CORNELL UNIVERSITY LIBRARY ESTATE OF CHARLES W. KUBBELL 3 1924 083 881 403 Cornell University Library The original of tiiis book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924083881403 Practical Marine Engineering FOR MARINE ENGINKERS AND STUDENTS WITH Aids for Applicants for Marine Engineers' Licenses Seventh Edition Revised and Enlarged By REAR ADMIRAL C. W. DYSON, U. S. N. BusSAU OP Stbam EnginBBring, UNIT8D Statss Navy. Author of "Screw Propellers and Kstimation of Fovrer for Propulsion of Ships''. New York Aldrich Publishing Compan> 461 8th Avenue 19J8 Copyright 1918 By Aldrich PublishinK Company Preface to First Edition THE purpose of the author in the preparation of this work has' been to provide help for the operative or practical marine engineer, either for the man who has already entered the profession, but who may wish to perfect himself more fully in many branches of the subject, or for the applicant for the lowest round of the ladder, or for the young man whose attention is first turning to this field, and who may wish some simple and fairly complete presentation of the subject from the practical standpoint. The treatment of the subject throughout has thus been with a view to simplicity, but without undue sacrifice of generality or exactness of statement. It has been the desire of the author to bring the subject, so far as treated in the present work, within the grasp of those who have not had the advantages of higher mathematical and engineering education, but who may wish, nev- ertheless, to fit themselves for positions of honor and responsi- bility in the field of operative marine engineering. With this end in view only such parts of the general field of engineering have been included as are of special interest to the practical marine engineer. On these topics, however, the attempt has been made to give the largest amount of useful information in the simplest and most compact form. In the marine field itself, likewise, selection has been necessary, and many interesting parts of the subject have been omitted or briefly referred to in order to give more room for the practical side of the subject. Thus the book does not treat of the designing of marine machinery except in an incidental way. For the operative engineer the topics of greater importance are construction, operation, management and care. The simpler parts of the subject of design are, however, represented by the U. S. rules regarding the design and con- PREFACE struction of marine boilers> and by many hints regarding propor- tions and relations scattered throughout the work. In the chapters deahng descriptively with engines, boilers and auxiliaries, it has been impossible, of course, to describe exhaustively every form of de'sign or appliance to be met with in marine practice. The purpose has been rather to describe typical or standard forms and to give the general conditions which the various parts must fulfill. The illustrations have been specially chosen with a view to supplement the text in these various par- ticulars, and it is hoped that they will form not the least instruc- tive and acceptable feature of the work. The subject of operation, management and repair has been given special attention, aiid it is hoped that this part of the work will be of value, especially to the young engineer lacking in prac- tical experience. In Chapter XIV is gathered a collection of miscellaneous problems and discussions, many of which, it is hoped, will be of value to the professional engineer in connection with the various questions likely to arise in his experience. The chapters on valve , gears and on indicator cards, while necessarily brief, are intended to present the fundamental features of the subject in such manner as to aid the novice and instruct and stimulate the professional engineer to a better understanding of these important branches of the subject. The chapter on propulsion and powering is neces- sarily brief, but the fundamental principles are given, with a few simple rules and the discussion of most of the problems commonly arising in practical engineering work. The chapters on refrigeration and on electricity on shipboard are added in order to give the marine engineer some notion of the funamental principles controlling the operation of refrigerat- ing and electric machinery, these two important auxiliaries of modern marine engineering practice. They are of necessity quite incomplete, especially Chapter X, but it is hoped that nevertheless they may be of aid to the marine engineer in understanding the mode of operation of such machinery, and in giving to it the proper care. In Chapter XV is given an elementary discussion of compu- tations for engineers, or rather of the mathematics UDon which such computations depend. A general knowledge of the subject is presupposed, but the more essentiar features of the elementary PREFACE mathematics usually required are given and illustrated with many problems. It is hoped that this feature of the work may be of aid to those who wish to drill themselves in such computations as the marine engineer is commonly called upon to make. Attention may also be called to the questions at the end of each chapter, each question with page reference to the part of the book where the answer may be found. The answer, of course, will not usually be found in the direct form suggested by the question, but a discussion of the subject will be found giving the information needed for the answer, which may be put into form by the reader for himself. It is believed that such an exercise will be of far greater value than the perusal of a series of ques- tions and answers in the usual catechism form. Throughout the work numerous problems have been scat- tered, accompanied usually by illustrative examples, showing the method of working. Numerous cross references have also been given to aid in the more complete explanation of any given topic, and in finding these use should be made of the table of contents, giving the page location of each section and bracket subdivision. A collection of miscellaneous problems is also added at the end of the book, as well as a set of steam tables for use in tb.e solution of the various problems requiring a knowledge of its various mechanical and physical properties. W. F. DURAND, Professor of Naval Architecture and Marine Engineering, Ithaca, N. Y., 1901. Cornell University. Preface to Sixth Edition IN the several editions which have been published since this book was first written, numerous changes have been made and much new material added. The third edition, published in 191 1, consisted of three separate and distinct parts written at different times. In the fourth edition, published in 1917, these parts were brought together to form one connected book of fifteen chapters and the material in the book was brought up to date, covering especially the latest practice in marine steam turbine machinery and auxiliaries and their operation, and also internal combustion engines, fuel oil burning and steam boilers. In the sixth edition the book has been enlarged by the addition of a chap- ter on miscellaneous machinery, including steering engines, cap- stans, windlasses, towing engines, and heating, ventilating, fire extinguishing and fumigating apparatus. As the installation, operation and repair of deck machinery form an important part of the work of the engineering force on board a modern steamship, the description of this machinery has been given in considerable detail and fully illustrated. The new edition of the book, there- fore, covers completely every branch of the work called for in a marine engineer's license and should prove useful as a guide to those who are taking examinations for a marine engineer's license. Due to the fact that the advance in marine engineering has been so rapid, it has been necessary to make descriptions as short as possible. In some cases this rule has been violated and ap- parently too much space has been devoted to the descriptions of comparatively unimporfant items. In these cases, however, no intelligent description could be given in any other way. The files of the Journal of the American Society of Naval Engineers must be credited with much of the new material, par- ticularly articles prepared for that journal by Lieutenant-Com- manders S. M. Robinson, J. J. Hyland and H. C. Dinger, U. S. N. Rear Admiral C. W. Dyson, U. S. N. Washington, D. C, 1918. TABLE OF CONTENTS CHAPTER I Principal Materials of Engineering Construction SECTION PAGE 1. Aluminum i 2. Antimony I 3. Bismuth • 2 4. Copper 2 5. Nickel 3 6. Vanadium 3 7. Iron and Steel 4 [i] Cast Iron 4 [2] Malleable Iron 9 [3] Wrought Iron ■ 11 [4] Blisters and Laminations 12 [S] Steel 13 8. Lead 28 9. Tin 29 ID. Zinc 29 11. Alloys 29 12. Testing of Metals 37 [l] Different Kinds of Tests 37 [2 Explanation of Terms Used 37 [3] Test Pieces for Iron '. 38 [4] Test Pieces for Steel and Other Materials 38 [S] Bending, Quenching and Hammer Tests 41 CHAPTER II Fuels 13. Coal 43 [i] Composition and General Properties 43 [2] Combustion , / 44 [3] Impurities in Coal, Clinker Formation 47 [4] Weathering of Coal. 48 [5 [ Spontaneous Combustion 49 [6] Corrosion 52 [7] Transportation and Storage 52 [8] General Comparison Between Bituminous and Anthracite Coal S3 14. Briquettes and Artificial Fuel 53 15. Liquid Fuel 54 [i] Composition S4 [2] Physical and Chemical Characteristics of Fuel Oil 56 vii CONTENTS CHAPTER III Boilers SECTION i6. Types of Boilers. PAGE 63 [i] The Scotch Boiler 66 [2[ Direct Tubular Boiler, Gunboat Type 66 [3] Direct Tubular Boiler, Locomotive Type 67 [4] The Flue and Return Tubular or Leg Boiler 67 [S] The Flue Boiler 68 [6] Watertube Boilers 69 [7] Relative Advantages of Different Types of Boilers 83 17. Riveted Joints 85 18. Materials and Construction 104 [i] Materials 104 [2] Joints 104 [3] Construction of Firetube Boilers 105 [4] Construction of Watertube Boilers 127 [S] Common Sizes and Dimensions of Scotch Boilers 129 [6] Common Proportions of Scotch Boilers 130 [7] Weights of Boilers 131 [8] Western River Boat or Flue Boilers 131 19. Boiler Mountings and Fire Room Fittings 133 'i] Safety Valves 133 2] Muffler 136 3] Stop Valve 137 4] Dry Pipe or Internal Steam Pipe 139 S] Feed Check Valve and Internal Feed Pipe 140 6] Surface and Bottom Blows 141 7] Steam Gages 143 8] Water Gage and Cocks 144 9] Hydrokineter Circulator ; 147 [10] Hydrometer 150 [11] Boiler Saddles 151 [12] Boiler Lagging 152 Draft 152 [i] Introductory 152 [2] Superheaters 161 Boiler Design in Accordance with the Rules of the United States Board of Supervising Inspectors of Steam Vessels.... 163 CHAPTER IV Oil Fuel Burning The Boiler Furnace and Its Accessories igi [i] Smoke Pipe Area ^ * ipi [2] Fire Brick , 192 [3] Atomization of the Oil 194 Mechanical Burners — The Principles Employed in Their Manu- facture and the Various Types Used 195 [i] Schutte-Koerting Burner igy [2] Thornycroft Burner ' 107 [3] Howden Burner ipg [4] Normand Burner [ jgn [5] Fore River Burner ' igg [6] Peabody Burner [] 200 viii CONTENTS SECTION PAGE 24. Air Cones, Registers or Tuyeres 203 25. Amounts of Air for Combustion 208 26. Air Chambers on Fuel Oil Lines 209 27. Aids to Combustion 210 28. Methods of Operating with an Oil-Fired Boiler 211 CHAPTER V MARINE ENGINES 29. Types of Engines : Introduction 218 30. Marine Reciprocating Steam Engines 220 [i] Types of Engines and Arrangement of Parts 220 31. The Turbine for Ship Propulsion 231 i] Advantages 231 2] Parsons Turbines 234 3] Curtis Turbines , 235 4 Combination Machinery 236 S] Reduction Gears 241 "6] Hydraulic Reduction Gearing 252 7] Electric Reduction Gear 256 32. Internal Combustion Engines (Explosion) 268 [i] Commercial Classification of Internal Combustion Marine Engines 268 2] Heavy Duty Engines 269 3] Racing Machine Engines 269 4] Semi-Speed Engines 271 S] Two Cycle and Four Cycle Engines 272 '6] Predominant Forms of Marine Engines in Service .273 7] The Large Engine 277 8] Starting and Reversing 279 9] Double-Acting Engines 283 [10] Cooling Systems 284 [11] Fuels 289 33. The Diesel Oil Engine (Progressive Combustion) 291 [l] Types of Diesel Engines According to the Stroke Cycle. . . . 294 [2] Description of Four- Stroke Cycle Diesel Engine 295 [3] Outline of the Operation of a Two Cycle Diesel Engine. . . . 297 [4] The, Harris Valveless Engine 299 34. Producer Gas Installations 305 [i] The Producer 30S [2] Operation of the Producer 306 [3] Producer Gas Engines 307 CHAPTER VI Description of the Principal Parts of Marine Engines 35. The Principal Parts of a Reciprocating Engine 310 [i] Cylinders 310 [2] Columns 31S [3] Bedplates 319 [4] Engine Seating 321 [5] Pistons 321 [6] Piston Rods 325 [7] Crossheads 327 [8] Connecting Rods 330 [g] Crank Shaft 332 ix CONTENTS SECTION PAGE 36. Construction of Parsons Turbines 33S [i] The Cylinder 336 [2] The Rotor 338 [3] Other Details 338 [4J Blading 340 37. Construction of Curtis Turbines 341 [i] The Cylinder 341 [2 The Rotor 344 [3] The Nozzles 344 [4 The Diaphragms 344 LsJ Blading 345 [6] Distributors 345 [7] Other Details 345 38. Other Turbines 346 39. General Details 347 [i] Line, Thrust and Propeller Shafts 347 [2J Bearings 350 40. Western River Boat Practice 359 [i] Doctor 36s 41. Engine Fittings 369 [i] Throttle Valve 369 [2] Main Stop Valve 372 [3] Arrangement of Throttle and Maneuvering Valves for Tur- bine Engines 374 4] Cylinder Drain Gear and Relief Valves . . . : 376 S] Starting Valves :^77 6] Reversing Gear 378 7] Turning Gear 381 8] Joints and Packing 382 [9] Reheaters 386 [10] Governors ■ 386 [11] Counter Gear 389 [12] Engine. Log System and Averaging Counters 389 [13] Lagging ; 396 [14] Lubrication and Oiling Gear 396 [15] Turbine Micrometer Gage 413 [16] Special Couplings 414 [17I Kingsbury Thrust Bearing 417 42. Piping 423 [i ] Systems and Materials ■ 423 [2] Expansion Joint 426 [3] Globe, Angle and Straightway Valves 427 [4] Balanced Expansion Joint 427 CHAPTER VII Auxiliaries 43. Circulating Pumps 430 44. Condensers 432 [i] Condensers for Turbines " " ' ^3,^ 45. Air Pumps ..!.'.'.' 438 46. Feed Pumps and Injectors 443 47. Auxiliaries for Turbines ^,g [i] Circulating Pumps 44g [2] Air Pumps '.'.'.'.'. 4^0 [3] Lubricating System ^58 [4] Water Service 4go X CONTENTS SECTION PAGE [S] Operating Gear 460 [6] Turning and Lifting Gear 460 48. Feed Heaters 461 49. Filters 466 50. Evaporators 467 51. Direct Acting Pumps 470 52. Blowers or Fans 474 53. Separators 475 54. Ash Ejector and Ash Expeller 477 55. Pneumercator 479 [l] Draft Indicator for Vessels 481 56. Time Firing Regulators _. 484 "l] Transmitter 484 2] - Indicator 487 3] Gong : 488 " " Operation 488 57. Steasn Traps ". 489 58. General Arrangement of Machinery 492 CHAPTER VIII Valves and Valve Gears 59. Slide Valves 493 'i] Simple Slide Valve 493 2] Double Ported Slide Valve 497 3; Piston Valve 498 4] Equilibrium Piston S02 S] . Equilibrium Rings 505 [6] Outside and Inside Valves S06 60. Motion Due to Simple Eccentric and Its Representation by Valve Diagrams 507 [i] Simple Eccentric 507 [2] Oval Valve Diagram 510 [3] Bilgram Valve Diagram .- 515 [4] Zeuner Valve Diagram 517 61. Stephenson Link Valve Gear S18 62. Braemme-Marshall Gear 524 63- JOy Valve Gear S28 64. Walschaert Valve Gear S29 65. Crank Valve Gear 531 66. Details of Stephenson Link Valve Gear 534 [i] Eccentric and Strap and Eccentric Rod S3S [2] Link 537 [3] Link Block and Valve Stem 539 67. Valve Setting S41 [i] Putting an Engine on the Center S41 [2] Setting the Valve 544 [3] Valve Setting from the Indicator Card S46 CHAPTER IX Refrigeration 68. General Principles S48 69. Refrigeration by Freezing Mixtures S49 70. Refrigeration by Vaporization and Expansion 550 71. Principal Features of Ammonia Refrigerating Apparatus 553 72. Carbonic Anhydride Refrigerating Machinery SS9 73. Ethyl Chloride Machines 560 xi CONTENTS SECTION PAGE 74. Sulphur Dioxide Machine 562 75. Refrigeration by the Expansion of Compressed Air 563 76. Principal Features of Compressed Air Refrigerating Apparatus. . 564 77. Operation and Care of Refrigerating Machinery 566 CHAPTER X Electricity on Shipboard 78. Introductory 570 79. The Dynamo S76 80. Wiring and the Distribution of Light and Power 582 81. Lamps 586 82. Operation and Care of Electrical Machinery 588 [i] Routine Care S88 [2] Faults .590 CHAPTER XI Propulsion and Powering 83. Measure of Speed 593 84. Propulsion 593 85. Screw Propellers 596 [i] Definitions 596 [2] Varieties of Propellers 602 [3] Materials 605 86. Paddle Wheels 609 87. Powering Ships 614 88. Reduction of Power When Towing or When Vessel is Fast to a Dock ; 617 89. Trial Trips 619 90. Special Conditions for Speed Trials 624 CHAPTER XII Operation, Management and Repair 91. Boiler Room Routine 626 [i] Starting Fires and Getting Under Way (Coal-Burning Boilers) 626 [2] Fireroom Routine 630 92. Engine Room Routine and Management 640 [i] Getting Under Way 640 [2] Routine Operation 644 [3]. Minor Emergencies and Troubles 646 93. Routine for Turbine Propelled Vessels — Preparations for Getting Under Way 650 [i] Engine Room and Fireroom 650 [2] Securing Main Engines After Coming to Anchor 652 [3] Instructions for Working Fires (Time Firing) 652 [4] Additional Notes on Firing 654 [S] Instructions for Burning Oil Fuel •.•••• i 655 [6] Preparations for Getting Under Way in the Firerooms (Watertube Boilers) 656 [7] Routine for Getting Under Way 657 [8] Routine for Coming to Anchor 6S9 [9] Care and Operation 661 [10] Work in Dry Dock 663 xii CONTENTS SECTION _ PAGE 94. Emergencies and Casualties 664 95- Boiler Corrosion 676 96. Boiler Scale 688 97. Boiler Overhauling and Repairs 697 [i] Inspection and Test 697 2] Leakage from the Joints of Boiler Mountings 702 3] Leakage About Shell Joints 703 4] Leakage at Internal Joints 704 5] Patches 70s 6] Cracks and Holes 706 7] Blisters and Laminations 706 8] Tubes 707 [9] Leakage About Stays and Braces 708 [10] Bulging or Partial Collapse of Furnace or Combustion Chamber Plates 709 [11] Split in Feed Pipe 710 98. Engine Overhauling, Adjustment and Repairs 711 Cylinders 71 1 Pin Joints and Bearings 712 Crosshead Guides 714 Crosshead Marks 715 Lining Up 716 Valve Gear 722 7 Thrust Bearings 722 Circulating Pump 722 Condenser 723 Air Pumps 724 Pumps in General 724 Piping 72s 99. Spare Parts 725 100. Laying Up Marine Machinery 726 8 9. [10 [II [12 CHAPTER XIII Steam Engine Indicators, Indicator Cards and Torsion Meters loi. Indicator Cards 731 [i] Descriptive 731 [2] The Indicator Card and the Operation of the Valve Gear . . 734 [3] Working Up Indicator Cards for Power 737 [4] Combined Indicator Cards 745 102. Steam Engine Indicators 749 [i] Descriptive , 749 [2] Reducing Motions •. 753 [3] Taking an Indicator Card 756 103. Torsion Meters '. 758 [i] Calibration of Shafting with Torsion Meter in Place 759 [2] Gary-Cummings Torsion Meter 763 [3] Hopkinson-Thring Torsion Meter 770 CHAPTER XIV Special Topics and Problems 104. Heat and the Formation of Steam 774 [i] Constitution of Matter 774 [2] Heat 775 l3l Steam ..., 780 CONTENTS SECTION PAGE [4] Total Heat in a Substance 786 [S] Latent Heat in Passing from Ice to Water 788 105. Steam Boiler Economy 789 [i] General Principles 789 [2] Evaporation per Pound of Coal 792 [3] Evaporation per Pound of Combustible 795 106. Steam Engine Economy 796 [i] General Principles ^ 796 [2] Relation of Expansion to Economy 80S [3] Economy of the Actual Engine ■ • 807 L07. Coal Consumption and Related Problems 808 108. Development of the Steam Turbine '. 813 [i] Principles of Action 814 [2] Superheat ■ 816 [3] Vacuum , .■•■.■ 816 icg. Definitions 817 no. Velocity Diagrams and Work by Steam 821 111. Action of the Steam in. Parsons Turbine 824 1 12. Action of the Steam in Curtis Turbine 826 113. The Lever Safety Valve and the Safety Valve Problem 829 114. The Boiler Brace Problem 832 lis. Strength of Boilers ' '. 837 1 16. Loss by Blowing Off 841 117. Gain by Feed Water Heating 844 118. The Proportions of Cylinders for Multiple Expansion Engines.. 845 119. Clearance and Its Determination 847 120. The Effect of Clearance in Modifying the Apparent Expansion Ratio as Given by the Point of Cut-Off 848 121. Engine Constant , 850 122. Indicated Thrust '. .. . 851 123. Reduced Mean Effective Pressure 852 124. Pressure on Main Guides , 855 125. Force Required to Move a Slide Valve ^ 856 126. Amount of Condensing Water Required 857 127. Work Done by Pumps 858 128. Discharge of Steam Through an Orifice , 860 129. Computing Weights of Parts of Machinery ....'. 861 [i] Units to be Used 861 [2] Approximation and Short Cuts 862 CHAPTER XV Computations for Engineers 130. Common Fractions 865 [-] Units of Measurement and Definitions ■. . .869 [2] Reduction of a Mixed Number to an' Improper Fraction. . . 870 [31 Reduction of an Improper Fraction to a Mixed Number. . . . 871 [4] Reduction of Fractions Without Change of Value 871 [3] Addition of Commori Fractions 872 [6] Subtraction of Fractions ^4 [7] Multiplication of Fractions 875 [8] Division of Fractions , 876 [9] Multiplication and Division by Fractions 876 [10] Complex Fractions 879 131. Decimal Fractions 879 l] Introductory 87p '2] To Reduce Decimals to Lower Terms 8g'o ^3] To Raise Decimals to Higher Terms 880 xiv CONTENTS SECTION PAGE [4] To Reduce a Decimal Fraction to a Common Fraction. .. . 880 [5] To Reduce a Common Fraction, Proper or Improper, to a Decimal 880 [6] To Add Decimals 881 [7] To Subtract Decimals 882 [8] To Multiply Together Two Numbers Expressed Decimally. 882 [9] To Find the Quotient of Two Quantities Expressed Decimally 882 132. Percentage 883 133- Compound Numbers 886 [1] Long or Lineal Measure -. 886 [2] Avoirdupois Weight or Measure. 886 [3] Square Measure 887 [4] Cubic or Volume Measure 887 [S] Liquid Measure 887 [6 Dry Measure 887 [7] Shipping Measure 887 [8] The Metric System of Weights and Measures 888 [9] Conversion Tables 888 [10] Reduction of Compound Numbers 889 [11^ Addition of Compound Numbers 890 [12] Subtraction of Compound Numbers 890 [13] Multiplication of Compound Numbers 891 [14 Division of Compound Numbers 891 134. Duodecimals 892 13s. Ratio and Proportion 894 [i] Simple Proportion _ 894 [2] Compound Proportion 897 136. Evolution and Involution ■ 899 [i] Introductory 899 [2] To Extract the Square Root 900 [3] To Extract the Cube Root 902 137. Mathematical Signs, Symbols and Operations 904 138. Geometry and Mensuration go8 [I [3] [4: [5: [6 17. [8 [9 [10: [II [12 [13 [14: [15 [16: [17: [18 [19] [?o 21 23 [34J Square .. . .- 908 Rectangle 909 Parallelogram 909 Trapezoid 910 Triangle r 910 A Right Angled Triangle 911 Trapezium 912 Regular Polygons .' 913 Irregular Figures ^". 913 Circle - -.913 Circular Ring^ or Annulus : 915 Sector of Circle 915 Segment of Circle 916 Ellipse 917 Figures with Irregular Contour 917 Prism 920 Cylinder 921 Any Solid with a Constant Section Parallel to the Base, Either Right or Oblique ; 922 Wedge 922 Right Pyramid 923 General Pyramid" 923 Right Circular Cone 924 General Cone 92S Frustum of Right Pyramid , ,,,,,,. 935 J5Y CONTENTS SECTION PAGE [25] Frustum of General Pyramid 926 [26] Frustum of Right Cone 926 [27] Frustum of General Cone 927 [28] Sphere 927 [29] Volumes of Irregular Shape 928 [30] Volume Generated by Any Area Revolving About an Axis. . 929 139. Problems in Geometry 929 [l] At Any Point in a Line to Erect a Perpendicular 929 [2] To Bisect the Distance Between Two Points 930 [3] To Find the Center from Which to Pass an Arc of Given Radius Through Two Given Points 930 [4] To Divide a Given Line Into a Given Number of Equal Parts 930 [5] To Construct a Triangle, Having Given the Three Sides. . . 931 [6] To Bisect a Given Arc or Angle 931 [7] To Construct a Mean Proportional Between Two Given Lines 931 [8] To Construct a Fourth Proportional to Three Given Lines. 931 [9] To Construct a Square Equivalent to a Given Rectangle 932 [10] To Construct a Square Equivalent to a Given Triangle 933 [ill With One Given Side, to Construct a Rectangle Equivalent to a Square 932 12] To Find the Length of an Arc of a Curve 932 13] To Construct an Ellipse 933 14] To Construct Any Regular Polygon 934 15] To Develop the Surface of a Cylinder 934 16] To Develop the Surface of a Cylinder Which is Intersected by Another Cylinder, the Two Axes Being in the Same Plane 935 17] To Develop the Surface of a Cone 936 18] To Develop the Surface of the Frustum of a Cone 936 19] To Develop the Segments of an Elbow 936 140. Physics 937 [i] Acceleration Due to Gravity 937 [2] Specific Gravity 937 [3] Heat Unit 938 [4] Specific Heat 938 [S] Expansion of Metals 938 141. Mechanics 939 [i] Introductory 939 [2] Force 939 [3] Specification of a Force 939 [4] Moment of a Force 940 [S] Resultant 940 [6] Work 940 \7] Power 940 [8] Energy 942 [9 Conservation of Energy 943 [10] Statics 943 [11] Dynamics 94j [12 Propositions in Statics 944 [13] Mechanical Powers 945 [14] Examples in Mechanics ! . . 952 CHAPTER XVI Miscellaneous Machinery 142. Steering Engines. Steam 958 [i] Indirectly Connected to Tiller 959 [2] Direct Connected to Tiller y^ xv: CONTENTS 149. ISO. ISI. 152- 153- 154- ISS- 156. 157. 158. 159. 160. .(a) (b) (c) (d) (e) SECTION Napier Screw Cear gg^ Rigidly Connedted Engine Room Steering Engine! '. '. 065 Wilson-Pirrie Gear 066 Wilson-Pirrie Gear (Compromise) g68 Diflferential Steering Gears 968 143. Electric Steering Gear 050 144. Steam Tillers '"" g-i 145- Electro-Hydraulic Steering Gear 973 146. Transmission .' n^g [i] Outside Packed Telemotor '. 077 [2] Inside Packed Telemotor '.'.'.'.'.'.'.'. 979 147. Anchor Windlasses and Capstans 082 '■''' Steam Windlass for Light Craft 982 Steam Capstan \ og. Combined Capstan and Windlass ; '. 984 Electric Capstan and Windlass 986 General Description of Engines and Windlasses 986 Directions for Operating Steam Capstan Windlass 988 148. . _ To Work Windlass by Steam Ahead and Heave in Chain. ^™ 2] To Stop the Windlass 989 3] To Reverse Windlass for Veering Chain 989 4 To Work the Windlass by Hand. 989 5] To Lock the Windlass 989 ^6] To Unlock the Windlass 989 ■7] To Obtain Double Purchase on Windlass 990 '8] To Veer Chain Without Using Engine 990 .9] To Run Capstan by Steam 990 [10] To Run Capstan by Hand ggo [11 Use of Pins in Capstan 990 [12 Use of Friction Bands 990 [13] Working the Pawls 991 [14] _ Directions for Keeping Windlass in Order 991 Towing Engines 991 Deck Winches 993 [i] Spur Geared Winches 994 (a) Cone Friction Winches 994 (b) Clutch Winches 995 2] Compound Geared Winch 996 3 Worm Geared Winches 997 4] Two-Cylinder, Double Drum Winch 997 5] Frictional Geared Winches 998 "6] Electric Deck Winches 1000 Arrangement of Winches dnd Gears for Cargo and Coal Hand- ling ,-■ lOOI BoaLCranes, Steafn and Electric 1002 Ash Hoists, Steam and Electric 1004 Surface Combustion (Hot Bulb) Engines 1006 Heating and Ventilation 1009 Combined Heating and Ventilation: The Thermofan loio Ventilation and Cooling ; Magazine Cooling 1017 Fire Extinguishing and Fumigating 1020 Applications of the System 1021 Description of Apparatus 1023 General Airangement of Piping 1024 Disinfectant Tank 1025 Air Compressors 1026 Steam Whistles and Sirens 1028 [i] Steam Whistles 1029 [2] Steam Sirens 1030 xvu CONTENTS SECTION ,_ PAGE i6i. Reducing Valves and Governing Valves 1032 [i] Reducing Valves 1032 (a) Outside Spring Reducing Valve 1033 (b) Inside Spring Reducing Valve ^. . , 1033 [2] Governing Valves for Pumps 1036 (a) "Constant Pressure" Valves 1036 (b) "Excess Pressure" Valves 1037 xviil Practical Marine Engineering CHAPTER I Principal Materials of Engineering Construction Sec. I. ALUMINUM The commercially pure metal, i. e., with less than i percent impurity, is white in color, soft, ductile and malleable. It melts at about i,i6o degrees F., has a tensile strength of about 15,000 pounds per square inch of section, but lacks in stiffness and resilience, or the power to withstand shocks. Aluminum does not oxidize readily under the influence of ordinary air, but when in contact with sea water, or in air charged with sea water, the corrosion is often .serious in extent. Aluminum cannot be welded except electrically, is not suitable for forging or rolling when hot, and cannot be tempere^d or hard- ened. It is, however, suitable for casting, and when cold can be rolled into sheets and drawn into wire, and in thiri sheets or small pieces may be spun or flanged, or worked under the hammer in various ways. Aluminum unalloyed is of comparatively small value to the engineer, but it enters into several valuable alloys, as described in Section 1 1, and its use in this way has increased to a consider- able extent within the past few years. Sec. 2. ANTIMONY The pure metal is whitish in color, quite brittle and crystal- line or laminated in structure, and has a melting point of about 840 degrees F. It is useless in the pure state for ordinary engi- neering purposes, but is a valuable ingredient of various alloys used for bearing metals, etc., as described in Section ii. 2 PRACTICAL MARINE ENGINEERING Sec. 3. BISMUTH The pure metal is light red in color, very brittle and highly crystalline in structure, with a melting point of about 510 degrees F. It is useless in the pure state for engineering purposes, but forms a part of various alloys used for bearing metals, etc., as described in Section 11. Sec. 4. COPPER In the pure state the metal is red in color, soft, ductile and malleable, with a melting point of about 2,000 degrees F., and a tensile strength of from 20,000 to 30,000 pounds per square inch of section. Copper is not readily welded except electrically, but, on the other hand, is readily joined by the operation of brazing. Attempts have been made to temper or harden it, but the operation has not been made a practical success. It is readily forged and cast, and when cold may be rolled into sheets or drawn into wire, and in sheets or small pieces may be spun or flanged or worked under the hammer in various ways. The tensile strength of copper rapidly falls off as the tem- perature rises above about 400 degrees F., so that at 800 degrees to 900 degrees the strength is only about one-half what it is at ordinary temperatures. This peculiarity of copper should be borne in mind when it is used in places where the temperature is liable to rise to these figures. Again, if copper is raised nearly to its melting point in contact with the air, it readily unites with oxygen and loses its strength in large degree, becoming, when cool, crumbly and brittle. Copper in this condition is said to have been burned. The possibility of thus injuring the tenacity of copper is of the highest importance in connection with the use of brazed joints in steam pipes. In the operation of brazing a joint, the surfaces to be joined are cleaned, bound together with wire or otherwise, then sup- plied with brazing solder in small bits, mixed with borax as a flux, and placed in a clear fire until the solder melts and forms the joint. The brazing solder, or hard solder, as it is often called, is usually a brass or alloy of copper and zinc. The melting point of all such alloys is below that of copper, and when copper is joined to brass, or two pieces of brass are joined together, the solder used must have a melting point lower than either of these metals. In the operation of brazing a copper joint, therefore, the greatest care must be taken in the selection of a solder and in MATERIALS 3 attention to the fire, .so that there may be no danger of burning the copper, and thus endangering the quahty of the metal in the joint. Copper unalloyed is used chiefly for pipes and fittings, espe- cially for junctions, elbows, bends, etc. For large sizes the ma- terial is made in sheets, bent and formed to the desired shape and brazed at the seams. Small sizes are either made by the same general process or from solid drawn pipe, which may be bent as desired after drawing. Copper is also largely used as the chief ingredient of the various brasses and bronzes, as described in Section ii. Sec. 5. NICKEL Nickel is a silvery-white metal with a strong lustre, not tar- nishing on exposure to air. It is ductile, hard, and as tenacious as iron. It is attracted by the magnet and may be made magnetic. The fusion point of nickel is about 3,000 degrees F. It is chiefly used in alloys with copper, and in the manufac- ture of steel to increase its hardness and strength. Steel in which nickel has been used possesses, the highly val- able characteristics of resistance to cracking, high elastic limit and homogeneity. Resistance to cracking increases as the percentage of nickel is increased. When the amount of nickel is increased to 27 or 30 percent, the steel becomes practically non-corrodible and non- magnetic. The elastic limit rises in a marked degree with the addition of about 3 percent of nickel, and in such places as shafts, axles, etc., where failure is the result of fatigue of the metal, this higher elastic limit tends to prolong the life of the piece, and at the same time, through the superior toughness of the metal, offers greater resistance to the sudden strains of shock. Sec. 6. VANADIUM Vanadium is a brittle, pale gray metal with a silver-white lustre, of a crystalline structure, and is non-magnetic. Its specific gravity is 5.5. It does not oxidize when exposed to the air, even at 212 degrees F., and does not decompose water at 212 degrees F. It fuses at 3,236 degrees F. Notwithstanding its high melting point, vanadium readily alloys with other metals. 4 PRACTICAL MARINE ENGINEERING Sec. 7. IRON AND STEEL Classification It will be convenient to give here a general classification of iron and steel products based on the methods of manufacture. The following is the classification used by Prof. J. B. Johnson in his text book on the Materials of Comtruction, MALLEABLE Wrought Iron. — Rolled or forged from a puddle ball ; it con- tains slag and other impurities and cannot be hardened by sud- den cooling. Steel. — Rolled or forged from a cast ingot and free from slag and similar matter. Soft Steel. — Will weld (with care), and cannot be hardened by sudden cooling. It is sometimes called ingot iron, and has the same uses as wrought iron. Medium Steel. — Welds imperfectly except by electricity. Will not harden with sudden cooling. Hard Steel. — Will not weld. Hardens by sudden cooling. Tool steel, etc. SEMI-MALLEABLE Steel Castings. — Malleable metal cast into forms. Malleable Cast Iron. — Non-malleable metal cast into forms and then brought to a semi-malleable condition. NON-MALLEABLE Cast Iron: Hard Cast Steel. — Non-malleable metal cast into forms. In describing these products at length it will be found con- venient to begin with cast iron. [1] Cast Iron This material consists of a mixture and combination of iron and carbon, with other substances in varying proportions. ( I ) Influence of Carbon. In the molten condition the car- bon is dissolved by the iron and held in solution just as ordi- nary salt is dissolved by water. The mixture or combination of the two elements is thus entirely uniform. The proportion of carbon which pure melted iron can thus dissolve and hold in solution is about 2% percent. If chromium or manganese is MATERIALS 3 present also, the capacity for carbon is much increased, while with silicon, on the other hand, the capacity for carbon is de- creased. In the various grades of cast iron the proportion of carbon is usually found between 2 percent and 4.5 percent. Now, when such a molten -mixture cools and becomes solid, there is a tendency for a part of the carbon to be separated out and no longer remain in intimate combination with the iron. The carbon thus separated or precipitated out from the iron takes that form known as graphite, and collects together in very small flakes or scales. The carbon which remains in intimate combina- tion with the iron is said to be combined, while that which is separated out is usually called graphitic. The qualities of cast iron depend chiefly on the proportion of total carbon and on the relative proportions of combined and graphitic carbon. With a high proportion of graphitic carbon the iron is soft and tough, with low tensile strength, and breaks with a coarse grained dark or grayish colored fracture. In fact the substance in this condition may be considered as nearly pure iron with fine flakes of graphite entangled and distributed through it, thus giv- ing to the iron a spongy structure. The iren thus forms a kind of continuous mesh about the graphite, which decreases th« strength by reason of the decrease of cross-sectional area actually occupied by the iron itself. Such irons are termed gray. As the relative proportion of graphite carbon decreases and that of combined carbon increases, the iron takes on new proper- ties, becoming harder and more brittle. Its tensile strength also increases to a certain extent, and the fracture becomes fine grained or smooth and whiter in color. When these characteristics are pronounced the iron is said to be white. When about half the carbon is combined and half separates out as graphite, . the effect is to produce a distribution of dark spots or points scattered over a whitish field. Such irons are said to be mottled. In a general way with a large proportion of total carbon there is likely to be formed a considerable amount of graphitic carbon, and hence such irons are usually gray and soft. With a large proportion of carbon also the iron melts more readily and its fluidity is more pronounced. As the proportion of total car- bon decreases the cast iron approaches gradually the condition of steel, whose properties will be discussed in a later paragraph. 6 PRACTICAL MARINE ENGINEERING Of the special ingredients in cast iron the combined carbon is one of greatest importance. It is that chiefly which, by uniting with the iron, gives it new quaHties, and the principal influence of other substances lies in the effect which they may have on the proportion of this ingredient. As between graphitic and com- bined carbon, the former does not affect the quality of the iron itself, but acts physically by affecting the structure of the casting; while the latter, by entering into combination with the iron, acts chemically and produces a new substance with different qualities. The following percentages of combined cai'bon are recommended for quaHties of iron as indicated. PROPORTION OF COMBINED, CARBON Soft cast iron o.io to .15 of one percent. Greatest tensile strength 1 about .45 of one percent. Greatest transverse strength... about .70 of one percent. Greatest crushing strength one percent or over. The proportions of combined and graphitic carbon are in- fluenced by the rate of cooling, and by the presence or absence of various other ingredients. Slow cooling allows time for the separation of the carbon and thus tends to form graphitic car- bon and soft gray irons. Quick cooling, or chilling in the ex- treme case, prevents the formation of graphitic carbon and thus tends to form hard, white irons. In addition to carbon, small quantities of silicon, sulphur, phosphorus, manganese and chromium may be found in cast iron. (2) Influence of Silicon. The fundamental influences of silicon are two. (a) It tends to expel the carbon from the com- bined state and thus to decrease the relative proportion of com- bined carbon and increase that of graphitic carbon, (b) Of itself silicon tends to harden cast iron and to make it brittle. These two influences are opposite in character, since an in- crease in graphitic carbon softens the iron. In usual cases the net result is a softening of the iron, an increase in fluidity, and a general change toward those qualities possessed by iron with a high proportion of graphitic carbon. This applies with a pro- portion of silicon from 2 percent to 4 percent. With more than this the influence on the carbon is but slight and the result on the iron is to decrease the strength and toughness, giving a hard but brittle and weak grade of iron. A chilled cast iron is an iron which if cooled slowly would be gray and soft, but, as explained in ( i ) , by sudden cooling, from MATERIALS 7 contact with a metal mold or other means, becomes white and hard, especially at and near the surface. Certain grades of cast iron tend to chill when cast in sand molds. This property is usu- ally' undesirable. In such cases the tendency can be prevented by the addition of silicon, which, by forcing the carbon into the graphitic state on cooling, prevents the formation of the hard, chilled surface. In all cases the actual eflfect of adding silicon will depend much on the character of the iron used as a base, and only a statement of the general tendencies can here be given. To sum up, a white iron which would give hard, brittle and porous castings can be made solid, softer and tougher by the addi- tion of silicon to the extent of perhaps 2 or 3 percent. As the silicon is increased the iron will become softer and grayer and the tensile strength will decrease. At the same time the shrink- age will decrease, at least for a time, though it may increase again with large excess of silicon. The softening and toughening influ- ence, however, will only continue so long as additional graphite is formed, and when most of the carbon is brought into this state the maximum effect has been produced, and any further addition of silicon will decrease both strength and toughness. (3) Influence of Sulphur. . Authorities are not in entire agreement as to the influence of sulphur on cast iron, some be- lieving that it tends to increase the proportion of combined car- bon, while others maintain that it tends to decrease both the combined carbon and silicon. It is generally agreed, however, that in proportions greater than about .15 to .20 of i percent it increases the shrinkage and the tendency to chill, and decreases the strength. Sulphur does not, however, readily enter cast iron under ordinary conditions, and its influence is not especially feared. An increase in the proportion of sulphur in cast iron is most likely to result from an absorption of sulphur in the coke during the operation of melting in the cupola. (4) Influence of Manganese. This element by itself de- creases fluidity, increases shrinkage, and makes the iron harder and more brittle. It combines with iron in all proportions. With manganese less than one-half, the combination is usually called spiegeleisen. With manganese more than one-half it is called ferro-manganese. One of the most important properties of man- ganese in combination with iron is that it increases the capacity of the iron for carbon. Pure iron will only take about 3^ percent 8 PRACTICAL MARINE ENGINEERING of carbon, while with the addition of manganese the proportion may rise to 6 percent or 7 percent. Manganese is also believed to decrease the capacity of iron for sulphur, and'to this extent may be a desirable ingredient in proportions not exceeding i percent to i^^ percent. (5) Influence of Chromium. This substance is rarely found in cast iron, but it has the property, when present in large pro- portion, of raising the capacity of the iron for carbon from about 3j4 percent up to about 12 percent. (6) Shrinkage of Cast Iron. At the moment of hardening, cast iron expands and takes a good impression of the mold. In the gradual cooling after setting, however, the metal contracts, so that on the whole there is a shrinkage of about ^ inch per foot in all directions, though this amount varies somewhat with the quality of the iron and with the form and dimensions of the pattern. In a general way hardness and shrinkage increase and decrease together. (7) Strength and Hardness of Cast Iron. The hardness of cast iron is chiefly dependent on the amount of combined carbon, as noted above in (i). The strength is also chiefly dependent on the same ingre- dient. As shown in (i), the greatest crushing strength is ob- tained with sufficient combined carbon to make a rather hard, white iron, while for the maximum transverse or bending strength the combined carbon is somewhat less and the iron only moder- ately hard, and for the greatest tensile strength the combined carbon is still less and the iron rather soft. Metal still softer than this grade works with the greatest facility, but is deficient in strength. Numerical values for the strength will be given at a later point. (8) Uses of Cast Iron in Marine Engineering. Cast iron is used for cylinders, cyHnder heads, liners, slide valves, valve chests and connections, and generally for all parts having con- siderable complexity of form. It is also used for columns, bed plates, bearing pedestals, caps, etc., though cast and forged steel are to a great extent displacing cast iron for some of these items. It is also used for grate bars, furnace door frames, and minor boiler fittings, and for a great variety of special purposes usually connected with the stationary or supporting parts of machines. MATERIALS 9 (9) Inspection of Castings. In the inspection of castings care must be had to note the texture of the surface, and to this end the outer scale and burnt sand should be carefully removed by the use of brushes or chipping hammer, or, if necessary, by pickling in dilute muriatic acid. The flaws most liable to occur are blow holes and shrinkage cracks. The latter, however, are not often met with when the molding and casting are properly carried out. The parts of the casting most liable to be affected by blow holes are those on the upper side or near the top. On this account a sinking head or extra piece is often cast on top, into which the gases and impurities may collect. This is afterward cut off, leaving the sounder metal below. The presence of blow holes, if large in size or in great num- ber and near the surface, may often be determined by tapping with a hand hammer. The sound given out will serve to indicate to an experienced ear the probable character of- the metal under- neath. (10) Special Operations on Cast Iron. Cast iron may be softened and toughened by the process of malleablizing, as de- scribed in (2). It may be somewhat hardened on the surface by arresting the usual process of malleablizing at a suitable point and then hardening as for steel. This operation arrested before completion results in the formation of a surface layer of material having essentially the properties of steel. Cast iron may be brazed to itself or to most of the common structural metals by the use of a brazing solder of suitable melt- ing point, and with proper care in the operation. Cast iron may also be united to itself or to wrought iron or steel by the oper- ation of burning. This consists in placing in position the two pieces to be united, and then allowing a stream of melted cast it on to flow over the surfaces to be joined, the adjacent parts being protected by fire clay or other suitable material. The result is to soften or partially melt the surfaces of the pieces, and by arrest- ing the operation at the right moment they may be securely joined together. [2] Malleable Iron (i) Composition and Manufacture. If a casting of hard, white iron, or one with a large proportion of combined carbon, be packed in some material which will not fuse at a red heat, W'hicli will exclude the air, support the piece and prevent deform- 10 ' PRACTICAL MARINE ENGINEERING ation when hot, and if it be then subjected to continuous red heat for some days, the combined carbon will be separated from the iron, but will not be able to collect together in flakes or scales or to form the same structure as in soft, gray cast iron. In conse- quence the iron crystals remain in more intimate contact, much as in steel, and the tensile strength and toughness are greatly in- creased. It has long been supposed that this operation involved an actual withdrawal of the carbon from the iron, and to this end the substances usually employed are either the common red oxide of iron in the form of hematite iron ore, or the black oxide in the form of mill scale, or the corresponding oxide of manganese. These have a decarbonizing effect; that is, under the conditions existing they will to some extent withdraw the carbon from the surface layer of iron'. Analyses of malleable iron show, however, that only to a slight extent is the carbon actually withdrawn as a whole, and that the principal change is in the condition of the car- bon, as above explained. The surface effect, however, extending in, as it does, for perhaps 1-16 inch, is undoubtedly a valuable feature, and while a good quality of malleable iron has been made by the use of river sand as a packing medium, the use of the sub- stances mentioned above is rather to be preferred. In order that the process may be successful, the iron must have nearly all the carbon in the combined state, and must be low in sulphur, as the latter substance is found to greatly in- crease the time necessary. It has been customary to use only good charcoal-melted iron in which the sulphur is very low, though a coke-melted iron is quite as suitable, provided the pro- portion of sulphur is correspondingly small. The process can rarely be applied to very large castings, because such, cooling slowly, usually show a considerable proportion of graphitic carbon. To carry out the pi-ocess the castings are embedded in the material selected. The whole is then enclosed in a cast iron box or pot and is subjected to a full red heat for from two or three days to as many weeks, depending on the size of the piece. (2) Physical and Mechanical Properties. Outside of the numerical information, to be given later, attention may be called to the ductility of malleable iron, which is from four to six times that of cast iron, though only about one-tenth that of wrought MATERIAL'S li iron. Nevertheless good malleable iron can be bent and twisted to a very considerable extent before breaking, and its ability to withstand blows or shocks is very much greater than cast iron. Malleable iron may with care be forged and welded, and it may be case hardened much as with wrought iron. (3) Uses in Marine Engineering. Malleable iron is used for junction boxes and for pipe fittings in certain varieties of watertube boilers, and to some extent for general pipe fittings on board ship. It would seem that the use of this material might with advantage be extended to many parts in which more strength and toughness are required than can be provided by cast iron of the ordinary type. [3] Wrought Iron ( I ) Composition and Manufacture. Wrought iron is nearly pure iron mixed with more or less slag. Nearly all the wrought iron tised in modern times is made by the puddling process. For the details of this process reference may be had to text books on metallurgy. It will only be noted here that in a furnace some- what similar to the open-hearth referred to in [5] (4), most of the carbon, silicon and other special ingredients of cast iron are re- moved by the combined action of the flame and of a molten bath of slag or fluxing material consisting chiefly of black oxide of iron. As this process approaches completion small bits of nearly pure iron begin to separate out from the bath of melted slag and unite together. This is helped along by the puddling bar, and after the iron has thus become separated from the liquid slag it is taken out hammered or squeezed, and rolled down into bars or plates. Some of the slag is necessarily retained in the iron and by the process of manufacture is drawn out into fine threads, giving to the iron a stringy or fibrous appearance when nicked and bent over or when pulled apart. The proportion of carbon in wrought iron is very small, ranging from .02 to .20 of one percent. In addition, small amounts of sulphur, phosphorus, silicon and manganese are usually present. The proportion of sulphur should not exceed .01 of one percent. Excess of sulphur makes the iron red short, that is, brittle when red hot. The proportion of manganese in malleable iron amounts gen- erally to about I percent, and appears to counteract the effect of 12 PRACTICAL MARINE ENGINEERING phosphorus. Excess of phosphorus makes the metal cold short, that is, brittle when cold. The proportion of phosphorus should not exceed .05 percent. The proportion of silicon may vary from .05 to .30 of i percent. The influence of the silicon and manganese is usually slight and unimportant. (2) Special Properties. Wrought iron is malleable- and ductile, and may be rolled, forged, flanged and welded. It can- not be hardened as steel, though by the process of case-hardening a surface layer of steel is formed and may be hardened. Wrought iron may be welded, because for a considerable range of temper- ature below melting (which takes place only at a very high tem- perature indeed) the iron becomes soft and plastic, and two pieces pressed together in this condition unite and form on cool- ing a junction nearly as strong as the solid metal. In order to be thus successful, however, the iron must be heated sufficiently to bring it to the plastic condition, yet not overheated, and there must be employed a flux (usually borax), which will unite with the iron oxide and other impurities at the joint, and form a thin liquid slag, which may be readily pressed out in the operation, thus allowing the clean metal faces of the iron to effect a union as desired. (3) Uses in Marine Engineering. In modern practice the place of wrought iron in marine engineering has been almost entirely taken by steel. It formerly was used for all moving parts requiring strength and toughness. It is still used to some ex- tent for the staybolts and braces of boilers, and for boiler tubes. [4] Blisters and Laminations With modern boijer material these defects are happily rare. In older practice, however, when wrought iron was the material employed for boiler plates such defects were quite frequently met with. A lamination consisted in the separation of the ma- terial of the plate into layers not welded together and therefore lacking the strength and solidity of the plate proper. The for- mation of such places was usually due to the presence of slag in the iron which in the operation of rolling the plates would be- come thinned out into a sheet or layer separating the two parts of the iron and preventing them from becoming welded together MATERIALS I3 and thus forming a solid homogeneous plate. Such places may vary in size from a trifling amount up to patches of several square feet in area. When a plate with such laminations is worked into the structure of a boiler, with the continual fluctuations of temperature and the consequent expansions and conti-actions, it very frequently happens that the two parts of the laminations become separated from each other, and in particular the thinner of the two will become raised, often to a considerable extent, thus forming a so-called blister. The chief danger from such a blister on the heating surface arises from the non-conductivity of the plate for heat at this point, and the consequent danger of its overheating and giving rise to a serious rupture. In examining a plate for laminations or small blisters not plainly shown to the eye, the hammer test is usually considered the most reliable. The plate is tapped over its surface, and judg- ing by the sound an experienced ear can usually detect the locality and approximate extent of trouble of this character. [5] Steel (r) General Composition. The properties of steel depend partly on the proportions of carbon and other ingredients which it may contain, and partly on the process of manufacture. The proportion of carbon is intermediate between that for wrought iron and for ca^t iron. In the so-called mild or structural steel the carbon is usually from i-io to 1-4 or 1-3 of i percent. In spring steel tlie carbon proportion is somewhat greater, and in high carbon grades, such as are used for tool steel, etc., the car- bon is from .6 to 1.2 percent. In addition to the carbon there may be sulphur, phosphorus, silicon and manganese in varying but very small amounts. From the proportion of carbon it follows that steel may be made either by increa;sing the proportion in wrought iron or decreasing the proportion in cast iron. The earlier processes followed the first method, and high grade steels are still made in this way by the crucible process. (2) Crucible Steel. In this process a pure grade of wrought iron is rolled out into flat bars. These are then cut and piled and Note. — ^Mild or structural steel is made wholly by the second general method — the reduction of the proportion of carbon in cast iron. There are two general processes, known as the Bessemer and the Siemens Martin or Open Hearth. 14 PRACTICAL MARINE ENGINEERING packed with intermediate layers of charcoal and subjected to a high temperature for several days. This recarbonizes or adds carbon to the wrought iron, and thus makes what is then called cement or blister steel. These bars are then broken into pieces of convenient size, placed in small crucibles, melted, and cast into bars or into such forms as are desired. (3) Bessemer Process. In this process the carbon and sili- con are burned almost entirely out of the cast iron by forcing an air blast through the molten iron in a vessel known as a con- verter. A small amount of Spiegel eisen or iron rich in carbon and manganese is then added in such weight as to make the propor- tion of carbon and manganese suitable for the charge as a whole. The steel thus formed is then cast into ingots or into such forms as may be desired. In this process no sulphur nor phosphorus is removed, so that it is necessary to use a cast iron very nearly free from these ingredients in order that the steel may have the properties de- sired. A modification by means of which the phosphorus is re- moved, and known as the basic Bessemer process, is used to some extent. In this, calcined or burnt lime is added to the charge just before pouring. This unites with the phosphorus, removes it from the steely and brings it into the slag. In the basic process the lining of the converter is made of gannister or calcined mag- nesia limestone, in order that it may not also be attacked by the added limestone and the resulting slag. In that form of Bessemer process first noted, and often known as the acid process in distinction from the latter or basic process, the lining of the converter is of ordinary fire clay or like material. The removal of the phosphorus by the basic process makes possible the use of an inferior grade of cast iron. At the same time, engineers are not altogether agreed as to the relative values of the two products, and many prefer steel made by the acid process from an iron nearly free from phosphorus at the start. (4) The Open Hearth Process. In this process a charge of material consisting of wrought iron, cast iron, steel scrap, and sometimes certain ores, is melted on the hearth of a reverbera- tory furnace heated by gas fuel on the Siemens Martin or re- generative system. The carbon is thus partially burned out in much the same manner as for wrought iron, and the proportion MATERIALS ■ ij of carbon is brought down to the desired point or slightly below. A charge of Spiegel eisen or ferro-manganese is then added in order that the manganese may act on any oxide of iron slag which remains in the tath, and which would make the steel red short if allowed to form a part of the charge. The manganese separates the iron out from the oxide, returns it to the bath, while the carbon joins in with that already present, and thus produces the desired proportions. Here, as with the similar operation with the Bessemer con- verter, there is no removal of either sulphur or phosphorus, and only materials nearly free from these ingredients can be used for steel of satisfactory quality. With very low carbon, how- ever, a little phosphorus seems to be desirable to add strength to the metal. This limitation of the available materials has led, as with the Bessemer process, to the use of calcined limestone, which unites with most of the phosphorus and holds it in the slag. Here, as in the Bessemer process also, it is necessary to use a basic lining for the furnace, and it is known as the basic open hearth process. By distinction the method without the use of the limestone has come to be known as the acid open hearth process. As between-the products of these two kinds of open hearth process, there is much difference of opinion among engineers. Either will produce good steel with proper care, and neither will without it. It is usually considered sufficient to specify the allow- able limits for the proportions of phosphorus and sulphur and leave the choice of the acid or basic processes to the maker. (5) Open Hearth agd Bessemer Steels Compared. Open hearth steel is usually preferred for structural material in ma- rine engineering. This is because : (a) It seems to be more reliable and less subject to unex- pected or unexplainable failure than the Bessemer product. (b) Analysis shows that it is much more homogeneous in composition than Bessemer steel, and experience shows that it is much more- uniform in physical quality. This is due to the process of manufacture, which is much more favoraible to a thor- ough mixing of the charge than in the Bessemer process. (c) The open hearth steel may be tested from time to time during the operation, so that its composition may be determined and adjusted to fulfil specified conditions. This is not possible i6 PRACTICAL MARINE ENGINEERING with the Bessemer process, and the latter product is therefore, not under so good control as in the open hearth. (6) Influence of Sulphur on Steel. Sulphur makes steel red short or brittle when hot, and interferes with its forging and welding properties. Mangane'se tends to counteract the bad effects of sulphur. Good crucible steel has rarely more than .01 of I percent, In structural steel the proportion may vary from .02 to .08 or .10 of I percent. When possible it should be re- duced to not more than .03 or .04 of i percent. (7) Influence of Phosphorus on Steel. Phosphorus increases the tensile strength and raises the elastic limit of low carbon or structural steel, but at the expense of its ductility and tough- ness or ability to withstand shocks and irregularly applied loads. It is thus considered as a dangerous ingredient, and the amount allowable should be carefully specified. This is usually placed from .02 to .10 of I percent. (8) Influence of Silicon on Steel. Silicon tends to increase the tensile strength and to reduce the ductility of steel. It also increases the soundness of ingots and castings, and by reducing the iron oxide tends to prevent red shortness. The process of manufacture usually removes nearly all of the silicon, so that it is not an element likely to give trouble to the steel maker. The proportion allowed should not be more than from .10 to .20 of i percent. (9) Influence of Manganese on Steel. This element is be- lieved to increase hardness and fluidity, ai)d to raise the elastic limit and increase the tensile strength. It also removes iron oxide and sulphur, and tends to counterfct the influence of such amounts of sulphur and phosphorus as may remain. It is thus an important factor in preventing red shortness. The propor- tion needed to obtain these valuable effects is usually found between .20 and .50 of i percent. (10) Semi-steel. A metal bearing this trade name has in recent years attracted favorable attention among engineers and has come into considerable use where somewhat greater strength and toughness are required than can be provided by cast iron. Semi-steel is made by melting up mild steel scrap, such as punchings and clippings of boiler plate, with cast iron pig, in the proportion of about 25 or 30 percent of the former to 75 or 70 percent of the latter. The presence of manganese and other MATERIALS I7 special fluxes in smal], proportions is also found to add essen- tially to the strength, toughness and good machining qualities of the product. In this way is obtained a material having a tensile strength of 35,000 pounds or over, and a toughness and ability to withstand shocks decidedly greater^ than for cast iron, and with fairly good machining qualities. Semi-steel casts as readily as most grades of cast iron, and its shrinkage and general manipu- lation are about the same. The chief drawback seems to lie in the danger of hardness under the lathe, planer or boring tool, but with the proper mixtures this is avoided, and a material very satisfactory for many pvirposes in marine engineering is thus produced. ^ (11) Mechanical Pfoperties of Steel. The tensile strength of the lowest carbon steel, say about .10 of i percent carbon, is usually not above from 50,000 to 55,000 pounds per square inch of section. The strength increases with -the increase of carbon, and with not above the usual proportions of sulphur and phos- phorus, quite uniformly. Experiments show that under these circumstances the strength will increase up to 75,000 pounds per square inch, or higher, at the rate of from 1,200 to i,5oo pounds per .01 of I percent of carbon added. At the same time, with the increase in strength the ductility decreases, so that a proper choice must be made according to the particular uses for which the steel is intended. With the best grades of tool steel with carbon ranging from ^ to i percent and over, the strength ranges from 80,000 pounds upward to 120,000 pounds, and even higher in exceptional cases. Flange and rivet steel must be tough and ductile in the high- est degree. Such steel has usually a tensile strength between . 50,000 and 60,000 pounds and an elastic limit of 30,000 to 40,000 pounds. Its elongation in 8 inches is from 30 to 35 percent, and re- duction of area at the ruptured section from 50 to 60 percent. It will bend cold on itself and close down flat under hammer or press, up to a thickness of ^ inch to i inch without a sign of fracture. Shell steel, used for boiler shells, etc., has usually a strength between 55,000 and 65,000 pounds; elastic limit from 33,000 to 45,000 pounds ; elongation in 8 inches of 25' to 30 percent, and re- duction of area of 50 to 60 percent. For shafting, the quality of the steel is about the same as for i8 PRACTICAL MARINE ENGINEERING shell plates. For piston and connecting rods the strength is rather higher, and ductility somewhat lower. For steel castings the strength required is usually from 60,000 to 65,000 pounds, with an ebngation in 8 inches of from 10 to 15 percent. (12) Various Specifications for Structural Steel. U. S. NAVY BOILER PLATES Roiling — Any plate to be incorporated in the shell or drum of a boiler and subjected to the boiler pressure must be rolled in the direction of the circumference of the shell or drum, and test pieces should be pulled in the same direction. Physical and Chemical Properties — The physical and chemical char- acteristics of steel boiler plate are to be in accordance with the following table : Mini- Maximum Tensile mum Elon- perqentage - strength elastic gation of— Without showing cracks or Class. Material. ; (pounds per limit (pounds (per- cent flaws, must cold bend about an inner diame- « square per in 8 ter — inch). square inches). P. S." inch). Equal to thickness of plate andthroughlSO" for plates f 65,000 }^T. } 22 1 inch in thickness and un- A /Open hearth 1 steel. to 1 ®- 0.035 0.035 der and equal to one and I 75,000 one-half times the thick- ness through 1 80 ° for plates over 1 inch' in thickness. Flat back through 180" for plates under 1 inch in f 58,000 «T. thickness and equal to thickness of plate through B do to S. } " .035 :035 ( 65,000 180" for plates 1 inch and over in thickness. C Open hearth or Besse- mer steel. To be in accordar ice with specifications for flange and boiler steel adopted by th e Assoc ation of American Steel Manufacturers, revised 1903. Number of Tests — One longitudinal tensile test piece and one bend- ing test piece (transverse for class "A" and class "B" and longitudinal for class "C" boiler plate) shall be cut from each plate as rolled at such points as may be designated by the inspector. The cold-bending test pieces may have their corners rounded to a curve the radius of which is equal to one-fourth the thickness of the plate. Surface Inspection — Boiler plates shall be free' of all slag, foreign substances, brittleness, laminations, hard spots, brick or scale marks, scabs, snakes, or other injurious defects. Shearing — Boiler plates shall not be sheared closer to finished dimen- sions than once the thickness of the plate along each end and one-half the thickness of the plate along -each side. MATERIALS 19 Variation in Thickness — Tolerance — A tolerance of o.oi inch below the ordered gage will be permitted for plates up to and including 100 inches in width, and for plates over 100 inches in width a tolerance of 0.015^ inch will be allowed, measured in each case at 'the thinnest point. Rivet Holes — In no case where boiler plate is subjected to the boiler pressure will punched holes be allowed. All such rivet holes will be drilled, this being done when the plates are in position to insure absolute accuracy. Treatment of Bent and Flanged Sheets — Boiler drum sheets when- ever bent, all flanged sheets, drum heads, headers, nozzles, and man and hand hole plates which are formed from boiler plate shall be formed hot. BOILER RIVETS Rods for Boiler Rivets CHEMICAL AND PHYSICAL REQUIREMENTS Material. Mini- mum tensile strength (pounds per square inch). Mini- mum elonga- tion (per- - cent in 8 inches). Maximum Amount of — ■ Class. P. - S. Bends. 2 A B. ... C Open hearth nickel or carbon steel. Open hearth carbon steel. Commercial steel. 75,000 68.000 23 28 0.04 .04 0.03.5 .035 Cold bend ISO'^about an inner diameter equal to one-half the thickness of the test piece for diameters up to and includ- ing 1 inch, and equal to the thickness for diameters over 1 inch; quench bend ISO" about an inner diameter equal to the thickness of the test piece for diameters up to and including I inch and equal to 1}4 times the thickness for diameters over 1 inch. Cold bend flat back through 180°; quench bend 180° through an inner diameter equal ,to one-half the thick- ness of the -test piece for diam- eters up to and including 1 inch and equal to the thick- ness for diameters over 1 in. 1 Elongation for rounds }4 inch and less in diameter shall be measured in an original length equal to 16 times the diameter of the test piece; for mateS-ial over }.^ inch up to and including 1 inch in diameter, the elongation shall be measured in a length of 8 inches; and for material over l^inch in diameter up to'and including 2 inches in diameter, the required percentage of elim^ticm,. measared in a length of 8 inches, shall be reduced by one for each increase in diameter of H inch or a fraction thereof above inch. 2 Quench test pieces to be heated to a dark cherry red, as seen m. daylight, and plunged into fresh clean water of 80° to 90° F. Surface and Other Defects— The. rods must be true to form, free from seams, hard spots, brittleness, injurious sand or scale marks, and •injurious defects generally. Tensile Test— One tensile test piece shall be taken from each ton or fraction thereof of rods rolled from the same heat. If, however, the rods in one heat are not of the same diameter, then the inspector will take such 20 PRACTICAL MARINE ENGINEERING additional test pieces as he may consider necessary according to tlie num- ber of different sizes of rods in the heat. When practicable, but one piece will be cut from each rod selected for the test. Upsetting Tests— S\\3.\\ stand hammering down cold, longitudinally, to one-half their original length without showing seams or other defects which would tend to produce imperfections in the finished product. COMPLETED BOILER RIVETS Description — Rivets must be true to form, concentric and free from injurious scale, fins, seams, and all other injurious defects. If the ma- terial is found to be very uniform and none of the tests made of a series of lots fails, the inspector may discontinue the tests after he has made enough to satisfy himself that the whole of the material on the order is satisfactory. Dimensions, and Weight of Head and Shank Diam. Greatest Depth I, east Weight Weight per inch of shanic of Diam. of of Diam, of of 10 Rivet Head Head Head heads Inches Inches Inches Inches Pounds Pounds 1-2 15-16 7-18 1-2 0.531- 0.0556 9-16 1 1-2 9-16 0,713 .0704 5-8 1 1-8 9-16 5-8 1,007 .0869 11-16 1 1-4 5-8 11-16 1.372 .1052 Vi 1 5-16 5-8 3-4 1.551 .1251 13-16 1 7-16 11-16 13--16 2.033 . 1470 - 7-8 1 1-2 11-16 7-8 2.258 .1703 15-16 1 5-8 3-4 15-16 2,871 .1956 1 1 3-4 13-16 1 3,584 .2225 1 1-16 1 13-16 13-16 1 1-16 3,910 .2512 1 Jl-8 1 15-16 7-8 1 1-8 4.761 .2816 1 3-16 2 7-8 1 3-16 5.170 .3137 1 1-4 2 1-8 15-16 1 1-4 6.215 .3477 1 5-16 2 1-4 1 1 5-16 7,391 .3833 1 3-8 2 3-8 1 1-16 1 3-8 8,490 .4207 1 7-16 2 1-2 1 1-8 1 7-16 9.941 .4599 1 1-2 2 S-8 1 3-16 1 1-2 11.507 .5006 1 9-16 2,3-4 1 1-4 ' 1 9-16 13,242 .5433 1 5-8 2 7-8 1 5-16 1 5-8 15.146 .5876 1 11-16 3 1 3-8 1 11-16 17.300 .6336 1 3-4 3 1-8 1 7-16 1 3-4 19.485 .6815 Tests — Samples from each lot must stand the following tests with- out fracture, test (o) being applied to one lot and (&) to a second, etc.: (o) Bend double, cold, to a curve of which the inner diameter is equal to the diameter of the rivet. , (6) Bend double, hot, through an angle of l8o degrees flat back. (c) The head to be flattened when hot without cracking at the edges until its diameter is 2J/2 times the diameter of the shank. id) The shanks of sample rivets to be nicked on one side and tjent cold to show the quality of the material. Purpose — Class A materiar shall be used for all rivets where class A plate is used. Class B material may be used with class B boiler plate. MATERIALS 21 Class C material shall be used boiler is not affected, such as — Air ducts. Ash dumps. Ash pans. Ash-pit doors. Blower casings and fans. Boiler casings, including that for watertube boilers. Circulating plates for boilers. Coal and ash buckets. for rivets where the strength of the Fireroom air screens. Furnace doors. Ladders. Oil tanks. Smoke pipes and covers. Platforms and gratings. Tallow and other tanks. Uptakes and uptake doors. Feed and filter, tanks. BOILER BRACING The physical and chemical characteristics of boiler bracing are to be in accordance with the following table : Class. Material. Minimum tensile strength (pounds per square inch). Minimum elastic limit (pounds per square inch). Elongation percent in^- 8 inches. 2 inches. A...'.. 75,000 75,000 60,000 60,000 40,000 40,000 32.000 32,000 23 23 26 26 26 A "Porfring^oppn hearth stpcl 26 B 30 B Forgings. open hearth steel 30 Class. Material. Maximum percentage of^ Bend- ing tests. Open- ing and clos- P. S. mg tests. A 0.04 .04 .04 .04 • 0.04 .04 .04 .04 a b c d • e A B ... e B (o) One test piece cut from each lot of class A shapes foT bracing must stand bending, cold, through an angle of i8o degJ'ees to an inner diameter equal to twice the thickness of the piece tested without showing a fracture on outside of bent portion. "A" Forgings Cold Bend — (6) One bar J^ inch thick, cut from each lot of class A forcings for bracing, must stand cold bending through an angle of i8o degrees to an inner diameter of I inch without showing a fracture on outside of bent portion. "B" Shapes Cpld Bend—(c) One test piece cut from each lot of Class B shapes for bracing must stand bending, cold, through an angle of i8o degrees to an inner diameter equal to once the thickness of the piece tested without showing a fracture on outside of bent portion. '^B" Forgings Cold Bend—(d) One bar J^ inch thick, cut from each lot of class B forgings for bracing, must stand cold bending through an 22 PRACTICAL MARINE ENGINEERING angle of i8o degrees to an inner diameter of 54 inch without showing a fracture on outside of bent portion. Opening and Closing Tests of Shapes— {e) Angles, tee bars, and other shapes for boiler bracing are to be subjected to the following addi- tional tests : A piece cut from i bar in 20 shall be opened out flat while cold without showing cracks or flaws; a piece cut from another bar in the same lot shall be closed down on itself until the two sides touch with- out showing cracks or flaws. Treatment— AW forged material for boiler bracing shall be annealed as a final process. Surface Inspection— AW boiler bracing must be true to form, free from seams, hard spots, brittleness, injurious sand, or scale marks, and injurious defects generally. BOILER TUBES Physical and Chemical Properties — The manufacturers, when order- ing billets or disks from which it is intended to manufacture tubes under these specifications, should give the quality and brand and the tests the material is expected to stand to insure the delivery of proper material. Seamless Tubes — Seamless tubes must be made from solid disks or billets of perfectly homogeneous steel by the process known as cold draw- ing and not by hot drawing with a cold finish, or they may be hot rolle,d. Seamless Tubes — Thicknesses — Seamless bqiler tubes vjill be ordered by outside diameter, and for sizes between i inch and s inches, both in- clusive, the following thicknesses, which have been adopted by the manu- facturers as standards, shall be designated in mils, as may be required : 95 109 120 134 148 i6s 180 203 220 238 Lap-welded Tubes — Lap-welded steel tubes must be made of steel of a perfectly homogeneous quality and of the grade which is found to in- sure the soundest welds. Iron Tubes — Iron tubes must be made of knobbled hammered char- coal iron ; pig iron only (and no scrap) is to be used in the manufacture of the blooms. TESTS Flattening and Opening Tests — A test piece cut from each end of each tube must stand flattening under a press or hammer immediately on being separated from the tube, without showing any defects on the out- side. Of these flattened pieces, 10 percent or more, each cut from a differ- ent tube, must on being opened for inspection show no defects on the inside. Expansion T?sts — The ends of each tube to stand expanding, cold, to one and one-sixth times the original diameter and have a flange turned all around the end of the tube equal in width to. one-eighth of the diame- ter of the tube without showing defects. Pressure Tests — Each seamless tube will be subjected to a hydro- static pressure of 1,500 pounds and each lap-welded tube to 1,000 pounds per square inch without showing signs of weakness or defects. MATERIALS 23 SURFACE INSPECTION AND GAGING Surface Defects — Tubes must be free from all injurious defects. The defects to be particularly avoided in seamless cold-drawn tubes are tears, snakes, checks, slivers, injurious scratches, rings, laps, pits, and sinks; in hot-rolled tubes they are slivers, scratches, seams or laps, and scale pits ; in lap-welded tubes they are defective welds, cracks, blisters, scale pits, and sand marks. Weights — A tolerance of s percent over and 3 percent under the calculated weight will be allowed for individual seamless cold-drawn and lap-welded tubes and 7 percent over and 2 percent under for seamless hot-rolled tubes, assuming that i cubic inch of iron weighs 0.280 pound and I cubic inch of steel 0.283 pound. SPECIAL REQUIREMENTS Annealing — All seamless cold-drawn steel tubes must be annealed, as a final process, in retorts or in an approved furnace in which the flame does not strike the tubes. The amount of scale due to the annealing on the inside of the boiler tube shall be reduced as low as possible. STEEL FORCINGS FOR MACHINERY The respective classes of forgings have the following properties : Maximum Minimum values values. +j Elonga- Cold bend witli- aass Treatment. Material. 0) a a •d tion. out cracking. g i - m tk H > ►J t-i Per- Per- Per- Per- Per- cent cent cent Lbs. Lbs. cent cent HG.. Annealed and. oil tempered. Nickel steel. 0.35 .045 0.04 96.000 65,000 21 18 180 degrees to in- ner diameter of 1 inch. An... Annealed Nickel steel. .35 .045 .04 80,000 50,000 25 21 180 degrees to inner dia. of Ac... Annealed and Carbon steel. .60 .045 .04 80,000 50.000 25 21 1 incli. B Annealed,, oil -Carbon .60 .045 .04 75.000 40.000 22 1« 180 degrees to spec- tempering steel. inner dia. of 1 ial optional. incli. B.... Annealed. . . . Carbon steel. .35 .04 .04 60,000 30.000 30 25 180 degrees to inner dia. of § ' inch. c .07 .07 50.000 18 15 1 steel. Nickel steel shall contain not less than 3 percent nickel. Class C forgings are not tested unless there are reasons to doubt that they are of p, quality suitable for the purpose for which they are intended. Connecting and Piston Rods and Valve Stems— HG. Thrusts, Line and Propeller Shafting— An or Ac. Crank Shafts— An or Ac. General Treatment of Forgings— h\\ forgings are annealed as a final process, unless otherwise directed, AH tempered forgings, if forged solid, 24 PRACTICAL MARINE ENGINEERING and if tnore than g inches in diameter in any part of their lengths, not including collars, palms, or flanges, are bored through axially before tem- pering, the bore being of sufficient size fo enable the manufacturer to get the requisite tempering effect. Forgings, such as crank shafts, thrust shafts, etc., may, previous to tempering, be machined in a manner best calculated to insure that the tempering -effect reaches the desired portions. STEEL CASTINGS CHEMICAL AND PHYSICAL PROPERTIES Chemical Composi- tion. Physical requirements. Grade. Not over Minimum tensile Minimum Minimum elonga- Minimum reduction Bending test; cold P. S. strength. yield point. tion. of area. bend (not less than). Pounds i}er Pounds per Percent square inch. square inch. in 2 inches. Percent F U.U6 .05 85,000 53,000 f45 percent 22 f 30' ' 120 degrees about an inner dia. of 1 inch. A .Ub .06 1 80,000 of tensile 17 20 90 degrees about an D....;. .05 .07 / [Maximum strength obtained. 'inner dia. of 1 inch. B .06 .05 J 80,000. ..do 22 25 120 degrees about an E .OH .07 fMinimum inner dia. of 1 inch. 1 60,000. C .OB 07 NoTB. — Class F castings shall contain 3.25 to 3.75 percent of nickel. U. S. INSPECTION REQUIREMENTS FOR BOILER PLATE Phosphorus: Not more than .04 of i percent. Sulphur : Not more than .04 of i percent. PHYSICAL PROPERTIES, STEEL PLATES When the tensile strength is less than 65,000 pounds, the minimum elongation shall be 25 percent for plates three-fourths inch and under in thickness, and 22 percent for plates over three- fourths incfi in thickness. The minimum reduction of area shall be 48 percent for plates three-fourths inch and under in thick- ness, and 42 percent for plates over three-fourths inch in thick- ness. The quench bend specimen shall bend through 180 degrees around a curve, the radius of which is three-fourths the thickness of the specimen. When the tensile strength is 65,000 pounds or greater, the minimum elongation shall be- 22 percent for plates three-fourths inch and under in thickness, and 20 percent for plates over three-fourths inch in thickness. The minimum re- duction of area shall be 45 percent for plates one-half inch and MATERIALS - 25 under in thickness, 40 percent for plates over one-half inch up to and including i inch in thickness, and 36 percent for plates over I inch in thickness. The quench bend specimen shall bend through 180 degrees around a curve the radius of which is one and one-half times the thickness of the specimen, AMERICAN BOILER MAKERS' ASSOCIATION REQUIREMENTS Phosphorus : Not over .04 percent. Sulphur : Not over .03 percent. Tensile Strength : 55,000 to 65,000 pounds. •Elongation (^ inch and under) : 20 percent in 8 inches. Elongation (% inch to % inch) : 22 percent in 8 inches. Elongation (% inch and over) : 25 percent in 8 inches. Cold Bending. — For plates Yz inch thick and under, specimen must bend back on itself without fracture. For plates over J4 inch thick, specimen must bend 180 degrees around a mandril one and one-half times thickness of plate without fracture. BRITISH BOARD OF TRADE REQUIREMENTS Tensile Strength of Plates Not Exposed to Flame: 60,480 to 71,680 pounds per square inch. Tensile Strength of Plates Exposed to Flame: 58,240 to 67,200 pounds per square inch. Elongation : From 18 to 25 percent in 10 inches. STANDARD SPECIFICATIONS ADOPTED BY THE AS- SOCIATION OF AMERICAN STEEL MANUFACTURERS Special Open Hearth Plate and Rivet Steel. Steel shall be of four grades, as follows : Extra Soft, Fire- bpx, Flange or Boiler and Boiler Rivet Steel. Extra Soft, Firebox 'and Boiler Rivet Steel: Maximum phosphorus, .04 percent ; maximum sulphur, .04 percent. Flange or Boiler Steel : Maximum phosphorus, ..06 percent ; maximum sulphur, .04 percent. > PHYSICAL PROPERTIES. Extra Soft and Boiler Rivet Steel. Ultimate Strength : 45,000 to 55,000 pounds per square inch. 26 PRACTICAL MARINE ENGINEERING Elastic Limit : Not less than one-half the ultimate strength Elongation: 28 percent. Cold and Quench Test: Bends 180 degrees flat on itself without fracture on outside of bent portion. Firebox Steel. Ultimate Strength : 52,000 to 62,000 pounds per square inch. Elastic Limit : Not less than one-half the ultimate strength. Elongation : 26 percent. Cold and Quench Test: Bends 180 degrees flat on itself without fracture on outside of bent portion. Flange or Boiler Steel. Ultimate Strength : 52,000 to 62,000 pounds per square inch. Elastic Limit : Not less than one-half the ultinjate strength. Elongation: 25 percent. Cold and Quench Test: Bends 180 degrees flat on itself without fracture on outside of bent portion. (13) Special Properties of Steel. Mild or low carbon steel may be welded, forged, flanged, rolled and cast. It can not be tempered or hardened with a proportion of catbon lower than about % of I percent. High carbon steel can be welded only imperfectly and if very high in carbon not at all. It can be forged with care, and cast into forms as desired. It can be tempered or hardened by heating to a full yellow and quenching iij cold water or by other means, and then drawing the temper to the point desired. Mild steel should not be worked under the hammer or flang- ing press at a low or "blue" heat, as such working is found in many cases to leave the metal brittle and unreliable. Steel in order to^ weld satisfactorily should have a low proportion qf sulphur, and special care is required in- the operation, because the range of temperature through which the metal is plastic and fit for welding is less than with wrought iron. In the operation of tempering, the steel after quenching i very hard and brittle. In order to give to the metal the prop- erties desired, the temper is drawn down by heating it up to a certain temperature, and then quenching again, or, better still, allowing it to cool gradually, provided the temperature does not rise above the limiting value suitable for the purpose desired. MATERIALS 27 If the reheating is done in a bath of oil the conditions may be kept under good control and the final cooling may be slow. If the reheating is in or over a fire the control is lacking and the piece must be quenched as soon as the proper temperature is reached. This is usually determined by the color of the oxide or scale which forms on a brightened surface of the metal. The following table shows the temperatures, corresponding colors, and uses for which the various tempers are suited : 430 degrees— Faint yellow. ) HarHe^t anH Wpp.np great elasticity or toughness, or for 600 degrees — Dark blue. J working very soft materials. (14) Special Steel. In the common grades of steel the valuable properties are due to the presence of carbon modified in some degree by other ingredients as already described. There are other substances which by uniting with iron in small propor- tions are able to give to the combination increased strength or hardness or other valuable properties. There are thus various special steels in which the properties may be due to the presence of both carbon and other ingredients, or due chiefly to special in- gredients other than carbon. Of these special steels it is desirable to note the following : Nickel steel, containing somewhere about 3 percent of nickel and varying amounts of carbon, is found to have increased strength and toughness as compared with ordinary steel. Nickel ' steel is most extensively used for armor plate, though to a large extent it has been employed in Government work for crank, pro- peller and other shafting and for boiler plates. For the former purposes it has given excellent satisfaction, but for the latter use difficulty has been met with in obtaining plates free from sur- face defects. Chrome steel, containing from .5 to 1.5 or 2 percent of chro- mium may be made excessively hard, but it is not always reliable, and is not regarded with general favor. Tungsten steel or mushet steel is a steel containing carbon and tungsten, the latter in proportions as high as 8 to 10 percent. 28 PRACTICAL MARINE ENGINEERING This steel must be forged with care and is excessively hard. The hardness is not increased by tempering, but is naturally acquired as the metal cools. Hence it is said to be self-hardening. Some specimens contain also small amounts of manganese and silver; Its chief use is for lathe and planer or other cutting and shearing tools where excessive hardness is required. Vanadium steel is steel containing a very small percentage of vanadium. The action of the vanadium is very powerful, and therefore it is only used in small quantities. Vanadium steels may be grouped in three classes: (i) Those containing vanadium alone, in which the tensile strength, elastic limit and resistance to shock increase up to i percent vana- dium content. (2) Those with vanadium and nickel, in which the vanadium causes the nickel steel to become more homogene- ous and decreases fragility which" nickel tends to produce. (3) Those with vanadium and chromium, in which the vanadium re- duces the hardness due to the chromium and facilitates machin- ing. . (15) Uses of Steel in Marine Construction. In modern practice mild or structural steel is used entirely in the construc- tion of ships. The same general class of material is used for all parts of boilers, though the tubes are still sometimes made of wrought iron. Cast steel is used for various parts of engines such as pis- tons, crosshead blocks, columns, bed plates, bearing pedestals and caps, propeller blades, and for many small pieces and fittings. Pistons are made almost exclusively of cast steel. For most of the other items mentioned cast iron is still used, probably to a larger extent than cast steel, especially where the castings . are large and complicated in form, as with columns and bed plates. Forged steel is used for columns, piston rods, connecting rods, crank and line shafting, and for many other smaller and minor parts. Sec. 8. LEAD Lead is a very soft, dense metal, grayish in color after ex- posure to the air, but of a bright silvery lustre when freshly cut. Commercial lead often contains small amounts of iron, copper, silver and antimony, making it harder than the pure metal. It is very malleable and plastic. In engineering, lead is chiefly of MATRRtALS 29 value as an ingredient of bearing metals and other special alloys. Lead piping is also used to some extent for water suction and delivery pipes where the pressure is only moderate, and where the readiness with which it may be bent and fitted adapts it for use in contracted places. Sec. 9. TIN Tin is a soft, white, lustrous metal with great malleability. Commercial tin usually contains small portions of many other substances, such as lead, iron, copper, arsenic, antimony and bismuth. It is largely used as an alloy in the various bronzes and other special metals. Tin resists, corrosion well and in con- sequence is often used as a coating for condenser tubes. It is also used for coating iron plates, the product being the so-called "tin plate" of commerce. It melts at about 450 degrees, which corresponds to a steam pressure of about 400 pounds per square inch. Due to this low melting point tin is often used as the com- position for safety plugs in boilers. Sec. ip. ZINC Zinc, or "spelter," as it is often called commercially, is a brittle and moderately hard white metal with a very crystalline fracture. The impurities most commonly found in zinc are iron, lead and arsenic. It is used chiefly as an alloy in the various brasses, bronzes, etc., and as a coating for iron and steel plates, rods, etc. The process of applying zinc for such a coating is called "galvanizing," and the product "galvanized" iron or steel. Electricity, however, is not used in the process, the articles, after being well cleaned, being simply dipped in a tank of melted zinc and then withdrawn. Slabs of zinc are also used in marine boilers to prevent corrosion. Sec. II. ALLOYS A mixture of two or more metals is called an alloy. The properties of an alloy are often surprisingly different from those of its ingredients. The melting point is sometimes lower than that of any of the ingredients, while the strength, elastic limit and hardness are often higher than for any of them. Mixtures of foppen and zinc are called brass. Mixtures of copper and .tin, or copper, tin and zinc, with sometimes other sub- Stances in small proportion, form gun metals, compositions and io PRACTICAL MARINE ENGINEERING bronzes. These terms are, however, rather loosely employed. Various mixtures of two or more.of the metals — copper, tin, zinc, lead, antimony — form the various bearing metals. Brass and composition are used for piping and pipe-fitting ; globe, gate, check and safety valves ; condenser tubes and shells ; sleeves for tail shafts, and for a great number of small fittings^ and attachments for which the metal may be suited. The bronzes are employed for many of the uses of brass where more hardness, strength or rigidity are required. They are used with especial success as a material for propeller blades. The white metals, supported or backed by some other metal, such as brass, cast iron or cast steel, to give the necessary strength, are now very largely used for bearing surfaces. PROPORTIONS OF INGREDIENTS FOR VARIOUS ALLOYS In the following proportions the numbers after the ingredi- ents denote the number of parts in loo of the mixture. They represent either the usual proportions, or the results of special analyses of samples, and have been collected from various sources. The alloys are arranged in the alphabetical order of their names to facilitate ready reference: Admiralty Bronze. — Copper 87, tin 8, zinc 5. Aluminum Brass. — Copper 63, zinc 34, aluminum 3. Aluminum Bronze. — Copper 89 to 98, aluminum 11 to 2. Anti-Friction, A. — Zinc i, iron .65, lead 78.75, antimony 19.6. Anti-Friction, B. — Copper 1.6, tin 98.13, iron trace. Anti-Friction, C. — Copper 3.8, tin 78.4, lead 6, antimony I1.8. Babbitt (Light). — Copper 1.8, tin 89.3, antimony 8.9. Babbitt (Heavy). — Copper ^.y, tin 88.9, antimony 7.4. Brass, XJommon Yellow. — Copper 65.3, zinc 32.7, lead 2. Brazing Metal. — Copper 84, zinc 16.^ Brazing Solder. — Copper 50, zinc 50. Bush Metal. — Copper 80, tin 5, zinc 10, lead 5. Delta Metal. — Copper 50 to 60, tin i to 2, zinc 34 to 44, iron 2 to 4. Deoxidized Bronze. — ^Copper 82, tin 12.46, zinc 3.23, iron .10, lead 2.14, phosphorus trace, silver .07. Gun Metal. — Copper 89, tin 8.25, zinc 2,75. MATERIALS 31 Magnolia. — Tin trace, zinc trace, iron trace, lead 83.55, antimony 16.45. Manganese Bronze. — Copper 88.64, tin 8.7, zinc 1.57, iron .72, lead .30. Muntz Metal. — Copper 60, zinc 40. Navy Brass. — Copper 62, tin i, zinc 37. Navy Composition. — Copper 88, tin 10, zinc 2. Navy Journal Boxes. — Copper 82.8, tin 13.8, zinc 3.4. Parsons White Metal.— Copper 1.68, tin 72.9, zinc 22.9, lead 1.68, antimony .84. Phosphor Bronze. — Copper 90 to 92, phosphide of tin 10 to 8. Steam Metal.— Copper 85, tin 6.5, zinc 4.5, lead 4.25. Tobin Bronze. — Copper 59 to 61, tin i to 2, zinc 37 to 38, iron .1 to .2, antimony .30 to .35. White Metal. — Lead 88, antimony 12. Proportions of ingredients and physical characteristics of non- ferrous metals as required by the U. S. Navy, also purposes for which suitable : Admiralty Metal — ^Composition A. Copper, not less than 70 percent. Tin, not less than i percent. Iron, not more than .06 percent. Lead, not more than .075 percent. Zinc, remainder. Suitable for condenser tubes, distiller tubes, feed water heater tubes, evaporator tubes. Brazing Metal — Composition F. Copper, 84 to 86 percent. Iron, not more than .06 percent. Lead, not more than .3 percent. Zinc, remainder. Suitable for all flanges for copper pipe and other fittings that are to be brazed. Commercial Brass Castittgs — Composition B-c. Copper, 62 percefit. Zinc, not less than 30 percent. Iron, not more than 2 percent. Lead, not more than 3 percent. Tin and nickel, remainder. Suitable for name and number plates, cases for instruments, oil cups, distribution boxes. Commercial brass for rods, bars, shapes, sheets, plates and piping. Rods, Bars and Shapes— B-c. Copper, 60 to 63 percent. Tin, not more than 0.5 percent. 33 PRACTICAL MARINE ENGtMBERlNG Zinc, 38 to 35^ percent. Lead, not more than 3 percent. Iron, .06 percent. Sheets, Plates and Piping — B-p. Copper, 60 to 70 percent. Zinc, 40 to 30 percent. Lead, not more than .5 percent. Iron, not more than .06 percent. Suitable for (brass sheet) liners, trim, etc.; (brass pipe), hand rails, oil' tubes and water pipes; (brass rod), for trim and purposes where ijtrength and incorrodibility are not required. Copper sheets, plates, rods, bars and shapes. Non-ferrous Metal Cu-r. Copper, not less than 99.5 percent. Tensile strength 30,000 pounds per square inch. Elastic limit 25 percent in 2 inches. Suitable for copper pipe and tubing. Gun Metal, Cast, or Composition G. Copper, 87 to 89 percent. Tin, 9 to II percent. Zinc, I to 2 percent. Iron, not more than .06 percent. Lead, not more than .2 percent. Minimum tensile strength 30,000 pounds per square inch. Minimum elastic limit 15,000 pounds per square inch. Minimum elongation in 2 inches 15 percent. The material is suitable for the following purposes : All composition valves 4 inches in diameter and above ; expansion joints, flanged pipe fitting, gear wheels, bolts and nuts, miscellaneous brass castings, all parts where strength is required of brass castings or where subjected to salt water, and for all purposes where no other alloy is specified. Composition valves. — Safety and relief, feed check and stop, surface blow, drain, air, and water cocks, main stop, throttle, reducing, sea, safety, sluice, and manifolds at pumps. Heads, shapes and water chests for condensers, distillers, feed water heaters, and oil coolers." Pumps. — Air pump casing, valve seats, buckets, main circulating, water cylinders, valve boxes, water pistons, stuffing boxes, followers, glands, in general the water end of pumps complete except as specified. Stuffing boxes. — Glands, bushings for iron or steel toxes. Blowers. — Bearing boxes. Journal boxes. — Distance pieces. Miscellaneous.— Grease extractors; steam strainers, separators, cas- ing for stern tube and propeller shafts, propeller hub caps. Bearings. — Main, stern tube, strut, and spring. Spring bearings. — Glands and baffles. Journal Bronze or Composition H. Copper, 82 to 84 percent. MATERIALS 3.1 Tin, 12.5 to 14.5 percent. Zinc, 2.5 to 4.5 percent. Iron, not more than .06 percent. Lead, not more than i.o percent. ^ The material is suitable for the following purposes: Bearings, jour- nal boxes, bushings, and sleeves, slides, slippers, guide gibs, wedges on watertight doors, and all parts subject to considerable wear, for recipro- cating engines in valve stem crosshead bottom brass, link block gibs and suspension link brasses. Manganese Bronze Ingots, Composition Mn-i. Copper — Maximum, £0 percent. Minimum, 55 percent. Zinc — Maximum, 42 percent. Minimum, 38 percent. Tin — Maximum, 1.5 percent. Minimum, 0.0 percent. Manganese — Maximum, 3.5 percent. Minimum, 0.0 percent. Aluminum — Maximum, 1.5 percent. Minimum, 0.0 percent. Iron — Maximum, 2.0 percent. Minimum, 0.0 percent. Lead — Maximum, 0.2 percent. Minimum, 0.0 percent. The sum of the specified elements must equal 99.9 percent. This material is suitable for the following purposes : Propeller hubs, propeller blades, engine framing, composition castings requiring great strength, such as main gearing in steering engine; worm wheels in windlass or turning gear for turrets. Manganese Bronze, Cast or Composition, Mn-c. Minimum tensile strength, pounds per square inch, 65,000. Minimum elongation in 2 inches, 20 percent. Copper, ss to 60 percent. Zinc, 42 to 38 percent. Till, i.s to o percent. Manganese, 3.5 to o percent. Aluminum, 1.5 to o percent. Iron, o to 2 percent. Lead, o to .2 percent. The sum gf the specified elements to equal 99.8 percent. GRADES. Oiily the best grades of virgin materials shall be used in the manu- facture of Grade A manganese bronze. Scrap resulting from the manu- facture of articles of the same composition as specified herein may be used, however, but heads, gates, and risers shall not be used. For Grade B manganese bronze, compliance with physical and chemical requirements will be reqtiired, but the materials used shall be left to the discretion of the manufacturer. 34 PRACTICAL MARINE ENGINEERING Grade A shall be used for propeller blades, propeller hubs, engine framing, and in general for all castings requiring igreat strength and piirity of material. Grade B material is required for all manganese bronze cast- ings where Qrade A is not specifically designated. Manganese Bronze, Rolled, or Composition Mn-r. Minimum tensile strength, i inch and below, 72,000 pounds; above I inch, 70,000 pounds per square inch. Minimum elastic limit, i inch and below, 36,000 pounds; above i inch, 3S,ooo pounds per square inch. Minimum elongation, 30 percent in 2 inches. Copper, 57 to 60 percent. Tin, .5 to l.S percent. Zinc, 40 to 27 percent. Iron, .8 to 2 percent. Lead, .2 percent. Manganese, .3 percent. SUITABLE FOR Rolled round rods requiring great strength where subject to cor- rosion and salt water — Valve stems, etc. Propeller blade bolts, air pump and condenser bolts, and parts re- quiring strength and incorrodibility. Muntz Metal, Cast, or Composition D-c. Copper, 59 to 62 percerit. Zinc, 38 to 41 percent. Lead, not more than 0.6 percent. Muntz Metal Sheets, Plates, Rods, Bars and Shapes, or Non-ferrous Metal D-r. Copper, 59 to 62 percent. Zinc, 38 to 42 percent. Lead, not more than 0.6 percent. Tensile strength, 40,000 pounds per square inch. Elastic limit, 20,000 pounds per square inch. Elongation, 25 percent in 2 inches. The material is suitable for the following purposes : Bolts and nuts not subject to action of salt water. Monel Metal Cast, or Composition Mo-c. Minimum tensile strength, 65,000 per square inch. Minimum elastic limit, 32,50^ per square inch. Minimum elongation in 2 inches, 25 percent. Nickel, not less than 60 percent. Iron, not more than 6.5 percent. Aluminum, 0.5 percent. Copper, remainder. The material is suitable for the following purposes : Valve fittings, plumbing fittings, boat fittings, propellers, propeller hubs, blades, engine MATERIALS 35 framing, pump liners, valve seats, shaft nuts and caps, and cotjiposition castings requiring great strength/ Rolled Monel Metal, Sheets, Plates, Rods, Bars, Etc., or Composi- tion Mo-r. Copper. Lead (maximum) Percent ' . . . Rem. ... 0.0 Iron (maximum) Nickd (minimum) Percent .... 3.5 60.0 5 Thickness. Ultimate tensile strength per square Yield point per square inch. Elonga- tion in 2 inches. } in#»li anA hi»lnw Pounds 84,000 80,000 75,000 Pounds 47,000 45,000 40,000 Percent 25 28 32 The material is suitable for the following purposes : Rolled rounds used principally for propeller blade bolts, air pump and condenser bolts, and parts requiring strength and incorrodibility, and pump rods. Naval Brass, Cast, or Composition N-c. Copper, 6o to 63 percent. Tin, .05 to 1.5 percent. Iron, .06 percent (maximum). Lead, .3 percent (maximum). Zinc, remainder. Normal composition copper 62 percent, tin I percent, zins 37 percent. The material is suitable for the following purposes: Hatch frames, hatch-cover frames, door frames, scuttle frames ; fittings for mess tables and benches ; skylight and chest hinges and fittings ; all joiner work fittings (except hardware) ; rail and ladder stanchions; brackets, clips, etc., for stowage purposes ; fittings for canopy frames ; all brass valves and fittings of ventilation system (except working parts); belaying pins, tarpaulin hooks, brass hatch and door fittings, brass pipe flanges. Valve handwheels, hand-rail fittings, ornamental and miscellaneous castings, and valves in water chests of condensers. Phosphor Bronse, Cast, Composition P-c. Minimum tensile strength, Grade i, 4S,ooo; Grade 2, 30,000 pounds per square inch,^ Minimum percentage elongation in 2 inches, Grade i, 20* Grade 2, 15. -' - - Phos- Iron Lead phorus , Grade. Copper. Tin. Zinc. maxi- mum. maxi-' mum. maxi- mum. Percent Percent Percent Percent Percent Percent 1 85-90 85-90 6-11 6-11 Not over 4.. Remainder 0.06 0.1 0.2 1.00 0,5 2 0.5 The material is suitable for the following purposes : Fittings exposed to the action of salt water, for gears, driving and 36 PRACTICAL MARINE ENGINEERING main nuts of steering gears and castings for other parts which require strength combined with good bearing qualities and incorrodibility. Grade i should not be specified where Grade 2 may answer. Phosphor Bronze, Rolled or Drawn — ^^Composition P-r. u u III S boo' Si fe 1^ m ft •3 -a? •?.§.a d (U las gas a ■S.Hs ats-r a" Is ft §• .,: u a N Percent (d) ? 3 a a u M ? 1 l-I i?' a*" 1 120,000 80,000 60,000 (0)90,000 (6)60,000 (<;) 45,000 Percent 25 Percent 94-96 Percent 5-4 Percent (d) Percent (d) Percent 0.10 2' 50,000 25,000 25 85-95 10-5 4 0.06 0.2 .15 (a) For diameters less than 1-8' inch. (6) For diameters 1-8 inch to 1-2 inch, inclusive. (c) For diameters over J inch. (,d) The total of these three impurities not to exceed 0.10 percent. The material is suitable for the following purposes: Grade i — For rods, pins, spring wire, etc. Grade 2 — Pump rods, valve stems, objects exposed to salt water. Rolled Naval Brass, Sheets, Plates, Rods, Bars and Shapes, or Com- position N-r. Copper. Tin. Zinc. * Iron, max. L ead, max. Percent 59-63 Percent 0.5-1.5 Percent Rem. Percent 0.06 Percent 0.2 Thickness. Tensile strength. Elastic limit. Elonga- tion in 8 inches. Elonga- tion in 2 inches. Bend 120O cold. Pounds per Square inch 60,000 58,000 54,000 Pounds per Square inch 27,000 26,000 25,000 Percent 25 28 2S Percent 35 40 40 equals thick- Over 1 inch , . . ness. The material is suitable for the following, purposes : Bolts, studs, nuts, and turnbuckles, especially if subject to corrosion or salt water, rolled rounds, used principally for propeller blade bolts, air pump and condenser Bolts and parts requiring strength and incorrodibility, and pump rods, tube sheets, supporting plates, and shafts for valves in water heads. Valve Bronze, or Composition M. Copper (minimum). Tin (minimum). Zinc. Iron (maximum). Lead (maximum). Percent 87 Percent 7 Percent Remdr. Percent 0.06 Percent 1 The material is suitable for the following purposes: Valves below 4 inches for steam and general purposes for which the material is not MATERIALS . 37 otherwise specified, manifolds and cocks, relief valves, composition lug sockets, and pad eyes not requiring special strength, hose couplings and fittings. Sec. 12. THE TESTING OF METALS [i] Different Kinds of Tests Metals may be tested for strength in various ways — in ten- sion, by pulling apart a test piece of specified pattern and size ; in compression, by crushing a piece of suitable dimensions ; in cross breaking, by supporting a bar at two points and breaking or bend- ing it in the testing machine by a load applied at an intermediate point; in torsion, by twisting apart a bar in a machine especially designed for the purpose ; in direct shearing, by breaking a riveted or pin joint connection in the usual machine ; for impact or shock, by letting a weight drop through a certain height and by its blow develop suddenly the stress in the material. [2] Explanation of Terms Used Ultimate Strengths — The ultimate strength of a test piece is the load required to produce fracture, reduced to a square inch of original section ; or, in other words, the ultimate or highest load divided by the original area. Thus if the area of the cross section of a test piece is .42 square inch and the load producing fracture is 28,400 pounds, the ultimate strength equals 28,400 -=-• .42 = 67,620 pounds per square inch. Elastic Limit. — The elastic limit is the smallest load, reduced to one square inch of area, which will produce a permanent set or distortion of the material. Thus in a tension test if the cross section is .68 square inch and a permanent elongation or set is just produced by a load of 27,600 pounds, the elastic limit is 27,600 -^- .68 = 40,600. Elongation. — A certain length being marked oflf on the test piece as described in. [3], [4], the percentage of elongation is found by dividing the actual extension of the length just before raipture by the original length, and reducing to percent. Thus if a length of 8 inches is marked off on the test piece and if the length between the same marks at fracture is 10.2 inches, the actual elongation is 2.2 inches and the pe^rcentage elongation is 220 -^ 8 = 27.5 percent. When a- test piece is first pvit under load the elongation is distributed nearly uniformly over its length.' This continues until the piece begins to neck down near the point of 38 PRACTICAL MARINE ENGINEERING final fracture. Nearly all of the remaining elongation is re- stricted to the immediate vicinity of this point. Hence the per- .centage elongation with short length of test piece may be much greater than with a long piece. A few years ago, for example, when test pieces 2 inches long were not uncommon, the actual elongation might be nearly i inch, and thus percentage elongations approaching 50 percent were found. In modern practice the length of a test piece is usually 8 inches and values of the percent- age elongation over 30 percent, even with vastly superior material, are rarely met with. In reporting elongation the length used should always be stated. Reduction of Area. — The percentage reduction of area is found by subtracting the final area of the section at the point of fracture from the original area at the same point, dividing the difference by the latter, and reducing to percent. Thus if the original area is .68 square inch and the final area is .36 square inch, the actual reduction is .68 — .36 = .32 square inch, and the percentage reduction is 3,200 -^ 68 =; 47.5 percent. [3] Test Pieces for Iron In modem practice the form of test pieces for iron is usually the same as for steel, and as described in [4] . The form of test piece fpr wrought iron plate prescribed by the United States Board of Supervising Inspectors of Steam Vessels is, however, some- what different, and is illustrated in Fig. i. If the plate is 5-16 inch thick or less, the width at the reduced section must be one inch. If the plate is over 5-16 inch in thickness, the width of the piece- must be reduced so that the cross sectional area at the re- duced section shall be about .4 square inch, but it must not be greater than .45 square inch nor less than .35 square inch. Fig. 1. Test Piece for Iron Plate [4] Test Pieces for Steel and Other Materials Fig. 2 shows the form of test piece for tension prescribed by the Navy Department for tests of steel plate for naval uses. MATERIALS 39 9.0 X J' r 8 ^ >- - 16V. 20" Fig. 2. Test Piece for Steel Fig. 3 shows the form prescribed by the Association of American Steel Manufacturers, and adopted by the United States Board of Supervising Inspectors of Steam Vessels. The test piece for plates is cut from a "coupon," as it is called, left on one corner of the plate as shown at A, Fig. 4. The United States law requires further that : T CM •I. X^ f*KAOius ^ / h tf — J \ gr- <•—- — 3T.6 <* — 3T.6= »f Fig. 3. Test Piece for Steel - "Every iron or steel plate intended for the construction of boilers to be used on steam vessels shall be stamped by the manu- facturer in the following manner : At the diagonal corners, at a Fig. 4. Plate with Coupon distance of about 4 inches from the edges and at or near the center of the plate, with the name of the manufacturer, the place where manufactured, and the number of pounds tensile strain it will bear to the sectional square inch." Fig: 5 shows the usual round form of test piece for all ma- terial except plates. 40 PRACTICAL MARIME ENGINEERING o oo oo rvi-IM OO o oo o OOCO o o © §f i-H •-io ^ (NO (N lO rn" vr o oo O om IN oonH lO(N O IN-*0 oooo CO 1^ u M CO o ooo >o CXJOO o OtD g > OO »o CO .^■oo o CO I o o CD r-l IVtO ooooo 0(N CO l-t < W h4 i^ W M w w o w t-H {H w O rt Ah & O < > a pq a" "a M rn o ooco C<1 (N ?^ ^■* CO OOtO "-I (N(N CO 1> o ,co ■00 C5 o CO ■* CO'* 03 lOCD O C 1-1 CO OiCO o u i_r to ri 15 tn •>i i-> W o. o *j ■ o« ^'\ O I 1 COO H to o "S e_o u 0*00 « CO -3 00 0° o o CO y Ct3 +j to O (U t\i o ^; w s M tn ^; M I-l ooooo ooooo o_o_^o_^oo ITS »0 »0 CDO (Ncoiraooira I I I I T' OOOOO OOOOO ooooo OO oo oo o o o I I I oo o oo o oo o oo o CD-* CO oo oo oo o o o §^ to oo i d, +.0 go 05 O -rt O Ss ■°- o ^-o (No i°-. CO r4 S w I— I s +-> : Sc3:S2Si •a^-^ i o o O OJ jr* tn O u m a a a o ci *iu MATERIALS 41 ::jp®C'CZ U---8"— Fig. 5. Round Test Piece. [S] Bending, Quenching and Hammer Tests The nature of these tests has already been described in. Sec. 5. (II). (12). Fig. 6. Bending Test Fig. 8. Angle Test Fig. 6 illustrates a cold bending test on a piece of steel plate. A drift test is also sometimes required. This is illustrated in Fig. 7, and consists in driving taper drifts of continually increasing size into a punched or drilled hole until the ^ameter is increased to at least twice its original size. The metal must stand this test with- out sign of fracture about the edges of the hole. T j I 1 _L o ■mm^i^mmhmmm Fig. 7. Drift Test Bending tests for angle and Tee irons, as referred to in Sec. 5, (12), are also illustrated in Fig. 8. 42 PRACTICAL MARINE ENGINEERING QUESTIONS Principal Materials of Engineering Construction PAGE What are the chief properties and uses of aluminum? i What are the chief properties and uses of antimony?/ . i What are the chief properties and uses of bismuth? 2 What are the chief properties and uses of copper? ^ 2 How does heat affect the tensile strength of copper? 2 Describe the operation of brazing 2 What is meant by burning copper? 2 What are the chief properties and uses of nickel? 3 What are the properties of vanadium? 3 What is cast iron? 4 What are gray, white and mottled irons? 5 What is meant by combined and by graphitic carbon? 5 What is the influence of silicon on cast iron? 6 What is a chilled cast iron? 6 What is the influence of sulphur on cast iron? 7 What is the influence of manganese on cast iron? 7 What is the influence of chromium on cast iron? 8 What is the shrinkage of cast iron? 8 On what is the hardness of cast iron chiefly dependent? 8 On what is the strength of cast iron chiefly dependent? 8 What are the chief uses of cast iron in marine engineering? .■ • • • ^ What chief points are to be kept in mind in the inspection of castings? 9 What is malleable iron and-how is it made? 9 What are its properties and uses in marine engineering? 10 What is wrought iron and how is it made? ^. u What is the effect of sulphur on wrought iron? 11 What is the effect of manganese on wrought iron? 1 1 What is the effect of phosphorus on wrought iron? 12 What special properties has wrought iron? 12 Describe the operation of welding. 12 What are its chief uses in marine engineering? 12 What is steel? , 13 Describe briefly the Bessemer and open hearth processes 14 Compare the two products IS What is the influence of sulphur on steel? 16 What is the influence of phosphorus on steel? 16 What is the influence of silicon on steel? - 16 What is the influence of manganese on steel? - 16 What is semi steel? 16 What are the leading mechanical properties of steel? 17 What special properties has steel? 26 Describe the operation of tempering 26 What is nickel steel? 27 What is chrome steel? 27 What is vanadium steel? ! . . 28 What is tungsten steel? 23 What are the chief uses of steel in marine engineering? 28 What are the chief properties and uses of lead? 28 What are the chief properties and uses of tin? 29 What are the chief properties and uses of zinc? 29 What is an alloy? • , . . 29 " What are the proportions of some common alloys? 30 To what tests are metals subjected? 37 What is meant by the terms ultimate strength, clastic limit, elongation, reduction of area? 37 What forms of test pieces are employed, and how are the various tests carried out? 39 . CHAPTER 11 Fuels Sec. 13. COAL [v] Composition and General Properties The principal fuel for engineering purposes is coal. It con- sists of the following chief substances. (A) Uncrystallised Carbon. (B) Volatile Hydrocarbons. Hydrocarbons are chemical substances formed of carbon and hydrogen in certain proportions. They often become partially oxidized* by the union of part of their hydrogen with oxygen, in the same proportion as in water. Upon the application of heat to the coal they escape in the form of gas, and are hence said to be volatile. (C) Nitrogen and Oxygen. These gases, the constituents of air, are also found, the latter in addition to this amount joined to the hydrogen "as above referred to. (D) Sulphur. This is found in small amounts, chiefly as a part of the mineral known as iron pyrites^. The proportion of sulphur is rarely above three percent and usually much less. (E) Ash. This consists of the earthy and incombustible sub- stances present as impurities in the coal. Coal may be roughly divided into two chief varieties. An- thracite and Bituminous, with intermediate grades. Semi-anthra- cite and Semi-bituminous, occupying the general middle ground between the two. In the present chapter the terms anthracite and bituminous will be frequently used as denoting the general divi- sion into the two chief varieties, as above noted. Anthracite coal is sold commercially in hard, compact lumps, showing a shiny, smooth surface when first broken. Bituminous coal is relatively soft and is sold commercially in lumps of irregu- ♦ Oxidized means united with oxygen. firon pyrites is a mineral formed of iron and sulphur in the pro- portion of 46.7 parts of iron to 53.3 of sulphur. 44 PRACTICAL MARINE ENGINEERING lar size, It crumbles easily, showing often a rather dull surface when broken. In anthracite coal the proportion of volatile matter varies from 3 to lo percent; in semi-anthracite and semi-bituminous, from lo to 20 percent, and in bituminous, .from 20 to 50 percent. The amount of ash in good coal should not exceed from 8 to 10 percent, while occasionally it falls as low as 5 percent. Anthra- cite coal is graded commercially, according to size, the chief terms being the following, in the order of increasing size : Buckwheat, pea, chestnut, stove, egg, broken and lump, [2] Combustion Combustion means simply the chemical union of a substance with oxygen. The oxygen is furnished by the air, which con- tains oxygen and nitrogen. These in air are not in chemical union, but simply as a mixture, in the proportion by weight of twenty-three parts of oxygen to seventy-seven parts nitrogen in one hundred parts of air. When bodies enter into combination, or into combustion with oxygen, heat is set free, and the products formed by the combustion are very much hotter than the original fuel and oxygen. > The manner in which coal burns or enters into combustion depends upon its composition and upon the nature of the fire and the supply of air. The elements available for the liberation of heat are the carbon and the hydrogen. Small quantities of sulphur are frequently present, but the amount is so small and the heat- ing power so feeble that its influence may be neglected. A pound of pure carbon requires for its complete combustion 2| pounds of oxygen, and the result is 3f pounds of carbonic acid or car- bon dioxide in the form of gas. The total amount of heat set free in this operation is about 14,500 heat units. Now, since the proportion of oxygen in the air is about 23 percent, the number of pounds of air required per pound of carbon will be 2f -f- .23, or 2.66 -4- .23, or about 12. Similarly a pound of pure hydrogen requires for its complete combustion, 8 pounds of oxygen, and the result is 9 pounds of water vapor. The total amount of heat set free in this operation is about 62,00a heat units. In the same way as above, it follows that the combustion of a pound' of hydrogen will require the presence of 8 -^ .23, or about 35 pounds of air. The amount of hydrogen, however, is FUELS 43 usually small, and allowing for the ash the amount of air neces- sary to barely furnish the oxygen required for one pound of fuel is about 12, or substantially the same as for one pound of carbon. In practice, however, it is found that this would be insufficient to maintain the draft, nor could it be expected that the air would be so distributed as to give exactly the right amount of oxygen at the right place. It is, therefore, necessary practically, to provide a large excess of air and the amount actually passing into the fur- naces is usually not less than i8 or 20 pounds per pound of coal, and may even considerably exceed this amount. At 12.5 cubic feet per pound this will give for the volume of air required per pound of coal from 225 to 250 cubic feet and upward. Consider now the process of combustion with bituminous or semi-bituminous coal. When such coal is put on the fire the first result is not a combustion of the carbon, but a dis- tillation oi' driving off of the hydrocarbons in the form of gaSj and until this operation is nearly completed there will be little or no combustion of the cai-bon. During this first operation of distilla- lation, heat is absorbed by the fresh coal from the remainder of the fire for the liberation of these gases which are substantially the same as those forming ordinary illuminating gas. After these gases are liberated from the coal they rise into the furnace and combustion chamber. Here, if they meet with a, suitable supply of air at a proper temperature, they will be burned, both carbon and hydrogen, and will thus set free all the heat which is obtain- able from tbem. If the air is insufficient in amount the gases will be only partly consumed, the oxygen uniting most readily with the hydrogen and leaving the carbon in fine particles to form smoke or soot, according as they float away with the products of com- bustion, or become closely packed together on some of the sur- faces of the boiler. If the air is not sufficiently hot likewise, there may occur a partial combustion resulting in burning the hydrogen into water vapor and in setting the carbon ffee as smoke or soot as before. If, however, the. temperature is too low the gases may become chilled and pass off ,33 a whole unburnt, thus carrying away not only their own heat of combustion, but also the heat which was absorbed for their liberation. If, on the other hand, hydrocarbon gases are subjected to a very high temperature be- fore being mixed with the air, they will become more or less broken up into free hydrogen and carbon in fine particles. If 46 PRACTICAL MARINE ENGINEERING these are kept at a temperature high enough for ignition and are supplied with oxygen, they will burn ; but if they fall below the proper temperature they pass off unburnt, the carbon constituting smoke or soot, as before. Smoke is, therefore, the sign of a fuel containing hydrocarbons, and of a more or less imperfect com- bustion. The actual amount of fuel lost in ordinary smoke is, however, quite small; so small that it is often considered as hav- ing no significant influence on the question of economy. Hence, smoke prevention is often considered as hardly worth special effort, so far as the saving of fuel alone is concerned. There may , be other losses, however, in connection with the general condi- tion of which smoke is an indication, and any mode of design and of general operation which reduces the smoke formation will usually tend toward economy of combustion. It has already been seen that the conditions for burning the hydrocarbon gas are high temperature and an air supply above, the grates and in the combustion chamber. This, then, is one of the reasons for providing openings for the proper admission of air above the grates as well as underneath. Now return to the residue left on the grates after the escape of the hydrocarbon gases. During this part of the opera- tion certain kinds of bituminous coal swell up and cake more or less firmly together on the grate. Such are called caking coals. The swelling up is due to the formation of gas in the midst of the coal and to its efforts to escape, while the caking is due to a par- tial softening or melting of the substance under heat as the hydro- carbons are set free. Other kinds of bituminous coal undergo little change in their external form, while still others break up into small particles or grains. Those latter varieties are called non- caking or free-burning coals. In any case the residue, after the hydrocarbons are set free, is called coke and consists of nearly pure carbon with ash. As has already been seen, the carbon burns by uniting with oxygen, and this must take place at the burning lump itself. Hence, it is necessary that the air should penetrate thoroughh all parts of the fire, and to this end it is brought in, in part at least, under the grate and by the draft pressure is forced upward through the mass of burning coal. If the fire is-rather thick the operation proceeds in the following way. The carbon and oxygen first unite in complete combustion, i pound of carbon to 2f pounds of oxygen, and the product, carbon dioxide, proceeds up- FUELS 47 ward through the fire. As this gas comes in contact, however, with the cooler coal in the midst or near the top of the bed of fuel it absorbs some of the carbon and becomes changed to a com- bination in the proportion of i pound of carbon to i^ pounds of oxygen. This gas is called carbon monoxide. In this oper- ation also is absorbed back again more than two-thirds of the heat which the first combustion had liberated. If the gas should escape unburnt, a serious loss would result, as only about 4,450 heat units or less than one-third of the heat available in the carbon would have been liberated. If, however, the gas finds air above the grate and a suitable temperature, the carbon which was absoi'bed is burnt out again and the corresponding beat is given back, so that the final result is the complete combustion of the carbon and the liberation of all the heat possible. The formation of carbon mon- oxide in this way shows again the need of admitting air above the grate, as well as underneath. This gas burns with the peculiar blue flame so often seen, especially after a fresh firing with anthra- cite coal, and the presence of this flame thus indicates the forma- tion and recombustion of carbon monoxide in the way described. After the coal has all been thoroughly ignited and raised to a bright glowing heat, the combustion into carbon dioxide is com- pleted at once, and there is little or no formation of carbon mon- oxide to be burned as a gas above the grate. The thinner the fire the more quickly is this condition reached. The combustion- of semi-anthracite and of anthracite coal proceeds in the same general manner as for bituminous coal, ex- cept that the period of distillation becomes shorter and less im- portant as the proportion of hyrocarbon is decreased. It thus results that an ordinary anthracite coal burns almost entirely in the manner described for the coke residue of bituminous coal, ex- cept that in consequence of the lowertemperature of thefuel during the early stages of combustion, there is apt to be a more pro- nounced formation of carbon monoxide for the combustion of which there must be a supply of air above the grate as already noted. [3] Impurities in Coal. Clinker Formation The chief impurities in coal may be divided as follows: (A) Nearly infusible slate, stone, and earthy matter either in separate lumps or distributed through the coal as a whole, thus giving it a low carbon value. (B) Mineral materials more or less fusible, 48 PRACTICAL MARINE ENGINEERING add thus capable of melting and forming a slag which uniting with the ash and slate forms clinker. Substances liable to be present in - coal and which are more or less fusible at the high temperatures in the furnaces are : Potash, soda, lime and silica. The melting point of these substances is also considerably lowered by mixing with iron oxide, which is always formed by the oxidation or com- bustion of iron pyrites. The presence of this substance in the coal will thus result in lowering the melting point of the other mineral earths and impurities, and in the greater liability to form clinker. This formation of clinker may be so considerable as to seriously interfere with the combustion of the coal, and in such cases its removal must he care.fully attended to from time to time in order to keep the fires in good condition. Iron oxide, or common iron rust as it is more familiarly called, will give to the ashes a reddish tinge so that such a color noted in the ash may usually be accepted as an indication of the presence of iron pyrites in the coal, with the various results which have been already noted. Its presence in any considerable amount is also usually shown by a yellowish or brassy appearance of the coal. For the formation of little or no clinker a coal should have little or no alkali, lime, or pyrites. . Such coal in burning gives a nearly white, soft and friable ash, [4] Weathering of Coal When coal is exposed to the air and weather for a consider- able period of time there is a slow absorption of oxygen, and thus a real combustion and wasting of the fuel value of the coal. It thus results that the coal during this operation is really burning up, though at a rate so slow that the heat developed is hardly appreciable and the change in the outward appearance of the coal is so gradual as to escape ordinary notice. The hydrocarbons are much more readily subject to. this operation of gradual oxidation or combustion than pure carbon, the latter entering only with great difficulty into union with oxygen at ordinary temperature. It thus follows that bituminous coals are much more subject to waste and change by weathering than anthracite coals. In addition to the loss due to this slow combustion there is often a gradual escape of gaseous hydrocarbons imprisoned within the lumps, or a gradual vaporization of liquid hydrocarbons and their escape as vapor. Such losses also are, of course, more marked with FUELS 49 bituminous than with anthracite coals. A bituminous caking coal often becomes changed to a non-caking coal after exposure to the air and weather for a considerable period of time. The chief external conditions which may influence weather- ing are moisture and heat. If the coal contains no iron pyrites, moisture is believed to slightly retard the operation of slow com- bustion, and thus to act beneficially rather than the reverse. If iron pyrites are present in the coal, the conditions are changed. Iron pyrites oxidize with comparative readiness at ordinary tem- peratures, both the sulphur and iron uniting with the oxygen. It thus tends to set up the operation of oxidation and to break up the lump into small bits, while the heat developed is a further aid to the continuance of the process. The oxidation of iron pyrites is, moreover, much aided by moisture, which, therefore, with such coals, becomes a distinct disadvantage. In any event a coal with iron pyrites may be expected to suffer more seriously by weathering than one free from this substance. In extreme cases the oxidation of the pyrites has caused the crumbling of the coal into such small bits that it has become nearly worthless for its original purposes. Heat in general always increases the activity of this slow combustion, and hence tends to increase the loss due to weather- ing. The heat developed by slow oxidation in the interior of large piles or masses of coal escapes with great difficulty and thus ac- cumula:tes and raises the temperature, making the conditions still more favorable for the continuance of the process. So far as this effect goes, therefore, the loss would be more serious in large piles than in small. This is, however, offset by the greater difficulty which the oxygen has in penetrating to the interior of the pile as it is larger in size. It results that With other things equal there is no great difference in the loss due to weathering with eoal either in large or in small bulk, [5] Spontaneous Combustion It has already been seen under the head of weathering that coal at ordinary temperature is subject to a very slow oxidation, or combustion, which gradually wastes away its fuel value. When the coal is freshly mined this oxidation seems to be especially active due to the property which carbon has of absorbing or con- densing gases upon its surface. The volume of oxygen that differ- 50 PRACTICAL MARINE ENGINEERING erent coals are capable of absorbing varies from l% to 3 times the volume of the coal. The oxygen thus absorbed is very active chemically, due to the fact that coming from the air it is absorbed more readily than the nitrogen, and is thus less diluted than in the air. This absorption is itself attended by the production of heat, and this heat, in conjunction with other conditions favorable to chemical action, brings about an oxidation of the hydrocarbons of the coal, thus generating still more heat. Now, if the coal is in small bulk and well ventilated, there will be little chance for the gradual accumulation of the heat and a consequent rise of temperature. A few lumps of coal exposed to the open air may lose much by weathering in the course of six months or a year, but the heat set free will readily escape and the rise of temperature will be unnoticeable. If, on the con- tray, the coal is in large bulk, or is confined in bunkers with little or no ventilation, the heat developed by slow oxidation will be im- prisoned and the temperature may gradually rise to the point where active combustion will proceed according to the supply of air available. It thus appears that there may be danger from no ventilation or from insufificient ventilation. Opinions dififer on these points, but it may probably be accepted that unless the ventilation can be made thorough, the compartment should be kept tight and the air excluded as much as possible. At the same time before such closed compartments or bunkers are entered with a light they should be thoroughly ventilated, especially if the coal is of a quality likely to freely disengage hydrocarbon gases. A further important point to be noted relates to the influ- ence which the initial temperature has on the rapidity of chemical actions of this kind. Below a temperature of loo degrees F. the action will go on slowly with little chance of undue heating taking place, but as soon as the temperature rises much above loo de- grees F., especially with certain coals, spontaneous combustion is only a question of time. It appears, therefore, that the true index of the danger of spontaneous combustion must be taken as the capacity of the coal for absorbing or condensing gases in its outer layers or near its surface. This in turn will be shown by the amount of mois- ture which it can absorb from the air. A coal which absorbs a large amount of moisture from the air will at the same time absorb FUELS SI a large amount of oxygen, and will, therefore, be relatively a dangerous coal as regards spontaneous combustion, while on the other hand a coal which absorbs but a small amount of moisture from the air will likewise absorb but little oxygen, and Avill be comparatively safe as regards spontaneous combustion. The per- centage of moisture which can be absorbed from the air by coal is found to vary from about 2.5 to 10 percent, and experience has shown that the liability to spontaneous combustion varies closely with this percentage. In general then the liability to spontaneous combustion de- pends on, (i) The size of the cargo or compartment, increasing as the bulk increases. (2) The size of the coal, increasing as the lumps are smaller, and thus present relatively more surface. (3) The presence of iron pyrites with moisture. Iron py- rites has sometimes been thought a possible direct cause of spon- taneous combustion, but the proportion of this substance is small, rarely rising above 3 or 4 percent, and the heat developed by the combustion of sulphur and iron is very much less per pound than for carbon and hydrogen. The heat developed by the oxidation of irdn pyrites is, therefore, hardly sufficient to do more than help along the general condition of slow combustion as referred to above. In another way, however, the presence of the pyrites may have an important influence on the result. The presence of mois- ture favors the oxidation of the pyrites and as a result of this it will swell and tend to split up the coal, thus decreasing the size of. *J- ji d t> o'S •» Kind op Oh,. a ■ a a a ^ u 0, a ri a V d E s P o 6 1 w" 0. •3 O °F. °F. 0.924 0.926 .966 180 216 311 200 240 230 19,060 19,481 84.60 83.26 81.52 10.90 12.14 11.01 1.63 0.50 0.55 2.87 Beaumont refined 3.83 California 6.92 Calorific Power of Various Descriptions of Petroleum, Etc. (Taken from Redwood.) Chemical composition W Heavy petroleum from West Virginia. . Light petroleum from West Virginia. . . Light petroleum from Pennsylvania. . . Heavy petroleum from Pennsylvania. . American petroleum .-..,... Petroleum from Parma Pechelbronn .- Pechelbronn Schwab.weiler Schwabweiler Hanover, Kddese Hanover, Wietze Bast Galicia West Galicia Shale oil from Ardeche, Vagnas Coal tar from Paris gas works Petroleum from'Balakhani Light petroleum from Baku . .". Heavy petroleum from Baku Petroleum residue from Baku factories. Petroleum from Java Heavy oil of pine (Landes) , , 0.873 0.8412 0.816 0.886 0.820 0.786 0.912 0.892 0.861 0.829 0.892 0.955 0.870 0.885 0.911 1.044 0.822 0.884 0.938 0.928 0.923 0.985 83.5 84.3 82.0 84.9 83.4 84.0 86.9 85.7 86.2 79.5 80.4 86.2 82.2 85.3 80.3 82.0 87.4 86.3 86.6 87.1 87.1 87.7 13.3 14.1 14.8 13.7 14.7 13.4 11.8 12.0 13.3 13.6 12.7 11.4 12.1 12.6 11.5 7.6 12.5 13.6 12.3 11.7 12.0 10.4 3.2 1.6 3.2 1.4 1.9 1.8 1.3 2.3 0.5 6.9 6.9 2.4 5.7 2.1 (NO) .2(OSNi 10.4 0.1 0.1 1.1 1.2 0.9 2.5 Calories 10,180 10,223 9,963 10,672 9,771 10,121 9,708 10,020 10,458 10,005 10,231 9,046 8,916 11,700 11,460 10,800 10,700 10,831 .10,081 FUELS 59 FuBt Oils (Taken from Lewes.) Carbon. Hydrogen. Oxygen, etc. American 84.9 86.6 87.8 85.6 84.9 86.4 13.7 12.3 10.78 11.03 13.96 12.10 1 1 1 Borneo 1 24 Texas 3 51 1 25 Burmah 1 50 Liquid Fusls (Taken from Lewes.) Specific gravity. Flasli point. Calorific value by bomb. Calories. B.T.U.'s. .886 .956 .945' .920 .958 .936 .875 .979 1.084 -F. 350 308 244 230 210 285 288 206 218 10,904 10,800 10,700 10,480 9,899 10,461 10,120 3,933 8,916 19,627 Russian Ostatki 19,440 Texas 19,242 18,864 17,718 Barbadoes *. Borneo 18,831 Shale-oil , 18,217 Blast-furnace oil 16,080 Heavy tar oil. ... 16,050 An examination of the above tables shows that these oils may be divided into certain groups which contain approximately the same percentage of chemical constituents and approximately the same heating value per gallon. However, these characteristics have in general very little to do with their proper burning. Before an oil is burned certain tests should be made to determine its characteristics, and some of these are required to be made before an oil is accepted, These tests are (i) determination of the gravity of the oil, (2) deter- mination of the flash point, (3) determination of the water and sediment, (4) determination of the calorific value, (5) deter- mination of the sulphur contents, (6) determination of the ulti- mate analysis of the oil, and, lastly, (7) the determination of its viscosity at various temperatures. (o) The gravity of an oil is found by filtering a sample of the oil into a 100 cubic centimeter cylinder and allowing a hydro- meter to float freely in this oil. The hydrometer has a scale grad- uated in degrees Beaume on its face, and also a temperature scale in degrees Fahrenheit. Both indications are noted, and by means of the tables supplied by Tagliabue the gravity at 60 degrees F. can easily be found by interpolation, in case the temperature of the oil is not 60 degrees F. The specific gravity of the oil can be found from the formula. 66 PRACTICAL MARINE ENGINEERING 140 Specific gravity = 130 X ° Beaume The tables prepared by the Inspector of Petroleum of the New York Produce Exchange Annex give the specific gravity of light oils for every i/io of a degree on the Beaume scale. (b) The flash point of an oil is the temperature to which an oil must be heated to give off vapors which, when mixed with air, form an explosive mixture. This test is usually found either by the open-cup method or the closed-cup method. The Navy Department and general practice usually give the flash by the Abel or Pensky-Marten closed-cup method. In the Pensky- Marten closed-cup tester the oil is first filtered to prevent foam- ing, in case any water is present. It is then placed in a brass cup of standard size and filled to a mark on the inside of the cup. This cup rests in an outer vessel which forms a water jacket, the outer vessel being supported by three legs and heated by an alco- hol burner placed below. The oil cup is fitted with a tightly fitting cover which carries a thermometer and allows it to extend into the liquid, a stirrer for agitating the oil, made of two paddles, and a srnall testing flame or wick. The cover has triangular holes cut in it, and these holes are covered by a circular plate which is rotated to expose the opening and at the same time actuates the wick which dips into the opening. In case the temperature of the oil is not near the flash the wick will be extinguished when dipped. As the flash point is neared the wick flame increases in brightness, and at the actual flash a bluish flame shoots up through the open- ing with a perceptible flash. The fire point or burning point of an oil is the temperature at which vapors are given off which, when ignited, burn con- tinuously. The fire test is made in an open tester. The fire point is usually about 25 degrees F. above the flash. (c) The test for water and sediment is now usually made with benzol as follows: 50 cubic centimeters of the oil and 50 cubic centimeters of benzol are placed in a high-speed centrifugal and revolved rapidly for some time and then the percentage of water is read off in terms of the total 100 percent. In case the sample contains a large percentage of water the test is made ,by the distillation method. (d) The calorific value of an oil is usually determined by the bomb calorimeter, Mahler's bomb calorimeter or any other FUELS 6i Standard make being used. Approximate formulae for determin- ing the British thermal units without a bomb calorimeter are as follows : British thermal units = 18,650 + 40 (Beaume reading— 10). British thermal units = 17,680 + 60 (Beaume reading). {e) The sulphur contents of an oil may be determined by any of the following methods : 1. Dry fusion with alkalies and subsequent oxidation with bromine. 2. Dry fusion with a mixture of alkalies and oxidizing agents. 3. Treatment with wet alkalies and oxidizing agents. 4. Oxidizing with fuming nitric acid at high pressures. 5. Burning in pure oxygen at atmospheric pressure. 6. Burning in a stream of pure oxygen. 7. Burning in a lamp in atmospheric oxygen. 8. Burning in a bomb calorimeter with pure oxygen under a pressure of 30 to 40 atmospheres. The last method is the best and most reliable and is the one usually used. (/■) The ultimate analysis of an oil is made by a chemist, the following being the constituents found : Carbon, hydrogen, nitrogen, sulphur, oxygen, water and sediment. {g) The viscosity of an oil is its rate of flow, of a certain amount, through a specific orifice at a certain temperature. There are various makes of viscosimeters used, namely, Engler's, Say- bolt's, Redwood's, Kunkler's and a great many others, each of which use a different liquid and a different volume as a standard. The Engler, which is the standard in the United States Navy, puts 240 cubic centimeters in the cup and allows 200 cubic centi- meters to run out, the comparison being water at 70 degrees F. as unity. The Saybolt puts 70 cubic centimeters in the cup and al- lows 60 cubic centimeters to run out, a stop watch timing the interval, and the second is the standard. It is pretty well established from recent investigations of diflFerent fuel oils, that it is impossible to get an explosive mixture from the gases given off by oils when heated and mixed in com- bination with air below the flash point of the oil. It was found that in order to have an explosive mixture i percent to 1.5 percent of vapor is nee(ied. The table following gives data of tests made to establish this fact ; b2 PRACTICAL MARINE ENGINEERING VAPOR TABLE KIND OF OIL. Mexican crude, 17.3, Beaumd, Mexican gas oil Lima oil Mexican crude, 17, Beaum^.i' Louisiana oil ^ Mexican crude, 15.4, Beaum^. Indiana oil Navy contract (Oklahoma)... California Star oil Temperature to which oil was heated. °C. 53 73 23 63 92 24 55 77 55 71 94 97 75 72 95 35 66 87 50 75 95 50 98 °F. 127 163 73 145 198 75 131 171 131 160 201 207 167 162 203 95 151 189 122 167 203 122 208 Oxygen, percent. 20,4 20.0 20.8 20.1 26.9 20.1 18.1 20.7 20,4 19.7 20.4 20.6 20.4 18.6 20.5 20,3 20.0 20.3 20.1 19,8 19,9 15,5 Vapor, percent. 1,00 1,10 .20 .90 1,40 .20 1,20 "ao .80 ] ,40 ,95 .70 .70 1,50 .30 .90 1.30 .50 1,0 1,40 ,55 1.37 Flash point. °C 52 64 55 70 130 94 54 73 85 °F. 126 47 .31 58 266 26 i 147 67 8.5 Another fact di.sclosed is that where oil is stowed in air-tight tanks, so that no oxygen is present, the gases are absolutely non- explosive because they cannot receive oxygen to support com- bustion. QUESTIONS Fuels PAGE What.are the chief constituents of coal? 43 What are the chief varieties of coal? 43 What are about the proportions of volatile matter and carbon in the different varieties? 44 What percent of ash is usually found in good coal? 44 Describe briefly the process of combustion with anthracite coal and with bituminous or semi-bituminous coal 44 How much heat is liberated by the complete combustion of 1 lb. of carbon? 44 How much for 1 lb. of hydrogen? 44 How much air is required to barely furnish the oxygen necessary for the combustion of an average lb. of coal? : 45 How much is actually required and why is the excess necessary? 45 What is soot and how is it formed? 45 What is clinker and how is it formed? ~. 47 What is meant by the weathering of coal? 48 What influence does iron pyrites have on weathering? 49 What is spontaneous combustion and what are the conditions on which it depends? 4g How many cubic feet bunker space are usually allowed per ton of coal? 52 What are briquettes? 53 What are the constituents of liquid fuel? 54 How does the evaporative power of Hquid fuel compare with that of coal? 55 What are the chief advantages of liquid fuel?. 55 What is the present chief difficulty attending the extended use of liquid fuel? ; jg What tests should be made to determine the acceptability of oil fuel? 59 What is the flash point of oil fuel? 60 What'is the fire Doint of oil fuel? fin CHAPTER III Boilers Sec. i6. TYPES OF BOILERS In the general sense, any receptacle in which steam is gen- erated by the application of heat is a boiler. A boiler must, there- fore, contain three fundamental features : A place for the fire, a place for the water, and a division or partition between them. The great variety of boilers arises from the different forms which these features take, and the different manner in which they are arranged. SHELL Fig. 9. Scotch Boiler The keynote of the development of steam boilers from the earliest forms is contained in the word subdivision; subdivision of the hot ,gases and of the water so that no particle of either shall be very far from the partition or heating surface, as it is called.^ If in addition to this subdivision provision is made for a definite flow of the hot gas along one side of the heating surface and of the water along the other in the opposite direction, the conditions for the 64 PRACTICAi. MARINE ENGINEERING most eflScient transfer of the heat of the gas through the surface into the water will be fulfilled. In modern boilers the principle of subdivision has been carried to a high degree of development, but the conditions for proper circulation are but imperfectly fulfilled. The subdivision is obtained by the use of a large number of tubes Am Dnwa for Aft I Other Hud Fgrvd Bfiinforcinff FUto !l(' Thick. I'BinU Fig. 10. Scotch Boiler, End View or tubular elements surrounded by a shell or casing. The chief classification of boilers is made according to the relation of the water and hot gas to these tubular elements. If the gas is led through the inside and the water is on the outside, the arrange- ment is known as a Hretube boiler. If, on the contrary, the gas is on the outside and the water circulates through the inside, the arrangement constitutes a watertube boiler. BOILERS 65 Firetube boilers may be divided into return tubular or Scotch boiler, the direct tubular or gunboat boiler, the locomotive boiler, the flue and return tubular or leg boiler, and the Hue boiler as used on western river steamers. These are illustrated in Figs. 9-14. o o o o Btecl Scnwed Bbijl 1s"m BatLot Thread InapMtad for (WOO Lb.t.S 000 Fig. 11. Scotch Boiler, Longitudinal Section Watertube boilers are found in great variety, depending on the details of arrangement of the tubes, and drums or headers of which they are composed. A few representative types are shown in Figs. 15-18 and 20 to 27. First will be given brief descriptions of the important features of these boilers, and then at a later 66 PRACTICAL MARINE ENGINEERING point will be taken up the subjects of theii" design and con- struction. [i] The Scotch Boiler In present practice, in the merchant marine," the Scotch boiler is used more than any other one type, and, in fact, more than all other types combined. This boiler, as illustrated in Figs. 9, 10, 11, consists essentially of a cylindrical shell containing one or more cylindrical furnaces, usually corrugated circumferentially for strength, opening into combustion chambers at the back end, from which a large number of small tubes lead again to the front end or head of the boiler. The grates are placed at about the center of the height of the furnace, and the fire and hot gases occupy the . upper part of the furnaces, the combustion chambers, and the in- side of the tubes, while the water and steam fill all the remaining parts of the shell, the water level being usually some 6 inches to 8 inches above the highest part of the tubes or combustion chambers. The hot gases pass from the fire on the grate bars into the com- bustion chamber, thence forward through the tubes and out through the uptake or front connection to the smoke pipe or fun- nel. Several varieties of this boiler are in common use. Thus the number of furnaces may be one, two, three, or four. They may be fitted with separate combustion chambers, or there may be one combustion chamber for all furnaces, or, as is common with four furnaces, there may be two combustion chambers — one for the two furnaces on either side. Again, the boilers may be single-end or double-end. Fig. 11 is an example of the first. A double-end boiler consists of two sets of furnaces opening from either end of a shell of double length. It is evidently equivalent to a pair of single-end boilers placed back to back, with the back heads removed and the shells joined. Such boilers may also have either separate combustion chambers for each end, or a common combustion chamber for both ends. The former arrangement is to be pre- ferred, and becomes necessary where forced draft is used. [2] Direct Tubular Boiler, Gunboat Type This boiler is rarely used except in former warship practice, where with low head room it has been occasionally employed. It consists of a shell with furnaces and combustion chamber some- what as in the Scotch boiler, but the tubes, instead of returning to the front, lead on to the farther head. To this head is fitted a BOILERS 67 smoke box of uptake leading to the funnel, In such cases the boiler for the same power is of smaller diameter and greater length than the Scotch type, and it is readily seen that the whole arrange- ment is simply a mode of exchanging diameter for length. [3] Direct lobular Boiler, Locomotive Type The locomotive type of marine boiler as illustrated in Fig. 12 consists of a cylindrical shell extended to the front and modi- field in form with flat sides and bottom, and flat or rounded top. Fig. 12 Locomotive Type Boiler The furnace is of rectangular cross section, and is surrounded by the shell at the front, leaving on the sides a narrow space known as the water leg and sometimes a like space underneath known as the water bottom. The gases take the same general course as in the gunboat type, the chief difference in the two being in the form of the furnaces and in the absence of the combustion chamber in the locomotive type. [4] The Flue and Return Tubular or Leg Boiler In this boiler, as illustrated in Fig. 13, the hot gases pass from the furnace through large tubes or Hues, as they are termed, to a combustion chamber at the farther end. They then return to the front through small tubes, and are led by an appropriate uptake to the funnel. The furnace is of rectangular cross section, and the front end of the boiler is modified on the sides and bottom to cor- respond to this form, as in the locomotive type. Water legs are also formed in the same way on the sides of the furnace, and from this feature the boiler receives its common name. This form of the front end of the boiler with flat sides and rounded top is some- times known as a wagon top. Very commonly, as shown in Fig. 13, an attachment to the shell, known as a steam chimney, surrounds 68 PRACTICAL MARINE ENGINEERING the lower part of the funnel, the office of which is to subject the steam to the drying and superheating- effects of the gases on their :.v.;. Fig. 13. Leg Boiler way through the funnel. Boilers of this type have been used to a considerable extent on tug. and river boats. [S] The Flue Boiler In Western river practice use is quite commonly made of the return flue boiler as illustrated in Fig. 14. This boiler is ex- ternally fired. The flames and hot gases pass back along the out- side of the boiler to a back connection and then enter the flues and return through them to the front, and thence to the uptake and funnel. Boilers of the locomotive type, or tubular firebox boilers as they are often called, are also used to a considerable extent in Western river practice. BOILERS 69 [6] Watertube Boilers Turning now to this type, a brief description will be given of the leading features, which may'^be combined in the greatest possible variety, thus giving the yast^number of forms of such boilers on the market at the present time. To aid in the descrip- Fig, 14. Return Flue Boiler tion a few typical forms of such boilers are shown in Figs. 15-18 and 20-27. Most boilers of this type have one or more cylindrical drums or chambers on top and one or more similar drums below, the two sets of drums being connected by sets of tubes. The feed usually enters first the upper drum, frequently passing on its way through a coil heater in the base of the smoke pipe or top of the boiler. It then flows down certain of the tubes to the lower drums. If these tubes are of extra large size and specially intended for down flow, the boiler is said to have special down How or down- cast tubes or pipes, as shown in Figs. 15, 16, 21. In some cases such tubes are omitted, and the feed must descend through part of the small inner tubes. In any case, after finding its way to the lower drum it enters the up Hozu or steam forming tubes, which are surrounded by the hot gases coming from the furnace below them. During the passage of the water upward it is partly converted into steam, and the mixture issues from the upper end of the tubes into the upper drum. There the steam is separated and led to the engine, while the water joins that already in thjs drum, and thus begins another round. In some cases the upper ends of the steam forming or delivery tubes are below the level of the water in the upper drum, and they are then said to be drowned or wet. In other cases they are above the water level and are said to be dry. In still other forms they enter at about the middle of the drum or about the water level, and may be wet 70 PRACTICAL MARINE ENGINEERING BOILERS 71 CO n < 72 PRACTICAL MARINE ENGINEERING or dry as the level varies. See the various cuts for examples. Watertube boilers are often divided into two general classes : large tube and small tube boilers. In the former they are usually 3 or 4 or even 5 inches diameter, while in the latter they are usually from I to ij^ or 2 inches diameter; in naval practice, however, boilers having tubes from i^^ inch diameter up, are known as the large tube type. Again, the tubular elements may be made up in a great variety of forms. In some they are straight, in others curved, Fig. 17. Babcock & Wilcox Boiler Arranged for Burning Oil Fuel and Equipped with Superheater as shown in the various figures. In small tube boilers they are very commonly curved or bent, while in the large tube types they are straight. Also in some types the elements are continuous between drums or headers as in Figs. 17, 18, 20, while in others, as in Figs. 15, 16, 27, they are made up of lengths or of different parts with screwed joints, elbows, returns, junction boxes, etc. BOILERS 73 74 PRACTICAL MARINE ENGINEERING In some they are expanded into the shells of the drums.; in others screwed. In some all joints are carefully protected from the direct action of the flame; in others screwed joints are freely ex- posed to the flame. In some the general direction of the tubes is nearly horizontal ; in others nearly vertical, and in others bent or curved in various forms. In some types, as illustrated in Figs. Forced- Circulatioa Accelerated CirculatioQ Fig. 19. Circulation Diagrams 24 and 25, the lawer drums are omittedj or consist merely of the lower portions of the tubes and headers, or members to which the tubes are connected. In all cases the grate lies below the tubes, and frequently between the lower drums, as shown in the various figures, while the whole is surrounded by a casing in- tended to prevent, so far as possible, the loss of heat by radiation. WATERTUBE BOILERS— CLASSED BY METHOD OF CIRCULATION OF WATER The classification of watertube boilers according to the method of circulation of the contained water is shown on Fig. 19. Class I. Limited Circulation. — Water flows down to the bot- BOILERS 75 torn of the tube element, then up, as indicated by arrows to the broken line which shows the water level. Here the steam frees itself and passes into the steam drum from \yhich it is drawn off for use. The combined tube area is large for the amount of steam drawn off and the velocity of flow in the tubes low, the flow being only sufficient to replace the amount which passes off as steam. To this class belong the Belleville, Almy and Roberts boilers. Class 2. Free Circulation. — In boilers with free circulation the water enters the drum A from which it flows down through a header or water chest into which connect a large number of tubes through which the water flows and becomes heated. The combined water and 'steam then pass into another header or chest through which it rises and returns to the steam drum A, whence tlje steam is drawn off for use. The velocity of flow is moderate, but is more than sufficient to make up for the amount of steam drawn off. To this class belong boilers of the Babcock & Wilcox, Ward and Niclausse types, although the latter type is slightly modified in its arrangement of headers. Class 3. Accelerated Circulaiion.-^-ln boilers of this type the tubes tend toward the vertical in inclination and may be either bent or curved. They are usually of small diameter and the total area for circulation is small as compared with the two preceding types. The feed may enter the upper drum, pass down through the outer rows of tubes to a lower drum and return to the upper drum through the rows close to the furnace, or it may enter the lower drum and, being baffled, pass up through the two outer rows of tubes to the upper drum, thence down through the central rows to the lower drum and return to the upper drum through the rows close to the furnace. The circulation is rapid when compared with the volume of steam drawn off from the upper drum. Such boilers are known as express boilers and are light in weight and in weight of contained water. The Thornycroft, Yar- row, White-Forster and Seabury boilers are examples of this type. In the three classes of boilers just described, the drums and interior volume of the tubes provide a reservoir for quite a large amount of water and thus guard against a temporary shortage of feed water while also giving surplus volume to contain a slight T(> PRACTICAL MARINE ENGINEERING BOILERS 77 78 PRACTICAL MARINE ENGINEERING > BOILERS 79 8o PRACTICAL MARINE ENGINEERING amount of excess feed. This provides an element of safety against rupture due to overheating and also is a serious element of danger when rupture occurs, as the contained water flows out into the boiler compartment, filling it with steam' and scalding water. Class 4. Forced Circulation. — In boilers of this type there is utter absence of steam and water drums. The feed water is forced into a manifold A or A\ and thence through a series ol elements Fig. 24, Lagrafel and D'Allest Boiler as shown, and passes off to the engine through a steam manifold A^ or A. Such boilers are generally known as "flash" boilers. There is no reserve of feed water in the boiler nor is there any res.erve volume to accommodate a surplus of feed. The feed sup- ply must exactly balance the amount of steam drawn off or either serious overheating of tubes or flooding of the engine results. In case of tube rupture, however, the water contents of the boiler being very small, the danger of serious disaster is reduced to almost nothing. The Talbot and the White boilers are examples of this type. BOILERS 8i Fig. 25. "Babcock & Wilcox Boiler (Coal Burning) 6 ESCAPE PIPE CAftRlEO AROUIfD 8M0KI PIPE TO BE AFT OF IT Ab6vE UFPfcR OECKl «) 5S 50 a iD Fig. 26. Arrangement of Fireroom with Babcock & Wilcox Boilers PRACTICAL MARINE ENGINEERING FEED OUTLET FROM.ecONOMISER reED INLET TO BOILER , AFTER LEAVINQ - ECONOMUSER Fig. 27. Belleville Boiler BOILERS 83 [7] Relative Advantages of Different Types of Boilers For large merchant ships under ordinary conditions and where the extremes of lightness or of speed on a given displace- ment have not to be attained, the Scotch boiler seems at present to be considered as fulfilling most satisfactorily the all around re- quirements for a marine boiler, and in consequence it is found pre- dominating in the mercantile deep sea marine, as well as on the Great Lakes, and to a large extent on inland craft of all descrip- tions, except those of small size. It is also used to sortie slight ex- tent in naval practice, though the use of watertube boilers has be- come almost general in this field, where their special features be- come of marked value. The present is a time of change with regard to types of boiler. It is not too much to say that in rnodern naval construction the watertube boiler is accepted as the standard type to the exclusion of the fifetube boiler. The watertube boiler is also making large advances in the mercantile field, and not a few modern ships of the mercantile marine are now equipped with this type of boiler. For tugboats, river steamers, and a variety of small craft, the various types of direct firetube and flue boilers have been much used. These boilers are more readily adapted to a variety of demands regarding size, farm and arrangement, and in small sizes are perhaps more cheaply built than Scotch boilers. In many cases, however, the preference for boilers of this type has doubt- less depended on local and special conditions quite independently of their relative value from the engineering standpoint. For fast yachts, launches, all craft of the torpedo boat type, and in fact in all cases where the highest speed is to be attained on the least weight, the watertube boiler has become a necessity, and in one or other of its many forms is universally employed. The weight of Scotch boilers without wateV, per square foot of heating surface, is usually from about 25 to 30 pounds; of watertube boilers of the lighter types from 12 to 20 pounds. The weight of the contained water per square foot of heating surface is usually from 12 to 15 pounds for Scotch boilers, and from, say, 1.5 to 3 pounds for watertube boilers. It results that Scotch boil- ers with water will weigh from, say, 35 to 50 pounds per square foot of heating surface, while watertube boilers will similarly weigh from 13.5 to 23 pounds. These figures are not to be consid- ered as giving absolute limits, but simply as representative values 84 PRACTICAL MARINE ENGINEERING for average types. It- should be noted, however, that a square foot of heating surface in a Scotch boiler seems to be somewhat more efficient than in a watertube boiler. It is difficult to estimate the difference numerically, but other conditions being equal, it would probably be safe to give to the watertube boiler additional heating surface to the extent of from ten to twenty percent._ On the other hand, it must be remembered that watertube boilers can stand forcing to a much higher degree than firetube boilers. With the latter supplying steam to triple expansion engines the ratio of heating surface to indicated horsepower can hardly be reduced below 2, while with the former this ratio has been reduced in many cases to less than one and one-half, and, as reported in cer- tain extreme cases, to between one-half and one. Watertube boil- ers have the further advantage that they are more readily con- structed for the higher and higher steam- pressure which modern practice is continually demanding. With watertube boilers, due to the construction and to the smaller amount of contained water, there is also less danger from disastrous explosion. With water- tube boilers steam may be raised much more quickly than with firetube boilers; from one-quarter to one-half hour is sufficient with the former, while from three to four hours should be taken with the latter. Watertube boilers are also much more portable than firetube. In many forms spare parts or even the whole boiler may be shipped in elements or sections across country by rail or to foreign ports by ship transport, put on board the steamer for which they are intended, and erected in place without difficulty. On the other hand, the watertube boiler imperatively requires fresh water feed. Under modern conditions this should be pro- vided no matter what the type of boiler in use, but if in emergency salt water must be used, the firetube boiler will receive the lesser injury. Again, from the small amount of water contained as a stock upon which to draw, the watertube boiler requires a more uniform feed than the firetube boiler, and is generally more sen- sitive to variations in the conditions under which it works. Again, the rupture of a tube is a more serious matter in the watertube. than in the firetube boiler. In the latter it may be plugged with- out disturbing the water and steam in the boiler, and with only a momentary interruption to its operation. In the former it is usually necessary to disconnect the boiler, draw the fires, blow BOILERS 8s down the water, and plug the split tube or insert a new one. Scotch boilers may be made in 2,000 horsepower units or even larger, while 4,500 is about the usual maximum for the watertube boiler, although, with oil fuel, this may be exceeded to a large extent. To summarize the general comparison between watertube and firetube boilers, the former have relative advantages in the following chief points: Weight, ability to stand forcing, suit- ability for high pressures, greater safety from disastrous explo- sion, quickness of raising steam, can be renewed without opening up decks and removal of deck houses. On the other hand, they have relative disadvantages in these points : A more rigid re- striction of the feed to fresh water, the necessity of greater regu- larity of feed, greater difficulty in dealing with leaky tubes, and general sensitiveness to variation in the conditions of use. To which may be added the present feeling of uncertainty as to their durability and efficiency under the conditions prevailing on deep water voyages, particularly with the class of men usually cai'ried by the merchant marine where the engineer force is so transient in its character that it can not be trained to the necessary degree re- quired to insure efficiency with the watertube boiler. All of these fears and doubts, however, are due to the over-conserva- tism of seagoing engineers who havfe had no experience with watertube boilers and are led astray in their judgment by fear of the, to them, unknown. Sec. 17. RIVETED JOINTS The various joints in a boiler are usually of the riveted form. The use of welded joints in various parts of boiler construction is increasing somewhat as greater skill is acquired in making them, but in ordinary practice the joints are riveted, and of various types, as follows : Riveted joints are divided into lap joints and butt joints, according as the plates lap over each other (see Figs. 32-35), or butt together at the edges, and are covered by one or two butt' straps (see Figs 36-40). They are also divided according to the number of rows of rivets into single, double or triple riveted joints (see Figs. 32-34). The rivets are usually staggered in arrangement, as shown in Figs. 33-40. Sometimes, though rarely, the chain arrangement, 86 PRACTICAL MARINE ENGINEERING as shown in Fig. 28, is used. While chain riveting is as strong, or perhaps even slightly stronger, than staggered riveting, the latter gives a better disposition of rivets for making a steam or watertight joint, and this fact leads to its more frequent use in boiler construction. In butt joints the arrangement of rivets is duplicated on each side of the joint, and the style of riveting is named according to the arrangement on one side. Thus, Fig. 36 shows a double-riveted and Fig. 37 a triple-riveted butt joint. A riveted joint may fail: (i) In the plate by tearing out or across from hole to hole, see Figs. 29, 30; (2) in the rivet by shearing; (3) in the plate or rivet by a crushing of the material. Fig. 28 The failure of a joint by the tearing out of the plate in front of the rivet, as in Fig. 30, is safely guarded against by placing the row of rivets at a proper distance from the edge of the plate. This, by experience, is found to be about one diameter in the clear, or one and one-half diameters from edge of plate to center line of rivets. In lap joints and butt joints with one cover, as in Fig. 31, the rivets resist shearing at one section only. In butt joints with double covers, as in Figs. 36-39, the rivets resist shear- ing at two sections. The total shearing strength of a rivet in double shear is usually taken as somewhat less than twice the strength in single shear. The British Board of Trade rules give 1% as the ratio to be used. With usual proportions the last mode of failure mentioned above is the leasj likely to occur, so that so long as the proper limits are not exceeded the resistance to crushing needs no especial examination. These limits will be given in detail at a later point. The strength of a riveted joint is, of course, determined by whichever is the weaker of the two, the plate or the rivets. In BOILERS 87 a properly designed joint the strength of the plate and that of the rivets should be equal, so that there will be no more likeli- hood of failure in one way than the other. It may be remarked, however, that since corrosion usually affects the plate only, it is often considered good practice to give to the plate a slight excess Fig, 29 Fig. 30 of Strength, so that even after some wasting by corrosion the joint may still be in fair proportion as to the relative strength of plate and rivets. No exact directions can be given for this in- crease, as it is simply a matter of judgment. The investigation of the strength of riveted joints by any simple theory is necessarily quite imperfect, because we do not know in just what way the stress is distributed through the re- maining part of the plate, nor through the section of the rivet, Fig. 31 nor what allowance to make for the frictional grip of the joint. Th€ proportions given by the following equations, however, are those which will give practically equal strength of plate and rivets, using the British Board of Trade rules. These rules represent standard and reliable practice, based on wide experience, and are substantially adopted by the United States inspection authorities. In thus considering a joint, take simply an element such as that between AB and CD in the following diagrams. It is clear in each case that the whole joint may be considered as made up of a series of such elements : 88 PRACTICAL MARINE ENGINEERING Liet p denote the pitch of the rivets ; that is, the distance from center to center. Where the rivets in one rovy are pitched twice as far apart as in another (see joints D, H, etc.), p denotes the larger of the two values. d denote the diameter of rivet.* » = p -^ d ^ number of rivet diameters in the pitch. * = thickness of plate. a j= t -j- d. T = tensile strength of plate per square inch of section. S = shearing strength of rivet per square inch of section. The ratio of 6" to T is taken as 23 : 28 or 5" = .821 T. The efficiency of the joint is the ratio between the strength of the joint and the original strength of the plate. ' It will be seen by the formulsegiven later that the efficiency of a joint is increased as d and p are made larger. There is, however, a prac- tical limit to the increase in d, due to the difficulty of heading up very large rivets, and a limit to the increase in p, due to the neces- sity of guarding against leakage. If the general proportions between d and t, as indicated later in connection with the various joints, are observed, the result will be a pitch within safe limits, and a joint agreeing well with the best practice. The largest permissible values of the pitch, according to the Board of Trade rules, are given by the following formula : p =C t + 1% ' where C is drawn from the following table : Form of Joint as Shown Below C Form of Joint as Shown Below C A 1.31 2.62 3.47 4.14 3.50 P G H 4.63 B 5 52 C 6 00 D I 6.00 E In no case should the pitch exceed 10 inches. Now proceed with the equations and proportions for various forms of riveted joints. * Strictly speaking, the diameter of the rivet hole should be used, as it is about 1/16 inch larger than the rivet before heading up. In the Board of Trade Rules, however, the diameter of rivet is used. The difference in proportion of joint is quite small, and probably not of practical importance. Joint A 89 Fig. Z% Joint A h = ly^ d B = 3d The element is A B C D, containing one rivet. Therefore, in this case: Strength of plate = t {p — d) T Strength of rivet = }i tt d' S = % ■^ iP X .821 T Since S = .821 T, for equal strength of plate and rivet: t (p — d) T = .821 TX rf= 4 .821 X ^ t p — t d= X d" 4 p d dp = .821 X -7854 X — = I .'. d d t d For equal strength of plate and rivet, P . d or n ^ I + .645 — d t = d (. + .6454J Efficiency = ■64s a + .645 The ratio d -h t may vary from 1.5 to 2.5, the lower values being more commonly employed with very thick plates on_ account of the difficulty of heading up excessively large rivets, and the *The exact figure is 644.8, and this difference between the actual figure and .645 produces a slight excess in efficiencies calculated by the n — I formula == efficiency. go PRACTICAL MARINE MGINEERING necessity of a moderate pitch to permit of proper calking to insure against leakage. In order, furthermore, to guard against danger of rupture by crushing, the upper limit, 2.5, should not be exceeded. The foregoing operations may be expressed also by the fol- lowing : Rule. ( I ) Select a diameter of rivet according to the thick- ness of the plate and the directions given. (2) Multiply this diameter by .645 and divide by the thickness of plate. (3) Add I to the result obtained in (2). (4) Multiply the diameter of rivet By the result ob- tained in (3), and the result will be the pitch suited to the diameter chosen. (5) Select the clearest working dimension, going usually above in order to give slight excess of strength to the plate. (6) To find strength of plate in the joint, subtract the diameter of rivet from the pitch, multiply by the thickness and by the tensile strength per square inch of section. (7) To find strength of rivet, find area of section, mul- tiply by the same strength per square inch as in (6), and then by .821. (8) To find original strength of plate multiply pitch by thickness of plate, and by the tensile strength per square inch, as in (6). (9) To find the efficiency, divide the lower of. the two results found in (6) and (7) by that found in (8). Example. To lay out a single riveted lap joint for j/i inch plates, using % inch rivets. 7 X. 645X2 Then % X .645 -^ y2= = 1.13 8 And 1. 13 -|- i.oo = 2.13. And 2.13 X Vs = 1.86 = pitch. Take the nearest eighth inch above and pitch =1% inches. Then taking the strength of the plate at 60,000 pounds per square inch : ' Strength of plate in joint = (iVb — Vs) X 'A X 60,000 = 30,000. Area of %-inch rivet = .60 square inch. Strength of rivet = .60 X 6o,coo X .821 = 29,556. Original strength of plate = 1% X H X 60,000 = 56,250. Efficiency = 29,550 -^ 56,250 = .525. BOILERS 91 Similarly, if 15-16 inch rivets should be taken, it would re- quire for equal strength in plate and rivet a pitch of 2.07 inches. If a pitch of 2yi inches, the efficiency will be .533. If 2.07 is taken, the efficiency will be .548. Joint B. Lap Joint. Double Riveted. Fig. 33. Joint B h = lyi d q not less than (.6 /> + .4 rf) fP = (.6 p+A dY (vJ^ .11 />' + .48 ^ d + .16 d? Hence H not less than V (i.i /> + .4 d) (.1 /> + .4 rf) B—zd+H Where ihere are two or more rows of rivets they must be placed at a sufficient distance apart, so that there may be no danger of rupture along a zig-zag line, as indicated in the diagram. To this end the British Board of Trade rules give certain values for the distance q as given above for this case. This distance is known as the diagonal pitch. The rules are derived from experi- ment. The distances resulting may be considered as the smallest allowable. In practice the values oi q are often made somewhat greater than would result from the rules. Having selected the distance q, the location of the second row of rivets is easily found from the first by constructing^ a triangle with base equal to p, and the two other sides each equal to q. In this case the element A B D C contains one whole rivet and two halves, or two rivets in- all. Then : Strength of plate = t (p — d) T Strength of rivets = H ^ d^ S t n — I 1.29 92 PRACTICAL MARINE ENGINEERING For equal strength of plate and rivets ; p d or M := I + 1-29 • d Efficiency := n 0+ 1.29 The values oi d ^ t may vary through about the same range as in joint A, above, and for the same reasons as there explained. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above : Rule: ( i) Same as for joint A (2) Use 1.29 instead of .645. (3). (4), (S)> (6) Same as for joint A. (7) Take twice the strength of one rivet, found as for joint A. - (8), (9) Same as for joint A. Example. To lay out a double riveted lap joint for J^ inch plates, using % inch rivets. 3 X 1.29 X 2 , Then 54 X 1.29 -^ Yz = ^ = I.93S 4 '^ And 1.935 + i.oo = 2.935. And 2.935 X Ya = 2.201 = pitch. Taking the nearest eighth above, p = 2]/^ inches. Then taking the strength of the plate at 60,000 : Strength of plate in joint = (2 14 — Ya) X /4 X 60,000 = 45,000. Area of Y i"ch rivet = .4418 square inch. Strength of rivets =: .4418 X 2 X 60,000 X -821 = 43,520. Original strength of plate = 2>4 X J^ X 60,000 = 67,500. Efficiency = 43,520 -^ 67,500 = .645. Similarly vv^ith % inch rivets, pitched 2% inches, the strength of plate and rivets will be nearly equal, and the efficiency will rise to .687. Ioi«t C. Lap Joint. Triple Riveted. h—iy,d q not less than (.6 /> + .4 rf) Hence H not less than V(i.i /> + .4 rf) (.1 /> + .4 d) BOILERS 93 B = z d -\- 2 H In this case the element A B D C contains two whole rivets and two halves, or three rivets in all. Then : Strength of plate = t (p — d) T Strength of rivets ^ ^ ■^ d' S Fig. S4. Joint C For equal strength of plate and rivets : P d or n = I + I.93S Efficiency == ■ t 1-935 n 0+1.935 The values of d -=- f may vary through about the same range as in joint A, above, and for the same reasons as there explained. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. Rule: (i) Same as for joint A. (2) Use 1.93s instead of .645. (3). (4), (5), (6) Same as for joints. (7) Take three times the strength of one rivet found as for joint A. (8), (9) Same as for joint A. Example. To lay out a triple riveted lap joint for J^ inch plates, using % inch rivets. 3X1-935X2 Then ^ X I-93S -i- J^ = = 2.903 And 2.903 + i.oo = 3.903. 94 PRACTICAL MARINE ENGINEERING And 3.903 X H = 2.93 inches = pitch. Take p = 3 inches. Then taking the strength of the plate at 60,000 : Strength of plate in joint = (3 — ^^ X J4 X 60,000 = 67,500. Area of ^ inch rivet = .4418. Strength of rivets = .4418 X 3 X 60,000 X .821 = 65,280. Original strength of plate = 3 X J4 >< 60,000 = 90,000. Efficiency = 65,280 -=- 90,000 = .725. Similarly with Ji inch rivets, pitched 3% inches, the efficienc becomes .764. Joint D. Lap Joint, inner row spaced one-half p. Triple riveted, with rivets i H ■ ^ ■ ^ H ■ 4- p -H ' Fig. 35. Joint D h — lyi d q not less than (.3 p -\-d) Hence H not less than V(.SS p + d) (.05 P + d) B = 3 d+ 2 H As seen below, the efficiency of this joint is superior to thi of joint C, but it is perhaps slightly inferior as regards tightnei agaihst leakage. In this case: Strength of plate = t (p — d) T Strength of rivets = ir d' S For equal strength of plate and rivets : p d — or »! ^ I + 2.58 — d t n — I 2.58 Efficiency = — — : + 2.58 BOILERS 95 The values oi d -^ t may vary through about the same range as in joint v4 above, and for the same reasons as there explained. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. Rule: (i) Same as for joint A. (2) Use 2.58 instead of .645. (3). (4), (5). (6) Same as for joint y4. (7) Take four times the strength of one rivet found as for joint A. (8), (9) Same as for joint yi. Example. To lay out a triple riveted joint as in D for J4 irich plates, using ^ inch rivets. 3 X 2.58 X 2 Then J4 X 2.58 -^ yi = = 3.87. 4 And 3.87 + i.oo = 4.87. And 4.87 X % = 3.65 inches = pitch. Take p = 3 11-16 inches. Then J/2 /> = i 27-32 inches. Then taking the strength of the plate at 60,000 : Strength of the plate in joint = (3Hie — %) X J^ X 60,000 = 89,062. Area of ^ inch rivet = .4418. Strength of rivets = .4418 X 4 X 60,000 X -821 = 87,050. Original streagth of plate = 3Hie X K X 60,000 = 110,625. Efficiency = 87,050 -=- 110,625 = .787. With % inch rivets spaced 2 7-16 inches in the middle row and 4% in the outer rows, the strength of plate and rivets would be nearly equal, and the efficiency would rise to .81. Joint E. Double Butt Straps. Double Riveted. h = iy2 d q not less than (.6 ^ + .4 rf) Hence H not less than V(i.i /► + .4 d) (.1 p + .4 d) B = 6 d-\- 2 H. Thickness of each baft strap not less than ^ the thickness oi plate. The arrangement of rivets is duplicated on either side of the joint line P Q. It is only necessary to investigate the part of 96 PRACTICAL MARINE ENGINEERING the joint on one side oi P Q. The element is then A B D C, as in joint B, except that the rivets are in double shear instead of single shear. For the total shearing strength of a rivet in double shear, as previously explained, it is customary to take i^ times -5K- h %^ — %i B I Fig. 36. Joint E the strength for a single shear instead of 2 times,- or to take the two strengths in the ratio 7 : 4. Then: Strength of plate — t (_p — d) T Strength of rivets ;= % ir iP S For equal strength of plate and rivets : p d or M = I + 2.26 d t n — I 2.26 Efficiency ^ a + 2.26 In all double butt strap joints d -^ t usually varies from i to iJ4- The lower range of values, as compared with joints in which the rivets are in single shear, is required in order to insure the joint against danger of failure by crushing. These operations may be expessed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. Rule: (i) Same as for joints. (2) Use 2.26 instead of .645. is)' (4). (5). (6) Same as for joint .4. BOILERS 97 (7) Take ^iV^ times the strengtli of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in E for i inch plates, using I yk inch rivets. 9 X 2.26 Then \% X 2.26 -^ i = = 2.54 8 And 2.54 + I = 3.54. And 3.54 X 9/8 = 3.98 inches = pitch. Take pitch = 4 inches. Then taking the strength of the plate at 60,000 pounds, as before : Strength of plate in joint ^= (4 — 1]/?,) X i X 60,000 = 172,500. Area of i ^ inch rivet = .994. Strength of rivets .= .994 X 3/^ X 60,000 X .821 = 171,376. Original strength of plate = 4 X i X 60,000 = 240,000. Efficiency = 171,376 ^ 240,000 = .714. Similarly with i inch plates and ij4 inch rivets, pitched 4% inches, the strength of plate and rivets will be about the same, and the efficiency is .737. Joint F. Double Butt Straps. Triple Riveted. h = lyi d q not less th an (.6 p -\- .^ d) Hence H not less than V(l.i /> + .4 rf) (.1 /> + .4 d) , , • Bz=6d + aH. Thickness of each butt strap not less than ^ the thickness of plate. The element of the joitlt is ^ 5 £> C, as in joint C, except that. the rivets are in dotrble shear. Taking, as before, the strength in double shear to that in single in the ratio 7:4: Strength of plate z=z t (p — d) T Strength of rivets = 2 1/16 ir d' S For equal strength of plate and rivets : p d — or M = I + 3.39 — d t «— I 3-39 Efficiencv a + 3-39 98 PRACTICAL MARINE ENGINEERING In this joint d -^ t usually varies from i to ij4, as explained for joint £. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. A -t c --1- h Fig. 37. Joint F Rule: (i) Same as for joint A. (2) Use 3.39 instead of .645. (3), (4), (S). (6) Same as for joints. (7) Take 5j4 times the strength of one rivet, as found for joints. (8), (9) Same as for joint /i. Example. To lay out a joint as in F with i inch plates, using I 3-16 inch rivets, 19 X 3-39 = 4-03 16 Then i 3/16 X 3-39 -4- I = ■ And 4.03 + I = 5.03. And 5.03 X I 3/16 = 5.97 inches = pitch. Take pitch = 6 inches. Then with strength of plate at 60,000, as before. Strength of plate in joint =(6 — i3/i6)XrX 60,000 = 288,750. BOILERS 99 Area of i 3/16 inch rivet = 1.108. Strength of rivets = 1.108 X SM X 60,000 X .821 = 286,500. Original strength of plate — 6 X i X 60,000 = 360,000. Efficiency = 286,500 -f- 360,000 = .796. Joint G. Double Butt Straps. Rivets as in Joint D. h C ig D Fig. 38. Joint G h = l]/i d q not less than (.3 p + d) Hence H not less than V (.55 P + d) (.oS P + d) B — 6 d + 4H. Butt straps to be of thickness not less than as given by the formula : 5(p — d) Thickness of strap = X (thickness of plate) ^ip—2d) the element of the joint is A B D C, as in joint D, except that the rivets are in double shear. Taking, as before, the strength in double shear to that in single shear in the ratio 7 : 4, Strength of plate = t (p — d) T Strength of rivets = 7/4 ^ d' S For equal strength of plate and rivets : p d or n = I + 4.52 d t PRACTICAL MARINE ENGINEERING n — I 4.52 EfBciency = a + 4-52 In this joint d -h t usually varies from about i to l^, as explained for joint E. These operations may be expressed by a rule similar to that for joint A, the numbered sections referring to that rule as given above. Rule: ( 1 ) Same as for joint A. (2) Use 4.52 instead of .645. (3)> (4), (S). (6) 'Same as for joint /4. (7) Take 7 times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. Example. To lay out a joint as in G with i>4 inch plates, using i^ inch rivets. 13 X 4-52 X 2 Then i^^ X 4-S2 ~ I'A = = 4-9 8X3 And 4.9 :+^ I = 5.9. And 5.9 X i^ = 9.6 inches = pitch. Take pitch for outer rows 9^and for inner rows 4 13/16. Then, with the strength of the plate at 60,000, Strength of plate in joint = (9^ — i^)Xi/4X 60,000 = 720,000. Area of i^ inch rivet = 2.074. Strength of rivets = 2.074 X 7 X 60,000 X -821 = 715, I57- Original strength of plate = 9^ X i>^ X 60,000 — 866,250. Efficiency = 715,157 -^ 866,250 = .826. Joint H. Double Bntt Straps. Triple Riveted, with double spacing in outer row on each side. ' h = iK' d q not less than .3 /> + .4 rf Qi not less than .3 p -\- d Hence H not less than V (.55 p -\- .4 d) (.05 /> + .4 rf) Hi not less than V (.55 p + d) (.05 p -\- d) . B = 6d + 2 H + 2 Hi Thickness of butt straps found by same formula as for joint G. The element of the joint is A B D C, containing four whole rivets and two halves, or five in all. These are all in double shear. BOILERS loi Taking, as before, the strength in double shear to that in single in the ratio 7 : 4, Strength of plate = t (p — d) T Strength of rivets = 3S/i6 t rf" 5" For equal strength of plate and rivets : p d or n = I + S.64 d t n — I 5.64 Efficiency = a + s.64 In this joint d -^ t usually varies from i to ij^, as explained for joint E. These operations may be expressed by a rule similar h f" H Fig. 39. Joint H to that for joint A, the numbered sections referring to that rule as given above. Rule: (i) ■ Same as for joint A. (2) Use 5.64 instead of .645. (3), (4). (5). (6) Same as for joint A. (7) Take 8^ times the strength of one rivet, as found for joint A. (8), (9) Same as for joint A. 102 PRACTICAL MARINE ENGINEERING Example. To lay oyt a joint as in H with i}i inch plates, using I 7/16 inch rivets. 23 X 5-64 X 8 Then I 7/16 X 5-64 -^ ^Vs — = 5.9 16 XII And 5.9 + I = 6.9. And 6.9 + I 7/16 = 9.92 inches = pitch. The limiting pitch by the Board of Trade rule for this case would be 9.87. This means that a pitch of 9.92 or larger would not be passed without special permission. If necessary to reduce below the limit, the joint should be re-designed with a smaller rivet. This case illustrates the point that these limiting values of the pitch, if rigidly adhered to, would prevent the attainment of the best joint efficiencies with thick plates. Assuming the right to proceed with the pitch derived from the formula, take 10 inches for the outer and 5 inches for the inner rows. Then taking the strength of the plate at 60,000, Strength of plate in joint = (10 — i 7/16) X i^ X 60,000 = 706,406. Area of i 7/16 inch rivet = 1.623. Strength of rivets = 1.623 X 8^ X 60,000 X -821 = 699,554. Original strength of plate = 10 X i^ X 60,000 = 825,000. Efficiency = 699,600 -^ 825,000 = .848. loint I. Double Butt Straps. Triple Riveted, outer row on each side being double spaced, and passing through inside butt strap only. h = lYi d q not less than .3 p -\- .4 d qi not less than .Z p -\- d Hence H not less than V(.55 P + -A d) (-05 P + A~d) Hi not less than V(.5S p + d) (.05 p + d) B = 6d + 2 H 5i=6rf + 2H + 2Hi Thickness of butt straps found by same formula as for joint G. The element of this joint is A B D C, with four rivets i:i double shear and one in single shear. Taking, as before, the strength in double shear to that in single in the ratio 7 : 4, Strength of plate ^ t (p — d) T Strength of rivets = 2 "■ (f 5" For equal strength of plate and rivets, p d — or n = I + S-i6 BOILERS T03 Efficiency ^ S.16 + S-I6 In this joint d -=- t usually varies from i to Ij4, as explained for joint E. ■ These operations may be expressed by a rule similar h H. 1 Fig. 40. Joint I to that for joint A, the numbered sections referring to that rule as given above. Rule: (i) Same as for joint A. (2) Use5.i6instead of .645. (3)>.(4), (5), (6) Same as for joint .^. (7) Take 8- times the strength of one rivet, as found for joint A. (8), (9) Same as for joint ^. Example. To lay out a joint as in I with i^ inch plates, using I 7/16 inch rivets. 23 X S.16 X 8 Then i 7/16 X 5-i6 -f- i?^ = = 5.40 16 XII And 5.40 -f- I = 6.40. And 6.40 X I 7/16 = 9.2 inches = pitch. Take 9^4 for the pitch of the outer row, and hence 4^ for I04 PRACTICAL MARINE ENGINEERING the pitch &f the inner rows. Then, taking the strength of the plate at 60,000, Strength of plate in joint = (9^ — i 7/i6) X i^ X 60,000 = 644,530- Area of i 7/16 inch rivet := 1.623. Strength of rivets = 1.623 X 8 X 60,000 X -821 =^.639,591. Original strength of plate = 9^ X i^ X 60,000 =;763,I25. Efficiency = 639,600 -^763,125 = .838 An examination of the values of the efficiency will show that these various joints for the same value of d -^ t stand, in this respect, in the order : H, I, G, F, D, E, C, B, A, Sec. 18. MATERIALS AND CONSTRUCTION [i] Materials ^ Open hearth mild steel is used almost universally as the material for boiler construction, and in standard practice is used exclusively for shells, drums, heads, furnaces, combustion cham- bers and braces. Both steel and wrought" iron are used for tubes, though seamless, cold drawn steel tubes may be considered as the better representing advanced engineering practice. Wrotight iron is also used to some extent for rivets, though in the best modern practice steel rivets are preferred. [2] Joints The various plates of a boiler are fastened together by riveted joints. These are of several varieties, as discussed in Sec. 17, and to which reference may be made. The holes in the plates are either drilled or punched. The former method is much the better, the plates being drilled in place. In the operation of punching, a thin skin of metal about the hole is so severely strained that its strength, and especially its ductility and toughness, are reduced far below what they are in the re- mainder of the plate. This is not the case with the operation of drilling, or, at least, not to anything like the same extent. Drilled holes may also be located more accurately than punched holes, and thus with the former the parts of a riveted joint may be more perfectly fitted than with the latter. The operation of drilling leaves, however, a sharp edge, which should be removed by a reamer in order to avoid any tendency to cut the rivet. In spite BOILERS J05 of the greater cost of drilled holes they are now generally ac- cepted as the best for all high class work, and in the majority of specifications no holes are allowed to be punched. Riveting is either by hand or by machine ; usually hydraulic. The latter gives much the better result, and is preferred where the machine can be made available. In many cases the construc- tion is such that the jaws of the machine cannot be brought to bear on the joint, and in consequence hand riveting must be employed. After being riveted the joints are calked to insure tightness against leakage. This operation consists in beating down the edges of the metal against the face of the opposite plate by means of special pneumatic driven or hand tools, as shown in Fig. 41. These rzT \ I Fig. il. Calking Tools are known as calking tools, and are of two types, square and round nosed, as shown in the figure. The latter form is usually employed in modern practice. For operations on board ship the common hand tool is, of course, most commonly used; but for extensive calking, as in the construction of boilers in the shop and where compressed air is available, the pneumatic driven tool is very largely displacing the hand tool. Where calking is employed, care must be taken that the surface of the lower plate of the joint is not cut by the calking tools, as such grooving may seriously we^en the plate, [3] Construction of Firetube Boilers The chief features of the construction of a Scotch boiler will now be considered. This will, at the same time, sufficiently illus- trate the operations involved in the construction of other types of firetube boilers. In the best practice the longitudinal joints are double butt strapped and triple riveted in order to give to the boiler in this direction the highest possible proportion of the strength of the io6 PRACTICAL MARINE ENGINEERING plate itself. The circumferential joints, those which run around the shell, are lapped and double or triple riveted. So far as in- ternal pressure is concerned the boiler is twice as strong to resist rupture around the girth as lengthwise so that a lapped circum- ferential or girth joint is quite enough for strength alone, and it only remains to make it steam and water tight and to insure the necessary stiflfness of the boiler as a whole. Single-ended boilers are usually made with two courses of plates, as in Fig. ii. Double- ended boilers are usually made with three courses. Each course consists of two or three sheets, varying with the diameter of the boiler. The heads are flanged, as shown in Fig. ii, and thus secured by riveting to the shell. In some cases the shell has been flanged instead of the head, hut such form of construction is rare. The head flanges are sometimes turned out, and sometimes in, as shown by the figure. Where machine riveting is to be used they must be turned out in order to allow the riveter to do its work. The back head is made usually in two pieces, with double or triple —Fox. — Purves. — Morrison. Fig. 42. Styles of Corrugation riveted lap joints. The front head is made in two or three pieces, according to size of boiler, usually with double riveted lap joints. The furnaces, as shown, are corrugated in order to give greater strength and elasticity. There are three styles of corru- gation 'in common use, as shown in Fig. 42. The furnaces are riveted to flanges formed on the front furnace sheet, and are con- nected by flanging to the sheets of the combustion chamber. Several different modes of connection are in use for this- pur- pose. In one the furnace end is left plain and the flange is all on the combustion chamber sheet, as in Fig. 9. In another the combustion chamber sheets are left plain and the flange is on the furnace, as shown in Figs. 11, 43 and 45. In some forms pro- vision is made for removal and renewal without disturbing the BOILERS 107 furnace head sheets. Thus, in Fig. 9 the diameter at the front is the same as, or slightly larger than, that on the outside of the corrugation, and so the furnace may be withdrawn through the opening in the front sheet. In other forms of connection, where the furnace is flanged, especial provision must be made for removal, as shown in Fig. 44. Here the back end of the furnace is necked in on the bottom and sides, and a flange is thus obtained which only extends out- side the outer diameter of the corrugation at the top. This flange Fig. 43. Flanged Furnace serves to attach the furnace to the combustion cHamber, and on cutting the joint loose the furnace may be taken straight to the front until the upper flange strikes the front sheet, and then swung upward and out of the front opening, as may be readily seen. In some cases where it is difificult to obtain the necessary room on the front head for the greater diameter of the outside Fig. 44. Removable Furnace of the corrugation, or where, for other reasons, it is not con- sidered preferable to have the furnaces removable without dis- turbing the front sheet, the furnace end at the front runs out on the smaller diameter, as shown in Fig. 45. Some one of the forms io8 PRACTICAL MARINE ENGINEERING favoring easy removal may be recommended as preferable in all ordinary cases. The combustion chamber, as shown, is built up of steel plates flanged and riveted together. The details of the construction vary somewhat with the form of furnace attachment adopted, with the Fig. 45. Non-Removable Furnace size of the boiler, and with the choice of the designer. The front plate is known as the back tube sheet. The top of the combustion chamber is sometimes flat, as in Figs. 9 and 66, and soinetimes rounded up, as in Figs. 1 1 and 46. _ Fig. 46. Rounded Top Combustion Chamber The tubes are secured into the tube sheets by "expanding," and "beading" or turning over at the back or at both the back and front ends. See Figs. 47, 48 and 49. Tubes are expanded by means of a tool as shown in Fig. 50, representing the Dudgeon expander. The tool is introduced into the mouth of the tube BOILERS log and the small steel rolls are forced out by means of the tapering steel mandrel on which they rest. The mandrel is then turned around, and this by means of the frictional contact with the rolls causes them to turn also, and thus to roll around on the inner surface of the tube, carrying the whole tool slowly round and Fig. 47. Tube End , Fig. 48. Tube End round. The mandrel is continually forced in and thus the rolls are forced outward against the tube. The action is thus a roll- ing of the tube out against the tube sheet, and in this way the joint is made thoroughly tight. Fig. 49. Tube Ends The Prosser expander, which was generally employed in former years,, is now but rarely used. It consists, as shown in Fig. 51, of a hollow tapering , plug divided up into separate ele- ments or sections which are held together by a steel band. ■ These Fig. 50. Roller Tube Expander are forced outward against the inner surface of the tube by driv- ing a taper mandrel into, the hollow between the elements. The action of the expander is thus to force the metal of the tube out against the edges of the sheet in a form of circular ridge as shown in Fig. 47. no PRACTICAL MARINE ENGINEERING Beading over the tube ends is usually done with a tool, as shown in Fig. 52, and the result is as shown in Figs. 47-49. In some cases the tube sheet is recessed out for the beaded end of the Fig. 51. Prosser Tube Expander tube, as shown in Fig. 48. The front ends of the tubes, as shown in Fig. 49, are usually swelled slightly larger than the rear ends to facilitate removal. The thickness of tl\e metal of plain boiler D Fig. 52. Beading Tool tubes is usually from 8 to 12 wire gage, or from about .17 to .10 inch. In addition to the plain tubes fitted as before described, stay Fig. 53. Stay Tube with Ferrule tubes are also frequently fitted. These are of extra heavy metal, usually about ^ inch thickness, and specially fitted to the tube sheets by screw joints, as shown in Fig. 53. These tubes act as stays between the tube sheets. Further reference to this point BOILERS in ^vill be found under the head of bracing. When stay tubes are fitted, it is customary to bead over only the back ends of the plain tubes, as in Fig. 49. Not infrequently, however, no stay tubes are fitted, and in such case the plain tubes must be beaded over on both ends in order that they may securely support the tube sheets. Instead of the ordinary form of boiler tube, the Serve Fig. 65. New Admiralty Ferrule Fig. 54. Serve Tube tube of cross section, as shown in Fig. 54, is frequently fitted. The ribs of metal reach down into the column of hot gas moving through the tube and furnish additional surface to absorb the -heat and help it through into the water. The surface on the fire side is thus much greater than the surface on the water side, while with the plain tube it is somewhat less. Such tubes are credited .; Fig. 58. Retarder with an increased evaporation per square foot of surface meas- ured on the water side. Their increased weight, however, offsets in a measure this increase of evaporative efficiencyper square foot of surface. Reference may also be made at this point to. the use of re- tarders in boiler tubes. These are long twisted strips of thin sheet steel, as shown in Fig. 56. They are simply laid in the tubes and serve to give the gases more or less rotary motion and to assist in' throwing them outward against the surface of the tube, thus 112 PRACTICAL MARINE ENGINEERING bringing every portion of the heated gas into contact with the tube surface. With forced draft and high rates of combustion the use of retarders has been accompanied with a mariied increase of economy. In some cases both Serve tubes and retarders have been fitted, but the special advantages of the combination may be called in question. As a measure of protection for the back ends of tubes under forced draft, cast iron ferrules are sometimes fitted. Fig. 55 shows the so-called Admiralty ferrule in place in a stay tube. The improved type of ferrule shown in Fig, 55 by reason of the air space is believed to act still more efficiently to protect the tube end than the form shown in Fig. 53. Bracing. It is now necessary to consider the bracing needed to make the boiler perfectly secure and safe under the Fig. 57. Adarason Ring Fig. :58. Bowling Ring pressures to which the various parts will be subjected. The gen- eral principles to be kept in mind are as follows : (a) Cylindrical surfaces subjected to pressure on the concave side are not helped by bracing. They must be made sufficiently strong by giving to the material a suitable thickness, (b) Cylindrical surfaces sub- jected to pressure on the convex side may be stayed like a flat surface, or they may be stiflfened by ribs running around them in planes at right angles to the axis, (c) Flat surfaces will support themselves if their area is sufficiently small in relation to their thickness and to the load per square inch, and it follows that large, flat surfaces must be subdivided into parts of such size that they may thus become self-supporting. As an illustration of (&), furnaces were formerly strengthened in this way, and the long favorite Adamson ring, as shown in Fig. 57, or the Bowling ring, as shown in Fig. 58, may be taken as good illustrations of this mode of adding support to cylindrical surfaces loaded on the convex side. The present corrugated fur- nace, especially the Purves type, as shown in Fig. 42, may be BOILERS 113 considered as a further illustration of the same principle. In modern marine boilers, aside from the furnaces, this mode of sup- port is chiefly used to stiffen the bottom of single combustion chambers where screw staybolts could not be readily fitted, and also in some cases the curved tops of combustion chambers. See Fig. 46. Coming next to flat surfaces as referred to under (c), the necessary subdivision is provided by the fitting of braces connect- mg the part to be supported to some point where the support can Fig. 59. Main Head Brace be provided, or by connecting together two surfaces urged by the steam pressure in opposite directions, as for example the two opposite heads of a boiler, as shown in Figs. 9 and 11. Occasion- ally als6 flat surfaces are aided by attaching to them stiffening ribs of angle or tee bar, as on the front tube sheet,' between the nests, of tubes, or between the tubes and the shell. Plates which are subjected to the direct action of the fire, as in the furnace and combustion chambers, are made relatively thin. This is done because a thin plate transmits heat better' than a thick one, and is subjected to less severe internal stresses due to the difference in temperature of its two faces. The thinner the plate, however, the less the area which will be self-supporting. Hence the braces for thin, flat plates are relatively small and closely spaced, while those for thick plates are larger and spaced . at greater intervals. 114 PRACTICAL MARINE ENGINEERING The main head braces are secured as shown in Fig. 59. A washer or strap is fitted on the outside to increase the supported area, and a nut is fitted both inside and outside so that the joint may readily be made tight, and that the brace may, if needed, act as a strut against pressure from without as well as a tie against pressure from within. In some cases a relatively thin plate is Fig. 60. Forked End Brace supported by a brace connecting it to a thicker or perhaps to a double plate, or to a plate not requiring support itself, but which furnishes a convenient point for carrying the load. In such case the attachment to the thin plate is often made, as shown in Fig. 60, in order the better to subdivide and distribute the support. In double-ended boilers, certain parts of the head, as for example those between the furnaces, are supported by braces running BOILERS IIS obliquely back to the shell and attached as shown in Fig. 6i. It often thus happens that braces must run at a slight obliquity in order to connect the parts to be supported with convenient points o o^ o o) Fig. 61. Flange Foot Brace of support. Other instances are often found in the braces con- necting parts of the back tube sheet below or between the tubes to the boiler head. In all such cases, wedge-shaped washers, as Fig. 62. Oblique Brace shown in Fig. 62, must be fitted under the nuts in order to get a good bearing between the nut and the shell. The braces connecting the relatively thin plates of the com- bustion chamber to the back head and shell of the boiler and to ii6 PRACTICAL MARINE ENGINEERING each other, are fitted by screwing them through into both plates, as shown in Fig. 63. The ends are sometimes riveted over and sometimes fitted with nuts. In some cases they are left threaded the entire length, in others the threads are raised on the ends, as Fig. 63. Screw Staybolt in the main head braces; The latter practice is much to be pre- ferred. These braces are commonly known as "screw stays," or "screw staybolts." This mode of fitting enables the screw stay- Fig. 64. Socket Bolt bolt to act both as strut and as tie, or to resist pressure in both directions. In some cases the older form of "socket bolt," as illus- trated in Fig. 64, is still fitted. In such case the head is riveted Fig. 65. Improved Screw Stay and the part of the bolt between the plates is provided with a hollow "socket." This acts as a strut and holds the plates at a proper distance apart. In some cases screw staybolts may be BOILERS "7 either hollow or drilled in at each end (see Fig. 65), to a point well beyond the inner face of the supported plate. The expansion and contraction of such parts of the boiler may have the effect of bending these bolts back and forth, and they thus in time become CBOWN BAB lii ijj ill] H 0000 COMBUSTION CHAMBER 0000 Fig. 66. Girder Brace or Crown Bar broken off, the break naturally occurring near the thicker of the two sheets where the bolt is held more rigidly. If this should , Fig. 67. Flanged Manhole and Fitting occur, or if the bolt should become badly corroded or pitted, especially near the plate, warning will be given of the fact by the escape of water or steam, and proper means must be taken for replacing the bolt. In this way timely warning is given of a condi- tion of aflfairs which, if allowed to go unnoted, might result in a collapse of the plate, or in a disastrous explosion of the boiler as a whole. ii8 PRACTICAL MARINE ENGINEERING The usual spacing of stays, such as that shown in Fig. 59, and supporting plates not directly exposed to the hot flames or gases is from 14 to 16 inches between centers, while for screw Fig. 68. Reinforce Plate stays supporting plates more or less directly exposed to the fire, the spacing is usually from 6 to 8 inches. For the support of the top of the combustion chamber, girders or crown bars are used, see Fig. 66. The load is transferred by means of the bolts from the combustion chamber plate to the p-O' "^ ^^O ^ V3/ )000000/^ FRONT OF SCOTCH BOItER Fig. 69. Manhole and Fitting- in Shell of Boiler Fig. 70. Reinforce Plate girder, while the latter is supported by the edges of the vertical plates forming the front and back of the chamber. These girders are made of two pieces of steel plate, usually from Yz to fi inch thick, bolted or riveted together with distance BOILERS iig pieces between so that the bolts which take the load from the flat plate may pass up between them as shown in the figure. The combustion chamber is sometimes secured to the back head of the boiler, or in double-ended boilers the two combustion chambers are secured together by plate braces fitted as shown in Fig. 46. Such are usually called gusset braces. In the general internal arrangement of the tubes, furnaces and combustion chambers, care must be taken to allow, as far as Fig. 71. Manhole Plate and Fittings possible, a ready examination of the various parts. In good modern practice a space of from 10 to 12 inches is left between the nests of tubes and between the tubes and shell, to allow the passage of a man from the steam space down through these spaces to the furnaces, and also to provide better circulation for the con- tained water. Manholes and Covers. For the purpose of entering, examin- ing and cleaning the interior of a boiler, man or hand holes are cut in the head or shell. These are then covered by manhole covers, plates or doors, as they are variously called. These are secured by bolts and dogs, as shown in Figs. 67-71. The usual size of a manhole is 11 by 15 inches, which are the dimensions required by the United States rules. It is of oval or elliptical 120 PRACTICAL MARINE ENGINEERING shape, so that the cover with its lip extending over the edge may be gotten in and out without difficulty. The joint is made on the inside in order that the pressure may tend to keep the joint tight. A handhole is similar in shape and fitting, and is simply smaller in size. In order to provide local strength and stiffness and to help support the load which comes on the feet of the dog, and also, when the hole is cut in the shell, to restore in some measure the metal taken out, a reinforce ring of metal is fitted about the hole. Such a ring of cast steel for a hole in the shell is shown in Fig. 69. The inner face is planed, so that the joint with the cover is readily Fig. 12. Furnace Front made. In order that the removal of the metal may affect as little as possible the strength of the shell, the longer axis of the hole should run around the boiler rather than lengthwise. For holes in the head of a boiler the metal is often flanged inward, as shown in Fig. 67, the joint being made against the dressed edge of the ring. Where a manhole or handhole comes close to through braces, as, for example, near the furnaces, the reinforcing plate may be formed, as shown in Figs. 68 and 70. At the angles or corners the plate is of sufficient width to let the threaded end of the brace come through, and the outside nut is then jammed down on the ring as shown. For heavy pressure the fitting illustrated in Fig. 71 may be recommended. The reinforcing ring is of flanged steel, and the cover of steel plate also, somewhat thicker BOILERS .121 than the metal of the shell. An angle iron, as shown, is riveted to the cover, making a neat fit within the reinforcing ring, and keeping the plate accurately to its seat. ' Furnace Fronts and Doors. The furnace front is a fitting attached to the mouth of the furnace, and carrying the furnace door. In Figs. 72 and 73, a common form of arrangement is shown. The front consists of a steel plate forming the outer part, and made with lugs or a flange for attachment to the furnace. The opening for the door is formed, as shown, within this front or door frame as it is sometimes called. Attached to this frame and with 'a space between is a second plate of cast iron forming the inner wall. This is pierced with a large number of small holes, while the frame is provided with a smaller number of larger holes. These are provided for the purpose of admitting air to the furnace above the grate. The inner plate is subject to the direct action of the fire, and although cooled somewhat by the air passing through it, it is liable to burn out from time to © © ® © iO©@©©0@0©Qtf O"®" © © ^© © ©00 0,4^.®'® * e o © @ ^^ o o I r @ o ^^- '@ © © ^ — • \ ""^ © © A © © m\ © @ @ e^ox @ © © \ © © © © IS \ tr\© ® \ 3 ©© m 1 Fig. 73. Detail of Furnace Front time. It is for this reason that it is made as a separate piece, and so is readily replaced as occasion requires. The door is formed in much the same way as the frame, and is provided with holes in a similar fashion and for the same purpose. Often a small covered peephole is provided for examining the fire without opeiiing the door. In some cases also a small opening is made through which a slice bar may be introduced for stirring or 122 PRACTICAL MARINE ENGINEERING breaking up the fire without opening the door. A form of slide or gridiron is also sometimes fitted so as to control the amount of air entering above the grates. In some cases the doors and frames are made entirely of flanged steel plates instead of cast iron, while much variety exists in the arrangement of the holes for the intro- duction of the air. Certain special fittings necessary to adapt the furnace fronts and doors to the application of forced draft will be referred to at a later point. Another type of door, known as a balanced inswinging door, has come much into favor in the last few years. Such doors are Fig. 74. Section of Furnace and Grate hinged at the top and swing into the furnace when open, the door being fitted with outside counterbalance weight's. These doors have the advantage of being much handier when coaling or working the fires and have the additional great advan- tage of closing automatically by sudden rush of pressure when internal rupture of tubes occurs, thus protecting the men from a sudden outrush of steam and hot coals into the fireroom. The ash pit door usually consists simply of a plate of thin sheet steel provided with 1:he necessary lugs and handles, and covering the front opening in the furnace below the grate bars. It is used chiefly as a damper in connection with closed stokehold forced draft. BOILERS 123 It may also be fitted to inswing and be counterbalanced similarly to the inswinging furnace door. Grate and Bridge Walls. The general arrangement of the inside of the furnace is illustrated in Fig. 74. The grate extends from the front of the furnace to the bridge wall as shown. The bottom of the door frame extends back a little way and drops down, forming a shelf for the support of the front ends of the grate bars. In some cases this extension of the door frame ex- tends back some distance, forming the so-called dead plate, uporJ. which bituminous coal may be piled when first fired, so as to pro- vide for the gradual distillation and combustion of its gases. The grate bars may be made in a large variety of forms. In Fig- 75 is shown the standard type of cast iron bar. There are £ ^ ^=^>=^ ■ 3 ¥ Fig. 75. Grate Bar usually two lengths of bar in the length of the furnace, supported by the door frame in front and bridge wall at the rear, and by bearing bars in the middle. These latter in turn are supported at their ends by attachment to the furnace. The bars are usually cast double, as shown, while for convenience in fitting grates of varying widths, a smaller number of single bars are usually pro- vided. The width of air space between the bars is usually made about equal to the width of the bar, or about one-half of the entire grate area, although this proportion should vary somewhat accord- ing to the fuel in use. The surface of the grate usually slopes slightly from front to rear, from i in 24 to i in 12, covering the usual range of angle. Cast iron grate bars often have a shallow groove running along the top. This fills with ashes and tends to prevent the clinkers adhering to the grate. In addition to the type of bar shown in Fig. 75, square wrought iron bars running the whole length of the furnace are sometimes used, and there is a large variety of patent and special 124 PRACTICAL MARINE ENGINEERING kinds of shaking grate. The purpose in grates of this character is to provide means for breaking up and working the fire without the need of opening the door. Many of them accomphsh this end to a considerable extent, but the greater simpHcity and cheapness of the plain cast iron grate, as in Fig. 75, insures for the latter a wide use, and it is still the favorite in ordinary practice. Turning now to the bridge wall, a common arrangement is shown in Fig. 74., A casting extends across the back of the fur- Fig. 76. Front ' Connections, Uptakes and Funnel Base nace and is supported by attachment at the sides. This supports the back ends of the grate bars, as already referred to, and , also a wall of fire brick which forms the back limit of the grate, and over which the products of combustion pass on their way to the combustion chamber. Instead of fire brick, the use of cast iron for bridges is becom- ing frequent in modern advanced practice. Such bridges are of ribbed or channeled form, and in use they become sufficiently covered with ashes to form a protection against the heat of the fire. Front Connections and Funnel or Smoke^Pipe. After leav- ing the tubes at the front end the gases and smoke must be guided BOILERS I2S to the base of the funnel. This is done by the front connection or smoke boxes and uptakes, as shown in the diagrams. Fig. 76 shows the connection made between two single-ended boilers and one funnel, used in common by both. The boilers are placed front to front in an athwartship fireroom. Fig. yy shows the connections between one double-ended boiler and the smoke-pipe. These connections are formed of sheet metal riveted up in two or more thicknesses with an air ?pace or non-conducting material be- Fig. 77. Front Connection's" and Uptakes tween. The term front connection refers more especiauy to that part of the passage directly in front of the tubes. This is provided with doors swinging upward to allow examination, cleaning and repair of the tubes. A swinging damper is often placed in the up- takes for controlling the draft as may be desired, especially where two or more boilers are connected to one funnel, The futinel is also made of sheet metal riveted up, and, in good practice, in two thicknesses with a considerable air space between. This tends to prevent loss of heat by radiation, and thus the temperature of the gases is kept as high as possible while in the funnel, as is neces- 126 PRACTICAL MARINE ENGINEERING sary for good draft. It may be remembered that for boiler economy the temperature of the waste gases at the front connec- tion should be as low as possible, while for the sake of the draft all further loss of heat while in the funnel should be prevented. Around the base of the funnel is fitted an additional air screen or passage, known as the air casing. See Fig. 78. This serves^ to OUTE R STACK Fig. 78. Funnel or Smoke Pipe ventilate the fire rooms and to protect the neighboring parts of the ship from the heat radiated by the funnel. The air casing is pro- tected from the weather by a sloping ring of metal attached to the funnel, as shown in the figure, and known as the umbrella. The weight of the funnel is usually carried by straps or lugs attached to the structure of the ship, and it is furthermore stayed by guys on deck in order to provide the necessary steadiness and support in a seaway. In small craft, however, the weight of the funnel is often taken simply by the uptakes and boilers. BOILERS 127 The funnel is often provided with a cover, which may be placed over the top when the ship is laid up, or when for other reasons the funnel is not in use. The cover is usually kept a little distance above the top so as to allow the escape of smoke from small fires used for warming and airing the boilers. A ladderway should also be provided on the funnel to assist in examination, adjustment of guys, fitting of cover, etc. In small craft a damper is often fitted in the funnel near the base to assist in controlling the draft. [4] Construction of Watertube Boilers Only a few points will require special notice under this head- ing. As has already been seen, many types of watertube boilers consist of one or more cylindrical drums above and one or more below, joined by a series of tubes. See Figs 15-27. These drums, which may be as much as 54 inches diameter, are made from steel plates usually by flanging and riveting in the usual manner. The heads alone of such drums require consideration as regards brac- ing. If of sufficient size to require it, they may be braced by through bolts as with boiler heads. In most cases, however, the heads are bumped or made of dished form, either concave or con- vex on the outside. The latter is preferable, as the pressure is then carried on the concave side, and according to the United States law such heads are allowed, without bracing, a pressure the same as that for a cylindrical shell of a diameter equal to the radius of the sphere of which the head forms a part. It is much preferable to form the heads in this way, avoiding the need of bracing, and thus leaving the interior of the drum freer for examination. To allow access to the interior, manholes or handholes with appropriate cover plates are fitted to the heads. Instead of forming these drums with riveted joints, drums with welded joints have recently come somewhat into use, but only to a limited degree. With boilers having headers formed by the space between two parallel sheets, the necessary arrangements are quite differ- ent. These sheets require special support, and this is usually pro- vided by screw staybolts or other equivalent stays worked between the two sheets, attached to the tube sheet between the tubes as convenient, and securely tying the two sheets together. In some cases the outer sheets are supported by rod stays passing from head to head through the tubes. In such case the tube sheets'are 128 PRACTICAL MARINE ENGINEERING left to be supported by the tubes which are thus thrown into com- pression, and the tubes must, therefore, be carefully expanded, especially on the inner side of the sheet, in order to give sufficient hold to support the sheets in this direction. In Sec. i6 [6], in speaking of the operation of watertube boilers, reference was made to a separation in the upper drum of the water and the steam as they are delivered from the upper ends of the tubes. This is usually effected by some form of baffle plate. A plate pierced with small holes is placed just in front of the tube openings, and against this the escaping jets of water and steam are directed. The water is supposed to collect on the plate and to run down to the lower edge, or to the water in the lower part of the drum, while the steam passes through the holes and enters the steam pipe beyond. In the Belleville boiler, as in Fig. 27, there is a series of baffle plates forming a more or less tortuous passage through which the steam must pass on its way to the outlet, while at the last there is a plate with holes which exercise a straining action in the manner described just above. Special separators are sometimes fitted in addition to these internal separating devices. The tubes of watertube boilers are of wrought iron or steel, and welded or seamless drawn. For the bent tube boilers seam- less drawn steel tubes are to be preferred. For straight tube boilers welded iron tubes are still in common use. The tubes are secured to the tube sheets either by expanding or by special fittings with screwed joints. In general there is a force tending to draw the tubes out of the tube sheet or junction box or other form of header, equal for each tube to its cross sectional area multiplied by the steam pressure. This force must be resisted by the tube fastening, and while it is not usually serious in amount, its ex- istence should not be forgotten, and the need of care in the fasten- ing is shown. In all high class boilers, however, the tubes are all seamless drawn steel, expanded into the drums or headers, and no screw stays or screw joints are permitted. The furnaces of watertube boilers are fitted with grate bars with a space below for the ash pit, all inclosed in the same general casing which surrounds the boiler as a whole, and as shown in the various figures referred to in the foregoing. Often a considerable amount of fire brick is used as a lining to the furnace, and for protection to the lower ends of the tubes. BOILERS 129 Due to the great variety of forms of watertube boilers, the details of construction often present the widest variation, and they cannot be so readily reduced to standard forms as in boilers of the firetube type. [5] Common Sizes and Dimensions of Scotch Boilers The furnace diameter for Scotch boilers is usually found between 42 and 48 inches. The upper limit comes about in the following manner. Taking into account the extreme ranges of temperature to which this part of the boiler is subjected, and based on general experience, it is usually considered that from y2 to y^ inch is about as far as it is desirable to carry at present the thickness of the metal for the furnace. Again the strength of the furnace increases with the thick- ness and decreases with the diameter. Hence for a given pressure and limit on the thickness, the diameter will be limited as well. With modem pressures and a general limit on the thickness as above, the limit on the diameter, therefore, results. Rarely fur- naces are met with up to 54 inches, but only with the more moder- ate steam pressures. The lower limit for furnace diameter is given by a consideration of the necessary space between the fire and the furnace crown. If this space or height is not sufficient the fires cannot be properly worked and the combustion will be incomplete, due to insufficient space for the admixture of air with the gases given off from the coal. In fact, for efficiency of combustion the diameter of the fur- nace should probably be larger than conditions will allow to be fitted. As a lower limit, however, it may be considered inad- visable to fit furnaces much smaller than 42 inches, though they are sometimes found down to 36 inches. The length of firegrate is usually found between 5 and 6 feet, though occasionally it extends to 6 feet 6 inches, or may be found as short as 4 feet 6 inches. The chief limitation here comes from the limit in the capacity of the average fireman to efficiently work his fire beyond a certain length. For average practice 5 feet 6 inches may be considered a good length, while it is doubtful if grate area added beyond this lehgth will be of any great value for steam production. It is more than likely to become partially choked with ashes and clinker, while a shorter grate of 5 feet or 5 feet 6 inches in length may be kept bright and efficient over its entire surface. 130 PRACTICAL MARINE ENGINEERING The Jength of the furnace itself being equal to the tubes wiT! be somewhat longer than the grate. The.differaice is usually from 12 to 24 or even 30 inches. This gives for the usual length of furnace and of tubes from 7 to 9 feet. The usual depth of the combustion chamber is from 24 to 30 inches. This will usually give a suitable volume, and will also provide a sufficient space within which a man may swing a ham- mer or make use of such other tools as may be necessary in caring for the back ends of the tubes. The usual thickness of the water leg or space between the back of the combustion chamber and the back head of the boiler is from 6 to 9 inches. It will thus be seen that the usual length of a Scotch single- end boiler will be found between 10 and 12 feet ; 10 feet 6 inches and 1 1 feet are quite common values. Comparing the construction of a single and double-end boiler it is clear that the length of the latter will be slightly less than twice the length of a single-end. This gives for the usual length of a double-end boiler from 18 to 21 feet. The diameter of the boiler will depend largely on the number of furnaces to be fitted, and on the steam pressure, low pressures requiring more volume above the water level for the steam than high ones, and on any limitations in the thickness of the plates em- ployed. Modern foUr furnace boilers are usually found between 15 and 17 feet in diameter. For three furnace boilers the diame- ters will similarly range from 13 to 14 feet, while for two furnace boilers the diameter may vary from 10 feet or less to 11 or 12 feet. The usual diameter for tubes is from 2^ to 3 inches. The smaller sizes are used with forced draft and the higher rates of combustion. For natural draft 2^ and 3 inches are common sizes. The thickness of boiler tubes is usually specified by sheet metal gage number. Plain tubes are usually No. 8, 10 or 12, cor- responding to .17 to .10 inch. Stay tubes are usually about No. 3 or ]4 inch in thickness. [6] Common Proportions for Scotch Boilers Grate Surface (G. S.) 10 to 15 indicated horsepower per square foot G. S. BOILERS 131 Heating Surface (H. S.) 2 to 5 square feet per indicated horsepower, or 25 to 40 square feet per square foot G. S. Coal Burned. 15 to 30 pounds per square.foot G. S. per hour, or J^ to I pound per square foot H. S. per hour, Water Evaporated. 6 to 10 pounds per pound of coal, or 4 to 10 pounds per square foot H. S. per hour. Section of Passage Over Bridge Wall. 1-6 to 1-8 G. S. Sectional Area of Tubes. 1-5 to 1-7 G. S. Sectional Area of Funnel. 1-6 to 1-8 G. S. Volume of Combustion Chamber. 3 to 4 cubic feet per square foot of G. S. Steam Volume. 0.3 to 0.4 cubic foot per indicated horse- power. [7] Weights of Boilers A modern four furnace single-end Scotch boiler will weigh in the neighborhood of 40 tons, or upward, while the water will weigh not far from 20 tons, making 60 tons or more for the boiler as a whole. A four furnace double-end boiler will similarly weigh not far from 70 tons, while the water will weigh not far from 40 tons, making no tons more or less for the boiler as a whole. For a modern three furnace single-end boiler the weights would be similarly about 25, 15 and 40 tons, respectively, for boiler, water and total, while for a three furnace double-end boiler they would be about 45, 25, and 70 tons, respectively, for boiler, water and total. Wide variations, of course, are found in the weights of boilers, and the above figures are only given to show the general nature of the weights involved. The weight of boilers with and without water, per square foot of heating surface, has already been noted in Sec. 14. From these various figures and propor- tions it results that Scotch boilers may be expected to develop from 20 to 30 indicated horsepower per ton according to conditions, while for watertube boilers the figures will run from 30 or 40 for the heavier types to 60 or 70 and even more for the lighter types, and with extreme rates of forced draft. [8] Western River Boat or Flue Boilers As noted in Sec. 16 these boilers are in common use on the western rivers of the United States. A few additional points may here be given regarding their construction and installation. 132 PRACTICAL MARINE ENGINEERING The length of such boilers varies from 20 to 30 feet, with a diameter of about 4 feet and with from 4 to 6 flues 10 to 14 inches in diameter. The shells are made up of several courses as shown in Fig. 14, the circumferential seams being single riveted and the longitudinal seams double riveted. The flues are usually made also in lengths, lap welded and telescoped together. When such boilers are arranged in battery they are placed side by side and are usually provided with a single setting, thus giving a common furnace for the entire battery. The length of grate bar is short, being usually about 4 feet 6 inches. The boilers are furthermore usually connected by a steam drum on top and by one or more mud drums at the bottom. The steam drum for the size of boiler referred to above may be from 18 to 24 inches in diameter, connected by legs 12 to 16 inches in diameter and spacing the boilers so as to give flame room of 9 to 12 inches between the shells. In order to make the setting of such boilers as light as pos- sible the brick work may be kept down to a single thickness of fire brick supported by a sheet iron casing. The ash pan is prefer- ably of steel plates lined with fire brick laid in cement. An in- teresting feature of the ash pan is the ash well which is frequently fitted. This consists of a 10 or 12 inch cylindrical passage leading from the surface of the ash pan down through the bottom of the boat, and through which the ashes are discharged overboard without further handling. The boiler fronts are of cast iron with suitable fire door and ash pit openings. The. uptakes and funnels, or chimneys as they are more commonly called, are made of heavy sheet iron and are supported by bracing carried down to the main deck beams which carry the boilers themselves. As noted below, the engines work non-condensing, and the exhaust, as a rule, is led first through the feed heaters to the "Doctor," as described later, and then to the base of the chimneys for forming a blast and forcing the combustion. Connections may also be provided for carrying the exhaust to an exhaust pipe lead- ing to the air, and also in part to the stern wheel if desired, in order to prevent the formation of ice in cold weather. Lever safety valves, as illustrated in Fig. 79, are usually em- ployed on these boilers, while gage cocks, fusible plugs, steam gages, and blow-off cocks are provided in accordance with usual practice. BOILERS- 133 The Steam, piping is usually of lap-welded wrought iron with flanged joints. One of the chief features of western river practice is the flexibility of the boat under different conditions of lading, and the necessity for allowing for such flexibility in the connec- tions between the. boilers and engines, and between the engines and wheel. Between the boilers and engines this is usually pro- vided by the introduction of long bends or special connections in- tended to allow for changes due to expansion, contraction, twist- ing, etc. In addition to the flue boiler, as illustrated above, the direct fire tubular or locomotive type of boiler, as illustrated in Fig. 12, is sometimes used on the western rivers, each boiler being thus self- contained, and the brick work setting of the flue boilers being dis- pensed with. The flue boiler, however, is the more used and must be considered as the typical boiler in this field of practice. Sec. 19. BOILER MOUNTINGS AND FIRE ROOM FITTINGS [1] Safety Valves The purpose of the^ safety valve is to provide for the escape of the steam in case the pressure should tend to rise above the safe working limit for which the valve is set. There are two kinds Fig. 79. Standard Lever Safety Valve of safety valves, known as lever and spring valves, according as the valve is kept down on its seat by a weight on a lever or by a powerful spring under compression. Fig. 79 shows the construc- tion of the standard United States lever valve. The valve itself has a plain conical face, and fits to a corre- sponding seat as shown. In its motion up and down it is guided by the double stem, so that it can by no means become jammed 134 PRACTICAL MARINE ENGINEERING in the chamber. The pressure of the steam comes on the bottom of the valve, and as it reaches or passes the limit for which the adjustment is made the valve lifts and the steam escapes about the edge, and thence is led by the escape pipe to the deck. The actual lift of a safety valve is very small, ^ inch being usually a large Fig. 80. Double Spring Safety Valve (Duplex) lift. The opening for the escape of the steam depends on the circumference of the valve and on the lift, rather than on the area and lift. Safety valves are, however, usually designated and de- termined according to their area. The weight acts by means of the lever, as shown, and may be adjusted so as to allow the valve to open at the pressure desired. In modern practice the lever valve is infrequently used, ex- cept in vessels engaged in smooth water (river) service, the spring valve being fitted almost universally. In this form of valve, which BOILERS 135 is shown in Fig. 80-81, the chief point of difference is in the sub- stitution of the spring for the weight and lever. The tension of the spring is adjusted by a screw at the top, so that the valve will not open until the limiting pressure is reached or exceeded. It is readily seen that as soon as the valve rises the spring is com- pressed and the tension is increased. It is also found that with the plain form of valve, as shown in Fig. 79, the pressure on the face decreases the instant the valve lifts. Due to these facts it follows that such a valve, especially when controlled by a spring, is apt to seat itself the instant after rising, lifting again the next instant in answer to the restored value of the pressure. This irregular action will lead to a rapid opening and closing of the valve, pro- ducing a chattering noise very undesirable in passenger boats, and interfering with the continuous and regular escape of the steam. Index plal Body Valve Adjustmg rini Valye Beat- Fig. 81. Duplex Safety Valve, showing Names of Parts To avoid this a lip of one form or another, as shown in Figs. 80, 81, 82 and 83, is fitted to the valve at or beyond the edge, so that it may catch the escaping jet of steam, and thus increase the effec- tive area of the valve after it has lifted from the seat. In such case the valve is forced farther from the seat, and while it still vibrates, it remains definitely open until the pressure has fallen some 4 or 5 pounds below that for which it opehs. The valve then touches the seat in one of its vibrations downward, and remains closed until the pressure again rises to the point for which it is set. The safety valve should always be fitted with a hand lifting gear, 136 PRACTICAL MARINE ENGINEERING so that it may be opened by hand when desired, and the spring adjustment should be protected by lock and key, so that it cannot be changed by unauthorized persons. For large boilers, instead of one large valve, safety valves are often fitted in groups of two or three. This reduces to the smallest possible limit the danger from sticking or other derangement of Fig. 82. Enlarged Section of Lip Fig. 83. Safety Valve and MuiBer the valve. The safety valve or valves should always be attached to a fitting leading, direct to the boiler, and with no possibility of closing it off by a stop valve. If both stop and safety valves are attached to the same fitting the latter must always be placed inside or nearer the boiler than the former. [2] Muffler This fitting, though not in the fireroom, may be properly re- ferred to at this point. It consists of a metal chamber filled with bits of metal or stone, marbles, wire-gauze, small spiral springs, or with thin plates in layers pierced full of holes and arranged in staggered fashion so as to provide a series of zig-zag passages for the steam. The steam from the safety valves and escape pipe BOILERS 137 makes its way to the air through this chamber, the purpose of the fining being to muffle or deaden the noise, which might otherwise seriously interfere with the giving of orders on deck. Fig. 83 shows a combined safety valve and muffler, the latter with plates as above described. Such an arrangement would be applicable for small or open craft having but one boiler, such as launches, small yachts, etc. Mufflers are not usually fitted on seagoing ships. [3] Stop Valve Each boiler is connected through a separate boiler steam pipe to the main pipe. The entrance of steam to this pipe is con- Fig. 8i. Boiler Main Stop Valve trolled by the boiler stop valve, which thus provides for the regula- tion of the supply of, steam to the engine, and for closing the boiler of? entirely from the main steam pipe if necessary. The usual type of valve employed is shown in Fig. 84, and consists of, a valve disk guided to its seat by wings, and raised or lowered by its connection with the screw spindle and handle as shown. As 138 PRACTICAL MARINE ENGINEERING also shown in the figure, the valve seat with wings and guide for the valve is very commonly a separate piece of gun'metal or bronze, specially fitted for its strength and wearing qualities. Commonly in warship practice, and to some extent in mer- cantile practice, such valves are made self-closing in case of rup- ture of the boiler. In fundamental principle such a valve is a form of non-return valve, as illustrated by the check valve of Fig. 85. The screw stem does not open the valve, but limits simply the extent to which the valve can open. A second plain stem passing through the first then allows the valve to be pulled open by hand, even if there is no definite difference of pressure to force it open. In case of accident which reduces the pressure back of the valve so that the rush of steam is in the reverse direction to its usual flow, the valve will be closed by this rush and held securely on its seat by the excess of pressure on its outer face, thus shutting ofif the injured boiler, and retaining the others intact for use. If such an arrangement is not fitted and the valve cannot be closed by hand, or until it can be thus closed, an entire battery of boilers may be thrown out of use by the rupture of any one of them, all of the steam formed escaping through the one opening. Such form of valve should be placed with the spindle horizontal, so that its own weight may not enter as a direct factor in the movement of the valve toward and from its seat. Another form of this type of valve carries a piston on the sliding stem, this piston working in a cylinder to which steam is admitted by opening a valve in an adjacent boiler compartment in case of accident, the pressure thus exerted driving the stop valve home on its seat. Such quick power-closing valves should always be fitted, whether the vessel be a war vessel or not, as they are of the utmost value in case of rupture of the boiler of any character. Boiler stop valves are made of cast iron, composition or cast steel, depending upon the grade of work required and the pres- sure to be carried. In case the valve is of cast steel or cast iron, a composition valve seat is usually fitted. Where superheated steam is used it becomes imperative to use cast steel with nickel or monel metal seat and valve disk, as the superheated steam tem- perature greatly weakens composition, while the corrosive and erosive action of superheated steam on steel and iron is excessive. BOILERS 139 [4] Dry Pipe or Internal Steam Pipe This is a pipe of relatively thin metal placed within the boiler, extending lengthwise, and close to the top of the shell. At the inner end it is closed, and at the outer end connects with the pipe leading to the safety valve chamber, stop valve and boiler steam pipe. Along the top or sides of the pipe are cut a large number of narrow slits, through which the steam enters the pipe. This Fig. 85. Boiler Check Valve arrangement has the efifect of drawing the steam from the highest part of the steam space, and of straining and drying out some part of the entrained water. A small hole in the bottom of the pipe provides for draining off the water which may gradually collect. The uniform draft of steam from the whole length of the boiler tends also to prevent the priming which might be caused by drawing it all from one point. I40 PRACTICAL MARINE ENGINEERING [s] Feed Check Valve and Internal Feed Pipe . The water from the feed pump comes to the boiler through the feed pipe, and then at the boiler passes through the feed-check. This is a screw-down, non-return valve, as shown in Fig. 85. The valve itself is entirely disconnected from the spindle, and the lat- ter simply limits the height to which the valve can rise, while by screwing down sufficiently, the valve may be forced shut and held there. This construction is adopted so that should the feed pump stop working or between the strokes of the pump there may be no escape of water backward from the boiler into the pipe. Two Fig. 86. Combined Check and Stop Valve such check valves are usually fitted to each boiler, one connecting with the main and the other with the auxiliary feed pumps. A stop valve is fitted between the check valve and boiler, in order that, if necessary for examination or repair, the check may be shut off from communication with the boiler. Such combined stop and check valves are frequently fitted in a single casing, the stop valve, of course, being placed next the boiler (see Fig. 86). The stop valve should always be so fitted as to open against the boiler pressure so that in case the stem should break the valve can be opened by the pump pressure. . After passing through the check valye the water enters the internal feed pipe, by which it is led to the point or points of delivery. The end of the pipe is usually closed, and the water is delivered through a large number of small holes distributed BOILERS 141 along the pipe. The delivery is usually below the water level, and often between the nests of tubes where it meets with the rising currents of water heated by them. In some cases it is led to the bottom of the boiler, where it mixes with the relatively cool water there found ; but this plan cannot be recommended, as it retards rather than assists circulation. In some cases also the water has been introduced as a spray into the steam space, but, while this plan has some advantages, it has not met with general favor. Fig. 87. Blow-off Cock In watertube boilers the feed water is usually fed into the upper drum, whence it joins the circulation in the boiler as noted in the description of boilers of this type. [6] Surface and Bottom Blows Cocks or valves and connecting pipes are fitted for blowing grease and scum, or mud sediment and water, out of the boiler into the sea — Fig. 87. The surface blow consists of a valve or cock attached to an internal pipe lying just below the normal water level, and either perforated with holes or leading to a shallow open pan. Outside the boiler there is a discharge pipe leading to an outboard valve, through which the discharge is effected. The scum and grease which collect on the surface of the water may by means 142 PRACTICAL MARINE ENGINEERING of this arrangement be blown out of the boiler, and thus disposed of. In early engineering practice the bottom blow was of great importance, as it was used not only to discharge mud and sediment, but also the relatively dense water in the boiler when blowing down to reduce concentration, or when emptying the boiler of water for purposes of examination or cleaning. In modern prac- tice with the surface condenser and the evaporator, blowing off to reduce concentration is no longer necessary, and blowing the water out of a boiler with its own steam is no longer considered good practice. The preferable. plan is to allow the steam to condense and'the water to cool down, and to then run it into the bilge or re- move it by pump connections suitably arranged. Due to these facts, bottom blow valves have been sometimes omitted. There may still, however, be occasion to use such valves for the dis- charge of mud and sediment, and, therefore, they are still quite generally fitted. In any event, there should be some valve and pipe connected with the lowest part of the boiler, and through which it can be emptied in one way or another. Both surface and bottom blows are usually fitted to water- tube boilers, especially to those types consisting of upper and lower drums with sets of connecting tubes. The surface blow is for scum and grease, while the bottom blow is essentially for mud and sediment, and is often attached to a special mud drum provided to collect such substances. In -many cases the inner end of the surface blow pipe ter- minates in a shallow pan located near the low water level in the boiler. The water within this pan will tend to remain more quiet than that outside, and the scum and impurities will thus collect therein, ready for removal by the use of the blow. The arrange- ment thus serves as a collecting pan for the surface blow, and by most engineers is believed to be quite efficient for the purpose in view. In other cases the pipe terminates in a closed end and is pro- vided with a number of longitudinal slits through which the scum is drawn from -the surface of the water. The cross sectional area of the bottom blow may be so pro- portioned as to give about one square inch for every 5 tons of water contained by the boiler, with perhaps somewhat larger area in the case of small boilers. The area for the surface blow may be usually made from J^ to 1-3 that of the bottom blow. BOILERS 143 Due to the rapid cutting out of the valve face and seat when an ordinary globe valve is fitted as a bottom blow, this type oi valve has been abandoned for this purpose in the best modern SECTIONS ON A-B & C-D Fie. 88 practice and a type of valve known as "seatless" has been adopted. An example of this type is shown in Fig. 881, [7] Steam Gages The steam pressure within the boiler, or rather the excess of the pressure within over the atmospheric pressure without, is shown by some form of steam gage, of which the best known and most used are those employing a Bourdon tube. In Fig. 89 is shown such a gage and tube, the cross section of the latter being an ellipse as shown. When the inside of the tube is sub- jected to the pressure of the steam it tends to become round in section, and the tube as a whole, being firmly held at one end only, tends to straighten out. This carries the free end outward, and this movement, by means of suitable connections, is made to give motion to the needle. These gages are graduated by comparison with a mercury column or other form of gage tester, or with a standard gage which has been thus graduated. Steam should not be allowed to enter these gages, as the change in temperature may aflfect the accuracy of the reading. To prevent this the pipe lead- ing to the gage is always provided with a loop or U bend, called a "goose neck," which serves as a trap for the water condensed beyond this point. In this way the Bourdon tube and part of the connecting pipe are kept filled with water, which in turn is acted on by the steam, and thus the pressure is indicated without the actual presence of steam within the gage. Steam gages require 144 PRACTICAL MARINE ENGINEERING comparison with a standard gage from time to time, in order to make sure that their indications are correct. They are often pro- vided in duplicate, and frequently one gage at-least is provided of sufficient range to allow of use in the hydrostatic boiler test, this Fig. 89. Bourdon Steam Gage test being usually carried as high as one and one-half times the working pressure of the boiler. [8] Water Gage and Cocks The level of the water within the boiler is shown by a ver- tical glass tube 'connected to fittings at each end, which in turn connect the one with the steam space and the other with the 'water space. As shown in Fig. go, the entire arrangement of glass and fittings is attached to a hollow mounting called the stand pipe, water column, or water gage mounting. To the top and bot- tom of this are attached pipes, one leading to the steam space at or near the top, and the other to the water space at or near the bottom. In connecting the pipe with the steam space care must BOILERS 145 be taken that the opening is not near a steam outlet, as the rush of steam past such an opening might disturb the pressure and render the indications inaccurate by showing a higher level of water in the glass than actually exists in the boiler. Care should also be taken that there are no bends in the steam pipe in which water can collect. If such bends exist a water trap is formed and the water will stand at a higher level in the glass than actually exists in the boiler. Such a false showing may produce disastrous consequences through heating surfaces becoming uncovered by Fig. 90. Water Gages water and overheating. At the bottom of the mounting a drain cock and pipe are provided, so that the glass may be blown through and cleaned as occasion requires. Screw plugs are also fitted above and below in a line with the base of the tube, so that if necessary a wire and swab may be run through the glass. Instead of the connections, as shown in Fig. 90a, and which are to be con- sidered as preferable, the ends of the water column are some- times connected by horizontal passages directly to the boiler, as in Fig. gob, which shows the fitting attached to the curved shell of boiler. With such a mounting the level of water in the glass is more liable to fluctuation and disturbance due to rolling of the ship or to priming than with the arrangement of a. Gage glasses are usually from 12 to 15 inches in length, and ^ to J4 inch diameter. Due to the fluctuations in temperature 146 PRACTICAL MARINE ENGINEERING and the accompanying expansion and contraction, they are liable to occasional breakage. To avoid danger or trouble from the escaping jet of water and steam, it is quite customary in modern practice to fit the connection carrying the ends of the glass with ball non-return valves, working on a similar principle with the Fig. 91. Reflex Water Gage safety stop valve described before. So long as the glass is in place and the pressure equalized, the balls by their weight remain away from the seat and leave the passages open. Upon the breakage of the glass, however, they are carried by the rush of water and steam, each against its seat, thus closing the openings and stop- ping the escaping jets of water and steam. When automatic closing is provided, the ball should always be so fitted as to rise vertically when closing, as if it is fitted in the horizontal position it is apt to roll to its seat when water is admitted to the column. In addition to the gage glass, small cocks, three or four in number, are usually provided. In some cases such cocks are attached to the mounting, and in other cases to the boiler itself. These cocks serve as a check on the gage glass, or for use in case the glass is not to be depended upon. The glass is usually so BOILERS 147 adjusted that when the water is at the bottom it is still some 3 ®r 4 inches above the level of the highest heating surface. The water cocks cover about the same vertical distance, though in some cases the lowest cock is placed nearly on a level with the top of the heating surface. On single-end boilers two such water gages are often fitted, one on either side at the front, and with water cocks at the back. Similarly on double-end boilers three would befitted, two on one end and one on the other. In the reflex water gage (Fig. 91) the glass tube of the or- dinary gage is replaced by a heavy cast steel or composition frame carrying at its back a block of heavy glass, having its front surface cut into deep vertical V grooves, while the front of the frame is open and carries a thick sheet of plate glass. The effect of the V grooves is to make the water appear black, so that the water level is always clearly visible. When the steam pressure carried exceeds 225 pounds per gage, the steam has a very heavy erosive effect on both tubular and reflex gage glasses, the portions of the glass subjected to the action of the steam eating away rapidly and producing weak- ness and leakage, while at the Same time the clearness of the glass is seriously impaired. To obviate this trouble, another type of plate glass gage, similar in outward appearance to the reflex gage, has been developed. These gages have the grooved reflecting plate of the reflex gages removed, the carrying frame having windows both front and back closed with sheets of heavy plate glass. In order to protect these glass plates from the steam, thin transparent sheets x>i mica, are fitted watertight on the water side of the glasses, thus keeping them entirely free from contact with the steam and water. These glasses are used very extensively in the nayal service and give much satisfaction. [9] Hydrokineter, Circulator The hydrokineter is an appliance used to force the circulation of the water in the boiler when raising steam. It consists, as shown in Fig. 92, of a steam jet and series of nozzles with frame perforated at the back for the entrance of water. The steam is furnished from another boiler, and by its inducing action a cur- rent of water is set up and driven along, as shown by the arrows. This arrangement is placed near the bottom of the boiler, and 148 PRACTICAL MARINE ENGINEERING thus serves to drive out the cold water which tends to collect there, and which is only slowly heated by the operation of natural circu- lation. Circulator. In order to aid in the circulation of the water in cylindrical boilers and thus maintain a more even temperature throughout the boiler for the purpose of reducing strains due to uneven expansion, circulating pipes, plates or a combination of both, are very often fitted. One of the most successful of these Fig. 92. Hydrokineter circulating systems is that known as the Eckliflf Automatic Circu- lator, which is shown in Fig. 93. The arrangement and operation are as follows : The circulator consists of tubes and piping so constructed and arranged that they may be inserted through the manholes into the interior of the boiler and detachably secured, to take in water from the lower portion of the boiler, heat it and discharge it into the upper part of the shell. The circulator consists of a horizontal tube 2 inches diameter, adapted to lie close to and extend longi- tudinally at the bottom of the boiler, as. shown by B, a tee (C) secured to one end, and a vertically extending tube (E), which is detachably attached to the tee at its lower end by a nipple (G) adapted to fit within the lower end of the tube (E). (E) is a 3- inch seamless tube extending upward alongside the fire chamber or furnace near one end, and is bent to the arc of the furnace. BOILERS 149 150 PRACTICAL MARINE ENGINEERING then formed with a short bend at point 5 and extending longi- tudinally along and adjacent to the upper side of the furnace in a straight run to near the opposite end of the furnace, where it is again bent slightly upward to aid the discharge. The tube run- ning along the top of the furnace is 3 inches diameter, and is preferably fla.ttened at points of contact on the furnace to give greater heating area. On the tubes at the bottom of the shell, elbows (A) and (D) are provided to open upward, to permit the water to freely enter the pipe and pass up into the vertical and horizontal tubes (E) and (F). There are two complete sets of tubes installed for each fur- nace requiring a circulator to permit one circulator to discharge at the front head and the other circulator at the opposite end of the boiler near the combustion chamber. The entire apparatus is shackled to the stay rods, braces and tubes and there is no danger of its becoming loose or displaced in any way. [10] Hydrometer The density of the water in the boiler is determined by an instrument known as the hydrometer, and shown in Fig. 94. It < I I I IIIIIIIIIIIIIII1II Fig. 94. Hydrometer may be of either glass or metal, and consists essentially of two bulbs with stem as shown. The upper and larger bulb is filled with air, and serves to give buoyancy to the instrument ; while the lower and smaller bulb is weighted and keeps it in the upright position. When a body floats freely, wholly or partly immersed in a liquid, the weight of the body equals the weight of the liquid displaced. Hence, in this case the denser the water the less the volume displaced, and the higher the stem out of water. Average sea water contains about i part in 32 of solid matter, and hydro- meters are usually graduated relative to this as a unit. That is, 2 means twice as much solid matter relatively as sea water ; 3, three times as much, etc., while o, of course, means fresh water. The density of water depends, furthermore, on its temperature, so BOILERS 151 that the scale on the hydrometer can only be used with the tem- perature for which it was graduated. This is usually 200 degrees F., though frequently three scales are provided; for 190 degrees, 200 degrees and 210 degrees, respectively. The water is drawn from the boiler through an appropriate pipe and connections into a deep, slender vessel called a salinomter pot. Soon after draw- ing, the water cools down through the temperature corresponding to the hydrometer scales, when its density is observed. [11] Boiler Saddles The weight of ttie boiler is supported on saddles, or bearers, which in turn are attached to the structure of the ship. A modern form of boiler saddle is shown in Fig. 95 and consists of two or Fig. 95. Boiler Saddle more supports on each side of the boiler of the form shown, and extending each one for some little distance longitudinally. An older form shown in Fig. 96 consists of a plate on edge con- nected with the structure of the ship, extending transversely under the boiler, and cut out to fit the round of the shell. The upper edge of this plate is fitted with angle irons on one or both sides to give a broader surface of support for the boiler. The form of saddle shown in Fig. 95 gives a better longitudinal support, and, moreover, makes access and examination of the bottom of the boiler more easy than with the other form. Single-end boilers usually have two such saddles on each side, while double-end boilers are given three or four. In addition, the boiler is held in place in its saddles by stays adjustable by screw turnbuckles, or by other like means. A knee- piece, or chock, is also often riveted to the structure of the ship. IS2 PRACTICAL MARINE ENGINEERING projecting just above the end of the boiler at the bottom, and thus preventing endwise motion. [12] Boiler Lagging To prevent loss of heat by radiation the boiler is covered with non-conducting, non-combustible felting, asbestos or mag- nesia, which in turn is held on by iron straps, or in some cases Fig. 96. Boiler Saddle This covering is known by a complete covering of sheet metal, as boiler lagging. Sec. 20. DRAFT, SUPERHEATER Draft is due to a difference in pressure between the uptakes or bases of the funnel and the ash pits. Due to this difference the air is driven up through the grate, thus supplying the amount re- quired for combustion, see Sec. 13 [2]. What is it that causes this difference of pressure ? To make the case simple, let AB, Fig. 97, denote a grate with burning fuel, and ACDB the funnel. Then the pressure downward on the top of the fuel will be equal to the weight of a column of air and gas of cross section equal to AB, and extending up to the limits of the atmosphere. The pressure upward at the bottom of the grate will be the regular pressure of the external air, and this will equal the weight of a column of air of the same cross section, G, H, and extending also up to the limit of the atmosphere. The differ- ence in the weight of these two columns is seen to lie in their lower ends, the bottom of one being composed of hot gas and the other of common air. The difference in pressure will, therefore, equal the difference in weight between the column of hot gas BOILERS 153 CDBA, and that of air EFHG. Actually, the column of hot gas will extend some distance above the top of the funnel before losing its heat or mingling with the air, so that the real height of the column is greater than the funnel. This difference is, how- ever, usually neglected, and the difference in pressure is taken as the difference in weight between the column of hot gas extending from the grates to the top of the funnel, and a like la ffw'wHnW ^ Fig. 97. Showing Principle of Natural Draft Fig. 98. Draft Gage column ot external air. The pressure per square inch will, of course, be likewise equal to the difference between two similar columns of one square inch section. This shows the conditions for producing the so-called natural or funnel draft pressure. In order that the combustion may proceed, however, it is not enough to produce simply a column of hot gas. Care must also be taken to provide for a free and full inflow of the outside air to the grates in order that the amount necessary for combus- tion may be on hand as required. Draft pressures are usually measured by an instrument known as a draft gage. As illustrated in Fig. 98, it consists of a bent U tube partly filled with water as shown, and with a scale between 154 PRACTICAL MARINE ENGINEERING the legs. In use, the two legs are connected by appropriate means to the two places between which the difference of pressure is desired, as for example the ash pit and funnel base, or external air and funnel base. In the latter case one leg is open to the air and the other is connected by a flexible pipe or other similar means to the uptake or funnel base. With equal pressure in both places the water will stand at the same height in both legs, but with a difference of pressure it will rise in one leg and fall in the other, the movement being toward the lesser pressure. The difference in pressure is then measured by the weight of a column of water equal to the difference in height between the two legs. This is usually read in inches, and hence draft pressures are usually ex- pressed in inches of water. With ordinary funnel draft the pres- sure is usually from J4 to yi or ^ inch, with assisted or light forced draft from yi inch to i inch, with forced draft on large ships from i to 3 inches, while on fast yachts and torpedo boats the pressure may rise to S or 6 inches or more. These pressures are for coal burning. Where oil fuel is used with forced draft these pressures vary from 3^^ to 6^- or 7 inches, depending on the arrangements of burners and registers for the admission of the air. In this connection it may be well to remember that an inch of water pressure is equal to a pressure of about 2-3 ounce per square inch. Since, as above explained, natural draft is dependent on the difference in weight between the hot gas in the funnel and the outside air, it follows that the lighter, and, therefore, the hotter the gas the stronger the draft; also the higher the funnel -the greater the difference and the stronger the draft. A strong natural -draft with moderate height of funnel requires, therefore, a high temperature of escaping gases, and since these carry away heat to the outside air, this means a loss of heat and hence of economy. Strong natural draft requires, therefore, either a very high funnel, or a very high temperature of escaping gases, with the resulting loss in economy. The usual temperature of the gases in the funnel base is from 600 degrees to 800 degrees F. At a lower temperature the draft will be very poor, while with a higher temperature the increase of draft will be obtained at the expense of economy. With natural" draft the rate of combustion will usually range from 12 or 13 to 20 pounds of coal per square foot of grate surface, dependent on the quality of the coa'. and other circumstances. BOILERS I5S From the preceding it is clear that with natural or funnel draft the ipovver which can be obtained from a square foot of grate surface soon reaches a limit, and under present conditions this is usually found at from lo to 12 indicated horsepower. In order to obtain more power per square foot of grate area, or in general more per pound of boiler, some form of assisted or forced dr^ft is necessary. In all cases where high power on light weight is required, as in war vessels, torpedo boats, fast launches, yachts, etc., the application of forced draft is a necessity, as the boilers required to develop the power under natural draft would occupy far more weight and space than could be assigned them. With assisted or moderately forced draft the power per square foot of grate surface may be raised to from 15 to 18 indicated horsepower, and if properly installed, without sa^crifice of economy. With harder forcing the power may be raised to 25 or 30 indicated horsepower per square foot of grate surface, or even more in ex- treme cases, but necessarily at the expense of a loss in economy. The immediate object of all forced draft appliances is to in- crease the difference in pressure between the ash pit and uptake over what it would be with the funnel alone, at the same time taking care to provide for the full supply of air to the grates as required by the rate of combustion desired. To this end there are four fairly distinct means as follows: ( 1 ) Closed fire room. (2) Closed ash pit. (3) Exhaust fans in the uptakes, or between them and the funnel. (4) Steam jets in base of funnel. In the closed fire-room system the air is forced by means of blowers into the fire room, which is closed air tight except for the outlet into the furnaces. The fire room is hence under a pressure greater than the other parts of the ship, and to enter or leave it an air lock is necessary, as illustrated in Fig. 99. Small air valves are provided by means of which the pressure in the lock may be equalized with that on either side, as may be desired, and this being done the door may be opened. To leave the fire room, for example, both doors of the lock being closed, the pressure inside is equalized with the fire room and the. door being opened the person enters and' closes it behind. The pressure in the lock is then equalized with that outside, the door is opened, 1 56 PRACTICAL MARINE ENGINEERING and thus exit is effected. The chief advantages of this system He in the fact that the boilers are left unchanged as for natural draft, and the shift from one system to the other is readily made. The necessary structural arrangements are also sometimes more readily effected than for the other systems, ^especially in warship practice, and this reason may in some cases largely determine the choice. Its chief disadvantages lie in the difficulty of making the fire rooms air tight, in the necessity of fitting air locks as above described, and in the more severe strain placed on the fire room force than with other systems, and also the evil effect on the Fig, 99. Showing Principle of Air Lock boiler of the heavy inrush of cold air to the furnaces whenever the furnace doors are opened. In the closed ash pit system the air is forced by means of blowers into conduits leading directly to the ash pits and furnaces, which are closed air tight from the fire room. The former are, therefore, under a pressure greater than in the fire room, and if the furnace doors were opened with the draft on, the flames and gas would be driven out into the the fire room. To prevent this, draft must be shut off when the. furnace or ash pit doors are opened, and to avoid accidents a locking arrangement is often provided which prevents the door from being opened while the draft is on, or the draft from being turned on till the doors are closed. The Howden forced draft, which is representative of this system, provides also for heating the air by means of the waste furnace gases before it enters the ash pits and furnaces. The general arrangement for the Howden draft is shown in Fig. lOO. In the uptake is fitted a nest of vertical tubes through which the furnace gases pass on their way to the funnel. The air from the BOILERS 15; 158 PRACTICAL MARINE ENGINEERING blower is delivered into a conduit which leads across the front of the boiler and within which these tubes are placed, as shown in the figure. The furnace gases pass, therefore, through the tubes ■while the entering air passes about them on the outside, and thus absorbs a part of their heat which would otherwise escape through the funnel. The heated air then passes downward to a kind of special front over the ash pits and furnaces. From these passages openings controlled by either sliding or hinged valves lead into the ash pits and into the furnaces above the grates. The supply of air to the fire may thus be regulated, and the relative amounts delivered above and below the grate may be adjusted as required for the best combustion. The ash pit and furnace doors are, of course, air tight to the fire room, and arrangements may be pro- vided for insuring the closure of the valves before opening the' doors as above explained. . Induced draft is represented by the Ellis and Ecuves system, as illustrated in Fig. loi. A large exhaust fan is so placed as to draw the gases along the uptakes and discharge them to the fun- nel, thus producing the draft by means of a reduction of pressure in the uptakes, rather than by an increase in the ash pit or fire room. Considering the uptakes and funnel base as representing the main passage, the fan is so placed as to draw from the former and deliver into the latter. Between the inlet and delivery is a slide or damper in the main passage, while the fan inlet may similarly be closed off. When the blower is in operation the for- mer of these is closed while the latter is open and the products of combustion are thus drawn from the uptake arjd delivered to the funnel base on the other side of the main slide. On the other hand, if it is desired to run without the fan the inlet may be closed off and the main slide or damper opened, thus giving ! the usual ariangement for natural draft. The entering air which in this case is supplied either by natural ventilation or by special blowers is heated before reaching the furnaces, usually, by being drawn around nests of tubes through which the gases pass on their way to the fan. These tubes are sometimes arranged vertically in front of the boiler as in the Howden system, and as shown in the figure, and sometimes horizontally in the spandrels over or between the boilers. The air thus heated is then led through passages at the side of the front connections of the ash pits, and to the spaces around the BOILERS 139 i n Tfio PRACTICAL MARINE ENGINEERING furnace frames. The furnace and ash pit fronts are closed from the fire room, and a certain proportion of the air is admitted above and below the grates according to the needs of the com- bustion. This system has the advantage of leaving the fire room open and of working the ash pit under practically atmospheric pressure. Furthermore all leaks between the fire room and the fire side of the boiler are inward, and thus the fire room is kept free from escaping gas, or from flame and gas when the furnace d9ors are opened. Its chief disadvantage lies in the large size and weight of fan necessary to handle the gases, as compared with the smaller size needed for the air alone in the closed fire room and closed ash pit systems and the temperature to which the fan is exposed. The action of steam jets in the base of the funnel is to pro- duce a reduction of pressure in the uptake, thus giving a form of induced draft. Turning the exhaust of a non-condensing engine into the funnel produces the same result, and may also be con- sidered as a form of induced draft. The latter arrangement is sometimes met with in tugs and other small craft, while the steam jet is much used throughout the whole range of tugs, yachts, launches, tenders and all forms of small craft. One. of the special advantages of the steam jet is its readiness for use as soon as a small head of steam is formed, and independent of any special auxiliary machinery. It is, however, a wasteful and ex- pensive mode of obtaining increased combustion, and is only to be recommended when simplicity and the saving of weight and space are of more importance than economy of steam. In this connection it must not, of course, be forgotten that the operation of the blowers used in the closed iire room, closed ash pit, or induced systems of draft requires also the consump- tion of steam and hence of coal, so that in no case can forced draft be obtained without paying for it in one form or other, ex- cept in cases where feed heaters using exhaust steam as the heat- ing medium are fitted or where the exhaust steam from the blower engines is further xrtilized in the steam receivers of the main engines, where reciprocating engines are used for propulsion, or in a low pressure stage of the turbines where these are fitted. General experience shows, however, that for a given increase in the rate of combustion, the use of a steam jet requires more steam than blowers, so that the latter are to be preferred except in such special cases as are referred to above. BOILERS i6i Reference may also be made to the practice of introducing jets of air under considerable pressure into the combustion cham- bers or furnaces of steam boilers. The result of such an arrange- ment is twofold : ( 1 ) It places the air in the immediate point where it may be of the most value in aiding to complete the eorabustion. (2) Its introduction under pressure insures its thorough mingling with the gases and the latter with each other, and thus still further aids in bringing about the conditions necessary for complete combustion. The introduction of air in this manner has met with considerable favor in many cases where it has been tried, especially in certain forms of watertube boilers where the voliame of furnace available for the combustion of the gases before they pass among the tubes is often limited or insufficient in amount. [a] Superheaters In order to insure that the steam when it reaches the engine shall be perfectly dry, and also very frequently, that it shall have a temperature higher than that corresponding to its pressure, such increase in temperature materially increasing the economy of the engine, superheaters are often fitted to boilers. For Scotch boilers and others of the cylindrical and kindred types the super- heater usually consists of a cylindrical drum built to form a por- tion of the uptake. This drum is fitted with tubes through which the gases from the boiler pass on their way to the funnel; the steam from the boiler passing through the drum around the tubes. In watertube boilers the general form of superheater is as shown on Fig. 17, where the superheating coils are located at what is called the end of the first pass of tlie gases across the tubes. In all arrangements, however, the idea is to still further rob the gases p£ combustion of what would otherwise be lost heat, as such recovery of heat causes a direct gain in efificiency, both of boiler and of engine. Roughly speaking, for every 10 degrees F. rise in tempera- ture of the steam above that temperature corresponding to its dry or saturated condition, the gain in efficiency is i percent. i62 PRACTICAL MARINE ENGINEERING Sec. 21. BOILER DESIGN IN ACCORDANCE WITH THE RULES OF THE UNITED STATES BOARD OF SUPER- VISING INSPECTORS OF STEAM VESSELS I. CYLINDRICAL SHELLS The working steam pressure allowable on cylindrical shells of boilers constructed of plates inspected as required by these rules, when single riveted, shall not produce a strain to exceed one-sixth of the tensile strength of the iron or steel plates of which such boilers are constructed; but wjiere the longitudinal laps of the cylindrical parts of such boilers are double riveted, and the rivet holes for such boilers have been fairly drilled instead of punched, an addition of 20 percent to the working pressure provided for single riveting shall be allowed. The pressure for any dimension of boilers shall be ascer- tained by the following rule, viz. : Multiply one-sixth of the lowest tensile strength found stamped on the plates in the cylindrical shell by the thickness — expressed in inches or part of an inch — and divide by the radius or half diameter, also expressed in inches, and the result will be the pressure allowable per square inch of surface for single rivet- ing, to which add 20 percent where the longitudinal laps of the cylindrical parts of such boilers are double riveted, when all the rivet holes of such boiler, including steam and mud drums, have been fairly drilled and no part of such holes has been punched. The pressure allowed shall be based on the plate whose tensile strength multiplied by its thickness gives the lowest product. 2. HEADS Requirements for Heads All plates used as heads, when new and made to practically true circles, and as- described below, shall be allowed a steam ' pressure in accordance with the following formula* CONVEX HEADS TXS p = R Where R = one-half of the radius to whicTi the head is bumped. 5" = one-fifth of the tensile strength. T = thickness of plate in inches, P = steam pressure allowable in pounds. BOILERS 16.3 CONCAVE HEADS For concave heads the pressure allowable shall be eight- tenths times the pressure allowable for convex heads. Note: — To find the radius of a sphere of which the bumped head forms a part, square the radius of head, divide this by the height of bump required; to the result add height of bump, which will equal diameter of sphere, one-half of which will be the required radius. Example. Required, the working pressure of a convex head of a 54-inch radius ; material, 60,000 pounds tensile strength and one-half of an inch thick. Substituting values and solving, .5 X 12,000 P = := 222 pounds 27 The pressure allowable on a concave head of the same dimen- sions would be 222 X -8 ^177 pounds. To avoid grooving, the flanging shall be well rounded at the bend. Bumped heads may contain a manhole opening flanged in- wardly, when such flange is turned to a depth of three times the thickness of material in the head. Material used in the construction of all bumped heads shall possess the physical and chemical qualities prescribed by the Board of Supervising Inspectors for all plates subject to tensile strain, as required by section 4430, Revised Statutes. FLAT HEADS OF WROUGHT IRON OR STEEL PLATE Where flat heads do not exceed 20 inches in diameter they may be used without being stayed, and the steam pressure allow- able shall be determined by the following formula : CXT' P = Where P =: steam pressure allowable in pounds. T = thickness of material in sixteenths of an inch. A = one-half the area of head in inches. C = 112 for plates seven-sixteenths of an inch and under. C = 120 for plates over seven-sixteenths of an inch. Provided, The flanges are made to an inside radius of at least ijE4 inches. Example. Required the working pressure of a flat head 20 inches in diameter and three-fourths of an inch thick. Substitut- ing values, i64 PRACTICAL MARINE ENGINEERING 120 X 144 P = =110 pounds. 157 3. MANHOLES, HANDHOLES AND HOLES FOR PIPE CONNECTIONS All boilers shall have a manhole opening above the flues or tubes of not less than 10 by 16 inches or 11 by 15 inches in the clear, and shall have such other manhole openings in other parts of the boiler as may be required, of sufficient dimensions to allow easy access to the interior of the boiler for the purpose of inspec- tion and examination. When holes exceeding 6 inches in diameter are cut in boilers for pipe connections, manhole and handhole plates, such holes shall be reenforced, either on the inside or outside of boiler, with reenforcing wrought iron or steel rings, which shall be securely riveted or properly fastened to the boiler, such reenforcing ma- terial to be rings of sufficient width and thickness of material to fully compensate for the amount of material cut from such boilers, in flat surfaces ; and where such opening is made in the circum- ferential plates of such boilers, the re-enforcing ring shall have a sectional area equal to at least one-half the sectional area of the opening parallel with the longitudinal seams of such portion of the boiler. On boilers carrying 75 pounds or less steam pressure a cast iron stop valve, properly flanged, may be used as a reenforcement to such opening. When holes are cut in any flat surface of such boilers and such holes are flanged inwardly to a depth of not less than ij^ inches, measuring from the outer surface, the reenforce- ment rings may be dispensed with. No connection between shell of boiler and mud drum shall exceed 9 inches in diameter, and the flange of the mud drum leg shall consist of an equal amount of material to that cut out of the shell of boiler. 4. HYDROSTATIC PRESSURE The hydrostatic pressure applied shall be in the proportion of 150 pounds to the square inch to 100 pounds to the square inch of the steam pressure allowed. 5. HOLES FOR STAYBOLTS AND TUBES, RIVET HOLES AND BUTT STRAPS All holes for staybolts and tubes shall be fairly drilled and no part punched. BOILERS 165 The diameter of rivets, rivet holes, distance between centers of rivets, and distance from centers of rivets to edge of lap for different thicknesses of plates for single and double riveting shall be determined by the following rules. The following formulas, equivalent to those of the British Board of Trade, are given for the determination of the pitch, dis- tance between rows of rivets, diagonal pitch, maximum pitch, and distance from centers of rivets to edge of lap of single and double riveted lap joints, for both iron and steel boilers: Let p = greatest pitch of rivets in inches. n = number of rivets in one pitch. Pa := diagonal pitch in inches. d = diameter of rivets in inches. T = thickness of plate in inches. V = distance between rows of rivets in inches. E = distance from edge of plate to center of rivet in inches. To Determine the Pitch Iron plates and iron rivets : d? X .7854 X n p = + d T Example, first, for single riveted joint: Given, thickness of plate {T) = >^ inch, diameter of rivet (d) = % inch. In this case n ^ 1. Required the pitch. Substituting in formula, and performing operation indicated, (?^)'X.78S4Xi 7 Pitch = (- - — = 2.077 inches. 1/2 8 Example for double riveted joint: Given ^ = >4 inch and d = 13/16 inch. In this case n = 2. Then-^ ( 13/16)' X. 7854X2 13 Pitch =: ■- 1 ^ 2.886 mches. y2 i6 For steel plates and steel rivets : 23 X rf' X .7854 X n /. = + d 28 xr Example for single riveted joint: Given, thickness of plate = Yz inch, diameter of rivet = 15/16 inch. In this case w = i. 23X(iS/i6)'X.7854Xi iS Pitch = — H = 2.071 inches. 28 X 34 16 Example for double riveted joint : Given, thickness of plate = Yz inch, diameter of rivet = % inch, n = 2. Then — i66 PRACTICAL MARINE ENGINEERING 23X(Hy-X. 7854X2 7 Pitch = 1 = 2.8s inches. 28 X 'A 8 For Distance from Center of Rivet to Edge of Lap 3Xd E = 2 Example: Given, diameter of rivet (d) = % inch; required the distance from center of rivet to edge of plate. 2X% E ^ == 1.312 inches, for single or double riveted lap joint. For Distance Between Rows of Rivets The distance (F) betweeii lines of centers of rows of rivets for double, chain riveted joints shall not be less than twice tht- diameter of rivet, but it is more desirable that V should not be less than 4d + i 2 Example under latter formula : Given, di?imeter of rivet = % inch. Then — (4X^)+i V = ^- = 2.25 inches. 2 For ordinary, double, zigzag riveted joints : V(ii/' + 4rf) (P + 4d) 10 Exwniple: Given, pitch =: 2.85 inches, and diameter of rivet = J^ inch. Then — V(iiX2.85 + 4X^) (2.8s+4X^) V — = 1.487 inches. 10 Diagonal Pitch For double, zigzag riveted lap joint. Iron and steel : 6p-\-4d 10 Example: Given, pitch = 2.85 inches, and rf = J^ inch. Then — BOILERS 167 (6X2.8s) + (4X^) ^ Mean diameter = least inside diameter + 2 inches.] Fox Type CXT P — D Where P = pressure in pounds. T =: thickness in inches, not less than five-sixteenths. D z= mean diameter in inches. BOILERS 171 C := I4, A a 0, eoooeocD CO CO CO CO CO ■NNrtOg ■ CO CO CO CO CO t oooscoco COCONNeDCQ.-^«o■*co1-HOJXl>w■*co£J^HOQOJco^-^cgto«2SNS3 0Dt»t»OeD»0U5»0»0^'*'*'^^C0C0C0C0C0eQC0C0C0C00)(NC^NN0INC««(N':N »OwcOO)»OCSICOb-COCllN'«*-< o OS 00 1> «o g »2 3; ;* M CO w pfl ^ j^ ^>.^»^-colCu^«^■*^■TJ^^^eocococococococococ^c^p^c^c^l^lo^fr^c^MO^NNe^ C4 C4 XOCDO OS to -^ OiOOt^COON-»OCO |>C0CD'0U3»0^'*^ 00 (N « 00 b- O CO ■«** -^ t^ O "3 -H OS t^ CD t* ^* 00 OS i-H ^ to O "* 00 CO ^ N CO « ffl ** O JO C00SU3»-'00cOC0'-'-'cotDoseob-.c«to--it;«coeootDNjn r-C0OlCOC0.-(O>b-'OC0C^'H01«b-CD»OTj^rtOSCD^COtHOWI^tD»O^COOIN»HOQOSWMt^b.b-cOtO'OiOiO^-^Tj( IOTt<^TtiC0C0C0C0C0C0NC^N|.HOOSOSOOb*t*COCOiOW3T*(Tt(»COCO«OI«i-00»OOU50'OOiOOiOOiOOWOiOOiOO»00 U3iOtOCOt^t*MMOSOiOO'-<'-00000>asOO<-c.-iC« rt rt rt ,-H i-ti-H iH i-H »-l rH rt t-l rH i-< 1-H 1-H 1-H 1-1 r-1 ^ « Cq N M Ol tOO'00''30»OOU30'OOiOO»OOiOO»00'OOU3piOO»00»OOU50iOO« t0r»b-x000S0SOO'-"-*MC^C0C0^'*»0V0tDt0b-r^00000S0)OO'-"-tC^C^JC0C0 - r-l rt rt rt i-< 1-1 1-t r-H rt r-H-l F^ r-l iH rt r-< r-l r-i r^ r-* (N N tiO(oj o c-i>-iooosa30ixoDoor<.t^b.i> «eH rt ,_, rt rt rt .-H .-H o o o o o ■«*MXo»0)0 WC4NMNN«M«Cg(NNCi|O)(NC0 OtOOtOOiCOiOOujOiOOiOOiO Tf>St»niO«3(OI>t^MODCJOSOOrHiH MWiMiNNC4NOJMO»(MCSCQCgweO i82 PRACTICAL MARINE ENGINEERING The figures (a) in table (page i8o) multiplied by square feet of grate surface give the area of safety valve or valves required. When this calculation results in an odd size of safety valve, use next larger standard size. Examples. Boiler pressure = 75 pounds per square inch (gage). Two furnaces: grate surface = 2 (No.) X S feet 6 inches (long) X 3 feet (wide) = 33 square feet. Water evaporated per pound of coal = 8 pounds. Coal burned' per square foot grate surface per hour = 12^ pounds. Evaporation per square foot grate surface per hour = 8 X I2j4 = ICO pounds. Hence JV = 100 and gage pressure = 75 pounds. From table the corresponding value of a is .230 square inch. Therefore area of safety valve ^ 33 X .23 = 7.59 square inches. For which the diameter is 3% inches nearly. Boiler pressure ^215 pounds. Six furnaces: grate surface = 6 (No.) X 5 feet 6 inches (long) X 3 feet 4 inches (wide) ^ no square feet. Water evaporated per pound coal = 10 pounds. Coal burned per square foot grate surface per hour = 30 pounds. Evaporation per square foot grate surface per hour = ip X 30 = 300 pounds. Hence W ^= 300, gage pressure = 215, and a ^ .270 (from table). Therefore area of safety valve = no X .270 = 29.7 square inches, which is too large for one valve. Use two. 29.7 = 14.85 square inches. Diameter = 4^ inches. 2 To determine the area of a safety valve for boiler using oil as fuel or for boilers designed for any evaporation per hour : Divide the total number of pounds of water evaporated per hour by any number of pounds of water evaporated per square foot of grate surface per hour (W) taken from, and within the limits of, the table. This will give the equivalent number of square feet of BOILERS 183 grate sufface for boiler for estimating the area of valve. Then apply the table as in previous examples. Example. Required the area of a safety valve for a boiler using oil as fuel, designed to evaporate 8,000 pounds of water per hour, at 175 pounds gage pressure. Make W =^ 200. 8,000 = 40, the equivalent grate surface, in square feet. 200 For gage pressure = 175 pounds and W = 200, from table, a = .218 square inch. .218 X 40 = 8.72 square inches, the total area of safety valve required for this boiler, for which the diam- eter is 3 5/16 square inches nearly. 18. WATERTUBE AND COIL BOILERS The working pressure allowable on cylindrical shells of watertube or coil boilers, when such shells have a row or rows of pipes or tubes inserted therein, shall be determined by the follow- ing formula: iD — d) XTXS P = DXR Where P = working pressure allowable in pounds. D = distance in inches between the tube or pipe centers in a Hne from head to head. d = diameter of hole in inches. T = thickness of plate in inches. S = one-sixth of the tensile strength of the plate. R = radius of shell in inches, n = number of tube holes in a pitch. When tubes on any one row are pitched unequally, nd must be substituted in the formula for d. Where rows of tubes are pitched diagonally, each diagonal ligament shall be not less than three-fifths of each longitudinal ligament. Example. Required the working pressure of a cylindrical shell having holes i inch in diameter, spaced 2 inches from center to center, in a line from head to head; material, one-half of an inch thick ; diameter of shell, 20 inches ; tensile strength of plate, 60,000 pounds. Substituting values, we have (2—1) X.SX 10,000 P = = 2S0 pounds. 2X10 i84 PRACTICAL MARINE ENGINEERING 19. MAIN STEAM PIPE The thickness of and pressure allowed on main steam pipe constructed of riveted iron or steel plates, shall be determined in the same manner as required to determine the pressure allowable on boilers. The thickness of and steam pressure allowable on all lap- welded or solid-drawn steam pipe of wrought iron or steel shall be determined by the following formulas : PXD T = + .125 10,000 (T — .125.) Xi<*,ooo D Where P = pressure of steam allowable in pounds. T = thickness of pipe. D = diameter of pipe. Example. Given P = 200 pounds pressure. /? = 5 inches in diameter. Substituting and solving for T, 200x5 T = 1- .125 = .225 inch. 10,000 Substituting and solving for P, (.225 — .125) X 10,000 := 200 pounds. 20. WELDED STEAM AND WATER PIPES From one-eighth of an inch inside diameter up to and includ- ing 30 inches inside diameter. The pipe shall be made of wrought iron or mild steel, smooth, straight, and free from defects. Threaded pipe of standard thickness shall be avoided as far as possible. In steam pipes it is a very serious matter and shall not be allowed in any case on standard pipe over 5 inches in diameter. All pipe over 2 inches in diameter shall be lap welded. 21. COPPER PIPES All copper pipe subject to pressure shall be flanged over or outward to a depth of not less than twice the thickness of the material in the pipe, and such flanging shall be made to a radius BOILERS i8s not to exceed the thickness of the pipe. No bend shall be allowed in copper pipe of which the radius is less than one and one-half times the diameter of the pipe, and such pipe shall be so led and flanges so placed that they may be readily taken down if required. The thickness of material, according to the working pressure, shall be determined by the following formula : PXD T = \- .0625 8,000 Where T = thickness in inches. P =1 working pressure. D ==: inside diameter of pipe in inches. Example. Required the thickness of material of a 5-inch copper pipe for a working pressure of 175 pounds per square inch. Substituting values, '^ 17s X 5 T = \-.062S = .171 inch. 8,000 Provided, however, That all copper pipe subject to pressure and installed for use on steam vessels after July i, 191 1, shall have a thickness of material according to the working pressure, to be determined by the following formula : PXD T = h .0625 6,000 Where T = thickness in inches. P =^ working pressure. D = inside diameter of pipe in inches. Example. Required the thickness of material of a 5-inch copper pipe for a working pressure of 175 pounds per square inch. Substituting and solving, we have 175 X 5 T = \- .0625 = .208 6,000 The flanges of all copper steam pipes over 3 inches in diame- ter shall be made of brass or bronze composition, forged iron or steely or open-hearth steel castings, and shall be securely brazed or riveted to the pipe : Provided, however, That when such pipes are properly formed with a taper through the flange, such taper being fully reenforced, the riveting or brazing may be dispensed with: And provided also, That when the pipe has been expanded by proper and capable machinery into grooved . flanges and the pipe flared out at the ends to an angle of approximately 20 degrees, said angle to be taken in the direction of the length of the pipe, and i86 PRACTICAL MARINE ENGINEERING having a depth of flare equal to at least one and one-half times the thickness of the material in the pipe, said riveting or brazing may be dispensed with. Where copper pipes are expanded into or riveted to flanges, it will be necessary for the -pipes with their flanges attached to withstand a hydrostatic pressure of two and one-half times the boiler pressure. Flanges shall be not less than four times the required thick- ness of pipe, plus one- fourth of an inch, and shall be fitted' with such number of good and substantial bolts as shall make the joints at least equal in strength to all other parts of the pipe. Any form of joint that will add to the safety or increase the strength of flange and pipe connections over those providfed for by this rule shall be allowed on any and all classes of steam pipe. t 22. CAST STEEL, SEMISTEEL, FERROSTEEL, CAST IRON, MALLEABLE IRON, HARD BRASS, BRONZE AND OTHER COMPOSITIONS MADE OF COP- PER, TIN AND ZINC Cast steel fittings of any size or character, and for any pres- sure may be used for any and all steam and feed pipe connections, and for boiler fittings, valves, cocks, and all appliances subject to steam or water pressure in connection with the boilers and engines of steam vessels, when made by regular processes and by manufac- turers who stamp such fittings and appliances with their trade mark or identifying stamp and who guarantee the castings to pos- sess" the following physical characteristics: Tensile strength, minimum, 50,000; maximum, 70,000 pounds per square inch; elastic limit, minimum, not less than 45 percent of tensile strength ; elongation in 2 inches, minimum, 25 percent. All steel castings shall be thoroughly annealed. The minimum thickness of steel fittings shall be determined by the following formula : PXD T = \- .188 7,000 Where P = working pressure in pounds. D := diameter in inches, T = thickness in inches. Malleable iron possessing a tensile strength of not less than 30,000 pounds to the square inch may be used for any casting or connection up to and including 6 inches in diameter, and for pres- BOJLERS 187 sures not exceeding 300 pounds, or a temperature of 417.5 degrees F. Such castings of 3 inches in diameter or over shall be extra heavy, beaded or banded, and stamped with the trade mark or identifying stamp of the manufacturer. Cast iron, semisteel, or ferrosteel, possessing a tensile strength of not less than 20,000 pounds to the square inch may be used in the construction of valves and fittings when such valves and fit- tings of 3 inches in diameter or over are stamped with the trade mark or identifying stamp of the manufacturer, and made in accordance with the following formula : PXD T = + .25 3,000 Where T = thickness of casting in inches. P = pressure of steam allowable in pounds. D = internal diameter of the largest opening contained in the cylindrical part of the casting. Cast iron may also be used in the construction of manhole and handhole plates. Hard brass, bronze, and other compositions, of which 95 per- cent is copper, tin, and zinc, possessing a tensile strength of not less than 30,000 pounds to the square inch, may be used in the construction of all fittings up to and including 12 inches in diam- eter and for all pressures not exceeding 300 pounds per square inch, and not exceeding a temperature of 425 degrees F. For all pressures of more than 300 pounds, and a temperature of more than 42s degrees F., no fittings other than steel shall be allowed. 23. EVAPORATORS, FEED WATER HEATERS AND SEPARA- TORS MADE OF CAST IRON AND SUBJECT TO BOILER PRESSURE When evaporators, feed heaters and separators are constructed of cast iron possessing a tensile strength of not less than 20,000 pounds per square inch, the shells being cylindrical and ends flat or convex, the castings sound and of uniform thickness, the work- ing pressure shall not exceed that found by the following for- mulas : Flat surface: Cylindrical shell: 20,000 X T' 3,500 X T P=- P = jy D t88 practical marine ENGINEERING ^ T - 20,000 3,500 Where P = working pressure per square inch in pounds. T = thickness in inches. Provided, i. That the thickness of ends of evaporators, feed heaters and separators shall be not less than three-eighths of an inch. 2. That to the resultant thickness obtained by the formula given above there shall be added, for cylinders having an inside diameter of i inch to 6 inches inclusive, one-fourth of an inch ; for cylinders having an inside diameter of over 6 inches to 15 inches inclusive, one-eighth of an inch. D =: diameter inside in inches. When the pressure is to be de- termined for a part of a flat surface which is a square, or rectangle in the flat surface formula, the value of D used shall be the diagonal of the square or rectangle, and when the ends are bolted to the shell the value of D used shall equal the diameter of the bolt circle. All flanges shall be substantial, and there shall be a good fillet all around the root, and when the ends and shell are cast solid there shall be a good and substantial fillet inside all around. The bolts or studs for the ends or doors shall not have a greater stress than 6,000 pounds per square inch, and the size of bolts or studs shall be not less than three-fourths of an inch in diameter. Evaporators shall be provided with an efficient safety valve of approved type, same to be set to blow at 10 pounds pressure, and it shall be the duty of the engineer in charge of the vessel to see that such valve blows off at least once in 30 days. QUESTIONS Boilers PAGE What are the two fundamental types of boilers? 64 Into what classes may fire-tube boilers be divided? 65 Give a general description of these various classes 66 How may watertube boilers be classified according to the circulation of the water? 74 Give a general description of a few leading types of watertube boilers. 75 Compare the two types watertube and fire-tube as regards their ad- vantages and disadvantages for marine use 83 In what way may a riveted joint fail? 86 What is meant by single and double shear? 86 Describe the various forms of riveted joints, and show how they may be proportioned so as to give approximately equal strength in plate and rivet section 88 What material is used for modern boilers? 104 Are rivet holes usually punched or drilled? 104 Compare the relative advantages of the two methods 104 BOILERS 189 PAGE What is meant by calking a joint and how is it done? 105 In Scotch boilers what form of joints is used for the longitudinal seam? what for the circumferential seams? , 105 Why should the longitudinal seams have a higher efficiency than the circumferential? 106 What is the relative strength of the boiler to resist rupture in these two directions? 106 How are the head plates usually flanged? 106 Describe the styles of corrugated furnace in common use 106 Describe various modes of connection between the furnace and the combustion chamber 107 What are the two usual forms of combustion chamber top? 108 How are the tubes secured in the tube sheet? 108 What are stay tubes and how are they secured? no What is the Serve tube and what advantages are claimed for it?. . in What are retarders and what is their use? in What is the Admiralty ferrule and what is its use? 112 What fundamental principles govern the bracing of a boiler? 112 How were furnaces stiffened before the invention of the corrugated form ? 112 Describe the various forms of braces used in modern boilers, and the method of fitting them up 113 Of what advantage is the hollow or drilled screw staybolt? 116 Describe the form of girder or crown bar with which the top of the combustion chamber is usually supported 118 What is a man-hole and cover, and what is its use? 119 Give approved methods of fitting them up 120 Describe the fitting up of the ordinary furnace door 121 Describe the usual form of grate bar and the methods of supporting , it in the furnace 123 ' What is the bridge wall and how is it fitted up? 124 Where do the gases pass after leaving the tubes? 124 Describe the usual style of front connections and uptakes 125 Describe the funnel and the usual method of fitting it up 126 What is the ratio of heating surface to grate surface? 130 How is the horsepower of a boiler related to the heating surface or to the weight? _ 131 Mention the various boiler mountings I33 Of what use is a safety valve?. . . . _. I33 Name the principal valves on a boiler 133 Describe the U. S. Standard safety valve 133 Describe the usual type of spring safety valve I35 What is a mufHer and what is its use? 136 What is the use of the boiler main stop valve? 137 What is an automatic closing valve, and what is its use? 138 What is the dry-pipe and how is it fitted up? 139 Describe the usual form of boiler check valve 140 What are the bottom and surface blows and how are they fitted? 141 Describe the usual form of Bourdon steam gage 143 Describe the usual manner of fitting up water cocks and water gages. 144 What is a hydrokineter and what is its use? 147 Describe the Eckliff circulator 148 What is a hydrometer and what is its use? 150 How are the boilers supported in the ship? 151 Describe the usual forms of boiler saddles 151 To what is draft due? '52 How is draft measured?. ...._. • .■ ' ' li,' ' J ' Vli l^l What are the chief methods in use for mcreasmg the draft? ....... . . 155 Describe briefly the closed stoke-hold system— the closed ash-pit system — the use of exhaust fans in the uptakes — and of jets in the tase of the funnel ■ '55 190 PRACTICAL MARINE ENGINEERING PAGE What advantages are there in heating the air introduced into the furnaces? 158 Describe briefly the Howden system of forced draft 156 Describe briefly the Ellis & Eaves system of induced draft 158 Give the U. S. rule for the pressure allowed on cylindrical shell boilers 162 What is the relation between the test pressure and the working pres- sure allowed? 162 What is the relation between the thickness of butt straps and the thick- ness of shell plates? 162 How would you compute the size of stays for a given steam pressure? 163 How would you compute for a given steam pressure the thickness of a flat plate supported by stays? 163, 177 Give rules for corrugated furnace flues 170 Give rules for ribbed furnace flues • 171 What are the proportions for flue lining subjected to external pressure? 171 How do you compute for a given pressure the necessary dimensions of crown bars? 1 76 How do you compute the thickness of a bumped head? 163 How do you determine the pressure allowed on unstayed flat heads . . . 163 How do you determine the pressure allowed for concave heads? 163 What are the rules for fitting manholes? 164 What are the rules for fitting safety plugs? 178 At what temperature does a safety plug melt? 178 What are the rules for fitting gage cocks? 179 What are the rules for fitting safety valves? 179 What considerations govern the area of a safety valve? 179 How would you compute for a given steam pressure the thickness of copper steam pipe? 184 What rules govern the use of iron and steel pipe? 184 In the construction of coil and tubulous boilers what provision is made for the use of cast steel manifolds, tees, retrun bends and elbows? 186 What special rules relate to the construction of drums for tubulous boilers? 187 CHAPTER IV Oil Fuel Burning Sec. 22. THE BOILER FURNACE AND ITS ACCESSORIES In successfully burning fuel oil under or in a boiler there are three principal factors to which the greatest attention must be paid, namely: (i) The boiler furnace and its accessories; (2) the oil-burning apparatus proper, consisting of the burners, the tuyeres or air cones or air registers, as they are called, and (3) the air regulation, oil regulation and aids used to make the combustion as perfect as possible. In order to burn oil properly there are three essential condi- tions : ( I ) The gases of combustion must be kept at the ignition temperature long enough to properly burn them; (2) there must be an intimate mixing of the particles of air and oil; (3) the air supply must be sufficient for combustion. In practice, the first condition is secured by providing proper furnace arrangements, ample combustion space and suitable re- fractory linings. The aim of furnace design should be to secure such shape, volume and arrangement that the combustion of the gases is completed in the boiler and that the gases are suitably retarded so that all possible heat is absorbed by the heating sur- face. Another essential point is to so locate the burners as to prevent the products of combustion, as they leave the oil-burning front, from impinging on the cold tubes and metal furnace walls of the boiler. It is especially important to keep the side and the bottom burners far enough from the side and bottom walls to prevent the formation of heavy masses of carbon by the oil spray. These masses will eventually produce poorer combustion. [1] Smoke Pipe Area Another point which has. not been definitely determined is the proper uptake or smoke pipe area to allow. The usual prac- tice in the United States Navy is to allow one square foot of 192 PRACTICAL MARINE ENGINEERING funnel area for each 300 pounds of oil burned per hour under the boiler. Thus far this area has been ample for good evaporation and smokeless combustion. Yarrow Boilsr. — Steam Prbssurb 240 Pounds; 4,500 Squars Febt Heating Surface •a 4t 3 5& n •° 2 il -3 § n^ u< h 15.90 .9809 12.57 .9750 9.62 .9730 15.90 .7383 12.57 .7327 9.62 .728 15.90 .4867 12.57 .4690 9.62 .4693 ■S«§ W 13.83 13.32 13.68 14.212 14.38 14.60 15.07 15.17 15.07 9 835 to 890 825 to 845 800 to 806 730 to 740 690 to 725 660 to 680 550 to 555 550 to 575 525 to 535 O o 13, 8 to 14.2 14.0to 14.2 14.6 to 14.8 13.2 to 14.0 14.0to 14.4 14.0 to 14.2 13.4to 14.0 13.0 13.6 to 14.0 SBS 5.90 5.50 5.40 4. 20 to 3.50 3.50 3.85 3.50 3,00 3.30 £i •33 > 3.50 3. 50 to 3.20 3,45 2. 15 to 1.91 2, 00 to 2.31 2.25 to 2.35 1.10 1.15 to 1.20 1.30 to 1.40' ^Full I' Experiments with reduced smoke pipe area have been con- ducted as shown in preceding table, which appear to indicate that the area can be considerably reduced from the usual practice with- out reducing the capacity of the boiler, but improving the com- bustion as indicated by the CO2 content of the escaping gases. [2] Fire Brick The use of fire brick or refractory lining for the furnace is to keep the temperature of the furnace high, and to retard, diffuse and distribute the flames until the combustion is complete. Fire brick should be made of the best fire clay procurable and the crushing should be as homogeneous as possible ; unless it will stand a temperature of 3,200 degrees F. without fusing or cracking, it is of very little use in an oil furnace. Poor fire brick necessitates frequent shut downs for repairs, and unless the boiler is shut down when a brick breaks up the casing becomes badly warped or a hole may even be burnt through it. There are shown in Fig. 102 three methods usually employed in securing fire brick. . . Furnace walls are rarely built in watertube boilers without the brick being secured by bolts in some way, as shown in Fig. 102, since otherwise the vibration of the boiler would quickly shake down^ the entire walls. Tests havs shown that the temperature of OIL FUEL BURNING 193 the furnace varies from 2,500 degrees F. near the burners to 2,800 degrees F. well inside the furnace, and in some cases rising as high as 3,100 degrees F. When such high temperatures as 2,800 degrees and upwards occur, some other substance than magnesia must be used as a lagging behind the fire brick, as magnesia dis- integrates at these high temperatures. When the oil and air are im- properly mixed, due to improper regulation, the temperature at ■^■'^sii* ^ SKETCH NO. 3 Fig. 102. Methods of Securing Fire Brick the burners has dropped in many cases to 1,900 degrees F. The necessity for good regulation of the air is shown by this. A high-temperature cement, both for laying up the fire brick and for effecting repairs to the broken brickwork and holes found due to bricks fusing, is required. It is generally used in the form of a light mortar, and is allowed to settle for a few hours and then hardened by lighting fires with one burner to give a gentle heat. In general, the ingredients are fire clay, cement, ground glass or silicate of soda, finely ground magnesia and lamp black. A mixture of car- borundum fire sand and silicate of soda made into a heavy wash or paste and applied with a brush forms an excellent coating on the brick work, which not only prolongs its life, but materially assists in maintaining the high temperature needed in the furnace, 194 PRACTICAL MARINE ENGINEERING [3] Atomization of the Oil There are three methods of atomizing oil fuel in order that it may be properly burned; these methods are (i) atomization by steam, (2) by air, and (3) by mechanical means. All steam and air atomizers, and these are the ones most usu- ally found in the merchant marine, can be divided into two gen- eral subdivisions, as follows : 1. Outside Mixing. — The oil and the atomizing agent meet outside the burner. 2. Inside Mixing. — The oil and the atomizing agent meet inside the burner. The above types may be further subdivided into five general classes as follows (Fig. 103) : Drooling Burner E Atomizer Burner Chamber Burner Fir. 103 1. Drooling Burner. 2. Atomizer Burner. 3. Chamber Burner. 4. Injector Burner. 5. Projector Burner. I. Drooling Burner. — The oil supply simply oozes or drools out, at the orifice over and on to the steam or air jet. The action is as follows : As the steam or air issues forth it expands within the layer or film of oil which is being carried into the furnace. OIL FUEL BURNING 195 2. Atomizer Burner. — In this burner the oil is brought through an orifice from which it is swept off by a brush of steam or air. It is a principle made use of in the ordinary cologne spraying devicA. 3. Chamber Burner. — In this burner the oil and steam are more or less mingled within the body of the burner and pass out from the tip or nozzle as a mixture, and then, owing to the ex- pansion of the steam, the oil is rapidly broken into minute particles. 4. Injector Burner. — Burners of this type are analogous to the injector used for boiler feeding and other purposes. Here the steam and oil rising, each through its own passage, mingle within cone-shaped passages and, as a mixture, pass through a con- tracted nozzle and then outward through a reversed flaring cone. 5. Projector Burner. — In burners of this type the oil is pumped to the oil orifice and from there is caught by a passing gust of steam and blown off. This might be regarded as a sub- classification of No. 2, the atomizer burner, except for the fact that the brush of steam is located some distance from the oil -orifice, and this sweeping brush of steam, as usually constructed, is arranged to entrain a certain amount of air as a further aid in spraying and for combustion. Practically every steam and air atomizer on the market is based^ ott one of these five general types, the variations met with being, many, but the principle of operation being identical. Sec. 23. MECHANICAL BURNERS— THE PRINCIPLES EM- PLOYED IN THEIR OPERATION AND THE VARIOUS TYPES USED In oil burning the atomization of the oil by means of a me- chanical burner under pressure as distinguished from vaporiza- tion or gasification in the burner is the preferred method for naval use. -Various advocates of burning oil, especially in the early days, insisted that the only way to burn oil was by some treatment of the oil which admitted it to the furnace in form of vapor. These systems, while successful in metallurgical work, are not successful in boiler work, where great capacity is needed. They also introduce a factor of danger. The mechanical burner sprays or atomizes the oil by means of pressure alone, without the use of compressed air, steam or any other exterior atomizing agent. igS PRACTICAL MARINE ENGINEERING Fig. 104. Schutte-Koerting Burner Fig. 106. Thornyctoft Burner Fig. 105 Fig.. 107. Howden Burner mmw/tw/iwtwt/mjr. Fig. 110. Norraand Burner Fig. 109. Oil Spray, Navy Department Burner Fig. 111. Fore River Burner Fig. 112. Peabodjr Burner OIL FUEL BURNING 197 Two methods are employed to accomplish this purpose : ( i ) By forcing the oil through a passage of helical form like the screw thread, and (2) by delivering the oil tangentially to a circular chamber (oil chamber) from which there is a central outlet. Before proceeding to describe the various burners that are built on the above principles it will be well to describe the re- quirements of a successful burner and at the same time correct various popular fallacies regarding them. Any successful burner must reduce its atomization to very minute particles, so that, when issuing from the burner, they will not drop "to the furnace bottom before combining with air ; and the friction in the central or oil chamber must be very small. It is quite possible to work out the coefficients of friction of different burners. Th^ velocity of. an oil issuing from a chamber = F = yj^gh, where h is tfte head due to oil pressure. The quantity Q passed through in a given time = Q ^ K y, V y. A, where A = area of the orifice and K = co- efficient of friction. Q and A are easily found and curves drawn, so it would be very easy to find KV and compare them. The idea that oil issuing from a burner tip pf the mechanical form goes out in a revolving spray is wrong. The oil issues in straight lines, in a hollow conical spray of various angles up to 90 degrees. The rotation is entirely within the burner, and is con- fined to the oil chamber proper. The three most familiar burners of the first type, namely, those that secure the rotating motion by means of a helical screw thread, are the Schutte-Koerting, Thornycroft and Howden. t [i] Schutte-Koerting Burner (Fig. 104) The tip of this burner is cut out to receive a small spindle, less in diameter than the oil chamber except at the end. A triple- parallel thread is cut on this spindle, which just fits the chamber and forms with it three helical passages which deliver the oil to a smaller chamber at the end of the spindle which communicates with the central ^outlet. The spindle is not adjustable, so the out- put is controlled by the temperature and pressure of the oil. The - burner is fitted with a yoke and hand screw which holds it in position and provides a ready means for disconnecting it. [2] Thornycroft Burner (Fig. io6) In this burner the oil receives a whirling motion, passing through a spiral groove into a central chamber communicating 198 PRACTICAL MARINE ENGINEERING with the outlet orifice of the tip. The tip fits on to a nozzle, in which there is a cylindrical hole about the same diameter as the central chamber and concentric with the axis of the burner. In the surface of this cylindrical hole a thread of square section is cut, of very slight depth at the end coinciding with the central chamber in the tip, but increasing rapidly in depth towards the opposite end of the burner at which oil is, admitted. A spindle fits into the cylindrical hole of the nozzle and on this spindle there is a corresponding thread, accurately fitting the threads of the nozzle and tapering to nothing at the end. When the spindle is screwed home the thread on the spindle bottoms on the tapering thread of the nozzle and no oil can get to the tip. As the spindle is unscrewed the marked taper of the two threads cause them to separate and form in combination a spiral groove, the sectional area of which rapidly "increases as the spindle continues to be un- screwed. The central chamber is formed by the combination of the end of the spindle and the burner tip. The output of the burner is controlled by the size of the outlet orifice and by the revolution of the spindle which regulates the area of the spiral oil passage. [3] Howden Burner (Fig. 107) The Howden burner, Fig. 107, is very similar to the Schutte- Koerting burner in principle, except that the regulation of the spindle permits the output to be controlled. The helical passages are not affected, however. The second type of mechanical atomization by delivering the oil tangentially to a circular oil chamber with a central outlet was first developed by the British Admiralty and is the type that is most generally employed in mechanical burner construction. There are many claims as to priority of patents covering the me- chanical burner, but not until the British Admiralty took hold of the matter was any combination of burners able to drive a boiler to full power and obtain good results. This they succeeded in doing. ' The angle of the conical spray differs with different burners, depending on the size and the thickness of the walls of the outlet orifice. The thicker the wall the narrower the angle, and vice versa for a given size of outlet orifice. No burner, however, pro- duces a greater spray angle than 90 degrees. The angle of the spray is usually about 60 degrees to 70 degrees, and variation OIL FUEL BURNING 199 within these limits has Httle or nothing to do with the efficiency of atomization. As noted in a previous paragraph, atomization depends on the friction and other elements of the design. A me- chanical burner that will atomize oil as finely as does the air burner is desired. The idea of some engineers is to have a valve as an inherent part of their burner, a high oil pressure being maintained up to and into the burner, and the output of the burner being throttled or regulated by this valve. This regulation is unneces- sary and undesirable. The simpler fhe construction of the burner the more hard usage it will stand, and the better it will accomplish its purpose. It is very doubtful whether burners having a valve as an inherent part of their design can be regulated so that each will spray the same amount of oil. If, however, the burner has no valve, but is run wide open under a constant pressure, then, providing the central orifices or outlets are the same size, each burner must deliver the same amount of oil per hour. This is of the greatest importance in properly regulating the air supply. In attempting to construct a burner on the tangential principle it was found that four tangential passages to the circular cham- ber, each having the same area as the central outlet and inclined at an angle of 26 degrees to the horizontal, being supplied by four holes, each also of the same size as the central outlet, gave a burner with a very good spray, efficiency and capacity. It was also found that the higher the oil pressure within certain limits the finer the atomization. The burner, however, works very well under any pressure above 75 pounds. This burner is shown in Figs. 108 and 109. [4] Normand Burner (Fig. no) In this burner eight small holes, each the same size as the cen- tral outlet, deliver the oil tangentially to the central chamber formed by a combination of the tip and the adjustable spindle. The oil chamber is recessed so that the movement of the spindle does not in any way close or affect these holes, its office being to form a wall of the central chamber and to throttle or close the central outlet. The tip is made separately and is held in place on the burner pipe by a hexagonal nut. [5] Fore River Burner (Fig. in) An adjustable spindle in this burner is arranged to throttle or close the central outlet and to vary the size of the central cham- 2O0 PRACTICAL MARINE ENGINEERING ber to which the oil is delivered through two tangential holes. The burner is provided with a quick detachable arrangement, practically similar to that of the Schutte-Koerting burner. The Newport News burner is practically the same as this burner. [6] Peabody Burner (Fig. 112) Oil is delivered under pressure to an annular chamber cut into the face of the nozzle upon which is screwed a tip having a small central chamber communicating with the central outlet. Between the nozzle and the tip a thin disk is inserted and held in place. This disk has a hole in the center corresponding with the diameter of the central chamber, and small slots four in num- ber, extending tangentially from the edge of the central opening outward toward the periphery of the disk, long enough to overlap the annular channel of the nozzle and put it in communication with the central chamber. Fig. 113 gives the curves of capacities of the Navy Department burner with various size outlets used with oil of about 26 degrees « im CURVES OF OIL DISCHARGE FOR BU. S.E. TYPE "H" BURNERS April 3, 1914 Notes:- Curves are results oe tests at Oil Burning Testing Plant with Texas and other light oils .90 specific Gravity heated to about 170* Fahr. -850 750 700 .N^ B«l< >ev'l- vt ^ TO -s- u -^ -^ g 600 ^ ^ n 1. V* , '0 " • net M 600 ^ tf^ v'l '3 Pt y ^ -^ -' ^ fe / ,-■ ^ -" " D 3 39) WO 250 200 Lloo / /' ^ V th pe^ BU cnei Tip y / ^ — « y / ^ ^ ^ -' -Tip -I / y " »; «T pet / ^ ■^ — ■ &; ypfr H-B am( rja '- 100 / X ^ ^ z^ — ~ -w 9 K M 15 lO S( w 2£ lU 3C M OilJDlactiarg^ Pressure at Baraeca, PouadB Qauge Fig. 113 OIL FUEL BURNING 201 B. gravity, heated to 170 degrees F. These curves can also be used for the Normand and Peabody burners. Naturally, new curves will have to be made for other oils of different gravity and temperature, but the above curves show the characteristic capaci- ties of various burners used with light oils. The characteristics of the oils have very little to do with their proper burning, but the viscosity of oil is the main point to consider in its proper burning. The viscosities of several oils at various temperatures are shown in Fig. 114. These data practi- cally cover the characteristics of oils from all over the world. Repeated tests have shown that in order to have good atomization and smokeless combustion the viscosity of the oil must be reduced by heating to 8 on the Engler scale. The use of additional heat to further lower the viscosity below 8 in no way improves the evap- oration. The pumping-capacity temperature curves, Fig. 115, of three heavy Mexican oils are given, and it has been shown by re- peated pumping tests that in order to be able to run full power, the viscosity of the oil has to be reduced to 375, Engler scale, to produce this result. An oil is heated for the purpose of reducing its viscosity, in order to be able to properly pump and atomize it. When the heating has accomplished this purpose the use of additional hedt is of no value. Heating an oil also aids in disassociating any water that may be in it. The capacity of a burner is increased by heating the oil up to a point called the critical point ; after this point is reached, additional heat lowers the capacity. This is shown in the temperature-capacity curve of a burner, operating at a constant pressure, the temperature of the oil being changed. Fig. 116. Sec. 24. AIR CONES, REGISTERS OR TUYERES The Schutte-Koerting register, shown in Fig. 117, is one of the first attempts made to regulate the air supply by means of a sliding sleeve working on the outside surface of the frustum of a cone and operated by rack and pinion gear, The sleeve permits the air opening to be entirely closed, in case the burner is not in use, or to open it to fixed amounts. On the earlier oil-burning vessels it was found that, in order to make this register work properly, the air and the oil had to enter the furnace in certain relative velocities, in order to prevent vibration, flarebacks, etc. This was 202 PRACTICAL MARINE ENGINEERING _4 (sqaaliq'e jIs8aj!^a0-4in'}'B!i3iI lu'dX- O I, f=< . ~ ■ iH i« Dj " 3 P •m mu « M^S fa SI 5^ - o . >. _ „ CO ."1 S _; tr 1-0 a!|. m m lis a. s a. oow 006S 0088 OOM 009£ ooes 00^8 0088 00S8 00T8 0008 006!! \ s ^ \ s \ ^ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ V \ \ \ \ 009^ OOW 0082 \ " e I \ •i- V $ \ t ^^ \ \ OOTK 0002 006t V ""A f^^ ^\ V A 'A j\ ^ ^ \ t % \ \ N) feV 008 OOi 009 4 S» , " % v\ \ s !1 f \ ooe 00^ 1 3 1 V \ ^ ^ f ' > \ 1 Ij S ^ I 1 -i •as- 001 ==a •^-^ — ' J ! ° ! it. i i ; < S s 1 s 3 s ; s ; s 5 ^ : ? : s ' s i i ; 5 I % 6 rH a'-' & Sf )|3qa3jqe,I easjaaa eanqfvjadiuax 204 PRACTICAL MARINE ENGINEERING 240 250 260 270 280 290 300 310 320 330 340 350 360 3T0 380 390 400 410 420 430 440 450 Founds o{ on per Burner per Hour , Fig. 116 accomplished by speeding up the blowers, giving a higher static pressure and closing in on the openings so that the volume of air remained the same but its velocity was increased. Fig. 118 Fig. 119 There are shown in Figs. ii8 and 119 various types of the Navy Department air registers. The idea in designing the;se regis- ters was to make the port area ample for any condition that might OIL FUEL BURNING 205 Fig. 117. Section Through Thornycroft Boiler, showing Schutte-Koerting Arrangement for Burning Oil Fuel A — Front plate of air casing; B — Balanced air door closing by back pressure from furnace; C — Air cylinder fitted with outer revolving casing, for regulating amount of air port openings; D — Handle for rotating air cone adjusting casing; E — Burner base casting; F — ^Burner clamp; G — Oil cock handle; H-^Strainer; J — Oil main. 206 PRACTICAL MARINE ENGINEERING be met, to impart a rotary motion to the air and to adjust the port area by means of the sliding sleeve so as to permit the velocity of the air to be increased at will. The essential difference between this type and the Schutte-Koerting is tliat the latter is almost a Fig. 120. Impeller Plates cylinder, is simply an air distributer, and imparts no rotary motion to the air. There are shown in Figs. 120 and 121 Peabody impeller plates, invented by Mr. E. H. Peabody, of the Babcock & Wilcox Boiler Company, and used by him with great success on the Babcock & Wilcox boilers, burning oil alone, or in combination with coal. Fig. 121. Peabody Impeller Plates. View from Furnace The impeller is fixed, the vanes being set at an agle of 45 degrees. The air' supplied to these impellers is regulated by draft doors on the oil-burning front. A rotary motion is imparted to the air. If the type of impeller is designed specially for the requirement ' of the boiler this impeller is as good as any on the market. There is one drawback : the plates which close off the impeller when not in use become red hot when closed and make it very hard to open them, once they are closed. OIL FUEL BURNING 207 With the burners and air registers as already described, forced draft with high static air pressure must be used to obtain the best results. Where natural draft is desired, the air register should Fig. 122. Casting for Furnace Front, showing Radial Vanes be capable of admitting the necessary air at low velocity, and on account of this low air velocity, the angle of the oil cone should be very great in order that the mixture of oil and air can take place well towards the front of the furnace. Fig. 123. Arrangement of Furnace for Natural Draft One method of using mechanical atomization with natural draft is that known as the "White" system, of which the points are shown in Figs. 122 and 123. It is essential that the air supplied for combustion be brought to as high a temperature as possible for economy, and also for the elimination of smoke. In the White system of natural draft front, this is done by forming a lining space fitted with radial 2o8 PRACTICAL MARINE ENGINEERING vanes, A, which conduct the heat from the furnace front to the air. The small sliding cone, B, affects the length and spread of the flame, and when set in proper position an intense white flame is obtained. The system of cones, C, allows the air admitted to be under complete control, and assures a perfect admixture of air and oil, and as is demonstrated in practice, complete combustion is obtained in the furnace flue itself. The gases of combustion" pass through the tubes as a consumed gas leaving the tubes with a temperature of around 500 degrees F. (shdwn at the base of the funnel). This system can be and is adapted for forced draft, either closed stoke-hold, or Howden hot air, and is generally regarded as efficient. The Navy Department and Peabody systems have also been adapted for use with natural draft, and are very successful. Sec. 25. AMOUNTS OF AIR FOR COMBUSTION To burn a pound of oil completely 15 pounds or 200 cubic feet of air are required. Attempting to burn oil with less than this amount of air results in incomplete combustion, forms a large amount of carbon monoxide, and causes vibration. In case a large amount of excess air is introduced an excess of oxygen results which will lower the evaporative power of the boiler. Forcing a boiler by burning more oil than that which the air supply will con- sume smokelessly is only wasting fuel and injuring the boiler. In burning oil under forced draft the fire rooms are generally closed up by means of air locks and airtight hatches. Turbine forced-draft blowers running as high as 1,800 revolutions per minute supply the air from an outside louvre or inlet opening to the atmosphere, and deliver it into the boiler, where it mixes with the oil and forces the gases up through the boiler. The proper regulation of air is of prime importance. No air should enter the boiler at any place except through the air cones, registers or tuyeres, where it will do useful work, and enter and mix with the oil spray in proper proportions. An airtight boiler casing is a necessity. All the joints, seams, etc., of the boiler casing should be made up with an asbestos gasket or similar material. Poor evaporation is to a great extent due to leaky air casings. One method of examining for leaks is to turn the blower over slowly and examine all the seams with a lighted candle. If the flame is drawn into the inside of the casing, or put out, then the casing leaks. Another method is to sample the gases in the furnace and OIL FUEL BURNING 209 also at the base of the funnel with a COj apparatus. If the re- sults are similar, the casing is tight; if the funnel sample indi- cates much lower CO2 than the furnace, the casing leaks. In order that data for design may be furnished the amount of air supplied to a boiler is measured. A Pitot tube is inserted in either the intake or discharge of the blower, where a uniform and steady flow of air can be obtained. This instrument measures the velocity of the air. Having this and the area of the inlet or PITOT TUBE Locations of Pilot Tubes 8UU0 Qewl-4-Vdooltj Fig. 124 INOLrNEO DIFFERBNTIAL GAOE outlet pipe, the quantity delivered can be obtained. This = Q = Fi X ^, where V^ = mean velocity of the air in feet per second, and A = the area in square feet of the blower discharge pipe. This velocity V^ = y/2gH, where //.= velocity head in feet of air. One inch of water is equivalent to a pressure of 5.2 pounds per square foot. Velocity head in inches of water Then i? = 5.2 X ' Weight of I cubic foot of air Let h = velocity head in inches of water = dynamic head — static head. p := density of air in pipe =: weight of i cubic foot of air. g = mean gravity = 32.17. V = velocity of air in feet per minute. h Then H = 52 X — P . .34X5-2XA V ±^ 60 V2 g H P ' P The velocity head is found by means of a differential gage attached, as sho^yn in the sketch. Fig. 124. I64.34 X 5.2 X A \ h = 60 "V = ''O97 \ — Sec. a6. AIR CHAMBERS ON FUEL OIL LINES A necessary condition for properly burning oil is- to have a uniform, steady pressure which will give a steady stream of oil PRACTICAL MARINE ENGINEERING into the furnace and prevent fluctuations in the discharging oil spray. Rotating plunger pumps have been built to accomplish this purpose. Two illustrations are shown of the above pumps, namely, the Kinney, Fig. 125, and the May-Nelson, Figs. 126-128. The principle of both is the same, namely, a disk set eccentrically on a shaft which has an eccentric movement imparted to it. They accomplish the purpose very well. Where these pumps are not Fig. 125. Kinney Pump Fig. 126. May-Nelson Pump Fig. 127 Fig. 128 provided, air chambers on the dead ends of the line and also on the line just before the oil reaches the burners are employed. These air chambers are charged with air at 90 pounds pressure per square inch, and the pump is started and the oil valve opened. If the air chamber is properly charged the fluctuation is practically eliminated. The oil, especially when heated, has a great affinity for oxygen, and it rapidly absorbs this element in the air, thus re- quiring the chamber to be recharged about twice a day. Sec. 27. AIDS TO REGULATE COMBUSTION The most useful guides to secure complete combustion of oil are (i) the use of the CO2 apparatus, (2) the amount of smoke produced, and (3) the color of the flame. In good com- OIL FUEL BURNING 211 bustion as high as 15 percent of COj is obtained; about 2 to 2.5 percent oxygen, and about 0.2 of i percent to 0.4 of i percent of CO. One authority gives 2 percent to 8 percent oxygen as the requisite amount for good combustion. The total gives about 18 percent, and the remainder, or 82 percent, is called the nitrogen difference. If the total does not approximate 18 percent then something is wrong with the CO, apparatus. With a gas analysis as above, there should be very little or no smoke, about No. i on the Ringlemann smoke chart being the proper amount. Dense black smoke indicates incomplete coni- bustion. . No smoke indicates an excess of air. The Ringlemann chart is a scale or chart graduated from o to 5 and showing vari- ous differences from no smoke, which is "6," to dense black smoke, ^hich is "5." By examining the flame a great deal can be learned. If ;the flame is pure white, and the back walls can be seen through it, "there is an excess of air; if the flame is yellowish-white, it is about right. If it is a dark yellowish-red, there is insufficient ^ir. An analysis of the gases by the use of the CO, apparatus is, how- ever, the best and surest indication of proper combustion. Sec. 28. ME'^j^S OF OPERATING WITH AN OIL-FIRED ^ w BOILER Su'p^se^flo steam is on the plant, the boilers all being cold sfeSm or air available. ' A hand pump is connected up to ilcharge end of the burner line and the hand pump suction taken from a five-gallon can filled with oil. The pump is started and the pressure brought up to and kept at about 200 pounds per square inch, the pressure being kept as steady as possible. For this purpose, a three-crank pump of the Schutte-Koerting type is a very good one. A torch made of a hooked rod with either waste or «sbestos-ball wicking on the end is dipped in the oil. The addition of a little kerosene or gasoline to the torch improves matters. The torch is lighted and held close in front of one of the burner tips. All the registers are opened wide to give as much air as possible to the boiler. Oil-burning boilers are not provided with dampers, a. .^\ u% -p; gl J 1 Z Ie -5 , ' t , t ^ r --^ -- -| r~ 5 . t ' ' "^ i =E § is — i^s^ r '• > M t, 1 u ''63 " ""iC"" :g 3 ' \ _ ^, ^ , . ii: :||t.. .1 .-. - _ _i s S ~-N "K g g g S 1 1 1 1 ^ 1 i u c o ^ « O (9 la ^ n OIL FUEL BURNING 213 of the oil is reduced by heat to 8 Engler or below, when the torch may be withdrawn. When steam pressure has reached 75 to 100 pounds, turn steam on the oilpumps and heaters and disconnect the hand pump. Turn steam on the forced draft blower and get ready to light the other burners ; start blower slowly, open air registers wide and light the burners. As soon as lighted, speed up the blower until there is sufficient air pressure to prevent vibration and flarebacks. Then set the vanes to the proper openings on the SIDE ELEVATION BABCOCK AND WILCOX BOILER HALF SECTION FRONT ELEVATION YARROW BOlLEl? Fig. 132 HALF SECTION REAH ELEVATION NORMAND BOILER air registers. Always run with the air registers throttled down, as it gives a.betfeer regulation and a higher velocity to the air and ensures ^mdother running. Until the boiler furnace is well heated an excess of air will Ijg^Jle^e^ to prevent smoke. When the furnace becomes heated .^e air can be cut down to the proper amount. Light other burners as needed, first being sure the registers are set and open to the proper amount. In case of vibration shut off a burner till the blower can be speeded up to give sufficient air. Run with very light smoke. Keep a half gage glass of water in the boiler ; if the watg^ level is too high the boiler will prime. It is a well known fact that as burners are added to a boiler, forcing it more, the water level rises, and. vice versa. This should be provided for in operating the feed pumps. Never shut off all the burners at one time on a boiler operating at full power. The water level will drop out of sight and. give many an anxious moment until in sight again. In addition, operating with oils of 12 degrees B. to 17 2t4 PRACTICAL MARINE ENGINEERING OIL FUEL BURNING 215 zi6 PRACTICAL MARINE ENGINEERING looo 3 -Isoo Br700 \ =600 1 foOO |400 -300 / ^-- ^ i!» — 1 a 79 ?i 78 Boile reffic ency ;urve — -^ ^ S 76 .^*— r ^ -^ ^ / Svapo 212° :atiot i". pei from poun and a oil^ ;i^ P^— — o — o / ^__ ■5 . ^ ^ stack temp :ratur B / 111 / o a • / / / 12 g, / / U*q- -,^ q / ^E apon tion f .per •oma q.ft.1 id at .S. / Ji-2 1 / / 0) J3 / / / "1 O ^ C / / / / f t 3 / / / ? 1 / v y s / / ^ y ' / > ^ -ur ) 4 6 t ' « 1. 1 1 1 2 1 3 1. 1 1 s Fig. 136. Tests of Babcock & Wilcox Oil-Burning Boiler degrees B. gravity, the relief valve of the oil pump shows a decided tendency to stick. If a boiler is shut down suddenly with the oil pump running, there is danger of bursting the oil lines and causing a fire. Slow the pump down until the pressure is low enough to cut it out altogether ; then close the burner valves. There are shown herewith diagrammatic cuts, Figs. 129, 130, 131 and 136, of the performances of Yarrow, Normand, and Bab- cock & Wilcox oil-burning boilers at the United States Navy fuel oil testing plant. It is very noticeable that the efficiency and general perform- ance of the Babcock & Wilcox boiler greatly exceeds the per- formance of the other two boilers, especially at the high rates. OIL FUEL BURNING 217 Fig. 132 shows the general design of these boilers, while Fig. 133 shows the furnace of a Scotch boiler arranged for oil fuel burning, and Fig. 134, a Thornycroft boiler fitted with Schutte-Koerting oil fuel burning apparatus. QUESTIONS Oil Fuel Burning PAGE What are the principal factors entering into the successful burning of fuel oil? igi What are the essential conditions concerning the air and gases of com- bustion? I 191 What is the U. S. Naval practice concerning smoke pipe area? 191 Describe the materials used for furnace linings 192 Describe the three principal methods of atomizing fuel oil for burning 194 Into what two general sub-divisions and what five classes may steam and air atomizing burners be divided? 194 Describe the general features of a good mechanical burner atomizing by pressure 195 What amount of air per pound of oil is required for complete com- bustion? 208 What are air chambers on the fuel oil lines used for and how should they be located? 209 By what means can the quality of combustion be gaged? 210 Describe method of operating an oil fired boiler • 211 CHAPTER V Marine Engines Sec. ag. TYPES OF ENGINES: INTRODUCTION From early in the nineteenth century until nearly its expiration the reciprocating steam engine, driving either paddle wheels or screw propellers, held the entire field of marine propulsion. Late in that century, however, a new form of marine engine appeared and rapidly demonstrated its fitness for the work to which it was proposed to apply it, and in some parts of the fielfl it showed marked superiority over the reciprocating engine. While the former is a pressure engine, the newcomer, the steam turbine, is a heat engine pure and simple. That is, in the first case pressure disappears and reappears as work, while in the second case heat disappears and work takes its place. The steam turbine has one serious drawback, however, which seriously handicapped it in some parts of the marine field, in its race with the reciprocating engine for supremacy. The latter machine can be worked throughout a great range of percentage of its designed power without serious loss in econ- omy. This is not the case, however, with the steam turbine, which loses rapidly in efficiency as its speed of revolution de- creases below the designed speed and as the volume of steam flow through the turbine is decreased below that for which the engine was designed. Combination of Turbine and Reciprocating Engines: The fact that the steam turbine uses the heat in the steam almost, if not c(uite, down to that corresponding to the vacuum in the condenser, while the reciprocating engine lower limit is well above the pres- sure corresponding to this temperature, was father to the idea of combining the two machines for the sake of increase in economy. There are several arrangements of combination machinery, the variations being caused by varying conditions of service. These arrangements and the reasons for the variations will be described later. MARINE ENGINES 2^9 Reduction Gears: The nature of the steam turbine requires a high speed of revolution of its moving part, the rotor, in order that a high degree of efficiency may be realized. In order to obtain a high propulsive efficiency with the screw propeller which drives a ship, a comparatively low speed of revolutions must be used. It is thus seen that the interests of the prime mover and of the propeller are, antagonistic, as to improve one the other must be sacrificed should it be desired to connect the turbine directly to the propeller shaft. In order to reap the benefits of both high speed turbine and low speed propeller, "reduction gears" have been introduced. These may be classed under three heads, as follows : a. Mechanical. b. Hydraulic. c. Electric The general term of "reduction gear" is generally applied to a, in which the power is transmitted from the turbine to the pro- peller shaft through a pinion or pinions on the turbine shaft gearing in with a gear wheel on the propeller shaft. The reduction by hydraulic means, b, is usually efifected through a series of centrifugal pumps, the supply pump being driven by the turbine, and the receiving pumps being carried on the pro- peller shaft. The arrangement is known as the "Fottinger trans- former." Electric reduction gear, c, is usually spoken of as "electric pro- pulsion," but the electric bind between the electric generator driven by a high speed turbine and the slow speed motor on the propeHer shaft can be justly classed, along with the mechanical and hydraulic binds, as "reduction gear." Internal Combustion Engines: These are a late development in the field of marine propulsion and appear to be a realization of one of the dreams of marine engineers, namely, the development of power in the engine cylinders by the direct use of heat gen- erated inibe cylinders themselves. In sodi^engines the power giving force is generated in the cyl- inders by the combustion of gas or oil directly in the engine cylinder, thus avoiding the heat losses which occur unavoidably in the boilers and piping of steam engines. Purposes for which each of the types is best fitted: Low speed, 220 PRACTICAL MARINE ENGINEERING low power; small variation in ordinary power and speed: Inter- nal combnstion engines, mechanical and hydraulic reduction gear, reciprocating engines. Moderate speeds, moderate to high power; large variation in speeds and powers : Electric reduction gear, mechanical reduction gear, hydraulic reduction gear, combination machinery, recipro- cating engines. High speeds, moderate to high power; slight variation in speeds and powers : Steam turbines, elec?tric reduction gear. High speeds, moderate to high power ; large variation in speeds and powers : Steam turbines with auxiliary turbines and reduction gear for cruising, electric reduction gear, mechanical reduction gear. The foregoing will give a general idea of the ground to be covered in a general consideration of the subject of marine pro- pelling machinery, The different systems will now be taken up more in detail, Sec. 30. MARINE RECIPROCATING STEAM ENGINES [i] Types of Engines and Arrangement of Parts The various types of marine reciprocating steam engines may be classified in different ways, according to the particular feature under special consideration. A typical engine as in Fig. 138 may be defined as a vertical, inverted, direct acting, multiple expansion, condensing, engine. The significance of these various terms will first be examined. In the early days of marine engineering the engines were often horizontal, as shown in Figs, 141 and 142, and such are still met with occasionally in special types of warship practice and elsewhere. An intermediate type, as shown in Fig. 143 and known as the inclined or diagonal engine, has been used to a considerable extent with paddle wheels. In modern practice, with rare excep- tions, the marine screw engine is vertical, as in Figs. 137-140. In the earlier vertical marine engines the cylinder was at the bottom and tne motion of the parts proceeded upward either directly, to the crank shaft, as in the oscillating engine. Fig. 144, or to a beam or intermediate mechanism. Fig. 145, whence it came back to the shaft. In the modem engine the cylinders are on top and the motion of the parts proceeds downward to the MARINE ENGINES shaft. Hence in comparison with the earlier types the modern engine is called inverted. Where the connecting rod and crank lie beyond the cross- head or farther end of the piston rod, as in Figs. 137-141, the 3tarine Enfftiuerhtg Fig. 137. Longitudinal Secticm, Compound Engine, Mercantile Type engine is said to be direct acting. In certa^ early types of hori- zontal engines in single screw ships, as represented in Fig., 142, the cylinder was sometimes placed close to the shaft and two piston rods were fitted passing beyond the shaft, one above and Hi PRACTICAL MARINE ENGINEBRING MARINE ENGINES 223 the other below. Then from a crosshead at this point the motion came back to the crank pin by a connecting rod in the usual way. Fig. 139. Triple Expansion Engine, End View Looking Aft Such engines were called return connecting rod or back acting. In still earlier times the same type of engine placed on end, with the cylinder at the bottom, and known as the steeple engine, was 224 PRACTICAL MARINE ENGINEERING frequently fitted in side wheel paddle steamers, and a modifi- cation ot this is occasionally met with abroad at the present time Fig. 140. Triple Expansion Engine; End View Showing Condenser in Back Framing In early marine engines the expansion of steam always took place in one cylinder only. In the typical modern engine the steam is passed through a series of cylinders from, one to another MARINE ENGINES 225 of increasing size. Such engines in general are termed multiple expansion. If the steam is thus used successively in two cylinders or the expansion occurs in two stages, the engine is said to be a compound; if in three cylinders or three stages, it is a triple or triple expansion; if in four cylinders or four stages, it is quad- ruple or quadruple expansion, etc. Where the steam after being used in the cylinder is exhausted into the air, the engine is said to be high pressure or non-con- 1 _ I Fig. 141. Horizontal Direct Acting Engine, Outline densing. In the typical modern engine the steam is exhausted to a condenser, thus giving the advantage of an increased ratio of expansion and a decreased back pressure. Such engines are called condensing. Reciprocating engines are often given special names accord- ing to the nature of the mechanical movements employed. In Fig. 143. Horizontal Back. Acting Engine, Outline the usual type, as has already beenseen, the motion is direct act- ing and proceeds through piston,"=^iston rod, crosshead, connect- ing rod, crank pin and crank shaft. In the beam engine^ as shown in Fig. 145, the motion passes from the piston rod to a crosshead and then by link or parallel motion to the beam. Thence from the other end of the beam it passes by the connect- ing rod to the crank pin and crank shaft. Such engines are espe- 226 PRACTICAL MARINE ENGINEERING daily suited to side wheel, paddle steamers, and for many years were considered the standard engine for use on river, bay and lake steamers. In more recent practice, however, the vertical direct acting engine with screw propeller is to a considerable ex- tent displacing the beam engine with paddle wheel, even in its own territory. In the oscillating engine, a favorite in British practice for side wheel paddle steamers, the cylinders are located below the Fig. 143. Inclined Engine, Outline shaft and are swung on trunnions, as shown in Fig. 144. The piston rod is connected directly to the crank pin, the piston rod and connecting rod forming thus but one member. This motion is made possible by swinging the cylinder on trunnions, as may be readily seen by the diagram. The trunk type of horizontal engine, as shown in outline in Fig. 146, was often fitted in former years where economy of transverse or athwartship dimension was necessary. In this engine the use of the piston rod was avoided by the large trunk, to which the connecting rod was directly attached, as shown. The stern wheel western river boat engine, as shown in Fig. 248, is a direct acting horizontal engine connected to the stern wheel, and provided with a peculiar type of valve gear. Refer- ence to some peculiar features of this engine will be made further on. The various members of a multiple expansion ma,rine engine may be arranged in a great variety of ways as regards the location of the cylinders, the crank angles, and the order in which the MARINE ENGINES 227 cranks follow each other around in the revolution. These are illustrated in Figs. 147-150. Of the many combinations which might be made, only the more important are mentioned. Through- out these diagrams the high pressure cylinder is denoted by H, the low pressure cylinder by L, the intermediate cylinder of a triple expansion engine by /, and the first and second intermediates Fig. 144. Oscillating Engine, Outline of a qtiadruple expansion by I^, and /j, respectively. Where the total cylinder volume is divided between two, each of half size, both of the latter are given the same letter. The course of the steam through the engine is also indicated by the arrows. For compound engines the usual arrangements are illustrated in Fig. 148. There may be two or three cylinders and one, two or three cranks. In the latter case the entire volume of low pressure cylin- der is divided between two cylinders, each of half the total vol- ume. The first arrangement with high pressure cylinder on top of low pressure is known as a single crank tandem compound, but is rarely met with in marine practice. The other arrangements may be placed, of course, with either end forward. The various 228 PRACTICAL MARINE ENGINEERING crank angles are shown in Fig. 147, at i, 2, 3, 4 and 5, the crank marked / in No. 5 being in this case one of the low pressure cylin- ders. With two cranks the angle between may be either 90 de- Fig. 145. Beam Engine, Side Elevation Jdarin* £nffint4rimg grees or 180 degrees, or slightly greater or less than 180 degrees, as 175 degrees or 185 degrees. Thego-degree angle is undoubtedly the best for all-around service. The 180-degree angle gives a bet- ter balance to the moving parts and admits of a simplification of valve gear, and is sometimes preferred for these reasons. There is, however, a liability of the engine's sticking on the center, thus making it hard to start, and the general readiness of handling is MARINE ENGINES 229 less than with cranks at 90 degrees. To overcome this, angles of 175 degrees or 185 degrees, as shown at 2, are sometimes used, the balance of moving parts in such case being substantially as good as with an angle of 180 degrees. L T^ — --^ :=r::rr:^i.. r 1 T r'-'T 1 1 1 / I Fig. 146. Trunk Engine, Outline With three cranks the angles are usually equal, and hence 120 degrees each. Occasionally they are slightly varied from these &0®(3 -% 8 9 10 Fig. 147. Various Crank Arrangements ■^ n 5^ T2 values in order to give a more uniform rotative effort, or to give a better balance to the forces causing vibration. V ^ ./ L H / 2 / I *-. ^1 H y / 1 / i / Fig. 148. Cylinder Arrangements for Compound Engine For the triple expansion engine the more important arrange- ments of cylinders are shown in Fig. 149. There may be three cylinders or more, and two, three or more cranks. The most com- 230 PRACTICAL MARINE ENGINEERING mon types have either three or four cranks, in the latter case the total low pressure volume being divided between two cylinders, each of half the total volume. The crank angles are usually 120 degrees with three cranks, and 90 degrees with four, though occa- dt <«s > L 1 i L 1 h/ 1 L H , \ / * / 1 4 ^ 1 L l[[ S]/ ' / y< 3 y 7 Fig. 149. Cylinder Arrangements for Triple Expansion Engine Y 1. 1. L H \ »■ i V L L 1. H/ / / ■» 3 M V 13 z Fig. 150. Cylinder Arrangements for Quadruple Expansion Engine sionally slight variations from these values are adopted in order to obtain a better balance of the forces causing vibration. Of the various arrangements of cylinders shown in Fig. 149, each may, of course, be placed either end forward in the ship. There may also be the various sequences and arrangements of cranks as indicated in Fig. 147, the changes of lettering where necessary being readily seen. Where four cylinders, two low pressure, are used, the best modern practice is to place the low pressure cylin- MARINE ENGINES 231 ders one at each end of the engine with the high pressure and intermediate pressure between, the high pressure crank being opposite its adjacent low pressure one, and the intermediate pres- sure crank opposite the other. For the quadruple expansion engine the more impoitant cylin- der arrangements are shown in Fig. 150. The number of cylin- ders may be four, five or six, with four or five cranks. With five cranks the angles are usually equal, and hence of 72 degrees, though as .with three and four cranks slight departures might be made to obtain a better balance of the forces producing vibra- tion. The arrangements of cylinders shown in Fig. 150 may be placed in the ship either end forward, and various crank sequences in addition to those shown in Fig. 147 may be easily arranged. One of the chief tendencies of modern practice is to pay especial attention to the balancing of the forces producing vibration. The use of irregular crank angles in this connection has been already referred to. In addition, and of not less importance, the larger cylinders with the larger and heavier pistons are now frequently placed inside, with the lighter moving parts on the outside, as in Fig. 149, Nos. 3 and S, or Fig. 150, No. 2. Sec. 31. THE TURBINE FOR SHIP PROPULSION The steam turbine now occupies a recognized position in its use and application for the propulsion of ships. Doubts that ex- isted only a few years ago have been dispelled by success and established records. [i] Advantages Among the features which give the turbine advantage over its original conipetitor, the reciprocating engine, itiay be noted especially the perfect safety and ease with which turbines may be run without approaching the dangers which follow ponderous or fast-moving reciprocating engines should they be oversped or race. Further, the almost inappreciable amount of vibration with turbines renders this machine a particularly desirable adjunct for pass'^nger steamers, as well as for warships; the absence of in- ternal lubrication saves much oil and returns feed water free from its deleterious effects. Moreover, the turbine is not seriously affected by the priming of the boilers, except as to a reduction of speed. For high speed ships running at full power some advan- tage is also gained in increased economy of steam consumption ; 232 PRACTICAL MARINE ENGINEERING its capaciity to deliver an excess in designed power is often claimed as of some advantage not possessed by Ordinary engines, but this advantage would not exist if the turbine were designed as Fig. 151. Three-Shaft Arrangement of Parsons Turbines closely to the required power as is the case with the reciprocating engine. In other words, turbines as usually designed are too large for the desired output of power. MARINE ENGINES Z33 Its cost and weight both compare I'avorably with reciprocat- ing engines. The space, however, occupied by marine turbines is not reduced materially, if at all, as compared with modern high Fig., 162. Four-Shaft Arrangement of Parsons Turbines on o Battleship speed reciprocating marine engines, and where additional cruising turbines are fitted for economy at lower speeds, the space required is considerably greater. This is due to the fact that their speeed of revolution has to be compromised to suit propeller speeds, in order to gain reasonable propeller efficiency. It is also claimed for turbine-driven ships that the duties of part of the engine room 234 PRACTICAL MARINE ENGINEERING staff are lighter in so far as the watching of the main machinery is concerned, the principal attendance consisting in the operation of the auxiliaries. [2] Parsons Turbines Arrangement in Ships. Installations with this type of tur- bine. Figs. 151 and 152, are with either three or four shafts, two shafts being used only in special cases as in destroyer work where such an arrangement has been used with great success. Various considerations are responsible for either arrangement. Four shafts are generally used in battleship designs and in ships where Fig. 153. Two-Shaft Arrangement of Curtis Turbines a minute subdivision of compartments is aimed at, as, for instance, transatlantic liners of the Mauretania and Lusitama class. Tor- pedo-boat destroyers have two or three shafts, while three shafts are used with a large nuajber of the ordinary type of passenger steamers. , The turbines are usually all placed in one compart- ment with three shaft arrangements, and, in two or more com- partments, with four shaft arrangements. For warships, either separate cruising turbines are fitted or they are made within the same casing as the main high pressure turbine, having separate by-pass valves. When arranged independently, they are always placed on the low pressure turbine shaft. They are fitted in naval vessels owing to the fact that low cruising speeds are impo'sed by tactical requirements for a great part of the time. When three shafts are used the main high pressure turbine drives the center shaft and each of the two low pressure turbines drives a wing shaft. In four shaft arrangements the high pressure turbines usually drive the outboard shafts, while the low pressure turbines drive the inboard shafts. The backing turbines are arranged MARINE ENGINES 235 within the casings of the low pressure turbines, or are entirely independent units. Some arrangements provide one on each shaft ; others only on two shafts. [3] Curtis Turbines Arrangement in Ships. Arrangements with Curtis turbines in ships are made with two shafts, Fig. 153, three shafts. Fig. 154, Fig. 154. Three-Shaft Arrangement of A. E. G. Turbines on a Battleship or four shafts, either arrangement being composed entirely of independent units on each shaft, both in so far as the turbines and 236 PRACTICAL MARINE ENGINEERING the necessary auxiliaries are concerned, of the steam may pass from the turbine on one shaft to and through the turbine on the other before passing to the condenser. In very large installations the turbine unit is usually divided in a separate high and low pressure turbine, but single turbine units are used also for in- stallations of considerable power. There are no separate cruising turbines with straight Curtis turbine installations, the power for low speeds being regulated by the throttle and by shutting off a certain number of the nozzles. [4] Combination Machinery There are two separate and distinct fields in which this type of machinery can be used with profit for the propulsion of ships, and these two fields are so widely separated in their requirements that radical differences in the designs of the machinery must be made according to the field in which it is to be utilized. The first field of use is that of the "merchant marine." In this field vessels are required to steam at nearly a constant speed when in free route. This being the condition of service, the ma- chinery is designed to develop approximately the power required for the designed speed, and economy at this speed is the result aimed for. The ordinary arrangement of machinery for such service is as follows: Number of shafts — Three, 2 outer or wing, i center. Engines — Triple expansion, vertical, inverted, reversible, re- ciprocating, on each wing shaft. Low pressure turbine on center. Pressure of Steam at Turbine — Twelve pounds absolute. Course of steam in the ahead motion : ' Through reciprocating engine on each wing shaft. Through change valve on each engine to low pressure turbine. Through low pressure turbine to Condenser. Course of steam, engines reversing : Valves of reciprocating engine set for reversing. Steam through reciprocating engines. Through change valves to con- denser. Change valves ; valves thrown by a steam or hydraulic piston or by the reversing shafts of the reciprocating engines, and chang- ing the course of the steam exhausting from these engines. There is only one condenser. There may or may not be MARINE ENGINES 237 arrangements for reversing the center shaft, but usually all re- versing is done by the reciprocating engines only. The economy realized by this arrangement is considerable, the water consumption per brake, or shaft, horsepower, while as good, if not better, than that of turbines only, is much better than that of reciprocating engines, and more than offsets the loss in propulsive efficiency due to the inefficient fast running propeller on the center shaft. The result is a net gain in water per knot and in fuel per knot. Turning now to the second field, a different condition of speed and power requirements will be encountered. This field is the one occupied by naval vessels of the battleship and cruiser classes. Such vessels must be capable of producing high power and speed when called upon and must produce them on as light a weight of machinery and as economically as possible. In addi- tion, the greater part of the steaming done by such vessels is at a much lower speed with correspondingly lower power than the maximum, and for the sake of economy and cruising fuel life of bunkers, it is absolutely necessary that as high a rate of economy as possible be realized at these cruising speeds. These variations in conditions between the two fields of use cause a radical difference in the design of and in the proportional part of the power developed by the engines and the turbine or turbines. In the first field, it has been shown that an ordinary triple expansion engine exhausting to the turbine at a pressure of about twelve pounds absolute is used. The proportion of power de- veloped by the two reciprocating engines is two-thirds of the total, the turbine producing the other third. In the second field, in order to prevent the turbine from becoming a drag upon the power developed and thus causing loss before, sufficiently low power and speed are reached, the initial pressure at the turbine is raised to about thirty pounds absolute and the turbine, when full power is being developed, produces approximately one-half of the total. In describing an installation of machinery of this type, a design proposed for the United States battleships Arkansas and Wyoming, in 1909, will.be taken as an example. In designing this machinery, advantage was taken of the fact that the initial turbine steam pressure, thirty pounds absolute, is 238 PRACTICAL MARINE ENGINEERING practically the same as the pressure' existing in the low pressure receiver of a modern high-power reciprocating steam engine of the most efficient type, using steam of 265 pounds absolute, in the high pressure steam chest. Further advantage was taken of the fact that while in a triple expansion reciprocating steam engine the thermal efficiency of the high pressure and of the intermediate pressure cylinders exceeds that of the high pressure turbine, the thermal efficiency of the low pressure cylinders is greatly ex- ceeded by that of the low pressure turbine. Utilizing the above facts, the usual low pressure cylinders of the triple expansion engines were omitted and the intermediate cylinders, having a ratio of about *2j4 to i to the area of the high pressure, became the low pressure. The engines were made double compound, with two high and two low pressure cylinders to each engine, the low pressure cylinders were adjacent to each other and a high pressure cylinder was at each end of the engine. Each high with its adjacent low pressure cylinder formed a com- plete engine, so far as the course of the steam was concerned, and either half unit could be cut out in case of trouble and the re- maining half unit still be operated. There were four shafts, two outer or wing, and two inner, the low pressure turbines driving the inner shafts, and each turbine received its steam from the exhaust of the compound reciprocat- ing engine on the adjacent wing shaft. Between each pair of low pressure cylinders was a large ex- haust receiver and the steam passed from these receivers through change valves, of the piston type, to the turbines. The reciprocating engines were made reversible and each inner shaft also carried a reversing turbine. There were two condensers, one for each pair of shafts. The change valves were operated directly from the recipro- cating engine reversing shaft, so that when the man handling the engine threw the reversing lever into either the ahead or astern position, the change valve followed the lever similarly to the steam valve gear links, and the exhaust steam from the compound engines was directed either to the ahead or to the backing, turbine, as desired. Calculations of economies indicated _ that this combination would be from 10 to 15 percent more efficient than either the straight reciprocating engine or the straight turbine drives at MARINE ENGINES 239 twenty-one knots -speed, and vrould equal the reciprocating and be about twenty-five percent better than the turbine drive at eleven knots. This installation was not made, but not from doubts as to the economy to be realized. However, in 1912, the French Govern- ment adopted a very similar arrangement for several new battle- ships, and while nothing definite as to their performances in active service has been obtained, it is understood that expectations have been realized. Combination Machinery for High Speed Vessels of High Power, In such vessels where turbines are used as the propelling engines at high speed, but where the usual steaming speed is only about one-half of the maximum speed, small, reciprocating engines are used in combination with the main turbines when steaming at the lower speeds. The usual arrangements are as follows : (a) With Parsons or Curtis turbines: Number of shafts three. Arrangement of turbines: High pressure turbine on center shaft exhausting to low pressure turbine on each wing shaft. Low pressure turbines exhausting each to its own condenser. Back- ing turbine on each wing shaft. No backing turbine on center shaft. On each wing shaft; forward of the low pressure turbines and coupled to the turbine shaft by a coupling which may be unccrapled, and with some types coupled, without stopping the machinery, is a small two-cylinder, vertical, inverted, compound engine, using high pressure steam and exhausting through a steam re-heater to the first regular high pressure stage of the high pres- sure turbine. The term "regular high pressure stage" is here used for the reason that in some cases, in order to obtain a small gain in economy after the reciprocating engines have been un- coupled, the high pressure turbine is fitted with one or more so- called "cruising stages" in advance of the first regular stage of that turbine, the blading of these cruising stages being propor- tioned for the reduced volume of steam required for the inter- mediate speeds. The reciprocating engines are, in some cases, fitted with re- versing gear which also controls a change valve in their exhaust, changing the flow of the exhaust from the high pressure turbine 240 PRACTICAL MARINE ENGINEERING to the backing turbines when the valve gears are thrown to the reverse position. In other cases the reciprocating engines are not fitted with reversing gear. When this is the arrangement, each cyHn^er is fitted with a large relief valve, so that should reversal take place without an opportunity to uncouple, undue compression of the steam confined in the cylinders is prevented by these relief valves lifting under the pressure and allowing free discharge of the con- fined steam either into the atmosphere or to the condensers. (b) With Curtis and similar turbines only: Number of shafts, two. Fig. 155 Complete turbine unit on each shaft, each unit discharging to its own condenser. Backing turbine on each shaft. On each shaft, forward of the turbine, is a small reciprocat- ing engine similar to those in (a) and arranged for reversing, coupling and uncoupling as in (a). Each engine, however, ex- hausts to the first stage of the turbine on its own shaft, and if fitted for reversing exhausts to the backing turbine on that shaft when going astern. For equal power with (a) the reciprocating engines in (b) would be slightly larger and more powerful than those in (a). (c) With Parsons turbines only: Number of shafts, two. High pressure turbine on one shaft exhausting to a low pres- sure turbine on the other. One condenser to which low pressure turbine and backing turbine exhaust. MARINE ENGINES 241 On each shaft is located a backing turbine abaft the main ahead turbines. Coupled to the low pressure turbine shaft, forward of that turbine is a small reciprocating engine which exhausts directly to the main high pressure ahead turbine. This engine is similar to those fitted in (a) and (b). For pianeuvering purposes, a direct connection from the high pressure turbine to the condenser is fitted; also a valve in the exhaust from that turbine to the low pressure one. In maneu- vering, the connection to the condenser is opened, and the exhaust valve to the low pressure turbine closed, live steam being used in both high and low pressure turbines, which are thus con- verted into independent units, although at a heavy loss in economy when being so used. [5] Reduction Gears (a) Mechanical Gears: The principal examples of the appli- cation of gear wheels and pinions to provide a suitable connecting link between the fast running efficient steam turbine and the slow turning efficient screw propeller are the Parsons and the Westing- house systems. Practically the only essential difference between these two systems is that while in the Parsons system the gear wheel and pinion shafts are supported in rigid bearings, depending entirely for alinement upon the rigidity of the bedplate and foundations supporting the- gears, in the Westinghouse system the pinion shaft bearings' are supported by hydraulic cylinders which permit that shaft to adapt itself to any change of alinement of the gear wheel shaft, tend to deaden the noise of the gearing and also give a ready means of measuring the power transmitted at any instant. The Westinghouse gear will here be explained in detail. The first idea of automatic adjustment of alinement originated with the late Rear-Admiral George W. Melville, U. S. N., for many years Engineer-in-'Chief of the United States Navy, and his partner in business, Mr. John H. Macalpine. The idea, as de- veloped by its originators, differed essentially from the fully de- veloped scheme, the alinement being taken care of by means of a flexible I-beam which carried the bearings of the pinion shaft. The original idea is shown by Fig. 155. A A is the double helical pinion, and B B is the large gear connected directly to the propeller shaft. The pinion shaft is 242 PRACTICAL MARINE ENGINEERING supported in three bearings in the frame C This frame is sup- ported at its center by a section of /-beam D, which is fixed to the bedplate of the gear casing. It will be seen that if the pinion shaft is flexibly connected to the shaft of the driving turbine, the elasticity of the supporting member D will allow the frame C to tilt in a clock-wise, or counter clock-wise direction to whatever extent is necessary to_ secure a proper alinement of the bearings of the pinion with respect to the bearings of the main gear. The Westinghouse Design While the Melville and Macalpine design fully demonstrated the correctness of the theory of the floating frame, Mr. Westing- house saw that the essential principle might be more advantage- Fig. 156 ously applied by supporting the pinion frame hydraulically. The advantages ofthe hydraulic support are threefold. First, the removal of all direct metallic connection between the floating frame and the gear casing eliminates in a large meas- ure the noise of operation. Second, the hydraulic medium, being constantly circulated, contains a small amount of air entrained with it, which has a valuable cushioning effect, that is not only further conducive to quiet running, but which also gives a degree of elasticity to the system that will prevent the rapid contacting of the teeth from producing a hammer blow effect that might eventually result in pitting or crystallization. Third, the hydraulic pressure automatically adjusts itself in direct proportion to the torque, so that by the addition of suitable MARINE ENGINES 243. indicating instruments, the gear becomes the most accurate dyna- mometer yet devised for the measurement of large powers. The Westinghouse design is illustrated diagrammatically in Fig. 156. As in Fig. 155, ^ /4 is the double helical pinion, B B the driven gear, and C C the frame carrying the pinion shaft bear- ings. In the lower side of the pinion frame are three cylinders with pistons D D D, which rest on a suitable beam or ledge in the gear casing, while three other cylinders, D D D, are fitted in the upper side of the pinion frame to take the thrust when the direc- tion of motion is reversed. E and E' are passages communicating with all of the cylinders. It is evident that if fluid under suffi- cient pressure be introduced at E, the pinion frame C will rise and will literally float on the fluid contained in the cylinders. It is also evident that the lift of the pinion frame may operate a relief valve on the fluid pressure system, in such a way as to maintain the pressure in direct ratio to the load on the floating frame. If in the arrangement shown in Fig. 155, the direction of ro- tation is such that the upper teeth in the pinion are moving toward the observer, the resistance offered by the gear B B will cause a downward thrust on the floating frame C, and the relief valve in the fliiid pressure system will maintain the pressure in .the hydrawiic cylinders at the exact point required to balance the weight of the floating frame, plus the downward thrust due to the tooth pressure between the gear and the pinion. If the load is increased, the downward thrust on the pinion frame is in- creased. The pinion frame is depressed slightly, closing the relief valve in the fluid pressure system sufficiently to restore equi- librium. Conversely, if the load decreases, the pinion frame rises slig^itly, opening the relief valve, and relieving the excess pres- sure in the hydrarfic cylinders, thus automatically bringing the system into balance again. From the foregoing, it will easily be seen that the pressure in the hydraulic supporting cylinders is at all times an accurate index of the intensity with which the gear is working. The re- lief valve on the fluid pressure system is opened by a device that multiplies the movement of the floating frame so that the total travel of the latter over a range of load between full capacity and zero is only a few thousandths of an inch. How THE Fluid Pressure is Maintained It is evident that the fluid pressure behind the supporting 244 PRACTICAL MARINE ENGINEERING pistons could be maintained by means of a pressure pump dis- charging into the passage E and E' through a flexible connection. Fortunately, however, there is a much simpler means which obvi- ates the necessity for the added complication of auxiliary pump- ing apparatus. For a long time it has been known that if oil is introduced into a rotating journal at the point of least pressure, and a means of egress is provided at the point of maximum pressure, the jour- nal will have a decided pumping action, and will build up an oil pressure substantially equal to the maximum bearing pressure. This action of bearing oil is taken advantage of in the follow- Fig. 157 is a cross section through the floating pinion frame at the middle bearing. A is the pinion shaft, which in this case is Fig. 157 located directly above the main gear shaft. B denotes the upper part of the gear case. C is the floating frame and D and D' are two of the opposite supporting pistons. E is an upwardly pro- jecting arm with oil passages F F' and G. H H and H' H' are oil chambers extending throughout the length of the floating frame and communicating with all three of the hydraulic cylinders on either side. The sections indicated by the letters H and H are not two separate chambers, the apparent dividing wall being a boss or post through which the oil passage carrying the high pres- sure oil to the bearings is drilled. Similarly H' and H' constitute a single chamber. K and K' are valves for automatically regulat- ing the oil pressure. L is a pivoted link connecting the floating frame to the side MARINE ENGINES 24s of the gear casing, so that when the floating frame moves side- wise slightly in accommodating itself to the load the upper end of the arm E will have a positive and magnified corresponding movement. The operation is as follows : Low pressure oil is introduced into the upper end of the passage G, through which it passes down to /, which communicates with the top of all three shaft bearings. If it is assumed that the pinion is rotating in the direction of the hands of a clock, the reaction between the teeth of the pinion and the gear will move th^ floating frame slightly to the right and the upper end of the oil passage F' will be sealed by the valve K'. Each bearing will draw in low pressure oil at the top from the passage / and discharge it through the opening on the right, past a ball check valve into the chamber H' H' and into the hydrau- lic cylinders in which the supporting pistons D' are located. Since the exit of the passage F' is sealed by the valve K', the oil pres- sure will build up behind the pistons D' until it just balances the side thrust of the floating frame corresponding to the load carried at the moment. The instant this pressure is exceeded, the pinion frame is forced slightly to the left. This movement causes the upper end of the passage F' to become unsealed by the valve K', and allows the surplus oil to escape into the gear case, whence it is returned through the lubricating system to the passage G. The valve K' throttles the discharge from F' sufficiently to main- tain the pressure behind the pistons D' constant at the degree re- quired to balance the thrust of the pinion frame. If the load on the gear increases, the arm E moves slightly to the right, throttling the discharge from F' sufficiently to raise the oil pressure behind the pistons D' to the point where the system will be in balance agam. Conversely if the load on the gear is decreased, the arm E moves slightly to the left, reducing the throttling of the dis- charge through F' so that the pressure behind the pistons D' is lowered until it just balances the decreased thrust of the floating frame. When the direction of rotation is reversed, the action is just the same, except that the valve K and the oil passages and sup- porting pistons at the left come into play. Measurement of Power Delivered From what has been explained regarding the automatic regu- 246 PRACTICAL MARINE ENGINEERING lation of the pressure of the oil which sustains the thrust of the floating frame due to the reaction of the tooth pressure between the pinion and the gear, it will- readily be perceived that the pres- sure of the oil is an exact measure of the force that is at the mo- ment being exerted at the pitchline of the gears. This force mul- tiplied by the pitchline speed in feet per minute and divided by 33,000 gives the horsepower that is being transmitted. Hence, by noting the pressure registered by the pressure gage connected to the oil cylinders, only a very simple calculation is required for calculating the power that is being developed. By connecting to the gear a continuous speed recorder, and a recording pressure gage, charts may be obtained from these in- struments which will constitute a continuous log of the power developed over any extended period of time. The gages connected to the oil cylinders may be located at any distance from the gear itself. When the gear is running, only one of the two gages indicates pressure. A reversal of the direction of rotation of the gear shifts the pressure reading to the other gage. If these gages were located on the bridge, the officer on duty could determine at a glance the direction of rotation of the turbine and the intensity with which it was working. These gages would also indicate unerringly the degree of promptness with which the engine room force carried out the instructions tele- graphed from the bridge. With a ready and accurate means of determining the power exerted, experience would doubtless indicate many ways in which this information could be utilized in detecting wastes and effecting important economies. For example, increased coal consumption without increased power would call for prompt investigation of the condition of the boilers, engines and auxiliaries. On the other hand, a comparison of the power developed, and the speed of the vessel, would avoid the necessity for any conjecture as to when it might pay to dock the ship for a general cleaning of the hull and an examination of the propellers. Lubricating of the Gear Teeth The lubrication of the gear teeth is copious and effective. Fig. 158, showing one-half of the floating frame, shows the longi- tudinal channel which distributes the low pressure oil to the bear- ings. This is the passage indicated by the letter / in Fig. 157. From this channel there are also small passages which discharge MARINE ENGINES 247 oil on the pinion. The oil is thrown off of the pinion by centri- fugal force. By referring to Fig. 159, which is a cross section through the floating frame and pinion, it will be obvious that the latter is com- pletely housed in, except for that portion of the circumference where the teeth engage with the teeth- of the main gear. The oil Fig. 158 thrown off by the pinion can therefore escape only by being pro- jected directly against the working face of the gear. Flexible Connection Between Turbine and Gear To avoid the necessity for absolutely rigid alinement between the turbine and gear, they should be coupled together by a reason- ably long flexible shaft. In order to obtain this desirable con- nection, without sacrificing any space, the pinion shaft is made Fig. 159 hollow, and the flexible driving shaft extends into the bore of the pinion shaft and is fixed to the latter at the end furthest away from the turbine. By this simple expedient, the gear may be set close to the turbine and still have the advantage of a connecting shaft of considerable length. The coupling between the turbine shaft and the flexible driv- ing shaft is so constructed as to allow the pinion to have a self- adjusting end-wise motion without affecting the longitudinal po- sition of the turbine shaft. Other Mechanical Gears, There are two other mechanical 248 PRACTICAL MARINE ENGINEERING gears in addition to the Parsons and the Westinghouse, which seem almost certain to extend the field of propulsion by means of toothed wheels. They are the General Electric and Bath Iron Works systems. In the General Electric system there is a chain of gears, the turbine driving the main pinion shaft, the pinions engaging with I'ig. 160. Gear Casing with Single Pinion Shaft Located Directly Above Main Shatt intermediate gears on two intermediate shafts, and these gears driving the main gear on the propeller shaft. In the Bath Iron Works system, the pinion teeth are all cut in the same direction instead of in opposite directions, as is the case in the other systems, and the steam thrust of the turbine through its pressure directly astern tends by its fore and aft com- ponent to balance a portion of the propeller thrust, thus easing up to some extent the work required of the main thrust bearing. The Efficiency of Mechanical Reduction Gear is very high, tests at the works of the Westinghouse Machine Company show- MARINE EXCINES 249 Fig. 161. Gear Case with Single Pinion Sliaft at Side o£ Main Shaft Fig. 163. Same as Fig. 161. Upper Half of Casing Removed 250 PRACTICAL MARINE ENGINEERING Fig. 103. Gear Case with Two Pinion Sliafts Fig. 16i. Same as Fig. 10^. Upper Half of Gear Casing Removed, Showing Two Pinion Shaft Supporting Cylinders at Right MARINE engines; 251 ing it to reacli 98.5 percent. This was, Ikaxtvci', measured for- ward of the thrust bearing. It is probable tliat tlie actual lirake horsepower transmitted to the propeller shaft and measured abaft the thrust bearing can be safely estimated at 96 percent of the power exerted by the turbine on the pinion shaft. Objections to Mechanical Gearing: These may be enumer- ated as, ( I ) Noise of the gearing, which increases with the pres- sure between the teeth and with the velocity of rotation of the Fig. 165. Main Gear Wheels tooth pitch circles. This can only be reduced by extreme ac- curacy in the cutting of the gears, accuracy of alinement of gears, efficient lubrication, and by use of different means for breaking up the metallic vibrations in gears and housing. (2) Undue wear of the gears. This can be guarded against by choice of proper grades of steel for pinions and gear wheel, accurate cut- ting of teeth, and ahnement of shafts, efficient lubrication. (3) Breaking of gear and pinion teeth. This can be avoided by mak- ing the tooth sections large and keeping the tooth pressure com- paratively low, by proper materials only being used, b)- accurate alinement of shafts, and by the use of a properly designed gear cover insuring the exclusion of all dirt and foreign substances from the gears. 252 PRACTICAL MARINE ENGINEERING Mechanical Gearing Used as an Auxiliary Cruising Unit. In the later battleships and destroyers of the United States Navy, cruising turbines driving reduction gears which are coupled to the main turbine shafts forward of those turbines have been fitted. In battleships these cruising turbines are used up to about fifteen knots speed, while in the destroyers they are kept in service up to twenty knots speed. Above these speeds the reduction gear is uncoupled from the main shaft and the main turbines only are used. The arrangement is precisely the same as that described in Sec 31 [4], the reciprocating engines of the combinations in that section being replaced with the cruising turbines and reduction gears. [6] Hydraulic Reduction Gearing Dr. Fottinger of the Vulcan Works, Stettin, Germany, has invented a differential water turbine transmitter, in which the primary water wheel, driven by the steam turbine shaft, transmits, with a certain velocity, water through guide blades or directly to a secondary wheel or wheels mounted on the secondary or propeller shaft in the same axial plane. In this way it is found possible to provide for transmission ratios of 3 to i up to 12 to I. By an arrangement of guide blades and buckets it is possible to have on the same shafts a reversing water turbine transmitter of somewhat similar design. The efficiency depends on the reduction ratio desired, it* decreases a little with the higher ratios, because it then becomes necessary to have relatively higher water velocities, which involve more friction. The transmitter (Fig. 166) consists of two chambers of cast iron, the after one for driving the propeller shaft ahead at a re- duced speed, and the forward one for driving it astern, also at a reduced speed. This arrangement may be altered so far as the disposition of the respective transmitters is concerned. Each of the transmitters is alike in principle. They consist of a primary water turbine wheel mounted on the primary or steam turbine shaft, and one or more — in this case two — secondary water tur- bines mounted on a secondary or propeller shaft, with one or more stationary guide wheels interposed at any place of the circuit. The wheels and blades are of bronze, and the wheels are keyed to the shaft. The series of primary and secondary wheels and guide blades constitutes a complete cycle, and the water moves in a con- Missing Page MARINE ENGINES 253 stant compact flow, the primary wheels taking the water again immediately from the last secondary wheel ; but guide blades may be interposed should this be considered necessary. The water impinges on the whole circumference of the turbine wheels. The water is given pressure and velocity in the primary wheel, which is coupled to the steam turbine shaft, and delivers the water, in the case of ahead circuit, directly to the first secondary wheel ; in this wheel only part of the energy, especially velocity, is absorbed in driving the propeller shaft. The water then flows through stationary guide blades, which are connected to the casing, and leaving these blades, passes through the secondary turbine, which absorbs the remainder of the energy; the water still flows at a certain velocity to the primary wheel. The first probably, and cer- tainly the second, secondary wheel is reactionary. The blades of the primary water turbine are curved back, while those in the first secondary water turbine correspond to ordinary impulse water wheel blades. The guide blades are similar to those in reaction water and steam turbines. The blades in the second secondary wheels are nearly radial and in some cases quite radial. The clearances are similar to those in ordinary steam turbine practice. All spiral casings and connecting tubes to the primary centri- fugal pump and secondary turbines are wholly dispensed with. Taking first the ahead transmitter, shown to the left of Fig. 166, the part marked A is the primary water wheel, B the first secondary wheel, C the stationary guide blades, and D the second secondary wheel. B, it will be noted, is connected to D, which is mounted on the propeller shaft. In the go-astern transmitter — that to the right of the section, Fig. 166 — the primary water wheel is marked A^, the guide blades attached to the casing C^. These, ^ will be understood, reverse the direction of flow of water to the secondary wheel D^, which drives the propeller shaft astern, being coupled to the wheels B and D in the ahead transmitter, and through them to the propeller shaft. From D^ the water passes again to the primary wheel A^. Between the ahead and the astern water circuit there is a diaphragm plate provided with two cham- bers to pass the water which would otherwise leak to the inoper- ative transmitter. These chambers communicate with drains lead- ing to a small tank at the bottom of the boat for the supply of a sm^ll auxiliary centrifugal pump. The amount leaking away has been measured and was found to be about i percent of the mass of water circulating through the turbine wheels. 254 PRACTICAL MARINE ENGINEERING The medium for driving the transmitter is fresh water, which is satisfactory from the point of view of friction and of density. No difference in efficiency has been noticed, even when large quan- tities of oil, salt, or other impurities have found their way into the water. The transmitter is supplied with water by the small cen- trifugal pump driven from the steam turbine through bevel gear upon an extension of the turbine placed at the forward end, as shown in Fig. i66. This absorbs about 0.5 percent of the power of the steam turbine. The pump maintains a constant, but slight, pressure in the pipes between the supply tank and the maneuvering valve, which consists of several chambers within a casing. The pump serves for supplying the water when maneuvering, and for replacing the leakage. It is beneath the water level in the feed tank, so that there is always a suitable column to ensure efficient suction. Nor- mally there is always sufficient pressure of water in the valVe chambers to enable the water supply to be withdrawn from one or other of the two transmitters, and to pass it to the other. The water is fed into the ahead turbine through the port / in the secondary wheel £), this port leading it to the suction side of the primary wheel A for ahead action, while for astern action the supply is through some hollow guide blades Q to the port adjoin- ing the suction point of the primary wheel A^. In describing maneuvering, it may be best to take first the reversing, which is accomplished by ari admission valve controlling the flow of water to the admission noziles or ports in the ahead or astern wheels. This valve is located in the chamber which sup- plies the water for making up leakage, and is under the level of the transmitter. The valve is horizontal, of the balanced-piston type, and the water either flows through the nozzle d to the nozzle of port / for going ahead, or through the nozzle d^, lead- ing to the port for the astern water. The valves are mounted on one spindle, so that d or rf^ cannot be opened unless the other is closed. Moreover, the seatings of the valves are so arranged that when d or d^ is opened to pressure water from the pump, the other is opened to the exhaust pipe to the small reserve tank. The same valve is fitted with traps so as to pass off any water from one or both transmitters; thus the action of the valve permits the water to pass from one of these drain traps into the main drain system. Stuffing boxes are fitted forward and aft of the trans- MARINE ENGINES 2SS mitter with metallic packings. These stuffing boxes are fitted on the hubs of the bearings in order to reduce the fore and aft space occupied. The efficiency of transmission in the ratio of 4.5 to i rises very rapidly, and from 600 revolutions of the primary shaft the efficiency is 78 percent, advancing steadily until 1,250 revolutions is reached, when the efficiency is 83 percent, at which it remains constant. The primary horsepower absorbed by the transmitter re- mains as a nearly constant power rate for a very wide range of secondary speed. At the secondary speed corresponding to the designed transmission ratio, 4.5 : i, it seems to be a minimum, the efficiency a maximum, about 85 percent. Between transmission ratios of 5 and 3.7 it exceeds 80 percent, between 6 and 3.5 it ex- ceeds 75 percent. This has been reached without any regulating devices. In case regulating devices, as in modern water turbines, should be employed, the range af highest efficiency will be still greater. This is of great importance for regulating the trans- mission ratio at reduced speed of steam turbines at cruising speeds. The secondary torque increases very rapidly when the sec- ondary speed diminishes, and is more than twice the designed torque when the secondary shaft is stopped. This is very im- portant for maneuvering. Also for a certain secondary speed, the siccindary torque is zero, so that the propeller may race or the propeller shaft might break down without any danger to the parts of the transmitter, because the secondary wheels then would only attain about twice the designed revolutions, and never exceed this. The system has very considerable possibilities. It enables the turbine to be overloaded without increasing the revolutions, of the twrUue^ and_ secures for a slow running propeller all the advan- tages of the turbineil with its high efficiency. and its freedfim from oil in the condensed water, a very important factor in marine in- stallations. The introduction of the reversing system permits of the continuous use of the economical high speed ahead turbine, irrespective of ahead or astern steaming ; and this, in ships which are frequently reversed, is an important factor. Moreover, the same power is available for going astern as for going ahead, while the adoption of large diameter and large area propellers gives 2s6 PRACTICAL MARINE ENGINEERING greater propulsive power in reversing and maneuvering. In the event of any fracture of the shaft or the propeller involving over- racing, the transmitter acts itself as a relief governor to the turbine. [7] Electric Reduction Gear Main Engines The installation of motors and generators on board ship for propelling purposes is an attempt to make use of the good effi- ciencies of high speed turbines without sacrificing the efficiency of low speed propellers. The weight of such an installation is less (as will be seen from figures given later on) and the space is less also than any of the present installations of either turbines or reciprocating engines. As compared with other methods of speed reduction, it has the advantages (i) that the ratio of reduction can be varied (that is, by winding the motors for different numbers of poles, the ratio of motor and generator can be varied), (2) that at low powers only part of the plant need be used (that is, if two gen- erators are installed, only one need be used at a time), and (3) that there is no need for a backing turbine, which is usually in- efficient and gives very little torque. It will be seen that these advantages are much more marked in a ship using wide ranges of speed and power, such as a battleship, than in a ship running always at nearly the same speed, such as a collier. The claims for electric propelling machinery are that it is lighter than either reciprocating engine or direct drive, takes up less space, and is more efficient than any other form of ship propulsion. The installation on the U. S. S. Jupiter consists of one Curtis turbo-generator, two induction motors, two water-cooled rheo- stats, and one main switchboard ; the excitation for the main gen- erator is taken from one of the ship's 35-kilowatt generators. The turbo-generator furnishes power to the motors, the func- tion of the generator and motors being solely that of a reduction gear. All changes of speed are made by changing the speed of the turbine, thus varying the frequency of the generator and con- sequently the speed of the motors. The generator is two-pole and the motors are thirty-six-pole. The speed reduction ratio is there- fore practically one to eighteen ; the slip of the motors will vary a little for different loads and alter the ratio a' slight amount. The motors are wound for only one number of poles and therefore the MARINE ENGINES 357 ELEVATION LOOKING FORWARD FROM FRAME 173 TO FRAME 163 Kg, 167, Arranrement of Machinery, Collier Jupiter, ElecKic Di'ive 258 PRACTICAL MARINE ENGINEERING speed ratio is not changeable as it would be for a battlcsbip iri- stallation ; the reason for this is that such change is not necessary, as the cruising speed of the ship is practically her maximum speed. The turbine wheels are made of forged steel and are pressed onto the turbine shaft, the diameter of which decreases slightly in steps from the low pressure end down to the high pressure end. There is a brass bushing betweeti the shaft and wheel which pre- vents the two from rusting together. The turbine shaft is solid forged steel. The casing of the turbine is cast iron : the intermediate dia- phragms are also of cast iron. The nozzles are of iron and are Pig. 108. Stator for U. S. Cullier Jupiter ]fi9. Kotor for I' Colli. Jiifitc cast into the intermediate dia])hragms. The expanding nozzles on the high pressure end are bronze and are renewable in sections. The packing rings on the intermediate diaphragms between stages are aluminum rings in two halves with very fine edges on the inside which form a labyrinth packing; the edges of this ring practically touch the shaft and wear their own clearances. The packing around the shaft at each end of the casing consists of carbon rings held together by garter springs which rest in grooves on the circumference of the rings. The rings are pre- vented from turning with the shaft by a stop secured to the garter springs. The carbon rings are supported by flat springs which MARINE ENGINES 2^g keep them flexibly centered with the shaft. There are four rings on the high pressure and two rings on the low pressure ends. In addition to the carbon packing each end of the casing is also packed with a steam seal. Fig. 170. Armature for U. S. S. Jul^iter The blades in the first stage are made of monel metal, which resists the erosive effect of the very hot, fast moving steam ; the blades in the seventh, eighth and ninth stages are also made of monel metal to resist the corrosive effect of anv water that might Fig. 171. Revolving Field for U. S. S. Jupiter 260 PRACTICAL MARINE ENGINEERING collect in those stages ; the blades in the second, third, fourth, fifth and sixth stages are made of bronze. The bearings are of the spherical, self-alining type and both upper and lower halves are water cooled, the water passing through coils embedded in the babbitt. Water for this purpose is furnished by the main circulating pumps or the salt water sani- tary pump. Oil is supplied, under pressure, to the bearings and also to the cylinder of the governor relay by a cycloidal gear pump Fig. 172. 4,00(|-Kilowatt, Nine-Stage Curtis Turbine for U. S. Collier Jupiter situated on tlie lower end (jf the governor shaft. The oil reservoir is in the bed plate of the turbine and is fitted with air vents and an indicator. Oil passes through a large strainer before going to the pump ; after leaving the pump it goes through an oil cooler which gets its cooling water from the same water service that the bear- ings do ; from the cooler the oil goes through a fine mesh strainer, then through a reducing valve (set at 25 pounds pressure per square inch) to the bearings, and returns by gravity to the reser- voir; the oil for the cylinder of the governor relay does not go through the reducing valve but goes direct to the cylinder and is maintained at 75 pounds pressure by relief valves which dis- charsje into the reservoir. MARINE ENGINES 261 The governor is mounted on a vertical shaft driven by a gear from the main shaft. It consists of weights resting on knife edges and acting by centrifugal force against a coiled spring ; the motion of the weights operates a small pilot valve which admits oil, under pressure, to the cylinder of the relay which operates a rack, gearing with a pinion on the cam shaft ; the position of this shaft determines the number of control valves that are open. At the end of the governor arm which operates the pilot valve is con- nected up a diamond shaped frame or parallel motion transmitter which is connected by a system of rods arid bell crank levers to the operating stand in front of the switchboard. The motion of a small wheel on this stand alters the fulcrum about which the governor acts on the pilot valve and consequently alters the speed which the governor will maintain. Steam is admitted to the nozzles through eight control valves. The number open at any time is regulated by the governor, as already explained. These valves are of the globe type, and are free on their stems to allow them to seat easily. The stem ex- tends through a stuffing box and is secured to the lower guide plate of the spring, which is compressed by an adjusting screw sufficiently to force the stem through the stuffing box and seat the valve. The valve is raised by a lever which has a roller on one end which rides on a cam on the cam shaft. The thru.st bearing for the generator turbine consists of a collar on the turbine shaft which works between blocks of cast iron with babitted faces, supported on the ends of lugs projecting from two disks, one at either end of the bearing. The hole in the block into which the lug projects has a spherical base, thus allowing the blocks to aline themselves automatically. The whole bearing as- sembles in one piece on the shaft and, on its outside surface, has a screw thread which rests in a large nut. On the after end of the thrust block is a worm wheel engaging with a worm, the shaft of which projects through the bearing and has a hand wheel on the end of it. By moving this hand wheel the whole thrust bearing will be moved forward Or aft in the large nut and thus change all the clearances on the inside of the turbine. The float in the thrust is set at .017 inch, but can be altered by changing the shims under the after disk. The throttle valve is a Schutte-Koerting balanced piston valve with a quick closing attachment, which can be tripped, either by 262 PRACTICAL MARINE ENGINEERING hand or by a trigger on the shaft, which flies out when the tur- bine speed rises above 2,300 revolutions per minute. The hand trip is also connected by a wire to a hand pull at the operating position at the switchboard. Steam for the steam seals is supplied from the main steam line through a reducing valve set at 25 pounds pressure per square inch. There is an auxiliary gage board on the after engine room bulkhead near the turbine. It has on its face a. steam gage, vacuum gage and first stage pressure gage. This board is for use when starting up the turbine. There is an absolute-vacuum gage con- nected to the base of the exhaust trunk of the turbine and secured to a stanchion near the turbine. The generator is totally enclosed, and the rotor has fans on each end which take air in at the bottom of the casing and blow it out through the windings, discharging into a duct on top of the generator casing ; this duct leads to the suction to the forced draft blowers, so that the heat generated by losses in the iron and copper in the generator is thus passed on to the furnaces of the main boilers. The fans use about 35 kilowatts at full speed. The exciting current for the revolving field is supplied to slip rings on the shaft by one of the ship's 35-kilowatt lighting units. The three power leads from the generator lead forward under the floor plates, being insulated from the ship by porcelain in- sulators. One lead goes direct to the two motors and the other two leads to bus bars on the main switchboard. The motor bearings are of the spherical, self-alining type and are self-oiling, being oiled by rings running in reservoirs in the lower halves of the bearings. The frames of the motors are of cast steel and are covered by sheet metal housings which confine and carry away the heated air and deliver it to the suction of the blowers. Each motor is installed in a watertight pit which cannot easily be filled with water from below. However, the motors are situated under the engine room hatches, so that water from that source would go into the pits, and for this reason the windings are all made waterproof and are intended for safe running when partially submerged. The rotor windings are connected to collector rings which MARINE ENGINES 263 are in turn connected to the water cooled rheostats. These col- lector rings can be short circuited by a slider operated by a lever and working on the motor shaft. The short circuiting device con- sists of a brass segment under each ring and a corresponding segment on the slider; the segments on the slider are made up of thin brass strips interleaved to form a spring, which will have to be compressed to slip under the solid segments. In addition to these devices, there is an auxiliary device working with each main device. This consists of a carbon block on the solid segment and a brass contact on thie slider ; the tips of the brass contacts are re- newable; these contacts are held in place by flat springs on their backs and will thus be forced into contact before the main con- tacts are and will leave the carbon blocks after the main contacts have let go ; the purpose of these auxiliary contacts is to prevent the main contacts from being burned when opening or closing thq circuit. There are two water cooled rheostats, one for each motor. The two weigh 5.8 tons. Each one consists of a top header, bot- tom header, three large porcelain cylinders, three small porcelain cylinders, and three non-inductive resistances. These resistances are made of calorite, and consist of spiral coils laid up on a wooden spindle and having alternate coils connected oppositely from the others so as to make the resistance non-inductive. The large porcelain cylinders rest on rubber gaskets on the bottom header ; the resistances go inside thes^ cylinders; a rubber gasket and a brass ring go on top of each large cylinder and the small cylinder sits on top of this ; the top header rests on rubber gaskets on the tops of the small cylinders. The rheostats have water entering at the outboard end of the bottom header, passing through the cylinders, and going overboard from the outboard end of the top header ; this water is furnished by the main circulating pumps or the sanitary pump. The object of these resistances is to give the motors high torque when backing or when starting from rest and also to keep the current in the circuit within bounds at these times. From an inspection of the speed torque curve of an in- duction motor it will be seen that when starting up or backing the torque is very low, and as the speed increases the torque rises to a maximum and then drops to zero at synchronous speed. This maximum torque will always be the same for any given motor, no matter how much resistance is introduced into the- rotor, but 264 PRACTICAL MARINE ENGINEERING The main switchboard weighs 3.2 tons with all its switches and instruments. It has "Ahead" and "Astern" oil switches for each motor, an ammeter for each motor, an integrating wattmeter for each motor, a voltmeter for the generator, an indicating^ watt- meter for the generator, a voltmeter for the exciter, an ammeter for the field circuit of the generator, a rheostat for the field cir- SECTfON A-A LOOKING *H III DIRECTION OF ARROWS n I li : + . I 11 ' I ;| I I <{ 1 ,i..±_j. 173. Water-Cooled Rheostat for Collier Jupiter cuit of the exciter, a switch for the field of the exciter and a switch for the field of the generator. On the gage board just above the switchboard, there are a frequency meter graduated in revolutions of both generator and motors, an auxiliary steam gage, an oil pressure gage, a first stage pressure gage, an auxiliary vacuum gage, and a clock. On the board secured to the star- board side of the switchboard are main steam and vacuum gages, a Smith^Cummings counter and a Gary-Cummings counter. The control stand for the turbine faces the main switchboard and con- sists of a small hand wheel working around a dial and operating MARINE ENGINES 265 a vertical shaft which has a worm on its lower end ; this worm en- gages in a segment of a worm wheel and the movement of the latter is transmitted by rods and bell crank levers to the governor gear. The operating levers and switches on the board are inter- locked as follows: The short circuiting levers are locked electrically by solenoids which are in series with the field circuit of the generator so that these levers can not be moved while the generator has current in its field circuit ; the "resistance out" ends of the levers have been filed so that they can be operated when current is on, but the locks will keep the levers held in this position strongly enough to pre- vent vibration from moving the levers ; the short circuiting levers and oil switches are locked mechanically so that the oil switches can not be closed when the rheostats are short circuited ; the two oil switches for each motor are mechanically interlocked so that both switches cannot be closed at the same time (that is, the ahead and astern switches of a motor can not be closed at the same time). A summary of the different weights previously given shows the total weight of the propelling machinery to be 166.5 tons. The Cyclops is a sister ship of the Jupiter and is equipped with reciprocating engines ; the weight of her propelling machinery is 260.8 tons. Method of Operating The operation of the machinery will vary according to dif- ferent conditions. Starting with all auxiliaries in operation, the turbine running,, and an exciter cut in on the field of a generator, the operation under different conditions would be as follows : (i) Getting underway, coming to anchor, going alongside a ship, or, in general, handling the ship where much reversing might be expected. Under these circumstances, the resistances would be kept in on both motors. This method would not give yery high motor efficiency, as the rheostats would cause considerable loss ; also the highest speed attainable in this case would be about three-quarters of the maximum speed, The operation in this condition is very simple; to go ahead or astern on either motor, simply close the ahead or astern switch ; this requires about one second for each motor. (2) When it is desired to do economical cruising: 266 PRACTICAL MARINE ENGINEERING It will be necessary to cut the resistances out of the motors ; both motors will, of course, be going ahead, as will also the ship; this operation is not performed in answer to a signal from the bridge, but is merely a change of cruising conditions. To carry out this change, first open the field switch of the exciter ; second, move the control wheel on the dial to very slow speed; third, move both short circuiting levers . so as to short circuit the rheostats; fourth, close the exciter field switch; fifth, bring the turbine up to the desired speed. The total time required for these operations is about twenty-five seconds; about fifteen of these seconds are required to allow the field circuit to die out suffi- ciently to allow the short circuit levers to be moved. (3) After having accomplished operation (2), a signal is received to back either one or both engines. First, open the exciter field switch; second, open the ahead oil switches; third, move the short circuiting levers so as to put the resistances in both motors; fourth, close the astern oil switches; fifth, close the exciter field switch. The total time re- quired for these operations is about ten seconds. The reason this operation does not require as much time as (2) is that it is not necessary to wait for the generator field circuit to die out before moving the short circuiting levers. It will be noted that since the speed of both motors is directly dependent on the speed of the turbine, the speed of the two motors must always be the same unless one of them is entirely stopped. In connection with the operation of the machinery there are several other conditions that might arise. The rheostats might become disabled, in which case the mechanical interlock between the short circuiting levers and the oil switches would be discon- nected, making it possible to move the oil switches with the rheo- stats cut out. The ship could then be maneuvered satisfactorily, but it would always be necessary to slow the turbine down to very slow speed before starting up or backing. Either motor might be disabled, in which case the ship could be propelled with one motor. In case of failure of the governor, the speed could be readily controlled by the throttle itself. To sum up the case of the electric drive, it seems to be well adapted to all ships of horsepowers of 5,000 and above. Un- MARINE ENGINES 267 doubtedly the ideal place for it, however, is on a battleship. The following list of advantages for it on a battleship are given : (i) It virtually gives duplicate means of propulsion. With two turbines and two motors, one of either of them could break down and still leave a means of propulsion; this is of course true in the case of direct-connected machinery, but in the case of the electric drive, if it is a turbine that is broken down, the pro- pulsion would still be twin screw. The two turbines would be so designed that either would be capable of giving about 17 or 18 knots and the normal method of running would be with one turbine and two motors. This makes it possible to overhaul the other turbine whether at sea or not. (2) The turbines are always operated under fairly good load conditions and hence always give good economy. Since only one turbine is used at the lower speeds, the load on it will always be twice as much as for direct connected machinery. (3) The turbines are always operated under fairly good speed conditions, and this insures good economy of the turbines. This is due to the fact that the speed reduction ratio is variable. This is accomplished by winding the stators of the motors for two different numbers of poles, either of which can be put into operation by simply throwing a switch. For example, if the generator has two poles and the motors are arranged to have either 30 poles or 50 poles, the reduction in the first case would be 15 to I, and in the second case 25 to i. This combination of good load conditions and high speed is really the vital point so far as economy at cruising speeds on a battleship is concerned, and it is an advantage that any other form of propulsion will find it difficult to overcome. (4) The governor absolutelj- eliminates all racing in a sea- way, with the attendant strains on shafting and danger of throw- ing propeller blades. (5) Speed can he. maintained with much greater accuracy than with any form of propulsion. This is of little importance to a merchantman, but it is not necessary to emphasize the im- portance of this on a battleship to any one who has been in the fleet. (6) The space taken up is less than required for other forms of propulsion.* * This does not necessarily hold when compared with geared turbines or the hydraulic transmitter. 268 PRACTICAL MARINE ENGINEERING (7) The weight of the machinery is less than for other forms of propulsion where direct connected engines are used. (8) The arrangement of the machinery is much more flex- ible than any other form of propulsion as the position of turbines and motors is not fixed. (9) The readiness with which repairs can be effected. There is hardly any accident that can be conceived of that could not be readily repaired by the ship's force. The reblading of the first stage of the Jupiter's turbine by the ship's force shows that this part of the work can readily be handled. ( 10) Due to the small size of the turbines, the upkeep would be very materially reduced. (11) The rapidity of operation is much greater than with other forms of propulsion. In considering the disadvantages of this method of propul- sion the first thing that occurs to any one is the danger from water. However, this danger does not exist, or at least not to any great extent; the generator can be placed high enough from the floor to insure its safety as long as anything could be operated; the motors can be placed in watertight pits and made secure against water from above. All leads could be taken from the top of the generator and thus be kept well out of danger. The danger to life from high tension current is practically nil, as all leads can be placed so as to be out of the way of accidental contact. The main thing to, remember in considering this installation is that it is not like a power plant with leads in all directions, but is simply a reduction gear between the generator and motors. This difference is also very important when considering the damage that might arise from short circuits; this damage would be en- tirely local and confined to the place where the short circuit oc- curred ; the generator itself would suffer no harm as it is not an enormous reservoir of power, as in the case of a power plant. The danger of such short circuits occurring is also very remote. Sec. 32. INTERNAL COMBUSTION ENGINES (Explosion) [i] Commercial Classification of Internal Combustion Marine Engines Internal combustion engines for marine work may be sub- divided roughly into three separate and distinct classes — namely, the heavy duty, semi-speed and racing machine types — each of which has its own particular field of application and its own sched- MARINE ENGINES 269 ule of allowances and limitations of design, construction and in- stallation. They may be further divided, according to the action of the gas in the cylinders, as two cycle or four cycle engines. [2] Heavy Duty Engines The heavy duty engine should be applied to the very full- bodied, heavily constructed boats of large displacement relative to their over-all dimensions, the speeds of which are compara- tively low, the proportionate actual running time very great, and where utmost reliability under constant service must be assured. These boats include most all commercial forms of cargo and work- ing-boats; also deep-sea yachts and heavy cruisers. Therefore, the heavy duty engine must be designed most conservatively as regards piston speed, compression pressure, bearing surfaces, and general factor of safety in proportioning the parts under stress. The horsepower rating must be particularly conservative. On account of the higher propeller efficiencies thereby secured, the rotative speed must be comparatively low. The fuel used must be cheap and easily obtained, and the consumption per brake horsepower per hour as low as ijossible. All parts must possess the greatest degree of accessibility, must be open to view for in- spection at all times, and be easily taken off for repair or adjust- ment without disturbing other parts. The cost of repair and gen- eral upkeep must be at the lowest possible figure, and general reliability must not appreciably suffer, even when a comparatively unskilled and low priced operating crew, picked at random, is placed in charge. First cost must be fairly low, and this should be assured through simplicity of both design and manufacture, the use of fairly low priced an^ easily obtainable materials, and the elimination of all "difficult" specimens of workmanship; due allowances for these conditions, for strength and durability, being generously provided for in the original design. Weight and size in this class of engine are generally among the last considerations, as restrictions on these heads are least felt in heavy duty marine service. [3] Racing Machine Engines To take the opposite extreme — the racing machine engine — these conditions are, for the most part, reversed. Such engines are required for the very lightest built and "finest" bodied ex- treme speed boats, which possess the least displacement for their length, which have been refined and restricted in every particular 2JO PRACTICAL MARINE ENGINEERING d n m a'^'S •a *- 1. 2 •i. a.3 Or is IJ g i o =i I.I P5 a ci —_ CO "< •B-3 B S S M '^ *-■ P S"^ sis-s 13 TJ' o o J5i^°" " 3" ■d BOSt s 8~SS « - " b X-2 = a C3 ni-^ O ,s " a SjT! ■5--; ^ »5 *** :ff -2 «_ 5 d a ■ o « l!| d 5" 2 "' I-:! 'I S'mi JJ^^S CM S' 555| so* ta •OS'S d-i aasvv III"! wi iH I* j«.*« o o >o »2 C^ jQ «^ S9 m d^-rt III 1^ 1^ §,■=•3 3 SE, 'Eg, ado ^ _ _; "ta p* .5 S -wS « &■= S S » "■. do " S-dw o 9qoUS -* " s-l a -a oj-O.fl'"' 3 <9 s •n 09 zs^t ggg.§l.§^|° o5 4 *? d o •3 S3 aaa^ *M *H d = 1 SO. .s .^^ -a d >« B o. 5 ^ ■** ■if as ■as •sgs* ffioSS! ^ h " g fe ^ "■ a a a g m m ta « I |a^|s|gi''lJl| '.2 OS :g = ■ S »« '■ &1 3 a •c ■o I s -as^g g I Sll 1 si ■»"■§ - s- -MARINE ENGINES 271 as to design, construction and material to the last possible de- gree, excluding all excess weight and paring down the factor of safety almost to the danger point. These boats include the speed record breakers, trophy winning challengers, torpedo and dispatch boats. Engines for such work must be built according to the same considerations. Material must be of the very highest grade that can be produced; the factor of safety in all parts must be very low; general and detail design should insure the greatest refine- ment and lightening of all parts; workmanship must be of the Tiighest class, whatever the cost. The greatest possible power output must be secured through highest attainable piston speed and compression pressure which will safely admit of a few hours' run at rnaximum speed — :all_ that is ever required. In connection with these, the rotative speed must be as high as a reasonable de- gree of efficiency, with a well designed propeller, will possibly permit, in order that the size and weight of engine may be con- siderably reduced and to lower the center of gravity. Fuel must be of the best quality as an appreciable aid to brake horsepower output. Actual running time is comparatively very short, and periods for adjustment and repair are permissibly frequent. First cost, cost of operation and upkeep, are relatively of little impor- tance, the main object befflg to actually secure the speed. [4] Semi-Speed Engines The semi-speed type of engine is, of course, merely a medium between the heavy duty and the racing machine types. These are meant for the lighter built, speedy cruisers, passenger and mail boats, coastwise yachts, revenue cutters, etc. Such boats are faMy refined as to design and construction^ with moderately "fine" lines, reasonable displacement for their over-all dimensions, must show very fair speed at low cost of fuel and upkeep, and prove reliable enough for practically continuous service. The cost, in racing engines, of increasing to the highest pos- sible degree the maximum brake horsepower output for a definite cylinder volume ; of securing proper propeller efficiency at high rotative speed ; of reducing size and weight of engine and acces- sories, and yet retaining a fair degree of reliability even for runs of only two 'or three hours' duration, becomes enormously expen- sive and most difficult as the very high values are reached — all out of proportion, in fact, with the results obtained. Therefore, the 272 PRACTICAL MARINE ENGINEERING semi-speed engine is found to cost very little more per maximum brake horsepower output than the heavy duty engine — only a fraction of the cost of the racing machine engine — and yet the speed qualifications are nearly as high as the latter, while the reliability under long, hard service is nearly equal to that of the heavy duty engine. The accompanying table (Table i) indicates, in a concise form, the average values of the most important factors for the three types of internal combustion marine engine as obtained in the best modern practice. 4 [5] Two Cycle and Four Cycle Engines The terms "two cycle" and "four cycle" will be used in speaking of internal combustion engines, and in order to give , ^gM B"* L ^F^-" ' w^Kmmtm -, wm I • \ - y 1 Fig. 174. Heavy Duty Type Stanc'ard Engine for Small Power a clearer understanding of the subject it is necessary to give a definition of these terms. "Tivo Cycle." or. Better, "Tzi'o Stroke Cycle": Consider the piston at the end of its stroke in the bottom position. All of the products of combustion have been exhausted and the cylinder is filled with the scavenging mixture of fuel and air at the exhaust pressure and this mixture is compressed on the return stroke. It becomes ignited just after the return down stroke begins. On this stroke, combustion, expansion of the gases, expulsion of the gases through the exhaust, and refilling of the cylinder with fresh air occur. It is thus seen that every down stroke of a vertical inverted engine is a power stroke. "Four Cycle" or "Four Stroke Cycle": In four stroke cycle MARINE EXGINES 27,3 gas engines of the ordinary explosion type a mixtnre of gas and air is admitted during what is called "the suction stroke," com- pressed in the following stroke, exploded by ignition at the be- ginning of the third or "power stroke," being expelled through the exhaust during the fourth or "exhaust stroke.' In this type of engine every other down stroke is a power stroke. [6] Predominant Forms of Marine Engines in Service For the small and medium size open pleasure launches, skitfs, dories, tenders, etc., meant for short runs around rivers, small Fig. 175. Six Cylinder Enclosed Uasc L^mb Engine lakes and harbors — boats which seldom require over 12 to 15 brake horsepower, and displace, generally, under 2 tons, the ser- vice conditions of which are extremely light, the actual running time very short and practically entirely optional, where even high fuel consumption does not entail great expense, and where first cost is generally the most important consideration — the tv^'o-cycle marine engine in single and double cylinder units is the most popular, and, no doubt, the proper type. This particular field is practically the two cycle engine's exclusive territory. As the service becomes harder and more forced, and as power required rises above 15 horsepower, the two cycle engine 2/4 PRACTICAL }[ARINE ENGINEERING meets sharp competition in the small four cycle type, and at 25 to 30 brake horsepower the four cycle engine, for the present at least, has undoubtedly proved itself most economical, reliable and generally advantageous for all branches of marine work. Various attempts have been made of late in the interest of large powers by those connected with the two cycle engine branch of the industry to obtain the required fuel economy and reliability through the adoption in various forms of separate preliminary Fig. 176. Six Cylinder Enclosed Base Sterling Engine charge compressing and scavenging cylinders, somewhat after the fashion of the Koerting and the Oechelhauser stationary two cycle engines ; also, by the introduction of the differential piston ; but, up to the present time at any rate, no great or commercial successes with the gasoline engine along these lines have been recorded or advertised for actual application. The single cylinder, four cycle engine, even in the smallest powers, is now practically obsolete, by reason of the inherent lack of mechanical balance and evenness of turning moment. Also, the immensely heavy flywheels necessary in connection with the large reverse gear, which must be heavy enough in all its parts to withstand the low frequency, therefore comparatively heavy, impulses, and the great proportionate weight of engine base and frame, combine to produce an entirely too large, heavy and other- wise inconvenient motor for even the heaviest of heavy duty boats requiring only very moderate power. Two cylinder units are somewhat more fitting and desirable, ,U.//?/.V/T C.VC/.VC.9 275 but even in this form the weight is generally excessive, mechanical balance is poor, turning effort is still very irregular, and carbure- tor difficulties too evident. _ Three and four cylinder units are more practical in these par- ticulars. Such engines may be applied with all assurance of good results .in the smaller dut}- and semi-speed boats, and even in some of the less important racing boats. For the medium size and large boats of all classes, however, the six cylinder engine guarantees probably the highest justifiable values of vibration, flexibility of speed variation, low center of i m i?,.i i 4 X: f 1 /-atss .■-:.i.. ' v*v/V 31 Bf - X, itm i3 1 -Ji'-'M « 1 i m _M I ^ L \ fltf^^ - - - . ^---- Fig, 177. 2ti-Horsepo\vei* Standard Mngine for High-.Speed Runabouts. Open Crank Case gravity, decreased size of all parts, increased vaporizer efficiency, least value of excess weight, and greatest reliability. Enclosed Grank Cask Type Until very recently it was general practice among most marine engine manufacturers to make all engines, whatever the class, of the enclosed base construction — of cast iron for heavy duty and of aluminum for the high speed types, such as are shown in Figs. 172-174. When splash lubrication of cylinders, main bearings and connecting rod brasses were applied, closed crank cases were, no doubt, very necessary. In the more recent designs, however, the main causes of gas engine uncertainty and unreliability, due to irregularity of oil control, resulting in fouled igniters, carbonized combustion cham- 2-]() PRACTICAL MARIXF. E\rGiyF.KRiyG bers, stuck and leaky piston rings, unevenly lubricated and cut cylinders, etc., as is constantly found to be common to the splash system of oiling, are practically eliminated through the application of mechanically operated, force feed, properly adjusted oilers to cylinders, main bearings, and also, through continuous, centrifugal oil rings, to the crank pins, thus eliminating such factors as luck, chance and guesswork from the oiling system. AVith such devices Fig. IVy. Six Cylinder Ojien Crank Case Holmes l"!nglne in use, there really exists very little or no excuse for the retention of the enclosed crank case in the four-cycle engine of any size or type. Open Cr.\nk Casi; Type An open crank case, secured in the smaller engines through the use of cast columns or struts upon which the individual cyl- inders are bolted, and which, in turn, are fastened to a cast chan- nel or tee shaped base frame, will reduce both weight and cost very considerably. For the larger engines, turned steel columns or stanchions, thoroughly cross braced, are preferably utilized to sup- port the cylinders. The base is more satisfactory if built up of cast bearing brackets or girders bolted securely to angle or channel iron sills. In each case a galvanized iron or sheet copper oil pan, deep enough to escape the swing of Ihe connectinic rod bolts, in con- Missing Page ;./.-i.aV.V/T n\'GINES 277 junction with easily removable vertical sheet brass or Russia iron oil splash guard plates fastened by spring clips to the columns and base, are efficient, light and inexpensive. Such construction pro- duces engines which are most accessible for inspection and repair, and which are, therefore, much more liable to be kept in good working order. A small size, high speed engine of this type is shown in Fig. 177, while Figs. 178 and 179 are fair examples of what is done in the small heavy duty type. Fig. 180 is a large, semi-speed, open Fig. 17 9. Oijen Crank Case Campbell Engine crank case, air starting and reversing engine rated at 300 horse- power. [7] The Large Engine The purely pleasure boating field has undoubtedly served a very great purpose in aid of development of the internal combus- tion marine engine, inasmuch as it has offered a very practical means for experimenting, for the trying out of ideas, and for determining the degree of advantage and superiority of one form of engine over another as to their theories, cycles, efficient vapor- ization and gas manipulation, valve timing, ignition, rotative speed, power output, number of cylinders, economy, balance, reliability, speed control, detail design, construction, installation and oper- ation, etc., for all classes and conditions of work. The pleasure boating field, however, really gave this industry only its initial start and impetus. It served as the advance agent of what is by far the largest and most important field — the com- mercial, freight and passenger carrying boats and ships, requir- 278 PRACTICAL MARINE ENGINEERING -c •& a M MARINE ENGINES 279 ing enormous power output. Such momentous enterprises, though already achieving their prototypes, are little more than fairly entered upon, comparatively. The field, however, is grow- ing rapidly, and bids fair to prove entirely successful, as many of the entries on the list. Table II, would indicate. Engines for such work are nominally of the heavy duty and the semi-speed Masses. [8] Starting and Reversing Considering, first, the smaller sizes, it is found sufficiently convenient to start eyen six cylinder engines up to about 7 or 8 inches diameter of cylinder by hand, especially when, as is usually the case, these engines are equipped for easy starting and for maneuvering about a dock, with a reversing gear in which a neu- tral position is provided, at which point the propeller remains sta- tionary, though the engine continues to run. A governor of an efficient type, should always be provided on such an engine, to prevent racing at this neutral point while maneuvering. As the cylinders begin to exceed 8 inches diameter it be- comes more expedient to provide a good compressed air starting device, operating from the camshaft. Engines so equipped are also provided with a small air compressor operated either from an eccentric on the engine crankshaft or from a crankpin mounted on the end of the camshaft. The air is compressed to a pressure of from 250 to 300 pounds per square inch, and is stored in one or more cold drawn, seamless steel tanks placed under the engine room floor, or immediately under the deck beams, against the planking or the bulkheads, where the space is otherwise generally useless. Such air compressors are equipped either with automatic or hand-operated cut-out devices acting upon the compressor inlet valve when the gage shows the required pressure in the tanks and throwing the compressor out of action. As this air is also used for blowing the whistle, the compressor is designed for nearly continuous operation. For heavy duty installations of 100 horsepower and over a separate small size, high speed auxiliary internal combustion en- gine outfit, starting by hand, is provided. This auxiliary engine is built on one base with an efficient air compressor of large capacity; also, with a dynamo for lighting the boat, operating a searchlight, for charging storage batteries, and sometimes for operating electric anchor winches. A large water pump is also 28o PRACTICAL MARINE liNGINEERING mounted on this base, and, when connected up through a mani- fold, may be used for pumping out the forward and after bilges, or for pumping sea water for anchor, or deck washing and for fire purposes. Such an auxiliary engine is shown in Fig. i8i. In medium slow speed engines of under lOO horsepower out- put, reversing is sufficientlv convenient when accomplished by means of the planetary reverse gear. For slow speed engines of lOO horsepower or over, however, the cylinders of which are 8 i • m 1 : i t ''m ».. ' - w| _.-**, ,^p| r >^ —^ '^ -:. Fig, 181. Four Horsepower Standard Auxiliary Fngine, Combining Air Compressor, Electrical Generator and \\'ater Pump inches or larger in diameter, the weight and size of a substantial planetary reverse gear become most excessive, and it is preferably discarded, and the engine itself is then made reversible, as well as compressed air starting. This is best accomplished through shift- ing the camshaft endwise, thus bringing into action an entireh; different set of cams, which are properly set for producing the reversal of the engine. The initial start of a day's maneuvering with a six cylinder engine is accomplished by means of compressed air. Subsequent starts, either ahead or reverse, are usually brought about by merely throwing in the ignition switch and properly shifting the camshaft, a sufficiently good charge remaining in at least two of the cylinders to ignite and to start the engine. MARINE ENGINES 281 In such an engine, cam operated compressed air valves are preferably mounted on all six cylinders in the single acting en- gine, and on either the six upper or the six lower cylinders in the double acting engine. These cam operated valves, in conjunction with six automatic check valves, admit compressed air to all the cylinders in proper rotation upon the explosion stroke only. Thus each cylinder is permitted to draw in its proper charge of explo- sive mixture from the carburetor during the suction stroke, after Fig. 182. lOO-Horsepower, Heavy Duty Standard Engine. Uiien Crank Case which it i)roceeds to properly compress this charge. Should igni- tion be accomplished when the sparker trips off, the higher explo- sion pressure in the engine cylinder prevents the compressed air check valve from opening, thus economizing in compressed air. Should the charge prove too weak to ignite, or should ignition fail for any other reason, the high pressure air, timed by the cam operated valve, opens the check valve against compression pressure only, and supplies the required impulse to that cylinder in its proper rotation for starting. Such an air starting and reversing engine (as shown in Fig. 182) is absolutely certain in its action, and operates as in- stantaneousl}- either way under load as any steam engine in long cut-off position. PRACTICAL MARINE ENGINEERING .MARINE ENGINES 283 I9] -Double-Acting Engines In cases where such high power is required that the.cyhnder bore exceeds 12 inches in diameter as a single-acting engine, it is more desirable to resort to the double-acting principle rather than to increase the number or. diameter of the cylinders. Only a very ,1 - . . Fit. 184. Cross Section of 300 Horsepower, Double- Acting -Engine f£w years ago the double-acting internal c.ofnbustion marine en- gine was generally considered an impracticable, if not well nigh impossible, venture for reliable heavy duty, marine service, prin- cipally because of the supposed difificultie's which. would be met with, first, in constfucting a piston rod stuffing, box which would remain cool^ gas tight, and which would not score the piston rod; then in preventing excessive heating of the piston ; also in insuring efficient cylinder lubrication; in equally cooling all parts of the cylinder and combustion chambers ; in securing proper carburiza- 284 PRACTICAL MARIXH ENGINEERING tion and distribution of the charge, and a few. other supposed troubles. As early as 1905, however, a six cylinder, double acting, com- pressed air starting and reversible marine gasoline engme, in a most practical, highly refined and successful form, was designed and built by Mr. Carl C. Riotte, and, shortly after, still further developed by him. This engine was a lo-inch by lo-inch engine, Fig. 18'). .^DIJ Ilursepower. Double .-\ctin.g Stan.iar.i [engine rated at 300 horsepower, and was installed in the racing boat Standard, which has several times since broken the existing world's speed records. As the list in Table II shows, several of these double acting engines, in units of 300 and 500 horsepower, have been Iniilt and successfully applied to various branches of marine service. A more recent design of the lo-inch by ioJ/-inch double- acting, air starting and reversing engine is shown in Fig. 183. A 500 horsepower, i2i/2-inch by 13-inch engine is shown in Fig. 185. In such engines a compressed air cylinder is used to shift the cam- shaft for reversing. [10] Cooling Systems A hollow or tubular link motion equipped with spring stuffing MARINE ENGINES 285 boxes leads a supply of water up through one side of the cross- head through the piston rod to the lower side of the piston. The heated water then passes out the. top of the piston, down through an inner tube in the piston rod, and to a discharge water rail through a duplicate tubular link motion connected to the opposite side of the crosshead. Thus the pistons and piston rods may be run practically cold, if desired, despite the great heat resulting from combustion both above and below the piston ; also, the inside surface of the piston rod stuffing box is thus most efficiently cooled. Stuffing Box The piston rod stuffing box itself is made up of hard gun iron rings, lap jointed in three places, and held in case hardened and ground steel retainers. The only pressure tending to cause wear between the gun iron rings and the piston rods is produced by a light circular band spring. The whole series of eight split rings is arranged to allow free side play of the piston rod should aline- ment become bad from wear of the crosshead -slipper. A water jacket completely surrounds this stuffing box, while lubricating oil is pumped through it in very small quantities. As a result of such, a construction the piston rods and stuffing boxes bid fair to outlast the entire engine. Valves In all engines of 8-inch diameter or over the exhaust valves should be water cooled; otherwise, even low compressions cause troublesome pre-ignitions, and the valves will fail to keep tight. (See Figs. 183 and 184.) In engines of 12-inch diameter the pis- tons, as well as both inlet and exhajust valves, are preferably water cooled, to allow of a fairly high compression pressure, free from pre-ignition — a common fault of the large cylinder volumes, unless such precautions are taken. In six cyjinder engines, particularly when of the double acting type, exhaust valves should be of the balanced form (see Figs. 183 and 184.) This allows of the use of much smaller and lighter, ^construction of all camshafts and valve-operating gear. >'° .i| Mechanically operated inlet valv^es in such engines are advis- ably interchangeable with the?' exhaus|. valves, as a matter of sim- plicity of design and reduction of cost. Piping All exhaust piping in large installations should be water PRACTltAL MARINE ENGINEERING < E-i MARINE ENGINES 287 288 PRACTICAL MARINE ENGINEERING jacketed, the discarded hot water from the engine being used for that purpose. For the sake of lightness, assured strength, and to admit of calking, these water jacketed pipes are more satis- factory when built up of large size boiler tubing or thin steel plating rolled into tubes, then shells being riveted to steel flanges, then galvanized. Elbows in the exhaust line are preferably un- cooled, but well lagged with asbestos, to prevent excessive heating of the engine room. Owing to the presence of innumerable delicate tubes, passages and sheet metal surfaces in the water circulating system of the large internal combustion marine engines, which parts would be seriously injured through galvanic action and salting up should the use of sea water be continued, a fresh water circulation is installed. Coolers In such cases, a cooler built very much after the fashion of the steam condenser is provided, the hot fresh water from the engine being cooled upon passing through a nest of fairly small copper tubes, while sea water passing around the outside of the tubes serves to carry away the excess heat. The flow of sea water in this cooler is induced partly by the forward motion of the ves- sel, aided and guided by suitable scoops properly placed below the waterline, also partly by thermo siphoning. The cooled fresh water is then led to a small reserve tank holding about as much water as is contained in the engine cylinder jackets. From this tank the water is once again pumped through the circulating sys- tem. At the first heating of the water the contained air is driven off. After that the water can cause practically no more rusting of iron or steel.parts than would a like quantity of oil. Although the internal combustion marine engine installation does not include any correspondingly great producers of heated air and waste gases such as are supplied in steam installations in the form of boilers, nevertheless, in medium and large size in- stallations of the newer type, a funnel is found to be almost a necessity. Besides adding to ttte general appearance of a vessel, a funnel installed on a gas driven boat become'^. a most efficient engine room and galley ventilator. When the engine exhaust muffler is placed in it with the muffler outlet about 2 feet below the top of the funnel, the ejector action thus set up induces a very strong draft, which keeps the engine room and galley as cool as could be desired and prevents the accumulation of explosive or debilitating gas mixture. MARINE ENGINES 289 A modern twin screw installation of two 300 horsepower, double acting, compressed air starting and reversing Standard engines, with auxiliary engine, funnel exhaust and water cooler, is shown in Figs. 186-187. [11] Fuels Owing to the ease with which gasoline in its entirety may be gasified, mixed with air and burned in the engine cylinder with- out expensive or bulky apparatus and at a minimum of resuling dirt or odor, compared with most other fuels, also owing to the heretofore small power output of the average internal com- bustion marine engine, no other fuel has been so generally used or experimented with. (See Table i.) The industry is fast grow- ing to such a point, however, where a most insistent demand is strongly felt for very large engines operating on the cheaper fuels, such as kerosene, fuel oil, refuse oil, crude oil and anthracite or bituminous coal gas. Though the size and weight of such installations may be somewhat greater per brake horsepower out- put than the gasoline installation, the great saving possible in fuel cost insures their extensive application, especially in the commer- cial working boat field. Though in the past an immense amount of capital has been invested in their development, until very recently the kerosene and the heavier oil engines gave little proof of eminently successful or anything like reliable operation for very long runs ; being pecul- iarly liable to self-ignition on even low compressions ; fouling of combustion spaces, igniters, and exhaust passages; sticking of pistons and their rings, also valves and movable igniter electrodes ; low power output in relation to cylinder displacement volumes; uncleanliness and bad smelling qualities, and difficulty of proper regfulation and control. Recent developments in oil engines clearly indicate that the pioneers failed principally : because of their in- ability to bring about the. complete atomization of the entire oil charge, inchKiiiig the very first and last drops injected into the cylinder per impulse •because, of their having employed hot tubes, bulbs, plates, etc., to bring aboiit the gasification of the oil, and in sonie cases to supply the means of ignition, which accessories nec- essarily produced premature self-ignitions, even on comparatively low compression pressures) in cylinders of any appreciable size, and if run at or nearly full load ; also because of their toleration of stratified, semi-explosive mixtures, varying in richness all the 2go PRACTICAL MARINE ENGINEERING way from a gas entirely unmixed with air, to air entirely devoid of gas, which stratification must in itself produce low mean efifec- tive pressure and an assured carbonization of the cylinders. Those oil engine builders who aimed to first gasify the oil charges in a separate chamber, heated either by the engine's ex- haust gases or with an external flame, and burning the gas thus generated immediately after in the engine cylinder, failed through their inability to secure at all conditions of load and speed a temT perature high enough to entirely gasify every atom of the oil,. yet not so high as to "crack" this oil up into the lighter and the, heavier carbons, gasifying the lighter and carbonizing or coking the heavier, the latter of which soon throws the engine out of commis- sion for the time being, until it can be thoroughly cleaned out again. ;. , A recent development in the kerosene gasifier line starts the engine on gasoline to warm up the gasifier, . and then atomizes the oil charges in a kerosene vaporizer, operating by reason of the engine suction into a veritable labyrinth of passages heated by the exhaust gases passing around them. This slightly aerated oil vapor is then passed through a spring loaded automatic mixing valve which admits enough auxiliary air to form a proper explo- sive mixture, which passes immediately into the engine cylinder. The correct degree of heat to gasify and yet not "crack" the oil is maintained constant by a simple "fool-proof" thermostat, arranged to by-pass a varying portion of the exhaust gases at varying loads and speeds when the temperature rises too high. Engines equipped with this device and operating on kerosene of .48 Baume scale consume .71 pint per horsepower hour and run with practically no carbonizing, even after weeks of running. Another development tending to make a fixed gas from Solar fuel oil acts through the suction of the intake, drawing a small charge of exhaust heated, air through an automatic differential valve, which atomizes a micrometrically regulated charge of fuel oil down upon a very broad surface of specially prepared porous clay, which has initially been brought to a cherry red heat through the application of a kerosene blow lamp. No gasoline is. required on board. Having once heated the porous material, the small air charge serves to support just sufficient combustion of the oil to keep the clay at its proper heat, and this necessary combustion i& ma- MARINE EXCISES 291 terially reduced by surrounding the gasifying chamber with an exhaust heated space. The gas thus produced is then passed through an automatic air-mixing valve and into the engine cyhn- der. Any of the heavier carbons being thrown down as coke on the porous material are burned to dust and ar^ passed out the en- gine exhaust in suspension, the proportion of this being so small that a continuous run of several weeks' duration does not produce a noticeable accumulation of dust in the engine combustion space. The automatic differential valve is so constructed as to perfectly regulate both the oil and the small air charge to suit the conditions of variable load and speed. The whole device is about the size of a properly propor- tioned muffler, and is placed directly alongside the engine. The quality of the gas generated is remarkably uniform, the service obtained is as reliable as any steam plant could give, and at a fuel consumption of .JJ pint of Solar fuel per brake horsepower hour. Sec. 33. THE DIESEL OIL ENGINE (Progressive Combustion) Thus far the most successful type of oil engine which me- chanically injects the liquid fuel directly into the engine cylinder is the Diesel oil engine. This engine, employing no ignition sys- tem other than the heat due to very high compression pressures, is Fig. 188. 300 Horsepower Diesel Engine 292 PRACTICAL MARINE ENGINEERING able to operate on the heavier oils, even on crude oil, because of at least two natural conditions. First, oils of .782 specific gravity (49 Baume), or heavier, fail to vaporize upon being atomized and mixed with atmospheric air, even if both oH and air be previously heated slightly. The Diesel engine, after compressing air only, to 450 or 600 pounds pressure, depending upon the temperature required to ignite the oil used, begins to inject atomized oil into the cylinder immediately after completion of the compression stroke. This oil, being pumped to the atomizer under pressure, is blown into the engine cylinder in an extremely finely divided state by a stream of air of from 150 to 300 pounds higher pressure than that existing in the cylinder. This mingling intimately with the highly heated air charge already in the cylinder immediately burns, the piston mean- while moving on the outward stroke, and the amount of oil ad- mitted being regulated by a suitable governing device. Extreme care must be taken in designing the atomizer to make sure, that the atomizing air charge begins to flow just an instant before the oil charge and that the oil charge stops first, otherwise the very first and last oil drops will not be atomized and will cause trouble. Then, too, the heavier carbons contained in oils of .782 spe- cific gravity, or heavier, though very incompletely burned at or- dinary gas and gasoline engine compressions, more readily com- bine with oxygen and burn at the extremely high compression pressures employed in the Diesel engine, and the latter is better able to run continuously on heavy oils without carbonization troubles. One of the peculiarities of the Diesel cycle is that though the compression carried is extremely high the heat in the engine cyl- inder is by no means as high as in the gas or gasoline engine, principally because the fuel is burned at constant pressure, and, therefore, a constant temperature — the pressure and temperature of compression. In the gas and gasoline engine the highest tem- peratures attained are from 1,900 to 2,200 degrees F., while in the Diesel engine the temperature ranges from about 1,000 to 1,100 degrees F. The marine Diesel engine installations, so far as present de- velopment has gone, are heavy if compared to gasoline installa- tions, but are lighter than a combination of gas engine and gas producer, and require considerably less space than the latter. MARINE ENGINES 293 Should the free use of modern high grade alloy steels and strict adherence to modern refinements of marine engine detail design be resorted to, however, the present difference in weight between the Diesel and the modern gasoline engine would be very considerably diminished or even wiped out entirely, as the mean eflfective pressures attained in the Diesel engine are somewhat higher than those of the gasoline engine, and also as, according to a recent opinion expressed by Dr. Diesel himself,the marine Diesel engine of the future will be of the two-cycle scavenging type. Attempts are now being made in Europe and in the United States to build double acting two cycle scavenging type Diesel engines. In oil engines, no bulky gas producers, scrubbers or other gas cleaning apparatus are required; also, as oil fuel contains about 40 percent more heat value, weight for weight, than coal, less weight per horsepower is necessary and considerably more space is made available for cargo carrying. Then, too, as the thermal efficiency of the Diesel engine is as high as 32 to 34 per- cent, the fuel consumption is extremely low, being in most cases about .4 pound per brake horsepower, which circumstance allows either a material reduction of fuel carried or a considerably in- creased radius of action. The fuel economy of the Diesel engine on part load is con- siderably higher than in any other form of prime mover, in one case having been found to be as follows : .4 pound per brake horsepower per hour at full load, .4175 pound per brake horsepower per hour at .three-quarter load, .47 pound per brake horsepower per hour at half load, .625 _ pound per brake horsepower per hou^-^t quarter load. With^uch general advantages, rfen, as the resulting gain in useful spaced dueto- the eJimination as well of boilers and their acces- sories ; the small size of fuel holders ; increased capacity for cargo, due to relatively small weights of the Diesel engine's fuel and accessories; utmost utilization of the otherwise Hrnited useful space taken for bunkers; gain in time and elimination of wages paid, due to elimination of bunkering and coal trimming; no stand-by losses; immediate readiness of the engine to start on a moment's notice; reduced and easier management; wages and space economy through reduction of operating force; reduced cost of fuel; cooler engine rooms and absence of stoke holds, resulting in increased mechanical capacity of engineer's staff, especially in torrid climates, etc., it is not strange that the 294 PRACTICAL MARINE ENGINEERING more recent development of the Diesel engine should have pro- duced units of horsepower output, considerably greater, in fact, than has ever been produced in any other form of the internal combustion marine engine. [i] Types of Diesel Engines According to the Stroke Cycle The Diesel engine, similarly to the explosive engines,, can be divided into two general classes; namely, the four-stroke cycle (four cycle), and the two-stroke cycle (tWo cycle). Describing the four-stroke cycle first, as it is the one, most generally used, the following series of actions is found : 1. In. the first downward stroke of the piston, air is sucked into the engine cylinder direct from the atmqsphere through a slotted cylinder, and thence through the main air inlet valve of the top of the cylinder. At the end of the stroke the cylinder is full of pure air at practically atmospheric pressure, ready for the compression stroke. 2. In the next stroke the air is compressed to the required pressure, recently about 500 pounds per square mch, while the temperature rises to between 1,000 degrees F. and 1,100 degrees' F., all the valves being closed during this operation. 3. During the early period of the third and power stroke the fuel oil is injected into the cylinder above the piston by a blast of air at a higher pressure than that in the cylinder (about 8co pounds per square inch), through a special form of needle valve. Combustion takes place during this period, as the tempera- ture of the compressed air is above the flash point of the oil fuel. The duration of this part of the stroke depends on the setting of the valves, but cut-oflf usually occurs not later than one-tenth of the stroke at full Ibad. After cut-off when the fuel inlet valve closes, combustion continues; for a . short period, ex- pansion then occurs and work is done on the piston for the rest of the stroke. Just before the piston reaches the end of its travel the exhaust valve begins to open and the ;pressure drops off rapidly. .. . ; : 4. In the final stroke the exhaust valve :remains: open and the burnt gases are expelled from the cylinder into the exhaust pipe,. arid; the cycle of operations begins once more. : In the two-stroke cycle engine, the general action is as fol- lows : MARINE ENGINES 295 1. The piston being at the end of its stroke at the bottom of the cylinder, the cylinder is full of air at nearly atmospheric pressure. This is compressed during the first or upward stroke of the cycle to the usual top compression pressure of 500 pounds per square inch, as in th6 second stroke of the four-stroke cycle. 2. During the second or down stroke, combustion, expan- sion, expulsion of the burnt gases to the exhaust and the filling of the cylinder with fresh air are the operations which must be ■effected. Fuel is sprayed into the cylinder through the " inlet valve by compressed air during the early part of the stroke, as before. This valve then closes and expansion occurs while the piston passes through about another 75 percent of its stroke, at which point the exhaust opens and the products of combustion begin to pass out. Air, under a pressure of about 4 to 8 pounds per square inch, then enters the cylinder through a separate valve or port in the cylinder, being supplied from a so-called scaveng- ing pump, which is quite separate from the air compressor for the provision of fuel ignition and starting air supply. All the exhaust gases are thus forced out through the exhaust ports, and at the end of the stroke the cylinder is left full of pure air with all the valves closed, ready for the first stroke of the next cycle. As far as constructional details go, the two-stroke cycle en- gine differs from the four-stroke cycle type in the arrangement of valves and the provision of a scavenge pump in the former case. Otherwise the engines are identical. No Diesel engine is self -starting on oil fuel. - The in- variable method of starting is to get the engine moving by mea^ of compressed air which is admitted to the cylinder through a separate starting valve in the cylinder cover, ar- ranged so that it cannot be in operation at the same time as the fuel inlet valve. The engine runs as an air engine until it has attained sufficient speed to take up its work as an oil engine, which it does after two or three revolutions. A supply of compressed air is therefore necessary both for starting the engine and for the blast for fuel injection into the cylinder when the engine is running. [2] Description of Four-Stroke Cycle Diesel Engine The engine selected to illustrate this type is known as the Werkspoor engine and is built by the Nederlandsche Fabrik 296 PRACTICAL MARINE ENGINEERING Van Werktingen En Spoorweg-Materieel of Amsterdam, Hol- land. The engine is shown in Fig. 189; a shows a front section of a 600 brake horsepower engine, built to run at 125 revolutions per minute. There are four cylinders, the two inner having the cranks set at 180 degrees with the outer pair. A single air pump is mounted on the end of the bed plate and is of the vertical two- stage type, and driven off the main crank shaft. In this engine a trunk piston is not used, but there is a crosshead and a short connecting rod, and though the length of the piston is dimin- ished since it no longer has to be of the usual bearing surface, the engine is necessarily higher than the ordinary trunk piston type. The crosshead has two bearing surfaces, the guides being bolted to the engine framing. A forked connecting rod end is used, as shown. All the main bearings are water cooled, as is also the piston, an unusual feature in a four cycle engine, cool- ing witn the Werkspoor type usually being adopted for cylinders of more than 100 horsepower. The arrangement for the piston cooling is shown in Fig 189. The piston rod is hollow and is secured to the piston, which is also hollow, by means of a flange forged on the piston rod and studs carried by the piston body. Two small pipes are connected to the water cavities in the piston, and these slide telescopically within two long tubes which are connected with the supply and delivery pipes for the cooling water. These tubes are provided with stufifing boxes at the telescopic joints to prevent leakage. The water outlet for the cooling water from the crank shaft bearings delivers into a cup at the front of each bearing, the rate of flow through the bearing being regulated by a cock, thus providing a ready means for controlling the temperature. The engine is also provided with forced lubrication for the crank shaft and connecting rod bear- ings, all of which are very accessible. The framing is of the box type, the cylinders, which are cast together, being supported directly on the framing, while addi- tional strength is provided by means of long vertical bolts which tie the cylinders rigidly to the bed plate. The crank chamber is entirely enclosed, a hinged door being provided in front of each connecting rod, and the piston rods pass through stuffing boxes in the box frame so that the crosshead bearings and wrist pins are in a cool atmosphere away from the heat of the cylinder. Missing Page MARINE ENGINES 297 Eccentrics, instead of the usual cams, are used for operating the valve levers, thus diminishing noise and increasing the smoothness of running. There is a horizontal eccentric shaft carrying these eccentrics. The eccentric rods are attached at their upper ends to horizontal levers, pivoted eccentrically on a horizontal spindle, and these levers thus receive an up and down motion. At the other end of these horizontal rods, the valve rods operating the valves rest upon them, and thus the motion of the eccentric is transmitted to the valves, which open and close vertically. For the starting valve, which admits compressed air for a few seconds in starting, the ordinary cam and cam shaft are used. The governor is arranged on the vertical shaft which drives the horizontal eccentric shaft, and regulates the speed of the engine by the duration of the opening of the suction valve of the fuel pump during the delivery stroke, and thus regulating the amount of oil admitted to the cylinder. There is a fuel pump for each cylinder, arranged in a common pump chamber and driven together by an eccentric from the vertical ggvernor shaft; [3] Outline of the Operation of a Two-Cycle DieSel Engine The two cycle engine, considered by many leading engineers as the ultimate type, consists of few essential parts and the function of each part will be described in the order of its re- spective action in the so-called Diesel Cycle. Scavenging Pump or Low Pressure Compressor: The func- tion of this pump or compressor is to draw a charge of air from the atmosphere and blow it through the working cylinder, thereby blowing out, into the exhaust pipe, the previously burnt charge and leaving the cylinder full of pure air, which will afterwards be compressed by the working piston on its inward stroke. Main or Working Cylinder and Piston with Connecting Rod, Etc.: The function of the main cylinder and piston is the same as in an automobile engine or any other internal combustion en- gine, except that it does not have to "suck in" its charge. In- stead, the piston, on moving inwards, ' compresses the charge of pure air placed in the cylinder by the scavenging pump, into the small space between itself and the cylinder head and to a pressure of approximately 500 pounds per square inch. Air, when compressed to this pressure, has a temperature of about 1,000 degrees F., and will ignite almost any kind of oil 298 PRACTICAL MARINE ENGINEERING that comes in contact with it, if the oil is broken up into fira« enough particles. Atomiser : The atomizer is an appliance to break up the oil into fine. particles or atomize it. It is situated in the cylinder head and, on opening, communicates with the inside of 'the cyhnder. The atomizer is in constant connection, by a pipe, with an air boftle wherein is stored the injection air. The air blows the contents of the atomizer directly into .the cylinder when the atomizer spindle is lifted by a push rod, operated by the rotation of the cam shaft. Fuel Pump: The function of the fuel pump is to receive the oil from the service tank and force it, under pressure, into the atohiizer, to lie there between the seat of the atomizer spindle and the inlet leading from the injection air bottle. The oil is then in such a position, in the atomizer, that immediately the atomizer spindle is Hfted, ever so slightly, the injection air be- hind will force the oil into the cylinder, where it will at once ignite. Multistage Air Compresor: The function of this com- ■pressor, which is driven directly off the cra^nkshaft of the engine, or by auxiliary means, is to keep the injection air bottle charged with the necessary pressure to blow the fuel oil into the com- pressed" hot charge of air in the cylinder. It also serves to charge, while running, the bottle of air used for initially starting the engine. The "foregoing briefly describes the main parts of a two cycle Diesel engine and their different functions. The cycle of opera- tions is: as follows : First: The fuel pump places a small quantity of crude or fuel oil in the atomizer at a certain time in the revolution of the engine and leaves it there. Second: The. scavenging pump blows out the previous charge through the exhaust and leaves a charge of pure air in the cylinder when the piston is at the end of its outward stroke. Third: The piston returns in the cylinder and compresses this charge of pure air into such a small space that it becomes heated above the ignition point of the fuel. Fourth: The atomizer spindle is lifted by the cam shaft, opening the passage into the cylinder, and the injection air forces the oil lying in the atomizer, into the hot charge of air in the MARINE ENGINES 299 form of a spray. The oil irrtmediately ignites and further heats the charge of air and causes it to expand behind the piston and thereby transmit power to the crank shaft as steam does in a steam engine. There is no explosion and the pressure does not materially exceed the 500 pounds compression pressure, but owing to the additional heat, supplied by the burning of the oil, the expansion creates the power. To illustrate an engine of this type, as an example, the Harris so-called valveless two-cycle engine, manufactured by the Southwark Foundry and Machine Company, of Philadel- phia, Pa., has been selected on account of its great simplicity and efficiency. [4] The Harris Valveless Engine Starting with the Diesel principlie as a foundation, the Harris valveless engine was designed with the object of producing an engine free from complicated mechanism, without delicate ad- justments, embodying the most desirable features of the best marine steam engine practice and at the same time eliminating what might be called weak points in existing Diesel engines, as follows : In the ordinary Diesel engine cold air at high pressure is admitted into the hot working cylinders to reverse or start up ; this air, being stored in bottles or tanks, at 800 pounds to 1,000 pounds per square inch for two-cycle engines, or 300 pounds to 800 pounds per square inch for four-cycle engines, acts on the pistons to cause the engine to revolve in starting or reversing. Air at these pressures, when expanded through a valve, drops in temperature below the freezing point and it is easily understood that this cold air, entering a cylinder heated to a high degree, is undoubtedly often' the cause of cracked cylinders, cylinder heads and pistons. This is especially true in the case of marine engines, where a vessel coming into port after per- haps several hours, or even days, continuous running in one direc- tion with its cylinders and pistons heated to a high degree; to berth this vessel at the wharf, possibly ten or fifteen orders may be "rung down" to the engine room in as many minutes. To carry out each of these orders the engine is turned for a few seconds with this cold air and the next second after it is cut off the contents of the cylinders are expected to be heated up 300 PRACTICAL MARINE ENGINEERING over i,ooo degrees. This sets up a very severe expansion and contraction. In the Harris valveless engine the scavenging pump or low^ pressure compressor is of the step piston type ; that is, the piston of the scavenging pump is an enlarged extension of the main piston, working in its own cylinder below the working cylinder. It is while reversing and starting the engine on compressed air that this scavenging cylinder and step piston play a prominent part, as follows: Each scavenging cylinder on the movement of the starting lever either "ahead" or "astern" becomes immediately con- verted into an air motor by the automatic cutting out of the suction and delivery valves, the air starting valves automatically come into play with the cam shaft and keep the engine running, owing to the compressed air acting on the step pistons instead of on the main pistons. By the continued movement of the handling lever the atomizers begin to open and the fuel com- mences to be supplied to the working cylinders, the engine still running on compressed air in the scavenging cylinder without having afffected the working conditions in the main cylinder, thereby avoiding the admission of the usual high pressure air into the working cylinders, just at the time when it is necessary to build up a temperature. This novel feature renders it an easy and quick engine to maneuver, also assuring certainty, as it is not necessary to shut off the fuel, nor interfere with the conditions in the main cylinders in any way, at any time, when reversing. Another interesting fact is that each scavenging piston, having a greater area than the main pistons, allows the engine to be started with 175 pounds air pressure instead of the usual 800 pounds to 1,000 pounds. Further, in starting and reversing, the atomizer valves do not operate while air starting until the operator wishes them to do so, consequently all the usual "by- pass" valves are eliminated and the temperature of the fresh charge of air in the cylinder is quickly raised, owing to the absence of the chilling effect caused by the blast air being al- lowed to enter through the atomizer valve without fuel on each stroke while air starting. In the ordinary Diesel engine of both two- and four-cycle types there are from two to seven valves in each cylinder head. This makes a complicated casting, and even special material and MARINE ENGINES 301 1. Main or Working Cylinder. 2. Main or Working Piston. 3. Scavenging and Air Starting Cyl- inder. 4. Scavenging and Air Starting Pis- ton. 5. Scavenging Air Inlet Valve. 6. Scavenging Air Outlet Passage, Starting Air In- let Passage. 7. Scavenging Air Delivery Valve. 8. Scavenging Air Manifold between Adjacent Cylin- ders. 9. Scavenging Air Iiilet to Working Cylinder, 9A. Scavenging Air Inlet Ports. 10. Air-Operated In tercepting Valve for Air Starting. 11. Outlet for Start- ing Air. Silencer for Start- ing Air Exhaust and Scavenging Air Inlet. Vents for Hous- ing Fumes. 14. Injection Air Sto- rage Bottle. 15. Removable Front Columns. 16. Cam Shaft. 17. Atomizer Actuat- ing Rockers (one Ahead, one Astern). j 18. .Radius or Atom- izer Push Rods (one Ahead, one Astern). 19. Atomizer Levers '(one Ahead, one Astern). 20. Atomizer Spindle. 21. Cylinder Head. 22. Exhaust Pipe. 22A. Exhaust' Outlet Ports. 23. Wrist Pin. 24. Connecting Roa, 26. Crank Pin. 26. Crank Shaft. 27. Bed Plate. 28. Housing. 29. Light Sheet Steel Removable Fronts. 30. Floating Packing Rings. 31. Crank Pit Drains to Filter. Injection Air from Compressor. By-pass to Start- ing Bottles, 12. 13. 32. Fig. 190, Cross Section of Harris Valveless Engine, Diesel Principle J02 PRACTICAL MARINE ENGINEERING most careful design have not eliminated the difficulties arising from the severe working conditions of pressure and temperature to wrhich it is subjected. The casting must be strong enough to withstand the high air starting pressure, must resist the high temperature of com- bustion and the frequent expansions and contractions previously mentioned without cracking or warping and be designed to pro- vide for efficient water cooling. The valves with their cams, two to each in a reversible engine, are noisy, require considerable attention and, each one is another risk of ja. breakdown. The Harris engine has no valves in its cylinder heads. The heads have only to withstand the normal working pressure and each cylinder has only one cam working, the atomizer cam, • St ep P iston ^Main Pieton Fig. 191. '■ Step Piston ti Harris Engine Avhen the engine is running in either direction. The ingenious method of using the step piston in air starting does away with the necessity of air 'starting valves in the cylinder head. The scavenging air is admitted to the working cylinder through ports in its circumference. The exhaust gases pass out through ports located opposite the scavenging ports and so arranged that the piston opens and shuts them at the correct time during its travel. In the building of the engine these ports are correctly located and consequently give the operator no further trouble or expense. Thus there remains only one small opeffling to be pro- vided in the cylinder head for the admission of the oil from the atomizer. In the ordinary trunk piston type of Diesel engine it is neces- sary to give the pistons considerable, clearance between the pis- ton and walls of the cylinder on account of the expansion, of the pistons. This is especially true in the case of a two-cycle en- gine and is far more necessary in Diesel engines than in ordinary internal combustion engines, owing to the high temperature of compression on the instroke and the heat created by combustion MARINE ENGINES 303 on the outward stroke. The wrist pin, being up inside of these hot pistons, receives considerable heat from them, which is also transmitted to the connecting rod and bearings. With this ex- cessive clearance the piston in a trunk type of engine has to take the side thrjist of the connecting rod, which sets up a side flogging with its consequent noise. The Harris valveless engine avoids these difficulties by using a step piston and in this case the wrist pin is comparatively cool in the step or lower piston, which practically does not ex- pand; therefore it can be a neat fit in the lower cylinder and acts as a circular crosshead guide for the main piston. The main pistons can have ample clearance between themselves and the walls of the cylinder and "let the rings do the work they are intended for." This type of engine is also built with a regular crosshead and guide. Another advantage of the step pistons acting as scavenging pumps is that they draw in^ upon themselves and around the working piston on its outgoing stroke a charge of atmospheric air for scavenging purposes. This air helps to cool the working pistons and the air itself at the same time is thus slightly heated. It is, therefore, apparent that when this scavenging air enters the working cylinders it is never cold, as is the case with four-cycle engines. It is, also, possible tb take ofif. the inlet valves of the scavenging pump and, owing to the peculiar design of engine, it will still continue to run. Thus if the inlet valve were to break down at sea it would not prevent the ship from working into port. In the ordinary Diesel engine governing is accomplished by having the governor act on a finger in the suction check valve; whii^ij^hen governing, lifts the suction valve of the fuel pumps off their seats, thereby allowing the charge of fuel in the pump to be returned or pumped backwards into the suction pipe. Fuel oil has an affinity for air and this by-passing thurns the oil, and when the governor allows the check to seat, the first few strokes give foam instead of a solid stream. Again, with this method the spring of the check valve has to be very carefully adjusted, so that it will not affect the working of the governor and yet so that the oil surging in the supply pipe from the service tanks, caused by the rolling of the ship, will not cause the valve to jump off its seat. 304 PRACTICAL MARINE ENGINEERING The Harris engine governs on a special variable stroke principle controlled by the governor. Once the line is cleared of air there is always a solid stream of oil from the service tanks to the atomizers and the slightest movement of the pump plunger produces a corresponding movement of the column of oil ; that is, if the plunger moves one thirty-second of an inch, then one thirty-second of an inch of oil by the diameter of the pump plunger is forced into the atomizer, or if thle stroke be increased by the governor a corresponding additional amount of oil will be supplied. The oil is delivered from the service tank to the pumps under air pressure, taken care of by the engine, which may be anything from 5 pounds to 100 pounds, making it immaterial where the service tank is located. There is no suction or pumping backwards, and if the gov- ernor cuts the pumps out of action entirely the oil in the line is stationary and under pressure, but ready to respond to the slightest movement of the pump plungers. No hand pumping is necessary when starting, even after weeks of idleness. In the ordinary Diesel engine it is necessary to hand pump the fuel to the atomizers before .starting, and in some cases while reversing, which is avoided in this engine. Like all other internal combustion engines, it is impossible to start the ordinary Diesel engine under load without a clutch or rnedium, as it is necessary first to build up a momentum by running the engine on air and then cut out the air supply, while the engine "takes hold" on fuel. There is an interval, during which the engine is turning by momentum only, and this interval is likely to be noticeable, in the case of a marine engine, reversing from "full head" to "full astern" while the ship is pnder way. In starting or reversing the Harris engine the action is similar to starting up a steam engine with an air pressure of from 175 pounds to, say, 300 pounds. This air, when allowed to act on the step pistons, will turn the engine over, even with its load on, so long as the engineer desires to do so, and, after the momentum of the engine is built up, the oil can be given to the main cylinders, the air still being allowed to act on the step pistons. This will augment the' power being developed from the main pistons, and, if the engineer desires it, both the main and MARINE ENGINES 305 the step pistons can be acting at the same time, the former on oil and the latter on air. As before stated, allowing this air to act on the step pistons in no way affects the working-conditions in the working cylinder, nor the step piston's normal function of acting as a scavenging pump, but is very desirable in vessels, as it allows the ship to respond more quickly and with more certainty in a case of re- versing from "full speed ahead" to "full speed astern" or vice versa. In the ordinary Diesel engine the common practice in re- versing is to move the cam shaft on end and it is necessary to lift all the valve levers off the cams first by means of compressed air. This requires considerable power to compress all the valve springs. After lifting them, the cam shaft is moved on end and these levers allowed to return onto a new set of cams, after which air is admitted to the main or working cylinders to initially turn the engine over. In the Harris engine the reversing is done by moving one rod "on each cylinder. IsTo power is required, except that which can be exerted by hand, by the engineer, regardless of the size of the engine. The same wheel or lever which admits the start- ing air and the fuel oil , controls the movement of these rods. This does avvay with a lot of small- air valves and by-pass valves, levers and extra shafting, and the loose feathers in the cam shaft, and the danger of .this important member shifting from its exact setting. Sec. 34. PRODXTCER GAS INSTALLATIONS [i] The Producer A producer gas plant consists primarily of the apparatus shown in Fig. 193, in which 7 is the producer in which the coal is burned, 15 is the scrubber in which the gas is cooled and washed, and 14 is the dryer from which, the outlet is led to the engine. The coal is fed into the producer through the automatic gas-tight hopper 4, which is provided with an automatic lock 5, which pre- vents the opening of the valve while the lid is open. The ashes are removed thTOUgh the ashpit door 10, about once a day. Special grates 12, make the fire easy of access and prevent coals of even small sizes from running. This presents a very simple type of plant, which with sHght modifications would be suitable for marine installations, for the 3o6 PRACTICAL MARINE ENGINEERING gas generator 'or producer 7, consists merely of a steel tank lined with firebrick and having a special readily cleared grate at its lower end and a hopper connection for coal on the top, and an outlet connection for the gas near the top. [2] Operation of the Producer The operation of this apparatus comprises building a fire on the grates -and keeping it built up to a depth of about 4 feet above the grate bars. Under these conditions, the air entering Fig. 193. Gas Producer through the grates will be evenly distributed and entirely con- sumed to carbon dioxide in the first 12 inches of the fire, and, ris- ing from that zone upward, the heated carbon of the fuel bed will rob the carbon dioxide of one atom of its oxygen, thereby chang- ing the contents of the gas to carbon monoxide, which is a com- bustible gas. In some designs of producers steam is also ad- mitted into the ash pit for the purpose of adding hydrogen to the gas constituent; but this may be a distinct disadvantage rather than otherwise — first, because to obtain the steam it J5 necessary to evaporate water in some form or other, MARINE ENGINES 307 which at sea would necessitate carrying fresh water, or a deposit o| salt in the evaporator, neither of which is desirable; and, on the other hand, hydrogen so formed in the gas, burning as it does at twice the rate of speed of the carbon monoxide, causes a flame propagation in the mixture in the cylinders in excess of all moderate and practical piston speeds. For this reason some marine gas producers have been designed which require no fresh water for their operation, and which generate a gas having abso- lutely no hydrogen, its sole active constituent being carbon monoxide, the rate of combustion of which is sufficiently slow to coincide with the best designs as to piston speed. In a gas-producing plant as designed for a small tow boat or cruising yacht the proportion of space required can be readily appreciated, because the necssary height over the top of the pro- ducer is taken care of by a small deckhouse, so that the operator may be able to poke his fires from the top of the producer with- out inconvenience. The space required around the producer is very small, being one-half the diameter of the producer itself, as the fire is entirely poked down from the top, and it is only necessary to open the lower doors for the removal of ashes once or twice a day. [3] Producer Gas Engines Regarding the engine equipment, it is well to bear in mind the fact that gas engines which have been designed to operate on gasoline fuel require modification before they will be suited for operation on producer gas, for two reasons: First, the valve areas will have to be larger, due to the necessity for taking in larger quantities of this weaker gas, and second, a higher com- pressioh will be necessary and advisable, in order to reach the best efficiency. It is desirable to have compression pressures from 150 to 180 pounds, although the engine will operate on any compres- sion from 100 pounds upward; still, the economy is very much greater with the increased compression. While on the subject of engine design it is well to note that there are several features existing in the design of gasoline engines which might prove troublesome with operating on producer gas. For example : When using a high compression, it is always very desirable that no uncooled points or areas should exist in the design of the cylinder, or that any pockets be allowed to exist 3o8 PRACTICAL MARINE ENGINEERING which might hold incandescent carbon, the result from either of these conditions being premature ignition and even back-firing. The simplest design of combustion chamber — one having the least number of irregularities in its shape, and, in fact, as nearly spherical as possible, will give the best results when operating on a lean gas, especially when combined with liberal valve areas. Many engineers favor a type of engine which employs valves operating directly into the compression space, but it must be borne in mind that the placing of the valve in this way is attended with a certain amount of noise from the camshaft, which may prove annoying to the operators in the boat, and that the slight gain in economy obtained by. this arrangement may be offset by greater inconvenience in taking down the engine, as compared to other arrangements of the valve mechanism where a valve pocket on the side of the engine is part of the design. It is a much mooted point whether the valves opening directly into the compression space are superior in all respects to the valves opening into a valve chamber. It has, however, been found in practice on large engines— say 500 horsepower and up- wards, designed for stationary work — ^that the valve opening directly into the compression space is far less liable to cause trouble from overheating, back firing, etc., than those valves opening into a valve chamber lying at the side of the cylinder. However, the condition of extreme heat developed per stroke on an engine with a cylinder bore of, say, 24 inches, is, of course, vastly greater than those encountered in small engines, such as would be used for the boats under discussion. The engine design which will be necessary to successfully handle the producer gas will be, first, good,. solid construction; second, piston speeds which coincide with flame propagation of the mixture to be burned in the cylinders ; and third, adequate ignition of the make-and-break type, magnetically or mechani- cally operated — in any case, however, being adjustable as to time ; fourth, ample bearing surfaces for the main bearings and positive force feed drips; fifth, an engine which can readily be taken down for repairs or replacement when necessary without the dismantlement of all the equipment. Given an engine possessing these qualities — and there are already several of them on the market— ^and a producer plant for furnishing the gas, capable of operation twenty-four hours MARINE ENGINES 309 per day continuously, and there results an ideal marine installa- tion, possessing the following qualifications : Moderate first cost. Ease of operation, as compared to a steam boiler and engine. Low cost of operation, the fuel con- sumption being under one pound of anthracite coal per brake- horsepower developed per hour. Reliability ; a plant of this kind will operate forty-eight hours at a stretch, and then need only be shut down to clean the ignitors on the engines. QUESTIONS Marine Engines PAGE What are the different types of engines and combinations of engines in use for marine propulsion?. 218 For what purpose is each type and combination best fitted?.... 2ig Explain the chief characteristics of the typical marine reciprocating engine . . . r 220 Explain the more important arrangements which may be made of the cylinders and cranks of multiple expansion engines ... 226 What are the advantages of steam turbines for ship propulsion? 231 Give brief description of an installation of Parsons turbines 234 Give brief description of an installation of Curtis turbines 23s What is meant by the term "combination machinery" ? 236 Give brief description of an installation of combination machinery, and state wherein the main difference occurs between such ma- chinery for merchant ships and for naval vessels, and why. . ; . . . 23 J' Describe an installation of combination machinery for vessels of high power and speed 239 What is meant by "reduction gears" ? 241 What are the different kinds of these gears ? , 241 Give brief description of a mechanical gear 241 Give brief description of a hydraulic gear : 252 Give brief description of an electric gear .,; 256 What are the advantages of reduction gears over direct-connected reciprocating engines or steam turbines ? : 267 Give the commercial classification of internal combustion engines. . . . 268 What is a two-cycle or two-stroke cycle engine ? 272 What is a four-cycle or four-stroke cycle engine ? 272 Give general description of predominant fornvs of explosive engines in general use .,.. 273 Give brief description of pipifig for such engines 285 Give brief discussion of fuels for such- engines 289 Give brief discussion of the Diesel engines, and state wherein it dif- fers from engines of the explosive type 291 Name principal differences between the construction and fittings of a two-stroke cycle and a four-stroke cycle Diesel engine 294 Describe the installation and operation of a producer gas plant 305 CHAPTER VI Description of the Principal Parts of Marine Engines Sec, 35. THE PRINCIPAL PARTS OF A RECIPROCATING ENGINE In describing the principal parts of the typical modern marine reciprocating engine, the stationary parts will be first taken and then the moving parts. [1] Cylinders As shown in Figs. 137-140, the cylinders are at the top of the engine and consist each of a cylindrical chamber containing the moving piston. The steam is received from the steam chest alternately in either end and thus forces the piston up and down. The motion is then transmitted through the piston rod and con- necting rod and thus, the revolution of the crank and the crank shaft is produced. Cylinders are made of cast iron of the highest grade. Each one, as shown in the figures, consists essentially of a cylindrical body, or barrel, with which is usually cast the lower or bottom head. With the barrel are usually cast also the valve casings and chests and all ports and passages, as well as the necessary feet for attachment to the columns, lugs for attaching braces, etc. The top head or cover is cast separately and is secured to an appropriate flange on the barrel by means of stud bolts. In some cases the head is made in a single thickness, conical in form to correspond to the piston, and ribbed on top for strength. In other cases it is made by a double shell or in two thicknesses with connecting ribs between. The lower head is formed in the same general way, but, as noted above, is usually cast in one piece with the barrel. In many cylinders, as shown in Fig. 194, liners are fitted within the barrel or cylinder proper. These are of extra hard and fine grained iron, and are fitted for one or both of the fol- lowing purposes: (i) To provide a working surface admitting of replacement in case of excessive wear. (2) To provide a jacket space between the barrel and liner in case the cylinders MARINE ENGINB DETAILS 3" are to have steam jackets. The space thus formed is filled with steam from the boiler or other source, thus providing a jacket or layer of steam entirely surrounding the steam cylinder. Such an arrangement is known as a steam jacket, and is used to increase the economy of the engine by decreasing the amount of condensa- tion of the steam within the cylinder. The liners are usually Marine Engheertng Fig. 194. Cylinder with Liner and Double Valve Chests secured at the lower end by a flange, as shown in Figs. 194 and 196, the joint between the end faces of the liner and barrel being carefully made in order to prevent leakage, especially if the space between the barrel and liner is to be used as a steam jacket. At the upper end the joint between liner and barrel may be made in a variety of ways. As shown in Fig. 195, a packing space is formed between the liner and barrel. This is filled with some form of elastic pack- ing held in place by a ring attached to the liner as shown. In this 312 PRACTICAL MARINE ENGINEERING way the upper end of the liner is free to come and go as ex- pansion and contraction may require, while the packing main- tains the joint steam-tight. In another mode of fitting, a groove of dovetailed cross section is turned out partly in the liner and partly in tfie barrel, and a ring of soft metal or packing is ex- panded into the space thus formed. In Fig. 197 is shown a liner as fitted to a high pressure cylinder, the cylinder being un jacketed. The liner is made a forcing fit in the cylinder casing at the points B, and bottoms fil s \ I I ^^^^: N V ^S ''^. :^^ / ^= E" / J Fig. 195. Joint Between Liner and Barrel Top, Fig. 196. Joint Between Liner and Barrel Bottom with a small clearance against the inner surface of the lower head, at the same time bringing up on the shoulder A. The upper end of liner is flush with the bearing face of the upper cylinder flange, so that when the cylinder upper head is in place the liner is held securely in position with sufficient clearance at the bottom to allow for difference in expansion between it and the cylinder casing. The bore of the cylinder or liner is made uniform, except near the top and bottom, where it is counterbored out slightly larger, so that at the extreme ends of the stroke the piston rings may overrun the counterbore, and thus avoid wearing a shoulder in the metal. Cylinders as well as steam jackets are usually.provided with MARINE ENGINE DETAILS .313 drain cocks and vdlves with suitable piping, so that water collect- ing within them may be drained away. In addition, automatic Fie 197 U S. S. Oklahoma. High Pressure Cylinder. Volumetric Cylinder *■ ■ Clearance Equals 10.75 Percent (Mean) . ' relief cocks or valves should be fitted, set to open under an ap- propriate pressure, and thus furnishing relief in case a large quantity of water finds its way into the cylinder. il'i PRACTICAL MARINE ENGINEERING The cylinders are supported directly upon the columns which are attached to facings on the lower head, or to lugs cast on the lower part of the barrel in case its diameter is not suffi- cient to reach out over the tops of the columns. See Fig. 198. For mutual support the cylinders are quite commonly tied to- Fig. 198. Double Inverted Y Columns gether by braces, or flanged and bolted to each other. In some cases, however, the cylinders are allowed to stand alone and in- dependently, while in the other cases of recent practice a form of connection has been adopted, consisting of a vertical tongue and grooved joint. This allows differences of expansion vertically and fore and aft, but provides mutual support transversely. The valve chests with the various ports, passages, etc., are also cast with the cylinders, as shown in the figures. These parts will receive further notice in connection with valves. MARINE ENGINE DETAILS 315 [2] Columns The columns serve to support the cylinders and to connect them with the bed plate. They also serve to support the guide surfaces for the crossheaSfs, and thus receive the transverse thrust of the connecting rods. Columns are made either of cast iron, cast steel or forged steel. When of cast metal they are usually in the form of an. inverted Y, as shown in- Figs. 198 tfarint MmgiiueTing Fig. 199. Inverted Y and Cylindrical Columns and 199, and of a box or I-formed section. When forged, the columns are usually cylindrical or slightly tapering, and some- times-hollow. Cast inverted Y columns both- front and back of the engine, as shown in Fig. 198, for many years constituted standard practice. More recently, however, cast inverted Y columns at the back of the engine and cylindrical forged columns in front, as in F^s. 199 and 200, are commonly employed in repre- sentative marine practice. In such case either one or two col- umns may be fitted in front and one in the rear. When the col- umns are all cylindrical, it is customary to provide four for each cylinder. Such columns are usually placed vertical, as in Fig. 3i6 PRACTICAL MARINE ENGINEERING 20I, though occasionally they are spread somewhat at the base, as in Fig. 199. Marin* Sngiiucrifii/ Fig. 200. Inverted Y and Cylindrical Columns, Warship Typ% In some cases of modern practice four vertical columns of / section have been provided for use with a crosshead as shown in Fig. 218. The columns stand in pairs, one forward and one MARINE ENGINE DETAILS 317 aft, and the wings of the crosshead carrying the sHde surfaces work between them on the guides carried on their inner faces. In some cases the condenser is placed back of the engine and on the bedplate, as in Fig. 140. In this case the back col- umns are either cast with the condenser shell or consists of short vertical columns standing on top of the condenser, which thus; constitutes a part of the support of the cylinders as shown. Haiitu Sngintering Fig. 201. Cylindrical Colunms To resist the racking and cross-breaking stresses to which the columns may be subject, it is necessary, especially with plain cylindrical columns, to provide transverse and ev^n longitudinal ties and braces. The usual arrangement of such bracing is shown in Figs. 199, 200 and 201. It will be noted in particular that the transverse bracing between a pair of columns, as in Fig. 201, unites them into a single girder, thus providing vastly more strength to resist lateral stresses due to rolling of the ship, etc., than could be furnished by the columns themselves and without the assistance which the bracing is able to provide. The guide surface for a crosshead is fitted in various ways 3iS PRACTICAL MARINE ENGINEERING according-to the style of crosshead, the style of columns andtype of practice. The simplest arrangement is as shown in the cross- section of Fig. 202, in which the guide surface is fitted directly on the inner face of the Y column. In the arrangement of Fig. 199 the guide surface is fitted on a separate slab of rather harder and finer grained cast iron, and hence better adapted for bearing purposes. Between the slab and the face of the column a space is left as shown, and through this may be circulated a stream of water to absorb the heat generated by the friction, and Fig. 202, Section of Cast Column, Showing Guide Surface thus to keep the bearing surface cool. With cylindrical col- umns the guide surfaceinust be fitted as a separate slab for each crosshead, and usually in the manner shown in Fig. 201. These slabs may be of cast iron, steel or bronze, and are carried on longitudinal bars attached to the columns. The form of cross- section may be either hollow for water circulation, or plain or ribbed on the back for strength, as the case may require. A common form is that shown in Fig. 201, thinner towards the ends and thicker in the middle as a girder, to provide the neces- sary strength at this point. MARINE ENGINE DETAILS 319 For further details of the giiide surfaces which depend on the form of crosshead used, reference may be made to [7]. [3] Bedplates The purpose of the bedplate is to support the feet of the columns, and thus to carry the weight of the cylinders and at- [0 ■ I Iq -j < qi ;_ _1 40 0' |0 ■ o T !o ... I9. II i 1 Vi 1 r y ^1 ill i f 1 1 1 1 V J '<\ J . V J i •i C3 1^ ll 05 ' J \ Uw ii Ifarint Enginttring Fig. 203. Bedplate for Triple Expansion Engine in One Casting tachments, to provide seatings and support for the crankshaft bearings, and generally to serve as the foundation piece upon which the engine rests, ^nd through which its weight and the Fig, 201. Details of Bed Plate in Fig. 203, Showing Main Pillow Block various stresses developed are transferred to the structure of the ship. As usually formed, it consists of a series of transverse box 320 PRACTICAL MARINE ENGINEERING or / girders, one for each crank shaft bearing, these beiiig con- nected together by fore and aft members, as shown in Figs. 203 and 205. Bed plates are usually made of cast iron or cast steel. Rarely bronze or special forms of plate girder may be employed. Large Fig. 205. Bed Plate in Sections. End View of One Section bed plates instead of being made in one casting are often made in sections and bolted together. The bed plate is secured to the ship by holding down bolts passing through the flanges of the 00 LONGITUOIMAL SECTION. TRANSVERSE VIEW. Fig. 206. Engine Seati'^g or Foundation plate and of the specially strengthened structure of the ship under- neath, known as the engine seating or foundation. Further ex- amples of bed plates may also be noted in Figs. 137-140, 198-200. In the design of the bed plates particular attention should be paid to the cross webs under the bearings to insure as wide a bearing on the foundation as possible in order to prevent fore and aft rocking of the shaft journal. MARINE ENGINE DETAILS 321 [4] Engine Seating This structure is a part of the ship, and serves to give the final support to the weight of the engine, and to lead the stresses due either to its weight or to its operation into the structure of the ship as a whole. The usual character of the seating is shown in Fig. 206. It consists of a cellular construction formed by longitudinal and transverse vertical plates, stiiifened and con- nected at the corners by angle irons, and usually forming a con- tinuous structure with a part, at least, of the regular internal members of the ship itself. The chief moving parts of the engine will now be considered. [5] Pistons The piston is the moving part of the engine upon which the steam directly acts, and which, by the steam pressure, is driven back and forth in the cylinder, and from which, through the piston rod, crosshead and connecting rod, the motion is trans- Marine £ngiiiienng Fig. 207. Conical Marine Piston mitted to the crank and crank shaft. The requirements for the piston are therefore: (i) It must be able to support the load which the steam pressure brings upon it. (2) It must be of such form as to admit of movement up and down in the cylinder, at ~the same time making a steam tight joint between its outer edge and the cylinder walls. (3) Provision must be made for its secure attachment to the piston rod, through which the forces are transmitted to the remaining moving parts of the engine. Pro- vision must be made against the steam getting behind the pack- ing of the joint between piston and cylinder wall and thus pro- ducing abnormal frictional resistance. The usual form of marine piston is shown in Fig. 207, and consists of a shell of conical form with a central boss or body for carrying the piston rod as shown. Around the outer edge of 322 PRACTICAL MARINE ENGINEERING the piston the metal is thickened up to provide for the packing rings, which are fitted to tnake a steam tight joint between the piston :and cyHnder walls. The fitting of these rings is shown in Fig. 2cfi. The rings are usually two in number, and are formed Marint Engint*rimif Fig. 208. Marine Piston, Enlarged View, Showing Packing Rings and Follower Plate of cast iron turned first to an outside diameter slightly larger than the bore of the cylinder. They are then cut as shown in Fig. 209, and enough is taken out so that they may be sprung together sufficiently to allow their entrance into the cylinder bore. CF TI SU TOP-RING w Xavine Eng\nnrtng Fig. 209. Marine riston, Joint in Packing Rings Care is taken to so locate the two rings that the cuts shall not come opposite each other and thus the opportunity for a direct leak through from one side to the other is avoided. In order to still further prevent such leakage, a tongue as shown in the figure is usually fitted across the opening. The tongue piece, which is usually of brass, is attached to the ring and overlaps the slitj as MARINE ENGINE DETAILS 323 shown. The joints between the ring and tongue piece are care- fully fitted so that in this way the ring may open and shut, as cir- cumstances may require, while the opening into the slit remains closed to the entrance of steam. When the piston is of any con- siderable size it is customary to aid the natural elasticity of the rings by steel springs, as shown in Fig. 210. These bear on the bottom of the recess formed in the piston, and on the inner surface of the rings, and thus the latter are forced outward against the surface of the cylinder. In the best practice, the sharp edges of the cuts at A and B (Fig. 209) are chamfered off to reduce the o Fig. 210. Marine Fiston, Steel Spring for Packing Rings tendency to dig into the cylinder wall and cause breakage, and in order to prevent steam getting behind the ring and setting it out hard against the wall, restraining lugs fitted with a clamp are se- ,cflred on each side of the cut, which limit the possible amount of expansion of the ring. In high pressure cylinders it is preferable to cast the rings solid and fit them so, centering them on the piston by means of springs, which will allow a slight play of the piston spider, as the solid part of the piston is called. In very large cylin- ders, the rings may be made in several sections, the openings being guarded by tongue pieces and restraining lugs and clamps. "^ The body of the piston itself, as shown in Fig. 298, is turned slightly smaller than the diameter of the cylinder, so that it clears the latter at all times, while the rings extend beyond and make the joint with the cylinder wall. The rings and springs are fitted as shown between the lower flange of the piston body and a plate known as the follower plate or ring. By removing the latter the rings and springs may be removed when necessary for overhauling and refitting. The follower plate is secured to the 324 PRACTICAL MARINE ENGINEERING piston by stud bolts and nuts, as shown in the figure. In the best class of work all joints between the piston, and rings, between the follower plate and rings and between the two latter are care- fully made by hand scraping and fitting, in order to reduce the chances of leakage to the smallest possible limits. Many variations are met with in the details of the form and fittings of pistons. In some- cases they are flat and either solid or hollow, as shown in Figs. 137 and 212. In some cases Ramsbottom rings are fitted instead of the rings of Fig. 207. These consist of two or three narrow rings turned slightly larger than the cylinder with a piece cut out so that they may be sprung on over the body of the piston, and into Fig. 211. Ramsbottom Rings grooves, as" shown in Fig. 211. No special springs are fitted, and the natural elasticity of the rings is depended upon to give the necessary pressure between the ring surface and the cylinder. It is easily seen that no follower plates being fitted, the rings cannot be examined or removed without removing the piston. To avoid this difficulty the arrangement of Fig. 212 is sometimes used. Here the rings are carried on a larger solid ring, as shown, and sometimes known as a bull ring. This is carried between the faces of the piston flange and follower plate, and thus by the removal of the latter the whole arrangement may be withdrawn and examined. There is usually some clearance between the MARINE ENGINE DETAILS 325 inner surface of the bull ring and the body of the piston, as shown in the figure. This allows the whole arrangement of rings to move transversely independent of the piston body, thus mak- ing allowance for lack of alinement between the axis of the piston rod and the axis of the cylinder, or for wear in the latter. While light packing rings of cast iron fitted as above de- scribed without the assistance of steel springs may prove satis- cn,.,. Fig. 212. Piston with Ramsbottom Rings on Bull Ring factory for small pistons, the more standard method of Fig. 207 is to be recommended for all cases where the pistons are of any considerable size, but care should always be taken to prevent undue friction between ring and cylinder. In present practice, pistons of the form shown in Fig. 207 are made of cast steel. Pistons of the form shown in Figs. 137, 212, are more commonly made of cast iron. Fig. 213. Piston Rod Marinr Snpiatlring The chief advantage of the conical form of piston lies in the saving of weight for the necessary strength and stiffness, as com- pared with other forms. This superiority has gained for it almost universal adoption in modern practice, and it may be considered as the present day representative form of marine piston, and the one which will naturally be adopted unless there may exist special reasons for the adoption of the older type. [6] Piston Rods The piston rod is that member of the moving parts which serves to support the piston, to carry the. forces due to the steam pressure througfh the stuffing box outside the cylinder, and through the crosshead to communicate them to the connecting 326 PRACTICAL MARINE ENGINEERING rod and other moving parts. The requirements are therefore as follows: (i) It must have sufficient strength and stiffness to safely carry the load coming from the piston. (2) It must be provided at the upper end for attachment to the piston, and at the lower end to the crosshead. (3) It must be of such form as to admit of readily making a steam tight joirtt where it pas.ses through the cylinder head. To fulfil these conditions the piston rod, as shown in Fig. 213, has the form of a uniform cylindrical rod except at the ends where it joins the piston and crosshead. The common form of attachment to the piston is shown in the Mariit^i^uuing. Fig. 214. Marine Crosshead figure. The rod is usually tapered where it lies in the piston, but is sometimes parallel. It is often relieved from direct bearing ex- cept near the top and bottom, so as to give definite points of bearing where it is most needed. A shoulder or ring is also fitted, as shown, so as to give a definite stop against which the body of the piston rests. The end of the rod is threaded and a nut on top completes the fastening. This nut is sometimes hex- agonal and sometimes cylindrical, with longitudinal grooves, a spanner wrench being used in the latter case to set the nut down. The fitting at the lower end of the piston rod depends on the style of crosshead used, and may be more appropriately de- scribed under that heading. In modern practice with conditions requiring the highest grade of material and most careful design, the piston rod is often made hollow. This practice also extends to most of the other cylindrical elements of the engine such as cylindrical columns, crosshead pins, connecting rods, crank pins, crank, line, thrust. MARINE ENGINE DETAILS 327 and propeller shafts. Inasmuch as this style of construction was first commonly introduced in connection with shafting, the reasons for such practice and its advantages may properly be discussed under that heading. [7] Crossheads There are several types of crosshead to be met with in marine practice. In Fig. 214 is shown one of the more common forms. It consists essentially of a cubical body A, through which in a vertical direction is the hole for the piston rod. Extending VaHiti BnginMrimg Fig. 215. Marine Crosshead, Slipper Type with Cotter Fastening for Piston Rod out on either side longitudinally are the two crosshead pins B and C. Then attached to the two remaining sides transversely are4he slides as shown. The connection between the crosshead and the piston rod is commonly by means of thread and nut, as shown in the figure, in the same way as for the connection to the piston. In some cases a pin or cotter joint, as shown in Fig. 215, is used instead of the thread and nut on the end. The slide sur- faces D and E rest on the guide surfaces of the columns, as above described, one side taking the load when going ahead and the other when backing, A crosshead of this type is therefore suit- able for double inverted Y columns where there is a guide surface on both back and front sides of the engine, ^here cylindrical columns are used, as in Figs. 199, 201, the slipper form of cross- head is commonly fitted. This is shown in Fig. 216, and so far as the part connected with the piston rod and carrying the cross- PRACTICAL MARINE ENGINEERING head pins is concerned -may be the same as in Fig. 214. Instead of two wings carrying sUdes, however, there is but one with the form shown in the vertical view. The corresponding form of guide is shown in Figs. 199, 201. When going ahead the face A VERTICAL VIEW. TRANSVERSE VIEW. Fig. 216. Marine Crosshead, Slipper Type of the slipper bears against the face B of the guide. Cheek pieces or, gibs C and D are secured to the column, thus forming guide surfaces on their inner faces E and F. Against these the faces G and H of the slipper bear when in backing motion. The go- ahead surface is therefore formed on the faces A and B of the Xarint Enginarmg Fig. 217. Crosshead Formed on Lower End of Piston Rod guide and slipper, as with Fig: 214, while the backing surface, in- stead of being provided on the opposite column and on another slide piece on the other side of the crosshead, is formed on the reverse side, G and H, of the slipper, and on the cheek pieces, as shown. MARINE ENGINE DETAILS 329 These types of crosshead are suited to the so-called forked type of connecting rod, as described below, for which the cross- head pins are a part of or fast in the crosshead, and are naturally two in number, one on either side fore and aft, as showp. In the other type of connecting rod which is frequently met with, the rod is not forked, and the pin is fast in the upper end, and is single rather than double, while the crosshead member fur- JfHrifle angtnttrwig Fig. 218. Marine Crosshead, Special Type nishes the bearing. This arrangement is shown in Fig. 217. The crosshead body is usually forged up on the lower end of the piston rod, and together with a suitable cap and bearing brasses iorras the bearing for the pin which is fast in the upper end of the connecting rod, as shown. The wings for carrying the slides may be attached and the slides may be fitted in the same general manner as in Figs. 214, 216, either double or of the slipper type.* A third form of crosshead occasionally found in modern practice was referred to in [2], and is here shown in Fig. 218. This type of crosshead is a marine adaptation' of a type very common in stationary engine practice. The slide surfaces are formed on the opposite faces of webs or wings extending out from the body of the crosshead, and bearing on the guide sur- faces formed on the columns. In Fig. 219 is shown a somewhat different foi-m of the same type of crosshead, the latter being suited to two columns and the former to four. 330 PRACTICAL MARINE ENGINEERING As noted in [6], the crosshead pins, in the most advanced practice, are often made hollow. In some cases the hole is parallel; in others its diameter decreases from the outer end "1 1 h^ \' — 1 /^r rWi^ai e ^^ 1 L.J .-J 'vl- Jfartn* Eagiiietring ,J||L J\ z-J /■ Fig. 219. Marine Crosshead, Special Type inwarc^^thus giving the most metal at the inner end, where the greatest stresses are likely to be found. See Fig. 214. -f¥W [ c^m MdfAat JBgg'tiMPiav Fig. 220. Marine Connecting Rod [8] Connecting Rods Fig. 130 illustrates perhaps the more common type of con- necting rod. At the upper end it is forked or formed into a U shape, each branch being provided with a bearing and connec- MARINE ENGINE DETAILS 33! tiohs for one of the crosshead pins. This type of end corre- sponds therefore to the type of crosshead shown in Figs. 214, 216. Fig. 221. Marine Connecting Rod Marin4jltigiv4CTin/ For connection to the crank pin, the lower end of the rod is fitted with brasses and cap, all secured to the forged out foot of the rod by through bolts as shown. Xarint Engintering Fig. 222. Marine Connecting Rod with Gib and Key Connections For the type of crosshead shown in Fig. 217 the rod is formed, as shown in Fig. 221, with a U-shaped upper end fitted to receive the two ends of the crosshead pin, which is thus made fast to the rod. This pin is then seated in a bearing in the cross- head, as described under that heading. The lower end of the rod is usually of the same form as shown in Fig. 220. 332 PRACTICAL MARINE ENGINEERING Rarely the gib and key foftfi of connecting rod end as illus- trated in Fig. 222 is found in marine practice. In external form marine connecting rods- usually, increase in transverse dimension from top to bottom. In some cases they are given a uniform taper from one end to the other, as in Figs. 220222, while in others the extra metal is planed off on the forward and after sides until the thitkness in the fore and aft direction is uniform from top to bottom. As noted in [6], the connecting rod, in the most advanced practice, is usually hollow, a hole of uniform bore being drilled from one end. to the other, as shown in Fig. 221. [10] Crank Shaft Modern marine crank shafts are of two principal types, forged and built up. Fig. 223 shows ^ a portion of a built-up ,.< ««!S,- ;j._ Fig. 223. Section of Built Up Crank Shaft crank shaft. It consists, as shown, of two crank webs or throws A and B, one crank pin C and two portions of shaft D, E. Built-up crank shafts are usually made continuous for the whole engine, and in such case the piece of shafting D connects the crank shown with the one next to it, and thus serves as a common member for the two. In this type of crank shaft the various sections of shaft, the crank pin and the webs, are all made separately, and then fitted and secured together. This is usually done by shrinking and keying the various cylindrical members into the sections of web as shown in the figure. Fig. 224 shows a section of a forged cranlc shaft. In this case a forging of suitable form is made, and the various parts MARINE ENGINE DETAILS 333 are then formed by cutting out and machining this forging. In many cases, moreover, the series of such sections for the entire engine are forged and machined in one piece, the result being a continuous forged crank shaft. In other cases the section for each crank, as shown in the figure, is forged and made sep- arately, the various sections being then secured together by flange couplings, as shown in Fig. 224. The advantage of making the shaft in sections lies in the fact that in many cases the sections may be made interchangeable, and thus a single spare section is sufficient for the replacement of any section which may become ^ h • p , ■ Fig. 224. Section of Forged Crank Shaft disabled through accident, and in any event a break will usually require the refitting of a single hew section instead of an entire shaft. Forged crank shafts are commonly used in naval practice, and in general where the type of construction is of specially high grade and the saving of weight an important feature. Their use in all departments of marine practice seems, more- over, to be on the increase. Built-up crank shafts, however, are still much used in the mercantile marine, especially where the conditions are easily fulfilled, and their somewhat greater vyeight is not a serious objection. As noted in [6], the cylindrical members of marine engines are oftea made, hollow, especially in the more advanced types of design. Fig. 224 shows a crank shaft section with hollow pin and shaft. As this feature was first commonly introduced in connection with shafting, and is more often met with here than elsewhere, the advantages of such construction may be now considered. , ^ The advantages of hollow cylindrical members such as a piston rod, connecting rod, crank pin, or length of shafting, are two in number, (i) It 15 stronger for a given weight, or for a 334 PRACTICAL MARINE ENGINEERING given strength less weight is required. (2) The central core of metal is removed, and this is. the most liable to contain cracks 'is «-, oA °'->fU ji Be . m >■'« u f^% s t< QU 7b V ** ei o.i- a ■ -S"5 H E o*^ <;murw or flaws, which might in time extend out into the remaining metal, and thus seriously weaken the member. Furthermore, the hole gives opportunity for the inspection of the metal on the MARINE ENGINE DETAILS 335 inside, and thus increases the opportunity for the detection of a flaw which might not extend to the outer surface, or which might there be so small as to be overlooked. For cross-breaking or for torsion the metal in the in- terior of a cylindrical member is of comparatively small value. Thus in a lo-inch shaft, the inner core 5 inches in diameter is worth no more than a shell of metal about .016 inch thickness lying next to the outer surface. Or, as a further illustration, a i6-inch shaft with a 10-inch hole is equal to a 15-inch solid shaft. In other words, a shell of metal % inch in thickness all around added on the outside of the 15-inch shaft will make up for the removal of the inner core of 10 inches diameter. In the lat- ter case the hollow shaft would weigh about 65 percent of the equivalent solid shaft. , The saving in weight for a desired strength may thus be very considerable, but it is probable that the advantages noted above under (2) are of still greater im- portance, and in some cases might justify the added cost of making the member hollow where such addition could not be justified by the saving of weight only. Sec. 36. CONSTRUCTION OF PARSONS TURBINES The Parsons marine turbine, Fig. 225, consists 'essentially of the following parts : 1. The cylinder, composed of a lower casing and an upper casing, bolted together at the center line flanges. 2. The cylinder heads, containing the stuffing boxes and the pedestals supporting the bearings. 3. The rotor. At each end of the rotor, or spindle, are se- cured cast steel wheels, into the hubs of which are forced the rotor shafts, made of high grade steel forgings. When placed within the same casing the backing drum is secured to the low pressure ahead drum. 4. The blading, arranged in a number of stages, or "expan- sions," is composed of stationary blades in the cylinders and movable blades on the rotors or drums. 5. The dummy pistons. The object of the dummy piston is to prevent the live steam from reaching the stuffing boxes, and also to regulate the amount of end surface necessary to counter- act the propeller thrust. 6. The steam-packed glands. 336 PRACTICAL MARINE ENGINEERING 7. The main bearings and the thrust bearing in the forward pedestal. 8. Steam, exhaust, drain and oil connections. [i] The Cylinder As will be noticed by studying the figure, the casing con- sists in reality of a number of cylinders of different diameters and lengths. At the inlet end the internal diameter is smallest, and then the successive diamfitfirs increase by steps. The differ- ence in diameter of each stage is provided in order, to accommo- 890a 670° eOO" 630° 660° 690° 720° 750° 780° 810° 840° ^Absolute Temperature of Steaia In Degrees F. In a Turbine System Fig. 226. Approxiidate Steam Speeds Through a Marine Turbine date the increase in the volume of the steam as a result of its expansion in flowing through the turbine. The exit areas be- tween the vanes should, theoretically, increase in the same ratio as the actual volumes, and thus follow along a. curve resembling the pressure-volume curve for steam expanding adiabatically. MARINE ENGINE DETAILS 337 This is, however, not done in practice, as it would require a different blade height for each row ; so what really occurs is a con- stantly increasing steam velocity at each vane row within a given "expansion." A fairly good idea of the steam speeds through a marine turbine may be obtained from the diagram shown in Fig. 226. The grooves turned in the cylinder range in depth and width to correspond with the size of blade. The width of the blades increases with the length. Nozzles for the steam inlet and exhaust are provided on the cylinder at suitable places. The main steam inlet is furnished with a separate steam strainer, to prevent any solid matter from entering the blading. Where the arrangement consists of three turbine units — viz., a high pressure and two low pressure turbines — self-closing valves are placed at each of the exhaust nozzles on the high pressure turbine connect- ing to the steam end of the low pressure turbines. This is done to render each low pressure turbine entirely independent of the other when used for maneuvering, as it must be carefully noted that, when backing, only the low pressure turbines are being used. For the purpose of maneuvering the low pressure turbine has a high pressure steam connection at each end — that is, to the backing turbine placed within the after end of the casing as well as the forward end of the low pressure turbine. Were the valves, mentioned above, not provided, the live steam let into the head end of one turbine would flow through into the high pressure turbine and in some arrangements into the ahead end of the other turbine, which would cause serious disturbance should, at the same time, this turbine be used for backing. With the self-closing valves shut, the high pressure turbine revolves in a partial vacuum, due to the drains being opened to the condenser. A similar arrangement of self-closing valves and drain con- nections is placed also on the cruising turbines, thereby causing them to revolve in a vacuum when not used. Self-closing valves, or any kind of valves, are not needed in the exhaust connection between the high pressure and low pressure turbines in four- shaft turbine arrangements. This is because the high and low pressure turbines on each side of the ship, taken together, form an independent unit. The main exhaust connection to the condenser is placed be- tween the ahead and backing turbines on the low pressure cylin- 338 PRACTICAL MARINE ENGINEERING der casing. It is made of large dimensions, in order to reduce the exhaust velocity to a low figure, ranging from 350 to 450 feet per second. [a] The Rotor The revolving or mobile part of the turbine consists of a uni- form diameter wrought steel cylinder called the rotor. It must be carefully balanced, both statically and dynamically, and one of the principal objects to be attained in its construction is rigidity. A center, or wheel, is firmly secured in each end of the rotor cylinder. Into each of these centers is shrunk and pinned a steel shaft hav- ing journals resting in bearings, which are placed in extending pedestals. These are made either in one piece with the turbine casing or otherwise firmly secured to it. Grooves for the blading, similar to those in the cylinder, but with small serrations cut concentrically In their entire depth. Fig. 227. Detail of Thrust »nd Main Bearing of Rotor Shaft are turned on the outer cylindrical surface. These grooves resist centrifugal action on the blading. [3] Other i)etails The rotor bearings. Fig. 227, are placed at each end of the turbine, and consist of white-metalled brasses held in place by screws. Oil grooves are cut in the surfaces to provide for effi- cient lubrication. Where the rotor shafts go through the turbine casing are placed steam-packed glands. Fig. 228, which consist of a cast iron casing with a series of loose fitting brass rings fitting in be- tween corresponding collars turned on the shaft. The high pressurte g:land is supplied with high pressure steam, while steam MARINE ENGINE DETAILS 339 of lower pressure is let into the low pressure turbine glands. By these means steam from the high pressure turbine is prevented from leaking out and air from leaking into the low pressure turbine. Drain cocks and pipes are fitted to all turbine casings and glands. All the casing drains connect to either condensers or air- pump channel way. Dummy pistons are placed at each steam end of the tur- bines. They consist of a number of collars turned in the ex- tension made on the rotor and corresponding parallel rings, fit- ting with a very small clearance against the collars, on the inside A. ShaCfr B . Sleeve C . Snap Rlnga 0. Packing Strii* Fig. 228. Steam Gland of a separate bushing bolted to the head. By successive expan- sions and superheating the steam volume is gradually enlarged and the steam leakage thereby effectually choked upon reaching the" last rings. The loss from leakage at these pistons is, never- theless, considerable, and their close adjustment is a source of great care. A thrust bearing is built forward of the forward rotor bearing. It consists of several rows of brass rings let into a sleeve imbedded in the pedestal. The bearing is split on the center line, and the lower parts of the rings form the thrust sur- face fpr ahead motion, while the upper parts take up the thrust when backing. Thrust collars are turned on the shaft, and ad- justment for wear is secured by a slight movement being given to the upper half of the bearing. 340 PRACTrCAL MARINE ENGINEERING [4] Blading The blading, Fig. 229, is a most important part of the tur- bine, as upon the accuracy of its dimensions and angles depends largely the efficiency of the turbine. As originally made, each blade and packing piece was placed separately by hand into the grooves provided in rotor and cylinder and then calked into place. Gi-oovo Into wbtch blades are calked, showing Eerratious. Blade Tip Blade Tip Showing saw cut ill blade; lacing fttrip not yet inserted .J3 ^^^ Lacing strip; soldei-ed in position ^^ in saw cut ; extending tfafougb \ all blades of the i-ow. Binding wire wound ai-ound blade and lacing strip, and trom one blade to the next, over the eutii-e i-ow. Radial view of pit>Jecting blades showing lacing sti-ipand binding wire . .Binding Wire Lacing Strip ^ Tjrpe of Caliiing Piece Fig. 229. Blading of Parsons Turbine The improved method consists of the so-called segment system, which means that several vanes are assembled into long seg- ments. These are put in as a whole piece at one time. Parsons segments are produced by building up blades and packing pieces in cast iron frames having grooves identical to those of the rotor and cylinder and furnished with stops" giving the correct angles. Packing pieces and blades are strung on brass wires, trued up, wire-laced, and then silver-soldered. The wire at the root of the blades and packing pieces is riveted at the ends and the seg- ment completed. By thinning the tip ends of Parsons blading the clearance may be reduced and the danger arising from contact somewhat diminished. Casing blades are subject chiefly to bending stresses, MARINE ENGINE DETAILS 341 due to the impulse of the steam when in contact with the vane surfaces. The rotor blades, on the other hand, are subject not only to bending stress, but also to a tensile stress, caused by the centrifugal force brought about by being in rotation. Slight serrations are provided in the grooves, in order to secure a bet- ter hold on the rotor blades, or wedge-shaped grooves are pro- vided. The stripping of blades is usually caused by suddenly start- ing up when, at the same time, water has been allowed to collect in the cylinder. Insufficient tip clearance, or melting out of the bearings, resulting from stoppage in the oiling system, or unequal expansion in warming up are also sometimes the cause. Sec. 37. CONSTRUCTION OF CURTIS TURBINES The Curtis marine turbine consists principally of the follow- ing parts, reference to which is given in Fig. 230: 1. The cylinder with the heads. 2. The rotor with the rotor shaft. 3. Nozzles. 4. The diaphragms. 5. The blading. 6. Distributors. 7. Glands. 8. Bearings, including thrust bearing. 9. Steam and exhaust nozzles, drain connections, etc. [i] The Cylinder The turbine cylinders are made in halves, and are strongly constructed. The ends are usually made of separate castings bolted to the main body. The cylinder is divided by means of diaphragms or standing buckets into as many compartments as there are stages. An extension nlade on the inside of the cylinder in-^ajgh stage carries the nozzles. Besides the nozzles there is bolted to the cylinder in each stage the distributor containing the stationary vane rows. Separate steam chests are bolted to the front and back heads. The steam chests contain the first-stage nozzles, which have separate valves for the purpose of shutting off their steam supply. The two principal parts of which the turbine cylinder is made consist of one part for ahead-going motion and another part 342 PRACTICAL MARINE ENGINEERING MARINE ENGINE DETAILS 34^ m. 9 be CD ^44 PRACTICAL MARINE ENGINEERING for backing motion, each having a separate and independent steam connection. The main exhaust nozzle is placed between them. [2] The Rotor The first few stages of the rotor consist of wheels, while in the remainder the drum construction is used. The moving blades are fastened to the rim of the wheels and drum. The number of vane rows depends largely upon the jet velocity. The wheels are built up of cast steel hubs, plate sides and forged steel rims. They are forcfed on the rotor shaft and keyed. The rotor shaft is a hollow forging, and carries the weight of the entire rotor. Each end, outside the cylinder, rests in a bearing. Where the power delivered at the turbine is great the turbine is usually divided into two or three units called the high pressure turbine, the intermediate pressure turbine (when the heat removal is accomplished in three stages) and the low pressure turbine. The high and low pressure turbines and the backing turbine of a two-stage unit are shown in Figs. 230-A and 230-B. A point of interest in the high pressure turbine is the reversal of flow of the steam at its low pressure end by which means the steam thrust is very effectively reduced. [3] The Nozzles The number and size of the steam nozzles are directly in- fluenced by the horsepower of the turbine, which, in a way, may be regulated by the number of nozzles open. In the first stage they are made expanding, giving a steam velocity of between 1,800 and 2,200 feet per second, all other stages having parallel nozzles with steam velocities between 1,000 to 1,500 feet per second. The nozzles adjoining each stage increase in number and size as the volume of the steam becomes greater by its expan- sion through the turbine. The early stages contain comparatively few nozzles, occupying only a part of the perimeter of the dia- phragms, while those in the low pressure zone cover the entire circle. [4] The Diaphragms Each stage is separated by a diaphragm dove-tailed in the cylinder. Where the rotor shaft goes through the diaphragm a close^tting grooved packing gland is placed to prevent undue steam leakage. The diaphragms are made of wrought steel plates MARINE ENGINE DETAILS 345 riveted to cast steel rims at the cylinder and forged steel hubs at the shaft. In modern practice they are made in halves for easy removal. [5] Blading The turbine blading consists of separate blades, fitting in dove-tailed grooves in the casing and the rotor, with distance pieces between. The distance pieces, after being driven firmly home, are securely calked, although calking strips forming a wedge-like securing piece along one side of the dove-tail may be used and alt the calking be done on this strip. [6] The Distributors These compose the stationary vane rows, the purpose of which is to guide the steam in succession to the various moving vane rows fastened to the wheels or drum. The distributors are bolted to the inside of the cylinder in line with the nozzles and occupy an arc somewhat longer than that occupied by the nozzles, which, in the first few stages, take up only a small part, or parts, of the wheel perimeter, but gradually increase to the entire cir- cumference for the later stages. [7] Other Details Around the shaft at each end of the turbine cylinder is placed a stuffing box packed with carbon rings having a light bearing on the shaft. Steam connections with drains to a stage containing a less pressure' are provided for the packing rings, to prevent air leakage into and steam leakage from the turbine cylinder. Horseshoe or other approved thrust bearings are placed either forward or aft of the cylinder. i Each stage is connected by a valve and pipe in such a way as to drain successively to the condenser. The following may be noted with respect to impulse turbines of the Curtis type : 1. For a given vane s"peed and pressure range the number of vane rows is less with impulse turbines than with turbines of Parsons type. 2. High initial steam pressures and superheat may be used to advantage. 3. Clearance in the vane system may be provided with ample allowance. 4. Balance and dummy pistons are not needed, but are grad- ually coming into use to a limited extent. 346 PRACTICAL MARINE ENGINEERING Sec. 38. OTHER TURBINES Some of the more noted turbines, also used for propulsion of ships, are the Zoelly, Ra- teau, Melms-Pfenninger and Westinghouse. The first named are par- tial admission impulse tur- bines, the Zoelly turbine hav- ing two velocity stages in each pressure stage, while the Rateau machine, Fig. 231, has one velocity stage in each pressure stage in the high pressure zone. In the low pressure zone the compound impulse - reaction system is used, the drum construction being here incorporated. The Melms - Pfenninger turbine consists of a partial admission high pressure im- pulse zone. With this system the steam inlets in the guide blades are not continuous, but they are distributed in sec- tions around the circumfer- ence. The clear circumferen- tial length between the sta- tionary vanes is accordingly reduced, which admits of longer blades being used, with less loss from clearance. The first reaction stage in the middle zone connects at the end of the impulse stage with a drum of smaller diam- eter. The end thrust on the offset forms an effectual means for balancing the rotor. The middle and low pressure zones are of Parsons turbine type; but, owing to the impulse rf « MARINE ENGINE DETAILS 347 action being used in the high pressure end, a shorter turbine is rendered. The Westinghouse marine turbine, Fig. 232, is constructed for high rotational speeds and intended to be used in connection with speed-reducing gears, which have a speed ratio high enough to give a low propeller speed. In this turbine all pipe connections Fig. 232. Westinghouse Marine Turbine are made on the lower casing, whereby it becomes possible to re- move the upper casing for examination without breaking joints. Sec 39. GENERAL DETAILS [i] Line Thrust and Propeller Shafts From the crank or main driving shaft the motion is carried Fig. 233. Detail of Flange Coupling and Bolt on to the propeller by means of a number of lengths or sections of shafting according to the distance from the engine to the stern of the ship. Of these sections, the one to which the propeller is at- 348 PRACTICAL MARINE ENGINEERING tached is known as the propeller shaft. One length must also be specially fitted to transmit the forward thrust of the propeller to the thrust bearing and thence to the ship. This section is known as the thrust shaft. Other intermediate lengths form the line shafting. These various lengths, with the exception noted below, are usually connected by flange couplings, as in Fig. 233, The Fig. 234. Flexible Coupling coupling from the engine to the next section of shafting aft in the^ case of reciprocating engines is occasionally made of such form as to allow a certain degree of flexibility between the line shafting and the crank shaft. A form of such coupling is shown in Fig. Marint £nginMrtng PROPELLER BOSS Fig. 235. Outboard Shaft for Twin Screw Ship 234. One of the coupling flanges is faced off, as shown, like the segment of a sphere, with a ball and socket joint at the center to keep the two parts in line. The coupling bolts are then set up with nuts bearing on some form of spring washer which will take up the slack as the shaft revolves, even when not exactly in line. MARINE ENGINE DETAILS 34^ The action of the coupling will be readily seen from a study of the figure. The thrust shaft will more naturally find its description with the thrust bearing. See [2]. In single screw vessels, the propeller shaft and stern tube shaft are in one. The propeller shaft is formed with the after end tapered and fitted with screw thread for a nut, as shown in Fig. 235c. The propeller is fitted with a corresponding taper, and is held in place by a nut and prevented from turning on the shaft by one or more keys, as indicated in the figure. In the case of twin screws, where the propeller shafts are outside the skin of the ship some distance forward of the stern. MariTU Snginterinif SECTION ON 0-D Fig. 236. Detail of Socket Coupling it is usual to form the stern tube and propeller shaft as two dis- tinct shafts, coupled together by couplings "of the muft, clamp or socket type. In all cases it is necessary to form one end of the section of shaft which passes through the skin of the ship with a plain end, so that it can be passed through the outboard bear- ing as described in [2]. In cases, therefore, where the propeller cannot be attached directly to the plain end, as in single screw ships, it becomes necessary to provide a; special form of socket coupling connecting the after pud of the last inboard length of shafting vvith the forward end of the length which passes through the ship. The general plan ^of .'this af rangenleht is shown in Fig. 23Sb, and the details of the coupling in Fig. 236. Such couplings vary somewhat in detail, but the form shown in the figure will serve to illustrate the type. It consists, as shown, of the enlarged end of the inboard shaft, in which is bored out a tapering socket of appropriate size to take the tapered forward end of the first outboard length of shaft. The two are then secured together by. keys and locking ring, as shown in the figure. 350 PRACTICAL MARINE ENGINEERING [2] Bearings The various types and forms of bearing and bearing surface to be found in marine engines may be conveniently examined under one heading. ( I ) Crosshead and Guides. The stationary part of this bear- ing has been already referred to in Sec. 35, and as there noted is usually of a hard and fine grained cast iron. The moving surface on the crosshead is usually of brass, bearing-bronze or wrhite metal. When of brass or bronze, it is in the form of 'a bearing piece secured to the crosshead, as shown in Fig. 214. When of white metal, a suitable slab of brass, cast iron or cast steel, with shallow pockets formed in its surface, forms the bearing piece. SECTION TNROUGH A-B SECTION THROUGH C-D Fig. 237. Main Pillow Block, Cap These pockets have slightly overhanging edges, and into them molten white metal is run, the general layout and arrangement being similar to that for the main pillow block bearings shown in Fig. 238. The wliite metal is then machined down to a bear- ing surface, in some cases being hammered with a round pehe hammer in order to compress or harden the metal. The spaces between the pockets thus become spaces between the sections of white metal, and serve for the circulation and supply of oil to all parts of the bearing surface. In some cases shallow channels or oil grooves are cut in the guide surface or stationary part a? well, but this is the least necessary with the arrangement of white metal as described. MARINE ENGINE DETAILS 351. Liners of packing pieces are often placed between the bearing piece and the crosshead, so as to allow for adjustment and take up in case of wear. (2) Crosshead Pins. The general arrangement for the bear- ings are indicated in Figs, 217, 220, 221. The crosshead pins are steel, and the bearing surface is brass, bronze or white metal. The bearing pieces are two in number, forming between them the hollow cylindrical bearing, and are held in place by steel caps as shown. From the fact that in former practice such bearing pieces were almost universally made of some grade of brass, they are still usually known as brasses. r SECTION ON C-D ' SECTION OX A-B Fig. 238. Main Pillow Block Bearing When white metal is used it may be fitted in the same gen- eral manner « above described for the crosshead slides, or in some cases, especially for small surfaces, the white metal sec- tions are turned down until a continuous bearing surface is ob- tained on both white' metal and brass. For the distribution of oil, grooves or channels are then cut to serve in place of the chan- nels between the sections of white metal, as in Fig. 238. (3) Crank Pin. The usual arrangement of this bearing is sufficiently shown in Figs. 220, 221. In modern practice the material used is commonly white metal in a brass backing or- bearing piece, as already described. In older practice, brass or bronze was commonly employed. 352 PRACTICAL MARINE ENGINEERING (4) Pillow Block or Crank Shaft Bearings. The usual ar- rangements are shown in Figs. 204, 237, 238. Here likewise in modern practice the usual surface is white metal in a brass backing piece. In all bearings for cylindrical elements, as the crosshead pin, crank pin, crank shaft, etc., the two brasses are held from separating by a cap and bolts as shown, and from JSarint Enffinterinff .C Fig. 239. Plain or Spring Bearing pinching the pin or shaft too tightly by filling pieces or liners. These by adjustment allow of take up for wear. In modern practice the lower pillow block brass is often made in the form of a half cylinder, as shown in Fig. 238, so that by the removal of the cap and upper brass the lower one may be slid around the shaft and so removed for adjustment or repair, or a new brass replaced without disconnecting the crank shaft and lifting it from its bearings, as is necessary when the lower brasses are of the shape shown in Fig. 204. MARINE ENGINE DETAILS 353 (5) Line Shaft or Spring Bearings. In these bearings the chief load is the weight of the shaft, at least so long as the bear- ings and shaft are in line and adjustment. It is therefore quite common to provide for such bearings simply a lower brass or bearing piece, usually in modern practice of white metal backed by brass, or in some cases by cast iron or steel. A bearing cap or cover is then fitted, not in contact with the shaft, and serving simply to protect the bearing surface and to support grease cups or other lubricating arrangement. A bearing of this type is shown in Fig. 239. (6) Thrust Bearing. At this bearing the thrust coming from the propeller is taken ofif the shaft and transferred to the ship: The length of shafting which is specially fitted for this purpose is known as the thrust shaft. The special provision on the thrust shaft consists of a series of rings or collars, as shown \m mi Mxrina Snginuring Fig. 240. Thrust Shaft in Figs. 240-242, while the bearing of the type shown in Fig. 241 has a icorresponding series of channels into which the shaft rings enter when the thrust shaft is in place. The bearing thus comes on the forward faces of the shaft rings and after faces of the in- termediate bearing rings when the propeller is turning ahead, and vice versa when backing. The faces of the bearing rings are usually of white metal, thus giving a steel on white metal pair of surfaces. In order to take the weight of the thrust shaft, .a support of brass or white metal of the usual spring bearing forai, is usually provided at the forward and after ends of the bearing casing. The casing is furthermore commonly made in the fotrn. of a rectangular box, so that it can be filled with oil and thus flood the bearing With lubricant. Where the shaft passes through the ends of the casing, a stuffing box or form of pack- ing ring is providted to prevent the oil from leaking through. At the bottom of the casing a hollow space is often provided con- necting freely with the general oil receptacle above, and through •vhich a pipe of copper or thin brass is led back and forth. Through this pipe cold water is circulated for cooling down the 354 PRACTICAL MARINE ENGINEERING MARINE ENGINE DETAILS 355 oil, and thus absorbing the heat of the bearing. The base of the bearing is secured to the ship through a seating specially strength- ened and stiffened to take the thrust from the shaft and thus transfer it to the structure of the ship. In Fig. 242 is shown a bearing somewhat more modern in type and very commonly met with in present day practice. It is known as the horseshoe collar bearing. The shaft is fitted the same as in Fig. 241, but the bearing, instead of being fitted with series of fixed rings and intermediate channels, is provided with Fig. 243. 3tarin« Sngintirinf Detail of Horseshoe Collar Thrust Bearing a series of separate collars of the form shown in Fig. 243. These collars are provided with ears or lugs A and B, by means of which they are carried on side rods attached to the bearing casing, as shown in Fig. 242. These lugs in turn bear against adjusting nuts on the side rods as shown. In operation the thrust is trans- ferred from the shaft rings to the faces of the collars, thence through the lugs and nuts to the side rods, thence to the bearing casing, and thence to the ship. It is readily seen that this arrangement allows of the indi- vidual adjustment of each collar as may be required by wear, or, if need be, of its removal and replacement by a spare collar 356 PRACTICAL MARINE ENGINEERING MARINE ENGINE DETAILS 357 even when under way, and without interfering with the action of the other parts of the bearing. The collars are usually of cast steel, or, in some cases, of brass or bronze, and the bearing surface of white metal, carried in pockets, as explained above. The arrangement of the casing as a receptacle for oil, the provision for spring bearings at the ends, and the provision of circulating pipes for cooling water, are similar to those above described in connection with Fig. 241. Fig. 244 shows a thrust bearing of the horseshoe type as fitted for forced lubrication, the main difiference between this bearing and the ordinary oae of the type being in the lips ex- tending out from the horseshoes to prevent excessive throwing of oil, and the care that must be taken with casing joints and shaft stuffing boxes to prevent oil leakage. The. thrust bearing is variously located. In some cases it is placed immediately abaft the engine with its base connected directly to the engine bed plate. In other cases it is placed at the after end of the inboard shaft, or just forward of the after shaft alley bulkhead, and in others at some intermediate point. (7) Stern Bearing. The general arrangement of the stern bearing for a single screw ship is shown in Fig. 245. The entire distance through the stern of the ship from the stern post to the after bulkhead of the shaft alley is lined with a tube A B, usually of cast iron. Within this are placed brass tubes C D, each perhaps about one-third the total length. These bearing tubes are pro- vided with longitudinal channels slightly dovetailed in section, as shown in the figure, and into these are forced blocks of lignum vitae for a bearing. The arrangement is therefore somewhat similar to that for white metal, as described above, except that lignum vitae is substituted for white metal, and is placed in con- tinuous channels running the entire length of the bearing tube with intermediate spaces between. The shaft itself is cased with a brass sleeve or casing, so that the bearing surfaces are brass on lignum vitae. It is found by experience that water is a liibricant for such a pair of surfaces, and it is chiefly for this reason that lignum vitae is so commonly used as the material for the stationary part of the bearing. The brass sleeve, which preferably extends the whole length of that part of the shaft within the tube, also pro- tects the shaft from corrosion. This part of the shaft is known 3S8 BRACTICAL MARINE ENGINEERING either as the tail shaft or propeller shaft. It is usually made a little larger than the line shaft to provide for corrosion, and also for the more violent shocks to which it is subject. At the for- ward end of the tube A is fitted a stuffing box, through which the shaft passes to the after end of the shaft alley. At the after end of the tube the water enters freely through the spaces between the lignum vitae and flows forward, thus serving to cool and lubricate the bearing. At the forward end the stuffing box pre- vents leakage through into the ship. It is desirable, however, to fit a small pipe and cock so that water may be drawn from the tube as desired, in order to judge by. its temperature as to the condition of the bearing. Instead of a pipe and cock the stuffing box follower is sometimes loosened up so as to allow a sufficient leakage to insure circulation through the tube, and to serve as an index of the condition of the bearing. In some cases, instead of water lubrication, the after end of the stern tube is closed against the water, and the tube is filled Fig. 246. Stern Brackets with heavy oil or tallow. Or if desired a stand pipe may be run up to a sufficient height, so that when filled with oil it will pro- duce a pressure in the tube slightly greater than that of the water outside, and thus the leakage will be outward rather than inward. With oil lubrication the lignum vitae bearing surface is replaced by white metal. In small craft the steel shaft without casing is often fitted directly in a brass bushing or bearing. In such case oil lubri- MARINE ENGINE DETAILS 359 cation is to be preferred, but very commonly the bearing is left to run with such lubrication as the water can provide. This type of bearing should, however, never be used when the vessel is to serve in waters carrying much mud or sand. For twin screw ships, as shown in Fig. 235, the same gen- eral arrangement is used, except that the length of the tube where it passes through the skin of the ship is shorter, and fre- quently the lignum vitae bearing extends the entire length in- stead of over a part of the forward and after ends. A similar form of bearing is also provided in the shaft brackets or struts just forward of the stern post. The general form of such brackets TOP VIEW MtttintXitgiMtriiig LONGITUDINAL SECTION Fig. 247. Stern Bracket Bearing is shown in Fig. 246. On each side is a heavy steel casting secured firmly at top and bottom to the structure of the ship, and carrying at the apex a boss for the bearing, as shown in Fig. 247. This bearing is formed by a tube carrying lignum vitae strips as previously described, and in this way, with twin screws, the ex- treme after ends of the shafts are supported. Sec. 40. WESTERN RIVER BOAT PRACTICE The peculiar conditions existing on the western rivers of the United States have resulted in the development of a special type of boat and propelling machinery. In the early days of river navigation the raft was first employed, and then came the flat- boat, which has stood as the type of all later developments. On 360 PRACTICAL MARINE ENGINEERING the rivers where at certain seasons, of the year the water is shal- low, the current swift and the channel narrow and tortuous, the usual style of keel boat would be of small service, while the light draft flat bottom craft seems admirably adapted for navigation under such difificulties. Of the two varieties of boat, side wheel and stern wheel, the latter is preferred as on the whole the better suited to the all-around conditions of river navigation, and the flat bottomed stern wheel craft may to-day be considered as the typical boat for western river navigation. Indeed this type of boat has met ^ariiu Ungineering ^"^ Fig. 248. Western River Engine, Elevation and Section through Valve Chests - with much favor for river, navigation in all parts of the world, and especially in South America, where they are largely employed. The type of engine used on western river boats is shown in Figs. 248-250. It is horizontal and of the simple non-condensing type. Two such engines are usually employed, one on each side placed close to the guards, with the axis of the cylinder's fore and Fig. 249. Western River Engine. Top View aft, and with the connecting rods coupled to the cranks on the stern wheel paddle shaft. MARINE ENGINE DETAILS J6i The cylinders are of relatively small diameter and long stroke, the dimensions in a typical case being 24-inch diameter by 96-inch stroke. The most peculiar feature of the engine, however, is found in the valve gear. The valves themselves are usually of the double beat poppet form, as shown in Fig. 248, and each cylinder is provided with four, two for steam and two for exhaust. These valves are actuated by a cam valve gear mechanism, as briefly described below. The steam valves with their connecting pipes are located on one side of the cylinder, while the exhaust valves and con- nections are on the other side. Each set of valves is operated by separate rocking cams or levers, which receive their motion through rockers and connections from a special cam located on the main paddle shaft. The cam type of valve gear possesses peculiar advantages, especially for long stroke, slow revolution engines such as are used in these cases. The motion of the valve may thus be made intermittent, giving a quick opening and closure, with interme- ' Marine Engineering Fig. 250. Western River Engine, End View and Section Showing Valves diate periods of rest or very slow motion. It is also peculiarly adapted to the elastic movements of the boat during the process of loading, unloading, etc., movements which continually vary the distance between the rnain shift and rock shaft, and which, with almost any other type of gear, would introduce serious dis- turbance into the movement of the valve and the distribution of the steam. 362 PRACTICAL MARINE ENGINEERING For the operation of these valves in the common type of gear two cams are used ; one known as the full stroke cam and one as the cut-off cam, When the engine is in full gear the full stroke cam operates all four valves, raising one exhaust and one receiving valve at opposite ends of the cylinder at the same Fig. 251. Full Stroke Cam with Yoke moment, and alternately at each end, thus distributing the steam as required to carry the piston back and forth continuously. The one cam does all the work in the full gear motion of the engine both ahead and astern, and is hence in its neutral posi- Fig. 252. Full Stroke Cam tion when the crank is at its dead point. The cut-off cam is so arranged as to be hooked on after the full stroke cam has given headway to the boat, and is used in the go-ahead motion only. This cam is so designed that the steam is cut off at any desig- nated point in the stroke, as at >4,>^, %, etc. The form of a full stroke cam with its yoke is shown in MARINE ENGINE DETAILS 363 Fig. 251, and oi & % stroke cut-off c5m in partly dotted lines. In Fig. 252 is shown the usual type of construction of the full stroke cam, and in Fig. 253 similarly the ^ cut-off cam. With this arrangement of gear the exhaust is opened and closed just at the end of the stroke, and hence neither early ex- haust opening nor closure for cushion can be obtained. A means of obtaining the former has been found by blocking up the exhaust lifters somewhat, so that the valve will be slightly open when the engine is on the dead point. This insures an earlier opening of the exhaust and so clears the cylinder for the return stroke, but it gives likewise a later exhaust closure, so that with the engine on the center both ex- haust valves are slightly open, and in full gear operation a slight "blow through" will occur. This disappears, however, when the Fig. 253. Three Quarter Cut-off Cam cut-off cam is engaged, because the opening movement of the latter is much slower than that of the full stroke cam. Various modifications of this simple cam gear have been introduced with a view of improving the general operation, especially by the provision of means for obtaining both steam and exhaust lead and compression, as well as independent move- ments for the go-ahead and backing motions. In the Sweeney valve gear two full stroke cams are era- ployed, one for go ahead and one for backing, each set so as to give suitable exhaust lead and compression, while a separate cut-off cam is fitted for the go-ahead motion. The crossheads of these engines are usually of the locomo- tive type, Ayjth long brass gibs bearing on the top and bottom • guides. The connecting rods are commonly of wrought iron or wood, with iron or steel fittings, and form one of the most pecu- liar features of these engines. Wood is often thus preferred 364 PRACTICAL- MARINE ENGINEERING over metal because it seems to be better capable of standing the shocks and peculiar twisting strains which come upon the rod, and in spite of the strangeness of the combination, there is found in some modern boats a fluid compressed nickel steel paddle shaft with a wooden connecting rod. The rods are very long, fre- quently as much as eight times the crank, and the best rods are made of Oregon fir, reinforced with iron straps which are let into the body of the rod and through bolted. The ends of the rods are fitted with brass boxes with straps, gibs, keys, etc., in the usual manner of fitting up such form of rod, and as illus- trated in Fig. 222. In some cases of modern river boats on the Pacific Coast many changes have been introduced looking toward a closer approach to usual marine practice. In a typical example of such improved practice the engines are horizontal tandem compound, the high pressure cylinder having piston valves and the low pressure cylinder slide valves, both operated by eccentrics and link work in the usual way. In this case there are two engines developing about 1,500 indicated horsepower each. The cylinders are 22^ inches and 38^ inches diameter, with a stroke of 8 feet, and are intended to make thirty revolutions per minute. The crank shaft for such engines is built up in structure, the two cranks being separately forged and secured to the pad- dle shaft by shrinking and appropriate keys. The shaft is usually fitted with hexagonal bosses where the wheel flanges are to be secured. The latter are usually of cast iron, heavily ribbed and reinforced by wrought iron bands shrunk on their hubs and outer circumference. These flanges are fitted to the hexagonal bosses on the shaft, and are secured with suitable keys. They are provided on one face with sockets for the wheel arms, which are of wood. These latter are further strengthened by circular bands of iron bolted near the outer ends, and also by oblique bracing which is worked between them. The buckets are also of wood, 2-inch oak plank of suitable width and length being a standard material. They are secured to the wheel arms by special clamp bolts, and are so located relative to the draft of the boat as to be immersed only some 4 to 6 inches when the steamer is running light. In some cases the buckets are divided at the center, forming really two sets, staggered with reference to each other, and thus reducing the shock of the wheel as it enters the water. MARINE ENGINE DETAILS 36s [i] Doctor This peculiar feature . of western river practice as illus- trated in Fig. 254, is a combination of feed pump and feed water heater. As here shown, the doctor consists of a vertical beam Fig. 254. Western River Boat "Doctor" engine with crank and flywheel operating four pumps. Two of these are simple lift pumps drawing water from the river and delivering it into the heating chambers overhead, while the other two are feed pumps proper, taking their supply from the heaters and forcing the water into the main boilers. Each lift and force pump is designed of sufficient capacity to supply the entire battery of boilers, so that one of either kind may be dis- connected for examination or repair without disturbing the 366 PRACTICAL MARINE ENGINEERING regularity of boiler feed supply. The various parts of the ma- chine are erected on a deep cast iron base plate which contains various ports and passages, forming the water connections be- tween the various pumps. The suction pipe from the river is connected with a vacuum chamber, and communicates through a passage in the base cast- ing with the suction side of the lift pump. The discharge from these pumps is then led by other passages to the columns, which serve as discharge pipes, supports for the engine beam and for the heaters. Valves are also located in these columns, by closing which the water in the heaters may be prevented from returning at such times as it is necessary to open up a pump for examination or repair. The heaters themselves consist of wrought iron shells riv- eted to cast iron heads, through which the exhaust steam from the main engines is led on its way to the exhaust pipe. The ex- haust steam thus comes in direct contact with coils of copper pipe that lie in the lower part of the heaters, and through which the feed water is forced and finally discharged below a dia- phragm. Beyond this the exhaust steam and water are to some extent in direct contact, the latter being finally led down through the pair of columns on the opposite side of the machine to the feed pump inlet valves in the base plate. The head of water in the columns is thus sufficient to flood the valves and prevent the pump from missing stroke, even with the hottest feed water which the heaters can furnish. The lift pumps are fitted with long pistons having either cup leather or square gum packing, while the feed pumps are of the common plunger type. The pump valves are flat disks of brass made quite thick so as to avoid the need of springs, and also to allow metal for re-facing. The engine part of the doctor is very simple and will call for no special comment, consisting simply of a steam cylinder for actuating the beam and thus giv- ing motion to the four pumps as described. In some cases of recent river practice injectors have taken the place of the "doctor," and if they can be depended upon they are of course much preferable, being easy to handle and occupying little or no space otherwise valuable. While it is probable that they can thus be used to advantage on certain of the upper portions of the western rivers, it is hardly possible MARINE ENGINE DETAILS 367 368 PRACTICAL MARINE ENGINEERING e > <: (0 that they could be used at all in many other localities on ac- count of the sand and grit which is held in suspension by the water, and which would cut out the injector tubes so rapidly that their use would be out of the question. For this reason it seems likely that the "doctor" will hold its own in all such locali- ties and that it will continue to be an important detail of west- ern river practice. MARINE ENGINE DETAILS 369 Sec. 41. ENGINE FITTINGS [i] Throttle Valve The purpose of the throttle valve is to provide a means for quickly opening or closing the main steam pipe near where it connects with the high pressure valve chest, and thus to provide for the quick control of steam 'to the engine when stopping and starting. A great variety of valves have been employed for this purpose. The necessity for quick operation, especially by hand gear, requires usually some form of balanced valve, though in very small sizes an ordinary globe or straightway or gate valve, as shown in Figs. 260, 262, may be used. Of these the straight- way valve is much to be preferred, as when open it leaves prac- tically an unobstructed passage for the flow of the steam. (i) Gridiron Valve. The gridiron is another form of unbal- anced valve sometimes employed as a throttle. This valve, as Fig. 258. Griditon Valve Fig. 259. Double Beat Poppet Valve shown in Fig. 258, consists of a series of bars and ports corre- sponding to a like series in the valve chest, and giving a series of openings for the steam, wider or narrower according to the position of the valve. With such an arrangement a considerable area of opening may be obtained with a comparatively small movement of the valve, and a screw or some other form of. slow motion gear may be employed without loss of quick opening and closure. This f-orm of valve is, however, but rarely met with in modern practice and on account of friction is objectionable. (2) Double Beat Poppet. The double beat poppet valve, as shown in Fig. 259, has been much employed as a form of bal- anced throttle. The upper disk is slightly larger in area than the lower, so that if the live steam is on the outside the net load on the valve is that due to the difference of the two areas, and this mav be made very small. The resistance to opening is thus no 370 PRACTICAL MARINE ENGINEERING more than can be readily overcome with a direct hand gear, as, for example, a simple lever or other like arrangement. The chief difficulty with this valve is in keeping it tight, var- iations of temperature and the consequent expansions and con- tractions often tending to slightly unseat one disk or the other. (3) Butterfly Valve. The butterfly valve has also been widely used as a balanced throttle. It consists of a disk of ellip- tical form carried on a spindle and swinging within a cylindrical casing. When closed it rests obliquely on the inner surface of the casing, thus closing the passage around its outer circumfer- ence. When full open it swings into a position with its plane lying along the pipe, thus leaving the passage nearly free for the flow of steam. This form of valve is quite perfectly balanced, but it is difficult to keep tight. If the angle of obliquity with the surface of the casing is too small, it may also be liable to stick fast, due to unequal expansion of the valve and casing. In an- other form of butterfly valve, as shown in Fig. 260, however, the ilarine Enginevrfng Fig. 260. Combined Stop and Throttle with Balance Piston disk is circular and when closed swings square across the line of flow, just fitting within a corresponding ridge of the casing. In such case the diameter of the opening must be made enough larger than that of the disk to avoid the danger of striking, and considerable leakage will usually result. (4) Disk Valve With Balance Piston. A plain disk with balance piston attached to the stem is quite commonly employed in modern practice for the throttle or for the stop and throttle MARINE ENGINE DETAILS 371 combined. Such an arrangement in combination with a butterfly valve is shown in Fig. 260. By this means the pressure on the piston nearly balances the load on the valve, and it may thus be operated by hand gear. Steam may also be admitted back of the piston by a pipe with stop valve operated from the working Fig. 261. Globe Valve platform. By this means the disk may be balanced when once off the seat, and closure effected as easily as opening. (5) Power Operated Throttle. In some cases with large en- gines the throttle is operated by steam power instead of by hand, steam being admitted tO' an operating cylinder by means of a hand lever or other like arrangement. Here the steam acts upon an auxiliary piston and by suitable connections produces the move- ment of the throttle as desired. In such cases the connections are often of the "floating lever" type, as in the reversing gear described in [5,] so that the valve will follow the hand lever in 372 PRACTICAL MARINE ENGINEERING its movements back and forth, and the combination becomes thus equivalent to a direct operation of the throttle by hand. When the throttle takes the form of a plain disk with bal- ance piston, as in Fig. 260, no additional stop is thought necessary, and such an arrangement is often known as a combined stop and throttle valve. In such case, however, a screw stem may be pro- vided with connections for bringing it into use when closing the valve down as a stop. [2] Main Stop Valve The throttle valve from its construction can rarely be closed sufficiently tight to prevent leakage of steam, often considerable in amount. To provide a shut-ofif without sensible leakage a stop valve is often fitted in addition. Such valves may be of vari- ous types, as shown in Figs. 261, 262, 263. • (i) Globe Valve. This valve, as shown in Fig. 261, consists of a metal chamber of globular or spherical form with flanges for connecting to the line of piping. Within the body is a partition separating the portions connected with the two openings, and in this partition is a hole with conical seat upon which the valve with corresponding conical face bottoms when closed. The valve is attached to a threaded spindle which works in a nut either formed in the neck which contains the stem, or carried outside on a girder supported by stud bolts, as shown in the figure. To the end of the stem a handle is attached, and by this means the valve is opened or closed as desired. The stem is packed by means of a stuffing box and soft packing compressed by a gland of the usual form as shown. In small sizes the gland is usually replaced by a form of nut threaded to the neck, which contains the stem, and compressing the packing between the nut and the bottom of the packing space. (2) Angle Valve. In this type of valve, which is an angle or elbow and a valve combined, the seat and valve face, as shown in Fig. 262, are placed square across one of the openings, thus shutting off all flow through it when the valve is closed. When the valve is opened, however, the passage is left free, according to the degree of opening, for the flow of the liquid or vapor around the angle and on into the following section of pipe. When the stop valve is of the disk form it is very commonly of the angle type and arranged to go in at a turn of the pipe, as MARINE ENGINE DETAILS 373 shown in Fig. 262. In this case also the valve is attached to a bulkhead and the arrangement will serve to show the method of carrying steam through a bulkhead and of making up the joints connecting together the steam pipe, the stop valve and the bulk- head plate. (3) Straightway' or Gate Valves. In this form of valve, which is shown in Fig. 263, the moving part consists of a special r -1— ' ■ ' ' — I y — I . V JUaiynt -UnffintaHng Fig. 262. Angle Stop Valve form of slide which is moved by a screw back and forth across the opening of the pipe. There are various special fofms and de- vices for securing tight contact between the valve and its seat when closed, and thus making the valve tight under steam pres- sure. The general arrangement of Fig. 263 will, however, serve to show the main features of valves of this type. When closed and with pressure on one side of the slide only, there is some- times some difficulty in opening the valve. To relieve this con- dition a small by-pass, as shown, is often fitted. This admits steam to the farther side of the valve, thus balancing the load and making the operation of opening much easier. In another form the valve slide is made of two parts, hinged together and 374 PRACTICAL MARINE ENGINEERING with the end of the spindle working between them in such way that when screwed hard down it is forced as a wedge between the two parts, thus forcing them against their seats. When the handle is turned in the reverse way the first action is to partly withdraw the stem from between the two parts of the slide, thus easing them from their seats and allowing them to be readily withdrawn as the stem is turned farther back. Large gate valves are usually made with renewal seats to assist in repairing. Jffarin* Snginttring SECTIONAL ELEVATION Fig, 263, Gate Valve SECTIONAL PLAN SHOWING BY-PASS [3] Arrangement of Throttle and Maneuvering Valves for Turbine Engines The working platform usually is immediately abaft the for- ward engine room bulkhead, upon which are located all the valves and other operating gear, such as gages, counters, telegraphs, etc. Composing the group of turbine operating valves (Fig. 264) are the angle, main steam stop valves, one on each side ; the starboard valve admitting steam from one-half of the boilers, and the port valve from the remainder. Pipes from these valves lead to a MARINE ENGINE DETAILS 375 distributing casting located amidships, at the bottom of which is a balanced throttle valve. At the bottom of the throttle valve casting is a steam strainer with two branches for steam to the main high pressure turbine, with a globe stop valve for steam to the intermediate pressure cruising turbine on the starboard side, and a globe stop valve for steam to the high pressure cruising tur- bine on the port side, where such units are fitted. On the horizontal arms of the distributing casting are two combination double beat valves (Fig. 265) for steam direct to the Fig. 264. Arrangement of Valve Working Platform with Turbine Engines low pressure ahead and astern turbines, these valves being used for maneuvering; the valve stems being actuated by a doub'e- ended lever controlled by springs, and so arranged that when one valve is opened the other is closed. One valve of the combination is for steam to the low pressure astern turbines and the other is for steam to low pressure ahead turbines. By turning the maneuvering valve hand wheel to the right the ahead valve is closed and the astern one is opened, thereby admitting steam to the low pressure astern turbine, the operation, of course, being vice versa for going ahead. All valves and castings are composition and all piping is of seamless drawn steel, with rolled steel flanges. 376 PRACTICAL MARINE ENGINEERING [4] Cylinder Drain Gear and Relief Valves A certain amount of water is likely to collect in the steam cjiests and cylinders, either carried in with or condensed from the entering steam, especially when warming up the engine pre- paratory to getting under way. Provision must be made for Fig. 265. Section Tlirough Maneuvering Valves for Turbine Engines getting rid of this water as occasion may require, and to this end the so-called cylinder drains and relief valves are fitted. The drains are usually plain cocks piped up and connected to the parts to be drained, and with the valve stems connected by levers and bell cranks to operating handles at the starting platform. The drains in the bottom of the cylinder or valve chest will naturally be placed at the lowest point at which water can collect. MARINE ENGINE DETAILS 377 or as near to such point as is practicable. Those in the upper end of the cylinder will be placed at such a height that the opening will not be covered by the piston when at the top of the stroke. For small engines, auxiliaries, pumps, etc., the drain valves are often plain globe valves piped into the cylinder at convenient points, and operated independently by hand. The discharge of the drains is piped away either into the bilge, or into a fresh water collecting tank. In addition to such gear, which is operated by hand, and when judgment may call for its use, it is necessary to provide automatic relief valves for the discharge of water in larger quan- tities should it find its way into the cylinder by priming or in other ways. Such a relief valve is in the form of a safety valve, and may be set to open at any pressure desired. Such valves are sometimes connected up with operating levers, also led to the starting platform, so that they may be operated by hand from that point. In such cases only the one set of valves is often fitted, automatic when necessary, and under hand control when desired. In some cases with large engines a double set of auto- matic relief valves is furnished, a pair of large valves not under hand control, and a smaller pair under hand control, as described above. [s] Starting Valves In order to assist in starting the engine, especially if the high pressure piston happens to be on or near the center, a valve and pipe are usually provided for admitting steam direct from the steam pipe or high pressure valve chest, to the first receiver, or intermediate pressure valve chest. This will give sufficient load on the intermediate pressure piston to start the engine, and carry the high pressure piston off the center, and thus give the engine a chance to start in the regular way. In case the high pressure and intermediate pressure cranks should be opposite, and thus both pistons on or near the center at the same time, the auxiliary pipe will lead to the second intermediate piston, or to the first cylinder, whose piston is not on the center with the high pressure. In some cases the passage of the steam to the next cylinder beyond the high pressure is effected by the open- ing of a valve connecting the steam and exhaust sides of the high pressure valve chest. Such valve being opened, the steam finds its way directly to the point where it is needed. 3?8 PRACTICAL MARINE ENGINEERING Valves for this general purpose are variously called pass- over, or starting valves, or monkey tails. They are either in tht form of a cock or of a small slide valve, in either case admitting of full opening by a single short stroke of a convenient hand lever, to which they are connected by suitable rods and con- nections, or they may be simple globe valves with stems extended to the working platform of the engine. [6] Reversing Gear The various lengths of a Stephenson valve gear are con- nected by side or bridle rods to arms on the rock or "weigh" shaft. To reverse or link up with such a gear, therefore, it becomes necessary to provide some means for turning this shaft back and forth, and for holding it under complete control at any positiion desired. The form of reverse gear most commonly employed in Fig. 266. Floating Lever Reverse Gear American practice is of the so-called "floating lever" type, and is illustrated in Fig. 266. It consists of a cylinder, AB, with piston and rod, D, con- nected by a link from £ to an arm on the engine rock shaft, and thus connecting with the links. As the piston is moved back and forth by the steam this arm will evidently be carried with it, and the various Stephenson links, or like parts of other types of valve gear, will be moved as desired, each through its connection with the rock shaft. The steam to the cylinder, AB, is controlled by a slide valve, V, either plain or of the piston type. This valve has very small lap, so that from the position when covering both parts but slight move- MARINE ENGINE DETAILS 379 ment is needed to uncover. To the stem of the valve is attached a link, LI, which at the latter point is joined to a bar, KH. The lower end, H, of this bar is attached to a lug, Q, on the piston rod, and, therefore, moves with the piston. The upper end, K, is connected through a link, KN, to a hand lever, which is pro- vided with means for clamping in any position desired. Suppose now the gear in the position shown and with the valve covering both ports. Let the hand lever be moved so as to throw KN to the left. For the moment H will be a fixed center, and with the connections shown the valve will be moved to the left also. With this arrangement of connections an in- side edge admission valve must be used, and, therefore, steam will be admitted to the left-hand end of the cylinder, AB, and the pis- ton forced to the right. Let the hand lever, carrying with it the valve, be thus moved over a certain distance and then held or clamped there, thus fixing. NK. The point, K, will thus become for the time a fixed center, and the movement of H to the right will carry the valve in the same direction, and thus finally close the ports, shutting off the supply of steam at one end and closing the exhaust at the other. The movement of the piston will thus be stopped and the gear will be held in the position reached. It is clear that for every position of the hand lever there will thus be some corresponding position of the piston, rock shaft arm and main valve gear, for which the admission valve will be brought to mid position and the gear thus brought to rest, and that the steam will carry the gear to this position and then automatically shut off and stop. If the hand lever is moved but slightly so as to barely displace the valve, the piston will move but a small dis- tance before again covering the ports and coming to rest. If the handle be moved to an extreme position the valve will be moved far over and the steam will rush the piston and gear over into the extreme corresponding position. In short, the position of the gear for equilibrium under steam will correspond exactly to that of the hand lever, and wherever the latter may be placed, the gear will run to the cprresponding position and then stop. It is also clear that if the hand lever be moved slowly, the piston and main links will follow along at equal pace, stopping when the handle is stopped and moving when it moves. Also if the handle be slightly displaced and left to itself the fric- tion of moving the valve will be usually more than that of mov- 38o PRACTICAL MARINE ENGINEERING ing the handle, and in consequence the point, I, will become for the time a fixed center, and the piston will move along, the valve remaining open and in connection, HKN, moving the handle over at equal pace with the link. This will continue till the handle comes against a stop at the end of its path. The point, K, will then become fixed, and the further movement of the j?isf:on will move the valve into mid-position, thus shutting off st^alm and bringing the gear to rest in the position corresponding fd Ihat of the hand lever. To take up sudden shocks and provide a safeguard against putting the link over too rapidly and thus overrunning at the end through the inertia of the parts, spring stops or buffers, R, are provided on a rod, S, against which the lug, Q, comes at the end of its run. It is thus seen that this gear furnishes a very perfect con- trol over the main valve gear, the action being the same as for a man operating the gear directly, and thus giving him readiness of control with the least mental effort, and the least liability of error in a moment of hurry or excitement. In addition to the spring buffers, as shown in Fig. 266, a form of plunger control is sometimes added. In this arrange- ment the piston rod of the reverse cylinder is continued back- ward and connected to a second piston or plunger working in a cylinder filled with oil. The operation of the plunger is to trans- fer the oil through a suitable pipe connection from one end of the cylinder to the other, and as this passage may be throttled at will by a stop valve, all possibility of slamming or of violent motion may be removed. A further advantage of this arrange- ment lies in the fact that with suitable pipe connections to a hand pump, the oil may be drawn from one side of the plunger and forced in on the other, thus giving a control over the valve gear by hand power in case of derangement of the power con- trol. Oi other forms of reverse gear the so-called all around gear is quite commonly met with in English practice. The main links are connected up to a small engine which makes a large number of revolutions in running the link over from one extreme to the other. This engine is under the control of a small link which is directly operated by hand. A form of lever stop is usually provided which will either reverse or middle the small MARINE ENGINE DETAILS 381 link and bring the engine to rest when the main links have reached either extreme of their travel. In engines for small yachts, launches, etc., the links are placed directly under the coi^trol of a hand lever. The various other types of valve gear may be operated by any of the forms of reverse gear described. With all valve gears, the reversing is effected by the movement of some piece of the gear from one positi9n or location to another, and so back and forth for the various degrees of linking up, etc. By suitably con- necting such piece to the power reverse gear the control may, therefore, be obtained in the same manner as for the Stephenson link as described above. [7] Turning Gear It is always necessary to provide some means for turning the engine other than by its own power. This is necessary for moving the engine when in port for adjustment of bearings, set- ting of valves, etc. The turning gear usually consists of a large worm wheel placed on the main shaft, geared down through worm and spur gearing to a small engine, usually a double simple engine with cranks at 90 degrees, or to an electric motor. The gearing ratio is such that many hundred revolutions of the turning en- gine may be required to one of the turning wheel or main en- gine shaft. This gear must be so arranged as to be readily thrown in and out of connection with the main turning wheel. This is usually accomplished by carrying the main worm on a shaft which is pivoted, and which can thus be locked in either of two positions, in one of which the worm is in gear, and in the other out of gear, or else by driving the worm on a shaft with a feather, thus providing for endwise motion, and for fix- ing it in either of two locations on its shaft, in one of which it is in gear and in the other out of gear. The latter is the arrangement more commonly met with. When a turning engine is not provided the turning wheel is usually arranged for operation by hand through worm gear- ing operated by a lever with pawl and ratchet arrangement, or by some similar device. In some cases the engine is turned by a hydraulic jack placed under a movable chock piece located; in sockets cast in the turning wheel. This chock is shifted from one socket to an- other as the jack shoves it upward, and thus \\i^ engine is slowly 382 PRACTICAL MARINE ENGINEERING In small engines the turning wheel is often simply a form of gear wheel with shallow teeth in which a pinch bar is worked, and by this means the engine may be slowly pried around. Such a wheel is known as a pinch wheel. [8] Joints and Packing The joints to be considered under this head are of two kinds, (i) Fixed joints as those between a cylinder or valve chest cover and flange, and (2) sHding or slip joints as those be- tween a piston rod and the stuffing box, or the slip joint in a length of steam piping. For making up stationary joints a great variety of packings are in use, the difference depending to some extent upon the temperature to which the joint is to be subjected. Thus for joints to stand high temperature, as with boiler manholes, cylinder heads, etc., sheet abestos either plain or in combination with other materials is used, but gaskets of plain, sheet asbestos must never be used where they would be subjected to the direct action of water, as they soften and blow out. There are also various kinds of packing in which rubber in one form or another is used either in combination with some fibrous material as sheet canvas, or as a constituent of some form of compound. The tendency, of I rubber by itself is to grow dry, hard and brittle, especially under the action of heat, and the purpose of the modern forms of rubber compound is to avoid this tendency, at the same time retaining its elasticity and joint making qualities. For joints not subject to 'action of high . temperature, similar forms of packing are used, though with a greater proportion of rubber, if desired. The strip or ring of packing which is cut out and fitted for the joint is called a gasket. In making up such* a joint it is well, to smear the surfaces of the gasket with a mixture .of black lead and grease or oil. This will, aid somewhat inVi^aking the joint> and very much in the removal of the cover and, gasket; at a later time withotit tear- ing the latter. With such precaution and", when the temperature is not high the same gasket may! be used several times over with- out loss of its joint, niaking/ qualities. In addition to gaskets made of such materials as described above, joints are also made with gaskets of corrugated sheet MARINE ENGINE DETAILS 383 copper, or of plain copper wire. For high pressures such gas- kets have proved quite successful. The soft copper is expanded between the harder metals of the flanges, and spreads, filling the surfaces where it touches, thus making a tight joint. For sliding joints as between a piston rod and stuffing box, the greatest variety of packings is likewise in use. They mav Marine Engintv^^^ Fig. 267. Plain Stuffing Box De broadly divided, however, into the two classes, fibrous and metallic. The fibrous packings are made of the same material as the sheet packings above described, and are either round, square or triangular in section. For use they are cut to such lengths as may be necessary and placed in the stuffing box in layers or turns, the joints between the ends being shifted so as not to come one above another. The stuffing box, as shown in section in Fig. 267, consists of a cylindrical chamber or box, EF, with cavity B. This is bolted by means of the flange, F, to the lower cylinder head. The part, CC, is known as the gland or follower ^84 PRACTICAL MARINE ENGINEERING and is carried by two or more studs, as shown. At the bottom or upper end of the box is a ring, as shown, just filhng in the space between the opening in the box and the piston rod. Fre- quently this ring is omitted and the metal of the box fits about the rod. The packing is placed in the box as described above, thus filling the space, BB, between the bottom of the box and the gland. The packing may then be compressed as desired and V ^ _ netring Fig. 268. Metallic Packing as may be necessary by means of the nuts on the stud bolts, thus forcing the gland down on the packing and making the joint tight. This is the general type of all such joints made with compressible packing, with, of course, variation in details. Joints of this character are used for piston and plunger rods, slide valve stems, globe and disk valve stems, joints about the shaft where it goes through a watertight bulkhead, joint in the thrust bearing casing, in slip and expansion joints, etc., etc. For metallic packing with joints of this character the form MARINE ENGINE DETAILS 3»S of the box is in general the same. In fact, in some cases, the box is so made that either soft or metaUic packing may be used. Here again the greatest variety in detail is to be found, but a single instance will serve to illustrate the essential features of such packing. In Fig. 268 is shown an example of metallic packing. The box or casing contains at its bottom, or upper end in the cut, a spiral spring, as shown. Next comes a brass ring, and next a series of babbitt or white metal rings carried in a casing or shell, as shown. These rings are conical on the outer circumference, and fit to a corresponding form of the containing shell. Next below is a second brass ring which supports the shell above, the joint between the two being ground to a tight fit. This ring rests on a casing below, the joint between the two being spherical and ground to a fit. The latter casing contains another spiral spring and then follows another series of rings, etc., similar to these above. The whole box contains, therefore, two similar sets of packing elements, each consisting of a spiral spring, white metal rings, containing shell, etc. Each of the white metal rings consists of two separate halves, the whole arranged so as to break joints from one ring to the next. It is readily seen that the action of the spring is to crowd the white metal pack- ing rings into the conical shell and hence against the rod, thus keeping the joint tight between the two. It is further seen that with this way of carrying the packing the latter is entirely un- constrained laterally, and may move in any way to accommodate itself to any slight irregularity in the rod without danger of dis- turbing the tightness of the joint. The two series of packing, as a whole, are held up into place by an outer ring, secured to the cylinder head by stud bolts. The joint between the packing sys- tems and the cylinder is made by a ring of copper wire, as shown, thus shutting ofif the leakage of steam from the packing space in this direction, while the various ground joints and pack- ing "ring- surfaces close it off in other directions. Among the various conditions which an ideal packing for piston and valve rods should fulfill those of chief importance may be stated as follows : (i) The packing should make a steam tight joint between rod and stuffing box, at the same time opposing the minimum frictiopal resistance to the modon of the former. 386 PRACTICAL MARINE ENGINEERING (2) It must be durable even under the temperature of mod- ern high pressure steam, and also easily removed or replaced with new when necessary. (3) The packing should be free to move about transversely to a sufificient extent to follow the rod, even if it is slightly bent or out of line, at the same time maintaining the joints steam tight between the rod and the packing, and between the packing and the stuffing box. Requirement (3) has given the greatest trouble and has led to many varieties of design intended to cover the point, one of which is illustrated as above in Fig. 268. No packing can be considered satisfactory for modern requirements which does not possess in good degree the qualities detailed above. [9] Reheaters A reheater is a collection of pipes placed in a receiver or ex- haust passage from one cylinder to the next. Within these pipes high pressure steam is circulated, and around them the exhaust steam passes. The high pressure steam will, therefore, give up its heat to the cooler exhaust steam, and thus tend to dry or even to superheat it as it passes on into the next cylinder beyond. The office of the reheater is, therefore, to exercise a drying and heating action on the exhatist steam as it passes from one cylinder to another in a multiple expansion engine. Under most condi- tions this will exert a beneficial influence on the economy of the engine by decreasing the amount of cylinder condensation, and to such action may be referred the benefit which the reheater seems to give. [10] Governors In order to control the revolutions of the engine and to prevent violent increasing or racing when the propeller is par- tially lifted out of the water by the pitching of the ship, some form of governor is frequently fitted. The early types of marine engine were usually governed by hand at the throttle, which was commonly of the butterfly variety, though occasionally auto- matic means of moving the valve were employed. With modern multiple expansion engines, however, it is impossible to satis- •factorily control the revolutions by the throttle. With such engines the control must come from the slide valve gear, the links of which may be linked up more or less, as required when the propeller is uncovered, and linked out again as it is sub- MARINE ENGINE DETAILS ^7 merged. Where no automatic governor is fitted, this must be done by hand control of the reversing gear. The modern auto- matic governor is intended to take the place of this hand con- trol. There are two modes of actuating marine governors. (i) By utiHzing the varying pressure under the stern. (2) By utilizing a variation in the revolutions from the reg- ular speed. In the first type a pipe is run from the outside water at the stern to some form of pressure chamber near the engine, within which is a flexible diaphragm held in position by a spring or other equivalent means. The water being admitted to this pipe, the air within is compressed according to the head of water over the outer end. The apparatus is so adjusted that at normal draft the diaphragm is in equilibrium between the two forces, due to the water pressure on the one side and the spring on the other. A change in the draft of the ship at the stern will cause a variation in the pressure which will be transmitted through the air and thus destroy the equilibrium, throwing the diaphragm in one direction or the other. This may be made to actuate a steam valve and thus through an auxiliary steam piston control the reversing lever, and through this the links. In former practice this type of gear was sometimes made sufficiently large to actuate the steam throttle directly, or sometimes a like valve in the exhaust pipe. The other type of governor is found in various forms. In many of them use is made of the centrifugal force of revolving balls or weights somewhat as in the ordinary stationary gover- nor. Through the force thus available a small valve is oper- ated, thus leading through a series of steps to the control of the reverse lever or other part which it is desired to operate. Again in other forms a revolving fan or propeller working in a box filled with liquid maintains the apparatus in a certain condition at a certain speed. With a sudden change of speed a corre- sponding change of resistance to the motion is met with, and this difference of force may be used to operate a small valve, and then, as before through the proper steps, the reversing lever is controlled. In another form a pump continually forces air into a chamber from which it escapes through a cock whose opening may be regulated at will. For a given size of outlet and speed 388 PRACTICAL MARINE ENGINEERING of pump the pressure will rise until finally as much escapes as enters and the pressure remains constant. If the speed changes, however, the pressure will change correspondingly, and this dif- ference of pressure will give a force which may be used as already explained. A still different type of gear operated by a change of speed but not driven by the use of a belt employs the forces due to inertia. As usually installed it consists of a weighted vertical rod pivoted at the top so that if unrestrained it could swing to and fro between a pair of stops. This weight with its point of suspension is then given a movement of reciprocation horizon- tally by attachment to any suitable part of the engine. If not prevented, it would therefore swing to and fro between the stops, due to the change in momentum imparted by the recipro- cating motion. It is, however, held by a spring against one of the stops, and the tension is so adjusted that movement will not result until the engine exceeds its normal speed, when the inertia forces overcome the spring, and the weight moves away from the stop. This motion, by means of an attached lever, may operate an auxiliary valve, piston, etc., and thus control the links. This type of governor is sometimes used only as a safety gear to quickly stop the engine in case of a breakage of the shaft or other accident permitting violent racing. In such case the gear is sometimes so arranged that the movement of the weight away from the stop will cause it to engage as a clutch with an arm or lever connected with the reverse lever,, and so adjusted that the motion given will just bring the links to the mid position. The instant the weight leaves the stop, therefore, the levers will be suddenly thrown over, the links middled and the engine stopped. All forms of marine governor are somewhat slow in con- trolling the variations of speed. The ideal governor would antici- pate the motion and close down or open up just in advance of the rise in speed. Instead of this they act only after the stern has risen or fallen, or after the change of speed has become more or less pronounced. It is considered good practice, however, to fit some form of governor, at least as an emergency control, so as to prevent an excessive increase of revolutions from any cause whatever. For this purpose only those forms which de- pend on a change of speed are suitable, and such are commonly fitted in modern practice. MARINE ENGINE DETAILS 389 [11] Counter Gear The revolutions of the engine are automatically registered by a counter of the common type, and consisting of a series of disks with numbers from o to 9 on their circumferences. The motion for the counter is taken from any reciprocating piece which has a convenient location and a motion of small range. This is connected up to the counter by appropriate links, bell cranks, etc. The motion operates directly on the disk to the right and moves it along one notch or figure for each revolution. As each disk reaches 9 it engages with the one of next higher order on the left and throws it over, thus carrying the count continuously along the disk from the first to the last. In this way the revolutions are registered one by one, the total number for any period of time being found by taking the difference of the two readings lor the beginning and end of this period. By this means the revolutions per minute, per hour, or per day are readily found as desired, [12] Engine Log System and Averaging Counters In both maneuvering and cruising of naval vessels the pri- mary requisite of keeping the position in line or column can be attained best when exact knowledge is had of the speed of the ship. Taking advantage of the uniform slip of propellers at any given speed, instruments to transfer automatically the revolutions of the propellers into distance traveled through the water have been developed. Such an installation has been fitted to the latest United States battleships and auxiliary vessels. This automatic method of indicating the speed and the revolutions promotes harmony between the engine room and the bridge, and does away with a great deal of trouble and with time consuming computations. It is no longer necessary to telephone down to the engine room for the revolutions of the engines, wait for the figure to be obtained, add up the totals for the several shafts and divide by the number of shafts, then divide again by the number of revolutions per mile to obtain the distance traveled, and then compute the speed. The distance is now worked out accurately and automatically every 100 turns of the, main engines and the revolutions per minute are given every 200 turns. The system is operated by the vacuum in the condensers or 390 PRACTICAL MARINE ENGINEERING by a small vacuum pum.p in such a way that connection between the condenser or pump and the instruments, in the chart house or conning tower, or on the bridge, is made every loo revolutions of the main engines. The indicator on the stop clock travels con- tinuously during the period between successive impulses and covers, therefore, the record of loo revolutions. This is trans- lated at once into revolutions per minute by means of the scale of reciprocals on the dial. In order to average up the revolutions of the shafts of ships driven by two, three or four propellers, an ingenious averaging counter is used which gives automatically and continuously the exact average of revolutions for the various propellers, instead of requiring this to be done manually, and at a definite cost in time. The valve controlling the connection between the con- denser and the instruments on the bridge is taken off from the averaged results, so that no corrections are necessary to the read- ings shown. To comply at the same time with naval requirements, which call for a continuous rotary counter, showing the total revolu- tions made by the engines, both ahead and astern, the con- nections to the averaging counter are provided with a "one- way gear," which runs the counter forwards, regardless of the direction of rotation of the shafts. In this way full credit is given on the counter for all motion of the engines, this item being needed in connection with the engineering competitions as between ships. The counter in the engine log moves up one unit for every loo revolutions of the engines. Two ciphers on the dial, as shown in Fig. 271, complete the reading. The little opening near the top, "Revolutions per knot," shows the revolutions required to make one nautical mile through the water at the desired speed. This figure m.ay be changed as the speed changes, by means of the knurled knob at the right. A change in this figure is carried, through an ingenious gearing device, to the clockwork operating the three hands, so that no matter what may be the number of revolutions required to make one nautical mile, the hands will travel a distance so proportioned to the revolutions, as shown near the bottom of the dial, that the distance covered in nautical miles and tenths of miles will be given accurately. The black hand, which in Fig. 271 points to 79, is carried MARINE ENGINE DETAILS 39' Fig. 269. Log Stand ^"^HiJiliL ^^M^^l^ F^^-fe^^ s^l K?^^^f. ^^^ Fig. 271. The Engine Log is both Revolution Counter and a Distance Indicator j^._ "^1 i 1. Fig. 270. Two-Shaft Averaging Counter (below) Connected to Electrically Controlled Course Indicator (at toil) Fig, 272. Direction Indicator by frictioh lipon the shaft of the main hand. This black hand, which is labeled "course," may be set at zero upon passing any buoy or mark, and will thus register the distance covered from any desired point. It may be set without interfering with the motion of the other hands, and, of course, shows distance traveled from any point, without the necessity for the usual calculations. This is of great vakie for navigating in a fog, or for covering any given distance on a certain course. 392 PRACTICAL MARINE ENGINEERING ■ Bridfo Fig. 273 This diagraiqmatic layout of the instruments indicates their relation to the pro- peller shafts and condensers, and shows a type plan of the system as applied to battleships and armored cruisers. Other vessels may be fitted with such portions of the system as requirements demand. By manipulating the three-way cock the revolutions per minute of each shaft or of the average of shafts will be indicated, at will of operator, on the stop clock. MARINE ENGINE DETAILS 393 The accuracy of this instrument (based upon the naviga- tor's abihty to estimate the revolutions required per mile) has, in actual tests, been found surprising. Shop tests at all different speeds, and lasting for nearly two months, failed to show any appreciable error. This is due, perhaps, to the very 'ittle work required of the parts, and to their slow movement and accurate register. The direction indicators are operated by means of pressure or vacuum produced by a small pump connected to each pro- peller shaft, as shown in the diagrammatic layout. For rota- tion in one direction the vanes within this pump produce a partial Fig. 274. Stop Clock. Located in En- gine Room, Chart House Conning Tower and on Bridge Fig. 275. Fbur-Sliaft Averaging Counter, Operated by Gears on Same Principle as Two-Shaft Counter vacuum resulting in throwing the pointer into the "ahead" posi- tion. When the direction of rotation of the shaft is reversed the vanes of the pump produce a definite pressure within the pipe leading to the indicator, thus throwing the pointer into the "astern" position. As soon as the shaft comes to rest the indi- cator returns to zero. The mechanism of the stop clock, Fig. 274, is similar to that of an ordinary stop watch. The vacuum in the connecting pipe drops the piston, thereby starting the hand. The vacuum in the pipe is broken when the rotary valve shuts off the condenser or pump connection, air then being admitted to the pipe, and the piston returned by a spring. As soon as the engines make 100 turns from time of starting the clock the pipe again opens to the condenser or pump, the piston descends and stops the clock. 394 PRACTICAL MARINE ENGINEERING The clock registers directly the number of revolutions per minute. The hand remains stationary for several seconds at the point where it was stopped, before being released and returned automatically to zero. The cycle is repeated every 200 revolu- tions, 100 being consumed in the motion of the hand and 100 in its reading and recovery. If the engines are making 200 revo- lutions per minute there will be an indication of the revolutions per minute once a minute. Stop clocks are usually fitted in both engine rooms, in addition to those in the chart house and else- where. An auxiliary dial around the circumference of the main dial on the stop clock is graduated in knots speeds, to fit each par- ticular ship. This can be altered when necessary, as, for in- stance, when the ship receives a new set of propellers, or some other change requires it. Another dial may be had for standard- ization purposes which carries, not the number of revolutions per minute, but the number of seconds and fifths of seconds, as in the ordinary stop watch. This dial and the one shown in the cut may be interchanged whenever it may be desirable to do so. An index may be clamped at the desired revolutions, indicating at a glance how nearly the engines are realizing what is required of them. The two shaft averaging counter, Fig. 270, contains three sets of counting wheels, one for the starboard revolutions, one for the port, and one for the average of the two. These are connected to the main shafts through a combination of gears and ratchets which divide the registering shaft always in one di- rection, regardless of the direction of rotation of the propeller shaft. By the introduction of this one way gear much trouble- some reciprocating motion in other types of counters has been eliminated. The use of gears in the averaging instruments does away with the errors inseparable from other methods of driving these counters. In addition to the averaging counters .this instrument, which is in the engine room, carries a dial for the revolutions per min- ute, operated by means of the knurled handle shown at the left. By keeping the teeth in contact for thirty seconds by the watch the record of revolutions per minute is shown. If more accurate results are required, or if it is desired to reduce the personal error in reading the watch, another gear may be thrown in and the MARINE ENGINE DETAILS 395 reading taken for five minutes, giving tiie average revolutions per minute over that period. This device permits the engineers to check up the revolutions per minute, independently of the instru- ments on the bridge. The auxiliary counter above the averaging counter, designed particularly for standardization of the propellers and for trial runs, contains two counting cylinders, A and B (Fig. 270). These are operated individually from the averaging counter be- low, one cylinder running while the other is stationary. This shows accurately the total "averaged" number, of revolutions for a given time or over a given distance. It is controlled electrically from the bridge or any other desired point. The observer on deck closes the circuit when the line is crossed, thus immediately starting the stationary counter and stopping the one which was running. When the circuit is again closed these operations are repeated. This instrument, especially useful in determining the revolutions for each period during a long run, enables the officer in charge to obtain an extremely accurate reading of the revolu- tions per minute, averaged over the period. It is fitted usually in one engine room only. On the bridge and in the conning tower of the latest U. S. naval ships are located indicator boxes for showing both the revo- lutions per minute and the speed of the ship in large figures visible from any position or distance at which the officer on duty may be. These "distance" indications are controlled by a quartermaster or other observer reading from the automatic revolution counter and stop clock in the same casing, and setting manually the large figures for the use of the commanding or other officer. At night these figures are illuminated by an incandescent light in the case, and at all times they are so arranged that the officer can see at a glance just what the engines and ship are doing. These are par- ticularly valuable in maneuvering vessels and in target practice. (See Fig. 269.) Should it be desired to print the readings of revolutions, the auxiliary counter already described may be fitted up for this purpose. This eliminates the possibility of error in making a reading. It has been found convenient to print the reading of a counter before going on a course on one side of the paper, and the reading after coming off on the other side. The differ- ence between the two will be the revolutions on the course. The 396 PRACTICAL MARINE ENGINEERING full record is thus on one piece of paper, which may be referred to at any time. This printing counter, designed for trial trip purposes only, is unnecessary for general use. The above refers mostly to twin screw ships, showing the averages of port and starboard propellers. For quadruple screw ships the same arrangement obtains except that there are more gears involved. One set averages the two shafts on the port side of the ship; another averages the two shafts on the starboard; the third averages these two averages. This device is illustrated (Fig. 275). The arrangei^nent for averaging the revolutions on a triple screw ship" is somewhat different in detail, but operates on the same general principles and gives the same dependable results. [13] Lagging The cylinders, cylinder heads, valve chests and covers are usually provided with some form of covering intended to prevent the loss of heat, and thus conduce to economy as well as render the engine less disagreeable to work near and about. Such cov- ering is known as lagging and consists usually of either wood in strips or-polished sheet brass or Russia iron, between which and the metal to be protected is placed the insulating material of magnesia, asbestos, or other non-conducting incombustible sub- stance. When of wood the strips are narrow, i to 2 inches in width, and often of alternate light and dark color to give a pleasing effect. They are usually matched together and secured by bands of brass or polished iron, or by brass headed screws taking into foundation pieces held in place by countersunk tap bolts. The cylinders of turbines are usually lagged with Russian or galvanized iron. [14] Lubrication and Oiling Gear (i) Lubricants. For the lubrication of the various rubbing surfaces and turning joints, except within the cylinder, use is made of vegetable, animal and the lubricating grades of mineral oil. Olive oil, cottonseed oil, peanut oil, castor oil, rape seed oil, whale oil, fish oil, neatsfoot oil and lard oil are all used to some extent, the more expensive combined with cheaper and poorer grades. For the lubrication of the internal surfaces nothing but the best mineral oil must be used. The grade commonly em- ployed is known as cylinder oil, and is heavy and viscid at ordi- nary temperatures, becoming qujte fluid, however, at the usual MARINE ENGINE DETAILS 397 temperatures of the steam. It is usually fed in by means of a sight feed lubricator. In addition to the liquid oils, various lubricating greases are used, often in combination with a certain proportion of graphite (black lead). Graphite alone or in combination with oil is also used, and its lubricating qualities are of the highest order. It seems to possess the property, especially with cast iron, of filling the pores of the iron, and of thus forming a kind of graphite metal skin on the surface, with a very small co-efficient of fric- tion. The place where the lubricant should be supplied to the bear- ing is a subject which has attracted considerable attention in the past few years. It seems now to be very well established that the following principles should govern: (a) The oil should always, where possible, be led into the bearing at a point which is under the smallest pressure. (b) The continuity of the oil film, where it is under the greatest pressure, should not be interrupted by oil channels or grooves. (c) The oil should be prevented, as far as possible, from escaping at those points which are under the greatest pressure. For journals such as main pillow blocks, etc., these princi- ples are very commonly violated, and in fact it can hardly be said that practice has as yet come to act upon them, though their correctness seems to have been well demonstrated. According to these principles the oil for the main pillow block bearings should be introduced near the division between the upper and lower brasses, and the oil scores or grooves in the metal of the bearing at the top and bottom should be omitted. Similarly for the crank pin and other cylindrical journals, the oil should be admitted at those points where there is the least pressure, and at the points where the pressure is greatest the .bearing surface should be smooth and not interrupted by grooves, or scores, or oil channels of any kind whatever. (2) Amount of Lubricant Required. As to the amount of oil to be used, practice differs widely, but from 5 to 8 pounds of oil per ton of coal may be taken as a fair allowance, or say from S to 8 pounds per 1,000 indicated horsepower per hour. In small sizes, for engines of the torpedo boat type, etc., the consumption will go up to considerably larger figures. 398 PRACTICAL MARINE ENGINEERING After a ship has been at sea for a few days and the machin- ery has settled into a steady running condition, the amount of internal lubricant may be gradually decreased uiitiL the only oil used for internal lubrication will be that which is carried into the cylinders by the piston rods. Particularly is this the case with vertical engines. With regard to the frequency of lubrication no definite rules can be given. The ideal system is, of course, as nearly con- tinuous as possible. Where, however, the continuous system is not in use and intermittent oiling must be depended on, the vari- ous joints and stuffing boxes will require attention and a fresh supply of lubricant at intervals of from perhaps twenty minutes to one hour. For the various pin and turning joints, main guides, etc., the lubricant is usually supplied by oil cups or cans of character suited to the particular use for which intended, while the piston and valve rods are lubricated by means of a swab charged with cylinder oil or special grease. The main guides are also in some cases lubricated by the swab rather than the can. With engines of the best type, especially where the steam is supplied by watertube boilers, and where the steam is always more or less moist, it is preferable to depend on water lubrica- tion for cylinder walls, and to avoid, so far as -possible, the use of internal lubricants. This end may be furthered by careful work- manship in the fitting up of valves and pistons, and by driving the engine by belt or otherwise in the erecting shop with the surfaces charged with graphite. The minute pores of the metal are thus filled with the graphite, and rubbing surfaces are developed which run very well without further lubrication. (3) Adjustment of Bearings. For a bearing in good adjust- ment the clearance or distance between the journal and bearing surface is proportioned to the size of the journal, and may be made about .002 or 1-5 of i percent of the diameter. With a lubricant of proper consistency and a load per square inch not too great, say not over 400 to 500 pounds per square inch of projected area, the film of oil will retain its place, and insure the proper lubrication of the bearing. If too thin a lubricant is used the bearing may heat and pound simply because the journal is not supported by the film of oil. The proper consistency of the oil as influenced by its natural viscosity and by the temperature MARINE ENGINE DETAILS 399 of the bearing may, therefore, determine to a considerable ex- tent the smooth running or pounding of the various joints and journals. DEVICES EMPLOYED FOR SUPPLYING LUBRICANT TO BEARINGS The more important devices for supplying oil and grease to the bearings, or to the points where required, are : (4) Wkk Cup. The plain wick cup consists of a receptacle, usually of cast brass, fitted with a cover, and placed at a conven- ient point for the delivery of the oil to the bearing. It is also frequently fonned as a part of the bearing cap, as in Fig. 239. Fig. 276. Wiper Fig. 277. Oil Cup witli Adjustable Feed A tube, as shown, enters through the bottom of the oil reservoir and rises within to a point above the level at which it is expected to carry the oil. This tube leads downward to the duct which carries the oil to the point of delivery to the bearing. The "wick" consists of a few threads of cotton wicking, one end of which is wrapped with a bit of wire, which then serves as a handle for pushing it down the tube or for pulling it out. In op- eration, one end of the wick is pushed down the tube and the other end dipped in the oil. Through the action of capillary at- traction the oil rises in the wick on the outside, and then by a combination of capillary and siphon action descends and drips down the tube to the bearing. The end of the wicK within the 400 PRACTICAL MARINE ENGINEERING tube should be pushed down below the level of the bottom of the cup so that this shall form the longer leg of the siphon. The size of the wick should be adjusted according to the amount of oil which it is desired to feed and to the quality of the oil as well. This adjustment of size is most easily effected by varying the number of strands of cotton in the wick. The amount fed may also be varied to some extent by regulating the distance to which the wick is pushed down the inner tube. For a sudden flush of oil the cups may be filled until they overflow into the inner tube, by which means the bearing may be flooded if desired. (5) Wiper. A wiper is shown in Fig. 276. It consists of an oil cup with a central blade or plate, A, extending above the edge, and attached to one of the moving parts of the engine. At a convenient point is placed a strip of fibrous material on to which the oil is fed from the source of supply. The strip and wiper are so adjusted that the latter in its motion to and fro wipes or scrapes along the lower surface of the former, and thus as soon as the strip is saturated with oil the wiper takes off a drop or more, which then runs down into the cup and thence to the surfaces to be lubricated. Naturally this mode of lubrica- tion is more especially suited to parts having a horizontal mo- tion. (6) Plain Oil Cup With Adjustable Feed. This consists of a simple cup, as shown in Fig. 277, mounted where convenient and connected by pipe or duct to the bearing to be supplied. The rate of feed is regulated by a needle or conical valve, which controls the size of opening through the discharge passage in the base. A cover is usually fitted to prevent spilling or the ad- mission of impurities. Where such a form of cup is used to ad- mit oil to a steam chest or other chamber under pressure, a strong scrpw cover is necessary, as shown in Fig. 278. To fill the cup in such case the valve is closed, the cover unscrewed, and the cup filled. The cover is then replaced and the valve opened according to the rate of feed desired. Another variety of cup used for this purpose has a body of cylindrical or globular form terminating at top and bottom in a neck or tube, each of the latter being closed by a valve. The lower neck joins the tube leading to the bearing as in other cups, while to the upper is fixed a shallow open cup. The chamber between the two MARINE ENGINE DETAILS 401 valves is filled by closing the lower valve, opening the upper and pouring into the shallow cup, which serves thus simply as a funnel. When filled, the upper valve is closed and the lower one opened according to the rate of feed desired. The use of this type of cup is strongly advised against, as they are extremely wasteful of oil. (7) Sight Feed Oil Cup. As shown in Fig. 279, this is es- sentially a plain cup with the addition of the "sight feed" attach- ment or feature. When in adjustment, the flow of oil is regu- lated by the conical valve to a drop at a time at such interval as may be desired. The space below the outlet of the cup is cut away so as to show the drop as it falls into the mouth of the Fig. 278. Oil Cup with Screw Cover Fig. 279. Oil Cup witli Sight Feed feeding tube. Very frequently a glass tube is fitted inside the brass framework, thus closing in the oil completely, but allowing the drop to be seen as it falls. For a sudden flush of oil it is only necessary to open up the conical valve sufficient to let the oil descend in a stream and flood the bearing. (8) Compression Grease Cup. In addition to oil, various forms of hard grease in cakes, or balls, or in bulk, are some- 402 PRACTICAL MARINE ENGINEERING times used for lubricating purposes. For feeding such lubri- cating material to bearings, two means are made use of. (i) If the bearing tends to become heated the heat devel- oped will soften the grease and allow it to run to the spot where it is needed. (2) Compression cups are used containing a piston or plunger on top of the grease and acted on by a spring under control by a screw operated by hand. (See Fig. 280.) The grease is thus forced either automatically or by hand through the feeding tube and to the bearing. The spring arrangement marut».^nffine4ring Fig. 280. Compression Grease Cup Automatic Lubricator Fig. 281. may be made adjustable so as to force the grease more or less rapidly, according to its degree of hardness, and to the rate of feed desired. (9) Lubrictor. For the introduction of cylinder oil into the valve chests or steam pipes, an apparatus known as a sight feed lubricator is very commonly employed. Such devices have been made in great variety of form, but the description of one will be sufficient to show the principle upon which they operate. The lubricator, shown in Fig. 281, consists of a main chamber, A, MARINE ENGINE DETAILS 403 with cgnnections for attachment to the ^team pipe or throttle valve casing at B, and for the attachment of a length of vertical pipe, P, leading in to the main steam pipe at C. D and E are two fittings for a short length of glass tube, as shown. From the top of the chamber a passage or pipe leads down to the lower fitting, E, while from D the passage leads into the steam pipe through the connection at B. The lower part of the chamber is connected to the vertical pipe leading up to C. There are also two connections, F, G, with glass gage between to show the level of the oil and water within the chamber. The operation of the lubricator depends on the difference in density between ifanm!Bngiimfing ' Fig. 282. Oil Pump the oil and water. The lubricator is first filled with oil through the plug H. The steam is then admitted to the pipe, P, where it will slowly condense and collect at the base of the chamber, in the pipe between D and E, and in the pipe P, thus furnishing a head of water acting on the oil and forcing it upward. As soon as the head is sufficient, oil will be forced a drop at a time as regulated by the valve V, out through the passage leading from the top of the chamber down to E and up through the water in the tube, DE, and so on to the steam pipe, where it is caught by the flow of steam and carried to the valve chest and cylinder. The passage of the oil drop upward is plainly seen, and thus the operation of the lubricator is under ready observa- tion. Such lubricator may be placed on the steam pipe or throt- tle valve chamber, or at any convenient point where the oil will be carried by the inflowing steam to the points where needed. 404 PRACTICAL MARINE ENGINEERING ( 10) Oil Pump. A simple arrangement f oj forcing cylinder oil into a steam chest is sometimes used when it is not con- venient to fit a lubricator. This consists, as shown in Fig. 282, of an oil pump operated by hand. The chamber being filled with oil the delivery valve is opened and the oil forced in as may be desired, through a connection attached to the pump delivery, as shown. (11) Modern Systems of Oil Distribution. In the preced- ing section have been described the principal devices used for supplying oil to a bearing, or to a steam pipe or chest. There will now be described briefly the general oiling system for the engine as a whole, involving such combination of these devices as may be found most desirable. The leading features of the modern gravity system consist in the provision of a small number of distributing centers from which oil is taken by piping as directly as possible to the various places where needed, each place having its own independent pipe and set of connections. Following is a brief description of such a system of oiling gear, and will serve to illustrate the methods now in use in good practice. A light cast brass box is provided for each cylinder placed at a point higher than any joint or bearing to be reached by the oil, and having a capacity sufficient to last several hours without refilling. These oil boxes are provided with sight feed cups with protected glass tubes from which pipes lead to wipers on the moving parts, or to tubes in the bearings and guides. Union joints are fitted where necessary, so that the oil pipes may be quickly taken down and cleaned. With few exceptions the oil for the various moving parts of the cylinder is supplied from this box. The main crank pin is oiled by means of a pipe and cup carried on the crosshead and taking oil from a drip supplied from the oil box as described. The pipe runs down the side of the rod, or frequently inside if the rod is hollow, and connects with the oil duct leading through to the pin. The crosshead guides are provided with oil through pipes connected with holes at about the middle of each forward and backing guide. The main pillow blocks are oiled by one or more wick cups deliver- ing the oil at the points desired. A cup for tallow or grease is also usually provided, and like- MARINE ENGINE DETAILS 405 wise sometimes a hole through which the hand may be passed to feel of the shaft as may be desired. The presence of this hole, however, is not in accord with the principles given above in ( i ) , and the practice cannot be recommended. If anything of the kind is to be fitted it is better to carry the hole simply through the cap, thus leaving the brass continuous. The latter may then be felt as desired, and a tendency to heat observed. The eccentric straps are fed from long narrow oil cups, receiving their oil through the drip pipes from the reservoir. The length of the cup is made such that some part of it is always under the drip in any position of the eccentric, and it will, there- fore, always receive its supply. The various other parts of the gear are similarly supplied with oil either from a drip or a wiper, as may be more convenient. The chief advantages of such a system consist in the cer- tainty and regularity of operation which may be assured with the minimum of time and attention on the part of the oiler. In modern naval practice the gravity system of oil supply for lubrication, particularly for engines of high power and speed, has, in the interest of economy and reliability, been replaced by what is known as the system of "forced lubrication." FORCED LUBRICATION Forced lubrication of engines is not a new idea. It has been successfully used for years in dynamo and blower engines of. high rotary speeds, and is today the general practice for turbine and internal combustion engines. The application of a forced lubrication system as used on dynamo engines is illustrated by the cut showing the section of a dynamo engine and generator. A small plunger pump, operated by an eccentric on the engine crank shaft, takes the oil through a strainer in bottom of crank pit and forces it through a system of pipes to each main bearing. From the main bearings the oil goes to the crank pins through a diagonal channelway drilled through crank web. From the crank pin the oil goes through a pipe alongside or inside the connecting rod to the inside of crosshead pin, and from the crosshead bearing the oil is directed to the slide, and drops down to the crank pin. The leakage at the various bearings also finds its way to the reservoir at bottom of crank pit and is used over again. New oil is supplied to make up any leakage through oil-tight casing. 4o6 PRACTICAL MARINE ENGINEERING Though old in principle, the application of forced lubrica- tion to large marine reciprocating engines is of recent develop- ment. Superior efficiency and economy of oil are the principal claims for the forced system of lubrication over other oiling arrangements. As a matter of fact, both claims have been estab- lished beyond question by installations now in operation. Wher- ever used the verdict has been nothing but praise, the only regret expressed being that it was not adopted years before. The question of economy is better appreciated when it is understood that with forced lubrication the oil is used over and over again and not wasted into the bilge after performing its function but once. In general, naval engines use about one gal- lon of oil per lOO indicated horsepower per 24 hours. It is, therefore, obvious that the daily saving in oil for a large vessel having engines developing from 20,000 to 25,000 indicated horse- power will be considerable. Several days' oil consumption would be sufficient to run a forced lubrication equipment for months. The installation, as applied to large reciprocating marine engines, is not the simple arrangement as fitted to dynamo or blower engines, consisting of a small oil pump actuated by an eccentric on the crank shaft and a few pipes from this pump to the various bearings to be lubricated. In principle it is similar, but it involves much more gear and complications, rendering the lubricating system a plant in itself of no small moment, requir- ing skill and attention for its proper manipulation. The following description of a typical installation is readily followed by reference to sketches as noted. In general the sys- tem consists of three steam driven oil pumps, one main supply oil tank and one water and oil settling tank for each engine, together with the necessary piping, valves and filters, arranged as ex- plained later. The crank pits are of oil-tight construction, fitted with an oil well, and are so designed that no bilge water or dirt can enter therein. An oil trough is thus formed at the base of each engine, to catch all the oil. The engine is cased in to a height of within two feet of the cylinder bottom with a light sheet iron casing to prevent splashing and waste of oil, but allowing sufficient clearance below the cylinder bottoms for observation of the running parts. MARINE ENGINE DETAILS 407 Designating the pumps as A, B and C (see Fig. 283), the pump A draws oil from the main supply tank and discharges it through oil filters to the main bearings only. The pump B is arranged primarily to draw oil from the crank pit oil well and discharge through filters to the main supply tank. The filters on "0-«n Fig. 283. Diagram Showing Piping Connection of Forced Lubrication System in Main Engines 1 — Suction from Main Supply Tank. 2— Oil Suction from Oil Well. 3— Water Suction from Oil Well. 4 — Discharge to Filters. 5- — Discharge to Main Supply Tank. 6 — Discharge to Water and Oil Settling Tank. 7 — Discharge to Main Bearing Oil Filters. 8 — Main Bearing Feed Line. 9 — Drain to Oil Well. 10 — Drain to Bilge. 11 — Cross Connection to Main Bearings. are provided in triplicate, as shown, two intended to be used at a time, while the other is being overhauled and cleaned. This pump can also be used as an auxiliary on the water suc- tion from oil well, with delivery to settling tank. The pump C is in the nature of a standby, principally intended to draw water and oil from the oil well and discharge to the settling tank, but 4o8 PRACTICAL MARINE ENGINEERING also arranged to perform the duties of either of the other pumps in case of emergency. The plant operates as follows (see Fig. 283) : The pump A draws the oil from the main supply tank via pipe i, and dis- charges through pipe 7 and the filter to either main-bearing Fig. 284. Diagram Showing Forced Lubrication Connections for Connecting Rod and Crank Shaft of Main Engine 8 — Main Bearing Feed Line. 12— Crosshead Pins. H — Stop Valves tor Service to Crosshead Pins. 17 — Stop 19 — Swivel Joint Water Service to Service to Bilge. A — Oil to Main C— Oil to Crank Shaft Axial Hole. Crank Pin Bearing. F — Oil Groove Straps. H — Oil to Crosshead Pins. J Stop Valves, Oil to Main Bearings. 13— Oil to same. 15 — Swivel Joint for same. IG — Water Valve for same. 18 — Stop Valve Oil for same. Bilge. 20 — Stop Valve for same. 21 — Water Bearings. B — Oil Groove in Main Bearings. D— Oil to Crank Pin Axial Hole. E— Oil to in Crank Pin Bearing. G — Oil to Eccentric —Axial Hole Covers. K — Oil to Main Bearings. feed line 8. Branch pipes K (see Fig. 284) conduct the oil to the main bearings through the holes A in the bearing caps. The quantity of oil supplied is regulated by the stop MARINE ENGINE DETAILS 409 valves 12. Annular grooves B distribute the oil throughout the main bearings and into the crank shaft axial hole via the radial holes C, one to each journal, and thence via holes D to the crank pin axial hole. The openings at the ends of axial holes are closed by oil-tight cover plates /. The crank pins are lubricated by the radial holes E, one for each pin, the annular grooves F distributing the oil to the bearing surface. Holes G are pro- vided for supplying oil to the eccentrics. The crosshead pins are supplied by pipes 13 and swivel joints 15; thence through holes H to the brasses, or the oil is led up through the connect- ing rod, as shown by Fig. 285. Stop valves 14 are provided for regulating the flow of oil. A water service supply pipe 16 is fitted to this connection, with drain 19 and 21 to bilge. Stop and check valves are fitted, permitting water alone or any com- bination of oil and water being supplied. All other parts of the engine are oiled in the usual manner, by gravity flow sup- plied from manifolds or cups. After performing, its function, the oil is forced out at the ends of the bearings and drains to the crank pit, which, as previously explained, serves the purpose of a trough for catching the oil. From the crank pit oil well the oil is drawn by the pump B (see Fig. 283) through the pipe 2 and delivered through pipe 4, oil filters and pipe 5 to the main supply tank, thus completing its cycle, which is repeated indefi- nitely as described. Should the oil show signs of water, due to water service waste and other sources, the pump C is put on the water suc- tion 3 from the oil well and discharges through pipes 4 and 6 to the settling tank, from which, after heating and allowing to settle, the oil is drained off to the crank pit through pipe 9 and the water to the bilge through pipe 10. The settling tank connects to no pump suction. Pressure gages as indicated (see Fig. 284) show the pressure at which the oil is supplied. Thermometers are also fitted in the main bearing caps for taking the temperature of the bearings, etc. Large storage oil tanks are provided for making up leakage and other waste and for replenishing the entire system when desired. In using this system care must be taken that an oil that does not saponify and which does not leave a gummy residue is 410 PRACTICAL MARINE ENGINEERING used. An oil that easily saponifies would, when brought in contact with water which will be present from small steam leak- age along piston rods and the churning movement of the crank, cause a lather to form, which may in time stop up the oilways. r<^ ''■''''^^'''^ Fig. 285. Connecting Rod with Forced Lubrication Any gummy residue left by the oil, either in the bearings or oil- ways, would also stop up the pipes and prevent proper lubrica- tion to some of the bearings. The strainers provided will guard against any dirt or mechanical impurities that may be left in the oil, but this does not guard against the saponifying or gumming action of the oil. Special oils having the proper qualities for use with forced lubrication are supplied by the principal oil manufacturers. MARINE ENGINE DETAILS 411 Fig. 286 illustrates the method of applying forced lubrication to a thrust bear- ing. In this case the bearing was fitted for a Curtis tur- bine. A is the main turbine shaft carrying at the for- ward end the thrust rings. BC are the horseshoes, faced with bearing metal D, and supported by the thrust bearing casting E. F is the main steady bearing fitted at -its after end with the oil baffle G, which en- gages with collars H on the shaft to prevent the escape of oil. / is the oil casing fitted with sighting and adjusting openings closed by the lids O. /is the supply pipe for cooling water to the horse- shoes, which circulates through the shoes and es- capes by means of the cor- responding pipe on the opposite side of the shaft. Xhe oil under pressure en- ters through the pipes' X on each side of the shaft and thence to the grooves ^shown on the faces of C 412 PRACTICAL MARINE ENGINEERING and thence to the oil b.ath 2. From 2 pipes lead the oil back to the central oil drain tank of the system. Openings closed by plates P are provided for access to 2 for cleaning out purposes. Fig. 287. Section of Dynamo Engine Fitted for Forced Lubrication Fig. 287 illustrates a dynamo engine fitted for forced lubri- cation. For marine purposes there is one serious error in the arrangement as shown, and that is in the arrangement of piston MARINE ENGINE DETAILS 413 rod stuffing boxes. With the boxes, as shown, large quantities of oil would be drawn up into the steam cylinders by the piston rods, and would find its way into the boilers. To guard against this, the cylinders should be raised sufficiently to prevent any part of the rod which travels within the crank case from entering the piston rod stuffing box, and the crank case stuffing boxes should be of sufficient depth to accommodate from three to four turns of soft packing. In the case of a large reciprocating engine with forced lubri- cation, where the stuffing boxes extend directly down into the running gear space, in order to guard against oil entering the Fig. 288. Turbine Micrometer Gage cylinders it becomes necessary to resort to the fitting of external stuffing boxes, called steam seal boxes, below the regular boxes. These boxes are provided with a chamber encircling the rod be- tween two successive packing rings. This space is filled with steam of a pres'sure above that of the atmosphere and slightly above that of the steam cylinder to which it is fitted. The seal is provided with a drain and steam trap. [15] Turbine Micrometer Gage In order that the fore-and-aft (axial) clearances between moving and stationary blades of turbines may be checked up at aqy time in order to guard against internal friction and possj- 414 PRACTICAL MARINE ENGINEERING ble loss of blading, due to their being in contact, gages similar to the one shown in Fig. 288 are usually fitted. 5 is a casting securely fastened to the turbine cylinder head and having an extension end passing through the head into the turbine. This end is fitted at C with a stop, as shown. In B, and guided by it, slides a spindle K, fitted with a spade handle H, and sliding through a threaded sleeve /, which works in a thread in B. I is turned by an adjusting micrometer v^^heel G, having a scale on its circumference passing under a pointer F. K also carries a spring for holding its end firmly against a faired surface of the rotor end D. The abutment for the spring on K also carries a pointer, indicating position of K on the scale E. It is evident the relative positions of the turbine end of K and the fixed standard B can always be determined from the indications on the scales E and G, and thus the blade striking points having once been determined they can be checked up at any time by turning the spindle K until its turbine end is clear of the stop C, then easing it gently until its end brings up against D and reading the scales. [16] Special Couplings (Figs. 289, 290, 291) With the introduction of cruising units, in addition to the main propelling turbines, in order to obtain greater fuel economy at low- speeds with naval vessels, it became necessary to provide some form of quick operating clutch between the main and the cruising element so that as little time as possible would be lost in coupling or uncoupling. Several such clutches have been developed, and three are here described. The first. Fig. 289, known as the Wetherbee clutch is purely mechanical and can be uncoupled^ but not coupled with, the njachinery in motion. The second. Fig. 290, is the Turner clutch. It is a mechani- cally operated friction clutch and can be operated either for coupling or uncoupling while the machinery is in motion. • The third, Fig. 291, is known as the Metten clutch. This- clutch is operated with oil pressure and can be coupled or un- coupled with the machinery in motion. While friction clutches have an advantage over the posi- tive mechanical engagement clutches in permitting both coup- MARINE ENGINE DETAILS 41S ling or uncoupling without the necessity of bringing the machin- ery to rest, they have one disadvantage not possessed by the other type. They must always be fitted in combination with a flexible coupling in order to prevent a sliding strain from being brought on the friction disk, due to the two shafts which are to be coupled being out of line with each other, or other means which must be provided to take care of such disalinement. 1. The Wetherbee coupling (Fig. 289). A, the operating hand wheel, is carried on a shaft extending horizontally over and supported by brackets on the coupling casing. This shaft carries two worms gearing into worm wheels B, fitted on the upper Fig. 289. Wetherbee Clutch ends of two vertical shafts, which carry at their lower ends the pinions K. These pinions gear into two racks /, one on each side of the shaft, and carried betvyreen the joining flanges Of the halves of. non-rotating shifting band H. This band or collar is carried between a flange and a screwed-on stop ring 7 of the coupling sleeve, G. G is fitted with teeth on its inner circumference engaging permanently with corresponding male teeth on the drum F car- ried by the cruising element shaft D, and engaging with similar • male teeth on the drum E when coupling up. E is carried on the main turbine shaft C, to which it is securely keyed. On its hub is cut a worm L gearing in with a worm wheel M and thus driving the cbuntergear. 4i6 PRACTICAL MARINE ENGINEERING 2. The Turner Coupling (Fig. 290). C is the cruising en- gine shaft and D the main turbine shaft. E is the inner coup- ling disk keyed to but having a slight sliding motion on C. F is the friction disk carried on ball bearings, working in races pro- vided on the shaft C. F is flexibly connected to D by means of parallel sided bolts carried by a flange on the forward end of D and working through bushed holes in F and providing for flexi- bility. L is an outer coupling clamp. H is a sleeve sliding on ^jrw PLAN OF TOGGLE HALF SECTION AT A. HALF SECTION AT B. Fig. 290, Turner Coupling and rotating with C and E. I is an outer non-rotating sleeve carried between shoulders on H, with ball bearings to reduce friction. / has a thread cut on its outer surface and has fore- and-aft motion given to it by means of the gear ring N. N carries worm teeth on its outer circumference gearing into a worm on the shaft W, this shaft being operated by the hand wheel V. As the sleeve / is carried aft along the shaft it carries with it H, to which are attached the spindles O, operating the toggles P- The toggles straighten out, draw -L and push E firmly against F and close the clutch. This clutch is apt to give trouble, due to oil working in between the friction surfaces and causing a slight amount of slip. This slip very shortly generates excessive heat and the clutch becomes inoperative. 3. The Metten Coupling (Fig. 291). A is the cruising en- gine shaft and B the intermediate shaft fitted with a flexible coupling at its after end. C is a casing firmly bolted to a flange on 4 and forming the forward outer wall of the oil chamber MARINE ENGINE DETAILS 417 E the inner friction clamp and D form the inner and the circum- ferential and the after wall of the oil chamber. // is a corrugated cylinder machined from a solid cylindrical steel forging of suffi- cient temper to prevent it taking a permanent set. H forms the outer and flexible circumferential wall of the oil chamber. To C is also securely bolted the circular outer clamp ring. This ring Fig. 291. Metten Clutch and E carry a special friction material on their engaging sur- faces. F is the friction disk securely bolted to a flange on B. The outer edge G of F is reduced greatly in thickness to provide flexibility and is slotted, as shown, to prevent warping. The oil pressure is provided either by a pump or by applying pres- sure from an air reservoir and is transmitted to the clutch through K, the central hole in the shaft A. [17] Kingsbury Thrust Bearing An interesting development in engineering is a thrust bear- ing, known as the Kingsbury. In this bearing the load is uni- formly distributed over the entire surface, and the slippers are free to adjust themselves at slight angles to the collar so as to glide or skiin over a film of oil which adheres to and moves with the collar, the action of a slipper being much the same as that 4i8 PRACTICAL MARINE ENGINEERING of a single hydroplane. As compared with the Usual types, the results which have been obtained with this bearing are remark- able and of great importance. In high speed bearings a pres- sure of 500 pounds per square inch is being carried, and in low speed 900 pounds. Although these pressures are unusually high, they are still far from the safe maximum pressure which can be carried, the factor of safety being ten or more. A test on a turbine thrust bearing showed that a pressure of about 7,000 pounds per square inch could be carried without the breaking down of the oil film. The following is a description of the Kingsbury thrust bear- ing which is illustrated in Fig. 292. The bearing consists of a body secured to the turbine cas- ing, in which are mounted in spherical seats two ringi which carry, also in spherical seats, the slippers which bear against opposite sides of a single thrust collar which is held on the shaft by a key and a nut. Each of the slippers, which are of steel with the rubbing surfaces lined with white metal, fits into a recess in the slipper ring which holds it in the correct position, preventing rotation around its longitudinal axis, and is held in its spherical seat by a helical spring held in compression between the slipper ring and the head of its retaining bolt which passes through a hole in the ring. Each of the steel slipper rings, which are carried in the spherical seats of the body, is held against rotation and sup- ported by a bolt which passes through a short slot with the spherical lower surface of its head resting on a thick washer on the supporting yoke; this yoke is carried by a tran.sverse bolt passing through lugs on the body. The cast steel body consists of a forward part which is screwed into an after part on a diameter exceeding those of the thrust collar and slipper rings, which are contained in the latter. The bearing clearance or "float" is adjusted by screwing the for- ward part in or out ; and as the after part is divided on top by a longitudinal slot through the threaded portion, the two parts can be clamped in the required position by the transverse bolt which passes through lugs on each side of the slot. The for- ward part of the body extends through the casing to which its flange is bolted. Under the flange there are brass liners, made in halves, by means of which the bearing can be adjusted to MARINE ENGINE DETAILS 419 give the required longitudinal position of the rotor. The body is centered in the casing at both ends. From a branch of the turbine oil service oil enters the annu- lar space in the forward body behind the slipper ring, and passes through the inlet channels into the inside ends of the radial supply spaces between the forward slippers. From 420 PRACTICAL MARINE ENGINEERING another branch oil enters the annular space in the after body behind the retaining bolts of the slippers, and likewise passes through the inlet channels into the inside ends of the supply spaces between the after slippers. From the supply spaces the oil passes radially outward through the corresponding exit pass- ages in the body, and fills the casing so that the bearing runs immersed in oil, which insures good lubrication and cooling. From the casing oil drains out into the adjoining main bearing reservoir, part of it passing through the space around the shaft, and the remainder through the holes in the upper part of the casing. From the supply spaces oil is drawn under the slippers, which, due to the action of the lubricant, "ride" on an oil film of appreciable thickness, so that there is no rubbing contact between the surfaces. As the slipper ring is free to move in its spherical seat, the forces transmitted through the slippers cause it to adjust itself so that the pressure is equally divided among the slippers ; and, as each slipper has similar freedom, the forces acting on its surface cause it to adjust itself so that the pressure is uniformly distributed over the surface. Therefore, the self-adjustment of the bearing automatically distributes the pressure uniformly over the entire surface; and, as there is an abundant supply of oil introduced between the surfaces, the unit pressure on the bearing surface is with safety carried much higher than usual. The pressures acting on the surface of a slipper are, of course, not equal. They are greatest at a point slightly beyond the center in the direction of rotation, and become less as the edge is approached in any direction. With relation to the sur- face as a whole, however, the pressures are balanced and, con- sidering the action of the lubricant, are uniformly distributed. The oil drawn under the leading edge of a slipper escapes from the three remaining sides, the major part of it passing out under the following edge. Therefore, the thickness of the film is greatest under the leading edge and least under the following edge. This diflference of thickness of the film causes the slipper to stand at a slight angle to the surface of the collar, and, so to speak, it "rides" on the film in a position which is required for the proper action of the lubricant. This is similar to the action in a cylindrical bearing, where the greater thickness of the film MARINE ENGINE DETAILS 421 Fig. 293. Thrust Bearing of Large Water-Wheel Generating Unit A:— Shaft B — Collar Seat. C— Thrust Collar. D — Bearing Seat. E— Slipper Ring. F— inside Oil-Retaining Ring. &— Slipper- Ad justing Wedges. H — Liners. I — Slipper Seat^ lever. J — Slipper Seat, upper. K — Slipper. L — Outside Oil-Retain- ing Ring. M — Casing. N — Oil-Supply Space. on the leading side causes the journal to run slightly eccentric to the bearing. However, due to the journal and bearing having approximately the same curvature, the action of the lubricant is not as perfect as in the case of the slippers with plane sur- 422 PRACTICAL MARINE ENGINEERING faces. In the usual types of thrust bearings, where the surfaces are held rigidh- parallel, the action of the lubricant is still less perfect, which accounts for the low unit pressures to which they are limited. The bearing, which has been described, illustrates in a gen- eral way the mechanical features of all Kingsbury bearings. Fig. '2Vi. Parts of Kingsbury Thrust Bearing for Turbine A — Thrust Collar. C — Collar Nut. C — Slipper. D — Slipper Seat. K — Retain- ing Screw. F — Slipper Ring. G — Bearing Seat (spherical). H — Dowel. I — Ad- justing Threads. J — Adjusting Ring and \\'orm Rack. K — Shaft Packing Ring. L — Collar-Nut Washer. M — Oil Holes. N — Oil-Supply Space. O — Locking Device. The details are varied somewhat to suit the conditions, but the principle of construction remains the same. The bearing shown in Fig. 293 is used to support the rotor of a large water wheel generating unit. It will be noted that the slippers have plane surfaces which rest on spherical seats, which in this case are convex to the slipper. The slipper seats are provided with wedges and liners by i7Teans of which the vertical position of the rotor can be adjusted. Each slipper can be adjusted independently and removed radially as shown. The center of support for the slipper is slightly beyond the geometric center of the surface in the direction of rotation, and corresponds with the theoretical center of pressure. This construction gives greater freedom to the slipper and slightly reduces the coefficient of friction. Oil is admitted to the reservoir formed by the bearing casing, and MARINE ENGINE DETAILS 423 passes out through an overflow pipe located at the oil level shown in the illustration. The bearing therefore runs in an oil bath and is subject to continuous circulation which removes the heat. In this type of bearing, where the thrust is always in the same direction, only one set of slippers is used. This type is also used in turbines and other horizontal machines where the thrust is always in the same direction. In marine turbines and other machines where the direction of the thrust changes, slippers must, of course, be provided on both sides of the collar. The single bearing illustrated in Fig. 294 is used in a steam turbine of a generator unit. This construction has been used in all turbine work of this class. Sec. 42. PIPING [i] Systems and Materials The principal systems of piping are as follows : (i) The main steam piping from boilers to engine. (2) The auxiliary steam piping from the auxiliary boiler or from one or more boilers specially selected, to the various auxiliaries which are to be operated by steam. (3) The main exhaust piping from cyHnder to cylinder and from the low pressure cylinder to the" condenser. (4) The auxiliary exhaust system, providing each auxiliar}' with its exhaust, either to the condenser or overboard, as de- sired. (5) The feed system, main and auxiliary for returning the condensed steam to the boilers. (6) The condensing system for bringing the condensing water to the condenser and for carrying it from the condenser to the sea again. (7) The drainage and bilge pump delivery systems for lead- ing water to the bilge pumps and from the pumps to the sea. (8) The fire system for leading water to the fire pumps and from the pumps to the fire plugs. (9) The sanitary system for delivering water to the water closets and heads. (10) The steam heating system. All pipes may otherwise be classified under three heads: steam pipes, exhaust pipes, and water pipes, while of the latter 424 PRACTICAL MARINE ENGINEERING there may be a further division into those carrying water to a pump or suction pipes, and those carrying water from a pump or discharge pipes. For steam pipes the materials in present use are copper, wrought iron, and steel. Copper pipes in small or moderate sizes may be made of seamless or solid drawn tubing; in large sizes they are made of sheet copper with brazed joints. Wrought iron pipes are lap welded, while steel pipes are also lap welded and are sometimes further fitted with a riveted longitudinal strap cov- ering the line of the weld. Seamless or solid drawn steel pipes have also been made to a large extent and should always be used for the highest grade work. For the various junctions, elbows, bends, tees, etc., steel or malleable iron castings are used with steel pipe, while with cop- per pipe sheet copper is used for these parts, bent and formed up by hammering into shape, and secured at the joints by braz- ing. The advantages of copper are its great ductility, freedom from corrosion, and the readiness with which it may be used to make pieces of an irregular form, such as the elbows, junctions, etc., referred to above. Its disadvantages are, greater cost, low tensile strength, the possibility of damage to the quality of the material in the process of pipe manufacture, and the possibility of a loss of ductility in service by repeated strains due to the expansions and contractions which result from changes in tem- perature. The metal close about a flanged joint seems especially liable to lose its strength in this way. This is probably due to the concentration of the strains due to expansions and con- tractions in the vicinity of a rigid connection such as a flanged joint, and to the development in this way of a line of weakness i-unning around the pipe. To render copper pipe more secure under high pressure it has been wound with copper or steel wire, or reinforced by wrought iron or steel bands. Such bands may be from J4 to 2 inches wide by J^ to J4 inch thick, and spaced with intervals of from 6 to 10 inches. These methods, especially the latter, have proven quite successful in strengthening copper piping for mod- ern advancing pressures. The chief advantages of wrought iron and steel pipes are, less MARINE ENGINE DETAILS 425 cost, greater tensile strength, less liability of the material to damage in quality in the processes of manufacture, and less liability to lose strength or ductility in service. Their disadvan- tages are, greater liability to corrosion, and greater weight of cast junctions and fittings than for copper. Welded pipe is made from rolled strips the edges of which are machine beveled for a lap joint. The requirements of manu- facture are such that for all except the largest sizes the thickness • is in excess of that needed for strength alone, at least with the pressures at present in use, so that when such material is em- ployed there is always an excess of strength. With wrought iron pipes the welded joint is trusted without reinforcement. With mild steel a covering strip or butt strap is sometimes riveted on, though with the later improvements in the welding quality of such material, experience shows that these joints are quite as reliable as those of iron. Flanges for wrought iron or steel pipes may be welded on, but more commonly they are riveted or screwed to the pipes or the pipe is expanded into the flanges. When riveted or screwed on the flanges are calked on both sides to make a steam tight joint. In small sizes and in a relatively cheaper grade of practice, ordinary commercial steam piping is used, fitted up with the usual fittings and screwed joints. For exhaust piping the same general character of pipe is used as for steam, with such differences as the decreased strength necessary may indicate. For water piping steel, iron and copper, and in cheaper practice the ordinary commercial pipe are all used. Steel and iron are usually considered less suitable for water than for steam piping on account of the greater danger from corrosion. This is especially true for feed piping, and in case such material is used for this purpose it is considered good practice to carefully galvanize the pipe both inside and out. It is likewise good practice to tin all copper piping which is under the floor plates or in the bilge, but this is rather to protect the ship than the pipe, the former being in danger of attack by electro-chemical action in case the copper and the metal of the ship obtain con- nection through a medium such as bilge water. All copper piping for use with salt water should be lined with a mixture of lead and tin for its protection, and zinc protectors should be 426 PRACTICAL MARINE ENGINEERING- provided. In connection with piping see also that heading under Section 19. [2] Expansion Joint The expansion and contraction of a length of piping under a change of temperature require some kind of joint or connec- tion which will allow of the change of length without buckling or straining the pipe. This is usually provided by an expansion joint, as shown in Fig. 295. This consists of a recessed portion Fig. 295. Expansion Joint on one part of the joint into which the other fits, as shown. The space left between the two thus forms a stuffing box into which packing is compressed by means of the gland. The two parts of the joint are thus free to slip a little way, one relative to the other, while the joint is kept tight by means of the stuffing box and gland in the usual manner. It is readily seen that the steam pressure within the pipe, especially if it contains a bend or elbow, will tend to force the two portions of the joint apart, and thus open the pipe at the joint. To guard against this, safety stays or ties should be fitted. In the figure, one of three such stays is shown by the bolt at the top. Care must be taken in adjusting such stays that sufficient freedom is left for the ex- pansion and contraction which the joint is intended to provide for. This type of joint is as usually fitted but it is incorrect in principle. The stays should be depended upon to insure the in- tegrity of the joint. The pipe should extend from a fixed anchorage to the male portion of the expansion joint, which should be securely anchored, leaving the pipe free to slip in and out of the joint the amount required by the expansion of its length between the anchorages. While, as stated, slip joints are MARINE ENGINE DETAILS 427 usually fitted, as shown, they are a source of danger and trouble when so fitted. In special and more complicated forms, known as balanced or equilibrium expansion joints, these forces are more or less completely balanced within the joint itself. [3] Globe, Angle and Straightway Valves For controlling the flow of a liquid, vapor or gas through a line of piping, various forms of valve are used. Chief among these are the globe, angle and straightway or gate types, as de- scribed in Section 41 [i], [2], and to which reference may be made. [4] Balanced Expansion Joint (Fig. 296) Such a joint may be installed in place of an elbow in the pipe, thus providing for expansion of the piping and for change Fig. 296. Balanced Expansion Joint in direction of flow of the steam in the same fitting. The closed end of the pipe opposite to the direction of flow of the steam provides for steam thrust in both directions along the axis of the pipe and thus provides for absolute balance in the joint, which therefore has no tendency to blow out. QUESTIONS Marine Engine Details PAGE "Explain the chief features of an engine cylinder 310 What is a liner and how is it fitted ? 310 Explain the different forms of engine columns and how they are fitted 315 How are cylindrical columns braced and why? 317 Explain the more common ways of fitting up the guide surfaces 317 Describe the usual form of bedplate 319 Describe the usual form of engine seating 321 428 PRACTICAL MARINE ENGINEERING pAge Describe the usual form of marine piston with its packing rings and springs 32i What other forms of piston are employed ? 324 What is the purpose of the piston rod and how is it fitted up?. .... . 325 Describe the various styles of crosshead to be met with in marine practice .• ; ■ • 3^7 Describe the various styles of connecting rod to be found in marine practice 33° Describe the built-up and the solid forged styles of crank shaft 332 What are the advantages of making shafting hollow ? _ ... 233 To what extent may the same practice be applied to other cylindrical members ? 333 Describe the principal features of a Parsons turbine 335 Describe the principal features of a Curtis turbine 34i Describe the usual form of thrust shaft , 347 How is the propeller or tail shaft fitted up at the after end, and how is it secured to the length of shafting next forward in the case of swin screws? 34^ Describe the usual forms of crosshead and guide bearings 350 Describe the usual form of bearing for the crosshead pins 351 Describe the usual form of bearing for the crank pin 351 Describe the usual form of bearing for the crank shaft '. . . 351 Describe the usual form of bearing for the line shaft 352 Describe the two leading types of thrust bearings 353 Describe the usual form of stern and bracket bearings 357 Describe the usual type of Western river boat engine 360 What are the essential features of the valve gear employed on such engines ? 361 What is a Western river boat "doctor" ? 365 What is the office of the throttle valve, and what forms of valve may be employed for this purpose ? 369 What is the office of the main stop valve, and what is its usual form? 372 Describe the usual forms of globe, angle and straightway valves 372 Give brief description of throttle and maneuvering valves for turbine engines 374 What is the office of the cylinder drain and relief valves, and how are they usually made ? 376 What are starting valves ? ,. . . . 377 What is the purpose of the reversing gear ? 378 Describe the "floating lever" type of reversing gear 378 What is the purpose of the turning gear, and what are its main fea- tures? / 381 Describe the various forms of packing used for making the various fixed joints about a steam engine 382 Describe the more common forms of packing used in the piston rod and valve stem stuffing boxes 385 What is a reheater, and what is its purpose ? 386 What is the office of the governor ? 386 Describe the usual principles on which marine governors are designed. 387 What is the office of the counter gear, and of what does it consist?. . 389 What is the purpose of lagging on cylinders, valve chests, etc.," and how is it usually fitted ? 396 What kinds of oil are used for lubrication, and what are their special characteristics ? 396 What other forms of lubricant are employed ? 396 At what point in a bearing should the lubricant be applied ? 397 About how much lubricant may be allowed per 1,000 I. H. P. per day in usual practice ? 397 In the adjustment of the bearing how much clearance may be left between the journal and bearing surface? 398 MARINE ENGINE DETAILS 429 PAGE Describe the various devices in use for distributing oil or lubricant to a bearing 399 Describe the leading features of a modern system of oil distribution. 404 Describe a forced lubrication system as fitted to a modern marine engine 40S What are the principal systems of piping found on shipboard? 423 What materials are in use for steam and water piping ? 424 What are the relative advantages of copper, wrought iron and steel ? , 424 What is the purpose of an expansion joint ? 426 Describe the usual form of expansion joint 426 What is a balanced joint? 427 CHAPTER VII Auxiliaries RECIPROCATING ENGINES Sec. 43. CIRCULATING PUMPS The office of the circulating pump is to draw the condensing water from overboard, force it through the condenser tubes, and thence overboard through the condenser discharge pipe or, as usually styled, the outboard delivery. The principal resistance to be overcome by the pump is the resistance to the flow of the water through the tubes, and this is but slight when measured Manna Engineering Fig. 297. Centrifugal Pump in pounds per square inch or in feet of head. On the other hand, the quantity of water to be handled is large, and hence the requirement is for a type of pump which shall be able to handle large quantities of water against a small head or re- sistance. These requirements are very perfectly fulfilled by the- centrifugal pump, as shown in Fig. 297. The moving part con- sists of a number of vanes or arms attached to a shaft and form- ing what is called the runner. This revolves within a casing fur- AUXILIARIES 431 nished with inflow and outflow passages, as shown in the figure. The pump being primed or filled with water and started, the rotary motion gives rise to a centrifugal force, in obedience to which the water moves outward toward the tips of the blades, where it escapes through the outflow passage into the discharge pipe. There is a corresponding loss of. pressure about the hub of the runner and a resulting inflow of water from the sea to take the place of that which leaves at the outflow. The opera- Fig. 298. Outboard Discharge Valve tion thus becomes continuous and results in a steady flow of water from the pump through the condenser tubes and back to the sea through the condenser discharge pipe and outboard delivery. In order to prevent the water from "short circuiting" or slipping back from the discharge space about the tips of the blades to the inflow space about the hub, a running fit is pro- vided between corresponding faces on the runner and casing as indicated in the figure. The discharge or outboard delivery valve ii usually a plain type of angle stop valve, as illustrated in Fig. 298. Its office is cimply to allow when open the discharge of the water from the 432 PRACTICAL MARINE ENGINEERING . condenser, and prevent when closed the inflow of the sea to the pump. Sec. 44. CONDENSERS The purpose of the condenser is to provide for converting the exhaust steam back into water. Condensers are of two types — jet and surface. The jet condenser consists simply of a chamber of rec- tangular or cylindrical form in which the steam and the condens- ing water are mingled together, the steam giving up its heat to AIR PUMP SUCTION Fig. 299. Surface Condenser, Longitudinal Section the relatively cool water, and thus being reduced to the liquid state again. The water is usually led into the top of the chamber and allowed to fall upon a plate pierced with a large number of small holes, and known as the scattering plate. This divides the water into small streams or jets and enables it to mix intimately with the steam which enters just below the plate. The condensed steam and condensing water then fall together to the bottom of the co_ndenser.. From here the water is removed by the air pump which delivers it overboard, the feed pump in the meantime taking enough for the boiler feed and returning it to the boilers. AUXILIARIES 433 The usual type of surface condenser consists of a chamber commonly of cylindrical form if separate from the main engine (see Fig. 299), or rectangular if forming a part of the engine colunms. This chamber contains, as shown, a large number of small brass tubes running between the inner walls of the heads, which are double, thus providing a connection between the ends of the various tubes. The condensing water is driven by the circulating pump through the tubes, the usual run being as shown in the figure. The water enters at the lower left-hand end and fills the lower half of the head, being prevented from filling the whole head by a partition half way up, as shown. It thus finds its way into the lower half of the tubes and flows through them to the right-hand head. It then rises into the upper half of the tubes, flows back to the left and out at the opening in the upper part of the left-hand head. The water thus traverses twice the length of the condenser forward and back, and from the bot- tom upward. The steam, on the other hand, enters at the top into the body of the chamber, and thus around the outside of the tubes. The steam and the condensing water are thus kept separate, and the steam is condensed simply by the surface action of the tubes. The steam thus condensed to water falls to the bottom of the condenser, whence with some air and vapor it is removed by the air pump and delivered to the hotwell, whence it is taken by the feed pump and sent back to the boilers. Baffle or diaphragm plates, as shown, are often fitted in the condenser to prevent the steam from rushing directly through from the inflow on top to the air pump passage on the bottom. Baffles should, in fact, always be fitted over steam inlets to the con- denser, as the impact of the hot steam and water on the tubes causes them to deteriorate very rapidly and finally to split. The steam is thus forced to fill the condenser as completely as possi- ble, and thus the condensing surface is more uniformly brought into action. In order to facilitate the rush of steam downward into the body of the tubes, thus bringing more quickly into action those in the lower part of the condenser, a few rows are often omitted in the upper part, thus forming branching passages lead- ing from the top downward, as shown in Fig. 300. In order to support the heads against the pressure from without, a certain number of longitudinal braces or struts are necessary, as shown in the figures. 434 PRACTICAL MARINE ENGINEERING Condenser shells are made of cast brass, cast iron, or sheet brass or copper or steel. When of rectangular form the sides are cast with the necessary webs to give them strength to stand the pressure from without. When of cylindrical form the neces- sary strength can be given by a suitable thickness of metal rein- forced if necessary by ribs running around the shell. When rela- tively thin sheet metal is employed, as in torpedo boat practice and the like, it is customary to fit one or more angle iron or tee iron stififeners running around the shell in order to provide the necessary strength. AIR PUMP SUCTION Marine Etyimering Fig. 300. Surface Condenser, Cross Section Condenser tubes are of thin brass, usually ^ to }i inch out- side diameter. In order to make a watertight joint between the condenser tubes and the inner heads or tube plates, and at the same time to avoid a rigid constraint of the tube, a great variety of condenser tube packings have been employed. The most com- mon type of packing in present practice is shown in Fig. 301. The tube plate is counterbored, as shown, and threaded for a ferrule with a tapering outer end. The hole in the outer end of the ferrule is thus of about the same size as that inside the tube, and hence smaller than the outside of the tube. Between the other end of the ferrule and the bottom of the counterbore is usually a ring of rubber or a few turns of some other elastic or fibrous material as packing. Screwing down on the ferrule compresses the packing, and thus makes the joint, while at the same time the tube is free to expand and contract .to a slight extent. The outer ends of the ferrules, however, prevent the AUXILIARIES 435 tube from crawling to such an extent as to free either end, a result liable to occur without some method of prevention. In the latest practice, for large condensers with straight tubes, the tube ends through which the water enters are expanded into the tube sheets which are made about i}i inches thick to withstand the strain due to this expansion, while the opposite ends are fitted Fig. 301. Ferrule and Tube Packing, Surface Condenser with ferrules and packing. In smaller condensers, the tubes are slightly curved, usually in the horizontal plane, to allow for ex- pansion under varying temperature, and both ends are expanded into the tube sheets. [i] Condensers for Turbines Ordinary condenser.s consist of the shell, tubes, exhaust in- take and circulating water in- and outlets. They are invariably made of the contra flow type, which infers opposite circulation of water and exhaust steam. The steam circulates usually out- side of the tubes and enters either at the top or bottom, the water in either event entering in an opposite position to the steam. The essential difference in the working- conditions of con- densers when used with reciprocating engines and turbines ex- 436 PRACTICAL MARINE ENGINEERING ists in the considerably increased steam volume issuing from a turbine as compared with the engine. This is due, of course, to the higher vacutim at which the turbine operates. Recognizing this fact, it becomes important to so design the tube distribution as to admit the steam into the tube nest with the least possible obstruction to flow. This is done, first, by giving to the exhaust nozzle an area such as at once to distribute the exhaust over the Fig. 302. Uniflux Condenser entire tube surface and, second, to so space the tube rows ad- joining the nozzle that the clear space between them becomes" nearly equal to the area of the nozzle. Guided by these consid- erations, condensers of the Uniflux type have been introduced in marine turbine installations. (i) The Uniflux Condenser. — The shell of this condenser is made of heart or triangular shaped, with sides formed of cir- cular arcs struck with appropriate radii. One side faces the ex- haust nozzle, with the point turning downward. The tubes, usually made ^ inch diameter, are divided in various clusters. AUXILIARIES 437 each with a different tube spacing. The center Hnes for the tube spacing make angles of from 30 to 45 degrees with the normal center line of the shell. Below the lowest tube row is a perforated continuous baffle plate. The air pump suction is at the lowest point and the circulating water enters the water chest at the bot- tom, where it passes through half of the tubes, returning in the remaining tubes, then discharging through the upper outlet. Due to the spacing diminishing towards the lower part of the condenser by a systematic method, a uniform velocity of steam flow is obtained, rendering all tubes equally efficient, at the same time increasing their capacity for heat transmission. With this condenser is allowed about .7 to .9 square foot of cooling surface per shaft horsepower. There are no baffles, except the one at the bottom. An end view of this condenser is shown in Fig. 302. The injurious effects caused by leaky condenser tube pack- ings are obviated by the use of curved condenser shells and tubes. The tubes in these condensers are expanded into the tube sheets, the curvature in these condensers taking up expansion caused by the heating up. Tightness and less priming in the boilers, with dryer steam, are some of the advantages obtained. (2) Condensing Surface. — The tube, or condensing surface, is determined with regard to the vacuum required, the tempera- ture and quantity of the injection water and the amout of steam to be condensed. If Q = actual quantity of steam in pounds to be condensed per hour, obtained by multiplying the total quantity used per hour in the turbine by the dryness fraction. to =: temperature of injection. h = temperature of discharge. T = temperature corresponding to the vacuum within the condenser. Hr = heat of vaporization at temperature T. S = heat transmission per square foot of tube surface per hour for each degree difference in temperature inside and outside qi tubes (varying between 300-600 B. t. u.). A = tube surface in square feet, then A = With A, Q and ^0 constant and fj approaching f„ in value, T diminishes and becomes a minimum when t^ -— to, a condition im- 438 PRACTICAL MARINE ENGINEERING possible. Increasing A both t^ and ^i may be increased without change in T, which means the maintenance of vacuum with hotter injection. But with A constant, increasing tg without adding to the quantity, renders T greater and the vacuum, therefore, lower. Condensation at low vacua requires ample tube surface ef- fectively disposed, low temperature injection, together with a liberal allowance in quantity. Air being heavier than steam or vapor, sinks to the bottom of the condenser, and, at ordinary vacuum temperature, occupies a large volume. This air must be extracted in order to render this part of the tube surface efficient. Sec. 45. AIR PUMPS It is the purpose of the air pump to remove from the con- denser the water and such small quantities of air as may enter by leakage or with the steam, and which would ultimately de- stroy the vacuum if not removed. As often stated, it is the office of the air pump to maintain the vacuum formed by the condensation of the steam. The usual type of air pump is shown in Fig. 303. A is the piston or bucket moving in the barrel B, and carrying bucket valves, D, opening upward, as shown. The foot valves at C also open upward and admit the contents of the condenser from be- low. Beginning with the piston in the position shown the opera- tion is as follows : As the piston rises, the air and vapor between its lower face and the foot valves become rarefied, with a resultant decrease of pressure. Soon a point is reached where the pressure in the condenser is decidedly greater than in the space above the foot- valves, and in answer to this difference of pressure the valves open and admit air, vapor and water from the condenser. This operation terminates with the piston at the top of the stroke. On the return stroke the foot valves close and the contents of the barrel are forced through the bucket valves D to the space above. On the next stroke the contents are lifted and forced out through the delivery or head valves at E, where the air and vapor escape, and the water flows to the hot well, whence it is sent by the feed pump back to the boiler. It is evident that the pressure in the condenser cannot be reduced below that necessary to raise the foot valvesj so that for this reason, as well as for their more ready response to AUXILIARIES 439 Jiarint Sngirutring ^ Fig. 303. Vertical Attached Air Pump 440 PRACTICAL MARINE ENGINEERING variation of pressure, they should be made as light as is consistent with a proper performance of their duty. As shown in Fig. 304 such valves in modern practice are usually made of light sheet metal disks controlled by spiral springs. In older practice vul- canized rubber was quite commonly employed. It is also evi- dent that the foot valves will respond the more quickly, the more- rapidly the pressure above them decreases as the piston begins to rise, and hence the less the clearance space btween the valves and the piston when in its lowest position. The air pump has the peculiarity in its action, that the load per stroke and hence the resistance often decreases with an increase of speed, and increases with a decrease of speed. Hence when the pump is operated by an independent engine, it may rvi Jtarine MIngtaeering Fig. 304. Air Pump Valve, Guard and Spring be liable, unless carefully designed, to race or run away to ex- cessively high speeds with an increase of pressure in the steam cylinder, or to slow down and stop with a corresponding de- crease. .It is apparent also that a certain time will be needed for the foot valves to open, and for the air, water and vapor to flow through. Hence, with excessive speeds, the valves may not have time to open between strokes, the vacuum will become poorer, and the condenser may become flooded with water. It thus fol- lows that with too high as well as with too low a speed, the vacuum will be poor, and the operation of the pump unsatis- factory. The air pump may be driven either by an independent engine or by attachment to the main engine. The attached air pump is usually operated by air pump levers, which derive their motion in most cases from the low pressure crosshead. The stroke of AUXILIARIES 441 the pump is thus reduced to usually less than one-half that of the main engine. One of the advantages of the attached air pump is that the number of strokes per minute is necessarily the same as for the main engine, and it can neither race nor slow down on account of variations in its own resistance. A further advan- tage is that the power required for its operation is obtained more economically than when operated by a separate engine. The chief disadvantage of the attached air pump is that with the modem increase of revolutions, the speed may be too great Fig. 305. Air Pump for High Speeds for the best results from the pump as usually designed. This, together with the advantage of having the condition of the con- denser under control independent of the main engine, furnish the chief reasons for the use of the independent air pump. When thus fitted as an independent auxiliary the number of double strokes per minute usually varies from 15 or 20 to 30 or more, while the revolutions of the main engine may be from 100 to 200 or more. For special cases where the revolutions are very high, as in torpedo boat practice, but where for simplicity or for the saving of space it is desirable to use an attached air pump, the Bailey type of pump is employed. In this pump, as shown in Fig. 305, the water flows by gravity into the barrel through ports 442 PRACTICAL MARINE ENGINEERING alternately opened and closed by the piston itself, which thus serves as its own valve. The air and vapor naturally expand and enter with the water, and the whole contents are forced out of the end of the barrel through delivery valves similar to those in the pump of usual type. In some cases the delivery valves are Fig. 306. Vertical Independent Air Pump •carried on movable heads, which thus become valves in them- selves, and available to relieve the barrel in case the smaller valves give insufficient opening. In some cases, as shown in Fig. 305, the smaller valves are omitted and the entire head serves as the delivery valve. With this design air pumps may be successfully operated at speeds of 400 or 500 revolutions and higher. AUXILIARIES 443 When operated independently the air pump is very com- monly made double, and operated by one form or another of special steam valve gear. A typical form of independent air pump is shown in Fig. 306. The general operation of the valve gear is as follows : The beam which positively connects the main piston rods of the pumps operates from a point near its center and by means of rod and bell cranks, the slide valve of the horizontal cylinder which lies between the main steam cylin- ders, as shown. The piston of this horizontal cylinder is really the driving engine of the maiti steam valves, a function which it performs by means of a system of internal levers. The adjust- able collars on the valve stem of the "valve driving engine" af- ford a means for regulating for full stroke at any speed, while suitable cushion valves give a further controL over the action during the stroke, in regulating the distribution of the work and preventing the slamming of the foot valves. Sec. 46. FEED PUMPS AND INJECTORS Comparing the feed and circulating pumps the former has to handle a very much smaller quantity of water — usually from 1/25 to 1/60 the amount — ^but against a very much higher pres- sure, viz., that in the boilers. In consequence an entirely dif- ferent type of pump is required. The feed pump may be attached to the main engine, or run as an independent auxiliary. When attached to the engine it is usually of the type known as the plunger pump and shown in Fig. 307. The moving part consists- simply of the plunger, AB, working in the stuffing box, KL, and operated usually from the air pump levers. There are two valves or sets of valves, in- flow and outflow, as shown at F and E. The level of the pump is usually below that of the hot well so that the water stands ready to enter through the inflow valves as the plunger rises and makes room for it. This is aided by the partial vacuum formed within the barrel as the plunger rises. On the other hand, as the plunger descends on the next stroke the inflow valve closes and the water flows out through the outflow valve in order to make room for the descending plunger. It is thus seen that the pump is single acting ; that is, that it delivers but once in two strokes, and that the amount delivered is measured by the volume of the plunger displacement. 444 PRACTICAL MARINE ENGINEERING This in turn equals the cross sectional area of the plunger multiplied by the length of the stroke. The actual delivery per stroke will be somewhat less than this due to leakage, and to failure of the barrel to completely fill on the up stroke. The stuffing box, KL, is of course accessible and adjustable from the outside, and with proper design the inflow and outflow valves may be examined by the simple removal of a bonnet. The Fig. 307. Plunger Feed Pump strong points of this pump are its simplicity, and the ready accessibility for examination and adjustment of all parts on which the operation of the pump may depend. In fitting up the attached feed pump it is necessary to pro- vide it with some form of safety or relief valve, else should the discharge or check valve jam or fail to operate, the feed pipe or pump or some part of its operating gear would become broken. Such a relief valve is usually a simple form of spring loaded safety valve, and similar to engine relief valves. In order that the valve may be effective in relieving the pump and entire line of pipe it should be placed on the pump chamber or in any event not beyond the pump discharge valve. AUXILIARIES 44S Where the feed pump is operated as an independent auxil- iary it is usually of the direct acting or positive motion type. For feed pump purposes the area of the steam piston is made from two to three times the area of the water piston or plunger in order to give on the steam side a pronounced excess of total pressure over th.e resistance on the water side. This will enable the pump to overcome the resistance to the flow of the water through the feed pipe and check valves, and thus to force water Fig. 308. Turbine Driven Multi-Stage Centrifugal Feed Pump, Upper Half of Turbine and Pump Casings Opened into the same boiler from which it draws its steam, or even into a boiler with a pressure somewhat higher than that from which its steam is drawn. For the general purposes of a feed pump the vertical or Admiralty style has come to be very generally used. Its chief advantages over the horizontal type are two in number. ( 1 ) It occupies less floor space and may be conveniently put up on a "bulkhead or elsewhere, in such manner as to occupy but little space otherwise available. (2) The valves in the water end, as shown in the figure, are more conveniently arranged for examination by the removal of a bonnet than with the horizontal type of pump. These considerations, and especially the latter, have made this general type of feed pump the standard in modern marine engineering practice. 446 PRACTICAL MARINE ENGINEERING Of late years centrifugal feed pumps (Fig. 308), driven by steam turbines, have been coming into favor. These are par- ticularly adapted for use on vessels which have practically a con- stant speedj requiring constant power, as this type of pump falls off rapidly in efificiency as its output is decreased. This, coupled with the decreased economy of the driving turbine at reduced revolutions, make the combination undesii'able for ves- sels having great ranges of powers. In such cases it is neces- sary to fit several feed pumps so that the number in use may be decreased as the power decreases. These pumps are built in Fig. 309. Injector Stages, a lower stage runner discharging to the next higher stage until the required pressure is obtained. In addition to feed pumps of the plunger, piston or centri- fugal types, an injector is often fitted as an auxiliary means of. feeding the boilers. There are many different varieties of in- jector, but a description of one will suffice to illustrate the prin- ciples involved. Referring to the diagram. Fig. 309", .S is a nozzle connected with the upper pipe, B, leading steam from the boiler. When steam is turned on by means of the handle, K, and at- tached valve stem and valve, it escapes in a jet which enters the slightly tapered passage VC. The air in the space around, and between these two orifices is caught and drawn along with the jet, thus causing a reduction of pressure at this point. This AUXILIARIES 447 space is connected through the lower pipe, B, to the water reser- voir, and when the loss of pressure is sufficient, the water rises the same as in the case of a pump. The water and steam are thus brought into contact, and pass on together into the com- bining and delivery tube CD. The steam is here condensed and the resultant jSt of water attains a very high velocity. A little further on, when this is reduced to the relatively low velocity of the water in the feed pipe, the pressure developed is sufficient to overcome the boiler pressure, to open the check valve, and to force the water into the boiler. It may aid the understanding of this seemingly puzzling re- sult if it is remembered that it is the energy of the steam which is the real motive power. This is transformed largely into motion in the combined jet, and this, when arrested, gives the pressure, as stated before. In the steam pump a steam piston is provided much larger than the water plunger in order to give a force suffi- cient to overcome the resistance of the feed pipe and at the check valve. So in the injector, in a somewhat similar manner, the energy of the steam in a relatively large pipe' is concentrated on a small jet of water, giving it the high velocity and later the pressure, as described. In passing it may be noted that as a boiler feeder a good injector has piractically a perfect efficiency, all heat used being carried back again into the boiler, except the small amount lost by radiation from the instrument and connecting pipes. An injector of the type shown in the figure is known as an automatic injector. This signifies that once the injector is ad- justed and working, should, the jet of water become broken by a jar or other accidental circumstances, it will restart itself without further adjustment. The capacity and working range of an in- jector are decreased as the lift is higher and as the water is warmer. With cold water and a moderate lift, say not exceed- ing 5 to 8 feet, a good automatic injector will start up with 25 or 30 pounds steam pressure, and will work with little or no further adjustment over a range of perhaps 100 pounds pressure. With feed water at about 100 degrees F., the same injector would start at 30 or 35 pounds steam pressure, and will work over a range of perhaps about 70 pounds or up to about 100 pounds. In addition to the automatic injector there is another type having two sets of tubes, one for lifting and one for forcing. 448 PRACTICAL MARINE ENGINEERING Such instruments are often termed inspirators to distinguish them from the ordinary automatic injector. When properly ad- justed the lifting set of tubes acts as a governor to the forcing set, supplying under a great range of steam pressure the proper amount of water to condense the steam in the final set of tubes. Such an injector handling cold water with a short lift, will work through a range of over 200 pounds, while with water as hot as 100 degrees F. and small lift it will work through a range of from 150 to 200 pounds. The operation of each set of tubes is on the same general principles as above described for the automatic injector. Sec. 47. AUXILIARIES FOR TURBINES All the auxiliaries used in arrangements with reciprocating engines are required also with turbine installations, together with a few others in addition. These latter concern principally appa- ratus for increasing the vacuum and for maintaining efficiently the forced lubrication in the rotor bearings. Among the auxiliaries which are directly influenced by the use of steam turbines are to be noted : Circulating pumps, con- densers, air pumps, oil pumps, oil coolers and appurtenances for the distribution of the oil. [i] Circulating Pumps The size of these pumps is made larger than those for reci- procating steam engines, in order to deliver greater quantities of cooling water needed for the higher vacua required with the steam turbine. . They are invariably made of the centrifugal type. When driven by reciprocating engines, there is one single runner of a diameter such as to give a velocity of discharge at the tip of the runner that its revolutions become suitable to the engine. II driven by a turbine, which revolves very much faster, the diameter of runner may be smaller and still give large enough peripheral runner velocity to sustain to- gether the discharge and velocity heads. Then, however, for large quantities of water it is advantageous to mount two runners on the shaft instead of one with very broad tips. Such pumps are now being used for large condensing apparatus. The quantity of cooling water required per pound of steam to be condensed depends on the vacuum as well as the tempera- ture of injection. If the temperature corresponding to a certain vacuum is T, and the heat of vaporization corresponding thereto AUXILIARIES 449 Hy, and the mean temperature of the injection water within the condenser tubes is t, then the temperature difference outside and inside of the tubes equals T — t in degrees F. If Q := cubic feet of water required to be delivered per miritte by the pump, W = pounds of steam to be condensed per minute, 62.3 := weight in pounds per cubic foot of water, then (T—t) X62.3 [2] Air Pumps In addition to the ordinary wet air pump used with recipro- cating steam engines, it is common practice with turbines to fit I I Fig. 310. Dry Vacuum Pump either dry vacuum pumps, vacuum augmentors or pumps of the dual (combined wet and dry) type. Other types, supposed to do in one operation what all of the foregoing do together, are the Rotrex, the Leblanc and the Kinetic rotary air pumps^and air ejector systems. Dry vacuum pumps are operated in connection with the wet air pumps in such a way that their suctions connect to the highest point on a suction air chamber- placed in the suction pipe between the condenser and the wet pump. Such an arrangement not oniy 4SO PRACTICAL MARINE ENGINEERING keeps a constant head of water on the suction side of the wet pump, but also, due to the vacuum created in the top of the cham- ber, induces a current of air and vapor in this direction, at the same time diminishing the condenser pressure and enhancing the vacuum. The vapor and air are discharged overboard. The dry vacuum pump, Fig. 310, used in this connection consists of two separate air cyHnders with packed pistons. They are driven by separate steam cyHnders connected to one shaft. Ports around the air cyHnders about at the middle connect the suction end with the discharge end of each cylinder. On the down stroke, after having passed the ports, the upper parts of the cylinder become filled with the vapor, which is compressed by the piston on the up- stroke, and is discharged through the head valves into the escape pipe. The pumps run at about 275 revolutions per minute, and increase the vacuum by from i to 2 inches. In more recent designs the wet and dry pumps are combined in one apparatus, called "Dual air pumps." They consist of sepa- rate wet and dry pump cylinders driven by a steam cylinder mounted on top of the wet air pump cylinder and a walking beam connected to the crosshead driving the dry pump. The dry pump suction connects with the suction of the wet cylinder, and the dry cylinder being water cooled, densifies the contents and increases its efficiency. In ordinary pumps the hot well temperature for a given vacuum is dependent on the air pump capacity or the vacuum it is able to produce. By making use of separate pump cylinders, handling the water independently of the air, and cooling the air in a separate cylinder by separate cold injection non-returnable to the feed tank, the temperature of the hot well remains at practi- cally the temperature of the vacuum. This system, as compared with separate wet and dry pumps, is simpler, and possibly more economical in operation. Referring to Figs. 311 and 312, the wet air pump is situ- ated below the steam cylinder, as this pump is the only one which works under considerable load; the dry air pump is driven by a beam in the usual manner. One connection is made to the condenser, but a branch' pipe is led to the dry air pump, the connection being made in such a manner that the water from the condenser will pass it to the wet pump. The dry air pump discharges through the return pipe and a spring loaded valve into the wet pump at a point below its AUXILIARIES 4SI head valves. When starting the pump the filling valve is opened for a minute or so to enable the vacuum to dra^? in a water supply for priming from the hot well pump. The valve is then closed and the water passes from the hot well of the dry pump by the pipe to the annular cooler, through which sea water circulates, and after being cooled passes into the suction of the dry pump ; then passing through the pump it becomes heated aad again passes Fig. 311. Weir Dual Air Pump to the cooler, and so on in a continuous circuit, any excess passing over the pipe to the wet pump. The spring loaded valve is adjusted to maintain a vacuum of about 20 inches in the dry pump hot well when the condenser is working at 28 inches vacuum, and this difference of 8 inches in vacuum is sufficient to overcome the friction in the cooler and to pass the water into the suction. The function of this cooling water is to reduce the temperature and, accordingly, the volume of the air handled by the dry air pump. The volumetric capacity of wet air pumps used in connection with marine turbines is made about 100 cubic inches per shaft horsepower. Single acting vertical air pumps should always be used when weight and space permit. 452 PRACTICAL MARINE ENGINEERING If D =: diameter of pump barrel in inches, S = stroke of pump piston in inches, N =: numbcE of single strokes per minute, S. H. P: = shaft horsepower, then D = u ■^4 S. H. P. NXS The capacity of dry air pumps in cubic feet of volume swept by the air pistons should be 40 to 50 times the volume of the con- densed steam. li W ^ steam condensed per minute in pounds for total S. H. P. D = diameter of cylinder in feet, S = stroke of piston in feet, N = number of revolutions per minute, then D = .6yl~ W NXS (i) Vacuum Augmentor. — The augmentor consists of a steam ejector proportioned to use either high pressure or low Fig. 312. Weir Patent Dual Air Pump, Cooler and Connections pressure steam as may be desired which is arranged with either an independent suction with an internal connection from the lower part of the condenser or with a suction connection from the top of the main air pump suction pipe leading to the bottom of the con- denser. The steam ejector discharges into a separate small con- denser called "augmentor condenser," in which the pressure be- comes from I inch to i J4 inches higher than in the main condenser. The function of this small condenser, which receives its circulat- ing water from the main condenser, is to condense the ejector steam and to densify the vapor and air drawn off from the main AUXILIARIES 453 Ohc Water Inlot to AugmeDtor Coudeu&cr AugmcDtor Ko2zle -,/Sleaiu to Augiueutor Fig. 313. Vacuum Augmentor condenser. The main air pump suction connects thorugh a water seal to both the main and the augmentor condenser, the increased pressure in which forces the mixture into the air channel-way. The water seal prevents the gases from re-entering the main con- denser. See Figs. 313 and 314. (2) Lehlanc Air Pump. — This pump is a rotary pump, which consists principally of a steam ejector and a fast revolving tur- bine wheel, with similar action to a "Sirocco" fan impeller. In Fig. 314. Vacuum Augmentor A Main Condenser. B — Air Suction. C — Steam Nozzle. D — Steam Pipe to Nozzle. E— Ejector Body. F— rVapor Inlet from Ejector to Augmentor. G — Scatter- ing Plate for Vapor. H — Augmentor. I — ^Augmentor Outlet. J — Water Seal. K — Air Pump Suction. L — Cooling Water Inlet. M — Cooling Water Outlet. — Con- densate Suction from Main Condenser. 4S4 PRACTICAL MARINE ENGINEERING operation, the ejector is first started, and, as soon as a sufficient vacuum is formed, causes the water to rise in the suction pipe con- necting the condenser and to enter the nozzle communicating with the turbine wheel. The wheel is driven by either motor or tur- bine, and runs as high as 2,500 revolutions per minute. Referring to Fig. 315, the water operating the pump, which, when used for ships, may be sea water, although this entails a loss of fresh water, enters pipe B and then through chamber C Fig. 315. Leblanc Air Pump into the wheel. Between the thin, solid sheets of water thrown off by the vanes large volumes of air and vapor from the con- denser become entrained. The velocity of the water, together with the tenacity of the film, renders discharge against the atmosphere possible. The discharge chamber of the wheel is, at the same time, the suction pipe from the condenser, and form? also the bore of the ejector. A separate hot well pump draws off all the condensed water, and, therefore, the water used by the wheel in throwing off vapor and air does not come into contact with any of the condensed fluid. Due to this fact, its temperature remains low, and it may also be used for circulating water in the main condenser. (3) Rotrex Air Pump. — This pump consists of a cylindrical casing and an eccentrically mounted rotor placed on a shaft carried by outside bearings. The suction and discharge compartments are separated by a radius cam, which is carried in independent AUXILIARIES 455 bearings. This radius cam is operated from the rotor shaft by a lever and crank. The rotor and cam are operated with close clearances, which are water sealed, enabling high vacua to be maintained. There are metallic discharge valves, but no suction valves. (4) Kinetic Air Pump System. — In the Kinetic system the air and non-condensible gases are removed from the condenser by the action of a steam jet followed by a special system of water jets known as the "Kinetic ejector." Jets of water moving at a high velocity through suitably shaped orifices have been used for many years for the purpose of producing a partial vacuum for various purposes, including the rarefication of the vapor spaces of condensers. A water jet has of itself a relatively low capacity for assimilating and withdraw- ing air, and, therefore, should this type of air extractor be em- ployed when the quantity of air to be removed is appreciable, then the quantity of water or the pressure necessary for the jet is large and the expenditure of power excessive. The air with- drawing capacity of any water jet device is, however, greatly increased if the air to be extracted is previously mixed with steam. In the case of the Kinetic plant the steam is introduced into the air suction pipe through a high velocity nozzle, thus entrain- ing the air and intimately mixing with it. This steam is con- densed on the secondary sprays of the Kinetic ejectors, and the resulting liquid carrying with it all occluded air and gases is ejected to the atmosphere by the main water jet. The steam jet is fed with live steam in the case of plants fitted with electrically driven pumps, or with exhaust steam at a pressure of about 20 pounds above the atmosphere, if this be available. The quantity of steam required varies according to the amount of air leakage and the size of the plant, but from 3^ to ^ of one percent of the steam to be condensed may be taken as an average figure for installations of considerable dimensions. The water for the Kinetic jet is water of condensation which has already been removed from the condenser, and the whole of the latent heat contained in the steam used in the steam nozzle is absorbed by this water, which is subsequently discharged to the feed tank at a correspondingly higher temperature than when it left the condenser. The water of condensation is withdrawn from the condenser 4S6 PRACTICAL MARINE ENGINEERING and discharged ^ against the pressure of the atmosphere by the action of two pumps of the centrifugal type, known as the "head" pump, and "pressure" pump respectively. The "head" pump works under the condenser pressure both on the suction and on the de- livery sides, and is designed so that it will pass the required quantity of water with an extremely low head on the suction side of the pump. The water is discharged from this pump into a stand pipe or receiver which provides a natural head of water on the inlet side of the "pressure" pump, by which the water is finally ejected against atmospheric pressure. This patented arrangement makes it possible to place the pumps only a few inches below the level of the condenser bottom, and a perfectly regular discharge is maintained at all loads, the amount corres- ponding to the quantity of steam condensed. Ordinarily centrifugal pumps have been successfully used for the withdrawal of the water of condensation from condensers both of the surface and jet types, but for satisfactory operation these pumps must invariably be placed at a considerable distance below the level of the condenser, a condition which in practice is often very difficult and costly, if not impossible of attainment. For marine use single centrifugal pumps are apt to work very irregularly due to changes in the relative levels of the condenser and pump consequent on the motion of the vessel. In the case of the Kinetic plant the vertical stand pipe be- tween the "head" and "pressure" pump maintains a practically constant head on the latter irrespective of the motion of the vessel. The claims made for this type of apparatus are : The energy lost from the system in a normally designed in- stallation does not exceed 0.0003 (or three ten-thousandths) of the energy developed by the total steam which is condensed. It will be noted that the whole of the energy in the steam jet, also that required to drive the air and water extraction pumps, is returned to the system, with the exception of : (a) The theoretical energy required for the extraction of the water, and (b) The theoretical energy required for the compression of the extracted air against atmospheric pressure. With the above exceptions which have been proved by direct experiment to be practically negligible, the whole of the energy AUXILIARIES 457 expended reappears in the form of heat in the Kinetic tank, whence it is returned to the boilers, subject only to a small further loss through radiation from pipes and other exposed surfaces. The energy expended, but again recovered as heat, takes the following forms : (a) Sensible heat in the steam jet. (fc) Latent heat in the steam jet. (c) Mechanical losses in the mechanism. (d) Fluid frictional losses in the pumps. (^) Energy used to produce the high velocity air extracting water jets. As these recoverable losses are many times as great as the irrecoverable losses named above, it will easily be seen how the extraordinarily high efficiency is obtained. Referring to the diagram, Fig. 316, rarefication of the con- denser is effected by steam jet (2) followed by the action of Fig. 316. Diagrammatic Illustration of Condenser with Kinetic Air Pumps 1 — ^Air- Suction Orifice on Condenser. 2 — Exhaust Steam Jet. 3 — Air Pipe to Kinetic Ejector. 4 — Kinetic Ejector. 5 — Suction Pipe to Kinetic Pump. 6 — Kinetic Pump Discharge Pipe. 7 — -Condensed Water Pipe to Head Pump. 8 — Stand Pipe between Head and Pressure Pumps. 9 — Pressure Pump Discharge to Tank. 10 — Non- Return Valve. 11 — Feed Water Delivery Pipe. 12 — Float Controlled Feed Delivery Valve. 13 — Kinetic Tank. 14^ — Pressure Equalizing Pipe. 15 — Exhaust Steam to Jet. 16 — Surplus Exhaust Steam. Kinetic ejector (4) supplied with water by the Kinetic pump through pipe (5) and discharging into the Kinetic Tank (13). Water of condensation flows through pipe (7) into the head pump whence through stand pipe (8) to the pressure pump, and 458 PRACTICAL MARINE ENGINEERING thence through pipe (9) and non-retnrn valve (10) into the Kinetic tank. The excess of water in the tank corresponding to the feed water is delivered by the Kinetic pump through pipe (11) and float controlled valve (12) into the feed tank which may be placed overhead. (5) Westing housc-Leblanc Air Ejector System. — The prin- cipal difference between this system and that last described is The Ejector may be incIiDecl to fbe vertical, but the an^e of inclination should not exceed 60.° Condensate Pump' Feed & Filter TankL I f To Peed ♦ Pump Fig. 317. Diagrammatic Arrangement of Westinghouse LeBlanc Air Ejector for Marine Purposes . ^ Note. — When the main engines are stopped and no steam is condensed in con- denser, but the vacuum must be maintained in the same, feed water is admitted to the condenser by opening the globe valve of the circulating pipe in order to circulate water through the condensate pump and to cool the feed water, the temperature of which would increase by the continuous supply of steam from the ejector. that there is no ejector fitted in the centrifugal pump discharge, this pump being especially developed for high efificiency under very low suction heads. The arrangement of the system is shown very clearly in Fig. 317. [3] Lubricating System Owing to the high number of revolutions at which steam turbines are operated, a highly efficient oiling arrangement is necessary. An unfailing oil supply, filtering and effectual cool- ing become, therefore, matters of great importance. The oil sys- tem comprises essentially such auxiliaries as oil pumps, piping, drain tanks, distributing tanks; oil coolers, and pumps furnishing circulating water for the oil coolers. The number and size of pumps and coolers are largely governed by the size of the turbine AUXILIARIES 4S9 Vapor Inlet installation, the oil pumps being usually furnished in duplicate units of whatsoever number of pumps each unit requires. In operation, the oil is supplied by forced lubrication to all turbine bearings, as well as line shaft bearings, under pressure varying from 15 to 35 pounds per square inch. The oil is pumped from the oil drain tanks, placed low down in the ship, into which tanks the oil drains by gravity from the bearings through one or more of the coolers to the various bearings. Another ar- rangement, which has the ad- vantage of absolute certainty in case of breakdown as regards any one of the oil pumps, is to pump the oil to a distributing tank, placed at a high point in the ship, from which the oil flows by gravity through coolers into bearings. Sight glasses are fitted at all return pipes from the bearings, to enable observation of flow. Therrnometers are fitted at both inlet and outlet of the coolers to ascertain the temperature of the oil. The coolers are made either witb plain tubes, or with tubes twisted into spirals. The shell is' made cylindrical, of sheet cop- per, heads and tubes being made of brass. The circulating water flows through the tubes and the oil within the shell and around the tubes. By means of baffle plates in the shell the oil travels four to six times the length of the shell, the direction of flow of the two liquids being in opposite directions. (Fig. 318.) The SECTION B-B Fig. 318. Zimmermau Oil Cooler. This may be used as Fresh Water Distiller, Better results obtained with oil and water interchanged from those shown. 46o PRACTICAL MARINE ENGINEERING flow of water and oil may, however, be changed, the water flowing around the tubes, but inferior results will be obtained. [4] Water Service Cooling water is not generally used through main turbine bearings or in line shaft bearings in turbine installations for tor- pedo boat destroyers, nor with large turbines of the Parsons type, the circulation of oil through these bearings being rehed upon to keep the bearings at a sufficiently low temperature. In heavy and large turbines of the Curtis type, however, a separate water service pipe, connected to the discharge side of the circulating pump, supplies water circulation to the spring bearings and main turbine bearings. The system as provided for the main turbine bearings, thrust horseshoe bearings, oil reservoir in thrust pedestal, and the cooling coils in oil drain tanks, usually takes the cooling water from the main circulating pump discharge and discharges it into the suction of the same pump. [5] Operating Gear Various systems are used in the arrangements of operating valves and throttle valves for the manipulation of the main tur- bines. An arrangement often used in torpedo boat destroyers having Parsons turbines, where all the valves controlling the steam to both ahead and astern turbines, as well as those to the cruising turbines, are grouped on the forward bulkhead at the working platform. (See Chap. VI.). Other arrangements consist of balanced throttle valves admit- ting steam from the main steam pipe to the ahead and astern steam chests, respectively, each entirely independent of the other, and controlled by hand wheels from the working platform. Ahead of the two throttle valves in the steam line is an emergency stop valve of the butterfly type operated by hand from the working platform. [6] Turning and Lifting Gear Means for turning over the rotors for examination and repairs are provided in the form of worm wheels on the shafts of the tur- bines. These wheels engage with removable worms and shafts, turning motion being transmitted either by a ratchet wrench or by regular turning engines, as may be required by the size of the installation. Lifting gear is provided for handling the rotor and the upper AUXILIARIES 461 casing of the turbine cylinder in the erection or dismantling of the parts. A motor acting through a system of worms and worm- wheels on threaded spindles at each end of the turbine will raise or lower either casing or rotor. The lifting yokes are guided so as to prevent damage to the blading while removing the respective parts. Sec. 48. FEED HEATERS The office of the feed heater is to raise the temperature of the feed water from that of the hot well as nearly to that within the boiler as may be practicable before the feed enters the boiler proper. Feed heaters are of two fundamentally different types, according as the heat used is drawn from waste furnace gases or from steam. If the former, as is very common with water- tube boilers, the feed heater is really a part of the boiler. The entire operation is thus performed in two stages, one in the heater, and one in the boiler proper. In the- first stage it is sought to raise the water as nearly as possible to the boiling point by use of the furnace gases after they have passed the main steam generating tubes. In the second stage, carried out in the boiler proper, the previously heated water is transformed from liquid into vapor. The resulting economy comes from being thus able to re- duce the products of ■ combustion to a temperature lower than they would otherwise have before finally getting rid of them. The addition of the heater will, of course, affect the draft, and the extent to v/hich heating surface, either in the form of steam generating tubes or feed heating tubes, can be added without seriously interfering with the draft is a point which must receive consideration. Moreover, since the feed heating surface might be put into additional main boiler tubes, thus giving the same total surface without a feed heater, the question may naturally be asked whether in such case the results would be as good. In other words, is it better to put the total heating surface all into main boiler tube surface, or to divide it up and put a part (usually quite small) into a feed heater located beyond the main part of the boiler? Experience seems to indicate the latter as the better design of the two, and the fundamental reason is that given above — viz., that it is thus possible to reduce the products of combustion to a lower final temperature than with main boiler tubes of the same aggregate surface. The reason for this is 462 PRACTICAL MARINE ENGINEERING found in the fact that the temperature of the feed water as it en- ters the heater is much lower than that of the steam and water within the main tubes. Hence with such a heater the gases as they leave the boiler pass over relatively cool surfaces, and the flow of heat will be much more pronounced on account of the greater temperature difference between the water and the gases, - TO CONDENSEH- . Haritw EnginMriblg eUPPLY TO SECOND PUMP Fig. 319. Feed Water Heater, Direct Contact and the gases will be more effectively cooled than by passing over an equal area of main boiler tube surface. Turning now to the other type of heaters an entirely different mode of operation is encountered. Here the heat given the feed water comes from steam which is drawn either directly from the main or auxiliary steam pipe, or from the receivers of the main engine, or from the exhaust of- some of the auxiliaries on its way to the condenser or to the escape pipe. There are two styles of heater working on this principle. In one the steam and feed AUXILIARIES 463 water are mixed together in the same chamber and the steam is condensed and thus joins the feed water, raising its temperature as may be determined by the conditions of operation. In the other style the steam is on one side of a coil or nest of tubes and the feed water on the other side, the heat passing through the metal of the tubes from the former to the latter while the steam condensed in consequence of the loss of heat is drawn or trapped out as may be required. Where the steam and feed water are mixed together the feed heater consists essentially of a chamber or drum, as in Fig. 319, provided with means for introducing the feed as a spray or series of cascades, while the steam is introduced in jets, and the two thus become intimately mingled. In the form here shown the feed enters through C and pass- ing out through a valve, D, falls as a cascade through the an- nular space between the pipe and the steam delivery drum which is pierced, as shown, with small holes. The steam enters through B, and passing through the holes in small jets becomes mingled with the water and thus imparts to it its heat, The two then fall to the bottom of the chamber from whence the feed pump takes its supply, and by means of which the water is finally sent to the boiler. The advantages of such a form of heater are simplicity in the apparatus itself and a quicker action than with tubes, as in the other form. The chief disadvantage lies in the fact that an ad- ditional feed pump must be provided ; one for forcing the water from the hot well to the feed heater and the second for taking it from the heater and forcing it into the boiler. Turning to the other style of heater, as illustrated in Figs. 320 and 321, there is a chamber or drum containing a nest of corrugated copper pipe. The feed water passes on one side of the pipes and the steam on the other, as shown, the heat passing through from the one to the other, as above described. Where such a heater is fitted to utilize the steam from an auxiliary ex- haust, the heater forms simply a part of the exhaust passage and the steam passes through continuously, simply leaving a part of its heat behind. In other forms of heater there is no continuous flow of steam through, but the steam is led to the steam side from the source selected and there gradually condensed by the loss of 464 PRACTICAL MARINE ENGINEERING heat, while the water thus formed is drawn off as may be neces- sary. The heater is thus kept clear for efficient operation, and the water is returned to the hot well or otherwise into tlie feed system. RELIEF VALVE .^ ^a^T'^'J'"'*'^^ BLOW-OFF Fig. 320. Feed Water Heater, Surface Fig. 321. Feed Heater. Film Type In heaters of this type the flow of water is continuous from the feed pump through the heater to the boiler, and no additional pump is required as with the other type referred to above. The difference is due to the fact that where the water and steam are AUXILIARIES 465 separated, the water side of the heater can be operated under the full pressure in the feed Pipe and thus made part of the feed circuit. Where the water and steam are mixed the interior of the heater cannot be operated under any such pressure, and thus two separate pumps are required. In heaters using steam from the steam pipe or from the re- ceivers, it is clear that all such steam would ultimately go to the condenser and thence back to the boiler as feed water, and hence that no heat is saved which would otherwise have been thrown away. In such cases it is not at first sight clear where the gain can come in, for the operation seems to be a simple shifting of heat from one part of the cycle to another without gain or loss in total amount. As a matter of fact the operation does consist of just such a shifting of heat, and here is where the gain in work comes in. The shifting of heat from one part of the cycle or routine of the steam to another introduces a change which brings the cycle a little nearer that for the highest efficiency. While, therefore, there will be no saving of heat as such, the engine may be enabled to better use the heat which is provided and thus to show a larger return in useful work. These points cannot be here discussed in detail, but it seems at least worth while to note in general terms the chief source of the economy experienced with such heaters. Especially will heaters of this type affect the routine of the steam favorably when they are arranged on the compound or step by step principle. In this arrangement the feed passes through a first chamber and receives heat from steam drawn from the low pressure receiver. It then passes on to a second chamber and there receives heat from steam drawn from the next higher receiver, and so on, in the last receiving a final addi- tion of heat from steam of full boiler pressure. This type of heater, when of sufficient capacity to raise the temperature of the feed nearly up to that of the water in the boiler, wijl effect a marked economy in the routine through which the steam is car- ried. In addition to the saving thus effected by feed heaters, many engineers believe that they are of use in reducing the strain and wear and tear on the boilers by furnishing a hot rather than a cold feed, and hence that they are of distinct advantage to the boiler as well as to the engine. -466 PRACTICAL MARINE ENGINEERING Sec. 49. FILTERS Feed water filters are provided for removing oil from the feed water before it enters the boiler. Such filters are made in various forms, the chief features being the kind of filtering material employed, and the arrangement of the flow of water through it. Animal charcoal, sand, gravel, broken pumice stone, etc., form one class of substances, while fibrous materials, such as sponges, bagging, toweling, etc., form another case. Of the first class, animal charcoal is the best, though somewhat expen- Marine Enghuning Viz. 322. Feed Water Filter sive. It may, however, be removed from time to time, washed in lye water and replaced, and thus made to do duty for a long period of time. The various fibrous materials, such as sponges or bagging, soon become clogged also with oil and impurities, and require either replacement or washing and cleaning. After a few repetitions of cleaning in this manner, such material must be re- placed with new. Filters also dififer, according to whether the flow of watei through the filtering material is forced by the pressure of the feed pump, or is due simply to the flow under the action of gravity. In gravity filters the flow may be up and down, two or AUXILIARIES 467 three times through the bed of filtering material, the course be- ing determined by suitable partitions or passages within the filter box. When the action is under pressure the filter forms a part of the feed pipe circuit and the water enters and passes through, urged by the action of the feed pump, though at a much lower velocity than through the feed pipe itself. In such case, if the filter should become choked, excessive pressure might be de- veloped between the feed pump and filter with the possibility of a rupture of the latter. To avoid this danger a by-pass pipe and safety valve may be arranged so that the valve will open under an excess of pressure and allow the water to flow around the filter to the continuation of the feed pipe beyond. The safety valve may also be maintained open by appropriate means and the filter shut off by stop valves, thus sending the feed through the by-pass pipe and leaving the filter free for examination and repair. In Fig. 322 a simple form of filter is shown with bypass pipe and valves for controlling the flow of the feed. From the explanation above the operation of the filter will be readily understood. Sec. 50. EVAPORATORS The office of the evaporator is to supply fresh water to make up the loss in boiler feed. Of the steam which the boilers supply not all can find its way back through the feed. Small steam leaks may occur at the various joints and stuffing boxes, some of the auxiliaries may not send their steam to the condensers, the whistle may be used (as in foggy weather), and so in various ways losses of fresh water will occur. The proportion of such loss varies widely with circumstances, but will often amount to 5 percent and more. In order to avoid making up this loss with salt water the evaporator is provided. A modern representative evaporator consists of a series of nests or coils of pipe contained within a chamber, as shown in Figs. 323 and 324. The chamber has a salt water inlet, and steam from the boiler or from one of the receivers is passed inside the tubes. The heat in the steam passes through the tubes and forms steam or vapor of lower pressure on the salt water side. The chamber is connected with the condenser or with the low pres- sure receiver, and the steam formed in the evaporator is thus 468 PRACTICAL MARINE ENGINEERING passed into the main circuit and serves to make up the loss as specified before. At the same time the water formed in the coils by the loss of heat is drawn or trapped out as it accumulates, and is returned to the feed, so that all steam formed on the salt water side is a net gain for the fresh water account The coils Fig, 323. Evaporator on the outer or salt water side naturally become coated with scale, so that they must be cleaned from time to time. To this end they are usually made removable or arranged so as to be readily accessible through manhole openings in the shell. It is, of course, essential that the tubes be kept clean for the most effi- cient working of the evaporator. AUXILIARIES 469 In the operation of the evaporator the chief point requiring attention is the proper proportion between the amount and tem- perature of the inflowing steam and the pressure within the chamber on the salt water side. If the pressure is low and Fig. 324. Evaporator of Return Flow Type steam is provided in excess, it may give rise to a violent ebul- lition or foaming, which will carry some of the salt water along with the vapor formed, and thus introduce salt into the circulat- ing system. This condition must be guarded against by a proper control of the amount of steam admitted. 470 PRACTICAL MARINE ENGINEERING In the way of general maintenance, the tightness of the tube joints and the condition of the tubes as regards scale are the chief points requiring attention Sec. 51. DIRECT ACTING PUMPS In early marine practice the fly wheel pump was a favorite type, and was used for all ordinary purposes where an inde- pendent pump was required, as for boiler feed, fire purposes, or for general purposes on shipboard. This pump consisted essen- tially of horizontal steam and water cylinders with the piston and plunger on a common rod and moving together. Attached to the rod was a crosshead with connecting rod leading to a crank and shaft carrying a fly wheel. The fly wheel served to carry the pump past the dead points, and the shaft served to carry an eccentric which actuated a simple slide valve on the steam cylinder. This type of pump, however, has almost entirely disappeared from modern practice, its place being taken by the direct acting pump with its greater compactness of form and better adapta- tion to the conditions of service. Now consider briefly the essential features of this type of pump, with a few examples drawn from modem practice. As illustrated in Fig. 325, the pump is horizontal and con- sists of two cylinders, one for steam and one for water, carried on a common piston rod. The steam end is operated by means of a suitable valve gear as a simple reciprocating engine, and thus communicates the same movement to the pump plunger or piston. Each end of the water cylinder is provided with both inflow and outflow valves, as shown, and thus the pump becomes double acting — that is delivering on each stroke alternately from one end and then the other. For operating the steam ends of pumps of this type, a great variety of ingenious valve gears have been devised. The need for special devices arises from the fact that there is no rotating part and no chance to use an eccentric, and that the valve cannot be operated directly from the main piston rod. Where it is thus required that a single set of principal moving parts be self operating, the valve gear usually consists of the following chief features : AUXILIARIES 471 (i) The main steam valve, often of special form, but usu- ally operating as a simple slide valve. (2) An auxiliary plunger or piston moving in a cylinder formed in the valve chest, and coupled or connected to the main valve. Jferfw Xni /i tue il ng Fig. 325. Direct Acting Independent Feed Pump (3) An auxiliary valve controlling steam and exhaust to and from the two ends of the auxiliary plunger cylinder. (4) Means for operating the auxiliary valve from the main piston rod. Such means may consist of levers, links, rods, cams, etc., operated by tappets on the main rod, whose location or point of operation may be adjusted according to the length of the stroke desired. The chain of operation is then, in general, as follows : Just before the end of the stroke the tappet or other piece 472 PRACTICAL MARINE ENGINEERING moved by the main piston rod gives motion to the auxiliary valve. This produces an adjustment of steam and exhaust for the auxiliary cylinder which results in a movement of the auxil- Fig. 326. Vertical Duplex Feed Pump Admiralty Type Staritu Engi»e4rtnfi Fig. 327. Vertical Single Feed Pump iary valve. This produces an adjustment of steam and exhaust for the auxihary cylinder which results in a movement of the auxiliary piston and hence the movement of the main valve as de- sired. The motion of the main piston is thus reversed and the AUXILIARIES 473 stroke takes places in the opposite direction, and so on continu- ously. In Fig. 325 the lower section is horizontal and taken through the auxiliary piston and auxiliary slide valve operated by the levers and links as shown. The upper view shows in vertical section the auxiliary piston and main steam valve. If two such pumps are placed side by side, it is found that the valve of each pump may be operated from the piston rod of the other. Hence by appropriate connections a pair of such pumps may be made self operative, the strokes being made alter- nately, and each piston rod running the valve gear of the other pump. Such an arrangement constitutes a duplex pump, a form which has enjoyed wide and continued favor among marine en- gineers for feed pumps and for other purposes with generally similar conditions. In the so-called "Admiralty" style of pump the motion of these parts is vertical, and the water valves are specially arranged with a view to ready examination and overhauling. This general style is quite commonly used for feed pump purposes. Such pumps may be either simple or duplex, but the duplex type is more commonly met with in this form, although the simple type is the more economical in steam expenditure. In Fig. 326 is shown one member of a duplex admiralty pump, the arrangement of the parts and operation of which will be apparent without fur- ther explanation. In Fig. 327 is shown similarly a single ver- tical type of feed pump with independent valve gear, the auxiliary piston being operated by the opening and closing of ports due to a rocking motion which is communicated to it by the levers and link work, as shown. Bilge pumps, when independent, and all general service pumps, are usually of the direct acting form, as above illustrated. The chief item of difference is found in the ratio of the areas of steam piston and water plunger. Where the water is to be de- livered under considerable pressure, as for feed pumps or for fire purposes, the area of steam piston will be from two to three times that of water plunger. Where the resistance to be over- come is less, as in a pump for freeing the bilge or for circulat- ing water throiigh distillers, evaporators, waterclosets, etc., the water plunger may be relatively larger and such pumps will be found with a water end only slightly smaller or equal in size or even larger than the steam end. 474 PRACTICAL MARINE ENGINEERING Such pumps are generally, though not always, so con- nected up as to enable them to be run from the auxiliary boiler! Sec. 52. BLOWERS OR FANS The centrifugal blower is the type universally used on ship- board for all purposes requiring the handling of large quantities of air under light pressure, as for ventilation and forced draft. As indicated in Fig. 328, such a blower consists of a series of flat or nearly flat steel vanes carried on a shaft and surrounded Fig. 328. Destroyer Forced Draft Fan, Vertical Unit, Open Type, Terry Turbine by a casing. The principle of operation is the same as with the centrifugal pump. The rotation of the vanes sets up first a cir- cular current or rotation of the air, and as a result of this motion, centrifugal force is developed which carries the air out toward the tips of the blades and develops an increase of pressure from the hub outward. If an outlet is then provided in the outer shell of the casing the air will be delivered at this point and the surround- ing air will flow in to take its place at the intake about the hub. So long as the rotation is kept up these conditions will continue, and there will be a continuous flow of air in at the hub and out AUXILIARIES 475 through the delivery passage under a pressure depending on the speed of rotation and other circumstances. Blowers are driven by either reciprocating or turbine steam engines or by electric motor direct connected to the shaft, and are made of various forms so as to readily find a place in almost any position desired, thus requiring the smallest possible amount of otherwise valuable space. In the operation of blowers the points of chief importance relate to the general care which must be given to the operating motor, whether electric or steam, and to the proper lubrication and care of the fan-shaft bearings. Sec. 53. SEPARATORS In many types of watertube boilers, special arrangements are provided for separating the steam from the water. These are usually located in the upper drum or chamber and consist HarvU^Ejagineerint Fig. ^29. Separator commonly of one or more metal plates pierced with holes through which the steam passes to the stop valve and steam pipe, and which exercise more or less of a straining or separating action on the water and steam. In addition to such arrangements located in the upper drum of watertube boilers, special devices known as separators are used wherever the steam is likely to have any considerable pro- portion of water. Such devices are found in great variety of 476 PRACTICAL MARINE ENGINEERING form, and utilize various principles in their operation. The most successful are those which employ for separating the water from the steam the centrifugal force developed by a rotation of the steam as it enters or passes through the separating chamber. The following description will serve to illustrate the oper- ation of a typical separator of this character. The separator, as shown in Fig. 329, consists of a vertical cylinder with an internal central pipe extending from the top downward, for about half the height of the apparatus, leaving an annular space between the two. A nozzle for the admission of the steam is on one side, the outlet being on the opposite side or on top as may be most con- venient in making the connections. The lower part of the apparatus is'" enlarged to form a re- ceiver of some considerable capacity, thus providing for a sudden influx of water from the boiler. A suitable opening is tapped at the bottom of the apparatus for a drip connection, and a glass water gage shows the level of the water in the separator at all times. The current of steam on entering is djeflected by a curved partition and thrown tangentially to the annular space at the side near the top of the apparatus. It is thus whirled around with the velocity of influx, and a centrifugal force is developed, which throws the particles of water against the outer cylinder. These adhere to the surface, so that the water runs down continuously in a thin sheet around the outer shell into the receptacle below, while the steam, following a spiral course to the bottom of the internal pipe, enters it abruptly, and in a dry condition passes upward and ovit of the separator, without having once crossed the stream of separated water, all danger of the steam taking up the water again after separation being thus avoided. The water thus separated from the steam collects in the lower part of the chamber and may be drawn out from time to time or it may be led to a steam trap of bucket or float type and trapped out, thus making the operation entirely automatic. The water thus obtained will, of course, be of high temperature and should be led directly to the hot well, where it will aid in raising the temperature of the feed water. The heat which it contains will thus be returned to the boiler,- and saved, and nearly all heat loss in connection with the operation will be avoided. AUXILIARIES Ml Sec. 54. ASH EJECTOR AND ASH EXPELLER Ashes are either hoisted in a bucket by a special hoist to a point on the main deck level and there dumped into an ash chute leading to the side of the ship and down into the water, or else disposed of directly from the fireroom by means of an ash ejector. Such a device is illustrated in Fig. 330. A represents a cast metal chute or pipe leading from the fireroom up and out through the side of the ship near or slightly above the waterline. Fig. S30. Ash Ejector. At the lower end this chute connects with a hopper, B, into which is led a pipe from the discharge of a pump. This pipe enters to a point near the lower end of the chute, into which its discharge is directed, and is contracted to a nozzle so that the water issues with a high velocity. The hopper may be closed by a cover, and if in this condition the discharge valve is opened and the pump started, a stream issues with high velocity from the upper and open end of the chute. If then the cover is removed and ashes shoveled into the hopper, they are caught by the stream, carried rapidly up, and ejected free of the ship's side in a mingled jet of ashes and water. It is found by experience that at the upper bend the wear on the metal of the pipe, due to the scouring action of the ashes, is very rapid, and it is usually, found necessary to make this bend in a separate piece of extra thick metal, or to fit a separate wearing piece in the pipe, and to provide: by rneans of a proper arrange- ment of joints for its replacement as occasion may require. 478 PRACTICAL MARINE ENGINEERING A similar device known as the ash gun is shown in Fig. 331. Where possible the lead of pipe from the hopper to the ship's side is made straight so as to avoid all bends and elbows. The principles of operation are the same as above explained. Ash Expellees When it is deemed inexpedient to cut holes above water for ash ejector discharges, as in the case of armored vessels, the Marin4 E;\j;inttriMg Fig. 331. Ash Gun ejectors are replaced by ash expellers. These discharge below the water level; and in many cases directly through the bottom of the vessel. They consist of a hopper to receive the ashes, which pass from the hopper through a quick opening and clos- ing gate or a revolving drum valve to a lower chamber, whence they are expelled either by air blast or hydraulic jet. They are liable to cause rapid wearing away of the paint on the ship's bottom, and if not properly located will cause ashes to be drawn AUXILIARIES 479 in through sea valves, plugging condenser tubes and producing other troubles. They are not regarded with much favor. Sec. 55. PNEUMERCATOR This is an instrument for measuring the amount of fuel in fuel oil tanks and also for use as a draft gage for measuring the draft of a vessel. The type of instrument installed is shown in Fig. 333, and Fig. 332 illustrates, in diagram, the general method of connecting the apparatus to the inner bottom tanks aboard ship. A balance chamber. Fig. 332, is installed in each fuel or cargo tank, from which a^ inch outside diameter lead pipe is led through an oil-tight connection in the tank tops, from which point a copper pipe of the same size is carried to the location of the indicating instruments. The indicating gages are mounted on slate boards attached to the bulkhead. Fig. 332. Diagram Arrangement of Method of Connecting the Apparatus to the Tanks Aboard Ship 48o PRACTICAL MARINE ENGINEERING AUXILIARIES 481 A connection is made from the ship's compressed air line, through a reducing valve, to two needle valves mounted on the boards, which in turn admit the air to the control valve- of each instrument and a pressure gage connected with the air line to register the air pressure available. The scales of the mercury gage are calibrated on one side in feet, inches and half inches, and on the other in the correspond- ing gallons of oil at 60 degrees F., temperature, or if desired the scale may be marked in pounds. An annunciator is mounted on each board which shows a signal and rings a bell when each tank is filled to the 95 percent full point. To accomplish this a low voltage electric current is con- nected to the mercury cistern of each instrument, and a copper wire inserted into the mercury tubes from the top reaching down to a point corresponding to the 95 percent full mark on the scales ; consequently when the mercury rises to this point the circuit is closed and the annunciator operated. While this method "of ascertaining when the oil has reached a predetermined height is of the greatest value, as it does away with the necessity of all electric wiring to the tanks themselves and electrical connections to floats or diaphragms in the tanks and the subsequent danger of short circuits and sparks in the vicinity of the fuel oil, it is not entirely satisfactory, as the spark caused by the contact of the mercury and the copper wire in the glass tube causes the tube to become clouded and brittle. This defect has been remedied by having the electric contact take place in an insulated tube parallel to and back of the regis- tering tube. This type of instrument is shown in Fig. 333. The instrument can also be arranged to operate an annuncia- tor when the tank is emptied to some predetermined point. The results, obtained by this instrument are most gratifying. Not only is it possible to ascertain, with accuracy at all times, the quantity of fuel oil in the various tanks, but a record of the oil burned on any run can be readily obtained, and with a degree of accuracy heretofore impossible, by merely taking the differ- ence of the gage readings at the beginning and end of the run. [i] Draft Indicator for Vessels Another application of the pneumercator is that of measur- ing the draft of vessels. ^2 PRACTICAL MARINE ENGINEERING ■----■i-,... s *d 1^ In this type of instrument, shown in Fig. 335, the balance chamber is placed in a casing, which in turn is connected with the sea itself by means of a i- inch sea valve. Two balance chambers are used, one forward and the other aft, the sea connec- tion being installed below the light draft trim of the vessel. Balance Chambei- and Sea Con- nection connected to the Registering Por- tion of tlie Instrument in same manner as m type of instrument. Fig. 333, pre- viously described The j4-inch copper tubing i§ then led from the balance cham- bers to the captain's office or the chart room. Fig- 334 shows in diagram a draft indicator installation, and Fig. 336, the indicating and registering instrument. AUXILIARIES 483 While the appearance of the balance chambers and register- ing instruments for the two models dififers materially, their oper- ation is practically the same. One mercury column, Fig. 336, is marked "forward" and the other "aft," and by noting the height of the mercury in Fig. 336. Pneumercator Registering Instrument for Draft Indicator these columns and applying this to the feet and inches scale placed parallel to them, the draft and trim of the vessel can be noted. Equidistant from these draft scales is a mean draft scale and a corresponding deadweight scale. When the knife edges which travel on rods beside the mercury column are placed exactly at the top of the mercury, a central knife edge automatically regis- ters the mean draft and the corresponding tons displaced. 484 PRACTICAL MARINE ENGINEERING If desired a third sea connection can be installed amidship and connected to its own mercury column, which will give the mean draft direct. ■ Furthermore, as the displacement or deadweight of a vessel represents its weight and all it contains, the amount of weight put on board or taken off a vessel can be readily ascertained by taking the difference between two successive readings of the dead- weight scale. Sec. 56. TIME FIRING REGULATORS In order to insure efficient handling of the boiler furnaces when burning coal, a proper regulation of the opening and clos- ing of the furnace doors must be possible, and time firing regu- lators accomplish this purpose. This apparatus is designed to signal predetermined firing time intervals from the engine .room to the several fire rooms, and to show in proper order which furnace to fire. The system consists of a transmitter, located in an engine room, and an indicator in each fire room. All instrument cases are of bonze composition, with separate covers for mechanism and junction box; soft rubber gaskets are provided to make the covers watertight. The system operates electrically through switch on the ship's switchboard. [i] Transmitter (Fig. 337) The transmitting instrument contains four separate electrical units — timer, transmitting relay and two contactor operating motors, besides a mechanical contactor and a hand-adjusting de- vice, necessary to make the desired changes in firing time indi- cations. The timer is a magnet with a balanced oscillating armature and a retractile spring to hold it away from the magnet poles. By means of a ratchet and gear mechanism, operated from the armature shaft, the retractile spring is made to drive a fan against air resistance, thus providing a constant timed retarda- tion to the retraction of the armature by the spring. A contact device in the operating circuit to the magnet coils, is so arranged as to be closed when the armature is drawn back by the retrac- tile spring, energizing the magnet again and drawing the arma- ture forward into the poles. This forward armature movement does not affect gears and retarding fan, as the connected ratchet AUXILIARIES 485 iB "^.^^^B^I^I^I^I^IIB 1 1 Fig. 337. Time Firing Kegulator Fig. 338. Time Firing Regu- lator Indicator is inoperative in that direction. At the end of this stroke the operating contact opens the circuit, which energizes the magnet coils and allows the retractile spring to be again operative, and, in retracting the armature, a pawl in the ratchet mechanism en- gages to drive the fan. In this manner the back stroke of arma- ture is timed to a certain definite interval. Since the inward movement of the armature, caused by the energizing of the coils, is practically instantaneous it is evident that ordinary variations in the pressure of the operating current will have no efifect on the timing action of the unit. The timer has no mechanical connection with any other part of the transmitting apparatus, and, controlling its own cur- rent, beats regularly and constantly without variation. The timer unit carries one other set of contacts which is arranged to open and close at every beat, intermittently ener- gizing from a line connection a wire leading to a common con- tact plate of a circuit changing device, located on and operated bv the transmitting motor unit. At this point the current is con- ducted to one of two other contact plates by a connecting brush, and these two contact plates are connected, respectively, to the two operating step motors of the screw feed contact device. 486 PRACTICAL MARINE ENGINEERING These motors are designed to drive a feed screw in oppo- site directions by certain definite movements at eacii beat or step. The feed screw carries a nut which forms an operating arm for two sets of contact brushes, one set being stationary, the other mounted on a movable block, adjustable by means of the hand screw on the exterior of case. The contact brushes on the movable block receive current from two contact bars which they engage and slide upon. One brush of each pair is connected to a lead which runs to a terminal of the transmitter magnet, the other brushes connecting to the leads ,of the screw operating motors. iiach of these motors carries two sets of related contacts, one closes when the armature is at rest and carries the operat- ing current for the opposite acting motor, providing a non-inter- ference system between the two motors ; the other contact closes as the motor armature is drawn into the poles connecting its own coils directly to the operating line from the timer, independently of the connection through the circuit changer on the transmitter. The contactor screw motors are connected to the feed screw by a special ratchet mechanism, so that at each beat of a motor and partial revolution of the screw, the contacting arm is moved a certain definite distance longitudinally. The continuance of screw action eventually brings the contacting arm against one of the contact brushes, closing the circuit between the operating line from the timer to the coils of the transmitting unit, energizing that motor and causing its armature to be drawn inward. This action moves the brush of circuit changer to the, operating con- tact plate for the reverse motor, so that the next beat of the timer will operate that motor and reverse that direction of the screw feed for the contact arm, which will continue to run in the new direction until it engages with contacts at the other end of the screw, when it again reverses. The transmitter armature also actuates another switch mechanism which closes the line to a common indicator operat- ing wire connecting to one side of all the cut-out switches in the junction box. A line is run from each of these cut-out switches to its individual indicator, and any indicator may be cut out of cir- cuit by opening its swifth in transmitter junction box. AUXILIARIES 487 The transmitting unit is provided with a timing or retard- ing mechanism similar to that used on the timing unit. At the time that the transmitter armature of this unit is drawn inward, , it is locked by a pawl which holds the indicator operating line closed. The armature falls back when the coils are de-energized by the opening of the circuit at the timer, being retarded on its back stroke for a certain definite interval of time by the opera- tion of the fan; when it has nearly returned to its stop, it en- gages and trips the pawl which holds the indicator line contact closed, thus allowing it to be opened under power from a re- tractile spring. This arrangement permits timing for the dura- tion of the indication, in order that it may be exposed quite long enough to be noted and then be cut out. An instrument lamp in the transmitter glows under a bulls- eye in transmitter cover when indications are changing in indi- cators ; the lamp is connected in the operating circuit. The cover of the transmitter case contains an oblong open- ing fitted with plate glass through which a dial, graduated to scale, and a pointer may be seen. The pointer is adjustable along the scale by means of a knob which projects from the front of cover. Another opening in cover contains a ground glass "bullseye" which is illuminated by a lamp when signals are being sent. The lower compartment of junction box contains the termi- nals for "line" and indicator operating wires, also the cut-out switches which control the indicators. The switch handles are mounted on the switch steps outside the junction box cover. [2] Indicator (Fig. 338) This consists of a watertight composition case divided into two compartments; the upper compartment contains the lamps and mechanism, the lower, or junction box, the binding posts for wirings. Both compartments have separate covers, made water- tight by soft rubber gaskets. A i2-inch bronze gong is attached to the upper part of the case. The cover for the upper compartment has a round opening, fitted with plate gl.'ss, through which two-inch figures can be seen. The figure dial is a thin metal disk, mounted on a rotating 488 PRACTICAL MARINE ENGINEERING shaft; the figures are stencil cut and are backed with a translu- cent white porcelain plate. Two instrument lamps, wired in mul- tiple, illuminate the figures from behind. The dial shaft is at- tached to ratchet mechanism, adapted to be engaged and rotated in one direction by a single step motor. One step of this motor turns the dial sufficiently to show a change from one figure to the next, and it is locked positively in each position by the ratchet mechanism. The dial motor carries a set of contacts so ad- justed as to be closed when the armature strokes inward anii opened when it falls back. One of the contacts is connected to the main line lead, the other to one terminal of the two lamps and one terminal of the bell solenoid. Single silk covered wire, .0079-inch diameter, is used for the dial motor coils. [3] Gong The gong is of the usual type but the striker is of special construction. It consists of a solenoid contained in an iron shell. The gong hammer consists of a brass head, adapted to strike the inher side of the gong and is attached to the upper end of an iron core which slides in a brass sleeve. The core carries at its lower end an iron disk of the diameter of the magnet shell, the whole forming the armature of the mag- net. Lost motion is provided between armature and hammer ; this allows the latter to rebound from the gong. Gravity returns the hammer to its original position. One terminal of the gong coil is connected to the indica- tor motor contact in common with the indicator lamps, and one terminal of motor is connected to the common return or line wire. When the indicator motor receives current from the trans- mitter, the motor armature operates to turn the dial one figure, closes contact to light lamps and energizes gong coil to strike the gong, When the motor coils are de-energized, the dial being locked, the armature falls back, contact opens, the lamps are cut out, and the gong hammer drops back. [4] Operation The operator in the engine room sets the pointer on the transmitter dial to the desired stoking interval, which, may be varied from 21 seconds to 10 minutes, by means of the hand ad- AUXILIARIES 489 justing knob. He has thereby moved the adjustable block and contact brushes along the contact bar to a point where it requires a definite number of beats of one of the operating motors to screw the contact arm into engagement with the contact brushes. The timing of these beats is governed by the regular beat- ing of the timer unit, which occurs once in three seconds, there- fore a certain time interval must elapse before a contact can be made. When the circuit is closed through the contact brushes, the transmitting relay operates and shifts the circuit to the other feed screw motor, thus reversing the direction of travel of the contact arm, and at the same time closing the circuit to the line to operate all the indicators in the several firerooms. At this time all indicator dial motors work simultaneously, changing fig- ures and closing circuit to lamps under dials, also operating the strikers of the attention signal gongs. After an interval of from five to six seconds, determined by its timing device, the trans- mitting relay breaks the circuit to indicators, allowing their motor armatures to fall back, cutting out lamps and causing the gong strikers to drop back, the figure set up on the dials, however, re- maining visible until the next change. The screw operating motor to which the timing circuit was last connected by the shaft of the circuit changer, will beat continuously every three seconds until a number of screw turns has moved the contact arm into engagement with the brush contacts at the other end of its travel, when all units again operate, as above mentioned. These opera- tions continue indefinitely, keeping equal time intervals between indications and signals until the pointer shall have been shifted over the dial. The pointer may be shifted at any time in either direction and changes of intervals for stoking signals are imme- diately produced. The dial is graduated to show 21 seconds, Yz minute, and from J^ to 10 minute divisions, and the pointer may be set at any point between graduations to produce any fractional sig- nalling intervals, as the minimum increment of adjustment is three seconds. Sec. 57. STEAM TRAPS , In order to collect water of condensation in steam cylinders and piping and to discharge it automatically to the feed tank or to the condenser, an apparatus called a steam trap is fitted. 490 PRACTICAL MARINE ENGINEERING These may be classed under three general heads, viz. : bucket traps, ball or float traps and expansion traps. (i) Bucket Trap. Fig. 339 shows a trap of the bucket type. The condensation follows the arrow, passing through the perforated strainer plate to the body of the trap, which gradu- ally fills until the upper edge of the bucket is reached. It then overflows into the bucket until the buoyancy of the bucket is overcome. This latter then sinks and opens the discharge valve- by means of the pipe lever, the water of condensation being forced out through this arm, as shown by the arrow, until the water Fig. 339. Bucket Steam Trap level in the trap falls below the level of the bucket edge, when the bucket slowly regains its buoyancy, rises and closes off the discharge valve. (2) Ball Float.Trap. Fig. 340. In this trap, the discharge valve is controlled by a spherical ball float, operating through a system of levers. As the float rises with the water level in the body of t"he trap, it gradually opens the valve until the amount of discharge exceeds the inflow of condensed water, when the water level falls, carrying the ball with it and closes the discharge valve. Both this trap and the preceding one can be used with any pressure and temperature of steam, but to insure proper opera- tion and to avoid the danger of clogging up the discharge open- ings and to insure that the proper operation of the discharge valve will not be interfered with by scale or grit collecting on the valve faces, the valves must be of large size; not less than one-half inch diameter is, required by the United States Navy, and efficient strainers must be fitted to the inlets. (3) Expansion Traps. These are especially suitable for AUXILIARIES 491 working with low pressures and temperatures of steam and should never be used with high. The trap has four principal parts : The most vital part of the trap is a crescent hermetically sealed tube spring. This tube is made of a high grade steel of high elasticity, and tempered. One end is fixed, while the other is free to move. The tube contains a liquid which is extremely volatile, and highly sensitive to any variations in temperature. Fig. 340. Ball Float Trap When steam comes in contact with the tube the liquid gasefies and the tube expands lengthwise. This expansion tends to straighten the tube, forcing the bronze cone shaped valve head against the tapered bronze valve seat, thereby preventing the steam from escaping. When con- densed steam accumulates, the tube contracts, comes back to its original shape, opens the valve and permits the water to flow through the outlet. The valve is made of bronze mounted on a steel spindle run- ning the length of the trap, and attached to one end of the tube so that it is positively operated by the expansion and contraction of tube. The valve is easily removed for regrinding or renewing. The valve seat is a tapered bronze seat driven into casing of trap and can be quickly and easily removed if ever necessary. The adjusting screw is for the purpose of adjusting the throw of the valve. This adjustment is very close and seldom, if ever, has to be changed. The valves, seats, regulating screws, and tube springs are 492 PRACTICAL MARINE ENGINEERING interchangeable and can be exchanged from one trap to another of equal size, or renewed at any time. ^ ^ ? M ? W ? Figs. 342, 843 General Arrangement Plans Sec 58. GENERAL ARRANGEMENT OF MACHINERY The various questions which ma> arise in connection with the problem of the general arrangement of marine machinery will not be discussed in detail as the ground to be covered is too ex- tensive, it will be sufficient for the present purpose to note the fundamental principles which must be held in view : AUXILIARIES 493 ( 1 ) Each piece must be located so as to favor, as far as pos- sible, examination and repair. (2) Each piece should be located with reference to handi- ness of care and control in routine operation, and in such way as to interfere to the smallest practicable extent with the routine care, examination and repair of other pieces. (3) Due regard must be had to economy of space and such combinations of the various pieces must be sought as will require the minimum total space, while giving the necessary freedom in accordance with the principles noted above. (4) The influence of the location of the various pieces on the arrangement of the piping must be carefully noted and due weight must be given to simplicity, shortness and directness of the various lines of piping. In Figs. 342, 343 are shown illustrations of a general arrange- ment plan in which the condenser is located in the engine fram- ing. The remaining features are independent, and include those most commonly met with in the auxiliary equipment of the engine room. QUESTIONS Auxrliaries PAGIC What is the office of the circulating pump ? 430 Describe the usual type of centrifugal pump and explain its mode of operation 430 Describe a usual type of outboard discharge valve 431 Describe the usual type of condenser 433 How are condenser tubes packed ? 434 What is the essential difference in the working conditions of con- densers for reciprocating engines and for steam turbines ? 435 Describe the Uniflux condenser 436 What are the advantages obtained by expanding condenser tubes into tube plates ? 437 What is the office of the air pump ? 438 Describe the usual type of construction and explain its mode of operation 438 What are the relative advantages and disadvantages of the attached and independent forms of air pumps ? 440 Why is the feed pump necessarily of different type from the circulat- ing pump ? 443 Describe the usual form of attached plunger pump and explain its mode of operation 443 Why is the area of the steam piston larger than that of the water plunger ? 444 What is the common ratio between these two areas ? 445 Describe a common form of injector and explain the principle of its operation 446 What is the difference between what are commonly known as auto- matic injectors and inspirators ? 447 494 PRACTICAL MARINE ENGINEERING PAGE What is meant by wet air pump ? by dry air pump ? 449 Describe the dual air pump; the vacuum augmentor; the Rotrex air pump; the Leblanc air pump; the Kinetic system of air ejection; the Westinghouse-Leblanc air ejection system 450 Describe essential features of lubricating systems for reciprocating engines ; for turbines 458 What is the purpose of the water service for a marine engine? 460 Give brief description of turning gear for marine engines, either re- ciprocating or turbines 460 What is the office of the feed heater ? 461 What are the two fundamental types of heater ? 461 What is the source of the gain in the case of heaters using the funnel gases as a source of heat ? 461 What are the styles of feed heater using steam as the heating agent? 462 What is the source of the gain in the case of heaters using steam as the source of the heat ? 465 What is the purpose of the feed water filter ? 466 What materials are used as the filtering medium? 466 What is the purpose of the evaporator, and of what does it consist?. . 467 What are the chief points to be observed in the operation of the evaporator ? 469 Describe a standard form of independent feed pump and explain its mode of operation 470 What advantage has the "Admiralty" type of feed pump over other forms ? 473 What are the uses of fans or blowers ? 474 Describe the usual form of centrifugal fan or blower, and explain its operation 474 What is the office of the separator ? 475 Describe a usual type of construction 475 Describe the ash ejector and explain its mode of operation 477 What is the difference between an ash ejector and an ash expeller?. . 478 What is the pneumercator and what is its use ? 479 What is a time firing regulator ? Give brief description of its method of operation 484 What are steam traps used for ? 489 What is a bucket trap ? 490 What is a ball float trap ? 490 What is the principle governing the action of expansion traps? 490 What principles govern the general arrangement of machinery on shipboard? 492 CHAPTER VIII Valves and Valve Gears Sec. 59- SLIDE VALVES [i] Simple Slide Valves In Fig. 344 VW represents a simple slide valve, supposed to be surrounded by live steam in the steam chest C C. P and Q are the ports leading to opposite ends of the cylinder as shown, Fig. 344. Plain Slide Valve, Mid Position while E is the exhaust port or passage leading to the condenser or to the air, as the engine is condensing or non-condensing. It is the business of the valve, as shall be explained later, to move Fig. 345 Plain Slide Valve, Position for End of Stroke back and forth, thus alternately uncovering the ports P and Q and admitting steam from the chest to the. ends of the cylinder. While the steam is thus being admitted at one end of the cylin- der, it must be allowed to escape from the other to the exhaust passage E, and thus the piston is moved to and fro in the cylinder and the operation of the engine becomes continuous. 496 PRACTICAL MARINE ENGINEERING If it is supposed in Fig. 344 that the valve is in the middle of its travel back and forth, or in mid posi- tion as it is commonly called, then the distance A Bhy which the edge of the valve on the steam side extends over the edge of the port is called the steam lap. Similarly the distance CD by which the edge of the valve ex- tends over the port on the exhaust side is called the exhaust lap. In Fig. 345 let the piston be at the end of the stroke and the valve in the position shown. Then the distance A B hy which the port is uncovered to steam is called the steam lead, while the distance CD by which the other port is uncovered for exhaust is called the exhaust lead. In general, therefore, lead is the amount by which the valve is open when the piston is at the end of the stroke. In Fig. 346 are shown a series of corresponding positions for valve and piston during a single stroke of the latter. The position a is the same as that of Fig. 345 and the port is open for the admission of steam on the left and for ex- haust on the right. The piston is at the end of the stroke dnd VALVES AND VALVE GEARS 497 4 just about to begin the stroke to the right. In b the piston has advanced about 10 percent of the stroke, and the valve has moved so that the port is nearly wide open. Up to this point the piston and valve have been moving in the same direction. In c the piston has advanced to about 60 percent of the stroke, while the valve has come back and has just closed the port to the entrance of steam. This is called the point of cut-off. Between b and c the piston has been moving on, but the valve has been moving back in the opposite direction. In d the piston has moved still further on while the valve is still moving to the left, and has just reached the point where the exhaust opening on the right is closed. This is called the point of exhaust closure, and the operation of com- pressing the steam in the end of the cylinder from this point to the end of the stroke is called compression or cushion. In e the piston is still nearer the end of the stroke on the right, while the valve has moved farther to the left, and is just about to open the port on the left for exhaust, thus allowing the escape of the steam which entered dui-ing the early part of the stroke. In / the piston has nearly reached the end of the stroke. The exhaust opening on the left is open still wider, while the port on the right is just about to open for steam. In g the piston is at the end of the stroke, the valve has moved-«o as to make the steam and exhaust openings still wider, and the return stroke is about to begin. This completes the history of the stroke, and the next or return stroke follows after it with like series of events, and so on con- tinuously. [2] Double Ported Slide Valve The valve shown in the above diagrams is called single ported because it covers but one set of ports or openings. A double ported valve is shown in Fig. 347. This is a form of valve within a valve. Thus taking one end of the valve there is at AB one set of edges respectively for steam and -exhaust, and zX. A^ B^ another like set. Steam surrounds the outside of the valve and is therefore ready to enter the port P past the edge A when the valve moves suflfi- ciently to the left. Steam likewise enters freely at the side into the passage S, and is therefore ready to enter the port P, past the edge A-^, as the valve moves to the left. Similarly as the valve moves to the right the ports P and P^ are open to exhaust past the edges B and B^, respectively. The passage E^ leads over the transverse passage S, and thus the entire exhaust finds its way into E the outlet passage. 498 PRACTICAL MARINE ENGINEERING With a double ported valve the area of the port opening required may be obtained with a travel of valve only one-half that for a single ported valve, or with the same valve travel, twice the area of port opening may be obtained. It is this feature which often leads to the use of a double ported valve where it is desired to obtain a relatively large opening with, small travel of valve. [3] Piston Valve The face of the valves in the types so far noted is a plane ; or in other words, they are flat slide valves. If now there can be imagined such a valve wrapped up so as to form a cylinder with LONGITUDINAL SECTION; Jtiannt £nffiiieering CROSS SECTION AND END VfF.W, Fig. S47. Double Ported Valve the valve stem for axis, there will result a cylindrical or piston valve is shown in Figs. 348, 351, 352. This consists essentially of two heads connected by an intermediate body, as shown. The steam enters past the outside edges, for example, and exhausts past the inside edges to the exhaust passage, in a manner entirely similar to that for the plain slide valve as above described. Other- wise the steam may enter past the inside edges and exhaust past the outside as described below for the inside valve. The steam port and passage consists of an annular channel surrounding the valve and connecting with a passage leading to the end of the cyl- inder in the manner shown. The valve is placed somewhat out of center with reference to this annular passage, so that it is quite shallow on the side opposite the cylinder, and gradually in- creases in depth toward the side nearest the cylinder. This arrangement, which is shown in Fig. 349, gives a cross sectional area of passage varying in proportion to the amount of steam VALVES AND VALVE GEARS 499 flowing through it, as may be seen by noting in the figure the natural direction of flow of the steam, radially outward through Fig. 348. Piston Valve the port opening, and then curving around to flow toward the cylinder. Comparing the two forms of valve it is readily seen that in the piston valve the outer circumference represents the active part .of the valve, and corresponds to the plate AB of the flat slide, as shown in Fig. 347. 500 PRACTICAL MARINE ENGINEERING The great advantage of the piston valve hes in the fact that it is perfectly balanced as regards the steam pressures which act upon it. It is readily seen that the flat slide valve is forced against its seat by the excess of the pressure on its back over that on its face, which excess will in the usual case be large, and will give rise to a heavy frictional load to be overcome by the eccentric acting through the valve stem. The piston valve, on the contrary, is forced equally in all directions, and hence moves Fig. 349. Section Tlirough Valve Chest and Cylinder freely so far as the steam forces are concerned, and with only such frictional resistance as may be necessary to insure tightness against steam leaks. In order to keep the heads of the valve steam tight they have been very commonly provided with one or more packing rings of similar character to those used on the main piston, but usually without auxiliary steel springs to force them outward. Such an arrangement is shown in Fig. 352. In the latest prac- tice, however, especially for quick moving engines, the special rings are very commonly omitted entirely, dependence being placed on a good working fit at the start and on the rapid re- versals of motion, to reduce the leakage to a negligible amount. VALVES AND VALVE .GEARS soi Such arrangements are shown in Figs. 348 and 351. In the latter a solid working ring is fitted as shown, in such manner that it may be readily removed and replaced with a new one as occasion may require. The valve seat is usually a separate piece of hard and fine grained cast iron, fitted as shown in Fig. 348. The ports in this seat instead of being continuous all around, thus dividing the seat into separate parts, are usually bridged over at several points distributed about the circle. The head of the valve is thus car- ried across from one side to the other, and is prevented from catching or jamming, as would very likely occur without such bridging. Where valve packing rings are used it is especially necessary to provide such bridging in order to prevent the ring from springing out into the port opening, and thus jamming the valve, or causing other damage. In Fig. 350 is seen the de- velopment or layout of the port for the valve shown in Fig. 352. Carina Engineering Fig. 350. Development of Piston Valve Port The bridges are placed on the slant so as to distribute as much as possible the wear on the valve rings. In the case of wear on the valve seat or rings, they may be replaced with new. When rings are not used the wear is usually less rapid, thus furnishing a further reason for their omission. The valve itself, however, will slowly wear, and as necessity may require a new head or new valve entire may be fitted. In some cases where a piston valve takes steam on the out- side, it is desired to lead the steam to the chest at one end only, and then to pass it down to the other end through the inside of the valve. In such case as shown in Fig. 352 the body of the valve is made hollow and as large as possible, thus connecting the steam chest at top and bottom as desired. The valve stem passes through the center of the valve and is usually secured with nuts at top and bottom, as shown in the figures. In case the valve is hollow for the passage of steam between the two ends, the stem must be carried in bosses sup- ported by radial arms connected with the valve heads, and as 502 PRACTICAL MARINE ENGINEERING small as possible in order to present the least resistance to the flow in either direction. [4] Equilibrium Piston The work of moving the valve up and down which is thrown on the eccentric may be much decreased by fitting an equilibrium or balance piston as shown in Fig. 352. The cylinder in which Figs. 351, 352. Piston Valves this is fitted is open at the bottom to the valve chest, and hence the full pressure of the chests acts constantly on the lower side of the piston. This may be so proportioned as to carry practically VALVES AND VALVE GEARS 503 about all the direct weight of the valve, which thus floats on the steam, requiring comparatively small effort on the part of the eccentric to move it back and forth. LovEKiN Assistant Cylinders The object of the assistant cylinder (Fig. 353) is to float the valve gear, so as to relieve it of the load under which it works. The reasons for relieving this load are obvious. At the high revolutions the valve gear works under a heavy load, which is due principally to the inertia of the heavy moving parts. Fig, 353. Lovekin Assistant Cylinder This load on the valve gear causes a great deal of friction, a great deal of wear on the eccentric bearings, and consequently frequent overhauling and repairing, which involves considerable expense. Hence, the object of the assistant cylinder is to relieve the valve gear of the load under which it works, in order to re- duce the wear on the bearings and the ensuing expenses. The action of the assistant cylinder may be compared to that of a spring dash pot. The steam in the cylinder is the elastic medium, which, when being compressed, acts as a spring. The steam in the cylinder so acts (governed by the laws of compression and expansion of steam) that the "predominating 504 PRACTICAL MARINE ENGINEERING force" in the cylinder is always approximately equal to the forces acting on the valve gear, and in an opposite direction. In re- ferring to the steam under compression, for clearness, it is as- sumed that the steam under compression is only the force acting on the piston of the assistant cylinder. Actually there is a steam pressure on each side of the piston, but it is only necessary to con- sider the difference in the two pressures (calling this the "pre- dominating force" acting on the balance piston). Thus the forces acting on the valve gear are neutralized, the valve gear is "floated," and the loads on it are relieved. At the beginning of the downward stroke the inertia force is at its maximum, and inertia and gravity act in opposite direc- tions. The "predominating force" at this point is approximately equal to the difference of these two forces and is in an opposite direction. In this case. Predominating force—/ — G. In the diagrams this is expressed thus: /^(top steam+gravity) — bottom steam. Thus : / — G=:top steam — bottom steam=the pre-, dominating force. As the valve descends, the forces acting on the valve gear are constantly decreasing; the predominating force is also de- creasing at the same rate and is always approximately equal to these forces. The inertia decreases until at some point of the stroke it is equal to the gravity force, and, being in opposite directions, the forces are neutralized, and there is no force acting on the valve gear. At this point the predominating force is approximately nil. After passing this point the direction of the forces acting on the valve gear changes from upward to downward, and also the predominating forces change from downward to upward. From this point, the forces acting on the valve gear continually increase until they reach the maximum at the bottom of the stroke. The predominating force increases at the same rate, and is always approximately of the same value until it reaches the maximum at the end of the stroke. At the bottom of the stroke the inertia force again reaches its maximum, and inertia and gravity are now acting in the same direction. At this point the forces acting on the valve gea:r reach their maximum and are in a downward direction. VALVES AND VALVE GEARS SOS Cylinder. — The assistant cylinder and the valve chest cover are cast in one. The sides and top of the cylinder are lagged. Steam Supply Port. — An annular steam supply port is located at the upper end of the stem guide and is opened and closed by the packed end of this stem. Enough steam is admitted through this port to the cylinder, from the valve che?t, to make up for condensation losses. Steam is supplied above the piston by ports, as shown. The ratio of pressures depends on the areas subjected to valve chest pressure and supply steam pressure. Let Pt = pressure per square inch in valve chest. ^s =: pressure per square inch of the supply steam. Ot = area of the piston subjected to the pressure of the steam in the valve chest. as = the area of the piston subjected to the pressure of supply steam. Then CEv : fls n^ pa : pv [5] Equilibrium Rings With a flat slide valve, as in Fig. 347, the full steam chest pressure acts constantly on the back of the valve, while a much decreased pressure will act on a part only of the other side. In Fig. 354. Section Through Equilibrium Ring consequence, the valve is forced with strong pressure against the seat and the frictional force thus developed must be over- come bv the eccentric. With large valves and where the lubri- So6 . PRACTICAL MARINE ENGINEERING cation is scanty this may become excessive, causing the valve and seat to cut, and throwing a great deal of unnecessary work on the eccentric. To relieve this condition, equilibrium or balance rings are often fitted on the back of the valve. Such an arrange- ment is shown in Fig. 354. The inner face of the valve chest carries a ring of metal within which is cut a groove, as shown. Within this groove is a ring which is forced against the back of the valve by springs and screw adjustment, as shown. The back of the valve is faced off and thus a joint is made between the two, while the space within the ring and between the back of the valve and face of the cover is shut off from the steam within the valve chest, and hence this part of the valve is relieved from the pressure of steam. In addition to this, the space is some- times connected by piping to the steam side of the condenser, thus bringing on this part of the back of the valve only the pres- sure in the condenser. In this way the load on the back of the valve and the resultant load on the eccentric may be much de- creased, and the operation of the valves will be correspondingly smoother, and less work will be thrown on the eccentrics and valve gear in general. There are several methods varying in detail for the fitting of the ring in such an arrangement, and in the formation of the joint between the ring and valve chest cover, but the principle is the same in all, and is sufficiently illustrated by the arrange- ment of Fig. 354. [6] Outside and Inside Valves In the preceding figures for valves the steam enters past the outside edges and exhausts past the inside edges. Such is known as an outside valve. In some cases, however, it is con- Fig. 355. Inside Valve venient to have this relation reversed, and to take steam past the inside edges, and exhaust past the outside edges. Such a valve is shown in Fig. 355, and is known as an inside valve. Live steam fills the space \<4 and enters the port P past the VALVES AND VALVE GEARS SO? edge C, while exhaust occurs past the edge F. The valve as here shown is in mid position and therefore C D is the steam lap and E F the exhaust lap. The only diflference in the two forms of valve is in the relative amounts of outside and inside lap. In each case, for reasons which will appear later, it is seen that the steam lap is greater than the exhaust, being in one case on the outside and in the other case on the inside. It is also clear that the outside valve moves with the piston at the beginning of the stroke, and opposite to it during the latter part, while with an inside valve it moves opposite to the piston at the beginning, and with it during the latter part of the stroke. Sec. 60. MOTION DUE TO SIMPLE ECCENTRIC AND ITS REPRESENTATION BY VALVE DIAGRAMS [i] Simple Eccentric It is now necessary to inquire by what means the valve can be given the motion necessary for the proper distribution of the steam, as above described. The simplest of such means is the plain eccen- tric, as shown in Fig. 356. This consists of a circular disk with center A set on the shaft eccentric or out of the center. The distance between the two centers is seen to be OA. This is called the eccentricity or throw of the eccentric* About the eccentric is a strap, ST, and attached to this is a rod, RR. As the shaft J" db — Fig. 356. Plain Eccentric, Skeleton of Motion turns, the eccentric turns with it, and thus gives to the rod a to and fro movement exactly as though it were a connecting rod attached to a crank OA. This principle of the equivalence be- tween an eccentric and a crank of equal throw is very important, and the motion should be studied until it is quite clear that the operation of an eccentric- is exactly the same as that of a small crank of throw equal to that of the eccentric, or to the distance * Some writers understand by the term throw, twice the above dis- distance. In the present work the term is to be understood to refer to the distance OA, as stated. So8 PRACTICAL MARINE ENGINEERING from the center of the eccentric to the center of the shaft. For purpose of illustration, therefore, the eccentric may be represented by a crank of equal throw. With this understanding again examine Fig. 346, on the left, when it is readily seen that the series of movements de- sired is exactly such as Avould be given by a small crank located at an angle somewhat more than 90 degrees ahead of the main crank. Or, in other words, with the valve stem attached to such a small crank or eccentric, the valve will be so moved that the piston will be forced to and fro in the manner described in Sec. 55 [i], and the main crank will follow the motion of the eccentric. This is what is meant by saying that with a slide valve connected, as in the diagrams, the eccentric leads the crank. In regard to the angle between the crank and eccentric it is clear from the diagram of Figs. 344, 346, that starting with the valve in mid position, it must move a distance equal to the lap before the port will begin to open. Hence when the piston is at the end of the stroke the valve must already have moved from its mid position by an amount equal to the lap plus the lead. Suppose now that the eccentric is loose on the shaft and may be \<^^ I ^y^ Manni.Engy3ieering Fig. 357. Diagram Showing Connections for Simple Valve Gear adjusted as desired. In Fig. 357 let C denote the crank on the center. Then suppose the eccentric first located 90 degrees ahead of C as shown at O A, where 0^ = 05 = eccentric throw. Then neglecting the slight effect due to the obliquity of the eccen- tric rod, the valve will be in its mid position, as shown in Fig. 344. Next, move the eccentric ahead until the valve has moved a distance equal to the lap plus the lead as in Figs. 345, 357. This gives the final location of the eccentric for the proper opera- tion of the valve, as already described. The angle AOB through which it is thus necessary to move the eccentric in order to effect this movement of the valve from its mid position, or more exactly the angle between the eccentric and the line at right angles with the crank is termed the angular advance. This term is sometimes VALVES AND VALVE GEARS 509 used in reference to the entire angle between crank and eccentric, but it is preferred to understand by the term the angle as defined above. The angular advance is usually denoted by the letter 8. With the arrangement of gear, shown in Fig. 357, the angle be- tween crank and eccentric will therefore be 90 degrees + 8. In regard to the direction of motion of the crank, it is clear that when the piston is at the end of the stroke and the crank on the center, the latter must start off in such direction as will in- crease rather than decrease the opening of the port for steam. If the connections and arrangements of a valve gear are known, no matter how complicated, this principle will always furnish an \ « I / ^ T Fig. 358. Inside Valve and Location of Eccentric answer to the question as to the direction in which the engine will turn. Thus in the direct connected gear, as in Fig. 357, with the piston at the end of the stroke, the crank moves in the same direction as the eccentric, or follows it, simply because that is the direction which opens the port still wider for steam admission. With an inside valve the eccentric is set 180 degrees behind or directly opposite the position for an outside valve, as shown in Fig. 358, or at OB^, Fig. 357. In such case the angle between the crank and eccentric is 90 degrees — 8 or the angle 8 is set oflf toward the crank from the 90 degree position. It is readily seen that this will bring the valve slightly open when the piston is at the end of the stroke, and that the crank will move leading the eccentric because this is the direction which opens the port wider for steam admission. It is also seen that to fulfill the same pur- pose the piston and valve at the end of the stroke must move in opposite directions. In some cases the valve rod instead of being directly con- nected to the eccentric rod is worked through a rocker arm, Sio PRACTICAL MARINE ENGINEERING which reverses the motion as compared with the direct connected gear. See Fig. 359. This provides a second mode of variation MarXTUi-EuBineaioil Fig. 359. Diagram for Valve Connections Through a Rocker Arm which may affect the arrangement of a valve gear, giving in all four combinations, as shown in the following table : Valve Connection Angle Between Crank Which Leads and Eccentric Outside Direct go + 5 Eccentric Leads Inside Direct 90 — s Crank Leads Outside Rocker 90 — s Crank Leads Inside Rocker 90 + 5 Eccentric Leads [2] Oval Valve Diagram It is now time to proceed to an examination of the effects due to varying the steam and exhaust laps, and the angle of ad- vance [i]. This may be done most conveniently by the aid of a diagram. In Fig. 360 let AB represent to any convenient scale the path of the piston. Then from the various points of AB corresponding to a series of successive piston positions, let the distance of the valve above or below its mid positions be laid off, and the points thus' found be joined by a continuous line. For a revolution or double stroke the result will be found somev/hat as represented by the curved line of the diagram. Thus at the lower end of the stroke, say at B, the valve will be at a distance BT above mid position. When the piston has gone on to 5" it will be at a distance SJ, at i? a distance RK, at P a distance PL, at N it Avill be in mid position, atid will then pass belmv' and reach - a distance AV at the end of the stroke A. On the return stroke, the valve will pass through a similar series of locations deter- mined by the distances from AB downward to the curve. With this arrangement of diagram the movement of the valve above VALVES AND VALVE GEARS 5" mid position is laid off above the line AB and vice versa. With an outside valve this shows above the line AB the events for the up stroke and below the line the events for the dozvn stroke. With an inside valve the relation is reversed, the events for the up stroke being shown beloiv the line and for the damn stroke above the Hne. It has already been seen that starting from mid position the valve must move a distance equal to the steam lap before the Fig. 360. Oval Valve Diagram WarineSni/iaeering port begins to open for steam. Suppose then, that BF is laid off equal to the steam lap on the lower end of the valve, and a line FL drawn parallel to BA. Then it is clear that the remaining distances from FL upward to the curve ZTKL give the dis- tances which the edge of the valve travels beyond the first edge of the port, and hence if the port is sufficiently wide, the actual widths of port opening. At R the farthest distance is reached, and the edge of the valve is at a distance OK beyond the first edge of the port. It is clear that the distance RK is the throw of 512 PRACTICAL MARINE ENGINEERING the eccentric, and that this is equal to the lap plus the greatest width available for port opening. If the width of port is equal to or greater than OK, then the total movement OK can be utilized for opening and will be its greatest value, while the vari- ous distances from FL to ZTKGL will give the entire history of the width of port opening for corresponding positions of the piston. Very often, however, the width of port is less than the distance OK. In such case draw a line // parallel to LF and at a distance from it equal to the width of the port. Then it is clear that the widths of port opening will be given by the distances from FL to the lines ZTJIL. Full opening is reached at / or with piston at S. This continues to /, or until the piston reaches Q. The port closes at L or when the piston reaches P. This is known as the point of cut-off or steam closure. Similarly the port opens at Z just before the end of the stroke, and at the end is open a distance FT, which therefore represents the steam lead. Having thus obtained a general idea of the nature of this diagram, the effects of a change in the steam lap can be ex- amined by its aid. This corresponds to raising or lowering the line FL, and it is readily seen that the results of an increase, for example, are as follows : earlier cut-off, steam opening nearer the end of stroke, decreased lead, decreased port opening all the way through. The results of a decrease of lap are, of course, in the opposite direction. In a similar manner may be examined the influence of a change in the exhaust lap. This is illustrated in the same figure where M Y is the lap line laid off at a distance B D from the center line, equal to the exhaust lap on the upper end of the valve; that is, on the end which opens the port to exhaust by moving above the mid position. It is thus seen that the valve opens to exhaust at Y with the piston a distance Y D from the end of the stroke, while at the end of the stroke it is open a dis- tance D T, the exhaust lead. Then during the following stroke the distance of the exhaust edge of the valve from the corre- sponding edge of the port is given by the distance from D M to the curve T K L M. At M the port closes, and for M C, the remainder of the stroke, the steam undergoes compression in the cylinder. Usually the width of port is somewhat less than the total distance available, so that the full movement of the valve cannot be utiHzed for actual opening. In such case draw a Hne VALVES ANto VALVE GEARS 513 G H parallel to il/ F and distant from it r.n amount equal to the w idth of port. Then full opening is reached at H with piston at W and continues to G with piston at U, the openings for the remaining portions of the stroke being given by the distance from M Z) to F r // and G M. An increase of exhaust lap is thus seen to produce the fol- lowing results : earlier exhaust closure and longer compression, exhaust opening or release later or nearer the end of the stroke, decreased exhaust lead, decreased port openings or decreased Marine Enginefing Fig. 361. Oval Valve Diagrams time during which the port is. wide open. A decrease of exhaust lap will, of course, produce results in the opposite direction. Having thus far been concerned with the influence of an increase or decrease in the steam or exhaust lap, it remains to examine the influence due to a change in the angle 8 the angular advance. If this angle is increased and the new series of valve movements plotted, as in Fig. 360, it will be found that the oval becomes narrower and touches the boundary lines nearer the corners, as shown in Fig. 361. Similarly with a smaller value of 8 the valve oval will become wider or rounder, and will touch the boundary lines farther from the corners, likewise in the figure as shown. Remembering this and comparing Figs. 360 and 361 it is readily seen with the same values of the lap that changes- in 514 PRACTICAL MARINE ENGINEERING the various quantities will take place, as shown in the tabular ar- rangement below. This table shows at a glance the variation in the various events due to change in the three items above the double line, as explained in the foregoing. Attention may also be called at this point to the diagram of Fig. 362, in which the various quantities for an outside valve are lettered and named in position. A careful study of this figure in connection with the valve positions of Fig. 346 will be of great aid in acquiring a good understanding of the operation of a slide valve, and of its representation by means of such a diagram. Angular Advance Increase Decrease Steam Lap Increase Decrease Exhaust Lap Increase Decrease Steam Opening Earlier Later Later Earlier Steam Closure Earlier Later Earlier Later Steam Lead Increase Decrease Decrease Increase Exhaust Opening Earlier Later Later Earlier Exhaust Closure Earlier Later Earlier Later Exhaust Lead Increase Decrease Decrease Increase Greatest Port Opening Same Same Decrease Increase If the measurements for the diagram are taken from an actual engine or from a properly constructed model, it will' be found that for the down stroke the curve is more humped or rounded than for the up stroke, as shown in the figures above. That is, for the same relative positions of piston the valve will be farther from the center line on the down than on the up stroke. This is an e'ffect due to the angularity of the connecting rod of VALVES AND VALVE GEARS 51S the engine, and it results that the various points of opening and closure, and the values of lap, lead and port opening cannot be made the same for both strokes. As is shown by the diagram the cut-off is usually later on the down than on the up stroke, and it cannot be equalized without a serious derangement of the other events. Instead of attempting to equalize any two fea- tures, such as steam lead, cut-off or port-opening, it is usually bet- ter to so adjust the steam and exhaust laps above and below, that the resulting combination of events shall represent the best com- promise possible under the circumstances. If it were not for the effect due to the angularity of the connecting rod, the curve would be an ellipse, and the distribution of the events for both strokes could be made the same. SCB-/^ SOB, 1 z 9 £ Ul Ecr./ \ TEAM LAP BOTTOM' H < -1 1 t- Ul 5 / H r ^ / \ y .-> ^ 00 ^ STEAM LAP T H • 2 y i 1 TSOT /SOT UJ ED -1 1 > < > 1.J S O T = steam opening bottom. EOT — exhaust opening top. EC B =^ exhaust closure bottom." 5 C T'= steam closure top. Fig. set. Oval Valve Diagram S C B ^ Steam closure bottom. £C7' = exhaust closure top. EO B=: exhaust opening bottom. S O T:= steam opening top. [3] Bilgram Valve Diagrams In Fig. 363 let a circle be described witli OP as radius equal to the throw of the eccentric' Then draw the radius OP at an Si6 PRACTICAL MARINE ENGINEERING angle S (the angular advance) with the horizontal or line AB. Then draw CD above AB at a distance LM equal to the lead. Then from the point P as center and with PQ as radius describe a circle tangent to CD. Also on OP as a diameter describe a circle as shown. Then let A^ be any position of the crank. Draw the radius A^^O and extend it back to cut the circle on OP at E. Then the properties of this diagram are such that the movement of the valve from mid position is given by the distance PE, while the port opening will be less than this by PQ or PF the radius of the circle about P as center. This radius equals the steam Fig. 363. Bilgram Valve Diagram lap, and the circle is for that reason known as the lap circle. It follows that EF is the port opening, or at least the travel of the edge of the valve beyond the edge of the port. The same con- struction holds for all other crank positions, so that there is here a means of representing by straight lines and circles the move- ment of the valve, and of thus determining the various events of the revolution. It must be understood, however, that while this construction shows with fair accuracy the relation between the movement of the vah'e and of the crank, it does not, without a further special construction, connect the movement of the z'alue with that of the piston. It is the special property of the oval diagram of [2] to VALVES AN.D VALVE GEARS $17 show this latter relation for an actually constructed gear or for a model, where both sets of measurements may be actually made. It is the special property of the Bilgram diagram, and others composed of straight lines and circles, to connect together with- out actual measurement the movement of the valve and crank for the ideal case when there is no angularity of eccentric rod. The error here involved is usually small, and since the diagram is so easily constructed, it may be preferred for many purposes of initial design. It thus appears that the distances of the edge of the valve be- yond the edge of the port are given by the intercepts (shown by the shaded part of the diagram in Fig. 363), between the two cir- cles, one on OP as diameter and the other, the lap circle, about P as center. In case the width of the port is less than the dis- tance G 0, an arc RS \s drawn from P as center, such that the distance HS equals the width of port. The widths of opening are then given by the intercepts between J K S R L and the lap circle with P as center. It is seen that the port opens for steam at J with crank at A^, and closes at L with crank at A^, while full opening holds from 5" to R. An entirely similar construction throughout with the ex- haust lap circle as shown by the small circle about P will give the various features of the movement on the exhaust side. The results of a change in the steam or exhaust lap, or in the angular advance 8 are readily examined by the aid of this diagram, and will be found to agree with the statements of the table in [2]. [4] Zeuner Valve Diagrams In Fig. 364 let ABCD be a circle described with radius OA equal to the throw of the eccentric. Let A denote the angular position of the crank at the end of the stroke, and let OB be drawn perpendicular to AC. Draw OP at the angle 8 (the angu- lar advance) with OB, and on OP as diameter describe a circle as shown. Draw also an arc of a circle with OL equal to the steam lap, as radius. Let OA^, be any position of the crank. Then the properties of this diagram are such that the travel of the valve from mid position is given by the distance OG, while the port opening will of course be given by EG the intercept between this circle and the lap circle MN. A similar construction holds for other locations of the crank, and it thus appears that steam 5i8 PRACTICAL MARINE ENGINEERING opening will occur at N with the crank in the position ON while closure or cut-off will occur at M with the crank in the po- sition OM. By describing a circle with center at and with radius equal to the exhaust lap, a similar construction gives the various features of the movement on the exhaust side of the valve. The history of the port opening for steam is thus given by the intercepts between MN and the circle on OP, as shown by the shaded part of the diagram. In case the width of port is less than the distance LP an arc RQ is drawn from as center such that the radial distance be- D Marine Engineering Fig. 364. Zeuner Valve Diagram tween MN and RQ equals the width of port. The history of the port opening is then given in the same way as for the corre- sponding case in Fig. 363, as there explained. The results of a change in the steam or exhaust lap, or in the angular advance 8, are readily examined by the aid of this diagram, and will be found in accord with the statement of the table in [2]. Sec. 61. STEPHENSON LINK VALVE GEAR The operation of a slide valve operated by a single eccentric has, so far, been examined in some detail. In the course of the discussion it has appeared that with such a gear the direction of motion of the crank relative to the eccentric depends on whether VALVES AND VALVE GEARS S19 the valve takes steam on the inside or outside, and on the nature of the connection between the eccentric rod and valve stem. With any one arrangement, however, motion in one direction only is possible ; and it is therefore clear that to enable the engine to re- verse — a fundamental requirement of all marine valve gears — some additional features will be necessary. The general problem of a reversing valve gear is one which has been solved in a great variety of ways, both with and with- out the use of eccentrics, as shall be seen later. With the use of eccentrics the simplest solution is furnished by the well-known JHuTine Engiiuering Fig. 365. Skeleton of Stephenson Link Stephenson link. This is illustrated geometrically in Fig. 365. C represents the crank on the center. A denotes one eccentric at an angle CO A on one side of the crank and B another at the same or approximately the same angle COB on the other side. AD and BE denote two eccentric rods connected by a link DE curved to an arc whose radius is the length of the rod AD or BE. To a block in this link is attached the valve stem DC Now it will be readily seen that with the arrangement of the diagram the valve is under the control of the eccentric A alone. The eccentric B simply pulls the link DE back and forth, causing it to swing about D, but in no way affecting the movement of the valve. Hence the engine will move entirely under the con- trol of the eccentric A, and with an outside valve direct con- nected, the direction of rotation will be right-handed, or from C toward A. Now to effect the reverse, it is only necessary to move the link over so that E comes to the center line and the valve and engine pass under the control of eccentric B alone. For the reasons already noted in Sec. 56 [i] the motion will 520 PRACTICAL MARINE ENGINEERING now be reversed and the rotation will be left-handed or from C toward B. The next condition to be considered is the motion of the valve stem when the link is only part way over, as shown by the broken lines in the diagram. In such case it is readily seen that the motion of the valve will be derived partly from the eccentric A and partly from B, the former giving the principal part of the motion, and the latter exercising a modifying influence. Without taking up the examination of this question in detail, it will be sufficient to state that within a very small error the result- ant motion will be the same as though it -were given by a single eccentric of somewhat decreased throw and increased angular advance as compared with A or B. A simple construction will Fig. 366. Construction for Equivalent Eccentric — Stephenson Link serve to determine the throw and angular advance of this equiva- lent single eccentric. This may be carried out as follows : ( 1 ) In Fig. 366 lay off the two eccentric throws OA and OB, with the proper angular advance as shown, and draw the line AB. (2) Divide the length of the link DE, Fig. 365, by twice the eccentric rod AD and multiply the quotient by the length AC, Fig 366. (3) Lay off the result from C to D, and through the three points A D B pass the arc of a circle, as shown. Then the arc ADB may be considered as representing the link, and to find the throw and angular advance of the equivalent eccentric for any given position of the link-block as F on D-^^E-^, Fig- 365. it is only necessary to take a corresponding point F on VAJJ'ES AND I'ALJ^E GEARS $21 the arc ADB, and draw the radius OF. The throw is then repre- sented by OF and the angular advance 8 by the angle POF. That is, if the link be put into the position shown by broken lines in Fig. 365 the movement of the valve will be, within a small error, the same as though it were operated by a single eccentric of throw OF, Fig. 366, and angular advance POF determined in the manner described. It is readily seen, therefore, that as the link is so moved as to bring the block from the end nearer and nearer the center, the corresponding point F, Fig. 366, will move from A nearer and nearer to D, and the throw of the equivalent eccentric will continually decrease while the angular advance will increase. As the link passes the center and the block approaches the other end the corresponding point F moves on from D toward B, and the throw again increases, while the angular advance changes to the other side and gradually de- creases as B is approached. With the hnk in full gear at either end, the corresponding point F comes to either A or B^ and the equivalent eccentric becomes the same as the real eccentric, with its throw and angular advance as constructed. ^ In some cases, especially with the double bar form (see Sec. 62) the link may be put over so as to bring the block even be- yond the points of attachment of the eccentric rods. See Fig. 380. In such case the throw and angular advance of an equi- valent eccentric will be given by extending the arc beyond A and B, as shown in Fig. 366, and by then taking a point F cor- responding to the relative location of the block and link. In such case it is seen that the throw is increased and the angular ad- vance decreased. The details of the motion for any given position of the link- block may, of course, be determined by the use of any of the methods given above for the case of a single eccentric. It is simply necessary to take the equivalent throw and angular ad- vance determined, as in Fig. 366, and use them according to the methods described in Sec. 56. In this way it may be found that as the gear is linked up, or the block approaches the middle, the valve travel and port openings decrease, the lead increases, and the cut-ofif becomes earlier. This is further illustrated by the two oval diagrams of Fig. 367. These are constructed as explained in Sec. 56 [2], and represent the effect of linking up. The larger diagram represents the movement for full gear position 522 PRACTICAL MARINE ENGINEERING as shown by the full lines of Fig. 365, while the smaller and nar- rower one represents that for a linked up position as shown by the broken lines of the same diagram. A gear arranged, as in Fig. 365, is known as an open gear or gear with open rods. That is when the crank is turned away from the cylinder the rods are open as shown. If instead of this the rods are crossed, as shown in Fig. 368, then it is called a gear with crossed rods. It will be noted that with the open gear the rods become crossed when the crank is turned toward the Figr. 367. Oval Valve Diagrams for Stephenson Link cylinder, while in the same position the rods in the crossed gear become open. It is, therefore, necessary to note the character of the gear by the appearance of the rods when the crank is turned azvay from the cylinder as stated above. It must now be re- membered that the construction given in Fig. 366 and the con- clusions drawn from it apply to the gear with open rods only. For the crossed rod gear, however, a similar construction applies, as shown in Fig. 369. The distance CD is here laid off toward the center and a like arc is passed through the three points ADB as shown. The diagram thus constructed is used in the same manner as with Fig. 366. It is thus seen as the link-block ap- proaches, the center of the link and the corresponding point F approaches D, that the equivalent angular advance increases, the equivalent throw, valve travel and port openings decrease, even more rapidly than with the open gear, while the lead decreases and the cut-off is earlier and earlier. The principal characteristics of these two types of Stephen- son link valve gear with regard to the effect on the various VALVES AND VALVE GEARS 523 events, etc., due to linking the gear up may be conveniently pre- sented in the following tabular form : STEPHENSON LINK EFFECT OF UNKING UP Type of Gear Open Rods Equivalent Eccentric Throw Decreased Angular Advance Increased Valve Travel Decreased Port Opening Decreased L^sd Increased Cut-off Earlier Crossed'Rods Increased Decreased Decreased Decreased Decreased Earlier Fig. 368. Skeleton of Stephenson Link Crossed Rods Fig. 369. Construction for Equivalent Eccentric with Gear of Fig. 368 The chief point of difference is seen to be in the lead, which increases with open rods and decreases with crossed rods as the gear is linked up. While both types of gear are met with, the open rod gear is more frequently employed. This is due to the fact that as the cut-off is made earlier by linking up, an increase of lead may be preferred to a decrease, and also to the fact that the width of port opening is decreased less rapidly by the open than by the crossed gear. 524 PRACTICAL MARINE ENGINEERING Sec. 62. BRAEMME-MARSHALL GEAR The Stephenson Hnk is by no means the only form of valve gear which will allow of reversal and which will give variable cut-ofif. Among the other arrangements are several known as "radial valve gears," and of these the more important may be briefly described. In Fig. 370 let C denote the position of the crank and E the position of a single eccentric located directly opposite the crank. Let FD be a slide pivoted on the horizontal Hne OX, and EB a rod attached to the eccentric at E and fitted with a pin joint and block at P so that the block may move in or on the slide FD. Then as the eccentric moves around the end E of the rod describes a circle, the point P describes a straight line FD back and forth, and other points between P and E de- scribe paths intermediate between these two. For a point such as Q this is found to be an inclined oval as shown in the diagram. For points beyond P, such as Q', for example, the path is found to be a somewhat similar oval as shown. Now it is found that the proper motion for a valve can be derived from a point moving as Q or Q' and that it is simply necessary to connect such point by a proper link valve stem as shown for Q. Instead of placing the eccentric at 180 degrees from the crank it may be placed with the crank, in which case in Fig. 370 the crank should be considered as at C. There are thus four arrangements of the gear according as the eccentric is with or opposite the crank, and as the point Q is between P and E or be- yond P. In all cases the gear must be so adjusted that when the crank is op either center as C, the point P is on OX, or at the pivotal point of FD. It is readily seen that if this condition is fulfilled for one center it will be likewise for the other. With regard to the kind of valve to be used (inside or out- side) and the direction in which the engine will run for any given arrangement of gear, the same principles may be applied as in the case of the single eccentric. Thus it is easily seen from the symmetry of the motion that Q will go as far above the center line as below, and hence that OX contains the middle of its \ertical motion. Hence in the arrangement of the figure with the crank on the top center the valve is below its mid position by the distance from to the center line OX. Hence to take VALVES AND VALVE GEARS 525 steam on the top of the piston an outside valve must be em- ployed, and the engine will go in the direction which will open the valve still wider. This must be that which will lower the valve, and hence that which will lower P, and hence that which \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ c '^K / \. , -V / /\ i 0. / 1 % / 1 / / y -■^___ y "c' Jfarine £ngi^ceHii^ Fig. 370. Braemme-Marshali Radial Valve Gear will carry E to the left, or right-hand rotation. If, on the other hand, the motion were derived from Q', the valve will be above its mid position, and hence to take steam on top it must be an inside valve. The engine in this case will turn in the direction which will raise Q' still further. This requires E to move to the right, and hence the rotation will be left-handed. 526 PRACTICAL MARINE ENGINEERING If FD be inclined in the other direction, as shown by the dotted line, it will be readily seen by the same rule that the direction of rotation in each case will be reversed. It is also found that as the direction of FD approaches the horizontal or OX, the cut-off becomes earlier and earlier, and it is readily seen that the valve travel and hence the port opening will de- crease. There is here, therefore, an entirely similar action to that which takes place in linking up with the Stephenson link. The means for changing the cut-off and for reversal are there- fore furnished by providing r, means for changing or reversing the obliquity of the slide FD, and for retaining it in any position desired. Since the point P comes to the center of the slide or pivot point when the engine is on the center, it follows that in this position the line EB, the point Q and the valve will have exactly the same location no matter v/hat the position of FD, and hence no matter what the point of cut-off. Hence the lead of the valve will be the same for all points of cut-off, or in other words, the lead is not affected by the change in cut-off. This is a feature which is possessed by the various forms of radial valve gear. With the Stephenson link the lead is variable with the cut-off as described in Sec. 57. As noted above, there are four arrangements of this gear depending on the location of the point Q, and the angle between the eccentric and the crank. Angle Between Crank and Eccentric 180° 180° Location of Q Inside P Inside P Outside P Outside P Valve Inside Outside Outside Inside These four arrangements are shown in the above table with the appropriate form of valve. The direction of rotation in each case will depend of course upon the direction of obliquity of the slide FD. The arrangement of Fig. 370 shows the earlier form of the gear. Another and later form is shown in Fig. 371 in which the slide FD, Fig. 370, is replaced by an arm PT^ pivoted atTi, and attached by a wrist pin to the rod EB. In this way the point P is caused to move in the arc of a circle F^ D^ inclined to the horizontal OX as shown. In such case the motion of the valve VALVES AND VALVE GEARS 527 is very nearly the same as if the point P moved in the line of the tangent F D, and except for secondary modifications it is there- fore equivalent to the motion of Fig. '370. The change of cut-off and the reversal are brought about by swinging the pivot Ty Fig. 371. Braemme-Marshall Radial Valve Gear about a center S, the intersection of FD with OX. In this way Ti is brought to a new position T^ and the line of motion is brought to F2 D2, thus reversing the direction of rotation ac- cording to the same principles as applied in the preceding case. It is evident that the same four arrangements as in the other 528 PRACTICAL MARINE ENGINEERING form of the gear, with the same relation between eccentric angles and type of valve as given in the table above may exist in this case. Fig. 372. Joy Radial Valve Gear Sec. 63. JOY VALVE GEAR In this form of radial valve gear no eccentric whatever is required. As shown in Fig. 372 F is a point on the connecting rod to whijch a link DF is attached pivoted to a swinging or sus- pension bar DK. The point F moves in an oval path as shown. The point D moves in the arc of a circle as shown. An inter- VALVES AND VALVE GEARS 529 mediate point as E will move in a path somewhat as shown. From this point on, the gear is similar to a Braemme-Marshall. Thus EP is a link pivoted at E and with the point P carried by a suspension bar PR exactly the same as PT of Fig. 371. The motion for the valve is similarly taken from a point Q as shown. It is thus clear that the Joy gear as here shown is the gear of Fig. 371 in which, however, the point E instead of moving in a circular path derives its motion from the connections shown in Fig. 372 and moves in a distorted oval path as there shown. It is clear that there will be the same two varieties of gear ac- cording as the point Q is taken between E and P or beyond P. The reversal is also effected in the same fashion by swinging PR, or the straight slide may be used as in the gear shown in Fig. 370. Sec. 64. WALSCHAERT VALVE GEAR In this gear, as shown in outline in Fig. 373, one eccentric E is used. MGK is a curved link pivoted at G. H is a block sliding on or in the link and connected by a radius arm to the valve lever AF. The end F of this lever is connected by a pin joint to the valve rod, and the other end A hy a short link to the main crosshead as shown. The valve is thus seen to derive its motion in part from the main crosshead and in part from the eccentric. The former part comes through the valve lever which pivots about D and thus communicates motion from C to F. The latter part comes from the curved link which is operated by the eccentric, causing it to swing about G and thus through the radius arm and valve lever the motion of the eccentric is communicated to the valve rod. The combination of these two motions is found to be such as to give a suitable movement to the valve. The linking up and reversal are accomplished by swinging the block H and radius rod from one side to the other of the mid-position or pivot G. As the block H is brought nearer to G the cut-off becomes earlier while the valve travel and port-open- ing are decreased the same as with the Stephenson link above described. In order that this gear may operate properly, certain ad- justments are required as follows : The radius of the curved link MGK must equal -the radius- rod HD. 530 PRACTICAL MARINE ENGINEERING Place the crank on, say, the top center, and bring the Hnk MGK into line with an arc struck from D as center with DH as radius. Then M should be so taken that the angle OMG is a right angle. Also the eccentric E is placed at a right angle from OM as shown. Then in this position the block H may be drawn to and fro along the link without moving the valve. — -> Fig. 373. Walschaert Valve Gear It is also clear that after the crank has gone i8o degrees the eccentric will be at E, and MG will be again in the same position and the block H may be drawn along the link without giving motion to the valve. It follows that the position of the valve when the crank is on the centers will be the same no matter where the block H may be located, and hence that the lead of the valve will be the same for all points of cut-oflf. It is clear that the arrangement of Figs. 370-373 will bring the valve chest on the side of the cylinder transversely instead VALVES AND_^ VAU'E GEARS 531 of fore and aft. The cylinders may, therefore, so far as valve chests are concerned, be placed nearer together than with the Stephenson link, with which the valve chests are forward or aft of the cylinders. The length of the engine as a whole may, therefore, be made somewhat less with the radial types of gear than with the Stephenson link, and it is this feature which gives to them their best claim of advantage. Such gears possess also, as has been seen, the property of giving the- same lead for all points of ciit-ofif, while with the Stephenson link the lead varies with the cut-off. With proper design, however, the variation in the latter case is not sufficient to constitute a feature of any im- portance, and the difference on this point can hardly be consid- ered as forming any noteworthy advantage for the radial gears. The general character of the valve movement and the distribu- tion of events in all cases is best studied by the aid of a diagram, ■ such as that of Fig. 360. It will thus be found that the results for these various cases will be quite similar, and that such dif- ferences as appear are of relatively small importance. Speak- ing broadly, it is perhaps fair to say that there is not sufficient difference in the operation of the valve itself to furnish any pronounced claim of advantage for the usual cases arising in marine practice. The choice must, therefore, be made rather by reason of structural considerations, such as the shortening up of the engine referred to above, or the details of construction of the gear as affecting the questions of breakage, wear and tear, readiness of repair, readjustment, etc. On the whole, the Steph- enson link seems to be usually preferred as the best fulfilling the all around requirements for the marine valve gear, and it may be fairly considered as the representative gear in present-day marine practice. Sec. 65. CRANK VALVE GEAR As has been seen in Sec. 56 [i] the action of an eccentric is equivalent to that of a simple crank of throw equal to the eccen- tric and set at a corresponding angle with the main crank. It is evident then that a series of cranks will operate a valve and gear in a manner identical with a corresponding series of eccentrics. Such cranks, however, on account of their small throw cannot readily be located or formed on the main crankshaft, and hence where used for operating the valves, are necessarily placed on a S32 PRACTICAL MARINE ENGINEERING special or auxiliary shaft. In Fig. 374 is shown the usual way of arranging the parts of this gear. 5" is the center of the main crankshaft, and ST the main crank. A, B and C are gear wheels, A attached to the crank- shaft, B an idler, and C attached to the valve shaft. is the center of this shaft and OP represents the throw and angular location of the small crank for operating the valve. The valve Fig. 3T4. Crank Valve Gear shaft will then turn in the same direction as the main shaft, and as may be readily seen, will operate the valve precisely in the same manner as an ordinary eccentric of the same throw and angular location. For reversing with this gear the usual plan is to have but one crank and valve connecting rod corresponding to one eccentric rod. The angular location of the crank must then be changed from a position such as OP in the figure to OP^. By comparing this with Sec. 60 [i] it is seen that such a change in the location of the crank will necessarily cause the engine to move in the opposite direction. To bring about this change in the location of the valve crank relative to the main crank, various mechanical devices may be used. Thus it may be seen that if after the engine has stopped the gear C were slipped out of the mesh with B, turned around through the angle POP^ and then slipped back into mesh again, the crank would be brought to OF-^ and if the engine were! started again it would go in the opposite direction. This, of course, it not a practicable form of reverse, since it cannot be carried out quickly enough, nor when the engine is in motion. VALVES AND VALVE GEARS 533 It does, however, serve to illustrate the necessary change to be made in the angular location of OP. In the usual mode of operation, some form of spiral cam is employed, as illustrated in Fig. 375. C is the gear wheel car- ried on a sleeve AB and connected to it by a key way and feather so that the sleeve may be moved back and forth axially and still remain coupled to the gear C so far as rotary motion is con- cerned. The gear C is also prevented by suitable stops from being carried out of mesh with the gear B, Fig. 374. This sleeve is carried on the shaft D to which is attached the valve crank, and Fig. 375. Crank Valve Gear Reversing Arrangement is loose on D and only connected with it by a pin P which pro- jects through a spiral groove RS cut in the metal of the sleeve. At E there is a circumferential groove in the sleeve, in which is fitted the end of a controlling lever F, by means of which the sleeve may be moved back and forth longitudinally. In the figure the sleeve is shown pushed in so that the pin is at one extremity of its travel in the spiral groove, and the valve crank will, therefore, be in a corresponding position with reference to the gear C and main crank, which will be supposed to be for full gear ahead. If now the sleeve be pulled longitudinally until the other end of ' the groove contains the pin, it is clear that the angular location of the pin relative to the gear will have been changed and hence that of the valve crank relative to the main shaft. If then the spiral groove be of suitable extent and location, such a change will serve to move the crank OP, Fig. 374, from its position for full gear ahead, to OP^ its position for full gear astern. Instead of one pin and spiral groove, two on opposite sides may be used, and other details may vary in many ways, but the arrangement will serve to illustrate the principles involved. While this form of valve gear is thus efficient for reversing, it is much less suitable for linking up or varying the cut-oflf than 534 PRACTICAL MARINE ENGINEERING the other forms of gear discussed above. Referring to Sec. 57 it was there shown how to find the equivalent simple eccentric for any adjustment of the Stephenson link, as shown by the line A D B, Fig. 366, for an open rod gear. Now it is readily seen that the form of reverse just considered is equivalent to taking the eccentric A and carrying it around from OA to OB, so that for the varying intermediate positions the virtual eccentric would be given by drawing a line from to the arc A B with OA as radius. From the principles discussed in Sec. 56 [2] it is readily seen that the effect on the valve will be as follows : Linking up will produce : Earlier cut-off. Earlier steam opening. Greatly increased lead. Earlier exhaust opening. Earlier and greater compression. The same valve travel and opening. While, therefore, the port opening is not decreased by link- ing up, the lead and compression may become excessive, and re- strict the practicable range of variable cut-off to narrow limits. In Fig. 374 reference was made to only one cylinder and valve operating crank, but the same arrangement may be applied, of course, to a series of cylinders for a multiple expansion en- gine. In such case the valve operating shaft has a series of cranks, one for each cylinder, and set at the proper angle from the corresponding main crank. Then with a reverse gear similar to that described in Fig. 375 all the cranks are moved together and are brought into the proper relation with their main cranks to operate the engine in the reverse direction. It is also to be noted that this arrangement brings the valve chests at the sides of the cylinders and that on this account it has the same effect in shortening up the engine as the vise of a radial valve gear. This type of gear has been used to some extent on launch, yacht and torpedo boat engines, but has not found favor for larger or slower running engines as used in ordinary mercan- tile and naval practice. Sec. 66. DETAILS OF STEPHENSON LINK VALVE GEAR In the present section will be given a brief description of the more important details of the Stephenson link valve gear as a VALVES AND VALVE GEARS 535 representative gear, and including as it does most of the elements of other forms of gear as described in Sec. 62-65. [1] Eccentric and Strap and Eccentric Rod The general construction of this part of the gear is shown in Figs. 376-379. The eccentric consists of a disk or sheave of circular form, and placed on the shaft eccentric or with its cen- ter set out from the center of the shaft. As shown in the figure the sheave is made in two unequal halves which join on the cen- ter line of the shaft, and are secured by bolts as shown. This brings the center of the disk at the point shown, the distance AB between this and the center of the shaft being the eccentric a J_ Fig. 376. Eccentric, Detail of Construction and Fitting throw as defined in Sec. 56. Once adjusted the eccentric is keyed in place and in addition set screws or binding bolts may be fitted, as shown. In the eccentric of Fig. 376 the larger part of the sheave is lightened out to save weight. In eccentrics of moderate size this is not usually done, and the bolts connecting the two parts are tapped into the larger part and hold the other portion in place by means of a countersunk head. The material of the eccentric is either cast iron or steel, or if small in size, brass is sometimes employed. The strap which surrounds the eccentric, as shown in Fig. 377, is also made in two parts bolted together, and the eccentric rod is attached by a flanged foot to the upper half, as shown in the figure. There are several w&ys of fitting the surfaces of the 536 PRACTICAL MARINE ENGINEERING strap and eccentric together, as shown in Fig. 378. In modern practice the strap is usually of cast steel or brass, lined with white metal for a bearing surface as shown at a. With this arrangement of eccentric sheave and strap, it is readily seen that as the former turns with the shaft the center of the sheave turns about the center of the shaft ; also that the center line of the eccentric rod which will always pass through the center of the sheave, will therefore move exactly as though it were a connecting rod with the distance A B between the two centers as a crank arm. Hence as noted in Sec. 56 [i] the mo- tion communicated to the rod will be exactly the same as would Marine Engineering Fig. 377. Eccentric Strap, Detail of Construction and Fitting be given by a crank and connecting rod the throw of former equal to that of the eccentric. The other eccentric strap and rod are fitted up in the same manner and two rods connect with the ends of the link in the manner shown in Fig. 379. In this figure is shown on the left the lower end of the eccentric rod with flange for securing to the upper strap as in Fig. 377. On the right is shown the upper end of the rod sometimes known as the eccentric rod fork. The form is more properly that of a U, the two sides VALVES AND VALVE GEARS 537 being fitted with bearing brasses and cap to provide a bearing for the pins by means of which the connection is made with the Hnk. [2] Link In Fig. 380 is shown the usual form of double bar link as it is termed. It consists of a pair of bars curved in the arc of a circle of radius equal to the geometrical length of eccentric rod ; Fig. SV8. Different Methods of Fitting Eccentric Strap that is, equal to the distance from the center line of the link to the center of the eccentric sheave. These bars are connected at the ends by bolts and by a block between so as to maintain the desired distance between them. Near the ends are fitted the pins A, B, C, D, which serve for connecting with the eccentric Fig. 379. Eccentric Rods, Fittings at Ends rods by means of the bearings in the upper ends, as shown in Fig. 379. Another pair of pins E, F, is fitted, either at the center as shown or as an extension of the pairs at the ends, or at some 538 PRACTICAL MARINE ENGINEERING intermediate point. To these are attached a pair of bars or links usualy known as side or bridle or reach rods, as shown in Fig. 381. These lead to the rock or ivcigh shaft, and serve to control the gear when linking up or reversing, and to hold it in any de- sired position. The rock shaft or weigh shaft is usually carried in bearings on the outside of the engine columns near the top, and is provided with arms, one each for the several links, and one for the connec- tpn .n nn ^W" 880. Stephenson Double Bar Link tion to the reverse cylinder by means of which it is operated as desired. In order to provide an independent adjustment for the valve gear of the different cylinders, the weigh shaft arm, as shown in Fig. 382, may be provided with a slot within which moves a block under control of a hand wheel and screw as shown. The bridle rods are attached to pins on the sides of this block, as shown on the right, and by this means without moving the weigh shaft at all, the links may be given an adjustment within the limits of the motion of the block in the slot. It is customary to so adjust the line of motion of this block that when the gear is in the go-ahead position, it shall lie nearly in the line of the bridle rod so that any movement of the block will be communi- VALI'ES AND J'ALVE GEAR€ 539 cated to the link without loss. In the backing position on the other hand, the line of movement of the block will lie across the line of the bridle rod at a considerable angle, and movement of the block back and forth will give but slight motion to the link. See also Fig. 384. T Marine Enyineerinj Fig. 381. Side or Bridle or Reach Rods This arrangement is often of use in adjusting the points of cut-oflf in the separate cylinders so as to divide as equally as pos- .sible the power among the different cylinders. See also Sec. 64 [4]. Fig. 382. Independent Adjustment for Cut Off with Stephenson Link [3] Link Block and Valve Stem The connection between the link and the valve stem is made by means of a link block, as shown in Figs. 380, 383. This con- sists of a central pin with wing pieces at the ends, as shown in the figure, the latter being fitted with bearing surfaces for con- 540 PRACTICAL MARINE ENGINEERING necting with the bars of the Unk, and permitting sliding motion between the two. The pin is connected with the lower end of the valve stem, which is formed in the usual manner with brasses and cap. See also Fig. 385. The valve stem is usually guided by means of a special guide or bearing, as shown in Fig. 384, which supports it against side stress, especially at the stuffing box just above. In good practice the valve rod stuffing box is usually packed with some form of metallic packing, and is of the same general form A ] r^ — ± — ^ ^ G ty IT | T| Marine' Engituerin J Fig. 383. Link Block for Stephenson Double Bar Link and arrangement as the piston rod stuffing box. Passing through the stuffing box the valve stem is attached to the valve, and thus the chain of connections between the eccentric and the valve is completed. The assemblage of these various parts of a Stephenson valve gear is further illustrated in Fig. 384, showing the upper ends of the eccentric rods, the link, link block, valve stem and guide, bridle rods, rock shaft arm and brackets for supporting the shaft, and independent cut-off control in rock shaft arm. When two piston valves are driven side by side as is very commonly the case on the low pressure or on intermediate pres- sure cylinders, the two valve stems are connected across by a yoke, as shown in Fig. 385, which in turn is connected to the link block by a form of bearing similar to that for the single stem. In such case the guide is very commonly attached to the yoke, the arrangement consisting of a dovetailed or gibbed slide and guide, the first formed on the yoke, and the second by a vertical VALVES AND VALVE GEARS S4i plate or bar projecting downward from the bottom of the cylinder head, as shown in the figure. Sec. 67. VALVE SETTING [i] Putting an Engine on the Centers One of the important features of valve setting is the placing of the engine on the centers or dead points in order to determine the lead. In a rough way this may be done by turning the engine and watching the crosshead slide as it approaches the dead points. Starine SnffinMrinff Fig. 384. Arrangement of Stephenson Link and Rock Shaft Connections The slide will move along the guide, more and more slowly, and will finally stop and begin to return. Just as the farthest point is reached, the crank is on the dead point. By moving the en- gine back and forth and watching carefully the movement of the slide relative to a light mark or score on the guide, the desired point may be determined with fair accuracy for purposes of valve setting. The difficulty in making an accurate determination by this method lies in the fact that when near the center the crank may 542 PRACTICAL MARINE ENGINEERING be moved to and fro through a sensible angle with hardly a no- ticeable movement of the slide. Hence while it is possible to N4 >i 1 2 3 1 Fig. 385. Yoke and Guide for Driving Double Piston Valves determine to a nicety the point on the slide which corresponds to the highest or lowest position of the piston, it is less easy to know just where to set the crank so as to have it accurately correspond VALVES AND VALVE GEARS 543 For more accurate setting the following to the same location, method may be used. The engine is placed with the crosshead slide at a small distance from the lowest or highest position. A mark A is then made on the slide and a corresponding mark B on the guide. The distance which the crosshead should be placed from the center when these marks are made depends, of course, on the size of the engine, but i or 2 inches, or say 1/20 to i/io the stroke, will Narine Engineexillg Fig. 386. Putting an Engine on the Center be a suitable distance. See Fig. 386. Another pair of marks P, Q, is next made on the forward end of the shaft and the adjacent brass, or on one of the coupling flanges and an adjacent block or bar set up for the purpose. The object is simply to have two pairs of marks, one on the crosshead slide and its guide, and one on the shaft and its support or guide or an adjacent and fixed object. The engine is then moved around continuously in one direction past the center till the crosshead slide moves back and the mark A again comes opposite B. The point P on the shaft in the meantime will have moved on to a new location, and a corresponding mark R is made on the bearing or stationary part of the engine on which the first mark Q was placed. The angle between these two marks Q R, on the shaft or coupling corresponds to the movement of the cro?.shead from the position of the first pair on to the end of the stroke and back again an equal distance. A mark 5" midway between Q and R, will give the proper location for the mark P when the crosshead is at the end of the stroke and the crank on its dead point. In this way by moving the shaft till P is brought opposite S the location of the crank for each dead point may be quite accurately found. 544 PRACTICAL MARINE ENGINEERING [2] Setting the Valve To return to the setting of the valve it should be first noted that the distribution of the steam to a cylinder by means of a slide valve depends on four chief items : (i) The throw of the eccentric. (2) The angular location of the eccentric relative to the crank. (3) The length of the valve stem. (4) The steam and exhaust laps. Let it be assumed that the parts of the valve gear are made, and that it simply remains to connect them up and make the proper adjustments. It is seen that but two items may be varied, or which enter into the question of the setting of the valve. These are (2) and (3) above. Adjustment should first be made for (3) and then for (2). It can readily be seen that an incorrect length of valve rod will give an improper balancing up of the events for the top and bottom of the cylinder. Hence the various events, for both ends must be examined and compared. To this end the entire gear is connected up according to judgment, the link being placed in the position intended for normal running ahead, and the necessary arrangements made for observing the movement of the valve. If the valve is a flat slide the valve chest cover is left off for this purpose. With piston valves, however, it is necessary to observe the movement of the valve by means of peep holes through the shell of the chest, such holes being fitted with screw plugs or covered by caps when the en- gine is closed up and ready for operation. In this manner the lead is observed while the engine is on the centers, and the points of cut-off and other items are observed for each end of the cylinder. The location of the valve on the stem is then varied until a fair balance between the two ends is obtained. It wlill be found that with anything like equal leads the cut-ofif will be later ©n the down than on the up stroke, or with an attempt to even the points of cut-ofF the lead and port opening on top will be- come too small and the lead on the bottom excessive. It will often be found that with something approaching equal leads on top and bottom, the points of cut-ofif will vary in the two ends by nearly or quite 10 percent, or even more. It is readily seen that similar derangements will result from VALVES AND VALVE GEARS 545 an attempt to balance the exhaust items. In general it is far better not to attempt to exactly balance any one item in the two ends, but simply to aim for the best all around combination of events which can be obtained in the given case. When a fair balance is thus obtained, the question of the point of average cut-oflf, steam opening, release and compression may be taken up. Changes in these items require a change in the angular location of the eccentric relative to the shaft, and it may be shifted according to the relations shown in the table of Sec. 60 [2] until the general character of the various items is made satisfactory. It thus appears that of the two items, length of valve rod and location of eccentric, the latter really fixes the general character of the various items, while the former makes it possible to ap- proximately even up or balance the various items between the two ends, according to what seems the most desirable average distribution. If the eccentric is shifted through any considerable angle from its first location it will be necessary to again examine the question of balance between the two ends, and to again adjust the length of valve rod. If by the adjustment of both valve rod and eccentric, the desired events, openings, etc., cannot be obtained, it means that the trouble lies with one or both of the other items, throw of ec- centric and steam or exhaust lap, and steps must be taken to modify these features as the conditions may require. The following table gives an illustration of the balancing up of the various items in the two ends of the cylinder. Top Bottom Steam opening 7 percent before end .4 percent before end of stroke - of stroke Steam closure or cut-off. ... 68 percent 59 percent Exhaust opening.. : 90 percent 91 percent Exhaust closure 85 percent 84 percent Steam lap 2.44 inches 2.40 inches Exhaust lap — -12 inch + .68 inch Steam lead 60 inch .52 inch Port opening for steam 2.08 inches 2.12 inches Angle of advance 33 degrees Throw of eccentric 4 15/16 inches The setting of the valve may, of course, be examined or re- adjusted at any time, as desired, by the use of the same general method. 546 PRACTICAL MARINE ENGINEERING [3] Valve Setting from the Indicator Card The indicator cards interpreted in accordance with the re- lations given in Sec. loi [2] furnish most valuable evidence as to the adjustment of the valve gear, and its suitability for operation under steam. In attempting a readjustment or resetting by the aid of the indications given by the cards, the question of balance between the two ends as afifected by the length of valve rod should be taken first, next the items depending on the angular location of the eccentric, and last the question of lap and eccentric throw. If the cards are pushed over to one side or show differences in the two ends it is evidence that the valve stem is not of the right length, and it must be changed accordingly. This is done first, cards being taken after each change until the twO' ends are fairly well balanced up. Attention is next given to the location of the eccentric. The points of cut-off, release and compression will show whether the angular advance is too large or too small, and the readjustment is made accordingly. A change in the angle of the eccentric for the purpose of adjusting any one item is more- over liable to disturb other items in such a way as to require a readjustment of the lap, and is therefore to be avoided unless considered necessary. Thus if the cut-off is too late, for example, and the eccentric is turned so as to increase the angular advance, the cut-off will be made earlier and the exhaust and compression as well, while the lead will be increased. If the change neces- sary to adjust the cut-off produces too great a disturbance in the exhaust and compression, or if in general a suitable and satisfactory arrangement of events cannot be reached by adjust- ment of the eccentric and valve rod only, it means that the lap is at fault or perhaps the throw of eccentric. Change in the lap can, of course, only be effected by removing the valves and cutting them down if it is to be decreased, or fitting a new valve or head if it is to be increased. Similarly change in the throw of the eccentric can only be effected by a removal of the old and fitting a new one of proper throw. QUESTIONS Valves and Valve Gears PAGE Explain the meaning of the terms steam lap, exhaust lap, steam lead, exhaust lead, cut-off, compression or cushion 496 Explain the general operation of a plain slide valve 496 VALVES AND VALVE GEARS 547 PAGE What is a double ported slide valve, and what is the purpose of this style of valve ? 497 What is a piston valve, and what is its chief advantage over the flat slide valve ? 498 What is the purpose of an equilibrium piston and how is it fitted up ? 502 What is the purpose of Lovekin assistant cylinder and how is it fitted up? 503 What is the purpose of an equilibrium ring on the back of a flat slide valve, and how is it fitted up ? 505 Explain the difference between an outside and an inside valve 506 What is an eccentric, and what is meant by its throw and angular advance ? 507 Explain the difference in the angular location of the eccentric relative to the crank in the case of an outside and of an inside valve 508 Explain the oval valve diagram for representing the movement of the valve relative to the piston, and for showing the various events and items of the operation 510 Explain the influence on the various events and items due to change in the three items, angular advance, steam lap and exhaust lap.. SH Explain the Bilgram valve diagram for showing the same features as mentioned above in connection with the oval diagram 515 Explain the Zeuner valve diagram for showing the same features as mentioned above in connection with the oval diagram 517 Describe the main features of a Stephenson link valve gear 518 When partly linked up, how may the motion of the valve be deter- mined ? 520 What is the difference between the two arrangements known as crossed rods and open rods ? 522 What arc the various effects due to linking up, and what is the dif- ference as regards the lead in the case of open and crossed rods ? 523 Describe the main features of the Braemme-Marshall valve gear. . . . 524 Describe- the main features of the Joy valve gear 528 Describe the main features of the Walschaert valve gear 529 What are the chief advantages of the radial types of valve gear?. . . . 531 Describe the main features of the crank valve gear, and explain its mode of operation S3i Describe the usual form of eccentric 535 How is it fitted up and secured to the shaft ? 535 Descrilse the usual form of eccentric rod and strap 535 Describe the usual form of double-bar link and the method of its control by bridle rods 537 Describe the usual form of link-block and valve-stem 539 How may an engine be put on the center or dead point? 54i How would you set the main valve of an engine? 544 In setting a valve what will be the result of an incorrect length of valve rod ? 544 What will be the effect of an incorrect angular location of the eccen- tric relative to the crank? ■ • •. 544 Can a perfect balance of steam and exhaust events and items be obtained? • .•■•■•■ S44 Describe the general operation of setting a valve by observation of the valve itself 545 Describe the use which may be made of indicator cards to the same purpose 540 CHAPTER IX Refrigeration Sec. 68. GENERAL PRINCIPLES In connection with the general principles of refrigeration reference should be made to the section in which the general nature of heat and its relation to matter is discussed. The funda- mental problem of refrigeration is the abstraction of heat from some body or substance A, or the maintenance of such substance ^ at a temperature lower than that of the surrounding air. This is most conveniently brought about by bringing the substance A into relation with another cooling substance B at a lower tem- perature, such that heat may readily pass by conduction from one to the other. The heat then flows A to B, and thus the end desired is brought about. It is clear, however, that unless there is a continuous renewal of the substance B, or some way of removing the heat which flows into it, then in the end the two substances A and B will come to the same temperature, and if this is lower than that of the surroundings, it will gradually rise until both A and B are in equilibrium with their general sur- roundings. Again it is seen that if the substance A is kept below the temperature of its surroundings there will be a constant flow of heat from these surroundings (structural material, earth, air, water, etc.) into it, and this heat must be as constantly removed by conduction into the substance B at still lower temperature, which again must be renewed in order to maintain its capacity for absorbing heat from A. Again there may be two different cases,, according as the substance A is cooled by the conduction of its heat directly into B, or first into some intermediate sub- stance such as air and then into B. In other words, the sub- stance B may affect A directly, or through the intermediate ac- tion of the air surrounding both of them. REFRIGERATION 549 Thus in making artificial ice the water to be frozen is brought as directly as possible under the influence of the cooling substance, whatever it may be, while in certain systems for the refrigeration of meat, etc., in a refrigeration or cold storage room, the meat is kept cool by the action of the cold air of the room, which, in turn, is cooled by the action of the cooling sub- stance, usually conducted through coils of pipe about the walls of the room. In other systems of refrigeration or cold storage, air itself is made the cooling substance, and the cooled- air is passed through the storage room, thus acting directly upon the substances stored therein. With the foregoing by way of a statement of general prin- ciples the subject of the production of the cooling substance is reached. In other words, how shall there be found or produced a substance whose temperature is far below the usual temperature of the air, and which may be made available for the purposes outlined above ? To this end there are two general methods ; one involving a change of state, either physical or chemical or both, and the other the compression, cooling and expansion of an elastic gas such as air. Illustrations of these methods will be found in the systems of refrigeration described in the following sections. Sec. 69. REFRIGERATION BY FREEZING MIXTURES If salt and ice are mixed there is a tendency for the mixture to pass into the liquid state. As to just why this is so need not be considered, but simply with the fact. In answer to this tendency the two substances pass rapidly from the solid into the liquid state, thus forming a brine, or, more exactly, the ice passes from the solid to the liquid state and the salt dissolves in the liquid. Now ice cannot pass from a solid to a liquid state without absorb- ing heat. This point is referred to in a later section, where it is also noted that the term latent heat is applied to the heat which is thus involved in a change of physical state- Heat must there- fore be supplied from somewhere in order that the change from ice to liquid may take place. Furthermore, due to the physical and chemical forces at work, this change takes place faster than heat can be. supplied from the general surroundings, and since it must come from somewhere it is drawn from the substances themselves, brine, salt and ice, which are thus reduced to a much lower temperature than they would have if separate. Thus a 550 PRACTICAL MARINE ENGINEERING mixture of ice and salt forms a brine having a temperature of about — 5 degrees F., or about 37 degrees below the freezing point of water. Such solutions or mixtures are known as freezing mix- tures, and the brine thus formed may then be used as a cooling or freezing agent in whatever way may be most convenient. Thus in the ordinary manner of freezing ice cream and ices the ice salt mixture is commonly used, inclosed in a casing which surrounds an inner vessel containing the substance to be frozen. In the manner above described then the ice will be melted, a brine will be formed, and heat will be withdrawn first from the freezing mixture itself, and then from the substance in the inner vessel, which thus becomes cooled down to its freezing point. Next its own latent heat will be drawn upon, and thus finally the substance becomes frozen as desired. There are many such mixtures composed of various chemi- cals, and by means of which temperatures from o to — 50 degrees F. may be obtained. For the general purpose of refrigeration, however, the use of such mixtures has not been found as efficient as other means, and it will not be necessary therefore to further refer to them in the present connection. Sec. 70. REFRIGERATION BY VAPORIZATION AND EXPANSION Next will be considered the application of substances like am- monia or carbonic acid, which are gaseous at the usual tempera- tures, but may be liquefied at low temperatures and under suitable pressures. Anhydrous ammonia (ammonia without water) has a boiling point under atmospheric pressure of 37 degrees below zero. With higher pressures the boiling point rises. As will be seen later, a liquid passing into the state of vapor absorbs a cer- tain amount of heat, and this latent heat, as it is termed, will be drawn either from the surroundings or from the liquid itself, or from both, thus lowering their temperatures. In order to utilize these properties of ammonia the refrigerating apparatus consists of the following : ( 1 ) A series of expansion evaporating coils which are placed in the refrigerator room or space to be cooled, or which in other .systems are surrounded by a liquid which is used as the imme- diate cooling agent in the coils of the refrigerator room. (2) A reservoir containing liquid ammonia which is allowed to flow as may be required into the expansion coils. REFRIGERATION 551 (3) -^ pump which withdraws the vapor from the expansion coils and then compresses it back into the coils of a condenser, which are surrounded by cool water. Here, under the influence of the pressure and moderate temperature, the vapor becomes condensed to liquid and then flows to the reservoir from which it started. The two fundamental parts of the process are there- fore (i) evaporation and expansion, (2) compression and con- densation. In this manner the continuous operation of the pump insures the formation and continuous flow of ammonia vapor at low temperature through the cooling coils. The vapor is thus in condition to absorb heat through the metal of the coils from the surroundings, either air or liquid, and thus the refrigeration is effected. Where a liquid is employed as the immediate cooling agent it is usually a brine made with common salt, which, after having been cooled down by giving up its heat to enable the ammonia to evaporate, is then circulated by a brine pump through the coils of the refrigeration room. It has been well said that the action of the ammonia in this round of operations is like a sponge. It vaporizes and expands in the. expansion coils and absorbs or soaks in the heat from its surroundings. Then it is compressed and the heat is forced or "squeezed" out, and it is ready for a new round, thus acting as a carrier of heat away from the substance to be cooled. It may aid further in understanding the action of the liquid ammonia in the refrigerating coils to note that relative to the air or brine surrounding these coils the ammonia is situated some- what like the water in a watertube boiler with hot gas on the fire side of the tubes. The furnace gases are hot relative to the water, and so heat tends to flow through the tubes into the water, thus forming steam. So is the temperature of the air or brine about the coils far above that at which ammonia would naturally exist in the liquid form under the pressure in the coils. In fact, the liquid ammounia when first admitted is itself far above this temperature, so that the first result is a tendency for the liquid to fly into vapor immediately, drawing on its own sensible heat to supply the necessary latent heat, and thus cooling the remain- ing liquid and the vapor formed. Then the heat from the sur- rounding air or brine flows in and thus the vaporization is com- pleted. It may thus be said that the liquid ammonia is boiled into vapor chiefly by the heat which it draws from the surround- SS2 PRACTICAL MARINE ENGINEERING ing air or brine. So likewise if a jar of liquid ammonia should be set into a snow bank, the latter would be warm relative to the boiling point of the ammonia under atmospheric pressure, and in consequence the snow would play the part of the fire in the usual case with water and supply the heat which would serve to vaporize the ammonia, the snow becoming thereby cooled by reason of its loss of heat. Having thus sketched the general outline of the process, the following additional points may be mentioned : The liquid ammonia is usually under a pressure of 125-175 pounds per square inch, corresponding to temperature from about 70 to 90 degrees. By the action of the ammonia pump, which draws the vapor from the refrigerating coils, the pressure in the latter is maintained at from 30 to 60 pounds, corresponding to temperatures from o to 30 degrees F. The ammonia condensing coils are in some cases immersed in water, which is renewed in order to maintain the temperature as low as convenient, while in other cases the condensation is brought about by allowing a spray of water to fall over them from top to bottom. Except for details of the apparatus employed, the principles outhned above, as well as the leading features of the equipment, are the same for a variety of substances which may be used as refrigerating agents. Thus, sulphur dioxide, carbon dioxide, sulphuric ether, me- thylic ether and still more recently liquid air may be and have been used in the general manner above described. The gases principally used as refrigerants in different com- pression systems are : Carbonic Anhydride CO2 Ammonia NH3 Sulphur Dioxide SOz Ethyl Oiloride QHnCl The mechanical operation is the same in the four systems with the exception of temperatures and pressures. The relative necessary cylinder volumes for equal effects are as follows : Ethyl Chloride Very great Sulphur Dioxide 13.78 Ammonia 5.60 Carbonic Anhydride 0.97 This shows that the cylinder volume of the carbonic anhy- dride machine needs be but about one-sixth of that of the am- REFRIGERATION 553 monia machine and about one-fourteenth that of the sulphur dioxide machine. The carbonic anyhydride machine therefore has the advantage of a smaller cylinder and most compact con- struction, but has the disadvantage of very high pressures, while the opposite is the case with ethyl chloride. Absolute Pressure Exerted by Various Refrigerants Temperatures AT Different Temp. Deg. Anhy. Ethyl Carbon Sulphur Fahr. Ammonia. Chloride. Dioxide. Dioxide. 30.8 4.1 314.5 10.3 5 34.2 4.7 335.0 11.9 10 38.3 5.4 362.8 13.4 15 42.9 6.1 391.7 15.3 20 48.0 6.9 422.5 17.1 25 53.4 7.8 455.7 19.4 30 59.4 8.7 490.0 21.6 35 65.9 9.7 526.2 24.3 40 73.0 10.8 565.2 27.0 45 80.7 12.0 607.2 30.1 50 89.0 13.3 650.0 33.4 55 97.9 14.8 696.7 37.0 60 107.6 16.3 745.0 41.0 65 118.1 18.0 795.5 45.2 70 129.2 19.9 8i9.3 49.7 75 141.2 22.0 9D6.5 54.6 80 154.1 24.2 937.0 59.9 Sec. 71. PRINCIPAL FEATURES OF AMMONIA REFRIGER- ATING APPARATUS In Fig.' 387 is shown diagrammatically the arrangement of apparatus in a system of ammonia refrigeration. In all such systems involving the compression of a gas it is most important that the compressed gas be as completely discharged as possible at the end of the stroke, else it will re-expand on the return stroke, thus preventing the inflow of a full charge of fresh gas and thus reducing the effective capacity of the machine. In the system illustrated in these figures this is accomplished by injecting into the compressor at each stroke a certain quantity of oil which fills all clearances and thus insures the delivery of practically the entire charge of gas. This oil likewise acts to lubricate the mov- ing parts and to seal the stuffing box, piston and valves, and thus to prevent leakage. It also acts to some extent to absorb the heat resulting from compression, thus to reduce the expenditure of work required. In Fig. 390 is shown the double acting com- SS4 PRACTICAL MARINE ENGINEERING prcssion cylinder used in this system. The two passages marked "suction" and "discharge," respectively, connect the compressor with the pipe system. On the up stroke gas flows through the lower section valve into the space behind the moving piston, while the gas above the piston, after being compressed to the condenser pressure, is dis- charged through the upper valves (in the loose head) into the discharge passage. .^^v.SS ^ ^Sn^'v^^^\S^^^\s^'.'s^\^^\^^\\\\\\S\^^\\\^^^S\S^V.'s\SV^^\\W . Fig. 387. Diagram Showing Arrangement of Ammonia Refrigerating Machinery On the down stroke gas flows into the cylinder through the upper suction valve, and the gas below the piston is compressed and passes through the lower discharge valves into the discharge passage. The piston in its downward course closes successively the openings of these two discharge valves. When the lower is closed, however, the upper one communicates with the chamber in the piston, and the gas and oil still remaining below the piston are discharged through its valves into the chamber and out by the upper discharge valve. The oil is injected directly into the compressor after the compression of the full cylinder of gas has commenced, and thus does not reduce the capacity of the machine. The compressed gas and oil thus delivered from the com- pressor cylinder pass on to the oil cooler. The cooled oil drops into the bottom of the tank, while the gas continues into the con- denser, where it is liquefied and collected in a second tank. Two forms of condenser may be employed. In one form the con- REFRIGERATION j i) k CoU of 134" Pipe ^ Coil of IJi" Pipe C j) i r a ►0 ( ) CO 1 I PIpo Room - 1 (j ]) s 2 t e. 1 K'Pll- ^ Coil ot IH'Plp" ( i If "^^ ^ ■ ■ ' ■ II 556 PRACTICAL MARINE ENGINEERING REFRIGERATION 557 densing coils are immersed in a tank of cold water, which, by -suitable pumping arrangements, is continuously withdrawn and renewed in order to maintain as low a temperature as convenient. In the other form of condenser water is sprayed over the coils, falling from top to bottom, while the gas enters preferably at the Fig. 390. Ammonia Compressor Cylinder Uarinf'Enijineeriytit Fig. 391. Ammonia Compressor Cylinder bottom and passes upward in a direction opposite to that of the water. The latter type of condenser is the more efficient of the two for the same amount of water, while it has the further ad- vantage that ammonia leaks are readily detected by the odor, while with the submerged condenser the escaping gas is absorbed by the water, and its escape is not so readily noted. From the collecting- tank the liquid ammonia passes through the expansion cock into the expansion coils. The latter may be located directly within the space to be refrigerated, Fig. 388, or S58 PRACTICAL MARINE ENGINEERING they may be surrounded by a brine, which in turn is pumped through the refrigerating coils proper, Fig. 389. The former method is the more efficient inasmuch as a loss always attends a multiplication of such processes. The chief objection to this method lies in the somewhat greater liability of ammonia leaks and the resulting presence of ammonia in places where it may be objectionable. The expansion cock must be capable of nice ad- justment in order to make possible the proper control of the flow of liquid ammonia into the coils. In the system here shown this is accomplished by making the orifice on the delivery side of the cock in the shape of a very narrow wedge, the point of which is the first to open. Movement is then imparted to the plug by a worm and wheels, thus insuring adjustment of the most delicate character. The point of chief importance in connection with the expan- sion coils, and, in fact, in connection with the entire piping sys- tem, is that of the joints. Screwed connections are far more liable to leak under ammonia than under steam, and the utmost care is needed in regard to this feature. For the best results, special joints are required. In a representative joint of this character the thread into which the pipe screws does not reach entirely to the outside of the fitting, but instead a smooth annular space is provided around the pipe beyond the termination of the thread. This recess is filled with solder, the pipe and fitting being well tinned, and thus a screwed and soldered joint is made which is found tight against ammonia under all pressures employed. The cooling efficiency of the refrigerating coils is also much increased by clamping to the pipes thin disks of cast iron. These disks are made in halves, and are placed at intervals of 6 to 10 inches on the pipes. They effect an increase in the surface in contact with the air, and thus an increase in the heat, which can be withdrawn from the air and conducted to the cooling substance within the pipe. In other systems of ammonia refrigerating machinery the same general principles are involved, but with some differences in the apparatus employed. The compressor, as shown in Fig. 391, is single acting, the gas being compressed on the upper side of the piston only. No oil is used to fill the clearance spaces, and the clearance is reduced to a negligible quantity by working the piston almost metal and metal against the head. This is made REFRIGERATION S5g practicable by making the pump head movable so that it may operate as a large valve the full size of the bore of the cylinder, and through the seat of which, if need be, the piston might pass without injury. Under normal conditions this entire head does not work as a valve, the discharge being through a small steel valve in the center of the head, as shown in the figure. The com- pressor cylinder is surrounded with the water jacket, wh,ich absorbs a part of the heat generated by the compression of the gas. For controlling the expansion in this system a special form of valve is used which provides for close adjustment of the open- ing and is fitted with an index and pointer so that the amount of opening may be ascertained and such adjustments made as have been by trial found to best suit each case. Sec. 72. CARBONIC ANHYDRIDE REFRIGERATING MACHINERY In these refrigerating machines, liquid carbonic anhydride serves-as the refrigerating medium. It evaporates at the low tem- perature of 124 degrees below zero F. under atmospheric pressure and during evaporation absorbs from its surroundings a quantity of heat corresponding to its latent heat of evaporation. In other words, while water boils at 212 degrees .F. under atmospheric pressure, and about 250 degrees at fifteen pounds pressure ; liquid carbonic anhydride boils at 124 degrees below zero F. under atmospheric pressure and at 30 degrees F. under a pressure of 34 atmospheres. The boiling point of water being far above the atmospheric temperature, heat must be applied to bring it to the boiling tem- perature.. The boiling point of liquid carbonic anhydride being very, much lower than the temperature of the atmosphere, it absorbs from its surroundings the necessary heat to cause it to boil or evaporate. Refrigeration is produced by the ebullition of the carbonic anhydride which is circulated through the cooling coils and re- turned to the refrigerating machine. The cycle of operation is the compression, liquefaction and evaporation of the carbonic anhydride. The refrigerating plant comprises three parts : 1. A compressor in which the gas is compressed. 2. A condenser in which the compressed warm gas imparts its heat to cold water" afid liquefies. 56o PRACTICAL MARINE ENGINEERING 3. Expansion coils in which the liquid carbonic anhydride re-expands into its original gaseous state, thereby absorbing heat and performing the refrigerating work. In order to make the operation continuous the three parts are connected; the charge of carbonic anhydride originally put into the machine being used over and over again, going pro- gressively through the process of compression, condensation and evaporation. Thus only a small quantity of gas is required to replace any losses. Carbonic anhydride is supplied in steel cylinders and can be procured in any part of the world. The cost of this gas is but a few cents per pound and the quantity required for a complete charge is very small. The compressor draws the gas from the expansion coils, com- pressing it to the liquefying pressure (which pressure depends upon the temperature of the cooling water in the condenser) . The compressed gas is discharged into the condenser where it imparts its heat to the water in the condenser and becomes a liquid. This liquid is then returned to the expansion or cooling coils, expanding through them and thereby absorbing heat. The surface of the cooling coils is so proportioned that all of the liquid evaporates as it passes through them. From there the gas again returns to the compressor to resume the cycle of oper- ation. The pressure of the gas in the coils is controlled by means of a valve. The compressor cylinders are made of solid open hearth steel forgings, the bore and valve ports being machined into these forgings. The working pressure in the cylinder varies from about 50 to 70 atmospheres (750 to 1,050 pounds). Owing to the very small diameter of the cylinder there is no difficulty in secur- ing a large factor of safety. The cylinder must be so designed that the clearance is brought to a minimum. The construction of the stufifing box must receive the most careful consideration on account of the high pressure. A con- tinuous working oil pump lubricates the stuffing box, valves and piston and seals the stuffing box, thereby preventing the loss of gas. Sec. 73. ETHYL CHLORIDE MACHINES Ethyl chloride is a very stable chemical, having a critical tem- perature of 365 degrees F., which, never being reached in the ma- REFRIGERATION 561 chines, there is no danger of the chemical breaking up and form- ing permanent gases. It has no reaction with air or water, hence no chemical change takes place should either gain entrance into the interior of the machine. It is chemically neutral, having no effect on metals, which allows a wide choice in the materials used in construction of the machines and the piping. It is neither poisonous nor of obnoxious odor and is but very slightly explosive. At a temperature of 70 degrees F. sulphur dioxide has a pres- sure of 49.7 pounds absolute, anhydrous ammonia 129.2 pounds absolute, carbon dioxide 849.3 pounds absolute and ethyl chloride only 19.9 pounds absolute, which is a low pressure and safe to Fig. 392. Rotary Compressor handle and it is obvious that the wear upon the machine will be much less than on those using a high pressure refrigerant. With this extremely low pressure the loss of refrigerant through the stuffing box of the compressor and valve stems will be small while with the high pressure refrigerant it is very great and re- quires long and heavy stuffing boxes. On account of its low specific heat and the resultant large volumes which must be used to produce the desired refrigerat- ing effect, reciprocating machines become unpractical, at least for use on board ship, and it is necessary to resort to compressors of the rotary type, one of which is shown in Fig. 392, an outlme of the entire machine being shown in Fig. 393. These rotary compressors are particularly adapted for use where large volumes at low pressures are to be handled. There are no valves, springs or other small pieces that can drop into the working parts. 56j PRACTICAL MARINE ENGINEERING The compressor consists of a cylinder with suction and dis- charge ports cast in the walls. A cast iron rotor is mounted on a chrome nickel steel shaft which is located eccentrically in the cyHnder, so that a line of contact is formed between the top of the cylinder and the revolving rotor. Four slots are milled radially in the rotor in which slide cast iron blades fitted with half round -Water Discharge -Water Suction Qaa Discharge- -Water Inlet 'Water Oatlefe Ga£ Suction^ Fig. 393. Outline Marine Type Ethyl Chloride Machine Steel packing strips which form the bearing surface against the cylinder. These blades are held apart by steel spacing pins which pass diametrically through the shaft and are prevented from eroding the blades by steel backing strips. The cylinder is capped at each end with cast iron heads in which are located the roller bearings supporting the shaft. A sight feed lubricant circulating system is employed which ensures a positive, continuous flow of lubricant to the bearings at all times after the machine is started. This compressor is noiseless in operation and requires no fly wheel or by-pass valves for starting. These machines, like the ammonia and the carbonic anhy- dride machines, operate both by direct expansion and by the use of the brine system of circulation. Sec. 74. SULPHUR DIOXIDE MACHINE In Fig. 394 is shown a type of the machines using sulphur dioxide gas as a refrigerant. One requirement of such machines .REFRIGERATION 563 is that moisture shall be completely prevented from having access to the gas in order to prevent the formation of sulphuric acid with its accompanying destructive effects upon the metal enter- ing into the construction of the machine. In the machine shown in Fig. 394, and which is known as the Audiffron machine, the compressor and expander are hermet- ically enclosed in the bells of the dumbbell, the compressor being in the right-hand bell. Communication between the bells is Fig. 394. Sulphur Dioxide Refrigerating Machine through the hollow bar connecting the two bells. This bar con- tains a pipe which conducts the gas, compressed into a liquid to the left-hand bell, where it expands into a gas and returns to the compressor through the hollow bar, passing around the pipe. The compressing and expanding are done by centrifugal force, the bells being rapidly revolved by means of an electric motor. The expander bell revolves rapidly in a brine bath and picks up the brine on its surface, throwing the collected brine into a col- lector at the top of the brine tank, whence it passes by gravity down through the cooling coils and thence back to the brine tank, the circulation through the coils being due to gravity only. These machines have proved very satisfactory and are well suited for refrigerating work on small vessels, such as yachts, destroyers and torpedo boats. Sec. 75. REFRIGERATION BY THE EXPANSION OF COMRESSED AIR The principles involved in the use of air as a refrigerating agent through compression, cooling and expansion will be next examined. 564 PRACTICAL MARINE ENGINEERING If compressed air is allowed to expand against a resistance, thus doing work, while at the same time no heat is allowed to enter, the air will lose a part of its heat, the equivalent in amount of the work done. That is, the work is done at the expense of the heat in the air, which gives it up as called for and becomes cor- respondingly cooled in consequence. Thus, for example, if air at 100 pounds absolute pressure and at a temperature of 70 de- grees were allowed to expand to 15 pounds pressure, and no heat be permitted to enter, the temperature would become reduced by nbout 220 degrees, or to about 150 degrees below zero. Actually the absorption of some heat could not be avoided, and hence the actual temperature reached would be higher than thus indicated. The equipment for utilizing these properties of air is substantially as follows : (i) A cylinder in which air is drawn from the atmosphere or from the refrigerating coils and compressed. The air thus be- comes heated and its temperature is raised. It is, therefore, sent next to (2), a cooling coil working after the manner of a sur- face condenser for steam, or for ammonia vapor, as above de- scribed. The difference here is, however, that no effort is made to condense the air, but simply to cool it down to somewhere about atmospheric temperature. The air is next sent to (3), a cylinder in which the air expands and does work and becomes thereby cooled. From this cylinder the cooled air on the return stroke is forced out through the refrigerating coils, and thus the cooling action is brought about. The compression and expansion cylinders are connected to the same crank shaft in such manner that the work done by the expanding air will aid in effecting the compression of the incoming fresh charge. The difference in the work of compression and that furnished by expansion plus the friction of the machine must be made up by the motor oper- ating the machine. Sec. 76. PRINCIPAL FEATURES OF COMPRESSED AIR REFRIGERATING APPARATUS The leading features of the Allen dense air refrigerating machine as illustrating this type of apparatus are as follows : Experiment has shown the advantage of using relatively high pressures throughout the apparatus. The air in the refriger- ating coils is, therefore, kept at about 60 pounds gage pressure. From these coils the compressor cylinder draws its air, REFRIGERATION 56s which is then compressed to 200 pounds, or oVer, and this, after cooling, is again expanded back to 60 pounds and sent to the coils again, so that the same air is used over and over. To make Fig. 395. Diagrammatic Sketch of Allen Dense Air Ice Machine up for leakage a small air compressor is added, capable of de- livering air at the lower pressure into the inflow pipe leading to the main compressor. Again the cold air on its way back from the coils at a temperature usually below freezing is used in a special cooler to further cool the compressed air at high pressure before it is sent to the expansion cylinder. 566 PRACTICAL MARINE ENGINEERING Referring to Fig. 395, the following are features of- the machines with their uses : (A) The steam cylinder which furnishes the power re- quired. (B) The air compressor cylinder. This is usually sur- rounded by a' water jacket to assist in cooling the air as it is compressed. — ■ "~^ (C) The cooling coil surrounded by water. Through this the air passes and thus becomes cooled nearly to the temperature of the external air. (C, C) The return air cooler for still further, cooling the compressed air by allowing it to give a part of its heat to the air returned from the refrigerating coils to the compressor inflow, as noted above. (D) The expansion cylinder. The cooled air is admitted to about one-third stroke and is then cut oflf. The charge is thus expanded to about' three times its original volume, and is thus brought to about the same pressure as it had when entering the compressor cylinder, but at a much lower temperature. The air is then discharged .through a pipe which leads it to the refrigerat- ing coils or to the point where its capacity for absorbing heat is to be utilized. (E) A trap through which the air passes after leaving the expansion cylinder and in which are gathered the lubricating oil carried by the air from the compressor cylinder as well as the frost which results from the freezing of the moisture in the air. This leaves the air pure and dry and in the best possible condi- tion for carrying out the refrigeration in the coils beyond. (F) A pump for supplying water for the water jacket around ; the compressor cylinder, for the bath around the cooling coils (C), and for the trap (I). , (G) A small air compressor for supplying the loss due to leakage. (H) A trap for taking the moisture from this supplementary air supply so as to have it enter the machine as dry as possible. Sec. 77. OPERATION AND CARE OF REFRIGERATING MACHINERY Before starting refrigerating machinery, whether newly in- stalled or after any considerable period of disuse, all piping and joints should be tested for leaks. This may be done, no matter REFRIGERATION 567 what the system be, using the compression pump to compress air into the piping up to whatever pressure may be considered suitable. The seriousness of the leakage may then be estimated by the rapidity with which the pressure is lost after allowing the pump to stop. The larger leaks may be determined by the noise made by the escaping air. For the smaller ones the joints are sometimes covered with soap suds so that the escaping air may show itself by blowing a cluster of bubbles. After the points which may show leaks have received proper attention, the system should, for a considerable time, hold the pressure without sensible loss. In this connection, however, it must be remem- bered that the air as it leaves the compressor will be heated by the work of compression, and as it loses this excess heat in the coils there will be a considerable loss of pressure. After equality of temperature with the outside air has been reached, however, the further loss of pressure should not be appreciable. With an air refrigerating plant the presence of leaks is of course of less importance than with ammounia or carbon dioxide. In the former a leak may result in a slight decrease in the capacity of the machine, while in the latter the capacity of the machine is not only aflfected, but the gases will be lost as well. With the air machine no further preliminaries are needed beyond the ex- amination neccessary to insure the proper mechanical condition of the compressor and steam cylinders. With the ammonia and CO2 machines, however, it is necessary next to exhaust the air from the entire system by working the pumps and discharging through valves provided for this purpose. When the gages show the highest vacuum which can be maintained, the valves are closed and the system is ready for charging. The ammonia or CO2 is usually provided in steel flasks con- taining a known weight of the liquid. To introduce the charge the flask is connected to the charging valve according to the direc- tions which usually accompany them. In the meantime the machine is run at slow speed with the suction and discharge valves open and the condenser ready for operation. The expan- sion valve is then closed and the valve of the flask opened, thus allowing the gas to be exhausted into the system. In this man- ner one flask after another is exhausted into the system until the liquid shows to a suitable height in the glass gage of the receiver. The charging valve is then closed and the expansion valve opened 568 PRACTICAL MARINE ENGINEERING and regulated until with the machine running at normal speed the pressure gages steady down to the pressures ususually main- tained, and a frosting of all parts of the expansion coils in con- tact with the air shows that the refrigerating action is in vigorous operation. The weight of gas in the flask being known, its com- plete discharge may be determined by weighing before and after r.Dnnection with the machine. For the routine care of refrigerating machinery the same principles apply as for steam engines and pumping machinery in general, and they need not be here repeated in detail. A few special points may, however, be mentioned. In ammonia machinery, through leaky stuffing boxes and in other ways, air may occasionally find its way into the system. Its presence will decrease the efficiency of the machine, and it must, therefore, be removed as soon as possible. The most no- ticeable symptoms of siich trouble will probably be a rise in the condenser pressure. Purging valves are usually fitted on the condenser or elsewhere through which such air may be drawn ofif. To this end it is desirable to stop the machine for a time to allow the air to collect. It may be then drawn ofif through a rubber hose or other suitable means and discharged under water. The rise of bubbles will show that air is escaping, while on the other hand the presence of crackling or snapping sounds will indicate that the air is all exhausted and that ammonia is es- caping and being absorbed by the water. Reference has been made to the importance of joints and piping. This part of the system must receive especial care both in the original installation and in the routine attention. For am- monia in particular, as already noted, special joints are usually required, and both ammonia and air will find smaller leaks than steam. It must also be remembered that the chemical action be- tween ammonia and copper renders impossible the use of copper, brass or bronze through all parts of the installation with which the ammonia may come in contact. With compressed air refrigerating machinery it sometimes happens that the ports or passages through which the air first passes in its expansion become clogged with a deposit of snow or ice, due to the freezing out of the moisture contained in the air. In the Allen dense air machinery, where the same air is used over and over again, additional moisture can only come REFRIGERATION 569 from the small make up air supply, and most of this is removed by the trap provided for this purpose. In operation this trap should be watched in order to make sure that its action is effi- cient and that there is no danger of the passage of water over into the expansion system. In routine operation it is usually desir- able to clean the machine by heating it up and blowing out all the oil and ice deposits. To this end the valves in the main pipes leading the air to and from the coils are closed, thus shutting off the machine from the remainder of the system. A by-pass is then opened, connecting the main expansion pipe beyond the oil and snow trap with the main return from the coils. Connections are then opened in the so-called hot air pipe leading from the compressor cylinder to the expander cylinder, and the expander inlet valve is partly closed. Live steam is then let slowly into the jacket of the oil trap in order to thaw out all ice and hard- ened oil, and the machine is run moderately for a time, during which the blow off valves of the trap and expander cylinder are frequently opened until everything appears clean. Then the machine is readjusted to its normal condition and run as before. If it should be suspected that any considerable quantities of oil and water have gotten into the pipe system and are clogging the surfaces, the pipes may be cleaned by running hot air through them and drawing ofif the oil and water at the bottom of the manifolds of the refrigerating coils. QUESTIONS Refrigeration Explain the general principles of refrigeration S48 How are these principles carried out by the use of freezing mixtures*' 549 How are they carried out by the use of ammonia or similar sub- stances ? 550 What are the gases principally used for refrigerating purposes? 552 What are their relative volumes ? S53 Give the principal features of ammonia refrigerating apparatus anci explain its operation 553 Give general features of carbonic anhydride refrigerating machinery? 559 Give general features of ethyl chloride machines .^ S^o Give general features of sulphur dioxide machines 5^2 How are the principles of refrigeration carried out by the use of a compressed gas ? 563 Give the principal features of compressed air refrigerating machinci";' and explain its operation • S64 What special points must be attended to in the operation and care (A refrigerating machinery ? 366 CHAPTER X Electricity on Shipboard Sec. 78. INTRODUCTORY In the present chapter are discussed briefly and from the practical standpoint the application of electricity on board ship for lighting, and as a source of auxiliary power. The limitations of space prevent, of course, the development of the subject in detail, and therefore shall be given by way of introduction a few t ■■^- 'D B>. / V. ^''■■-- — -.<1. "Marine Bngineering Fig. 396. Simple Bar Magnet, Showing Lines of Force statements and definitions which must be taken for granted by those not already famiHar with the elements of electrical theory (i) It is first supposed that the reader is familiar with a common magnet and its more well known properties. (2) The name magnetic field is applied to the space around a magnet and through which the magnetic forces act. Let PQ, Fig. 396, be a magnet, with one pole at E and one at A, and sup- pose the latter to correspond to the north end of a compass needle. ELECTRICITY ON SHIPBOARD 571 It must be understood that the magnetic forces act really in closed paths, as indicated by the dotted lines in the figure. That is, if the direction in which the north end of a long, thin magnet would be urged, beginning with A, should be mapped out it would trace out a path ABCDE. That is, a north magnet pole, if free to move by itself, would tend to move along the path from A around to E, in the direction of the arrow, and would so move unless prevented by some external force. Hence the magnetic force acts all along this line from one end to the other, thus marking out what is called a line of force. Now, to complete the circuit it is considered that the same force acts on through from Fig. 397. MaritM EnginMrinff • Horseshoe or Bent Magnet, Showing Lines of Force E tb A inside the iron or steel, although it is not possible to measure the actual force there in the ordinary way. The entire space around and within a magnet is thus occupied with these lines of force, and in its widest sense therefore the magnetic field, or field of force of a magnet, would include all space. As the immediate vicinity of the poles is departed from, however, the force becomes weaker and weaker, and finally at no great distance becomes very small- Practically, then, the field of force includes only that part of space within which the magnetic forces are measurably large in amount. By changing the form of the magnet, as in Fig. 397, the sensible part of the field becomes limited to the space between the two poles, as shown by the dotted lines, and it also becomes quite uniform in strength. (3) All the phenomena connected. . with what are called 572 PRACTICAL MARINE ENGINEERING electric currents in wires or other conductors take place as though a current of something was flowing around the closed circuit. Scientists do not assume that there is in reality anything actually flowing within the wire. In fact, the nature of electricity and of the electric current are not satisfactorily known, and so in the absence of more definite information the term electric current is used simply as an aid in the discussion. (4) The fundamental principle which seems to connect magnetism with electric currents is found in the following fact: A wire or conductor in which an electric current is flowing is surrounded by a field of magnetic force, as shown in Fig. 398. If the current is flowing away from the observer, or along the direction in which he looks, then the direction of the force is such that a free north magnetic pole would tend to go round and round the wire in circular paths in the direction shown by the dotted lines. -. ^ B .^ Marine Engineering Fig. 398. Lines of Force About a Wire Carrying an Electric Current (5) If the wire in which the current is flowing is bent into the form of a circle, as in Fig. 399, then these separate effects combine and there exists a field of force just the same as though the wire circuit were a very short, flat magnet, the two poles being very close together. If there are many turns of wire on a spool then all these effects are added, and there is a magnetic field of still greater force and distributed almost exactly as though the core of the spool were a bar magnet. If, in fact, a piece of soft iron for the core of the spool is used, then the iron itself becomes magnetized, and adds its force to that of the current, thus producing a still greater field of force. A rather more exact way of stating this is to say that the current which flows tends to produce a magnetic field, but that there is a certain resistance to the setting up of this force, and that this resistance depends on the substance through which it is to be set up. If there is no metal core, then the magnetic force must pass through ELECTRICITY ON SHIPBOARD 573 air around the entire circuit. It so happens that the resistance to the setting up of magnetic forcfes is very much less in iron than in air, so that if an iron core is put in, the total resistance in the cir- cuit of the magnetic forces is very much reduced, and the same electric current can then set up a much stronger field than through air all the way. (6) The fundamental principle upon which the operation of the electric generator depends can now be stated. If a wire is so moved as to cut across the lines of magnetic force, then there will be generated a force tending to set up a current of electricity in the wire. This is known as the electro- motive force, and is usually abbreviated into E.M.F. If, then, the ends of the wire are connected so as to form a closed circuit. Marina Etigbuennj Fig. 399. Lines of Force About a Coil Carrying an Electric Current and the movement is such that the amount of magnetic force which passes through the circuit of the wire undergoes a change, either increase or decrease, then a current of electricity will be set up in the wire, and will continue as long as such change is in progress. Thus, in Fig. 400, on the right, if the loop of wiru should be moved from a strong to a weak field, as shown, then the amount of force passing through the circuit would decrease and a current would be set up, as shown, and lasting as long as the change was in progress. If, further, the coil should move 01. fropi the weak to a strong field, there being no change in the di recfion of the lines of force, then a current would be developed in the opposite direction to that developed by the moveme:.-. from strong to weak. If, however, at the same time the directioi 574 PRACTICAL MARINE ENGINEERING of the lines of force should change, then the direction of the cur- rent would remain unchanged, as shown in the figure. If also, as shown on the left, the loop were to be turned sideways, so that a smaller amount of force could pass through, then also a cur- rerit-would be set up and would last as long as the change was in progress. In all such cases the direction in which the current will flow may be determined by the following rule: If the loop is looked at along the lines of force in the direction in which a free north magnetic pole would tend to move, and the change in the amount of force passing through the loop is a decrease, then the current will flow in the right-hand direction, or with the hands of a watch. If the change of force is an increase, the current will of course flow in the opposite direction. The generation of electricity in all forms of electric gener- JUarine £ngintertng Fig. 400. Development of Electro Motive Force by Moving a Coil of Wire in a Magnetic Field ators, and its use in all forms of motors, depend fundamentally upon the few principles explained above. Electro Motive Force. — :The force in answer to which the electric current is set up and maintained is known as -the electro motive force. Relative to the electric current this force plays a part quite similar to that played by steam pressure, or a difference, of steam pressures, in causing a flow of steam from one place- to another.. In fact, the term electric pressure, or diflference of ejectric pressures, is now quite commonly used by engineers in- stead of electro motive force. The phrase electro motive force is commonly abbreviated to E.M.F. The unit of E.M.F. is known as the volt. ^ Resistance. — The electric current, in flowing around the cir- cuit, meets with a certain resistance, and it is in fact this resist- ELECTRICITY ON SHIPBOARD S7S aiice which the E.M.F. must constantly overcome. This resist- ance to the flow of the electric current may be likened to the resistance of a pipe to the flow of water within it. Electric resistance depends on the material of the circuit, on its length, and on its cross sectional area. The greater the length the greater the resistance, and the greater the cross sec- tional area the less the resistance, both in direct proportion. Sub- stances are usually divided into conductors and non-conductors. There is no substance so good a conductor, however, but that it opposes some resistance to the passage of a current, and there is no non-conductor so perfect that it will not allow the passage of minute currents, especially under very high pressures. The unit of resistance is called the ohm, and is defined as the resistance which is opposed to the passage of an electric current by a tube of pure mercury of a certain size and length.* The result, then, of the action of electro motive force against electric re- sistance is to produce an electric current, and the unit of current thus produced is called the ampere. This is defined as the current which will be produced by an E.M.F. of one volt acting through a resistance of one ohm. It signifies a certain rate of flow, just as if a special name would be given to a flow of say 20 gallons of water per minute through a pipe. Electric power is represented by the product of E.M.F. and rate of flow, just as in the case of the flow of water in a pipe it is represented by the product of the pressure per square foot and the rate of flow expressed in cubic feet. The unit of electric power is called the watt, and is the power required to maintain for a minute a flow of one ampere under a pressure of one volt. Similarly a current of 8 amperes under a pressure of 50 volts will require 400 watts. To connect electric with mechanical power it is found that in round numbers 746 watts equal one horsepower. This must not be taken to mean that one indicated horsepower in a steam engine will give 746 watts in a generator. There are losses between the two due to the fact that the electric generator cannot transform all the mechanical energy it receives into electric energy, and thus wastes a certain amount, which appears chiefly as heat. The number 746 gives the ratio which would exist if there were no losses of any description whatever. * Cross section of one millimeter square, or about 1/25 inch, and length 1063 millimeters, or about 42 inches. 576 PRACTICAL MARINE ENGINEERING The ordinary commercial unit of electric power is the kilo- watt, or i,ooo watts. It is thus equivalent to about i 1/3 horse- power of mechanical work. Ohms Law. — The fundamental law which gives the relation between the current, the E.M.F. and the resistance will now be stated. It is simply that the current in amperes equals the E.M.F. in volts divided by the resistance in ohms, or in symbols C = E -^ R or E=CR. Likewise, if the electric power is denoted by P p = CE - C'R. This measures the power which is required to maintain the cur- rent in the circuit. If no other effects are produced it is wholly expended in heating the circuit, and the heat thus developed will be measured by the power multiplied by the time or in symbols H = C'Rt. Now, without further discussion of the principles of elec- trical engineering, a brief description of the apparatus more com- monly met with on shipboard will be proceeded with. Sec. 79. THE DYNAMO The dynamo may be considered simply as an apparatus de- signed for the development of electric current, or for the trans- formation of mechanical into electrical energy. It consists essen- tially of two electro-magnets, which may be called A and B. A is stationary, and between its poles B rotates, carrying its coils of wire through the field produced by A. The rotating magnet and its coils is known as the armature, and the fixed magnet and coils as the poles and Held coils. In Fig. 401 is shown one of the rotating coils A of the armature, while its successive positions are shown by i, 2, 3, 4. The field of force due to the field coils and poles is also indicated by the arrows. In accordance with the principles above stated an E.M.F. is thus generated in the armature coils. It may be likewise seen that the E.M.F. will act alternately in opposite directions in these coils, changing as their plane is about midway between the poles, or in the position shown at A. All these elementary forces thus generated in the separate coils of an actual armature are gathered together and produce the full pressure at the terminals. Electric generators are of two chief varieties, direct and alternating current. In the latter the E.M.F. generated is allowed to produce the current in the circuit back and forth, alternating ELECTRICITY ON SHIPBOARD 577 in direction as the coils pass between the poles. The current may thus be likened to a series of surges to and fro, but without continuous flow in either direction. In the former, or direct current machine, these impulses are so taken up by the commu- tator that they are all adjusted or turned in one direction, and there is, therefore, a continuous flow rather than a series of surges back and forth. It is found by experience that either form may be used for the development of light by either the incandescent oi arc sys- tem, while also either, by the use of appropriate motors, may be used for the development of mechanical power. Marine Enginttring Fig. 401. Action of Single Coil of an Electric Generator For use on board ship the direct current form is usually em- ployed. A discussion of the relative advantages and disadvant- ages of the two forms is beyond the present limits, but it may be said in a word that for lighting the limited space of a single ship the alternating current system does not possess the advantages which it may in the case of distribution over a wider area, and for the operation of motors its use would entail some advantages and complexity from which the direct current system is free. Restricting the text, therefore, to direct current machinery, the simplest is found in the so-called series dynamo. In this 578 PRACTICAL MARINE ENGINEERING type the circuit as a whole leads continuously around both the armature and the field coils, thence into the external circuit at one terminal, and around back to the machine at the other ter- minal. If instead of this arrangement the wires are led as in Fig. 402, the current leaving the armature is divided, and one part flows around the field coils while the other goes through the external circuit. This constitutes the so-called shunt wound dy- namo. In such case the field coils consist of many turns of fine wire, while in a series machine they consist of a few turns of larger wire. A combination of the series and shunt windings constitutes the so-called compound wound machine. For the purpose of Harine Engineering Fig. 402. Shunt Wound Electric Generator, Outline Diagram delivering a constant potential or electric pressure the shunt wound machine is usually employed, and it is this type which is commonly met with on shipboard. A brief description of a modern electric generator applicable to marine purposes will now be given. According to size the typical marine generator is made with four or six poles, distributed uniformly around the circumfer- ence of the armature, which is of the ring type, as shown in Fig. 403. The machine is shunt wound according to the diagram of Fig. 402. The commutator, as shown in Fig. 404, consists of a series of bars of special bronze or copper formed into a cylinder ELECTRICITY ON SHIPBOARD 579 or drum, and with mica or other insulating material between them. Each bar 6f the commutator is joined to the winding on the armature, and the connections are such that the E.M.F. gen- Fig. 403. Ring Armature aforiM Enffinteriny Fig. 404. Commutator erated in the entire series of coils is so directed as always to urge the current out through one of the brushes and in through the other. The brushes are usually in the form of a block of carbon, s8o PRACTICAL MARINE ENGINEERING and are carried in metal holders, as shown in Fig. 405, and pro- vided with means for holding them by adjustable spring pressure up to their contact with the commutator, while at the same time the frame which carries them may be rotated as a whole about the axis of the machine, thus bringing them to bear on diflferent parts of the commutator for purposes of adjustment with vary- ing load. With a four pole machine the brushes are usually placed one nearly on top and one at about right angles. This makes them more accessible than if placed at opposite sides of the commutator, as is necessary in two pole machines. CLAMPING SCREW BRUSH PRESSURE SPRING ADJUSTING SCREW In the selection of such a generator special attention should be paid to points of mechanical excellence, especially in connec- tion with the bearings and balancing of the armature, the con- struction of the brush carriers, the binding posts, and other like points entering into the construction of the generator as a ma- chine. 'The capacity of the generator should be such that it will be able at its normal rating to supply the expected demand for light and power. Generators are expected to be able to stand a certain amount of over load, and if of proper design and in a ELECTRICITY ON SHIPBOARD 581 cool and well ventilated room will run safely far above their rated pow£r. It must be remembered, however, that the dynamo room of a ship is rarely cool or well ventilated, and that the over- heating of armature and field coils is the chief limitation on the capacity of an electric generator. Hence in the unfavorable situ- ation in which such machines are usually installed, they should not be expected to carry any considerable over load. The typical marine generating set consists of a generator as above, together with engine set on one base and coupled direct together. The usual number of revolutions at which such sets are operated ranges from perhaps 300 to 500, according to size. The engine may be either a simple or compound, or even a triple- expansion, though the latter are but rarely employed in marine practice, while turbine driven generators are rapidly displacing those driven by engines of the reciprocating type. In many cases heavy oil engines of the Diesel type are used. In the design and construction of such engines, either for steam or oil, the chief points to be held in view are solidity and strength, especially an the running parts, but without undue excess of weight, generous bearing surfaces and provisions for continuous and sure supply of lubricant. With such small high speed steam engines the presence of water in the cylinder is likely to produce serious damage, and especial care should be taken in regard to the relief and drainage valves, both hand and automatic systems being preferably fitted. The governor provided with engines of all types is of the shaft automatic type, and should control the revolutions within about 2 percent for change from full load to no load, or vice versa. In the care and operation of such engines no points are in- volved which have not already been discussed in connection with other engines, and it will not, therefore, be necessary to further consider these topics. Motors Electric motors have come into use on shipboard for a variety of purposes, connected with the application of auxiliary power, but chiefly for running hoists and ventilating fans. It will be sufficient for present purposes to note that a motor is essentially the same as a generator, and only differs in the manner of its use. With the latter mechanical energy is supplied and electric 582 PRACTICAL MARINE ENGINEERING energy withdrawn. With the former electric energy is supplied and rriechanical energy withdrawn. The motor contains the same parts as a generator, and similarly related, and differs only in being thus operated in the inverse manner to the generator. Sec. 80. WIRING AND THE DISTRIBUTION OF LIGHT AND POWER The conductors used for the ^distribution of electricity may be either of single copper wire, varying in size according to the current to be carried, or of several small wires made up into a cable and of corresponding capacity. The insulation must be of extra good quality in order to stand the severe conditions to which it may be subjected on shipboard. The materials available for the insulation of wire are rubber, either gum or vulcanized, gutta percha, and various special com- pounds, together with braided or wrapped coverings of cotton, linen or silk. Gutta percha is rarely used except for submarine cables and for other special purposes. It must be understood that none of these substances singly and no combination of them is a perfect non-conductor There is always a small leakage through the insulation and air, and the purpose of the covering is to re- duce this leakage to a safely negligible amount. For marine work it is especially necessary to protect the insulation against the eifects of dampness and corrosion, as under these influences deterioration may set in, causing a breaking down of the resist- ance to the passage of the current and an increase in the leakage. The usual form of marine lighting wire is insulated with vul- canized rubber or other special compound, covered with braided cotton, the whole covered with a coating of waterproof and pre- servative material. For switchboards and mountings for fixtures and all attachments, slate, marble and porcelain are used. The conductors are run either in iron pipe, in double wooden mouldings or the wire is armored with lead and is run in the open. The latter system is to be preferred, as the conductors are thereby given the protection of the armor and at the same time open for examination, while no nesting place is provided for vermin. The conduit and armored systems are, however, much more expensive than the moulding system, and the latter is, therefore, more commonly employed, except in warship work and where high first cost is not an objection. The chief point in any system is to give to the wires and to ELECTRICITY ON SHIPBOARD 583 the various junctions and connections the greatest possible pro- tection from mechanical injury and from the action of dampness and water, and all parts of the distributing system exposed to the weather or to the sea should be made as nearly watertight as the limitations of first cost will permit. The method to be adopted for the distribution of electricity depends somewhat on the purpose for which it is to be used. The most common use on board ship is for operating incan- descent lamps, where as nearly as may be the same pressure Marine Engineering Fig. 406. Distribution in Parallel is required at each lamp. For this purpose the so-called dis- tribution in parallel is required. This is illustrated by the dia- gram of Fig. 406, where G is the generator and II the lamps. It is seen that each lamp has its own bridge across from the two mains, LL, and may thus be turned on or off independent of the operation of the others. In the early days of electric installations on shipboard the iron or steel hull was frequently made a part of the circuit, or, as it was sometimes stated, the return was made through the hull. To use the hull in this way it was simply necessary to connect one pole of the generator to the ship, and then connect one lead from each lamp to the hull likewise. Great difiSculty, however, was experienced in making and keeping good contact between the conductors and the ship. Corrosion was especially active at these points, and they were found to be the source of constant trouble. The presence of stray current returning through the ship was also believed to be a S84 PRACTICAL MARINE ENGINEERING factor in the corrosion and deterioration of parts of the ship's machinery, particularly the salt water piping. This system was, therefore, open to grave objections, and is now rarely met with. The modern practice is to employ a com- plete wire conductor for the external circuit, and to keep the cur- rent insulated entirely from the hull, as indicated in Fig. 406. Arc lamps are very commonly operated in series, as shown in Fig. 407, each lamp thus receiving the same current which flows around the entire circuit. On board ship the chief or only use of arc lamps is for the searchlight, and the number, therefore. Marine Enifineering Fig. 407. Distribution in Series will usually not be greater than one or two, except for warships, where a larger number may be employed. Current may also be required at various special points for the operation of motors for running ventilators, hoists, etc. The entire distribution may, therefore, comprise various cir- cuits according to the use to be made of the current and the point at which it is to be » delivered. It is furthermore found desirable to split up the incandescent lighting distribution into a series of circuits, each of which is led from a main distributing point. The entire distribution will thus comprise several main circuits, all of which, however, will be led frofn the central point. This distribution point is acually furnished by the switch- board, a slate or marble slab, on which are mounted the various instruments, switches, circuit breakers and connections needful for safely carrying out the distribution in the various ways in which it may be required. The more important items usually grouped on the switch- board are: ELECTRICITY ON SHIPBOARD 585 Switch or Cut Out. — The object of a switch or cut out is to break the circuit and thus stop the flow of current. With a single pole switch the circuit is broken at one point only. This is the usual form fitted in the sockets of electric lamps, etc. With a double pole switch the circuit is broken at two points. The switches mounted on the switchboard are usually of this type, and are to be preferred, since by this means the line is entirely cut off from connection with the generator. Fuses. — A fuse is a short piece of fusible alloy, so adapted to the proper current in the circuit that any marked increase in current strength will cause the fuse to melt, due to the increase in the heating effect. The result of this will be a break in the circuit and an interruption of the current. This is, therefore, an automatic device for preventing the rise of the current strength beyond a certain value. In the same manner as with switches, there may be single pole or double pole fuses. The latter are to be preferred, as they give a double chance of breaking the circuit, and hence a greater relative mar- gin of safety. Circuit Breakers. — It is found that the ordinary fuse does not satisfactorily provide protection against momentary varia- tions of current strength due to excessively rapid fluctuations in the generator or in the outer circuit. To prevent possible dam- age from such cause a magnetic circuit breaker is often employed. This consists of an electro magnet, through the coil of which the m.ain current flows. Any sudden increase of current will cor- respondingly increase the magnet strength, and the armature is so adjusted that in answer to this excess of pull it will move toward the magnet poles, thus breaking the circuit by the motion produce4, and interrupting the current as desired. Ammeter. — This is an instrument through which the current is passed in order to measure or indicate its strength. The in- dication is shown by a finger moving over a dial, graduated usually so as to read the current in amperes. The ammeter must be connected in series with the machine and main circuit. Voltmeter. — ^This is an instrument which measures or in- dicates the E.M.F. or difference of electrical pressure between the two points to which its wires are attached. It serves a sim- ilar purpose to that of the steam gage for the boiler. The indica- tion is shown by a finger moving over a dial graduated usually so S86 PRACTICAL MARINE ENGINEERING as to read the pressure volts. It is usually connected with one wire to each pole of the generator so as to give entire pressure in the external circuit. Rheostat.— This is simply an arrangement for varying the total resistance of the external circuit, and thus of varying the pressure available for that part beyond the instrument. It con- sists essentially of a series of coils of wire, more or less of which can be brought in and made a part of the circuit by moving a handle across a series of contact points. Rheostats are often required in connection with the use of arc lights, or with the governing and control of shunt wound gen- erators and motors. The complete installation of instruments, switches, connec- tions, etc., thus brought together on the switchboard has as its object the possibility of shifting the load from one generator to another, of connecting the various circuits singly or in different combinations with any one or any combination of generators, and at the same time providing for safety and for the proper measurement of the pressure and current. Sec. 8i. LAMPS Electricity is used on shipboard for operating incandescent or glow lamps for general lighting, for operating arc lamps for searchlights, and for operating motors, and very lately for main propelling machinery. Incandescent Lamps. The usual style of incandescent lamp consists of a filament of carbon in a glass bulb exhausted of its air and sealed air tight. The carbon filament is connected to metal terminals, through which connection with the external cir- cuit is made. The resistance of the carbon filament is very high and the passage of the current gives, therefore, a heating effect, which is sufficient to raise it to the luminous point. If the air were not exhausted from the bulb the carbon would be imme- diately burned up or converted into carbon dioxide by union with the oxygen. Since, however, the oxygen is almost entirely removed such combustion is limited to the smallest fraction of the filament when the current is first turned on, and it then re- mains nearly unchanged for a period of time ranging from 600 to 1,000 hours. Gradually the filament seems to disintegrate or lose its strength, and finally fails by snapping in two, or the bulb becomes blackened by a deposit of carbon on its inner sur- ELECTRICITY ON SHIPBOARD 587 face. The usual lamp for ship fitting is one of 16 candle power, requiring about no volts pressure, and taking about J/^ ampere of current. It thus follows that such a lamp will require about 55 watts of electrical energy. To supply this will require the equivalent of not far from 75 at the steam engine, or about i/io horsepower. It follows, then, that roughly about ten such lamps may be operated per indicated horsepower at the engine. More powerful lamps, such as 32 or 50 candle power, will require more current, and hence more energy and more horsepower in pro- portion. Arc Lamps. — The simplest form of arc lamp is shown in Fig. 408. It consists of a pair of carbon rods, separated by a . .Marine Engiiuering Fig. IflS. Arc Lamp, Simple Form slight gap as indicated. These carbons form part of an electric circuit, which is completed by the leads to the generator, as shown. To start the lamp the rods must be brought together, thus com- pleting the' circuit and permitting the current to flow. The in- stant the current is set up, however, the rods are separated a slight distance. The space between the two is then filled with hot air and carbon dioxide, and across this the current is able to pass. The resistance is so great, however, that intense heat is developed, and this brings the gases and the particles of car- 588 PRACTICAL MARINE ENGINEERING bon which are torn off and hurled across the gap all to a state of incandescence. As the lamp burns, the carbons are slowly consumed and the gap thus widens. There is always some width of gap for which the lamp operates best, and a constant adjustment must, therefore, be made. It is found further that the two carbons do not wear equally or similarly. Referring to Fig. 408, the current is supposed to flow through the lamp downward, and the upper or positive carbon will then wear in a crater like form, while the lower or negative carbon will take a more rounded or pointed form, as shown. The positive end will also wear away about twice as fast as the nega- tive end, and this will require a special form of adjustment in order to keep the gap at the same place in reference to a lense or mirror. It is also found that most of the light comes from the crater like cavity, so that the carbons must be so mounted as to allow the maximum amount of Hght to escape from this source. A lamp of this character, mounted and provided with suit- able lenses and adjustments for controlling the carbons and for manipulating and turning the beam of light in any direction as desired, constitutes a searchlight, as installed on board ship. No description of the modes of automatic adjustment for the carbons or of the optical parts of the lamp will be attempted, as the present purpose is to give only a general idea of the engi- neering side of the problem. Such lamps require a pressure of from 50 to 60 volts and a current of from 50 to 150 amperes. This corresponds to from 4 to 10 horsepower at the lamp, or say 5 to 12 at the engine. Sec. 82. OPERATION AND CARE OF ELECTRICAL MACHINERY [i] Routine Care In looking over a generator for the first time the whole machine should be carefully examined, both as to its electrical and mechanical features. All the leads of the wires should be followed through and the binding posts and contacts examined to insure that they are iji proper condition. The commutator and brushes should be carefully looked over to see if the seg- ments of the former are in good condition, and if the surface is smooth and free from scores and uneven spots. Carbon brushes are very commonly employed in modern marine practice, but whatever the form of brush the fit of its ELECTRICITY ON SHIPBOARD s8g end on the commutator should be noted, and if necessary it should be refitted so as to bed suitably on the surface. The final ad- justment of the brushes cannot be made until the machine is running, but the adjusting and holding devices should be carefully examined and the brushes placed in approximate adjustment, ac- cording to judgment. The bearings and journals and provision for oiling should then be examined, and carefully cleansed if the condition requires it. The armature should be turned by hand to make sure that there is the necessary clearance between it and the pole pieces, and that it has the proper freedom of motion. These various points having been attended to and every- thing being in a satisfactory condition, the machine may be started. A shunt machine usually excites or builds up best when the external circuit is cut out, so that it operates simply through its own armature and field coil. As the voltage rises, as indi- cated on the voltmeter or pilot lamp, the external circuit may be switched in and the generator will then settle down to its work. The proper lead or adjustment of the brushes is the next thing to be attended to. This must be ascertained by trial until a posi- tion is finally found where the sparking is reduced to the smallest limits. If in modern machines the sparking at the brushes is in any degree pronounced, it may be taken as a safe indication that the brush adjustment is not quite as it should be. The exact adjustment will, however, vary as the load changes, and hence in case the load is changing rapidly there will be more sparking than with a steady load. If excessive sparking occurs and cannot be controlled by the brush adjustment, the machine should be shut down at once, as this is an indication that it is out of electrical balance, and to continue running it would mean the possibility of burning out the armature or seriously injuring the commutator and brushes. In some cases such sparking may be due to a dirty commutator, and may be corrected by simply cleaning it. The presbure of the brushes on the commutator should also receive attention, as if too heavy undue wear will occur, while if too light they may jump and run irregularly, thus causing sparking. A very small amount of lubricant on the commutator is usually found to aid in smooth running and in saving the sur- face from scoring. In amount it should be very small ; a drop or two of hydocarbon oil or a little vaseline or a rub of one of the standard preparations sold for the purpose is sufficient. Sgo PRACTICAL MARINE ENGINEERING [2] Faults " One of the most troublesome features connected with the operation of electric machinery is the possibility of the occurence of more or less sudden failure at some point, resulting in the sudden extinction of a certain group of lights or the stoppage of a motor, or even the interruption of the entire plant in case the fault lies at the generator itself. In all such cases the immediate cause of the trouble is the interruption of the current, either in whole or in part. This may be due to a variety of causes, as follows : ( i ) The resist- ance in the circuit may be enormously increased, thus cutting down the current strength proportionately. (2) The current may be diverted in some other direction, finding an easier path, and thus avoiding the circuits in which it belongs. (3) The gen- erator itself may fail to develop the necessary E.M.F., and hence while the circuits may be in perfect condition the current will be weakened in corresponding degree. The increase of resistance in a circuit may be due to poor contact at binding posts or junctions, arising from improper mechanical construction or fitting, or from the presence of oxide due to corrosion, or from the reduction in the cross section of a conductor due to corrosion, or to any like cause which de- creases the cross section of the conductor or changes its electric conductivity. In case the conductor is broken or the separation is complete, the resistance across the air gap becomes practically infinite, and the current is completely interrupted. The current may be more or less shunted or diverted from its proper path by the accidental establishment of other paths, and the consequent re-arrangement of the current distribution. The generator may fail entirely to develop the E.M.F., if, for example, the field coil circuit should become broken and the cores thus lose their magnetism. In locating a fault the circuit in which it occurs must first be determined, and then the various points at which it might exist must be examined, one after another. The circuit in which the fault is located can usually be inferred from the extent of the disturbance. If only a single light goes out, it is evidently limited to the circuit belonging to that light alone, and may be looked for in the lamp itself or in the fuse block, if it has one. If all the lights on a single circuit go out, but no others, the trouble is of ELECTRICITY ON SHIPBOARD 591 course limited to that circuit, and may probably be found at the junctions with the main feeders. If, on the contrary, the lights in all the circuits go out or fall off in candle power, the trouble is in the main circuit and must be sought for at the switchboard or generator itsjlf. At the switchboard the cut outs and fuses must be examined, and if the trouble is here it will be soon located. At the generator the brushes should be examined to make sure that they run with proper contact on the commutator. The contact between the brush and holder and all binding posts and contacts about the machine should also be examined, in order to make sure that the trouble is not in a poor contact at these points. If nothing is found here, it is probable that the fault lies in the armature or field coils, and that possibly they have be- come burned out or unsoldered or otherwise disconnected at some point. Leakage faults may occur where the insulation is partially or wholly destroyed, and the result of such leakage will be a loss of effect in the lighting and power circuits. Thus, for ex- ample, the insulation between the brush carriers and the base of the machine may become faulty by wear or by the accumulation of copper dust and oil and thus form a more or less ready path from one brush to the other through the base of the machine. In such case the current traversing both the field coils and ex- ternal circuit will be cut down, and due to the former the strength of the magnetic poles will be diminished, and the E.M.F. devel- oped will fall off correspondingly. In case these leakage con- tacts are good, the entire machine will shut down, due to failure of current in the magnet coils and consequent failure of the magnetic field. In order that such trouble may exist, both brushes must be thus connected to the base. If one only is con- nected, the machine is said to be grounded. No immediate trouble may occur, but if any accidental connection is set up be- tween the external circuit and the structure of the ship the leak- age circuit will be complete and trouble will develop immediately, its character and extent depending on what point of the external circuit is thus grounded with the machine. The repair of a fault in the external circuit is often a simple matter of cleaning and readjustment. In the generator itself, however, the exact location and repair of a fault may require a 592 PRACTICAL MARINE ENGINEERING complete dismantling, and perhaps a partial re-building of the machine. QUESTIONS Electricity on Shipboard PAGE Explain the fundamental properties of a common magnet 570 What principle serves to connect magnetism with electric currents?.. 572 What are the fundamental principles upon which the operation of the electric generator depends ? 573 Define the following terms : Electromotive force, volt resistance. Ohm, Ampere, Watt 574 What are the two leading sub-divisions of electric machinery? 576 Which form is commonly used on shipboard? 577 What are the leading features of a modern marine generating set?. . 578 How does a motor differ from a generator ? 581 For what are motors chiefly used ? 581 Explain the method of distribution of electric current for incan- descent lamps 583 What is the purpose of the switchboard? 584 Mention the chief instruments and appliances found on the switch- board and give their uses 585 Describe the usual type of incandescent lamp 586 Describe a simple type of arc lamp 587 What points are of chief importance in the operation and care of electrical machinery ? 588 What are faults, and how may they be located ? 5go CHAPTER XI Propulsion and Powering Sec. 83. MEASURE OF SPEED For measuring the speed of steamships the customary unit is the knot. While this term is often used as a distance, it is really a measure of velocity. As adopted by the United States Navy Department, it is a speed of 6,080.27 feet per hour. The British Admiralty knot is a speed of 6,080 feet per hour. For all ordinary purposes the United States and British knots maybe con- sidered the same. It is often necessary to reduce knots to feet per minute or vice versa. To this end we divide 6,080 by 60 and find 101.33 feet per minute as the equivalent of one knot. Hence the following rules : To reduce knots to feet per minute multiply by 101.33. To reduce feet per minute to knots, divide by 101.33. In the inland waters of the United States, and to some ex- tent on the coast for tugs, yachts, launches, etc., the tnile per hour is used as the unit, instead of the knot. A statute mile consists of 5,280 feet. Hence one mile per hour equals 5,280 -=- 60, or 88 feet per minute. Hence : To reduce miles per hour to feet per minute, multiply by 88. To reduce feet per minute to miles per hour, divide by 88. Also: To reduce miles per hour to knots, divide the former by I-I5IS- To reduce knots to miles per hour, multiply the former by I-I5IS- Sec. 84. PROPULSION To propel a ship through the water some kind of a propul- sive thrust must be obtained. This is the fundamental problem of propulsion. Thus when a boat is poled along a shallow creek the thrust is obtained as a reaction from the bed of the creek 594 PRACTICAL MARINE ENGINEERING , against the end of the pole and thence to the man who is pushing it, and thence to the boat. In the usual case, however, there is no bottom to be reached, and the only thing outside the ship which can be gotten hold of for the purpose of gaining a reaction is the air or the water. For all cases with which the engineer is concerned it comes to the latter, and so the problem is to get from the water a reaction or force directed forward by means of which the ship may be . pushed through the water. To understand how this is possible it is necessary to remember the property of inertia, one of the fundamental properties of matter. It is this property which en- ables all matter to resist any efifort made to change its condi- tion of rest or relative motion, and to react back on the means by which such a change is effected. Thus a push of the hand may serve to set in motion a weight hanging by a rope, but while the condition of rest is being overcome the weight will react back on the hand with a force equal and opposite to that which the hand exerts upon the weight. Similarly, when a shot is fired from a gun, the inertia of the shot causes it to react back against the gas and so to the gun, catising the well known recoil. From the fundamental principles of mechanics it follows that to obtain a thrust or reaction forward it is only necessary to produce in a certain mass of water an increase in velocity, such increase being directed from forward aft, or at least having a component in that direction. There will then be a reaction directed from aft forward, or having a component in that direc- tion, and such reaction exerted on the means used to produce the change of velocity may be utilized as a propulsive thrust. This is carried out in practice by either a screw propeller or paddle wheel, and remembering the principles above stated, it appears that the immediate purpose of the propeller or paddle wheel is simply to produce an increase in the velocity of the water directed from forward aft. In consequence of this the water will exert a forward reaction on the propeller or paddle wheel, and thus reduce the thrust required to propel the ship through the water. It may be added that this increase of ve- locity from forward aft, referred to above, may be obtained either by taking hold of water at rest and giving it a motion stern- ward, by taking hold of water already moving sternward and giving it a still higher velocity in the same direction, or by taking PROPULSION AND POWERING S9S 596 PRACTICAL MARINE ENGINEERING hold of water moving forward and decreasing such forward mo- tion, stopping it and leaving it at rest, or reversing it to a stern- ward motion. In all cases it is the change of velocity which is of importance. Thus a change from rest to 5 feet per second aft, or from 3 feet per second aft to 8 feet per second aft, or from 5 feet per second forward to rest, or from 2 feet per second forward to 3 feet per second aft, will each give the same forward thrust. The theory of propulsion will not be gone into further, but in the next section will be given certain definitions relating to screw propellers and the solution of a few simple problems. Sec. 85. SCREW PROPELLERS [i] 'Definitions A screw propeller, as shown in Figs. 409, 410, consists of a hub and a certain number of blades, usually two, three or four. The blades have on their rear or driving face an approximately helical surface — that is, .a surface similar to that which forms the faces of an ordinary screw thread. In this view a two bladed screw propeller may be considered as a small part of a double threaded bolt, the threads being cut very deep, and all portions being cut away down to the hub except the parts retained for blades. Similarly a three or four bladed propeller may be con- sidered as a small part of a triple or quadruple threaded bolt similarly cut away except for the parts retained for blades. The Imb or boss is the central portion to which the blades are attached, and through which they receive their motion of rota- tion in a transverse plane relative to the ship. A propeller is said to be right hand or left hand, according as it turns with or against the hands of a watch when looked at from aft and driving the ship ahead. The face or drhnng face of a blade is to the rear. It is that face which acts on the water and so receives the forward thrust. The hack of a blade is therefore on the forward side. Care must be taken not to confuse these terms. The leading and folloimng edges of a blade are respectively the forward and after edges. The diameter of a propeller is the diameter of the circle swept by the tips of the blades. The pitch of a propeller is the same as the pitch of the screw thread, of which it may be considered as forming a small PROPULSION AND POJVP.RING 597 part — that is, it is the longitudinal distance between the succes; sive turns of the helical surface. This definition \\ill hold, how- ever, only when the pitch is the same over the entire face of the blade. In many cases the pitch varies from one point to an- other, and the term must, therefore, be understood as relating, in such cases, to a small element of the driving face only. From this view the pitch may be defined as the longitudinal distance which the ship would be driven for one revolution were this ele- JUarinc Enpi'ieermff Fig. 410. Screw Propeller, Detachable Blades ment to work on a smooth, unyielding surface, as, for example, the corresponding surface of a fixed nut. The pitch thus defined will depend on the location and inclination of the surface at the point or element considered, and its value may thus vary from one point to another over the entire face of the blade. The pitch is thus said to be uniform or variable, as its value remains the same or changes from point to point over the driving face. If it increases in going from the hub to the tip of the blade it is said to increase radially. If it is greater on the following than on 598 PRACTICAL MARINE ENGINEERING the leading edge, it is said to increase axially. The latter is usually implied by the simple increasing or expanding pitch. The pitch ratio is the pitch divided by the diameter, or the ratio of pitch to diameter. The areaj developed area or helicoidal area of a blade is the actual surface of the driving face. For the propeller as a whole it is the sum of the areas of all the blades. The projected area is likewise the area of the projections on a transverse plane, of one blade or of all the blades collectively. The disk area is the area of the circle swept by the tips of the blades, including the area of the hub. The pitch has been defined as the distance which the pro- peller in one revolution would drive the ship if it worked on a smooth, unyielding surface. Instead of working on such a sur- face, however, the propeller works on the water, a yielding me- dium, and in consequence the water recedes somewhat under the action of the propeller and the ship moves forward per revolu- tion a distance less than the pitch. The difference between the pitch and the distance the ship actually moves per revolution is called the apparent slip, or, more concisely, the slip per revolu- tion. The ratio of this slip to the pitch is called the slip ratio, or simply the slip stated in percent as a slip of 20 percent, 30 percent, etc. Let p denote the pitch of the propeller in feet. R denote the revolutions per minute. V denote the velocity of the ship in knots. s denote the slip ratio. Then 101.3 v -^ R is the distance traveled by the ship per revolution, and /> — (101.3 z/ -^ 7?) is the slip per revolution. Hence for the slip ratio; 101.31' R Multiplying both terms of the fraction by R : p R — 101.3 V (I) PR The term pR is the distance the ship would go per minute if PROPULSION AND POWERING spg there were no slip, while 101.3 v is the distance which is actually made good. The difference or pR — ioi'.3 v may, therefore, be called the slip in feet per minute, and the quotient of this by pR is the slip ratio. This later equation for .r is the one by means of which its value is usually computed. It may be well to note at this point that while slip implies a certain loss of effectiveness in the propeller, it is a loss which is necessary in the very nature of the case. It has already been seen that to obtain a propulsive thrust it is necessary to give to a certain body of water an increased velocity sternward. This means that the water must yield under the action of the propeller, and it is this yielding or falling sternward which thus gives rise at the same time to both the sHp and the propulsive thrust. As it is impossible to have the thrust without the slip, it becomes necessary to accept the latter to obtain the former. A further consideration must now be introduced. Slip has been defined as the difference between the pitch on the driving face and the advance per revolution. The latter admits of being defined in two ways according as is taken for the point of refer- ence a point in the outlying still water, or a point in the water about the stern of the ship and in which the propeller works. So far as the movement of the ship through the water as a whole is concerned the former is the natural point of reference. For va- rious considerations connected with the operation of the propeller itself, however, the latter is considered the more important in most of the investigations of propulsion. Let briefly the condition of the water close about the stem of the ship and in which the propeller works be noted. The ship in moving through the water will throw into for- ward motion a skin of water extending from the surface of the ship for several inches outward. Very near the surface of the ship this will move with nearly the velocity of the ship, while as the distance from the surface is increased the velocity will rap- idly decrease and soon become insensible. The water thus given forward motion by the skin of the ship will finally be found at the stern, where, still further influenced by wave and stern line motion, it forms the so-called "wake." The forward velocity in the wake at different points in a transverse plane at the stem is quite irregular, rising as high as 50 to 75 percent of that of the ship at points near the surface and near the stern post, and de- 6oo PRACTICAL MARINE ENGINEERING creasing irregularly and gradually to nothing at the outlying still water. For single screw ships the average value in that part of the wake directly influenced by the screw is usually from lo to 20 percent of the speed of the ship. For twin screws located somewhat aside from the strongest part of the wake the values are usually found between 6 and 12 percent of the speed of the ship, while with very fine lines and twin screws there may be no wake or even a negative wake in the location where the pro- pellers are working. Now with reference to the propeller, it is evident that so far as it is concerned individually and as an appliance for developing thrust, it should be judged relative to the water immediately about it and in which it works rather than relative to, an outlying body of undisturbed water upon which it has no direct influ- ence. The slip which is given by taking the speed relative to the wake is, therefore, called the true slip, while that given by taking the speed relative to the outlying still water (the speed as usually considered) is called the apparent slip. To show the relation between the true and apparent slips let w denote the forward velocity of the wake and v that of the ship as before, both measured in knots and relative to the outlying still water. Then (v — w) is the speed of the advance of the pro- peller through or relative to the wake. Also using the same no- tation as above, p R — 101.3 (v — w) is the true slip per minute, while, as before, p R — 101.3 z; is the apparent slip per minute. Denoting the latter by S^, and the former ^'2, we have : Si = p R — 101.3 V. S2 ^ p R — 101.3 (v — w) = 5"! + 101.3 w. It thus appears that the difiference between the two slips in feet per minute is simply the wake velocity, as should be ex- pected. To reduce to slip ratio use p R as the divisor in each case, and denoting the resulting ratios by ^-^ and s^ : pR — 101.3V as before, and pR p R — 101.3 (v — iv) 101.3 w PR PR PR'OPULSION AND POWERING 6oi Where the term slip is used without special definition, the apparent sHp is usually intended. In the preceding discussion of slip the term pitch has been used as though it were of constant value over the entire surface of the blade. If such is not the case, then the term must be un- derstood as referring to a mean or average value. Such an aver- age value of the pitch of a propeller might be defined in a variety of ways, but engineers are not as yet agreed upon the method most suitable. This point, however, is one which cannot be fur- ther developed in the present work. Problems (i) To find the apparent slip. From the preceding value of the apparent slip ratio j the following may be derived: Rule : ( I ) Multiply the pitch by the revolutions per minute. (2) Multiply the speed in knots by 101.3. (3) Subtract the result in (2) from that in (i) and divide the difference by the result in ( i ) . The quotient will be the slip ratio. Example: Given speed of ship, 11 knots; pitch, 20 feet; revolutions, 72. Find the apparent slip. Operation: 20 X 72 = i44o. II X 101.3 = III4-3- (1440 — 1114,3) -^ 1440 = 3257 -i- 1440 = 22.6 per- cent. Ans. (2) To find the speed of ship in knots having given the other items. From the preceding equation derive the following value for v: pR(^i—s) V =■ (2) 101.3 Whence the following: Rule:—{i) Multiply the pitch by the revolutions. (2) Subtract the slip percent from i.oo. (3) Multiply the result in (i) by that in (2). (4) Divide the result in (3) by 101.3. The quotient will be the speed in knots. Example: Given pitch, 18 feet; revolutions, no; apparent slip, 18 percent. Find the speed. 6o2 PRACTICAL MARINE ENGINEERING Operation: i8 X no = 1980- i.oo — .18 = .82. .82 X 1980 = 1624. 1624 -r- 101.3 = 16.03 knots. Ans. (3) To find the revolutions, having given the other items. From the preceding equation derive the following value for R: 101.3 V R = (.3) p(i — s) The use of this formula w^ili be illustrated by the following example : Given speed, 22 knots; pitch, 26 feet; apparent slip, 16 percent. Find revolutions. Operation: 101.3 X 22 = 2228.6. (1.00 — .16) X 26 = 21.84. 2228.6 -H 23.52 = 102.04 revolutions per tnin. Ans. (4) To find the pitch, having given the other items. From the preceding equation derive the following value for p: 101.3 V P = (4) R (i-s) The use of this formula will be illustrated by the following example : Given speed, 28 knots; apparent slip, 21 percent; revolu- tions, 380. Find the corresponding pitch. Operation : 101.3 X 28 = 2836.4. 380 X (100 — .21) = 300.2. 2836.4 -^ 300.2 = 9.4s feet. Ans. [2] Varieties of Propellers Screw propellers are found in the greatest variety according to the number, shape, style and arrangement of blades. In mod- ern practice the number of blades is usually either three or four, the former being perhaps more commonly met with in twin screws and the latter in single screws. The shape of the blades may be oval or elliptical, as in F"igs. 409, 410, or broadening somewhat toward the tip with rounded PROPULSION AND POWERING 603 comers, or of any intermediate or similar form which may be desired. The oval or generally rounded form of blade is most commonly met with in modern practice. The blades may also be bent or curved in various ways. Thus in propellers for small boats the blades are often bent back, as in Fig. 409, so as to throw them somewhat farther from the stern post. They are also sometimes curved in the plane of rotation so that the en- tering edge is well rounded as it enters the water in going ahead. Combined with these there may be various modifications of pitch, as above referred to. The normal or standard pro- peller in modern practice may, however, be considered as one having plain blades of uniform pitch, of oval or elliptical form, and standing at right angles to the axis, as in Fig. 410. Most of the variations from this type are based on fancy rather than on definite engineering reasons. So far as is known at present, the simple normal type, as specified above, is the equal of any of those of variable pitch or of special form or shape of blade, and while it may be that some special combination of pitch, shape and form of blade may give a higher efficiency than can be obtained from the normal type, yet up to the present time such results have not been proven. Small propellers are usually made complete or in one cast- ing, as in Fig. 409. Large propellers are made either in one casting or with separate or sectional blades, as in Fig. 410. In the latter case the root of the blade carries a circular flange fit- ting into a corresponding recess in the hub. This serves to se- cure the blade to the hub by stud bolts passing through the flange and fitted with nuts countersunk below its outer face. The general details of this arrangement are shown in the figure. The holes in the flanges are usually made slightly oblong, thus providing for a slight change in the pitch by turning the flange back and forth, and thus changing the average obliquity of the blade to the axis of the propeller. Once adjusted as desired the holes are filled by packing pieces so that no further change can result from the accidental slipping of the flange under the nuts. In this connection it may be noted that the change of pitch re- sulting from such a twisting of the blade is not the same for all parts of the blade, but varies from root to tip. It follows, if the blade is made of uniform pitch that it will remain so only so long as it is set at the corresponding angle, and that if it is 6o4 PRACTICAL MARINE ENGINEERING twisted to and fro the pitch will be increased and decreased, but not uniformly ; so that in all positions but this one the pitch will no longer be uniform, but variable. For a moderate angle of twist, however, the change from uniformity is but slight, and changes of average pitch up to perhaps lo to 15 percent may be made without serious departure from the average. The chief advantages of the separate blades lie in the possi- bility of varying or adjusting the pitch as just described, and in the readiness with which repairs may be executed. A separate blade broken or defective may be readily removed and replaced with a new one, this operation in small vessels being sometimes accomplished without placing the vessel in dry dock. One or two blades may also be carried as spare parts or shipped by rail, or otherwise, much more readily than an entire propeller. The attachment of the propeller to the shaft is shown by the figures. The taper is usually about i inch in the diameter per foot length. The propeller is prevented from turning on the shaft by one or more keys fitted, as shown. The after end of the shaft is fitted with a nut which serves to hold the propeller against any tendency to slip off when backing, and this is often covered with a conical tail piece, as shown, in order to reduce the eddy formation just aft of the boss. It may be noted that for a right- hand propeller the nut is usually left hand, and vice versa, it be- ing considered that this arrangement reduces the liability of loosening or backing off, but the necessity for this is not ap- parent. If water is allowed to come into contact with the taper of the shaft on which the propeller boss is secured it may give rise to considerable corrosion, and this may set the boss so firmly on the shaft that great difficulty will be experienced in its removal. In order to prevent the contact of water with the taper, various . means may be employed. In one method the brass liner on the shaft is carried along nearly to the forward end of the taper, and a rubber ring is placed just forward of the boss or in a counter- bore. As the boss is forced on, the rubber ring is compressed between the boss and the liner, and thus a watertight joint is made. See Fig. 410. In other cases the liner is carried into a counterbore in the boss and a red lead joint is made between the two. For the examination or repair of the stern bearing it may PROPULSION AND POWERING 605 become necessary to remove tlie propeller and withdraw the tail shaft forward into the ship. This is, of course, an operation re- quiring the docking of the ship. For the removal of the pro- peller the first attempt may be made with steel wedges between the forward face of the boss and the stern post, or after end of the stern bearing. The space between the two is made up with the metal blocking necessary, and the wedges are then inserted and driven one from either side. In this way a tremendous strain can be exerted and the boss will be started unless seriously corroded or jammed unduly tight. In the latter cases recourse must be had to hydraulic jacks, or to a heavy ram or to heating the boss in order to expand it in size and break the connection with the shaft. Once the boss is started the weight of the pro- peller may be taken by chain hoists suspended from the counter, and the shaft may then be drawn forwai-d into the tunnel. In the case of twin screw ships with the common forai of strut, the same general means may be employed, except that it should be remembered that the strain set up is carried on the strut, and the means taken should not go so far as to produce its rupture or undue straining of its fastenings. [2] Materials Cast iron, cast steel, brass, gun metal, monel metal and the various bronzes are the materials used for screw propellers. Cast iron is the cheapest, but is relatively weak and brittle, and the blades must necessarily be thicker and less efficient than if made of steel or bronze. Cast steel is stronger than cast iron, and the sections may be accordingly decreased with a resultant gain in efficiency. The surface of cast steel is naturally not as smooth as with cast iron, but with improved methods of produc- tion the difference is not important. Monel metal, brass and the various bronzes have naturally a smoother surface, and seem furthermore to have a lower co-efficient of skin resistance. This added to their strength and good casting qualities, makes possi- ble a smooth and relatively thin blade with sharp edges, all of which are features favorable to good efficiency. With the best bronzes the ultimate strength may vary from 50,000 to 60,000 pounds per square inch of section. With cast steel the ultimate strength will reach still higher, or, say, to 65,000 pounds per square inch. With gun metal an ultimate strength of 25,000 to 35,000 pounds may be expected, while with common brass and 6o6 PRACTICAL MARINE ENGINEERING cast iron not more than 20,000 to 25,000 pounds can be depended on. Of the various materials available, manganese bronze may perhaps be considered as possessing the best combination of desirable qualities, such as strength and stiffness, good casting qualities, resistance to corrosion, etc. Care is needed in the manipulation of the various bronzes in melting, pouring and cooling, in order to insure uniformity and the full reahzation of the valuable properties of the alloy. The greater cost of such bronzes restrict their use, however, to warships, yachts and launches, ocean liners and other cases where the importance of Fig. 411. Measurement of Pitch a saving in propulsive efficiency may be considered worth the in- creased cost of the propeller. The durability of propeller blades is usually in the order: monel, bronze, cast iron, cast steel. The two latter usually suffer by general corrosion and local pitting, the average life being usually from five to ten years. The life of monel and bronze blades is practically indefinite. [4] Measurement of Pitch To determine the pitch of a given propeller three measure- ments are necessary. See Fig. 41 1 . These are : (i) The radius 0^ at which the pitch is desired. (2) The angle or part of the complete circumference cor- responding to the distance on the blade between A and B, the two points between which the pitch is to be found. PROPULSION AND POWERING 607 (3) The advance BC parallel to the Une of the shaft, corre- sponding to this part of a complete revolution. In the figure, A and B are points on the face of the blade, and are at a constant distance OA from the shaft centerline 00. AC \s an arc of a circle which lies in a plane through A and per- pendicular to the shaft. The angle ^OC is, therefore, the one re- ferred to in {2), and the distance BC is the corresponding ad- vance. Then BC is the same fraction of the entire pitch that AOC is oi 3i complete circle, or the same fraction that the length ^C is of a complete circumference with OA as radius. This complete circumference will be 6.2832 X OA. Hence the pro- portion : AC : 6.2832 X OA : : BC : pitch, 6.2832 XOAXBC or pitch = AC It is not, however, as easy to measure AC as AB, so that for AC may be put its equal and then, pitch 6.2832 XOAXBC y^AW—BC A brief outline of the operations is as follows : (i) Select the points A and B at and between which the pitch is desired, making sure that they are at equal distances from the shaft centerline. This can be done by squaring down from a straight edge or other reference line PQ, PR, placed across the hub and at right angles with the shaft. Then measure the length AB. (2) The propeller being leveled up, measure the distance BC from a level through A vertically down to B. Or if the pro- peller cannot be leveled, measure from B in a' direction parallel to the shaft out to a line through A in a. plane at right angles to the shaft. Or measure from Q down to A and from R down to B and take their difference BC. (3) Multiply the distance OA or its equal PQ by 6.2832, and by the length BC all in the same units of measure. (4) Square the lengths AB and BC, subtract the square of the latter from that of the former and extract the square roct of the difference. 6o8 PRACTICAL MARINE ENGINEERING (5) Divide the result found in (3) by that found in (4) and the quotient will be the pitch desired. Thus, for example, suppose AB = 20 inches, BC = 13 inches and OA = 48 inches. Then 6. 2832 X 48 X 13.= 3920-7- Also V 400 — 169 = V 231 = iS-2. Then 3920.7 -^ 15.2 = 258 inches = 21 feet 6 inches = pitch. If the pitch is variable instead of uniform, the operation is precisely the same, but the result found must be considered merely as the mean or average value of the pitch between the Marine Enginee^ilJ Fig. 412. Measurement of Pitch points A and B. For other parts of the blade a similar process will give the pitch at those points. When the propeller is in place on the ship it is sometimes more convenient to carry out the principles involved in this method of measuring pitch somewhat differently, as follows : Let the propeller be turned so as to bring one of the blades horizon- tal. Then select the place at which the pitch is desired, and hang over the blade at this point a cord with two weights, as shown in Fig. 412. Care must be taken that the two points A and B at which the cord touches the edges of the blade are at the same distance from the center. It is then readily seen that the points A and B of Fig. 412 correspond to the siihilar points of Fig. 411, except that in Fig. 412 they are of necessity taken on the ex- treme edges of the blade. Then level up a bar PQ and meas- PROPULSION AND POWERING 6og ure the distances, AB and BC, as noted above, using them in the same way for finding the pitch. Or measure AC directly and use this with BC in the proportion above. As a rough and ready rule it may be remembered that the pitch of a propeller will equal the .length of a circumference at the place on the blade where the slope of the face is 45 degrees, or where it is equally inclined to the shaft and to the transverse direction. Starting near the shaft, the inclination to the longi- tudinal is small, but increases toward the tip, passing at some point through the value 45 degrees. At this point let the radius be r. Then pitch ^ 2 irr ^ 6.2832r. In this way an approximate idea may often be quickly obtained of the pitch of a wheel by estimate without special measurement, except for the radius or diameter at which the blade has the slope of 45 degrees. The details of the above methods for finding pitch may vary considerably, but the description given will serve to show the principles involved, and with reasonable mechanical skill no trouble will be found in carrying out the measurements required. Sec. 86. PADDLE WHEELS In addition to the screw propeller the paddle wheel is the other appliance used for ship propulsion. In Fig. 413 is shown Fig. 413. Radial Paddle Wheel, Skeleton Diagram in skeleton a common radial paddle wheel. In this type of \v'heel the paddles or floats are rigidly fixed to the arms, the lat- 6io PRACTICAL MARINE ENGINEERING PROPULSION AND POWERING 6ii ter being connected at their inner ends to a hub, which is carried on the shaft. In this manner the motion of the shaft is transmit- ted to the floats, and these, acting ort the water, drive it stern- ward and thus receive the forward thrust which is required for the propulsion of the vessel. In Fig. 414 is shown a feathering paddle wheel. In this ar- rangement the floats are hung on axes and are swung in such way that they enter and leave the water nearly in an edgewise direction. In this way there is less disturbance of the water and a smoother action of the wheel is obtained. Such arrangement is especially suitable for ships operating under widely varying conditions of draft, for the floats of a deeply immersed radial wheel enter and leave the water at a great obliquity and there would be considerable loss by oblique action. There are two chief methods by which the proper motion may be given to feathering floats, depending on whether the pad- dle shaft has an outer or spring bearing on the outside of the paddle box or is overhung; that is, provided simply with a bear- ing on the rail, the paddle wheel itself being then mounted on the overhung end of the shaft. In the former case the arrange- ment will be understood from the skeleton drawing of Fig. 415. The stationary eccentric A has its center forward of the wheel center, as shown. To the eccentric strap is attached a drive link HB, connected by pin joint to an arm BC, carrying a float DE. The other floats, mounted in a similar manner, are connected by pin joint links to the eccentric strap, as shown. As the wheel turns the drive link HB carries the strap around the eccentric sheave, and with it the series of connected links. This gives a see- saw motion to the ends of the arms BC and thus ?wings the floats in the manner desired. When the paddle shaft has no outer bearing, as in the ar- rangement shown in Fig. 414, the disk carrying the links may be mounted on a supporting pin carried on the outer side of the gtiard. It may then be given motion through a drive link and connections, as shown, giving a similar see-saw motion to the floats, as in the former case. In modern practice the arms, of paddle wheels are made of steel, the hubs of cast iron or cast'steel, and the floats of wood or boiler plate ; in the latter case often curved in cross section. In estimating the pitch of the paddle wheel or what corre- 6l2 PRACTICAL MARINE ENGINEERING sponds to pitch in the screw propeller, it must be considered as the circumference of the circle traveled by the floats. Since, how- ever, a float as a whole is made up of a series of strips or ele- ments at varying distances from the center, each such element will have its own circumference and, therefore^ its own pitch, and will try to drive the ship at a speed corresponding to such pitch. The paddle wheel as a whole has, therefore, a varying pitch, increasing from the outer to the inner edge of the float. The resultant mean pitch is considered as the circumference traveled by a point called the center of effort. The proper basis for the determination of this point, and hence of the true mean pitch of a paddle wheel is, however, not definitely known, and can Fig. *15' Paddle Wheel, Skeleton of Arrangement for l^'eathering Floats only be determined by the aid of extended experimental investi- gation. In the absence of such definite basis it is sufficient for all practical purposes to take it at the center of the float radially, though its true location would lie somewhat outside this point. Counting the circumference through this point as the pitch, the actual distance traveled by the boat per revolution is less by the amount of the slip, which is usually found from 15 to 25 or 30 percent. The circle whose circumference is equal to the distance trav- eled per revolution is sometimes known as the rolling circle. It is so called from the fact that the speed of the boat is the same as though it were carried on wheels along a smooth, level road. PR'OPULSION AND POWERING 613 •The solutions of problems relating to the revolutions, diam- eter and slip of paddle wheels are found in the same general man- ner as for the screw propeller, and the resulting equations are similar to those found in Sec. 85 [ i ] , with the substitution for p of D, as defined below, and 88 for 101.3. Let D = diameter of pitch circle. R = revolutions per minute. V = speed in miles per hour. s = slip ratio. Then, as with the screw propeller, we have: DR~88v ttDR ■jrDR (i — j) (I) " = ^ (2) 88 ^ = ~-^r T- (3) tD(i— .f) - 88t; D = (4) Ti? (l— j) These may be illustrated by the following examples : (r) Given diameter of pitch circle, 24 feet; revolutions, 30 per minute ; speed, 19 miles per hour. Find the slip ratio. Operation : ■K-DR = n- X 24 X 30 = 2262. 88w = 88 X 19 = 1672. (2262 — 1672) -^ 2262 ^ 590 -i- 2262 = 26.1 percent. (2) Given diameter of pitch circle, 18 feet ; revolutions, 45 per minute, what speed can be made, allowing a slip of 28 percent ? Operation : ttDR = tt X 18 X 45 = 2545. I — J = I — .28 = .72. .72 X 2S4S = 1832. 1832 -^ 88 = 20.8 miles per hour = 18.1 knots. (3) Given a speed of 18 miles per hour, a sHp of 24 percent and a wheel whose pitch circle has a diameter of 20 feet. Re- quired the number of revolutions per minute. Operation : 88 X » = 88 X 18 = 1584. I — J = I — .24 = .76- ttD (l — s) = T X 20 X 76 = 47.7S-. 1J84 -L. 47.75 = 33.3 revolutions per minute. 6i4 PRACTICAL MARINE ENGINEERING (4) Given a speed of 14 miles per hour; revolutions, 49 per minute; slip, 28 percent. Find the corresponding diameter of pitch circle: Operation : 88 X I* = 88 X 14 = 1232. I — J = I — .28 = .72. TTi? (i — j) = IT X 40 X -72 = 9048. 1232 -;- 90.48 = 13.6 feet. Sec. 87. POWERING SHIPS The subject of the powering of ships is one which can be here only referred to in a brief and elementary way. The usual problems are to find the power required to drive a given ship at a proposed speed, or the probable speed for a given ship with a given power. Such problems require a knowledge of the relation between power, speed and the ship. In the present state of in- formation on this subject, such relation cannot be accurately ex- pressed by any ordinary formula or -equation. Several approxi- mate formulae have, however, been employed for the solution of such problems, and among them none has perhaps been of wider general usefulness than the so-called Admiralty coefficient formula. Let H = indicated horsepower. A = displacement in tons. V ^= speed in knots. K =: & coefficient. The base formula is : H and solving for speed : AVst/S K v=-yj- HK A 2/3 or solving for the coefficient : K = H The whole point in the use of the formula is to properly se- lect the values of the coefficient K in accordance with the special features of the case, including the form and size of the ship, pro- posed speed, probable efficiency of propulsion, etc. The safest plan is to find values of K from the trial data of actual ships of about the same size, character of form and speed, as the pro- posed case, and to be guided by such values in the selection of PROPULSION AND POWERING 615 the coefficient for the proposed case. There are other special methods for obtaining from the trial data of ships of similar form, by the so-called law of comparison, the suitable values for a proposed case, even when the sizes and speeds differ consider- ably from those of the proposed case. These methods will not, however, be dealt with here. Some general suggestions regard- ing the value of K with a few illustrative examples must suf- fice. It is found by experience that in general the value of K is greater (and hence the I.H.P. relatively less) as the ship is larger, but more especially as she is longer, also as she is nar- rower in proportion of length to beam, and as she is finer in form, especially in the waterlines. In the reverse cases the values of K will be smaller, and the I.H.P. relatively larger. The values of K are also smaller and the I.H.P. relatively larger as the speed is higher in proportion to the length, or, more exactly, as the speed is higher in propor- tion to the square root of the length. For small launches and such craft driven at speeds in miles or knots greater than *\/-^ i" feet, the values of K will be quite small, ranging perhaps from 100 to 150. At lower speeds equal to or less than ^/L the values will rise to perhaps 200 and more with fine form and small pro- portion of beam to length. For yachts and craft of similar form, moderately fine and at fairly high speeds, values of 200 above and below will be found. For torpedo boats, with their narrow proportions and fine form, their excessive speeds carry them into a set of conditions where the coefficients are larger and the power required relatively less than might be expected. Varying with size and "other conditions, values of 200 above and below are found for boats of this character. For mercantile vessels of moderate size, rather full form and moderate speed, the values will be usually found from perhaps 220 to 250. For larger mer- cantile vessels at moderate speeds or for those of moderate size under exceptionally good conditions the values may rise from 250 to 300. For fast passenger boats varying with size, and other conditions, values from 220 to 280 may be expected. For naval vessels, cruisers and battleships, from 200 to 250 is the usual range. These various values are not intended as marking definite Note : L — Length of ship nn feet on the load waterline. 6i6 PRACTICAL MARINE ENGINEERING limits, nor can they enable a person without individual judgment to properly select a suitable value for a given case. They are intended simply as general suggestions of the range of values commonly met with. A few examples to illustrate the use of this formula will now be solved. Note that A^^^ means the cube root of the square, or the square of the cube root of the displacement in tons, and hence with a table of squares and cubes or square and cube roots, the value desired may be readily found. In some hand books values of A"^^ are given directly. (i) Given A = 3200, z/ = 12 and take K = 230. Required the power. From a table of squares (32)- = 1024, and hence (3200)^ = 10,240,000. Looking in the column of cubes of numbers of three figures the nearest cube is 10,218,313, and that the number corresponding is 217. This will be sufficiently near for all prac- tical purposes, and is therefore taken as the value of A^/^ Also (12)^ = 1728. Hence 217 X 1728 H = = 1630 Ans. 230 (2) Given a yacht of displacement 366 tons, to be driven at a speed of 18 knots. Assume K = 200 and find the necessary power. In this case (366) ^ = 133,956 and the number corre- sponding to the nearest cube is 51.2. Also (18)=' ^ 5832. Hence SI .2 X 5832 H = = 1493. 200 (3) Given A = 7243, 7/ = 16 and take K — 240. Find the power. Without important error the last 3 tons may be dropped so as to bring the number within the range of the usual tables of squares and cubes. Then (724)^ = 524,176, and hence (7240)- = 52,417,600. The number corresponding to the nearest cube is 374. Also (16)^ = 4096. Hence. 374 X 4096 H = = 6283. 240 (4) What speed may be expected from a liner of 15,400 tons displacement and 26,000 I.H.P. ? Take, in this case, K = 250. PROPULSION AND POWERING 6iJ Then (154)= = 23,716 and hence (15400)= = 237,160,000. The number corresponding to the nearest cube is 619. Then * = \ 20,000 X 250 • = ^ 10,500 = 21.9. 619 (S) Given A = 8320, z^ = 13 and H = 3400. Required the value oi K. (832)2 = 692,224 and hence (8320)= = 69,222,400. The number corresponding to the nearest cube is 411. Also (13)' = 2197. Hence 411 X2197 K = = 26s. 3400 Sec. 88. REDUCTION OF POWER WHEN TOWING OR WHEN VESSEL IS FAST TO A DOCK It is well known that the power developed by the engine when the ship is towing is less than when she is running free, the steam pressure and cut-off being the same; also that at a dock trial (engines running, but ship fast to the dock) the power is considerably less than may be developed in free route under the same steam pressure and point of cut-off. To explain these results, first assume that the ship, boilers, engine and propeller are all properly designed for a given speed. This means that with a given boiler pressure (say 180 pounds) the boilers will .be able to supply steam enough to drive the en- gines at the designed revolutions (say 100) and thus develop the designed power, while the propeller with a certain slip (say 20 percent) will drive the ship at the designed speed (say 16 knots). Now it must first be noted that all of these conditions go together, and if any one of them is disturbed it will react on all the others. The next point is that a constant set of pressures throughout the engine means a constant reduced mean effective pressure, a constant turning moment on the shaft and a nearly constant thrust, and hence a nearly constant resistance over- come. Now at the regular speed, if the resistance is increased, as by taking up a tovir, what will be the immediate result ? Evi- dently the speed will decrease until at some reduced speed the nearly constant thrust will balance the resistance, and the mo- tion will become uniform again. The greater the increase in re- sistance at the regular speed — that is, the larger the tow — the 6i8 PRACTICAL MARINE ENGINEERING lower the speed at which the nearly constant thrust will be able to balance the resistance and thus produce steady conditions. The whole question as regards power developed now turns on the revolutions at this reduced speed. In other words, how do revolutions and speed vary for a constant turning moment, and a nearly constant thrust developed or resistance overcome? This is best answered by experimental data, which give a relation similar to that shown in Fig. 416. Revolutions are laid off hori- 10 15 14 13 12 11 CO S" h 6- 4- 3- / / / / / / ' / / / / / / / / / / . ^ 19 30 40 60; -\6p- REVOCUTIoTilS 80 ZP Too Sneering Fig. 416. Diagram Showing Relation Between Revolutions and Speed for Constant Turning Moment zontally and speed vertically. Assume that revolutions and 14 knots are the designed conditions, as indicated on the curve, then the diagram shows how the revolutions and speed vary for a constant thrust. In particular the curve shows, as the tow is increased in amount and the speed for a given thrust decreases more and more, so likewise do the revolutions decrease, though at a slower rate. Hence with the decrease of speed the slip con- stantly increases. The relations as shown by this curve furnish the key for the solution of all questions regarding the variation of the power. The work done by the engine is a product of the revolutions into other factors, and since these other factors in- clude merely dimensions of the engine and mean effective pres- sure, and since by assumption all of these remain constant, it is evident that under the conditions assumed the power developed will vary directly with the revolutions. Hence the diagram shows PROPULSION AND POWERING 619 the relative decrease of power with decreasing speed, as well as the actual decrease in revolutions, provided always that the mean effective pressures in the cylinders remain constant. If the tow be added to indefinitely a condition similar to that of a vessel tied to a dock would finally be reached ; that is, a con- dition where the speed has become reduced to nothing and the revolutions reduced in quite marked degree. The exact relation between revolutions in free route and when fast to a dock will, of course, depend on the special circumstances. The mean ef- fective pressure remains the same, however, and the work done and power developed will, therefore, vary simply with the revolu- tions, according to a law similar to that shown in the figure. To sum up the matter, therefore, the power falls off because the revolutions fall off, and the revolutions fall off because the speed falls off, and because at the reduced speed and increased slip the constant turning moment of the engine can no longer turn the propeller at the original number of revolutions. The reason why of the facts expressed by the curve in Fig. 416, on which the whole matter turns, is to be found in the funda- mental relation between revolutions, slip, thrust, etc., a complete discussion of which is, of course, beyond the present purpose. Once these relations accepted as experimental truth, however, the desired explanation is seen to flow from them as a necessary consequence. Sec. 89. TRIAL TRIPS The general purpose of a trial trip is to determine the power or speed which may be maintained for a certain distance or time. In addition to these fundamental purposes, information relating to the general problem of resistance and propulsion may also be gained, as well as that bearing on other points which may be the object of special inquiry. It is not necessary to refer especially to the determination of power, as that has been already suffi- ciently treated. For the determination of speed alone it is sufficient to ob- tain observations of distance and time. The revolutions should, however, be also taken, in order that the slip of the propeller may be found. For speed trials a long course may be used, as, for example, from 20 to 100 miles or more, over which but one run, or, more commonly, one run in each direction is made ; or, 020 PRACTICAL MARINE ENGINEERING on the other hand, a short course of I or 2 miles, over which as many runs may be made as desired. For marking off the course, buoys or ships at anchor are often used for the long course, while range marks on shore for the limits and buoys for the direction and location are commonly employed for the short course. At each end of the short course there should be plenty of room for making turns and gathering headway before entering the course for the return run. The free space available for this purpose should be not less than from one-half to one mile, although the actual space required will de- pend upon the length and speed of the vessel. To eliminate the error due to the tide on the long' course run, tidal observations should be made from vessels anchored along the course by means of a patent log or equivalent device, and from the results the average tidal influence may be deter- mined. To eliminate the tidal error on short course trials the runs are made in both directions and an average is taken. This may be either a simple average or the result of a "continued average," as illustrated below. Suppose four runs made, two in each direction, and let the resulting speeds in order be those entered in the column on the left. 17.10 An average is first made of Nos. i and 2, then of 2 and 3, and then of 3 and 4, and these are put in the second column. Then these are averaged in like manner and put in the third column, and these are again averaged for the final result, which, in the above case, is 17.10. With six runs the operation is car- ried out in the same way. While this is often considered as the only correct way of averaging such a series of runs, it may be shown that such is by no means the case, and, as a matter of fact, that under ordinary conditions the simple average will give quite as probable a result as the more complex method. In the above case the simple average would give 17.05, as against 17.10, a difference of .05 knot, and the former value is quite as likely to be correct as the latter. North 17.2 South 16.8 17.00 17-075 North 17-5 17-15 17.125 South 16.7 17.10 PROPULSION AND POWERING 621 In some cases it is desirable to make a complete speed trial and thus obtain a series of values of the power, revolutions and speed from full power conditions down. This may be done on the measured mile or short course by making runs in pairs, the conditions for each pair remaining as nearly constant as possible, while from one pair to another the conditions change over the complete range to be included in the trial. The average results 20 18 16 M I- Ml 10 • ^ / '/ ' / / / / v y / / / 1 a D 3 4 3 5 D 6 7 8 9 10 REVOLUTIONS Fig. 417. Diagram of Revolutions and Speed JUarine Enginetring in speed, power and revolutions are then used for plotting the curves showing the various relations desired. Such a curve showing the relation between revolutions and power is shown in Fig. 418, together with the spots which may represent the actual single observations. The curve may then be drawn through and among the spots as a method of getting a graphical average ; or otherwise the values may be averaged numerically and plotted as a series of averages, and the curve then drawn through them. As a somewhat shorter method, a series of runs may be taken in each direction, beginning at the highest, and at con- 622 PRACTICAL MARINE ENGINEERING stantly decreasing revolutions. The results for speed and revo- lutions are then plotted, as shown in Fig. 417, and a fair curve drawn through and among the spots. This is then taken as the relation between revolutions and speed. The relation between revolutions and power is also plotted, as in Fig. 418. Then, by 9000 8000 7000 cooo xSOOO 4000 3000 2000 1000 iz~tz 1 'M * J * 10 20 iO 50 60 REVOLUTIONS 70 80 90 100 Marint SngivMring Fig. 418. Diagram of Revolutions and Horsepower the aid of these two, the speed-power curve may be plotted, as shown in Fig. 419. The computations arising in connection with such trials will now be noted briefly, the observations entering into the computations being simply time and revolutions. Let the course be a measured mile (marine or statute, as the case may be), and let the time on the course be t, expressed in minutes and decimals. This is usually determined by a stop- watch reading the half or quarter second. The value cannot, however, be depended on as accurate to much within i second. Then if v denotes the speed : z> = 60 -^ t. The revolutions will be obtained from the counter by sub- tracting the readings at the entrance and end of the course. This PROPULSION AND POWERING 62' will give the number of revolutions for the course. Let this be denoted by R. Then R Revolutions per minute = - — . t ywu / 7000 6000 / 1 /. d! / 4000 / / 3000 / A ^ y ^ 2 4 6 8 10 12 11 ppcCD fN KNOTS Fig. 419. Diagram of Speed and Horsepower 16 18 20 ^tarint Snginttrmg Also let p = pitch of propeller. Then assuming the course to be a nautical mile pR — 6080 (pR — 6080) = slip in feet, and pR = slip ratio. These computations may be illustrated by the following ex- ample : Let the course be a mile of 6,080 feet, and let the following data be taken : Counter at Entrance Counter at End Time Run north 106,248 106,654 4 m. 26 sec. Run south 107,112 107,542 . 4 m. 33 sec. Pitch of propeller 18 feet. Required the mean speed and slip for the two runs. For the run north the revolutions are 106,654 — 106,248 = 406, 624 PRACTICAL MARINE ENGINEERING For the run south the revolutions similarly found are 430. The average revolutions are then 418. The speed north is 60 -^ 4.433 == 13.53. The speed south is 60 -f- 4.55 = 13.19. The mean speed is then 13.36. The slip in feet = (418 X 18) — 6080 = 7524 — 6080 = 1444. 1444 ■ The slip ratio = = 19.2 percent. 7524 Sec. 90. SPECIAL CONDITIONS FOR SPEED TRIALS In speed or power trials the purpose is often the develop- ment of the maximum speed or power, and in the present section will be noted the more important points connected with the ful- filment of these purposes. Boilers. Where there is a record performance to be made there must be no loss of evaporating efficiency due to accumula- tions of soot and ashes on the fire side, or of oil, scale or mud on the water side. Hence especial care must be taken to see that the boilers are thoroughly clean on both fire and water sides. Fuel. If possible, the fuel should be of the highest grade and carefully selected with reference to clean, free burning qualities. Engines. The engines should be adjusted with the various joints sufficiently loose to avoid danger from heating, and at the same time not sufficiently loose to hammer seriously. Special attention must be paid to oiling gear, and also to the provision for supplying water in case the bearings tend to become hot. Ship. The ship should be brought to the displacement con- dition desired or which may be required by the terms of the builders' contract. The bottom of the ship should also be thor- oughly clean and fresh painted, or, if coppered, clean and pol- ished, if not too large. The propeller should also be looked after, and if there is opportunity it should be cleaned and the edges sharpened. QUESTIONS Propulsion and Powering What is the unit of speed used in havigation, and what is its vaJue in feet per hour ? ^p. How may knots be reduced to feet per minute ? cg^ How may miles per hour be reduced to feet per minute? 593 PROPULSION AND POWERING 62s PAGE Explain briefly the fundamental problem in propulsion 593 Describe a screw propeller, and name its various parts and pro- portions 596 What is slip or slip ratio, and how is it computed ? 598 What is the condition of the water in which the propeller works ? . . S99 What is the difference between the true slip and the apparent slip?. . 600 Describe various forms of screw propellers 602 When the blades are cast separately, how are they secured to the hub ? 603 Describe the attachment of the propeller to the shaft 604 What materials are used for screw propellers ? 60s Describe methods of measuring the pitch of a screw propeller 606 Describe the radial paddle wheel 609 Describe the feathering paddle wheel 611 Describe the two methods employed for operating the floats in the feathering wheel 611 What is the "rolling circle" ? 612 How is the slip of the paddle wheel estimated ? 613 Give the Admiralty coefficient formula for powering ships 614 In general, how does the coefficient vary with the speed and geo- metrical characteristics of the ship ? 614 Name average values for typical cases 615 Explain the reduction of power developed by a ship when towing, or when undergoing a dock trial 617 What are the general purposes of trial trips ? 619 For the determination of speed alone, what observations are neces- sary? 619 Describe various ways in which tidal influence may be eliminated .... 620 Describe the manner in which such information may be plotted or represented graphically 621 Describe the various conditions which should be attended to in trials intended to develop the maximum speed and power 624 CHAPTER XII Operation^ Management and Repair Sec. 91. BOILER ROOM ROUTINE In the present section it is the purpose to give brief hints and suggestions- regarding the routine of operation and manage- ment in the fireroom in getting under way and on the voyage, first supposing tliat everything is working smoothly and with- out trouble, and then to notice the chief emergencies which may arise. Suppose that firetube boilers are in use, in the first in- stance, and later give such supplementary suggestions as may be suitable for watertube boilers. [i] Starting Fires and Getting Under Way (Coal-Burning Boilers) A general examination must first be made of the boiler and fireroom equipment in order to make sure that everything is in readiness for getting up steam. Among the more important points to be attended to the following may be mentioned : See that the coal bunker doors are in proper working order and if the bunker is partly empty it may be well to air it by open- ing the door and taking off the deck plates. See that the coal handling gear is on hand and in proper condition. See that the necessary fire tools are provided, and dis- tributed as needed. Examine the grate bars, bridge walls and back connections, and note whether the area of passage above the bridge walls is properly proportioned. For usual conditions it should be from 1/5 to 1/7 the grate area. Note the condition of the tubes, both from the front and back connections. Examine the dampers in uptakes and funnel to see if they are in working order, and open them preparatory to lighting the fires. OPERATION, MANAGEMENT AND REPAIR 627 Examine carefully all valves, cocks, piping and connections and make sure that everything is connected up as it should be, and that no valves are open which should be closed nor closed which should be open. See that no waste or other inflammable substances have been left about by workmen on the tops of the boilers. If the water has not been previously run up in the boilers, this may be under way in the meantime. In modern practice the boilers are always filled with fresh water where possible, ob- tained from a hydrant on the dock or waterboat alongside, and put in usually by a hose through an upper manhole. If, how- ever, the boat is lying in fresh water, or if by necessity the water is to be taken from overboard, it is then run in through the bot- tom blow and Kingston (sea) valve. In the meantime examine the connections leading to the water gage and cocks. Clean the glass if necessary, and make sure by means of a wire that the openings through the cocks are clear. The packing of the gage glass should also be examined and renewed if necessary. When the water appears in the gage glass and shows from one-half to two-thirds full in each boiler, it may be shut off. All open manholes may then be closed, and the boilers are ready for the fires. Notice of the time when steam is required should have been given not less than from six to eight hours in advance, and many engineers prefer a still longer time in which to bring along everything into working condition. With hard coal a certain amount of wood is necessary in starting the fires. With soft coal less wood is required, and if necessary oily waste may be made to answer the purpose. If fires are up in the donkey boiler, a little live coal may be taken from them to assist in starting. As soon as the fires are going the hydrokineters are put on if such appliances are fitted. In some cases arrangements are made for drawing the water by the donkey or auxiliary feed- pump from the bottom of the boiler by the bottom blow and re- turning it through the feed pipe, thus producing a forced or as- sisted circulation. Where there are no appliances for forcing circulation during this period, it is considered good practice to light first the fires in the center furnaces, and later, by one or two hours, those in the wing furnaces. The natural circulation thus produced will more nearly even up the temperature within 628 PRACTICAL MARINE ENGINEERING the boiler than if all fires are lighted at the same time. After the fires are fairly going the funnel or uptake dampers may be partly closed so as to hold the fires back, and bring them along at a moderate gait as desired. While the boilers are thus warming up and before steam has formed, a last look may be given to the boiler mountings and their connections. The various cocks and valves should be worked, and especially the stop and safety valves, in order to make sure that none is jammed or in any way out of order. The oil lamps for the steam and water gages may also be trimmed and lighted, or the electric bulbs cleaned, if such are provided. During this period the steam pipe drains and safety valves are usually open to allow of the escape of the air and of the con- densed vapor as formed. In some cases, however, the safety valves are closed, and the stop valves being open, the air and vapor are expelled along the steam pipe and through the engine, thus beginning the process of warming up. Many engineers, however, prefer to keep the boiler stop valves closed until steam is formed and to discharge the air through the safety valve, or in some cases through a specially fitted air cock. If steam is already up on some of the boilers or if there is no auxiliary steam pipe and the pressure from the donkey boiler is on the main steam pipe, then of course the stop valves must be closed on the boilers in which steam is being raised, and they must re- main closed until the pressure on the boiler is equal to that in the steam pipe. In opening a boiler stop valve connecting with a pipe in which there is no pressure the following precautions should be taken : (i) The pipe should be thoroughly drained and especial care should be taken that there are no sags, bends or U's unpro- vided with proper drains, and in which a pocket of water may have collected. (2) The valve should be very carefully eased from its seat and opened only from a quarter to a half turn until the pipe is under full boiler pressure and has taken the temperature of the steam, and the drains are discharging steam instead of water. In opening a boiler stop valve connecting with a pipe in which there is approximately the same pressure as in the boiler, it is simply necessary to ease the valve from the seat and note by the sound whether there is a sufficient difference of pressure to cause OPERATION, MANAGEMENT AND REPAIR 629 any violent flow in one direction or the other. As soon as the absence of such evidence indicates an equaUty of pressure on both sides of the valve, it may be opened out as desired. The two fundamental principles underlying much of this routine and detail are simply as follows: (i) To prevent as far as possible sudden changes in the temperature condition of the boilers, piping and machinery, and (2) To prevent throughout the steam pipe system the accu- mulation of water at any point. If these two points are kept clearly in view and good en- gineering judgment used in carrying them out, the life of the boilers and machinery will be prolonged, and danger of ruptured pipes through the effects of water hammer will be avoided. After steam is formed and the pressure has risen to some 40 or 50 pounds the hydrokineters may be shut off, especially if the ship is to get under way as soon as ready. If, however, the boil- ers are to stand some time with steam up, it may be advisable to turn on the hydrokineters from time to time, at least as long as the pressure in the donkey boiler is sufficient for the purpose. The fires in the meantime have been kept simply in good condition without forcing, and even if they work under a forced draft system, only enough air should be provided during this stage to bring them along at the gradual pace which will allow the boiler properly to accommodate itself to the change in tem- perature and other conditions. The fireroom auxiliary machinery should also be examined during this period, and tested under steam from the donkey boiler if possible. The feed pumps should first receive attention, in order that there may be no question as to the proper supply of feed water when required. The fan engines should be examined, oiled and, turned over under steam. The ash hoist gear and engine, or ash ejector and pump, should be examined and put in working order. If steam for these purposes is not to be had from the donkey boiler, then as soon as a sufficient head is formed on the main boilers these auxiliaries must be examined, taking in all cases the feed pump first. Soon after lighting fires it may be desirable to slacken up somewhat on the funnel guys on deck, in order that the expan- 630 PRACTICAL MARINE ENGINEERING sion of the funnel may not bring an undue stress upon the guys and their connections, or upon the funnel and its supports. After the ship is away and the funnel has taken its temperature for running conditions, the guys may be tightened up so as properly to support the funnel in a sea way. [2] Fireroom Routine Suppose that full head of steam has been formed on the boilers, that the fires have been brought up to proper condition, and that the ship has gotten under way for the voyage. As soon as possible the operations in the fireroom should be brought to a regular routine. This will involve the following chief features, which shall be considered separately: (i) Firing. (2) Water tending. (3) Disposal of ashes. (4) Qeaning fires. (s) Sweeping tubes. Firing. — The routine of firing should be so arranged that no two furnaces in boilers connected to the same funnel shall be open at the same time. If this is not practicable, then care must be taken to avoid at least firing at the same time furnaces in op- posite ends of double end boilers, especially if there is a common combustion chamber. Two furnaces in a single end boiler, or in the same end of a double end boiler, will, of course, never be fired at the same time. It is now well understood that firing light and often is better than heavy and at great intervals. There is, however, a limit to this, for the oftener the firing the more are the furnace doors open and the more is the draft subject to disturbance, while the arrangment of a suitable routine be- comes more and more difficult. Light and frequent firing, especially with watertube boil- ers, is now, however, the rule where the best results are to be obtained. The furnace door should be opened smartly and kept open only the minimum time needed to get the coal on. Hard coal is spread in as even a layer as possible over the grate. For firing soft coal two methods are available. When firing for coal efficiency, that is to get the most heat out of a pound of fuel, the coal should be first charged in front and coked, and then should be pushed back and burned. When firing for weight efficiency, that is to get the most power out of the boiler, the former method would be too slow and the coal must be spread over the fire and burned without waiting for the separate dis- tillation and combustion of its gases. Where the coal runs ir- OPERATION, MANAGEMENT AND REPAIR 631 regular in size the large lumps should be broken into pieces not larger than the fist. The thickness of the fires varies with the conditions, from six to ten or twelve inches, or even thicker un- der a heavy forced draft. With a given speed of fan the air pressure in the ash pits will vary widely with the thickness of the fire, rising as it is thicker, and falling as it is thinner and the air finds more ready passage through. With a thick fire it will, therefore, be easy to get a strong draft pressure in the ash pits, while with a thin fire it will be perhaps impossible, even with a much higher speed of fan. A strong draft pressure will not, however, produce the corresponding rate of combustion unless the thickness and condition of the fire are such that the pressure is able to drive through it the necessary amount of air. For the best combustion the thickness of the fire should be so adjusted to the draft pressure that the latter is able to drive the necessary air through, and keep it in a state of active combustion through- out from fire grate to upper surface. Care must be taken to keep the grates evenly covered, especially at the back, and to prevent the formation of relatively thin or bare spots. A spot which is relatively thin allows the passage of relatively more air. This further increases the combustion at that point and the spot becomes still thinner, thus allowing more and more air to escape freely instead of passing through the remainder of the fire as it should. In the intervals of firing the pricker and slice bars may be used to clear away the ashes and clinker, if such is forming. Care should be taken to prevent the formation of dull or dead spots due to the accumulation of ashes or clinker, especially at the corners of the grate. Among old firemen a familiar saying relating to this point is : "Take care of the corners and sides of the fire and the middle will take care of itself." The ashpits should also be kept clear of ashes, for if allowed to accumulate they will prevent the passage of air to the grate, especially at the back. If the passage of air is thus interfered with to any con- siderable extent there will be also danger of overheating the grates and of bringing them down into the ashpits. In connection with the use of the slice bar, it must not be forgotten that every opening of the furnace door means an in- rush of cold air into the furnace, a checking of the draft, a distur- bance of the combustion, and often severe strains on the struc- 632 PRACTICAL MARINE ENGINEERING ture of the boiler, due to the sudden chilling and contraction which the heating surfaces undergo. If shaking grates are fitted, much of this cleaning may be done without opening the door, though no form of grate is quite able to deal satisfactorily with coal showing a decided tendency to form clinker. In thus working the fires a certain amount of fine unbumed or partly burned coal will be shaken down into the ashpit. In some cases this forms so large a part of what comes through the grate, that it may be immediately thrown on the fire and burned over again, In most cases a sifting or washing of the ashes and (r^ a oa Marine XngiMering- Fig. 420. Test for Water Gage and Glass separation of the combustible form of non-combustion would show a surprisingly large percent to be available as fuel, and some saving could usually be effected in this way. It is rare, however, that anything of the kind is attempted, as with ordinary prices of coal it may be doubted whether the additional appli- ances and labor would be paid for by the saving effected. Water Tending.^The care of the water is the most important and responsible of the duties in the fireroom. The ideal method of feeding is to keep the water regularly flowing inward through the check-valves at about the same rate as it is flowing outward as OPERATION, MANAGEMENT AND REPAIR 633 steam through the steam pipe. This requires constant watch and adjustment of the valves, closing down where it is entering too rapidly and opening up where it is entering too slowly. Instead of this method it is often the custom to put the feed on strong first on one boiler and then another, in order, according to the firing, feeding the boiler up when the fire is at its best, and shutting down when it is freshly coaled. The steady and uniform feed is, however, better, because it approaches more nearly to a uniform condition of the boiler, especially on the water side. The position of the water is determined, of course, from the water gage and cocks. It is necessary, of course, that the gage and its connections be clear of any obstruction in order that the height of the water may be properly indicated. To make sure that everything is clear the gage glass and connections are blown through by the "double shut off" method as follows : In Fig. 420, G represents the glass, A the drip cock, B and C the cocks connecting to the stand, and D and E those connecting the stand to the boiler. First, B and E are closed, and A is opened. If steam blows through, it shows that A, G, C, D are clear. Second, C and D are closed and A is opened. If water blows through, it shows that A, B, E are clear. The action of the water in the glass will usually show to an experienced eye whether or not the connections are clear. If the water is lively and follows the rolling of the ship, it is a good indication that the passages are clear. Otherwise it indicates that an obstruction exists which must be sought out without delay. In the meantime the water cocks are relied upon, and in fact many experienced water tenders prefer the indications of the cocks to those of the glass, while they should, in all cases, be freely used as a check on the glass. To those without experience, however, the glass is less apt to be misleading. The indications of the water cocks are sometimes difficult to interpret, because frequently it is not easy to tell whether water or steam is blowing off. With high pressure steam especially, a jet of water issuing at a temperature of 350 de- grees to 400 degrees is instantly surrounded with a shell of vapor formed by the vaporization of part of the jet. Furthermore, if the water in the boiler is in active ebullition near to the surface so that the jet would be drawn from a mixture of steam and water, then on issuing it becomes practically a jet of moist steam. On the other hand if the water is well below the cock so that the 634 PRACTICAL MARINE ENGINEERING jet would be drawn from steam alone or from moist steam, then on issuing it will become dry and usually superheated. It is also a fact, especially with watertube boilers, that due to a kind of lifting action, a cock will often discharge moist steam or a mix- ture of water and steam, even if the water level is somewhat below the mouth of the cock. It is hence readily seen that the indications from the cocks must be interpreted with judgment, and that some experience is necessary in order always to draw correct conclusions from them. It is often difficult to distinguish between an empty glass and one entirely full. In order to make sure, close the cock B, Fig. 420, and slightly open A. If the gage is full of water, the surface will gradually descnd, first coming into view in the top of the glass and then passing out of view at the bottom. If then A is closed and B is slightly opened, the water will rise again in the glass and pass out of view at the top. Blowing off. — Blowing off the boilers to reduce the concentra- tion or density of the water is now rare in good practice. In- stead of reducing density by introducing sea water for feed make up, evaporators are installed for providing fresh water make up, or for short runs additional fresh water is often carried in double bottoms or spare tanks provided for the purpose. In modern practice the purpose of blowing off is (i) to get rid of mud or slush in the bottom of the boiler or in the special mud drums of a watertube boiler, and (2) to get rid of oil and scum at and near the surface of the water. For the former a bottom blow or special mud cock is required, while for the latter the surface blow is used. In ordinary experience on deep sea voyages where evaporators or other fresh water make up are pro- vided, the use of the surface blow is all that is needed to keep the water in good working condition. It must not be forgotten that the use of the blow-off means a direct loss of heat, and hence it should be used with discretion, and no more frequently than is needed for the purpose in view. An idea of the condition of the water in the boiler near the surface may be obtained by drawing off a little water from a cock fitted into the surface blow pipe, or from a gage cock fitted directly to the boiler. The water, being allowed to cool and settle, is then poured into a glass jar, when its condition is readily noted, and the need of using the blow determined. It may be well to speak at this point of the proper method of OPERATION, MANAGEMENT AND REPAIR 635 testing, from the outside, the correct position of a plug cock han- dle for "closed" and for "open." Instances have been known where there was no mark on the head of the plug, and the han- dle becoming bent or being wrongly placed, the cock was left shut when it was supposed to be open, or open when supposed to be shut, with the possibility of most serious consequences, especially in the latter case. A careful examination of the cock, aided if need be by placing the ear to the chamber, will suffice to tell whether or not the cock is open and water or steam passing through. Then the cock being open let it be turned in one direction until it is just closed, and then back in the other direction until it is closed again. Half way between these two positions it will be wide open, and at right angles to the latter position it will be full shut. Taking the Saturation or Testing the Density of the Water. — The density of the water is determined by the use of a hydro- meter or salinometer as it is often termed. Under modern con- ditions where evaporators provide fresh water make up, the density rises but slowly, and it is usually only necessary to ob- serve its value once or twice a day. It is usually not allowed to rise above two or two and one-half on a scale of 32. Disposal of Ashes. — For the disposal of ashes two chief means are in use. According to the older methods they are sent up and disposed of through an ash chute leading overboard, and down the side of the ship to the water, and this method is still extensively used in large and deep ships. In the more modern system they are disposed of from the fireroom direct by means of an ash ejector. In either system it is usually sufficient to disfKJse of the ashes once in a watch, and they are coljected, wet down and either''hdisted in buckets or shoveled direct into the ash hopper usually between 6 and 7 bells. ^^.. ,- Cleamng of Fires. — The routine working of fires spoken of above will suffice to keep them in fairly good condition for sev- eral hours, provided the coal is of fairly good quality. It usually becomes necessary, however, to give to each fire from time to time a more thorough cleaning than is possible in the manner previously referred to. To this end the fire should be taken when partly burned down, but not too far, lest there be nothing left after cleaning on which to build up again. One side may be cleaned first, working the good coal over to the other si4e, 636 PRACTICAL MARINE ENGINEERING separating out the clinker and ashes, and hauling out the latter. Then similarly with the other side, working the good coal over to the side first cleaned and pulling out the clinker and ash. The live coal is then spread over the grates, fired lightly, and so brought up again into regular conditions. In some cases there is so little left after a thorough cleaning that live coal must be borrowed from another furnace to save the fire. Only judgment and ex- perience can determine the best conditions at which to clean a fire so as to insure the minimum loss of heat, and at the same time have enough coal left to nicely build up again. Some engineers prefer to burn the fire almost completely down to the ashes and clinker, and then pull the entire contents of the grate out and start afresh. This method, however, chills the furnace and more seriously interferes with the operation of the boiler, and is not to be recommended. It must, of course, not be forgotten that heat is lost with the clinker and ashes withdrawn, and the general operation should be so conducted as to keep this loss down to the minimum possible. Under usual conditions the fires will need cleaning in this way at intervals of from 12 to 16 hours, or at least once a day. Sweeping Tubes.-^n addition to the cleaning of fires the tubes will require cleaning from time to time, dependent on the character of the coal and other circumstances. With soft coal and moderate draft they will soon become partly filled with soot and ashes, thus choking the draft still further, and preventing the transfer of heat to the water through the metal of the tube. To prepare for sweeping tubes the draft is checked, ashpit doors put on, furnace doors opened and front connection doors raised. Care should be taken to wait until the fire is burned partly down before doing this, so that the circulation of air through the grates may not be shut oiif while the fires are too heavy, thus endangering the ^rate- bars. For cleaning the tubes the ordinary wire tube brush may be used. This consists of a mounting carrying wire bristles and fitted usually with a jointed handle by means of which it is pushed and pulled through the tubes, thus cleaning out the soot and ashes collected there. A more modern method consists in blowing through the tubes with a steam or air jet. The mounting of this appliance consists of a flange or conical ring fitting closely to the end of the tube arid provided with a steam or air nozzle directed along the center of OPERATION, MANAGEMENT AND REPAIR 637 the tube. A handle is provided for holding and guiding the appa- ratus, and steam or air is led to it by means of a flexible hose. By this means the ashes and soot are driven out of the tubes into the combustion chamber. By still another form of apparatus the jet is not directed into the tube but across the front end, pro- ducing a suction, and thus drawing the ashes and soot to ihe front connection and discharging them up the funnel. The operation of sweeping tubes is one that is necessary to maintain the continued efficient operation of the boiler, but it must not be forgotten that it involves a serious disturbance to the draft of the whole battery, that the chilling of the heating surfaces and interruption to the regular routine are hard on the boiler itself, and that hence, it should only be done when neces- sary and then as quickly as possible. Stopping Suddenly. — With everything going along its regu- lar schedule, suppose that the engine is suddenly stopped. The dispositions to be taken will depend on whether the stoppage is momentary or whether it is expected to last for some time. Here again the caution regarding a sudden change in the conditions must be kept in mind. If the stop is but momentary it will probably be sufficient to shut off the draft, close the dampers and put on the feed strong, standing by to ease open the safety valves in case the pressure rises too near the point of blow- ing off. If the stop is to be longer it may be necessary to still further check the fires by putting up the ashpit doors and open- ing the furnace doors, although this latter should only be done as a last re:ort. Caution must be exercised in thus checking the flow of air through the grates lest there be danger of overheating the bars, or even of bringing them down into the ashpit. Of these various steps for checking ,the fires the opening of the furnace doors and the suddea chilling of; the heating surfaces is the most objectionable and- should not; be resorted to unless necessary. As an additional means the fires may be freshly coaled, especially with dampened coal. This will check the formation of steam and provide fuel for bringing them into good condition for the next start. A period of stoppage like this may also be taken advantage of to clean such fires as. may be in need of it. In addition to checking the formation of steam, that which is formed may o^ten be used in a variety of ways. If evapor- 638 PRACTICAL MARINE ENGINEERING ators are provided, it may be turned on to them and thus go toward increasing the store of fresh feed water. The bilge pump may also be put on strong, and if its exhaust is saved there will be no loss of fresh water. In some cases with independent air and circulating pumps a bleeder is provided for taking the steam direct from the main steam pipe to the condenser. Here it is condensed and then sent by the feed pumps back to the boilers, thus avoiding blowing ofif at the safety valves and the loss of fresh water, and allowing the fires to be gradually reduced to the condition desired for the period of stoppage. Here again in all of these operations general principles are often worth more than a multitude of minor directions. These principles are ( i ) Sudden chilling of the boiler heating surfaces must be avoided as far as possible. (2) Fresh water in the form of steam should not be wasted, and (3) Care must be taken not to allow the grate bars to melt down. So far as relates to the general securing of the machinery and gear in the fireroom, the hints given in connection with getting under way will be a sufficient guide in reversing the process. Supplementary Hints Relating to Watertube Boilers. — In watertube b6iler« the circulation is usually more nearly natural than in firetube boilers, and circulating devices are not, there- fore, required. Steam may be raised in such boilers in from twenty minutesto one hour, depending on the type, character of the draft, etc. With this type of boiler it is especially neces- sary that for the best results the firing be light, often and regu- lar, and that th^ fires be kept as nearly as possible in a uniform condition. If is'also necessary that the feed be regular, and the water must be carefully watched, since from the small amount contained, any lack of feed in a given boiler -will be followed by rapid lowering of the level, and by a rapidly increasing likeli- hood of danger to the tubes. In watertube boilers it is especially necessary that ngthing but fresh water be used as feed, and great care must be taken to keep the condenser tight and the fresh water make up ample in quantity. The tubes of watertube boilers become coated with soot and ashes on the outer or fire side, and it is usually a very difficult mat|:er to satisfactorily clean them without the use of a steam jet. Irv iContinUjEd steaming for long periods, it wiil usually be OPERATION, MANAGEMENT AND REPAIR 639 found necessary from time to time to let the fires die down some- what and to use what methods are available for blowing off and dislodging the soot from the tubes. When stopping or standing by, the same general means may be adopted as in firetube boilers. As regards injury through sud- den change of temperature, the watertube boiler is somewhat less liable than the firetube. This is due to the nature of the con- struction, which, especially with curved or built up elements, is much more elastic than in the firetube boilers. It is always bet- ter, however, to avoid sudden temperature changes where possi- ble, and the same principles may be properly applied here as pre- viously discussed in reference to the other type of boiler. Coming Into Port. — When coming into port notice should usually be given some hours in advance, so that the fires may be worked into a condition in accordance with their expected disposition after arrival. If they are to be drawn and the boilers opened up for examination and repairs, they should be allowed to burn down as low as possible so as to use no more fuel than necessary, and to leave as small an amount as possible to finally haul, while at the same time sufficient steam must be maintained to bring the ship safely to her anchorage or dock. If, on the other hand, the fires are to be banked, they should not be allowed to burn so low. It may be recommended to bank fires on the front of the grates, as in such case the air is heated as soon as it enters the furnace and the boiler is kept at a more nearly even temperature than if they are banked at the back of the grate. As the fires are banked they should be cleaned and enough fresh coal put on to hold them in the condition desired. If th^ fires are properly managed there will be little extra steam after the engines are stopped, and this may be readily disposed of by means of the evaporator, bilge pump, bleeder, safety valve, etc. Loss of fresh water at this time is, of course, less objectionable than when on the voyage, and if desired the steam may all be blown off through the safety valves. Many engineers, however, object to using the safety valves and escape pipe for this purpose except as a last resort, and prefer other means as mentioned. In passenger vessels the noise occasioned is usually considered ob- jectionable, though to obviate this a muffler is frequently fitted in the escape pipe. If the boilers are to be opened, fires are allowed to die out or 640 PRACTICAL MARINE ENGINEERING are hauled immediately. If time permits, the former plan is pref- erable, as the change in the condition of the boiler is more gradual. When the fires are finally out, the ashes, soot and clinker are wet down and piled away until they can be disposed of to the ash barge, as few harbor regulations allow the dumping of ashes overboard. In wetting down the fires after they are hauled out on the fireroom floor, or in wetting down ashes at any time, care should be taken not to wet the fronts of the boilers or the mouths of the ashpits. The local chilling will not im- prove the quality of the steel, and the alternate wetting and dry- ing will increase the opportunities for surface corrosion. For the same reason damp ashes should never be piled up in contact with the boiler or furnace plates, as in many instances serious cor- rosion has resulted from a neglect of this precaution. The fires being burned out or hauled, some engineers pro- ceed to blow the boilers down immediately. This plan, however, cannot be recommended and should not be adopted unless the time available for examination and repairs is so short as to make it absolutely necessary. It is far better to let the steam condense and the water gradually cool, and then draw it out by means of a pump, or in some cases run it into the bilge. In this way the boiler cools more gradually and the structure is left in better condition, while on the water side the scale and incrustation will usually be made softer and more easily removed than when the boiler is blown down with steam on. Sec. 92. ENGINE ROOM ROUTINE AND MANAGEMENT [i] Getting Under Way In the engine room, the same as in the fireroom, a general inspection is first in order, more or less detailed and extensive, according to the time the machinery has been out of use, and the degree of acquaintance with. its various features and pecu- liarities. If the engine has been laid up for any length of time, a detailed examination will, of course, be required. It is here assumed, however, that no such general overhauling is needed, and that the machinery is to be supposed in a working condi- tion. A good general idea should first be obtained of the lead of the principal piping systems, and especially of the main and auxiliary steam and feed systems. These lines of piping should OPERATION. MANAGEMENT AND REPAIR 641 be looked over, the location of the valves noted, and where per- missible the valves should be opened or closed to insure their being in working order, and then left in the condition desired for getting up steam. The various parts of the main engine should be looked over so as to insure, so far as an external examination can, that every- thing is in proper working order. The various auxiliaries should be looked over in the same way, and the results of this general examination being satisfac- tory, steps may be taken to test the various parts of the machinery under steam as soon as it is ready. Already in Sec. 91 has been pointed out the importance of trying the feed pumps and getting them into working order as soon as possible, in order to insure the proper supply of feed water to the boiler. Next in order may come the circulating pump, the engine of which is started at moderate speed, the main injec- tion and discharge valves being first opened. In starting all of this auxiliary machinery, proper precautions must, of course, be observed in regard to freeing the steam cylinders of condensed water by means of the relief valves, as noted in Sec. 86 in con- nection with the feed pump. The circulating pump being usually below the level of the water outside the ship, it naturally floods itself so that no trouble should be met with in getting it to take water. Assuming the air pump independent, this may be started next and put at a moderate pace, or sufficient to maintain a vacuum of 15 to 20 inches. The electric light engines, if not in operation from the donkey boiler, should also be looked after and started in due time, as well as any other auxiliary machinery whose operation may be required for getting under way. In case the main engine since the last time used has been subjected to any adjustment or overhauling, it will be well to turn it completely over with the turning engine once or twice in order to make sure that everything is clear and in running condition. In the meantime, while the auxiliaries are being gotten into operation, the steam will have been admitted to the jackets, if there are any, and to the cylinders through the main stop and throttle valves. Here, as noted in Sec. 91, the object in view is to avoid any sudden change in the temperature or heat condi- 642 PRACTICAL MARINE ENGINEERING tion of the machinery. A good method of gradually warming up the engine is to just unseat the main stop and throttle valves, and then with the links in the ahead gear, say, to slowly turn the engine over ahead with the turning engine. This will allow the steam to work its way through the engine, warming up the entire series of cylinders and bringing them practically up to the working temperatures. The water condensed must, of course, be allowed to escape by reopening the relief and drain valves. During chis period the reversing gear should also be warmed up and tried ander steam until it works properly and throws the links smoothly from one side to the other. When the engine has thus become well warmed up, the turning gear should be disconnected and locked out of gear, and immediate preparations made for turning over under steam. At this point the question of lubrication must be borne in mind, and while the regular schedule of oiling, etc., need not be started until the ship is fairly under way, still a moderate provision of oil may be made to the more important bearings, and if the en- gine has been out of use some little time, it will be well to work oil into the principal bearings during the preceding operation of the main engine with the turning gear as suggested above. Before turning over under steam the deck oflEcer should be notified in order that the hawsers securing the ship to the dock may be looked to if necessary, or the presence of anything about the stern which might foul or jam the propeller may be re- ported back to the engine room. Everything being in readiness, the main stop valve is opened slowly to full opening, and steam is turned on the reversing gear. Then the main throttle being still closed the links are thrown back and forth a few times, the passover or starting valves opened, and the throttle opened moderately. If the engine does not start off in one direction the links are thrown into the other gear, and if everything is in the proper condition, the engine will start in one direction or the other after a few see-saws of the links. The hand relief valves are, of course, operated at the same time in order to aid in freeing the cylinders of any water which may collect there, or which may enter with the steam. Often the engine will move a little way, but the high pressure, or one of the other pistons will not pass the center. This is on account of the water in the cylinders, and is especially liable to occur if the engine has not OPERATION. MANAGEMENT AND REPAIR 643 been well warmed up, or if the steam pipe has not been properly dramed. In such case the water must be worked out through the relief and drain valves, the links in the meantime being moved back and forth. In answer to this the piston will see- saw up and down, getting gradually nearer the center, and finally when the water is sufficiently cleared out, passing over and con- tinuing the revolution. As the main engine is thus started the circulating pump and air pump, if independent, should be started up at the increased pace suitable to the amount of steam passing through the engine and into the condenser. After thus running for a few minutes, or until everything seems to be in proper running order, the engine is stopped, word sent to the deck that the engines are ready, and the signal for the regular start is awaited. The object of thus turning over under steam is simply to make sure that everything is free and in working condition. Little, of course, can be told regarding the adjustment of the various bearings, etc., or their liability to heat or pound. If the machinery is new or has undergone any considerable readjust- ment, or has been out of use a long time, it should have a dock trial of some considerable time, in order to determine the various points, and to bring out any defects liable to present themselves in the course of a continuous run. Naturally the time when the ship is to start will be known to the engineer, and these various preparations should be so timed that soon after the final turning over under steam, the signal for the regular start may be expected. Passage of Steam. Through the Engine. — In connection with the operation of a marine engine it will be instructive to note in order the names of the various parts through which the steam passes from the boiler until it returns again as feed water to its starting point. Starting, then, with its formation in the boiler, it traces the following route for the case of an ordinary triple- expansion engine: Dry pipe — Safety valve chamber — Boiler stop valve — Boiler steam pipe — Main steam pipe — Main stop valve — Main throttle valve — High pressure valve chest — Steam ports and passages — High pressure cylinders — Steam passages and ports— Exhaust side of valve — Exhaust passage— Exhaust pipe to intermediate valve chest and cylinder as above for the high pressure— Ex- haust pipe to low pressure valve chest and cylinder as above for 644 PRACTICAL MARINE ENGINEERING the high pressure — Exhaust pipe to condenser — Condenser — Air- pump suction valves — Hot well — Feed pump suction — Induction valves — Feed pump barrel— Discharge valves — Feed pipe — Check- valve — Feed stop valve — Boiler. In addition a separator may appear between the boiler and the engine, and the filter and feed water heater between the feed pump and the boiler. [2I Routine Operation In the routine operation of the main engine and of the other machinery in the engine room, the following are the points requiring chief consideration : (a) The supply of oil and other lubricant in suitable quanti- ties and at proper intervals, or continuously, according to the nature of the oiling gear in use. (b) A constant watch over the general conditions of oper- ation of the machinery in order that any symptom or sign of derangement or disturbance may be noted, and the proper steps taken for its control or removal. The chief points relating to the lubrication have been already discussed. The watch over the general conditions extends to all features and depends to such an extent upon the special circum- stances that only a few general hints can be given. First, regarding the sounds which accompany the operation of the machinery and the part the ear may take in detecting symptoms of disturbance. The operation of the main engine and of the various parts of the machinery individually is ac- companied by more or less plainly marljed sounds or noises or combination of sounds. These in the end tend to combine them- selves into a kind of resultant rumble, click, and rattle, which often remains quite constant in character, and so comes to have a kind of individuality of its own. To a person accustomed to the regular sounds of the engine room, the ear is often a deli- cate means of detecting any departure from the regular routine, and often the first indication of some disturbance will be fur- nished by a change in the character of the sounds produced. In particular, any unusual pound, jar, squeak or rattle should be located as soon as possible, and its cause investigated. In some cases assistance in the detection or location of a pound or knock may be gained by the use of a convenient piece nf rretal, such as a spanner, or bit of pipe, one end being placed OPERATION, MANAGEMENT AND REPAIR 64s to the ear and the other against the cyhndcr, valve chest, or other point nearest to where trouble is suspected. At the same time too much reliance must not be placed on the ear to the neglect of other means of observation. In fact in the hiodern engine room all of the available senses keenly on the alert will be found none too many for the proper watch and care over the machinery in use. The danger of heating, due to insufficient lubrication, poor adjustment or bad condition of bearing, is one which the ear will often aid in detecting, but the chief reliance must be placed on the senses of feeling and of smell. With the necessary skill most of the important bearings may be felt by the hand. Caution must be used, however, so that the hand may not be caught or jammed. This part of an engineer's training is one which can be learned only by observation and cautious trial. If the heating of the bearing passes beyond a moderate elevation of temperature, the oil will become correspondingly heated and will give off a burnt odor, or perhaps will smoke freely, thus showing plainly the existence of trouble. The nose and eye will thus come in as factors in detecting trouble of this character. Small steam leaks at joints, stuffing boxes, etc., will make themselves plainly visible, and should receive such treatment as the circumstances may require, in order that they may be closed up. It must not be forgotten that every steam leak means a loss of both heat and fresh water. The vacuum in the condenser will depend not only on the proper operation of the air pump, but also on the reduction of all possible air leaks which might admit air to the low pressure cylinder during the exhaust, or to the steam side of the conden- ser. All such stuffing boxes, joints, etc., must therefore receive careful attention, especially if the vacuum is not what it shojld be. Water coming over into the cylinders from the boilers pro- duces a crackling or snapping noise, which is readily recognized. The automatic relief valves may, of course, be depended on, or the hand gear may be operated to aid in removing the dis- turbing cause. In stopping momentarily the throttle is closed and the links are run to midgear, no other change being made, and every- thing remaining ready to start again at an instant's notice. In 646 PRACTICAL MARINE ENGINEERING stopping for a known period of time of any considerable dura- tion, means should be taken to stop the flow of oil to the bear- ings by the closure of the feeding valves or the withdrawal of wicks, according to the means in use. If the stop is only tem- porary, and the engines are to be kept in readiness for starting again, the further steps taken will be only such as will serve to bring the machinery into its condition just previous to getting under way. That is, the circulating and air pumps, so far as in- dependent, may be slowed somewhat, while by the aid of the steam jackets, if fitted, and steam which is allowed to flow past the stop and throttle valves, the main engine is kept warmed up and ready for operation at short notice. If the stop is to be of longer duration and the steam is to be shut off the engine, the stop and throttle valves will be closed, the air and circulating pumps shut down, and steam shut off the reversing engine, jackets, etc. The various drain valves and drips will be left open so as to free the machinery, as far as possible, of all the water formed by the gradual condensation of the steam. At the same time the flow of oil to the bearings will be shut off and such measures taken with respect to the oiling gear as the circumstances may require. [3] Minor Emergencies and Troubles The steps to be taken in the event of the more commonly occurring troubles, some of which have been mentioned in the preceding paragraph, will now be briefly considered. ( 1 ) Derangement of the Oiling Gear. — In sightf eed apparatus this is readily detected, and without loss of time and trouble must be located and remedied, the oil in the meantime being supplied to the bearing in question by hand. The trouble in such cases usually arises from a clogging up of some of the pipes or pas- sages, and all such pipes should be put up with union joints so that they may be readily taken down, cleaned and replaced. (2) Hot Bearings. — This is one of the most important of the minor troubles which may arise in the engine room, and one which may lead to serious consequences in case the proper steps for its control are not taken in time. A hot bearing may arise from a variety of causes, among which, the following are the more important: (a) Lack of lubrication. OPERATION, MANAGEMENT AND REPAIR 647 (b) Lubricant too thin so that it will not remain in place in the bearing and sustain the load. (c) Improper adjustment, the amount of clearance between journal and brass being too small. (d) Lack of alinement in the machinery, as a result of which the bearing is excessively severe on certain parts, thus forcing out the lubricant and causing the surface to nip and abrade. (e) Bearing surface not of sufficient area to carry the load or take the work put upon it without an undue rise in tem- perature. This means, of course, either that the design is faulty or that the machinery is worked beyond the loads for which it was intended. (f) Bearing surfaces rough and uneven, due to poor work- manship, or as a result of serious heating on a previous occasion. If the trouble is due to a lack of lubrication simply, and is discovered in time, an abundant supply of oil will be usually sufficient to control the condition and to gradually bring the bearing back to its normal temperature. If, however, the tem- perature rises considerably, the journal may expand more than the bearing brasses, so that the clearance will be decreased and the brasses will pinch the journal, thus introducing a further source of trouble as noted in (c) above. If this is not soon relieved, the metal surfaces will nip and the softer of the two yviW begin to abrade or "cut." This is always the bearing metal, and the resulting condition, in consequence of which the smooth- ness of the surface is destroyed, will tend simply to make matters still worse, to generate more heat, expand the parts still more, perhaps nip the surfaces still more tightly, and so cut the worse, until the bearing metal melts and runs out. The treatment of a heated bearing involves two chief items, viz., the removal of the cause and the restoration of the bearing to its normal condition. The cause may be removed entirely, of course, by stopping the engine, and in an advanced case of trouble, such as just described, this may be necessary. Otherwise it may be reduced by slowing down somewhat, and thus decreasing the amount of work thrown on the bearing. It may further be decreased by easing up the bearing cap and thus increasing the clearance be- tween journal and bearing surface. This, however, can only be 648 PRACTICAL MARINE ENGINEERING done to a slight extent, else trouble will be met with from too great clearance and the consequent pounding. A plentiful supply of oil, or other lubricant, will also aid in decreasing the cause and in restoring matters to their proper condition. A decrease in temperature will also usually aid in removing the cause, and is, furthermore, of course, one of the chief steps in bringing the bearing back to its normal condition. To this end in the extreme case, it may be considered neces- sary to turn a stream of water on the bearing, thus to absorb and carry away the heat, and in many cases full power trials are run with streams of water playing for a considerable part of the time on various parts of the machinery in order to carry of? the heat and so control the temperature. Water, however, is doubt- less used far more than is absolutely necessary, and far more than good engineering would authorize. If sprayed or run from a hose on the bearings, it is almost certain to find its way in and on to the bearing surfaces, where it will prevent action of the lubricant. For this reason its use once begun, it may be neces- sary to continue, simply because the lubricant cannot lubricate in the presence of water. In the best modern practice, provision is made for circulating water through hollow bearing blocks and brasses, and thus in the most effective way the water is able to remove the- heat generated without coming into contact with the bearing surface itself. In case the machinery is not properly lined up, or the bear- ings are of insufficient area, or not in proper condition, only tem- porary relief can be looked for from the various means suggested above, the most effective of which will presumably be the oper- ation of the machinery at a low or moderate power until such time as the needed readjustments, changes or repairs can be effected. To sum up the treatment for a hot bearing, the measures taken may be selected according to judgment and the special circumstances from the following : Lubrication. Easing up bearing caps. Slowing down and consequent reduction of load. Application of water. (3) Pounding. — This condition may arise from several causes, chief among which are the following : OPERATION, MANAGEMENT AND REPAIR 649 (a) Bearing not in proper adjustment, too much clearance being allowed between journal and bearing metal. (b) Lubricant too thin and thus unable to retain its place in the bearing. (c) Valve events not properly adjusted, especially the ex- haust closure and following compression. Furthermore, an engine will often show at dififerent speeds a marked difference in this respect, such diflference being chiefly due to the increasing efifect of the inertia forces with increase in the revolutions. If the trouble arises from the nature of the lubricant in use, a change to a heavier oil may show an improvement. If, however, as is more commonly the case, it is due to faulty ad- justment, either of bearing or valve gear, or both, but little can be done while the engine is in operation, and the first oppor- tunity for overhauling and readjustment must be taken for a study of the conditions, both as regards the bearings themselves, and the possibility of improvement by an adjustment of the compression. If the pounding becomes very severe, it may be- come necessary to slow down the engine and operate under less than the regular or full power until the proper examination and readjustment can be made. (4) Priming or Lifting Water. — This emergency has been more particularly referred to in Sec. 91. In small quantities water produces a crackling or snapping sound in the cylinders, and the automatic relief valves may be allowed to take care of the situation, or if desired, the hand reliefs may be operated as well. If, however, the water comes over in large quantities the engine will slow down and work with an irregular and labored motion, which may be readily recognized as denoting this con- dition. In such case the throttle or main stop valve should be partially closed and the water gotten rid of as quickly as possible by the use of the relief valves. The engine will then operate at the reduced speed permitted by the partially closed valve, pre- sumably without further trouble. If on opening out again the tendency to lift water at full or ordinary power is persistent, the power must be reduced until the trouble is removed and the engine will operate continuously without disturbance of this character. (5) Vacuum Falls. and Becomes Poor While the Condenser 6so PRACTICAL MARINE ENGINEERING Becomes Hot. — Following are the chief causes which may lead to such a condition : (a) Insufficient condensing water from any cause. (b) Division plate in condenser head carried away so that water goes directly from inflow to outflow without going through the tubes. (c) Excessive inflow of steam caused by leakage either past low pressure piston or slide valve, or possibly in the "bleeder" of "silent blow" if such is fitted. (d) Condenser air bound, that is air has collected in upper tubes and prevents the flow of condensing water through them. (6) Vacuum Falls and the Condenser Remains Cool. — In such case the indications are that this condition is due to the presence of air not removed by the air pump, as may be caused by any one or a combination of any of the following : (a) Air pump valves defective. (b) Leak in the condenser, either at the head joints or through a crack or in the exhaust pipe joints. (c) Soda or drain cocks open or leaking. (d) Low pressure piston rod stuffing box leaking air inward during exhaust stroke. (e) With "inside" piston valves on the low pressure cylin- der, leaky valve stem stuffing boxes. (f) Leak or obstruction in the pipe leading to the vacuum gage. (g) Drain cocks or steam cylinders of auxiliary engines left open to atmosphere. Sec. 93. ROUTINE FOR TURBINE PROPELLED VESSELS- PREPARATIONS FOR GETTING UNDER WAY [i] Engine Room and Fireroom Start forced lubrication pumps. Start main air and circulating pump 2j^ hours before time set for getting under way, maintaining from 8 to 10 inches vacuum in the condenser. In starting any pump, first open the drains, then the suction and discharge of the pump, then the exhaust, and, last of all, crack the steam valve to warm up the pump. The steam valve may now be gradually opened and, when the pump is free from water and running well, close the drains. In starting the main circulating pump it must be first jacked over one turn and left OPERATION. MANAGEMENT AND REPAIR 651 in starting position. It may be necessary to put a vacuum on the auxiliary exhaust line before this pump can be started. Open automatic stop valves, main steam line, and drain maneuvering valves, 2 hours before time set for getting under way. In opening the automatic valves care must be exercised to crack the valves in order to warm up the line. As the line becomes hot the valves may be opened full, and when full opening is reached, remove the pins and caps on the end of the valve stems. Turn steam on turbine gland line 2 hours before time set for getting under way. See counter gear oiled and everything clear for turning, i]^ to 2 hours before time set for getting under way. Start jacking rotors, with throttle by-passes open Yz turn, ij4 to 2 hours before time set for getting under way. In case the engines have been standing by for getting under way with the gland steam turned on, it will usually not be neces- sary to jack the engines, as the steam from the glands will furnish sufficient heat to keep the engine warm. Take out jacking gear 45 minutes before time set for getting under way. Take counter reading before turning engines. Inspect oil and water systems i hour before time set for getting under way. , Turn engines, ahead and astern each side, with each throttle, yi hour before time set for getting under way. Report ready after engines have been tried, 34 hour before time set for getting under way. Try steering engine 45 minutes before time set for getting under way. Drain whistle and siren 30 minutes before time set for get- ting under way. Test engine room and fireroom telegraph, etc., 30 minutes before time set for getting under way. Shift auxiliary exhaust to main condenser when started, 2 hours before time set for getting under way. Fire and bilge pump ready 30 minutes before time set for getting under way. Turn steam on vacuum augmentors 10 minutes before time set for getting under way. 652 PRACTICAL MARINE ENGINEERING After getting under way, close turbine drains. Shift to cruising combination, when fitted, as soon as both engines are signalled to go ahead at same speed. Take a set of turbine dummy clearances. Watch carefully all bearings for signs of heating. It is important to note that a cruising combination should not be used until it is certain that the steam pressure is high enough to make the required number of revolutions with the combination it is intended to use. [2] Securing Main Engines After Coming to Anchor Give necessary orders to firerooms about disposition of fires. Close main automatic stop valves. Shut steam ofif turbine glands. Secure anchor and steering engine. Secure forced lubrication pumps and oil cooling pumps about an hour after engines have stopped. Start evaporators to use up extra steam if not already run- ning. Shift auxiliary exhaust to auxiliary condenser shortly before main condenser is secured. Put in jacking gear. Read and record engine counters. Open turbine drains, turbines being jacked to drain points After about two hours, secure main circulating and air pumps. Air pumps are run this length of time in order to draw all vapor and water out of turbines and thus keep them dry in order to prevent internal corrosion. [3] Instructions for Working Fires (Time Firing) The following instructions are typical of those issued where time firing is to be used. The two-number method will be used for working all fur- naces, and it will be as follows ; the boilers having five fire doors each: Forward boiler. 34512 Upper number painted red 12345 Lower numbers brass. After boiler. 25351 Upper numbers painted red. 53124 Lower numbers brass. OPERATION, MANAGEMENT AND REPAIR 653 The system of firing will be as follows : Suppose the intervals to be three (3) minutes. No. I rings up on the time firing annunciator then : (a) Push back and level fires of No. i brass (lower) number and at the same time (b) Coal No. I painted number. In three minutes from the time No. i rang up the firing in- terval annunciator will ring up No. 2, which interval will give plenty of time to work the furnaces marked No. i. " When No. 2 rings (a) Push back and level fires No. 2 (brass numbered) furnace. (b) Coal fires No. 2 (painted number) furnace. This system will continue through all five furnaces of each boiler in numerical order, thus insuring that each fire will be coaled and pushed back at regular intervals, and it will also give enough bright fire to maintain an even steam pressure and consume the smoke to the greatest possible extent. At each firing three shovels of coal will be used as a "charge" no more, no less. The slicing of the fires will be done at the direction of the water tenders when in their opinion it is deemed necessary. It must be remembered also that too much slicing hinders a man in keeping good fires, and is bad for coal economy. This system must be strictly carried out when the firing device is in operation, and by its use each man will be required to do his share of work without being told, giving the water tenders more time for other important work and for obser- vations. Each watch will burn down and clean (when hot) their own fires. While cleaning fires the fire signals will, of course, be dis- regarded for that door. When hoisting or ejecting ashes the signals must also be followed. A short delay in getting ashes out is not to be con- sidered so important as the continuous handling of the fires. It is essential that all men of the fireroom force should be familiar with the system, and they should be required to follow it out to the letter. Where any change in the time of the signals is deemed necessary the chief water tender on watch should report to the engine room the desired time. 654 PRACTICAL MARINE ENGINEERING When coaling, raking or cleaning fires firemen should work quickly and close the furnace doors promptly. When cleaning fires in any boiler the draft should be checked by partly closing the damper and putting on ash pan doors of furnace being cleaned. When it becomes necessary to check the fires it should be done by the use of dampers and ash pan doors ; never by opening or cracking furnace doors. It may, at times, be advisable to carry dampers partly closed when boilers are steaming easiljf, Water tenders should regulate the feed so as to keep the water at from one to three inches from the bottom of the glass, and should determine what valve opening will maintain this level. The practice of opening the valve, allowing the water to rise high in the glass, and then closing the valve is wrong. The feed should be continuous and regular. All conditions of varying demand for steam, when there are many and frequent changes of speed, cannot be met by any system or rules. In such cases regular firing is not practicable, but whenever abandoned for sufficient cause the system should be taken up again as soon as possible. One of the principal sources of inefficiency in firing is the leakage of air through boiler casings and a too great opening of furnace doors. Water tenders should keep a vigilant lookout for leaks around boiler casings and have all possible leaks stopped up. A too great opening of dampers when steaming easily under natural draft is often a source of waste, since too much air is put into the boiler. The damper should be regulated to suit the rate of combustion. Care must be exercised that dead boilers connected with the funnel in use are kept shut tight on fire side and that their damp- ers are securely closed. [4] Additional Notes on Firing When using slice bar run it along grates, but do not break up fires. Do not break up fires with hoe. Only level oflf and fill air holes. Remove clinkers as soon as noticed and cover bare spot with live coal. Keep ashpit doors on top notch of pawl when open where OPERATION, MANAGEMENT AND REPAIR 655 automatically closing doors are used. Do not put fire tools or anything in ash pans that would prevent doors from closing in an emergency. ' ' Clean fires in one boiler at a time. Pump a little more water m than usual, and close dampers during whole operation. Keep other fires well built up so that steam pressure will not fall. Keep fires pushed back from furnace doors. There should be no fire on dead plate at any time, nor resting against cheek plates. Regulate steam pressure by use of dampers in preference to ashpit doors. At end of watch leave good round of coal on floor plates for relief. Blow through all gage glasses and use try cocks once an hour. Pump firerooms bilge dry each watch. Keep strainers clear. Blow down and sweep tubes only as directed. If draft is poor, request deck officer of the watch to have ventilators trimmed. Keep accurate tally of coal or oil burnt. [5] Instructions for Burning Oil Fuel These instructions apply to combination oil and coal burn- ing boilers using Schutte & Koerting, Peabody or Bureau of Steam Engineering, Navy Department burners (mechanical atomizers). One of the best indications of the proper degree of com- bustion of oil is, as in the case of coal, the smoke made. Ex- perience has shown the following facts to be proved : Insufficient air gives a thick, black, oily smoke. Too much air gives a thick, white, oily smoke. When the air is just sufficient the smoke is not noticeable. Experience has further shown that proper mixture of air and oil cannot be obtained by using too large burner tips. It has been found that one millimeter tip burners give the best atomiza- tion, and if an increase in the amount of oil burned is desired the number of burners should be increased, and not t\\e size of the tips. Where oil is being burned alone and in a furnace properly proportioned for combustion, the size of tip used can be in- creased very considerably above this size and efficient atomization and combustion be obtained. 6s6 PRACTICAL MARINE ENGINEERING With existing installations on board United States naval ves- sels, the following method of burning oil has been found to be the most satisfactory. Keep a bed of clinkers over the entire grate, about 8 to 12 inches thick. About the center of the grate keep a ridge of clinkers and ashes high enough for the flames "from burners to strike. Watch the grate carefully and keep all holes in the clinker bed filled up with coal. Keep all openings in the furnace, ash pan doors, furnace doors, etc., closed, except the opening immediately surrounding the burners. Watch the smoke from time to time. If black and thick, speed up the blowers ; if white and thick, slow down the blowers until a sufficient amount of air is being supplied and no more, and no smoke can be seen. A further check on the proper degree of combustion may be obtained by watching the flames of the burners. If short and white, the combustion is good; if long and yellowish, the com- bustion is poor. Officers in charge of steaming firerooms should keep all these facts in mind and endeavor to burn oil as economi- cally as possible. The following instructions are those used in the naval service and can, as far as possible, be applied in the merchant service to advantage. [6] Preparations for Getting Under Way in the Firerooms (Watertube Boilers) Before lighting fires examine boiler for water level; open air cock, try cock and gage glass cocks and valves. Make cer- tain that valve and pipe leading to pressure gage are open and clear. See that surface and bottom blow valves are shut. See that proper firing tools are at hand; shovels, hoes, slice bars, ash wetting hose, etc. Find out from what bunker coal may be used, and that it is opened and that coal buckets are handy. Examine grate bars and brick work; see that dampers are open. If wood or loose paper is available, use for covering grate bars, on top of which spread a layer of coal about 6 inches deep. Orders being received to "light fires," do so, using live coal from other steaming boilers burning coal. Care must be taken until green coal is ignited ; then regulate fires with dampers. OPERATION, MANAGEMENT AND REPAIR 6:7 Steam should form on a Babcock & Wilcox boiler one hour after fires are lighted. If possible, another hour should be used in getting steam pressure up to blowing-oflf point. When steam is formed air and pressure gage cocks will be closed, main stop valve opened full and closed one or two spokes of its handwheel. As steam pressure rises to 20 pounds and upward, all new gaskets and joints will be examined and set up on, boiler looked over for possible leaks, try cocks and gage glasses blown through. Loose coal that has fallen through grate bars should be raked out of, and usually a little sea water be put into ash pits. As pressure nears blowing-ofF point safety valve lifting gear should be tested, if circumstances will allow it, by raising valves ; forced draft blowers, made ready for use, oiled and turned over, gage glass lamps seen in order. Let steam come up to blowing- off point, note at what pressure safety valve lifts, then stop firing, close dampers and check fires. When connecting boilers to steam line, great care must be taken not to open the communicating or "feeder" valve quickly. This is the valve on the boiler steam pipe next to the main line of steam pipe. This valve will be slowly unseated and the pressure in boiler and steam line allowed to equalize. This can be done by consulting boiler and line pressure gages. The man handling this valve should always be provided with a wrench, so that the feeder valve can be promptly shut, if found necessary to do so. From 3 to 5 minutes should be given to equalizing. The feeder valve can then be opened full, but not jammed open. The feed check and stop valve should be properly regulated to give the feed water required, and carefully examined to see that neither of these valves is closed off or blanked and that the feed pump is in working order. Care should also be taken that two or more boilers do not reach the connecting point at the same time. An interval of from 10 to 20 minutes should be allowed to avoid confusion and possible accident. All coal placed on floor plates from bunkers should be care- fully measured in buckets and a careful record kept of the num- ber of buckets taken from each bunker. [7] Routine for Getting Under Way The following is a set of instructions in force on a large re- ciprocating engined vessel fitted for forced lubrication : 6s8 PRACTICAL MARINE ENGINEERING Four and one-half hours before engines are to be ready Hght fires in one extra boiler. (Only to be done if only one boiler is in use for auxiliary port purposes.) Three hours before time of getting under way : (a) Steaming watch goes on duty. (b) Drain down boilers to be used, to steaming level. (c) Prime furnaces. (d) Light fires, using fireroom auxiliary boilers. (e) See air cocks and gage cocks open on all boilers to be lighted. (f) See all gage glasses in good condition. (g) Inspect to see that all sighting holes into furnaces and tube nests have plates on. (h) Inspect to see that all double bottoms are closed and manhole plates dogged down. (i) Blow out sea chests of main condensers with steam to clear out marine growth. Two hours and one-half before time of getting underway : (o) Connect additional boiler first lighted. (b) Open by-pass valves to main steam line. (c) Turn steam on cylinder jackets. (d) Start main air and circulating pumps. (e) Turn exhaust into main condensers. (/) Cut out auxiliary condensers. (g) Shut down evaporators. Two hours before time of getting under way : (a) Test out water service. (b) Warm up and test out additional main feed pump. (c) Warm up an oil service pump in each engine room and test out oil service. (d) Start additional hotwell pump. (e) Warm up one auxiliary feed pump. One and one-half hours before time of getting under way: (a) Have oiler stand by steering engine. (b) See exhaust open and turn steam on steering engine. (c) Lift safety valves of boikrs by hand. One hour before time of getting under way: (a) Test out gage cocks in all boilers. (b) See exhaust valves on anchor engine line open. (c) Have man on watch in evaporator room stand by to start evaporators. OPERATION, MANAGEMENT AND REPAIR 6S9 When steam pressure in main steam line has risen to point where main and auxiliary steam pressures are equalized. Open feeder valves in steaming firerooms and close by-pass. As pressure in boilers newly lighted rises : (a) Inspect bottom blows and see that they are tight. (b) Regulate by use of dampers and ash pit doors so that pressure in boilers comes up one at a time. (c) Allow each boiler to lift safety valve by steam. (d) Connect boilers, one at a time, cracking boiler stop valve until pressure has equalized between boiler and main steam line, then open stop wide. Three-quarters of an hour before time for getting under way : (c) See that all engine room annunciators, telegraphs, voice tubes and bells are tested from the bridge. (b) Set links at full gear. One-half hour before time for getting under way: (a) Get permission from deck to try out main engines. (b) Start lubricating oil pumps. (c) Try out main engines. (d) See pressure on fire main. As soon as all boilers are connected : (a) Start additional main feed pump. (b) Start other feed heater. (c) Start evaporators. (rf)- Report ready to chief engineer. (e) Report ready to the deck. While warming up main engines see that cylinder drains are open at all tin^s and frequently move the main steam valves by use of the reversing lever. The evaporators should be started as soon as sufficient boilers are connected. [8] Routine for Coming to Anchor Two hours before time of anchoring: (a) Deck should notify the engineer officer of the watch. (b) Clean ash pits and eject all ashes. (c) Find out what boilers are to be used for auxiliary pur- poses. One-half hour before time of anchoring: (a) See that exhaust to anchor engine is open. (b) Turn steam on anchor engine. 66o PRATTICAL MARINE ENGINEERING (c) Start pump on fire main. {d) Take extra feed to bring level in feed tanks above center of upper gage glass, {e) Run links out to full gear. (/) Shut steam off low pressure piston rod steam seal packing. ig) Swab all piston rods with vaseline. (ft) Find out which engine room auxiliaries are to be kept in operation. (z) Notify dynamo room to have sufficient generators run- ning for power on cranes. (;') Burn down fires in boilers to be disconnected, taking care that full pressure of steam is kept. Fifteen minutes before time of anchoring: (a) Notify chief engineer. (&) Have men detailed to stand by annunciators and cylin- der drains. (c) Have men stand by evaporators. When anchored : (a) Notify firerooms that anchor has been let go. {b) Start evaporators. When word has come to secure: (a) Shut down lubricating oil pumps. {b) Shut down water service. (c) Let fires die down in boilers to be disconnected. (rf) Transfer all coal on floor plates to fireroom containing auxiliary boilers. {e) Start auxiliary air and circulating pump of auxiliary condenser to be used. (/) Slow down main feed pump. When fires in boilers have burned down enough to handle : {a) Fill boilers to within an inch of top of glasses. (&) Close feeder valves to main steam line. (c) Relieve pressure on main steam line by by-passing steam line and separator traps. {d) Watch main steam gage. The pressure will rise, but if it does not exceed five pounds in five minutes after draining line, shut down main condensers and start 'auxiliary conden- sers. If pressure rises, set up tighter on feeder valves. {e) Shut down spare main feed pump, spare hotwell pump and spare feed heater. (/) When fires have died down in boilers to such an extent OPERATION, MANAGEMENT AND REPAIR 66i that steam can be held, disconnect these boilers. Leave ash pit doors on and close up boilers. Fires are never to be hauled till dead, except in case of accident. (g) Bank fire well up against water leg nipples. (h) Clean up engine and firerooms and put away tools and firing implements. (t) Dismiss steaming watch and set auxiliary watch. [9] Care and Operation (a) Routine Orders for Engine Room in Port — Be careful to secure pumps, air compressors, etc., when they are no longer needed. Clean engine room bilges each week on day assigned. Allow no one in engine rooms or firerooms from 9 P. M. to 5 A. M. except men on watch and those on duty. No smoking in engine room hatches. Men will be kept out of hatches except those detailed there for cleaning stations. Keep all unnecessary lights turned out at night. In general, run evaporators on ship's tanks from 8 A. M. until they are full, then shift below to reserve feed tanks for the night. This will avoid overflowing ship's tanks during the night. Jack, daily, auxiliaries not in use. The oiler on watch should always know who are the officer and chief petty officers on duty. Their names should be entered on the auxiliary watch list or condition blank kept at engine room log desk. In case of any accident or derangement the officer and chief petty officers on duty will be informed. (b) Special Orders for Operation Machinery, Engine Room. General — The vacuum should be kept as high as possible in main condenser, but not by undue speeding up of main air pump. Run circulating pump so as to have about 100 degrees F. overboard discharge. Great care should be taken against mixture of salt water with the oil service at such places as the thrust bearing. A careful watch should be kept against loss of oil, particularly at the thrusts. Clean bilge and oil strainers every watch. Keep from 5 to 15 pounds (special direction on each vessel) back pressure on auxiliary exhaust line. If line fills with water, 662 PRACTICAL MARINE ENGINEERING use drains or lower back pressure occasionally to clear line of water. Every efifort should be made to keep feed temperature as high as possible. Keep about 5 to 10 pounds oil pressure on bearings fitted with forced lubrication. A somewhat higher pressure may be neces- sary at pumps or in oil lines^ but a high oil pressure is conducive to waste of oil. (c) Turbines — Have all throttles, especially backing throt- tles, warmed up when coming to anchor. Take turbine clearances regularly, and especially after a combination of turbines has been changed. Keep careful watch on thrust bearings whenever a change of speed or shift of combination is likely to cause considerable load on thrust. Keep gland steam carefully adjusted so as to avoid excessive leaks of steam into engine room and air leaks into turbines. (rf) Reciprocating Engines — Do not swab piston rods ex- cept when ordered and in accordance with special directions. Run cut-offs out full before getting under way or coming to anchor. Test reversing gear before anchoring. {e) Engine Room Aids — On Watch — The officer on watch is usually at the desk in the starboard engine room, and near by should be found the following : Port and sea routine (preferably in a bulletin board). Book of routine orders. Morning order book (contains for the night and following morning orders additional to the routine and routine orders). Muster lists of steaming, sections, auxiliary watch, etc. Tables of feed water in double bottoms, per inch, as sounded. Condition blanks, showing what machinery is in operation, etc. Booklet of skeleton pipe plans (in the desk). Table showing heaters and pantries on each heating circuit. Counters, tachometers, revolution indicators, clinometers, rudder indicator and time-firing device are installed near oper- ating station. Steaming Data Table. This consists of a table giving speeds, corresponding revolutions for full, standard, 2/3 and 1/3 speed, pressures and valve setting or turbine combination; fuel required and boiler power required. Other data mav also OPERATION, MANAGEMENT AND REPAIR 663 be added, such as air pressures, time firing intervals, feed pumps required, etc. This is useful in determining immediately what changes are needed for modifications in speed and avoids con- fusion and inaccuracy on this point. A copy of this table should be on the bridge for the information of the officer of the deck watch. A copy of speed and corresponding revolutions is sometimes placed on a cylinder in a case with arrangements for turning it, so that the particular speed required can be turned to the opening. It is also found useful to have a clip upon which is placed a slip of paper on which appear the standard speed and revolu- tions called for. Boiler Room. — Run auxiliaries at least once a week by steam. Clean fireroom bilges every week on day assigned. Obtain permission from the deck to blow soot from tubes or eject ashes. Keep unnecessary lights turned out. Keep bilges pumped dry. Keep fireroom floor plates cleared up. Allow no one in firerooms from 9 P. M. to 5 A. M., except men on watch or duty. Water tender on duty should inform officer on duty when- ever a bunker runs empty and obtain instructions about bunker to be opened. Water tender on duty should inform officer on duty and offi- cer in charge of station (or petty officer of sub-station) whenever any derangement occurs to machinery or boilers. [10] Work in Dry Dock While in dry dock, all openings in hull below water line should be closed at end of working hours. All sea valves should be removed, examined and ground in if necessary. Sea chests should be examined for corrosion, and cleaned out. Bolts and rivets securing sea chests should be carefully ex- amined for corrosion and should be tapped with hammer to see if they have become brittle. 664 PRACTICAL MARINE ENGINEERING Outboard strainers should be cleaned and bolts and niits securing them should be carefully inspected. Valve stems of sea valves should be inspected for corrosion and condition of thread noted and any stems in bad condition be renewed. Zincs should be examined and renewed if necessary. Stufifing boxes should be repacked. All bolts, nuts and joints of sea chests and valve chests should be carefully inspected. Before entering dock have spare protective zincs ready. Make out a detail for work in dock on the following lines: Each station should take care of its own valves and other work. Extra machinists on auxiliary station should be assigned to engine room. Select good men for helpers for each machinist. Detail men for any other special work, such as cleaning propellers. When flooding dock have necessary floor plates up so that all valves may easily be seen. Have a man standing by each valve, who should report any leak discovered. The officers should inspect the valves they overhauled while dock is being flooded. I. Stern Tube Stuffing Boxes. — Packing should be inspected and renewed if necessary. 2. Propellers. — Inspect blades to see if bent or injured in any way. Smooth blades as much as possible. Examine studs and nuts securing blades to hub. Examine nut on end of shaft. Measure amount shaft is down. Remove plug from coupling casing and see that casing is filled with tallow. Before docking see that there are a sufficient number of spare zincs on hand. Keep a record of work to be done in dock. When in dock make a note of work which will probably be necessary at next docking. Sec. 94. EMERGENCIES AND CASUALTIES (i) Foaming and Priming.— These terms refer to a dis- turbed condition of the water in the boiler, of such a nature that OPERATION, MANAGEMENT AND REPAIR 665 the water level is more or less uncertain in location, and the steam space is partially filled with foam or a mixture of foam and water. In severe cases of foaming, steam seems to be given off from almost the entire mass of water in the boiler, causing it to rise bodily as foam and water and fill the whole steam and water space, thence entering the steam pipe and passing on to the engine. In other cases the water seems occasionally to rise in gulps, nearly unmixed with steam, and entering the steam pipe pass on to the engine. The terms foaming and priming are often used as meaning practically the same thing. Where a difference is implied, foaming is understood to apply more especially to the uplifting of the mixed steam and water as foam, while prim- ing may refer more particularly to the lifting of water as such, and its passage over into the engine. There is, however, no clear line of distinction between the two kinds of disturbances, and there are all grades intermediate between the extremes. Foaming may be due to the presence of certain forms of oil or grease, or to the excess of soda used for scale prevention, or to other impurities in the water, or to the demand for steam too large in proportion to the steam space in the boilers or, in the case of watertube boilers, to a salting up of the feed water. A sudden change in the character of the feed water may also produce foaming. In former days when jet condensers were in common use, boilers were liable to foam in passing from sea water to fresh water, especially if the latter was muddy, and again in passing from fresh water back to sea water. In modern practice foaming is due either to the presence of oil, to the ex- treme demand for steam from the boiler or to salting up of the feed. In the former case the oil must be removed from the boiler by a free use of the surface blow, and kept out by a proper filter. In the latter case the engine must be slowed and the demand for steam reduced to an amount which the boiler can supply without the danger of such disturbance. As a result of foaming the engine slows down, power and speed are lost, while due to the possible inability of the relief valves to handle all of the water coming into the cylinders, there may be serious danger of breakdown. There is also danger to the boiler in foaming, because the water level cannot be known with certainty, and plates or tubes may become overheated, with danger of collapse and rupture. The tendency to foam is, there- 666 PRACTICAL MARINE ENGINEERING fore, a symptom of serious import, and no steps should be neg- lected to discover and, if possible, to remove the cause. (2) Feed Pump. — In modern practice an auxiliary feed pump is always provided except perhaps in very small craft. If then the main feed pump refuses to work, the auxiliary pump must be brought into use while the otlier is under examination. The chief causes which may disturb the operation of a feed pump are the following: (a) Jamming of check valve or other closure in the delivery pipe. (b) Water in the steam cylinder. (c) Derangement or sticking of the steam valves. (d) Jamming or sticking of the water or steam plunger in its cylinder. In addition to these causes which may affect or prevent the motion of the pump, the following causes may prevent it from throwing water into the boiler, even though its movement may be entirely regular: (e) Split in the feed pipe, or valve open, allowing the es- cape of the water at some unexpected point. (/) Excessive wear of water plunger. (g) Split or leak admitting air on the suction side or into the suction pipe. (h) An excessively high temperature of the feed water. (i) Derangement of the suction or discharge valves. To make sure that the delivery pipe is free, one or more feed checks and the air cock on the pump may be opened. If there is no movement of the pump or no discharge from the cock it may be concluded that the trouble is located elsewhere. The drain valves in the steam cylinder should then be blown out freely, and if there is still no inclination to start, the trouble is presumably with the valve gear. A fresh supply of oil should be admitted to the valve chest, and an attempt may be made to work the tappets or other valve mechanism by hand. In many cases this will suffice to start the pump off at its regular gait. If it does not, the chances are that the trouble is more serious, involving the stopping up or clog- ging of some of the auxiliary ports or passages, or the sticking, jamming or excessive wear of some part of the valve gear. A removal of the bonnets and complete overhaul can alone lead to a discovery of the difficulty in such cases. OPERATION. MANAGEMENT AND REPAIR 6&7 The jamming or rusting of the steam or water pUtngers in their cylinders could only result from long disuse and gross neglect, and can hardly be considered as of likely occurrence in routine work. If the feed pump is worjcing properly and throwing water into the boiler, the chamber of the check valve will be relatively cool, there will be a click as the valve rises and falls, the air cock at the pump will show a stream, and the water will rise in the boiler gage glass. At the same time an experienced eye and ear will detect by the manner of the pump, by the way it moves and by the character of the sounds, whether or not it is throwing water. If then the pump works, but does not seem to be throw- ing water, we must have resources to causes such as those men- tioned in (e)-(i). There are here two chief questions to be answered. First, is the pump getting water? and second, if it is, where is it going? The air cock will usually serve to answer the first question. If water appears here, and if the pump shows by its action that it is handling water, it is evident that there must be escape at some unexpected point. The feed pipe must then be carefully ex- amined for leaks, and all valves or connections leading to or from it should be examined to make sure that the water is not escap- ing in some such way. In one case the main feed pipe was fitted with a small branch leading to the forward tank. This branch was closed oflf from the feed pipe by a globe valve. Due to the ignorance or carelessness of some attendant, this valve was jammed wide open instead of being jammed hard shut. At low or moderate pressure the feed pump would throw enough water to feed the boiler in spite of this leak. The trouble was, there- fore, not discovered until a full power run being started, the de- mand for water was greater and the leakage as well, so that the boiler was soon short of water, and the run was lost. If no trouble is found in the feed pipe, the difficulty may be sought in a very loosely fitting or badly worn water plunger. Such a plunger will discharge water into the air or even against a low boiler pressure, but may not be able to force it against the regular pressure in the boiler. If from the evidence of the air cock and general behavior of the pump it is evident that no water is being handled, the suction pipe and plunger rod packing should be examined for air leaks. 668 PRACTICAL MARINE ENGINEERING Where there is some considerable lift from the hot well to the feed pump, an unusually high temperature of feed water, on account of the vapor formed, will sometimes prevent the pump from taking water. In good practice, of course, the hotwell is above, or at least not below the feed pump, so that this difficulty is not likely to arise. If such should prove to be the troubles the feed water must be cooled and the difficulty will be removed. If none of these causes seems to explain the failure to draw or discharge water, then the trouble is probably to be found in the suction or discharge valves, and the necessary bonnets or covers must be removed to allow of examination. In any search for the cause of the trouble in the feed pump, the details may, of course, be modified according to the circum- stances, and the above suggestions are more especially intended to illustrate the principle that in such a search the trouble has often to be found by a continued elimination of one thing after another, taking those which are most readily examined, and thus localizing the difficulty as quickly and as readily as possible. (3) Check Valve Jammed. — If the feed pump seems to be in proper condition except that it slows down and stops when out- lets excepting a particular check valve are closed, if furthermore the check valve chamber is hot, there is no click, and the water does not rise in the glass, the probabilities are that the check valve is jammed on its seat. In former years this was sometimes due to unequal expansion of the valve and seat, and nipping of the former by the latter. In modern practice with good design and an angle of valve seat not steeper than 45 degrees, such an oc- currence is very rare. The valve may also become jammed by the bending or other derangement of the stem or wing guides, or by the lodging of some foreign body within the chamber. If the trouble is due simply to unequal expansion, the usual treat- ment is to wrap the valve chamber in waste or cloths, and then to pour on cool water, thus reducing the temperature. At the same time the chamber may be tapped near the valve seat with a hammer or bar. In any ordinary case of sticking due to unequal expansion the result will be to free the valve from its seat. If this does not avail, then the stop valve between the check valve and boiler must be closed and the check valve cover removed, so as to allow an examination of the interior. In good modern practice at least two check valves, main and auxiliary, are pro- OPERATION, MANAGEMENT AND REPAIR 669 vided for each boiler, so that there should be no danger of low water. If, however, only one check is provided, or if there is any question of shortness of water while the necessary repairs are being made, the steam stop valve should be closed to stop the draft of steam and the usual' precautions taken when stopping suddenly. (See [2] above.) (4) Bursting of Water Gage Glass. — This occurrence is by no means uncommon, and under ordinary circumstances is of relatively small importance. With the type of gage glass fitting having self-closing valves the flow of water and steam is auto- matically shut off and the new glass is readily put in. Without such provision the shut-off valves must be shielded from the discharge in the manner most readily effective, and then quickly closed. In setting a new gage glass care should be taken to see that the fittings are well lined up, so that when screwed down there will be no bending strain on the glass. If any pronounced strain is thus set up on the glass by the fitting, it will be almost sure to break in a short time. The packing rings should also be screwed down no tighter than barely sufficient to keep the joint tight. In order to insure against a possible blocking up of the steam and water passages to the gage, the shut-off valves should be opened to their greatest extent. (5) Lozu Water. — The occurrence of low water or the ab- sence of water from the gage glass is one of the most serious emergencies which can arise in the fireroom. Immediate action is called for, and the most serious consequences may result from a mistake, or indeed may result in spite of whatever may be done. If there is reason to believe that the water has but just dis- appeared from the glass and the lower gage cock gives indica- tions of water or of very moist steam, it may be fairly assumed that the level of the water is not below the tubes or combus- tion chamber tops, and in such case there will be no immediate danger of overheating or collapse, at least so far as the level of the water is concerned. The "feed may, therefore, be put on strong without hesitation, and if the diagnosis has been correct the water will soon reappear in the glass and the incident is at an end. It may be considered prudent, however, to check at the same time the draft of steam from the boiler, and to deaden the fires tp some extent by some of the methods referred to below, 670 PRACTICAL MARINE ENGINEERING When the water reappears the boiler can then be put on its regular work as before. In the more serious case when the location of the water is quite unknown and the gage cocks and glass give no indica- tions, there is some diversity of opinion as to the best procedure. The chief point of difference relates to the propriety of imme- diately putting on a strong feed. It has been claimed that if the plates were red hot, so much steam would be suddenly gen- erated as to rapidly increase the pressure, and burst the boiler. On the other hand, it has been pointed out that the amount of steam which can be thus formed is in reality comparatively small, and that its formation cannot be instantaneous, nor even especially rapid, since its formation will extend over the period while the water is rising over the heated surfaces. In no way then could any great amount of steam be generated with especial rapidity, and it is hard to see how its formation could take place more rapidly than would be provided for by the natural outflow to the engine, and by the safety valve, if need arose. To obtain some deflnite information on these points, experiments were car- ried out by a steam boiler insurance company some few years ago, in which the plan of putting in cold feed upon overheated plates was followed. The boiler could not be burst by the operation, and no very pronounced elevation of pressure was produced. So far as the results of these experiments went, it would seem to be safe to put on the feed immediately in such an emergency as is now being discussed. This conclusion seems also to be borne out by- the results of such practical experience as is obtainable. There are, however, differences of opinion on this point, and while some would follow this plan in such a case, it should not be denied that many good authorities would consider it unwise, at least in the earliest stages of the measures, to be taken. Aside- from getting the feed into the boiler as soon as pru- dence will; permit, the other great point is to deaden the fire. If the heating surfaces have not collapsed when the condition is discovered, it is hardly likely that, the plates can be at more than a very dull red, and if the supply of heat can be effectually checked, further trouble may be averted. To this end a plan often followed, especially in former years, was to haul the fires. This, however, seems very unwise indeed. While being hauled the fires will burn up all the more OPERATION, MANAGEMENT AND REPAIR 671 fiercely, and for a few moments the heat supply will be in- creased rather than decreased. Instead of hauling directly, some engineers prefer to have the fires dumped into the ash pits by dislodging a few grate bars, and then to haul from there. This plan seems but little better than the other, and in any event the immediate result will be to increase the amount of heat given ofif at the very time when it should be decreased. A far better plan seems to be to deaden the fire with either moist ashes or coal. If a pile of wet ashes is at hand they should be thrown immediately on the fire, and will be found a most effective means of deadening the burning coals. In default of wet ashes, wet or even dry coal may be thrown on and the fire simply smothered. At the same time the dampers should be put up and furnace doors left open, thus checking all draft and stopping the formation of heat. As between these two operations, the deadening of the fire and the getting in of feed water, there is no question that the deadening of the fire is of the more immediate importance, and should be attended to first, because if will produce the most im- mediate effect over the whole heating surface, and will serve most effectually to rapidly check the further heating of the plates. Putting in the feed water will then complete the cooling, but the direct operation is slower, and more local in its influence, and is therefore of relatively less importance. In all such emergencies much, of course, will depend on the special circumstances, but if the two principles be kept in view that the fire must be deadened and the water restored, the details may be left to good engineering judgment to execute. After the water has again appeared in the glass, and if no ill effects seem to have resulted to the boiler, the fire may be again gotten into condition and the boiler put on its regular routine. If, however, there be any doubt whatever regarding the possible results to the boiler, no chances should be taken, but the boiler should be disconnected from the others, the safety valve raised and the steam blown down, while, the fires should be hauled or allowed to die out and the boiler allowed to cool down. It should then be carefully examined for symptoms of distress or collapse, and if any such are found they must receive proper attention before the boiler is again set to work. Probably the best rule to follow is, if there is any doubt 672 PRACTICAL MARINE ENGINEERING as to the length of time the water has been out of sight, deaden the fires with ashes, close steam stop valve, close damper and ash pan doors and allow fires to die out. (6) Collapse of Furnace Crowfis or Combustion Chamber Plates. — The collapse of a part of the heating surface is due either to an overheating of the plates or tubes, or to a gross error in the design. The latter is not liable to occur. Overheating may result from either low water, or from a coating of scale or of oil and scale on the water side. In the former case with no water to absorb the heat the natural result is an overheating of the plate until it becomes red hot, followed by its collapse and rupture. When the overheating is due to the presence of a coat- ing of scale, the gradual bulge or start toward a collapse may result in cracking off the coating and in letting in the water to the plate. This will cool the metal, restore its strength, and thus put an end to the operation. In some cases when the covering is a mixture of scale and oil, the overheating of the plate will result in burning off or volatilizing the oil, leaving the scale as a fine powdery deposit. This readily admits the water to the plate, and thus the metal may be cooled and restored in strength, and further bulging prevented. This nice adjustment of heating, burning or crack- ing bff, cooling and re-strengthening before final rupture can hap- pen, does not, however, always occur. Before the re-cooling is effected rupture only too often results, and the contents of the boiler are more or less completely emptied into the fireroom, with consequences always severe and sometimes fatal. If it is discovered that the furnace crowns have come down, but without final rupture, or if any portion of the heating sur- face has suffered collapse or bulging, but without final rupture, it may be assumed that the overheating was due to scale or oil, and that the change of form or the overheating has resulted in getting rid of the coating, and in readmitting the water to the plate. So that if rupture has not yet occurred, it is probable that the plate is safe for the time being, and in such case the fire may be first deadened and then hauled, the boiler shut off from the others and allowed to cool down, and then examined as to the nature and extent of the injury sustained. (7) Collapse and Rupture of Furnace Crowns or Combus- tion Chamber Plates. — In the event of rupture following upon OPERATION, MANAGEMENT AND REPAIR 673 collapse, the chief thought after the safety of human life must be for the remaining boilers while the fireroom is in such condition that it cannot be entered. The general nature of the steps which may be taken in such case are discussed in the following section, and while naturally judgment must be depended on for many details, it is readily seen that the two main points are as follows : (a) To isolate the injured boiler. (i) To safeguard the remaining boilers from injury due to low water. (8) Serious Leakage in Boiler Tubes. — A serious leak may suddenly develop in one or more of the tubes. A split in the metal, a collapse due to overheating, or perforation due to deep pitting or general corrosion, may give rise to such an occurence. If the hole or holes are not too large, the immediate consequence will not extend beyond a more or less complete filling of the fire side of the boiler with water and steam, and a more or less pronounced checking or deadening of the fire. In such case the feed should be looked after to see that the water does not get low in the boiler, while preparations are made for plugging the tubes. For this purpose a tube stopper or plug is used, of which there are many varieties. A standard type of stopper consists of two heads or tapered plugs which make a joint within or against the ends of the tube, and are held in place by a rod run- ning through the tube, threaded at the ends and provided with nuts for holding them up to their position against the ends of the tube. To fit this stopper it is necessary to enter the combustion chamber to adjust the back end, but once properly fitted, it may be depended upon to fulfill its purpose. There are also special forms of tube stoppers which may be inserted and adjusted from the front end only. It is more difficult to make a tight joint with the latter than with the former stopper, but they can be fitted without drawing the fire, and therefore in an emergency may prove of great value. Plugs of soft pine are also used for temporary purposes. These are pushed in from the front until they cover the leak, and the expansion due to soaking with hot water is depended on to make a tight joint. If, however, the holes in the tubes are of considerable size, so great a quantity of water and steam may be liberated as to make it impossible to remain in the fireroom. In such case the 674 PRACTICAL MARINE ENGINEERING fire will usually be put out as well, or at least so deadened that no further danger of collapse due to overheating need be feared, even should the water become low in the boiler. The general safety of the boiler itself is thus secured, but the other bdilers, ■ connected through the main steam pipe, will continue pouring out their steam through this leak, and as long as this condition continues it will thus remain impossible to return to the fire- room to attend to the other boilers. The first care after escaping from the fireroom, or before effecting escape, if possible, should be to close the stop valve which connects the boiler to the others, and thus to localize the trouble to the one boiler. If the stop valves are arranged so as to be worked from the deck above, as is frequent in good modern practice, this may be readily accom- plished. If at the same time the safety valve on the injured boiler can be opened, the pressure will soon be blown down, and with good ventilation from the fireroom it will be possible in a short time to re-enter it and give the needed attention to the other boilers. In the meantime also, the engine may be slowed down so as to reduce the demand for steam. Where the feed pump is located in the engine room, it will be possible, if the checks have been left open on the other boilers and closed on the injured boiler, to feed by judgment at a rate which will keep these boilers safe from all danger of low water. The object of these various steps is, of course, to isolate the injured boiler and safeguard it from anything more serious, and to provide for the safety of those remaining ; and while circum- stances may alter the details of the measures which should be taken, the above suggestions will serve to illustrate the main points to be looked after. When return to the fireroom is possible, and after the other boilers have received the necessary care, attention may be given to the injured boiler; the fires may be hauled, and after cooling down, the nature and extent of the damage investigated. (9) Rupture of Steam Pipe. — In case of a ruptured steam pipe the valves controlling the flow of steam to the point of rup- ture each way should be closed at the earliest possible moment, as the escape of steam will soon make it impossible to remain in the fireroom with safety. If it is arranged to work the stop valves from the deck above, this is readily eflfected, and the trouble thus gotten under control. Self-closing valves are also OPERATION. MANAGEMENT AND REPAIR 675 often provided in modern practice. It is not possible, however, to so fit these that they will always act, or that they will shut off the steam in more than one direction. In one way or another, however, the first attempt must be to shut off the escape of steam. The next thought must be for the boilers, to safeguard those which may have been shut off from the engine from danger due to increase of pressure, and those which still remain connected to the engine from danger due to low water. The particular steps suitable for attaining these objects have been already suf- ficiently discussed, and no further mention will be here necessary. (10) Casualties With Watertube Boilers. — With watertube boilers the same general emergencies are liable to arise as with fire tube boilers, and may be met in the same general way. It should be remembered, however, that, due to the small amount of water carried, the results due to shortness of water will come much more rapidly than with fire tube boilers, and promptness in action is all the more necessary. In such boilers the tubes are most liable to suffer through shortness of water, and any considerable overheating is likely to result in their rupture. With the small tube type the most serious results of such an accident are usually confined to the emptying of the contents of the boiler into the fire, and the effectual deadening or extinction of the latter. Here, as before, however, with more than one boiler the trouble must be localized by shutting off the boiler with the ruptured tubes from connection with the others. In other cases, however, with large tube types especially, or with the rupture of steam or water drums, the consequences may be more serious, resulting in driving every one from the fireroom, or even in loss of life. The same general principles apply here, however, as with firetube boilers, and good judgment must be depended on for the details suitable to the occasion. With boilers of the watertube type, in-swinging doors that close with a sudden rise of pressure in the furnace, are usually fitted. In the case of tube rupture in such cases and also in cases where oil fuel is being burned, when under forced draft, speed up the forced draft blowers to their utmost speed immediately; also, in the case of oil fuel, shut down the fuel pumps. With coal burning the fire will be extinguished by the rush of steam and water into the furnace, while the increased forced draft pressure in the fireroom «will prevent the steam from escaping 676 PRACTICAL MARINE ENGINEERING in that direction and will cause it to pass out by way of the uptake and smoke-pipe. This latter paragraph is of the highest importance and should be so thoroughly drilled into the mind that the movement towards the blowers would be instinctive in case of accident. Sec. 95. BOILER CORROSION No sooner has a boiler been completed than the various corrosive and destroying influences with which it is surrounded set to work on its destruction. Corrosion may conveniently be considered as of two kinds, that due to oxygen and that due to an acid. These two are, however, by no means independent, and are often combined in very complex ways. The process by which oxygen combines with another substance is called oxidation, and the product of such a process an oxide. In the case of iron and steel the typical product is the ordinary red iron rust, or ferric oxide (Fcj O3), consisting of about 56 parts by weight of iron and 24 of oxygen. In order that oxidation or rusting of iron may continuously proceed at ordinary temperatures, how- ever, it is not enough that oxygen and iron shall be in contact. It requires the additional presence of moisture and carbon di- oxide (CO,), small proportions of which are always present in . the atmosphere. Oxygen and moisture alone act feebly and very slowly on iron, but when the four substances, iron, oxygen, mois- ture, and carbon dioxide, are all present together, the operation of rusting proceeds continuously and with vigor. Oxide is first formed, and this is reduced by the carbon dioxide to a carbonate, and this in turn breaks up, forming hydrated oxide (FeHOs). setting free the carbon dioxide to continue the process. The hydrated oxide thus formed is furthermore electro-chemically negative to iron, and thus helps on the operation as explained at a later point. If either the moisture or the carbon dioxide is absent, the oxygen will have little or no effect, and the iron will be protected. This is shown by the non-rusting of iron in perfectly dry air, even though there may be some carbon di- oxide present; or again, by its preservation in a weak alkaline liquid, as lime water, in which there^ can be no free carbon dioxide. The piano wire used in certain forms of deep sea sound- ing apparatus, for example, is thus kept from corrosion under OPERATION, MANAGEMENT AND REPAIR 677 conditions which would naturally soon destroy its regularity and value for the purpose used. Acid corrosion means the attacking of a substance by an acid, the breaking up of the latter, and the formation of a new substance known as salt, and composed of a part of the acid and of the substance attacked. Thus hydrochloric or muriatic acid (HCl), as it is commonly called, is sometimes present in boilers. This is composed of hydrogen and chlorine. When it is brought into the presence of iron or steel the chlorine leaves the acid, and joining with the iron, forms a salt known as ferrous chloride, or chloride of iron (FeClj). With iron rust and muriatic acid the result would be similar, the chlorine would join with the iron and form ferrous chloride, while the hydrogen of the acid would join with the oxygen of the oxide and form water. As before stated, acid corrosion and oxidation are very commonly both present, especially in the latter operation, and in fact the continued progress of oxidation with iron, moisture and carbon dioxide is dependent on the combined action of both operations. The chemical details of corrosion in general will not'be further dealt with, but a brief consideration of the causes, effects and remedies as related to corrosion in marine boilers will be undertaken. Taking first the exterior of boilers and of all exposed iron and steel work in general, it is clear that the conditions for con- tinued rusting are all present on board ship. The air is moist and there is likely to be present carbon dioxide in abundance. The only safe protection is, therefore, a covering which shall keep the air, moisture and carbon dioxide from contact with the iron. To this end metal paint or other equivalent coating is used wherever possible. Many small fittings, especially about the deck, are of galvanized iron, that is, iron covered with a thin coating of zinc. The latter metal is but slightly affected by the process of oxidation, and it, therefore, forms an efficient pro- tection for the iron. Brass, bronze and copper are also oxidized but slightly, and the oxide formed serves as a protective covering to the metal underneath. For this reason, among others, many of the fittings about boilers and elsewhere are, as has already been seen, made of these metals. Passing now to the fire side of the boiler, the application of paint or other protective coating is found impracticable. Here 678 PRACTICAL MARINE ENGINEERING the heat, which will so dry the air that it is no longer moist, must be depended upon. That is, while water vapor may still be present in the air, there is so little compared with the amount the air could naturally contain at that temperature, that it is held by the air and is no longer free to enter as a factor into the op- eration of oxidation. Rusting in the usual way is, therefore, very much retarded or prevented. To this fact is owed the general preservation of the furnaces, ash pits, etc., from serious and continued corrosion. Another danger is, however, run into in the extreme case when oxygen is present in excess, and both the oxygen and iron are very hot. The oxygen in such cases enters more readily into union with the iron, and oxide is formed, the black, or magne'tic oxide (Fcg O4), the same as the mill scale or forge scale, which forms when iron is worked at a red heiat. The oxide thus formed may presumably be swept away by the scouring action of the draft, thus exposing a fresh surface to renewed attack. The back ends of the tubes seem especially liable to attack in this way, and particularly with hard forced draft. The cure for this trouble is found in the use of cast iron ferrules, as previously described. These ferrules protect the tube ends from the extremes of temperature, and also provide something for the hot oxygen to attack, while they are readily renewed. Turning now to the water side of the boiler, a more serious trouble is found here than with the fire side. There is likely to be more or less air in the feed water, either entering with the make-up feed, or occasionally drawn into the feed pump and sent on to the boiler. There may also be free carbon dioxide liberated from the salts entering with the make-up feed, and thus all the conditions for continuous rusting may be present. Even if free carbon dioxide is not present the formation of iron oxide, combined with electro chemical reactions, as referred to later, may result in serious local corrosion. Furthermore, as the feed water is heated the air is liberated, and the oxygen just at the instant of liberation seems to be especially active chemi- cally, and is thus all the more likely to attack exposed places than if allowed to remain in solution in the water, as at ordi- nary temperatures. Turning next to acid corrosion, mention may first be made of the serious trouble formerly experienced from the use of ani- OPERATION, MANAGEMENT AND REPAIR 679 mal and vegetable oils for cylinder lubrication. Such an oil is a compound of a fatty acid and glycerine. When exposed to a high temperature the fatty acid and the glycerine become separ- ated. If a substance such as soda or potash is present, the fatty acid combines with it and forms soap. This process is called saponification. If, however, no such substance is present, the acid will be free to attack other substances as it may be able. Fatty acids attack iron feebly, but if long continued the result may be a serious corrosion, resulting in the formation of what is known as an iron soap. The temperature within the cylinders and boilers was quite sufficient to thus decompose the oil, and there would, under such circumstances, be set free in the boilers an amount of fatty acid depending on the amount of oil used in the cylinders and finding its way into the condenser and feed water. There were thus present all the conditions necessary for the corrosion of the interior of boilers by fatty acids, and many serious cases were laid, in part at least, to this cause. These troubles appeared especially with the introduction of the surface condenser, and the part which fatty acids might play being un- derstood, the use of animal and vegetable oils for the lubrication of the cylinders was abandoned, and in their place hydrocarbon or mineral oils are now used. Such oils are derived as one of the constituents of crude petroleum, and are not compounds of a fatty acid and gylcerine. They are compounds of carbon and hydrogen, and belong to an entirely dififerent class of cihemical substances. They do not produce a fatty acid on being heated, and cannot, at least directly, take part in the process of boiler corrosion. In modern practice, therefore, nothing but the best hydro- carbon oil, entirely free from animal or vegetable admixture, should be used for cylinder lubrication. With lubricant of this character modern boilers should be free from corrosion charge- able to the action of fatty acids. These are, however, not the only acids which have given trouble in the way of boiler corrosion. Under certain circum- stances free hydrochloric or muriatic acid is found in boilers. This is presumably due to the breaking up of magnesium chloride, forming hydrochloric acid and magnesium hydrate. The most dangerous feature of the corrosion due to hydro- chloric acid is that under conditions which may exist within 68o PRACTICAL MARINE ENGINEERING steam boilers the chloride of iron first formed may become broken up, giving rise to other neutral compounds of iron, and setting free the acid to continue its ravages. There are also possibilities of the development of nitric acid from the organic matter which in small quantities may occasion- ally find its way into steam boilers. Except as it may be modified by electro chemical action, the presence of such an acid usually results in a general surface cor- rosion, at least of all surfaces not protected by a sufificient layer of lime scale. The most troublesome feature of boiler corrosion has not been, however, a general or more or less uniformly distributed effect, such as would naturally be charged to the action of an acid diffused throughout the boiler. It has been rather in the so-called pitting. This term refers to the formation of small pits or depressions from the size of a pin head upward, and conical or cup shaped in form. The depth of such pits may be anything from a slight depression to a hole cut entirely through a boiler tube. They are found in no fixed locality, though more commonly on the tubes, furnaces, and combustion chambers than elsewhere. When found they are usually filled with a blackish or brownish pasty mass, consisting chiefly of iron oxide with a slight admixture of lime salts, oily matter, and other substances. This deposit within the pits is often covered with a skin of somewhat different composition, consisting of lime salts and iron oxide in more nearly equal proportions. To account for the formation of these pits, various explana- tions have been suggested, most of them involving electro chemi- cal action as a more or less pronounced feature. To under- stand the nature of this action a few explanations must first be given. Nearly all substances are in a different electrical condition, or at a different electrical potential, as it is called. This differ- ence is found not only between substances of different kinds, but also between similar substances at different temperatures, or in different physical conditions, as, for example, between two pieces of iron or steel, one of which has been hammered or worked more than the other. Due to this difference of elec- trical potential there is a tendency to set up a flow of electricity from one to the other, and as a further result to so change the OPERATION. MANAGEMENT AND REPAIR 68i two substances as to bring them into electrical equilibrium. In other words, the result of such a difference of electrical con- dition is always to bring about changes which will cauee the dif- ference to disappear, and so bring the two substances into equilibrium. These chemical changes of the two substances, which tend toward electrical equilibrium, may be much helped or hindered by the medium in which the bodies are immersed. If they are in dry air, for example, no such activity takes place, and the difference of electrical condition continues unchanged. If, however, they are immersed in water, or especially in salt or slightly acid water, the operation will usually be much assisted by the activity of the medium for the substances. It may also happen that the medium and substances are so related as to bring about a series of chemical changes, of which the first are those which would naturally be associated with the transfer of electricity and the development of equilibrium, while the second counteract these changes chemically, and bring the substances back to their original condition, and so keep them constantly in the condition of electrical difference. There is as constantly the attempt to restore equilibrium, and hence so long as these conditions continue there will result this continued series of chemical actions, accompanied by a constant flow of electricity from one substance to the other. In order, however, that this flow of electricity may be thus constant and so constitute a cur- rent of electricty, as it is termed, there must be a path for a complete circuit or flow in one direction through the medium which produces the chemical changes, and in the other direction outside of this medium. The substance from which the current flows in the medium is known as the electro positive element, and the other the electro negative. The chemical activity pro- ceeds and the current is formed, in general, at the expense of the electro positive element. These operations are illustrated in the ordinary voltaic cell or battery, such as those used for ringing bells, etc. In most of these batteries, however, the action is not self-sustaining, and if allowed to continue for a little time, a condition of electrical equilibrium is reached, or, as ordinarily stated, the battery is run down. In others used for telegraphy and other purposes the operations are self-sustaining and continuous until the chem- ical substances are exhausted. 682 PRACTICAL MARINE ENGINEERING In a boiler these conditions for a more or less continued electro chemical action may be fulfilled in a variety of ways. Parts of the structure of widely differing temperatures or of different physical or chemical compositions may provide the elements in a different electrical condition. Still more likely is such a difference to be found between iron and its oxides, especially the magnetic oxide or mill scale (Fe^ O4), or between a particle of carbon in the steel and the surrounding metal, or between a place in the steel and the surrounding metal, or between a place in the steel where the proportion of carbon is much greater than the average and the surrounding metal, or between a bit of slag or other impurity in wrought iron and the surrounding metal. Copper, either in the form of oxide, or es- pecially in the metallic form, would also supply a substance dif- fering strongly from the iron. The exciting liquid is the water in the boiler, and its action will be more vigorous according as it is more acid in reaction, higher in temperature, and denser in concentration. With a high pressure, boiler water of high density and quite acid in character, and with the usual lack of homogeneity or uniformity in the structure of the boiler, the effects of electro chemical action should, therefore, be shown in marked degree. It happens, furthermore, that iron is electro positive to copper, to carbon, and to its own oxides, so that in all cases likely to occur the operation will proceed at the expense of the iron. From the very nature of these electro chemical actions their effects are necessarily local in character, and so far as understood they seem to provide a fairly good explanation of the formation of pits as already described. It is not unlikely, however, that in some cases they are due rather to simple chem- ical action, and that their localization to a small spot is due to special or accidental causes, such as the protection of the sur- rounding metal by lime scale, or a peculiar weakness against chemical attack at that point, due to peculiarities in chemical or physical structure. The possibilties of deposits of copper on boiler surfaces has been already mentioned. These were first noted in connection with the corrosion accompanying the general introduction of the surface condenser. It was believed that the copper of the condenser tubes was attacked by the pure water resulting from OPERATION, MANAGEMENT AND REPAIR 683 the condensation of the steam, or by the fatty acids formed as above explained, and was then carried over into the boiler and deposited on the surfaces. To prevent such action the con- denser tubes were tinned, thus covering the copper from the action of the water or the fatty acids. Neither this step nor the substitution of hydrocarbon oil for that containing fatty acids has made any very marked difference in boiler pitting, and at the most the presence of the copper can have been only one among a number of causes as suggested. Where two metals, one electro positive to the other, are brought into proximity in the steam space of a boiler, the de- struction of the electro positive element seems to be aggravated. Thus in watertube boilers brass baffle plates to aid in drying the steam are often encountered. Where this is the case rapid destruction of the tube ends which enter the steam drum above the water line is almost certain to occur. There has been much difference of opinion and difference in experience regarding the question whether wrought iron or steel boiler tubes were the more liable to corrosion. It was pointed out that wrought iron was less homogeneous than steel, and therefore the latter should be the better. The early experi- ence with steel hardly bore out this claim, and in fact the gen- eral opinion seems to have been that wrought iron tubes were found to corrode less readily than steel. In explanation of this, it may be said that while wrought iron was less homogeneous physically, the steel was perhaps less homogeneous chemically, and in any event contained a larger proportion of carbon than the iron, so that it would by no means follow that it would neces- sarily be less subject to electro chemical action. The latest and best products of the steel makers for such purposes, however, are extraordinarily low in carbon and very homogeneous, and experience with such grades of material seems to show them superior to wrought iron in this respect. The causes of corrosion on the water side of steam boilers have here been developed in some detail, so far as they are understood. For the prevention of such effects their causes must be removed or counteracted. For reducing the amount of oxidation and the possible re- sults due to electro chemical action, the presence of air in the feed water must be avoided by preventing as far as possible the 684 PRACTICAL MARINE ENGINEERING entrance of water from overboard into the feed. The Iiotwell or feed tank should also be of good size and kept full, so that there may be no danger of its getting too low from time to time, and thus allowing the pump to take air. The piston rod on the low pressure cyHnder should be kept well packed, so as to pre- vent the entrance of air during the exhaust of the stroke. The feed pump rods on the water end should be kept well packed for the same reason. To prevent acid corrosion the formation of the acids must be prevented as far as possible, and such as may form must be neutralized within the boiler. The prevention of the formation of fatty acids has been considered above. It has also been seen that the formation of other acids is due chiefly to the presence of salts contained in sea water, or to organic substances. There is therefore simply an additional reason for keeping all such substances out of the boiler as far as possible. To neutralize such acid as may form, bicarbonate of soda, or soda ash, as it is known in the trade, may be used from time to time, and in such quantities as may be found necessary. To test the water for acidity the litmus test is used. Blue Htmus paper turns red when dipped in water slightly acid, while if the water is alkaline it re- mains blue, or the red color caused by an acid is changed to blue. By this means the condition of the water may be tested from time to time and soda used accordingly. Care must be taken not to use it in too great excess, as it may cause foaming. The soda is introduced by means of a soda cock on the con- denser. Instead of keeping the water alkaline by the use of soda, dependence is often placed on the zinc slabs used to pre- vent electro chemical corrosion. These are gradually dissolved, forming zinc chloride, and this will undoubtedly tend to neutral- ize free acids and to keep the water alkaline. Whether sufficient or not, can of course be readily determined by the litmus test before referred to. For the prevention of electro chemical action the causes must also be removed or neutralized as far as possible. This cannot be realized entirely, but it is clear that the results will be the better, as the following conditions are the more nearly ful- filled : (a) The structure of the boiler should be of material as homogeneous as possible in its chemical constitution and physi- cal condition. OPERATION. MANAGEMENT AND REPAIR 685 (b) Causes liable to produce oxidation or the presence of foreign substances should be kept out of the boiler as far as possible. (c) The water in the boiler should be made as nearly neu- tral or non-exciting relative to the iron as possible. This in a general way will be attained by keeping it slightly alkaline rather than acid, and by avoiding very high densities. In addition to these means for reducing the causes, there remains one further step, and that is: (d) The provision of a substance which shall be electro positive to iron, and readily attacked, so that the activity will be diverted from the iron to the protecting substance, and the operation will proceed at the expense of the latter rather than of the former. Such a substance is found in zinc, and its use for this purpose is very general and seemingly beneficial. It may be also noted that the formation of zinc chloride as referred to in the foregoing will aid in keeping the water alkaline in reaction, thus reducing its natural activity, and contributing further to the general decrease of electro chemical action. In order to be effective as a protection to the iron in the manner described, the zinc must be in actual metallic contact with the structure of the boiler. It is usually in the form of rolled or cast slabs, weighing 8 to 12 pounds each. These are often placed in perforated sheet metal baskets hung from the stays or at- tached to other portions of the boiler. Where the basket is at- tached to the boiler there should be bright metal contact, and the attachment should be by screwed joint or other equivalent means, so that the separation of the two surfaces by the formation of scale or corrosion between them may be prevented. The zinc should also be connected to the basket by through bolts or other means which will insure continuous metallic contact. In some cases the zincs are hung by a through bolt without other means of support. In such case, as the zinc becomes used it may fall apart and the pieces may lodge where they will obstruct the cir- culation, or be otherwise undesirable. In any event, they will no longer protect the part of the boiler confided to their care, and their period of usefulness may, therefore, be less than when supported and connecled to a basket, as described above. The number of zincs fitted varies greatly, according to the judgment of dififerent engineers. In some cases not more than 10 to 12 686 PRACTICAL MARINE ENGINEERING would be assigned to the protection of a large double end boiler, while in others as many as 40 or 50 would be used. The latter number is the better representative of good modern practice. In any case they should be distributed as nearly uniformly as possi- ble throughout the boiler, in order" that the latter, may be thus subdivided into parts, each more especially under the influence of a given slab. In connection with the use of zinc it may be noted that for such boilers as may be used for distiUing purposes, that is, for the provision of fresh water for drinking and cooking, where evaporators are not fitted, the zincs should be omitted, as the presence of any considerable amount of zinc chloride will render the water unsuitable for such uses. Instead of depending on the zinc to prevent or divert electro chemical action, as above described, some engineers prefer to depend simply on reducing the activity of the water by keeping it alkaline by the use of soda, introduced as the litmus test may show to be necessary. When spots are found in a boiler, showing the presence of pronounced corrosion, they should be cleaned ofif thoroughly, washed with soda solution, and, if not on heating surface, cov- ered with a thin wash of Portland cement. This will attach itself to the iron and protect it in a manner similar to the lime scale. The beneficial effect of scale in thus protecting the surfaces of boilers from corrosion is well recognized, and there is no doubt that its presence as a thin wash or layer is of great value. In order to be effective, however, it must be so firmly and closely attached to the iron as to prevent contact of the water with the surface, else the corrosive action may proceed under the scale and result all the more seriously because it is protected from in- spection until the scale is thoroughly removed. On the tubes and other heating surfaces of the boiler, with their changes of temperature and consequent expansions and contractions, the scale is especially liable to be cracked off or partially separated irom the iron, with possible results, as here noted. This is still more likely to be the case as the scale becomes thicker and the metal more liable to become overheated. It has also been sug- gested that a very heavy scale may result in an overheating of the metal sufficient to decompose the moisture present, thus lib- erating oxygen and forming the magnetic oxide of iron or black OPERATION, MANAGEMENT AND REPAIR 687 mill scale (Fcg O4). This is highly electro negative to iron, and thus it may give rise to harmful elctro chemical reactions. Laying Up Boilers. — When boilers are to be laid up, the prin- ciples already explained will indicate the nature of the means suitable for preventing corrosion. On the outside, paint or other like coating may be used, as already noted. On the fire side of watertube boilers protec- tion is sometimes gained by building a slow fire of tar or resin- ous material, the tarry smoke from which condenses on the tubes and furnishes protection from the air with its moisture and carbon dibxide. Use is also made of quicklime in trays renewed from time to time. This absorbs the moisture and so keeps the air dry. Where oil fuel is used a spray of fuel may be played into the furnace, and being drawn through or among the tubes by the draft, will coat all the fire surface with a protective coating of mineral oil. Oh the inside, all boilers when laid up should be either empty or entirely full. If a boiler stands for any considerable length of time partly full, corrosion, is likely to occur about the water line. If they are to be out of use for a short time only, they may be filled full of water made slightly alkaline by the ad- dition of soda, the condition of the water being determined by the litmus test already referred to. If they are to be laid up for a longer time it is better to lay them up dry. To this end the water is removed, the manhole plates taken off and the interior thoroughly dried out by the introduction of trays of burning charcoal or coke. The boiler is then closed up, except a lower manhole, through which a tray of freshly burning charcoal is in- troduced, and the manhole cover is put on. The charcoal will consume most of the remaining oxygen, and the boiler will thus be protected. Instead of the final introduction of a tray of char- coal, trays of quicklime may be used to insure the absence of all moisture, and the boiler then closed as before. It is readily seen that these various methods are simply ways of carrying out the necessary conditions for preventing oxidation, as already discussed, and if these principles are kept clearly in view the means most conveniently at hand may be suitably adapted to provide the protection desired. 688 PRACTICAL MARINE ENGINEERING Sec. 96. BOILER SCALE It is well known that sea water contains in solution a certain amount of solid matter, while even ordinary fresh water is not wholly free from similar substances. As long as the water re- mains in its natural condition these solids remain in solution ; but under the change of conditions to which the water in a steam boiler is subjected, they are liable, as explained later in detail, to separate out from the water and thus to form scale or sludge, according as the circumstances may determine. The proportion of the solid matter in ordinary sea water is about (by weight) i part in 32, or 1/32. This is the same as about 5 ounces per gallon, or 2 pounds per cubic foot. The solid matter consists chiefly of chloride of sodium or common salt, with small quantities of calciuni sulphate and carbonate, magnesium sulphate and chloride, with smaller quantities of other substances. An average composition of this solid matter is about as follows : Percent Chloride of sodium (common salt) 76 Chloride of magnesiun^ 10 Sulphate of magnesium 6 Sulphate of calcium (gypsum) S The remaining 3 percent consists of small quantities of other salts with a little organic matter. The proportion of the solid matter in river and lake water is quite variable with the locality, and no representative or average analysis can be given. The amount held in solution may vary from perhaps 10 to 250 parts in 100,000 or from .015 ounce to .30 ounce per gallon, or .1 ounce to 2.5 ounces per cubic foot. It is composed chiefly of the carbonates of calcium and magne- sium with smaller quantities of the sulphates of calcium and magnesium, and other substances. In addition to the substances in solution, quantities of sand, mud, organic matters, etc., may be carried in suspension, dependent entirely on the locality and special circumstances. Boiler scale from sea water is composed chiefly of calcium sulphate or sulphate of lime, as it is commonly called, while that from iresh river or lake water is composed chiefly of calcium carbonate or carbonate of lime, as commonly called. With brackish water, as might be expected, the proportions of the two are more nearly the same. Following are analyses of boiler scale OPERATION, MANAGEMENT AND REPAIR 68g by Professor Lewes which may be considered as typical of the incrustations formed by river water, brackish water and sea water, respectively: Constituents River Brackish Sea Calcium carbonate 75.8s 43-65 0.97 Calcium sulphate 3.68 3478 85.53 Magnesium hydrate 2.56 4.34 3.39 Sodium chloride 0.45 0.56 2.79 Silica 7.66 7.52 1. 10 Oxides of iron and alumina 2.96 3.44 0.32 Organic matter 3.64 1.55 ' trace Moisture 3.20 4.16 5.90 100.00 100.00 100.00 It thus appears that scale from river water may be looked on as an impure calcium carbonate, that from sea water as an impure calcium sulphate, while that from brackish water is a mixture of the two in more nearly equal proportions. Sodium chloride or common salt is soluble in water until the proportion exceeds some 25 or 30 percent. This corresponds to a density of 8 or 10 on the usual hydrometer, and is far greater than that reached by the water in marine boilers. This substance, therefore, gives no trouble so far as helping to form icale is concerned, and the small amount found in analysis of boiler scale is probably due to the shutting in, so to speak, of a small amount of water during the formation of the scale. In discussing the formation of boiler scale for present purposes, it will be sufficient to refer to the behavior of the salts of calcium and magnesium. Calcium carbonate (CaCOg) is practically insoluble in water, while calcium bicarbonate (CaCaOg) is quite soluble, and it is in this form that the substance exists in solution in water. If now the water is heated to the boiling point carbonic acid (CO2) is driven away from the bicarbonate, it becomes reduced to the simple carbonate, and being now insoluble it separates out as a more or less powdery deposit. Mixed With other salts, however, especially calcium sulphate, or if there is a little sulphuric acid in the water, it may collect on the heating surfaces and form a hard and closely adhering scale. Magnesium bicarbonate is in a similar manner reduced to the simple carbonate, which is in- soluble, and is then deposited in the same fashion. Calcium sulphate is soluble in cold water to a slight extent, 690 PRACTICAL MARINE ENGINEERING as found in sea water. As the water is heated, however, or as the density becomes greater, the proportion of sulphate which it can retain in solution becomes less and less. When the tempera- ture rises to 280 degrees or 290 degrees (corresponding to from 35 to 45 pounds gage pressure) the water can no longer retain any of the sulphate in solution, and it is all deposited. It is also largely deposited, even at a temperature of 212 degrees, if the density rises to 3/32 or above. The other sulphates become like- wise insoluble and are completely deposited, if the temperature rises to about 350 degrees or over, corresponding to about 120 pounds gage pressure. These sulphates of lime and magnesium thus deposited tend to attach themselves to the surfaces within the boiler, and to form a very hard and crystalline scale. As to the effects of this scale, its presence in a very thin layer is often considered beneficial as a protection to the surface of the boiler from corrosive influences. On the other hand, how- ever, it is a much poorer conductor of heat than metal, and its presence on the heating surfaces retards the transmission of heat from the fire through to the water. In the extreme case the heat may be so effectually shut off from the water that it simply be- comes banked up, so to speak, in the metal, and in this way the tubes and other heating surfaces may become seriously over- heated with resulting damage to the boiler. The scale may also in extreme cases become so collected between the tubes or be- tween the combustion chamber and boiler sheets as to impede the circulation of the water and thus lead to overheating and its dangers, as referred to above. In watertube boilers the accu- mulation of scale on the inside of the heating tubes is of special danger, as the circulation becomes in such case rapidly ob- structed and the danger of overheating and rupture is corre- spondingly increased. In a similar manner the accumulation of scale in the interior of tubular feed water heaters rapidly de- creases their efficiency as heaters, if no worse results follow due to the burning out of coils, or to the resulting shortness of water in the boilers. Scale Prevention, Fresh Water. — The best way of preventing scale is simply to keep it out of the boiler. If the scale forming substances find entrance to the boiler, it will be found very diffir cult to prevent its formation, at least to some extent. On boats navigating inland waters the jet condenser is still OPERATION. MANAGEMENT AND REPAIR 691 for the most part used, the feed is ordinarily taken from the con- denser, and therefore practically from overboard. In such boilers, therefore, the formation of the usual fresh water scale, consist- ing chiefly of calcium carbonate, may be expected. For the treat- ment of fresh water scale a great variety of methods have been proposed. In some cases the substances proposed act chemically, in others mechanically. From the great variation in the char- acter of the solid matter contained in fresh water, it can hardly be expected that any one method of treatment or substance will prove equally good in all cases. If a feed water heater is used, and is effective in heating the water, it will be found that most of the scale will be deposited in the heater, especially if it is of sufficient size to allow of proper time. In this way the scale may be kept out of the boiler proper. The heater, however, should be so made as to readily admit of cleaning, especially if the water contains any considerable pro- portion of scale forming salts, otherwise it will soon become choked and ineffective. Among the various substances which have been recom- mended for • the prevention of fresh water scale the following may be mentioned : Oak and hemlock bark and other like substances which contain tannic acid are more or less effective in waters contain- ing carbonates of calcium or magnesium. The tannic acid, how- ever, will attack the iron of the boiler and may lead to serious corrosion. Molasses, cane juice, fruits, distillery slops, vinegar and other like substances containing acetic acid have also been used with success where no sulphates are present. The acetic acid, however, is still more injurious to the iron than the tannic acid, and the organic substances will form a scale with sulphates if they are present. Salammoniac when used with a feed water containing cal- cium carbonate brings about an exchange between the two sub- stances as a result of which ammonium carbonate and calcium chloride are formed. The former of these is soluble and quite volatile and passes off mostly with the steam. The latter is quite soluble and thus the deposition of the calcium carbonate is avoided. This operation by itself, however, would result in the gradual accumulation of calcium chloride in the boiler, thus rais- 692 PRACTICAL MARINE ENGINEERING ing the density of the water to a point where ultimately it would begin to deposit. This condition may, of course, be controlled by a suitable use of the blow. Tannate of soda is well recommended for general use, but with water containing sulphates a small amount of soda ash should be added. In all boilers, however, where the use of scale preventing mixtures containing much soda is prolonged, care should be taken that all seams below the water line are well calked on the water side, as evidence exists that the soda which enters between the laps of the plates has a very destructive effect upon the metal of the plates and rivets, and rapidly robs them of their strength. Among the substances which act mechanically, crude petro- leum and kerosene oils are probably the most widely used. The latter may be recommended as the better of the two, as the crude oil will sometimes aid in scale formation. They seem to act best in cases where there are some sulphates present, as in slightly brackish water, or in the waters of certain geographical regions. Kerosene seems to act by preventing the particles of scale from sticking closely together or from tightly adhering to the heating surfaces, so that much of the matter will collect as a sludge in the bottom of the boiler, and that on the heating surfaces will be more easily removed. In all cases where there is reason to expect the accumula- tion in the bottom of the boiler of deposits thrown down in a loose or powdery form, the bottom blow should be freely used so as to prevent the accumulation of too great a quantity, or op- portunity for its hardening into scale. In spite of all modes of treatment there may be found some scale on the heating surfaces, and provision must be made for entering the boiler and removing it with appropriate tools as the occasion demands and circumstances permit. In many of the inland waters the amount, of scale forming substances is so small that no special treatment is thought neces- sary, and little attention is paid to the matter except to remove the accumulation at the periods of regular inspection and over- haul. Scale Prevention, Salt Water. — Turning now to boilers in • bich sea water may form a portion of the feed, it will be of in- OPERATION, MANAGEMENT AND REPAIR 693 terest to first note briefly the historical development of the mod- ern situation. In the early days of marine engineering, the temperature and pressure of the steam were low, and the jet condenser was in general use. The feed water which was drawn from the min- gled condensing water and condensed steam was but slightly fresher than sea water, so that large amounts of solid matter were thus fed into the boiler. In consequence the density would have risen rapidly had it not been kept down by blowing off a part of the water in the boiler of relatively high density and re- placing it with the salt feed of lower density. Had the sulphates of calcium and magnesium thus brought into the boiler been completely deposited, enormous quantities of scale would have been formed, and this method of operation would have been quite impracticable. Due, however, to the moderate pressure then in use and to the fact that the density was kept usually be- tween 1% and 2, the salts were held fairly well'ln solution, and but a moderate amount of scale was deposited. As steam pressures advanced, however, beyond 40 or 45 pounds, conditions were reached under which first the calcium sulphate and later magnesium sulphate and other salts are com- pletely deposited. Under such circumstances blowing off to re- duce the density of the water will only make matters so much the worse, for the lower the density is to be maintained the greater must be the amount blown off, and hence the greater the amount of extra feed, and the greater the amount of scale form- ing salts brought into the boiler, all of which will be deposited. It became, therefore, necessary to abandon the use of the jet condenser and salt feed. Its place was taken by the modern sur- face condenser. So long as this condenser is perfectly tight the feed water consists of the condensed steam, and is therefore al- most perfectly fresh water. Due, however, to steam leaks at the various joints, seams and glands, to the occasional use of the steam whistle, and to the use of steam in certain auxiliaries from which it is not returned to the condenser, there will be a con- tinual shortage in the feed water, which under usual conditions will be found between, say, 2 and S percent. Until recent years this shortage was made up by the use of sea water obtained usually by opening, as circumstances required, the salt water cock connecting the salt water side of the condenser with the 694 PRACTICAL MARINE ENGINEERING steam side. It is very difficult to keep the tubes of a surface condenser packed perfectly tight, and in some cases the con- denser was allowed to run a little leaky, simply to make up in this way the salt feed required. Due to this admixture of salt feed, the scale forming salts of which are all deposited in the boiler, there will be a gradual formation of scale greater or less, according to the length of the run and the proportion of salt feed make up. In recent years experience has clearly shown that the dan- gers of overheating and the general bad effects due to the pres- ence of scale are more and more pronounced as the pressures are higher. It has become, therefore, more and more important to prevent so far as possible the entrance of any sea water into the boiler, and thus avoid the formation of scale with its troubles and dangers. To this end, in modern practice, the make-up feed is provided by an evaporator, or in some cases by feeding one boiler with salt feed and thus restricting the scale formation to this boiler, while the condensed steam from all the boilers is re- turned to the other ones as feed. In all such cases it will be noted that this scheme amounts to a transfer of the use of salt water and the formation of scale from the boilers in general to the evaporator, or to the particular boiler in which it is allowed to accumulate. For short trips, as, for example, those met with in bay, har- bor or channel service, or on short coasting voyages, fresh water for make up feed may be carried in tanks instead of providing it by means of an evaporator. By many engineers this is consid- ered the preferable method whenever tanks of sufficient size can be provided, and in some cases with the double bottom style of construction, double bottoms have been utilized to a consid- erable extent for this purpose. It is rare with packed tubes that the condenser can be main- tained perfectly tight, so that even under the best practicable conditions there is apt to be some passage of sea water into the steam side of the condenser, and thence into the boiler. Under the best conditions the amount of scale formed, however, is so small that commonly no special treatment is attempted, and the scale is allowed to deposit, and is then removed at the regular periods of inspection and overhaul. Some attempts have been made to prepare sea water by the OPERATION. MANAGEMENT AND REPAIR 695 removal of the calcium sulphate in a separate vessel before en- tering the boiler. This may be done by the use of sodic fluoride, which causes the sulphate to separate out and settle to the bot- tom as a fine powder. The remaining water is practically free from this substance and may be used for boiler feed without fear of causing scale. Soda ash and other alkalies have sometimes been used in boilers, with feed water containing sulphate of lime. They act by converting the sulphate into a carbonate, and thus into a somewhat less objectionable form. Barium chloride acts in a somewhat similar fashion by pro- ducing barium sulphate and calcium chloride. The use of zinc in boilers is also by many believed to prevent to some extent the formation of scale by the reaction of the alka- line zinc chloride on the scale forming salts. With sea-going, as with inland boilers, the bottom blow should be used occasionally and as the particular circumstances may demand, so as to remove the accumulation of such sub- stances as may be thrown down as a powder or sludge and thus collect in the bottom of the boiler. However careful the provisions for keeping sea water out of the boilers or no matter what methods may be used to -pre- vent scale formation, it is almost sure to gradually accumulate, and assurance of safety from the troubles and dangers which may result can only be obtained from periodical examination and scaling as may be found necessary. All marine boilers must, of course, be provided with manholes for this purpose, and the internal arrangement of tubes, braces, furnaces, etc., should be made, so far as possible, with a view to furthering this neces- sary operation. Combinations of Oil and Scale. — Reference thus far has been made to scale formed simply from the solid matter in the feed water. The combinations which may be formed by the de- posited salts and oil from the cylinders as it may enter with the feed water are, however, of even still greater importance, and must now be noted. Oil coming in thus with the feed water is caught by the cir- culating currents and distributed more or less throughout the boiler, though by reason of its lesser weight it will tend grad- ually to rise and accumulate as a scum at the surface of the 696 PRACTICAL MARINE ENGINEERING water. In thus wandering about, a drop may come in contact with a bit of solid matter separated from the water. The two join together, the oil forming a coating about the sulphate, and they journey on, meeting and joining with other like particles. The combination- of the oil and sulphate may have about the same specific gravity as the water in the boiler, and hence these particles will readily move with the circulating currents, either up or down, as they happen to be flowing. They are thus swept along the heating surfaces, to which they attach themselves all the more readily by reason of their oily covering, and on either the upper or lower side as they happen to be moving with a down or up-flowing current. In this way the coating gradually in- creases until it has attained a thickness sufficient to seriously interfere with the passage of the heat. In other cases, when the scale and oil are lighter or the water is denser and heavier, there seems to be formed at the surface of the water in the boiler a kind of oil and scale blanket or layer floating about, and perhaps ultimately by the gradual increase of weight sinking and covering some portion of the heating surface. Especially is this oil "pancake," as it has been called, liable to settle should the density of the water in any way be suddenly decreased. Still otherwise, should the boiler be blown down by the bottom blow, such an oil blanket would naturally settle and attach itself to some part of the heating sur- face. Should the boiler be then filled again, the coating would remain where attached. This shows that under such circum- stances a boiler should never be blown down with the bottom blow without first using thoroughly the surface blow to remove as far as possible all such accumulations of oil or of oil and scale from the surface of the water. The danger to be feared from this combination of scale and oil is not in its close adherence to the surfaces, but in its non- conductivity of heat. Experiments show that 1/16 to 1/8 inch cf such covering is far worse in this respect than perhaps r/2 inch or more of scale alone. The danger to be feared is there- fore overheating and collapse, and not a few cases of the col- lapse of furnaces and other parts of marine boilers are believed to be due to this cause. So far as these effects are concerned it is seen that it is bet- ter to carry a high density in the boilers than a low one, so as OPERATION. MANAGEMENT AND REPAIR 69^ to keep such oil and scale combinations at the surface of the water, where they may be disposed of by the surface blow. As it is practically impossible to prevent the entrance of some scale forming materials into the boiler, the danger of trouble with oil and scale combinations is most surely prevented by keeping the oil out. To this end a cylinder oil should be used having a high point of vaporization, as the higher this point the smaller the amount carried into the condenser. Of this oil the minimum amount necessary should be used in the cylinders, and the feed water should be filtered to remove whatever oil it may contain. Sec. 97. BOILER OVERHAULING AND REPAIRS [i] Inspection and Test Suppose that after some considerable term of service, and preparatory to a general overhauling, a battery of boilers are to be carefully and thoroughly examined. The more important points may be now considered. (i) Furnace Fronts. — The furnace fronts and doors may be found warped and cracked, and if this is the case to such an ex- tent as to interfere with the proper closure of the furnaces, or with the proper and convenient care of the fires, the necessary re- pairs or renewals should be made. (2) Grates and Bearers. — The grate bars will often be found warped and twisted, or badly burned, and at various points sunk- en below or sprung above their proper level. Such irregularities in the grate may occasion loss of coal at some points, while they will further the accumulation of ash and clinker at others, and will make it almost impossible to give to a fire the proper atten- tion, or to get from a square foot of grate surface the power which it should be able to give. The bearers may also be the cause of trouble ty warping or settling from having been over- heated, and all of these points must be attended to before the boiler can be considered again ready for proper service. (3) Bridge Wall. — The bridge wall is liable to be found more or less burnt out and dilapidated, while on the front side clinker and bits of brick may be found fused together in irregular masses. All of this must be removed and the bridges built up again with fresh bricks to the proper height as referred to in Sec. 91. 698 PRACTICAL MARINE ENGINEERING (4) Tubes. — The tubes will, of course, be swept and properly cleaned on the fire side. The existence of small leaks must be carefully looked for, the evidence being the presence of soot and scale burned to the metal where the water has come through and evaporated. The back and front tube sheets and the inside of the tubes must be carefully examined for any such evidence. Signs of especial wear should also be looked for at the back ends of the tubes, and if ferrules are used some will probably be found so worn and burned out as to require renewing. In watertube boilers any special warping or change in the shape or curvature of the tubes should be carefully noted, as it may indicate overheating due to faulty circulation caused by a clogging of the tube by scale and sediment. A split or badly ruptured tube will, of course, show itself by the resulting leak, but in a watertube boiler such leak may be very difficult to locate without the removal of several of the tubes in the vicinity of the one giving the trouble. These points depend entirely on the type and style of construction, and no general rule can be given for definitely and immediately locating such a tube in a watertube boiler. (5) Joints and Seams. — The joints and seams throughout the boiler, both in the combustion chamber and on the outside, should be carefully examined for small leaks, either between the plates or about the rivets. If the leakage is not serious, calking will serve as a sufficient remedy. In other cases, however, the removal of old rivets and the insertion of new ones may be found necessary. (6) Front Connections and Uptakes. — The front connec- tions, uptakes and fittings should be examined to make sure that the plates are not warped or broken from their fastenings, and that the dampers and their operating gear are. in proper condi- tion. (7) Fittings. — The valves and cocks are likely to be found more or less worn on their seats and leaky in consequence. These will require regrinding and refitting, or replacing by new where necessary. The operating gear, such as valve spindles, wheels, levers, chains, gear wheels, etc., should be examined for any breakage or derangement of parts. The various joints and fittings about the steam and water pipes must also be examined for signs of leaks, distress, corrosion, or other derangement. OPERATION. MANAGEMENT AND REPAIR 699 (8) Bracing. — The manhole plates will, of course, have been removed to facilitate examination of the interior. The braces, especially where pin joints and like connections are used, should be carefully examined for defects in the con- nections and fittings, and also for any symptoms of buckling or distress in the braces themselves. (9) Scale. — The scale present in the boiler should be ex- amined as to its amount, distribution and character — whether hard or soft, greasy or otherwise, closely adhering or readily cracked off. Accumulation of scale between the tubes or screw stays, and of scale and sludge in the bottom of the boiler must also be looked for and noted. In some cases an oily or greasy coating with little or no mineral matter and forming a coating over the scale and on the heating surfaces may be ob- served. This will indicate large quantities of oil in the boiler, and insufficient use of the surface blow. (10) Corrosion. — It is, of course, of the highest importance to examine carefully for signs of corrosion and pitting through- out the interior of the boiler. The following locations, however, are those in which it is most apt to be found : On the sheets at and near the water line. Occasionally also severe corrosion is found in the steam spaces. On the braces near the water line. On the tubes and combustion chamber tops. On the furnaces near the grate level. In watertube boilers at the tube ends and just inside these ends at which the water enters the tubes in its course of circu- lation. The nature and distribution of this corrosion must be care- fully noted, in order that the, most suitable steps may be taken for its arrest and prevention in the future. When they can be reached, corroded spots may be scraped and scrubbed clean with water made alkaline by the addition of soda or weak lye, and if not on a heating surface, coated with a thin wash of Portland cement. If on a heating surface, a redistribution of the zincs may prove of service, while in general a more careful attention to the various means suggested in Sec. 95 may be recommended. The zincs and their fittings, as discussed in Sec. 95, must also be carefuily looked after. Many of the zincs will probably be found to have wasted away to only a small part of their original size, 70O PRACTICAL MARINE ENGINEERING and to have become changed in physical structure to a blackish or brownish crumbly or brittle mass. In some cases remnants of the slabs may be found lodged between the tubes and screw stays, avji often more or less covered or imbedded in deposits of scale. On the exterior of the boiler the points most liable to cor- rosion are on the fronts about the bottom, where damp ashes may have collected, or about the saddles and on the under side, where dampness and water are liable to be formed. Thorough clean- ing, followed by a coat of paint, ashpaltum varnish, or other like material, is the usual remedy in such cases, at least where its application is practicable. Before the application of any such coating, the plates should te thoroughly dried, else it will be of little use. The presence of moisture on the plates causes the especial difficulty connected with the effective application of paint in such places, and where convenient the use of a portable sheet iron drying stove contain- ing burning charcoal or coke may be found of use. This may be placed under the surfaces to be covered so as to furnish an ascending current of warm air, thus aiding in keeping them dry during the application of the paint. For the structural material in bilges and bunkers a coating of Stockholm tar put on hot and then sprinkled with Portland cement is highly recommended by some engineers, as also are some of the bitumen preparations. (ii) Manholes and Covers. — The faces on which the man- hole cover joints are made should be examined for corrosion or scale, or anything which may affect their evenness, or make difficult the fitting of a tight joint. (12) Drill Test. — Where the boiler has seen long service, or where there are evidences of serious corrosion, or doubt exists as to the thickness or quality of the plates, they must be drilled at such points as may be selected. In this way the thickness of the remaining good metal may be ascertained, and the safe? pres- sure to be carried may be fixed in accordance with the evidence thus found. (13) Hydraulic Test.— When the boiler has been over- hauled and put in proper condition, at least as far as anything which may affect its strength is concerned, the hydraulic test may be applied. To this end the boiler is filled full of water and pressure is put on, usually by means of a special pump connected OPERATION. MANAGEMENT AND REPAIR 701 for the purpose. The test pressure is usually one and one-half times the working pressure desired. It is considered that this pressure is not sufficient to seriously try or injure the boiler should it be properly constructed, and of suitable factor of safety throughout, while at the same time it will be sufficient to de- velop small leaks, and should the boiler be unduly weak at any point, the bulging or yielding or distress at such point should become apparent. If no such evidences appear, then it is con- sidered that the boiler is abundantly strong for the working pres- sure as desired. To prepare the boiler for the test the springs should be withdrawn from the safety valves and lengths of pipe of suitable size substituted, so that the valves may be screwed down fast. All stop valves and gage glass connections should then be tightly closed, as well as the connection to any pressure gage which will not indicate up to the test pressure. While the test is under way the boiler is subjected to the most careful examination, both inside and out. The furnaces, combustion chambers and back tube sheets are examined from the outside. Small leaks are watched for and stopped by calk- ing, if possible, or if about the tube ends, by re-expanding. Es- pecial care must also be had in watching for any signs of bulging, buckling or other deforhiation or distress. Where the test is to be carried out with especial care, ex- tension and compression gages are provided in the furnaces and combustion chambers, and at other points, as may be desired. These serve to indicate and to measure the actual amount of dis- tortion which results from the gradually increasing pressure. If the distortion or bulging at any point should become abnormal, the pressure should be relieved by letting off a little water, in order to see if any permanent set has been made. The con- tinuance of the test should then be made to depend upon the be- havior of the part showing this relative weakness. For a thor- oughly satisfactory test, all gages should return to the original setting when the pressure is removed, showing no permanent set at these points. It will usually be found very difficult to so tighten the vari- ous valves that there will be no leakage. An idea of the amount of leakage may be obtained by watching the rapidity with which the pointer on the pressure gage moves backward when the pump 702 PRACTICAL MARINE ENGINEERING is stopped, as well as by the amount of pumping required to maintain the pressure at its full value. The pressure gage pointer will also frequently indicate by its more or less sudden movement backward, the sudden development of leaks about the riveted joints or tube ends. It has sometimes been urged against the hydraulic test that it may severely strain some part of the boiler where the yield or distress is difficult to observe, and thus so weaken it that a further yield or rupture may occur under a much smaller load at a later time. The hydraulic test is, however, very generally employed, both in the naval and mercantile marines, and if care- fully conducted and with a pressure not exceeding one and one- half times the working pressure, it is not likely that harm will result, while the test will develop the small leaks and minor defects, and may be the means of exposing serious faults of workmanship or design. The same test is, of course, applied to new boilers as a final preliminary to the getting up of steam. In some cases the water test has been carried' out by filling the boiler and then lighting wood fires within the furnaces. The expansion of the water will furnish the increase of pressure de- sired, which may be eased by the safety or stop valve, as neces- sary. It has been claimed that the boiler being in this way heated, was more nearly in its regular service condition. While this may be so to a slight extent, the boiler is, nevertheless, far from regular service condition, and the method has the serious disadvantage that it does not allow examination of the furnaces, combustion chambers and back tube sheets while it is under way. It is also under less ready control than the pump method, and is now but rarely employed. BOILER REPAIRS In the following suggestions regarding boiler repairs refer- ence shall more esf>ecially be made to such as may become neces- sary at sea or under emergency conditions, rather than to those which may result in the course of a thorough overhauling in port. [2] Leakage from the Joints of Boiler Mountings Such leakage by soaking through the lagging and keeping the plates wet- may give rise to surface corrosion on the boiler shell. OPERATION, MANAGEMENT AND REPAIR 703 The first care must be to stop the leakage by screwing down, re-calking or re-making the joints, as may be necessary. If there is reason to suspect corrosion of the boilers as well, the lagging should be removed and the corroded surfaces scraped clean and painted with good metal paint or other suitable cov- ering. [3] Leakage About Shell Joints Usually calking will be sufficient to stop any ordinary small leak in these joints. If it is serious and calking gives but little improvement, it may indicate a loose rivet or one with the head gone. In such case leakage about the rivet will usually be pres-, ent also, and will thus sei-ve to locate the trouble. Such rivets, must, of course, be replaced, in order to effectually stop the leak. Where a rivet has blown out and a quick repair is desired, , the hole may be drilled or reamed true and then tapped out. Fig. 421. Patch for Leaky Joint Then fit a bolt with corresponding thread and cut it partly through near the root with a hack saw. Screw this in, knock off the projecting end, rivet down the remainder and the job is complete. In some cases instead of replacing loose or broken rivets, or where for other reasons calking seems to be inefficient in stop- ping the leak, it may be considered desirable to put a patch over the seam, rivets and all. In such case a so-called "soft-patch" is applied. This is illustrated in Fig. 421. The patch is flanged and made with a recess of suitable size and form to accommodate the rivet points. It is then filled with a stiff putty of red lead and secured by bolts as shown. Such an application is really a red lead poultice, kept in place by a suitably formed steel cover, and secured to the shell, as explained. It is unnecessary to make such a patch of metal more than 3/16 or 1/4 inch thick, since' it is not intended to add strength to the shell, but simply to keep the red lead putty in place, and- thus stop the jet of leaking steam or water. , th The chief difficulty with lealcs in the shell seams and with the outside of boilers in general arises from the trouble in sub- 704 PRACTICAL MARINE ENGINEERING jecting them to the proper examination due to the presence of the lagging. As usually fitted, this covering is difficult of re- moval, and small leaks thus covered in may continue for long periods of time, keeping the outer surfaces wet and causing rust and corrosion where its existence may not be expected. A form of boiler lagging admitting of ready renewal and replacement in sections is much to be desired, and if full advantage were taken of such a form of covering to keep closer watch of all joints on the outer surface, much trouble might be avoided by taking the first appearances of trouble in time. [4] Leakage at Internal Joints The internal joints, on the whole, give more trouble than those on the outside. This is only to be expected, due to the thinner plates, the enormous range of temperature differences which exist, and the resultant expansions and contractions; The w//Mm/^ymm/Mmi'WMmmmmmmm Soft Patch, Locomotive Patch. Hard Patch. Fig. 422. Different Forms of Patclies difference in expansion between the furnaces and tubes is es- pecially liable to give trouble with the joints connecting the furnace to the combustion chamber, and several varieties of joint have been proposed to reduce this trouble to a minimum. With some forms of joint the greater expansion of the furnace tends directly to open up the joint, while vvith others the result is a shear on the rivets but no direct tendency to open the plates. In the latter case, however, the rivets are more directly exposed to the fire than in the former, and thus the points between the two joints are very nearly balanced. The joints producing shear on the rivets, however, allow a more ready removal of the furnace, and on this account it is often selected rather than the other type. Leaky joints on the combustion chamber should be first carefully re-calked. This operation, however, cannot be carried OPERATION, MANAGEMENT AND REPAIR 705 un indefinitely, for after calking to a certain extent, the edge must be chipped oflf to get a fresh calking edge. This, if re- peated, will leave the metal between the rivets and edge too narrow for safety. If careful and judicious calking does not remedy leaks in these seams, it is evident that the rivets need renewal, and in carrying this out especial care should be taken to see that the hales are fair in the two plates, and that the rivets fil' them completely. [5] Patches Turning now to the patching of boilers and to the different kinds of patches employed : It must first be remembered as a general principle that any thickening of metal on the heating surfaces is undesirable and to be avoided as far as possible, or reduced to tne lowest possible extent. If, therefore, a patch on a heating surface is to be considered as a permanent fixture, the faulty metal should be cut out, thus doubling the thickness only over the necessary width for the fastenings. A patch put on in this way with rivets beaded up as in regular boiler work is known as a hard patch, and is illustrated in Fig. 422. In some cas^s the patch must be put on from one side only, or is more temporary in character, In such case either the locomotive or the soft patch is used. The former is a patch put on with tap bolts, as illustrated in Fig. 422, and usually without cutting out the metal. The soft patch has been already referred to. In its more usual form, as shown in Fig. 422, it is made by lipping down a plate of steel so as to contain and hold in place a coating or layer of red lead putty. It is more suitable for temporary repairs, or where the surfaces are so rough and uneven that a patch of the other forms could not be fitted. The soft patch is sometimes secured with tap bolts, and sometimes with through bolts and nuts, as may be most convenient with the case in hand. As to whether a patch should be put on the water or fire side, much will depend on location and convenience. Where it is possible the water side may be chosen so that the steam pressure will tend to keep the patch in place. Usually, however, the fire side of the plate is more readily accessible, and in many cases there is no choice but to put the patch upon this side. In any event with either the hard or locomotive patches, the edge will require careful calking as the final closure and making of the 7o6 PRACTICAL MARINE ENGINEERING joint. With the soft patch, calking the edge is not necessary, as the putty is depended upon to stop the leak, and the office of the patch is merely to hold it in place. [6] Cracks and Holes A small crack is usually treated by drilling a hole at each end to prevent its extension, and then covering with a patch, according to location and convenience. Very small cracks are sometimes drilled and tapped out as close together as the holes will stand, and then filled with soft iron or steel bolts, riveted down so as to overlap and thus completely close the crack. Small isolated holes not accompanied by a general thinning of the metal may be treated in a similar fashion by drilling and tapping out the hole and riveting in a bit of soft iron or steel Fig. 423. Patch for Boiler Tube Sheet bolt. Larger holes, or where many are located near each other, or where they are accompanied by pronounced thinning of the metal must be treated by patching. In general it may be noted that plugging as above described, is only suitable for the mere stopping of a leak, and that it adds nothing whatever to the strength of the plate. If, then, the conditions are such as to make additional strength desirable, a patch must be fitted. - '• Where a crack is found in a tube sheet it usually extends from tube to tube. Such a crack may be covered by a patch extending over the crack and taking enough good metal to obtain a secure hold. The patch must have holes cut in it, of course, to correspond to the tube ends as shown in Fig. 423. [7] Blisters and> Laminations With modern boiler material these defects, are happily rare. In former years, and especially with iron plates, they were only OPERATION, MANAGEMENT AND REPAIR 707 too frequently met with. The chief danger from these defects is due to the weakening of the plates and the liability Of over- heating, due to poorer conductivity for heat. Such defects if very small are often left undisturbed, with careful watching and measurement from time to time. If small and the metal quite thin on one side, the thinner part was cut away, leaving the thicker side to do duty for both. In some cases also a dog and supporting bolt was fitted to support the remaining metal. For some serious cases, however, it was usually considered preferable to cut out the metal thus affected, and cover the hole with a patch. In all cases where patches are put on, or in general where new material is put into the boiler, it is well, if convenient, to select it of stock as nearly like the boiler as possible in physical and chemical consitution. This will tend to decrease the pos- sible sources of electro chemical action as discussed in Sec. 95. [8] Tubes The repairs to boiler tubes comprise re-expanding, plug- ging, and renewals. Expanding has already been explained, and a repetition of the process may be required from time to time, to keep the tube ends tight. The immediate cause of the leakage of boiler tubes is often the accumulation of dirt and scale about the tube ends and on the tube sheet. These points should therefore be carefully looked after, or the re-expanding will be of little use. Care must be taken that the operation of re-expanding is not repeated too often, or the metal of the tube end may become so thinned and hardened that there will be danger of weakness or brittleness at this point. For stopping a tube which has split or in any way developed a serious leak, a tube stopper or plug is used. Temporary stop- pers of pine wood are often employed. Such a plug closely fitting the tube and twelve or fifteen inches long may be forced in from the front end to a point where it covers a split or hole, and thus provides a temporary repair. The swelling of such a plug caused by the action of the water and steam will cause it to stick closely in place and thus more efifectually stop the leak than would a metal plug in the same location. For more per- manently plugging a tube, tapered cast iron plugs are used, one at each end, driven in to a tight fit and held in place by a rod passing through them from one end of the tube to the other 7o8 PRACTICAL MARINE ENGINEERING and set up with thfead and nut. The plugs and nuts should be faced so that when set up with a copper washer or turn of cop- per wire underneath, a steam tight joint between the plug and nut may be made. To plug a tube in this manner the fire must, of course, be drawn and the back connection entered in order to insert the back plug in place and adjust the rod and nut. When a tube is to be renewed the old one must first be drawn. To this end the back end is closed down so as to readily pass through the hole in the tube sheet. A rod is then passed through the tube and a nut and washer are fitted to the back end, the washer being of such size that it will bear on the tube end and at the same time will pass through the hole in the tube sheet. The front end of the rod passes freely through a dog or strong-back whose feet rest on the tube sheet, and is provided with a nut bearing on the face of the dog. The nut being then forced down, the rod is withdrawn and with it the tube. To facilitate withdrawal the front end of -the tube is usually made of slightly larger diameter than the back end, and the tube once started is readily withdrawn the remainder of the way. Before inserting the new tube the metal of the tube sheets about the holes should be carefully examined to see that the holes are smooth and fair and that no reason exists why the expansion of the new tube may not make a steam tight joint. The new tube may then be inserted, the ends expanded, beaded over at the back end or at the front and back ends if no stay tubes are fitted, and the operation is complete. [g] Leakage About Stays and Braces Leakage at these points may be due to corrosion about the joint, or to loosening due to repeated" expansion and contraction, or to bending or distortion of the plate or stay caused by bulging or partial collapse of the plate. If the leak is not serious, setting up on the nut, or calking about the joint between stay and plate may prove suiificient. If not it will usually be necessary to re- move and rdit the stay. For screw, stay bolts this will usually require the reaming out and retapping of the holes for the next larger size. For braces fitted with nuts or nuts and washers, the same size can usually be replaced, but especial care should be taken to insure the proper smoothness and fairness of surface about the holes, as well as the proper fit and adjustment of the nuts and washers, .so that the usual fitting will provide tightness of joint. OPERATION, MANAGEMENT AND REPAIR 70g [lo] Bulging or Partial Collapse of Furnace or Combustion Chamber Plates There has already been discussed in Sec. 93 the causes of bulging or collapse, and the steps most suitable to insure im- mediate safety. When the time comes for examination and re- pair the following steps may be taken : If the bulge is quite small, it may be decided" to leave it undisturbed, assuming that its strength is practically as great as before. In such cases, however, a template should be fitted to the bulge, and this should be a;, plied from time to time in order to detect any signs of further yielding at this point. In other cases special girders or through braces may be fitted to support the bulged portion, the details of the arrangement depending, of course, wholly on the circumstances of the injury. In other cases the bulged part may be more or less com- pletely forced back into place. This, however, is an operation requiring both skill and car€, and should not be undertaken with- out making the preparations necessary to carry it out in the proper manner. A portable grate or furnace for burning coke or charcoal is first provided of such shape and with such arrangements that the burning fuel may be brought close up to the bulged surface. An artificial draft may be provided by mean-s of a blower from ^ hand forge fitted with a suitable conduit, or otherwise as may be most convenient. In the meantime a cast iron former block should be provided, shaped on its face to correspond to the sur- face of the plate when forced back into position. A hydraulic jack or other like appliance must next be provided, taking es- pecial care to arrange for the distribution of the load on the base over a considerable area of plate so that no harm may be done by the reaction from the head. To this end a support of heavy timbers is usually the most convenient to arrange. These various appliances being in readiness the bulg.ed plate is heated to a low red, the former block and jack are adjusted in position, and the plate is carefully forced back into shape. Several ap- plications of the heat and of the jack may become necessary before the plate is restored to its original form. It is thought by many that the partial heating of a steel plate in this way with no later opportunity for general annealing is liable to injure its homogeneity and toughness, especially if 710 PRACTICAL MARINE ENGINEERING the operations are carried on at too low a temperature, or ap- proaching what is known as blue heat. This was undoubtedly true for much of the earlier products of the steel makers, and there is no doubt that the homogeneity of the metal is thus somewhat disturbed. With the latest and best grades of boiler plate, however, little danger, as regards strength at least, need be feared on this score, and but little hesitation is now felt in reducing to shape a bulge of moderate depth. [ii] Split in Feed Pipe A small split in the feed pipe may sometimes be temporarily repaired by wrapping with heavy canvas and marline, or copper wire. It is, however, difficult to make a tight joint with hand wrapping, especially with modern high pressures, and a more effective plan is to form up a patch of sheet copper and secure it in place by bolted strap clamps, with a sheet of good elastic packing, pure rubber, or a thin layer of stiff putty between the patch and the pipe to make the joint. A small hole in the feed pipe may, if the metal is thick enough, be stopped by drilling and tapping out and riveting in a small screw plug. Soft solder when applied with skill may also be used to stop pin holes, or to aid in securing a suitable plug in a larger hole. If, however, the hole is of any considerable size, or if the metal is thin about its edges, some form of patch, as described above, must be made use of. All such repairs are, of course, only temporary, and at the earliest convenient opportunity the damaged length of pipe should be replaced with new. In some cases with copper pipes, however, where the neces- sary materials and skill are available, it may be desired to under- take a more permanent repair by brazing a patch over the hole or split. To this end the metal about the defective spot is first cleaned with file, emery cloth and acid. The patch similarly cleaned is cut from sheet copper of about the same thickness as that of the pipe, formed to fit over the defective spot and wired in place. A clear coke or charcoal fire is then prepared on a forge and the pipe placed in position. The spelter or hard solder, mixed with borax as the flux, is then placed in position on the inside of the pipe and the whole carefully heated. At the proper temperature the spelter will melt and run in between the patch and pipe, thus forming a joint between the two. Care must be OPERATION. MANAGEMENT AND REPAIR 7" exercised in this operation in order to avoid danger of overheat- ing or "burning" the copper, as serious loss of strength will result. Sec. 98. ENGINE OVERHAULING, ADJUSTMENT AND REPAIRS A few hints regarding the more common- operations involved in the overhauling, adjustment and repair of marine machinery will now be undertaken. [i] Cylinders First, in the main engine, the cylinder covers must be re- moved at frequent intervals, and attention given to the condition of the wearing surfaces and of the piston rings. The troubles most liable to be found are cutting and scoring of these sur- faces, and derangement or breakage of the springs. The nuts of the follower studs and all other forms of screwed fastenings should be examined, in order that any tendency toward loosen- ing up or backing off may be noted and checked. To examine the condition of the piston the follower plate is lifted and the springs and packing rings removed. The latter, if wearing properly, will be of uniform thickness around the en- tire circumference, and of uniform polish on the outer surface. If the piston rod is bent or cylinder bore not quite in line with the motion of the rod, the ring will wear wedge shaped in cross section. In replacing, care should be taken to note the degree of tightness of the ring when set out with its springs. This should be such as to supjxjrt the ring anywhere along the bore, but not so much that the ring cannot be pushed along by hand, using moderate force. In closing up the cylinder or valve chests, especial care should be taken to see that all nuts, split pins, etc., are properly secured in place, and that no tools, waste or other foreign substance are left within. Neglect of this latter point has often been the cause of serious trouble, resulting in broken cylinder heads, bent piston rods, broken valves, port metal, etc. To test the tightness of the joints of the cylinder liners, the cylinder being open, steam is admitted to the jacket and the joints are carefully examined top and bottom. Where there is no manhole on the lower head, as is common with small cylinders, a leak of any significance will become evident by opening the lower indicator cock. In order to test the tightness of the piston under steam, the cylinder head being in place, proceed as follows : Put the engine 712 PRACTICAL MARINE ENGINEERING and links in such position that a little steam can be admitted on top of the piston and then open the bottom indicator cock. Then admit the steam, usually through the starting valve, and if it blows through the lower cock the piston is thus shown to be leaky. For a thorough test it will be well to try the leakage in both directions ; that is, from top to bottom, as above, and similarly, from bottom to top. [2] Pin Joints and Bearings The various pin joints and cylindrical bearings will need attention according to the special circumstances of the case. The manner in which a joint or bearing has been working, both as to noise and temperature, will often serve as a guide to those which require the most attention. To examine the crosshead bearings the main points of the operation may be outlined as follows : (i) The crosshead with piston rod and piston must be se- cured near or at the top of the stroke. This is sometimes done by inserting pins or bolts in the upper edge of the slide through the holes for securing the slipper, and allowing such to project over the top of the guide. Or otherwise it may be done by shoring in such a way as may best be suited to the details of the case in hand. (2) The outer caps and brasses are removed. (3) A wooden chock lashed to the connecting rod is fitted between its upper end and the guide. This will serve to support the upper end when free from the crosshead. (4) The connecting rod sloping in such a way as will bring the support of its upper end upon the chock, the turning engine is used to revolve the crank down until the parts are sufficiently clear to admit of the examination desired. To remove the crank pin brasses the maiiv points of the operation may be outlined as follows : (i) Starting with crank near its lower position the bottom cap is removed and landed on a bed suitably prepared for it. (2) The turning engine is then used to carry the crank up nearly or quite to the top of the stroke, where the crosshead is secured by hanging up or shoring as described above. (3) The upper brass is then secured and the crank is rotated down until the parts are sufficiently clear for the purpose in view. OPERATION, MANAGEMENT AND REPAIR 713 For like examinations of other parts, similar means will readily suggest themselves. For removing the lower brass of the main pillow block bear- ings where it is in the form of a half cylindrical shell, it needs simply to be rotated out. A method sometimes used for this purpose is to clamp to the crank arm a bar of steel carrying a projecting pin or bolt so placed that it will engage with the top face of the brass when rotated around. The upper cap and brass being then removed, the shaft is rotated carefully by means of the turning engine, and in this way the lower brass is forced around and up until free from its bed. Bearings and journals of this character may simply require readjustment, or refitting and adjustment as well. When the wear has been considerable, the liners or chock pieces between the brasses will need thinning, in order to reduce the clearance between the journal and the bearing to the proper amount. In order to measure the clearance under any given adjustment, a piece of lead wire is employed, of somewhat greater diameter than the clearance is to be. This wire is placed on the journal Such an operation is called taking a lead. Several leads, if de- the journal and the brass. The cap is then removed, and from the resulting thickness of the wire the clearance at any point between the journal and the brass may be readily measured. Such an operation is called taking a lead. Several leads, if de- sired, may be taken at once from a bearing, and will thus serve to map out quite satisfactorily the distribution of clearance, and thus to show them when the proper adjustment has been made. The proper amount of clearance in any given case is somewhat a matter of judgment, and will, of course, vary with the size of the journal. In ordinary cases it may be made about .002 of the diameter. If time is limited the adjustment may be efifected without the taking of leads, as follows: The chock pieces or liners are taken out and the nuts are tightened up till the brasses bear full on the journal. Their positions are then marked, and they are then backed oflf an amount determined by judgment or experience with the particular circumstances of the case, and the liners are stripped to fit this adjustment. While this method is not as satis- factory as with leads, it is much quicker, and with experience good results mav be obtained. 714 PRACTICAL MARINE ENGINEERING In connection with the marking of the nuts for such pur- poses it may be recommended as a good plan to mark permanent- ly with a line and a numeral i, 2, 3, 4, 5, 6, the faces of all the large nuts likely to be used in making adjustments. An adjacent reference line on the bolts or on the metal of the bearing caps will then furnish means for making a record of each adjustment, or if no permanent record is desired, such means will greatly facilitate making the adjustment in any given case. The refitting of bearings and journals on shipboard does not usually extend beyond removing or smoothing rough spots caused by overheating and scoring. This may be done by filing followed by "lapping" with oil stone powder or dressing with an oil stone. In some cases emery is used, but great care is then necessary in order to remove all particles, as if allowed to re- main, they will give trouble by continued cutting and grinding in the bearings. The brasses are similarly redressed, usually by scraping. The nature of the contact between the brass and the journal is tested by lightly smearing the latter with red lead and then applying the brass in place and lightly rotating back and forth. The high spots will then be shown by the red lead and may be further dressed down till a satisfactory fit is obtained. It may be noted that where brasses are thus fitted up each one may show a satisfactory fit when tried separately and without external constraint, and yet when in place they may be unable to come to the same relative positions on the journal and make satisfactory contact with it. For this reason it is preferable to test the contact with the brasses together and regularly secured in place. This is not always possible, however, by reason of the additional time required, and judgment in all such cases must be used, having in view the various circumstances of the case in hand. [3] Crosshead Guides The main guides and crosshead slides must receive attention, both as regards cutting or uneven wear, and as regards the ques- tion of adjustment. The result of wear is to throw a cross break- ing stress on the piston rod at each stroke, as the crosshead is forced over by the oblique action of the connecting rod to a bear- ing on the guides. Care must therefore be taken that when the engine is turned without a load, the guide surface remains in full contact with the face of the slide, and therefore in a condition OPERATION, MANAGEMENT AND REPAIR 7^5 to support and guide the lower end of the piston rod in a path consistent with the movement of the rod in the axis of the cylin- der. If this condition is not fulfilled, the necessary adjustments must be made in the manner best suited to the structural arrange- ments of the case in hand. To remove the slipper or bearing piece for examination or refitting, screw eyes may be screwed into holes in its upper edge made for .the purpose, and from these the slipper may be sup- ported by means of wire rope or stout wire wound around a baf suitably supported and secured above the slipper. The bolts holding the slipper to the crosshead are then removed and the crosshead forced over by screw or hydraulic jack or other con- venient means, sufficient to ease the pressure between the slipper and the guide. The slipper may then be lowered by using the bar as an axle and the rope or wire will readily follow down between the crosshead and guide surface. [4] Crosshead Marks In connection with adjustment of the moving parts of the engine it is well to have a mark on the crosshead and correspond- ing marks on the guide, showing the extreme positions of the piston when in contact with the cylinder heads, top» and bottom ; also two marks placed slightly within the latter and showing the ends of the natural stroke, and a mark placed midway between the two latter, showing the location of the piston when in mid- stroke. The distance from the extreme marks to these showing the ends of the stroke, shows the amount of clearance proper between the piston and the cylinder heads when the former is at the ends of the stroke. This will vary with the size of the engine and character of the workmanship, but it is usually found between ^ and ^ or J4 inch, being a little more at the bottom than at the top, to allow for the general tendency of the parts to lower rather than to rise through the effect of wear. To determine these extreme or striking points a convenient reference mark is first placed on the crosshead. The connecting rod may then be disconnected and the parts hoisted up as far as they will go, or until there is contact between piston and head. A rhark is then made on the guide corresponding to that on the cross- ' head. The parts are then lowered down as far as they will go, or 7i6 PRACTICAL MARINE ENGINEERING until there is contact between the piston and the lower head, and another mark is made on the guide corresponding to that on the crosshead. The distance between these is then taken, and from it is subtracted the length of stroke. The remainder is then divided between the two clearances, top and bottom. Midway between the two inner points a point may be placed to indicate the location for mid or half stroke. Thus, if the stroke is 36 inches and the distance found as above is 37 inches, the i inch difference is to be divided between the two clearances, giving to the upper, say 7"i6, and to the lower 9-16 inch. These differences are then laid off within the outside marks, and the points thus given will serve at any time as a guide for the adjustment regarding clearance proper, while the movement of the piston may be readily brought to conform to these limits by suitable adjustment of the liners or chock pieces in the joints and bearings of the connecting rod and crank shaft. The 36 inches may then be divided equally and the mark placed to show mid stroke, such a point being sometimes of use in connection with the setting of the valve. Another method of determining the clearance which is avail- able when the cylinders have manholes is as follows : The man- holes are removed and a number of balls of stiff red lead or other putty and faced with plumbago are distributed on the top of the piston and on the inside of the lower head. The engine is then given a revolution by means of the turning engine and the balls are collected. This method serves to show just how the clearance is distributed, and is therefore a valuable test for a bent piston-rod, a condition which will throw the piston out of position and give greater clearance on one side than on the other. [5] Lining Up An important feature, both of the original setting up of machinery and of its overhauling and adjustment, is the de- termination or correction of the alinement of the various moving parts. It is clear, of course, what the condition of proper aline- ment is. For a marine engine it may be briefly stated as follows : (i) The centers or axes of the main pillow block bearings should all be in one straight line, which will coincide with the crank shaft axis, and which will be taken as a standard or line of reference. OPERATION, MANAGEMENT AND REPAIR 7^7 (2) The axes or center lines of the cylinders should all be in the same vertical plane containing the centerline of (i), arid they must also be' at right angles to this line. (3) The same vertical plane should also contain the axes or center lines of all the crosshead pins. (4) The axes or center lines of the crank pins or crank pin bearings in the connecting rods must also be parallel to the cen- terline in (i). (5) The surfaces of the main guides must be parallel to the plane in (2). (6) The line shaft must be in line with itself, and unless a flexible coupling is provided between this and the crank shaft it must also be in line with the crank shaft, as determined by the line in (i). The same general principles, of course, control the aline- ment of the valve gear and the various other moving parts, such as the starting, handling and drain gear, attached pumps, etc., but into these there is no necessity to go into further detail. The implements used in establishing the relation between these various lines and planes will naturally vary with the circum- stances, but are usually found among the following: The level, plumb line and square. The straight edge. The stretched wire or cord. Provision for using a line of sight. A straight line, such as that for a Hne of shafting, may be determined by either of the latter. The sag in a piano wire of known size and length and stretched with a known weight over a pulley is a matter which may be found by a computation, or, better still, it may be determined in the open air by the aid of a surveying instrument with the usual cross hairs. A table giving the sag at various points between the ends for known lengths and for a known stretching weight will then give a ready means of establishing a straight line on board ship, by stretching the wire under the same conditions, and then setting upward at the various points the amount of the sag. A series of levels may thus be found which will give a true, straight line within the limit of the error in measurement. When a line of sight is used the following method may be employed : A board is fitted to the bearings at the extreme ends 7iS PRACTICAL MARINE ENGINEERING of the line to be run, a hole of some considerable size being made in the board at about the center. This hole is then covered with a piece of thin sheet metal having a small hole, say 1-16 to 1-8 inch in diameter. These sheets of metal are adjusted by measure- ment until the small hole, as accurately as may be, is brought to the center of the bearing. Similar boards are then prepared for the other bearings or points at which it is desired to establish the line. A light is then placed at one end beyond the further hole, and the eye at the other end. An assistant then adjusts the intermediate pieces of sheet metal until the light reaches the eye through the entire series of holes. The centers of these holes will then serve to establish a series of levels which may be marked on the pedestals, bulkheads or other convenient points, and which will serve to establish the line as desired. In lining up and adjusting the engine itself so that the vari- ous conditions (i)-(5) above are fulfilled, very much will depend on the accuracy and care with which the various parts have been machined in the shops. The gaps in the bed plate, which receive the main bearing boxes, should be planed out so that they are all in line. This is a matter which may be tested by a straight edge, or by measurements from a stretched wire. If the bottom brasses are then adjusted, all to the same thickness, they will evidently support the crank shaft in line. This may also be further tested by reference to a line of levels, each of which is obtained by measuring the same distance upward from the bottom of each gap, and locating on the bed plate at any convenient point the level thus determined. This adjustment, it may be noted, will bring the axis of the crank shaft parallel with the bottom of the gaps. Passing now to the columns, the seatings for their feet should have been planed at the same time as the gaps. This will bring the bottom of the feet in a plane parallel with the bottom of the gaps, and hence parallel with the axis of the crank shaft. The columns and cylinders may now be erected and temporarily secured in place. The center line for each set of moving parts may be next determined as follows : A piece of board is placed across the top of the cylinder and secured at each end and over one or more stud bolts. Then, by careful measurement or the use of a beam compass, the center of the bore at the top of the cvlinder is located on the board. A small hole is then bored at OPERATION, MANAGEMENT AND REPAIR ■ 7i() this point and a fine wire is passed through and attached to a little frame, which will allow a few inches of the wire to show above the board. The lower end of the wire is then located in the crank shaft axis by suitable measurement from the faces of the bed plate. The wire is then stretched between the two points, and the adjustment of the upper end verified by renewed meas- urement. If these parts come accurately to place, the wire will be truly central relative, to the opening left in the lower head for the stuffing box, and hence it may be taken as the true center line for the cylinder as a whole. The wire will also be found at a constant distance from the guide surface on the column, thus proving the latter parallel to the center line, as required by (5) above. The wire will also be found at right angles to the crank shaft axis, as required by (2) above, and, of course, in a general way, at right angles to the bed plate transversely. Supposing these various conditions fulfilled for each center line separately, then it must be ascertained whether they are all in the same fore and aft plane as referred to in (2) above. To examine this point it is necessary to look the wires "out of wind," as the expression is, by standing aft or forward and trying, by sighting fore and aft, to bring all the wires accurately behind the nearest one. If these various conditions, for each wire sep- arately and for all collectively, are not fulfilled, then the necessary adjustments must be made until they are brought into the re- quired relations as above specified. As a further adjustment to be made at this time, a wire may be stretched fore and aft along or near the guide surfaces, and at the same horizontal distance from each vertical center line. This will serve to show whether the guide surfaces stand in the right direction fore and aft, and hence, whether the plane of each is parallel to the central plane defined in (2) above. In setting up attached auxiliaries, such as air, circulating or feed pumps, the principles used will be similar to those al- ready discussed, while the methods used will depend upon the particular circumstances of the case. If the seatings are located in the bed plate they will probably be planed at the same time as the main bearing gaps, and if the pump bases are faced at the same time they are bored, their axes will come at right angles to the seatings, and hence parallel to the axes of the main cylinders, and thus properly in line. 730 PRACTICAL MARINE ENGINEERING In order to test the line of the crosshead pins the connecting rod may be hung from the upper end and allowed to swing partially free at the bottom. Then, by turning the engine into, various positions in the revolution and measuring the fore and aft clearance between the crank webs and the faces of the lower end of the rod when thus relieved of constraint, the accuracy of the adjustment can be determined. This operation may be car- ried out in the following manner: Assuming that it is desired to test the adjustment in the case of an engine completely set up, the cap on the lower end of the connecting rod is removed and the crosshead is shored up in any convenient manner. The engine is then turned slightly by hydraulic jack or turning en- gine in such direction as to carry the crank pin away from the rod and thus leave the latter free in a fore and aft direction, so far as direct contact with the pin is concerned. Measurements are then taken, and the engine is next moved around so as to bring the pin against its bearing again, and then on to a new position. Here the crosshead is again shored, the pin backed off measurements taken as before, and so on. In this way the piston, crosshead and connecting rod are carried around by resting on the crank pin, and then in each position the connecting rod is freed by shoring the crosshead and backing off the crank pin. In case the clearance between the crank- pin brass and the faces of the webs is too small to allow a possible irregularity of move- ments to show itself, the regular brass may be taken out and a dummy brass or wooden block, with sufficient clearance for all possible motion, may be fitted in its place. In locating a line shaft, a wire or line of sight may be used in the general manner previously described. After locating the center of the stern tube at the stern post, the line is run to the after end of the crank shaft or on through the forward end, as may be desired, such point being located by measurement according to the drawings of the ship, engine seating and bed plate. In twin screw ships the centers at the after struts are located by measuring at the proper height the necessary distance out-» ward from the centerline of the stern post, at the same time squaring from this centerline so as to bring both centers at the same height above the keel. The two lines are then set at the forward end at equal distances from the keel at the proper height, in accordance with the drawings. In most cases the shafts are OPERATION, MANAGEMENT AND REPAIR 721 not parallel with the keel, either in a vertical or horizontal direc- tion, usually inclining outward from forward aft and either up- ward or downward, according to the size of the ship and other circumstances of the case. In the examination of the adjustment of machinery which has been already in operation, as in the routine care of marine engines, it is not to be supposed that the preceding operations in all their details will be necessary. Judgment must be used, having in view the particular points to be examined, and the best means of effecting such examination in accordance with the general principles above discussed. Thus the fairness of the line shafting must be tested occa- sionally, lest, as time goes on, wear in the bearings or changes in the structure of the ship may throw it seriously out of line. For this purpose the following method may be used : Three or more laths or battens are provided with a straight edge on one side. These are then placed across the shaft on the upper side, as nearly horizontal as judgment may indicate, being located at suc- cessive points along the line of shafting to be examined. A line of sight is then taken along the projecting lower edges of the battens and by adjustment they are brought parallel to each other. Then, if they can all be brought into one line the shaft itself is in line. If not, the shaft is out of line in the vertical direction, and, by blocking or other similar adjustment, until the battens are all brought into one line the amount by which the shaft is out at one point relative to two others is readily de- termined. In a similar manner the line in the horizontal direction may be tested by holding the battens vertical against the side of the shafting. This method presupposes, of course, that the shafting throughout the part tested is all of the same size. Instead of placing the battens on the shafting they may be placed on the couplings quite as well, supposing, of course, that the latter are all of the same size. Another test which is sometimes used consists in slacking the coupling bolts at a coupling near which it is suspected that the shaft is not in line, and noting whether there is any tendency for the two parts of the coupling to open out on one side or another. Such an opening out then shows an unfairness in the line in one way or another, according to the side on which it appears. 722 PRACTICAL MARINE ENGINEERING [6] Valve Gear In the routine examination of tlie valve gear the points to be looked after are wear and lost motion in the eccentrics and eccentric straps, in the link block brasses of the Stephenson link, or in like parts of other forms of valve gear, in the various pin joints and connections, and abrasion or uneven wear in the valve faces or seats. In the case of the eccentrics and straps and various pin joints, the wear may be taken up by the adjustments usually provided and in the general manner already outlined for other similar parts. Excessive or irregular wear in a flat slide valve or seat may require either resurfacing or renewal, accord- ing to the circumstances of the case. With piston valves, es- pecially if not fitted with rings, excessive wear in either valve or seat will mean a serious steam leak, and will usually call for new parts, either for valve or seat or both. [7] Thrust Bearings The most common trouble with thrust bearings is scoring or irregular wear of the bearing surfaces, or a general wear which may allow the thrust shaft to move forward sufficiently to put a pronounced thrust on crank shafts. This will result in heat- ing and wearing, and may throw the crank shaft bearings out of line. A little clearance is usually allowed in the shaft couplings and in the fitting up of the crank shaft and shaft pin bearings, so as to insure freedom from end thrust for the crank shaft as a whole. If the wear at the thrust collars should exceed this, then a part of the thrust would be transmitted to the crank shaft, with effects as above noted. With adjustable or horseshoe collars this trouble is readily adjusted by moving the collars back by means of the adjusting nuts provided. With the plain type of thrust bearing the bearing as a whole must be moved slightly aft by means of the screws provided for the purpose. [8] Circulating Pump The engines for operating such pumps require the care necessary in all machinery of such type, the principles of which have been already discussed. The runner simply needs examina- tion from time to time to make sure that it is running freely, but without undue clearance on either side in its casing. Trouble is often met with in the maintenance of circulating pumps by the choking of the inlet passage, valve or strainer by marine OPERATION. MANAGEMENT AND REPAIR 723 growth of one form or another. To aid in freeing the strainer and inlet passage a connection is often made with the deHvery of one of the fire or other auxihary pumps, or by providing a steam jet, by means of which they may often be cleared without the need of regular overhauling. The runner shaft inside the pump casing should also be examined at intervals to insure that it is not wasting away through the action of the sea water. [g] Condenser The chief troubles to be expected with condensers are as follows : ( 1 ) Leakage about the tube ends through the packings from the salt water to the steam side. (2) Corrosion and pitting of the tubes, resulting ultimately in the development of holes or the breaking of the tubes and similar leakage, as in (i). (3) Fouling of the tubes with oil deposit on the condensing surface, thus decreasing the heat conductivity of the metal and the efficiency of condensation. The condenser heads or bonnets must therefore be taken off from time to time and the condition of the tube ends and pack- ings examined with reference to the matter of leakage and general condition. To test the condenser for leakage the main inlet and out- board valves should be tightly closed, and the connections to the low pressure cylinder and air pump closed by blank flanges. The consdenser heads may then be taken off and the steam side filled with water while a watch is kept for leaks on the tube sheets at each end. Where available, air pressure in place of Hydrostatic may be used for this test, all possible points of leak- age being searched with a candle flame while the pressure is on ; the existence of a leak will be indicated by the blowing of the flame. It is also desirable to put, by means of a hand-pump or otherwise, a pressure of 15 to 20 pounds per square inch on the contained water, thus making the development of the leak more certain. It is sometimes desirable to be able to identify both ends of the same tube. This may be readily done by passing a wire through from one end to the other. In some cases a lamp held at one end will serve the same purpose. When provided with bonnets for the purpose, the steam side 724 PRACTICAL MARINE ENGINEERING of the condenser must also be occasionally opened and the tubes and interior surfaces examined, with refetence to grease coating and general condition. Where there may be any doubt as to the condition of the tubes in the interior, a few should be drawn when the heads or head bonnets are removed, and their condition determined. So far as the accumulation of grease is concerned, the con- denser may be cleaned by the use of hot soda or lye water, care being taken to wash it out thoroughly so as to remove any excess of the alkali. When soda is used for the boilers it is some- times introduced into the condenser, there entering the feed water and then passing on to the boiler. It may be questioned, however, whether this is the best plan, as accumulations of grease only partly converted to soap may thus be carried into the boiler, there giving trouble, as already referred to under that head. Zinc plates are often used on the salt water side in condenser heads to protect against corrosion, in a similar manner as ex- plained for boilers in Sec. 95. The condition of these plates and of their attachment to the shell should be carefully noted when the condenser is opened, and such repairs made as may be re- quired. [10] Air Pumps The head, foot and bucket valves require the most frequent and careful examination. They often tend to become coated by an accumulation of a black, greasy paste formed from the cylin- der oil and the material of the wasted zinc plates, if such are used. This accumulation may prevent their proper working, and they should be carefully cleaned as occasion may offer. With air pumps attached to the main engine, and where the number of strokes is usually greater than with the independent pump, the valves sometimes give trouble by severe pounding against their seats and guards. This is due to their inertia, and is likely to be more severe, as the valves are heavier and have more lift. Light metal valves of sufficient number and size to allow of moderate lift are therefore to be preferred for all such pur- poses. [11] Pumps in General The chief troubles to be expected in the operation of the OPERATION, MANAGEMENT AND REPAIR 72$ various forms of independent pumps found on shipboard are as follows : (i) In the water end the plunger rings or packing or the barrel may become worn, thus allowing considerable leakage or "slip," especially under high pressure, as in boiler feed pumps. (2) The water valves, either inflow or delivery, may be- come worn or deranged, and thus fail to hold the water as they should, so preventing the proper operation of the pump. (3) In the steam end the piston rings or cylinder barrel may become worn, allowing steam to blow from one side to the other and decreasing the effective steam load on the piston. (4) The main steam valve or more often some part of the auxiliary steam operating gear may become worn or deranged so that the pump can no longer properly operate under steam. These various troubles must be guarded against by periodi- cal examination of the points mentioned with a view to the detec- tion of wear or derangement of any kind whatever. [12] Piping Steam piping of copper if improperly constrained may be- come brittle and weakened in spots by long continued expansion and contraction. An indication of this may often be found in the wavy or irregular condition of the surface. Such pipe should, of course, be replaced at the first opportunity. A repair may, however, be made by banding with screw clamps made of strap iron or steel and closely spaced over the suspected part. Small holes which may sometimes develop may be treated with a soft patch held in place by a screw clamp, by filling with solder, or by a patch as in Sec. 97 [2] (10), according to the cir- cumstances of the case. Leakage and like trouble with steel piping may be treated by the same general means as for boilers, and as discussed in the preceding section. Sec. 99. SPARE PARTS In order to provide for the results of regular wear, and for the possibilities of accident it is customary to carry a certain number of spare parts, especially of those most likely to require replacement, either as the result of wear or accident. The pieces carried and their number will depend entirely, of course, on the 726 PRACTICAL MARINE ENGINEERING extent to which it may be necessary or desirable to fit out the ship with provision for such wear and emergency. No attempt will, therefore, be made to give any complete list of such parts, but among those more commonly carried the following may be mentioned : Grate bars, bearers and dead plates, furnace and ash pit doors, boiler tubes, manhole and handhole plates with fit- tings, safety valve springs, boiler gage cocks, fittings for boiler water gages, feed check valves, bottom blow valve, surface blow valve, piston and pump rods for the various pumps, valves, valve guards and springs for the various pumps, follower bolts, nuts and springs for the various steam pistons, brasses for the various bearings, horseshoes for the thrust bearing, propeller blades, valve stems, metallic packing for the various stuffing boxes where it is used, shaft coupling bolts, emergency shaft coupling, condenser tubes and glands, evaporator and distiller tubes, evaporator coils, one section of crank shaft, if made in sections. Sec. 100. LAYING UP MARINE MACHINERY The chief dangers to marine machinery when not in use arise from the likelihood of rust and corrosion. Fundamental principles relating to these chemical changes have been discussed in Sec. 95, and by reference to that point it will be seen that the chief points to be attended to relate to the protecion of the sur- face from moisture and corroding acids. Where appplicable a good metallic paint well laid on will be found the most efficient and satisfactory. In such case the surfaces must be dry and well cleaned in accordance with the principles discussed in Sec. 92 [i] (10). For finished surfaces or bright work generally, where paint would not be suitable, a coating of heavy cylinder or other like oil or vaseline may be used, or perhaps even more commonly a mixture of white lead and tallow in about equal proportions. Any of these will efficiently protect the surfaces and will remain for a long period of time without becoming too hard to admit of ready removal, especially with the aid of a little kerosene or other light oil. One of the most important features connected with the lay- ing up of marine machinery is the draining out of water con- tained in the various cylinders, pipes, bends, valve chambers, etc. The draining off of the water is, of course, of importance relative to the question of rust and corrosion, but it may be of even still OPERATION, MANAGEMENT AND REPAIR 727 greater importance relative to the question of freezing and pos- sible rupture of the chamber, casing, or pipe containing the water. Many a cracked cylinder or valve chest or globe valve chamber, or split in pipe elbow or bend, or in boiler or condenser tube, etc., has been due to incomplete drainage of water and subsequent freezing. In laying up marine machinery, therefore, where there is any liability of freezing, a systematic study must be made of the piping systems, pockets, etc., where water might collect and by freezing result in damage. These remarks apply especially to piping and fittings, to small auxiliaries, to the con- denser, and to watertube boilers. If the proper drains are not fitted and the water cannot be gotten out in any other way, then the necessary joints should be broken and the water removed in this manner. QUESTIONS Operation, Management and Repair PAGE A general examination of the boiler and fireroom equipment is to be made previous to getting up steam. Mention the more im- portant points to be attended to in such an examination 626 How are fires laid and started ? 627 After lighting fires what points may receive special attention ? 627 What precaution should be taken in opening a valve connecting a boiler with a pipe in which there is no steam pressure? 628 What fundamental points should be kept in view throughout the entire course of these operations ? 629 What steps may be taken when steam is foraied and a moderate pressure is developed ? 629 What auxiliary machinery in particular should receive attention at this time ? 629 What attention should be paid the funnel guys during this period?.. 629 Describe briefly the routine of firing 630 What difference of method may be employed according as the coal is hard or soft ? 630 What is the usual thickness of the fire ? 631 How is the thickness of the fire related to the draft pressure? 631 What is the result if thin spots are formed ? 631 What means are available for working, cleaning and caring for the fire in the intervals of coaling ? 631 Describe the duties of the water tender 632 Describe the "double shut-off" method of making sure that the gage glass is clear 633 For what purposes is blowing off now employed ? 634 What is the especial use of the bottom blow? Of the surface blow?. . 634 How may a plug cock be tested to ascertain whether it is open or closed ? 63S What means are available for ascertaining the density or saturation of the water ? 635 Describe the various means available for the disposal of ashes 635 Describe the method of cleaning a fire 635 728 PRACTICAL MARINE ENGINEERING PAGE What mear.s are available for removing the soot and ashes which accumulate in the tubes ? 636 What preparations are made for sweeping tubes, and hovif is the operation carried out ? 636 What dispositions may be taken when making a momentary or very short stop ? 637 If the stop is to be of longer duration what dispositions may be neces- sary or suitable ? 637 What principles lie at the foundation of these various steps ?. 638 What mode of firing is usually most effective with watertube boilers? 638 Why with such boilers is it especially necessary to pay strict attention to the feed ? 638 What trouble is met with on the fire-side of the tubes of watertube boilers ? 638 What dispositions may be made just previous to coming into port, or to a long stop, during which the fires are to be hauled and the boilers opened ? 639 What are the first steps to be taken in connection with getting under way in a ship with whose machinery you are not familiar ? 640 Mention the various auxiliaries which must be examined and tested. . 641 Describe the process of warming up the engine 641 Mention the various steps to be taken in connection with turning the engine over under steam 642 Trace in detail the passage of the steam from its formation in the boilers through its entire round, and to its return to the boilers as feed water 643 What dispositions are made when stopping the engines momentarily? What if the stop is to be of some little duration, but with the engines ready for immediate start? What if of longer duration and steam is to be shut off the engine ? 645 What derangements are likely to occur in the oiling gear ? 646 What causes may lead to a hot bearing, and what measures may be taken to control the situation ? 646 What are the causes of pounding, and what measures of relief may be taken ? 648 What are the evidences of priming or lifting water, and what should be done under such conditions ? .- 649 What causes may lead to a poor vacuum with a hot condenser? 649 What causes may lead to a poor vacuum with a cool condenser?. . . . 650 What are foaming and priming, and what steps may be taken to con- trol these conditions ? 664 What causes may affect the working of the feed pump, and what steps may be taken to locate and remove the trouble ? 666 What may be done in case the check valve is j ammed ? 668 What may be done in case the water gage glass bursts ? 669 What steps may be taken in the case of low water in the boilers?. . . . 669 What steps may be taken in the case of collapse or rupture of furnace crowns or combustion chambers ? 672 What steps may be taken in the case of serious leakage in the boiler tubes ? 673 What steps may be taken in the case of a ruptured steam pipe? 674 What are the necessary conditions in order that rusting may pro- ceed continuously at ordinary temperatures ? 676 What means does this suggest for preventing the formation of iron rust ? 676 Describe the process of corrosion by an acid 677 Why are brass, bronze and copper used for many fittings which might otherwise be made of iron ? 677 What is black or magnetic iron oxide and how is it formed? 678 OPERATION, MANAGEMENT AND REPAIR 729 PAGE What is one of the purposes of the ferrules sometimes fitted in the back ends of boiler tubes ? 678 How may air and carbon dioxide gain access to the inside of a boiler ? 678 Explain the nature of animal and vegetable oils and how they may give rise to the formation of a fatty acid 679 Explain the troubles which were formerly met with due to the pres- ence of fatty acids in boilers 679 How are these difficulties now avoided ? 679 What other acids may be present in the boiler ? 679 What is meant by pitting ? 680 Explain briefly what is meant By electrochemical action and its rela- tion to boiler corrosion 680 What are the various means which may be employed to reduce or prevent the internal corrosion of boilers ? 683 What are the special conditions necessary to reduce or prevent electro- chemical action ? 684 How does the use of soda aid in preventing corrosion? 684 How does the use of zincs aid in this purpose ? 685 How shouW the zincs be fitted in order to be most effective? 685 Should zincs be fitted in boilers used for distilling purposes? 686 What treatment should be applied to spots in the boiler showing marked corrosion ? 686 Explain the beneficial action of scale in preventing corrosion 686 What means may be taken for the protection of boilers which are to be laid up ? 687 What is the proportion of solid matter in ordinary sea water? 688 What is the average composition of this solid matter? 688 What is the chief component of the solid matter in ordinary fresh water? 688 What are the chief constituents of boiler scale from river water, from brackish water and from sea water ? 688 Explain the manner in which calcium carbonate is deposited from solution 689 Explain the manner in which calcium sulphate is deposited from solution 68g What ill effects may arise from the accumulation of scale in the boiler ? 690 State some of the various ways in which the formation of fresh water scale may be reduced or prevented 6go Explain why the present condition with regard to the formation of salt water scale is quite different from that existing in former years with the very light steam pressures then common 693 Why was blowing off and making up with salt feed then admissible, while now inadmissible ? 693 What is the present condition with regard to make-up feed, and how is it preferably obtained or carried ? 694 State some of the various ways in which the formation of salt water scale may be reduced or prevented .' , 69s In what manner may sea water be prepared for use in the boiler by the removal of the scale- forming constituents ? 695 Can scale formation be entirely prevented, and if not what steps must be taken to insure the safety and efficiency of the boiler? 695 Describe the combinations of oil and scale which may be formed . within a steam boiler 695 What is the surest means of preventing the formation of such com- binations ? _ 696 In the inspection of boilers after use what points should be specially looked for in the furnace fronts, in the grates and bearers, in the bridge wall, in the tubes, in the joints and seams, in the front connections and up-takes, in the bracing, in the fittings ? 697 730 PRACTICAL MARINE ENGINEERING PAGE What special points should be held in view in examining the character and amount of scale ? 699 What special points should be held in view in looking for corrosion?. . 699 What is the hydraulic test and how is it carried out? .- 700 What steps may be taken in the case of leakage about the joints on boiler mountings ? 702 What steps may be taken in the case of leakage about shell joints?. . . 703 What steps may be taken in the case of leakage about the various in- ternal joints of a Scotch boiler? 704 What is a soft patch and how is it applied ? 70S What is a hard patch and how is it applied? 70S Describe various means for taking care of small cracks or holes 706 What are blisters and laminations, and what may be done with them ? 706 How may leaky tubes be treated ? 707 What steps may be taken in the case cf leakage about braces and stays ? 708 What steps may be taken in the case of bulging or collapse of furnace and combustion chamber plates ? 709 What may be done with a small split in the feed pipe? 710 In the case of overhauling and repairing the main engines, what spe- cial points must be looked for in the cylinders ? 711 What points in the various pin joints and bearings ? 712 What methods may be used in adjusting the bearings? 713 What points in the crosshead and guides ? 714 Explain the general operation of lining up and adjusting a marine engine 716 What points in the valve gear ? 722 What points in the thrust hearings ? 722 What troubles are liable to be met with in the condenser, in the air pump or in other pumps ? 723 Mention the spare parts usually carried 725 Describe the general methods in use in laying up marine machinery and the points requiring special care 726 CHAPTER XIII Steam Engine Indicators, Indicator Cards and Torsion Meters Sec. 101. INDICATOR CARDS [i] Descriptive An indicator card is a diagram showing for each point of the stroke in both directions the steam pressure on the piston. Thus Fig. 424 represents an indicator card showing the steam pressure above the piston, say, for both the down and up strokes. RS is the line of zero pressure from which all pressures are measured upward according to the scale of the diagram. This is called the absolute pressure line. A is the beginning of the down stroke, B the point of cut-off, C the point of exhaust Fig. 424. Indicator Card opening, and D the end of the stroke. The line AB is called the steam line and shows the steam pressure on the upper side of the piston from the beginning of the stroke to cut-off. The line BC is called the expansion line and shows the decreasing values of the pressure during that part of the stroke. At C the exhaust opens and the pressure drops suddenly as shown by CD. For the return or up stroke, D is the beginning, E the point of exhaust closure or beginning of compression above the piston, and F the point of steam opening just above the beginning of the tiext down stroke. CDE is the exhaust line and shows the nearly con- stant pressure during this period. EF is the compression line 732 PRACTICAL MARINE ENGINEERING and shows the increasing pressures on the return stroke after the closure of the exhaust valve. FA is the admission line and shows the sharp upward turn as the steam is admitted again just before the beginning of the next down stroke. The line PQ drawn when the space below the indicator piston is shut off from the engine cylinder and connected to the air is called the atmospheric line. The distance PR between RS and PQ thus represents the pressure of the atmosphere, 14.7 pounds per square inch, its length depending of course on the scale of the diagram. Thus for the down stroke the varying pressures on the top of the piston are shown by the varying distances from RS to ABCD, while Fig. 425. Pair of Indicator Cards for the up stroke the pressures on the same side of the piston are shown by the distances from RS to DBF A. There will be, of course, a similar design for the other end of the cylinder showing the pressures below the piston for both the up and down strokes in the same manner as for the diagram - described. Such a pair of diagrams taken from actual practice is shown in Fig. 425. Let a comparison now be made of the cards of Figs. 424, 425 with Fig. 426, the latter showing a so-called ideal card ; that is, a card which would be given if the valves opened and closed in- stantaneously, if when closed they were tight against all leakage, if there were no loss of^pressure due to friction of steam in the passage, and if the expansion and compression lines were equi- lateral hyperbolas. Instead of these conditions the valves open and close gradually ; even when cldsed there may be some leakage ; there is always some loss of pressure due to friction or resistance to the flow of steam, especially through a gradually closing or opening port and the expansion and compression lines are not true hyperbolas. Added to these is the inertia of the indicator piston, which prevents it from following with absolute exactness all the variations of pressure as they occur. INDICATORS AND TORSION METERS 733 As a result of these various causes the actual engine and in- dicator give the diagrams of Figs. 424 and 425 rather than such as Fig. 426. The gradual opening and closure of the valve rounds off the various corners, while the steam line instead of being horizontal, drops somewhat, due to the loss of pressure through the ports and passages. The piston, of course, moves faster as it approaches mid stroke and hence the steam must flow in at an increasing velocity to fill up the space behind the advancing piston. The higher the velocity the greater the loss of pressure, and hence there is a continual slope down from the beginning of the stroke as shown in Fig. 425 and often to a far more pro- Fig. 426. Ideal Indicator Card nounced degree. The actual point of cut-off is also not always easy to locate, rounded off as it is by the gradual closure of the valve. It may, however, be properly considered that the point of actual final closure is where the curve changes direction of curvature, that is, from convex to concave, as at or near P, Fig. 425. It is sometimes considered that the point of equivalent cut- off is more nearly obtained by continuing the curve back as shown by the dotted line to Q and supposing a sharp cut-off at this point. The result would then be an expansion line from Q similar to that which is obtained by the gradual closure in the actual case. The steam engine indicator diagram is valuable for two chief purposes. (a) It enables to judge of the operation of the valve by noting the various events, steam opening and closure, the loca- tion relative to that of the piston, the resulting piston pressure, and to answer various questions relative to the general problem of the distribution of steam to the cylinder. (b) It enables to answer all questions which depend on the J'34 PRACTICAL MARINE ENGINEERING amount and distribution of steam pressure on the piston and thus to determine the mean pressure, and knowing the revolutions to find the indicated horsepower ; also the turning effort at the various points of the revolution, and the mean effort for the entire revolution. [2] The Indicator Card and the Operation of the Valve Gear Now consider briefly the more important derangements which may be met with in the valve gear, and the results as shown by the indicator card. Fig. 427. Indicator Cards with Angular Advance too large (i) Eccentric too far from a line at right angles to the crank; that is, angular advance 8 too large. Results: Cut-off too early, steam lead large, exhaust opening and closure early. In short, the whole round of events is ahead of time. See Fig. 427. (2) Eccentric too near a line at right angles to the crank ; that is, angular advance 8 too small. Restdts: Cut-off late, steam lead small or even negative, compression small, steam opening late, exhaust opening and closure late. In short, the whole round of events is behind time. See Fig. 428. Fig. 428. Indicator Card with Angular Advance too small. (3) Steam lap too large. Results:- Cut-off early, steam opening late and lead small or even negative, port opening small with a probable wire drawing of the steam, and drop of pressure on steam line. See Fig, 429. INDICATORS AND TORSION METERS 735 (4) Steam lap too small. ^^•sitlts: Cut-off late, steam opening early and lead large, port opening large. See Fig. 430. Fig. 429. Indicator Card with Steam Lap too large. Fig. 430. Indicator Card with Steam Lap too small (5) Exhaust lap too large. Results: Exhaust closure early and compression large, ex- haust opening late and exhaust lead small. See Fig. 431. Fig. 431. Indicator Card with Exhaust Lap too large Fig, 432. Indicator Card with Exhaust Lap too small (6) Exhaust lap too small. Results: Exhaust closure late and compression small, ex- haust opening early. See Fig. 432. (7) Compression excessive. Results: The pressure in the cylinder may be carried above that in the valve chest before the steam valve opens, thus forming T},6 PRACTICAL MARINE ENGINEERING a loop as shown in Fig. 427. This may be due to either ( i ) or (5) above. (8) Expansion Excessive. Results: The pressure in the cylinder may fall below that in the next receiver or exhaust space beyond, thus forming a loop as shown in Fig. 433. Fig. 433. Indicator Card with Excessive Expansion (9) Valve Stem too long. Results: This means that the middle of the stroke of the valve is placed too high relative to the ports. The results for an outside valve will be to give too much steam lap on top and exhaust lap on the bottom, and too little steam lap on the bottom and exhaust lap on top. Hence there results : Steam opening in top late and small and cut-ofF early. Steam opening in bottom early and full and cut-off late. Exhaust opening on top early and full and closure late. Exhaust opening on bottom late and small and closure early. See Fig. 434. Fig. 434. Indicator Card with Valve Stem too long or too short ( 10) Valt^e Stem too short. Results: Similar to those for (9) but oppositely related to the ends of the cylinder. To these may also be added the following; (11) Leaky piston or piston rod stuffing box. Results: The expansion line will be steeper than it should be. The compression line may also flatten off somewhat near the top. INDICATORS AND TORSION METERS 737 (12) Port openings or Passages too small. Results: Wire drawing or loss of pressure on the steam line and rise of pressure on the exhaust line. See Figs. 425, 429. It will be noted in the above that different causes may pro- duce similar results, so that in interpreting a given set of cards caution must be used in working back from result to probable cause and remedy. This operation may be aided by the following general hints: It will be noted that the general effect of a valve stem too long or too short is to effect the two ends of the cylinder in Fig. 435. Indicator Card Showing Combination Effect opposite directions, thus giving the cards the appearance of having been pushed over in one direction or the other as in Fig. 434. On the other hand, if the valve stem is of proper length but the eccentric is improperly set the results will be of the same kind in both ends of the cylinder as shown in Fig. 427. Various com- binations of these may exist in the same engine. Thus a pair of cards as shown in Fig. 435 indicates an incorrect length of valve stem, an incorrect adjustment of the laps, with perhaps too large an angular advance. The combination nearly corrects certain difficulties and makes others still worse. Various special features may combine to make the so-called "freak" cards, but no further examination of this part of the sub- ject will be made, as such freaks are of rare occurrence, and a careful study of the results of the various single derangements as given above in (i) to. (12) will usually be sufficient to show the nature of the trouble. [3] Working Up Indicator Cards for Power From the principles of mechanics it is known that zuork is the result of a force or effort acting through a distance, and is meas- ured by the product of the force in pounds by the distance in feet. This gives the measure of the work in foot pounds. Power 738 PRACTICAL MARINE ENGINEERING measures the capacity to perform a certain amount of work in a given time. The common unit is one minute of time. Hence to find the power of an engine there are two chief steps : ( 1 ) To find the foot pounds of work done per minute. (2) To reduce this to horsepower by dividing by 33,000. It may be noted here that the term Indicated Horsepoiver means simply the horsepower as determined from the indicator cards. Now by definition the foot pounds per minute for the steam engine will be the product of the acting force multiplied by the distance through which it acts in one minute. The acting force equals the mean load on the piston, and this equals the mean effective pressure per square inch multiplied by the area in square inches. The distance acted through per minute must be measured in feet, and equals twice the stroke multiplied by the number of revolutions per minute. Let p = mean effective pressure in pounds per square inch ; A = area of pistbn in square inches ; L = length of stroke in feet ; A^^ = revolutions per minute. Then pA = acting force or mean total load on the piston measured in pounds, and 2LN = distance moved per minute in feet = piston speed. Hence foot pounds of work per minute equals product (pA) X (2LN) or what is the same thing 2pLAN. Hence the formula: 2pLAN Horsepower = 33000 This is the usual formula for finding the indicated horse- power, and is commonly employed for working up indicator cards for this purpose. The reason for measuring L in feet and A in square inches will be readily seen from the following considerations. Work is composed of two factors, the force factor and the distance factor. The first must be measured in pounds and the second in feet. The product pA is the force factor, and since p is usually measured in pounds per square inch, A must be measured in square inches in order that pA may be the total mean load in pounds. The product 2LN is the distance factor, and hence 2L the distance traveled per revolution must be measured in feet, in order that 2LN may be the distance traveled per minute meas- ured in feet. The product (pA) X (zLN) or 2 pLAN will then INDICATORS AND TORSION METERS 739 give the work measured in foot pounds as has been seen above. The rule for the operations necessary to find the indicated horsepower as expressed by the formula above is: Rule — Multiply together the mean effective pressure in pounds per square inch by the length of the stroke in feet, and this product by the area of the piston in square inches, and this product by the number of revolutions per minute, and this product by 2, and then divide the final product by 33,000. The quotient will give the indicated horsepower. Fig. 436. Mean Effective Pressure from Indicator Card The various factors which enter ihto either' the formula or rule for horsepower, the length of stroke and area of the piston come from the dimensions of the engine, and the revolutions per minute from the counter, or by actually counting them, watch in hand. There remains the mean effective pressure p, which must be found from the indicator cards, and to this part of the operation now turn. The mean pressure for a single card such as Fig. 436 gives simply the mean of the pressure in one end of the cylinder, say the top. To obtain this mean pressure a number of different ways may be followed. Fundamentally the mean of such a series of pressures as given by the indicator card, is found by dividing the area of the card by the length. This gives the side of a rectangle which would have the same area as the card. Thus in Fig. 436 if the rectangle ABCD has the same area as the card, then the side AD of the rectangle is the mean height of the card, and to the proper scale will give the mean pressure desired. Hence any method which will give the area of the card may be used for finding a mean height, and hence a mean pressure. In Chap. XV. are given various rules and methods for finding the measure of an irregular area, illustrated by the example of an indicator card, and any of these may be used as there explained. The method most commonly used is to measure the ordinates on 740 PRACTICAL MARINE ENGINEERING the clotted lines as in the figure there shown, take their sum, and divide by their number, lo. This multiplied by the scale of the indicator spring will give the mean pressure desired. The sim- plest method of locating the intervals for these dotted ordinates is that explained in Chap. XV. To carry this out proceed as follows : Let the card be represented in Fig. 437, then draw the lines at the ends as shown, perpendicular to the atmospheric line OA \ I-.^ r^ ^ — \ -J ^ N ht s 3^ \ \ \ \ \ \\, Fig. 437. ^bdivision of Indicator Card for Obtaining Mean Ordinate and tangent to the card, thus fixing its length. Then lay off the line OB at an angle and on OB lay off first a half division Ox, then nine whole divisions, and then a half division as shown. The divisions may be taken from % to J^ inch in accordance with the length of the card. Then drawing a line from B to A and other parallel lines from the points of division on OB to OA, the locations for the ordinates are determined, and they may be drawn as shown. Where a large number of cards are to be worked up in this way, time will be saved by the use of a form of template or pattern for locating these points. Such an imple- ment is shown in Fig. 438 and consists of a piece of hard wood with small steel points set in to the edge, spaced according to the lay out of points along, 05, Fig. 437. This distance between the extreme points is somewhat greater than the length of the longest card likely to be met with. Instead of steel points set in a block of wood, a thin plate of steel may be cut out and filed up so as to leave the points projecting at the desired intervals. In using this device it is simply necessary to draw lines tangent to the ends of the card, as shown, and then to place one end of the template on one boundary line PR at any convenient point as P, and swing it to such an angle as will just bring the other end Q to the other line OS. The template is then pressed down so as to INDICATORS AND TORSION METERS 741 mark the paper with the points, and lines parallel to those at the ends are drawn through the points thus marked, as shown by the lines of the figure. In this way the ordinates spaced in the man- ner desired may be rapidly laid out and drawn in. For summing the ordinates the method by the use of a strip of paper as explained in Chap. XV. may be recommended as the i i 1 i i i 1 i 1 1 1 i Fig. 438. Subdivision oi Indicator Card for Obtaining Mean Ordinate simplest, quickest and most satisfactory available for the purpose. Having thus in one way or another found the mean effective pressure for one card, the other one of the pair is taken in like manner, thus giving the mean effective pressure for the other end of the cylinder or other stroke. These two values may then be averaged, and the result taken as the mean effective pressure for the revolution, thus furnishing the final factor p required in the formula or rule for horsepower. It must be noted that this operation is slightly in error by reason of the difference in area between the upper and lower sides of the piston. On the upper side the entire area is effective while on the lower side the piston rod takes out a small area in the center. To take account of this, compute the indicated horse- power for each end of the cylinder separately. To this end take each card by itself, say the head end first, and find the mean effective pressure, which may be denoted by p^. Let the entire piston area be Aj.. Then as before the mean load or average acting force is the product of the two, piA,^. The distance acted through is L for each down stroke, and the number of down strokes per minute is equal to the number of revolutions N. 742 PRACTICAL MARINE ENGINEERING Hence the distance per minute for the down strokes is LN and the indicated horsepower for this end of the cylinder will be : p^A^LN PtLA-.N Hi = or 33000 33000 In a similar manner find the mean efifective pressure for the bottom of the piston is obtained, which may be called A^. Then taking from A^ the area of the piston rod, the efifective area of the bottom of the piston is obtained, which may be called A^. Then similarly as in the head end for the indicated horsepower in the crank end, piAiLN P1LA2N H2 = or 33000 33000 The total indicated horsepower will then be the sum of these for the two strokes up and down, or : pN I. H. F.-H^ + H2 = ipi A, + p, Ai) 33000 For illustration see example (7) below. Mean Effective Pressure by the Aid of the Planimeter. The planimeter, an instrument for measuring areas, is also frequently used for working up indicator cards, and where the number is large will be found of great service. Such instru- ments may be obtained of most makers of indicators or of deal- ers in mathematical instruments. General directions for their use will accompany them. The following hints may be given for their use with indicator cards. Where the instrument has an adjustable bar it should be set so as to read the area in square inches. Where the bar is not adjustable the instrument is usually already set to read in terms of this unit. The order of procedure is then as follows : (i) Draw lines at the ends of the card at right angles to the atmospheric line so as to be able to determine its length. (2) Place the instrument and card in a suitable position, and read the record wheel, putting down the result, say 3.26 as below. (3) Then trace around the contour, usually in the direction with the hands of a watch for a second reading greater than the first, and come back carefully to the starting point. Then read again and set down the result, say 7.08 below the first as shown. INDICATORS AND TORSION METERS 743 (4) Then repeat, tracing around as before, read and set down the result, say 10.92, below the others as shown. In mak- ing the last reading it will be noted that on the instrument itself could be read only 0.92, but the increase upward from 3 to 7 shows that the wheel has passed the starting point and begun again, so that we must add the ten and write 10.92. Readings Differences Average First 3.26 Second 7.08 3.82 Third 10.92 3.84 3.83 (5) Then take the difference of the readings, the first from the second and the second from the third, and set down as shown, and then average these two numbers, thus finding in the present case 3.83 for the area in square inches. The reason for going around the area twice is to have two measurements, so that each will give a check on the other. If they differ widely an error somewhere is certain and they must be repeated, while if nearly the same, as in the case given above, the error is no more than must be expected with such means, and the average may be taken as the value of the area desired. (6) Next divide the area by the length of the card. Thus suppose in the case in hand that the length is 4.2 inches. Then 3.83 -H 4.2 = .912 inch. This is the mean ordinate of mean height of the card in inches. (7) Next multiply by the scale of the indicator spring and thus find the mean eiTective pressure desired. Thus sup- pose the spring to be 60 pounds to the inch. Then 60 X .912 = 54.72 pounds. This is then the mean effective pressure for the stroke as given by the card thus measured-. Proceed similarly with the other card, and use the results for the determination of horsepower in the manner already explained. Illustrative Examples ( 1 ) The area of an indicator card is 2.87 square inches and its length is 3.8 inches. What is the mean height? Solution: 2.97 -=- 3.8 = .755 inch. (2) The» scale of the indicator spring is 40 pounds per inch. What is the m. e. p.*? Solution: .755 X 40 = 30.2 pounds. (3) The ordinates measured in inches taken from an indi- cator card divided up as in Fig. 437 are as follows : * This abbreviation is often used for the term mean effective pressure. 744 PRACTICAL MARINE ENGINEERING .91, 1.30, 1.44, 1.40, 1.3s, 1.20, .95, .80, .70, .25, and the scale of the indicator spring is 60 pounds per inch. Find the m. e. p. Solution: Adding the lengths as given the sum = 10.40. Hence dividing by 10 the mean ordinate equals 10.40 h- 10 = 1.04. Hence the in. e. /"^ is 60 X 1-04 ^ 62.4 pounds. (4) The total length between marks on a strip of paper used to measure the ordinates is found to be 6.3 inches. The scale of the spring is 20 pounds. Find the m. e. p. Solution: 6.3 -h 10 = .63 inch = mean height, and .63 X 20 = 13 pounds ■= 1)1. e. p. (5) Given an indicator card with ordinates spaced as in Fig. 437. The pressures measured by a scale corresponding to the indicator spring are as follows : 18, 26, 28.4, 27.8, 2y, 24.2, 19, 16, 14.3, 7.2. Find the m. e. p. Solution: Add the pressures and find the sum 207.9. Divide this by 10 and the quotient 20.79 or 20.8 pounds = the value of the ;;/. e. p. (6) From the two cards of a pair the values of the m. e. p. are found to be 28.6 for one and 32.2 for the other. The piston area is 1,213 square inches, the stroke 39 inches and the revolu- tions 102. Find the indicated horsepower, neglecting the eflfect due to the area of piston rod. Solution: The m. e. p. for the whole revolution is the mean of the values for the two ends or 111. e. p. = (28.6 + 32.2) -4- 2 = 30-4- Then stroke in feet := 39 -4- 12 ^ 3.25. 2 X 30.4 X 3-25 X 1213 X 102 Then I. H. P. = 33000 Multiplying out the factors of the numerator and dividing by the denominator, indicated horsepower = 741 Ans. (7) Given the following: Diameter of cylinder = 24 inches. Diameter of piston rod ^= 5 inches. m. e. p. from head end or p^ := 63.4 pounds. m. e. p. from crank end or p^ = 58.8 pounds. Stroke = 36 inches. Revolutions no. Find the indicated horsepower both with and without the al- lowance for the area of piston rod. INDICATORS AND TORSION METERS 74s Solution: Area of 24 inch piston or J = 452.4 square inches. Area of 5 inch piston rod or a ^ 19.6 square inches. Effective area of lower side of piston = difference, or A^ = 432.8 square inches. Then neglecting the effect of the rod : m. e. p. = (63.4 + 58.8) -=- 2 = 61. 1, and I. H. P. (2X6i.iX3X4S2.4Xiio\ 33000 / Working this out : Indicated horsepower = 552.8. Taking account of the piston rod area for the head end : 63.4X3X452,4X110 Hx = = 286.8 33000 For the crank end: 58.8x3X432.8X110 H2 = = 254.5 33000 Adding : H = 54I-3- There is thus seen to be in this case a difference of 11.5 horsepower, constituting an error by the first method of some considerable amount. It is readily seen that this error will be relatively less the larger the cylinder, especially in the cylinders of a multiple expansion engine. Thus in the case given which was for the high pressure cylinder of a triple expansion engine the error is 1 1.5 horsepower, or about 2 percent. For the intermediate pressure cylinder the error would be not far from 4.5 horsepower, or about .8 percent, while for the low pressure cylinder it would be perhaps two horsepower, or about .3 percent. This would give a resultant error of about i percent for the engine as a whole. While these figures would vary with particular circumstances, they will serve to illustrate the nature of the error, and the methods given show how to avoid it when so desired. [4] Combined Indicator Cards The cards taken from the various cylinders of a multiple expansion engine, as for example those of Fig. 439, may be com- bined in such a manner as to show very instructively the continu - ous history of the expansion of the steam, that is, the continuous relation between volume and pressure as the steam passes through the engine. To effect this combination it is necessary to lay down 746 PRACTICAL MARINE ENGINEERING the various cards in one diagram and all to the same scale of vol- ume and pressure. The details of the operation may be sketched out in the following steps : ( I ) In Fig. 440 take the two lines at right angles, OX and OY, the former as an axis of volume and the latter as an axis of pressure. ATMOSPHERIC LINE ATMOSPHERIC LINE Xarint £ngintering Fig. 439. Set of Indicator Cards from Triple Expansion Engine (2) Determine in cubic feet for each of the cylinders the volume of the clearance and the volume swept by the piston. (3) Lay off the lines AB, CD, EF at such distances from OF as to represent respectively the clearance volume in the high pressure, intermediate pressure and low pressure cylinders, taking INDICATORS AND TORSION METERS 747 care to select the scale of volume such that the low pressure volume plus its clearance as measured between the lines Y and GK will come within the desired limits of the diagram. (4) Lay off on each card the line of zero pressure or the perfect vacuum line, as shown by OX in the small diagram a. (5) Take next the high pressure card, as at a for example, and select any point, such as P. Measure in any convenient units the distcmces MP and MN; multiply the volume of the cylinder by the former and divide by the latter. This will give the volume Marina Sngineuring Q X Fig, 440. Combined Cards from Triple Expansion Engine swept in the high pressure cylinder from the beginning of the stroke to the point P (6) The corresponding point P of the combined diagram is then found by measuring from AB a distance, HP representing this volume, and from OX a distance, JP representing the pressure PQ on the card. This will give the point P, and other points are found in a similar manner, as many as may be needed to determine the form of the card as shown. It is to be especially noted that the high pressure card of the combined set is the same as that at a, but drawn simply with different scales, and therefore more or less distorted in appearance. (7) The points necessary to determine the other cards of the combination are found in a precisely similar manner, remem- 748 PRACTICAL MARINE ENGINEERING bering that in each case volume is measured from the clearance line CD or EF, while the pressure must be measured from the line of zero pressure for the card and laid off from the corresponding line OX of the combined set. This diagram shows the general manner in which the steam expands on its way through the engine. An expansion line, PQ, shows tlie general law of expansion as a continuous operation. PR is an ideal expansion line laid down as a hyperbola, all points in the curve corresponding to the condition that the product of volume by pressure shall be constant, or in symbols, pv = Con- stant. This shows the result of the so-called true hyperbolic ex- pansion law, and as appears from the diagram, the actual expan- sion line is somewhat below this ideal line. The equation to the actual expansion line may be expressed in the form of pi^ = Constant, where n is an exponent having values usually lying between 1.15 and 1.2. The equation pv^ ■'^^ may be taken as very commonly representing this line in good ■ average practice. The extent to which the area bounded by the line PR and the clearance lines on the left is well filled in, is an indication of the degree to which the performance of the actual engine approaches that of an engine having true hyperbolic ex- pansion and w'ith indicator cards as shown in Fig. 426. The rela- tion between the actual engine and such an ideal case is usually expressed by a percentage factor known as the "card factor." For good practice with triple expansion engines, this factor will be found from .60 to .70. With quadruple expansion engines repre- sentative values are found from .55 to .60. The diagrams of Fig. 439 are reproduced from an actual case, and may be considered as representing good modern prac- tice in general character and form. At this point reference may be made to the effect on the dis- tribution of power in a compound or multiple expansion engine, of linking up or cutting off earlier in the intermediate or low pressure cylinders. Taking first the case of a compound, linking up or shortening the cut-off on the low pressure cylinder will in- crease the power in this cylinder and decrease it in the high. This result at first sight seems contradictory to common experience, because in a single cylinder it is usual to associate an earlier cut- off with decrease of power. In the case of the compound, how- ever, cutting off earlier in the low pressure cylinder gives a INDICATORS AND TORSION METERS 749 higher back pressure in the high pressure cyHnder and a conse- quently higher initial pressure in the low pressure indicator card area, instead of a decrease as in the case of a single cylinder. At the same time the area of the high pressure card will be reduced and the power developed in this cylinder will be decreased cor- respondingly. Similarly for a multiple expansion engine and in general, cutting off earlier in any of the cylinders beyond the first or high pressure, will result in an increased back pressure for the next preceding cylinder, and in a higher initial pressure for the cylinder itself, and thus in an actual addition to the area of the indicator card and a corresponding subtraction from the area of the card for the cylinder preceding. Thus in Fig. 440, cutting off earlier in the low pressure cylin- der will result in raising the upper line of the low pressure and lower line of the intermediate pressure cards, and thus in increas- ing the area of the former and decreasing that of the latter. In like manner cutting off earlier in the intermediate cylinder will result in raising the upper line of the intermediate pressure and the lower line of the high pressure cards, and thus in increasing the area of the former and decreasing that of the latter. In like man- ner cutting off later in any cylinder beyond the high pressure will result in similar changes, but in the opposite direction. Thus a later cut-off in the intermediate pressure cylinder will decrease the power developed in that cylinder, and increase the jx>wer de- veloped in the high pressure cylinder. It thus results that a com- bination of changes such as a later cut-off in the intermediate pres- sure cylinder and earlier cut-off in the low pressure will both tend to decrease the power developed in the intermediate pressure ; while an earlier cut-off in the intermediate cylinder and a later cut-off in the low pressure will both tend toward an increase of power developed in the intermediate pressure. Sec. 102. STEAM ENGINE INDICATORS [i] Descriptive The indicator card has already been described in Sec. loi. It is the purpose of the indicator to draw this card. It must therefore provide for the proper combination of these movements. ( 1 ) A movement in step with the piston and proportional to it in amount so that all horizontal distances on the card shall bear a constant proportion to the corresponding parts of the stroke. (2) A movement at right angles to that in ( i ) and in direct pro- 750 PRACTICAL MARINE ENGINEERING portion of the pressure per square inch on the piston in the end of the cyHnder to which the indicator is connected. The combination of these movements will then result in a diagram such as those shown in Sec. loi, and giving at each point of the stroke the pressure on the piston as desired, the upper line JWll I lM ^IgilMtftTIg Fig. 441, Steam Engine Indicator showing the pressure which urges the piston forward on one stroke and the lower line the pressure which resists its movement back- ward on the return stroke. In Fig. 441 a modern inside spring indicator is shown, while Fig. 442 shows one of the outside type in which the spring is located outside of the cylinder and does not have its temperature and elasticity affected by the steam temperature. Referring to Fig. 441, ^ is a drum to which the paper is attached by means of the clips, as shown. This drum is given a motion back and forth about its axis by means of a connection with the crosshead through INDICATORS AND TORSION METERS 751 the so-called "reducing motion." By this means the drum is given a motion of some three to five inches in extent, just in step with the motion of the piston and proportional to it in amount. B is the indicator cylinder or barrel connecting with the end of the engine cylinder from which the card is taken. Within the cylinder, as shown, is a piston with a coiled steel spring above, resisting pres- sure from below the piston upward. To the piston rod is attached a linkage carrying at the end of the arm P the pencil point which is to trace the diagram upon the paper carried by the drum. The connection between the linkage and the piston rod is such that the former may be swung freely about the cylinder upon a ring to which it is attached. The pencil may thus be brought into con- tact with the paper on the drum or withdrawn from it as desired. An adjustable screw stop is provided, and so arranged as to arrest the movement of the pencil motion when swung around by the hand, and thus allow only light contact between the pencil point and the paper. In some cases a brass point is used instead of a pencil, the cards being of paper specially prepared, so that the brass will leave a black mark upon it. Such points are strong and require no sharpening except at long intervals. The object of the linkage which forms the pencil motion is to magnify the movement of the indicator piston, and thus to allow the use of stiff springs with a corresponding small move- ment of spring and piston. With high revolutions especially, this is found necessary in order to reduce as far as possible the disturbance in the diagram due to the inertia of the moving parts of the indicator. The linkage is thus a form of multiplying mo- tion, or a reducing motion reversed, and it should give to the pencil a movement exactly proportional to that of the piston, but 3 to 5 times greater as may be desired. The relation between the pressure per square inch and the actual movement at the pencil point fixes the so-called scale of the spring. This depends also on the actual area of the indicator piston, which is, however, usually about one-half square inch. Thus a 40 pound spring means a spring such that a pressure of 40 pounds per square inch on the indicator piston, or say an actual load of 20 pounds, will produce a movement of one inch at the pencil point. By means then of the piston, spring and linkage, the second of the necessary movements, as mentioned above, is thus pro- duced. 752 PRACTICAL MARINE ENGINEERING -Returning to the drum the first of the motions above noted is obtained by some form of reducing motion as described below. The connection between the drum and the reducing motion is Fig. 442. Outside Spring Steam Engine Indicator i — Spring lock nut. 2 — Spring lock nut screw. 3 — Spring swivel nut. 4 — Spring swivel. 5 — Spring swivel screw. 6 — Upper piston rod. 7 — Spring sleeve. 8—? Spring sleeve top adjusting nut. 9 — Barrel. 10 — Piston rod guide. 11 — Vibrating arm. 12 — Vibrating arm screw. 13 — Long link. 14 — Long link pin. 15 — Steady link. 16 — Steady link screw, 17 — Steady link bolt. 18 — Pencil lever. 19 — Metallic point. 20 — Link swivel body. 21 — Lower piston rod. 22 — Piston. 23 — Sleeve. 24 — Sleeve stop screw. 25 — Sleeve stop screw lock nut. 26 — Sleeve stop screw handle. 27 — Steady link post. 28 — Steady link post nut. 29 — Cylinder plate. 30 — Cylinder plate lock nut. 31 — Cylinder. 32 — Indicator plate. 33 — Tail piece. 34 — Coupling. 35 — Drum spindle. 36— Cord guide bracket. 37 — Cord guide bracket swivel. 38 — Cord guide bracket thumb nut. 39 — Swivel set screw. 40 — Cord pulley. 41 — Drum base. 42 — Drum spring. 43 — Drum key. 44 — Drum stop screw for plate. 45— Sleeve stop post. 46 — Drum spring head. 47 — Drum spring base. 48 — Paper clip. 49 — Drum spindle collar. 50 — Bushing. 51 — Steady screw for spring sleeve. 52 — -Drum. 53 — Sleeve pivot screw. 54 — Swivel cap. 55^Swivel cap set screw. 56 — Detent body. 57 — betent lever.' 58 — Detent body screw. 59 — Deteiit lever handle. 60 — Spring sleeve bottom adjusting nut. 61 — Spring stop screw for base. INDICATORS' AND TORSION METERS 753 usually made by means of a cord C wrapped around a groove in the base as shown. The cord thus serves to pull the drum around in one direction while the return stroke is made by means of a coiled spring in the base. This spring opposes the motion given by the cord, and is therefore coiled up during the forward stroke. As soon, however, as the pull of the cord ceases the spring takes charge and uncoiling carries the drum in the reverse direction as fast as tlie cord will allow, thus keeping the latter taut and insuring the motion of the drum in step with the main piston in both direc- tions as accurately as the fonn of reducing motion may determine. A separate indicator may be provided for each end of the cylinder, or by suitable pipe connections and a three-way cock. ^o U' Fig. 443. Reducing Motion Fig. 444. Reducing Motion. one indicator may be made to serve for both ends. In any case, the cock which shuts oflf the indicator must be so arranged that when shut ofif from the cylinder the space below the piston will be connected to the outside air. The piston with equal air pressure on both sides will then come to a position of equilibrium, and the atmospheric line may be drawn. [2] Reducing Motions The purpose of the reducing motion has already been stated. There are many different ways in which the desired movement may be given to the drum, some of them accurate in geometrical principle and some only approximate. One of the most common is by means of links, levers and bell cranks. The simplest of such forms is shown in Fig. 443. A is a pin attached to the crosshead. AB is a short link connecting 754 PRACTICAL MARINE ENGINEERING the crosshead to a lever BD pivoted at C. The point D will then move in step and nearly in constant proportion to the piston, and from D the motion for the drum may be taken, either by a cord direct, or from the end £ of a rod DE moving as shown. In such cases the cord should run in continuation of the line DE and not off at an angle as EF or DH. As a general rule in all such cases, the reducing motion should be so adjusted that the cord part should not undergo changes of angular direction, or, at least, such changes should be made as small as possible. Thus in Fig. 444 suppose the point from which the motion is taken to move through Fig. 445. Reducing Motion a path AB, and the indicator guide pulley to be at P. Then at one extreme the cord will be represented by PA, and at the other by PB. Such a change in the angular direction of the cord relative to the line of motion AB will result in error, and should be avoided by bringing P over AB or AB under P. It is not necessary that the motion of the point E, Fig. 443, should be vertical so long as the gear is so arranged as to reduce to a minimum all angular Fig. 446. Reducing Motion changes in cords and connecting Hnks. Thus the arrangement of Fig. 445, while containing a large number of joints and parts, may be as nearly correct as the simpler form- of Fig. 443. Instead of taking the motion direct from D a link DG con- nects this point with a bell crank GHI pivoted at H. Then a second link // connects this to second bell crank JKL and a rod LE guided at M gives a point E from which the motion may be taken, or if more convenient the rod LE may be dispensed with and the motion taken from L direct. Such a complication of gear is of course not desirable, and the arrangement is shown simply INDICATORS AND TORSION METERS 755 as an illustration of a combination of links and bell cranks which would still give the motion required. All such forms of reducing motion are approximate and not geometrically exact. The error is, however, in most cases small and is usually neglected, though, if desired, its nature and extent may be investigated by a suitable geometrical analysis of the gear. Instead of taking the motion from the crosshead by means of a short link as AB Fig. 443, a lever BD, Fig. 446, is sometimes Fig. 447. Pantograph Reducing Motion Fig. 448. Lazy Tongs Reducing Motion provided, having a forked end and pivoted at C or D. A pin on the crosshead working in the slot or forked end gives the to and fro motion to the lever, while from D or C the desired motion is taken. Instead of attaching the cord direct to C, for example, a sector of wood PQD with center at D is attached to the arm, and the string is led off from the face of the sector. Such a sector may also be employed with the arrangements shown in Figs. 443 and 445. None of these motions is geometrically exact. A form of pantograph consisting of jointed rods as shown in Fig. 447, may sometimes be used when there is room for it to work freely. A is attached to the crosshead and Z? or £ is the fixed pivot. Then the other point E or D will provide a motion for the indicator drum which is geometrically exact. Here again, however, the string should be so led that its angularity will not vary. Instead of this arrangement of links the so-called lazy tongs as shown in Fig. 448 is sometimes employed. This is also geo- 75fi PRACTICAL MARINE ENGINEERING metrically exact, and is, in fact, an equivalent to the pantograph in Fig. 447, without requiring quite as much room. Various combinations of pulleys may also be used, as illus- trated in Fig. 449. AB is an ami projecting from the crosshead and moving with it. To the end B of this arm is attached' a cord wrapping around a light pulley P. Q is a smaller pulley on Fig. 449. Reducing Motion the same -axis and moving with P Wrapped on this is a cord CD^ which may be led ofif in various directions tO' the indicator as shown by CD, CD^, CZ^j- This gear is geometrically exact. » Various other forms of reducing motion are also to be met p/lo AllB a 6 « • Fig. 450, Putting on an Indicator Card with, but those described will be sufficient to show the forms most commonly available for marine practice. [3] Taking an Indicator Card The instrument should first be examined and put into proper condition and adjustment. This should include the following points : (i) The joints should all work freely, but without lost motion. (2) The piston should not bind nor should it be so loosely fitted as to allow serious leakage. , A slight leak is, however, better than' too snug a fit. (3) The working surfaces of the barrel and piston should be carefully wiped and oiled. This should be repeated from time to time when a series of cards is being taken. The joints of the INDICATORS Ai\D TORSION METERS 757 pencil motion should also be lubricated with clock oil, a non- gumming oil, as often as may be required. (4) The pencil points should be sharpened and the screw step so adjusted that the point can rest only lightly on the paper. The operation of taking the card itself is briefly as follows ; ^ The indicator is attached to the cock, a blank card is placed on the drum and the cord connection is adjusted so that the drum will have the proper stroke without coming against the stop at either end. In attaching the blank card the most convenient way will be to bend the sheet of paper around and grasp both edges between the thumb the forefinger, as at AB in Fig. 450a. Then slip over the drum and under the clips so that the latter will come outside the paper, as shown at PQ, b. Then slip the paper down into place, pull and adjust so that it fits snugly, and bend the edges back as in c. The cord is then hooked on to the reducing mo- tion and the drum takes up its movement with the main piston. The cock is then opened at the end of the cylinder from which the diagram is desired, and the pencil immediately takes up its motion corresponding to the varying pressures of the steam. The indicator piston should be allowed to work in this way for a few strokes, or until everything is warmed up into working condition. When everything is in readiness the pencil motion is moved up against the stop so that the pencil, resting lightly on the paper, will trace ils path for a complete revolution or longer if desired. Then remove and shut of? the indicator from the cylinder. This will connect, it with the air, the indicator piston will come to equi- librium under atmospheric pressure, and the atmospheric line may then be drawn. The drum connection is then unhooked, the paper removed, a fresh one replaced and the next card taken when desired. If one indicater is used for both ends of the cylinder, both cards should be taken on the same paper with as small an interval between as possible. The cock is swung ever for one end and the card taken, and then immediately swung over for the other end and the second card taken without loss of time. The cock is then closed ofif, thus connecting the indicator with the air, and the atmospheric line is then drawn. Each card as it is removed from the indicator should be marked with sufficient data to identify it, and make possible its use for the purpose intended. This should include at least the following items : 758 PRACTICAL MARINE ENGINEERING ( 1 ) Cylinder. (2) End from which card is taken. (3) Revolutions. (4) Scale of spring. (5) If a scale of cards is being taken, the time and serial number should also be set down. The various other items usually printed on the back of the card may be filled in at a later time, as may be convenient. When cards from both ends are taken on one paper, it is necessary to be able to assign each to its proper end of the cylinder. The most certain way of determining this is to shut off the connection to one end of the cylinder entirely, and then take the card from the other end. It will thus show how the card from this line lies on the paper, whether with admission line to the right or left, and this will indicate how to mark the entire series of cards taken with the same arrangement of reducing gear, etc. Sec. 103. TORSION METERS As the work performed in a steam turbine is due to heat which is converted into kinetic energy by the velocity created by expansion of the steam, no satisfactory means exists to measure this work in a manner similar to that used in "indicating" recipro- cating engines. Methods have, therefore, been devised to measure the torque transmitted to the line shafting of marine turbines by means of torsion meters, which indicate the torsional deflection of the shaft. All torsion meters, for measuring the shaft horsepower devel- oped by a turbine, are based on the same principle. This involves the quality of ordinary materials possessing perfect elasticity when the stresses, to which they may be subjected, are well below the elastic limit of the material. When a revolving shaft trans- mits power it always twists slightly throughout its length, the amount of twist varying directly as its length, directly as the moment of the load applied, inversely as the rigidity of the mate- rial, and inversely as the fourth power of the diameter. Having established the true "modulus of rigidity" for the shafting, the horsepower may be obtained from eiTN H. P. = where CL 6 = torque in degrees, D = diameter of shaft in inches, INDICATORS AND TORSION METERS 759 N = number of revolutions per minute, C = constant varying with the "modulus of rigidity," L = length of shafting in inches. In order to apply this formula the "modulus of rigidity" — that isy how much the shaft will twist with a given static load ap- plied af the end of a lever of known length — must be known. The torque in degrees (6) is ascertained by the use of the torsion meter. [i] Calibration of Shafting with Torsion Meter in Place The torsion meter used in this instance consists of a tube, the lengtTi varying for different shafts, installed within a hollow section of line shafting, one end secured within the shaft by pointed set screws, the other end, carrying the pointer mechanism, riding free within a ball bearing at the flange of the shaft. A lever which actuates the pointer mechanism passes through a slot in the flange, the slot being large enough to permit the free movement of the lever within the radius of movement of the pointers. With no load on the shaft the two pointers, when correctly adjusted, lie in the same plane of rotation, but as the load varies the pointers separate a distance directly proportional to the twist of the shaft. A recording apparatus makes it possible to obtain at any time this distance. The object of calibrating the torsion meter is to determine the relatiort existing between the movement of the pointers and the horsepower transmitted by the shaft. The calibration test described was for the port shaft of a United States destroyer. The method pursued was as follows : The forward end of the shaft was rigidly secured to a heavy casting clamped to the bed of a large boring machine. The after end rode freely in a ball bearing just abaft the flange, likewise rigidly secured. To the after flange was bolted a lever, X Y, with ten-foot arms, for applying the torque. Square marks were placed on the flanges to show any slipping of the shaft or lever. The two pointers, A, B and C, D (eight-foot arms), for determining the angle of twist were clamped securely to the shaft six feet apart. All measurements were accurately checked. Cards were secured in position at A, B, C and D for recording the pointer refadings, and on small boards for taking the meter readings. "Squares and sharp pencils were provided for marking pointer positions. Beam scales were placed in 760 PRACTICAL MARINE EXCINEERING INDICATORS AND TORSION METERS 761 S.0 OS ^ / / / / 2.1 2.2 2.0 1.8 1.6 1.4 1.2 1.0 .8 CALIBRATION DATA, PORT SHAFT, U.S,S. DUNCAN. / / ^ a / / s a / /" / ,<-^V / ^ o^P r f / «. .f ^ —- .5 / ____ --' .4 « / / stCo :rect il -^ / ^ ^ ^ 1000 8000 3000 4000 5000 6000 7000 8000 9000 Total Load on Levera, Pounds Fig. 452. Calibration Record Curves position at each end of the lever, suspended from a crane at one end and secured to heavy weights at the other. The upward pull was obtained by means of a differential purchase, the down- ward pull by a bolt and nut. The pull on the lever was taken on knife edge bearings at each end. The moment required to produce an overload of 25 percent above the designed horsepower of the shaft was determined from the formula. S. H. P. X 33,000 M =■ — . 2tR.P. M. Where 5. H. P. = shaft horsepower. R. M. P. = revolu- tions per minute. This result was used in calculating the pull to be applied to tlie lever arms. At a bell signal the zero positions were recorded with no load on the lever. Then a load of approximately 500 pounds was placed on each arm, the bell was rung, the figure "i" was displayed to denote the number of the reading, and pointer positions were a< a + 1 i ■< W d Q < a a 1 +.04 0. 0. 0. 0. 0, 1 500 135 635 1167 .33 .37 .03 .03 .15 15 03 15 12 2 1195 740 1935 2467 .74 .78 .10 .085 .32 .32 .09 32 ?,3 3 1915 1360 3275 3807 1.18 1.22 .18 .16 .55 .53 .17 ,54 37 4 2640 2030 4670 5202 1.63 1.67 .27 .255 .75 .74 .26 .745 485 5 3265 2730 5995 6527 2.08 2.12 .37 .35 .99 .97 .36 .88 62 6 4005 3415 7420 7952 2.52 2.56 .48 .47 1.23 1.20 .475 1 215 74 7 4470 3900 8370 8902 2.84 2.88 .59 *.38 .56 1.44 1.15 1.42 1.13 .575 1.43 .855 8 3960 3500 7460 7992 2.53 2.57 .56 *.33 .34' 1.33 .97 1.30 .94 .38 1.14 .76 9 3280 2775 6055 6587 2.07 2.11 .51 *.28 .52 .27 1.15 .77 1.11 .76 .335 .955 .62 10 2590 2090 4680 5212 1.64 1.68 .46 *.22 .45 .22 .95 .58 .93 .57 .275 .765 .49 11 1900 1370 3270 3802 1.20 1.24 .40 *.15 .40 .155 .76 .39 .74 .37 .22 .575 .355 12 1200 690 1890 2422 .75 .79 .33 *.09 .335 .09 .57 .19 .54 .19 .15 .38 .23 13 490 155 645 1177 .34 .38 .27 *.00 .27 .00 .37 .00 .36 .00 .09 .19 .10 14 + .03 .00 —18 —18 — .18 — .17 SECOND RUN + .03 0. .00 0. .00 0. 1 500 160 660 1192 .35 .38 .04 .04 .17 .175 .04 .17 .13 2 1165 725 1890 2422 .75 .78 ,.11 .11 .34 .345 .11 .34 .23 3 1915 1380 3295 3827 1.19 1.22 .18 .18 .55 .55 .18 .55 .37 4 2600 2105 4705 5237 1.64 1.67 .24 .24 .74 .74 .24 .74 .50 5 3345 2775 6120 6652 2.09 2.12 .32 .32 .94 .94 .32 .94 .62 6 4045 3460 7505 8037 2.53 2.56 .37 .37 1.14 .113 .37 1,135 .765 7 4100 4025 8125 8657 2.74 2.77 .41 .41 1.225 1.22 .41 1.22 .81 7A 4505 3985 8490 9022 2.86 2.88 .43 .405 1.27 1.27 .42 1.27 .85 8 3995 3500 7495 8027 2.53 2.55 .42 .38 1.14 1.13 .40 1.135 .735 9 3300 2790 6090 6622 2.09 2.11 .38 .34 .965 .95 .36 .955 .595 10 2595 2095 4690 5222 1.65 1.67 .33 .29 .78 ,77 .31 .775 .465 11 1885 1390 3275 3807 1.19 1.21 .22 :22 .58 .57. .22 .575 .355 12 1205 700 1905 2437 .75 .77 .16 .16 .38 .37 .16 .375 .215 13 500 155 655 1187 .34 .36 .08 .08 .19 .19 .08 .19 .11 14 + .02 .00 .00 .00 .00 .00 [2] Gary-Cumniings Torsion Meter (Description: Calibration of Shafting Without Torsion Meter in Place) Figure 453 shows this instrument as supplied to the U. S. S. Florida. A tube A, about fourteen feet in length, was installed 764 PRACTICAL MARINE ENGINEERING Fig. 453. Gary-Cummings Torsion Meter inside a section of the propeller shafting-. l^One end of this tube had clamped on it a spider casting B, as shown at tne left, and in section at X-X. Each leg of this spider carried a spindle C, which is a close fit in B, with one end turned to a sharp point and the other cut to form a feather that fits in a tapered keyway on screw IXDICATORS AKD TORSION METERS 76s D. The three keyways in D are about 3/i6-inch deep at the left end of screw, and taper to about i/32-inch at the right. A long- handled socket wrench fits nut E, and is actuated from the left end of shaft. The screw plug D is thus drawn to the left, and since the keyways in which spindles C fit are .tapered, the points on C bite into tlie shaft, tlius binding the spider and the left end of tube rigidly to the inner wall. F is a lock washer which serves to prevent E working loose. The right end of tube A had a casting G clamped on it, and this rested in a ball bearing fitted into a spider set into the end of shaft and held firmly by means of tapered screws H. The arrangement described above permits the tube A to re- main free from torsion while the shaft is transmitting power. The left end is clamped to the shaft, but the right end is permitted to turn freely in its ball bearing, and will do so in case there should be any angular displacement of the shaft at this end. It is evident that there will be such a movement and the amount will be propor- tional to the twisting moment, or torque, transmitted by the shaft. It remains, then, to provide a means for measuring and re- cording this movement. A lever L was secured to the right end of tube A and lies in the slot S, cut for this purpose in the face of flange on the shaft. The width of this slot is such as to freely per- mit the small movement of lever caused by the slight angular move- ment of tube relative to shaft. A top piece M, secured to L by screw /, simply serves to transmit the movement of -L to, the rcr cording mechanism. A double arm T, made of tubing to give the maximum strength on minimum weight, is fitted in a block U that is centered at KJ and actuated by M. At each end of / is a ger- man silver recording needle, secured by binding screw not shown in figure. The ball 0, section Y-Y, is held against the screw P by the spring Q and pin i?, thus providing for taking up all lost mo- tion due to wear. Since / and are both firmly secured to the block U moving about K-K as a center, any movement of L vsfith respect to the flange on shaft causes one of the two points A'^A'' to go to the left and the other to the right. It still remains to provide means to record this movement, that is, the distance between the circular paths traced by the two points NN as they revolve with the shaft. At the lower right-hand corner of the figure is shown the device for holding the small sheets of metal coated paper for tak- 766 PRACTICAL MARINE ENGINEERING ing the record from the needles NN as they revolve in the paths yy. Several sheets of this paper are placed loosely in the pocket provided, and by pushing the rod W the top sheet is moved until it becomes tangent to F-F and receives the record. Z is a handle for moving the paper holder so that if it should be found that only one needle touches, the plane of the paper can be slightly changed so that both needles will mark. S' is an adjusting screw for mov- ing the paper holder in and out from the center of the shaft. The linear distance between the lines traced by NN is a direct measure of the twist of shaft when corrected for the zero reading. This is obtained by dragging the propeller in order to cause the shaft to revolve when transmitting no power. Both points can be made to mark the same line by careful adjustment of the screw P; but this is inadvisable, since the shaft must be stopped to make the adjustment and a zero reading of as much as o.i inch is of no disadvantage. The proportions of the Florida's instruments are such that one-half degree angular displacement of shaft is equivalent to 1.9 inches of displacement between the two recording points. This ratio was found in shop tests with a calibrating instrument espe- cially devised for the purpose. The results of these tests are plotted in the upper right hand corner of the figure, and show that ratio between angular displacement and distance between lines on the record is constant for all powers. The tests were made first by adjusting the arm in the slot, using a micrometer gage to place it in the exact position required. The arm was then locked in this position and the calibrating instrument run in a lathe and cards taken while running. It was also shown by these experiments that the speed of rota- tion does not afifect the reading of the instrument. Centrifugal force only tends to increase the diameters of the circles traced by the needles, andlhere is no tendency to vary the distance between the planes of these circles. The linear distance between marks on a card when laid flat is directly proportional to the angular twist of shaft. It is thus seen that one constant serves for all powers and speeds. To obtain the horsepower constant the shafts were calibrated in the shop by applying a known moment and measuring the angle of twist in a known length by means of battens. Thus determin- ing the horsepower constant for No. 2 shaft on the Florida the following method was employed : INDICATORS AND TORSION METERS 767 From calibration data it was found that one-half degree of twist in 100 inches of length of shaft corresponds to 171,371 foot pounds of moment. One inch reading on torsionmeter card cor- responds to 0.263 degree of twist. Hence 0.263 degree of twist when the shaft is transmitting power must correspond to 0.263 X i7i>37i X 2 = 90,312 foot pounds of twisting moment or torque. 27r X Af X R.P.M S. H. P. = , . 33,000 where M = twisting moment in foot pounds. If the torsion- meter reading is one inch for M could be substituted the number 90,312, but the reading varies directly with the torque in all cases, and 2^ X (90,312 X r) X R. P. M. S. H. P. = — ^ = 17.19s X T X R. P. M., 33>ooo where T = the corrected torsionmeter reading in inches. The above expression applies to a length of 100 inches in No. 2 shaft of the Florida. In any shaft the constant is inversely proportional to the length of the shaft under consideration. It is therefore possible to cut the tube A of such length that the constant will have a value of 10, and the work of calculating horsepower from the torsionmeter reading can be thus greatly facilitated. This instrument possesses the advantage of being housed in the shaft, where it is entirely out of the way. There are few parts to get out of order, there is no chance for lost motion to de- velop and the weight is less than in other torsionmeters. It is ap- plicable only to hollow shafting. The tube and attachments must be placed there permanently and cannot be adjusted or even exam- ined without removing tlie section of shaft in which installed. The parts are rigidly constructed with locking devices on all pieces that could otherwise work loose. When carefully installed it is be- lieved that there will be no necessity for further adjustment of these parts. Formulae The moment M, caused by the pull W on an arm of length r^=W'X,r. From the results of calibration experiments a curve is constructed, the ordinates giving the values of M in foot pounds and the abscissae the corresponding readings of the torsion- meter. From this curve the moment corresponding to any reading of the torsionmeter, when the shaft is transmitting power, may be obtained. 768 PRACTICAL MARINE ENGIKEERISG The shaft horsepower (S. H. P.) is equal to 2 X '^ X ^V X R. P- I\I- M X R. P- M. (i) ' ^ = ' 33,000 5,252 From applied mechanics it is known that the angle of torsion, for a shaft within the elastic limit, 2 X »i X / ^ ^9 (2) 0^ = =^ , where EXiXd r 180 =^ the angle of torsion in circular measure ; 6 = the angle of torsion in degrees ; A = the linear deflection measured on a circumference of radius r; m = the twisting moment in inch pounds; I = the length of shaft in inches ; d = the outside diameter of the shaft in -inches; di = the inside diameter of the shaft (if hollow) in inches; E = the modulus of elasticity of the shaft ; Trd? 1 =: the modulus of the section = for solid shafts, nr 16 16 d It is more convenient to foot pounds, express the twisting moment in Making this (3) M = - change, EXiXd X M-. "■X» 12 == X £Xrf* -X » 360 X 12 X / 16 360 X 12 X / Substituting this value of M in formula (i) for horse- power, 2 X '^ X M X R- P. M. 2 X 't' X £ X d' X « X R. P- M. (4) S. H. P. = — ■ ■■ = 33,000 360 X 16 X 12 X 33,000 X ' E (f X « X R. P. M. X ■ for solid shafts. 36,782,000 / Similarl}' for hollow shafts, E (rf* — di*) X»XR. P. M. (5) S. H. P. = X — : , 36,782,000 From (3) is obtained 360 X 12 X 16 X / X M 7,003.2 XlXM 583.6 XlXm ♦ (6) E = — : : = __:. ■^Xd'x^ d' — e d'—9 for solid shafts; and similarly. (7) E = for hollow shafts. INDICATORS AXD TORSIOX METERS 7,003.2 X / X ^/ 583.6 XI X III r6g (.d' — d,') X" (rf' — rf.') X» From (6) or (7) the modulus ■ may be calculated when the results of calibration of the shafting have been obtained. This has been done for the shafting of a large number of vessels, and the results are given in the following table : Out- side Inside Ship. Shaft. Shaft Shaft Shaft diam. diam.. No. 1. No. 2. No. 3. No. 4. inches inches. North Dakota 11,495,800 11,590.800 14 8 Preston 11,825,555 11,926,444 11,825,555 6J^ 3M Flusser 11,548,000 12,100,000 11,730,000 6M Wi Reid 11,500,000 12,030,000 11,810,000 6 14 3M Menaghan. . . 11,550,000 11,675,000 11,360,600 634 33^ Terry 11,219,000 11,396,000 ll,-505,000 6M ^y2 Chester 11,622,702 11,820,000 11,840,000 11,755,405 8,' oHd Salem 11,373,947 11,687,837 9M 5 Perkins 11,490,000 11,551,000 8 4 Sterett 11,484,000 11,635,000 8 4 McCall 11,685,887 11,891,530 11,825,966 634 3M Burrows 11,952,038 11,895,519 11,878,224 6^ Wa Florida 11,695,300 11,659,600 11,616,600 11,844,666 121^ 6 A rkansas. . . . 11,936,903 11,962,910 11,893,953 11,818,720 121^ 8 Test shaft... 11,577,071 IMs olid These results do not show great variation, but the difference is sufficient to justify the rule that all shafting on which a torsion- meter is to be used must be calibrated. It is probable that the re- sults would have approximated more closely to a mean value if the axial hole had in all cases been exactly central and of the cor- rect diameter throughout, and also if the experiments had been carried out under the same conditions by' the same observers. When calibration is impracticable, approximately 'correct re- sults 'in the case of high grade steel 'shafting will be obtained by assuming a value for E of 11,750,000. Substituting.this value in (4) and (5), rf* X ^ X R. P. M. (8) S. H. P. = — — - for solid shafts, and (9) S. H. P. for hollow shafts. (rf*- 4-13 X / -rfi') X^XR.P.M. 3-13 X I 770 PRACTICAL MARINE ENGINEERING [3] Hopkinson-Thring Torsion Meter The principle of this apparatus is a differential one, and con- sists in the observation of the twist between two adjacent points on the shaft by means of two beams of light projected on to a scale from a fixed- and a movable mirror. The beam projected on the Fig, 454. Torsion Meter Mounted Complete on Shaft scale by the fixed mirror is taken as the zero point, while the beam projected by the movable mirror indicates the amount of torque on the shaft. Both mirrors revolve with the shaft, but even at mod- erate speeds the reflections appear as continuous lines of light across the scale. Fig. 455. Scale Box with Lamp, for Torsion Meter The Torsionmeter is shown in Fig. 454, mounted complete on a shaft, and the scale box in Fig. 455, while a diagrammatic ar- rangement of the complete apparatus, is shown in end elevation and plan in Figs. 456 and 457. A collar A, clamped to the shaft of which the torque has to be measured, is provided with a flange projecting at right angles to the shaft and an extension (Fig. 457). A sleeve B (Fig. 457) provided with a similar flange and ex- tension at one end, is clamped at its further end on to the shaft in such a manner that its flange is close to that on the collar A, while INDICATORS AND TORSION METERS 77^ its extension overlaps that of the collar A, on which it is supported to keep it concentric. Both the collar and sleeve are quite rigid, and it is obvious that when the shaft is twisted by the transmission of power, the flange on the sleeve B will move relatively to that on the collar A, the movement being equal to that between the two Fig. 456 Fig. m parts of the shaft on which these fittings are clamped. This move- ment is made visible by one or two systems of torque mirrors mounted between the two flanges, which reflect a beam of light, projected from a lantern, on to a scale divided in a suitable man- ner on ground glass. Each system of torque mirrors consists of a mounting, pivoted 772 PRACTICAL MARINE ENGINEERING top and bottom on one or other of the flanges, in which two mir- rors are arranged back to back. This mounting is provided with an arm, the end of which is connected by a flat spring to an adjust- able stop on the other flange. Any relative movement of the two flanges will turn the torque mirror and thereby cause the beam of light to move on the scale, the deflection produced being directly proportional to the torque applied to the shaft. Hence, if the rigidity of the material and the number of revolutions per minute are known, the horsepower transmitted can be readily calculated. With the arrangement described, a reflection will be received from each mirror at every half revolution of the shaft ; but where the torque varies during a revolution (as with reciprocating engines), a second system of mirrors may be arranged at right angles to the first system, so that four readings can be taken during one revolution; or, if two scales are used, eight readings can be taken. Fig. 456 shows how the beam of light reflected by the mirror when in its highest position passes through the upper part of the scale ; while the second reflection will occur when the mirror is in the position occupied by the zero mirror, the beam of light passing through the lower part of the scale. The position of the torque mirror in Fig. 457 is such that the reflected beam strikes the scale to the right of the zero line, but when the shaft has made a further half revolution, the reflected beam from the other mirror will strike the scale to the left of the zero line. Obviously, the deflec- tion on both sides should be equal. The fixed mirror is attached to one of the.flanges (in Fig. 457 to the flange of the sleeve B). This must be adjusted so that the beam of light reflected from it is received at the same point on the scale as those from the movable mirrors when there is no torque en the shaft. To facilitate the erection and adjustment of the apparatus, the box containing the scale and carrying the lamp is fitted with trunnions, so that it can be inclined as required. If the position of the apparatus becomes altered relatively to the scale owing to the warming up of the shaft or from' other causes, this is indicated immediately to the observer by an altera- tion in the position of the zero as reflected by the fixed mirror. Hence, the zero can be adjusted by moving the scale so that its zero coincides with the reflection from the fixed mirror. It will be obvious that it is not necessary to move the scale, as the mean of INDICATORS AND TORSION METERS 772, the two readings will be the same. It will readily be understood that a movement of tlie torque mirrors can only occur through a relative movement of the two flanges, so that vibration of the shaft or of the ship will not influence the readings. The constant of the instrument, viz., the factor which, when multiplied or divided into the product of the torsion meter reading and the revolutions, gives the horsepower, may be calculated with- in 2 or 3 percent, if the section of shaft within the instrument is uniform. A direct calibration of the shaft, with the instrument in position, is recommended before the former is put into the ship. This is effected readily by applying a known twisting couple, as previously described. QUESTIONS Indicators and Torsion Meters PAGE Describe briefly wliat is shown by an indicator card and name the various lines 731 In what manner does an actual card differ from an ideal card, or a card referring to ideal conditions ? 732 To what are these differences due ? 722 What are the two chief uses of indicator cards ? 733 As shown by the indicator card, what is the result on the steam dis- tribution of setting the eccentric too far ahead of a line at right angles to the crank; that is, of too large an angular advance?. . . . 734 What is the result similarly with too small an angular advance? 734 What is the result with the steam lap too large ? 734 What is the result with steam lap too small ? 735 What is the result with exhaust lap too large ? .' 735 What is the result with exhaust lap too small? 735 What is the result with excessive compression ? 73S What is the result with excessive expansion ? 736 What is the result with valve stem too long or too short ? 736 What is the result of a leaky piston or piston rod stuffing box? 736 What is the result with ports and passages too small ? 727 Describe in detail the method of working up indicator cards for power, both by ordinates and by the planimeter 737 Describe and explain the method of combining a set of indicator cards from a triple or multiple expansion engine 74S Describe a steam engine indicator, name its various parts and state their uses 749 What is the object of the reducing motion ? 753 Describe various kinds of reducing motions 7.53 In examining and adjusting an indicator for service on the engine, what are the chief points to which attention should be given?. . . . 756 Describe the operation of taking a card 757 How is the atmospheric line drawn ? 757 What information should be placed on each card as it is taken? 758 Describe method of calibrating a shaft 759 Describe a torsion meter and the method of using it 763 CHAPTER XIV Special Topics and Problems Sec. 104. HEAT AND THE FORMATION OF STEAM [i] Constitution of Matter For the purpose of explaining or discussing the relations between matter and the forces of nature, all substances are sup- posed to be composed of enormously large numbers of infinitely small parts called molecules, each one of which is supposed to be, in fact, the smallest portion of the substance which can exhibit its various properties. These molecules are furthermore not at rest, but are supposed to be in a state of more or less violent agitation or motion. If the motion of each molecule is about a fixed center, so that they all retain their average positions fixed in the body, it is said to be a solid, or in the solid state. If the motion of the molecules is about centers which themselves are free to move about in any direction, so that the average position of the molecules is not fixed and the body readily changes its form, -it is said to be a liquid, or in the liquid state. If the motion of the molecules is in straight lines hither and thither, bound to no center or location, but ever striving to fly as far apart as possible, the substance is said to be a gas, or in the gaseous state. In the solid and liquid states the molecules are bound together by forces of molecular attraction, so that they tend to maintain about the same average distance apart, and thus to fill the same volume. Any attempt to change this average distance between the molecules and thus to make the volume larger or smaller must deal with these molecular forces. The only practicable way of doing this is through the agency of heat, as shall be seen in the next sec- tion. In a gas the forces binding the molecules together have been overcome, and the molecules have been separated so much further apart that all traces of these attractive forces have disap- SPECIAL TOPICS AND PROBLEMS 775 peared, and instead there exists a repulsive force acting between the molecules and urging them as far apart as the limits of the vol- ume which contains them will allow. Due to this property a gas will expand and fill any volume, no matter how large, the repul- sive force or force of expansion, however, becoming weaker as the volume increases and the average distance between the mole- cules becomes greater and greater. [2] Heat ( I ) Heat and Its Relation to Matter. — Energy is known as the capacity for doing work; also the energy of motion is called kinetic energy, while the energy of position or location relative to a given force, is called potential energy. Heat is one of the many forms of energy. It is, in fact, the energy of the molecule, and the heat in a body means therefore simply the amount of such molecular energy which the body pos- sesses. This energy of the molecule is partly kinetic or due to its motion, and partly potential, due to its position relative to the molecular forces which act upon it. The addition of heat to a body, or its subtraction from a body, means therefore the addition or subtraction from the energy of its molecule, and hence the addi- dition to or subtraction from its store of molecular energy. This addition or subtraction of heat is always accompanied by a series of changes in the state or condition of the body. Thus, if heat be added to a lump of ice at the melting point, or 32 degrees F., it first melts, or changes from' a solid to a liquid, remaining at the constant temperature of 32 degrees, and slightly contracting in volume meanwhile. If heat is still further added the water grows warmer to the touch, as shown by the thermome- ter. At the same time it continues to contract slightly till it reaches a temperature of about 39 degrees F., and then slowly ex- pands. If under atmospheric pressure the increase of tempera- ture and volume will continue with the addition of heat until the thermometer marks a temperature of 212 degrees F. Then the further addition of heat occasions no further elevation of tem- perature, but instead, a new change of state. The water now passes into the state of vapor or steam, the temperature of both the water and the vapor formed from it remaining meanwhile constantly at the fixed temperature of 212 degrees. After the water is completely vaporized, if the vapor be inclosed in a cham- ber of fixed volume and heat still further added, it will then be 7y6 PRACTICAL MARINE ENGINEERING found that the pressure and temperature will continue to increase so long as additional heat is supplied. If, instead, the pressure is kept^constant, the volume and temperature will increase as heat is added. If the temperature is kept constant, the pressure will fall as the volume is increased. From the start, then, as more and more heat has been added, the water has exhibited successively the three states of matter: As ice it is a solid ; in its usual state, or between 32 degrees and 212 degrees under atmospheric pressure, it is a liquid, and after it is completely vaporized and heat is still further added so as to carry the conditions considerably beyond those at which the Vapor was formed, it becomes a gas. It is necessary to explain here the difference which may be im- plied in the words gas and vapor. When a substance first changes from the liquid to the gaseous state, or while the pressure, volume and temperature are near those corresponding to such a change, the substance is more strictly called a vapor, or is said to be in a vaporous condition. If the substance is in the gaseous state, but with pressure, volume and temperature conditions far removed from those corresponding to the change of state, the substance is more generally called gas. There is no sharp line of difference between a vapor and a gas. The former means simply a substance in the gaseous state, but at or near the conditions corresponding to the process of change from one state to the other, while the lat- ter means likewise a substance in the gaseous state, not far re- moved from the conditions corresponding to the process of change of state. There are thus two chief kinds of change which the applica- tion of heat may produce. (a) It may change the temperature of a substance accom- panied by a change of pressure or volume, or both, but without change of state. (b) It may produce a change of state, asfrom sohd to liquid, or liquid to vapor, accompanied usually by a change of volume, but without change of temperature. If, however, the pressure varies during -the change of state, then the temperature at which the change occurs will also vary, but there will be no change of tem- perature directly accompanying the change of state. In conse- sequence, during the change from solid to liquid, or vice versa, the temperatures of both are the same, and similarly during the change SPECIAL TOPICS AND PROBLEMS 777 iruin liquid to vapor, or vice versa, the temperatures of both arc the same. It must be understood when changes are referred to as de- pending on the addition of heat, that the subtraction of heat will produce changes in exactly the opposite direction. Thus, if the addition of heat causes a body to expand, the subtraction will cause it to contract; if the addition causes an increase of pressure the subtraction will cause a decrease ; if the addition causes a change of the state from liquid to vapor, the subtraction will cause a change from vapor to liquid, etc. (2) Sensible and Latent Heat. — Heat which causes a change of temperature in a body, as when water is heated and becomes hot- ter to the touch or to the thermometer, is called sensible heat. This corresponds to a change in the kinetic energy of the molecule, so that increase of velocity of the molecule and increase of its kinetic energy correspond within the substance to the growing hotter to the touch and to increase of temperature as observed on the outside. Heat which is involved in a change of state but which pro- duces no effect on the temperature of the substance (as in the melting of ice at 32 degrees or the boiling of water at 212 degrees) is called latent heat. This corresponds to a change in the potential energy of the molecule so that an increase in the average distance between the molecules (acquired in opposition to the molecular forces acting) , and a consequent increase in their potential energy corresponds within the substance, to the change of state at con- stant temperature as observed on the outside. It must be understood that there is really but one kind of heat, and that this division into sensible and latent is only a matter of convenience in order to signify the particular energy change which is effected within the body. The heat required to raise the temperature of a body or to increase its sensible heat is thus expended in increasing the velocity of the molecules of the body, and hence in increasing tlieir kinetic energy. The heat required to effect a change of state, or to increase the potential energy, is expended, on the other hand, in increasing the average distance between the molecules, and in increasing the volume of the body against whatever external forces may exist. The gradual expansion of a body with increase of tempera- ture "is accounted for by assuming that as the velocity of the 778 PRACTICAL MARINE ENGINEERING molecules, is increased, their average path is increased also, and hence their average distance apart, and hence the volume of the body. (3) Temperature. — It has been shov^fn above that temperature refers to the condition of a body as regards its sensible heat, or the kinetic energy of its molecules. Two bodies are said to be at the same temperature when there is no tendency for heat (that is, molecular energy) to flow from one to the other. This con- dition is measured by the thermometer, an instrument too well known to require particular description. The Fahrenheit scale, which is commonly used by engineers in the United States, is graduated as follows : The temperature of melting ice is called 32 degrees and that of boiling water 212 degrees. The interval between the two is then evenly divided into 180 parts, and the same divisions are extended above and below as far as may be desired. On the Centigrade scale the temperature of melting ice is called o degrees and that of boiling water 100 degrees. The in- terval is then evenly divided into 100 parts, and the divisions extended above and below as may be desired. For transforming temperatures from one scale to the other the following equations are used : E = 9/5 C + 32 degrees. C — S/9 (P — 32 degrees). where F and C denote respectively the temperatures on the Fahrenheit and Centrigrade scales. Examples: Transform 20 degrees C into F. Operation : ^ = 9X20-^5-1-32=36+32=68 degrees. Transform 20 F to C. Operation: C = 5/9 (20 — 32) = 5/9 (— 12) = — 62/3 de- grees, or 6 2/3 degrees below zero. Transform 77 F into C. Operation : C = s/9 (77 — 32) = S/9 X 4S = 25 degrees. Transform — 22 degrees F into C. Operation: C = s/9 (— 22 — 32) = 5/9 (— 54) = — 30 degrees. (4) Heat Unit.— Care must be taken to distinguish between quantity of heat and temperature. The first refers to the total amount of heat energy present in the substance, the second to the kinetic energy of a molecule. A large cup of warm water and a small cup of hot water may both have the same quantity of heat, but not the same temperature. A cup of hot water and a barrel full of hot water may have the same temperature, but the quan- tities of heat will be very different. SPECIAL TOPICS AND PROBLEMS 779 For measuring quantities of heat, use is made of a heat unit defined as the amount or quantity of heat required to raise one pound of water one degree in temperature. Inasmuch, further- more, as the amount thus required would va?ry sHghtly at different temperatures, it is necessary to fix the temperature at which the unit is to bedefined. The temperature thus taken for the defini- tion of the heat unit has sometimes been at the freezing point, or again at the point of maximum density of water, which is about 39 degree F., or again at about 62 degrees, or from 62 degrees to 63 degrees. It is very difficult to determine the amount of heat required to raise water one degree at or near the freezing point, while between 60 degrees and 70 degrees, or at about an average atmospheric temperature, the measurements are most readily made. For this reason a temperature within this range is to be preferred for definition of the heat unit. The heat unit thus defined is often known as the British Thermal Unit, the name being usually abbreviated to B. T. U. (5) Joule's Equivalent. — Since heat is but a form of energy it follows that it should be possible to transform heat into me- chanical work, and vice versa. It is for the first purpose that the steam engine is used, while instances of the latter transformation are constantly in evidence, as in the heat developed by the friction of a bearing, or in turning a chip from a bar of steel, etc. It therefore becomes of importance to know the ratio of transformation, or how much mechanical work measured in foot- pounds corresponds to one heat unit as above defined. This has been made the subject of careful experiment extending over the past one hundred years, and the latest and most reliable results seem to give for this ratio the value 778. That is, one B. T. U. is equivalent to 778 foot-pounds of mechanical work. This means that when in a steam or other heat engine heat is transformed into mechanical work, for every B. T. U. so transformed and dis- appearing as heat, 778 foot- founds of work will be obtained; or again, when mechanical work is transformed into heat, for every 778 foot-pounds so transformed and disappearing as work, one B. T. U. of heat will appear. This number or ratio, 778, is known as the mechanical equiva- lent of heat, or freouently as Joule's equivalent, though its value as determined by Joule was somewhat smaller than the value given above. 78o PRACTICAL MARINE ENGINEERING (6) Transfer of Heat. — Heat may be transferred from one body or place to another in three different ways : by radiation, by conduction, and by convection. By radiation is meant the transfer of heat through space' in straight lines, as from the sun to the earth, or from a furnace fire to the face when the door is opened. By conduction is meant the transfer of heat along a body from one molecule to the next, as when a slice bar becomes warm at one end if red hot at the other. By conductioti.is meant the transfer of heat along a body of a liquid or gas to another by means of currents set up in the liquid or gas and carrying the heated molecules from one place to another, as in the circulation set up within a Scotch boiler. Two other operations are also concerned in the transfer of heat from one substance to another. These are emission and ab- sorption. By emission is meant the giving off or transfer of heat from the molecules from one body to those of another. By absorption is meant the converse of this, the receiving of heat by the molecules of one body from those of another. The heating of water in a boiler is due, at least in part, to all of these processes. The fire in the furnace radiates heat to the crown sheet; convection and draft currents convey the hot gas to the heating surface ; there is emission from the hot gases and absorption by the metal of the heating surfaces ; there is con- duction through the metal from the fire to the water side; there is emission from the metal and absorption by the water; and finally there are convection currents, developed in the water by means of which the temperature is more or less uniformly raised. [3] Steam S'teaun or the vapor of water is the substance almost univer- sally used as the medium through which the heat set free by the coal is transformed intoi the mechanical work of the engine or pump. Its properties are therefore of great importance for the engineer, and it is proper to study briefly the more important at this point. (i) Formation of Steam.— Let AB in Fig. 458 be a very. tall vessel open at the top and having an inside cross section of one square inch. Let it be supposed at the start that there, is in the bottom of this vessel one cubic inch of water at say 60 degrees SPECIAL TOPICS' AND PROBLEMS 781 temperature. On top of the water let there be a piston as shown which suppose to move without friction, and to be without weight. In other words, it is simply something to separate the water from the air. Then on the surface of the water there will be just the atmospheric pressure of say 14.7 pounds per square inch. Now let heat be applied at the bottom of the chamber. The first result u Marbu Sngineirinff Fig. 458. The Fdrmation of Steam will be a transfer of heat through into the water, and a resultant lise in temperature of the water near the heating surface. In consequence of this the water will expand somewhat and thus become lighter than the other water above and farther from these surfaces. The heated water will thus tend to rise to the top and so displace the cooler water there, which will in conse- quence sink and thus in turn be brought into contact with the heating surfaces. There is set up in this way a general ascending current of warmer water and a corresponding descending current of cooler water by means of which the whole mass is gradually raised in temperature. -In this manner are formed the convection currents referred to in the preceding section, and to their formation in a steam boiler is due the circulation of the water, especially in those of the fire-tube or tank type. '_ In this way then the temperature of the water will gradually rise until it reaches 212 degrees. The temperature then ceases 782 PRACTICAL MARINE ENGINEERING to rise and steam begins to form, rapidly increasing the volume below the piston and thus forcing it upward. The steam formed is of the same temperature, 212 degrees, as the water of which it is formed, the only changes being the increase of volume and the change of state. If the supply of heat at the bottom is con- fined and it is prevented escaping from the sides of the tube or chamber, the water will thus gradually be all converted into steam, just balancing by its own pressure the atmospheric pressure on the top of the piston. The volume of steam just formed would be 1,663 cubic inches, or in other words the tube would have to be 1,663 inches or 138.6 feet high to allow of the operation to take place. Suppose now that at the beginning the piston is loaded down with a weight so tha-t the total load on the water is 20 pounds instead of 14.7. Then let heat be supplied as before. A like series of changes will follow, but the water instead of beginning to change state from liquid to vapor at 212 degrees must be heated to 228 degrees before the change begins, while the final volume will be only 1,244 cubic inches. If the initial pressure were 100 pounds, then the temperature at which the change of state would begin would be 328 degrees, and the final volume would be only 275 cubic inches. Similarly for 200 pounds pressure, the figures are 382 degrees and 144 cubic inches. On the other hand, if by means of an air pump the pressure on the water were decreased below that of the atmosphere the temperature 'of change would become lower, and the volume greater. Thus if the pressure is 10 pounds, the figures are 193 degrees and 2,385 cubic inches, and if 5 pounds, they are 162 de- grees and 4,576 cubic inches. Similarly, to boil water at 32 de- grees, or the freezing point, it would be necessary to reduce the pressure to .089 pound, while the volume of vapor formed would be about 21,170 cubic inches. In general it is found that as the pressure is increased or decreased there is a corresponding rise or fall in the temperature at which the formation of vapor begins, and that it remains fixed at this temperature during the process of change of state and that the temperature of the vapor formed is also the same as that of the water from which it is formed. It thus appears that steam is simply the vapor of water, or water in the vaporous state, as defined in [2]. The process of SPECIAL TOPICS AND PROBLEMS 783 Steam formation as above described is known as boiling or ebul- litioii, or sometimes in the general sense as vaporization. The temperature at which the change of state occurs is known as the boiling point or point of ebullition. At lower temperatures there is always a certain amount of slow vaporization going on, the pressure of the vapor formed being limited to that corresponding to the temperature of the water. It is by means of such slow vaporization that water is carried up for the formation of rain clouds from the surfaces of rivers, lakes and oceans, or tliat mud dries up in the roads, or clothes when hung out to dry. Thus if the temperature is 100 degrees, the maximum vapor pressure is about one pound. Con- siderable vapor will thus be formed, which will gradually find its way upward into the air, at least so long as the air is i>ot saturated ; i. e., already charged with vapor of the full pressure corresponding to the temperature. This is, however, a branch of the subject that cannot be pursued further here. When, however, the temperature is such that the vapor ;gressure is sufficient to just balance the entire pressure on the surface of the liquid, then the vapor is formed with freedom, and more or less from the body of the liquid, producing the agitation and other conditions which constitute boiling or ebullition as re- ferred to above. An examination in some detail has thus been made into the formation of steam at constant pressure. Let an equally brief examination be made into its formation at constant volume, the case which corresponds to its generation in a steam boiler. The boiler being first open to the air through the safety valve, the water is subject simply to atmospheric pressure. The heating of the water and first formation of steam proceed accord- ing to the process as described above. The air is thus displaced from the boiler and driven out through the safety valve or other escape. The safety valve or escape is then closed and in con- sequence the steam which is formed tends to increase the pres- sure, and as this rises the temperature of the boiling point will rise also. In this way as heat is added, a part of it is used in raising the temperature of the water and steam up to the ever- rising boiling point, while the remainder goes for the vaporization of a fresh portion of steam. In this way the volume of vapor remains practically constant, but the pressure and temperature 784 PRACTICAL MARINE ENGINEERING rise together according to the regular law which relates the one to the other, while the increase of vapor is accommodated in the constant volume by the increase in density or decrease in volume required per pound as the pressure rises. It is thus seen that the temperature and volume of steam are closely dependent on the pressure to which it is subjected. For engineering purposes pressure may be measured from two different starting points. The true or so-called absolute pressure is measured from the zero or no-pressure condition, and is the true or total pressure exerted by the gas or vapor in ques- tion. The ordinary steam gage, however, does not measure the absolute pressure, but simply the difference between this and the pressure of the atmosphere. This is due to the fact that the gage is subjected to the pressure of the steam on one side of the tube and to that of the atmosphere on the other side. It thus measures simply the difference between the two. This is commonly called "gage pressure." The absolute pressure is greater than the gage pressure, therefore, by the pressure of the atmosphere. This varies with the altitude and with other circumstances affecting the barometer. For engineering purposes it is very commonly taken at 15 pounds per square inch. A more correct average for the sea level is, however, 14.7, as noted above. It results there- fore that having given the gage pressure the absolute pressure may be found by adding 15 or 14.7, as may be chosen, according to the degree of accuracy needed in the case in hand. (2) Saturated and Superheated Steam. — When steam and water are present in the same vessel together and there is no tendency for the water to change into steam or the steam into water except as heat is added or taken away, the water and the steam are said to be in thermal equilibrium. When steam is thus in equilibrium in contact with water, it is said to be saturated. Thus during the entire process of steam formation illustrated in Fig. 458, the steam is saturated. When there is no moisture or water in the liquid condition suspended in or mixed with the vapor, the steam is said to be dry. When there is moisture or water suspended in or mixed with the vapor, the steam is said to be moist or wet. In such case the steam or vapor part of the mixture must itself be in the saturated condition as defined above, so that wet steam is simply a mixture of saturated water vapor and liquid water. SPECIAL TOPICS AND PROBLEMS 785 When steam is free from all suspended moisture, but is still in the saturated condition as determined by its pressure, tem- perature and volume, it is called dry and saturated. Thus the condition of the steam in the vessel of Fig. 458, just as the last bit of vapor is formed, is dry and saturated. During the opera- tion the vapor would be dry and saturated provided it contained no suspended moisture. Practically this is a condition difficult to realize. The greater or less violence of the ebullition is apt to carry up a certain amount of water in the shape of fine mist into the steam space, from which it settles back only slowly, and so is liable to be carried over into the engine. The steam furnished by the average boiler under good conditions contains usually not less than from i to 2 percent of moisture, while under poor con- ditions the amount may rise to 5 percent and more. Suppose now, referring to Fig. 458, that after the last bit of water has been vaporized, heat is still further applied, the pres- sure on the piston remaining the same. The temperature which during the process of valorization has remained stationary will now begin to rise, accompanied also by an increase of volume. If the three stages are recalled through which the water has passed, all at constant pressure, it appears that during the first stage there was a rise in temperature of the water to nearly con- stant volume: during the second stage (that of steam formation) there was an increase of volume at constant temperature : during the third stage, as just described, there is increase of both volume and temperature. If in this last operation instead of keeping the pressure con- stant the piston were held fast, thus keeping the volume constant, it would be found that with the addition of heat both the tempera- ture and the pressure would increase. Steam in the condition resulting from these operations is said to be superheated. As compared with saturated steam its temperature and volume are greater for the same .pressure, or its temperature and pressure are greater for the same volume, or its volume is greater and pressure less at the same temperature. It is clear that superheated steam cannot be in contact with water and remain superheated. It cannot therefore be moist. If it were brought into contact with water, it would lose its super- heat and become saturated, forming by the heat given up, a little more vapor from the water present. 786 PRACTICAL MARINE ENGINEERING The relation between saturated and superheated steam may be put into the following form : Saturated steam contains only as much heat as is absolutely necessary for its maintenance as steam at the given pressure. Superheated steam at the same pressure contains more heat than saturated. The temperature and volume per pound for saturated steam correspond with the pressure as in the process of vaporization, and are respectively the lowest temperature and smallest volume at which steam of the given pressure can exist. The temperature and volume per pound for superheated steam are both larger for the same pressure than for saturated steam. [4] Total Heat in a Substance (i) Total Heat of Steam. — The total heat of a body in a given condition is the total amount of heat required to produce this condition, reckoning from some starting point agreed upon. For steam this point is usually taken at 32 degrees F., or the freezing point of water. The total heat per pound of steam at a given pressure and temperature, means then the total amount of heat, both sensible and latent, required to produce one pound of steam of the given pressure and temperature, from water at 32 degrees. These quantities of heat are used in the solution of problems relating to the heat required for evaporation, boiler efficiency, gain by feed water heating, etc. The value of the total heat in terms of the temperature is very closely given by the following approximate equation : H = 1083 + .3* while the latent heat is similarly given by the ' equation : L = 1114 ^ .7* In these equations, H denotes the total heat, L the latent heat, and t the temperature. Instead of using these or other similar equations, the values are more conveniently taken from tables prepared so as to give the various quantities for regularly varying values of the pres- sure. Thus from the Table it appears that at 14.7 pounds pres- sure absolute, or at the pressure of the atmosphere, it requires 180.9 B. T. U. to heat the water from 32 degrees to the boiling point 212 degrees, and then 965.7 B. T. U. to completely vaporize it at this point. The great excess of the latter or latent heat over the former or sensible heat may thus be noted. It is also seen SPECIAL TOPICS AND PROBLEMS 787 that according to the table the heat required to raise the water from 32 degrees to 212 degrees is not exactly measured by the difference in degrees, which is 180. The excess is due to the fact that the B. T. U. is defined for i degree rise from 62 degrees to 63 degrees, while the amount required to make i degree difference at other temperatures is slightly different, increasing on the whole for higher temperatures, so that between ^2 degrees and 212 de- grees the average is slightly greater than from 62 degrees to 63 degrees. It thus results that the sensible heat per pound of water involved in a temperature change is slightly greater than the num- ber of degrees which measures such change. This difference is, however, so small that for most engineering purposes it may be neglected if more convenient, and the number of heat units per pound of water may be taken equal to the number of degrees difference in temperature. (2) Total Heat of a Mixture of Steam and Water. — Steam as actually used is usually moist ; that is, it contains a small frac- tion of water. To find how much heat is required to produce one pound of such a mixture of steam and water, a given fraction being steam and the remainder water, it is necessary to remember that all of the water must be raised to the temperature of boiling, while only the given fraction is vaporized. If therefore 6" denotes the sensible heat and L the latent heat, while x is the fraction which is steam, or the quality of the steam as it is called, then the heat H required to produce one pound of the mixture will be : H = S + xL The quality x is usually expressed on the percentage basis. The following examples will illustrate the use of the steam tables : ( 1 ) Find the sensible heat, the latent heat and the total heat in one pound of steam at 120 pounds gage pressure.* Ans. from the table, 322.1, 866.6, 1 188.7. (2) Find the heat in i pound of feed water at a temperature of no degrees. Ans. no — • 32 = 78. (3) How' much heat would be required to produce the steam in example (i) from the feed water in (2) ? * For present purposes, and in the following problems, it will be sufficiently accurate to take the pressure of the atmosphere as iS pounds per square inch. The absolute pressure is therefore found from the gage pressure by simply adding IS- 788 PRACTICAL MARINE ENGINEERING Ans. — The difference between the two, or 1110.7. Remark: These three examples show how the heat necessary to produce a pound of steam of given pressure from feed water of any given temperature may be found. (4) How much heat is required to make i pound of steam at 150 pounds gage pressure from feed water at 130 degrees? Ans. 1095.5. (5) How much heat is required to produce i pound of moist steam of 92 percent quahty at 150 pounds gage pressure from feed water at 120 degrees ? Solution : The sensible heat per pound of steam is. 338-4 The sensible heat per pound of feed is 88.0 The difference is 250.4 The latent heat for one pound is 855.1. But since only 92 percent is vaporized, only .92 of this will be required. There- fore : H = S + xL — 250.4 + .92 X 855.1 = 1037. Ans. (6) One engine requires per indicated horsepower per hour, 16 pounds of steam of 96 percent quality at 150 pounds gage pressure, the feed being at a temperature of 140 degrees. An- other engine requires 20 pounds of steam of 90 percent quality at no pounds gage pressure, the feed being at a temperature of no degrees. Find the amounts of heat required per hour in the two en- gines, and hence their real comparison as heat engines. By the methods illustrated above there is found as follows : For the first engine 16,821 B. T. U. per hour. For the second engine 20,436 B. T. U. per hour. The second engine requires, therefore, 3,615 B. T. U. per hour more than the first, and in consequence is about 21.5 per- cent more expensive in terms of the heat required. Further illustrations of these principles will be found in Sec. 105. [s] Latent Heat in Passing from Ice to Water It has been seen in [2] ( i ) that a certain amount of heat is absorbed in the melting of ice at the constant temperature of 32 degrees. It is thus rendered latent or is taken up in effecting the change of state in the same general manner that heat is rendered SPECIAL TOPICS AND PROBLEMS 789 latent in passing from liquid to vapor. It may be of value to note here the quantity of heat thus rendered latent. This amounts to about 143 heat units, or B. T. U., per pound of ice melted from 32 degrees into water at the same tem- perature. Sec. 105. STEAM BOILER ECONOMY [i] General Principles There may be several different bases for boiler economy ac- cording to the particular feature held in especial prominence. The output of the boiler is estimated in terms of the steam pro- duced, and there may be the following kinds of economy: (i) Economy in coal consumption, increasing with the out- put of steam per pound of coal burned. (2) Economy in weight of boiler, increasing with the output of steam per pound of boiler. (3) Economy in first cost, increasing with the output of steam per dollar invested in the boilers. (4) Economy of maintenance or total life, increasing as the life of the boiler is longer and the amount necessary for repairs is smaller. It is never possible to fulfill in the highest degree the condi- tions for these various kinds of economy, and a compromise must always be made among them, though usually (i) or (2) will take the first place in the order of importance. Without special note, however, the term economy is under- stood to refer to (i), though the considerations relating to the others should always be kept in mind. In some cases, as in tor- pedo boat and like practice, (2) may assume first place in the order of importance, and, perhaps, require some sacrifice relative to the others. Now consider more especially the economy re- ferred to under (i). From the standpoint of coal economy or efficiency, the boiler is charged with all the coal that is thrown through the furnace doors, and is credited with the steam which it sends to the engine. Or, to state the matter more definitely, it is charged with all the heat which could be gotten from this coal by perfect and complete combustion, and is credited with the heat which is transferred through and actually used in the formation of steam. If the efficiency were perfect, or if there were no loss, these two amounts of heat would be equal. Actually there are many losses, 790 PRACTICAL MARINE ENGINEERING large and small, and, in consequence, the latter is considerably less than the former. The ratio of the two is known as the boiler efficiency. In practice its value varies from about 50 to about 75 or 80 percent. Following are the more important sources of loss which occasion this drop in efficiency. In the first place, a little of the fuel may fall unburned through the grate into the ash pit. Again, a little in the form of dust and small bits may be carried by a strong draft, either un- burnt or only partially burnt, through into the tubes, uptakes or funnel. Still another small portion may escape as smoke, which consists almost entirely of very fine particles of unburnt carbon formed from the gases which are distilled away from the coal in the process of combustion. Still another portion of these gases may escape unchanged and unconsumed. Again, there may be an incomplete combustion of the carbon forming carbon mon- oxide, and giving only about 4,450 heat units per pound, instead of 14,500 which result from the complete combustion into carbon dioxide. Hence, whatever carbon escapes in the form of carbon monoxide is only partially burned, and may be considered as car- rying away over two-thirds of the heat which would be liberated by complete combustion. These losses all occur in the furnace, and are due to poor firing and to imperfect combustion. To reduce them to the lowest limit, the fireman must know his business, and be willing to attend to it with ceaseless care and diligence. In addition, there must be provided, by proper design, the necessary supply of air both above and below the grate, together with such arrangements as experience may show are needed for good combustion with the fuel in hand. At best this loss may be reduced to perhaps 2 or 3 percent, while with carelessness or poor design, or both, it may easily reach values from 10 to 20 percent. The heat being thus more or less perfectly liberated in the furnace, is then passed on to the boiler heating surface, whose duty it is to transfer it through into the water on the other side. The energy is still to exist as heat, but it is to be transferred from the hot gas to the water, thus converting the latter into steam. This, however, cannot be perfectly accomplished, and thus arises a further loss. A part of the heat, instead of passing through the heating surface, goes up the funnel carried by the escaping gases, and so gets away into the outside air. Another and smaller part SPECIAL TOPICS AND' PROBLEMS 79i escapes by radiation into the fire room. These losses it is im- possible wholly to avoid. It would be necessary to avoid all loss of heat by radiation, and to reduce the temperature of the pro- ducts of combustion in the funnel to that of the outside air. The latter, especially, cannot be done for the best of reasons. In the first place, the temperature cannot be reduced below that of the steam and water in the boiler, because heat always flows naturally from a hot body to a cooler one, and it will, therefore, flow from the gas to the water only so long as the latter is the cooler of the two. The actual temperature of the escaping gases must be considerably higher than that of the steam, because in the first place sufficient heating surface to reduce them to nearly the same temperature could hardly be allowed ; and, again, aside from blowers, the strength of draft is dependent on the tempera- ture of the hot gas in the funnel, and for a satisfactory rate of combustion it is necessary to discharge the products of combus- tion at temperatures not less than 450 to 600 degrees. This loss is one, therefore, which exists in the nature of things, and cannot be reduced below some 20 or 30 percent. On the whole, then, the entire losses under the best condi- tions can hardly be reduced much below 25 percent, while with poor conditions they may aggregate 40 to 50 percent. The re- maining fraction, or the 50 to 75 or 80 percent, represents then the efficiency of the boiler as defined above. Since a pound of average good coal has available some 13,000 to 14,000 heat units, and of fuel oil from 18,500 to 19,300, it follows that the heat actually utilized per pound of coal is usually found between say 7,000 and 11,000 units, and between 9,250 to 15,400 per pound of fuel oil. In general the conditions favorable to high efficiency are the following : (i) A free burning coal of good quality, with suitable fur- naces and air supply for complete combustion, and in the case of fuel oil, an oil of low specific gravity and flash point. (2) Moderate draft. (3) Abundant heating surface. Or, as a combination of (2) and (3), may be put: (4) Moderate evaporation required per square foot of heat- ing surface. The opposite of these conditions will cause necessarily a loss in efficiency more or less pronounced according to circumstances. 792 PRACTICAL MARINE' ENGINEERING [2] Evaporation Per Pound of Coal The efficiency of a boiler is often roughly estimated by the number of pounds of water evaporated into steam per pound of coal burned on the grates or per pound of oil injected into the furnace. This, according to conditions, may, with coal, vary from 6 or 7 to perhaps 11, while with oil it rises to from 12 to 16. Re- membering that it usually requires rather more than 1,000 heat units per pound of steam, the general agreement between these figures and those above for the heat utilized per pound of coal is readily seen. In fact, the figures for the heat utilized are derived really from a measurement of the pounds of steam evaporated per pound of coal, together with a knowledge of the heat required per pound of steam, the latter being derived, of course, from the conditions of the evaporation. When the great difference in the amount of heat required per pound of steam, depending on the temperature of the feed, the temperature of the steam, and whether the steam is moist or dry, is remembered, it is clear that for any fair measure of boiler performance in terms of steam formed per pound of coal, these differences must be allowed for, especially in comparisons be- tween boilers working under different conditions. To this end it is customary to reduce the number of pounds evaporated to what it would be if the steam were dry and the temperature of both feed and steam were 212 degrees. In such case it would require to make one pound of steam simply the latent heat at 212 degrees, or 966 B. T. U. (British thermal units). This is known as the reduced evaporation, or the equivalent evaporation from and at 212 degrees. It is really the number of pounds of steam which would be formed if each required 966 B. T. U., and is, therefore, simply a measure of the B. T. U. put into the steam per pound of coal or of oil. The ratio betwen the number of B. T. U. actually required and the 966 is known as the' factor of evaporation. These factors are often arranged in tabular form, assuming dry steam in each case, but with temperature of feed water and steam varying over the usual range. The application of these various principles relating to boiler economy will be better understood by the solution of the follow- ing illustrative problems. In these problems for convenience con- SPECIAL TOPICS AND PROBLEMS 793 sider the pressure of the atmosphere as 15 pounds per square inch, and the absolute pressure, therefore, as 15 pounds greater than the gage pressure. (i) Temperature of feed no degrees, steam pressure 150 pounds, gage. Thermal value of the coal 14,000 thermal units per pound. Efficiency of boiler .64. Find the pounds of water evaporated into dry steam per pound of coal. Operation : From the steam tables: Heat in the water at boiling point 3384 H^t in the feed =110 — 32 = 78 Difference 260.4 Latent heat 855.1 Heat required per pound of dry steam mS-S Heat available per pound of coal = .64 X 14,000 = 8,960. Hence pounds of steam evaporated = 8960 -=- 1115.5 ^= 8.03 Ans. (2) Temperature of feed 140 degrees. Steam pressure 200 pounds, gage. Quality of steam 96 percent. Thermal value of coal 14,400 thermal units per pound. Efficiency of boiler .70. Find the pounds of water evaporated per pound of coal into steam of the given quality. Operation : Heat in the water at boiling point 36i-3 Heat in the feed — 140 — 32 108 Difference 253.3 Latent heat per pound = 838.9. ■ Take .96 of this 805.3 Heat required per pound of moist steam 1058.6 Heat available per pound of coal = .70 X 14.400 = 10,080. Hence pounds of steam evaporated = 10,080 -f- 1058.6 = 9-52- (3) Temperature of feed 100 degrees. Steam pressure 120 pounds, gage. Evaporation 8 pounds per pound coal. Assum- ing dry steam, what is the evaporation from and at 212 degrees, and what is the factor of evaporation ? Operation : /94 PRACTICAL MARINE ENGINEERING Heat in the water at boiling point 322.1 Heat in the feed = 100 — 32 = 68.0 Difference 254.1 Latent heat per pound 866.6 Heat required per pound of dry steam 1 120.7 Heat utilized per pound of coal = 8 X 1 120.7 = 8965.6. Evaporation from and at 212 degrees := 8965.7 -^ 966 = 9.28. Factor of evaporation = 1 120.7 "^ 9^6 = 1.16. Evidently also Equivalent evaporation ^ 8 X i-i6 ^ 9.28. (4) Same as in example (3) but assuming the steam of 95 percent quality, what are the results? Operation : Heat in the water at boiling point 322.1 Heat in the feed = 100 — 32 ^ 68.0 Difference 254.1 Latent heat per pound = 866.6. Take .95 of this 823.;^ Heat required per pound of moist steam 1077.4 Factor of evaporation = 1077.4 -^ 9^6 = 1.115. Equivalent evaporation = 8 X i-ii5 = 8.92. (5) Temperature of feed 160 degrees. Steam pressure 200 pounds, gage. Quality of steam 97 percent. Evaporation 8.8 pounds steam per pound coal. What is the equivalent evapora- tion from and at 212 degrees, and what is the factor of evapora- tion? Operation : Heat in the water at boiling point 361.3 Heat in the feed := 160 — 32 = 128.0 Difference 233.3 Latent heat per pound = 838.9. Take .97 of this 813.7 Heat required per pound of moist steam 1047.0 Factor of evaporation = 1047.0 -i- 966 = 1.084. Equivalent evaporation = 8.8 X 1.084 = 9-54- (6) Compare the economy in (3) and (5). Ans. in the ratio 9.28 : 9.54 or i : 1.028. (7) Which is the more economical of the following cases? (a) Coal at $4.00 per ton, 9.2 pounds of steam per pound of SPECIAL TOPICS AND PROBLEMS 795 coal; qualit}' of steam 98 percent; steam pressure 150 pounds, gage; temperature of feed, no degrees. (b) Coal at $3.20 per ton; 8.0 pounds of steam per pound of coal; quality of steam 96 percent; steam pressure 135 pounds, gage; temperature of feed 120 degrees. By the methods of the preceding examples it is found that the equivalent evaporations in the two cases are as follows : (a) : 10.46. (b) : 8.85. The cost of steam in the two cases will therefore be in the compound ratio. (See Chap. XV.) : 4.00 : 3.20. : 8.8i : 10.46. -. 4.00 X 8.85 : 10.46 X 3-20. : 1.058 : I, (a) : (b) or -^(a) : (h) Whence (a) ; (b) or case (a) is nearly 6 percent more expensive than (b). Note. — In solving the above examples the heat in the water at boiling point has been taken from the tables. Somewhat more quickly such problems may be solved by taking the heat in the water at boiling point as measured simply by the difference in temperatures, as explained in Sec. 104 [4] (i). The difference is small and is very commonly neglected. In the above examples, however, the more exact values have been preferred. The sim- pler form of solution will be illustrated by solving example (5) in thia way, and the result will serve to show the nature of the difference between the two. Thus : Temperature of steam 387.7 Temperature of feed 160 To raise one pound feed to boiling point 227.7 Latent heat for one pound =: 839.9. Take .97 of this 813.7 Heat required per pound moist steam 1041.4 Factor of evaporation = 1041.4 -=- 966 = 1.077. Equivalent evaporation = 1.078 X 8.8 = 9.49. [3] Evaporation Per Pound of Combustible In discussing further the details of steam boiler perform- ance, it is often desirable to make the necessary allowance for the ash in the coal, or for the ash and moisture, so as to obtain the evaporation per pound of actual combustible matter. To 'this end it is only necessary to divide the evaporation per pound of coal determined as above by the fraction of the coal which is 796 PRACTICAL MARINE ENGINEERING combustible, or what is the same thing, the result per pound of coal may be increased in the ratio in which the coal is greater than the combustible. The result will be the evaporation per pound of coal exclusive of ash or of ash and moisture. This result may relate, of course, either to the actual evaporation under the given conditions, or to the equivalent from and at 212 de- grees. This will be illustrated by the following examples : (8) In example (5), suppose the ash to be 12 percent, what are the actual and equivalent evaporations per pound of moist combustible ? Ans. Actual evaporation = 8.8 -^ .88 = 10 pounds. Equivalent evaporation = 9.54 -=- .88 = 10.84 pounds. (9) Under the same conditions, suppose the ash and mois- ture to be 15 percent, what are the evaporations per pound of dry combustible ? Ans. Actual evaporation = 8.8 -^ .85 = 10.35. Equivalent evaporation = 9.54 -H .85 = 11.22. Sec. 106 STEAM ENGINE ECONOMY [i] General Principles In the following discussion it will be assumed that the reader has a general knowledge of the chief properties of steam and of its relation to the heat which it contains. A discussion of the principles governing its economical use in a steam engine will now be taken up in an elementary way. At the very outset it must be clearly understood that the work of the engine is derived from the heat which the steam contains, and not from the steam in itself. The steam is simply a carrier for the heat and the operation of the engine is simply a means for transforming into useful work a fraction of the heat which comes into the engine, and then rejecting the remainder with the steam, which is its carrier. The larger the fraction of the heat which can be transformed into useful work the better the efficiency of the engine, and the constant aim is therefore to turn into useful work the largest possible fraction of the heat which enters with the steam. It may be asked, why not turn all the heat into work, and so realize a perfect efficiency? Unforunately a series of natural laws and limitations seems to prevent all hope of realizing such SPECIAL TOPICS AND PROBLEMS 797 an ideal, and actually it is necessary to be content with turning into useful work a comparatively small fraction of the total heat supplied. First and foremost among the causes of this reduction in efficiency is a principle or law sometimes known as the second law of thermodynamics. This law fixes a limit on the fraction of heat which can be transformed into useful work, such limit de- pending on the extreme temperatures between which the sub- stance is worked ih the engine. Thus if t^ is the temperature of the steam at admission and tz that at exhaust, so that t^ and ^2 are the two temperatures between which the steam is worked, and (?i — ^2) is the range, then the law asserts that no engine, no matter how perfect, can transform into useful work a fraction of the entering heat greater than (^^ — fj) -^ (^1 + 461)- A? another way of stating this relation, the temperature may be supposed to be measured from a point 461, or more accurately 460.7 degrees, below the ordinary zero of the F. scale. This is called the absolute zero, and temperature measured from this zero is called absolute temperature. The difference of the tem- peratures would be the same no matter whether measured from the ordinary or absolute zero. The numerator of the above frac- tion is therefore the difference or range of temperature, while the denominator is the absolute temperature of the entepng steam. The fraction of heat converted into useful work can therefore never exceed the temperature range divided by the absolute tem- perature of the entering steam. Thus to illustrate, suppose that t^ ^ 370 and ^2 = 140- Then the fraction becomes (370 — 140) -^ (370 + 461) or 230 -=- 831 = .277 or slightly over one-quarter. These figures represent the limits for steam of about 160 pounds gage pressure, and it therefore appears that for engines operating between these limits this law steps in, and at one stroke reduces the ideal efficiency from one to about one-quar- ter ; or in other words it is necessary, due to the operation of this law, to throw away about three-quarters of the total heat, and at the very best with the most ideally perfect engine only trans- form into useful work the remaining one-quarter. Such, then, is the very best that could be done by a so-called ideal engine. The working substance in the simplest form of such an engine must be carried through a series of changes or operations, four in number, and specified as follows : (i) The first operation must consist of an expansion at con- 798 PRACTICAL MARINE ENGINEERING stant temperature, and all heat received from the source of sup- ply must be received during this operation. (2) The second operation must consist of an expansion with decrease of temperature during which, however, no heat as such is allowed to either enter or leave the substance. (3) The third operation must consist of a compression during which the temperature remains constant and all heat re- moved from the body must be removed during this operation. (4) The fourth operation must consist of a compression with increase of temperature, during which, however, no heat as such is allowed to either enter or leave the substance, and at the end of which the substance must find itself in the same condition as at the beginning of number ( i ) . Work is done by the substance during operations (i) and (2) and work must be done on the substance during (3) and (4). The difference between the work done by and on the substance will be the net work obtained from the heat in the substance, and the ratio of this to the total heat supplied during number ( i ) or the efficiency of the engine will be exactly measured by the difference between the temperatures of operations (i) and (3) divided by the larger increased by 461 ; or in symbols : tl — <2 Efficiency ^ tl + 461 This is then the cycle and the efficiency of an ideal engine in the simplest form. There may be certain related variations in the operations (2) and (4) making a more complicated cycle, but with the same efficiency. This ideal marks, then, "the highest possible limit of efficiency for any and all engines working be- tween the given temperature limits fj and fj- In the table are shown the values of this limiting efficiency for engines with gage pressure as indicated, all condensing and supposed to have a back pressure of 2.8 pounds absolute, or a lower temperature, t^, of 140 degrees. An examination of this table shows that with the ideal con-.-, ditions which correspond to the operation of this engine, the fraction of heat utilized with modern boiler pressures would range from 25 to 30 percent. These conditions, however, are far from those which actually exist in practice. Every one of the conditions specified above is violated in greater or less degree, and the result is that with the operation of the engine SPECIAL TOPICS AND PROBLEMS 799 under the best conditons obtainable in actual practice, the frac- tion realized will be only some 60 to 80 percent of the figures for the ideal case as given in the table below. These figures, 60 to 80 percent in the best practice, really measure the efficiency of the engine so far as the engineer is responsible. That is, nothing which he can do will serve to avoid the loss which re- duces the hmiting efficiency down to that for the ideal engine as given in the table above. His efforts are therefore limited to approaching as nearly as possible to the conditions of the ideal engine, and the figures 60 to 80 percent measure the de- gree of approach which modern engineering practice has ma'de Table Gage Pressure Limiting at Engine Efficiency 100 248 no 253 120 .259 130 264 140 269 ISO 273 i6o 278 170 281 180 285 190 289 200 292 210 29s 220 299 230 301 240 304 250 307 to this ideal. Thus, for illustration, if the ideal engine could transform 25 percent of the heat into useful work, a good actual engine working between the same temperature limits will be able to transform from 15 to 20 percent, and similarly for other con- ditions. To put the matter a little differently, any and all engines fail to transform into work all of the heat supplied to them. In the ideal engine as specified above, the part not transformed but rejected as heat is the least possible for all engines working be- tween the same limits of temperature t^ and t^. In any actual engine the amount not transformed into work but rejected as heat is greater than in the ideal case. Such additional amounts of heat rejected and not transformed into work are called wastes or losses. That is, all differences between the performances of 8oo PRACTICAL MARINE ENGINEERING the ideal and actual engines are considered to be due to these so- called zvastes or losses. These various wastes may be classified as follows : (a) Radiation and Conduction Waste. This consists of heat which is radiated away from the hot surfaces of the cylinder, or conducted away through the columns and bed plate. The heat thus escaping avoids transformation into work and is therefore counted as a heat waste, or as an ex- pense from which no corresponding return is received. (b) Initicl Condensation. At the instant the steam valve opens, the steam rushes into the cylinder to find itself in contact with surfaces which have but recently been exposed to the influence of the condenser or ex- ternal air. They are, therefore, at a temperature much lower than the steam, and in consequence a part of the heat is absorbed and a corresponding part of the steam is condensed. The heat thus absorbed by the surfaces of the cylinder and piston will be given up later during the exhaust period of the revolution, and thus communicated to the condenser. It thus appears that a thin skin of metal on the inside of the cylinder and on the faces of the cylinder head and piston may be considered in a sense as a place of hiding into which a portion of the heat slips on the entrance of the steam, and from which it escapes to the con- denser or air without having taken part in the cycle of the en- gine, and hence without having contributed its part to the useful work done. The heat so escaping appears thus as an expense, but without any corresponding return in work, and therefore con- stitutes a heat waste. (c) Irregularities of the Cycle. There have been specified above the four fundamental opera- tions of the ideal engine cycle in its simplest form. In the actual engine none of these is realized, and the variations are all such as to count against the efficiency. The details of these points will not be considered here, and the broad statement must suffice that with but few exceptions, the variations from the routine specified above for the ideal engine will count against the efficiency and occasion a heat waste greater or smaller as the circumstances may determine. The Improvement of the Steam Engine.- — From the preceding section it follows that there are two fundamental methods open SPECIAL TOPICS AND PROBLEMS 801 for the improvement of the steam engine from the standpoint of economy. (i) An increase in the temperature range and thus an in- crease in the ideal or limiting efficiency. (2) The saving of some of the various wastes as noted above. The first raises the ideal efficiency and hence with a given proportion of wastes will raise the actual efficiency as well. The second raises the actual efficiency by carrying it a little nearer to the ideal. The temperature range may be increased in two ways, — the initial temperature can be raised, and the final temperature can be lowered. The continually advancing pressures in modern practice means a constant rise in the upper temperature, a constant in- crease in the ideal efficiency, and with the same proportion of losses, a corresponding rise in the actual efficiency. This is then the real significance of high pressures in modern practice so far as they are related to the question of economy. Again by decreasing the back pressure from say 18 pounds for a non-condensing engine to say 3 pounds for a condensing engine, and to less than i pound for a turbine, a very considerable decrease in the final temperature is obtained, a corresponding in- crease in the temperature range, and a resultant increase in actual efficiency. This is likewise the real significance of the in- fluence of the condenser on the economy of the engine. In general, then, the proportion of heat wastes being the same, the economy will be better as the initial pressure is higher, and the back pressure is low^er; or in general, as the range of pressure and temperature worked through is the greater. Turn next to the problem of reducing the wastes of the actual engine, as specified under the three heads above. The waste due to radiation and conduction cannot be wholly avoided, but the former, which is by far the larger of the two, may be much reduced by suitable lagging or non-conducting covering. With such provision the loss under this head is usually very small compared with the other losses mentioned. The waste due to the so-called initial condensation is one which may be reduced, but not wholly avoided. Before dis- cussing the means suitable to this end some further explanation of the nature of the loss will be required. 8o2 PRACTICAL MARINE ENGINEERING As already pointed out, the action of the metal walls in pro- dticing this loss depends on their capacity when at a lower tem- perature, for absorbing heat from the steam (as during admis- sion) and for giving it up when at a higher temperature (as dur- ing exhaust). The action depends, then, on the range of tem- perature between admission and exhaust, and on the particular readiness with which the walls absorb and reject heat according as they are cooler or hotter than their surroundings. There are therefore two distinct features to be considered — the range of temperature, and the readiness with which the iron absorbs and rejects heat under the conditions mentioned. Now it is found that if the expansion through the entire temperature range is split up into a series of steps, each carried out in a cyhnder by itself, the loss under consideration is less than if the entire expansion should take place in one cylinder. Carrying out this principle, there results, of cqurse, the multiple expansion engine with its total range of operation divided among several cylinders in series. This, then, is the real significance of the multiple expansion (compound, triple, quadruple, etc.) engine, so far as its relation to economy is concerned — the splitting of the total expansion or of the total temperature range into a series of steps is found to reduce considerably one of the wastes, and so raise the actual efficiency of the engine. Next turning to the other controlling feature of this loss, — ' the readiness of absorption and emission — it seems to be the case that once the internal surfaces become wetted or covered with a film of moisture, the absorption and emission of heat into and from the metal proceed with much greater readiness than when they are dry. In other words, the passage of heat between metal with a moistened surface and moist steam is much more rapid than between the same metal with a dry surface and dry or superheated steam. In the ordinary steam engine there exists, therefore, an action of the walls due to the range of temperature employed, and to the natural capacity of cast iron or steel to absorb and emit heat from and to the steam. This is further greatly augmented by the presence of a more or less complete film or layer of water over the surface, which arises from the condensation of the first entering saturated steam. SPECIAL TOPICS AND PROBLEMS 803 The use of superheaters, reheaters and jackets is found in a general way to decrease the readiness with which heat ex- changes occur between the metal and the steam, and thus to decrease the amount of waste due to their actions. Thus in an engine using moderately superheated steam there should exist the same general tendencies as noted above for the operation with saturated steam, but less augmented because of the smaller amount of moisture formed. In an engine using steam super- heated to such an extent as to remain above the point of satura- tion during its entire passage through the cylinders, no moisture is formed and the action of the surfaces is limited to that which can take place between their dry surfaces and the dry super- heated steam. The office of superheating is then simply to re- duce the readiness with which the exchange of the heat between the metal surfaces and the steam is effected. The results show that in such case the reduction is real and productive of a con- siderable increase in economy. Regarding the use of reheaters it seems likely that their beneficial action will be well marked in proportion as they are able to superheat the steam passing through them, and thus act as a superheater in stages, each for the cylinder next beyond. The beneficial results gained by the use of steam jackets are in large measure due to action of the same character. The jacket containing steam at a temperature higher than that in the cylinder transfers heat into the inner surface of the cylinder walls and thus tends to keep it dry and to reduce the amount of heat exchange, and hence the corresponding waste. The steam jacket acts also to some extent to modify the character of the cycle as noted below, but most of its useful action- may probably be put down to the hindering of heat exchanges between the walls and the steam in the cylinder. It must not be forgotten, however, that whatever gain is thus effected within the cylinder is obtained at the expense of the heat drawn from the jacket, and the whole operation is there- fore an attempt to reduce one loss by introducing another. If the latter is less than the saving in the cylinder, the net result will be a gain equal to their difference. If the latter is the greater of the two, the net result will be a loss, and if they are equal the net result will be no change in the economy of the engine. These re- lations account for the varying experience with jackets, but it 8o4 PRACTICAL MARINE ENGINEERING now seems well assured that when properly fitted and operated, the result will show a gain of from 5 to 10 percent over similar conditions unjacketed. The last principal division of the wastes of the actual steam engine are now arrived at, — those due to irregularities in the cycle, or in other words to variations from the routine of opera- tions which would give the efficiency of the ideal engine as dis- cussed above. In this respect but little can be done to improve matters. The use of jackets and reheaters may possibly affect the routine in such a way as to bring it somewhat closer to the ideal conditions, but this is by no means certain, and the benefit due to these appliances comes mostly from the decrease in cylin- der condensation as explained above. There are methods, however, of modifying the cycle of the engine by the use of a series feed water heater, in such way as to bring it somewhat nearer to the ideal cycle. Such a feed heater for a quadruple expansion engine may consist of say three chambers or heaters through which the feed passes in series. In the first it is heated by steam drawn from the low pressure re- ceiver. It then passes on to the second chamber, where it is heated by steam drawn from the second intermediate pressure receiver, and then goes on to the third chamber, where it meets with steam drawn from the first intermediate pressure receiver. As the feed water thus becomes hotter and hotter it meets with steam of higher and higher temperature drawn from the suc- cessive higher receivers in the engine, and it is-thus brought nearly to the temperature of the water in the boiler. The ex- haust from pumps may also be turned into the first chamber, thus making it a means of taking heat from their exhaust and of re- turning it with the feed to the boiler. In some cases also live steam of full boiler pressure has been used in a last chamber to still further raise the temperature of the feed. Various modifi- cations may be worked out in the details of the operation of such feed heaters, but in all cases their significance lies in the fact that the cycle of operations as a whole may in this way be brought a step nearer to the ideal cycle than would otherwise be the case. All such changes, if made in accordance with the proper princi- ples, may therefore result in a saying of heat and in a gain in the economy of the engine, and in this fact lies the chief signifi- cance of the feed water heater as a feature of modern engineer- ing practice. SPECIAL TOPICS AND PROBLEMS 80s [2] Relation of Expansion to Economy The question of the expansion of steam and its influence on engine economy has long held an important place as perhaps the chief factor in engine economy, and it may therefore he well to refer to this feature in somewhat further detail. From the stand- point of the preceding discussion of the question it should be said that the expansion of steam is favorable to economy because it brings the cycle of operations nearer to that for the ideal engine. These points may, however, be treated differently and in a more elementary manner, and the question may be discussed by the actual comparison of the two indicator diagrams given by an engine working with and without expansion. Consider the two cards C D I H and C D E F H oi Fig. 459. The first is the card that would be given by using the steam in an engine with stroke C D following to the extreme end, and then exhausting along D I H. The second card is such as would G Fig. 459. The Expansion of Steam be given by the same steam used expansively, cut-oflf taking place at D and the stroke continuing expansively to E. The back pressure in each case is represented by the line H F. The area C D I H represents the work in one case and the area C D E F H in the other, so that the difference ovD E F I represents the gain by expansive working. In other words, if the steam full pressure is used up to D and then exhausted, an amount of work measured hy D E F I which might be saved by expansive working is thrown away. It is likewise true that the exhaust opening at E causes a loss of work E J F which might be saved by continuing the expansion down until the forward pressure falls to the back pressure as at /. It is rare, however, that it is possible to afford cylinders of sufficient size to carry the expan- sion to such a point, and, as may be seen, the amount thus lost 8o6 PRACTICAL MARINE ENGINEERING is smaller and smaller as the final pressure £ G is nearer the back pressure F G. To illustrate the gain by expansive working, suppose the initial pressure Z, C = loo pounds, the back pressure L H = t, pounds, and that the cut-off is at a series of points .1 .2 .3, etc. Then neglecting the effect due to clearance, the number of ex- pansions will be as 10, 5, 3.3, etc., and the ratio of saving will be as given in the following table. The numbers in the column headed e give values of the ratio D E F I ^ C D I H, or the ratio of the amount saved by expansion to the amount done before expansion begins. Point of Cut-off Expansion Ratio e ,1 10. 2.11 .2 5- i-SS .3 330 1.18 .4 2.50 .91 .5 2.00 .69 .6 1.66 .51 .7 1-43 -36 .8 I.2S .23 .9 I. II .11 .10 1. 00 .00 It will be understood that the figures of the above table refer to indicator cards such as those of the diagram in which there is no allowance for clearance, compression, rounding off of cor- ners, etc. These conditions are of course taken in order to simplify the necessary computations. The nature of the results would, however,, be the same in the actual case, and these figures may therefore be taken as a sufficiently close indication for illus- trative purposes. It thus appears that the gain is proportionately greater the larger the number of expansions, and for the highest efficiency the expansion should be carried to the highest limit. Practically there are two considerations which fix an early limit to this extension of the expansion range. The first is the limit of size. The greater the number of expansions the larger the engine and hence, especially for marine engines, it is seldom possible to afford weight enough to give the number of expansions which other considerations might warrant. The second limitation comes from the increase of internal or cylinder condensation which increases with the number of expansions until finally the resulting waste would off-set the gain due to the increase in ideal efficiency. SPECIAL TOPICS AND PROBLEMS 807 This loss is decreased by the compounding of engines, so called, or by the splitting up of the total expansion into a series of steps in separate cylinders. Hence with multiple expansion engines it is possible to employ higher rates of expansion with- out corresponding losses from cylinder condensation than with a single cylinder; and this, as has been seen in [i], is the real sig- nificance of the use of multiple expansion rather than simple engines. [3] Economy of the Actual Engine It has already been shown that the highest possible efficiency of. an ideal engine under usual conditions will be found between 25 and 30 percent, while the actual engine at the best will realize only some 60 or 70 percent of these figures, or an efficiency of say 15 to 20 percent in good practice. Now one horsepower is 33,000 foot pounds of work per minute, and from the value of the work equivalent of heat this is equal to 33,000 -^ 778 = 42.42 heat units per minute. Hence one horsepower means the transformation of 42.42 heat units per minute into mechanical work. It follows that the heat which must be supplied to the engine in order to provide for one horsepower will be given by dividing the number 42.42 by the efficiency at which the trans- formation is effected. But 42.42 -^ 15 ^ 283. + and 42.42 -^ 20 = 212. -\-. Hence, placing the limits a little more broadly, it appears that in good practice there will be required from say 200 to 300 heat units per minute for each horsepower developed in the engine. This corresponds to a range of 12,000 to 18,000 heat units per hour. Now remembering that each pound of steam brings to the engine roughly 1,000 heat units, it is clear that this will correspond to a range of steam consumption of say 12 to 18 pounds per indicated horsepower per hour. These figures may be taken as covering the range of good practice from about the best at present attainable to a value only mod- erately fair for modern triple expansion engines, or good for the usual type of compounds. Again each pound of coal burned may be expected to fur- nish under good conditions some 9,000 or 10,000 heat units to the water in the boiler, or to transform some 9 or 10 pounds of water info steam. Hence the coal required per indicated horse- power per hour will be given by dividing the heat units or the pounds of steam required by the amount of either which may be 8o8 PRACTICAL MARINE ENGINEERING expected from one pound of coal. This will give a coal con- sumption of from about 1.2 to 1.8 pounds per indicated horse- power per hour, which may also be considered as representing the upper part of the range of good practice for triple and quadruple expansion engines under from moderately good to the best conditions at present attainable. In a few exceptional cases by the use of feed heaters, superheated steam and all means favorable to economy the consumption has been reduced to i.o pound coal per indicated horsepower per hour. For compound and simple condensing engines under good to moderate conditions the steam consumption will rise to from 20 to 30 pounds of steam, corresponding roughly to from 2 to 3 pounds of coal with good boiler economy, and to perhaps 2.5 to 3.5 pounds with poor boiler economy. Farther along the line will come engines perhaps non-con- densing, and of still lower efficiency, such for example as electric light, centrifugal pump, blower, winch, and steering engines, the steam required for them may rise to from 40 to 60 pounds or more per indicated horsepower per hour, corresponding to a coal consumption of from perhaps 4 to 8 pounds, according to the boiler efficiency. Still lower in the scale of economy we find the ordinary direct acting pump. Such pumps operate in the steam cylinder with almost no steam expansion, and the piston speed is very low, thus giving full time for the transfers of heat which cause cylinder condensation. Due to these and other less important causes the steam consumption may rise to 200 pounds and more per indicated horsepower per hour, while rarely can it be brought as low as 100 pounds. This corresponds to a coal consumption from say 10 to 25 pounds, depending somewhat on the efficiency of the boiler. In terms of absolute efficiency these figures cor- respond to from about i to 3 percent, the values thus ranging downward from the 15 to 20 percent given above as the highest values at present attainable. Sec. 107. COAL CONSUMPTION AND RELATED PROBLEMS As has already been seen in Sec. 106, the coal required per indicated horsepower per hour in good practice is usually found between say 1.5 and 2.0 pounds. Where especial attention is given to economy the figure may be reduced below the lower SPECIAL TOPICS AND PROBLEMS 809 value down even to i pound per indicated horsepower per hour, while by the neglect of due attention, or in cases where the con- ditions are such that economy must be sacrificed, the value may rise above the higher limit. Let : c denote the pounds of coal per indicated horsepower per hour. H denote the indicated horsepower. Then cH = pounds of coal per hour, cH -=- 2,240 = tons of coal per hour, and 24 cH 3 cH cH , or , or = tons of coal per day. 2240 280 93.3 As a thumb rule for a quick estimate, remember that at a coal consumption of 1.86 pounds per indicated horsepower per hour (a figure only moderately good), the coal required per day will be 20 tons per i,cxdo indicated horsepower. The use of the above formulas may be illustrated by the following examples : (i) With a coal consumption of 1.78, how much coal will be required in the bunkers of a ship making a seven-day trip, the indicated horsepower being 2,400 and a margin of 10 percent being allowed for emergencies? 3 X 1.78 X 2400 Coal per day = = 45-75 tons. 280 Tons Coal for 7 days = 7 X 45-75 = 320.25, say 320 Margin 32 Coal in bunkers = 352 (2) Which will require the more coal per day, a ship with 9,800 indicated horsepower at 1.82 pounds per indicated horse- power per hour, or two ships each of 4,000 indicated horsepower at 2.20 pounds per indicated horsepower per hour? For the first: 3 X 1.82 X 9800 =: 191 tons per day. 280 For the second: 3 X 2.20 X 8coo = 188.S tons per day. 280 Difference, 2.5 tons. (3) How long time can a vessel steam on 213 tons of coal 8io PRACTICAL MARINE ENGINEERING and how far on a speed of 12 knots, the indicated liorsepower being 3,600 and the coal consumption being 1.68? 1.68 X 3600 Coal per hour = = 2.7 tons. 2240 Time 213 -;- 2.7 = 78.9 hours. Distance = 78.9 X 12 = 947 miles. (4) A vessel's log shows 420 tons of coal used in a period of 9 days, 16 hours. The average indicated horsepower was 2,120. What was the coal consumption per indicated horse- power per hour? Kumber of hours = 9 X 24 + 16 = 232. 420 X 2240 Amount used per hour = 4055 pounds. 232 4055 Coal consumption ;= = 1.91 pounds. 2120 As a further development of the same problem it may be desired to find the coal burned per mile, or per ton mile of displacement, or per ton mile of cargo. These may be illus- trated by the following examples : (5) Given: Displacement = 9,486 tons. Indicated horsepower =^ 12,000. Speed := 18 knots. Coal consumption =1.8 pounds per indicated horse- power per hour. Cargo := 2,ODO tons. Then: Coal per hour := 1.8 X 12,000 = 21,600 pounds. Coal per mile = 21,600 -^ 18 ^ 1,200 pounds. Coal per ton mile of displacement = 1,200 -=- 9,486 = .127 pound. Coal per ton mile of cargo = 1,200 -^ 2,000 = .6 pound. (6) If the same ship were to be driven at but half the speed, only about one-eighth the indicated horsepower would be re- quired, or say 1,500 indicated horsepower, while the cargo might be increased to say 5, 000 tons. With the same engine economy there would then be re- quired : Coal per hour 1.8 X 1,500 = 2,700 pounds. Coal per mile = 2,700 -f- 9 = 300 pounds. SPECIAL TOPICS AND PROBLEMS 8ri Coal per ton mile of displacement = 300 ^ 9,486 = .316 pouncj. Coal per ton mile of cargo = 300 -^ 5,000 = .06 pound. (7) Again a case similar to one of the large modern ocean freighters : Displacement = 27,000 tons. Speed =13 knots. Indicated horsepower = 6,600. Cargo =r 15,000 tons. Coal consumption = 1.3 pound per indicated horsepower per hour. Then: Coal per hour = i .3 X 6,600 = 8,580 pounds. Coal per mile = 8,580 ^ 13 ^ 660 pounds. Coal per ton mile of displacement := 660 -^ 27,000 = .0244 pound. Coal .per ton mile of cargo = 660 -^ 15,000 = .044 pound. At the other extreme take a torpedo boat of the destroyer type as follows : Displacement ^ 310 tons. Indicated horsepower = 6,200. Speed ^31 knots. Coal consumption -^= 2.2 pounds per indicated horsepower per hour. Then: Coal per hour = 2.2 X 6,200 = 13,640 pounds. Coal per hour = 13,640 -^ 31 = 440 pounds. Coal per ton mile of displacement = 440 ~ 310 = 1.42 pounds. These examples illustrate the principle that per ton mile, less coal is burned as the ship is larger and goes slower, while more is burned as she is smaller and goes faster. This is the result of the two facts. (i) As the ship increases in size the power required per ton of displacement for a given speed decreases, and accordingly the larger the ship the less the coal required per ton at a given speed. (2) For a given ship, as the speed increases, the power and hence the coal required increase nearly as the cube of the speed ratio, while the time for a mile or for a given voyage is reduced 8i2 PRACTICAL MARINE ENGINEERING only in the simple ratio o'i the speeds. Thus to illustrate: If the speed is increased lo percent, or say from lO knots to li knots, then the power will be increased nearly in the ratio 11^ -H -lo^ = (i-i)^ = I-33I. while the time on the mile or on a a given voyage will be decreased in the ratio lo -=- ii. Hence the I. 331 10 coal will be changed in the compound ratio X — or 1.21 I II to I. Hence it appears that in such case the increase of speed in the ratio I.I to i will increase the coal per mile or per voyage in the ratio of 1.21 to i. Or briefly an increase of 10 percent in the speed will mean an increase of about 20 per cent in the total coal required. Similarly, of coiirse, a decrease of 10 percent in the speed would mean a decrease of about 20 percent in the total coal required. If there were no other principle involved, it would follow that the slower a given vessel goes the more cheaply could she make a given voyage. This would be true if only the power in the main engine were considered, and assume for it a constant coal economy. This cannot be done, however, in the case of a single ship going at different speeds, because as the power in the main engines is decreased below its normal amount the coal re- quired per indicated horsepower increases continuously. Further- more, the power required for the various auxiliaries never decreases in the same ratio as the power of the main engines, and for certain auxiliaries the power is hardly affected by the change in the main engine. The coal required for the auxiliaries becomes therefore greater and greater relative to that required for the main engine. Due to these facts it follows that as the speed is decreased a point will be reached below which the saving in the total coal required per hour will be more than offset by the in- crease in the time required, so that for a given voyage the total coal expense will begin to increase rather than decrease. This point is known as the "most economical speed" and is the speed at which a given voyage can be made with the least expenditure of coal. Its value will depend largely on the amount and char- acter of the auxiliary machinery in operation, but is often found at a speed somewhat above half the full power speed. In the mercantile marine it is rare that ships are operated at speeds other than those corresponding to normal full power conditions. SPECIAL TOPICS AND PROBLEMS 813 so that the determination of a most economical speed is not of great importance in such cases. In the naval service, however, where economy may be of more importance than the reduction of time required for a voyage, ships are often operated at or about the most economical speed, and its determination and the principles fixing its location are of importance in such cases. Sec. 108. DEVELOPMENT OF THE STEAM TURBINE The steam turbine, in contradistinction to the water turbine, in which is transformed the potential energy possessed by water, transforms the heat energy possessed by steam into kinetic energy and motion. A species of reaction steam turbine was known as early as 120 B. C, or 1900 years earlier than the reciprocating engine invented by James Watt. This turbine, which was invented by Hero, and is described in his celebrated work, "Spiritalia Seu Pneumatica," consisted of a boiler, above which was mounted a sphere on two trunnions connected through the pedestals to the boiler. The sphere had two diametrically placed pipes in form of slightly bent nozzles, through which the steam raised in the boiler issued under pressure, and, by its reaction on the atmosphere, caused the ball to revolve. Another steam turbine of the impulse type, invented by Branca in the sixteenth century, consisted of a paddle wheel, which was made to rotate by the impact of a jet of steam from a nozzle connected to a boiler in which steam was generated. Doubtful though it be that these turbines were of practical value as prime movers, in them must be recognized the embryo idea from which has been developed the turbine of to-day. Among present-day turbines especially noted for successful and practical application are found the following well-known names: De Laval, Parsons, Curtis, Rateau, Zoelly, Melms- Pfenninger, Schulz, Westinghouse, Stump f-Riedler, A. E. G. turbine, Brown-Bovery, Lindmark, Elertra, Terry, Kerr, Bliss, Ljungstrom, etc. The two first-named turbines were invented in 1884. The subsequent development of the steam turbine has grown into such vast capacities of power, and its application has become so gen- erally favored both for stationary and marine purposes, that the 8i4 PRACTICAL MARINE ENGINEERING fundamental principles of its operation should be known generall}- at least to engineers. All of the foregoing turbines are well adapted to work in sta- tionary practice, and the Parsons and Curtis are now being used extensively for propelling ships. Other makes, like the Rateau, Zoelly, Melms-Pfenninger, Westinghouse, the A. E. G. turbine, the Ljungstrom and a modified De Laval, are, also being used in some notable marine installations. It should be borne in mind that a steam turbine is primarily a motor which must be run at high rotative speeds to render good efficiency, and that the propeller speed must not exceed speeds defined by limiting conditions to return also a reasonable efficiency. The turbine must, therefore, be of such construction that its speed becomes suitable for the propeller, thereby returning a good com- bined propulsive efficiency. In order to understand fully all of the underlying principles, therefore, a great deal of the theory of both the turbine and the propeller should be written; but, owing to the limited space allotted to this subject, only the most fundamental data, or features of greatest importance, can here be incorporated. [i] Principles of Action The principal difference in the action of the steam in the reciprocating engine and the steam turbine exists in the utiliza- tion of the heat energy possessed by the steam. In the former, this energy is converted into force by expanding back of a piston, while in the latter it is converted into kinetic energy by the velocity developed in the steam during expansion from a higher to a lower pressure. The expansion of the steam in the turbine takes place either in nozzles or in suitably arranged vanes, and the different arrangements and means by which the expansion is accomplished and the manner in which the energy is absorbed have given rise to a number of different designs of steam turbines, which may be classified under the following heads : 1. Single Stage Impulse Turbines. 2. Multiple Stage Impulse Turbines. 3. Compound Impulse Reaction Turbines. SPECIAL TOPICS AND PROBLEMS 815 By the foregoing division it is to be inferred that steam tur- bines depend for their action upon impulse alone or impulse and reaction together. Impulse is imparted to the vanes when jets of steam flow, under a uniform pressure, tangentially through the vanes, exerting a dynamic pressure on these vanes during passage through them. Impulse and reaction occur when a similar jet of steam enters a vane at a certain pressure and leaves it at a lesser pressure. This is caused by expansion of the steam be- tween the entrance and exit points of the vanes. In the first class, to which belong turbines of the De Laval type, the expansion of the steam takes place entirely within noz- zles. After having expanded, the steam issues, in form of well- defined streams or jets at a very high velocity, ranging between 2,500 and 4,000 feet per second, upon vanes placed securely on a revolving disk. This disk absorbs the greater part of the jet energy, and, for maximum efficiency, the peripheral disk speed should be about one-half of the steam speed. It may be mentioned that this is never carried out in practice, owing to the very exces- sive speed of rotation it would require. Even with the lesser speed of rotation it is necessary to use gearing to obtain a prac- ticable transmission ratio. In the second class the expansion of the steam takes place, as in the De Laval turbine, in nozzles — but the velocity, and there- fore, the energy, of \\-ie jet is absorbed in steps by several disks, whereby it is possible to use a much lower peripheral disk speed and still obtain good efficiency. To this class belong the Curtis, Zoelly and Rateau turbines, all of which are successfully used for marine purposes. In the third class, in which is noted especially the Parsons turbine, the principal expansion of the steam occurs in the vanes. The steam velocity is quite moderate in this class of turbine, but, in order to secure maximum efficiency, the peripheral speed of the revolving drum should be between .7 to .8 of the steam speed. Steam speeds in a Parsons turbine range from 175 feet per second in the high pressure end to 700 or 800 feet per second in the low pressure end. This type of turbine, owing to its low steam speeds, and, therefore, low rotor speeds, lends itself particularly well for marine propulsion. 8i6 PRACTICAL MARINE ENGINEERING [2] Superheat The usual gains arising from using superheated steam aig: first, decreased condensation; second, diminished loss as aflfected by leakage in clearance spaces; third, increased steam volume at equal pressures with saturated steam. All taken together, in- creased steam economy should be the result of the use of super- heated steam. In Parsons turbines superheated steam is not used in marine installations. This is principally because of constructional fea- tures, such as the steam being in direct contact with the vanes and their attachments to cylinder and rotor. High pressure super- heated steam of high temperature expands the materials to a con- siderable amount, and, owing to the fact that the tip clearance of the vanes is made as small as practicable, and the fact that vanes, rotors and cylinders are made of different materials with different coefficients of expansion, the clearance spaces become danger- ously reduced, and the strains caused by the expansion of the calking pieces bring strains on rotor and cylinder beyond the elastic limit of the metal of which they are made. In the Curtis turbine, or turbines of that type, the correspond- ing parts are not affected nearly in the same degree. This will be understood by the fact that the high temperature steam enters the nozzles first, where it is expanded, and its temperature, inci- dent upon the fall in pressure, is accordingly greatly reduced. The gain from using superheated steam amounts approxi- mately to I percent in steam economy for each 10 degrees F. of superheat applied to the turbine. [3] Vacuum The thermodynamic gain from high vacua is due to the com- paratively greater amount of heat contained in steam for each de- gree of low pressure over that at the higher pressures. Thus, for adiabatic expansion the available energy in thermal units per pound of steam when expanding from 200 pounds absolute to 138 pounds absolute, or for a temperature range of 30 degrees F., is 30.6 B. T. U., while for similar expansion from 2.87 pounds absolute to 1.23 pounds absolute, which is also equivalent to a tem- perature range of 30 degrees F., the available energy is equivalent td 41.2 B. T. U. SPECIAL TOPICS AND PROBLEMS 817 Expansion down to 27^ or 28 inches of vacuum is readily accomplished in the turbine, and is maintained with less than a difference of i inch in the condenser, while operating in conjunc- tion with a reciprocating engine the actual pressure at the comple- tion of expansion in the engine would be not less than 10 pounds absolute, with an actual back pressure of from 2 to 4 pounds absolute in the condenser. The reasons are to be found in the practical impossibility of providing great enough expansion ratios between the low and high pressure cylinders for the reciprocat- ing engine. High vacua in steam turbines give, besides the thermodynamic advantages shown previously, mechanical advantages in lessened friction on drums or disks when rotating in a steam fluid of small density. In the reciprocating engine, on the other hand, there is only a slight gain thermodynamically in the use of vacua above 26 inches; owing to the increased cylinder condensation, caused partially by the great difference in inlet and outlet temperatures of the steam, and also by the fact that due to the restricted port areas for the exhaust to the condenser, the back pressure in the low pressure cylinder can very seldom be brought much below 4 pounds absolute with the engine developing its designed full power. The effect of temperature variation is also greatly aug- mented by the fact that each end of the cylinder is alternately an inlet and an outlet end. A gain of approximately 4 percent in steam economy is ob- tained for increases in the vacuum from 26 to 27 inches, 5 percent from 27 to 28 inches and from 6 to 7 percent from 28 to 29 inches. Sec. 109. DEFINITIONS Steam Jet is a defined stream of steam, issuing from a noz- zle or vanes, moving at a certain velocity under a given pressure. Steam Turbine. — A steam turbine is a prime mover, com- posed of stationary and mobile parts, which converts the heat energy possessed by steam into kinetic energy. The mass of the steam, by its velocity, impinges, in form of jets, upon the moving vanes, and causes them to revolve. Energy. — The capacity for performing work is called energy. It exists both as potential — as, for instance, the heat in steam and the pressure exerted by water when under a certain head — and kinetic, as, for instance, the force of a moving body. 8i8 PRACTICAL MARINE ENGINEERING Mass. — The mass of a body is equal to its weight divided by g, the acceleration due to the force of gravitation. The mean value of g = 32.16 feet per second. If the weight of a body = W pounds and M = its mass, then W M = and W = Mg. g Moreover, if a stream (jet) of water, gas or steam moves with a velocity V in a certain direction, the force which it exerts is equal to W F — MV = V. 9 li W = the weight of a substance — for instance, steam passing an orifice of a given cross sectional area at a velocity V feet per second — the work which this steam weight is capable of perform- ing by virtue of its velocity and mass is 1 WV K = — MV = , 2 2g which is the measure of the actual or kinetic energy of the sub- stance. Per unit weight, or when W ^ 1, this becomes = . 29 The energy of a steam jet of constant cross section is, there- fore, proportional to the square of its velocity. Expressions of Equivalents. — The measure of kinetic energy is foot-pounds and of heat the British Thermal Unit (B. T. U.). One B. T. U. is that quantity of heat which is required to raise the temperature of one pound of water one degree Fahrenheit when the water is at its greatest density (39.1 degrees F.). The mechanical equivalent of i B. T. U. is 778 foot pounds, which means that i B. T. U. and 778 foot pounds of mechanical energy are mutually convertible. I I foot pound = B. T. U. 778 I horsepower = 1,980,000 foot pounds per hour. I horsepower := 33,000 foot pounds per minute. I horsepower = 550 foot pounds per second. I horsepower ^= 2,545 B. T. U. per hour. I horsepower = 42.42 B. T. U. per minute. I horsepower =; 0.707 B. T. U. per second. SPECIAL TOPICS AND PROBLEMS 819 Heat. — The measure of heat in the United States of Ameri- ca and in Great Britain is the British thermal unit. Specific heat of steam, or the coefficient for its thermal capacity, is the ratio of the heat required to raise its temperature one degree and that required to raise the temperature of water one degree from the temperature of greatest density 39.1 degrees Fahrenheit. Specific heat of saturated steam = .48 Specific heat of superheated steam = .yy Total Heat of Steam (H) is that quantity of heat which is required to generate one pound of steam from water at a tem- perature of ,32 degrees F. to any given temperature and pressure. It is made up of the latent heat of evaporation and the sensible heat, indicated by the thermometer. H = 1,082 + .305 t, where t = temperature of the steam. Latent Heat of Steam (L) is that quantity of heat which is required to transform one pound of water into steam at a given pressure, together with an amount of heat required to produce the external work done by increasing the volume of the water. Internal heat -f- external heat = latent heat of steam. L = 1,114 — .ytj where t = temperature of the steam. For the properties of saturated and superheated steam the reader is referred to special works called "Steam Tables." Adiabatic Expansion. — When steam at a certain pressure, flowing through a nozzle or the vanes placed within the annulai space of turbines of Parsons type, expands without receiving or being deprived of heat, and at the same time is performing no work except in displacing its own molecules, the expansion is termed adiabatic. All the work done by the steam during this process of expansion has been done at the expense of its in- ternal heat, and, as a result, there is a gradual drop in tempera- ture and pressure. Also, a certain portion of the steam con- denses, forming water, and its original volume is diminished. The expansion in a reciprocating engine is termed hyperbolic. Dryness Fraction. — It is very important to be able to deter- mine the exact volume of the steam at any point of the nozzle or stage of a turbine. This becomes manifestly true from the fact that the velocity, and, therefore the work of the steam, is de- pendent on the volume in conjunction with the area of the steam passage. The relation between the amount of dry steam after expansion and that before is called "dryness fraction," which is 820 PRACTICAL MARINE ENGINEERING also a measure of the quality of the steam. Due to the frictional resistance to flow between the passage walls and the steam itself, heat is generated and part of the moisture formed is re-evaporated into steam. Owing to this fact, the steam, strictly speaking, does not expand along true adiabatic lines, but in a way of its own peculiar to the turbine. The following formula gives a close approximation for the determination of the dryness fraction : yXHi £qi — E„2 + El X = 1 , where H. E, H-i = heat given up by steam expanding adiabatically between absolute pressures P^ and P2, corresponding to absolute tem- peratures Ti and T^. H-r = heat of vaporization at Tj. jBiii = entropy of the liquid at Ti. E (Tt — T,) = 326 B. T. U. with above values inserted. Sec. no. VELOCITY DIAGRAMS AND WORK BY STEAM In dealing with problems pertaining to the work done by steam flowing through a turbine, it is necessary to determine the velocity attained by the steam in the different nozzles and rows <3 Fig. 460. Velocity Diagram, Single-Stage Impulse Turbine of vanes at any point of the turbine as a result of expansion and the heat given up by the steam; also, to determine the absolute velocity at which the steam leaves the vanes, with vane speed and steam friction duly taken into account. The steam expansion in impulse turbines takes place wholly within the nozzles, an inappreciable amount only occurring in the 822 PRACTICAL MARINE ENGINEERING vanes, In the impulse reaction turbine, on the other hand, the steam expansion takes place within the vanes, and, to a small de- gree, in the space around them. In Fig. 460, representing the velocity diagram of a single* stage impulse turbine of the De Laval type, BC = Vi is the absolute jet velocity from the nozzle. EC = y^ is the relative jet velocity to the vanes. FG = Vi is the relative steam velocity leaving the vanes. HG = Vt is the absolute steam velocity leaving the vanes. BE = FH = Fv is the vane speed. In Fig. 461, representing the velocity diagram of a multiple Fig. 461. Velocity Diagram, Multiple-Stage Impulse Turbine stage impulse turbine of the Curtis type (one out of the several "expansions" of which the turbine is composed), Vi is the jet velocity from the nozzle, absolute entrance to the vanes. F2 is the jet velocity from the nozzle, relative entrance to the vanes. F3 is the vane steam velocity, relative exit from vanes. Vi is the vane steam velocity, relative entrance to the vanes of the first stationary row of vanes. Vs> ^e, similarly exit velocities from the first stationary row of vanes, and ^7^ ^s) entrance velocities to the second row of moving vanes. SPECIAL TOPICS AND PROBLEMS 833 ^9» f^io> f^ii. ^i2> ^i3> ^n> ^'15 and Fie being those of second stationary row of vanes, the third moving row of vanes, the third stationary row of vanes and the fourth moving row of vanes, Fi, stationary Vanes in Cylinder ^^^ Stationary Vanes in Cylinder ry Vanes I | I B I linder M M M W M Fig. 462. Velocity Diagram Impulse-Reaction Turbine being the absolute velocity with which the steam leaves the last row. In Fig, 462, representing the velocity diagram of an impulse- reaction turbine of Parsons type : V-i is the velocity at which the steam enters any one vane row, and Fg is the velocity at which the steam leaves the same row as a result of V^ and the expansion of the steam taking place within the vanes. Ft is, as before, the vane speed per second obtained from revolutions per minute and the diameter taken at the mean length of vanes. The energy absorbed by the wheel of the single stage impulse turbine is equal to the difference between the kinetic energy due to the absolute jet velocity Fj from the nozzle and that due to the absolute exit velocity F4 after the steam has passed through the vanes. 824 PRACTICAL MARINE ENGINEERING Similarly is the energy absorbed by the wheel of the multiple stage impulse turbine equal to the sum of the energy obtained by adding the energy absorbed by each moving vane row with respect to absolute entrance and exit velocities for each row. The stationary rows in the multiple stage impulse turbine serve only to deflect and guide the steam into the moving rows, while in the impulse reaction turbine this purpose is not only met, but expansion takes place within them and velocity is created to the steam entering the next moving vane row. The energy absorbed by each vane row in the impulse reaction turbine is that due to the difference between the energy created by the leaving steam velocity and that of the entrance velocity to any one vane row. The general formulas for energy absorbed per unit weight of steam are: Impulse type, K = , where V» > Fi 29 f V - Fe= Impulse reaction type, Ki = , where Vi > F« Ve and Fi are respectively the entering and leaving velocities in accordance with foregoing designation. If //j = heat units given up in creating energy, then = 778 Hi for impulse turbines. 2ff = 778 Hi for impulse reaction turbines. 29 Sec. III. ACTION OF THE STEAM IN PARSONS TURBINE After admission- to the steam chest the steam enters the first row of stationary vanes around the entire circle and attains veloc- ity as a result of expansion. When leaving this row of vanes the jets simultaneously enter and act upon the first row of moving vanes to which they have been guided by the stationary row. The moving rows, being attached to the rotor, receive impulse upon entrance of the steam and pressure by reaction of the steam when leaving the vanes. This is repeated continually from row to row throughout the whole turbine, the pressure diminishing and the volume increasing, the heat contained in the steam meanwhile being converted into kinetic energy as the steam passes each row SPECIAL TOPICS AND PROBLEMS 825 of vanes. The steam pressure being greater when entering the vanes than when leaving them, a pressure in the direction of flow is produced. This is of considerable magnitude, and is counter- acted by suitably proportioned balance pistons in land turbines. In marine turbines the unbalanced pressure on the vanes is taken up by the thrust of the propeller. The propeller thrust being greater than the unbalanced pressure is further counteracted by end thrust on the rotor provided by a diminution of the diameter of dummy piston. Any discrepancy in the opposing thrusts is allowed for in the thrust bearing. Referring to Fig. 462, which is a diagrammatic sketch show- ing steam and vane velocities through the blading, V^ is the ab- solute . velocity with which the steam leaves the vanes, V^ the relative velocity with which it enters, and V^ is the mean vane velocity. The absolute velocity in feet per second, V = where A Q = steam weight in pounds passing the turbine per second. S' = actual volume per pound in cubic feet =: specific volume at pressure existing times dryness fraction. A ^ exit area, in square feet, between vanes in any one row. If L = vane length in inches, a = angle which the vane makes with a plane vertical to the axis, C := circumference in feet at mean vane height, then L ^ = sin a X X C. 12 The clear exit area changes with length of vane, the angle oc and the circumference C. The heat given up per unit weight of steam in creating the change from velocity V^ to V^ = H-, — H,, H^ and H„ being respectively the heat in the steam before entering and after leav- ing a vane row. The work of the steam transformed into kinetic energy, disregarding friction, = (Hi — H.) 77&- 2g Were there no losses in the turbine, all of the available heat H^ — H2 would be converted into kinetic energy. Actual losses, however, do occur from the following sources : 1. Steam leakage over vane tips and by dummy pistons. 2. Steam frictional resistances in vanes. 826 PRACTICAL MARINE ENGINEERING 3. Velocity of exhaust. 4. Fluid friction on rotating surfaces. 5. Radiation. 6. Friction in bearings. All these losses have a certain equivalent value in heat units, which, when deducted from the available heat in the steam, leaves a definite amount available for useful work. The efficiency, or the relation between heat utilized and available heat supplied, may, therefore, be expressed — Available heat — heat due to losses Efficiency = Available heat If g = steam used in pounds per shaft horsepower (S.H.P.), B. T. U. = available heat per pound of steam within a cer- tain pressure range P^ — P^ and E = efficiency, then 1,980,000 = B. T. U. X 778 X £ In marine turbines the efficiency range is between 55 and 65 percent. Sec. 112. ACTION OF THE STEAM IN CURTIS TURBINE The Curtis marine turbine is of the compound impulse type, also sometimes called "velocity compounded." The steam ex- pands in sets of nozzles arranged for the different pressure stages successively from the initial pressure to that of the exhaust. The jet energy is transformed into work by impulse on the moving disks or drum. The number of vane rows (velocity stages) employed in each pressure stage depends on the jet velocity used, and are arranged in numbers varying from 3 up to 9. Good efficiency demands that certain proportions of steam and vane velocity be observed throughout the turbine. The steam action is essentially as follows: After expan- sion in the first stage nozzles the steam issues in solid jets against the first row of moving vanes, or buckets, which absorb a part of the jet energy, and, after passing through these buckets, meets the first row of stationary vanes placed on the distributors. The purpose of these vanes is to guide the steam into the second row of moving buckets, which, in their turn, take up another portion of the kinetic energy still possessed by the fast flowing steam, at the same time diverting it to the second row of stationary buckets, SPECIAL TOPICS AND PROBLEMS 827 which deflect the steam on the third row of moving buckets, where, again, more of the energy is taken up. This is repeated in a fourth and even a fifth row in the first stage, when the jet ve- locity is very high, but usually not in any other stage where con- siderably lower velocity exists. Thus, it will be understood, with a succession of rows, the original jet velocity is absorbed, and yet the bucket speed has at all times been only a fraction of the steam speed. Due to the fact that the velocity of the steam is gradually diminished by the continuous absorption of energy, while the steam volume remains practically constant, the bucket passages must be enlarged. This is done by making the length in the suc- cessive rows longer and longer, as well as by increasing the bucket angles. On entering the nozzles of the second stage the steam again expands, whereby new velocity is given, and now acts in the vari- ous rows of buckets of that stage exactly as it did in the first stage and so on right through the turbine. The number and size of nozzles must conform to velocity and volume, as well as to the steam quantity needed by the power to be transmitted. Due to the fact that velocities decrease and steam volumes increase suc- cessively in the stages removed from the first, the number and size of nozzles must increase successively in stages following the first. In order to reduce the steam pressure within the cylinder to a safe limit, the first stage velocity is made of such magnitude as to bring down the pressure in that stage to less than one-third of the original steam chest pressure. Working pressures prevailing in a seven stage Curtis tur- bine are given in the table appended, which conveys to the mind a clear illustration of conditions : TABLE Absolute Absolute Throat Throat Absolute Inlet Steam Pressure Area Nozzle ' Area Pressure Pressure in Nozzle of End Nozzle Kind Stage Pounds Pounds founds Nozzle Pressure in End. of per per per in Pounds per Square Nozzle. Square Square Square Square Square Inches. Inch. Inch. Inch. Inches. Inch. 1 265.0 79.0 152,9 1.339 95.7 1.52 Exp. i 79.0 41.7 45.58 4.24 45.58 4.24 " 3 41.7 21.2 24.0 ^ 7.8 24.0 7.8 " 4 21.2 10.4 12. "iZ 14.84 12.23 14.84 Parallel 5 10.4 4.9 6.0 29.25 6.0 29.25 •' 6 4.9 2.2 2.83 60.66 2.83 60.66 " 7 2.2 1.0 1.27 135.0 1.27 135.0 828 PRACTICAL MARINE ENGINEERING The jet velocity, or tlie velocity of the stream of steam which flows from the outlet end of the nozzle, depends essentially upon the proportions chosen in the areas of throat and outlet end and upon the initial and terminal pressure at the orifice and outlet. A definite relation exists always between the initial pressure and that at the throat when the orifice is well rounded. Thus, if P signifies the initial pressure, the throat pressure will be .577 P if the outlet pressure be equal to this or any other pressure below -577 P down to a perfect vacuum. This occurs in either a parallel or an expanding nozzle. The steam weight discharged is directly due to the throat velocity and the area of the throat, as well as to the specific volume, and, therefore, the higher the initial steam pressure the greater the steam weight per unit of time. The energy of the jet, however, corresponds to the outlet velocity as well as the weight. Steam velocities through the buckets of the first stage in a turbine with fixed bucket speed are shown diagrammatically in Fig. 461. The steam weight W in pounds per second passing through a turbine nozzle depends essentially upon: 1. Throat area ^ A, in square inches. 2. Actual volume of the steam after expansion = v, in cubic feet" per pound. 3. Velocity of flow at the throat = V, in feet per second. AXV W = z'X 144 From the general formula for the relation between kinetic energy and heat per unit weight of steam = 778 (Hi — H^) (I —A)), where 29 y ^ friction constant, V = velocity in feet per second, g = 32.16, Hi ^ total heat in steam at pressure Pi, H2 = total heat in steam at pressure P2. The throat velocity in a nozzle may now be figured, assuming F^ is the absolute pressure at the orifice, and P^ = .577 Pi. Example : Pi = 26s pounds absolute. Pi = -577 X 265 = 152.8 pounds absolute. SPECIAL TOPICS AND PROBLEMS 829 Hi — H2 = 46.1 B. T. U. y = 15 percent (assumed). V = ^ 2g X 77SX 46-1 X (i — .15) = 1,250 feet per second. The steam weight may be found from the formula previ- ously given. The outlet velocity may be found in a similar manner by sub- stituting the outlet pressure for the throat pressure. Sec. 113. THE LEVER SAFETY VALVE AND THE SAFETY VALVE PROBLEM The spring loaded safety valve is used almost exclusively in modern practice. The ability to solve problems relating to the weighted arm safety valve is, however, required of all candidates for United States engineer's licenses, so that it is of importance to thoroughly understand the method of solving the various prob- lems which may arise in this connection. These problems are all special cases of the general problem in mechanics which has to deal with the equilibrium of a body under the action of a system of forces, and for a clear understanding of the matter the principles discussed and explained later in Chap. XV, must be kept well in mind. The arrangement of a weighted arm safety valve is shown in skeleton in Fig. 463. The steam presses upward on the lower T Fig. 463. The Safety Valve Problem T face of the valve V, and is opposed by three forces tending to keep the valve on its seat as follows: ( 1 ) The weight of valve and spindle direct. - , (2) The weight of the lever with center of gravity at some point N and pivoted at the fulcrum 0. (3) The weight proper at M acting with a leverage or arm equal to MO. Now just as the valve is about to open, these two sets of forces, the one acting upward and the other acting downward, will balance. It is furthermore a principle of mechanics that when such forces are just on a balance, the product of the forces by their arms or leverages must make the same sum in each §30 PRACTICAL MARINE ENGlNEERlNC direction. Thus in the present case the up force at 5 may be considered as tending to cause motion of the lever about the fulcrum O, in the direction of the hands of a watch, while the down forces at B and W tend to cause motion about the same fulcrum in the opposite direction. Therefore measure the arms from the fulcrum point 0. Now if A is the area of the valve in square inches and p the steam pressure in pounds per square inch by the gage, the total steam load on the valve will be the product pA. This acts directly upward, and, as noted above, is directly opposed, as far as it goes, by the weight of the valve and spindle. Denote this weight by V. Then the difference (pA-V) is the actual or net force transmitted from the valve to the lever at S, and tending, as noted above, to turn the lever about from left to right. Let a denote the arrr for this force, or the distance SO from the center of the spindle to the center of the fulcrum. Then (pA-V)a is the product of force by arm for the upward forces. Keep this and turn next to the remaining or downward forces. Let W denote the amount of weight at M, and / the arm or distance MO from the center of gravity of the weight to the fulcrum. Also let B denote the weight of the lever, and c the arm or dis- tance NO, from the center of gravity of the lever to the fulcrum. Then (Wl + Be) is the sum of the products for the downward forces. By condition these are equal when the two sets balance and the valve may be considered as on the point of opening. Hence as an equation : ' ■ Wl + Bc>=(pA-V) a, or Wl + Bc = pAa-Va. From this equation can be found the value of any one- quan-- tity desired, provided all the others are known. Thus suppose all but W are known. Then : .pAa — Va — Be W= (I) i Similarly if all but / are known : pAa—Va — Bc l = - : — -(2) W and if all but p, the pressure per square inch at which thp valve will open with a given weight and location, m + Bc+Va ' P = (3) Aa SPECIAL TOPICS AND PROBLEMS 831 The operations represented by these equations may be readily ex- pressed as rules: Rule (i) To iind the weight knowing the other quantities. Multiply together the pressure per square inch, the area of the valve in square inches, and the distance from the center of the valve spindle to the center of the fulcrum. From this subtract the product of the weight of the valve and spindle by the same arm SO, and also the product of the weight of the lever by its arm NO. Divide the remainder by the weight arm MO, and the quotient will be the weight desired. Rule (2) To find the location of the weight or length of the arm MO knowing the other quantities. Find the same diflference as in rule (i) and divide by the weight W. The quotient will be the length of the arm MO. Rule (3) To find the pressure at which a given valve and weight will lift. Multiply the weight JV by its arm MO; also the weight of the lever by its arm NO, and the weight of the valve and spindle by its arm SO. Add these three products and divide the sum by the product of the area of the valve times the arm 5*0. The quotient will be the pressure desired. Example : Let MO or / = 28 inches. Let NO or c ^ 12 inches. I-et SO or a ^ 4 inches. Let diameter of valve = 3% inches. Then area of valve or A =z 9.62 square inches. Let weight of lever or S = syi pounds. Let weight of valve or K := 4 pounds. Let steam pressure or /> := 80 pounds per square inch. Then pAa = 80 X 9-62 X 4 = 3078.4. Fa = 4 X 4 = 16. Sc = sH X 12 = 66. Then 3078.4 — 16 — 66 =: 2996.4 and W =: 2996.4 -f- 28 = 107 pounds in round numbers. Or if PF were known and / required, the same numerator 2996.4 would be found, and then : / = 2996.4 -f- 107 = 28 inches in round numbers. Or if p is desired we should have Wl ^ 107 X 28 = 2996 Be = 5}4 X 12 = 66 Ka = 4 X 4 = 16 Sum 3078 832 PRACTICAL MARINE ENGINEERING Aa — 9-62 X 4 = 3848. Then /> = 3078 -^ 38.48 = 80 pounds in round numbers. General Remarks on the Problems. — The arm I is to beTneas- ured from the center of gravity of the weight W to the fulcrum or turning point 0. Usually the weight is of regular form, cir- cular or rectangular in elevation, so that its center of gravity is readily found. If the lever turns about a pin, then the arm i must be measured to the center of the pin. If it is provided with a link and knife edge bearing then / is measured to the bearing edge. If the center of gravity of the weight W and the fulcrum are not on the same horizontal line, then the arm / must be measured as the horizontal distance between verticals drawn through these points. The center of gravity of the lever arm must be obtained practically either by measurement or by balancing on an edge in the familiar manner. If it is practically a uniform straight bar the method of measurement will be quite accurate ; if it is taper- ing or irregular the method by balancing may be preferred. In any event, with usual proportions, as seen in the example above, the influence of the lever is relatively small, so that a slight error in the values relating to its weight or center of gravity would be of much less importance than a like proportional error in the weight W or its arm /. The area of the valve. A, should be that, of course, of the lower face, or more accurately, of the opening at the lower edge of the seat. The weights of the various parts are obtained by weigh- ing. If this is not practicable, a fair approximation may be made by computation based on careful measurement. In such case the volumes are found by the most appropriate means ac- cording to the shape of the figure and then by the use of the known weights of the substances per unit volume, the weights may be found. The general United States regulations relating to safety- valves will be found among the extracts from the Rules of the United States Board of Supervising Inspectors. Sec. 114. THE BOILER BRACE PROBLEM As has been shown before, all flat surfaces of any consider- able size, in a boiler, require some support in addition to that SPECIAL TOPICS AND PROBLEMS 833 which can be furnished by their own strength. In fact the whole idea of bracing is to subdivide by the braces a large flat sur- face into a sufficient number of smaller surfaces, each of which shall be self-supporting between the points where the braces are connected to the plate. The braces are then designed so as to be able to carry the entire load as a whole, and the parts of the plate between the braces are simply required to support, without undue change of form, the part of the load which comes upon them. To illustrate by a diagram let Fig. 464 represent a part of a boiler head requiring bracing. Now imagine the plate entirely Fig. 464. Boiler Bracing cut out around the dotted line, and then fitted in so exactly as to make a steam tight joint. The part thus cut out is therefore entirely separated from the remainder of the head, and without some especial support would be blown out immediately when steam was raised. Now suppose the braces to be so designed that they may be safely depended on to carry the entire load on the plate, and thus keep it securely in place in the head. It simply remains then for the parts of the plate between the braces to support themselves without losing their proper shape, and the support is thus made complete. In the actual boiler head, or in all cases where a flat surface has to resist pressure, the design of the braces is worked out exactly along these lines, and no account is taken of the strength of the plate for the general sup- port of the load as a whole. In designing boiler braces it is necessary to consider two things : 834 PRACTICAL MARINE ENGINEERING (i) The total load to be supported arid number of braces, or simply the load upon one brace as determined by their spac- ing and the steam pressure. (2) The safe load per square inch of section of brace. The total load depends on the area to be supported and on the gage pressure. In figuring out the area, as in Fig. 464, it is customary to consider that a narrow strip of metal around the outside will be well supported by the shell or by the tubes. The width of such strip is usually taken as 2 or 3 inches, though there seems to be no good reason why it should not be taken as half the spacing or pitch of the braces. This amounts to con- sidering the shell and tubes as effective bracing or support for that part of the plate near them, in the same manner and to the same extent as for the braces themselves. If the area thus found is multiplied by the gage pressure, the total load results. The spacing of the braces must then be Marine Engineering Fig. 465. Boiler Bracing ' taken in accordance with the principles and rules given in an earlier chapter. The total number of braces is thus determined, and the average load per brace may be found by dividing the total load by the number. Or otherwise, after the spacing is decided upon, the load on each brace may be found by multiplying the area which it supports by the pressure per square inch. Thus in Fig. 4650 the surface supported by the brace is considered as the dotted square, and the spacing being the same both ways, its area equals the square of the pitch. In some cases the spacing is not the same in both directions, as in Fig. 465&. In such case the. supported area is found by multiplying together the two pitches. Sometimes, again, the braces are irregularly distributed, and the area supported by one brace may be roughly triangular or of other irregular shape. In such case the area which the brace may be fairly called upon to support must be taken by approxima- SPECIAL TOPICS AND PROBLEMS 835 tion, using the best judgment which can be brought to bear on the special circumstances. When the braces are arranged in rows and columns as in Fig. 464, it will usually be found that due to the necessary spac- ing about the edges, the average load is slightly less than that which would correspond to an entire square or rectangle, and in consequence it is usually safer to take the load as determined directly by the area supported. Thus in Fig. 4650, let the side of the square be 7 inches; then the supported area is 49 square inches. Likewise in Fig. 465 fc, let the pitch be 14 inches in one direction and 16 inches in the other: then the supported area equals 14 X 16 or 224 square inches. Again, suppose that three braces are to be used to support an approximately triangular area on the back tube sheet. In such case make a fair allowance for the support about the edge, sketch in the area which the braces may be called on to support, sketch in the braces so as to divide the area as evenly as possible, and either compute the area of the whole triangle and divide by 3, or compute the smaller areas separately. Turning now to the second chief question, the safe load to be allowed per square inch of section of brace, the United States Rules provide that iron braces shall not be allowed m.ore than 6,000 pounds per square inch of section; while for steel, if in- spected . according to regulation, the allowance may be as fol- lows : From i J4 inches diameter to 23^ inches diameter, not to ex- ceed 8,000 pounds ; and above 2 J^ inches diameter, not to exceed 9,000 pounds, each per square inch of section. It must be noted that in all cases the diameter is measured at the root of the thread or at the smallest section. For this reason the threads are usually raised so that the diameter at the bottom is not less thati that of the body of the brace. There have been thus discussed the determination of two neces- sary items — the load which the brace is to support, and the safe load per square inch of section. It is clear then that if the latter is divided into the former, the quotient will be the necessary cross sectional area of brace. Having found the area, find the diameter by means of a table of diameters and areas, or by the proper rule or formula of mensuration. See Chap XV. These various operations may be expressed in the form of rules as follows: 836 PRACTICAL MARINE ENGINEERING ( 1 ) Find the area to be supported by one brace, and multiply this by the gage pressure per square inch. The product will be the load to be supported by the brace. (2) Take the safe load per square inch of section in accord- ance with the rule above given. (3) Divide the total load as found in (i) by the safe load as taken in (2) and the quotient will be the necessary area in_ square inches. (4) Find the corresponding diameter either by the help of a suitable table or by means of the proper formula or rule of men- suration. To illustrate the foregoing a few examples will be of aid. (i) In Fig. 464, suppose the total area to be supported is found by measurement to be 3,784 square inches, the steam pressure being 160 pounds gage. Find the total load. Ans. Load = 3784 X 160 = 605,440. (2) In Fig. 465a, suppose the braces spaced 14 inches each way, the steam pressure being the same as in (i). Determine the load on one brace. Ans. Load = 14 X 14 X 160 = 31,360. (3) Suppose, instead, that it was wished to space the braces 14 inches one way and 16 inches the other. Find the load on one brace. Ans. Load = 14 X 16 X 160 = 35,840. (4) Suppose that screw staybolts are spaced 6 inches by 6 inches. Find the load on one brace. Ans. Load = 6 X 6 X 160 = 5,760. (5) Suppose in (4) that the spacing weire 7 by 6j^. Find the load. Ans. Load = 7 X 6>4 X 160 = 7,280. (6) What would be the area and diameter of & steel brace in (2), allowing 8,000 pounds per square inch of section? Ans. Area = 31,360 -=- 8,000 = 3.92 square inches. Corresponding diameter = 2j4 inches nearly. (7) What would be the area and diameter of a steel brace in (3), allowing 8,000 pounds per square inch of section? Ans. Area = 35,840 -^ 8,000 = 4.48 square inches. Corresponding diameter = 2 7/16 scant. Probably 2J/2 inches would be employed. (8) What would be the area and diameter of an iron stay m SPECIAL TOPICS AND PROBLEMS 837 (4). allowing 6,000 pounds per square inch of section? Ans. Area = 5,760 -^ 6,000 = .96 square inch. Corresponding diameter = i}i inches nearly. (9) What would be the area and diameter of an "iron stay in (5), allowing 6,000 pounds per square inch of section? , Ans. Area = 7,280 ~ 6,000 = 1.2 13. Corresponding diameter 1% inches nearly. (10) Suppose that screw staybolts are spaced 7 by 7 inches, the steam pressure being 200 pounds gage. Find the area and A E Q (J ^' \ - — \ J t V B F H D JUorine Engineering Fig. 466. The Strength of Boilers diameter of a steel stay, allowing 8,000 pounds per square i::;'. of section. Load =z ^ X 7 X 200 := 9,800 pounds. Area = 9,800 -=- 8,000 = 1.225 square inches. Corresponding diameter = i}i inches nearly. Load on Oblique Braces. In case the brace is not at right angles to the surface to be supported, proper allowance must be made for the increase of load on the brace due to the angle of obliquity. This problem is explained in Chap XV. Load on Forked Ends of a Brace. The load on the forked ends of a brace is greater than one-half the load on the brace, in a ratio depending on the angle of obliquity. This problem is ex- plained in Chap XV. Sec. 115. STRENGTH OF BOILERS In order to examine the relation of the strength of a boiler shell to its diameter, thickness and the steam pressure, consider first a hollow chamber, as in Fig. 466, with parallel sides, AC and BD, a face AB perpendicular to these sides, and for the other end any other curved or irregular surface CD. Let this contain steam 838 PRACTICAL MARINE ENGINEERING under pressure. Now it is a well-known fact of experience that under such circumstances the chamber will remain in equilibrium, and it will not move as a whole, and in particular will move neither to the right nor to the left. Hence the internal force acting to the right must equal that to the left. But the force acting to the right is the total resultant of all the forces acting on the curved surface CD, while the force acting to the left is the resultant of the parallel forces acting on the plane face AB. Hence numer- ically these two resultants must be equal, and this will be the same, no matter what the shape of the surface on the right, as, for example, EF or GH. Now AB is called the projected area Q Marine Engineering Fig. 467. The Strength of Boilers of any curved surface, such as CD, EF or GH, the direction of projection being of course parallel to the sides AC and BD. Hence it can be said that the total resultant force in any direction due to the pressure of steam or of any gas or vapor acting on the curved surface will equal the pressure of the projected area of such surface, the projection being taken in the direction of the resultant desired. This is a very general and very important principle in mechanics, and has many applications, one of which is to the problem of the strength of a boiler, as will be shown. In Fig. 467 let ABCD denote a cross section of a cylindrical boiler with steam pressure acting on the curved surface, as de- noted by the arrows. Suppose a plane of division AB, and let us consider what it is which keeps the two halves from separating under the action of the steam pressure. The surface ACB is urged upward and the surface ADB is urged downward, while SPECIAL TOPICS AND PROBLEMS 839 they are prevented from separating by the strength of the ma- terial at A and B. Now the force tending to thus separate the two parts is evi- dently measured by the force urging ^C5 upward or ADB down- ward. As has just been seen, this equals the force on the pro- jected area which is represented by AB. Suppose the axial length of the section to be one unit, or one inch, and denote the diameter by d, the radius by r and the thickness of the shell by t. Then the area of AB equals d square inches, and if p is the pressure per unit area the total load on AB is pd. But as has been seen this is numerically the same as the force which urges ACB up- ward and ADB downward, and which is opposed simply by the strength of the material at A and B. The cross sectional area on each side will be f x i or t; hence the total area of material will be 2t. Let 5" denote the stress developed in the material per square inch of section. Then 2^5" is the total stress developed, and this must equal the load pd. Hence the equation 2tS ^^ pd ■=■ 2pr, (i) and pd 2S (2) 2tS tS P = = (3) d r In these equations (3) gives the value of the steam pressure p, which would produce the stress 6" in the metal of thickness t. If, however, a shell, as in Fig. 467, were formed with riveted joints the strength of the metal in the joint would be less than that of the plate itself in the ratio given by the efficiency of the joint as previously discussed. Hence, if .S" is to be the safe working stress in the metal of the joint, and e is the efficiency, the working pressure p must be reduced in the ratio of the effi- ciency, or from p to ep, in order to keep the stress in the joint down to the value 5". Also if T is the ultimate strength of the metal, it is not desired that 5" rise above a certain fraction of T. The number by which to divide T to find the safe stress 6" is called the factor of safety. Denote this factor by f. Then in (3) substituting for 5" its value T -^ f and allowing for the efficiency of the joint: 2 etT etT P = = , (4) df rf 840 PRACTICAL MARINE ENGINEERING and fpd (5) 2 eT In a similar manner consider the strength of the boiler to withstand rupture around the shell. In this case the area of the head is wd'^ -H 4 and the load is pwd'^ -=- 4. The section of metal carrying this load is measured by the circumference multiplied by the thickness, or by -rrdt. Hence if S is the stress developed per unit area, the total stress in the metal carrying the above load is Trdts. Equating the load and the total developed stress : V dtS = AtS 2tS (6) d r Comparing this with (3) it is seen that in the case of the shell without seam or joint the pressure necessary to produce rupture around the circumference will be just twice that required for rupture along the length ; or, in other words, the boiler is tvice as strong for rupture around the circumference as for rup- ture along the length, and this is an important principle which should be borne in mind in dealing with questions relating to the strength of a cylinder against pressure from within. It also fol- lows that the longitudinal seams must be made with the greatest care and of the highest efficiency, while joints of lower efficiency, so long as they insure tightness against leakage of steam, will be sufficient for the circumferential seams. To take account of the factor of safety and of the efficiency of the joint it is necessary to introduce in (6) the factors / and e, the same as in (3). This will give: 4 etT 2 etT P = = , (7) fd fr and fpd t = — — (8) 4et For a bumped boiler head, as referred to in section 21, con- sider that the head is a part of a sphere, and that all parts of such a surface are equally strong. Now for a sphere as a whole the total load on a circumferential section equals the pressure p multiplied by the projected area of the hemisphere. But the SPECIAL TOPICS AND PROBLEMS 841 latter is ird^ -4- 4, and therefore the load is npd^ -f- 4. The total section of metal is Trdt, and if 6" is the stress developed per unit area, then the total stress is irdtS. Hence : Trp(P = w dts 4ts d But, as seen above, this is the same as the value for a cylin- drical shell for rupture around the circumference. Hence the principle that a sphere has the same strength in all directions as a cylinder of equal diameter for rupture around the circum- ference. It will be noted that this relates simply to the strength of a sphere or part of a sphere for pressure on the concave sur- face. For the strength of a head bumped inward or convex on the inside, there is no method of treatment by simple mechanics. For the mechanics involved in the computations relating to plain boiler bracing reference may be made to Chap, XV. Sec. 116. LOSS BY BLOWING OFF In the days of the jet condenser, and when blowing off to reduce the density of the water in the boilers was the usual prac- tice, the loss of heat occasioned by this operation was necessarily the subject of consideration, and it became necessary to be able to compute this loss in any given case. This is most easily done by the simple application of algebraic methods. Let F denote the pounds of feed water in any given time, and / its density. Let B denote the pounds of water blown out in the same time, and b its density. Then (F — B) ^pounds of water evaporated into steam in the same time. Likewise fF represents the amount of solid mat- ter brought into the boiler during the given time, and bB repre- sents similarly the amount blown out in the same time. Since the density of the water in the boiler remains constant at b, the amount of solid matter in the water must remain constant, and hence as much must be blown out as comes in by the feed, or : fB = bB. (i) From this is readily derived the following relations : 842 PRACTICAL MARINE ENGINEERING F b ~S~' f F—B b—f (2) (3) B f Now let h =: temperature of feed, t2 = temperature of steam, H = total heat in one pound of steam at given pr«ssure. Then B (t^ — h) = heat blown out, and (F — B) [H — (Jj — 32)] = heat put into the steam formed. Then (F — B) (H + 32) + 5f, — Ff^ = total heat. Hence ratio of loss e is given by : B (h — k) " ^ (F — B) (H + 32) +Bk — Fh By the aid of the ratios above, this expression is readily re- duced to the following form : f(k-h) '~ (&-/) (H + 32)+fU-bh These algebraic operations may be expressed by the fol- lowing : Rule — (i) Multiply the density of the feed water by the dif- ference between the temperatures of the steam and of the feed. (2) Subtract the density of the feed from the density of the water blown out. (3) Add 32 to the total heat of i pound steam. (4) Multiply together the results in (2) and (3). (5) Multiply the density of the feed by the temperature of the steam. (6) Multiply the density of the water blown out by the tem- perature of the feed. (7) Add the results in (4) and (5) and subtract from the sum the result in (6). (8) Divide the result in (i) by that in (7) and the quotient expressed in percent will give the percentage of loss. Examples : (i) Density of feed, f = 1. Density maintained in boiler, 6^2. Pressure of steam ^ 100 pounds gage. Temperature of feed ti = 100 degrees. Then from tables : U = 337-8, and FI = 1185. 337.8—100 Then loss ratio, e = (1185 + 32) +337.8 — 2 X 100 SPECIAL TOPICS AND PROBLEMS 843 237-8 17.S percent. I3S4-8 The details may be followed through somewhat differently, as follows: The loss of heat per pound of water blown off equals {t^ — t^). This equals 337.8 — 100 or 237.8. The heat required per pound of water evaporated is H — {t^-. — 32). This equals 1185 — (100 — 32) or 1117. Now from (3) it appears that the amount evaporated is to the amount blown out as {b — /) is to / or as i is to i. That is, the amount evaporated equals the amount blown out. Hence for every 11 17 heat units put into a pound of steam 237.8 are lost. Hence the percentage loss on the total heat employed is 237.8 -h (237.8 + 237-8 or e = = 17.5 percent, as before. 1354-8 (2) Density of feed, f = %. Density maintained in boiler, b = i^. Steam pressure = 60 pounds, gage. Temperature of feed ti = 92 degrees. Then from tables: t,^ = 307.4, and H = 11 75.7. Then percentage of loss, Vs (307-4 — 92) 3i (117S-7 + 32) +% X 307.4— iHX 92 7 X 21S-4 1507.8 ::= 18.4 percent. 6 X 1207.7 + 7 X 3074 — 13 X 92 82.02 Or again by analysis: The loss of heat per pound of water blown off equals (t^ — h)- This equals 307.4 — 92 = 215.4. The heat required per pound of water evaporated is H — (fi — 32). This equals 1175.7 — (92 — 32) = 1115.7. Now from (3) it appears that the amount evaporated is to the amount blown out as ^ is to J^ or as 6 : 7. Hence for every 6 pounds evaporated there will be 7 pounds blown out. The corresponding loss of heat is 7 X 215.4= 1507.8. The corresponding amount of heat put into steam is 6X 1115.7 = 6694.2. The total heat used is 1507.8 + 6694.2 = 8202. The percentage of loss will be then 1507.8 e = = 18.4 percent, as before. 8202 844 PRACTICAL MARINE ENGINEERING Sec. 117. GAIN BY FEED WATER HEATING As has already been seen, a certain fraction of the heat is lost by way of the funnel. In certain forms of feed water heat- ers, a part of this loss is prevented by placing the heater at the base of the funnel to absorb the heat of the gases after they have left the tubes. In watertube boilers such arrangements are especially common, the heater consisting usually of a con- tinuous coil of pipe jointed up with elbows or return bends, and through which the feed water passes before going to the upper drum, or point of regular feed entrance. It thus becomes a question of interest as to how much sav- ing may be effected by the feed water heater thus arranged to utilize a part of the heat in the waste funnel gases. This will be best illustrated by an example. (i) Temperature of feed no degrees. Pressure of steam 160 pounds gage. Assuming dry steam, what will be the per- centage gain by heating the feed water to 170 degrees? From Table I for the first condition: Total heat in i pound steam = 119S Heat in feed water =; 1 10 — 32 = 78 Heat required to form i pound steam ^ 1117 For the second condition the heat units saved are measured by the difference in the feed water temperatures, or in this case by 170 — 110= 60. Hence 60 heat units have been saved out of 11 17, and in this case the heat required per pound of steam formed will be 1117^60 =: 1057. The percentage saving is measured by 60 -H 1117 ^ 5.7 per- cent. In case the feed water is heated by exhaust steam which is not sent to the condenser, and of which the heat would be other- wise wasted, the gain is found in the same manner by dividing the rise in the temperature of the feed water by- the number of heat units needed to form one pound of steam without the heater. In case the feed water is heated by live steam from certain of the receivers, or by any steam which might otherwise have been used or the heat of which might have been saved, then the question of heater economy becomes much more complicated and cannot be determined by any process of simple computation. SPECIAL TOPICS AND PROBLEMS 84s It becomes simply a question of where it is most advantageous to use the heat, whether in the heater or elsewhere, a question which m general can only be answered by the actual trial. Sec. 118. THE PROPORTIONS OF CYLINDERS FOR MULTIPLE EXPANSION ENGINES The total expansion of the steam in the multiple expansion engine is attained by expanding it in the high pressure cylinder from the point of cut-off to the end of the stroke, and then handing it over to a series of cylinders of continually increasing size until the steam which first filled the high pressure cyhnder to the point of cut-off, finally fills the low pressure cylinder, and the expansion is complete. It would seem at first that the total num- ber of expansions would be given by dividing the volume of the low pressure cylinder by that of the high pressure up to the point of cut-off. It is not quite true, however, that the volume of the entering steam is measured by the volume of the high pressure up to the point of cut-off, nor that its final volume is that of the low pressure cylinder. These simple relations are modified by the clearance. Due to the clearance the actual number of ex- pansions will usually be from .5 to i less than the apparent num- ber given by dividing the high pressure volume up to the cut-off into the low pressure volume. The number of expansions suitable in any given case will vary with the initial steam pressure and with the other conditions to be fulfilled. With steam having an initial presi)Ure of 150 to 180 pounds ahd used in triple expansion engines che number will usually vary frorti'say 8 to 12; toward the lower values as the importance of the development of power per ton of machinery is greater, ^nd the importance of coal economy is less, and toward the higher limit and perhaps even beyond in the reverse cases. With higher steam pressure, say from 180 to 220 pounds, and quad- ruple expansion engines, the number of expansions will be 'com- monly found between 10 and 15, varying in one direction or the other according to the same general considerations as given above for the lower pressures. In naval practice with initial pressure as high as 265 pounds per gage, the expansion used is about 12 at full power, the ratio of low pressure to high pressure cylinder, including clearances, being 10. 846 PRACTICAL MARINE ENGINEERING Of this total expansion range not more than 1.4 to 1.6 is usually obtained in the high pressure cylinder with the usual cut- off between .55 and .75 of the stroke, and taking into account the effect of the clearance. This leaves the remainder to be obtained from the ratio between the volumes of the high pressure and low pressure cylinders, and assuming the same stroke this will equal the ratio between the areas of the cylinders. Hence with from 8 to 12 total expansions the ratio between the piston areas of the low pressure and high pressure will usually be found say from 5 to 7, while with a higher steam pressure and from 10 to 15 total expansions the ratio will be from say 7 to 10. The details of the proportions of the cylinders of multiple expansion engines will not be entered into here, and it will be sufificient to add to the foregoing the following simple rules by which suitable values for the diameters of intermediate cylinders may be found having given those of the high and low. (a) For triple expansion engines — (i) Take the square root of the high pressure diameter. (2) Take the square root of the low pressure diameter. (3) Multiply together the results of (i) and (2), and the result will give a value for the intermediate diameter. Example : Diameter of low pressure = 50 inches. Diameter of high pressure := 20.25 inches. V 50 = 7-07- V 20.25 = 4.5. 4-S X 7-07 =31-8. It is usually considered better to take the actual value slightly under rather than over the value given by the rules, and therefore take 31 or ^lyi as a suitable diameter for the inter- mediate cylinder. (b) For quadruple expansion engines — ( 1 ) Take the cube root of the high pressure diameter. (2) Take the cube root of the low pressure diameter." (3) Square the result found in (i). (4) Multiply together the results found in (2) and (3) and the product will give a value for the diameter of the first inter- mediate pressure. (5) Square the result found in (2). (6) Multiply togther the results found in (i) and (5) and SPECIAL TOPICS AND PROBLEMS 847 the product will give a value for the diameter of the second inter- mediate pressure. Example : Diameter of high pressure =; 27. Diameter of low pressure = 80. V^= 3- V 80 = 4.31. (3)^ = 9. 9 X 4-31 = 38.79- (4.31)' = 18.58. 3 X 18.58 = SS.74. Here also it is usually considered better to take the actual diameters slightly under rather than over the values given by the rule. Hence in taking shop dimensions go under rather than over, and in the present case take say 38 and 55 as suitable values for the diameters of the two intermediate pressure cylinders. Sec. 119. CLEARANCE AND ITS DETERMINATION The term clearance is used in two senses. Clearance proper denotes the actual distance between the face of the piston and that of the cylinder head when the former is at the end of the stroke. That is, it is the least distance between the piston and the cylinder head. In amount it may vary from % to yi or }^ inch, being naturally larger the larger the engine. The clearance volume or the percentage clearance on the other hand is the actual volume contained between the face of the valve and the face of the piston when the latter is at the end of the stroke plus the volume of the steam port up to the valve seat, or it is such volume expressed as a percentage of the volume swept by the piston. The clearance should be deter- mined either by measurement and computation from the draw- ings, or by filling it with water and measuring the amount re- quired. There are several methods of procedure. In the iirst place the valve must be disconnected and blocked in mid position, thus covering the ports. Care must also be takert to provide by the use of putty, if necessary, against leakage at either the valve or piston. Then place the engine on the center and by means of the indicator pipe fill the clearance volume with water by pail- fuls, weighing each pailful before pouring in, and the amount left over in the last pailful. Then knowing the weight of the pail, the total weight of water poured in may be found. This reduced to volume by taking 62.5 pounds to the cubic foot will give the clear- 848 PRACTICAL MARINE ENGINEERING ance volume in cubic feet, and this divided by the volume of the piston displacement will give the clearance percentage. If salt water were used, 64 instead of 62.5 would be used in reducing to volume. Somewhat differently the mode of procedure may be as fol- lows : Place the engine just one inch off the center as shown by measurements on the guides. Fill up the volume as before and note the weight required. Then move the engine up to the center slowly, catching the water as it is forced out and weighing as be- fore. The amount forced out corresponds to i inch of piston dis- placement. Subtract this amount from the total, and the re- mainder represents the water in the clearance. Divide the latter by the amount representing one inch of piston travel, and the quotient is the number of inches corresponding to the clearance. This divided by the stroke will give the clearance percentage. As an illustration of the first mode of procedure, suppose diameter ^ 22 inches, stroke = 40 inches, weight of water to fill clearance = 85 pounds. The volume of clearance = 85 -=- 62.5 = 1.36 cubic feet. The volume of piston displacement = 3.1416 XiiXiiX40-f- 1728 = 8.8 cubic feet, nearly. Heiice clear- ance percentage = 1.36 -f- 8.8 = 15.45 percent. For the second mode of procedure let the figures be as fol- lows : Total weight of water with engine i inch off center = 99 pounds. Weight of water forced out when engine is brought to center = 13.5 pounds. Difference = 85.5 pounds. Then 13.5 pounds represents l inch of piston travel, and 85.5 pounds the whole clearance. Hence 85.5 -^ 13.5 = 6.33 inches = number of inches of piston travel giving a volume equal to that in the clearance. Hence 6.33 -H 40 inches = 15.8 percent = clearance percentage. Sec. 120. THE EFFECT OF CLEARANCE IN MODIFYING THE APPARENT EXPANSION RATIO AS GIVEN BY THE POINT OF CUT-OFF As was shown in Sec. 119, the clearance volume is defined as the volume or space between the piston when at the end of the stroke and the face of the valve. It comprises the "clearance proper" or space between the piston when at the end of the stroke and the cylinder head, together with the volume of the ports or passages leading from the valve face to the cylinder. SPECIAL TOPICS AND PROBLEMS 849 The volume of the clearance expressed as a fraction of the vol- ume swept by the piston is usually known as the clearance ratio or percent, and is usually found in marine practice from .07 to .15, though in some cases it may rise as high as .23. The steam within this volume takes part, of course, in all expansions and compressions to which the steam in the cylinder as a whole is subjected, and its influence on the apparent expansion ratio must therefore be considered. If there were no clearance volume, then the expansion ratio would be given by dividing the total volume swept by the piston, by the volume up to the point of cut-off. But this would be the O A Marine t/ngineering p Fig. 468. The Effect of Qearance on the Expansion Ratio same as taking the reciprocal of the cut-off ratio. Thus, for example, if the cut-off were at J^ stroke, the expansion ratio would be 2; if at 1/3 stroke, 3; if at 2/3 stroke, 3/2 or 1.5, etc. With a clearance volume, however, this is modified as shown by Fig. 468. Let AB denote the volume swept by the piston and OA the clearance volume to the same scale, or otherwise let AB denote the length of the stroke and OA the clearance volume re- duced to stroke by dividing the volume by the piston area. Then if cut-off is at some point X, the actual volume of steam within the cylinder and ready to expand is denoted by OX rather than by AX. Again at the end of the stroke when the piston reaches B, the final volume of the steam is OB. Hence the real expan- sion ratio \s B -^ O X and denoting its value by r: AB + OA ~ AX + OA Now dividing both numerator and denominator of this frac- tion by AB: 8so PRACTICAL MARINE ENGINEERING OA AB AX OA AB AB Now AX -^ AB is the cut-off ratio, and OA -^ AB is the clearance ratio or percent. Denote the first of these by a and the second by c. Then i + c a-\- c Examples : (i) Cut-off at ^ stroke, clearance lo percent. Find the true expansion ratio. Operation : o = H = -SO c ^z lo percent = .10 i.oo-|-.io 1. 10 Hence r = = =; 1.83 Ans. ■So-f.io .60 (2) Cut-off at 60 percent, clearance 15 percent. Find the true expansion ratio. Operation : i.oo+.is 1. 15 r = = = I.S3 Ans. •60 + .15 .75 Sec. 121. ENGINE CONSTANT The horsepower formula is : 2PLAN /■2LA \ L H. P. = = ipN) ( 1 33,000 \ 33,000 / Now the factors 2LA -^ 33,000 are always the same for any one cylinder, while the other two {pN) will vary according to the conditions. Therefore compute in advance the value of the factor {2LA -f- 33,000) and then to find the horsepower simply multiply these by the other two, of which one, p, mean effective pressure, is found from the indicator cards, and the other. A'', number of revolutions per minute, from the counter. This factor 2LA -^ 33,000 is called the "engine constant," and is often thus computed as a matter of convenience, especially when large num- bers of cards are to be worked up. For the power in one end of the cylinder only simply take the factors LA -^ 33,000 with A'' and the value of p found from SPECIAL TOPICS AND PROBLEMS 851 the corresponding card. To allow for the area of the piston rod on the lower side of the piston in the formula for the full power, use the average area top and bottom with the average mean effec- tive pressure. When there is a difference in the values of the mean effective pressure top and bottom, this will not give quite the same result as if the two ends were taken separately. The difference, however, is in all ordinary cases quite unimportant. Example : Given a cylinder of diameter =: 36 inches, stroke = 42 inches, diameter of piston rod = 5 inches. Find the constant neglecting the piston rod, and also allawing for it as above explained. Area of cylinder = 1017.9 square inches. Stroke = 3.5 feet. Constant = (2 X 3-5 X 1017.9) -H 33,000 = .2159. Next to allow for the piston rod, its area = 19.6 square inches. Taking this from 1017.9 there remain 998.3 square inches as the area of the lower side of the piston. The mean of the upper and lower sides is then 1008. i. It may be noted that in all such cases the mean may be most easily obtained by taking from the upper area one-half the piston rod area, or in this case, by taking 9.8 from 1017.9, giving 1 008.1 as above. Then Constant = (2 X 3-S X 1008.1) ^ 33,000 = .2138. Sec. 122. INDICATED THRUST The indicated thrust in pounds may be defined as the indi- cated power in foot pounds divided by the product of the pitch of the propeller multiplied by the revolutions per minute. Let H = indicated horsepower. p =z pitch of propeller in feet. N = revolutions per minute. T = indicated thrust. Then by formula : 33,000 H^ T in pounds = pN This may be reduced to tons by dividing by 2,240, and 33,000 H 1473^ T in tons 2,240 pN pN Dividing the above value of T in pounds by the value of the reduced mean effective pressure as given by equation ( i ) in Sec. 123, and 8S2 PRACTICAL MARINE ENGINEERING T 33,000 H 2LNA 2 LA X pm pN 33,000 H p It thus appears that the ratio of the indicated thrust to the reduced mean effective pressure is measured by twice the stroke times the low pressure area divided by the pitch of the propeller. All of these are constants for any given engine, and it thus follows that the ratio between the indicated thrust and the reduced mean effective pressure is a constant, or in other words that the former is in a constant ratio to the latter. The indicated thrust which is often considered as a rather vague quantity is thus related to the reduced mean effective pressure, a much better known quantity. The indicated thrust may also be considered as the actual thrust which would be exerted if the propeller worked without slip, and if all the power developed in the cylinders were used in driving the ship forward at the speed thus produced. Actually a part of the power is lost in the friction of the engine and in the water due to the operation of the propeller, while the latter does not operate without slip. In consequence the actual thrust ex- erted on the thrust block is usually found somewhere about one- half to seven-tenths the indicated thrust, computed as above. Example: The indicated horsepower is 1,640, the pitch 13 feet, and revolutions 148. Find the indicated thrust in pounds and in tons : 33,000 X 1,640 T in pounds = = 28,130 13 X 148 T in tons =: 28,130 ~ 2,240 = 12.56. bee. 123. REDUCED MEAN EFFECTIVE PRESSURE In the multiple expansion engine the power is developed in the various cylinders, as equally as the designer is able to bring about. The reduced mean effective pressure may be defined as the mean effective pressure which, acting in the low pressure cylinder alone with the same piston speed, would produce the same power as the actual engine with its series of cylinders. Taking the usual formula for power 2 PLAN H — 33,000 and solving for p 33,000 H 33,000 H p= = /,) 2 LAN (2LN)A SPECIAL TOPICS AND PROBLEMS 853 Hence if the entire power were to be developed in the low pressure cylinder the necessary mean effective pressure would be found by the operations indicated by this equation, and such would be the reduced mean effective pressure, or the mean effec- tive pressure reduced to the low pressure cylinder. The opera- tions indicated by the above equation may be expressed by a rule as follows: Rule: (i) Multiply the indicated horsepower by 33,0(X). (2) Multiply twice the length of the stroke in feet by the revolutions (giving piston speed) and this by the area of the low pressure piston in square inches. (3) Divide the result found in (i) by that found in (2) and the quotient is the reduced mean effective pressure desired. To obtain a somewhat different expression for the reduced mean effective pressure denote the areas of the three pistons high pressure, intermediate pressure and low pressure of a triple expansion engine, for example, by A-^, A 2, A^, and the corres- ponding values of the mean effective pressure in these cylinders Pi> p2, p3- Then the total power H of the formula (i) above may be expressed as follows X2 LN) p^. + (2 LN) p^, + (2 LN) Ms H = - 33.000 According to ( i ) this value of H is to be multiplied by 33,00x3 and divided by 2LN times A^ the low pressure piston area. This will give the following as the value of the reduced mean effective pressure : Ax Ai P = Pi \-p^ 1- ^a (2) Aa A3 According to this formula the procedure for finding the re- duced mean effective would be as follows : ( 1 ) Divide the mean effective pressure for the high pressure cylinder by the ratio between the low pressure and high pressure piston areas. This reduces the high pressure mean effective to the low pressure piston. (2) Divide the mean effective for the intermediate pressure cylinder by the ratio between the low pressure and intermediate pressure piston areas. This reduces the intermediate pressure mean effective to the low pressure piston. 8s4 PRACTICAL MARINE ENGINEERING (3) Add together the results found in (i) and (2) and the mean effective for the low pressure. The sum will be the total mean effective pressure reduced to the low pressure piston. Example: Given for a triple expansion engine the following: Diameter high pressure cylinder = 24 inches. Diameter intermediate pressure cylinder = 38 inches. Diameter low pressure cylinder =: 60 inches. Length of stroke = 42 inches. Revolutions ^ 106. From sets of indicator cards suppose the mean effective pressures found as follows: For the high pressure pi = 61.9. For the intermediate pressure pi = 30.2. For the low pressure p3 = 13.8. Find the total indicated horsepower and the reduced mean effective pressure. For the piston areas, from a table of areas of circles : Ai = 452.4. A2 = II34-I. A3 = 2827.4. Then finding the indicated horsepower in each cylinder: Indicated horsepower in high pressure cylinder = 629.6 Indicated horsepower in intermediate pressure cylinder = 770.2 Indicated horsepower in low pressure cylinder = 877.2 Total indicated horsepower =: 2277.0 Then according to rule ( i ) for the reduced mean effective : 33,000 X 2277 p = = 35.82 7 X 106 X 2827.4 According to rule (2) for the same: 452.4 II34-I p = 61.9 X h 30.2 X h 13-8, 28274 2827.4 or /> = 9-9 + 12.12 + 13.8 = 35.82. The results are of course the same, since the two operations are simply two methods of computing the same quantity. If the indicated horsepower, revolutions, length of stroke and low pres-. sure piston area are given, then' the first method would be used. If the mean effectives in the various cylinders are given, together with the revolutions, length of stroke, and piston areas, then the second method may be used without necessarily finding the indi- cated horsepower at all. SPECIAL TOPICS AND PROBLEMS 8SS Problems : (i) Given indicated horsepower = S,i20. Low pressure area =: 5,612. Stroke = 48 inches. Revolutions = 112. Find the reduced mean effective pressure. Ans. 33.6. (2) From a pair of high pressure indicator cards the mean effective pressure is found to be 72.6 pounds. The diameters of the high pressure and low pressure cylinders are respectively 18 and 48 inches. Find the high pressure mean effective reduced to the low pressure piston. Ans. 10.2. (3) In the same engine as in (2) the mean effective pressure for the intermediate pressure cylinder is found to be 33.2 pounds, and the low pressure diameter is 29 inches. Find the intermediate pressure mean effective reduced to the low pressure piston. Ans. 12.1. (4) In the same engine as in (2) the low pressure mean effective pressure is 14. i pounds. Find the entire reduced mean effective pressure. Ans. 36.4. Sec. 124. PRESSURE ON MAIN GUIDES The load on the crosshead guides comes from the load on the connecting rod and the obliquity of its line of action. The mechanics of this problem is considered in Chap. XV, and the maximum value of the load, which is found when the crank is at right angles to the centerline, is readily computed in the manner there shown. It thus appears that the maximum load on the guide will bear the same relation to the load on the piston that the length of crank does to the connecting rod. This method of computing the load will be illustrated by an example. (i) At about mid stroke given the pressure on the top of the piston 180 pounds per square inch and on the bottom 88 pounds per square inch. The ratio of connecting rod to crank is 4.5 to I. The area of the piston is 404 square inches. Re- quired the maximum load on the guide. Net pressure on the piston = 180 — 88 = 92 pounds per square inch. Net load on the piston = 92 X 404 = 37. 168 pounds. Maximum load on guide = 37,168 -:- 4.5 = 8,260 pounds. The safe load on guides is usually taken at from 50 to 70 pounds per square inch. In this case therefore taking 60 pounds as a safe load per square inch 856 PRACTICAL MARINE ENGINEERING Area of crosshead slipper needed = 8,260 -^ 60 = 138 square inches. Sec. 125. FORCE REQUIRED TO MOVE A SLIDE VALVE The net load on a slide valve is the difference between the steam loads on the two sides. On the back there is a load due to the full steam pressure in the steam chest. On the inside there is a more variable load due partly to the pressure in the steam chest or cylinder, and partly to the exhaust pressure. For the low pressure cylinder exhausting into the condenser the exhaust pressure is small and is usually neglected. The area of the face subjected to pressure from the cylinder is also relatively small, and for the purposes now in view is usually omitted. The load on such a valve is therefore taken simply as the load on the back, the pressure per square inch, multiplied by the area in square inches. Denote the pressure by p and the area by A. Then the total load will be pA. The resistance of the motion of the valve which must be overcome by the valve rod will be the load pA multiplied by the coefficient of the friction between the valve and its seat. Let / denote this coefficient, and F the force necessary to move the valve. Then F = fpA. The values of / will depend on the condition of the surfaces and on the lubrication. With well fitted and lubricated surfaces its value should not exceed .01 to .02. With dry surfaces, es- pecially if they should begin to abrade, its value may rise to .10 and more. Example: Given a low pressure slide valve with dimensions 50 inches by 60 inches : average excess of pressure in valve chest over condenser, 26 pounds. Coefficient of friction .02. Find load on valve stem. Area = A ^= 50 y, 60 = 3,000 square inches. Load =pA = 26 X 3,000 = 78,000. Load on valve stem = fpA = .02 X 78,000 = 1,560 pounds. In designing a valve stem relative to such a load it must be given a large factor of safety in order to provide for starting the valve from rest or where partly stuck to the seat, and also for extra stresses due to the effects of inertia. For a flat slide valve on a high or intermediate cylinder, an SPECIAL TOPICS AND PROBLEMS 857 estimate must be made of the load on each side and the differ- ence taken. Without serious error the net pressure may be taken as the difference between the average pressure in the valve chest and in the next following receiver. If then p^ and p2 are these" pressures, (p^ — p^) will be the difference, and iPi — Pi) ^ the average load on the valve. The remainder of the operation is, of course, the same as explained above for the low pressure valve. Sec. 126. AMOUNT OF CONDENSING WATER REQUIRED It has already been shown how to find the amount of heat required to form one pound of steam of given temperature and pressure from a pound of feed water of given temperature. To condense the steam and reduce it back to the condition of the feed water will require the subtraction of the same amount of heat. Hence the heat to be taken from each pound of steam in the condenser may be found in exactly the same manner. Now suppose the condensing water as it comes in to have a tempera- ture of ti, and as it is discharged, a temperature of t^. Then the temperature of each pound will be raised (t^ — fj) degrees. This means that it will absorb (t^ — t^) units of heat. Then if this is divided into the number of heat units which must be taken from each pound of steam, it will give the number of pounds of condensing water which must be provided to con- dense one pound of steam. Then if the amount of steam to be condensed is known, the total amount of condensing water is readily found. This may be illustrated by the following example: Pressure of steam at exhaust = 3.5 pounds, absolute. Corresponding' temperature = 148 degrees. Temperature of condensed water = 130 degrees. Temperature of condensing water at entrance or t^ = 62 degrees. Temperature of condensing water at discharge or ?2 = 98 degrees. Then from the steam tables it is found that 1,029 heat units per pound must be subtracted in order to condense the steam and reduce it to the condition of the water in the condenser. Also fa — fi = 98 — 62 = 36 = number of heat units absorbed per pound of condensing water. Then 1,029 -^ 36 = 28.6 = number of pounds of condensing water per pound of steam. 858 PRACTICAL MARINE ENGINEERING Suppose an engine of 2,000 indicated horsepower requiring 16 pounds of steam per indicated horsepower per hour to be con- densed under these conditions. Then for the total weight of water IV, W = 2,000 X 16 X 28.6 = 915,200 pounds per hour. And 915,200 ^ 60 = pounds per minute = 15,253. Then 15,253 -^ 64 = cubic feet sea water per minute = 238. In all ordinary cases the number of heat units to be sub- tracted will not differ much from 1,000, and for a rough estimate this number is often taken without detailed computation from the steam tables. Then, varying with the season of the year and the locality, it may be expected that each pound of condens- ing water will absorb from say 25 to 50 heat units, and hence that the condensing water required per pound of steam will vary from 40 to 20. For turbines the amount required is usually from 50 to 60. Sec. 127. WORK DONE BY PUMPS It is sometimes desired to find the net work done by a pump in handling a certain amount of water. This may be computed closely if the conditions under which the pump operates are known. It is shown in mechanics that work may be divided into a volume factor and a pressure per unit area factor, and this form of the expression for work is usually most convenient for use in such cases. Take first the case of a boiler feed pump feeding against a gage pressure of 160 pounds and supplying 16 pounds water per indicated horsepower per hour for 2,100 indicated horse- power. Then the amount of water supplied will be 2,100 X 16 = 33,600 pounds per hour. This equals 33,600 ^ 60 = 560 pounds per minute. Taking 62.5 pounds per cubic foot this will occupy a volume of 560 -^ 62.5 = 8.96 cubic feet. This volume of water is pushed into the boiler against a total pressure of 160 + 14.7 or say 175 pounds per square inch or 175 X 144 := 25,200 pounds per square foot. Hence : Work per minute ^= 25,200 X 8.96 = 225,792 foot pounds. Reducing this to horsepower: horsepower = 225,792 -^ 33,000 = 6.84. This is the net work, and assuming that there is no leakage or loss of steam. Actually there will be such a loss, raising the amount of water which the pump must deliver by from 5 to 10 percent or more. Now between the steam cylinder where the total work is SPECIAL TOPICS AND PROBLEMS 859 developed and the net delivered work as above determined, there is a series of losses. These may be classified as follows : (i) Loss due to the friction of the water in the pipes and to the inertia or resistance of the valves. These items form an extra resistance which must be overcome in addition to the regular pressure in the boiler. (2) Loss due to the friction of the pump itself. This like- wise forms an extra resistance as in (i). (3) Loss due to the slip of the pump. The pump plunger and valves are rarely tight and a certain amount of "slippage" to the water is sure to occur. It results that the volume displaced by the pump plunger will be greater than the volume delivered to the feed pipe, and the work to be done in the water cylinder will be increased in about the same ratio. The slip is quite a variable feature, being quite small with good workmanship and careful attention, and large under contrary conditions. With the usual run of boiler feed pumps, however, it will rarely be less than 5 percent, and with lack of care may readily rise to from 10 to 20 percent. The sum of losses (i) and (2) will be found usually between 15 and 20 percent, and hence the sum of the total losses may be expected to vary between perhaps 20 or 25 and 40 percent. In the present case, for illustration, assume the loss by leak- age of steam at joints, etc., as 6 percent. Then the water ac- tually delivered to the boiler will require a net work of 6.84 -f- .94 = 7.28. Assume the total losses between steam cylinder and feed pipes to be 33 percent. Then the indicated horsepower in the steam end will be 7.28 -^ .67 = 10.87, and it should be ex- pected that under moderate to fair conditions such a pump would require from 10 to 11 indicated horsepower. With the pump plunger and valves leaking badly, stiff working parts and gener- ally poor conditions, the amount will, of course, rise far above these figures. The full capacity of the feed pump would also be, of course, considerably above these values. The question here is, however, simply an estimate of the power actually required and the net power delivered under a given set of conditions. Again consider the case of a centrifugal pump for the same engine handling, say, 30 pounds condensing water per pound of steam condensed. Then the total amount of water handled per hour will be 2,100 X 16 X 30 = 1,008,000 pounds. 86o PRACTICAL MARINE ENGINEERING In this case the resistance to be overcome is due chiefly to forcing the water through the condenser tubes. In some cases also the discharge outlet is slightly above the surface of the water and this additional lift increases the work to be done. The most convenient method of computation in this case is to estimate the total head equivalent to the resistance occasioned by the condenser tubes, and the lift of the water above the sur- face. This will be the total height of water which would pro- duce the same pressure as must be overcorne by the pump at the tips of the vanes. In iisual cases the head corresponding to the resistance in the condenser tubes may be assumed at from 4 to 5 feet. If the water is discharged a:t or below the water level this will then be the total head against which the pump works. In case, however, the pump draws from the bilge as when used for freeing the ship of water, then the total head will be the total lift plus the head due to the condenser tubes, and its value may rise in such cases to 20 feet and more. In such cases the work done is the product of the weight of water handled as the force or resistance factor, multiplied by the head as the distance factor. In the present case, assuming a total head of 6 feet : Work per minute = 16,800 X 6 = 100,800 foot pounds, or horsepower = 100,800 -^ 33,000 = 3.05. The efficiency of such pumps is usually found between .30 and .50. That is, between 50 and 70 percent of the power de- veloped in the steam engine operating the pumps is lost, chiefly in the slip of the pump. Hence under fair conditions it may be assumed that this 3.05 horsepower will be about 40 percent of the indicated horsepower of the engine. Hence the latter will be greater than 3.05 in the ratio of 100 to 40 or 2}^ times. Hence indicated horsepower required = about 2j4 X 3.05 = about 7.5. These examples will serve to show the methods to be used in working such problems, and if the principles involved are kept clearly in view, they may be similarly applied to the solution of many problems likely to present themselves in engineering work. Sec. 128. DISCHARGE OF STEAM THROUGH AN ORIFICE It may be sometimes convenient to be able to compute ap- proximately the amount of steam which will escape into the atmosphere from a chamber under a given pressure through an aperture of given area. SPECIAL TOPICS AND PROBLEMS 86i Let p be the pressure, supposed to be not less than 25 pounds, absolute. Let A = area of aperture in square inches, and W = weight discharged in pounds per second. Then Napier's rule for the approximate value of W is as follows : PA Wz= . 70 Thus given ^ = .5 square inch and p = 140: 140 XI iV = = I pound per second. 70X2 Take the following problem : What weight of steam would be discharged per hour through a small hole. or crack of area .005 square inch under a pressure of 200 pounds per square inch ? Using the formula: 200 X 005 X 3600 IV = = 51.4 pounds per hour. 70 The importance of small leaks may thus be realized. Sec. 129. COMPUTING WEIGHTS OF PARTS OF MACHINERY The determination of the weights of various parts of marine engines and boilers is often necessary as a part of an estimate of costs for repairs or for other purposes. Such determinations are usually made by numerical computation, and consist in find- ing first the volume of the piece in question, and then its weight by the use of factors such as those given in the table of unit .weights of material. The chief part of the computation is there- fore mensuration, the principles of which are given in Chap. XV. Some general suggestions regarding the application of these rules, with some adc'itional methods which may be used in special cases, ^re heie added. [i] Units to be Used The dimensions will usually be taken either from a drawing or directly frorn the piece in question. It may be recommended as a general rule to reduce all dimensions to inches as the unit rather than feet or feet and inches, the latter requiring the use of duo-decimal notation and methods as explained in Chap. XV. Where the pieces are small and fractions of an inch are to be dealt with, it will usually be most convenient to reduce them to decjmal form rather than to express them as cQmmon fractions. 862 PRACTICAL MARINE ENGINEERING In brief the inch as the unit and numbers expressed decimally are recommended as a general rule in such computations. The factors for reducing cubic inches to pounds are then used as given in tables of unit weights of material, and the weight is readily found. [2] Approximation and Short Cuts In computations of this character absolute accuracy does not exist. In fact with no physical measurement can absolute accuracy be obtained. In practical life simply an approximation is desired, a value sufficiently near for the purposes in view; a value so near that the' error is not of commercial or financial , importance. All engineering measurements and computations recognize this principle, and of the acquirements which may come to the engineer with experience, none is of greater value than that which enables him to know where to stop his compu- tations, how far to carry his measurements and approximations, what error will be of importance, and what -insignificant. Thus if the dimensions of a coal bunker are desired in order to compute its volume, it is evidently absurd to note the figures to the frac- tion of an inch. There is no surety that the length, for example, is uniform within any such limit, and the difference due to a variation of 34 or J^ inch either way will be insignificant for the purpose in view. On the other hand, if a journal is to be measured in order to make a new one which shall fit in the same bearing, the admissible error in only a few thousands of an inch, and the utmost attainable accuracy will be in order. So likewise in finding the weight of a sheet of boiler plate an error of }i inch in the length or breadth will introduce no significant error in the final result, while such an error in the thickness would cause a most serious error in the result. The former would make a difference of perhaps one part in 1,000 or so, while the latter might cause an error of one part in 8 or 10. Another point which may also be remembered is that a large relative or percentage error is more permissible in some small part of the whole than in a large part. Thus in a boiler an error of 10 percent in the weight of the tubes may be of less importance than one of i percent in the weight of the shell and heads, while an error of 50 percent in the high pressure cylinder cover, for example, might make less difference than one of 10 percent in the low pressure cover. Of course there should be no excuse for SPECIAL TOPICS AND PROBLEMS 863 making any 50 or 10 percent errors, but the principle may be borne in mind as a legitimate means of saving time when a roughly approximate value must be determined. The most common approximations are those which make the computation of volume simpler by substituting for the actual 2farine Engineering Fig. 469. Approximate Area of Segment of Circle Marine Enjtnetr^tf' Fig. 470. Approximate Area of Boiler Plate body some other of simpler form, and with such dimensions as to be of equal volume so far as judgment may be able to deter- mine. Such substitutions are often employed, but they must be used with judgment and care in order that the possible error in- 864 PRACTICAL MARINE ENGINEERING troduced may not be larger than permissible. No general rules can be given for such approximations, but the most common consist in substituting a rectangle or triangle or sometimes a cir- cle, for a more irregular area ; or a cylinder or regular prism or plate for some irregular volume. Thus in Fig. 469, if it is desired to find quickly an approxi- mate value of the segment of the circle ABC, sketch in a tri- angle ADC, so taking the sides that the area left out shall be judged equal to that taken in, and hence the area of the triangle may be taken as an approximation to that of the segment. This area is then readily found by the usual rule for a triangle. Again, in computing the area of a front boiler tube sheet, as shown in Fig. 470, for a first approximation substitute by judg- ment for the actual contour a rectangle ABCD, and thus quickly obtain a value which may be sufficiently close for the purpose in hand. Again often add by judgment something to one of the dimensions of a piece in order to provide for additional or irregular parts which would not be included in the regular geo- metrical figures dealt with. Thus in finding quickly the approxi- mate weight of a cylinder casting, provision may be made for the flanges by adding by judgment an appropriate amount to the length of the casting; or similarly for a piece of shafting with flanged couplings at the ends. It is often necessary to divide a more or less complicated piece into several parts, each of which may be of some relatively sim- ple form. In some cases the volume of one simple form may be subtracted from that of another, thus giving as the remainder the volume of a more or less irregular form. Thus, to find the volume of a pair of brasses with square backs and sides, find the volume from the outside dimensions as though the block were solid, and then the volume of the cylindrical hole, and take the one from the other. Many such little devices will suggest themselves in connec- tion with the details of the work, but it will be unnecessary to here enter further into the subject. In connection with the rule of Pappus, Chap. XV, the fol- lowing method of applying it to the determination of the weight of such forms as a piston, cylinder head, etc., may be noted. The operations are as follows: SPECIAL TOPICS AND PROBLEMS 86s ( 1 ) The cross sectional drawing is supposed to be at hand. ' (2) A copy of the half cross section, as shown for a piston in Fig. 471, is prepared on thick, uniform paper, and then cut carefully out with a sharp pointed penknife. (3) This is weighed on delicate scales, and also balanced on the knife edge, the line AB containing the center of gravity be- ing thus found. (4) A square of the paper containing any convenient num- ber, say 100 square inches of area, is also cut out and weighed. lfttriM.£ngineeHiv Fig. 471.' Volume of Piston by Eule of Pappus This divided by the area' will give the weight of the paper per square inch. (5) The weight of the paper half section is divided by that of the square inch. The quotient will be the area of the paper half section in square inches. (6) This area is multiplied by the square of the scale ratio of the drawing. Thus if the drawing is to a scale i inch = i foot, it is in the ratio i : 12 with the original, and multiply by 12 X 12 or 144. If the scale is ij^ inches = i foot, it is i : 8, and multi- ply by 64. If to a scale of 3 inches = i foot, it is i : 4 and multiply by 16. The result thus found will be the area of the actual full sized half section in square inches. (7) Then multiply the distance AG scaled off according 866 PRACTICAL MARINE ENGINEERING to the scale of the drawing and expressed in inches, by 6.2832, and the product by the area as found in (6). The result will be the volume in cubic inches. Instead of the preceding, the area may be found less ac- curately by taking it in parts and using substituted simpler forms, as above explained. Then by judgment assume the location of G and then proceed as above in (7). Thus, for example, suppose as follows: Scale of drawing i>^ inches = i foot. Weight of paper section 240 grains. Weight of paper per square inch 36 grains. Arm AG = 1.7 inches on the paper or 13.6, as scaled from the drawing. Then area = 240 -h- 36 = 6.67 inches. This multiplied by 64 gives 426.7 square inches as the area of the actual half section. Then volume — 13.6 X 6.2832 X 426.7 = 36462 cubic inches. QUESTIONS Special Topics and Problems .PAGE In what three physical states may bodies exist? 774 Name the characteristics of each 774 Describe the results of continually applying heat to a lump of ice 775 What is the difference between a gas and a vapor? 776 What are the two chief kinds of change which the addition or sub- traction of heat may produce ? 77^ What is meant by the terms sensible heat and latent heat, and how are each related to the energy of the molecule ? 777 What is meant by the term temperature ? 778 How. is it measured? 77^ What thermometer scales are in use and how are they related? 778 How is heat measured as to its quantity ? 778 What is the heat unit employed ? 779 What is meant by Joule's equivalent or the mechanical equivalent of • heat, and how much is it ? 779 In how many ways may heat be transferred from one body or place to another ? 780 Describe emission and absorption 780 Describe radiation, conduction and coni'ection 780 Describe how these various operations (mter into the heating of the water in a boiler 780 Describe the formation of steam from wi'ter , 780 How does the temperature of the boiling poirjtvary with the pressure? 782 What is saturated steam ? 784 What is moist or wet steam ? ' 784 What is dry and saturated steam? 785 SPECIAL TOPICS AND PROBLEMS 867 PAGE What is superheated steam ? 785 What is meant by the total heat of steam ? 786 How do you find the total heat of a mixture of steam and water?. . . . 787 Mention various ways in which the economy of a steam boiler may be considered 789 Describe in particular the conditions affecting fuel economy 789 What is meant by the evaporation per pound of coal, and how is it found ? 792 What is meant by the evaporation per pound of combustible, and how is it found ? 795 Describe the cycle or routine corresponding to the so-called ideal engine 797 Upon what does the efficiency of such an engine depend? 798 Describe the various heat wastes which prevent the actual engine from realizing the efficiency of the ideal 799 In what fundamental wayS may the efficiency of the actual engine be improved ? 800 In particular what methods may be taken for reducing the heat wastes of actual engines ? 801 Explain the gains which may result from the use of superheaters, re- heaters, jackets, feed heaters 80,3 Explain the relation of expansion to gain in efficiency 805 State for various representative types of engines the economy which may be expected in terms of coal per I. H. P. per hour and pounds of steam per I. H. P. per hour 807 What is an impulse turbine ? 815 What is a compound impulse turbine? 815 What is an impulse reaction turbine ? 815 Explain action of steam in each type 821 Derive the formulae required for a general discussion of the lever safety valve 829 Explain the suppositions made in connection with the subject of boiler bracing, and show how the principles of mechanics are applied to these problems 832 Derive the formulae for the strength of cylindrical boilers, for both longitudinal and for circumferential rupture, and show that, aside from the influence of the riveted joints, the boiler is twice as strong in the latter as in the former direction 837 Derive the formulae for the strength of a bumped boiler head 840 Derive the formulae required for the discussion of the loss by blowing off, and show how to apply it to special cases 841 Explain the operation of the different types of feed water heaters, and how they may effect a saving in the heat required 844 How may the various diameters for the cylinders of triple and quad- ruple expansion engines be proportioned? 845 What is a clearance volume ? 847- Describe methods for its determination 847 How does the clearance affect the apparent expansion ratio as given by the point of cut-off ? 848 What is the "engine constant" for power, and how is it found? 850 What is meant by the term "indicated thrust," and how is it found? 851 What is meant by the expression "reduced mean effective pressure," or "mean pressure reduced to the L. P. piston ?" 852 How is this redteed pressure found, and what is its relation to the indicated thrust? 852 How may we compute the load on the main guides ? 855 How may we compute the force required tp mov? a slide valve? 856 868 PRACTICAL MARINE ENGINEERING PAGE How may we compute the number of pounds of condensing water per pound of steam for any given set of conditions? 857 How may we compute the work done by pumps, knowing the de- livery head and the amount of water handled ? 858 How may we compute the discharge of steam from an orifice? 860 Explain some of the short cuts and convenient methods which may be employed in the computation of the weights of parts of marine machinery 861 CHAPTER XV Computations for Engineers Sec. 130. COMMON FRACTIONS* [i] Units of Measurement and Definitions One of the principal duties of the engineer is to measure things. Thus he may be called on to find the length of a sec- tion of shafting, the diameter of a piston rod, the weight of a screw propeller, the volume of an oil tank, or the capacity of a coal bunker. Measuring consists in nothing more or less than comparing the quantity to be measured with another quantity of the same kind, and so finding how many times the latter is contained in the former. Thus in measuring a length of shaft with a foot rule the length of the shaft is really compared with the length of the rule, and so found, for example, that the shaft is 14 feet in length; that is, that it is 14 times as long as the rule, or that its length contains the length of the rule 14 times. All these are simply different ways of saying the same thing. Now the foot rule or the foot in such an operation is called the unit. Again, in measuring the weight, say, of a screw propeller, the operation really amounts to making a comparison between the weight of the propeller and the standard weight called the pound. Here likewise the pound is the unit. It is easily seen that the unit must be the same kind of quantity as the thing to be measured, else no direct comparison can be made between them : thus a unit length to measure length, a unit area to measure surface, a unit volume to measure volume, a unit weight to measure weight, etc. * The reader is supposed to be somewhat familiar with the general subject of fractions as presented in the elementary text books of arithmetic. The present section is not intended as a complete discussion of the subject, but rather as a short compendium of the more important operations, based on a point of view somewhat different from that given in the usual text books. 870 PRACTICAL MARINE ENGINEERING When fractions are being handled simply for exercise in arithmetic, it is not necessary always to stop to ask what kind of a unit it is, or what kind of a quantity is being dealt with. For an exercise in arithmetic it makes no difference, but the engineer in actual problems always knows what he is dealing with, and what kind of a unit is meant. In the usual way of writing fractions, as —-, ^e' To' "ih' etc., the number below the line is called the denominator and shows into how many equal parts the larger or principal unit is divided in order to furnish the smaller or fractional unit. The denominator thus shows the relation of the fractional unit to the principal unit. The number above the line is called the numerator and shows how many of these fractional units are used to measure the quantity in question. Proper Fraction. In a proper fraction such as % the nu- merator is less than the denominator, showing that the quantity measured is less than the principal unit. Improper Fraction. In an improper fraction as ^%2, the numerator is greater than the denominator, showing that the quantity measured is greater than the principal unit. Mixed Number, or Whole Number and Fraction. Such an expression means that the quantity is measured in terms of two units. Thus 7%2 means seven principal units and five frac- tional units, the latter unit being one-twelfth the former. This is exactly similar to the measurement of length in feet and inches, or weight in pounds and ounces. Thus if the foot is the principal unit, 7%2 means simply 7 feet and 5 inches, or if the pound is the principal unit, 8%6 means 8 pounds and 9 ounces. [2] Reduction of a Mixed Number to an Improper Fraction This means simply the reduction of the measure all to terms of the smaller or fractional unit, just as a measure in feet and inches may be reduced all to inches. Thus to reduce 7?i2 to an improper fraction it is seen that in each pf the seven prin- cipal units there are 12 fractional units, and hence 7 X 12 or 84 such units in the whole number. In addition, there are 5 more fractional units, and therefore 84 + 5 or 89 in all. The reduced value is therefore *%2. In a similar way if the principal unit were the foot, reduce 7 feet and 5 inches to inches by multi- plying the 7 by 12 and adding in the 5, giving 89 inches similar to the 89 twelfths (%) above. Therefore the following: COMPUTATIONS FOR ENGINEERS 871 Rule. — Multiply the whole number by the denominator and add in -the numerator. The result is the numerator of the im- proper fraction, and the denominator is the same as before. Problems. — Reduce to improper fractions the following: 2^, 84, I2-I-, 8iA. 12i-i 1713. 26^113. 6' T ^"=16' lY' 16' '45"' ^TTT' AnS. i-I, 1-5.. 199 107 206 788 86139 6 7' 16' la' lu' "To"' 144 ■ [3] Reduction of an Improper Fraction to a Mixed Number To reduce an improper fraction such as ^%2 to a mixed number, find first how many principal units there are. Since 12 fractional units make i principal unit, it is evident that the num- ber of principal units will be found by dividing 31 by 12. The quotient will then give the number of principal units and the remainder will give the remaining number of fractional units. Thus 31 -H 12 = 2 principal units and 7 remainder, or 7 frac- tional units over; or % = 2%2. Hence the lollowing: Rule. — To reduce an improper fraction to a mixed number, divide the denominator into "the numerator and the quotient will be the whole number, while the remainder will be the numerator of the fraction, and the denominator will be as before. Problems. — Reduce to mixed numbers the following: 76 198 289 56 95 143 264 764 13 144 101' 21' 76 117 84 19 Ans < 11 t3. 2_87_ 2.Z. t1 t2 ,1 An*. ^as. 5^3-, i-g, 2—^, 2^, i_, i_, 3_, 40^. [4] Reduction of Fractions Without Change of Value If the size of a unit of measure is changed, the measure of the quantity is changed in like proportion. Thus, for example, the number measuring the diameter of a bolt in sixteenths as a unit will be twice as great as if measured in eighths as a unit. Thus %o and % represent the same quantity, one measure being in sixteenths and'the other in eighths. It follows that both terms of a fraction (the numerator and denominator) can be multi- plied or divided by the same number without changing its value. Thus %, %, %, i%5, ^%i, ^%4, 2%o, 4%3, etc., all represent the same quantity measured in terms of different units, and it is seen that the % may be changed into any of the other forms by multi- plying both numerator and denominator by the same number, and similarly any of these latter forms may be reduced back to the % by dividing both numerator and denominator by the same number. 872 PRACTICAL MARINE ENGINEERING 2X7 i6-^8 Thus — i%i and = %. 3X7 24-^8 It may often be convenient to reduce a fraction to another of equal value, but having some particular or specified denomi- nator. To this end divide the denominator desired by the denominator of the fraction, and multiply both terms of the fraction by the quotient. That is, multiply both numerator and denominator by some number which will produce the desired denominator. Thus to reduce % to a fraction whose denominator is 42, divide 42 by 3 and find 14. Then multiply both terms of % by 14 and thus find ^?42 as the fraction desired. Lowest Terms. A» fraction is said to be reduced to its lowest terms where there is no whole number which will divide both numerator and denominator without a remainder. Thus in the foregoing-string of fractions % is in its lowest terms while none of the others is. To reduce a fraction to its lowest terms, seek a factor which will divide both numerator and denominator and divide, continuing the operation until no further reduction can be made. Exanlple. — Reduce Wm to its lowest terms. It is first seen that 2 will divide both terms without remainder. Dividing there remains %2 as a reduced value. It is then seen that 3 will again divide both terms, and thus find % as the lowest reduction. It may also be noted at first that 6 will evenly divide .both terms, and thus find % by a single operation. Problems. — Reduce the following to their lowest terms: 72 360 116 864 42 231 66 72 19 216' 770' 48' 1728' 81' 183l' 44' 24' 57' Ans 1 -5- 2-5- 1 14 21 T 3 -3 1 Addition, Subtraction and Multiplication of Common Fractions Considering fractions as representing the measures of va- rious quantities, it may be required to perform upon them the four fundamental operations of mathematics — addition, subtrac- tion, multiplication and divisioiv These will be briefly con- sidered in order. [s] Addition of Common Fractions Two-thirds and three-fourths cannot be combined into a single quantity any more than can 2 feet and 3 inches, or 6 miles COMPUTATIONS FOR ENGINEERS 873 and 8 feet. The reason is that the units are not the same in the two quantities which are wished to be combined, and before the combination can be effected it is necessary to reduce the measures to the same unit in each. To this end take advantage of the operations explained in [4] and reduce the fractions to a common denominator or common unit of measure. As small a number as possible is naturally sought for this denominator, and hence proceed according to the common rule for finding the L. C. M. {least common multiple) of the denominators. Then proceed to express the various fractions all with this L. "C. M. as the common denominator by the method explained in [4]. Then" add the numerators and reduce the result as may be pos- sible. This is the foundation for the usual rule, which may be expressed as follows: Rule, (i) Find the L. CM..* of all the denominators for a new denominator. (2) Divide each denominator into this L. C. M. and multiply the corresponding numerator by the quotient for a new numerator. (3) Add the new numerators thus found, and the re- sult is the numerator of the sum desired. (4) -Write this numerator over the L. C. M. or com- mon denominator, and reduce to the lowest terms. * For the convenience in connection with these operations is given as follows the rule for finding the least common multiple of a series of num- Ijers — t. e., the smallest number which will contain each without a re- mainder. Rule — Write the numbers in a line (as [i] below), and select any number (as 4 in this case) which will divide at least two of them without remainder. Divide and set down, the quotients underneath, except where the division would not be exact, in which case bring down again the number itself (as shown in line [2] below). Proceed with this line the same as with the first, and so continue until no two numbers have a com- mon divisor. Then multiply together all the numbers remaining on the last line, together with all the divisors, and the product will give the least common multiple desired. Ejeample— Find the L. C. M. of 8, 36, 20, 6. Operation : 4) 8 36 20 6 Line (i) 3) 2 9 S 6 Line (2) 2) 2 3 S 2 Line (3) I 3 5 I Line (4) L. C. M. = 4X3X2X3X5= 360.— Ans. 874 PRACTICAL MARINE ENGINEERING Examples. Add %8 and Vi. The L. C. M. of i8 and 4 is 36. Then 10 + 9 36 Add %6, % and %. The L. C. M. of 16, 3 and 6 is 48. Then 9 + 32 +40 %6 + % + % = = ^1/48 = by reduction 2%6. 48 If there are but two fractions to be added and both have I for a numerator, a short rule for their addition is as follows : Write the sum of the denominators over their product and the fraction thus formed is the sum desired. Thus % + 1/6 = "/48 = %4. [6] Subtraction of Fractions Thib operation requires reduction to the same unit of meas- ure in the same way and for the same reason as in the case of addition. Hence the usual rule, which may be expressed as fol- lows : (i) Find the L. C. M. of the two denominators for a new denominator. (2) Divide each denominator into this L. C. M. and mul- tiply the corresponding numerator by the quotient for a new numerator. (3) Subtract the new numerators, and the result will be the numerator of the difference desired. (4) Write this numerator over the L. C. M. or common denominator, and reduce to lowest terms. Thus to subtract Vi from %8, proceed as follows : 14 — 9 Mi-Vi- 36 If both numerators are i a short rule for the subtraction of the fractions is as follows: Write the difference of the de- nominators over their product and the fraction thus formed is the difference desired. Thus % - % = ?io. Problems in Addition and Subtraction of Fractions: Perfom the following additions: ^2^ 3^ 7 '^8~3~12-'' \ i T 3>' \5' 10)' VTT'tTj COMPUTATIONS FOR ENGINEERS 87s Perform the following subtractions : (i. 1 \ ( n _J_\ / 814 18 \ /-4_30. 104 \ / IT n V8 12';' V16 2 J' 144 le-" V8 6 4 2 8 8/' V6 4 iJ Ans. I-5-, li, 2i., 2-3-, is^, J-, ■^, 4i?-i, -5i_, a_ 42' 8' 9' lo' ■'48' 24 48' ^144' 432' 64 Note. — In the operation of multiplication and division it is always necessary to distinguish between the operator and the subject or thing operated on. Thus in 6 times 5, the number 6 is the operator and 5 is the subject. The latter is usually the measure of some quantity. The former is the sign of an opera- tion to be performed, and this distinction, which is most im- portant, must not be forgotten. [7] Multiplication of Fractions First consider the operator as a whole number and the sub- ject as a fraction. Thus suppose that it is desired to multiply %2 by 6. The operation is exactly the same as if it were desired to multiply 5 inches by 6. The result in the latter case is 30 inches and in the former it is 30 twelfths, or as it may be written : ^%2, or by reduction % or 2%. This illustrates the familiar prin- ciple that to multiply a quantity it is necessary to multiply its measure, and since in a fraction the numerator is the measure, multiply the numerator to multiply the fraction. Furthermore, it is plain that if the denominator of a frac- tion is multiplied, the size of the fractional unit is decreased, and hence with the same numerator or same number of such units the value of the fraction is decreased in like proportion. Similarly if the denominator is divided the size of the fractional unit is increased, and hence with the same numerator or same number of such units the value of the fraction is increased in like proportion. Hence to divide the denominator of the frac- tion by the given multiplier and leave the numerator the same, will have the same efifect as multiplying the numerator and leav- ing the denominator the same. Thus %2 X 3 = %■ This may also be seen by first multiplying the numerator and then reducing to lowest terms. Thus %2 X 3 = ^^2 = by reduction Vi. Hence the following rule for multiplying by a whole number: , Rule. — Multiply the numerator of the fraction or divide the denominator of the fraction by the given number. Problems. — Perform the following multiplications : 8/6 PRACTICAL MARINE ENGINEERING |X2, f X3, 3^X4, ^X6,lfX7, fix 12, j^X36. Ans. li, 2, 2-^, 3-|, 9^, 7, 2X. [8] Divisions of Fractions As before, first consider the divisor or operator as a whole number, and the dividend or subject as a fraction. Then remem- ber that division is simply the inverse of multiplication, and that by inverting the procedure for the later the former will be effective. Thus to divide % by 2, divide 18 by 2 and have %3 as the result. Or again, multiply the denominator, thus dividing the value of the fractional unit and thus dividing the value of the fraction as explained in [7]. Thus ^%3 -^ 2 = %. This being reduced to its lowest terms gives %3 as before. The operations on fractions involved in multiplication and division by whole numbers may be summarized. as follows: Multiplying the {----5- ^} ] ^f " | its value, and di- •J- ..1- S nuemerator ) /divides I -.^ „„i„„ viding the ] denominator [ (multiplies \ '*= ^•>'"«- Problenus. — Perform the following divisions: Ano 3 2 3 3 4 5 7 TT' JJ' 17' 3 6' TS" ~6~ IT [g] Multiplication and Division by Fractions In these operations the operator is expressed as a fraction, and the latter in this case is therefore not the measure of a quan- tity, but the sign of something to be performed. When the frac- tion is used "as a multiplier it is simply a shorthand way of ex- pressing two operations : ( i ) a multiplication by the numerator, and (2) a division by the denominator. Thus if % is used as a multiplier it is simply a shorthand way of expressing a multi- plication by 2 and a division by 3. Thus 8 X % is another way of expressing 8X2-^3or8-=-3X2. Similarly and since division is exactly the inverse of mul- tiplication, when a fraction is used as a divisor it is simply a shorthand way of expressing two operations: (i) a division by the numerator, and (2) a multiplication by the denominator. Thus if % is used as a divisor it is simply a shorthand way of expressing a division by 2 and a multiplication by 3. Thus 8 -^ % is another way of expressing 8-^2X3or8X3-T-2. COMPUTATIONS FOR ENGINEERS 877 When the thing operated on is also a fraction these prin- ciples work out as follows : % X % means that % is to be multi- plied by 2 and divided by 5. But it is possible to multiply by multiplying the numerator, and to divide by multiplying the denominator. Hence 3X2 % X % = — = %o = ?io. 4X5 Hence for the multiplication of one fraction by another the usual rule results, as follows: Rule. — Multiply together the two numerators for a new numerator and the two denominators for a new denominator, and the fraction thus formed is the product desired. Similarly for division, % -f- % means that % is to be divided by 2 and multiplied by 5. But this is the same as the pair of operations expressed by using % as a multiplier. Hence %.^%=% X V2 = ^%. Hence for the division of one fraction by another the usual rule again results, as follows: Rule. — Invert the terms of the divisor and proceed as in multiplication. This might naturally be expected by remembering the rela- tion between multiplication and division, and that one is the exact inverse of the other. For the multiplication of a series of fractions into each other these principles work out as follows : 1^ X % X ?^ X % means that ^ is first considered as a subject and % as an opera- tor. Then the result of this is the subject and % is the operator and so on. The final result will be therefore 1X3X2XS = 3%3o. 2X5X7X9 In this result there is a numerator 30 whose factors are the nu- merators of the individual fractions, while similarly the denomi- nator 630 has for its factors the individual denominators. Apply- ing here the principles of [4], cross out from numerator and denominator any pair of common factors. This will shorten the operation and give the result in its lowest terms. Thus shortened the above case becomes : 1 X ^ X ^ X ^ ^ 1_ JZx^xTx^ 21 878 PRACTICAL MARINE ENGINEERING The propriety of striking out a common factor in both nu- rherator and denominator may also be seen by remembering that such a pair of factors denote, one a multipHcation and the other a division by the same number. These operations will offset each other and may therefore be omitted entirely. Cancellation. This striking out of common factors from both terms of a fraction is known as cancellation, and is often of great value in simplifying an operation before proceeding with the actual multiplication and division. The following are addi- tional illustrations: ^ 7 2 14 _i6 21 22 ;^ X ;^ X ^; X ^^ 14 33 ^ 42 "" 8 ^ 18 - ^^ X ^^ X ^ X ;^ - 27 ^3 9 4 15 16 _27 ^ K ^ X 1^ X p I '8l''l6^"6^''V = ^;x;^x^^x 2 - 6 Expressions like 2X3X16 9X8 in which the number of factors in numerator and denominator is not the same are often encountered. All such expressions represent a series of multiplications of whole numbers and frac- tions as % X % X 16, or they may be considered as denoting a series of operations of multiplication and division, and in either case it follows that their reduction may be effected by cancel- lation as just described. Still otherwise such expressions may be considered as consisting of a numerator and denominator each resolved into factors, and hence in ready condition for reduc- tion by cancellation. Thus in the expression above 3 3 x^x ^^ _ 4 f^ T 3 Problems. — Perform the following operations : ^fXf)' 1X|). (f Xl|), (^Xf Xf), (JLxi^Xi), (|x-|x^) \3 ' tJ' -9 3-'' ^144 • 24^' Vo5 ' 13/' ^23 ' 16/' V3 ' ~i'J' Ans 1 -I- 3_6 -2_ lA li. oi li il li 128 4 ■ 7' 20 77' 27' 68' 3' ^' 3' 78' 5' 161' 17' COMPUTATIONS FOR ENGINEERS 879 [10] Complex Fractions In complex fractions either or both numerator and denomi- nator may consist of fractions or mixed numbers. Thus for example : 2^ % % ~%' IT" 1^' All such expressions may most conveniently be considered as ways of indicating operations, the numerator being the sub- ject of the operation and the denominator being the operator expressed as the divisor. Thus 2^ % % % = %-^3% = %-"/6 = %X-%6 = i^ 3% The reduction of such expressions becomes therefore simply a matter of the application of the rules and methods already given. Problems. — Reduce the following: 3% %+2ii %-%-.% +^^ 8% %-%X-^A 2%X%-i% Ans. 5^, 10%, %. Sec. 131. DECIMAL FRACTIONS' [i] In decimal fractions the denominator is always 10, 100, 1000, etc., or some power of 10. Instead of writing them in the usual way, however, a device is made use of to indicate the denominator without actually writing it. This is simply to write the numerator and to place a dot at such a point that there shall be as many figures on the right as there are ciphers in the de- nominator, using ciphers to the left of the significant figures if necessary to make up the needed number of places. In writing a mixed number the whole number part stands on the left of the dot or decimal point, which thus becomes a point of separation between the whole number and the fraction. Thus j-fl is written .7 100 "z 88o PRACTICAL MARINE ENGINEERING Too^ " " '007 O Q 10 .OOJ3 2-1-0 " " 2.7 ^^^TfI^ " " 162.043 In each case it is seen in the decimal that there are as many places on the right of the dot as there are cyphers in the de- nominator, and in this way the value of the denominator or unit of measure is indicated. There are no principles involved in decimal fractions different from those already discussed in common fractions, and the only difficulties in using them arise from the peculiar manner in which they are written. Without further discussion the rules for the handling of decimals will be given, all of which may be seen to follow from the principles already laid down. [2] To Reduce Decimals to Lower Terms Evidently all ciphers standing on the right of the decimal may be struck off as they disappear from both numerator and denominator. Thus .3500 = .35. [3] To Raise Decimals to Higher Terms Add ciphers to the right of the numerator as may be de- sired. Thus .35 = .350 = .3500. [4] To Reduce a Decimal Fraction to a Common Fraction Write the numerator and denominator as in common frac- tions and reduce to lower terms if possible. Example. — Reduce .35 to a common fraction. Operation : •00 100 20 [5] To Reduce a Common Fraction, Proper or Improper, to a Decimal Take the numerator for the dividend and the denominator for the divisor and proceed as in division of whole numbers, add- ing ciphers to the right of the dividend as may be necessary. Then point off according to the following rule : If the numerator or dividend is less than the denominator or divisor, the first figure of the quotient must stand on the right of the decimal point as many places as the number of ciphers added to the right of the dividend in order to enable it to contain the divisor. If the dividend is greater than the COMPUTATIONS FOR ENGINEERS 881 divisor, place the point after the figure of the quotient given by bringing down the last figure of the dividend in the opera- tion of division. It should be noted that this gives the general method for dividing one whole number by another and expressing the re- sult decimally. Examples. — Reduce ^%50 to a decimal. 2so)i6oo(.o64 1500 icwo 1000 Two ciphers are annexed in order to obtain the first figure 6 in the quotient. Hence this figure must stand in the second place to the right of the decimal point, and a cipher is added on the left of the 6 to bring it to this position. Reduce ^^*%5 to a decimal. Operation : 25)1647(65.88 220 150 200 147 200 125 200 The figure 5 of the quotient is given by bringing down the last figure 7 of the dividend, and hence the decimal point must come between this and the next figure of the quotient. Problems. — Reduce the following to decimals : 2. i_2 122 18 1 7 1 8 143 172 1 18 14 23 5' 5 ' 5 ' 250' 130' 4' 5o' 1440' 9600' 1900' 7' Ans. .4, 2.4, 24.4, .072, .1307 -I-, 4.5, 2.6, 1.1951 -f-, .001875, .007368 -|-, 3-2857 +■ [6] To Add Decimals Set down the decimals in a column so that the points shall all stand under each other. Then add as in whole numbers and bring down the decimal point in the sum under those standing above. Example. — ^Add .025, .64, .231, .4685, .003. Operation : * * If desired, the numbers may be filled out all to the same number of places, by adding ciphers on the right, such operation being, in fact, the reduction of the decimals all to the same denominator or unit of measure. In the summing, however, such ciphers play no part, and therefore the filling out is unnecessary in the actual operation. 882 PRACTICAL MARINE ENGINEERING .025 .64 .231 .4685 .003 1.367s [7] To Subtract Decimals Set down the subtrahend under the minuend, the two deci- mal points one under the other, adding ciphers to the right if necessary to fill out to the same number of places. Then sub- tract as in whole numbers and bring down the decimal point un- der those above. Example. — Subtract .263 from .83. Operation : .830 .263 .567 [8] To Multiply Together Two Niunbers Expressed Decimally Multiply as in whole numbers and point off for the decimal portion as many places as there are in the two factors taken together. Examples: .16 X 24, = 3.84 72. X 0004 = .0288 .162 X .041 =: .006642 21.14 X 13- = 274.82 21.14 X .13 = 2.7482 21.14 X 1-3 = 27.482 Problems. — Perform the following multiplications: 2.72 X 1.4 143.26 X 24.2 12.16 X 018 4214.3 X 22.3 .14 X .21 .06 X .0084 Ans. 3.808, 3466.892, .21888, 93978.89, .0294, .000504. [9] To Find the Quotient of Two Quantities Expressed Decimally Clear both dividend and divisor of decimals by moving the point to the right an equal number of. places in each, adding ciphers as may be necessary. The number of places moved will be that necessary to clear the term of higher order. Thus modified, consider the two terms as whole numbers and proceed with the division, pointing off according to the rule given above for the reduction of a common fraction to a decimal. COMPUTATIONS FOR ENGINEERS 883 Examples: .16 .16 -^2.5, or = -iJ_ = .o64 2.5 -"• 1.6 1.6-^2.5, or = i|=.64 2.S '' 1.6 1.6^ .25, or =:ilo=6.4 ■25 16 16. -^ .025, or = i«o'") = 640. .025 ^^ .016 .016 - 250, or = jj^lr^ = .000064 250 1.6 1.6 H- .243, or = ^^- 6-5761 + •243 Problems. — Perform the following divisions: 7.25 -^ 16 72.54 ^ 6.4 .00864 -i- .14400 8.64 -^ .0144 .96 -^ .024 1.25 -H .0025 Ans. .4531 +, 11,334 +. 0000006, 600, 4000, 500. Sec. 132. PERCENTAGE [i] In percentage, fractional relations are expressed deci- mally, but it is understood that the denominator shall always be 100. The fractional unit is therefore always one one-hun- dredth of the principal unit, and therefore occupies to it the same relation as that of the cent to the dollar. The word per- cent is commonly represented by the symbol %, so that 16% is the same as 16 percent or .16, while 5% equals similarly .05, etc. Care must be had not to fall into confusion with the use of both the decimal point and % mark. Thus .4% is not .4, but .4 of one percent or .004. A number written in percentage is usually an operator, and not a quantity, or measure by itself. Thus 16% is not a quantity by itself, but rather expresses the relation between two quantities, or represents an operation to be performed on one quantity in order to obtain another. The handling of percentage is the same as that of decimals, re- membering that the term percent is simply a special name for a fractional unit one one-hundredth of the principal unit, what- ever the latter may be, and that it is with this fractional unit 884 PRACTICAL MARINE ENGINEERING that all quantities are measured in percentage operations. Re- membering the rules for decimals the following is readily seen: Examples : i6 percent of 80 = 80 X -iS = 12.8. 3 percent of 2.1 =2.1 X .03 = .063. 23 percent of $i45-24 = $i4S-24 X -23 = $33-4052, or $33.41. From the above it follows that: To reduce any number expressed in percent to terms of decimals, divide by lOO and express the result decimally, or shift the decimal point two places to the left; while to reduce any decimal to terms of percent multiply by ICXD or shift the decimal point two places to the right. Thus Percent .16 = 16. 1.60 = 160. .016 := 1.6 .0016 = .16 To Find the Percentage Ratio Between Two Numbers Rule. — Multiply the dividend or numerator by 100 and then divide and express the result as a decimal according to the rules of Sec. 131 [9]. Thus 7 -=- 25, or -2^ = .5^ percent = 28 percent. Similarly Percent 3 -f- 5° or = 6 SO 7 7 -^ ID or = 43.7s 16 6.4 6.4 -f- 160 or = 4 160 6,4 6.4 -f- 16 or = 40 16 6.4 6.4 -^ 1.6 or • = 400 1.6 6.4 6.4 -i- .16 or =; 4000 .16 In percentage problems it is usually required to find certain percentages of various quantities, or to find the percentage re- lations between various quantities. The only difficulty likely to COMPUT AXIOMS FOR ENGlNEliRS 885 arise is not with the operations themselves, but with a correct interpretation of the. problem and a clear imderstanding as to the relations desired. Examples: (i) A broker buys a ship for $160,000 and sells her for $172,000. What percent does he gain? Solution: The amount of gain is $12,000. To find what per- cent this is of $160,000, proceed as above and find 12,000 -=- 160,000 = 7.5% = .075. (2) A broker buys a ship for $160,000 and sells her so as to gain 6%. What was the selling price? Solution: Six percent of $160,000 ^ .06 X $160,000 := $9,600. Hence selling price = $160,000 + $9,600 = $169,600. (3) A broker sells a ship for $171,200 and thereby gains 7% on her cost. What was the cost ? Solution: Since he gains 7% or 7 cents on every dollar of cost, there will be $1.07 in the selling price for every $1.00 in tVie cost price. Hence the cost price will be as many dollars as 1.07 is contained in 171,200 or 160,000. Problems: (4) Thirty-six pounds of gun metal contain the following: Pounds Copper 32 Tin I Zinc 3 Total 36 Find the percentage composition. Ans. Percent Copper 32/36 or 88.89 Tin 1/36 or 2.78 Zinc 3/36 or 8.33 (5) A ship starts on a voyage of 2,200 miles. After going 800 miles what percent of the voyage remains to be covered? Ans. 63.6%. (6) A ship starts on a voyage of 1,800 miles. After three days she has made 42% of the distance. With 12% increase of speed for the rest of the time, how long will it take her to finish the voyage? Ans. 6.699 days — Total on voyage. (7) A marine engine requires 2.1 pounds of coal per indi- !:86 PRACTICAL MARINE ENGINEERING cated hori:2power per hour. After certain changes are made the figure is reduced to 1.89 pounds. What is the percentage gain? Ans. 10%. In one ton of coal (2,240 pounds) there was found to be 250 pounds of ashes. What percent of the coal was combustible ? Ans. 88.8%. Sec. 133. COMPOUND NUMBERS WEIGHTS AND MEASURES [i] Long or Linear Measure Inches. Feet. Yards. Rods. Furlongs. Miles. Meters. I •0833 .0278 .00505 .000126 .000016 • 0254 12 ■333 .0606 .00152 .000189 • 305 36 3 .182 •00455 .000568 .914 198 i6>^ sV^ ^i • 025 •00313 ^•°ll 7920 660 220 40 =1 • 125 201 . 166 63360 5280 1760 320 8 =1 1609.3 39-371 3.281 1.094 .199 •00497 .000621 "' . Special 6 feet =z 120 fathoms — 6080.27 feet =1 6080 feet — 3 nautical miles =: Measures fathom, cable's length. nautical mile (United States), nautical mile (British), marine league. [2] Avoirdupois Weight or Measure Ounces. Pounds. Tons. Drams. Long or British. Short or Legal. Kilos. I 16 256 573440 512000 564^38 .0625 = 1 16 35840 32000 35^27 ■ 0039 .0625 = I 2240 2000 2 . 2046 .000446 = 1 . 000984 .0005 1. 12 = 1 .001102 •02835 •4.536 1016 907 = I COMPUTATIONS FOR ENGINEERS [3] Square Measure Square Inches. Square Feet. Square Yards. Square Meters. I 144 1296 1550 .00694 9 10.765 . 000772 .1111 = I 1. 196 .000645 .0929 .8360 = I [4] Cubic or Volume Measure Cubic Inches. Cubic Feet. Cubic Yards. Cubic Meters. I 1728 46656 61033 .0005788 27 35^32 •037 1.308 • 0283 •764s = I = [5] Liquid Measure Cubic Gills. Pints, Quarts. Gallons. Barrels, Inches. U.S. British. 8.665 34 659 69.318 231 277.274 ■ -1154 4 8 32 1008 .02885 •25 2 8 8 252 .0144 ■125 •50 = 1 4 4 126 •00433 •03125 •125 •25 = 1 1.2 3I>^ .00361 • 3125 •125 •25 .833 "31^^ .003175 •003175 - [6] Dry Measure Cubic Inches. Pints. Quarts. Pecks. Bushels. I 33-6 67.2 537^6 2150.42 .02976 ^2 16 64 .01488 •5 = 1 8 32 .00x86 .0625 •125 = 1 4 .0004641 .015625 •03125 • 25 = 1 [7] I register ton I United States shipping ton I British shipping ton Shipping Measure ^ 100 cubic feet. ( 40 cubic feet, or ' 32.14 United States bushels. !42 cubic feet, or 32.72 imperial bushels. PRACTICAL MARINE ENGINEERING [8] The Metric System of Weights and Measures Measures of Length 10 millimeters (mm). 10 centimeters 10 decimeters 10 meters 10 dekameters 10 hektometers =: I centimeter cm. = I decimeter dm. = I meter m. =: I dekameter Dm. hektometer Hm. kilometer Km. Measures of Surface (Not Land) 100 square millimeters (mm'') = i square centimeter cmj 100 square centimeters = i square decimeter dm'' 100 square decimeters ^ i square meter m" Measures of Volume 1000 cubic millimeters (mm°) =: i cubic centimeter cm' looo cubic centimeters =: i cubic decimeter dm' 1000 cubic decimeters = i cubic meter m' Measures of Capacity centiliter cl. deciliter dl. liter 1. dekaliter Dl. hektoliter HI. kiloliter Kl. (mi). lo milliliters lo centiliters 10 deciliters . 10 liters 10 dekaliters.. 10 hektoliters Note : — The liter is equal to the volume occupied by i cubic decimeter of pure distilled water at its temperature of maximum density, or 39.2 degrees F. Measures of Weight 10 milligrams (mg). 10 centigrams 10 decigrams 10 grams 10 dekagrams 10 hektograms 1000 kilograms Note : — The gram is the weight of i cubic centimeter of pure dis- tilled water at a temperature of 39.2 degrees F. ; the kilogram is the weight of I liter of water ; the ton is the weight of i cubic meter of water. [9] Conversion Tables English Measures Into Metric I centigram eg. I decigram dg. I gram g. I dekagram Dg. I hektogram Hg. I kilogram Kg. I ton T. English. Inches to Feet to Pounds to Gallons to Millimeters. Meters. Kilos. Liters. I 25.4001 .304801 • -45359 3-78544 2 50.8001 . 609601 .90719 7 57088 3 76.2002 .914402 1.36078 "•35632 4 loi . 6002 I. 219202 1.81437 15-14176 5 127.0003 1.524003 2.26796 18.92720 6 152.4003 1.828804 2.72156 22.71264 7 177-8004 2.133604 3-17515 26.49808 8 203 . 2004 2.438405 3.62874 30.28352 9 228.6005 2-743205 4.08233 34.06896 COMPUTATIONS FOR ENGINEERS Metric Measures Into English 889 Metric. Meters to Meters to Kilos to Liters to Inches. Feet. Pounds. Gallons. I 39-3700 3.28083 2 . 20462 .26417 2 78.7400 6.56167 4.40924 -52834 3 118.1100 9 84250 6.61386 ■79251 4 157-4800 13- 12333 8.81849 1.05668 5 196.8500 16.40417 11.02311 1.32085 6 236.2200 19.68500 13-22773 1-58502 7 275.5900 22.96583 15-43235 I. 84919 8 314.9600 26 . 24667 17.63697 2. I 1336 9 354.3300 29.52750 19.84159 2.37753 Use of the Conversion Tables Example: Change 243.6 feet into meters. 243.6 = 200 + 40 + 3 + .6. These parts separately may all be directly converted from the table by an appropriate use of the decimal point. Thus, keeping simply three places of decimals 200 feet =: 60.960 meters. 40 feet =. 12.192 meters. 3 feet = .914 meters. .6 feet = .183 meters. Hence, adding: 243.6 feet =: 74.249 meters. Other examples may be solved in an exactly similar manner. [10] Reduction of Compound Numbers Example — (i) Reduce 7 miles, 12 rods, 10 feet to feet. This may be done in two ways : (a) Reduce the rods to feet and add in the 10 thus: 12 X i6>4 + 10 = 198 + 10 = 208. Then reduce the miles to feet and add in the 208 thus : 7 X 5.280 + 208 = 36,960 + 208 = 37,168 feet; or (b) reduce the miles to rods and add in the 12 thus: 7 X 320 + 12 = 2,240 + 12 = 2,252. Then reduce the rods to feet and add in the 10 thus: 2,252 X i6>^ + 10 = 37.158 + 10 = 37,168 feet. The result will, of course, be the same in either case. The factors for mak- the reductions may be either taken from the tables of Sec. 133 or readily found by separate computation. Example — (2) Reduce 37,168 feet to miles, rods and feet. This is the inverse of the above and may likewise be solved in two ways : (a) Reduce the feet to miles with feet as a remain- 890 PRACTICAL MARINE ENGINEERING der, thus: 37,168 -=- 5,280 = 7 miles and 208 feet remainder. Then reduce the feet to rods with feet again as a remainder, thus: 208 -=- iSyz = 12 rods and 10 feet remainder. Hence 37,168 feet = 7 miles, 12 rods, 10 feet: or (b) reduce the feet to rods with feet as a remainder, thus: 37,168 -=- 161^ = 2,252 rods and 10 feet remainder. Then reduce the rods to miles with rods as a remainder, thus : 2,252 -^ 320 = 7 miles and 12 rods remainder. Therefore, as before, 37,168 feet = 7 miles, 12 rods, 10 feet. These examples will sufficiently illustrate the mode of pro- cedure so that all similar problems may be readily solved. Addition, Subtraction, Multiplication and Division of Compound Numbers [11] Addition of Compound ,Numbers Example — Add the following: 16 miles 43 rods 12 feet 21 miles 308 rods 9 feet 7 miles 318 rods 7V2 feet 44 miles 669 rods 2854 feet or 46 miles 30 rods 12 feet The columns are added as in whole numbers and the sums are brought down. This gives a correct result, but it is not in its simplest form, since 28J/2 feet are more than i rod, and 669 rods are more than i mile. Therefore reduce the feet to rods, giving I rod and 12 feet, and then carry the i to the column of rods, giving 670. Then reduce the rods to miles, giving 2 miles and 30 rods, and carry the 2 to the column of miles, thus giving the final result as stated in the second line of the answer. [12] Subtraction of Compound Numbers Example — In the following subtract the lower from the upper : 36 miks 18 rods 14 feet 21 miles 43 rods 6 feet In the column of rods, the 43 being greater than the 18, it is necessary to borrow i mile or 320 rods from the 36 miles, thus putting the minuend into the form as follows: COMPUTATIONS FOR ENGINEERS 891 35 miles 338 rods 14 feet 21 miles 43 rods 6 feet 14 miles 295 rods 8 feet Then subtract each column as in whole numbers, thus giv- ing the result as shown. In the actual operation the borrowing may be done mentally, thus making it unnecessary to rewrite the minuend as shown. [13] Multiplication of Compound Numbers Example — Multiply 14 miles, 276 rods, 12 feet by 5. Operation : 14 miles 276 rods 12 feet 5 70 miles 1,380 rods 60 feet 74 mile? 103 rods 10^ feet First multiply each term by the multiplier 5 and obtain the re- sult entered in the first line below. This is correct, but not in its simplest form, since 60 feet are more than i rod and 1,380 rods more than i mile. Therefore reduce the feet to rods, giv- ing 3 rods and loj^ feet, and carry the 3 to the column of rods, giving 1,383. Then reduce the rods to miles, giving 4 miles and 103 rods and carry the 4 to the column of miles, giving the final result as stated in the second line of the answer, [14] Division of Compound Numbers Example — Divide 142 miles, 296 rods, 15 feet by 6. Operation : 6)142 miles 296 rods 15 feet 23% miles 49% rods 2^4 feet First divide each term separately by the divisor 6 and obtain the result as written below the line. This is correct, but not in its simplest form, since % mile may be reduced to rods and feet, and ^A rod may be reduced to feet. Therefore simplify as follows : 23 49 25^ 213 II 23 262 I3J4 Since there are 320 rods in i mile, we have % miles := % X 320 rods = 213?'^ rods. Set down the 213 in the column of rods, and, adding the % to the other % belonging with the 49, we have 892 PRACTICAL MARINE ENGINEERING % rod in addition. Since there are i6^/^ feet in i rod, % rod = % X 16*/^ = II feet. This enter in the column of feet and add, giving the final result as shown. These examples will sufficiently illustrate the principles in- volved in the addition, subtraction, multiplication and division of compound numbers, so that all similar problems may be readily solved. Sec. 134. DUODECIMALS It is often necessary to determine areas or volumes, the dimensions of which are given in feet and inches. To this end it is necessary either to reduce the dimensions to feet and deci- mals, or treat them directly by the method of duodecimals. In this system of expressing numbers, us6^ is made of a series of numerical units, each one-twelfth of the unit of next higher order. The fundamental unit will be either the linear foot, the square foot, or the cubic foot, according to the geometrical nature of the quantity to be expressed. Lengths are thus expressed in feet, inches and twelfths; or, as they are termed feet, primes and seconds. Similarly areas are expressed in square feet, primes and seconds, and volumes in cubic feet, primes and seconds, the prime in each case being one-twelfth the foot, and the second one-twelfth the prime. Duodecimals should be written with a series of accents thus : 6° — 7' — 10". The ° stands for the fundamental unit, the foot, which may be a length, an area or a volume, according to the problem ; the single accent ' stands for the prime, and the double accent " for the second.* Thus, if the unit were a foot of length, the above expression would mean 6 feet, 7 primes or inches, and 10 seconds or ^9i2 inch. If the unit were a square foot it would mean 6 square feet, %2 of a square foot and % of M2, or ^%44 of a square foot. Hence, in all, 6 square feet and 94 square inches. If the unit were a cubic foot it would mean 6 cubic feet, ''A2 of a cubic foot and ^9i2 of M2, or ^%44 of a cubic foot. Hence, in all, 6 cubic feet and 1,128 cubic inches. The importance of noting the character of the fundamental unit is thus clearly indicated. * Care must be taken to avoid confusion between this method of writing duodecimals and the common method of expressing feet and inches by one and two accents. COMPUTATIONS FOR ENGINEERS 893 Addition of Duodecimals. The addition of duodecimals is carried on exactly as in compound numbers, quantities of the same order being written under each other and their sums, where necessary, reduced to units of higher order by division by 12. Example — Add 17° — 8' — 10" 14° — 2' — 9" 7° — i' — 8" Sum = 38° — II' — 27/12" = 38° — 13/12' — 3" = 39° — I' — 3" Subtraction of Duodecimals. The subtraction of duo- decimals is carried on exactly as in compound numbers, quan- tities of the same order being borrowed where necessary. Multiplication of Duodecimals. This operation, which is the one of greatest importance in the treatment of duodecimals, is carried on according to the following: Rule — Set down the two quantities, with terms of the same order under each other. Multiply each term of the multiplicand by each term of the multiplier. The order of any such product will be determined by adding the indices of the two terms used. If the product is greater than 12, reduce to the next higher order by dividing by 12, and set down the quotient and re- remainder in their proper columns. Proceed in this way, taking care in the product to set down terms of the same order under each other. Then add and reduce where necessary to the higher order by dividing by 12. Example — Multiply together : 6° - - 10' - -4" m 4°- - 8' 4 6 2 8 3 I 8 24 4 4 31° II' 2" 8'" First 8' X 4" = 32'" = 2" — 8'", which is set down. Next 8' X 10' = 80" = 6' — 8", which is set down. Next 8' X 6° = 48' = 4°, which is set down. In the same way use the other term of the multiplier, 4°, and then add and reduce the columns as shown. For purposes with which the marine engineer is concerned, feet and inches are alone involved, and operations with duo- decimals are correspondingly simplified. 894 PRACTICAL MARINE ENGINEERING Examples — (i) Find the area of a boiler plate 12" — 5' long by 6° — 7' wide. Multiplying as before, find for the product 81" — 8' — 11", or taking the result to the nearest prime, 81" — 9' or 8i?i2 square feet or 81 square feet — 108 square inches. (2) Find the volume of a bunker 26° — 4' by 9° — 7' by 7° — 10'. Taking first the product of 26° — 4' by 9" — / there results 252° — 4' — 4". Then multiplying this by 7" — 10' is obtained i,gy6° — lo' 11" — 4'", or taking the result to the nearest prime, 1,976° — II', or i,976i'/i2 cubic feet or 1,976 cubic feet — 1,584 cubic inches. Sec. 135. RATIO AND PROPORTION [i] Simple Proportion The ratio between two numbers is simply their numerical relationship expressed as the quotient of the first divided by the second. Thus the ratio of 6 to 3 is 2; of 1.2 to 3 is .4; of 4 to 5 is .8, etc. Ratio is often expressed by the sign : which is simply an abbreviation of the sign of division ->. Thus 6 : 3 = 2; 1.2 : 3 ^ .4, etc. Ratio is- also expressed by the sign of division or in the form of a fraction. Thus 6 : 3, or 6 -H 3, or % = 2 1.2 : 3, or 1.2 H- 3, or 1% = .4, etc. [i] A proportion is a statement of the equality of two ratios. The equality is commonly expressed by the symbol : : Thus : 6 : 3 : : 4 : 2 (i) A. proportion may also be written in other ways, as follows : 6:3 = 4-2 (2) % = % (3) A proportion always contains four terms, two for each ratio, and when written as in (i) and (2) the first and last terms are called extremes and the second and third are called means. To solve a proportion three terms must always be known and then the remaining terxn can always be found. From the na- ture of a proportion it follows that the product of the extremes must equal the product of the means, and this gives the usual rule for solution as follows : Rule — If the unknown term is an extreme, multiply together COMPUTATIONS FOR ENGINEERS 895 the two means and divide by the other extreme. If the unknown term is a mean, multiply together the two extremes and divide by the other mean. In either case the quotient will give the re- maining term desired. In a proportion two of the terms always relate to one kind of quantity, while the other two relate to another. Likewise two of the terms always relate to one set of conditions, while the other two relate to another set. In problems to be solved by proportion, therefore, where three terms must be given, two terms will be of one kind and the remaining term will be of another and of the same kind as the answer. Also two terms will relate to the given set of conditions, and the remaining term to the set involving the unknown term or answer. Again, proportions are of two kinds, direct and inverse. In a direct proportion the relation between the two quantities dif- ferent in kind is such that both increase or decrease together. In an inverse proportion the relation between these two quantities is such that one increases as the other decreases. Thus if the question involves the relation between distance and speed, the time being the same, the proportion is direct, because, for a given time, the more speed the more distance, or the more distance the more speed. On the other hand, if the question involves the relation between speed and time for a given distance, the pro- portion is inverse, because for a given distance the more speed the less time, or the more time the less speed, and vice versa. General knowledge of the relation between the quantities in- volved will thus enable to determine whether the proportion will be direct or inverse. Excmiple of a direct proportion : If a ship steams 1,400 miles in 5 days, how far will she steam in 8 days at the same rate? Here two of the given terms are days and one is miles, be- ing of the same character as the answer desired. Also two relate to one performance or set of conditions (1,400 in 5 days), while the other relates to another set (the desired performance in 8 days). The right to solve this example by direct proportion lies in the fact that the relation between the 5 days and 1,400 miles must be the same as that between the 8 days and the distance desired, and hence there must be an equality in the ratios showing these relations, and similarly for problems of like char- acter. 896 PRACTICAL MARINE ENGINEERING A simple direct proportion, like that involved in the example above, may be stated in various ways, of which two will serve the present purpose. (2) (2) (i) (i) (a) Ans. (miles) : 8 (days) : 1400 (miles) : S (days) (2) (i) (2) (i) (b) Ans. (miles) : 1400 (miles) : : 8 (days) : 5 (days) The numbers in () relate to the two sets of conditions, the first being the set given, and the second being the set for which the distance is desired. It is thus seen that the proportion may be stated as in (a), with each set of conditions forming a ratio, the items of proportion alternating: miles, days, miles, days; or it may be stated as in (b), with the set of conditions alternating 2d, 1st, 2d 1st, the two items of each ratio being the same. Example of an inverse proportion. If a ship at 10 knots does a certain trip in 5 days, how many days will be required at 12 knots? The relation between time and speed is such that, for a given distance, the more speed the less time, or the less speed the more time. The time is, therefore, said to be in such case inversely proportional to the speed. That is, for example, if the speed is doubled the time will be hah'ed, etc. An inverse proportion may be stated as follows : (2) (I) (I) (2) (c) Ans. (days) : 10 (knots) : : 5 (days) : 12 (knots) (2) (I) (I) (2) (d) Ans. (days) : S (days) : : 10 (knots) : 12 (knots) The difference between these methods of statement ind those above for direct proportion will be readily seen by com- parison. As another general way of stating a proportion whether ' direct or inverse, proceed as follows : Put the answer, or letter representing it, for the first term, and the other quantity of the same kind for the second term. Then, according to the first term or answer should be greater or less than the second term, write the third and fourth terms in the same order. That is, if the relation of the quantities is such that the answer should be greater than the second term, write the third and fourth terms in the order greater — lesser; or if the answer should be less than the second term, write the third and fourth terms in the order lesser — greater. COMPUTATIONS FOR ENGINEERS 897 After having become familiar with the methods of stating a proportion, the names of the quantities and tlie numbers de- noting the sets of conditions may, of course, be omitted, and there would be instead of (a) and (b) Ans. : 8 : : 1400 : 5 Ans. : 1400 : : 8:5 Solving either of these according to the rule given Distance = 8 X 1400 -^ S = 2240 Ans. Likewise instead of (c) and (d) Ans. : 10 : : 5 : 12 Ans. : S : : 10 : 12 Solving either of these Days =: 5 X 10 -;- 12 = so -^ 12 = 4 1/6 Ans. [2] Compound Proportion In many cases the result depends on more, than one chang- ing condition. In such case the problem is treated by the method of compound proportion as illustrated in the following example. When coal is $4.20 per ton the fuel bill for a ship requiring 34 tons per day on a voyage of 2,100 miles is $1,020. At the same speed what would be the bill on a 2,800-mile voyage, with coal at $3.60 per ton, and a consumption of 40 tons a day? The resulting cost evidently depends on three conditions, and the proportion is stated as follows: 3.60 : 4.20 Ans. : 1020 : : 40 : 34. 2800 : 2100 This consists really of three simple direct proportions, each stated exactly according to the rules already given, as may be readily seen. For the solution of such a proportion the same rules may be used, but the "product of the means" or the "product of the extremes" must here be understood to mean the product of all separate numbers forming these terms. Thus for the foregoing proportion, multiply together the means and divide by the extremes, giving as follows : 3.60 X 40 X 2800 X 1020 Ans. = = $i37-43- 4.20 X 34 X 2100 Cancellation can usually be made to assist in the reduction of such expressions, and thus readily bring the answer as stated. Where the relations are such that the answer is inversely SgS PRACTICAL MARINE ENGINEERING proportional to certain of the varying conditions, the ratio in- volving this part of the proportion will be inverse instead of direct. In fact, each of the ratios in the second part of the proportion should be carefully examined in order to make sure whether it should be stated direct or inverse. Example involving both direct and inverse proportion. When coal is $4.00 per ton, the fuel bill for steaming a certain distance at a speed of 12 knots, with a ship requiring 48 tons per day, is $1,800. For the same distance, what would be the bill if the ship steams 10 knots on 40 tons per day, with coal at $3.20 per ton? The statement would be as follows : 3.20 : 4.00 (direct) Ans. : 1800 : : 12 : 10 (inverse) 40 : 48 (direct) In this case 1800 X 3-20 X 12 X 40 Ans. = = $1440. 4,00 X 10 X 48 Problems in Proportion ( 1 ) An engine with 34 pounds mean effective pressure gives 1,400 indicated horsepower. All other conditions remaining the same, what would the engine give with 39 pounds mean effective pressure ? Ans. 1,606 indicated horsepower. (2) An engine making 98 revolutions per minute gives 1,800 indicated horsepower. All other conditions remaining the same, what would the engine give if the revolutions were 90? Ans. 1,653 indicated horsepower. (3) An engine with stroke of 3 feet gives 900 indicated horsepower. All other conditions remaining the same, what would be the power with stroke of 42 inches ? Ans. 1,050 indicated horsepower. (4) An engine cylinder whose area is 1,200 square inches gives 800 indicated horsepower. All other conditions remaining the same, what would be the power with an area of 1,000 square' inches ? Ans. 666.67 indicated horsepower. (5) A given engine has mean effective pressure 33, revolu- t ns 120, stroke 42 inches, and gives 1,800 indicated horsepower. COMPUTATIONS FOR ENGINEERS 899 Other conditions remaining the same, what would be the power with a mean effective pressure of 38, revolutions of 100 anc stroke of 4 feet? Ans. 1,974 indicated horsepower. (6) A boiler with tubes 7 feet long and 2^ inches diameter has 2,168 square feet of tube-heating surface. What would be the surface, with the same number of tubes, 7 feet 6 inches long and 2^ inches diameter ? Ans. 2,112 square feet. (7) An engine with 34 pounds mean effective pressure and 98 revolutions develops a certain power. If the mean effective pressure were 38 pounds, what revolutions would give the same power ? Ans. 87.7 revolutions. (8) A given engine has a mean effective pressure 33, revo- lutions 120, stroke 42 inches, and develops a certain power. With mean effective pressure of 38 and stroke of 3 feet, what would be the revolutions for the same power? Ans. 121.6 revolutions. (9) A pump making 40 double strokes per minute can empty a tank in i ^ hours. In what time could the same pump, making 30 double strokes per minute, empty a second tank, 20 percent larger than the first? Ans. 2.4 hours. (10) A propeller at 100 revolutions and 20 percent slip gives a speed of 18 knots. What will be the speed at 120 revo- lutions and 25 percent slip ? Ans. 20.25 knots. Sec. 136. EVOLUTION AND INVOLUTION* [i] Evolution is the operation of raising a number to successive powers, or of multiplying it into itself as a factor a certain number of tim.es. The number of times the number is used as a factor is called the index of the power, and is indicated by a small figure written to the right and above as follows : * Hand books with convenient tables of powers and roots are so common at the present day that the engineer has small use for the actual operations of raising to powers or of extracting roots. In practice the use of such tables is always counseled as tending toward accuracy and speed. The importance of these operations, however, merits a brief outline of the process as given herewith. 900 PRACTICAL MARINE ENGINEERING 5' = SXSXS =125 3° = 3 X3X3 X3X3 = 243 Evolution involves, therefore, simply continued multiplica- tion. The powers most commonly used by the engineer are the second and third, or square or cube, as they are commonly called. Involution is the inverse of evolution, and consists in finding a number which, used on itself as a factor a certain number of times, will produce a given number. The former is then called the root of the latter. The number of times the root is used as a factor is called the index, and is represented either by writing this number at the upper left hand angle of the sign of involution, V , or by the use of a fractional index, written as in evolution. The roots most commonly used by the engineer are the square and cube roots, corresponding to the second and third or square and cube powers. When square root is indicated by the symbol V , it is customary to omit the 2 from the upper angle. Thus: 1/27 or (27)! = 3 because 3 X 3 X 3 = 27. •1/49 or (49) i = 7 because 7 x 7 = 49. Occasionally the engineer has to deal with the index f, which is simply a short way of indicating two operations, (i) Raising to the square. (2) Extracting the cube root. Thus (64) ' means the 3d root of the 2d power of 64, or the 2d power of the 3d root of 64. Either order of operation will give the same result. Thus: (64) = 1/64 X 64 = 1/4096 = 16 or (64)^ = [Vel] = 4' = 16 [2] To Extract the Square Root This is best illustrated by an example. Find the square root of 746.2. Rule* — (i) Point off the given number into periods of two * The brackets [ ] contain the numbers in the example which corre- spond to the special indication of the rule, and thus make its application to the given case more easily followed. COMPUTATIONS FOR ENGINEERS 901 figures each, beginning at the right hand or at the decimal point, if there is one, and in the latter case point both ways, adding ciphers on the right of the decimal as may be necessary to com- plete the periods. Thus : Number Pointed Off 2643 2643 867 867 424.362 4-24.36-20 .024 .0240 .6 60 (2) Write a on the left, thus heading two columns (i) and (2), as shown. Find by trial the greatest number [2] which when squared is equal to or less than the left hand period. Put this on the right as the first figure of the root. U) (2) o 7-46.20(27.316 ■+■ 2 4 2 346 2 329 40 1720 7 1629 47 9120 7 5461 540 363900 _3 543 3 5460 I 5461 I 54620 (3) Place this figure [2] under the in column (i) and add. Multiply the sum [2] by the root figure [2], and place the product [4] under the left hand period in column (2). This product will be, of course, the square of the root figure. Sub- tract and bring down the next period for a partial dividend [346]. (4) Again place the root figure [2] on the left and add [4]. Annex a and the result [40] will be a trial divisor for the next root figure. (5) Divide and take on trial the resulting whole number for the next root figure [7] . 902 PRACTICAL MARINE ENGINEERING (6) Bring down this figure [7] in column (l) under the 0. Add and multiply the sum [47] by the same root figure [7] and place the product [329] in column (2) under the partial dividend. Subtract and bring down as before for a new partial dividend [1720]. (7) Place the root figure [] again 1n column (i), add and annex a cipher for the new trial divisor [540]. (8) Find another root figure as before and proceed in this manner till as many figures are obtained as desired. If the product found, as in (6), is greater than the partial dividend, it indicates that the trial figure was too great, and the next lower must be taken. If at any time the trial divisor is greater than the partial dividend, enter a in the root, bring down the next period in column (2) for a new partial dividend, annex an on the right in column ( i ) for a new trial divisor and proceed as before. [3] To Extract the Cube Root This is best illustrated by an example. Find the cube root of 12,593. (1) 3 (2) 4 12.593 (23.26 8 2 2 i 4593 4167 — — 1^^^ 4 66 2 3 1200 189 426000 320168 60 690 3 2 1389 198 105832000 — 63 692 3 2 158700 1384 694 2 160084 1388 6960 I6I47200 'jf?M/^— Point off the given number into periods of three figures each, beginning at the right or at the decimal point, if there is one, and in the latter case point both ways, adding ciphers on the right of the decimal as may be necessary to com- plete the periods. Thus : COMPUTATIONS FOR ENGINEERS 903 Number Pointed Off 1724 1724 17243 17243 17-24 17-240 .64 .640 .0032 .O03'2O0 (2) Write ciphers' on the left thus, heading the columns (i), (2) and (3), as shown. Find by trial the greatest number [2] which when cubed is equal to or less than the left hand period. Put this on the right as the first figure of the root. (3) Place this figure under the in column (i), add, multi- ply sum [2] by root figure [2], place product [4] in column (2), add, multiply sum [4] by root figure [2] again, and place product J8] in column (3) under left hand period. This product will be, of course, the cube of the root figure. Subtract and bring down the next period for a partial dividend [4593] - (4) Again place the root figure [2] in column (i), add, mul- tiply sum [4] by root figure, put the product [8] in column (2), and add [12]. (5) Again place the root figure [2] in column (i), and add as before [6]. (6) Annex one o to the result in column (i) [60] and two os to that in column (2) [1200]. The latter is then a trial divisor for the next root figure, which is thus seen to be probably 3. (7) The same process of bringing down, adding and multi- plying in columns (i), (2) and (3) is then repeated as just described, and as shown in the example. Continue in this way until as many figures of the root are found as are desired. If the final product to be entered in column (3) is greater than the partial dividend, it indicates that the trial figure was too great, and the next lower must be taken. If at any time the trial divisor is greater than the partial dividend, enter a o in the root, bring down the next period in column (3) for a new partial divi- dend, annex one in column (i) and two os in column (2) for a new trial divisof, and proceed as before. It will be noted that in these methods for square and cube root the former requires for each root figure two operations in column (i) and one in column (2), while the latter similarly requires three operations in column (i), two in column (2) and one in column (3). Care should be taken that none of these is omitted, and that the entire process is carried through with regu- larity and order. 904 PRACTICAL MARINE ENGINEERING Sec. 137. MATHEMATICAL SIGNS, SYMBOLS AND OPERATIONS Mathematical signs are simply shorthand methods of indi- cating mathematical language. Those most commonly met with are the following: + The sign of addition called plus. This means that the two numbers or quantities between which it is placed are to be added. Thus 12 + 3 is read 12 plus 3 and means that 12 and 3 are to be added, the result being 15. — The sign of subtraction called minus. This means that the number or quantity which follows the sign is to be subtracted from that which preceeds it. Thus 12 — 3 is read 12 minus 3 and means that 3 is to be taken from 12, the result being 9. X The sign of multiplication. This means that the two numbers or quantities between which it is placed are to be mul- tiplied together. Thus 12 X 3 is read 12 times 3 or 12 multi- plied by 3, the result being 36. -^ The sign of division. This means that the number or quantity which precedes the sign is to be divided by that which follows. Thus 12 -^ 3 is read 12 divided by 3, the result being 4. / A sign of division. A fraction is really a mode of ex- pressing division, and a common way of writing a fraction all in one line is to make use of the oblique line. Thus 12/3 means the same as -V- or 12 -=- 3 or 4. Frequently the horizontal line — as shown is used, thus : ^, J4, 1-2 all indicate one-half, or i divided by 2. The horizontal line used in this connection must not be confused with the minus sign ; usually the sense is plainly indicated by the connection in which it is used. . Placed before and in line with the bottom of a number is a decimal point, showing that the number is the numerator of a fraction which has some power of 10 for its denominator; as .1 ~ h' '^5 ^' M' whi'^h reduced to its lowest terms is 1-4. : The sign of ratio. This signifies the ratio or numerical re- lationship of the two quantities between which it is placed, and is equivalent to a sign of division, since the quotient of the first quantity divided by the second is the measure of the ratio be- tween them. Thus 12 : 3 is read the ratio of 12 to 3 or 12 is to 3, and the real measure of this ratio is 12 -^ 3 or 4. : : The sign of proportion or equality of ratios. This sign is placed between two ratios and signifies that they are equal. COMPUTATIONS FOR ENCmEERS 90s Thus 12 : 3 :: 20 : 5 is read 12 is to 3 as 20 is to 5, or the ratio of 12 to 3 equals the ratio of 20 to 5. This is seen to he the case, since 4 is the measure of each ratio. = The sign of equality. This signifies that the two quanti- ties separated by the sign are equal in value. Thus 12 -^ 3 = 4 is read 12 divided by 3 equals 4, and thus states the equality be- tween the two sides of the relationship. Equation. Two quantities or expressions related by the sign of equality, =, form an equation. Thus 4 + 2 = 6 = 3 a-\- b^ c ()'[]> { }• Parentheses or brackets. These symbols mean that all numbers or quantities within a parenthesis or pair of brackets are to be considered as one quantity and thus treated in all numerical operations. Thus 2 (3 + 4) means that 3+4 is to be taken as the single quantity 7, and then multiplied by 2. Similarly 2 (3-1-4 — 2)=I0 3[i6 — 2(3 + 4 — 2)] = i8 Notes: The sign, multiplication, X, is often omitted between a number and a parenthesis or bracket containing a quantity into which it is to be multiplied, as in the expressions here shown. In some cases a bar or vinculum is drawn over numbers thus to be taken together. Thus 2X3 + 6 means 2 multiplied by the quantity 3 + 6, or 2 X 9, or 18. The difference between 2 X 3+6 and 2X3 + 6 or 12 will be noted. In reducing quantities thus affected by the signs +, — , X, -^ and connected by brackets, the difference in significance between the sign +, — and X, -^ must be carefully noted. Thus 2X3 + 6 means 2 times 3 added to 6 or 12, and not 2 times (3 + 6) or 18. As a general principle, it may be remembered that the signs + and — effect a separation of the expression into separate terms, while the signs X and -^ bind together the- two quantities between which they stand into a single term. Examples — These principles are further illustrated by the following : 3 Xi6 — 2X3+4 — 2 + 4X3— I =SS 3 [16 — 2 X 3 + 4 — 2 + 4 X 3 — I =69 .3 [16 — 2 (3 + 4) — 2 + 4 (3 — 1)1 = 24 3 [16 — 2 (3 + 4 — 2)] + 4 (3 — I) =26 9o6 PRACTICAL MARINE ENGINEERING V This sign placed over a quantity denotes the extraction of a root. If no number is placed at the upper left angle, it denotes the square root;, otherwise a root corresponding to the index thus indicated. 3 Thus V49 denotes the square root of 49 or 7, y/27 denotes the cube root of 27 or 3, ^/i6 denotes the fourth root of 16 or 2, etc. 3^ or 4^ or a*- A small number written to the right and above another number or quantity is called an index or exponent, and signifies that the lower number or quantity is to be used as a factor on itself a number of times equal to the index. Thus 4''=:4X4X4 = 64 o*=oXaXoXo ' " These signs set to the right and above any figure or figures (superior) signify feet and inches. These signs are much used in dimensioned drawings. I Signifies perpendicular to. Z. Signifies angle. L Signifies right angle. Signifies hence or therefore. Signifies because. TT Denotes the ratio between the circumference and diameter of a circle. Its value is usually taken as 3.1416. □ Square ; as 220 pounds per □" or per square inch. % Signifies percent or per hundred. Formulae A formula is simply a brief way of denoting a series of mathematical operations. Once understood, the directions given by a formula are much more readily followed than when given in the form of a rule. In fact a formula may be considered as simply a brief or short hand way of expressing the same direc- tions as are given by the rule in ordinary words. In formulas, quantities are usually represented by letters, as in the well-known horsepower formula: 2pLAN I. H. P.= 33,000 COMPUTATIONS FOR ENGINEERS 907 In this formula p denotes the mean effective pressure per square inch of piston area, L the length of stroke in feet, A the piston area in square inches, and N the revolutions per minute. In thus writing letters to represent quantities the sign of multiplication, X, is usually omitted. Thus in the foregoing the numerator 2 p L A N means the same asaX/'Xl-X^XA'^, or that the continued product is to be taken of these five factors. It must be noted, however, ^that where both factors are numbers the sign for multiplication cannot be omitted. Thus, 23 does not mean 2X3, but 20 + 3 or 23. Division may be expressed by the usual sign, but it is more commmonly indicated by writing the dividend as the numerator and the divisor as the denominator of a fraction. Or, in general, multiply by putting a factor in the numerator, and divide by putting a factor in the denominator. • Thus in the horsepower formula the product 2 p L A N istohe divided by 33,000. As a further illustration, take the formula Tt 6R In this formula p is the pressure per square inch in a boiler, T is the tensile strength of the material of the shell, t is the thick- ness of the plate in inches, and R is the half diameter or radius of the shell in inches. The whole gives the pressure per square inch allowed by United States rules on marine boilers. The formula directs, in order to find the desired pressure, to mul- tiply together T and t and to divide the product by 6 times R; or, in the words of the United States rule: "Multiply one-sixth of the lowest tensile strength ... by the thickness . . . and divide by the radius or half diameter." In this formula all dimensions are in inches and the result is the pressure per square inch allowed on the boiler. Thus let T == 60,000, ^=114 inches and R = 6 feet or 72 inches. Then 60,000 X I -25 p := = 174 pounds per square inch. 6X72 Take again the formula 112;" P = In this formula p is the pressure per square inch allowed on 9o8 PRACTICAL MARINE ENGINEERING a flat surface of a boiler supported by staybolts, t is the thickness of the plate expressed in sixteenths of an inch, and L is the pitch of the bolts, or distance from center to center in inches. The formula thus directs to multiply 112 by the square of the thickness of the plate in sixteenths, and then to divide the product by the square of the pitch of the bolts. Thus let the thickness be 9-16 inch and pitch be 7 inches. Then: 112 X 9X9 p = = i8s pounds per square inch. 7X7 Sec. 138. GEOMETRY AND MENSURATION* [i] Square A square is a figure, such as A B CD, having four sides all equal, and four angles all equal, each being a right angle. Diagonal, A C. To find the length of a diagonal, A C, hav- ing given a side of the square, as ^ B: B C * The following definitions are here given as introductory to this section. Other definitions will be given as the terms are introduced. An angle is formed when two lines, O A and O B, having different directions meet in a point as O. The angle refers then to the difference in direction of the two lines, and its measure is a measure of such difference in direction. An angle is usually denoted by three letters, the one at the apex being placed between the other two. Thus, in Fig. a the angle would be called A O B ox B A. c Fig. b in such a way that the Fig. a When a line, C D, meets another line, A B, four angles at E are all equal, the two lines are said to be perpendicular to each other, or, in more common terms, one line is square with the other. An angle such as those formed at E is called a right angle. An angle less than a right angle, as /4 OB, Fig. a, is called an acute angle. An angle greater than a right angle, a.s F E B, Fig. b, is called an obtuse angle. / COMPUTATIONS FOR ENGINEERS 909 Rule — Square the side, multiply by 2, and take the square root; or A C= ^/z'aTB'; or Rule — Multiply the side by 1.4142. Example: A B =^ 16. Then ^ C = V 2 X 256 = v 512 = 22.627, or ^ C = 16 X 1.4142 =3 22.627. Area, A B C D. To find the area of a square, having given the length of a side, sls A B: Rule — Square the side, or multiply it by itself ; or Area = A B" =A B X A B. Example: A B — 6. Then area =: 6 X 6 = 36. [2] Rectangle A rectangle is a figure, such as A B C D, having four sides, the opposite sides being equal and parallel (A B := D C and B C = A D), and four angles all equal, each being a right angle. Diagonal, B D. To find the length of a diagonal, B D, having given the two sides, as B C and C D: Rule — Square the two adjacent sides, add, and take the square root; or j5 D = ^ WC^ + t^. Example: B C — 6,C D =8. Then S I> = V 36 + 64 = V 100 = 10. Area, A B C D. To find the area of a rectangle, having given the two sides, as A B and A D: Rule — Find the product of the two adjacent sides; or Area — A B X A D. Exa^nple: A B— 6,A D = 8. Then area = 6 X 8 = 48. [3] Parallelogram A parallelogram is any figure, such as A B C D, having four 9IO PRACTICAL MARINE ENGINEERING sides and four angles, the opposite sides being equal and parallel, and the opposite angles being equal. A E Area, A B C D. To find the area of a parallelogram, hav- ing given a side and the perpendicular distance between this and the side opposite : Rule — Multiply one side by the perpendicular distance be- tween it and the side opposite; or Area = ADXEF; = also A B X G H. Example: A D = 16, E F = g. Then area = 9 X 16 = I44- [4] Trapezoid A trapezoid is any figure, such as A B C D, having four sides and four angles, two of the sides, as S C and A D, being parallel. Area, A B C D. To find the area of a trapezoid, having given the parallel sides and the perpendicular distance between them : B__E__c A F D Rule — Multiply the half sum of the parallel sides by the perpendicular distance between them ; (BC + AD \ I X £ ^. Example: (io-|-i6\ 1X8= 104. [5] Triangle A triangle is any figure, such as A B C, having three sides and three angles. In a triangle placed as in the figure, A C is called the base, and B D — the perpendicular distance from B tq A C — is called the altitude- COMPUTATIONS FOR ENGINEERS 911 Any Side, A B. To find the length of any side, having given the other two sides and the angle included between them : Rule — Square the other two sides and add, and according as the angle between them is greater or less than 90 degrees, D C add or subtract twice the product of one of these sides by the projection* of the other upon it. Then take the square root of the result thus found; °r A B = V -Jc^ _|_ Bci — 2ACXD C. Similarly B C= ^-^TW' + TC — 2 A C X A D, and A C— '^~aB' X BC^+ 2 B C X B E. Example: A C = 12, B C = 9, D C = 8. Then A B= V 144 + 81 — 2 X 12 X 8 = Vir= 5.745. Area. To find the area of a triangle, having given the triangle complete, or any side and its perpendicular distance from the opposite vertex: Rule — Multiply any side by the perpendicular distance from the opposite vertex to such side (produced, if necessary, to meet the perpendicular), and take half the product thus found; or take half the product of the base by the altitude; or Area = J4 (^ C X -B D), ^y2(BCxAE), = yi{ABxCF). Example: A C ^ 120, B D =: 32. Then area = P2 (120 X 32) = i>920. [6] A Right Angled Triangle In a right angled triangle one of the angles, as C, is a right angle. The side opposite is called the hypothenuse. Hypothenuse, a B. To find the length of the hypothenuse, having given the other two sides : * Let B D he drawn perpendicular to A C. Then D C is called the projection of 5 C upon A C. Similarly A D\s the projection oi A B upon A C, A F the projection oi A C upon A B produced, and E C the projec- tion oi A C upon B C produced. 912 PRACTICAL MARINE ENGINEERING Rule — Square the other two sides and add, and take the square root of the sUm; oT A B = VXC^ + WC^ Example: A C =^9,B C —12. Then ^ 5 = V 8i + 144 = V 225 — . 15. Side, ^ C or 5 C To find the length of one of the sides about the right angle, having given the hypothenuse and the other side: Rule — Square the hypothenuse and the given side. Subtract the squares, and take the square root of the difference; or A C = ^ A B^ — B C\ Example: A B = i5, B C= 12. Then A C = V 225 — 144 = V 81 = 9. Area, ABC. To find the area of a right angled triangle, having given the two sides about the right angle: Rule — Multiply together the two sides about the right angle, and take half their product ; or Area=:: ^ (A C X B C). Example: A C = g, B C ^ 12. Then area == }4 (9 X 12) ^ 54. These rules are special cases of those for the general tri- angle, as in [5]. [7] Trapezium A trapezium is a figure, such as A B C D, having four angles and four sides, no two of the latter being parallel. ^r 1 "'k" /0\ \ \ / \ \\ ^ ^ A"--_- COMPUTATIONS FOR ENGINEERS 913 AreAj a B C D. To find the area of a trapezium, having given the figure complete: Rule — Divide the trapezium into two triangles, and proceed with each separately, and then add. [8] Regular Polygons A regular polygon is a figure, such as A B X^ D E, having any number of equal sides and a like number of equal angles. They are named as follows : Number of Sides Names 3 Triangle 4 Square 5 Pentagon 6 Hexagon 7 Heptagon 8 Octagon 9 Nonagon 10 Decagon Area. To find the area of any regular polygon, as A B C D E, having given the figure complete : Rule — Divide the polygon into as many triangles as there are sides, the apexes all being at the center. Find the area of one of these and multiply by the number of sides. [g] Irregular Figtures Area. To find the area of a figure, such asABCDEFG, having given the figure complete : C A F G Rule — Divide into triangles in any convenient way; pro- ceed with each separately and add the results. [10] Circle A circle is a figure bounded by a curved line, every point of which is equally distant from a point within, called the center. The distance across from one side to the other through the center is called the diameter (see A B or F G). The diameter 914 PRACTICAL MARINE ENGINEERING is usually represented by D. The distance from the center to the curved boundary line is called the radius, and is plainly one- half the diameter (see A C, F C, etc). The radius is usually represented by r. The curved boundary line A F H B G K A, is called the circumference. Any part of the circumference, as A F, F H, etc., is called an arc. Circumference. To find the circumference, having given the diameter: Rule — Multiply the diameter by 3.1416, or more exactly 22 by 3. 141 5927, or less exactly by — . This ratio is frequently 7 denoted by the symbod ir. or Circumference ^ 3.1416 X Diameter = tt Z?. Example: Diameter = 11. Then circumference = 11 X 3.1416 = 34.5576. Diameter. To find the diameter, having given the circum- ference : Rule — Divide the circumference by 3.1416, or more exactly 22 by 3. 141 5927, or less exactly by — . 7 or Diameter =: Circumference -f- 3.1416, or Diameter = Circumference X .31831. Example: Circumference = 48.7. Then diameter = 48.7 ^ 3-1416= 15.50 + Area, A H B K. To find the area of a circle, having given the diameter or the radius : Rule — Multiply the square of the diameter by .7854, or 3.1416 -^ 4; or multiply the square of the radius by 3.1416, or find half the product of the radius by the circumference; or Area = .7854 X (Diameter)" = . COMPUTATIONS FOR ENGINEERS 9i5 = 3.1416 X (Radius)^ = T r, = H (Radius X Circumference). Example: Diameter = 10. Then area = .7854 X 100 = 78.54. Length of Arc. To find the length of an arc, as A F, having given the corresponding number of degrees and the cir- cumference or diameter : Rule — Divide the circumference by 360, and multiply by the number of degrees in the arc; or multiply the number of degrees by .008727 and the product by the diameter; Circumference or Length A F t= X (Number of Degrees) 360 or Length A F =^ (Number of Degrees) X .008727 X Diameter. Example: Find the length of an arc of 60 degrees in a circle whose diameter is 20. Length =: 60 X .008727 X 20 := 104724. [11] Circular Ring or Annulus The surface lying between two circles, as shown by the snaded part of the figure, is called a circular ring or annulus. Area. To find the area of a circular ring, having given the radii of the two circles : Rule — Find the difference between the areas of the two circles. or Area = 3-i4i6 OB' — 3.1416 O A' = 3.1416 (O B' O A'). [12] Sector of Circle The surface lying between two radii and the corresponding part of the circumference, as shown by the shaded part of the figure, is called the sector of a circle, or a circular sector. Area, ABO. To find the area of the sector of a circle, having given the corresponding number of degrees and the diameter : 976 PRACTICAL MARINE ENGINEERING Rule — Find the area of the entire circle, divide by 360 and multiply by the number of degrees in the sector ; Area of Circle or Area ^= X (number of degrees in sector) ; 360 or, by proportion, 360° : Number of Degrees in Sector : : Area of Circle : Area of Sector ; or, otherwise, find half the product of the arc by the radius, or Area = Yz (^0 A X A B). Example: Find the area of a sector of 60 degrees in a circle whose radius is 10. Area of entire circle =: 78.54, 78.54 . 78.54 hence, Area = X 60 = ;=: 13.09. 360 6 [13] Segment of Circle A line, such as A B, cutting across a circle is called a chord. A part of the surface of a circle between a chord and the cir- cumference, as shown by the shaded part of the figure, is called a segment of a circle. KviEK, A C B. To find the area of the segment of a circle, having given the angle, A B, and the diameter or radius of the circle: Rule — Find the area of the sector, O ^ C B, as in [12], and of the triangle ^ B, as in [5], and subtract the latter from the former ; COMPUTATIONS FOR ENGINEERS 917 or Area =14 (A C B X O A — O E X A B). Example: O A =:io, O E= s, A B — 17.32, A C B = 20.944, then Area = ^ (20.944 X 10 — 5 X 17.32) = 61.42. [14] Ellipse If the surface of a circle, as shown by the dotted Hne, be uniformly stretched in one direction (horizontal in the figure) until the diameter, A^ B^, becomes equal to A B, the circum- ference will be changed into a curved line, A C B D, and the figure thus formed is called an ellipse. The two lines, A B and C D, are called the diameters of the ellipse. Area, A C B D. To find the area of an ellipse, having given the two diameters : Rule — Multiply the product of the two half diameters by 3-1416; or Area != 3.1416 X O C X O B. Example : O C = 5, O B = 8. Then area = 3.1416 X 5 X 8 r= 125.664. [15] Figures With an Irregular Contour To find Area, A B C D, representing, for example, an indi- cator card. This cannot be done with absolute exactness, but there are a number of rules for finding the approximate area as closely as may be desired. Divide the base O X into any appropriate number of in- tervals, usually ID for an indicator card and d'-^w lines across the card as shown. Rvle (i) — {Trapezoidal). Measure the successive ordinates or breadths on the full line and from their sum subtract one- half the sum of the end ordinates. Multiply the remainder by the length of the interval or by X -^ 10, and the product is the area desired ; 9i8 PRACTICAL MARINE ENGINEERING or calling the breadths ^o. Ju 3'2. etc., there results by formula in this case: OX Area = OAyo + Jii + yz + ys + yi + 3^ + Jio + y? + > + J'' + 10 Myio) • As a slightly different and preferable mode of pijocedure with this rule the breadths may be measured midway between the lines of division as indicated by the dotted lines. Their sum, without modification, is then multiplied by the length of the in- terval as before. Any number of spaces as desired may be employed with this rule. Rule (2) — (Simpson's or Parabolic) . Measure the ordinates as before. Take : Once the first and last. Four times every other one beginning with the second. Twice the remaining. (These multipliers are shown in the figure below the line X). Add the products and multiply by one-third the interval, or in this case by Z H- 30 ; or by formula in this case : OX Area = — (> + 4311 -|- 23(2 -|- 4313 + 2314 + 4y> + 2316 -j- 431, -|- 2318 + 30 4y» + 3'io). With this rule the number of spaces must be even. Rule (3) — (Durand's). Measure the ordinates as before. To their sum add one-twelfth the sum of those next the end and subtract seven-twelfths of those at the end. Multiply the result by the interval and the product is the area desired ; or by formula in this case : COMPUTATIONS FOR ENGINEERS 919 OX f y, -f- Jli + yj + 3I3 -j- ;V, -f yj -)- y, -j. y, _|- jl, -|- yj ^ 3ll„ A Area = -^+M2(j'i + >) \ 10 I — %2 (yo + yio) j With this rule any numher of spaces as desired may be employed. The measurement and addition of ordinates as in rules (i) and (3) may be quickly effected by means of a strip of paper on f, I ■ ■ ■ 1 1 A B which their lengths are marked off directly from the card and without the use of a scale, joining the end of one to the be- ginning of the next and thus effecting mechanically the addi- tion desired. To a reduced scale the strip when marked would resemble the figure, the ordinates being as indicated on the margin. The sum total is then directly found by means of a scale. Example: Suppose that the ordinates of an irregular area at one-half inch intervals are found by measurement to be as follows in column ( i ) : (I) (2) (3) . Ordinates ^ Multipliers Products yo .44 I -44 yi 1.42 4 5.68 yj 1. 61 2 3.22 yj 1.56 4 6.24 yt 1.51 2 3.02 ys 146 4 S.84 • ys 1.20 2 2.40 y7 .95 4 3.80 ys .71 2 1.42 y> .49 4 1.96 yi9 .18 I .18 Sum 11.53 34-20 Then according to rule (i) Sum of ordinates = II.53 }4 sum of ends =: .31 Difference = 11.22 Interval = .5 Area = Product =: 5.61 square inches. According to rule (2), the multipliers and products are given in columns (2) and (3). Then Area = % X .5 X 34-20 = 5.70 square inches. According to rule (3), from column (i) : 920 PRACTICAL MARINE ENGINEERING Sum of ordinates M.2 sum of next to ends. Sum %2 sum of ends = II.S3 =: .16 = 11.67 = .36 •Difference = 11.31 Area = .5 X ii.3i = S-66 square inches. Areas of irregular figures, such as indicator cards, etc., may also be found by an instrument called the planimeter. In this instrument a pointer is traced around the contour of the figure, \yhile the area is read ofif from a wheel, which is given appro- priate motion by the movement of the pointer. Such instru- ments, with instructions for use, may usually be obtained from the makers of steam engine indicators or from dealers in mathe- matical instruments. [16] Prism A prism is a solid body, bounded by two , equal and parallel ends and by three or more sides or faces, forming at their junc- tion a like number of parallel edges. When the sides are perpendicular to the ends, and are there- fore all rectangles, the solid is known as a right prism. When the sides and ends are all square, the solid is known as a cube. Surface. To find the surface of any prism, having given the figure complete : Rule — Find the area of the base (or top) by such of the preceding rules as may be appropriate. For the side or lateral surface, multiply the perimeter or boundary of the base by the perpendicular or shortest distance between any two correspond- ing lines of the base and top (as X" L in Fig. a). Volume. To find the volume of any prism, having given the base and altitude: COMPUTATIONS FOR ENGINEERS 921 Rule — Multiply the area of the base or end by the altitude or perpendicular distance between the two ends. Right Prism. In a right prism the preceding general rules hold, but the lateral faces are all rectangles, and the perpen- dicular distance between their ends, as K L; the length of an edge, as M N, and the altitude or perpendicular distance between the ends, all three become equal. Right Prism, with Rectangular Base. In a solid of this character (see Fig. b) the preceding rules still hold, but the sides and ends are all rectangles, and the rules may be simplified as follows : For the Lateral Surface : Rule — Multiply the perimeter of the base by the altitude, or Lateral Surface = Length A B C D A X A E. For the Volume : Rule — Multiply together the length and breadth of base and the product by the altitude, or Volume =ABXADXAE. Example: A B = 8, A D = 6, A E = 10. Then lateral surface = (8 + 6 + 8 + 6) X 10 = 28 X 10 = 280, and volume = 8 X 6 X 10 = 480. [17] Cylinder A solid with a circular cross section of constant size is called a cylinder. If the center of the top is vertically over the center of the base, the solid is called a right cylinder. Lateral Surface of Right Cylinder. To find the lateral surface of a right cylinder, having given the diameter of base and the altitude : Rule — Multiply the circumference of the base by the altitude, or Lateral Surface = Circumference ABCDXAE = 3.1416 XACXAE. Example: A C ^ 10, A E = 20. Then lateral surface = 3.1416 X 10 X 20 = 628.32, 922 PRACTICAL MARINE ENGINEERING Volume of Right Cylinder. To find the volume of a right cylinder, having given the base and altitude: Rule — Multiply the area of the base by the altitude, or Volume = Area ABCDXAE = .7854 ZT^ X A E. Example: A C = 10, A E =: 20. Then volume = .7854 X lOG X 20 = 1,570.8. [18] Any Solid With a Constant Section Parallel to the Base, Either Right or Oblique Such a solid is the general case of which the prism and cylinder are but special examples. The rules will therefore be similar to those of [16] and [17]. Surface. To find the surface of such a solid, having given the figure complete: H K Rule — Find the area of the base (or top) by such of the pre- ceding methods as may be appropriate. For the side or lateral surface, multiply the perimeter or boundary of the base by the perpendicular or shortest distance between any two corresponding lines of the base and top (as K' L in figure a) : or Lateral Surface = Length ABCDEAXKL. Volume. To find the volume of such a solid, having given the figure complete : Rule — Multiply the area of the base by the perpendicular distance between the base and the top, or Volume = Area of Base X Vertical Altitude. Example: Area of base = 120, altitude = 40. Then volume = 40 X 120 = 4,800. [ig] Wedge A right prism with a triangular base, as in b above, having two sides equal, as A C and B C, is called a wedge. To find the Surface or Volume, use the same rules as in [16]. COMPUTATIONS FOR ENGINEERS 923 [20] Right Pyramid A solid, bounded by a base and by triangular sides meeting in a point or apex, as P, is called a pyramid. If the base is a regular polygon [8] and the apex is vertically over the center of the base, the solid is called a right pyramid (see figure a below). Lateral Surface. To find the lateral surface of a right pyramid, having given the figure complete: Rule — Take one-half the product of the perimeter or bound- ary of the base by the perpendicular or shortest distance from the apex to one of the sides of the base, as P F, l^ngthABCDEAxPF or lateral surface = . Jtariat Engintering Volume. To find the volume of a right pyramid, having given the base and altitude : Rule — Take one-third of the product of the area of the base by the altitude, as P O, (Area of Base) X (Altitude) or volume r= . 3 Example: 180 X 16 Area of base = 180, altitude = 16. Then volume = = 960. [21] General Pyramid For definition see [20] , also Fig. b above. Lateral Surface. To find the lateral surface of any pyramid, having given the figure complete: Rule — ^The surface will consist of a series of triangles, simi- lar or not, according to the nature of the pyramid. ' These must be computed according to the rules for triangles and the re- sults added. 924 PRACTICAL MARINE ENGINEERING Volume. To find the volume of any pyramid, having given the base and altitLide : Rule — Take one-third the product of the area of the base by the vertical altitude, as G H, (Area of Base) XGH or volume = . 3 Example: 48X18 Area of base ^ 48, G H = 18. Then volume = = 288. 3 [22] Right Circular Cone Any solid having a base with curved or irregular boundary, an apex and straight sides, is called a cone in general. If the base is a circle and the apex is vertically over the center, the solid is called a right circular cone (see figure). D Lateral Surface. To find the lateral surface of a right circular cone, having given the base and the slant height: Rule — Take one-half the product of the circumference of the base by the slant height, CircumfereHce^ B C D AxAE or lateral surface = . 2 Example: 3.1416 X 10 X 20 Diameter ^ 10, A E ^ 20. Then surface = = 314.16. 2 Volume. To find the volume of a cone, having given the base and altitude : Rule — Take one-third the product of the area of the. base by the altitude, Area of Base ^ B C £> X -E ^ or volume = . 3 Example: .7854 X 64 X IS Diameter = 8, £ F = 15. Then volume = = 251.328. COMPUTATIONS FOR ENGINEERS 92S [23] General Cone For definition see [22] . Volume. To find the volume of any cone, having given the base and vertical altitude: Rule — Take one-third the product of the area of the base by the vertical altitude, as F G, Area of base X F G or volume = Example: 240X40 Area of base := 240, F G = 40. Then volume = = 3,200 3 [24] Frustum of Right Pyramid The solid contained between the base of a pyramid and a parallel plane, zs E F G H, is called the frustum of a pyramid. ^t -J^D B/ Lateral Surface. To find the lateral surface of a frustum of a right pyramid, having given the figure complete: Rule — ^Add the perimeters or boundaries of the base and top, and multiply the sum by one-half the perpendicular or shortest distance between two corresponding lines of the base and top, which may be denoted by h, (length AB CD + lengthEFGH) Xh or latitude surface = 2 Example: A B=zio,A D = i2,E Fz=6,E H = 7.2, h = 5. Then surface = (44-1-26.4) X5 = 176. 926 PRACTICAL MARINE ENGINEERING Volume. To find the volume of a frustum of a right pyra-' mid, having given the base and top and vertical distance between them Rule — Add together the areas of the base and top and the square root of their product, and multiply the sum by one-third the vertical altitude, which may be denoted by k. (ABCD + EFGH+VABCDxEFGH)Xk or volume = 3 Example: Area A B C D := lOO, area E F G H ^ 42, k = 12. Then volume = ( ICO + 42 + V 4,200) X 12 = 827.2. [25] Frustum of General Pyramid, as [21] To find the Lateral Surface: Rule — The surface will consist of a number of trapezoids, similar or not, according to the nature of the frustum. These must be computed according to [4] and the results added. To find the Volume: Rule — Same as for [24], [26] Frustum of Right Cone The solid contained between the base of a cone and a parallel plane, as E F G H, is called the frustum of a cone. Lateral Surface. To find the lateral surface of a frustum of a right cone, having given the base and top and slant height : Rule — ^Add the circumference of the base and top, and multi- ply the sum by one-half the slant height, as A E, (Cir.ABCD+CW.EFG H) XAE COMPUTATIONS FOR ENGINEERS 927 Example: Diameter A C =12, diameter £ G = 10, /I £ = 8. Then surface = (3.1416 X 12 + 3-1416 X 10) X 8 = 276.47. 2 Volume. To find the volume of a frustum of a right cone, having given the base and top and vertical altitude : Rule — Same as for [24]. Or in slightly different form, the following : Rule — Add together the square of the upper diameter, the square of the lower diameter, and their product, and multiply the sum by the vertical altitude and by the number .2618, or volume = .2618 I J (EG'- + ZC^ + EGX AC). Example: £G=6, ^C = 8, 7/^4. Then volume = .2618 X 4 (36 + 64 + 48) = 155. [27] Frustum of General Cone, as [23] To find the Volume : Rule — Same as for [24]. [28] Sphere A solid inclosed by a curved surface, every point of which is equally distant from a point within called the center, is called a sphere. The distance, A B, from one side to the other thfongh the center is called the diameter. The distance, A 0, from the surface to the center is called the radius, and is plainly one-half the diameter. Surface. To find the surface of a sphere, having given the diameter : , Rule — Square the diameter and multiply by 3.1416, or Surface = 3-i4i6 (Diameter)^. Example: Diameter = 20. Then surface = 3.1416 X 400 = 1,256.64. Volume. To find the volume of a sphere, having given the diameter or radius ; Q28 PRACTICAL MARINE ENGINEERING Rule — Multiply the cube of the radius by 4.1888, or multi- ply the cube of the diameter by .5236, or volume = 4.1888 A O" = 4/3 ir r" or volume = .5236 A B' = 1/6 t d' [29] Volumes of Irregular Shape Volumes of irregular shape in which the areas of a series of equally spaced sections may be found. Y Rule — Find the areas of a series of equally spaced cross sec- tions and treat them by the rules given in [15], using areas for ordinates. The result will give the volume desired. Examples: (i) Find the volume of an irregular box, 12 feet long; area of one end, 6 square feet; of the other, 15 square feet, and of a section midway between, 10 square feet. The interval is 6 feet. Then with Simpson's rule. Volume ^ 2 X (6-^-4X10+ 15) = 122 cubic feet. (2) Find the volume of a coal bunker, 20 feet long, having cross sections every 4 feet, as follows : Taking rule (3) in [15]: 297 8.3 Square Feet Ao z= 40 A. = 46 A2 = .SO A, = .S2 A. = S4 A, irz 55 Sum = 297 305.3 55.4 249.9 4 999.6 ; or, say, 1,000 cubic feet. COMPUTATIONS FOR ENGINEERS 929 [30] Volume Generated by Any Area Revolving About an Axis To find the surface or volume of such a body, the so-called "Rules of Pappus" are most readily applicable. These may be illustrated by the example of the Torus or Ring as in the figure. Surface. To find the surface of a ring, having given the necessary dimensions : Rule — Multiply the length of the generating line by the length of the path followed by its center of gravity. Example, as in the figure. The length of the generating line is 2 tt r. The length of the path of the center, C, is 2 w a. The surface is •'■ 2 ir r X 2 ir a = 4 w^ o r. Volume. To find the volume of a ring, having given the necessary dimensions : Rule — Multiply the generating area by the length of the path traveled by its center of gravity. Example, as in the figure. The generating area is tt r^- The length of the path of the center, C, is 2 it a. The volume is •'• 2 i^ a r'. The same general rules apply, no matter what the form of the generating area, and they will often be found of use in solving problems not readily treated in any other manner. Sec. 139. PROBLEMS IN GEOMETRY [i] At Any Point in a Straight Line to Erect a Perpendicular Let be the given point in the line L M. Then take points A and B such that A = OB. From A and B as centers with f 5CC G- L A B M ;fD any radius greater than A or B, describe arcs cutting in C or B, or if preferred, in both. Then a line drawn through and C or and D will be perpendicular to L M, or the line may 930 PRACTICAL MARINE ENGINEERING be drawn through C and D, in which case it will also contain O and be perpendicular to L M as before. [2] To Bisect* the Distance Between Two Points In the figure for problem [i] \et A and B be the two points. Then finding points C and £> as in [i] it is plain that the point determined by drawing the line C D will be the middle point between A and B as desired, and that A ^ B. [3] To Find the Center from Which to Pass an Arc of Given Radius Through Two Given Points In the figure for problem [i] let ^ and B be the points. Then finding points C and Z? as in [i] it is plain that any point 1 2 345 in the indefinite line E F will be at equal distances from A and B. Hence from A or 5 as a center and with the given radius cut the line E F in a point, as G. This is the point desired. [4] To Divide a Given Line Into a Given Number of Equal Parts Let A B denote the given line. Draw a line A D at sl small angle with A B, and lay off upon it as many equal divisions A a. B « A a b, b c, etc., as it is desired A B shall have. These divisions should be so chosen that the total length A f shall not widely dififer from A. B. Now draw B f and then a series of parallels through the points of division ab c, etc. The points where these lines cut A B will give the points of division desired. * To bisect a geometrical quantity means to divide it into two equal parts. COMPUTATIONS FOR ENGINEERS 931 [5] To Construct a Triangle, Having Given the Three Sides Let a b c denote the sides. Take A B =z c, and from A as center and with b as radius, describe an arc D E, and similarly from B as center and with a as radius describe an arc F G. These arcs intersect in C, and drawing lines A C, B Cj the construction is completed. [6] To Bisect a Given Arc or Angle Let A B denote the angle and A B the arc. From A and B as centers, and with any radius greater than half the distance between A and B, describe arcs intersecting in some point C. Then a line C will bisect the angle A B and at D the arc A B. aA D_ E [7] To Construct a Mean Proportional* Between Two Given Lines Let the two lines be denoted hy A B and B C placed end to end. Find the center of the line A C, and describe a semi-circle ADC. Draw 5 £ at right angles to A C. Then 5 £ is the desired mean proportional, and AB : BE : :_S_£ : B C or, ABXBC = BE' [8] To Construct a Fourth Proportionalf to Three Given Lines Let a, b and c denote the three lines, and let the desired pro- portion be: a:h::c: () *A mean proportional between two quantities a and c is a third quantity b, such that a : b : : b : c or, b'=:ac or, & = Vac. See also Sec. 6. fA fourth proportional to three quantities a, b and c is a quantity d such that a : b : c : d. See also Sec. 6. 932 PRACTICAL MARINE ENGINEERING Lay oS A B = a and A C =^ b. Then at any convenient angle lay off A K and take on it a distance A D = c. Draw B D and C E parallel to it. Then A E is the fourth term desired and c yf / / y yf 1 / / ' / / / / / / / / , . 1 or, tC B C - AB : AC : : AD : AE ABXAE=ACXAD [g] To Construct a Square Equivalent in Area to a Given Rectangle Find by problem [7] a mean proportional between the sides of the rectangle, and this will be the side of the square desired. [10] To Construct a Square Equivalent in Area to a Given Triangle Find by problem [7] a mean proportional between the base and half the altitude, or between the altitude and half the base. This will be the side of the square desired. [11] With One Given Side, to Construct a Rectangle Equivalent to a Square This is equivalent in [7] to having given A B the side of the rectangle and B E the side of the square. Find by the use of the construction in problem [ i ] a point on A B At equal distances from A and E and describe the semi-circle. Then S C is the remaining side of the rectangle desired. [12] To Find the Length of an Arc of a Curve Let A C D B denote the given arc. Take a strip of paper M N and lay with an edge just neatly tangent to the curve at A. Mark a point opposite A on the strip. Then, placing the pencil at C, a point near where the curve and edge of the paper strip begin to separate, bear down slightly and rotate the paper about C as a center until the edge is tangent at C or at a point slightly beyond. Then move the pencil along to a point D and repeat, and so on until the strip has been thus rolled along the curve to B. The distance A■^ B^, between the point opposite A on the strip at the start and the point opposite B at the end, will be very close to the true length of the curve. A little experience will enable COMPUTATIONS FOR ENGINEERS 933 the points C D, etc., to be so chosen that the error will be very small. A check on the operation may be obtained by reversing the process and rolling the paper back to the original position. If the point A^ comes again to A it shows that no slip has been ./^^ made, and the distance found may be accepted as a very close approximation to the true length of the curve. [13] To Construct an Ellipse Of the many methods available, three are given as follows: ( I ) Given the two diameters A B and C D. Take B Q equal to C and then O P equal to O Q. Draw P Q and find R its middle point. Then take Q H — Q R, and E, F, G all equal H. Through E, F, G and H draw lines as shown. Then with H and F as centers draw arcs / K and / L, and with E and G as centers draw arcs L K and / /. These arcs join and complete the contour. While this method is only approximate and does not give a true ellipse, it answers very well for draft- ing purposes where a good representation of an ellipse is all that is desired. (2) This method is exact in principle. Given A B and C D the two diameters as before. With C as center and C Q ^= B as a radius, find the points P Q. These are the foci of the ellipse. Then adjust a thread P C Q secured at P and Q and of a length PC-\-CQ=AB. A pencil carried around in the bight of this thread, as shown in dififerent positions at E, C, F, will trace the ellipse desired. 934 PRACTICAL MARINE ENGINEERING (3) This method is also exact in principle. Given A B and C D the two diameters as before. Prepare a strip of cardboard or thin wood with holes P, B, Q, such that P B equals one-half A B and B Q equals one-half C D. Then move the trammel, as it B F — V -- ^ t-x is called, so that P shall always move on the vertical YY and Q on the horizontal X X. The point B will then trace the ellipse desired. If points on the curve only are required, this method is readily applied. [14] To Construct Any Regular Polygon (Approximate) Let A ,B denote any diameter of the given circle within which the polygon is to be inscribed. Divide A B into as many parts as there, are to be sides in the polygon. From A and B as centers and radius A B describe arcs cutting in D. From D draw a line D C through the second of the points of division. Then 5 C is the side of the polygon desired within a very small error. For the square or hexagon, or when the number of sides is 4 or 6, the construction is exact. [15] To Develop the Surface of a Cylinder Let A B C D denote the cylinder. Lay off £ F = the alti- tude and E H = the circumference of the base, = tt X diameter COMPUTATIONS FOR ENGINEERS 935 = 3.1416 X diameter. Then the rectangle E F G H represents the development desired. H [16] To Develop the Surface of a Cylinder Which is Intersected by Another Cylinder, the Two Axes Being in the Same Plane The developed form of the intersectior> is the only part requiring special notice. Let A B. C D and E F G H denote the two cylinders. Draw any line T T to denote the element C D in the developed surface oi A B C D. Then the developed form of the intersection will be symmetrical about T T. Project E and H over to £1 and H^ for the top and bottom of the curve. Then to find intermediate points proceed as follows : Draw any line K L parallel to P Q and denoting the edge of a plane perpendicu- lar to the paper and cutting both cylinders. On F G as diameter, describe the circle as shown, and on A D the semi-circle W D X. Make A'' O equal to M K and project over to S, thence up to R and then over to T T. Rectify the arc 5" D and lay off Z U and Z V each equal to the rectified length. Then will U and V be points on the curve as desired. Other points may be found in a similar manner and the curve filled in. To develop the form of the smaller cylinder proceed as fol- lows: 936 PRACTICAL MARINE ENGINEERING Let Ci Di denote in the development the element H G. Lay off A^ Bi = the circumference I F J G. Then for the points cor- responding to the plane K L take C^ E^ ^ C^ F-^ =: the developed length of the arc G M. Then draw E^ H-^ and F^ /^ each equal to K R. This will give two points, //j and I^, and others may be found similarly and the curve filled in as shown. [17] To Develop the Surface of a Cone Let ABC denote the cone. With ^ C as radius and any point as center, draw an arc, G H K. Then lay off the circum- ference of the base A B (=3,1416 Y. A B) on a strip of paper, and lay off in this length by rolling as in problem [12] from G to some point J. Then the arc G H I ^ circumference oi A B and the sector G H J is the developed surface of the cone. G/ [18] To Develop the Surface of the Frustum of a Cone Referring to the figure for the preceding problem, let A D E B denote the frustum. Then, after proceeding as in that prob- lem, take next a radius L =z C D and describe the arc L M N. Then will the sector L M N represent the surface of the cone C D E, while the strip L G H J N M represents that of the frustum. [19] To Develop the Segments of an Elbow These are portions of a cylinder cut by oblique planes. Let A B C P denote such a segment. Draw L M perpendicular to A B and construct the semi-circle L Q M. L M may be placed at any convenient location between B C and A D. In the develop- ment let E F denote the element A B. Make F O = B L and then draw perpendicular to E F lines N O = P = each to the semi-circumference L Q M. Then N P is the development of COMPUTATIOXS FOR ENGINEERS 937 L M. Lay off jY G ^ P / = il/ C as shown. Then to find inter- mediate points on G F I take any line R S and project down to T. Develop L Q T and lay off the developed length at [/ and O V. Then make V Y and U W each equal to K R, and Y and W will be points on the development of B C. Other points may be found in a similar manner and the development oi B C com- pleted as shown by the curve G F I. The curve H E [ as the development of A D may be found in an entirely similar man- ner, and if S C and A D are equally inclined to the elements of the cylinder, L M will naturally be located midway between them, and H E J will be symmetrical with G F I about N P, and both may thus be found at the same time by laying off above and below A'' P the distance determined as above shown. Sec. 140. PHYSICS [i] Acceleration Due to Gravity In engineering computations there frequently enters a quan- tity known as the acceleration of gravity or the acceleration due to gravity, and denoted by the symbol g. This is the change per second which the gravity or attraction of the earth is able to bring about in a freely falling body. For engineering purposes its value is usually taken at 32.16 or 32.2. [a] Specific Gravity The specific gravity of a given substance is the relation be- tween the weights of equal volumes of the given substance, and 938 PRACTICAL MARINE ENGINEERING of some standard substance, usually water. Thus a specific grav- ity of 8 means that, volume for volume, the given substance is 8 times as heavy as water. [3] Heat Unit Heat is measured in terms of a unit defined as the amount of heat required to raise i pound of water i degree in temperature at 62 degrees F., or from 62 degrees to 63 degrees. [4] Specific Heat The specific heat of a substance is the relation between the amount of heat required to raise it i degree at the given tem- perature and under given conditions as to pressure or volume, and the unit of heat as just defined. Thus a specific heat of .32 means that under the given conditions it will require to raise the temperature i degree, .32 of the heat necessary to raise i pound of water from 62 degrees to 63 degrees. [5] Expansion of Metals Nearly all substances expand with the addition of heat, and usually with nearly equal amounts per degree rise of temperature, especially where the substance is not near its melting or boiling point. The following table gives the coeffi,cient of linear or length expansion for various substances. This is the expansion in unit length for i degree F. rise of temperature. Substance. Aluminum. . . Brass, cast. . . Brass, drawn. Brick Bronze Bismuth Concrete Copper Glass Coef. 0000123 0000096 .0000105 .0000031 . 0000099 . 0000098 . 0000080 . 0000089 .0000045 Substance. Iron, cast Iron, wrought. . Lead Mercury Steel, cast Steel, wrought. Tin Zinc Coef. 0000056 0000065 0000157 .0000333 0000064 , 0000069 .0000116 .0000141 To find the expansion in the length of any bar for any given rise in temperature proceed as follows: Rule — Multiply the coefficient taken from the table by the number of degrees, and this by the length of the bar, and the product is the expansion desired. COMPUTATIONS FOR ENGINEERS 939 Example: What is the expansion of a steel bar 20 feet long between 60 degrees and 350 degrees F. Ans. .0000069 X 290 X 20 ^ .04 foot = .48 inch. The coefficient for area or surface expansion is taken twice that for linear expansion, and that for cubic or volume expansion is taken three times that for linear expansion. Example: What is the increase in area between 60 degrees and 300 degrees F. in a copper sheet having an area of 54 square feet? Ans. .0000178 X 240 X 54 = -231 square foot = 33.3 square inches. What is the increase in volume between 100 degrees and 200 degrees F. in a piece of brass having a volume of 2}^ cubic feet ? Ans. .0000288 X 100 X 2.5 = .0072 cubic foot = 12.44 cubic inches. Sec. 141. MECHANICS- [i] It is a general law of nature that all bodies tend to remain unchanged as regards their condition of rest or relative motion. A body at rest does not move unless caused to do so by some outside agency. A body in motion continues to move until it is brought to rest by outside agencies such as friction, resistance of the air, or of water, etc. [2] Force Any agency which changes or tends to change the condition of a body as regards its rest or relative motion is called a force. For engineering purposes force is measured by the pound or ton as unit. In marine engineering the ton, unless otherwise stated, is usually of 2,240 pounds. [3] Specification of a force A force has three characteristics or particulars: (i) Its line of direction, as north and south. (2) The way it acts in that line, as north. (3) Its magnitude. A force may therefore be completely represented by a line A B oi length to represent the magnitude, and drawn in the direction of the line of action of the force. A B 940 PRACTICAL MARINE ENGINEERING Thus the force A B would mean a force represented in amount according to some scale by the length A B, and acting along the line A B from A to B. The direction of action is also frequently denoted by an arrow point, thus : A B > [4] Moment of a force This is the product of the magnitude or measure of the force multiplied by the perpendicular distance from its line of action to a given reference point. Thus in the figure let the full line represent a force, P denote ■^0 its measure, and O the reference point. Then P X O A is the moment of the force P about the point 0. In the term moment of a force a point of reference is therefore always implied. [5] Resultant The resultant of a system of forces two or more in number with their lines of action all meeting at a common point, is the single force which represents the combined action or result of the system. [6] Work Work is done when a force (or resistance, as it may be called in such case) is overcome; as, for example, when a weight is lifted or a ship is forced through the water. Water is measured by the product of the resistance by the distance through which it is overcome. The two essential factors of work are therefore force or resistance on the one hand, and motion or distance on the other. The unit of work is the foot pound or the work done in raising one pound weight one foot in height. Thus if 16 pounds be lifted 20 feet, the work done is 20 X 16 = 320 foot pounds. [7] Power Work in itself is independent of the time required to do it, and depends simply on resistance and distance. Power means a certain amount of work performed in a given time. The com- COMPUTATIONS FOR ENGINEERS 94i mon unit is the horsepower, which is 33,000 foot pounds of work performed in one minute. The added element involved in power should not be forgotten. Thus 33,000 foot pounds of work per- formed in I hour would not mean one horsepower, but only 1/60 of such amount, while 33,000 foot pounds of work performed in I second would mean 60 horsepower. Likewise 550 foot pounds per second represents i horsepower as also 1,980,000 foot pounds per hour. To find the horsepower in any given case, therefore : Rule — Find the foot pounds of work performed per minute and divide by 33,000. Example: An engine in one-half hour performs 118,800,000 foot pounds work. What is the horsepower? 1 18,800,000 Horsepower ^ = 120 30 X 33,000 From the above general expressions for work and power there come two forms of especial interest to the engineer. These relate to the work done by or on a fluid in a cylinder with a moving piston, as in a steam engine or a pump. Let A = the area of the cylinder in square inches. p := the average working pressure per square inch. L = the length of stroke in feet. N = the number of revolutions or double strokes per minute. Then pA = the average total pressure or load on the piston. This is the force factor. 2LN = the distance per minute assuming the engine or pump to be double acting. This is the distance factor. Then Work per minute = (pA) X (2LN) foot pounds (a) or as it is frequently written by changing the order of the factors, Work per minute = 2pLAN foot pounds (ai) To reduce this to horsepower, simply divide by 33,000 and have : 2PLAN Horsepower = (oz) 33.000 Now for the second form let the factors be arranged thus : Work per minute = {p) X {2LN A). Then multiply p by 144 and divide A by the same number. This will not change the value, and 942 PRACTICAL MARINE ENGINEERING 2LNA Work per minute = (iz^ />) X (2LNA-\ 144 J The first factor (i44/>) is the pressure per square foot. Also A -^ 144 is the area of the piston in square feet, while 2LN is the distance it moves through per minute measured in feet. Hence 2LN A -^ 144 is the volume swept through per minute. Hence the following form : Work per minute = (pressure per unit area) X (volume swept through per minute (b) In this form it must be noted that the unit area and the volume must both refer to the same unit, and since work is measured in foot pounds, this unit must be the foot. Hence more definitely : Work per minute = (pressure per square foot) X (volume swept through in cubic feet) (bi) In a still more general sense when a liquid is moved under pressure, volume moved or change of volume may be put for the second factor, and thus Work per minute = (pressure per square foot) X (volume moved in cubic feet) (bj) [8] Energy This is the capacity for performing work, and depends on special conditions of motion or location. For convenience, energy is considered of two kinds. Kinetic Energy is the energy possessed by a body in virtue of a condition of motion. Such a body resists an attempt to stop it, and it will overcome a certain resistance through a certain distance before being brought finally to rest. This kind of energy is measured bv the formula Wii' E = 2g where W is the weight in pounds, v is the velocity in feet per second, and g is the acceleration due to gravity or 32.2. Sinca energy is directly convertible into work it must be really similar in character to work, and therefore so many foot pounds of energy may be spoken of just as well as so many foot pounds of work. Potential Energy is the energy possessed by a body in virtue of its location or condition relative to the forces acting on it. COMPUTATIONS FOR ENGINEERS 943 Thus a weight lifted to the top of a building has potential energy relative to the street because it could do work if allowed to move downward. Similarly a compressed spring or a compressed gas has potential energy because either, if properly allowed to return to the condition toward which it tends, will perform work. Po- tential energy is measured by the work which could be thus per- formed, or by its equal the work which must be done upon the body in order to produce the given condition; as, for example, the work done in lifting the weight to the top of the building, or in compressing the spring or gas. Potential energy is therefore measured directly in foot pounds. [9] Conservation of Energy It is a fact of universal experience that energy can neither be destroyed nor created. The seeming appearance or disappear- ance of energy or work is always the result of a change of form. Energy may exist in a variety of forms, as (i) Mechanical, (2) Thermal, (3) Electrical, (4) Chemical, and when there is an in- crease in any one form there must be a decrease in the other forms of exactly the same total amount, and likewise -when there is a decrease in any one form there must he an increase in the other forms also of exactly the same total amount. There may be a like exchange between kinetic and potential energy, the one in- creasing as the other decreases, and znce versa. Thus with mechanical energy if there is no change to other forms it will be found that the sum of the kinetic and potential energies is always the same, and that one increases as the other decreases and mce versa. In this view work simply appears as an attendant upon the exchange of energy, or more definitely, as a measure of the exchange. Again, if attention is fixed upon one body, its changes of total energy measure the work which it receives or gives out. If its energy increases, it has had work done upon it. If its energy decreases, it has given out work to some other body. [10] Statics If the forces which act on a body are properly related or balanced, the body remains at rest. The conditions necessary to the realization of this state of rest under the action of forces form the subject of statics. [11] Dynamics If the forces are not so related, the body does not remain at 944 PRACTICAL MARINE ENGINEERING rest and motion results. The amount and nature of such motion and its relation to the system of forces form the subject of dynamics. [12] Propositions in Statics Following are a few simple propositions in statics given with- out proof: (i) A force may be transferred along its line of action with- out changing its effect. (2) Two forces equal and directly opposite will balance or produce equilibrium. (3) Paeallelogram of Forces. If two forces whose lines of action meet in a point are represented in amount and direc- A c tion by the lines A and B, then will the resultant of these two forces be represented also in amount and direction by the diagonal C of the parallelogram A C B erected on O A and B as adjacent sides. (4) A force C^ represented by the diagonal C reversed will balance C or the resultant, and therefore will balance P and Q. (5) Polygon of Forces. Let there be a system of forces represented as in (a). In (b) starting at any point O^ and 0^ A^ equal and parallel to O A. Then from A.^ as starting point draw Ai B^ equal and parallel to B, and so on, drawing finally £1 Fi equal and parallel to F. Then will the closing line Oj F, in direction and amount represent the resultant of the system of forces, while Oj Fj reversed, or F^ 0^, will represent similarly the COMPUTATIONS FOR ENGINEERS 945 balancing force of the system ; that is, the single force which will balance the system and with it produce equihbrium. In the construction in {b) the order in which the forces are taken is in- different, but they have been here supposed to be taken in regular order to the right, beginning with A and ending with F. It is readily seen that this proposition is a generalization of (3) extended to cover the case of .any system of forces. It follows from this proposition that if any system of forces may be repre- sented as in (b) by the sides of a completely closed polygon, then such system will produce equilibrium, for the resultant in such case would be zero. Again, in such case any force may be con- sidered as the balancing force for the system composed of all the others, and any force reversed may be considered as the resultant of the system composed of all the others. (6) Components. In the figure the two forces P and Q are at right angles. In such case they are known as the com- O O B^S ponents, or, more correctly, the rectangular components, of their fesultant R along the lines D and E. In g--al, the co norent 5 of any force C along any hne £ is found by drawing from C a line C B perpendicular to E, thus detenmn- '"^*7)^'c?NDiTioNS FOR EQUILIBRIUM. The Conditions for the equilibrium of any body are as follows : ■ (a) The sum of all the components of all the forces actmg on the body taken along any line, or, more particularly, along any pair of lines at right angles, must balance. (b) Taking any point as origin, the sum of the moments of all the forces tending to turn the body in one direction about this origin must equal or balance the corresponding sum in the other ''^Tf°ail the forces act through a single point, only the first of these conditions is necessary. If instead they act through dif- ferent points of a body, both conditions are necessary. 946 PRACTICAL MARINE ENGINEERING (8) Parallel Forces. The resultant of a system of parallel forces is the algebraic sum of the forces. The center of a system of parallel forces is a point such that if a force equal and opposite to the resultant be here applied, the whole system will be maintained in equilibrium. Or otherwise, it is the point at which the resultant of the whole system may be considered as acting. The center of gravity of a body is the center of the system of sensibly parallel forces due to the attraction of gravitation. Or otherwise, it is the point at which the entire weight of the body may be considered as centered, or through which it may be considered as acting. Or otherwise, it is the point of the body which, if supported, the whole body will be supported in equilibrium and perfectly free to turn into any position. [13] Mechanical Powers Lever. A lever consists essentially of a bar which supports a weight or applies a force at one point by means of a force ap- plied at another point, the bar in the meantime being supported at or turning about a third point called the fulcrum. According to the relation of these three points, levers are divided into three classes as below : Lever of the First Class. In this the fulcrum R is be- '. / tween the points of application of the forces P and W. The fol- lowing proportions and equations apply to this case: P : W :: b : a or P a=W h P : P + W : : b ■ I or P I = {P + W) h W : P +W : : a: lov W I— {P -\-W) a b b WW P = W= {P + W). a= b = ; a I P p^w a a P P W — — P = {P—W). b= 0= ./ b I W F-(- W Lever of the Second Class. In this the weight lifted or resultant force W is between the applied force P and the fulcrum 'R. The following proportions and equations apply in this case : COMPUTATIONS FOR ENGINEERS 947 P : W : : b : I or P l':!=lV h P : (lV — P)::b:aorPa=:z(iy — P)b W : (,W — P) :: I : aovW a— {W — P) I b b W — P W — P P = IV = {W — P). a— b = ; la P W II P P p = — iw—p). b= — ; = ha W W—P ^ '- --1 .. -_^ Lever of the Third Class. In this the applied force P is between the weight lifted or resultant force W and the fulcrum R. The following proportions and equations apply to this case: P : W :: I : a or P a = W I (P—W) : W : : b : a or {P — W) a = W b {P —W) : P : : b : I or {P —W) 1 = P b II WW P = - W = (P—W). a= ;= b a b P P — W a a P—W P—W W = P = {P+W).. b= ; = a lb W P f 1 ^ An ordinary crowbar, a pair of scissors, an air pump lever, are all examples of a lever of the first class. A pair of nut crackers, an oar (the water being the fulcrum), and often many of the levers about the starting and drain gear of an engine, are ex- amples of a lever of the second class. The forearm (the elbow being the fulcrum), or a ladder when raised against a house, are examples of the third class. Windlass and Crank. In this device a barrel B is carried on an axle supported in bearings at A and C, and operated by a crank D. The weight W may then, by means of a rope wound on the barrel, be raised or lowered by the action of a force P applied at the crank. The following proportions and equations give the relations between the various quantities concerned : P : W :: r ■ R or P R=W r 948 PRACTICAL MARINE ENGINEERING r p ■=z ;/■ R R ir = — P r P r = R W W R = r P r = radius of barrel. R =^ radius of crank. Wheel and Axle. This device is the same as the pre- ceding, except that the wheel A takes the place of the crank. The same proportions and equations apply as for the windlass and crank above. Illustrations of the principles involved in this and the preceding figures are found in all forms of windlasses, deck winches, etc. r = radius of barrel. 7? = radius of wheel. Geared Hoist. This device is similar to the two preced- ing, with the addition of gearing between the force P and the weight W. The following equations apply to this case : P W P W = RlR:- R1R2 R1R2 IV COMPUTATIONS FOR ENGINEERS 949 Most deck winches are illustrations of a simple geared hoist. Rt = radius of A n = radius of B i?2 ^ radius of C Yi = radius of D Single Fixed Pulley. /4 is a pulley or sheave supported from R and turning about its center. 5 C is a single rope led over the pulley, to one end of which the force P is applied, and to the other end of which the weight W is attached. The follow- ing equations apply to this case: P = W R— P+IV = 2P Velocity oi W ^ velocity of P. A single whip used for raising light weights is an illustration of this purchase. ^ Single Movable Pulley. ^4 is a pulley or sheave to the frame of which is attached the weight W. B C is the rope rove around the sheave, having one end made fast to the support D^ while to the other is applied the force P. The following equa- tions apply to this case : IV = 2P W i? = P = 2 Velocity oi JV =: i-2 velocity of P. Tacks and sheets on light sails are illustrations of this form of purchase. Luff Tackle. In this purchase there are two sheaves at A and one at B. The rope is led as shown from the frame of B up around one of the sheaves A, then down around the sheave B and up over the other sheave A to the point P, where the power is applied. The following equations apply to this case: R= 3 P R = 4P ?S0 PRACTICAL MARINE ENGINEERING If upper block is fixed, velocity oi W = 1/3 velocity of P. If lower block is fixed, velocity of i? = 1/4 velocity of F. In order to obtain the greatest advantage with this purchase, therefore, B should be the fixed block. 6 A 9 B w A Pair of Blocks^ as in the Luff Tackle Figure, with ANY Number of Sheaves in Either Block. = total number of ,ropes at the lower block, passing through P and attached. R P total number of ropes at the upper block, passing throflgh and attached. Thus in the figure the number of ropes at the lower block is 3 and the number at the upper block is 4, which, according to the rule, would give the same relations between P, R and W as in the equations above. Differential Pulley. In this purchase there are two sheaves at A fastened together, or made in one piece, and one sheave at B. A rope or chain is rove as shown in the figure, and the force is applied at P, while the weight W is supported from the lower block. The following equations apply to this case : R = radius of larger upper pulley. r = radius of smaller upper pulley. IV 2R Then = P R — r COMPUTATIONS FOR ENGINEERS 2R or W ~ P 951 R—r R — r Velocity of f^ = (velocity of P) 2R The differential pulley is commonly found in all engineer'? out- fits on board ship. P^B Inclined Plane. W h b — = or W = P P h h h and P = W b Wedge. R h h = or R = P Pa Q 952 PRACTICAL MARINE ENGINEERING and P = R h Screw. p = pitch of screw. P = force applied at radius r. W = pressure exerted. P : W : : P ■■ 2 v r or P : W : : p : 6.283 r 6.2832 r ovW = P P = 6.2832 r W Examples of the applications of the last three figures will be too familiar to need special mention. [14] Examples in Mechanics Below are given the solutions of a few simple examples as illustrations of the preceding principles of mechanics. In all cases the effects of friction are omitted. COMPUTATIONS FOR ENGINEERS 953 (1 ) In a lever of the first class as shown, a = 48 and & = 8. With a pull P of 160 pounds, what weight W can be raised? a ■ 48 IV = P = X 160 = 960 pounds. b 8 (2) In a lever of the second class as shown, / = 72 inches and Z? = 12 inches. What force P will be required to raise a weight JV of 600 pounds? 6 12 P =: IV = X 600 = 100 pounds. / 72 (3) In a lever of the third class as shown, / = 40 inches and 11' = 30 pounds. Where must a force P of 80 pounds be lo- cated so as to maintain equilibrium? IV 30 a = / = X 40 ^ IS inches. P 80 (4) The dimensions of a windlass and crank as illustrated are as follows : Radius of crank = 14 inches. Radius of barrel ^ 41^ inches. What weight can be raised with a force of 60 pounds applied at the crank? R 14 W = - — P = X 60 = 186 2-3 pounds. r 4J4 (5) With a wheel and axle as illustrated, the diameter of the wheel is 6 feet, and of the axle 10 inches. What force P will be required to hoist a weight W of 600 pounds? S P = W = X 600 = 83 1-3 pounds. R 36 (6) The dimensions of a geared hoist as illustrated are as follows : Diameter oi A ^24 inches ; number of teeth in 5 =: 16; number of teeth in C =;:= 96; diameter oi D = 10 inches. What weight W «an be hoisted if P = 100 pounds ? Since the diameters and radii of wheels are in the same ratio as their number of teeth : i?i i?2 12 X 48 X 100 IV = P = := 1440 pounds. nr, 8X5 (7) With a single movable pulley as illustrated, what weight can be raised with a pull P of 90 pounds? IV = 2 P — 2 X 90— 180. 954 PRACTICAL MARINE ENGINEERING (8) With a luff tackle purchase as illustrated, what force P will be required to raise a weight W of 372 pounds, and what will be the load at RF W =3 P ot P = W ^ 3=372 -^ 3 — 124. i? = 4P=4X 124 = 496. (9) The dimensions of a differential pulley as illustrated are as follows: Larger diameter, 13 inches; smaller diameter, 11 inches. With a pull P of 80 pounds, what weight IV can be raised ? 2R 2X6y2'X8o W = P = = 1040 pounds. R — r . 61^ — 5'/^ (^10) An inclined plane as illustrated has dimensions as fol- lows: Slant length, h =^ 72 inches; height, A = 18 inches. With a pull F of 40 pounds, what weight W can be moved up the plane ? b 72 W = P = X 40 = 160 pounds. h 18 (11) A wedge as illustrated has the following dimensions : Back, a =: 4 inches; length, /i = 26 inches. What resistance R can be overcome by a force P of 216 pounds? h 26 R = P = X 216 = 1404 pounds. a 4 (12) A screw as illustrated has the following dimensions: Pitch, p — J4.inch; radius, r = 12 inches; force, P = 60 pounds. What pressure JV can be exerted? 6.2832 X 12 X 60 W ~ — = 18095.6. 'A (13) Given a boiler brace A with crowfoot or forked at- tachment to the plate B C. With a known load on A, required the load on 5 and C. Evidently the three forces on ^, S and O C keep the joint in equilibrium. If represented according to the polygon of forces [12] (5), they must form a closed triangle. This is represented by ^ D, where A represents the force on the COMPUTATIONS FOR ENGINEERS 95S brace, A D that on B and i? that on C. Hence \i A is laid down to some convenient scale to represent the load on the brace, then A D and D respectively will, according to the same scale, represent the loads on B and O C. (14) Given a boiler brace A oblique to the shell C D. With a known load in the direction B O, required the load on A. The point of attachment O is again maintained in equilibrium by the action of the three forces, one along A, one in the "direction B 0, and a third, C, existing as a tension in the plate. The triangle of forces in this case is represented by S ^. Hence if O jB is laid off to any scale to represent the known load, then ^ill A represent to the same scale the resulting load on the brace. (15) Let C A B O represent the moving parts of an engine. With a known piston load acting along C A, required the re- sultant loads on the connecting rod and on the guide. The point A is kept in equilibrium by the action of the three forces, one acting down along C A, one acting up the rod along B A, and one acting from the guide along DA. It is the two latter which are required. The triangle of forces in this case is 956 PRACTICAL MARINE ENGINEERING represented by A E F. Hence \i A E is laid off to represent to any convenient scale the known piston load, then to the same scale will A F and E F represent the loads on the connecting rod and crosshead respectively. It thus appears that the load on the connecting rod is in general greater than that on the piston rod, and that it is greater in the same ratio that any length A F \s greater than the corresponding distance A E. (16) Let the diagram represent a davit C D supporting a weight W and braced, by a stay A B. With a given weight W, required the tension on the stay and the forces at the foot of the davit. The tension T may be represented by its two components P and Q, and the reaction at C by two' components N and R. In this case, the use of both conditions of equilibrium is required, and without giving all details, simply write the equations and the resulting values of the forces. Equating vertical forces W X Q = N. Equating horizontal forces P = R. Taking moments about C W a= Ph. Also b P = T. I and COMPUTATIONS FOR Q = h I T. From these equations P = a h W. Q = a b W. T = la bh ■ w. R = a h ■ w. CHAPTER XVI Miscellaneous Machinery Steering Engines; Windlasses ; Boat Cranes; Anchor En- gines; Ash Hoisting Engines; Towing Engines; Ventilating, Heating and Cooling Apparatus ; Sirens and Whistles; Fire Ex- tinguishing and Fumigating ; Reducing Valves; Regulating Valves. In the early days of steamship development when ships were small, of slow speed and of limited carrying capacity, the questions of steering, cargo handling, ventilating and heating, were all very simple. The steering was done by means of man power acting through the wheel, tiller ropes and tiller ; the cargo was handled by similar power assisted by the yard arm tackle ; the ventilation was accomplished through metal ventilators assisted at times by the temporary canvas windsail, while the ships were heated by means of stoves located in their living quarters. As the years rolled by, the size and speed of ships gradually increased, until finally they had reached such proportions that the application of man power to accomplish the necessary tasks of steering and of handling boats, anchors and cargo became too puny for the tasks involved. It then became necessary to resort to machinery, and the present-day steering engines, deck winches, boat cranes and anchor engines are the outcome of the necessity. As the sizes of vessels increased, their interior construc- tion became so involved that natural ventilation and the use of stoves for heating became impracticable, and as a result various systems of heating and ventilating were developed to meet the increased requirements and difficulties. In the present chapter some few of these machines will be described. Sec. 142. STEERING ENGINES— STEAM Steam steering gears may be divided into two general classes, the first being: Where the engine is independent of the tiller, MISCFJJ.AMEOUS MACHINERY 9S9 connection between the two being made by means of tiller ropes or chains, spur pinion and arc on rudder head, or by rigid con- necting links driven by blocks carried on a right-and-left-hand screw driven from the steering engine. The second class is that type known as "steam tillers," where the engine is carried on the tiller and moves with it. [i] Indirect Connected Steam Steering Gears American examples of this class are the "Williamson" steer- ing gears, built by the American Engineering Company, of Phila- delphia, Pa., and those constructed by the American Shipbuilding Company, of Cleveland, Ohio. The principle upon which such type of steering gear is built is that it must be reliable in operation and simple in design. It must give the same movement to the rudder when the steering wheel is operated as obtained with the old type hand gear. It is, therefore, necessary, to have the steam valve automatically con- trolled, so that the movement produced by the engine is kept proportional to the movement given the steering gear by the helmsman. The engine controlling valve must start to move at once in response to any movement of the steering wheel in either direction, and the engine must keep moving only so long as the control valve is kept in motion by the steering wheel. To function in this manner, the use of what is commonly called a floating lever valve gear for handling the steam valves of the steering engine is necessary. The application of the float- ing lever principle to the "Williamson" engine is as follows : Rotary motion is given to the shaft A, Fig. 472, from the rotation of the steering wheel in the pilot house. The threaded shaft B, which is prevented from rotating by the follow-up gears E and F when the engine is at rest, is pulled endwise by the rota- tion of miter gears C and D upon rotation of the shaft A. The gear D, which is threaded to fit the shaft B, is held longitudinally by the bearing G. This makes it a block through which the shaft B is drawn. The endwise motion of the shaft B controls the opening of the change valve, which admits steam to the main valves of the engine cylinders. Steam having been admitted to the cylinders during the turning of the shaft A, the revolving of the drum shaft rotating the follow-up gears E and F returns the change valve to a neutral position, when the shaft A ceases to turn, thereby stopping the 960 PRACTICAL MARINE ENGINEERING flow of steam to the main valve and causing tlie steering engine to stop. It is seen that the movement of the steering wheel in the pilot house admits steam to the engine, while the motion of the engine itself cuts off the steam. Stops are fitted to the automatic attachment to regulate the number of turns of the wheel from "hard over" to "hard over." % 4 \[j Fig. 472 These stops are adjustable to agree with the distance the rudder should travel to avoid bringing up against the chocks at the "hard over" position, thus preventing the bringing of undue strains on the chains and connections between the rudder quad- rant and the engine. The steam-steering wheel, made of small diameter, is used only for opening the engine valve. It is mounted on .a pedestal of brass or iron and is connected with the valve motion of the M ISC ELLA NEOUS MA C MINER Y g6i engine by means of shafting and gearing. The number of turns of the wheel from "hard right" to "hard left" varies from six to ten, according to the size of the vessel, a tell-tale or indicator be- ing located on the top of the column to show the angle through which the quadrant or rudder has moved. While the engines may transmit their power to the drum, around which wind the tiller ropes by spur gears or by worm gearing, the latter is to be preferred on account of its greater freedom from noise. Fig. 473 shows an arrangement of such worm gearing. The worm WW is of steel or brass and is driven from the crank shaft by feathers, allowing a sliding motion. The adjust- able bearings BB take the thrust, independent of the main jour- nals of the crank shaft, and take up the lost motion due to any wear of the worm or wheel. This prevents any back-lash or noise in reversing the engine. Adjustment is accomplished by slacking the bolts DD and tightening the screws 5'5". To determine whether the adjustment is too tight the engine should be turned over by hand by m'eans of the crank wheel. 962 PRACTICAL MARINE ENGINEERING Adjustment should be made as soon as any lost motion is discovered, so that the teeth may always be kept in proper bear- ing. Excessive lost motion should be taken up by gradual ad- justment — not all at once. The worms are self-lubricated by Fig. 474. Combined Hand and Steam Steering Gear means of an oiling attachment, L, consisting of a wheel revolving in an oil reservoir and always in contact with the worm. The large wearing surface and perfect lubrication of this style of cut gear make it far superior to the very best of spur gearing. This type of steering engine and gear may be of the "steam only" type or may be of the "combined hand and steam" type. MISCELLANEOUS MACHINERY 96J In this latter type only one wheel is used for both hand and steam steering. The drum is clutched to the worm wheel and is disconnected by means of the small hand wheel F, Fig. 474, on the column, when steering by hand. This same movement throws clutch K on the automatic shaft into contact with the pinion. The lever which operates K has a spring attachment which, if the clutches Fig. 475 do not meet fairly, allovvs it to give until the movement of the steering wheel brings it into the engaging position, thus prevent- ing any danger of jamming the clutch. When it is desired to have frequent and rapid changes from steam to hand steering and vice versa, the type of connection shown in Fig. 475 is used. The steering engine drum is clutched through a cone friction to the worm wheel and is connected and disconnected by means of the small chain drum shown, which is operated through the small chain A hy a small hand wheel lo- cated on the side of the pilot house. The steering engine drum should be connected by means of the tiller ropes leading direct to the tiller or quadrant chain without purchase, and the ropes from the hand gear in the pilot house may be connected either to the rudder direct or to the quadrant chain. .)04 I'K.ICTICAL MJRIXE EXGINEERING [2] Direct Connected Steam Steering Gears r.y direct connected steam steering gears is meant all those in which there is a direct connection between the steering engine and the rudder head, thus elimhiating all chains, ropes, sheaves and fair leads. Such gears are peculiarly suitable for vessels having their propelling machinery located far aft. Where the machinery is located well forward, the advantages of this type are partially oftset by the necessarily long steam anci exhaust pipes required. (a) Napier Screw Gear One of the oldest direct connected types, the Napier Scrciu Gear, shown in h'ig. 476, is fitted with auxiliary hand gear having I'ig. 470. Napier Screw Gear large steering wheels. This arrangeinent brings the engine close up to the rudder stock and produces a very compact machine. With this type of steering engine, the rudder crosshead is operated by two links ,-/, connected to blocks B, actuated by a right-and-left-hand screw C. The screw mav be driven from the engine by helical, spur or worm gear, as may be desired. The right-and-left-hand screw C can be operated from the deck carry- ing the steering engine, with one or more large wheels D mounted directly uiion the extension of the screw shaft or upon a separate shaft connected to the screw shaft bv suitable gearing or from the deck above bv shatting and bevel gearing. /\ modification of this same gear as applied to smaller ves- sels than that for which the gear shown in Fig. 476 is suitable is illustrated in Fig. 477. MlSCliLL.lXBOL S MAClllXERV 96s {b) Engine R.00M Steering Engine For the purpose of operating steering gears at the rudder head by means of engines located in or near the main engine room i-ig. 47 Napier Screw Gear r\Ioditied for Small Vessels aiul thus doing a\\"a\' wdth all necessit}- for running long lines of steam and exhaust piping to the stern of the shiji, the engine ,-~-i-:,^W,i'_^ Fig. 4 7 shown in Fig. 47S has been dc\'elopcd. This t_\-pc nf engine is connected to the right-and-left-hand screw steering gear of the preceding section by a long line of shafting. 966 PRACTICAL MARINE ENGINEERING These engines have proved very efficient in operation, and, owing to the cylinders being suspended below the bed plate, the valve gear and pistons can be removed in the compartment directly below the engine. Fig. 479 (c) WiLsoN-PiRRiE Steering Gear In large ocean-going steamers, steam steering gear of this type has found much favor. It has the advantage of being direct connected to the rudder head through spring quadrant gear. The MISCELLANEOUS MACHINERY 967 springs absorb all shocks between the rudder and the engine and relieve the engine and gear to a marked degree. Two vertical engines are provided, each with two cylinders, which actuate pinions on the crank shaft end farthest from the rudder head, and, through the medium of spur gears and bevel gears, transmit this motion to the two pinions, one for each en- gine, which mesh with the quadrant itself. One engine only is used at a time, the other remaining as a spare gear. The idle en- gine is thrown out of gear and can be overhauled at any time without disturbing the operation of the rudder. Although this machine is different from the one shown in Fig. 479, the arrangement of quadrant, main tiller, spare tiller and spring gear is the same. Referring, therefore, to that illus- tration, it will be noted that the two springs / are connected to the end of the main tiller and to the quadrant. The latter runs loose upon the rudder stock, to which both the main tiller and the spare tiller are keyed. It is evident, therefore, that the springs will transmit power from the quadrant to the tiller and that their elasticity will prevent shocks being sent in the reverse direction from the tiller through the quadrant to the engine. A demand for a cheaper type of the direct connected gear produced a modified form of the Wilson-Pirrie gear. With this type the quadrant is keyed to the rudder head, the springs are omitted and all overstrain is taken by the friction clutch. There is one horizontal engine with two cylinders, though sometimes two engines are fitted. The gearing between the engine and the quadrant consists of a worm and worm gear and a single pinion, the latter being upon the same shaft with the worm gear. Between the worm gear and the pinion is the clutch, which consists of two half bands inside the casing, hinged at one end and expanded at the other end by means of a right-and-left-hand screw, operated by a worm and worm gear from a pinion on the worm shaft. This pinion is operated by the large gear which encircles the worm-wheel shaft and which is operated by a large hand-wheel encircling this same shaft. Operation is combined steam and hand, the steam valves being controlled through a small shaft. The valve gear may be operated selectively through wire rope transmission, shafting, or by a trick wheel directly on the engine, or by hydraulic tele- motor, which will be described later. 968 I'R.ICTIC.IL M.lkL\'Ji n\'GlNElUilNG (d) Compromise Wilson-Pirrie Gear The gear shown in Fig. 4iSo is a compromise between the Wilson-Pirrie gear and that last described. Like the Wilson- Pirrie gear, there is a spring connection between the (juadrant and the tiller, thus providing fijr the absorption of all shocks. The arrangement of engines, gears and methods of valve con- trol are, however, similar to those last described. (e) Differential Steering Gears All direct connected steering gears require careful alinement and maintenance. This feature, which forms in many cases a source of wear and trouble, together with the wasteful use of steam, especially when using only small angles of rudder, has tended to produce a more economical gear known as "Differential Steering Gear." h'or the double purpose of saving steam consumption by the steering engine and of obtaining a differential leverage, increas- Fig. 480 ing as the rudder is moved away from its amidship position into areas of greater resistance from the water, the dift'erential link connection between the rudder head and the quadrant shown in Fig. 481 has been developed. This permits the rudder to be moved more quickly with little resistance near amidships and consequently the ship responds more quickly to the helm. The quadrant is made a complete circle and so arranged that it can be adjusted to any one of four different positions, thus allowing for wear during the life of the machine. The pins con- necting the differential link to this quadrant are at a smaller radius from the center than are the pins on the rudder head. T^e ratio IS such that for a fortv-five degree movement of the rudder MISCELLAXEOUS MACIUXERV 969 the gear quadrant moves about 70 degrees. This makes a differ- ential leverage, which increases the farther the rudder is moved. When hard over, the links approach the condition of a toggle joint. One feature of this trapezoidal connection is that the middle joints between the two pairs of pins do not remain the same dis- tance apart. In order to allow for th"is variation, the gear quad- rant is so arranged that it can swing about the pinion shaft as '^^tJSJ' required. Instantly, this ability to move ehminatcs the careful adjustment and maintenance necessary in other direct-connected gears. By the use of eccentricity of the middle joint between the rudderhead pins, the movement mentioned is limited to 5/32 inch. The differential gear arrangement takes less space than any other type, less even than the screw gear machine. The steering engine itself is compact and self-contained, having no require- ment for alinement except with the rudder stock. There are no expensive brackets and sheaves to be made and suitably secured. Aside from the base plate of the engine, there is simply the bracket for transmission to the deck above. The pinion and gear can readily be adjusted to suit any height of transom or rudder head. Sec. 143. ELECTRIC STEERING GEAR As an auxiliary to steam steering for commercial use, the electric motor has occasionally been found desirable. An ar- rangement of this sort is shown in Fig. 479, where the gear may 970 PRACTICAL MARINE ENGINEERING Fig. 482. Elevation of Steam Tiller Fig. 483. Plan of Steam Tiller be operated either by steam or by electricity, the steam engine or the motor being coupled in as desired. MISCELLANEOUS MACHINERY 971 Sec. 144. CLASS 2; STEAM TILLERS The essential qualities required for an ideally perfect steer- ing gear are sometimes summed up as follows : 1. The steering engine should be attached to the rudderhead without intervention of chains or ropes. 2. It should let go the rudder when unduly strained, and when. the abnormal strain has gone, return automatically to its former position. 3. The connection from steam to hand gear, and vice versa, should be effected without the use of jaw clutches or the slipping of bolts into holes — which operations are difficult to effect when the ship is rolling at sea with the rudder adrift. 4. The communication from the bridge to the machinery aft should be of a kind which dispenses with rods, chains and shafting, all being equally troublesome to the shipbuilder to ar- range and to the officers of the ship to keep in order. With reference to condition 3, it is a common practice to fit rubber brakes on ships where clutches are the means of connec- tion ; but as simplicity and fewness of parts are of first importance in steering gear, it is better that such a connection between the steering engine and the rudder, or the hand gear and the rudder, should be one which will act both as a clutch and a brake. To meet these conditions as far as possible, the steam tiller has been designed. In the accompanying illustration. Fig. 482 shows an elevation with hand steering gear, Fig. 483 being the plan. The prominent feature of this gear, in which it differs from all others, is that advantage is taken of as long a lever as will reach from the rudderhead to the limits of the poop deck, which, in the greatest number of ships, varies from 7 to 10 feet, and in the largest class of vessels has reached the length of 17 feet. It will be obvious that the strains at the end of such a lever will be reduced to the smallest possible amount and that the gear necessary to give the requisite power to steering the ship will be of the simplest form. The tiller A shown in Fig. 482 is keyed to the rudderhead B, and at its other end a jaw C is fitted with gun metal bearings in which a driving pinion D works, gearing into the toothed seg- ment E, which is bolted securely to the deck. The steering en- gines, two in number, are carried on the tiller and move with it, receiving and exhausting their steam through a double stuffing 972 PRACTICAL MARINE ENGINEERING box F, which also contains the reversing valve and is mounted on the axis of the rudderhead. The steam cylinders G are of ordinary construction fitted with piston valves. Motion is communicated to the pinion D through the intervention of an expanding friction clutch H, which is lined with wood and engages the worm wheel /, which in turn engages with the worm /. Motion is given to this worm by the steam engine, as shown in Fig. 483. The clutch H is expanded by a screw bolt and worm . wheel K, which turns in and out of the nut L at one end, the other abutting against a series of laminated springs M, so that by turning the worm A'' by a handle, provided for the purpose, to the right or left, the steam gear is engaged or disengaged at any position the rudder may be in, and at the same time it forms an efficient brake to hold the rudder in a seaway. In practice it is usual to expand this friction brake or clutch sufficiently tight to put the rudder hard over at full speed trials; but the springs in any case have not sufficient force to hold the connection tight enough to fracture any part of the machinery. In the event of a heavy sea striking the rudder, it immedi- ately slips, allowing the rudder to move out of position. This motion, however, opens the steam valves and the engines then bring the rudder back to position. As the steam tiller is in- tended for use on open as well as on closed decks, the entire machinery ie placed in a watertight casing, which forms the frame- work of the steering engines, access to these being given by the doors 00. The oiling of the various parts is efifected automatically by two valveless oil pumps PP, driven off the valve rods of the engine. These throw the oil from a well in the bottom of the casing through the hollow piston rod into the reservoir Q, and from there a copious supply of oil is supplied to every working part, as well as to the piston and valve rods. The pinion end of the tiller is carried up by gun metal slip- pers and spiral springs under the lugs RR, which can be ad- justed. As there is always a tendency for the tiller or quadrant to shake or chatter when there is no strain on, the rudder being fore and aft, the slippers in that position work upon inclined planes SS, which gives sufficient brake action to prevent any vibration. When putting the helm over to such an extent that MISCELLANEOUS MACHINERY 973 the pinion bears hard on the rack, the slippers run down on to the flat part of the toothed segment, when the springs slack off and only hold up the weight of that end of the tiller. The hand gear consists of a strong standard T bolted to the deck and carrying a worm wheel and worm with hand wheels and friction clutch exactly similar to that described in the steam gear. At the lower end of the shaft there is a pinion similar to D, which engages the toothed segment U, which is securely bolted to the steam tiller. The operation of changing from hand to steam or steam to hand by means of the clutch brakes can be accomplished very quickly. It is claimed that with this system of hand gear the friction is only one-third of that of the double screw system with nuts and connecting rods to a crosshead on the rudderhead, Fig. 476. The steering valve is operated by the lever V, which causes the piston valve to turn on its axis inside the trunnion casing, and as the tiller moves round it carries the valve face with it and closes the port. The lever V is connected to the motor cylinder ^ff the telemotor gear, which will be described later, by two pipes of small diameter, leading up to the bridge. In case of accident to these pipe communications to the bridge, a steering station is provided aft, which can be connected to the steering valve. It is claimed for this type of gear that it has the fewest num- ber of parts possible, namely, one pinion, one worm wheel and cne worm, which is due to the fact that the toothed segment in a tiller represents a steering wheel whose radius is the tiller, and this toothed rack, being shrouded to the crowns of the teeth and bolted at short intervals to the steel deck, is very secure. See. 145. ELECTRO-HYDRAULIC STEERING GEAR— HELE- SHAW MARTINEAU TYPE The ever-increasing use of electric motors and internal com- bustion engines has forced the subject of variable transmission more and more to the front, and in the field of auxiliary ship machinery has created a demand for an electrically-operated vari- able transmission for ship-steering gears. As a result of this de- mand, the Hele-Shaw Martineau electrical hydraulic steering gear has been developed. This steering gear, which has met with great success and an extended use abroad, consists, briefly, of the following parts : 974 PRACTICAL MARINE ENGINEERING One electric hydraulic unit consisting of a constant speed electric motor, direct connected to a variable stroke, reversible, hydraulic pump. It is on this pump that the basis for the whole system is founded, combining the capability of being run at high speed, positive action and power of giving and sustaining very great pressure, perfect balance, high efficiency and compactness with minimum wear. There are two or more hydraulic cylinders and rams (Fig. 484) operating a crosshead, to which the tiller is attached and which in turn operates the rudder. The control Rudder Head .Hydraulic 1 CyliudeE Fig. 484. Diagram Illustrating the Principle of the Hele-Shaw Martineau Electric Hydraulic Steering Gear from steering stations may be by either electric or hydraulic tele- motor, rope, shaft or other transmission gear. A diagrammatic view of a conventional application of this type of gear is shown herewith, and a general description of the method of operation follows : •By this diagram it will be seen that the rudderhead A is operated by rams working in two cylinders B'^ and B^. The rams themselves are actuated by oil which is supplied from a rotary variable stroke pump C. The pump itself is driven by the electric motor D. The operation is as follows : £ is a rod con- trolling the operation of the pump in such a way that when it is in mid-position no oil is being pumped. According as it is moved in or out from the central position the oil is transmitted under pressure through one or other of the pipes F^ and F"^ to the cylinders B^ and B"^. In this way, by the mere movement of the spindle E, the rudderhead can be put over to port or starboard as required. The actual operation of the spindle E is effected by means of a floating lever G, coupled near its middle point to the spindle E and controlled at one end by a lever H, which is con- MISCELLANEOUS MACHINERY 975 nected with the telemotor, and by means of the latter k operated from the briuge. The other end of the floating lever G is con- nected by means of the link L to the tiller head. Thus, as the link H is moved, the other end of the lever G being for the moment fixed, the spmdle E starts the pmnp in operation, and as a consequence the tiller head begins to move. In doing this, the link L mo^-es the other end of the lever G, and hence tends to bring the spmdle E to its middle position and so stops the pumping action (although the pump continues rotating) and in doing so the rudderhead is left exactly in the position correspond- ing to that which the wheel and telemotor have been made to take up. The only other essential feature is the pipe P connecting with the two ram cylinders (Fig. 485), in which is placed a Hydraulic Rams spring-loaded by-pass M, so arranged that if the rudder be sub- jected to any shock which would bring about more than certain predetermined stresses the rudderhead is able to yield by the transfer of oil from one ram cylinder to the other, and, since the floating link is thereby moved, the pump is automatically set in operation and the rudder restored to the position corresponding to that of the steering wheel f without the intervention of the steersman). There is practically no leakage, but what little there is, is taken back into the make-up tank, which is conveniently placed below the level of the system. It is obvious that as the flow is reversible fthe pressure and suction sides being interchangeable) the two sides of the pump must each be connected with the tank 976 PRACTICAL MARINE ENGINEERING by a pipe having a non-return valve, and, by means of these two non-return valves the leakage is returned to the circulating sys- tem. The pump, owing to the introduction of a new mechanism, has a very high efficiency for a large range of pressures and can work at a high speed, thus enabling it to be coupled direct to an electric motor. Some of the advantages claimed for this type of electric steering gear are that its extreme sensitiveness of operation per- mits of a rudder movement of but a small fraction of a degree; that the incompressibility of the oil pumped into the cylinders insures the rudder in holding its position ; that relief from shock and an automatic return of the rudder to the precise angle held before the shock is insured, and that the extreme simplicity of the system and the use of lubricating oil as a medium of operation practically eliminates all wear on the pump and other moving parts. The points on which great economy is claimed for this steering gear is that its precision will shorten a ship's voyage, due to straighter course steered, that it requires a minimum of atten* tion and adjustment, and that, owing to the electric motor and the hydraulic pump being in motion at the time the rudder i^s required to be moved, the static resistance to be overcome is very much less than in gears where motor and pumps have to be started in order to move the position of the rudder. Sec. 146. TRANSMISSION The type of transmission to be used between the pilot house and valve gear of any steering engine becomes an important item when the steering engine is located aft at the rudderhead. The use of shafting and gears is very undesirable, owing to the set- tling and shrinkage of decks, resulting in throwing the shafting out of alinement and causing parts of the transmission gear to bind. It thus follows that shafting and gears should be used for short distances only. When a clear runway is available, such as is to be found on freighters on the Great Lakes, a sliding-shaft transmission has been successfully used. The shaft, running fore and aft, is sup- ported on rolls and has a rack fitted at each end. These racks en- gage with pinions, of which the forward one, rotated by the wheel in the pilot house, gives endwise motion to the shaft. The motion thus transmitted rotates the after pinion, thus controlling the MISCELLANEOUS MACHINERY 977 Opening of the steam valve by operation through suitable lever connections. A transmission in common use for long distances consists of a wire rope drum forw^ard, and another aft, connected by ^-inch diameter flexible wire cable. This type of transmission is thor- oughly reliable. In fitting it, provision should be made for taking By pass Cock J > a(i Return Pipe L Cheese Cloth Strainer On Top of Tank Filling Tank B Filling Pump A Fig. 486 Up the slack due to stretching or other causes, without disconnect- ing the rope ends. By the use of fair leads, this rope can be run around obstructions and other places which would be impossible for shafting. [i] Outside Packed Telemotor Another very flexible transmission gear is the hydraulic tele- motor. Fig. 486 shows the controlling cylinder of an outside packed telemotor, also the hand operated pump for filling the cylinder of the telemotor and for making up for any slight leakage which may occur during operation. The transmitting 978 PRACTICAL MARINE ENGINEERING cylinder in the pilot house is connected with the controlling cylinder at the steering engine by copper pipe of small diameter. The whole system is charged with a fluid consisting of water and refined glycerine in equal parts, or with telemotor oil manu- factured especially for this purpose. This hydraulic combination forms as nearly as possible a frictionless means of transforming the revolving motion of the steering wheel in the pilot house to rectilinear motion in the valve gear of the distributing valve of the steering engine. Provision is also made, when desired, for con- necting the steering wheel on the bridge to the pilot house trans- mitting gear. A by-pass valve is usually fitted in the system to provide a ready means of connecting it with the filling tank. Having two independent columns of water with no connecting passages ex- cepting this by-pass, there can be no leakage altering the relative position of the plungers in the transmitting and controlling cylin- ders. All leakage taking place at the stuffing boxes is immedi- ately visible and is reduced to a minimum by hydraulic leather packing. Where leakage occurs, it is made up from the filling tank through the by-pass. Instructions for filling the telemotor system and for central- izing the rudder are given below, the letters referring to the diagram Fig. 486. Instructions for Filling Systems 1. When first starting, fill from aft end. 2. Open cocks C, D and by-pass cock /. 3. With pump A, fill system from tank B, pumping until fluid returning from pipe L is free from air bubbles. Care should be taken to keep tank B well filled and pipe M well under fluid, so as not to pump any air into system. 4. Close cock D. 5. Let oflF any pocket air at relief E and F, keeping pump moving slowly. 6. Close cocks E, F, and C. 7. Fill supply tank /. 8. Open cocks G and H to let air out, then close. 9. Turn steering wheel K to right and left to work out entrained air. ID. Close by-pass cock /. MISCELLANEOUS MACHINERY 979 Instructions for Centralizing 11. With engine in operation, turn steering wheel K until lamp lights up, showing that rudder is amidship, then stop. 12. Open by-pass cock /, then bring king spoke up with center marked C on rack, fair with pointer. 13. Close by-pass cock /, then forward and aft telemotor are centralized. [2] Bridge Transmitting and Inside Packed Controlling Telemotor The object of the telemotor is to supply a means of com- munication as nearly frictionless as possible, no matter how tortuous the communicating lines may be. The method by which this end is obtained is by a hydraulic device shown in Figs. 487, 488 and 489, which is suitable for large vessels where the com- municating lines must pass around corners, under decks, etc., in order to avoid cabins and other important spaces. In the telemotor an important function is performed in pass- ing the zero point amidships, by which, should the indicator not correspond with the actual position of the rudder, an automatic adjustment of position is produced. Fig. 487 shows the vertical section of a pump A fitted with a piston B, which is moved up and down by a rackC. Into* C gears a pinion D, fixed to a shaft which is caused to revolve by means of the hand steering wheel through the pinion G and the wheel F. The cylinder A, when the piston is in mid-position, as shown in Fig. 487, admits of a free passage of water above and below the piston, dividing A practically into two cylinders, an upper and a lower. The distance between the upper and lower cylinders is so small that the piston leather packings pass freely over the valve ports from one cylinder to the other without damage. From the by-pass valve S, which is connected to the top of the upper cylin- der by the pipe H and directly connected to the bottom of the lower cylinder, two pipes H and /, Fig. 487, pass and connect to a cylinder K, Fig. 488, of the controlling telemotor. These pipes correspond to the pipes M and L, Fig. 488. The cylinder K is fitted with a piston N, and with a piston rod and connecting link 0, which is attached by a lever to the follow-up mechanism of the steering engine, or in the case of a steam tiller connects directly gSo PRACTICAL MARINE ENGINEERING to the control valve lever. The piston rod has crossheads P and P, between which are two spiral springs Q and Q, the object being to cause the piston end to return into mid gear, unless prevented from doing so by pressure of water on either side of the piston. As the common diameter of the cylinders of the bridge trans- mitting telemotor is exactly the same as that of the controlling telemotor cylinder, it follows that when the system is completely Fig. 487 Fig. 488 filled with fluid, any movement of the steering wheel will bring about a corresponding movement of the controlling telemotor piston in cylinder N and in the valve gear of the steering engine. The transmitting telemotor on the bridge is fitted with an indicator, shown in Fig. 489 at R, which, when everything is in proper condition, will show the actual position of the helm. It is possible, however, that the leather packings may become so worn as to admit of considerable leakage. This may cause the piston to work entirely in one cylinder, so that when the ship is MISCELLANEOUS MACHINERY 981 steered on a straight course the indicator will indicate many de- grees of helm angle. To readjust the indicator and the position of the helm, it is only necessary to move the wheel until the indicator is brought to zero and the piston B then enters the mid-position, when the compressed springs aft will immediately bring everything into correspondence. As, however, the piston B in steering a ship is always passing the mid-position in porting or starboarding, even Fig.489 Fig. 490. Bridge Transmitting Tele- motor and Steering Wheel to the smallest extent, the tendency is for the piston N in the cylinder K always to attempt to get into mid-position, and the steering by the telemotor on the bridge is to disturb the position of the piston A'^ and move it in either direction from the center of the cylinder. It is sometimes necessary to set the gear so that this central position does not actually represent the rudder as true fore and aft, but a certain amount of permanent helm is given to counter- act the action of the propeller in steering, and this is done by making the connecting links O longer or shorter, as the case may require. In some exceptional cases, where i-t migl.it be inconvenient to 982 PRACTICAL MARINE ENGINEERING adjust the gear by running the indicator into its mid-position by the steering wheel, and so momentarily affecting the straight course of the ship, there is provided a by-pass valve S, which, when opened, gives a free communication between the upper and lower cylinders and so allows the indicator to be brought to zero without moving the rudder aft. A small tank V is provided with a gage glass at the end, as shown. This is usually charged with a mixture of glycerine aiid water, one part of the former to two or three of the latter. It is very important that the whole system of pipes and cylinders should be fully charged and that no air should be present. This being the case, it is necessary to provide for the ex- pansion and contraction of the fluid due to changes of tempera- ture. For this purpose, a relief valve W is fitted at mid-position of the cylinders, a section of which is shown in Fig. 487. They contain each an inlet and outlet valve about yi inch diameter. The outlet is simply an ordinary safety valve loaded above the working pressure, which is about 150 pounds per square inch. When the temperature rises, as in the case of the sun shining on the pipes, a portion of the fluid is blown into the tank V, and when the temperature falls, the fluid contracts and takes in the necessary quantity through the inlet valve. The entire telemotor on the bridge is constructed of gun metal, so as not to affect the compass. The motor cylinder a-ft is of similar material, and the pipes are of solid drawn copper, of diameters varying from ^ inch to % inch, according to the length of the vessel. Sec. 147. ANCHOR WINDLASSES AND CAPSTANS For handling heavy anchor chains and heavy hawsers the power windlass, the power capstan and the power combined wind- lass and capstan have been developed. The power employed is usually steam, although in many cases the steam engine is re- placed by the electric motor. [i] Steam Windlass for Light Craft Fig. 491 shows a type of the steam windlass which has been designed principally for light craft. It is of the spur-geared type with the engine self-contained on the same bedplate with the windlass. In this type of windlass, as it must be of extremely MISCELLAMEOUS AfACHINERV 983 light construction, all of the parts are made of one of the strong bronzes. [2] Steam Capstans As an example of the steam capstan, Fig. 492 is shown. In this type the engine is carried by the same deck as the capstan but underneath it, the power being transmitted to the capstan by means of a worn: driven b)- the engine, gearing into a worm wheel carried on the shaft of the capstan. The engines are usually made non-reversing. Pawls are provided on the lower part of the cap- stan barrel to keep the engine from turning backward when iMg. 491. Spur Geared Steam Windlass for Light Craft Stopped, due to the hawser strain. The capstan shown is fitted with sockets for the fitting of capstan bars when desired to oper- ate by hand. In the ex-ample given two speeds are provided, whether oper- ated by hand or by steam. When quick speed and light power are desired, the block key A is inserted in the capstan head, thus locking the barrel to the Iieafl. For the slow speed and heavy ])(jwcr, tlie Ijlock key is placed in the base, thus locking the gear plate which carries jdanetary gears meshing with an internal gear in the lower rim of the barrel. To fit the capstan for operating by hand, the engines are disconnected Ijy removing a I)lock Is-ey from the worm gear, thus allowing it to turn freely on its shaft. 984 PRACTICAL MARINE ENGINEERING [3] Combined Capstan and Windlass As an example of the combined capstan and windlass, Fig. 493 is shown. The capstan is geared to the windlass shaft by bevel gearing. A clutch is fitted on the capstan shaft so that the capstan can be disconnected when it is desired to work the wind- lass only, and also the windlass can be disconnected from the en- gine when the gypsies only are required to be used. The capstan Fig. 492 Steam Capstan provides a very satisfactory means of working the windlass by hand, the capstan being provided with gearing in the base and an arrangement of pawls such that when the capstan head is turned in a right-hand direction, the capstan barrel turns in the same di- rection as a simple capstan, but when the capstan head is moved in the reverse direction, the capstan barrel continues to turn in the same direction as formerly but at a decreased speed of about 3 to I, thus making a power capstan. MISCELLANEOUS J\IACI11NERY 98s I'ig. iOa. Combined Steam Capstan and Windlass; Spur Geared Type Fig. 494. Vertical Steam Capstan Windlass with Engines Inclosed in Base Another form of the combined capstan and windlass is shown by Fig. 494. Such an arrangement is intended for installation 986 PRACTICAL MARINE ENGINEERING on steamships where there is no space under the deck available for the installation of the engine. [4] Electric Capstan and Windlass The steam engines shown in the foregoing illustrations may all be replaced with electric motors, a windlass so fitted being shown in Fig. 495. The motors may be direct connected to the driving shaft or through reduction gears, the former being pre- ferable for quickness of operation, but the latter requiring a much smaller motor of higher speed. The connection between the Fig. 495 Electric Windlass motor and the driving shaft may be made by means of either a positive jaw or a friction clutch. [5] General Description of Engines and Windlasses In general; the steam engines used with anchor windlasses are of the same type, simple engines; sometimes being built as simple, two cylinder, vertical inverted engines, both cylinders working on the same crank shaft. In othier cases there are two single cylinder engines arranged diagonally, as shown in Fig. 496, the two engines driving the worm shaft by cranks at the same end, while in other cases the engines are single cylinder, hori- zontal, driving the worm shaft by cranks at its opposite ends, as shown in Fig. 494. The engines are usually made reversible, the reversing being accomplished by means of either a slipping MISCELLANEOUS MACHINERY 987 eccentric whose position on the shaft can be changed from behind to ahead of the crank at will, or by means of a reverse valve by which the flow of steam to the ports can be reversed. The windlasses are all constructed on the same general prin- ciples, as follows: _ Figs. 496 and 497 show a windlass of the horizontal type, having a capstan connection. Beginning at the right hand, A is what is called the gypsy, for handling light lines and hawsers; Fig. 496. Plan of Steam Capstan Windlass next in order is one of the main supporting bearings; then B is a handwheel for throwing in and out the locking device which locks the "wild cat" C to the main windlass shaft. Over C passes the anchor chain, C being cast of such a pattern as to fit the length of link of the chain which the vessel carries. Adjacent to C is seen R, which is a friction drum on which fits a friction band controlled by means of the lever M. Next to R is D, a. worm wheel locked to the main shaft by pawls, by means of which the windlass can be driven by hand from the capstan P through the worm I. Next in order is the middle main bearing of the windlass shaft. E is the main worm wheel for power driving of the windlass, the power being transmitted from the engine N through the worm shaft and worm F. E can be locked or unlocked from the main shaft as desired by means of pawls, so that the capstan P can be driven independently through the 988 PRACTICAL MARINE ENGINEERING worm /, worm wheel H and shaft 0. G is a locking wheel for locking H on 0. Reversing is accomplished by means of the reverse valve A', which is operated by means of the hand lever L working on a notched link. Fig. 497. Side Elevation of Steam Capstan Windlass In some makes of windlasses the engine worm gearing is replaced by spur gearing, as shown in Fig. 493. Sec. 148. DIRECTIONS FOR OPERATING STEAM CAPSTAN WINDLASS (All references are to Figs. 496 and 497) [i] To Work Windlass by Steam Ahead and Heave in Chain For Windlass with Reverse Valve: Lock the windlass. Start ahead by opening the throttle in steam pipe and push the hand lever L of the reverse valve K forward and control the running of the engine by means of the lever or by the throttle valve as is most convenient. MISCELLANEOUS MACHINERY 989 For Windlass zuith Slip Eccentric: Lock the windlass. See that eccentric is set for running ahead, open the throttle valve and control by throttle. On either style of windlass, if it is not desired to run the cap- stan at the same time, throw out the pawls in the capstan worm gear H by turning the hand wheel G to the right hand, until it brings up. When running ahead, it is better to keep the backing pawl in the engine worm gear E thrown out, avoiding the noise it otherwise makes. [2] To Stop the Windlass Windlass with Reverse Valve: Bring the reverse lever L back to central position if only stopping for a short time. If stopping for a long period, close the throttle valve. Windlass with Slip Eccentric: Close the throttle valve. [3] To Reverse Windlass for Veering Chain See that the backing pawl in the engine worm wheel E is thrown in and the two pawls in the hand worm wheel D are thrown out, then For Windlass with Reverse Valve: The throttle being open, pull the reverse lever L aft and control by throttle. For Windlass with Slip Eccentric: See that the eccentric is put into the backing position and start and control the windlass by means of the throttle valve. [4] To Work the Windlass by Hand See that the backing pawl in engine worm wheel E is thrown out, the two pawls in the hand worm wheel D are thrown in; drop the locking keys or pins into the holes provided in the lower part of the capstan barrel P and turn the capstan "with the sun." [S] To Lock Windlass Turn the hand wheel B from forward aft, making sure that the face of the projections on the wild cat C do not come in direct contact with the face of the projection on worm gears E or D, but that they go by and bring up against the rims of the worm gears in such a way that one projection will engage the other as in a clutch. [6] To Unlock Windlass Turn the hand wheel B in the opposite direction until the nut brings up against the stop in the shaft. 990 PRACTICAL MARINE ENGINEERING [7] To Obtain Double Purchase on Windlass Throw out the go-ahead pawls in engine worm gear E and keep them out by set screws provided for that purpose. See that the pawls in the hand worm gear D and capstan worm gear H are thrown in. Start the windlass, and the capstan worm / on the forward end of the engine crank shaft will drive the upright shaft or capstan spindle 0, which in turn will drive the windlass through the hand worm / and gear D. It is unnecessary to use this pur- chase under ordinary circumstances. [8] To Veer Chain Without Using the Engine Unlock the wild cat C by turning the hand wheel B forward and until the nut brings up on stop in shaft, and control the wild cats by means of the friction brake levers M. [9] To Run Capstan by Steam Throw in the pawls in the capstan worm gear H. See that the pins are in the holes in the lower part of the capstan barrel P and run the engines ahead as when running the windlass, at the same time having the wild cats thrown out. If it should be desired to run the capstan constantly, without working the windlass, the go-ahead pawls in the engine worm gear E may be thrown out and kept out by set screws provided for that purpose. [10] To Run Capstan by Hand Pull out the two pins in the lower part of capstan barrel P. Holes will be found in the base to hold these pins while not in use. Use as an ordinary hand capstan, turning head "with the sun" for speed, and "against the sun" for power. [11] Use of Pins in Capstan The pins or toggles connecting capstan to shaft are only re- moved when capstan is to be worked by hand. [12] Use of Friction Bands Ride only by friction bands and with windlass unlocked. It is then ready to pay out chain at an instant's notice. Windlass should be locked only when heaving in chain. Do not use oil on the fric- tion bands. Keep the turnbuckles free from rust so they can be screwed up at any time. M ISC ELLA NEC I 'S }L I CM EVER Y 991 [13] Working the Pawls To throw out the backing pawl in the engine worm gear E and the two pawls in the hand worm gear D, pull the pawl lifter cam away from its seat one-eighth inch and give it half a turn to the left. To throw the same pawls in, turn the pawl lifter cam to the right or in the opposite direction. To throw out the pawls in the capstan worm gear H, turn the hand wheel G to the right or "with the sun" until it brings up. To throw these pawls in, turn the hand wheel G to the left, ''against the sun" or in the opposite direction from above, until it brings up. [14] Directions for Keeping Windlass in Order Oil holes will be found in tlie wild cats, in the nuts, and in the rims of the worm wheels. Turn windlass by hand occasionalh", to insure the oil working under the rims of worm wheels. Use sperm oil on all parts of windlass that are exposed, or where ordinary oil would "chill." Sec. 149. TOWING ENGINES For the purpose of heavy towing at sea in all kinds of weather and under conditions which would make a rigid connection Ije- Fig. 498. Automatic Steam Towing Machine tween ships a source of danger, the automatic steam towing ma- chine, of which that shown in Fig. 498 is a type, has been devel- oped. The distinctive feature of this machine is the combination of the elastic steam cushion and the automatic relief to the hawser, 992 PRACTICAL MARINE ENGINEERING without which the latter would be continually straining and fre- quently breaking. Practical tests demonstrate that the operator is always in complete control of the vessel or barges being towed. The distance between the vessel in tow and the towing ship or tug may be altered at will. This is a great advantage in a crooked channel or going through canals or under bridges, for it obviates all necessity of stopping and taking in the hawser, as was formerly done. The machine, as shown, is built without any bedplate, the main frame being so designed as to provide sufficient rigidity for the whole machine, and so can be bolted directly to the deck. The frame includes the side bitts and all the main bearings of the machine. It carries the two steam cylinders, overhung on the after end, with steam checks and control valves between them. The main drum is mounted low in the center of the frame in order to reduce the straining effect produced by the pull of the towing hawser in a heavy sea. The drum is driven by a heavy cast steel spur gear wheel mounted- on the same shaft and into which engages a cast steel pinion carried on the crank shaft of the engine. In the engine illustrated the tow line is taken to the drum over the cylinder end of the machine, thus reducing the liability to fouling any moving parts, in addition to allowing the bulky part of the ma- chine to be set close up to the deck house, the cylinder of the en- gine being out in the clear for overhauling. The engine is fitted with a reverse valve, which forms a complete separation between the steam and exhaust ports and which is fitted in the same casting with the automatic towing valve, both valves being controlled by one lever. The mechanism for controlling the smaller or automatic valve consists of two spur gears shown on the side of Fig. 498, two pinions and a finger con- trolled by a cam which engages in the reach rod actuating the lever connected to the valve stem. The entire automatic arrange- ment is controlled by a lever, which allows it to be thrown in and out of service, the latter condition being for controlling the towing machine by hand. This mechanism is very simple and cannot well be put out of order. It is always in position and does not require any atten- tion before being put into use. The automatic towing valve opens and shuts gradually according to the variations in the pull on the line. MISCELLANEOUS MACHINERY 993 The automatic valve performs the double function of con- trolling the steam supply to the cylinder when towing automatic- ally and of shutting off the steam entirely from the reverse valve, thus reducing to a minimum the pressure on this large, flat valve when it is necessary to reverse the engine. The throttling is done by the independent automatic towing valve, or may be done by a valve in the main steam pipe, if desired. The two spur gears already mentioned as the initial parts of the automatic mechanism, are of different diameters and re- ceive their motion from two pinions connected to the drum shaft. When these gears are revolving, it is at a different number of turns per minute. This difference between the two gears ac- tuates the finger engaging in the reach rod for controlling the valve. It is so arranged that when the line is paying out and this finger has left the slot in the reach rod, the cam between the two gears draws the finger in flush with the periphery of the outer ring. This allows a large amount of line to be paid out without any interference from the finger, which remains out of view and out of contact for the maximum amount of rope that the machine is designed to pay out. The finger will continue in this position when the line is being recovered until approximately 30 or 40 feet is left, then the cam controlling this finger forces it out to engage again in the slot of the reach rod. This closes the valve, thus recovering automatically all the hawser that has been paid out. The periphery of the outer ring contains three fixed dogs. The function of these is to engage the reach rod when the ma- chine is recovering the line and to close the valve to a safety opening, thus preventing racing of the engines when working under a very light load. Sec. ISO. DECK WINCHES For the purpose of handling cargo, coal, ashes from the fur- naces, boats and other heavy weights with ease and rapidity, power winches of some type are fitted on board modern vessels, both merchant and naval. Such winches may be classified in a number of ways, as fol- lows: (a) According to method of transmitting power frorp motor to winch drums. 994 PRACTICAL MARINE ENGINEERING (b) According to type of motor engine. (c) Wiiere steam engines are used, according to the method of obtaining reversal of motion. (rf) According to the number of winch drums carried by the machine. (a) Winches may have the power transmitted from the motor engines to the winch drum (i) by means of spur gearing or (2) by means of friction gearing, the engine driving a spur or friction pinion engaging with a spur or friction wheel carried on the drum spindle. (5) The type of motor engine used is usually one or more single cylinder steam engine or electric motor, (c) Where steam engines are used, the reversal is accomplished either by use of the ordinary Stephenson link by which the gov- erning eccentrics are shifted into or out of direct control of the valve functions, or by means of a reverse valve by which the flow of the steam is changed, exhaust ports becoming steam ports and vice versa, (d) Where a winch may be called upon for more than one operation at the same time and the speeds of these operations are different, it becomes necessary to fit two or more winch drums having independent motors, the motors having dif- ferent speeds or the speeds of the drums being varied by means of different trains of gears. [i] Spur Geared Deck Winches Spur geared deck winches have three different methods of operation. First, by means of a cone friction drum; second, by link motion, and third, by a positive clutch on the crank shaft. Each of these methods of operation is described below. (a) Cone Friction Winches The cone friction drum, fitted loose on its shaft, has a conical flange fitting into a corresponding cone on the gear wheel, the latter being keyed fast to the shaft. The cones of the drum and gear wheel are forced into contact by means of a spiral operated by a hand lever, the resulting friction providing the driving force. A spring is provided which operates and releases the drum when the lever is thrown out. When the cones are thrown out of contact in this manner, the drum, which is loose on the shaft, would be overhauled by the load, except for a powerful adjustable strap brake lined with wood, which controls the motion of the MISCELLANEOUS MACHINERY 995 drum and is operated by a properly adjusted foot lever The drum can also be controlled while lowering its load by the cone friction arrangement. This practice, however, causes the cones to wear ver)- rapidly, and, as it necessitates frequent renewals, should never be used, the brakes being used instead to control in lowering the load, while the friction is only used for hoisting. The link motiou arrangement is used for reversing winches and is best adapted for cases where one load is raised while an- other is being lowered, thus handling two loads at the same time. Winches of this type are sometimes called winding or elevator winches. The link motion arrangement can also be used for or- Fig. 4'J9. Sjjui' Cleared Winch dinary hoisting, and luwering can be made much sluwer Ijy its means than by the brake. (b) Ci-UTCH Winches With the clutch winch the drum and gear wheel are keyed fast to the shaft, the former having a flange for a strap brake. The gear wheel is driven by a pinion clutched to the crank- shaft fsee Fig. 499). In hoisting, the load is raised to the desired height and the winch then stopped. The strap brake is then ap- plied to the drum and the clutch on the crank shaft thrown out of gear with the pinion. This puts the load, in lowering, under control of the strap brake only. 996 PRACTICAL MARINE ENGINEERING For controlling the lowering of very heavy loads requiring especially careful handling, a relief valve is fitted to the steam c)linders. This, when opened, allows the load to overhaul the engine without throwing out the clutch, thus providing perfect control at all times, as the load may be lowered or hoisted from or stopped at any position desired. In Fig. 499, A is the lever controlling the reversal of the en- gines, B that one controlling the pinion coupling, while C is a foot lever controlling the strap brake which is carried on the far side of the large spur gear wheel. Another type of the spur geared winch is shown in Fig. 500. [2] Compound Geared Warping or Mooring Winch This extra heavy double-cylinder winch is a type suitable for the largest transatlantic liners and heavy warships and is used particularly for "warping ship" and heavy hoisting. The large drum may be used for coiling rope. The large winch heads are at a considerable distance from the engine in order to get them well out towards the sides of the " ^L » i.-2!K- Fig. 500, Spur Geared Winch ^•essel, each being supported by its own heavy outboard bearing or bitt. For convenience in shipping and assembhng, the shaft carrying these heads is made in three sections, with suitable couplings just outside the engine frame. The two outside sections may be made of any length desired, thus permitting the heads to be located at any point called for by each individual case. The large winch heads are driven by single spur gears for fast, light hoisting or by compound gears for heavy, slow work. The change of gear is made by means of a clutch. The small winch heads, set close to the machine on the intermediate shaft, are driven from the crank shaft by spur gearing; the engines are MISCELLANEOUS MACHINERY 997 made reversible, the reversing being accomplished by means of a reverse valve. In some makes of geared winches the cut of the gear teeth is changed from the spur, the ordinary spur gearing being re- placed by helical gears for greater quietness in running. [3] Worm Geared Winches W here a wmch is designed for great power, worm gearing (as shown in Fig. 501) is used in place of the ordinary spur or Fig. 501. Worm Geared Winch helical gearing. The engine is reversed by valve motion. The drum is clutched to the worm gear in the same manner that it is unclutched and remains idle while operating the warping heads on the ends of the main shaft. In winches of the type shown, the drum can be used for the .storage of rope, as the drum can remain idle while the remainder of the winch is in use. [4] Two-Cylinder Double Friction Drum Deck Winch For handling two lines or loads at the same time, the ma- chine shown in Fig. 502 has been developed. The drums are of the cone friction type already described, and are independent of each other. As a result, when one is hoisting, the other can be lowering or can remain stationary, holding the load. Each drum has its own spur gear and there is a solid center bearing between the gears, adding much to the rigidity of the machine. There is an overhauling device for each drum. This device 998 PRACTICAL MARINE ENGINEERING consists of a pinion on the crank shaft, having a plain face, which drives an idler held in a swinging yoke operated by a lever. The I'ig. 50:2, Double Friction Drum \\'incli hus reversing idler pinion works on the wide flange on the drum, tl the direction of the drum. The friction brakes are next to the gears. [5] Frictional Geared Hoisting Winches Frictional geared winches are designed for fast hoisting and quick operation without risk of breaking the machine. The smooth and quiet operation of the friction gear fits them par- I'ii:. [>^)o. Double Cylinder irictional Gcareii W inch ticnlarly for use on the decks of ships. The simplicity of hand- ling for controlling the hoisting, holding and lowering of loads, which is all done with one lever, renders them reliable and safe, even in the hands of unskilled operators. These winches are MISCELLANEOUS MACHINERY ggg proportioned for faster work but lighter loads than are the spur gearing winches with engines of the same size. Single cylinder frictional geared winches are fitted with a governor attachment, so constructed as to be wide open when the lever is in position for hoisting. This attachment is closed when the lever is thrown back on the brake, holding the load, and has sufficient lap to remain closed when the lever is in the neutral position or has eased up on the brake for lowering. A starting or pass-over valve, is used for giving steam to keep the winch running when the governor valve is closed, so that sufficient speed can always be maintained to prevent stopping on the center. The governor valve is adjusted for a desired amount of movement. There is a center punch mark on the head of the casting and a ring turned on the stem of the governor. The dis- tance between these marks when the wheels are thrown in gear for hoisting should be a fixed distance, depending upon the de- sign, accurately measured. Whenever the wear of the brake band increases the movement of the valve to or beyond a given amount, depending upon the design of the machine, it should be shortened by the screw at the end of the brake band. If the lever A, Fig. 503, has too much movement toward the crank, the links on each side of the winch, connecting the eccen- tric bearings and the brake shaft, should be shortened both alike, thus bringing the lever back to its original position. The gov- _ernor attachment should be examined at intervals to see that it is exactly in the right position. For operation of this winch, the starting valve is opened with the brake lever thrown over; so that the brake is on and the wheels out of gear. This lets steam into the cylinder without passing through the governor valve, and runs the engine slowly. Then the lever B, operating the stop valve, is opened far enough to take care of the load to be lifted and the speed required. Moving the lever A over, throwing the gearing into mesh and opening the governor valve, all the steam which passes through the stop valve is allowed to enter the cylinder and the load is thus raised at the speed corresponding with the opening of the stop valve B. When the load reaches the required position, the lever is thrown back and the governor valve, by shutting off the steam, slows down the engine. Then, by easing up on the looo J'RACTICAI. MARINE ENGINEERING lever, the brake allows the load to be lowered at any speed de- sired, the engine meanwhile running ahead slowly to avoid dead centers. In uniform hoisting, after the lever B has been set to suit the load and speed, it is unnecessary to handle any lever except A for the operation of hoisting, stopping and lowering. In fast hoisting, however, even though the load and the speed desired be uniform, it is advisable to regulate with the lever B in such way as to start slowly until the load is clear, then open up for fast speed and slow down again before throwing on the brake. With the double cylinder winch, the governor valve is not generally used, and the speed of the engine is controlled through the throttle by lever B, Fig. 503. The throttle valve on these winches should be used, starting the load slowdy and then slowing down or stopping v/hen the load approaches the required height. This prevents the whip of the slack rope, resulting from throwing the load on the brake when running at high speed. [6] Electric Deck Winches In all the above described winches the steam engines may be replaced by electric motors as shown in Fig. 504. »-.A l'"ig. 504. Electric Deck Winch (a) This figure shows a winch of the double drum type, elec- tric driven, where A is the controlling lever, B is the motor and C the resistance box. (b) Fig. 505 shows another arrangement of the electric MISCELLANEOUS MACHINERY looi double drum in which each drum has its individual motor to which it is connected through worm gearing. Both drums are shown grooved for use with wire rope, one drum being used for hoisting, the other for topping the boom. Sec. 151. ARRANGEMENT OF WINCHES AND GEARS FOR CARGO AND COAL HANDLING Fig. 506 shows clearly the arrangement of winches and the necessary gear for handling cargo from the ship overside or from the overside into the ship. The particular cargo being handled in Fig. 505. Electric Double Drum Winch the illustration is coal, for which a clam shell bucket for holding the winch load is fitted. The winches are fitted in pairs, as shown, A being called the "hoisting" winch and B the "swinging" winch. A is a winch of the double drum type, carrying on one drum the holding, or hoisting rope, while on the other drum is wound the rope for closing and keeping closed the clam shell bucket. These ropes lead from the drams A through the fair leader blocks C, to the fair leader block D, which can travel fore-and-aft on the slack stay rope shown. After leaving D, these ropes pass through the sheaves in the traveling fair I0O2 PRACTICAL MARINE ENGINEERING leader E, to the grips on the bucket. The line for hauling the bucket, or rather swinging it, outboard leads from its drum on B, there being two drums on a common shaft, through the block G on the mast, the sheave / at the end of the boom, back to the eye on the outboard end of the fair-leader block E. The inswinging Fig. 506. Arrangement of Cargo Handling Gear rope leads through G to H and back to the eye on the inboard end of E. Sometimes the winches A and B are so arranged that the different operations may be all controlled by one operator. Sec. 152. BOAT CRANES— STEAM AND ELECTRIC The crane is of the built up girder construction and carries at its outer extremity a guide sheave fitted with a guard to prevent the load rope from slipping out of the sheave groove; The rope passes over this sheave to another, D, at the head of the main crane post. The rope on leaving this sheave passes MISCELLANEOUS MACHINERY 1003 down through the axis of the crane post, over the guide sheave A, which turns on an axis carried by the main post, thence over the guide pulley B, which is secured to the deck and along the deck to a deck winch, which may be either steam or electric. The crane post is fitted at its foot with a large worm wheel into which J'ig. 507. Boat Crane gears the worm E driven by the engine G through the spur gear- ing C. There are many forms of these cranes, another of which is shown in Fig. 508. This electric mast hoist has two friction drums with band brakes, ratchets and pawls complete. The swinging gear is mounted on the side of the mast opposite the drums. Through bevel gearing and a vertical shaft it drives a pinion which meshes with internal teeth on a ring bolted to the foundation. The hoist is actuated by a series wound motor, using direct current. The controller is of the railroad type, special resist- ances being mounted in the bedplate of the hoist. Hand levers mounted in a rack operate the friction drums. Foot levers oper- ate the brakes. The swinging gear is controlled by a horizontal lever attached to the mast. The strength and rigidity of the bedplate are made very great 1004 PRACTICAL MARINE ENGINEERING and the method of mounting on the mast is such as to insure an absence of vibration and makes a solid and safe construction. In operation one of the drums is used for the topping lift and one for the hoisting line. By means of the swinging gear, the mast and boom, \\ith the hoist, are swung in either direction. Fig. 50S. Double Drum Electric Mast Hoist with Boom Swinging Gear Fig. 5flt). Electric .\sli Hoist The o])erator, standing on the platform, always has his load in plain view. Sec. 153. ASH HOISTS— STEAM AND ELECTRIC Among its many adaptations, the winch has been found of great use for hoisting ashes from the firerooms of steam vessels. Fig. 510 shows the arrangement of winch adapted to such a ])ur])ose. The machine has been designed especially for use on vessels where it is both necessary and desirable to stop the ma- chine automatically after having hoisted to any desired height and to vary this height at will without any special adjustment. It is fitted with a double cylinder, piston valve engine, with drums keyed direct to the crank shaft and connected through spur gearing to the automatic operating device. In operation, the machine is controlled by a hand wheel, so MISCELLANEOUS MACHINERY 1005 connected through the automatic to the operating valve that the engine starts when the hand wheel is turned, and continues to run as long as the wheel is kept in motion and stops automatically when the wheel is stopped ; also at the limit of travel and when the bucket reaches the fireroom floor. The operating wheel can be placed at any point distant from the winch or connected by shafting and gearing, so that the winch can be worked from either the fireroom or the deck abov& Fig. 510. Reversible Ash Hoisting Winch Ash hoists may also be driven by electric motors, the motor speed being geared down to the speed of drum desired and the motor being controlled automatically as in the steam machine. Fig. 509 shows such a machine. The motor is controlled auto- matically. The operator applies the current for starting, and the action of the motor itself follows up automatically through the chain of gears shown, and closes the current. The brake is applied by a spring weight when the circuit is open, and is held off by electromagnets when the motor is either hoisting or lower- ing. ioo6 PRACTICAL MARINE ENGINEERING Sec. 154. SURFACE COMBUSTION (HOT BULB) ENGINES To the use of steam driven deck winches, there are several serious objections, as follows : 1. Requires the use of steam boiler for the production of the necessary power. 2. Requires the use of long lines of steam and exhaust piping Fig, 511. Section of Surface Combustion (Hot Bulb) Oil Engine laid along open decks; and as they are exposed to the weather and to seas coming on board, excessive corrosion occurs. 3. Causes great loss in economy, due to excessive radiation from long lines of exposed piping. 4. Are a source of danger, due to excessive condensation taking place in long lines of piping, resulting in excessive water hammer and consequent rupture of piping when steam is sud- denly turned on winches without first thoroughly draining the lines. 5. Danger of rupture of winches and of .piping in cold IS MISCELLANEOUS MACHINERY 1007 weather, due to steam leakage into the lines, condensation and freezing. All of these objections, except the first, are removed when electric winches are employed, and even the first is removed when the generators developing the necessary electric current are driven by internal combustion engines of one type or another. One of the most favored of these engines for this purpose what is called the "surface combustion" or "hot bulb" type, This type of engine is also often spoken of as the "semi-Diesel." A cut of this engine is shown in Fig. 511, and its operation is as follows: The engine works on what is known as the 2-cycle principle, that is to say there is one impulse each revolution. The working cycle is as follows : When the piston A at the end of its upward stroke is moving towards the ignition chamber E, the necessary air for combus- tion is drawn through the air valves B into the enclosed crank housing, and at the same time the air in the cylinder D is being compressed. When the piston A has reached its top position, a certain amount of oil is injected into the ignition chamber E through the nozzle F and the fuel charge explodes, the expanding gas driving the piston downwards towards the shaft. During this downward stroke of the piston, the air in the crank housing is compressed. As the piston nears the end of its stroke, the exhaust port G opens and immediately after the inlet air port H. The burnt gases escape by the exhaust port G, while the com- pressed air in the crank housing entering the cylinder by the port H completes the scavenging work, and furnishes the cylinder with air necessary to make up the next fuel charge. It will be noticed that the ignition chamber E has two ports ; by this means it is blown through with fresh air every revolution, an important feature for securing a rapid and effective ignition. The piston is now on the upward stroke again and the cycle is completed. The engine receives its name of "hot bulb" from the fact that the necessary heat for ignition of the fuel is obtained from the hot walls of the chamber E, the preliminary heating before starting being accomplished by means of a torch applied to the ioo8 PRACTICAL MARINE ENGINEERING outside of these walls. The engine shown is also known by the name of its makers, "Bolinder." It is one of the favorite engines used for auxiliary propelling purposes in sailing vessels, and for such uses it has the following advantages: (a) No water injection is required, rendering all fresh water tanks for the motive power unnecessary. In eliminating the water injection, this has been done in an entirely different way than hitherto in the existing types of engines of similar pattern; it is carried out in such a manner that the exhaust is both odorless and smokeless, with the natural consequence that the life of the wearing parts of the engine will be much lengthened. (b) The amount of lubricating oil is much reduced. (c) A perfect combustion, resulting in very clean cylinders and consequently less wear. (d) The running of th'e engine has been very much sim- plified. Such parts as the ignition bulb, which is subject as a rule to great differences in temperature, never in this engine becomes more than just visibly red when running on an overload, and is quite black when running at normal load, which is sufficient guarantee that it is not subject to undue wear. (e) Above all, this type of engine is more flexible. It is a well-known fact that with the ordinary internal combustion engine the power rapidly decreases should the engine be brought to reduced speed by means of an overload or otherwise — the power, in fact, falling much more rapidly than the speed. With this engine it is claimed that this is not the case at all, and this fact permits it to adapt itself to much broader running conditions than what can generally be obtained. (/) The working pressure of the engine is about one-third that of an engine built on the Diesel system. The importance of this fact cannot be exaggerated, as all the troubles to which engines of the Diesel system are so liable can be traced directly or indirectly to the abnormally high pressure under which the engine has to work. (g) Greater simplicity, half the number of working parts, no valves either for "admission" or "exhaust" — greatly reduced wear and tear of the engine as a whole. (h) Possibility of running at somewhat reduced load with- out using air compressor in case of a minor mishap to same. MISCELLANEOUS MACHINERY loog. This is A total impossibility with engines of the Diesel type : any mishap to their compressor renders the engine useless at once. (0 The governing of the engine is by the "hit and miss" principle, thus entirely eliminating the centrifugal governor, which is not so suitable for marine oil engine work, where, more often than not, the handling is by unskilled labor. Sec. 155. HEATING AND VENTILATION Heating: Vessels of small size are usually heated by means of steam radiators located wherever it may be desired and taking steam from a steam main extending throughout the ship. The water condensed in these heaters passes from them through drain lines to steam traps, whence it is discharged to the main feed tanks in the engine rooms. Where compartments are very re- mote from the steam heating and drain mains, long leads of branch steam and drain piping are required to connect up the radiators in these compartments. It is preferable, therefore, in such cases to fit electric heaters when sufficient electric current obtains on the vessel to permit of its use. This latter method of heating is very expensive as compared with steam heating and its use is only justified in extreme cases, where leads of branch pipes would be exceedingly long, and drainage, due to length of drains and unavoidable pockets in drains, difficult. Ventilating: Where vessels are small and the internal ar- rangements simple, efficient ventilation is readily obtained by means of fixed ventilating pipes leading to and well above the upper decks, by means of which the fresh external air is en- trapped and led down to the various compartments, those diffi- cult of access by these ventilating pipes receiving ventilation when needed by the simple expedient of opening hatches con- necting with ventilated compartments. Where the internal structure of the vessel is complex and the . number of compartments great, with many of them very remote from any possible connection with the outside air, artificial ventilation becomes a vital necessity. In such cases ventilation is provided by locating power fans driven by electric motors or by steam engines at several points in the ship and connecting these fans by suitable ducts to the outside atmosphere and to ducts leading throughout the vessel, with branch ducts leading off from these latter mains to the loio PRACTICAL MARINE ENGINEERING ' • different compartments which it is desired to ventilate. These branch ducts at their outlets are known as louvres and are fitted with shutters which can be opened or closed to any desired amount. Where air is taken from the outside atmosphere and is forced to the different compartments, the method of ventilating is spoken of as the "plenum" system. Where the air is taken from the compartments and discharged to the outside atmosphere, the supply of fresh air to the compartment being supplied by leakage into it, the system is called an exhaust system. The "plenum" system is usually to be preferred for comfort, as the supply of fresh air by it is positive. The "exhaust" sys- tem is usually considered the more healthful, as by it the foul air in each compartment is taken from the compartment and dis- charged directly into the outside air instead of being driven throughout the open spaces of the vessel as it passes freely from each compartment to the outer air. In some cases butterfly valves are fitted at the ventilating fans, by means of which the suction and discharge sides of the fan are made interchangeable. This makes it possible to work on either the "plenum" or the "exhaust" systems, as may be desired at the time. Sec. 156. COMBINED HEATING AND VENTILATION— THE THERMOFAN Where both heating and artificial ventilation are required, the weight necessary to install each system separately is very great. In order to simplify the systems and to save the weight of practically one complete system, an apparatus called the thermofan has been developed and is to-day in use on board many large vessels, both merchant and naval. The thermofan consists simply of a series of steam coils located in the discharge duct of a ventilating fan in order that the air, in passing into the ship, may be heated up to any de- sired degree before being delivered to the compartments. To merely heat this air is not sufficient. It must be made suffi- ciently humid to prevent bad effects upon the mucous mem- branes of the noses and throats of those who must breathe it. This humidification of the air is affected by discharging either jets of finely divided salt water or steam into the current of air after it has passed the heating coils. MISCELLANEOUS MACHINERY ion i I \ Ail Duct F ^/fv^ F ELEVATION CVlBy LOOKING Two Wb7 Atr-Suotlon Damper K v. I ^S^TOhAlTbilM ON A Talre PLAIj Fig. 512. Open Deck Type Thermofan Thermofans are constructed as three types, depending upon their location on board ship : (i) Open Deck Type, arranged for exposed or weather deck. (2) Awning Deck Type, arranged for deck open to the at- mosphere but having a protective deck over. (3) Between Deck Type, arranged for lower decks. These three types are all similar in everything except the ar- rangement, of ducts for bringing the air to the heating coils, so a description of the features of the main part of the apparatus applies to all types. A general arrangement of the open deck type is shown, Fig. 512. Referring to the letters: — A is the heater, which is cylin- drical ; steam is led into it through the stop valve and piping a; the condensed water is taken off through the steam trap and exhaust valve h. The heater is surrounded by a sheet steel casing C. Air is drawn from the atmosphere through the intake duct /; is directed to the fan D by the damper K and discharged into the annular space E. It is heated by contact with the shell in its upward passage and further heated in its downward pas- sage through the tubes B. The fan D is constructed with loia PRACTICAL MARINE ENGINEERING two-way discharge controlled by the damper N. When N is in its lowest or horizontal position all the air is discharged through the heater. As N is gradually moved towards the vertical posi- tion part of the air is discharged into the mixing chamber / with- out being heated, thus, by adjusting the position of damper N, any temperature of the air desired can be discharged through the distribution ducts FF. The damper is moved by a quadrant which is geared to a small motor of about ]/% io % horsepower. ^Humldlflet TalTi Stcnm Supply Valve CihauBt VqIto k Steam Trap PLAN Fig. 513. Open Deck Type Thermofan Supplying Warm Air to Living Quarters A reversing switch operated by the thermostat already referred to controls the motor. Any variation in the atmospheric tempera- ture immediately puts the motor into operation and supplies more cold or more hot air as required. In place of the small electric motor a steam cylinder may be used to operate the damper, the movement of the piston which opens and closes the steam ports being under control of two electric solenoids. The thermofans are designed in various sizes, delivering from 1,000 cubic feet of air per minute to lo.oco cubic feet; the de- livery, however, of each machine can be varied by regulating the speed of the fan motor. The open deck type as shown supplying air to the compart- MISCELLANEOUS MACHINERY 1013 ments (Fig. 513) draws its supply of fresh air from one of the shelter decks and thus avoids all smoke from the smoke pipes or foul smells from galley exhausts, etc. The fresh air is drawn in by duct /, directed to the eye of the fan by damper K, then heated and discharged as already explained. The exhaust damper U is up and the waterproof cover down, thus closing the annular space from the atmosphere. Humidifier Valve' Steam Supply VaWi Exhaust Valve and' Steam Trap Fig. 514. Open Deck Type Thermofan Exhausting Air from Living Quarters The Upper and lower exhaust dampers and U operate simultaneously ; O is fixed to spindle S, which is screwed into nut N. The extension of the spindle 6" below the nut N engages the fixed nut on the lower damper U in such manner that as the upper damper rises the lower one falls, ultimately taking up the positions shown on Fig. 514. Round the edge of the upper damper O is an angle iron which runs between rollers at one end of the lever L; the other end of the lever engages the rod R, which operates the lever of the inlet damper K. As the damper O rises it forces the damper K over the position as shown. The fan damper F is set in the horizontal position. The thermofan I0I4 PRACTICAL MARINE ENGINEERING 5 v/^ r^~ ELEVATION Humidifier Valve Steam Supply Valve ExLauBt Valve and Steam Trap PLAN END ELEVATION Fig 515. Shelter Deck' Type Thermofan Exhausting Air from Living Quarters. Same as Open Deck Type, Except Air Supply is Taken Through Waterproof Cowl now draws the air from the ship and discharges it to atmosphere, as indicated by the arrows in Fig. 514. ■ '^miimtmi ^^ ■.\% ELEVATION Eibtuot Talve &.8teua.!]^p END ELEVATION I PLAN ! Fig. 516. Shelter Deck Type Thermofan Exhausting Air from Ship and Discharging to Atmosphere MISCELLANEOUS MACHINERY loiS In principle the between deck type shown supplying air (Fig. 517) is the same as the other two types. The double exhaust dampers are replaced by a single -damper O, which closes or opens the discharge duct leading to the atmosphere; as shown, the discharge duct is closed and the tubes open. ^ExhauBt Valvo and Steain Trap Steam Valve Fig. 617. Between Deck Type Thermofan Supplying Warm Air to Living Quarters The between deck type exhausting air from the ship and dis- charging to atmosphere is shown in Fig. 518. The discharge to the atmosphere is open and the tubes closed by exhaust damper 0. Great efficiency is claimed for this system of heating and ventilating, and as evidence in support of this claim the curves of temperature-rise, shown in Fig. 519, are purported to be those obtained from actual tests. The diagram Fig. 519 speaks very strongly in favor of the thermofan system on board ship. The heating surfaces in both ioi6 PRACTICAL MARINE ENGINEERING ^Exhaust Valve and * Steam Trap Steam Valvo Fig. 518. Between Deck Type Thermofan Exhausting Air from Living Quarters h 1 1 s 1 o r?, 35 r 36 ID Ihoi ra ic direc t hea ting by th ermc fan -^ . ■ » . — o c f-- ■ 1 ^ ^ 1 y s / Srls ein hou rsili ect h eatlJ B H o / __ _ J^ -"^ B /^ - . — -J :( 8 « — ' \ Time in Hours Fig. 519. Diagram of Comparative Tests, Showing the Advantage of Indirect Heating and Ventilating on the Thermofan System, Compared with Direct Steam Pipe or Radiator Heating with Ventilation MISCELLANEOUS MACHINERY 1017 tests were equal and the atmospheric conditions the same, the tests being made simultaneously. Sec. 157. VENTILATION AND COOLING— MAGAZINE COOLING In a previous chapter has been described the application of refrigeration machines for ice making and for the refrigeration of storage spaces on board ship. In this section will be given ELEVATION END ELEVATION DiEcbarge fo Foul Air Dbohuga Water 8«pantoT- ^ Fig. Dense AlrlOatlet i PLAN 520. Cooling Thermotan for Battleships and Cruisers a description of another use of these same machines either with- out or in combination with thermofans for maintaining a con- stant temperature in fruit chambers of fruit carrying steamers and in the magazines of fighting ships. When fitted for this purpose, without the use of the ther- mofans, there is practically little difference between the in- stallation and that for refrigeration except that the work desired of the machine is less in the case being here treated, the main point of difference being in the arrangement of the cooling coils ioi8 Cooled Air Supply toMagaziae — PRACTICAL MARINE ENGINEERING KreBh Air Supply Foul Air Discharge FRONT ELEVATION SECTIONAL ELEVATION Fig. 521. Diagram Showing Thermofan Cooling and Renewing Air in Magazine through which the cooling brine is circulated. These should be located close up to and well distributed over the under surface of the overhead deck in order to insure as nearly an equality of temperature throughout the compartment as possible, while under the coils of piping should be drip pans fitted with proper means of drainage to catch and carry away any condensed moisture dripping from the coils. Where cooling and ventilation are combined, the apparatus known as the thermofan is very efficient and satisfactory. In Fig. 520 is shown a thermofan specially designed to meet the requirements for magazines on battleships and cruisers. The air is drawn from the atmosphere, cooled, the water of con- densation eliminated, passed into the magazine and finally dis- charged back to atmosphere (see Fig. 521). This method of ventilating and cooling, however, entails great waste of thermal units, and the method hereafter described is generally con- sidered more suitable. Fresh Air SapplK Fonl AixZDiscfaaz^ Cooled Ait. Supply toMa^zine — FRONT ELEVATION SECTIONAL ELEyATION Fig. 522. Diagram Showing Thermofan Cooling and Circulating Air in Magazine MISCELLANEOUS MACHINERY 1019 The air is drawn from the magazine, cooled, the water of condensation eliminated, then' discharged back to the magazine, this process being continued to take up the heat radiated to the magazine from the surrounding compartments. (See Fig. 522.) Referring again to Fig. 520 : the cooler A is cylindrical in form. Dense air is supplied through the inlet valve a, circulated through the cooler and discharged through valve h to be returned to the refrigerator. The cooler is thoroughly insulated and en- closed in a sheet steel casing C. A four-way damper box and damper / is provided, the several openings being connected up as follows: Two connections to atmosphere through cowls K and L; one to the air return from the magazine A and the fourth to the fan inlet D. By means of this damper, as already explained, the air may be either circulated or renewed (see Figs. 521 and 522). The air is discharged from the fan into the lower space E, up through the cooler into space F, from there to the water sep- arator G, thence by insulated ducts to the magazine. The water of condensation is collected, part in lower casing E and part in separator G and is drained ofif at C and D. The dense air inlet valve A is controlled by a thermostat placed in the magazine. When the temperature rises above a predetermined point, the valve A opens and admits dense air to the cooler, shutting it off as soon as the temperature is at the proper point. When a number of magazines are cooled by the same thermofan, part of the air is by-passed from the cooler. A thermostat is placed in each magazine connecting through a signal lamp and relay with an electric solenoid which operates the mixing damper, thus con- trolling the temperature of the air supplied to each magazine and so gives a constant temperature. The signal lamp serves the purpose of showing if, due to any abnormal reason, the maga- zine remains at too high a temperature, and investigation can immediately be made. The importance of these points cannot be overestimated, as variations in temperature, or too high a temperature, are not only dangerous but cause great variations in the ballistic value of the powder. Thermofans can be run in connection with carbon anhydrous refrigerators in place of the dense air and will give the most satisfactory results, brine being used as the carrying medium from the refrigerator to the thermofans. Fig. 523 shows the 1020 PRACTICAL MARINE ENGINEERING extra arrangement called for. Brine is led from the refrigerator to circulating pump P and is pumped through the cooler, to cool the air on its passage to the rnagazines. The pump P is driven by chain from the fan motor C. On the end of the motor shaft is fitted a magnetic clutch M, on the loose disk of which is the chain wheel W, which drives the pump. So long as the magazines are cool enough the pump is inoperative, but a very slight rise of temperature above the predetermined point immediately starts the pump, which remains in operation till the magazine is again Magnetic Clutch Operated by Thermostat in Magazine Pipe from Brine Tank Fig. 523 Brine to Cooler cooled down. The system of control in other respects is exactly the same as that applied to the dense air. Sec. 158. FIRE EXTINGUISHING AND FUMIGATING For fire extinguishing on board ship, dependence- may be placed on the fire hose, on perforated water pipes in compart- ments, all being supplied with water from the fire pumps ordi- narily fitted, by flooding valves located in compartments below the level of water outside or by utilization of the flue gases from the boilers. Fumigation is ordinarily accomplished by the burning of sulphur or other disinfectants in open pans in widely scattered parts of a vessel, but it also may be accomplished by this same utilization of the flue gases. Effectiveness of the Utilization of Flue Gases In an ordinary fire the supply of oxygen necessary for com- bustion is obtained from the atmosphere, which contains 21 per- cent of that gas. If the percentage of oxygen in the air supplied to t he fire b e reduced, combustion takes place more slowly. MISCELLANEOUS MACHINERY 1021 If the oxygen is only present to the extent of 14 or 15 percent of the air suppHed, the flames of the fire are extinguished, and with a further reduction combustion ceases altogether. When coal is burnt in an ordinary marine boiler furnace, a large proportion of the oxygen in the air combines with the carbon in the coal, and a gas is produced which contains only about 8 to 10 percent of oxygen. This percentage can be re- duced considerably by increasing the depth of the fire and obtain- ing a good draft. It is, therefore, evident that the gases in the uptake of an ordinary marine boiler are exceedingly valuable as a means of preventing and extinguishing fires. The system here described makes use of the gases for these purposes. As regards the quantity of gas available on board ship, the supply is almost unlimited, for every ton of coal produces at ordinary temperature and pressure about 400,000 cubic feet of free gas. It is further known that animal life cannot exist for any length of time in an atmosphere containing less than 10 percent of oxygen, especially if carbonic acid gas be present. This important property of flue gas is also taken advantage of for destroying rats and other vermin on board ship. Flue gas, although it has all the properties necessary for extinguishing fires and destroying vermin, has no injurious effect whatever on steel or woodwork, nor does it destroy the most delicate materials in cargo, as happens when water is used for extinguish- ing fires. The flue gas used is fire extinctive, whether coal or oil fuel be used. The plant is therefore admirably adapted for use in oil tank steamers. In vessels fitted with internal combustion engines the ex- haust gases are washed and used in the same way as described for flue gases. [i] Applications of the System Preventing Fires Spontaneous combustion is possible only when air is present to a greater or less extent in the body of the cargo. If this air be replaced by a gas with a sufficiently low proportion of oxygen, combustion cannot take place. Flue gas has all the properties necessary for replacing the air in the holds so as to make com- bustion impossible. The gas is forced in at the bottom of the holds and gradually displaces the air, filling up all the holes and crevices in the body of the cargo. In a hold or bunker filled with flu? gas, fire cannot take place. to22 PRACTICAL MARINE ENGINEERING A hold can be filled with gas as easily as a ballast tank can be filled with water. The delivery valve controlling the hold which is to be filled is opened and the valves for all other holds shut. The water supply valve to the washer is then opened and the fan is started. If at sea, the suction valve to the main boiler uptake is opened when the plant is started, and the valve to the donkey boilers closed. When working the donkey boiler in port, the valve to the main boilers is closed. The damper in the donkey boiler uptake should be above the suction valve, and this should be closed also to prevent air being drawn down the donkey funnel. The gas will be all the more effective if the fires are kept thick and well supplied .with coal. If the vessel is fitted with Howden's forced draft, the valves supplying the air to the top of the fires should be closed. The passage of the gas through the cargo is regulated by the hatch covers. The ventilators should all be closed up, and one of the hatch covers at the end of the hatch away from the inlet pipe should be partly opened. Thjs will allow the air to escape freely. Extinguishing Fires Should a fire break out in a hold, that hold should be filled with gas as described above. When the hold is filled with gas the fire is under control, but it may take some hours before the cargo is sufficiently cooled down to prevent the recurrence of the outbreak. The current of gas which the fan keeps pouring through the cargo in large volumes carries away the heat from the smouldering mass, and finally extinguishes the fire altogether. Fumigating — Disinfecting The system of fumigation can be used whether the holds are full or empty. The flue gas does not destroy the most delicate cargo, nor does it attack the structure of the ship. Rats only live for a few minutes in a hold filled with the gas. It is not claimed that flue gas alone will kill disease germs, but should it be necessary to disinfect any part of a ship or cargo this can readily and cheaply be done by introducing small proportions of such powerful germicides as formalin, carbon bisulphite, etc., into the gas by .means of the special apparatus provided for this purpose. MISCELLANEOUS MACHINERY 1023 [2] Description of the Apparatus This consists of a turbine or motor-driven blower, and a washer for purifying the gas. A simple installation of piping described below completes the installation. If disinfecting is required also, a small tank, for holding the disinfecting fluid, is fitted beside the washer. The blower draws the flue gas from the uptake of either the main or donkey boiler, so that the plant is available either at sea or in port. Before entering the blower, the gas passes through the washer, where it comes in contact with a series of cold water sprays. This has the effect of cooling the gas, besides removing from it soot and dust. The gas is then forced through the dis- tribution pipes to the holds or bunkers. An air valve is pro- vided so that air can be blown in large quantities into the holds to clear away the flue gas after a fire extinguishing or fumigating operation. The plant can also be used as a positive means of ventilating the ship. Figure 524 shows the general appearance of the plant and illustrates the apparatus supplied and fitted on the U. S. marine Fig. 524. Fumigating and Disinfecting Apparatus hospital ship Neptune. This vessel is stationed on the Delaware River at Marcus Hook. The apparatus is used for disinfecting all vessels entering the port of Philadelphia from infected ports. Thorough tests were made for over a year with preliminary apparatus before it was finally decided to discard the old method of disinfecting and install the present equipment, which has been found to be eminently satisfactory. 1024 PRACTICAL MARINE ENGINEERING [3] General Arrangement of Piping This is clearly shown in Figs. 525 and 526. On the suction side of the blower a pipe leads from the uptake to the cooler. On this pipe there are fitted valves to enable the gas to be drawn from the main and also from the donkey boiler uptakes. There Fig. 525 is also a branch to enable the fan to draw in air and force it to the holds for ventilating purposes (Fig. 527). The fan delivers into a 6-inch galvanized steel riveted pipe, which runs as far fore and aft as is necessary. From this pipe branch pipes controlled by sluice valves lead down to the bottom of the holds and bunkers. At the lower end of these branch Fig. 526 pipes there is a specially constructed rose, which prevents the cargo getting into the pipe, but allows the free escape of the gas. Branches are led on deck to a hose coupling for disinfecting and fumigating the passengers' and crew's quarters. The inlet branches are so arranged that the air or gas in the holds will be displaced as rapidly as possible. If necessary the main pipe can be led through the ballast tanks or along the bilge, the valve handles being extended through protecting casings to the main deck. In certain cases the gas can be led through the bilge pipes to the various compartments in order to save the initial cost of the piping. MISCELLANEOUS MACHINERY 1025 [4] Disinfectant Tank This apparatus, Fig. 52S, is a liokler for formalin, carbon- bisulphire or such other powerful germicide as may be used to disinfect. These are poured in liquid form through funnel F of the upper chamber, making sure that cock C, connecting upper Fig. 527 Fig. 528. Disinfectant Tank and lower chamber, is closed. Before introducing the germi- cide into the upper chamber, air cock AC must be open. The lower chamber contains a copper steam coil. The germi- cides are admitted to the lower chamber by opening cock C, and in this chamber are vaporized, passing through vapor outlet P^C, thence to hose carrying flue gas. There is fitted to this lower chamber relief valve RVj pressure gage G and water gage IV G. To drain the lower chamber, open drain cock DC. The connection SI is for steam to the coil; directly opposite this there is another connection, which is the drain from coil ; this is not shown in the cut. Care must be taken that cock C and drain cock DC are closed before steam is introduced into the lower chamber. 1026 PRACTICAL MARINE ENGINEERING Sec. 159. AIR COMPRESSORS For use on board ship with pneumatic tools, for sweeping boiler tubes and for the ejection of gases from guns on fighting ships, small air compressors are coming more and more into use. Of these compressors a type usually identified with the well-known Westinghouse air brake is one of the most useful. This machine is made of the simple or single stage or of the Fig. 529. Section of Steam Driven Air Compressor cross-compound two-stage type. The first is the type usually fitted on board ships. The simple or single stage type is shown in Fig. 529. As indicated in Fig. 529, this type of compressor has two cast iron cylinders arranged vertically, with the steam cylinder uppermost, and connected by a suitable centerpiece. Both cylinders are double acting ; that is, steam is admitted alternately on either side of the steam piston, and air is compressed and delivered on both up and down strokes of the air piston. Both steam and air pistons are rigidly connected to one piston rod, the latter MISCELLANEOUS MACHINERY 1027 being made of high grade steel to exacting specifications. The admission and exhaust of steam to and from the steam cylinder is controlled by a slide valve in conjunction with a main valve by which it is operated. The movements of the main valve are governed by a reversing valve which is actuated by the steam piston. The steam valve motion is substantial and compact, being entirely within the top cylinder head, and all its parts are arranged readily to permit of examination and replacement. Two air inlet valves (shown on the left in Fig. 529) and two air discharge valves (shown on the right in Fig. 529) are made of the best steel and specially designed for continuous operation. All corresponding parts in like sizes of compressors are standard and are interchangeable. The main steam valve in the top cylinder head consists of two main valve pistons of unequal diameter, connected rigidly to a valve stem. The latter fits into a suitable cavity in the top of the slide valve, so that any movement of the main valve causes a corresponding movement of the slide valve. The space A between the two main valve pistons and above the slide valve is always filled, during operation, with steam of working pressure. Space E to the left of the small main valve piston is always con- nected to the exhaust. The space to the right of the large main valve piston is alternately connected to steam pressure and ex- haust, thereby causing the main valve to operate. Of the three ports in the slide valve seat, that on the left leads to the bottom of the steam cylinder; the middle one leads to the exhaust; and that on the right connects with the top of the steam cylinder. When steam is admitted to the space to the right of the large main valve piston, the latter becomes balanced, having the same pressure on both sides ; this leaves the small main valve piston with steam pressure on the right and exhaust pressure on the left, and the main valve and slide valve is forced to the left, con- necting the bottom of the steam cylinder with the exhaust, allow- ing steam to enter the top of the steam cylinder, and causing a downward stroke of the steam and air pistons. When the space to the right of the large main valve piston is connected to the exhaust, both main valve pistons are unbalanced, having steam pressure on one side, and exhaust pressure on the other ; as the main valve piston on the right is larger than the other, an excess 1028 PRACTICAL MARINE ENGINEERING of pressure now exists toward the right, causing main valve and slide valve to move in that direction to the position shown in the cut, thereby connecting the top of the steam cylinder with the exhaust, admitting steam to the bottom of the cylinder and causing an upward stroke of the steam and air pistons. The space to the right of the large main valve piston is con- nected either to steam or exhaust by means of the reversing valve and rod, Fig. 529. A steel plate bolted to the upper sur- face of the main steam piston is arranged to move this rod up- ward and downward at the respective limits of its stroke. This movement of the rod causes a corresponding movement of the reversing valve, and the ports in the seat of the latter are so arranged that when it is down, the space to the right of the large main valve piston is connected to the exhaust; and when up, steam pressure is admitted to this space. In this way, a full stroke of the steam and air pistons is established in either direc- tion. A down stroke of the air piston draws free air into the upper part of the air cylinder, through the upper inlet valve; and compresses the air in the lower part of that cylinder until the pressure is sufficient to raise the lower discharge valve, and enable it to pass into the discharge pipe. During the upward stroke, the reverse obtains ; viz. : free air is drawn into the lower part of the air cylinder through the lower inlet valve, and com- pressed in the upper part until it discharges by the upper dis- charge valve. Drain cocks are provided in the steam cylinder at points where steam condensation may collect. An oil cup is provided for lubricating the air cylinder. An oil soaked "swab" is made to fit around the piston rod between the stuffing boxes of the center piece and furnishes thorough lubrication at this poini All valves are readily accessible, and will permit of individual inspection without disturbing other parts of the machine. The steam and air connections are shown in Fig. 529. Sec. 160. STEAM WHISTLES AND SIRENS For purposes of signalling to passing vessels, designating the course intended to be followed in passing in order to pre- vent collision, for warning purposes in case of fog, for signalling by sound from ship to ship, to distant ship's boats or to the shore, steam whistles are fitted. MISCELLANEOUS MACHINERY 1029 [i] Steam Whistles Steam whistles are of two types, the single tone type and the chime. Fig. 530 shows a whistle of the first type, there being a metallic bell closed at the top and open at the bottom, the edge of the lower circumference E, made thin in order that it may be easily started vibrating, these vibrations being then Fig. 530. Steam Whistle— Single Tone Type transmitted to the full bell wall area. The bell should be of sufficient length to prevent breaking up of the nodes of vibration thus permitting the metal to develop its full tone sound, which is dependent upon the diameter of the bell. In the chime whistle, the inner volume of the bell, through- out its length, is divided into two or more segments of unequal length of arc, but the arc lengths being so made that, while each [030 PRACTICAL MARINE ENGINEERING produces a different note, the notes are in chord and the result is a composite pleasing musical tone. The supply of steam is regulated by the valve A, which opens against a weak spring, the opening force being applied to the stem B through the lever C, by means of the whistle pull leading from the ship's bridge or pilot house and making fast to the lever C at its upper end. The opening force may also be applied electrically by operating the valve A by means of a solenoid. When A has been opened, the pull on the lever C can be re- leased and the valve will close by the pressure of the spring, rather slowly against the steam rushing under it through the valve seat, thus allowing the sound of the whistle gradually to die out. The sound is produced by the rush of the steam in a thin cylindrical sheet, through the opening D, directly against the edge E, of the whistle bell in which the vibrations necessary to generate the sound are produced. [2] Steam Sirens For emergency signalling purposes, such as a signal to close watertight doors when a collision with another vessel is im- minent, when a torpedo threatens, and in all cases, where the ship's crew being thoroughly accustomed to (and hence inatten- tive to) the other steam whistle, on account of its frequent use, some more rarely used alarm is required, the steam siren is fitted. This may be operated by hand or electric pull, as in the case of the steam whistle, and the steam valve may also be sim- ilar. The method of producing the sound is, however, entirely different. If a stationary disk pierced with small holes at an angle to its faces is placed directly in front of a similar disk, free to rotate, but having the holes at the same radial distance from the disk center piercing its surface, at an opposite angle, and air, steam, or any other gas be blown through the stationary disk, the reaction of the gas on the walls of the holes in the revolving disk will cause this disk to revolve. As the speed of revolution increases, the rapid interruption of the flow of the gas streams will gradually produce a musical sound, which will increase in both volume and height of tone as the velocity of revolution aug- ments. By locating the two disks at the base of a trumpet and allowing the gas to escape into the outer atmosphere through the bell mouth of the trumpet, the volume of the sound becomes MISCELLANEOUS MACHINERY 1031 very much increased, as in tHe case of the ordinary megaphone with which every one is famihar. The disks may be replaced by concentric cyhnders, one fixed and one stationary and pierced with slots or holes similarly to the disk. Fig. 531 Fig. 532 Such an apparatus is shown in Fig. 531, the outside appear- ance of the complete apparatus, including the trumpet, being shown in Fig. 532. In Fig. 531, A is the spinner or revolving cylinder pierced with the slots C. B is the stationary cylinder, 1032 PRACTICAL MARINE ENGINEERING with its corresponding slots D. A is carried on a spindle K working through a long bushed bearing, and is accurately ad- justed in position by means of two adjustment screws H and lock nuts L. The upper and lower housing castings are supplied with clamp doors G to provide access to H and L. £ is a screw plug provided to allow inspection of adjustment. F is the drain which, in the cases of both steam whistle and siren, should lead to a suitable trap. In many cases, however, the steam pipes to both of these instruments are led up inside the smoke pipe in order that the heat thus obtained will prevent any condensation in these pipes. The trumpet is secured to the flange at the upper end of M. In some cases the joint between M and the trumpet is made in such form as to permit the trumpet to be revolved, thus permitting the bell to point in any direction desired and thus throw the major part of the sound waves generated in this desired direction. Sec. i6i. REDUCING VALVES. GOVERNING VALVES [i] Reducing Valves For manufacturing reasons and also for cases where steadi- ness of operation is desired, it is necessary that the steam pres- sures to which the greater part of the auxiliary machinery on board ship is subjected should be fixed not to exceed a certain amount. This is accomplished by means of valves inserted in the steam supply lines which wire draw the steam through them and thus reduce the pressure from that of the boiler to that desired for the particular machine supplied. Such valves are called "pressure reducing" valves. There are several types of these valves, but two general types only will be described here, namely, the outside spring type and the inside spring type. Operation. — The steam enters valve at A (Fig. 533) and, flowing in the direction indicated by the arrows, passes out at B. In its course it enters chamber D, through port E, closing valve 4 against the opposing power of the springs 34. Any increased pressure on the diaphragms overcomes the resistance of the springs, lifting valve 4 toward its seats. Should the delivery or reduced pressure decrease, the springs overcome the pressure on the diaphragms and force valve 4 open. An equilibrium is thus instantly established. The desired delivery pressure is controlled by adjusting nuts 36 — turning to the right increases and to the left decreases the delivery pressure. MISCELLANEOUS MACHINERY 34s 1033 Fig. 533. Outside Spring Pressure Regulator. These regulators may also be applied on service other than steam — for instance, the manufacture of caustic soda, ammonia liquid, gas, etc. (a) Outside Spring Type of Reducing Valve (Fig. 533) ^umt er Name of Part Number Name of Part I Body 19 Diaphragm (set — consisting 2 Upper valve seat of one or more) ^ Lower valve seat 20 Diaphragm jamb nut 4 Main valve (or clapper) 21 Hood ■; Bottom flange (or plug) 22 Spring bolt bracket 6 Valve (or clapper) stem 23 Spring bolt bracket bolts 7 Valve stem nut 24 Spring bolt bracket and hood 8 Valve stem jamb nut bolt nuts q Valve stem jamb nut cotter- 25 Hood bolts pin 26 Port screw TO Bottom and top flange 27 Toggle lever base screws 28 Toggle lever TT Gasket 29 Toggle lever links 17 Top 30 Pivot washer IS Top liner 31 Plain yoke T4 Valve stem levers 32 Lock yoke 1=; Valve stem pin 33 Lock-yoke wrench t6 Cotter pin for 15 34 Springs (two to a set) T7 Diaphragm center 35 Spring bolts t8 Diaphragm center pin 3t) Spring bolt nuts 37 Diaphragm chamber plug Inside Spring Reducing Valves (Figs. 534-535) Operation. — Steam entering at A passes through main valve port H to outlet B. The initial pressure passing through port C, enters chamber P, thence to the top of piston 2, through 1034 PRACTICAL MARINE ENGINEERING >Fig. SSi Fig, S36 (&) Inside Spring Reducing Number Name of Part 1 Main valve 2 Piston 3 Yoke 4 Yoke guide stem 6 Diaphragm 7 Spring adjuster screw 10 Adjusting spring 11 Body 12 Piston rings 13 Bottom flange 14 Auxiliary valve disk 15 Auxiliary valve spring 16 Locking device cap 17 Upper spring washer A— Inlet B— Outlet C — Controlling port D — Diaphragm chamber E — Port to diaphragm cham- ber G — Equalizing ports H — Main valve opening Valves (Figs.- 534 and 535) Number Name of Part 18 Lower spring washer 19 Upper auxiliary valve plug 20 Lower auxiliary valve plug 21 Auxiliary valve top 22 Main valve spring 28 Lock nut 29 Spring chamber 30 Body studs 31 Body stud nuts 32 Piston cylinder 33 Seat ring 34 Bottom flange bushing 35 Port bushings J — Piston chamber L — Ports from auxiliary to piston chamber O— Tell-tale port P — Auxiliary valve chamber R — Drain (should be piped to trap) ports L, thereby opening the main valve I. The delivery pres- sure, passing through port E, raises the diaphragm 6 against the pressure spring 10, and allows the spring 15 to close the auxiliary valve 3. The pressure in chamber / is then equalized by the reduced pressure passing through ports G, to the underside of MISCELLANEOUS MACHINERY 1035 piston 2, and thus allows the spring 22 to close the main valve, which is then held to its seat by the initial pressure. Upon any reduction of the delivery pressure acting on the diaphragm, the spring 10 forces it down and opens the auxiliary valve 3, admitting steam to top of piston 2, as before explained. The delivery pressure is adjusted by screw 7, tightening the tension of spring 10 increases the discharge pressure and vice versa. The adjustment once made, the delivery pressure will remain constant, regardless of any variable volume of discharge or variation of the initial pressure, so long as the latter is in excess of the delivery pressure. Turning to the right increases and to the left decreases the delivery pressure. A variation of the inside spring type valve is shown in Fig- 535- The operation of the valve is as follows: The pilot valve M is opened by the tension of the spring C against diaphragm G, acting on the end of the valve M. Steam entering the valve passes up port Q through the pilot valve M and passage L on top of the piston P, pressing P down and opening the main valve Rj allowing steam to pass to the outlet side. The outlet or re- duced pressure acts on diaphragm G through port K, and as the reduced pressure increases above that for which the valve is set (by the action of nut B on spring C), this increased pressure raises the diaphragm and allows the pilot valve M to close, or partially close. This action of the pilot valve decreases the pressure above piston P, while the increase on the reduced side acting under P partially closes the main valve and reduces the reduced pressure, until a balance is obtained. In case the reduced pressure is lowered by a greater demand for steam, the reverse takes place. Spring .S" merely acts to take the weight of valve R and to close it when the steam is cut off. An important feature of the apparatus is the construction of the main valve. The valve is constructed with a collar which is beveled off as indicated. This collar allows of greater move- ment of the valve for small demands for steam than would be the case if the valve was of the ordinary type. Also any wire- drawing of the steam will cut away the collars and not injure the seat or valve face. 1036 PRACTICAL MARINE ENGINEERING [2] Governing Valves for Pumps In the use of pumps on board ship there are two conditions to be met, the first being those in which for certain reasons it is desirable to limit the discharge pressure of the pump to a cer- tain amount, as in the supply of hydraulic pressure to hydraulic auxiliary machinery ; second, where, as the resistance to the hy- draulic discharge from the pump increases, this increase in pres- 10 11 12 13 14 15 16 17 18 19 22 23 24 25 26 30 31 PARTS Main valve (or clapper) Piston Thimble Diaphragm top Spring adjusting nut Diaphragm Auxiliary valve stem Capstan stuffing-box nut Auxiliary valve-seat Pressure spring Body Piston rings Bottom plug Stanchion Thimble nut Restricted bushing Top flange Stanchion retaining screw Drain plug Main valve spring Retaining washer Packing Stuffing-box nut Liinit screw Body bolts Body bolt nuts A Inlet B Outlet Controlling port 30 D Diaphragm chamber 17 G Equalizing ports 11 H Main valve opening ^ Piston chamber Auxiliary valve port Aux. valve chamber Drain Discharge connection Fig. 536. Constant Pressure Pump Governor. See Key sure automatically tends to increase the steam supply to the steam ends of the pumps and thus maintain a governing excess of pressure in the steam ends over that in the water ends. For such purposes pump regulators, or, as they are termed, pump governors, are fitted. Those fitted to work under the first con- dition are known as "constant pressure" governors, while those operating under the second condition are called "excess pressure" governors. One of each type will be described. (a) "Constant Pressure" Governor (Fig. 536) Operation. — Steam enters at A and passes through port C MISCELLANEOUS MACHINERY , 1037 and auxiliary valve seat into chamber P and down through ports L to piston-chamber / and on top of piston 2, which forces main valve open and allows steam to pass through seat H and outlet B to pump. As the discharge pressure accumulates on the diaphragm 6, itsdepresses same against the power of the spring 10, and forces the stem 7 down on the auxiliary seat, closing off high pressure steam from piston chamber and allowing main valve to close, thus slowing down or stopping the pump. On governor for fire service, connection should be made at plugged opening R to drain or suction of pump, and plug cock inserted in line. In case of fire, by opening of plug cock it will relieve the pressure instantly from the diaphragm chamber and ' throw valve wide open, admitting full steam pressure to pump cylinder. After a fire, plug cock should be closed, when the valve will automatically govern discharge pressure as before. The plug cock should always be closed under normal conditions. A J^ inch pipe is run from union connection S (top of governor) to discharge pipe from pump, or when deUvering to a tank, connection should be run direct from tank. Turning adjusting nut 5 to the right will increase and to the left will decrease the discharge pressure. (&) "Excess Pressure" Governor (Fig. 537)' Fig. 537 shows the arrangement of a governor valve in relation to the steam and hydraulic lines of the pump, while Fig. 538 shows a sectional elevation of an "excess pressure" governor. The governor shown is an oil-controlled, piston-actuated pressure controlling valve for governing pumps for salt or fresh water, oil, ammonia, air, etc. It is made in several styles for use both where the pressure desired from the pump is fixed, and where it is necessary that the pressure be variable. The ma- terial used in the construction of these governors for high duty service is navy composition bronze or steel. For less exacting service steam composition or cast iron may be used. The governor is extremely sensitive, with an oil body in the hydraulic pressure cylinder, against the lower head of the hy- draulic pressure actuated piston. This body of oil prevents the liquid being pumped from reaching the hydraulic pressure cyl- inder, and thus prevents any sticking of the piston due to 1038 PRACTICAL MARINE ENGINEERING corrosion, or to sediment in the liquid being pumped. The oil con- stantly bathes the cylinder walls, piston and packing in lubricant. Fig. 537 shows the correct method of installing an automatic pump governor. The governor is placed in the steam line be- tween the throttle and the pump, as close to the pump steam chest as possible, with the arrow following the direction of flow of steam to the pump. The governor of the make shown must -I:aw T'ension E^rinff Fig. 537 Fig. 638 invariably hang vertically, with steam valve up, and pressure cylinder, oil trap, etc., down. To charge oil trap and cylinder: shut cut-ofJ valve Aj open drain cock B, oil cup C, and vent cock D. When trap is drained, shut drain cock B, fill with heavy bodied mineral cylinder oil through oil cup C until oil shows at vent cock D, close vent cock D, oil cup C, open cut-ofif valve A and the governor is in work- ing order. Automatic governor shown in Fig. 538 is of the variable pressure type, for use where decidedly different pressures are de- sired from one pump, at different times, for different work to be done. It is loaded with two springs, the first for low pres- sures, to which may be added the load of the second spring by MISCELLANEOUS MACHINERY 1039 a lever tension, in any amount required to build up and maintain any higher pressure. Otherwise its construction and action are similar to thp "constant pressure" type, and its uses include those of that type, and others made possible by its variable pressure control. Another feature of this type is its ability to act as a stop valve if the spring tension lever is reversed by hand to an upward position on the quadrant and locked, holding the valve closed until the lever is moved into the central (low pressure) or the lower (high pressure) positions on the quadrant. QUESTIONS Miscellaneous Machinery ,,M , . . . PAGE Why are steering engines necessary in vessels of large size or high speed ? 958 Into what two classes may steam steering engines be divided? 958 What is meant by "indirect connected" steam steering gears ? 959 Upon what principle are they built ? •. . . gcQ Sketch and describe the "floating lever valve gear" 959 Describe a steam steering engine of the indirect connected type 959 What is meant by "direct connected" steam steering gears and what are the advantages of such gears ? 964 Describe the Napier screw gear 964 What is the advantage gained by locating steering engines in the ship's main engine room ? 965 Describe the Wilson-Pirrie steering gear and its modifications 966 What are differential steering gears ? 968 What modification in arrangement is made to change from steam to electric power for steering ? 969 What are "steam tillers" ? 971 What are the principles leading to its use ? 971 Describe a steam tiller 971 What is meant by the term "hydro-electric steering gear?" 973 Give brief description of the Hele-Shaw Martineau gear 973 How is motion transmitted from the steering wheel in the pilot house to the governing valve of the steering engine? 976 Describe an outside packed telemotor 977 Describe an inside packed telemotor 979 Why are anchor windlasses and capstans fitted on ships ? 982 What is a steam capstan? Give brief description 983 What is a steam windlass ? Give brief description 984 Give brief description of engines and windlasses 986 Make sketch of combined windlass and capstan and give, briefly, descriptions for operating 988 What is a "towing engine" and why is it desirable to fit them to vessels designed for towing purposes ? 991 Give brief description of towing engine 992 What are the purposes for which winches are fitted on board ship? 993 How may winches be classified ? 993 Wherein does a cone friction winch differ from a clutch winch? Give brief description of each _. 994 What is meant by "compound geared winch" and why is the com- pounding necessary? 996 1040 PRACTICAL MARINE ENGINEERING PAGE Why are two-cylinder, double-friction drum winches fitted and what are their advantages ? 997 What are the advantages of frictional-geared winches? Describe their general characteristics 998 Sketch and describe a typical arrangement of winches and gears for cargo or coal handling looi Describe a steam or electric boat crane 1002 Describe a steam or electric ash hoist 1004 What is the distinguishing characteristic of a surface combustion engine ? Describe one 1006 What are the claims as to advantages of such an engine? 1008 What are its uses on board ship ? 1008 What are the different methods employed for heating and ventilating ships ? 1009 What is meant by "combined heating and ventilating ?" loio Describe the various methods of installing the "Thermofan" system, ion Give a brief description of the methods employed for magazine cooling 1017 By what means may fires be extinguished on board ship? 1020 What are the advantages of using carbonic acid gas for this pur- pose and for fumigation? I02i Describe a fire-extinguishing and a fumigating carbonic acid gas system , 1023 Why are small air compressors fitted on board ships? 1026 Describe the Westinghouse air compressor 1026 What is the purpose of and principle of operation of the steam whistle ? . 1028 Describe a steam whistle 1029 What is the purpose for which fitted and the principle of operation of the steam siren? 1030 Describe a steam siren 1031 What is a reducing valve and why are they used? 1032 Describe an outside spring reducing valve 1033 Describe an inside spring reducing valve 1034 What is a pump-governing valve ? 1036 What types of governing valves are there and what conditions decide the type to use? 1036 Describe a constant pressure governor 1036 Describe an excess pressure governor 1037 MISCELLANEOUS EXERCISES (i) One ton of coal is found to contain 300 pounds of ashes. What percent is combustible and what percent ashes. (Sec. 126). Ans. 86.6 percent and 13.4 percent. (2) In a certain boiler it requires 1,120 heat units to evap- orate one pound of water. With the addition of a feed heater this is reduced to 1,030. Find the percent of saving. (Sec. 126). Ans. 8.04 percent. (3) A ship steams 2,800 miles in 11 days. How long will it require to steam 740 miles at the same rate? (Sec. 129). Ans. 2.9 days. (4) A given engine with a reduced mean effective pressure of 36 pounds, stroke 33 inches and revolutions of 120 develops 1,200 indicated horsepower. With revolutions 140 and stroke 30 inches, what would be the reduced mean effective pressure for 1,300 indicated horsepower? (Sec. 129 [2]). Ans. 36.77. (5) A propeller at 90 revolutions and 24 percent slip gives a speed of 12 miles per hour. With 100 revolutions and 26 percent slip what speed will be attained? (Sec. 129). Ans. 12.98. (6) How many gallons of oil will be contained in a tank of rectangular form, 4 feet long, 27 inches wide and 2 feet high? (Sec. 127 [5], Sec. 132 [16] ). Ans. 134.6. (7) An oil tank 55 inches long has trapezoidal cross sec- tions. The two parallel sides are 28 inches and 40 inches, and the distance between them is 40 inches. Find the capacity in gallons. (Sec. 127 [5], 132 [4] [16]). Ans. 323.8. 1042 MISCELLANEOUS EXERCISES (8) What is the capacity of a pump in gallons per minute if the cylinder is 9 inches in diameter, 10 inches stroke and 60 strokes per minute ? (Sec. 127 [5], 132 [17] ). Ans. 165.2. (9) A coal bunker of rectangular form is 18 feet fore and aft, 40 feet wide by 13 feet deep. Find the capacity in tons, al- lowing 42 cubic feet per ton. (Sec. 132 [16]). Ans. 223. (10) A coal bunker of irregular form has three cross sec- tions, as follows : The first is a rectangle 12 feet by 18 feet. The second is a trapezoid with parallel sides 12 and 10 feet by 16 feet between them, and the third is a trapezoid with parallel sides 12 and 8 feet by 14 feet between them. These sections are 24 feet apart. Find the capacity in tons of 44 cubic feet each. Solution. The areas of the three sections are as follows. 216, 176, 140. Then by Simpson's rule. Sec. 138 [15] [29] the volume is found as follows: V = (216 + 4 X 176 + 140) -^ 3 X 24, or Volume ^ 8,480 cubic feet. Then tons = 8,480 -^ 44 = 192.7. (11) An oil can in the form of a frustum of a cone is il inches high, and the diameters of the base and top are respect- ively 5 and 4 inches. Find the capacity. (Sec. 132 [26]). Ans. .76 gallon. (12) Will a boiler 60 inches diameter, ^ inch thickness of plate stand as much pressure as a boiler 48 inches diameter, %6 inch thickness of plate? (Sec. no). Ans. 0.76 gallon. (13) Find the required weight for a safety valve whose diameter is 4 inches, fulcrum 3 inches, length of lever 34 inches, weight of lever 12 pounds, weight of valve and stem 6 pounds, steam pressure 65 pounds. (Sec. 108). Ans. 65.5 pounds. (14) What would be the safe working pressure of a boiler 1.08 inches thickness of plate, tensile strength 60,000 pounds per square inch, diameter of boiler 12 feet? Ans. 150 pounds per square inch for single riveting oi 180 pounds per square inch for double riveting. PRACTICAL MARINE ENGINEERING io43 (15) The diameter of a boiler shell is 15 feet. The work- ing pressure desired is 180 pounds per square inch. The strength of the material is 60,000 pounds per square inch. Find the thick- ness with double riveting. Ans. 1.35 inches, or say 1%. (16) The diameter of a steel screw staybolt at bottom of thread is ij4 inches. The area supported by each is 49 square inches. Find the pressure allowed. Ans. 200 pounds per square inch. (17) What wotild be the thickness of plate required for the same boiler as in (16) the spacing being 7 by 7 inches, and the bolts being simply riveted over on ends? Ans. 17-32 inch. (18) For other problems in boiler bracing see Sec. 109. (19) Temperature of feed 160 degrees. Steam pressure 180 pounds gage. Quality of steam 97 percent. Thermal value of coal 13,800 thermal units per pound. Efficiency of boiler .68. Find the pounds of water evaporated per pound of co&l into steam of the given quality. (Sec. 100). Ans. 8.76 pounds. (20) With a coal consumption of 1.80 per indicated horse- power per hour how much coal will be required in the bunkers of a ship making a lO-day trip, the indicated horsepower being 1,800 and a margin of 12 percent being allowed for emergencies? (Sec. loi). Ans. 388.8 tons. (21) A corrugated furnace has a diameter of 44 inches and thickness of J4 inch. Find the pressure allowed. Ans. 170 or 159, according to the style of corrugation. (22) Find the necessary thickness of a copper steam pipe for 200 pounds working pressure, the diameter of the pipe being 9 inches. Ans. 0.287s inch. (23) With cut off at 62 percent of stroke and clearance of 12 percent, what is the expansion ratio? (Sec. 115). Ans. 1. 51. 1044 MISCELLANEOUS EXERCISES (24) The indicated horsepower is 2,100, pitch of propeller 18 feet, revolutions 100. Find the indicated thrust in pounds. (Sec. 118.) Ans. 38,500 pounds. (25) What is the weight of a rectangular piece of boiler plate 14 feet long, 5 feet 6 inches wide and iy& inches thick? Ans. 12,474 cubic inches = 3,530 pounds. (26) Given speed of ship 12 knots, revolutions no, slip of propeller 20 percent, find the pitch. Ans. 13.8 feet. (27) Allowing an Admiralty constant of 280, what would be the indicated horsepower required for a displacement of 8,600 tons with a speed of 10 knots? Ans. 1,500. (28) Given speed of ship 18 knots, revolutions no, pitch 20 feet. Find the slip ratio. Ans. 17. 1 percent. (29) Given the pitch of a propeller 54 inches, revolutions 360, slip 21 percent. Find the speed in miles per hour. Ans. 14.54. (30) Given the diameter of the rolling circle of a paddle wheel 30 feet, slip 28 percent, revolutions 24. Find the speed in miles per hour. Ans. 18.5. (31) Given displacement 120 tons, indicated horsepower 420. Allowing an Admiralty-Constant of r6o, what speed may be expected? Ans. 14.03 knots. (32) Given indicated horsepower = 33,000, D = 20,000, speed ^ 23 knots. Find the Admiralty-Constant. Ans. 272. (33) Allowing an Admiralty-Constant of no, what would be the indicated horsepower required for a displacement of 4 tons at a speed of 7 knots ? Ans. 7.86. PRACTICAL MARINE ENGINEERING i04S (34) On a trial trip over a course of two nautical miles, suppose the observations as follows : Run North 2 minutes 36 seconds. Revolutions 648. Run South 2 minutes 24 seconds. Revolutions 604. Pitch of propeller 24 feet. Find average speed and slip of propeller. Ans. 24 knots, 19 percent. (35) Given the ship in example (27). With the same Ad- miralty-Constant, what percentage increase in power would be required for 30 percent increase in displacement? Ans. 19 percent. (36) Given the ship in example (27). With an Admiralty- Constant of 250, what percentage increase in power would be required for a 30 percent increase in speed ? Ans. 146 percent. 1046 PROPERTIES OF SATURATED STEAM* a I i Total Heat ffl .^s f-i ga 1 ^^ £■1 it above 33 " V. m 9 ® "^ '^S as ctiJ In the In the .*3 5 Water h Heat- Steam H Heat- i"i •||5 ©0 ^^" H units. units. 3- r^ ^.a 29.74 .089 32 1091.7 1091.7 208080 3333.3 .00030 29.67 .122 40 8 1094.1 1086.1 154330 2472.2 .00040 29.56 .176 50 18 1097.2 1079.2 107630 1724.1 .00058 29.40 .254 60 28.01 1100.2 1072.2 76370 1223.4 .00082 29.19 .359 70 38.02 1103.3 1065.3 54660 875.61 .00115 28.90 .502 80 48.04 1106.3 1058.3 39690 635.80 .00158 28.51 .692 90 58.06 1109.4 1051.3 29290 469.20 .00213 28.00 .943 100 68.08 1112,4 1044.4 21830 349.70 ,00286 27.88 1 102.1 70 09 1113.1 1043.0 20623 334.23 ,00299 26.85 2 126.3 94.44 1120,5 1026.0 10730 173,23 .00577 23.83 3 141.6 109.9 1125.1 1015.3 7325 117.98 .00848 21.78 4 153.1 121.4 1128.6 1007.2 5588 89,80 ,01112 19.74 5 162 3 ' ' 130.7 1131.4 1000.7 4530 72.50 .01373 17.70 6 170.1 138.6 1133.8 9j5.2 3816 61.10 .01631 15.67 7 176.9 145.4 1135.9 990.5 3302 53.00 .01887 13.C3 8 182.9 151.5 1137.7 986.2 2912 46.60 .02140 11.60 9 ■ 188.3 156.9 1139.4 982.4 2607 41,82 .02391 9.56 10 193.2 161.9 1140.9 979.0 2361 37,80 ,02641 7.52 11 197.8 166.5 1142.3 975.8 2159 34,61 .02889 6.49 12 202.0 170.7 1143.5 972.8 1990 31.90 .03136 3.45 13 215.9 174.7 1144.7 970.0 1846 29.58 .03381 1.41 14 209.6 178.4 1145.9 967.4 1721 27.50 ,03625 Gauge Pressure lbs, per. 14.7 212 180.9 1146.6 965.7 1646 20.36 .03794 sd. in. 0.804 15 213.0 181.9 1146.9 965.0 1614 25,87 .03868 1.3 16 216.3 185.3 1147.9 962.7 1519 24.33 ,04110 2.3 17 219.4 188.4 1148.9 960 5 1434 22.98 ,04352 3.3 18 222.4 191.4 1149.8 958.3 1359 21.78 .04592 4.3 19 225.2 194.3 1150.6 956.3 1292 20,70 .04831 6.3 20 227.9 197.0 1151.5 954,4 1231 19,72 .05070 6.3 21 230.5 199.7 1152.2 952.6 1176 18.84 .05308 7.3 22 233.0 202.2 11530 950,8 1126 18.03 .05545 8.3 23 235.4 204.7 .7 949.1 1080 17.30 .05782 9.3 24 237.8 207.0 1154.5 947.4 1038 16,62 ,06018 10.3 25 240.0 209.3 1155.1 945.8 998.4 15,99 ,06253 11.3 26 242.2 211.5 .8 944.3 962.3 15.42 ,06487 12.3 27 244.3 213.7 1156.4 942.8 ,928.8 14.88 .06721 13.3 28 246 3 215.7 1157.1 941.3 897.6 14.38 .06955 143 29 248 3 217.8 .7 939,9 868.5 13.91 ,07188 15.3 5»« — _ 30 250.2 219.7 1158.3 938.9 841.3 13.48 .07420 * Reprinted, by permission, from Powek Catjiohism, PROPERTIES OF SATURATED STEAM. 1047 Sd tn Total Hiat w^ . ^i 3 A 3.^ above 32= f. 60a In the In the Water h Heat- Steam Heat 1- < EH units. units. 3 " ^B ^ 16.3 31 2.32.1 221.6 .8 937.2 815.8 13.07 .07652 17.3 32 254.0 223.5 1159.4 935.9 791.8 12.68 .07884 18.3 33 255.7 225 S .9 934.6 769.2 12 32 .08115 19.3 34 257.5 227.1 1160.5 933.4 748.0 11.98 .08346 20.3 35 259 3 228.8 1161.0 932.2 727.9 11.66 .08576 21.3 36 260.8 230.5 .5 931.0 708.8 11.36 .08806 22.3 37 262.5 232.1 1162.0 929.8 690.8 11.07 .09035 23.3 38 264.0 233.8 .5 928.7 673.7 10.79 .09264 24.3 39 265.6 235.4 .9 927.6 657.5 10.53 .09493 25.3 40 267 1 236.9 1163.4 926.5 642.0 10.28 .09721 26 3 41 268.0 238.5 .9 925.4 627.3 10.05 .09949 27.3 42 270.1 240.0 1164.3 924.4 613.3 9.83 .1018 -28.3 43 271.5 2414 .7 923.3 599.9 9.61 .1040 29.3 44 272.9 242.9 1165.2 929 3 587.0 9.41 .1063 30.3 45 274.3 244.3 .6 921.3 574.7 9.21 .1086 31.3 46 275.7 245.7 1166.0 920.4 563.0 9.02 .1108 32.3 47 277.0 247.0 .4 919.4 551.7 8.84 .1131 33.3 48 278,3 248-4 .8 918.5 540.9 8.67 .1153 34.3 49 279.6 249.7 1167.2 917.5 530.5 8.50 .1176 35.3 50 280.9 251.0 .6 916.6 520.5 8.34 .1198 36.3 51 282.1 252.2 1138.0 915.7 510.9 8.19 .1221 37.3 52 283.3 253.5 .4 914.9 501.7 8.04 1243 38.3 53 284 5 254.7 .7 914.0 492.8 7.90 .1266 39.3 54 285.7, 256.0 1139.1 913.1 484.2 7.76 1288 40.3 55 286.9 257.2 .4 912.3 475.9 7.63 1311 41.3 56 288.1 258.3 .8 911.5 467.9 7.50 .1333 42.3 57 289.1 259.5 1170.1 910.6 460.2 7.38 .1355 43.3 58 ♦ 290.3 260.7 .5 909.8 452.7 7.26 .1377 44.3 59 , 291.4 261.8 .8 909.0 445.5 7.14 .1400 45.3 60 292.5 262.9 1171.2 908.2 438.5 7.03 .1422 46.3 61 293.6 264.0 .5 907.5 431.7 6.92 .1444 47.3 62 294.7 265.1 .8 906.7 425.2 6.82 .1466 48.3 63 295.7 266.2 1172.1 905.9 418.8 6.72 .1488 49.3 64 296.8 267.2 .4 905.2 412.3 6.62 .1511 50.3 65 297.8 268.3 .8 904.5 406.6 6.53 .1533 51.3 66 298.8 269.3 1173.1 903.7 400.8 6.43 .1555 52.3 67 299.8 270.4 .4 903.0 395.2 6.34 .1577 53 3 68 300.8 271.4 .7 9 2.3 389.8 6.25 .1599 54! 3 69 301.8 272.4 1174.0 901.6 384.5 6.17 .1621 55.3 70 302.7 273.4 .3 90n.9 379.3 6.09 .1643 56.3 71 303.7 274.4 .6 900 2 374.3 6.01 .1665 57.3 72 304.6 275.3 .8 899 5 369.4 6.93 .1687 ssis 73 305.6 276.3 1175.1 898,9 364.6 5.85 .1709 59.3 74 306.5 277.2 .4 898.2 360.0 6.78 .1731 1048 PROPERTIES OF SATURATED STEAM. ¥ e Press- s. per I inch. II Total Heat above 32° F. 1^ . ■a -B Wl g m 4-1 I! In the In the "i £2 Water h Heat- units- Steam Heat- units, 6° U ■*s (D 60.3 75 307.4 278.2 .7 897.5 355.5 5.71 .1753 61.3 76 308.3 279.1 1176.0 896.9 351.1 5.63 .1775 62.3 77 309.2 280.0 .2 896.2 346.8 5.57 .1797 63.3 78 310.1 280.9 .5 895.6 342.6 5.50 .1819 64.3 , 79 310.9 281.8 .8 895.0 338.5 5.43 .1840 65.3 80 311.8 282.7 1177.0 894.3 334.5 5.37 .1862 66.3 81 312.7 283.6 .3 893.7 330.6 5.31 .1884 67.3 82 313.5 284.5 .6 893.1 326.8 5.25 .1906 68.3 83 314.4 285.3 .8 892.5 323.1 5.18 .1928 69.3 84 315.2 286.2 1178.1 891.9 319,5 5.13 .1950 70.3 85 316.0 287.0 .3 891.3 315.9 5.07 .1971 71.3 86 316.8 287.9 .6 890.7 312.5 5.02 .1993 72.3 87 317.7 288.7 .8 890.1 309.1 4.96 .2015 73.3 88 318.5 289.5 1179.1 889.5 305.8 4.91 .2036 74.3 89 319.3 290.4 .3 888.9 302.5 4.86 .2058 75.3 90 320.0 291.2 .6 888.4 299.4 4.81 .2080 76.3 91 320.8 292.0 .8 887.8 296.3 4.76 .2102 77.3 92 321.6 292.8 1180.0 887.2 293.2 4.71 .2123 78.3 93 322.4 293.6 .3 886.7 290.2 4.66 .2145 79.3 94 323.1 294.4 .5 886.1 287.3 4.62 .2166 80.3 95 323.9 295.1 .7 885.6 284.5 4.57 .2188 81.3 96 324.6 295.9 1181.0 885.0 281.7 4.53 .2210 82.3 97 325.4 296.7 .2 884.5 279.0 4.48 .2231 83.3 98 326.1 297.4 .4 884.0 276.3 4.44 .2253 84.3 99 326.8 298.2 ,6 883.4 273.7 4.40 .2274 85.3 ICO 327.6 298.9 .8 882.9 271.1 4.36 .2296 86.3 101 328.3 299.7 1182.1 882.4 268.5 4.32 .2317 87.3 102 329.0 300.4 .3 881.9 266.0 4.28 .2339 88.3 103 329.7 301.1 .5 881.4 263.6 4.24 .2360 89.3 104 330.4 301.9 .7 880.8 261.2 4.20 .2382 90.3 105 331.1 302.6 .9 880.3 258.9 4.16 .2403 91.3 106 331.8 303.3 1183.1 879.8 256.6 4.12 .2425 92.3 107 332.5 304.0 .4 879.3 254.3 4.09 .2446 93.3 108 333.2 304.7 .6 878.8 252.1 4.05 .2467 94.3 109 333.9 305.4 .8 878.3 249.9 4.02 .2489 95.3 110 334.5 306.1 1184.0 877.9 247.8 3.98 .2510 96.3 111 335.2 306.8 .2 877.4 245.7 3.95 .2531 97.3 112 335.9 307.5 .4 876.9 243.6 3.92 .2553 98.3 113 336.5 308.2 .6 876.4 241.6 3.88 .2574 99.3 114 337.2 308.8 .8 875.9 239.6 3.85 .2596 100.3 115 337.8 309.5 1185.0 875.5 237.6 3.82 .2617 101.3 116 338.5 310.2 .2 875.0 235.7 3.79 .2638 J.02.3 117 339.1 310.8 .4 874.5 233.8 3.76 .2660 PROPERTIES OF SATURATED STEAM. 1049 2j m 1 Total Heat u 2-S 4 aB hi II above 33° F. ■S-sS g's In the In the ^i ■32 = |l ■Water Heat- Steam R Heat- 00 u '0^ 12 1- E< units. units. 3 1^ ^£ ^G 103.3 118 339.7 311.5 .6 874.1 231.9 3.73 .iCSl 104.3 119 340.4 312.1 .8 873.6 230.1 3.70 .2703 105.3 120 341.0 312.8 .9 873.2 228.3 3.67 .2724 106.3 121 341.6 313.4 1186.1 872.7 226.5 3.64 .2745 107.3 122 342.2 314.1 .3 872.3 224.7 8.62 .2766 108.3 123 342.9 314.7 .5 871.8 223.0 3.e:9 .2788 109.3 124 343.5 315.3 .7 871.4 221.3 3.56 .2809 110.3 125 344.1 316.0 .9 870.9 219.6 3.53 .2830 111.3 126 344.7 316.6 1187.1 870.5 218.0 3.51 .2851 112.3 127 345.3 317.2 .3 870.0 216.4 3.48 .2872 113.3 128 345.9 317.8 .4 869.6 214.8 3.46 .2894 114.3 129 346.5 318.4 .6 869.2 213.2 3.43 .2915 115.3 130 347.1 319.1 .8 868.7 211.6 3.41 ,2936 116.3 131 347.6 319.7 1188.0 868.3 210.1 3.38 .2957 117.3 132 348.2 320.3 .2 867.9 208.6 3.36 .2978 118.3 133 348.8 320.8 .3 867.5 207.1 3.33 .3000 119.3 134 349.4 321.5 .5 867.0 205.7 3.31 .3021 120.3 135 350.0 322.1 .7 866.6 204.2 3.29 .3042 121.3 136 350.5 322.6 .9 866.2 202.8 3.27 .3063 122.3 137 351.1 323.2 lisy.o 865.8 201.4 3.24 .3084 123.3 138 351.8 323.8 .2 865.4 200.0 3.22 .3105 124.3 139 352.2 324.4 .4 865.0 198.7 3.20 .3126 125.3 140 352.8 325.0 .5 864.6 107.3 3.18 .3147 126.3 141 353.3 325.5 .7 864.2 196.0 3.16 .3160 127.3 142 353.9 326.1 .9 863.8 194.7 3.14 3190 128.3 143 354.4 326.7 1190.0 863.4 193.4 3.11 .3211 129.3 144 355.0 327.2 .2 863.0 192.2 3.09 .3232 130.3 145 355.5 327.8 .4 862.6 190.9 3.07 .3253 131.3 146 356.0 328.4 .5 862.2 189.7 3.05 .3274 132.3 147 356.6 328.9 .7 861.8 185.5 3.04 .3295 133.3 148 357.1 329.5 .9 861.4 187.5 3.02 .33W . 134.3 149 357.6 330.0 1191.0 861.0 186.1 3.00 .3337 135.3 150 358.2 330.6 .2 860.6 184.9 2.98 .3358 136.3 151 358.7 331.1 .3 860.2 183.7 2.96 .3379 137.3 152 359.2 331.6 .5 859.9 182.6 2.94 .3400 138.3 153 359.7 332.2 .7 859.5 181,5 2.92 .3421 139.3 154 360.2 332.7 .8 859.1 180.4 2.91 .3442 140.3 155 360.7 333.2 1192.0 858.7 179.2 2.89 .3463 141.3 156 361.3 333.8 .1 858.4 178.1 2.87 .3483 142.3 157 361.8 334.3 .3 858.0 177.0 2.85 .3504 143.3 158 362.3 334.8 .4 857.6 175.0 2.84 .3525 144.3 159 362.8 335.3 .6 857.2 174.9 2.82 .3546 145.3 160 368.3 336.9 .7 856.9 173.9 2.80 .3567 1050 PROPERTIES OF SATURATED STEAM. u i Total Heat H . as„- ^S iA (D M a) above 32 ° F. glll 3I 11 In the In the cS 3— « o ® ^ Water h Steam CO ^t D* < Heat- units. Heat- units. ^" <3 °ti U6.3 161 363.8 336.4 .9 856.5 172.9 3,79 .3588 147.3 162 364.3 336.9 1193.0 856.1 171.9 2,77 .3609 148.3 163 364.8 337.4 .2 855.8 171.0 2,76 .3630 149.3 164 365.3 337.9 .3 855.4 170.0 2,74 .3650 150.3 165 365.7 338.4 .5 855.1 169. 2.72 .3671 151.3 166 366.2 838,9 .6 854.7 168.1 2.7] .3692 152.3 167 366.7 339.4 .8 854.4 167.1 2.69 .3713 153.3 168 367.2 339.9 .9 854.0 166.2 2.68, .3734 154.3 169 367.7 340.4 1194.1 853.6 165.8 2.66. .3754 155.3 170 368.2 340.9 .2 853.3 164.3 2.65 .3775 156.3 171 368.6 341.4 .4 852.9 163.4 2.63 .3796 157.3 172 369.1 341.9 .5 852.6 162.5 2.62 .8817 158.3 173 369.6 342.4 .7 852.8 161.6 2.61 .3838 159.3 174 370.0 342.9 .8 851.9 160.7 2.59 .3858 160.3 175 370.5 343.4 .9 851.6 159.8 2.58 .3879 161.3 176 371.0 343.9 1195.1 851.2 158.9 2.56 .8900 162.3 177 371.4 344.3 .2 850.9 158.1 2.55 .3921 163.3 178 371.9 344.8 .4 850.5 157.2 2.54 .3942 164.3 179 372.4 345.3 .5 850.2 156.4 2.52 .3962 165.3 180 372. -8 345.8 .7 849.9 155.6 2.51 .8983 166.3 181 373.3 346.8 .8 849.5 154.8 2.50 .4004 167.3 182 373.7 346.7 .9 849.2 154.0 2.48 .4025 168.3 183 374.2 847.2 .1 848.9 153.2 2.47 .4046 169.3 184 374.6 347.7 1196.2 848.5 152.4 2.40; .4066 170.3 185 375.1 348.1 .8 848.2 151.6 2.45 .4087 171.3 186 375.5 348.6 .5 847.9 150.8 2.48 .4108 172.3 187 375.9 349.1 .6 847.6 150.0 2,42 .4129 173.3 188 376.4 349.5 .7 847,2 149.2 2.41 .4150 174.3 189 376.9 350.0 .9 846.9 148.5 2.40 .4170 175.3 190 377.3 350.4 1197.0 846.6 147.8 2.39 .4191 176.3 191 377.7 350.9 .1 846,3 147.0 2.37 .4212 177.3 192 378.2 351.8 .3 845.9 146.3 2.36 .4233 178.3 193 378.6 351.8 .4 845.6 145.6 2.S5 .4254 179.3 194 379.0 352.2 ,5 845.3 144.9 2.34 .4275 180.3 195 379.5 352.7 .7 845.0 144.2 2.33 .4296 181.3 196 380.0 353.1 .8 844.7 143.5 2.32 .4317 182.3 197 380.3 353.6 .9 844.4 142.8 2.31 .4337 183.3 198 380.7 354.0 1198.1 844.1 142.1 2.29 .4358 184.3 199 381.2 354.4 .2 843.7 141.4 2.28 .4^79 185.3 200 381.6 554.9 .3 843.4 140.8 2.27 .4400 186.3 201 382.0 355.3 .4 843.1 140.1 2.26 .4420 187.3 202 382.4 355.8 .6 842.8 139.5 2.25 .4441 188.3 203 382.8 856.2 .7 842.5 138.8 2.24 .4462 PROPERTIES OF SATURATED STEAM. los: CD . Is CO II EH Total above C Heat 2° F. 1^ . ^s CO Wl 3 Relative Volume, Vol, of water at 39° F. = 1. CD O u 11 Ss In the Water h Heat- units. In the Steam II Heat- units. MOO 189.3 204 383,2 356.6 .8 842.2 138.1 2.23 .4482 190.3 191.3 192.3 193.3 194.3 205 206 207 208 209 383.7 384.1 384.5 384.9 385.3 357.1 357.5 357.9 358.3 358.8 1199,0 .1 .2 .3 .5 841.9 841.6 841.3 841.0 840.7 137.5 136.9 136.3 135.7 135.1 2.22 2.21 2.20 2.19 2.18 .4503 .4523 .4544 .4564 .4585' 195.3 196.3 197.3 198.3 199.3 210 211 212 213 214 385.7 386.1 386.5 386.9 387.3 359,2 359.6 360.0 360.4 360.9 .6 .7 .8 .9 1200.1 840.4 840.1 839.8 839.5 839.2 134.5 133.9 133.3 132.7 132.J 2.17 2.16 2.15 2.14 2.13 ;4605 .4626 .4646 .4667 .4687 200.3 2U1.3 202.3 203.3 204.3 215 216 217 218 219 387.7 388.1 388.5 388.9 389.3 361.3 361.7 362.1 362.5 362.9 .2 .3 .4 .6 .1 838.9 838.6 838.3 838.1 837.8 131.5 130.9 130.3 129.7 129.2 2.12 2.12 2.11 2.10 2.09 - .4707 .4728 .4748 .4768 .4788 205.3 215.3 225.3 235.3 220 230 240 250 389.7 393.6 397.3 400.9 • 362.2* 366.2 370.0 373.8 1200.8 1202.0 1203.1 1204.2 838.6* 835.8 833.1 830.5 128.7 123.3 118.5 114.0 2.06 1.98 1,90 1.83 .4852 .5061 .5270 .5478 245.3 255.3 265.3 2