wHHiiMiiwnminmiiinwHumwimimiR^^ ic'iHANic^ iTsl'STiTrrri''^ 14T.ir%i*^f^f"?'(iri W^m €W^ i::?iD J fl. V 'K tim '£ ^' Qlgitii^by, Microsoft® Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004638965 Cornell University Library TJ 275.C93 Notes on steam.engineering, preparedjor 3 1924 004 638 965 NOTES ON STEAM ENGINEERING PREPARED FOR THE USE OF STUDENTS AT THE ROCHESTER ATHENAEUM AND MECHANICS INSTITUTE ROCHESTER, N. Y. BY ALLEN S. CROCKER, S. B. (Mass. Tech.) SUPERINTENDENT DEPARTMENT OF INDUSTRIAL ARTS AT MECHANICS INSTITUTE MEMBER OF AM. SOCIETY OF MECHANICAL ENGINEERS Copyright 1907 by The Rochestbk Athene um and Mechanics Institute Rochester, N. Y. KEY. F. — Fahrenheit. C. — Centigrade. B. T. U. — British Thermal Unit or the Heat Unit. lb.— Pound. wt. — Weight. cu. ft. — Cubic Foot. No. — Number. H. P. — Horse Power. B. H. P. — Boiler Horse Power, and in some cases Brake Horse Power. F. and a. 212 degrees F. means that the water is evaporated from a temperature of 212 degrees F. into steam at 212 degrees F. L. P. — Low Pressure H. P.— High Pressure. M. E. P. — Mean Effective Pressure. I. H. P. — Indicated Horse Power, r. p. m. — Revolutions per minute. Av. — Average. NOTES ON STEAM ENGINEERING To the student who is about to enter on steam engineering study there is generally the one idea of being able to run an engine, leaving the boiler plant as a necessary evil to be looked after by the fireman. Neither is the importance of the steam generating part of the plant appreciated in most cases by the manufacturer or owner, and in many plants will be found ef- ficient engines and elaborately laid out engine rooms, while the boiler room suffers for it, inasmuch, as money is lost in the boiler room faster than it is saved in the engine room. The student must not neglect the study of the all important element in steam engineering, i. e., steam ; nor must he neglect the study of the source of steam, the boiler plant, and fully half of the time spent in this Institute will be devoted to the study of this foundation and source. Starting at the very basis we must un- derstand. HEAT. Heat is a form of energy generated (for steam engineering purposes) by combustion, which is in itself a chemical change. The term heat is often misused for temperature, where tempera- ture means the degree or intensity of heat. The unit of temperature is the degree Fahrenheit or the de- gree Centigrade, obtained in the following way. Heat generally causes expansion, and if a glass tube contain- ing mercury is held in ice water the level of the mercury is marked 32 degrees on the F. scale and o degrees on the C. scale. If this same tube of mercury is now placed in steam at atmos- pheric pressure the mercury will rise to a higher point in the tube ; this point is marked 212 degrees on the F. scale or 100 de- grees on the C. scale, giving us 212 degrees F. or 100 degrees C, as boiling points ; 32 degrees F. or o degrees C. as freezing points. This corresponds to 212 minus 32 or one hundred and eighty de- 3 grees between the freezing and boiling points on the F. scale, and IOC minus o or loo degrees between the freezing and boiling points on the C. scale. Therefore a rise of loo degrees C. equals a rise of i8o degrees F., or each degree rise on the C. corresponds to 1.8 degrees on the F. scale. The unit of heat is the British Thermal Unit, abbreviated B. T. U. It is the amount of heat necessary to raise one tb. of water from 62 degrees to 63 degrees F., or roughly speaking it is the amount of heat necessary to raise one lb. of water one de- gree. Water at the freezing point or 32 degrees is taken as contain- ing no heat or no B. T. U., while each pound at say 40 degrees F. would contain 40 minus 32 or 8 B. T. U., and 20 lbs. at 60 de- grees F. would contain 20x(6o minus 32) equals 20x28 equals 560 B. T. U. This gives us a means of figuring how much heat we have in our feed water before it goes to the boiler, or how much heat we put in it by raising its temperature. Example : Suppose we wish to raise one ton of water from 40 degrees F. to 65 de- grees F., how many B. T. U. are necessary. To raise one pound of water from 40 degrees to 65 degrees takes practically 65 minus 40 or 25 B. T. U., therefore, to raise a ton, requires 2,000x25 o"" 50,000 B. T. U. FUELS. Fuels can be compared by their heating qualities, and the heat- ing quality is determined by the number of heat units each pound of the fuel gives off, or as it is called, its heat of combus- tion. One lb. of coal after the ash has been deducted gives about 14,000 B. T. U. if Semi-Bituminous or Anthracite ; while Bi- tuminous gives about 13,000 B. T. U. In regard to wood we gen- erally consider a cord of hard wood equivalent to a ton of coal, or one lb. coal equals .4 lbs. wood. Petroleum, heavy, has about 20,000 B. T. U. per pound, Natural Gas 1,000 B. T. U. per cu. ft., and Producer Gas about 120 B. T. U. STEAM. When heat is first applied to bottom of vessel containing water the air contained in the water rises to the top as bubbles. The 4 water at the bottom near the hot surface is formed into steam, which as it rises through the colder water is condensed, or changed back to water. This condensation is the cause of the singing noise we hear when water starts io boil. Finally the entire volume of water reaches 212 degrees F. or the boiling point at atmospheric pressure, and the gas given off is called steam, the singing noise then stops. If we start with one lb. of water at 32 degrees F. and raise it to 212 degrees F. it will take 212 minus 32 or 180 B. T. U. (i. e.) (180 Heat Units) called the heat of the liquid. Now if we change this pound of water at 212 degrees F. into steam at atmospheric pressure we will need 965.8 more B. T. U. This 965.8 B. T. U. is called the heat of vaporization, and the sum of the heat of the liquid (180) plus the heat of vaporization (965.8) equals 1,145.8 B. T. U. and is called the total heat. If we enclose the water in a tank or boiler and close the exit for steam when it is formed, we will find that the pressure rises within the tank when heat is applied, and also the temperature ; that is raising the pressure raises the boiling point. For example : if we hold the steam back until the pressure has risen to 22 lbs. by the gage, a thermometer placed in the liquid would register 263 degrees, or the heat of liquid or number of heat units in each pound of the water before it is changed over into steam is 263 minus 32 or 231 B. T. U. PRESSURE AND VACUUM. One cu. ft. of water weighs 62.4 lbs. If we take a vessel, the inner dimensions of which make it a cube, one foot on each edge, the vessel will contain one cu. ft. or 62.4 lbs. of water. This wt. 62.4 lbs. comes on the bottom of the tank, distributed over an area of one sq. ft. or 144 sq. inches, and therefore 62.4 di- vided by 144 or .43 of a lb. comes on each sq. inch of the bottom, or we say the pressure is .43 lbs per sq. inch. If the tank were built two ft. high the pressure would be twice .43 or .86 lbs. per sq. inch ; or in other words to find the pressure per sq. inch multiply the height or head of water in feet by .43. If .43 lbs. pressure is obtained from one foot head one divided by .43 or 2.3 ft. head will give one lb. pressure per sq. inch. This is equiva- lent to saying that it takes as much power to pump water to a height of 2.3 ft. as it does to pump water into a boiler against a pound pressure. 5 Mercury is 13.6 times as heavy as water (this is called its Specific Gravity) so that one cubic ft. weighs 62.4x13.6 or 848.64 lbs., and the pressure for the foot depth would be 848.64 divided by 144 or 5.88 lbs., or for one inch height it will be 5.88 lbs. di- vided by 12 or .49. If a glass tube over 30 inches high and closed at one end is filled with mercury, and its top covered while inverting it and placing its open end under the surface of a cup of mercury, the mercury in the tube will not all run out, but will stand in the tube at a level about 30 inches higher than the surface of that in the cup. It is caused to stay at this height by the pressure of the atmosphere on the surface of the mercury in the cup. We saw that the pressure due to a column of mercury one inch high is .49 lbs., therefore, a column 30 inches high will have a pressure of 3OX.49 or about 14.7 lbs. per sq. inch. This tube in the mer- cury bath is our barometer, or instrument which tells us the pres- sure of the atmosphere, and as you know, this pressure varies from day to day. If we take a vessel closed on all sides and extract the air from it we will relieve the atmospheric pressure and have what is called a vacuum. To measure this amount of vacuum we have vacuum gages, some reading from o" to 30", while others read from o to 15 lbs. Those that read from o to 30 have the same graduations as a barometer, i. e. (inches of mercury), and if one of these gages when placed on a tank registers 26 this means that 26 inches or 26X.49 equals 12.7 lbs. of the atmospheric pressure has been taken away. Those gages which read from o to 15 read directly in lbs. vacuum per sq. inch. From above we get the rule to change from inches of mercury to lbs. vacuum. Multiply the reading in inches by .49. In steam engineering work, our starting point on the pres- sure scale is absolute vacuum, or zero pressure, or absolute zero as it is called. If a pressure gage stands at o this is called zero gage pressure or practically 14.7 lbs. absolute pressure. If a pressure gage stands at 40 lbs., this is 40 lbs. gage pressure or 40 plus 14.7 equals 54.7 absolute pressure. THREE KINDS OF STEAM. Wet Steam, Dry Steam, Superheated Steam. Dry Steam is steam at the temperature of the water from which it comes, and which contains no moisture, or, as this moisture is called, priming. Wet Steam is steam at the temperature of the water from which it comes, but which contains moisture or is primed. In other words this steam when it leaves the water takes some water with it, or if dry when it leaves the surface of the water it will be wet if carried any considerable distance on account of condensation. Superheated Steam is steam at a temperature higher than that of the water from which it comes, in other words it is steam which has been heated after leaving the water. Steam contains in the total heat the heat of the liquid and the heat of vaporization. Since dry steam is all steam and has had no added heat after leaving the water one pound of such steam at atmospheric pressure contains heat of the liquid (212 minus 32 or 180 B. T. U.) plus the heat of vaporization 965.8 or for its total heat the sum of these or 1,145.8 B. T. U. Wet steam contains moisture, and suppose we have a pound of wet steam at atmospheric pressure containing 5^ priming, its total heat will be made up of the heat of the liquid 180 plus 95 per cent of the heat of vaporization or .95x965.8 or 917.5 B. T. U., since only 95% of the water has been vaporized. This gives its total heat 917.5 plus 180 or 1,097.5 B. T. U., or shows it to con- tain less heat than dry steam at the same pressure. Superheated steam contains all the heat in dry steam and also a certain number of B. T. U. absorbed while being heated after leaving the water, so if we have a lb. of steam at atmospheric pressure and 250 degrees F. it is said to be superheated 250 minus 212 or 38 degrees F., and as it takes .48 B. T. U. to super- heat a lb. of steam one degree F. it has taken 38X.48 or 18.2 B. T. U. The total heat is therefore 1,145.8 plus 18.2 or 1,164 B. T. U. The water in the wet steam is so much dead material to carry along, while in the superheated steam its extra heat and higher temperature allows it to be cooled several degrees before any con- denses, thus making it very efficient. Other reasons for the in- efficiency of wet and the extra efficiency of dry steam will be given later. STEAM TABLE. i To deal with steam scientifically we must thoroughly under- stand the use of a steam table as given below. The first two columns relate to the temperature of and heat in the feed water as it goes to the boiler, and has been explained before. At 32 degrees F., or freezing, water is considered to have no heat, at 40 degrees F. one lb. will contain 40 minus 32 or 8 B. T. U. Our table gives us 8.06, this is due to the fact that it takes a slightly different amount of heat to raise a lb. of water one degree at different points of temperature. The remaining five columns relate to steam. Column No. 3 gives the absolute pressure of the steam, that is gage pressure plus atmospheric. Column No. 4 gives the temperature of the water from which the steam comes, or the temperature of the steam unless it is superheated. Column No. 5 gives the heat in a lb. of the liquid just before it is changed over into steam. Col- umn No. 6 gives the heat of vaporization, or heat necessary to change a fb. of the water ,when at the temperature given in col- umn 4) into steam at pressure given in Column No. 3. Column No. 7 gives the total heat in i lb. of dry steam at pressure given in column No. 3, and is the sum of column Nos. 5 and 6, i. e., — heat of liquid plus heat of vaporation. Example (i) i lb of water at 60 degrees F. is changed into dry steam at 35 lbs. gage pressure, how many B. T. U. are re- quired ? 35 lb. gage is practically 35 plus 15 or 50 lbs. absolute pres- sure. The total heat at 50 lbs. is 1,167.6 B. T. U. The heat of liquid at 60 degrees F. is 28.12 B. T. U. There has been put into this water 1,167.6 minus 28.12 or 1,139.48 B. T. U. Example (2) i lb. of water at 60 degrees F. is to be changed into wet steam at 35 lbs. gage, carrying 4^0 moisture, how many B. T. U. are required? Since only 96% is vaporized only .96 of the heat of vaporization or .96x917.4 B. T. U. or 880.7 were used in changing the water into steam. The total heat, then, in a lb. of this steam is the heat of the liquid 250.2 plus .96 times 917.4 or 1,130.9 B. T. U. Sub- tract from this the heat of the liquid for the feed water, or 28.12 B. T. U., and we have the required number of B. T. U. as 1,130.9 minus 28.12 or 1,102.78 B. T. U. Example (3) i lb. of water at 60 degrees F. is changed into 8 superheated steam at 35 lbs. gage pressure and 300 degrees F. temperature. How many B. T. U. are required? To change i lb. of water at 60 degrees F. into dry steam at 35 lbs. gage pressure requires 1,139.48 B. T. U. as shown by Ex. No. I. The temperature of dry steam at 35 lbs. gage pressure is 280 degrees F. Therefore this steam is heated 300 minus 280 or 20 degrees F. after it leaves the water, or is superheated 20 de- grees F. To superheat one lb. of steam one degree requires .48 B. T. U., therefore to superheat it 20 degrees requires 20X.48 or 9.6 B. T. U. 1,139.48 plus 9.6 or 1,149.08 B. T. U. gives B. T. U. required. I 2 3 4 5 6 7 , remp. Heat of L. Pr. Temp. Liq. Vapor Total. 32 0. I 101.99 70.0 1043. 1 III3.I 35 3.02 5 162.34 130.7 1000.8 II3I-5 40 8.06 10 193.25 161.9 979.0 1 140.9 45 13.08 15 213.03 1 81. 8 965.1 1 146.9 50 18.10 20 227.95 196.9 954-6 II5I-5 55 23.11 25 240.04 209.1 946.0 "55-1 60 28.12 30 250.27 219.4 938.9 1 1 58.3 65 3312 35 259.19 228.4 932.6 1161.0 70 38.11 42 270.08 239-3 925.0 1 164.3 75 43" 44 272.91 242.2 923.0 1 165.2 80 48.09 46 275.65 245.0 921.0 1 166.0 85 53-06 48 278.30 247.6 919.2 1 166.8 90 58.04 50 280.85 250.2 917.4 1 167.6 95 63.02 52 283.32 252.7 915-7 1 168.4 100 68.01 54 285.72 255-1 914.0 1169.1 no 78.00 56 288.05 257.5 912.3 1 169.8 120 88.10 58 290.31 259-7 910.8 1 170.5 130 98.10 60 292.51 261.9 909-3 1171.2 140 ro8.2 62 294.65 264.1 907-7 1171.8 150 1 18.3 64 296.74 266.2 906.2 1 172.4 160 128.4 66 298.78 268.3 904.7 1 173.0 170 138.5 68 300.76 270.3 903-3 1 173.6 180 148.5 70 302.71 272.2 902.1 "74.3 190 158.6 72 304.61 274.1 900.8 1 174.9 200 168.7 74 306.46 276.0 899.4 "75.4 205 173.7 76 308.28 277.8 898.2 1 1 76.0 212 180.8 78 310.06 279.6 896.9 1 176.5 80 311.80 281.4 895-6 1 177.0 Pressure Temp. Iviquid Vapor Total. 82 313-51 283.2 894-4 1 177.6 84 315-19 285.0 893.1 1 178. 1 86 316.84 286.7 891.9 1 1 78.6 88 318.45 288.4 890.7 1 179. 1 90 320.04 290.0 889.6 1 179.6 92 321.60 291.6 888.4 1 1 80.0 94 323-14 293.2 887-3 1180.5 96 324.64 294.8 886.2 1181.0 98 326.12 296.4 885.0 1181.4 100 327-58 297-9 884.0 1181.9 102 329.02 299-4 882.9 1 182.3 104 330-43 300.9 881.8 1 1 82.7 106 331-83 302.3 880.8 1183.1 108 333-20 303-8 879-8 1 183.6 no 33456 305-2 878.8 1 184.0 112 335-89 306.6 877-8 1 184.4 114 337-20 308.0 876.8 1 1 84.8 116 338.50 309-4 875-8 1 185.2 118 33978 310.7 874-9 1 185.6 120 341-05 312.0 874.0 1 186.0 122 342.29 313-3 873-0 1 186.3 124 343-52 314.6 872.1 1 186.7 126 344-73 315.9 871.2 1187.1 128 345-93 317-I 870.3 1 187.4 130 347-12 318.4 869.4 1 187.8 132 348.29 319.6 868.2 1188.4 134 349-45 320.8 867.7 1 188.5 136 350.60 322.0 866.9 1 188.9 138 351-73 323-2 866.0 1 189.2 Above tables are taken by permission from Professoi r Pea- body's "Tables of the Properties of Saturated Steam." BOILERS. Boilers are rated as to size by the Boiler Horse Power they will generate, one boiler horse power being equivalent to the evaporation of 34.5 fbs. of water per hour from a temperature of 212 degrees F. into steam at atmospheric pressure, this, as you can prove from your steam table, is equivalent to the following definition often used, i B. H. P. equals 30 lbs. evaporated from lOO degrees F. into steam at 70 lbs. gage pressure, in both cases the number of heat units used is practically the same, 33.320 B. T. U. Essentials and Proportions for a Good Boiler. (i) Grate Surface: — Sufficient to burn the required amount of fuel under the draft available. The plain cylindrical boiler has about 1/3 of a square foot of grate surface per B. H. P. and burns from 8 to 15 tbs. coal per sq. ft. of grate surface per hour, under natural draft. The water tube boiler with drum has about y^ sq. ft. grate surface per H. P. and burns from 9 to 16 tbs. of coal per sq. ft. grate surface, under natural draft. The Locomotive Boiler has about 1/15 sq. ft. grate per B. H. P. and burns from 50 to 120 lbs. coal per sq. ft. grate under induced draft. The Scotch Marine Boiler has i/io to 1/15 sq. ft. grate per B. H. P. and burns from 35 to 50 tbs. coal per sq. ft. grate per hour. Natural Draft is that obtained from a stack, due to its height. Induced draft is obtained by blowing steam into the stack, as in a locomotive, or by a fan placed in the stack to draw the gases through. Forced draft is obtained by a fan blowing air into the ash pit, as on the underfeed stokers. The grate bars have space between them amounting to from 25 to 50% of the grate surface to allow air for combustion and also to prevent the grate from burning. This space is larger for soft than for hard coal. (2) Combustion Space : — Sufficient for the gases to thoroughly mix, and for complete combustion. This includes the space over the grate and back of the bridge wall. This space is not as large for anthracite as it is for bituminous gas and flame produc- ing coal : On the ordinary horizontal multitubular boiler 24 inches is required above the grates for anthracite and 27 to 30 inches for soft coal, on the vertical Cahall boiler the arch is carried higher for soft coal, than for hard, and the arch after being heated thoroughly is claimed to be a smoke preventative, inas- much as it is hot enough to ignite any incompletely burned gases, — this is questionable, however. Setting a boiler too low, or giv- ing it insufficient combustion space often makes it smoke. In a Scotch Marine boiler 3 to 4 cu. ft. of combustion space is al- lowed per sq. ft. grate surface. (3) Draft Area: — Passage of gases must be free, that is noth- ing must obstruct their easy access to the chimney. The draft area in a fire tube boiler is the area through the tubes, or sum of cross sectional area of all tubes. Ashes, dirt, soot or scale in the flues is therefore bad. If too little air can pass through the flues we will have incomplete com- bustion, while if too much air passes through it passes so quick- ly that it does not have time to give up its heat to the boiler, and the stack temperature is too high. Proportion 1/7 to % of grate surface. (4) Heating Surface: — Sufficient to absorb heat from hot gases before they escape from the boiler. Baffling surface in- creases the efficiency of heating surface. There are two kinds of heating surface, the water heating and the steam heating or superheating surface. Thick plates or plates covered with scale make poor heating surface, as they do not allow the water to cool the outer surface of the plate so quickly, or allow heat to get to water. Water Tube Boilers use from 7 to 11 sq. ft. of heating surface per B. H. P.; Fire tube 12 to 15, and have the heating surface 35 to 40 times the grate surface. Locomotives use 4 to 5 sq. ft. heating surface per B. H. P. and have this 60 to 70 times the grate surface. Scotch Marine Boilers use 2 to 5 sq. ft. per B. H. P. and 25 to 40 times the grate surface. "Engineering News" gives the following rule for obtaining quickly and approximately the B. H. P. of a tubular boiler. Mul- tiply the number of tubes by their length in feet; multiply this product by the diameter of tubes in inches, and divide the latter product by 50. (5) Water Space: — Sufficient to prevent too great a fluctua- tion in the water level when an irregular demand for steam takes place, it is often made twice the steam space. A large water space serves for a reservoir of heat and therefore makes it easier to run with a steady pressure. It takes longer to raise the pres- sure when starting, however. (6) Steam Space : — Should be of sufficient size to keep a steady pressure during irregular demand. It is often taken equal to the volume of steam used every 20 seconds, or in the cylindrical fire tube boiler about .85 cu. ft. per B. H. P. In water tube boilers a steam drum is often used to give the required steam space. .3 to .4 cu. ft. steam space per B. H. P. is often used in Scotch Marine Boilers. (7) Free Water or Disengaging Surface :— This must be of sufficient area so that the flow of steam from the surface of the water when coming at a rate corresponding to filling the steam space three times per minute will not give wet steam. The water surface raises a little as the steam leaves it, and if the surface is so small that the steam has to leave at a high rate of speed, it will take water with it and be primed. This gives another cause for the steam drum on a water tube boiler. The proportion >^ sq. ft. per B. H. P. is sometimes used. BOILERS CLASSIFIED. According to use into Stationary, Locomotive and Marine. Marine and stationary are subdivided into shell, sectional, fire tube, water tube, internally and externally fired boilers, and the stationary boilers still further into horizontal and vertical boil- ers. Advantages and disadvantages of shell and tubular or section- al boilers, and we can say as a general rule that the same differ- ence exists, or same advantages and disadvantages occur if in- stead of classifying shell and sectional, we classify, fire and water tube boilers: — Advantages of Shell : — Cheap, easy to make, easy to clean that part which can be cleaned, give sufficient body of water to store heat, therefore they carry steady pressure and water level; suf- ficient steam space, therefore steadier pressure in case of sudden drains ; sufficient free water surface for disengagement of steam, therefore, generally dry steam, unless unduly forced or using dirty water. Disadvantages of Shell: — Size is limited by capacity and pres- sure. Thickness equals pressure times radius divided by safe tensile strength. Thicker plate has to be used than on sectional boilers, therefore, heating surface less efficient. Poor circulation in some, as in Scotch boiler, where the lowest part, where the coldest water settles is the coldest, and heating surface is not well distributed. In getting up steam in a hurry it is sometimes customary to draw water from bottom and return it near the 13 top, in which case unequal expansion and contraction cause straining and leakage. They are bulky for transportation, require side of building or deck to be removed to install. Slow steaming. Require more careful and skilled attendance for safety, as element of safety is not contained in them. Advantages : — Water Tube or Sectional. Quick steaming, generally good circulation and better distri- bution of the heating surface. Thin tubes, well exposed to hot gases. Easily installed in inaccessible places (down the smoke stack of a naval vessel for instance as in the 3-61-65 monitors) Monterey's boilers rebuilt without change in structure of the ship. Easily repaired by carrying spares. Safety boilers as a rule, for even those with a shell or drum for water storage or steam, have this drum either entirely with- out the path of the hot gases, or are exposed to those gases only after they have passed and repassed the tubes, and are sufficient- ly cooled to cause little danger to the drum. Light, powerful and compact, well adapted for forced drafts, as there are no tube or crown sheets to leak. Disadvantages of Sectional Boilers: — Many joints, numerous hand holes, in some types do not always separate steam prop- erly, requiring a separator. Small body of water in some and. therefore, steam pressure not so steady. In case of poor water, scale badly, although vertical boilers, as a general rule not so easily scaled. One of the disadvantages of the externally fired boiler is the extra amount of coal necessary to heat up the boiler setting, many engineers claiming that they fire twice as much coal in the morning as in the afternoon. On the Scotch Boiler although poor circulation, we have the lower part to act as a cool settling chamber, and in case of brine, the deposit of salt on this surface can be blown out with a hose, while in a dififerent boiler it might cause scale and cake on. On the water tube boilers as used in the navy it is hard work to keep them tight on account of the pitching and working loose of the parts due to the vibration and movement of the ship. BUYING A BOILER. Buying a Boiler: — In buying a boiler the following five import- ant points are given in the order of their importance. (i) Safety, (2) Convenience of Manipulation, (3) Steaming Properties, (4) Durability, (5) Cost. 14 The principal points to consider or examine in regard to safety are the quality and thickness of metal used, the kind of joints and the staying. The double cover plate butt joint is considered the best, as it requires no bend to be put in the sheet, and there is less straining action when contraction and expansion are set up in the boiler. The specification on steel for boiler plate gen- erally calls for Open Hearth fire box steel of not less than 55,000 nor over 60,000 lbs. tensile strength, not less than 56^ reduction of area and 25% elongation in 8 inches, ability to be bent double when cold and also at a red heat without showing cracks. Tests, however, have shown that although this bending can be done at these heats yet bending the plate when slightly above the temperature of the steam the boiler is using has de- veloped cracks. BOILER DESIGN. If we were to order an 80 B. H. P. horizontal multitubular boil- er 15 ft. long to run at 90 lbs. pressure we would expect some- where near the following proportion if hard coal and natural draft were used. Take 34J4 lbs. of water evaporated F. and a 212 degree F. as a boiler H. P. and we must evaporate 80x341/^ or 2760 lbs. per hour. If one lb. of coal evaporates 9 lbs. of water we will require 2760 divided by 9 or 307 lbs. of coal per hour. Taking the grate as burning 12 lbs. of coal per sq. ft. of grate surface per hour we require 307 divided by 12 or 25.6 sq. ft. grate surface. Draft area, or area through the tubes equals 2/15 grate surface or 2/15x25.6 equals 3.41 sq. ft. or 3.41x144 sq. in., equals 492 sq. inches. Tubes are generally used one inch in diameter for each 5 ft. in length for hard coal, and 4 ft. for soft coal. This on a 15 ft. boiler gives 15 divided by 5 or 3 inch tubes. Boiler tubes are given by their outside diameters. A 3, inch tube is .109 inches thick and its internal area is 6.07 sq. inches. For sufficient draft area we will require 492 divided by 6.07 or 81. Taking one cu. ft. of steam space per B. H. P. we will require 80 cu. ft. and twice this or 160 cu. ft. of water space. To find the space occupied by the tubes we have 81 tubes, 3" diameter each and 15 ft. long. The cross sectional area of a 3" tube is .0491 sq. ft. 15x81 equals 1,215 ft. length of tubes. 1215X.0491 equals 59.6 cu. ft. We now have the capacity of the boiler as 15 being steam space 80 cu. ft., plus water space 160 cu. ft., plus tube space 59.6 cu. ft. or 299.6 called 300 cu. ft. The end area of the boiler is equal to its volume divided by its length, or 300 divided by 15 equals 20 sq. ft. The diameter of a circle whose area is 20 sq. ft. equals the square root of (20 divided by .7854) or practically 5 ft. Next see if the heating surface is sufficient, for this take the outside of all the tubes and the lower half of the shell. From table of boiler tubes a tube 3" diameter and 1.273 ft. long gives i sq. ft. heating surface, so that our 1,215 ^t. gives 1,215 divided by 1.273 or 954 sq. ft. The circumference of the 5 ft. diameter shell is 15.7 ft. So the lower half gives us ^xi5.7x 15 equals 118 ft. or a total of 1072 sq. ft. Dividing heating surface by the grate surface we have 1072 divided by 25.6 equals 41, or the heating surface is 41 times the grate surface, which is a good ratio. Dividing the heating surface by the B. H. P. or 1072 divided by 80 equals 13.4 sq. ft. heating surface per B. H. P. For thickness of metal to use in this 5 ft. drum our rule is thickness equals pressure times radius in inches divided by the allowable tensile strength of the metal. Although the metal will stand 60,000 lbs. we use only 1/6 of this or 10,000 lbs. thus giving what is called a factor of safety of 6. Thickness equals 90 times 30 divided by 10,000 equals .27" add to this 1/16" for corrosion and our plate will be 5/16" thick as a stock size. The tube sheet is generally made %" thicker than the plate. PIPING. The feed pipe should place the water in the boiler where it will not retard circulation, and also where this feed water, if cold, will not cause undue expansion and contraction in the plates, and as the heavier or colder water is circulating down- ward at the back of the boiler in most of the sectional and shell boilers, the best place for the feed pipe to discharge is at the sur- face of the water at the back of the boiler, and as the regulating valve is generally required at the front of the boiler the feed pipe is led through the front head to back of boiler. This helps to heat the water slightly. Pipes are sometimes perforated or the feed pipe feeds into a pan in the steam space, the water overflowing from this in a thin sheet. The ease with which a boiler steams is affected more by the location of feed entrance, than in the manner of feeding. 16 There is less danger from siphoning from one boiler to another or back to the pump, etc., if the feed pipe is high. Feed pipes should have a globe valve near the boiler and a check between this valve and the pump, so if the check sticks it can be removed after closing globe valve. This check, when in working order prevents siphoning or the working of any scale or hot water back to the pump, where it would cause trouble. The feed pipe should be of such size that the velocity of flow of water need not be over 400 ft. per minute, and pipe larger than this if there is any scale to form or work into it. The steam pipe should rise from the boiler and pass along without pockets for water to collect in and hammer, and most steam pipes are made to pitch >4" to i" in 10 feet in the direction of the flow of steam, and the ends of all horizontal runs of any considerable lengths are provided with drips. Allowance should be made for expansion both at the boiler and throughout the length of the pipe. At the boiler this may be taken care of by running the pipe up, then from an elbow over, and from an elbow here attach the main line. Expansion along the pipe is taken up by carrying the pipe on chains, or if very heavy, on rollers or using expansion joints. The size of the steam pipe should be such that the velocity of steam in the pipe shall not be over 6,000 ft. per minute. Blow-off pipes, where they run from the bottom of the boiler back through the wall often burn off, since there is no circula- tion in them, and they may fill with scale. To prevent this a pipe is often run from just below the water line to the outside of the back wall, and down to the blow off pipe, this is provided with suitable valves so that it may be used either as a surface or bottom blow off. A cock valve is generally used in the blow off pipe as it is not easily clogged by dirt or scale hardening around it. SAFETY VALVES. A safety valve, to act as such, should have an area of opening large enough to allow the steam to pass away from the boiler as fast as it is formed, even if all other outlets from the boiler are closed. This makes them of such a size that they are seldom built to do this. They will lift, however, and give the attendant warning to check his fires. In case a safety valve sticks and the pressure has run above the safe pressure on the boiler, do not 17 lift the safety valve, for this relieves the pressure so suddenly that much of the water will flash into steam, and this quick ex- pansion has been the cause of many explosions. If the feed pump delivers water into the boiler where no danger will occur from contraction and expansion the pressure may be lowered by this means, in connection with checking drafts, and banking fires with ashes or coal. Do not pull the fire at once for this stirring causes extra heat. If it does not relieve the pressure too quick- ly extra machinery may also be started to use the steam. Safety valves are now of two kinds, the lever and ball, and the pop or reactionary valve, held on its seat by a spring. There are many rough rules for determining the area through the seat of the safety valve, varying from i sq. in. in area to i sq. ft. grate to i sq. in. area to 3 sq. ft. grate. The safety valve can be made smaller for a certain grate surface with high pressure steam than it can for the same surface of grate with low pres- sure steam. Forced draft on a grate also means more steam formed per sq. ft. of grate and therefore a larger safety valve. The higher pressure steam will flow faster than the low pres- sure for the rule is that the number of pounds of steam that will flow through an orifice in a second is equal to the area of the orifice in sq. inches times the absolute pressure of its steam divided by 70. This shows rate is increased directly as the pres- sure, or double the pressure and the amount which will flow through the same orifice per second will be doubled. To calculate the pressure at which a lever and ball valve will blow off or where to set the ball to blow off at a given pressure, measure the following: (i) Diameter of Seat D. (2) Distance A. or center of valve spindle to center of ful- crum. (3) Distance C. center of weight to center of fulcrum. (4) Distance B. center of gravity of lever to center of fulcrum. To get this last distance balance the lever on a knife blade to determine point A. (5) weigh the ball, (6) weigh the lever. (7) Find area of the valve seat by multiplying its diameter by its diameter and this product by .7854. To find the distance C. to set for a certain pressure, ist. Mul- tiply the area oi valve seat by the pressure, and then multiply this product by distance A. 2nd. Subtract from this last product the product of weight of the lever by distance B. 3rd, Divide 18 this difference by the weight of the ball, and the quotient will be the pressure ajt which the steam will blow off. The U. S. Law requires A. to be more than 4 inches, and L not over 40 inches. Safety valves should be lifted daily to insure their easy rising, as corrosion is liable to make them stick if seated for any length of time. SAFETY VALVE, Cut and description of the pop or reactionary valve will be given in the class. One of the great advantages in the pop valve is due to the reaction back and forward on the valve of the steam as it starts to leave the boiler, this causes the valve to open widely and quickly relieves the pressure, closing again after it has dropped a few pounds. WATER LEVELS. If either top or bottom valve leading to the water glass is closed, the level of the water will rise in the glass for, I St. When upper valve is closed the steam in the upper part of the glass is condensed and the water rushes up to fill this space. 2nd. When lower valve is closed condensation in glass causes level to rise. 19 When fire is stirred up under a horizontal boiler which has been banked, the water level rises in water glass, since circula- tion is from front to rear, being maintained by difference in level, and conversely, level falls when a boiler which has been steaming freely is checked. When foaming (or violent boiling on account of dirty water or undue forcing) occurs it may be hard to tell where the water level is, and, occasionally the use of steam may have to be partially stopped in order to tell where the water level really is, and if the foaming is due to dirty water the boiler should be blown oiif as soon as practical, and filled with new water. Do not, however, blow off while the boiler is too hot. If the main pipe leading to the gage glass and try cocks becomes choked with scale it is possible to tell where the water is by using a hammer on the front head, and telling by the sound of the tap whether you are above or below the water line. This, however, should not allow any engineer to run after the pipe is stopped up. LAYING UP A BOILER. When not in use boilers should be dry inside, or entirely filled with water from which the air has been expelled by boil- ing. In the American Navy, boilers are dried out and painted with mineral oil. In the English Navy the boilers are dried, glowing charcoal placed in them to consume the oxygen in the air, and quick lime introduced to absorb mosture. FUSIBLE PLUGS. They are made of brass with a conical filling of Tin and Lead and sometimes Bismuth is added ; or Zinc, Lead and Bismuth are used. This filling is of such composition that it is made to melt at the required temperature, generally from 300 degrees upward. They are placed just below the low water line and if the water uncovers them they melt and give warning of low water. Low water alarm whistles and water level regulators are, however, much used now. The objections to the fusible plugs are two; ist. they may become covered with scale and not melt when they should, or 2nd. they may melt even when covered with water. They are inserted in the following places: — Back Head of cylindrical tubular boiler about 3" above tubes. Crown Sheet of Locomotive firebox. In lower tube sheet of vertical boiler or in one of the tubes a little above that tube sheet. In lower side of upper drum of water tube boiler. TESTING QUALITY OF STEAM. Steam Tables give the temperature of steam for different pressures when the steam is not superheated, and if we were sure that the steam were not superheated we could take its tem- perature and look in the steam table for its pressure, this pres- sure would be the same even if the steam were wet. If the steam is superheated take both its temperature and pressure, as for ex- ample suppose the steam pressure is 105 gage and the tempera- ture is 350 degrees F. From the Steam table we find that the temperature of steam at 105 gage or 120 absolute is 341.5. The steam is therefore superheated 350 minus 341.5 or 8.5 degrees F. In case of over 3 fo moisture in the steam an instrument very similar to the separator is used for determining moisture. There is a gage glass on the side of the tank and this is calibrated so that we can tell how much water there is in the tank by the height in the glass. The steam in passing through this separa- tor has to travel over baffling plates, which take the moisture out and this is left in the separator and the weight measured by the height of water in gage glass. The steam then flows to the air through an orifice of known size, from which the weight is figured, i. e. weight that will pass in lbs. per second is equal to the area of orifice in sq. inches times the absolute pressure of the steam divided by 70. Example: Steam flows through an orifice J4 'i^ch area for ten minutes at 85 lbs. pressure gage, or 100 absolute, and the gage shows 15 lbs. of water collected in separator, the . of water 1 142.6 B. T. U. Heat added to 800 lbs. of water 800 914080. 914,080 divided by 965.8 equals 947 tbs. of water that would have been evaporated from and at 212 degrees F. 947 divided by 34.5 equals 27.4, equals Boiler Hoste Power. Second : If steam carries 2% moisture. 98% will be steam, 2% or .02 of 800 equals 16 lbs. of water. In the steam there will be 98% of 914,080 B. T. U., equals 895,798 B. T. U. Heat of liquid at 94.7 tbs. absolute pressure will be 293.8. 293.8 minus 38. 1 (heat of liquid feed water) equals 255.7 B. T. U., equals heat added to each lb. of water. 16 times 255.7 B. T. U. equals 4,081 B. T. U., the heat added to 16 lbs. 895,798 plus 4,081 equals 899,879 B. T. U. total. 899,879 divided by 965.8 equals 932 tbs. that would have been evaporated from and at 212 degrees F. 932 divided by 34.5 equals 27.0, equals B. H. P. Third : If steam is superheated and at a temperature of 350 degrees F. To superheat one tb. of steam one degree takes .48 B. T. U. Temperature of saturated steam at 80 tbs. gage pressure is 323.6 degrees, therefore this steam is superheated 350 degrees minus 323.6 degrees, or 26.4 degrees F. To superheat one pound 26.4 degrees F. requires 26.4 times .48 B. T. U. or 12.672 B. T. U. To superheat 800 tbs. requires 800 times 12.672 equals 10,137 B. T. U. Total heat of 800 tbs. if steam were dry (from number one) 914,080 Heat due to superheating 10,137 Total 924,217 B. T. U. 924,217 divided by 965.8 equals 957, equals number of lbs. that would have been evaporated F. and A. 212 degrees F. 957 divided by 34.5 equals 27.8 B. H. P. 24 SAMPLE BOILER TEST. Duration of test, hours loo Average air pressure, lbs 14.9 Average steam pressure (gage), lbs 104.0 Average temp, of feed water, degrees F 1 16.0 Kind of coal used Per cent moisture in coal 3^ Description of Boilers, Horizontal Inclined, Water Tube. 90 Tubes, 4" dia. 18 ft. iij^ in. long. Area sq. ft. 1,786 9 Tubes, 4" dia. 4 ft. 6 in. long Area sq. ft 42 2 Drums 3 ft. dia. 19 ft. iij^ in. J^ Area sq. ft. . . . 188 Grate surface 6' — 6"x7' 45.5 Water heating surface sq. feet 2,016 Ratio water heating surface to grate surface .... 44.3 lbs. coal fired — including coal equivalent of wood 45,000 Average coal burned in 15 minutes 112.5 Unburned fuel, if fires are drawn Coal burned — including wood equivalent 45,000 Total refuse from coal 6,490 1. Total combustible 37.i6o 2. Average combustible for 15 minutes 92.9 3. Average tbs. of air for 15 minutes i)S4i 4. Air per tb. coal _ 13.7 5. Air per lb. combustible 16.6 6. Quality of steam .974 7. Water apparently evaporated 390,200 8. Water apparently evaporated per ttJ. coal .... 8.67 9. Evaporation factor 1.1172 10. Water actually evaporated 380,055 11. Equivalent evaporation F. & A. 212 degree F. 435.931 12. Equivalent evaporation F. & A. 212 degree F. per lb. coal 9-7 13. Equivalent evaporation F. & A. 212 degree F. per lb. combustible 11-7 14. Coal burned per sq. ft. grate surface per hour 9.9 15. Water evaporated F. & A. 212 degrees F. per sq. ft. Heating surface per hour 2.16 16. Boiler horse power developed 126.5 17. Heat Units per pound of coal as fired 13,500 18. Boiler efficiency 69.4% (i.) Is found by substracting total refuse and moisture from 25 LAP WELDED CHARCOAL IRON BOILER TUBES. s 1 .2 » 1 i .0 la 1 1 03 Of u a 1 •3 a t-H i Sq. in. Internal Area Sq. ft. Sq. in. External Area Sq. ft. u II "S -S p. g •0 § ■" 41 Xi (fi 1 1 u I m 1.560 •095 4.90 5-49 1.91 •0133 2.40 .0167 2.448 2.183 2.316 1-65 2 1.810 ■095 5.68 6.28 2.57 -OI79 3-14 .0218 2. no 1.910 2.010 1.91 2X 2.060 ■095 6.47 7.06 3-33 .0231 3-97 .0276 1-854 1.698 1.776 2.16 2% 2.282 .109 7.16 7-85 4-09 .0284 4.90 -0341 1.674 1.528 1.601 2-75 2H 2.532 .109 7.95 8.63 5-03 •0350 5-94 .0412 1.508 1-389 1.449 3-04 3 2.782 .109 8.74 9-42 6.07 .0422 7.06 .0491 1-373 1-273 1.322 3-33 3X 3.010 .120 9-45 10.21 7-11 .0494 8.29 -0576 1.269 I -175 1.222 3-96 3K 3.260 .120 10.24 10.99 8-34 .0580 9.62 .0668 1.172 1. 091 1. 132 4.28 .3?< 3-510 .120 11.02 11.78 9-67 .0672 11.04 .0767 1.088 1.019 I-QS4 4.60 4 3732 ■134 11.72 12.56 10.93 .0760 12.56 .0873 1.024 -955 .990 5.47 4J^ 4.232 .134 13.29 14-13 14.06 .0977 15-90 .1104 •903 .849 .876 6.17 5 4.704 .148 14-77 15-70 17-37 .1207 19-63 .1364 .812 .764 .788 .6';6 7.58 6 5-670 .165 17.81 T8.8.S 25-25 .1750 28.27 .TQ'i'! .674 .6^7 TO.I 26 coal. (6) Is found by calorimeter tests. (7) Is water actually fed to boiler. (9) Is found by dividing the heat necessary to change one pound of water at 116° F. into steam at 104 tbs. pres- sure (i. e. steam that is 97.4% dry steam and 2.6% moisture) ^y 965-8. This 965.8 is the heat necessary to change one pound of water at 212" F. into steam at 212° F. (i. e. into steam at at- mospheric pressure.) (11) Is found by multiplying (7) by (9.) (16) Is obtained by dividing 11 by ico hours to get evapora- tion from and at 212° F. per hour, and then dividing this quotient t>y 34-5- (17) Is found by use of Mahler bomb or Parr Calori- meter. (18) Is obtained by dividing B. T. U. furnished per pound of coal, as shown by evaporation, by B. T. LJ. per pound of coal as shown by calorimeter, i. e. 9.7X965. 8-=-i3.5oo. MISCELLANEOUS. Steam Traps: — Their object is to drain condensation from steam pipes without allowing steam to escape. Tank traps are traps placed below the surface they are to drain, and which dis- charge into tanks or to the atmosphere, that is, they discharge against a pressure less than that of the line they drain. Return traps are traps set at least 3 ft. above the water line of the boiler and discharge to the boiler. When this return trap is fed by a pump or receiver it is known as the single system ; when fed by a tank trap a Duplex System. Traps depend for their action on floats, expansion of metals or gases, heights of water columns or counter balancing weights. The trap feed to the boiler is used only when hot water can be obtained and is the most ef- ficient way to feed water into a boiler in that case. The objec- tion to it is the uncertainty of the action of the traps and the lack of regulation in the speed of feeding the water in, also the intermittent feed. Corrosion or rusting is general in its action, i. e. a plate as a whole may waste away, and it is hard to detect such wasting. Pitting is local in its action, and is caused by unhomegenity of the metal, or galvanic action, pits or holes being formed. The inside of the boiler is allowed to slightly scale with lime or is painted to prevent this. Grooving is caused by expansion and contraction of a poorly stayed plate, where more or less bending motion or buckling is allowed. Scale is formed by the deposit from the water and is due to 27 the many impurities the water contains. There are various scale preventing compounds on the market, and as many of them con- tain acid, they should not be used. Send a sample of the water to a chemist and let him analyze and prescribe what is to be used in the feed water to prevent this scale. One of the worst scales is formed by oil in the boiler mixing with the impurities of solid matter. This forms a fluffy or pasty and porous scale which is an extreme non-conductor of heat. Oil should be taken from the exhaust by an oil separator or tank containing straw, through which all exhaust should pass. This straw or hay should be renewed weekly. The scale prevents the water from cooling the plate, thus al- lowing the plate to become dangerously overheated, and it also prevents the water from absorbing the heat, thus lessening the efficiency of the boiler. INJECTORS— PARTS— LIFTING NOZZLE— STEAM NOZ- ZLE—COMBINING TUBE— DELIVERY TUBE— OVER- FLOW VALVE. Injectors: — Are divided into two classes, lifting and non-lift- ing, or those that draft their water, or take it under a head. Automatic : — Regulate automatically the quantity of water which flows to the boiler. Restarting: — Start automatically when the injector breaks, without having to shut off the steam supply. Size : — The size of an injector is given from the diameter of the smallest opening of the delivery tube. Thus a number 8 in- jector is one in which the diameter of the smallest opening in the delivery tube is 8 millimeters, or about 8/25 of an inch. The principal difficulty is their inability to draft excessively hot water. The reason that an injector forces water into a boiler is due to the fact that the steam gives sufficient velocity to the water to overcome the boiler pressure and enter the boiler. Steam issuing from a nozzle at 180 lbs. pressure attains a ve- locity of 3,600 ft. per second, while water issuing at the same pressure attains a velocity of only 164 ft. or about 1/22 of that of steam. The steam, therefore, has more momentum and power of doing work. The momentum of i lb. of the steam, (weight 28 discharged per second times the velocity per second), equals 3,600 times one or 3,600. For the same reason the momentum of I lb. of water would be 164 times i or 164. Therefore, it would take 3,600 divided by 22 lbs. of water dis- charged per second to equal this momentum. Therefore the steam could easily enter the boiler if we could reduce it to the size of the water nozzle. Let us take an example. Let i tb. of steam at 180 lbs. pressure feed 10 lbs. water to the boiler, and we will find what pressure it will overcome. We will say that the vacuum caused by con- densation of the steam lifts and draws into the combining tube this 10 lbs. of water at a velocity of 40 ft. per second. Its mo- mentum equals 40 times 10, equals 400, and the momentum of the entire jet now in the combining tube is theoretically 3,600 plus 400 equals 4,000 and its velocity 4,000 divided by 11 or 366 ft. per second. Now this particular experiment has been tried and it was found that the velocity in the combining tube instead of be- ing 366 ft. was ig8 ft. per second. This loss of velocity is caused in part by eddies, etc., the steam and water not meeting exactly in the line of discharge. We saw, however, that we only needed a velocity of 164 ft. to enter the boiler, while we have 198 minus 164 or 34 ft. higher speed than we need, and as water under head of 206 lbs. has a velocity of 198 ft., we could feed against a boiler at that pressure. Of course we need some of this extra pressure to lift the main check valve and overcome the friction in the feed pipe. Only one or two per cent of the energy in the steam taken is used to force the water, the remaining energy is used in heating the feed water. The principal objections are cannot handle ex- ceedingly hot water and are a severe drain on the boiler if not used at proper times, also uncertain. ENGINES. The definition of heat as a form of energy has been given, but one form of energy may be changed to another. For instance the chemical energy expended in combustion is changed into heat energy, and in the case of the engine the heat energy in the steam is changed into mechanical energy, which causes motion in the parts to be moved. There is a definite relation between the amount of mechanical energy and the amount of heat energy developed by it. 29 The unit of mechanical work is the foot pound, or the raising of one pound one foot, or the overcoming of a pressure of one pound through a distance of one foot. If we take a drum as shown in the cut and carrying the blades which revolve in the water, and allow the weight of 778 pounds to fall one foot, the stirring of the water would raise one pound one degree F. or generate one B. T. U. is\v\\\\\\\\\\\^ ^M\\\\\\\\^^ That is 778 ft. lbs. is equivalent to i B. T. U. and therefore we would expect to get 778 foot lbs. out of every B. T. U. when we transformed it, but on account of much of the developed me- chanical energy being used within the steam itself we do not get this. The Engine Horse Power, abbreviated H. P. is the performance of 33,000 ft. lbs. of work per minute, or overcoming a resistance of 33 lbs. through a distance of 1,000 feet in a minute. 33,000 di- vided by 778 gives 42.42 B. T. U. per H. P. per minute, or to gen- erate one H. P. for an hour 60x42.42 B. T. U. on 2,545.2 B. T. U. Engines however use from 1,000 to 225 B. T. U. per H. P. min- ute. One heat unit is equivalent to 778 units of work or foot pounds. 30 We saw that i lb. of good coal developed 14,000 units of heat, now 14,000 heat units equals 14,000x778 foot pounds, equals 10,- 000,000 approx. There are 33,000 foot pounds in a H. P. Now in generating a H. P. for one continuous hour, we would generate 33,000x60 or approx. 2,000,000 foot pounds, therefore 10,000,000 divided by 2,000,000 gives us 5 or we would expect 5 H. P. per hour from each lb. of good coal. As a matter of fact our best engines take over i lb. of coal per H. P. hour. In actual prac- tice let us see how many lbs. of water each lb. of coal will evaporate. We found in our problem on the B. H. P. that it took 966 B. T. U. to vaporize i lb. of water at 212 degrees under the pressure of the atmosphere; according to this each lb. of coal would evaporate 14,000 divided by 966 or approx. 14^^ lbs. water. STEAM CYLINDER. This is of cast iron, truly and smoothly bored, and counter bored larger at each end. This counter bore is for two reasons : istj when one piece of metal slides back and forth over another it wears a hollowing space, allowing the sliding piece to over travel the seat tends to wear an even surface. 2nd, as the piston wears the cylinder out of round we have the old counter bore to line up from again. Also it is an advantage in boring out the cylinder to allow the tool to over travel. In some cases cylinder liners are put in, especially so in pumps, or water cylinders, in which case instead of reboring, a new liner can be put in. The thickness of the cylinder walls is generally determined by the ability to rebore rather than the question of strength, and is seldom less than J^" thick except in small engines. One head is generally cast with the cylinder, and also contains the stuffing box. On the top of the cylinder is cast the part for the steam ports, or passages for the steam to enter and leave the cylinder. In some cases the steam chest is cast with the cylinder. The parts should be of sufficient size to prevent wire drawing, or the fall of the steam pressure in the cylinder during admis- sion, due to restricted passages, and can be figured by allowing 6,000 ft. travel per minute of the steam, and if possible 2 times this area for area of exhaust ports. Most engines have to exhaust from same port, and the ports are of sufficient size to allow for this exhaust. Often times the valve does not fully uncover for admission but does for exhaust. Wire drawing may occur not 31 only in the engine but also in the piping if it is too small, or con- tains too many bends. The top of the steam chest, upon which the valve slides is also raised to allow overtravel of the valve, in order to wear a more even surface, and to allow for refacing as well as to give the cut- ting tool a drop or over travel. The seats are scraped as well as the valve that runs upon it. That is they are scraped together. The valve is of various kinds, the simplest being the plain slide valve. This, however, does not have so good a motion and gives slow cut off and is not balanced unless of special design. ENGINES. A Simple, Non Condensing engine consists of one in which the steam cylinder or cylinders use steam at boiler pressure, and exhaust into the atmosphere or tanks. That is, there is neces- 32 sarily a back pressure greater than the atmospheric pressure. By back pressure we mean the pressure on that end of the cylin- der that is not taking steam, or the pressure during exhaust. Therefore, in this engine we must throw away steam at a low pressure, depending upon the number of expansions allowed in the cylinder, and therefore this steam thrown away is wasted as far as the engine is concerned, although it may be used for heat- ing or drying. The Simple Condensing engine differs from the non condens- ing in exhausting at a pressure less than that of the atmosphere. In all work on steam we work from the absolute o pressure, i. e., 14.7 lbs. per sq. in. lower than o pressure on the gage. Therefore, if we can exhaust at a pressure less than atmospheric, we are getting so much more work out of our steam, or carrying our expansions farther. Relieving the pressure on one side of our piston is the same as increasing it upon the opposite side, and the condensing engine makes use of the pressure due to the atmosphere, or in other words, instead of having a back pressure we have a vacuum. This vacuum is obtained as follows: Each pound of steam at atmospheric pressure occupies a volume of 26.6 cu. ft. A cubic ft. of water weighs 62.4 lbs. and each pound of water occupies a space of 1/62.4 of a cubic foot. If we had this one pound of steam enclosed in a tank of 26.6 cu. ft. capacity and con- densed it to occupy the above volume of water we should have almost a perfect vacuum. This is in reality what we do in a con- densing engine. We condense the steam or change it back to water, which, occupying a smaller volume than the steam, creates a vacuum. CONDENSERS. This is condensed in one of two kinds of condensers. Name- ly the surface or jet condensers. In the surface condenser the exhaust steam is passed over a series of pipes through which the cold water passes. The steam striking this cold surface is con- densed. In the jet condenser the exhaust steam intermingles with the jet of condensing water and is condensed, giving us the name jet condenser. 33 COMPOUND ENGINES. The compound engine has, generally, two cylinders, one being three to four times the size of the other by areas. The high pressure steam is admitted to the smaller cylinder in which it expands and does work, from here it exhausts directly to the larger or low pressure cylinder, or else to a receiver first and then to the low pressure cylinder where it does more work, and ex- hausts to the atmosphere or the condenser. If the steam from the high pressure cylinder exhausts into a large receiver, the back pressure on the high pressure cylinder and the pressure during admission on the low pressure is more uniform. Also this re- ceiver is sometimes made reheating by inserting coils of pipe con- taining high pressure steam. In so doing the condensation that takes place in the high pressure cylinder may be evaporated, or in other words we have dry steam again for our low pressure cylinder, and in some cases even superheated steam. The volume of the L. P. cylinder at cut off equals the volume of the high pressure cylinder, since at each stroke the low pres- sure cylinder takes the same weight of steam as exhausted from the high pressure cylinder. If a receiver is not used and the H. P. exhausts directly into the L. P. cylinder, the two cylinders must commence and end their strokes together, otherwise we would have a detrimental high back pressure at one part of our stroke, and one piston act- ing against the other. In this case the engines must act either on the same crank pin or on crank pins i8o degrees apart. In the case of using a receiver the cranks can be set at any angle, as the stroke can be made at any time, besides they are generally set at 90 degrees to get rid of dead center, and thus give cer- tainty of action, and a more handy arrangement. Compounding increases the economy if the steam pressure is sufficiently high for this reason : — One of the principal losses in the steam engine is that occurring from the heat absorbed by the wall of the steam cylinder. It is a good conductor of heat. The colder a body is the more quickly it will cool off the warmer body. If we are using high pressure steam this steam is at a very high temperature, now when we expand it, its temperature falls and if we expand it down to atmospheric pressure there is a large drop from its initial or entering temperature to its final or exhaust temperature. Therefore, the steam on leaving the steam cylinder has cooled way below the temperature of the 34 entering steam, and when the steam enters on the next stroke a heavy condensation occurs on the cylinder walls, and an accom- panying requirement for more steam. If we exhaust this steam bpfore it has been expanded so far, or in other words before its temperature has dropped so much, there is less difference be- tween the temperature of the entering steam and that of the cyHnder walls ^nd consequently less condensation on the walls. And this also applies to the L. P. cylinder. Compound engines, under proper conditions, have shown a gain of io% and more over simple engines, and this is attributed to the lesser interchange of heat between the steam and cylinder walls, by having less fluctuation from admission to exhaust in both stages of exhaust. Besides we have the mechanical advantages if it is a large en- gine of smaller cylinders to assemble, more even distribution of work during the stroke, as you see in using one cylinder we would have a severe pressure at the start. Also we obtain a smaller initial stress on our crank pin. Compound engines are often made with two L. P. cylinders, both fed from the same receiver, and exhausting to the condenser. To make an even stroke, and to do away with the dead center, cranks are generally set at 120 de- grees. If a receiver is not used, of course the piping which con- nects the cylinders and the L. P. steam chests must act as re- ceiver§. This is quite often allowed in marine work, but of course we have the fluctuation in pressure just the same, but economy in room. Compound engines are again subdivided into Tandem and Cross Compound. The Tandem arrangement consists in having the cylinders in line, or in other words both pistons on the same piston rod, an arrangement very well adapted for use without re- ceiver, as it requires little or no piping. In the Cross Compound Arrangement the cylinders are side by side with separate piston rods, cross heads, connecting rods, etc., and the cranks generally set at right angles. Before leaving the question of compound engines it would be well to quickly go over the reason for having engines compound- ed. Steam enters a cylinder at a temperature corresponding di- rectly to its pressure. On striking the cylinder walls some of it condenses, requiring more steam to be drawn into the cylinder. This moisture, or condensed steam remains on the cylinder walls until exhaust, during which time the pressure lowers in the 35 cylinder. Decreasing the pressure decreases the boiling point and under this exhaust or low back pressure, this condensation which is very hot, re-evaporates, and lessens our efficiency still more by forming steam and increasing the back pressure. Suppose we are using 35 tb. gage steam, its temperature equals 280 degrees. Now suppose we exhaust to the atmosphere, leav- ing the exhaust steam at practically atmospheric pressure or 212 degrees F. We have had a drop of 280 degrees minus 212 de- grees or 68 degrees, and now the new steam on entering strikes cylinder walls at 212 degrees or 68 degrees lower than its own temperature, and therefore condenses on cylinder walls. Should we use a condensing engine you see the exhaust pressure is still lower and, therefore, the cylinder walls cooled to a greater degree. Now let us feed the same cylinder with steam at 100 lb. gage pressure, such steam has an initial temperature of 337 de- grees F., and if we exhaust to the atmosphere or cool the cylinder walls to 212 degrees, the entering steam must meet walls at a temperature 337 minus 212 or 125 degrees lower than its own, and of course this would give a greater loss than in the first case. To prevent this loss due to cylinder wall condensation, three remedies are resorted to. Jacketing, Compressing or Cushioning, Compounding. In jacketing there is an outer compartment to the cylinder, in which steam at boiler pressure is maintained, thus keeping the cylinder walls at such a temperature as to help prevent con- densation. It has been found in some tests that jacketing the cylinder heads increased the efficiency much more than jacketing the cylinder walls, and you can see the reason for this in a short or early cut off engine, on account of the cylinder head area being a large part of the cooling surface. Of course jacketing is the more necessary the greater the degree of expansion or the slower the piston speed. When we use jackets there is the extra expense of supplying them with steam, which is constantly condensing, and requires renewal. Cushioning or Compressing : — To heat the cylinder heads up to the temperature of the incoming steam, the exhaust is shut off before the end of the stroke and the enclosed steam compressed up to the pressure of the incoming steam, thus raising its tem- perature, and that of the cylinder head, piston and ports. This 36 acts as back pressure and requires work to be expended on the opposite side of the piston, and a corresponding cutting down of the area of the steam card as we shall see later. Compounding as we have seen reduces the change of tempera- ture in the two cylinders, and increases the economy with high pressure steam. INDICATING. Letters refer to cut showing indicator card. H. — Admission. M.— Cut Off. N. — Exhaust or Release. S. — Compression. A. B. — Line of Boiler Pressure. C. D. — ^Atmospheric Line or Line Atmospheric Pressure. E. F. — Absolute Vacuum or Line of Zero Pressure. A. E. — Clearance Line. L. — Length of Stroke. H. K. — Admission Line. K. M. — Steam Line. M. N. — Expansion Line. N. O. — Exhaust Line. O. S. — Back Pressure Line. . S. H. — Compression Line. A. B., A. E., and E. F. are drawn after the card is removed. INDICATOR CARD. The indicator card enables us to tell at what part of the stroke admission, cut off, compression and release come, or in other words, if the valve is set correctly, also if the steam pipes and 37 ports are large enough to prevent a reduction of pressure in the steam cylinder or wire drawing as it is called. Leaky valves, will be shown by a poor expansion line. Excessive moisture in the steam will be shown by an expansion line which goes down by steps. Too small steam pipe is shown by taking a card from the steam chest. This card should be a straight horizontal line, cor- responding nearly to the height due to boiler pressure, if a fall occurs it shows that the cylinder takes steam faster than steam pipe can supply it. Too small ports for admission or too slight opening of the valve will be shown by a low steam line. Small exhaust ports or small or crooked exhaust pipes will show high back pressure. The approximate steam used per H. P. per hour can also be figured from the indicator card, although this method gives results which cannot be relied upon to any degree of ac- curacy. The main use of the indicator is to determine the in- dicated H. P., i. e., the H. P. developed by the engine, even in- cluding that used in running the engine itself. For this deter- mination the indicator card gives us the average pressure acting throughout the stroke upon the piston, or the mean effective pressure, M. E. P. There are two ways of obtaining this M. E. P. from the card. ist. Divide the card into ten or more vertical strips, having the same horizontal lengths, draw vertical lines in the centers of these. Measure each center line and add these measurements. Divide by the number of lines added, and this gives the average height. This multiplied by the scale of the spring gives the M. E. P. 2nd, The more accurate way to iind the M. E. P. is by the plani- meter, a small instrument which measures accurately the area of the card. Divide this area by the length L, this equals average height. Multiply average height by scale of Spring this equals M. E. P. To find the I. H. P. ist, Multiply the area of the piston in sq. inches by the length of the stroke in feet and divide by 33,000. This gives the engine constant. 2nd, Multiply engine constant by the M. E. P. and this product multiply by the number of strokes per minute, the final product is the I. H. P. To find the actual useful work done outside of the engine a brake H. P. test is conducted. The brakes are of various kinds, two of which you will have experience with. In the rope brake 38 test, weigh the frame in place with blocks loose, start the engine and tighten brake just enough to keep the engine running at the speed governor is set for, tightening more would slow the engine below its running speed. Weigh the frame now, and take the speed of the flywheel upon which this brake is attached. Multi- ply the r.p.m. of the flywheel by its circumference in feet and multiply this product by the difference in weights taken. The latter divided by 33,000 gives the brake H. P. The scale meas- ures the difference in tension upon the two ends of the rope, which is the continuous force exerted or overcome at the rim. Multiplying this force exerted by the linear speed of the pulley rim gives foot pounds developed. Dividing this by 33,000 gives B. H. P. With the band brake measure accurately in feet the distance from the center of shaft to knife edge, which distance call R. Find weight of brake exerted on scale when engine is still and band is loose. Start engine and tighten as before. Measure weight on scale and r. p. m. of pulley. Multiply the difference in weights by 6.28 times R, and multiply this product by r. p. m. Divide the latter product by 33,000 and the quotient equals B. H. P. If the engine is indicated at the same time the difference be- tween the indicated H. P. and the Brake H. P. gives the fric- tional H. P. For the efficiency of the engine a water consumption test is run, that is at the same time that the brake and indicated H. P. is determined the steam from the exhaust is condensed and weighed. The weight caught per hour divided by the I. H. P. gives the water consumption in lbs. per I. H. P. or if divided by the Brake H. P. it gives the water consumption per B. H. P. per hour. The following is the data and solution for the indicated and water consumption test on a compound engine in which a steam jacket on the low pressure cylinder was supplied with steam. H. P. equals High Pressure. L. P. equals Low Pressure. H. E. equals Head End. C. E. equals Crank End. An engine constant is worked up for both ends of each cylin- der, as for extremely accurate work this is necessary in order to deduct area of piston rod from crank end side of piston. Scale of springs 20 and 10 lbs. H. P. Cyl.— Dia. Piston 16.01" Rod 2.19" Stroke 30". Eng. Constant — H. E. — .01525, C. E. — .01497. 39 L. P. Cyl. — Dia. Piston 24.06, Rod. 2.16, Stroke 30''. Eng. Constant, H. E. — .0345, C. E. — .03417. Revs, for 60 min. 4896 — Boiler Pressure 47.5. Steam used in cylinder — 1,513.5 lbs. In L. P. Jacket 104.1 lbs. R. P. M. equals 81.6 — Barometer 29.8 Area Card. Length Card. Av. Height. M. E. P. H. P. H. E. 2.83 3.60" .787 15.74 H. P. C. E. 2.54 3.62 ,702 14.04 L. P. H. E. 2.86 3.61 .792 7.92 L. P. C. E. 2.75 3.60 .764 7.64 Horse Power H. P. Cylinder. C. E. H. E. .01497x81.6x14.04 plus .01525x81.6x15.74 equals 36.73 H. P. Horse Power L. P. Cyl. C. E. H. E. .03417X81.6X 7.64 plus .0345 x8i.6x 7.92 equals 43.60 H. P. Total 80.33 H. P. Lbs. steam per H. P. hour. 1513.S plus 104.40 equals 20.74 lbs. at 47.5" Boiler Pressure. 80.33 or 47.5 plus 29.8 times .491 equals 63.13 lbs. Absolute. VALVE SETTING. In nearly all valve setting, unless valve is set by the indicator card, the engine must be set on the dead center. This is most accurately done as follows. Put the Crosshead near the center of its stroke and mark a point on the crosshead and the point that it lines with on the guides. At the same time mark a point on the fly wheel or crank disk and a point on a stationary object opposite this point. Turn the engine over until the cross- head comes back to its original position, and mark a point on the fly wheel or crank disk opposite the stationary point. Bisect the two distances between the marks on the fly wheel or crank disk and when the engine is turned so that either of these mid- points comes opposite the stationary mark, the engine will be on the dead center. 40 Always turn the engine in the direction it is to run to take up all backlash. Definitions: — Angular advance equals angle over 90 degrees that the eccentric is ahead of the crank. Lead equals amount the valve uncovers the port when the engine is on the centre. Port openings equals distance from edge of port to edge of valve. In case of maximum port open- ing this may be more than the width of port for exhaust, to ensure free exhaust, or to make sure that the valve will remain open long enough. Dead center, the position when the connecting rod and piston rod are in the same straight line. To set the plain slide valve for equal lead : Put engine on dead center and give the valve the proper lead and the eccentric the approximate angular advance, or give the eccentric proper (ap- prox.) angular advance and the valve the proper lead by adjust- ing the length of the valve spindle. Turn engine over to other dead center and if leads are unequal correct half the error by shifting the eccentric and half by changing length of valve spindle. Repeat this process until leads are equal. Where no link, rocker or radial form of valve gear is used an engine may be set in a simpler manner for the equal lead, for the valve set with equal leads will have equal maximum port openings. Method: — ist, set engine on dead center, loosen the eccentric on shaft and turn it around to reciprocate the valve, and make the valve spindle of such a length that the maximum port openings will be equal on both ends. Then give the valve the proper lead by moving the eccentric and the eccentric will then have the correct angular advance. This method is much easier than the former on a heavy engine as we do not have to turn the engine over. SETTING VALVE FOR EQUAL CUT OFF. Set engine on head end dead center and give the eccentric proper angular advance by previous method and valve proper lead as near as possible. Move engine forward until cut off occurs and mark position of crosshead on slides, turn the engine over until cut off comes on return stroke, and if crosshead is not at same distance from beginning of stroke as before, correct for this difference in length of valve spindle, i. e., if cut off is too early on head end, valve spindle is too long, and conversely. 41 Trams may be used for setting the valve without taking the steam chest cover off. In this case the tram fits into a punch mark on the valve rod and one on the steam chest or stuffing box. In this position the valve has proper lead. Two trams may be used and the same punch marks or two sets of punch marks and one tram. Scratches may be put on shaft and eccentric after once properly set. The plain eccentric motion allows the engine to run either way that the angular advance is laid off, that is by shifting the eccen- tric the engine may be reversed. To obtain an early cut off and still have the other events of the stroke come in a practical position, to do away with the severe pressure on top of the slide valve, or to obtain quickly full open- ing and rapid closing of valve, many valves and valve motions have been designed. The Corliss gear is one of the most widely used, and is a four valve type with a drop cut off. The admission valves take steam on inner edge. The linkage made up of the valve crank, valve rod and wrist plate is designed to give a slow motion when the valve is closed and a rapid motion when opening or closing. The governor sets a trip arrangement which allows the steam valve to drop at the desired part of the stroke, thus governing by the change of cut off instead of throttling, and giving a sharp, quick cut off. Therefore after the valve starts to close no ap- preciable amount of steam can pass to the cylinder, and we do away with the loss of steam from this slow closing in valve gears which are not quick closing. It is customary to give a small lap to the steam valves, conse- quently, as with a plain slide valve the eccentric has a small angu- lar advance. Therefore the eccentric will be on line of dead centers, and its valves will have their greatest displacements when the crank has moved through go degrees minus the angular advance, i. e., before half stroke, and if the cut off by the de- tachment gear has not occurred it will not occur until near end of stroke, its position being determined by angular advance and lap, as in the plain slide valve. There the range of cut off on the ordinary Corliss motion with one wrist plate is up to J4 stroke. To increase this range, two eccentrics and two wrist plates are often used, one for the exhaust and compression valves, set with small angular advance to give these events near end of stroke, and one to give admission and cut off set with clearance, 42 rather than lap, and having a negative angular advance, by which arrangement cut off can be carried beyond half stroke. This is quite often desirable in low pressure cylinders of com- pound engines and is known as the "Long Range Cut Off" type. An advantage in the 4 valve type of gear is that the live steam does not have to go through the exhaust passages which have been previously cooled by the low pressure and consequently low temperature steam. Gridiron or several port valves are used in the Brown and other engines, and they give a quick full opening and rapid clos- ing on account of small travel necessary. MEYER VALVE GEAR. Cylinder. Meyer or Double Valve: — Main Valve and cut off valves moved by different eccentrics. The lower or main valve is set with equal lead, and takes care also of the compression and re- lease, either of which may be equalized. The upper or cut off valve consists of two plates on the valve spindle. This valve spindle has left and right hand thread, and a swivel joint where it connects at valve rod head. This valve rod extends through stuffing box in further side or head end of steam chest, is squared on end and provided with hand wheel, therefore, valve may be adjusted by wheel while engine is running. It regulates Cut off, and readmission by cut off must not come before cut off by main valve, otherwise we will have a double admission. This is used considerably on air compressors. The cut off valve is set with a large angular advance, in some cases nearly opposite the crank. 43 PISTON VALVES. The piston valve is in the shape of two pistons, connected by a pipe or sleeve. Steam is generally supplied to the middle of the steam chest, and is exhausted from the ends. By this ar- rangement the live and exhaust steam are well separated and thus heat cannot easily pass from one cylinder to the other, and valve rod stuffiing box is exposed to exhaust steam only. However, in a condensing engine, this arrangement is not very advisable since the leakage of air past the stuffing box, is more objection- able than the leakage outward of steam. In taking steam on the inside, the inside laps control admission and cut off, while outside laps control the exhaust and compres- sion. On vertical engines the top end steam lap is the larger to hasten the cut off on the down stroke and to delay it on the up stroke. For same reason the top end exhaust lap is made the smaller, in some cases a clearance, this hastens the compression on the down stroke and delays it on up stroke. The piston valve is of course balanced as far as pressure on the seat is concerned. They are generally well made and sup- plied with packing rings, and are therefore no more liable to leak- age than the piston of the engine. Occasionally these are made without rings, depending on their fit for a seat, notably in pumps. These work well, but have to be renewed more often and valve chest rebored and bushed, or a new piston supplied . BALANCING. Where the difference in pressure between live and exhaust steam is large, the pressure on the slide valve is so great that this pressure is balanced to prevent the excessive friction. This takes some work off of the engine, does not strain the valve gear so much and wears the valve seat less. In some cases the underneath side of the steam chest cover is finished and the flat valve moves between its seat and the cover plate with enough clearance to avoid friction, but not enough to allow for leakage, just as a piston valve moves in its cylin- drical seat. Sometimes a steam tight ring is placed between the top of valve and valve plate or steam chest cover, this prevents steam from coming on top of the valve. The Atlas people use a hood to protect the top of the valve 44 and as this hood is held down by springs it allows the relief of an excessive back pressure by permitting the valve to lift slightly. FEED PUMPS. Their sizes are given by placing diameter of steam cylinder first, then diameter of water cylinder and last the length of stroke. Thus a 6"x4"x7" has 6" steam cylinder, 4" diameter water cylinder and a 7" stroke. The suction pipe should be of such a size that the velocity of flow shall be not over 200 ft. per minute, while the water in the discharge should not have over 400 ft. velocity, and it is better to have both less than the above. 100 ft. piston travel per minute is sometimes allowed on the water piston, but this is often excessive on short stroke pumps, and 60 to 80 ft. piston travel is allowed, thus giving less wear on the pump. The size of a boiler feed pump is often figured on the basis that the boiler is using 30 lbs. of water per horse power hour and making the pump capable of supplying 3 times this amount at ordinary speed. For example, find the size of feed pump to sup- ply a 150 H. P. Boiler. Let us take 80 ft. travel of the piston per minute. 150 H. P. requires 30x150 or 4,500 lbs. of water per hour. Allowing the pump to be able to pump 3 times this amount we have 3x4,500 or 13,500 lbs. per hour or 13,500 divided by 60 or 225 lbs. per minute, or 225 divided by 62.4 or 3.61 cu. ft. per minute. The area of the piston or plunger in sq. ft. times speed in ft. per minute equals the number of cubic feet pumped per minute, or if we know the amount to be pumped and the speed, divide the amount to be pumped by the speed and this wlil give the area of the piston in sq. ft., or in this case 3.61 divided by 80 equals .045 sq. ft. There are 144 sq. in. in a sq. ft. so .045 sq. ft. equals .045x144 or 6.48 sq. in. If the area of a circle is 6.48 sq. in. its diameter is found as follows : Divide the area by .7854 and extract the sq. root. 6.48 divided by .7854 equals 8.25, and the sq. root of 8.25 is about 2.9, or we would have 3 inch diameter for our water cylinder, and as for our length of stroke we could pick out a stock size of pump with a 3" water cylinder, or we could call for the length of stroke we wanted as a 3"x7" in the latter case the 7" stroke would give us the speed of the pump in strokes per minute as 80x12 divided by 7 or 137. 45 The area of the steam piston for boiler feed pumps is made from 2 to 4 times the area of the water piston. Roughly up to and including 23/^" water cylinders make the steam piston 4 times the area. From 2J/4" to 4" make steam piston 3 times the area of water pistons, and above this twice the area. On this 3" water cylinder use a cylinder 3 times as large in cross sec- tional area for the steam end. An easy way to do this is to multiply the diameter of the water cylinder by itself, this gives us for this case 3x3 or 9. Multiply this by 3 again giving 27, now find the number that multiplied by itself gives 27 or find the square root of 27 equals 5.19, or the diameter of the steam cylin- der would probably be 5 inches. Air chambers are placed on both suction and discharge ends of large pumps and are often made 2^ of the capacity of pump per minute. Pumping against a certain head or raising water a certain dis- tance can be changed over to pumping against an equivalent pressure in pounds per square inch. In the preceding part of these notes we found that a column of water 2.3 ft. high gives one lb. pressure to the square inch, or that each foot head is equivalent to .43 lbs. pressure. Pumping water to a height of 300 ft. is the same as pumping water into a boiler against a pressure of 300X.43 or 129.00 lbs. pressure, or conversely pumping against 129 lbs. pressure is the same as raising the water 300 feet. This gives us the means of telling the theoretical horse power necessary to feed water to a boiler. Ex. Find H. P. used in feeding 500 gallons of water per minute to a boiler against 100 lbs. pressure. 500 gallons equals 500X 8 1/3 or 4167 lbs. Pumping against 100 lbs. pressure is the same as raising the water 100x2.3 or 230 ft. high. Raising 4,167 lbs. 230 ft. in one minute gives 4,167x230 or 958,410 ft. tbs. or 958,410 divided by 33,000 equals 29 H. P. If this pump lifted its water 20 ft. we would have added 20 times .43 or 8.60 tbs. to the 100 tbs. in figuring the H. P. Feed pumps are of three kinds : Power, Direct Acting Steam and Flywheel steam pumps. The Power pumps are driven by belt from the main shaft or by electric motors. If driven from the main shaft the pump can be stopped by means of loose pulley and there are two ways to regulate the amount of water fed to the boiler while the pump 46 does not change its speed, ist. Partly close valve in suction pipe, this prevents the pump from filling completely each stroke. This however is the cause of pounding on the return stroke, when the plunger or piston comes up against the water. 2nd. A by-pass is put in from discharge pipe to suction pipe, or run- around as it is called, by opening this, part of the water can be carried back to suction and through the pump again. Check valves should be used on the discharge in this case. Relief or safety valves should be used on power pumps. On the electrically driven power pump the speed is regulated in the rheostat. The direct acting steam pump has one piston rod for both steam and water pistons, the motion is direct from steam piston to water piston. Of course these may be regulated by the amount of opening of the steam valve. To make these pumps pass the dead center auxiliary steam valves are used. The flywheel pumps have a crank and shaft and rely on the momentum of the flywheel to take them over the dead center, this requiring a certain amount of speed for perfect running. Regulation below this speed must be made by one of the meth- ods used on the power pump. The steam pump needs the fullest pressure at the end of the stroke for it is then doing the most work. This means that we must carry steam full stroke in the direct acting pump, making a very inefficient method of running. The stored energy in the flywheel pumps enables some of the expansive force of the steam to be used. Pumps for boiler feed often take from 70 to 200 lbs. of steam per H. P. hour. As the power for a power pump is generated in the engine, which is using from 10 to 50 lbs. of steam per H. P. hour it is the most efficient. With the exception of the electrically driven power pump all the machinery must run to operate the pump, however. Pumps using hot water must be set below the supply, for when a suction stroke is made it relieves the pressure on top of the hot water allowing some of it to vaporize, which vapor spoils the vacuum, or the water may be so hot as to give off vapor continually. 47 Index Boilers 10-16, 19, 20, 23-27 Boiler test 24, 25 Boiler tubes 26 Calorimeter 22, 23 Engines 29-36 Fuels 4 Heat 3, 4 Indicating 37-40 Injectors 28, 29 Piping 16, 17 Pressure 5, 6 Pumps ., 44-47 Safety valves 17, 18, 19 Steam 4, 7, 8, 9, 10, 21 Steam traps 26 Vacuum 5, 6 Valves and Valve Setting 40-44 48