1 Pi flu ■II iii i : ill ill 111 in ■■ ji|jjij!iijiiij 111!! Hill! POWER PLANT TESTING Published by the McGrow-Hill BookCompany N 3 4 u 1 bo ft ^oj£. 80° E kpsssL .a 2 I 3 1 3?~ 3Qf_ _2iil_ _L0° 100° 150° 200° 250° 300° 350 400 Difference between Reading of Thermometer and "Room" Temperature in Degrees Fahr. Fig. 46. — Exposure Corrections for Thermometers of the "Sleeve" Type. In practice for carefully conducted tests of engines or turbines opera- ting with superheated steam corrections as indicated should always be added to the thermometer readings to obtain the correct temperature MEASUREMENT OF TEMPERATURE 39 and superheat. In steam turbine tests, when a high degree of super- heat is used, this correction is often as much as from 5 to 10 degrees Fahrenheit. Recording Thermometers. Recently instruments for recording auto- matically low as well as high temperatures have been very satisfactorily developed. A typical example is shown in Fig. 47. It consists of a Fig. 47. — Typical Recording Thermometer with Flexible Tube. sensitive bulb (Fig. 48) suitable for being inserted into a pipe fitting and is attached by a capillary connecting tube to the recording instrument. The sensitive bulb and capillary tube are filled with either mercury or ether, which is sealed in the bulb and tube under pressure. The instru- ment is operated by the expansion of the vapor of these liquids. Vapor thermometers consist essentially of a metal bulb partly filled with a liquid which, when heated, gives off a vapor which exerts a pressure 40 POWER PLANT TESTING on a pressure gage through a small capillary tube. The following liquids are used, depending on the range of temperature : Liquid sulphur dioxide (S0 2 ) 15 to 200 degrees Fahrenheit. Ether (free of water) 95 to 250 degrees Fahrenheit. Water 212 to 450 degrees Fahrenheit. Heavy hydrocarbons 410 to 700 degrees Fahrenheit. Mercury 650 to 1350 degrees Fahrenheit. miimmimutmminmm Fig. Fig. 48. — "Sensitive" Bulb for a Recording Thermometer. The capillary tube may be made 100 feet long, and such instruments are suitable for " distant reading," but varying the temperature of the capillary tube by exposure will alter the observations. The whole length of the bulb must be exposed to the temperature to be measured, and complete immersion of the bulb is sometimes difficult in lines of piping of small size. In instru- ments using mercury vapor the bulb has a volume of about one cubic inch in outside dimension per 100 degrees Fahrenheit range of temperature. Those filled with ether are of about half the volume required for mercury. One of these instruments is shown in Fig. 49 with the cover removed so that the mechanism can be seen. It is exactly the same as that of a recording pres- sure gage (see page 13). 49. — Mechanism of Thermometer. Recording MEASUREMENT OF TEMPERATURE 41 In general appearance and in the operation of the recording mechanism and clockwork, these recording thermometers are like the recording- pressure gages now in general use. Some of these recording instruments, Fig. 50, have a short rigid connection between the bulb and the record- ing mechanism, making it necessary to locate the instrument always immediately adjacent to the bulb. In Fig. 47 there is a flexible connec- tion of capillary tubing attached to bulb permitting the setting up of the Fig. 50. — Recording Thermometer, Short Bulb Type. instrument on a wall near by. This capillary tube must, however, be handled very carefully to prevent causing a serious leak, making the instrument useless. Pyrometers. Temperatures over 600 degrees Fahrenheit are usually measured by instruments known as pyrometers. Various types are in use particularly for the measurement of temperatures in flues and chim- neys of boiler plants. Thermo-electric Pyrometers. When two wires of different metals are joined at both ends, so as to form a complete metallic circuit, as in Fig. 51, and if the two junctions H (hot) and C (cold) are at different 42 POWER [PLANT TESTING Fig. 51. — Diagram Illustrat ing Action of a Thermo couple. temperatures, an electro-motive force is generated which can be measured with a galvanometer or commercial milli-voltmeter. If the cold junc- tion is always maintained at a constant temperature the scale of the galvanometer can be graduated to read di- rectly the temperature of the hot junction. In practice it is usually impracticable to main- tain a constant temperature at the cold junc- tion so that usually a compensating device is arranged to eliminate the error. One of these devices (Fig. 52) consists of an air-tight glass bulb partly filled with mercury into the top of which a U-shaped platinum loop is fused. This platinum loop is long enough to extend into the mercury and its ends are connected to be in series with the thermo-couple at the cold junction. When the temperature ' of the leads or outside circuit falls, the voltage due to the couple increases because of the greater range of temperature at the " hot junction," but the mercury in the bulb contracts so that the current must pass through a greater length of the high-resist- ance platinum wire in the loop. The net effect is that the increased resistance neu- tralizes the greater voltage produced at the " hot junction." Another method of com- pensation is to attach a small mercury thermometer to the cold couple and put a wire resistance in series with the circuit, which can be cut out in varying amounts by adjusting a lever on a dial graduated to make the resistance correspond to the tem- perature. There are two general types of such in- struments (1) high resistance; (2) low re- sistance. The high-resistance type has a couple formed of two wires of small diameter. One wire is of platinum and the other is an alloy of 90 per cent platinum and 10 per cent rhodium. 1 To protect the fine and delicate wires against breakage and also because platinum deteriorates in the silicon, phosphorus and other " gases of reaction," the couples of the high-resistance type are always protected by porcelain or iron tubes. If the temperature never much exceeds 1500 degrees Fahrenheit iron tubes are satisfactory. For higher temperatures porce- 1 Formerly iridium was used for alloying but it volatilizes rapidly at over 1500 deg. Fahr,, causing a gradual lowering of the voltage produced. Fig. 52. — Mercury ting Device for Thermo-couples. MEASUREMENT OF TEMPERATURE 43 lain tubes are used, but they must be handled carefully as they are easily cracked. Base-metal or low-resistance types of couples are usually made of alloys of nickel, iron, and copper. Couples used very largely in America for temperatures up to about 1500 degrees Fahrenheit are made of nickel-steel and copper; another is made of one wire of nickel and the other of an alloy of nickel and chromium. Such couples made of cheap metals can be made of larger rods and at less cost than the high-resistance type. Even though they are not quite as accurate they are generally preferred for industrial work. There is also the advantage that a broken couple can be readily replaced by rods of iron and copper fused together at one end. A calibration curve for the couple is easily made to be accurate enough for practical purposes. The principal consideration in selecting rods for such couples is to get them of uniform chemical composition and they should be annealed preferably in an electric fur- nace to a temperature higher than that to which they are to be exposed. If rods in a couple are not of uniform composition, parasitic currents are produced which oppose that produced by the couple at the junction. Since these wires can be made comparatively large, usually about ^-inch diameter, the current generated will be large compared with the high- resistance types and its change in resistance with change in temperature will be small, so that a cheaper low-resistance galvanometer can be used. Low-resistance couples are usually protected by an iron tube, mainly because the steel wires deteriorate in the presence of sulphur gases and the asbestos insulation needed for separating the rods along their full lengths is likely to last longer with this protection. Low-resistance pyrometers have often the leads of the same metals as the couples so that the so-called " cold-junction " is at the terminals of the galvanometer, and the leads are then usually made long enough to permit the instrument being placed where the temperature can be main- tained at about normal " room " temperatures. Variation in the " cold junction " temperature from the calibration temperature produces more error in low-resistance than in high-resistance types. When iron is a constituent of a couple, it should not be used for tem- peratures above 1300 to 1400 degrees Fahrenheit as this temperature is a " transition point " for this metal and its physical and also its thermo- electric properties are changed. Thermo-couples made of platinum and a platinum-nickel alloy pro- duce twice the voltage of a platinum-rhodium combination, but it should not be subjected to temperatures above 2000 degrees Fahrenheit. If the couple is made of one wire of pure platinum and another of an alloy of platinum and about ten per cent of rhodium, temperatures nearly as high as the melting point of platinum, or nearly 3500 degrees Fahren- heit, can be measured, although 3000 degrees Fahrenheit is considered 44 POWER PLANT TESTING the safe limit. This pyrometer with a platinum " couple " is known generally as a Le Chatelier type (Fig. 53). Electrical Resistance Thermometers are based on the principle that the electrical resistance of some metals increases considerably as the temperature is raised. Platinum is usually selected because for a given temperature it has a remarkably constant resistance and it does not deteriorate at high temperatures. A resistance thermometer of the simplest type is made of a coil of pure annealed platinum wire W wound upon a mica framework (Fig. 54) in " series " with a very small coil in a casing C intended to be exposed to the temperature to be measured. The variation of resistance is measured by a Wheatstone's bridge method. Fig. 54. — Resistance Thermometer Fig. 53. — Le Chatelier Pyrometer. The current from one electric battery passes through the wire in C, and the current from another battery passes through the coil W in the cover of the box. When the two circuits are connected so that the electro- motive forces of the two batteries are opposed, the resistance in the cover is adjusted by means of a connection on a stylus S so that there is no current passing through a telephone receiver R or a sensitive galvanom- eter placed at the junction of the two circuits. For making observa- tions this stylus is moved along the " scale " wire in the cover to a point where the humming noise due to the electric current ceases. The tem- perature can then be read on the graduated scale opposite the position of the stylus. By means of a switchboard any number of " heating " elements can be connected to the same indicator box, which may be located at any distance from the source of heat. MEASUREMENT OF TEMPERATURE 45 Commercial instruments of this type are usually arranged so that the " bridge " indicates the temperature in degrees. Up to 1000 degrees Fahrenheit the error should be less than 3 V degree and at 2400 degrees Fahrenheit not more than \ degree. A delicate galvanometer sensitive for small currents is required. A large current in the necessarily small wires would by its own heating change the resistance and impair sensitive- ness. For many classes of work, particularly if there is rough usage, the platinum coil C must be protected by a porcelain or iron tube. This protection introduces a time lag, so that very delicate instruments are not protected by a casing. The junctions of the platinum wire of the thermometer with the wires going to the resistance measuring device must be placed in the cooler part of the circuit, where the temperature should be the same as when the instrument was calibrated, or com- pensators may be used as explained on page 42. Electric resistance thermometers are readily calibrated at the temperatures of melting ice, steam at varying pressures (from 212 to 350 degrees Fahrenheit), and boiling sulphur (832.5 degrees Fahrenheit). In- termediate temperatures are computed. 1 Metals like copper, tin, and zinc when pure remain at a quite constant temperature for about a half hour when cooling slowly and passing from the liquid to the solid state. Metallic or Mechanical Pyrometers (Fig. 55) consist essentially of two rods made of metals having different rates of expansion connected by gears and levers to rotate a pointer on a gradu- ated dial. Generally the rods are made of iron and brass, or of graphite and iron. Although the use of such instruments is very common they are generally very unreliable, and should never be used for temperatures above 1000 degrees Fahrenheit. There is always a tendency for the zero of the instrument to get higher with use at even moderate temperatures. Beckert and Wein- hold found that in a number of cases the zero changed from 200 to 400 degrees Fahrenheit in two months. In order to obtain readings corre- sponding to the graduations the entire length of the tube enclosing the rods should be placed in the chamber of which the temperature is being measured. Calibrations of " Indicating " Pyrometers such as the thermo-electric, resistance, and mechanical types are best made by comparison with a 1 Bulletin No. 7, U. S. Bureau of Standards. Fig. 55. — "Mechanical' Pyrometer. 46 POWER PLANT TESTING special standard electric resistance thermometer of which the error is known and which is used only for standardizing work. The couple to be calibrated and the standard should be fastened together closely with only a sheet of asbestos between them. The two couples thus bound together should be put into an electric furnace in which the temperature can be controlled and raised very slowly. Then at different points in the scale, at intervals of about fifteen minutes, readings for comparison can be taken. If a standard resistance thermometer is not available a cali- bration can be made by comparison in a furnace of constant temperature with a good mercury thermometer. 1 Such thermometers in which the capillary tube contains rarefied nitrogen above the mercury can be obtained to measure temperatures with a fair degree of accuracy, when new, up to 1000 degrees Fahrenheit. The method of calibration suggested by the Power Test Committee of the A.S.M.E. is as follows: "Compare pyrometers for calibration at low ranges under proper con- ditions with a mercurial thermometer of known accuracy (both being placed for example in a current of hot air or flue gases of which the temperature is under control). Determine the errors at higher tempera- tures by plotting the results obtained as above on a chart, finding the curve of error, and continuing the curve to the higher ranges desired." For extremely high temperatures such as that of a boiler furnace or the bed of coals in a gas producer, the radiation optical and pneumatic pyrometers may be used. (See pages 46 to 51.) Pneumatic Pyrometers depend for their action on the variation of the flow of gases through orifices due to heating. Uehling's pneumatic pyrometer is shown diagrammatically in Fig. 56. As shown flue gas is con- tinuously drawn through two orifices A and B by a constant suction pro- duced by an aspirator D. So long as the air has the same temperature in passing through A as it has in passing through B, there is no change in the partial vacuum in the chamber be- tween the two apertures; if, however, the air has a higher temperature when passing through A than when passing through B, the suction or vacuum in the chamber between the two orifices 1 3 4 rv - — ^r ^^ =—1000 §- 800 =— 600 =- 400 =— 200 1 JE Fig. 56. — Pneumatic Pyrometer. Usually temperatures vary considerably inside a furnace so that the couple and thermometer should be bound together in order to be sure they are exposed to the same temperature. MEASUREMENT OF TEMPERATURE 47 will increase in proportion to the difference in temperature between A and B, because the volume of air varies directly with the temperature. In the application of this principle orifice A is located in a nickel tube which is exposed to the heat to be measured, while orifice B is kept at a uniformly lower temperature. Filters are provided for keeping the orifices clean. The instrument can be made to record and indicate the temperature at a distance. In order to maintain a constant vacuum or suction at B the steam pressure at the nozzle D must be maintained constant by means of a good reducing valve or other means. Recording Pyrometers are ffiost frequently of the type of recording thermometers illustrated and described on pages 39 to 41. Such instru- Fig. 57. — Combined Indicating and Recording Pyrometer. ments can be constructed, when the sensitive bulb is filled with a gas instead of a liquid, to register accurately temperatures as high as 1200 degrees Fahrenheit. Another type operated by the expansion of the vapor of mercury is shown in Fig. 57. This is a combined indicating and recording instru- ment. The sealed tube A is to be inserted in the chimney or flue in which the temperature is to be observed. Radiation Pyrometers. For temperatures above 2500 degrees Fahren- heit radiation pyrometers similar to the one illustrated in Figs. 58, 59 and 60 are most suitable. They can also be used in many places where it is almost impossible to locate a pyrometer of any of the other types. 48 , POWER PLANT TESTING The principle of operation is that the energy radiated by a so-called " black " body is proportional to the fourth power of its absolute tem- perature. The instrument illustrated consists of a cylindrical case set upon a tripod. This case contains a concave mirror and a lens (or lenses) which when properly adjusted and focused on a hot body concen- Fig. 58. — An Optical (Radiation) Pyrometer in Use. trate the heat rays upon a small thermo-electric couple 1 inside the case. Copper wires connect this couple with a very sensitive portable galva- nometer (Fig. 59) located where it can be read conveniently. The most 1 Some of these instruments have a metal coil made up of a pair of strips of metal of widely different coefficients of expansion which replaces the thermo-couple. The principle is the same as in the metallic pyrometers (page 45). MEASUREMENT OF TEMPERATURE 49 modern instruments of this kind are provided with scales indicating directly degrees of temperature. Fig. 60 shows a section of the telescope used in connection with this pyrometer. The concave mirror M receives the heat rays and focuses them at F, where a small thermo-couple is located. To assist in pointing the telescope an eye-piece E is provided through which a reflected image of the hot body can be seen. The rack R and the pinion P, moved by a thumbscrew outside the case, serve for adjusting the focus of the mirror. In the center of the field of view, as seen in the eye-piece, the thermo-couple is seen as a black spot, and this must be overlapped on all sides by the image of the hot body to obtain the correct temperature. It is interesting to observe that the distance of the telescope from the source of heat does not affect the reading of the 59. — Sensitive Galvanometer of Fery Radiation Pyrometer. Telescope of Fery Radiation Pyrometer. instrument. When the telescope gets nearer the hot body the mirror M receives of course more heat, but at the same time this greater amount of heat is distributed over a larger image and the intensity of the heat remains the same. Radiation pyrometers are calibrated in terms of the radiation from a so-called " black body," which is approximately realized by a uniformly heated enclosure. It is only for " black bodies," such as carbon, coal, etc., that the temperature is exactly proportional to the fourth root of the heat energy. Readings obtained when measuring the temperature of a body not inside a closed chamber with hot walls will in some cases be very much lower than the true temperature. For a piece of heated coal the error is very small due to lack of enclosure, while in the case of molten copper or tin with a clean surface the temperature reading may be 100 degrees Fahrenheit too low. Conditions as regards enclosure are, 50 POWER PLANT TESTING however, satisfactory in most practical cases where the instrument is frequently used, such as taking the temperature of boiler furnaces, gas producers and retorts, annealing and hardening furnaces, etc. Error due to the furnace door being open for an instant when the observation is to be made is practically negligible, especially as these instruments are actually calibrated under this condition. If excess of air in a fur- nace is likely to reduce the temperature while sighting, a large tube of cast iron or fire-clay closed at the end toward the fire can be built into the furnace wall. By sighting through the open end upon the closed end which should be at the furnace temperature very satisfactory results are obtained. Observations made with such pyrometers of incandescent bodies or gases do not give the true temperature. It is generally assumed, how- ever, that they can be used to measure fairly accurately the temperature of heated chambers when focused upon the walls, 1 because of the reflec- tion going on in all directions. In most cases the flame temperature can be taken the same as that of the surrounding walls. A relatively large area is usually required to sight radiation pyrometers. It is stated that the distance from the telescope to the hot body can be as much as 30 times the diameter of the hot body and the telescope can be taken as much nearer as desired without changing the reading of instrument. Before taking observations the pointer of the galvanom- eter must be set at zero, the instrument receiving no heat rays during this adjustment. The readings of temperature made with such instru- ments are obviously the difference between the temperatures of the hot body and of the room. Optical Pyrometers. Another type of pyrometer, based in principle upon the measurement of the brightness of the hot body by comparison with a standard lamp, is shown in Fig. 61. In order to use this instru- ment, known as Wanner's, the incandescent (osmium filament) lamp must first be standardized by comparison with an amylacetate oil lamp of constant candle power. Then after standardizing it is only necessary to focus the instrument upon the hot body to be measured and the tem- perature is read directly on the graduated scale at the eye-piece. Temperature readings from optical pyrometers are actual and are not differences depending on the temperature of the room. Both the Fery and Wanner pyrometers have a satisfactory range from 800 to 4000 degrees Fahrenheit. At the lower temperatures the average error of such instruments is about 3 degrees Fahrenheit and the maxi- mum error at temperatures above 3000 has been shown to be not more than 20 degrees. 1 " Heat Energy and Fuels," by Hanns von Juptner, page 76. MEASUREMENT OF TEMPERATURE 51 Furnace temperatures can be determined approximately from the values correspond- ing to the color of the fire. All temperatures are in degrees Fahrenheit. Red — just visible 900 Orange 2000 Dull red 1250 White 2350 Cherry red 1600 Dazzling white 2700 Radiation and optical pyrometers are invaluable for determining the temperatures of the various parts of a furnace, of the walls of the setting of a steam boiler, of various portions of a bed of coals, etc. It is some- times stated that an optical pyrometer is a means for measuring tem- peratures of objects " miles away." Diffusing Glass -f%jj j — "f*j " Flame Gage Fig. 61. — Wanner Optical Pyrometer in Position for Standardizing. Calorimetric Pyrometers. If the specific heat and weight of a body are known, its temperature can be obtained by observing the rise in temperature of a known quantity of water into which the body is thrown. More in detail the method consists in the determination of temperature by putting a ball of metal or other refractory material into the medium of which the temperature is to be measured. When the ball has become heated uniformly throughout its mass to the temperature of the medium it is transferred quickly to a cup heavily jacketed with non-conducting material in which there is a known weight of water at a known tem- perature. Copper, wrought iron and fire-clay are suitable materials. Specific heats of these materials at about 500 degrees Fahrenheit are respectively .097, .110 and .180. Since metals are readily attacked by furnace gases they should be protected when used in this way in a cru- cible of refractory material. This method is often very serviceable in places or at times when accurate pyrometers are not available. On account of the " personal " error liable to enter, such determinations should be repeated several times to check the results. Calculations required are as follows. 1 1 A more complete description of calorimetric pyrometers and the precautions to be observed for accuracy will be found in Transactions of the American Society of Mechanical Engineers, vol. VI, page 712. 52 POWER PLANT TESTING Let Wi = weight of the ball, pounds. w 2 = weight of the cup (only the " inner " vessel), 1 pounds. w 3 = weight of the water in the cup, pounds. ti = initial temperature of water, degrees Fahrenheit. t 2 = final temperature of the water, degrees Fahrenheit. to = temperature of the heated ball, degrees Fahrenheit. Si = specific heat of the ball. s 2 = specific heat of the cup. Then W1S1 (t t 2 ) to (W 2 S 2 + W 3 ) (tj - ti), (w 2 S 2 + W 3 ) (tg - ti) W1S1 + t 2 (2) Seger Pyrometer Cones. For many purposes when a pyrometer cannot be well placed fusible Seger cones are used. Such cones are made of several different oxides mixed in a manner to give a definitely known melting point for each one. The melting points range from 590 degrees to 1850 degrees Centigrade by steps of from 20 to 30 degrees, each having a standard number. These cones are carefully graded, so that if one has had some experience with them, temperatures can be estimated to about the nearest ten degrees in Centigrade. Four of these cones are shown in Fig. 62. Fig. 62. — Seger Cones after Use. When a series of cones is placed in a furnace the one having the lowest melting point begins to turn over first. The temperature corresponding to the cone number is reached when the tip of the cone has bent over and just touches the surface on which it is standing. Hence the highest temperature reached when the cones shown in the illustration were used was about half way between that corresponding to each of the two middle cones. According to the numbers on the cones the temperature, 1 It would be more accurate, of course, to use in the calculation the water equiva- lent of the whole vessel, as is done in coal calorimetry. See page 210. Units given are in pounds and degrees Fahrenheit, but other units, provided they are correspond- ing, can be used in the equation given. MEASUREMENT OF TEMPERATURE 53 as given by the following table, was between 830 and 860 degrees Centi- grade. The greatest disadvantage with this system is that there is no way of observing a decrease in the temperature, or, in other words, only the maximum temperature is indicated.^ The following table gives the temperatures, in degrees Centigrade, at which the Seger cones will begin to melt: Seger Temp. Seger Temp. Seger Temp. Cone No. Deg. C. Cone No. Deg. C. Cone No. Deg. C. 022 590 04 1070 15 1430 021 620 03 1090 16 1450 020 650 02 1110 17 1470 019 680 01 1130 18 1490 018 710 1 1150 19 1510 017 740 2 1170 20 1530 016 770 3 1190 015 800 4 1210 26' i650'' 014 830 5 1230 27 1670 013 860 6 1250 28 1690 012 890 7 1270 29 1710 011 920 8 1290 30 1730 010 950 9 1310 31 1750 09 970 10 1330 32 1770 08 990 11 1350 33 1790 07 1010 12 1370 34 1810 06 1030 13 1390 35 1830 05 1050 14 1410 36 1850 Two types of mercury thermometers protected by heavy metal cases are illustrated by Figs. 63 and 64. It will be observed that a very satis- factory thermometer well is a part of the casing. The one shown in Fig. 64 has graduations for reading both temperatures and pressures. A thermometer of this type is particularly useful in pipes carrying hot boiler feed-water. When the temperature is above 212 degrees Fahren- heit the thermometer will indicate that the water is being heated at a pressure higher than atmospheric. For water heated in closed vessels or pipes there is for every temperature a corresponding pressure as given in tables of the properties of saturated steam. 1 Relative Accuracy of Thermometers and Pyrometers. For low- temperature work mercury thermometers are generally preferred as they can be made to almost any degree of accuracy required. For tempera- tures above 500 degrees Fahrenheit electric resistance thermometers and pyrometers come into use. When provided with a delicate galva- nometer electric resistance thermometers can be used with a very high degree of accuracy, and in fact temperature differences can be determined with them very much more accurately than with the best mercury ther- 1 Short and very much abbreviated tables of the properties of saturated steam are given in the Appendix. 54 POWER PLANT TESTING mometers. Next in degree of accuracy are probably thermo-electric pyrometers; and it is interesting that a pyrometer of this kind can be readily made by twisting together at their ends, rods of wrought iron and Fig. 63. - — Combined Thermometer Well and Protective Casing. Fig. 64. — Combined Thermometer and Pressure Gage for Boiler Feed-water Pipes. nickel. It is not essential that the ends should be welded but welding (preferably electric) gives the couple greater permanency, by preventing the accumulation of dust interfering with electrical conductivity. The loose ends can be connected up to the binding posts of a millivoltmeter by insulated copper wires and calibrated. The only disadvantage will be that it will not have a scale reading directly in degrees of temperature. The wrought-iron and nickel rods should be covered with a winding of asbestos tape to keep them separated. Mechanical pyrometers are not very accurate. Optical and radiation pyrometers have a special field beyond the limits of the other types. CHAPTER III DETERMINATION OF THE MOISTURE IN STEAM Unle33 the steam used in the power plant is superheated it is said to be either dry or wet, depending on whether or not it contains water in suspension. The general types of steam calorimeters, used to determine the amount of moisture in the steam, may be classified under three heads : 1. Throttling or superheating calorimeters. 2. Separating calorimeters. 3. Condensing calorimeters. Throttling or Superheating Calorimeters. The type of steam calorim- eter used most in engineering practice operates by passing a sample of the steam through a small ori- fice, in which it is superheated by throttling. A very satis- factory calorimeter of this kind can be made of pipe fittings as illustrated in Fig. 65. It con- sists of an orifice O, discharg- ing into a chamber C, into which a thermometer T is in- serted, and a mercury manom- eter is usually attached to the cock V 3 , for observing the pres- sure in the calorimeter. It is most important that all parts of calorimeters of this type, as well as the ■ connec- tions leading to the main steam pipe, should be very thoroughly lagged by a covering of good insulating material. One of the best materials for this use is hair felt, and it is particularly well suited for covering the more or less temporary pipe fittings, valves, and nipples through which steam is brought to the calorimeter. Very many throttling calorimeters have been declared useless by engineers and put into the scrap heap merely because the small pipes leading to the calorimeters were not properly lagged, so that there was too much radiation, producing, of course, con- 55 Fig. 65. — Simple Throttling Calorimeter. 56 POWER PLANT TESTING densation, so that the calorimeter did not get a true sample. It is obvi- ous that if the entering steam contains too much moisture the drying action due to the throttling in the orifice may not be sufficient to super- heat. It may be stated in general that unless there is about 5 to 10 degrees Fahrenheit of superheat in the calorimeter, or in other words unless the temperature on the low-pressure side of the orifice is at least about 5 to 10 degrees Fahrenheit higher than that corresponding to the pressure in the calorimeter, there may be some doubt as to the accuracy of results. 1 The working limits of throttling calorimeters vary with the initial pressure of the steam. For 35 pounds per square inch absolute pressure the calorimeter ceases to superheat when the percentage of moisture exceeds about 2 per cent; for 150 pounds absolute pressure, when the moisture exceeds about 5 per cent ; and for 250 pounds absolute pressure, when it is in excess of about 7 per cent. For any given pressure in the main the exact limit varies slightly, however, with the pressure in the calorimeter. In connection with a report on the standardizing of engine tests, the American Society of Mechanical Engineers 2 published the following instructions regarding the method to be used for obtaining a fair sample of steam from the main pipes. It is recommended in this report that the calorimeter shall be connected with as short intermediate piping as possible with a so-called calorimeter sampling nozzle made of |-inch pipe and long enough to extend into the steam pipe " nearly across to " the opposite wall. The end of this nipple is to be closed so that the steam must enter through not less than twenty |-inch holes " equally distributed from end to end and preferably drilled in irregular or spiral rows, with the first hole not less than f-inch from the inner wall of the pipe." "The sampling nozzle should not be placed near a point where water may pocket or where such water may affect the amount of moisture con- tained in the sample. Where non-return valves are used, or where there are horizontal connections leading from the boiler to a vertical outlet, water may collect at the lower end of the uptake pipe and be blown up- ward in a spray which will not be carried away by the steam owing to a 1 The same general statement may be made as regards determinations of super- heat in engine and turbine tests. Experience has shown that tests made with from to 10 degrees Fahrenheit superheat are not reliable, and that the steam consumption in many cases is not consistent when compared with results obtained with wet or more highly superheated steam. The errors mentioned, when they occur, are probably due to the fact that in steam, indicating less than 10 degrees Fahrenheit superheat, water in the liquid state may be taken up in " slugs" and carried along without being entirely evaporated. 2 Transactions American Society of Mechanical Engineers, vol. 21; and the Journal, Nov., 1912, pages 1713-14. DETERMINATION OF THE MOISTURE IN STEAM 57 lack of velocity. A sample taken from the lower part of this pipe will show a greater amount of moisture than a true sample. With goose- neck connections a small amount of water may collect on the bottom of the pipe near the upper end where the inclination is such that the ten- dency to flow backward is ordinarily counterbalanced by the flow of steam forward over its surface; but when the velocity momentarily decreases the water flows back to the lower end of the goose-neck and increases the moisture at that point, making it an undesirable location for sampling. In any case it should be borne in mind that with low velocities the tendency is for drops of entrained water to settle to the bottom of the pipe, and to be temporarily broken up into spray whenever an abrupt bend or other disturbance is met." If it is necessary to attach the sampling nozzle at a point near the end of a long horizontal run, a drip pipe should be provided a short distance in front of the nozzle, preferably at a pocket formed by some fitting, and the water running along the bottom of the main drawn off, weighed, and added to the moisture shown by the calorimeter, or better, a steam sepa- rator should be installed at the point noted. In testing a boiler the sampling nozzle should be located as near as possible to the boiler, and the same is true as regards the thermometer well when the steam is superheated. In a turbine or engine test these locations should be as near as practicable to the throttle valve. In the test of a plant where it is desired to get complete information, especially where the steam main is unusually long, sampling nozzles or thermometer wells should be located at both the boiler and the engine, so as to obtain as complete data as may be required. The sample of steam should always be taken from a vertical pipe as near as possible to the engine, turbine, or boiler being tested. Good examples of calorimeter nipples are illustrated in Figs. 67 and 74. Never close and usually do not attempt to adjust the discharge valve V 2 (Fig. 65) without first closing the gage cock V 3 . Unless this pre- caution is taken the pressure may be suddenly increased in the chamber C, so that if a manometer is used the mercury will be blown out of it, and if, on the other hand, a low-pressure steam gage is used it may be ruined by exposing it to a pressure much beyond its scale. Usually it is a safe rule to begin to take observations of temperature in calorimeters after the thermometers have indicated a maximum value and have again receded slightly from this maximum. The quality or relative dryness of wet steam is easily calculated by the following method. Using the symbols, pi = steam pressure in main, lbs. per sq. in. abs. P2 = steam pressure in calorimeter, lbs. per sq. in. abs. t c = temperature in calorimeter, deg. Fahr. 58 POWER PLANT TESTING T] and qi = heat of vaporization, and heat of liquid corresponding to pressure pi, B.t.u. per pound. H 2 and t 2 = total heat (B.t.u.) and temperature (deg. Fahr.) corre- sponding to pressure p 2 . c p = specific heat of superheated steam. Assume 0.46 for low pressures existing in calorimeters. 1 Xi = initial quality of steam (a decimal). ioo (i — Xi) = initial moisture in steam, per cent. Total heat in a pound of wet steam flowing into the orifice is xir x + qi, and after expansion, assuming all the moisture is evaporated, the total heat of the same weight of steam is H 2 + c p (t c - t 2 ). Then assuming no heat losses and putting for c p its value 0.46 we have, Xtfi + qi = H 2 + 0.46 (t c - ;ta), (3) H 2 + 0.46 (t c - t a ) - q, . ,, or Xi = ^ (3') Ti Charts for Moisture Determinations. A small section of the total- heat-entropy chart as provided in modern steam tables is shown in Fig. 66. It is arranged particularly for determinations of the quality of steam with a throttling calorimeter without using the equations above. Horizontal lines in the chart are those of constant total heat of the steam, and represent the process in a throttling calorimeter. To illustrate the application of the chart let the initial pressure of steam be 165 pounds per square inch absolute and the reading of the thermometer on the low-pressure side of the calorimeter be 270 degrees Fahrenheit. The pressure in the calorimeter is 15.2 pounds per square inch absolute. To find the quality x start at the intersection of the temperature line for 270 degrees with the 15.2 pounds pressure line and go across the chart horizontally to the 165 pounds line, then the " lines of constant quality" indicate that the quality of the steam is 0.979. When a U-tube manometer is used to determine the pressure in a calorimeter of the type illustrated in Fig. 65, this pressure can be obtained very accurately, and an excellent means is provided for calibrating the thermometer in the calorimeter just as it is to be used. The calibration would be made, of course, by the method of comparing with the tempera- ture corresponding to known pressures explained on page 34. In order to avoid having superheated steam in the calorimeter for this calibration 1 Average values for the specific heat of superheated steam for any pressures and temperatures are given on page 309. DETERMINATION OF THE MOISTURE IN STEAM 59 the felt or similar material usually needed for covering the valves and nipples between the main steam pipe and the calorimeter should be kept saturated with cold water. The Barrus Throttling Calorimeter. An important variation from the type of throttling calorimeter shown in Fig. 65 has been introduced quite widely by Mr. George H. Barrus. In this apparatus the tempera- ture of the steam admitted to the calorimeter is observed instead of the pressure and a very free exhaust is provided, so that the pressure in the calorimeter is atmospheric. This arrangement simplifies very much Fig. Entropy Chart for Determining Quality of Steam with any Throttling Calorimete the observations to be taken, as the quality of the steam Xi can be calcu- lated by equation (3') by observing only the two temperatures ti and t c , taken respectively on the high- and low-pressure sides of the orifice in the calorimeter. This calorimeter is illustrated in Fig. 67. The two ther- mometers required are shown in the figure. Arrows indicate the path of the steam. 1 The orifice in such calorimeters is usually made about ^V inch in diameter; and for this size of orifice the weight of steam 2 discharged per 1 Transactions American Society of Mechanical Engineers, vol. 11, page 790. 2 Formulas for calculating the exact weight of steam discharged from a nozzle are given on pages 189 and 190. In boiler-tests corrections should be made for the steam 60 POWER PLANT TESTING Fig. 67. — Barrus Throttling Steam Calorimeter. hour at 175 pounds per square inch absolute pressure is about 60 pounds. It is important that the orifice should always be kept clean, because if it becomes obstructed there will be a reduced quantity of steam passing through the instrument, making the error due to radiation relatively more important. In order to free the ori- fice from dirt or other ob- structions the connecting pipe or calorimeter nipple to be used for attaching the calorimeter to the main steam pipe should be blown out thoroughly with steam before the calorimeter is put in place. The connecting pipe and valve should be covered with hair felting not less than f inch thick. It is desirable also that there should be no leak at any point about the apparatus, either in the stuffing box of the sup- ply valve, the pipe joints, or in the union. Fig. 68 is a diagram for the determination of the quality of steam which is particularly suitable for use in connection with calorimeters of the Barrus type. Abscissas in this diagram are temperatures in the calorimeter t c , and the ordinates are the initial temperatures ti of the steam before expansion in the calorimeter. With the help of such a diagram the Barrus calorimeter is particu- larly well suited for use in power plants, where the quality of the steam is entered regularly on the log sheets. The percentage of mois- ture is obtained immediately from two observations without any calcu- lations. A very good design of throttling calorimeter recommended by the Power Test' Committee of the A.S.M.E. to be accepted as the standard for tests is shown in Fig. 69. The calorimeter is made practically throughout of ^-inch pipe fittings and has an orifice -fy inch in diameter in a flat plate. (Fig. 70.) This orifice is of a suitable size to throttle steam at the usual boiler pressures down to atmospheric. The wooden box should be filled with hair felt, 85 per cent magnesia, or an equally discharged from the steam calorimeters. The Power Test Committee of the A.S.M.E. suggest the use of Napier's formula, believing it to be sufficiently accurate for this kind of work. DETERMINATION OF THE MOISTURE IN STEAM 61 Temperature in Calorimeter, Degrees Fahi". v 240 250 260 270 280 290 300 310 7T " ~~ /-: ff±- ■--/:::- ESliEffll^ M— 4h— . i^fe^.; -f ^ :::l::::|::" ;: ±i Biliilif' ;:7 ?:i: 77 ;: ;: l Jaml 1 W .H^^H^^- ::4?;;;l£;|j{| ~iz -H --/- ^4^t^ |i : ;:J^-/::-i . .. :-4j::ilJ:i;;H ttt^L ;■ , : : ,'] -i" 7 .']::-:' -t^rt ^J 777 T- : -";S j I; 7 !; 7 ;; ijili tjl^'l^r^l SfffUW ; : :j. 7 :::|n 77 p I : : -R~FI7 r :T'7 ^/: r. V j"::. 7 i :~[ ::: iiltf lb; Vi '- f '■ 'f*- ■ Sv ||||||| jr::: [J A[ lew It ■ :; | -C i;:- ; r : : : j j TTT/T 1 "- ^ „j: " trp^j-T"t>'- r >frr- r PPJ^ Hg^ Hi RIM fr :: ■ ' ; 1 : /• -^—\ '4- -_.-... ■---■■..; - M^ii::! ■: r; |H ;:-::i::::: .:■; III 7 [ -+-"4-4- | iff +t£- -r+t— -rj- ;rfe4 * 240 250 260 270 280 290 300 310 320 (! y + Vi + 2/2 + II. By Durand's rule, A = w (0.4 y + 1.1 y x + y 2 + y 3 + • III. By Simpson's rule, A = \w {y n + 4 2/1 + 2 y 2 4- 4 y 3 + + yn-i + $y n ). + y n - 2 + l.li/„_x + 0.4j/ B ). + 2y B _ 2 + 4y n -i+.j/n). A very convenient method of measuring areas by the use of a " line pattern " has been devised by Granberg. 1 A sheet of tracing cloth or thin celluloid is prepared with parallel lines on it, equally spaced, and with dotted lines (Fig. 79) as shown, located at each end of the figure at one-fourth the distance between the unbroken lines first drawn. This " line pattern " is then laid upon the area to be measured so that the 1 Granberg, Technische Messungen, page 48. 74 MEASUREMENT OF AREAS 75 ends of the area fall on the " solid " parallel lines at opposite ends. The sum of the lengths of the " solid " lines included by the outline of the area added to one-half the sum of the lengths of the two dotted lines included at the ends when multiplied by the distance between the parallel " solid " lines (b) gives the required area. The various lengths required for both Granberg's and the trapezoidal rules can be conveniently added by laying them off with a dividers one after the other along a straight line and finally measuring the total length of the line. Areas are also frequently calculated by the method of mean ordinates, as given on page 142, for finding the mean effective pressure in engine cylinders. Planimeters. The most accurate and generally approved method of obtaining the area of irregular figures is by means of integrating in- struments called planimeters. Instruments of this kind may differ in many details, yet all of them are based, in theory, on the original Amsler polar planimeter. Polar Planimeters. One of the simplest forms of the polar type of planimeters is shown in Fig. 80. It consists essentially of two arms PO and TO pivoted together at O. When in use the point P is not to be moved, and is held in place by means of a pin-point upon which a small weight rests. There is a tracing point at T intended to be moved around the border of the area to be measured. Attached to the arm TO is a small graduated wheel W carried on a short axis which must be placed accurately parallel to TO. Any movement of the arm TO except in the direction of its axis will, of course, move the wheel W on the paper or other surface on which it is placed in such a way that the amount of its movement gives a record indicating the area measured. A vernier V placed opposite the graduations on the wheel, assists in reading the instrument accurately. The arm TO is usually made of such a length that the move- ment of the tracing point T around an area of one square inch (for English units) will move the wheel one-tenth of its circumference. Graduations of the vernier indicate usually one one-thousandth of a revolution of the wheel, or in English units one one-hundredth of a square inch. When the tracing point T is moved around an area in a clockwise direction the wheel will roll in the direction of its graduation, and the area is found by subtracting the final reading from the initial. Amsler planimeters are often constructed with the arm TO adjustable in length, so that it can be set to indicate areas in various units, as, for example, square inches, square feet, square centimeters, etc. The vernier V has ten graduations, and the total length of these ten divisions is one-tenth less than the length of those on the wheel so that it represents, counted from zero, so many hundredths of a square inch. 76 POWER PLANT TESTING To explain the method of using the vernier, Fig. 81 has been inserted, showing the wheel W and the vernier V in a drawing of larger scale than in Fig. 80. Readings of the graduations on the wheel W are always taken opposite the zero mark on the vernier, so that the reading indicated Fig. 80. — Amsler Polar Planimeter. in Fig. 81 without the help of the vernier would be a little more than 4.7. The graduation on the vernier which is exactly coincident with a gradu- ation on the roller wheel is the third from zero and indicates three hundredths. The complete reading is therefore 4.73 as determined by the vernier. ^1- 1 Fig. 81. — Typical Vernier for Planimeter. P w Fig. 82. — Position of the Arms of a Polar Planimeter to Draw the "Zero" Circle. Theory of Polar Planimeters. As this instrument is constructed neither of the points T nor W can pass over the arm PO (Fig. 82). If the arms PO and TO are clamped so that the plane of the graduated wheel W intersects the point P, x that is, when the'angle TWP is a right angle, and then the arms thus clamped are revolved around this point, the wheel will be continually slipping without any rolling motion in the 1 As regards the theory it is immaterial whether W is between O and T or on TO extended. Some planimeters are made one way and some the other. MEASUREMENT OF AREAS 77 direction of its axis, and consequently it will not revolve. When, how- ever, the arms are not clamped and if the construction of the instrument will permit the tracing-point T to be moved out so far that the axis of W will lie in the line PO, then an arc described by the movement of T will produce only a rolling motion of the wheel. Obviously with the arms in any position intermediate between that of the clamped right angle and the one with W in line with PO, the wheel will partly slip and partly roll, the amount of slipping and rolling depending on the size of the angle between the arms. It follows, then, that when circumscribing a closed figure the radial components cause only slipping of the wheel and need not be considered, while the circumfer- ential components produce a resultant rolling which must be taken into con- sideration. The path described by the tracing point T when the arms are clamped, as indicated in Fig. 82, is called the zero-circle for the planimeter. If the tracing-point is moved in any path outside the zero-circle in a clockwise direction a positive record will be indicated on the graduated wheel, while if it is moved in a path in the same direction as before but inside the zero-circle there will be a negative record. According to the theory of polar planimeters, they are designed so that the rolling of the wheel for a given circumferential motion of the tracing-point T is proportional to the area included between the path of T, the radial lines from P (Fig. 83) to the initial and final points of the path taken by T, and the arc of the zero-circle included between these radial lines. In other words, the area referred to is QTT'Q' in Fig. 83. In the discussion of this theory, the circumferential motion of the tracing- point T around the point P, with the angle WOP (marked a) remaining always at a constant value, is to be taken up first. 1 Now let us suppose the tracing-point is moved from T to T' in the figure through a very small angle, TPT' (marked e), keeping, however, the angle a constant; then the graduated wheel W will move through the arc WW', partly rolling and partly slipping. The component of this motion producing Fig ■ Theoretical Diagram for a Polar Planimeter. 1 In the mathematical discussion following, the graduated wheel will be considered as if it were a part of the arm TO, with its plane exactly at right angles to the axis of this arm. 78 POWER PLANT TESTING rolling will be perpendicular to the axis of the wheel; or, in other words, this component will be perpendicular to OT in all its positions, and without appreciable error for small values it may be represented in this figure by the line WX, making WXW a right-angled triangle of infinitesimal proportions. When the tracing-point has moved from T to T' the point O has moved through the arc 00' and the tracing-point subtends in its movement an angle WPW, which is equal to the angle TPT', marked e, which was passed over by T. Then the following relation is easily obtained: WW' = PW X c. In this equation the symbol c is a constant, expressing the ratio (for a given angle WPW) of the length of an arc to the corresponding radius for any value of this radius. In other words, in terms of the calculus this constant would be expressed in radians. In general for every angle there is a constant value which when multiplied by the radius gives the length of the arc for that radius. The component of WW' corresponding to the rolling of the wheel is WX, which is approximately equal to the arc WW times cos WWX. That is, WX = PW X c X cos WWX (8) But if PY is drawn perpendicular to T'W produced PW cos WWX = WY, (9) and combining (8) and (9), W'Y = ^ (10) c ' v Since the angle WPW is very small, WW may be taken as being per- pendicular to WP. Now WX is perpendicular to T'Y and the angle WWX is equal to the angle PWY. The trigonometric relations reducing the above to terms of the length of one of the arms of the planimeter and the constant angle a are as follows: WY W'Y = ^^ = PW'cosPWY = PO / cosPO'Y-WO' = PO / cosa-WO / , c then WX = c (PC cos a- WO') (11) This is an expression for the amount of rolling of the wheel when the tracing-point moves from T to T'. To express the relations required, the area will now be expressed trigonometrically in similar units. From geometry the area of sector TPT' = 1/2 arc TT' X PT, but arc TT' = PT X c, or area TPT' = 1/2 c X PT 2 . MEASUREMENT OF AREAS 79 We can write also, PT = VpQ 2 + OT 2 + 2 PO X OT cos a, area TPT' = 1/2 c (PO 2 + OT 2 -f- 2 PO X OT cos a). . (12) But the area represented by the amount of rolling of the graduated wheel is that part of the sector outside the zero-circle (see page 77), and this is the area TT'Q'Q. Now the radius r of the zero-circle, referring again to Fig. 82 ,* is easily obtained from equations expressing the relations of the sides of the right triangles in that figure for the particular case when there can be no rolling movement. Thus, PO 2 = WO 2 + PW 2 , (13) PW 2 = PT 2 - WT 2 = PT 2 - WO 2 - 2 WO X OT - OT 2 . . (14) Combining equations (13) and (14), PO 2 = WO 2 + PT 2 - WO 2 - 2 WO X OT - OT 2 . But PT = r, the radius of zero-circle, therefore, r = VpO 2 + 2 WO X OT + OT 2 . .... (15) Also from geometry, as explained on the preceding page, Area QPQ' - 1/2 r X c X r = 1/2 c X r 2 = i/2c(P0 2 + 2WO XOT + OT 2 ) (16) Subtracting equation (16) from equation (12), Area QTTQ' = c X OT (PO cos a - WO). . . . (17) Equation (17), which is the expression for the area outside the zero- circle, will be observed to be equivalent to the roll of the graduated wheel as given in equation (11), times the length of the arm OT from the pivot to the tracing-point. If, therefore, for a given area A, we call the reading of the wheel R and the length of the arm from pivot to tracing-point L, then, A = LR . (18) It should be noted further that this equation is independent of any other dimensions of the instrument. That this demonstration applies to areas not adjacent to the zero- circle or partly inside and out can be readily shown by subtracting in a given case the area between the zero-circle and the required area. 1 It will be remembered that with the arms of the planimeter in the position shown in Fig. 82 the tracing-point T describes the circumference of the zero-circle. 80 POWER PLANT TESTING Area of Zero-Circle by Experiment. The area of the zero-circle of a planimeter may be found readily by passing the tracing-point around the circumference of two circles each larger than the zero-circle. Pref- erably for this operation the fixed point of the instrument is placed at the center of the circles. If the calculated areas of these circles are respectively Ai and A 2 , and r is the radius of the zero-circle, then since readings of the graduated wheel show only the areas outside the zero- circle represented by Ri and R2, we obtain Ai = xr 2 + Ri, A 2 = Trr 2 + R 2 , 2 Trr 2 = Ai + A 2 - (Ri + R 2 ) (19) After r has been found 1 it is not difficult to calculate the proper length of the arm OT for any linear units (compare equation 15). In fact very many polar planimeters are constructed with the arm OT adjustable, so that the instrument can be used for any scale or for various units. The exact lengths required for both the English and metric units (inches and centimeters) are usually stamped on the adjustable arm. Mean Ordinate of an Area. 2 If we call m the mean ordinate and 1 the length of a given area A, then A = ml. From equation (18) we have A = LR, whence ml = LR, m = y R (20) 1 If instead of measuring and calculating the circles both larger than the zero-circle, one of the two is made smaller than the zero-circle, then the reading of the instrument is again the difference between the area of the circle and that of the zero-circle, but the value of this difference is now negative, so that if Ai is the area of the circle larger than the zero-circle and A 2 is the area of the one smaller, then using the other symbols as before, Ai = xr 2 + Ri, A 2 = Trr 2 - R 2 , 2 Trr 2 = Ai + A 2 - (Ri - R 2 ). Although this latter method does not fall in with the general demonstration so well, it is, however, usually preferred, as it will give greater accuracy than can be obtained with two circles both larger than the zero-circle, unless one of these is made unusually large. 2 Engineers must calculate mean ordinates most often when determining the mean effective pressure (m.e.p.) of engine indicator diagrams. MEASUREMENT OF AREAS 81 When, therefore, the tracing-point arm is adjustable it may be set as shown in Fig. 84 1 to make it equal to the length of the area measured. Then, obviously, the height of the mean ordinate will be equal to the reading of the graduated wheel expressed in the same units. For ex- ample, if the subdivisions of the wheel are fortieths of an inch, the result will be the mean ordinate also in fortieths. This scale of the wheel is not determined by the diameter of the portion of the wheel which is graduated, but by the diameter of the edge which comes into contact Fig. 84. — Polar Planimeter with Adjustable Arms for the Rapid Determination of Mean Ordinates. with the surface over which the wheel rolls. If then d is the so-called diameter of " rolling " of the wheel, its circumference is xd. Now by dividing the number of divisions on the circumference (usually 100) by 7rd, the "scale" of the wheel is obtained. It may also be found by measuring a rectangular area of the same length as that of the tracer arm and one inch wide, when the reading from the wheel will give the number of divisions per inch. For those instruments of which the radius of the wheel is one centimeter (.795 inch diameter) and having 100 divisions, the scale is almost exactly 40 divisions to the inch. Coffin Planimeter and Averaging Instrument. This planimeter is made commonly in two forms, illustrated by Figs. 85 and 86. As re- gards details the former is somewhat the simpler and will be explained first. In principle the two are exactly alike. As will be observed in the figures, this instrument has a single arm to which a suitably graduated 1 To facilitate the adjustment of the arm to the length of the diagram or area meas- ured, sharp points M and N are attached to the back of some planimeters. The point M is often conveniently placed a short distance away from the tracing-point T, and the point N must then be the same distance and in the same direction away from the pivot O. Then obviously the distance between M and N will be in all cases equal to the length of the adjustable arm. 82 POWER PLANT TESTING wheel is attached on an axis parallel to the line joining the ends of the arm. One of the ends of this arm is for tracing the outline of the area measured while the other slides up and down in a suitable slot. One of the advantages of this instrument over the polar planimeter, although it is not so generally adaptable, is that the wheel is made to move over a specially prepared surface, preventing unnecessary slipping. On mate- c-f : WSj/p* warn Fig. 85. — Coffin Planimeter. 3. — Coffin- Ashcroft Averaging Planimeter. rials having a rough, fibrous or, worst of all, an uneven surface, the movement of the wheel of any planimeter will not be the same as when rolling over a smooth flat surface. The Coffin planimeter may be discussed as a special form of the general polar type in which the pivoting point O, instead of swinging about the fixed point P (Fig. 8o), moves back and forth in a straight line. The angle between the arms PO and OT, as indicated by the dotted lines in Fig. 87, is really invariable at 90 degrees. Obviously, then, the equation (17) expressing the area traced by a polar planimeter outside the zero- circle becomes, referring to Fig. 83, area = c X OT(- WO); likewise equation (11), expressing the roll of the wheel for the Coffin planimeter, becomes equivalent to Roll or record of the wheel = c (- WO') = c (- WO). Using, as before, in equation (18), the symbols L and R for, respec- tively, the length of the arm OT and the reading of the wheel, we have, just as for the polar planimeter, A = LR (21) MEASUREMENT OF AREAS 83 As an averaging instrument the Coffin planimeter is very much more convenient than the typical forms of polar planimeters. For finding the mean ordinate of an area the use of the polar type of these instru- ments was explained on page 80. The sliding vertical straight edge shown at the right in Figs. 85 and 86 is for the purpose of making the operation of finding the mean ordinate of an area (or the " mean effec- tive pressure " of an engine indicator diagram) as simple as possible. P \ V Fig. Theoretical Diagram for a Coffin Planimeter. For this operation the straight edges C and K should be adjusted so that when the tracing pin passes over the extreme end of the area to be measured it will just touch both of them. Now if the tracer is started at either end of the area and moved around to the starting point and then moved upward along the vertical straight edge until the reading of the wheel is the same as when starting to trace the area, this last distance traced from the starting point along the vertical straight edge is the mean ordinate. To demonstrate this statement the symbols used on page 80 will be continued. Representing the mean ordinate by m, the length of the area A by 1, the reading or rolling of the graduated wheel in going around the area by R, and the length of the arm carrying the tracer by L, then as before A = ml. Now, when the tracing-point T moves over a vertical line, the angle DOT, represented by Z in Fig. 88, remains constant. If we call the vertical distance moved V, and remember that only the movement of the wheel at right angles to its axis produces rolling, then the reading corresponding to the rolling R is R = VsinZ. (22) 84 POWER PLANT TESTING But for the position shown in Fig. 87 when the tracer T is at the right- hand end of the outline of the area, we have 1 sinZ whence VI L Substituting this value of R in the general equation (20) for the mean ordinate m of a polar planimeter, then, LV1 XT < \ m= TT (23) This relation can be illustrated more simply, however, by referring to Fig. 89, which is a typical indicator diagram from a steam engine. In Fig. 88. — Theoretical Diagram for a Coffin Planimeter. V, Fig. 89. — Diagram Explaining the Method of Mean Ordinates with a Coffin Planimeter. this figure the tracing-point of the Coffin instrument is shown at O, with the tracing arm represented by VO. A rectangle OXYZ, indicated by dotted lines, is shown, of which the area is equal to that of the indicator diagram. Starting at O and moving the tracing-point around the in- dicator diagram once, the difference in readings is the area. Now if the tracing-point is moved in the opposite direction around the rectangle and again back to the starting-point at O it will measure a negative area equal to the first area and the reading of the graduated wheel will be the same as when first started around the indicator diagram. The MEASUREMENT OF AREAS 85 movement of the graduated wheel as the tracing-point moves from X to Y is equal and opposite to that in going from Z to O, so that these two cancel each other. The motion of the tracing-point from Y to Z requires the axis of the graduated wheel to be parallel to YV and con- sequently during this movement the wheel will not be moved. The only movement that is therefore producing a net change in reading of graduated wheel during the reverse tracing of the rectangle is in going from O to X. Consequently after going around any irregular area like an indicator diagram in a clockwise direction from the starting-point at O at the right-hand end of diagram, if the tracing-point is moved in a vertical direction from the starting-point at O until the reading of the graduated wheel is the same as when first started, this vertical distance moved, measured from O, will be equal to the mean height of the indi- cator diagram. — ^=^^\ \vx "lllllll R 2 \ 3 l-= Fig. 90. — A Typical Roller Planimeter. Although measurements of areas may be made with the Coffin planim- eter as with the regular polar types with the area in any position as regards its length and breadth, yet when the mean ordinate is to be obtained, its value in a definite position is required and the area must be placed so that its length with respect to which the mean ordinate is to be obtained will lie along the horizontal straight edge shown in the figures. Then the mean ordinate measured along a vertical straight edge will give the result required. Roller Planimeters. For the measuring of very large areas a planim- eter differing slightly in theory from the polar type has been designed by G. Coradi, of Zurich, Switzerland. It has the advantage of being adaptable for measuring surfaces of indefinite length and as wide as the length of the tracer arm. This instrument is illustrated in Fig. 90* 86 POWER PLANT TESTING It is supported at three points — the two rollers R 1 and R 2 and the trac- ing pin f, or its support s. These two rollers are attached to the shaft A. On the face of one of these rollers is a minutely divided miter-wheel engaging with a small pinion revolving the horizontal shaft carrying the spherical segment K. At the center of the frame B, and in the same vertical plane with the two shafts already mentioned, a vertical shaft carrying the tracer arm is supported. The spherical segment K causes merely by friction contact the movement of the cylindrical "measuring" roller shown at its right. This roller is supported on the auxiliary frame M, of which the tracer arm is a part. The " meas- uring" roller moves back and forth with respect to the spherical seg- ment to correspond with the movement of the tracing-point; but at the same time the rotation of the segment itself imparts rolling motion of the entire instrument. 1 Calibration of Planimeters. Tests are made by comparing the read- ings of the instrument with that calculated for a given area. For such calibrations it is necessary to use an area which can be gone over accu- rately with the tracing-point preferably held mechanically. This is done usually by using a metallic testing rule, shown in Fig. 91. It is usually 1 ' I 1 1 # Fig. 91. — Planimeter Testing Rule. made in the shape of a narrow strip from three to five inches long. At the end marked zero on the graduations a needle point is set which is kept in place by an overlapping screw. At each line of the graduations there is a very small conical hole into which the tracing-point of the pla- nimeter can be placed. The beveled end of the testing rule has the index line set accurately at the starting mark, so that this point can be very carefully located. With the tracing-point T in the testing rule and the fixed point P of the planimeter in approximately the position shown in Fig. 92, observe the reading of the instrument corresponding to the area of the circle described by the tracer moving clockwise, in the positions shown. 1st. When the fixed point P is on the left-hand side of the tracing point. 2d. When P is on the right-hand side. 1 Since this instrument is not often used by engineers, those interested in its theory are referred to Coradi's book of directions (in English) accompanying each instrument, or to Handbuch der Vermessungskunde, by W. Caville. MEASUREMENT OF AREAS 87 If the reading obtained is greater in tne first position than in the second, the end of the shaft carrying the graduated wheel nearest the tracing-point must be shifted toward the right to make the instrument accurate, and vice versa. Otherwise the error, if there be one, can be eliminated by taking the mean of the results obtained for the two positions. 1 Another test to be made, if there is doubt about the accuracy of a planimeter after the axis of the wheel has been adjusted, is to determine whether the settings of the adjustable arm marked on the instrument are correct. For this determination circles with several different diameters can be measured with the testing rule, and if there is a nearly constant \ percentage error, say x per cent too large, then the adjustable arm must be lengthened x per cent to make the planimeter readings correct, and vice versa. For accurate results the fixed point P should be placed as indicated by ^ 92 _ Me ^ ds "" f Testing the dotted lines in Fig. 92, so that Planimeters. when the tracing-point is near the center of the area to be measured the two arms will be approximately at right angles. Durand-Bristol Integrating Instrument. This instrument, illustrated in Fig. 93, has been recently developed by the Bristol Company for ob- taining the average radius of records traced on circular charts of uniform graduations like those used in recording gages, thermometers, etc. It is a simple device for obtaining quickly the average value of pressure, temperature, draft, watts, volts, amperes and other records generally taken on circular charts. This instrument consists of a wooden base in which there is a metal socket for supporting a rotatable pin slotted for receiving a horizontal shaft to which the integrating wheel is rigidly attached. On this shaft between the integrating wheel and the pin there is an adjustable tracing- point and at the opposite end of the shaft there is a triangular support for the shaft, also adjustable. The general principle of this instrument is due to Professor W. F. 1 For ordinary requirements a testing disk can be used in place of the rule, although it is not usually so accurate. On this disk circles of 1, 2, and 2| inches diameter are usually engraved; and if neither a testing plate nor a disk is available, tests can be made by using circles drawn with a pencil compass on a flat sheet of well-calendered paper. 88 POWER PLANT TESTING Durand 1 of Leland Stanford University. Its application hinges on the condition that the chart to be measured has a uniform radial scale, the Fig. 93. — Bristol-Durand Integrating Instrument for Circular Charts. same as there must be a uniform vertical scale for indicator and other similar diagrams in order that they can be averaged with the ordinary planimeters. Obviously the mean value of the radius of a circular Fig. 94. — Diagrammatic Drawing of Bristol-Durand Integrating Instrument. diagram cannot be determined with ordinary planimeters, since the area of a diagram in polar co-ordinates is proportional to the square of the 1 Transactions American Society of Mechanical Engineers, vol. 29 (1908). MEASUREMENT OF AREAS 89 radius and to the angle. 1 In Fig. 94 AB is an irregular curve, considered for this theoretical discussion as traced by a point moving in and out on a straight radial line. The center of the chart is at O, and at this point there is a socket, in which a rod O'P slides freely back and forth, permit- ting a tracing-point P to draw a curve AB. A graduated wheel W attached to O'P serves the same general purpose as the integrating wheel in the ordinary planimeter. Obviously this wheel will be moved only by circumferential motion, and for any radial movement of the rod in the direction of its length it will remain stationary. The amount of move- ment will be proportional to the radius WO, which differs from PO by a constant distance PW. The resultant movement of the wheel W is proportional, therefore, to the angle moved by the arm O'P and to the radius OW varying from point to point along the curve. Assuming for the present, but as will be shown later, the reading for any part of the curve, as AB, to be proportional to the product of the angle subtended between the points A and B, AOB, and the mean radius for the curve between these points, then if this reading is divided by the subtended angle expressed in circular measure the quotient will be proportional to the mean radius. Now if to the value of this mean radius the constant distance WP is added, the true value of the radial ordinate OP is ob- tained. When, as is usually the case in practice, the curve AB repre- sents values of radial ordinates with reference to a base circle of constant radius as the datum or " zero line," then if the radius of this base circle is subtracted from OP the remainder will be the true value of the ordi- nate. By making WP equal to the radius of the base circle, as may readily be done by a suitable adjustment of the instrument, the two corrections will be " balanced " and the mean value of the radial ordi- nate will be given directly as the quotient of the reading of the wheel and the subtended angle AOB expressed in circular measure. For a chart corresponding to twenty-four hours for a circumference, the angular measure to be used as the divisor will be .2618 per hour. The quantity to be determined in such diagrams is the time-mean of the quantity measured by theradialordinate. But since angular motion is made proportional to time, we may represent the desired mean by the following integral formula: rd0 (24) Now, in Fig. 95, let ABCD denote a curve drawn by a tracing-point 1 With the ordinary planimeter the mean square of the radial ordinates can be determined, and we can, of course, take the square root of these values, but in most cases this is not the same as the mean radius. 90 POWER PLANT TESTING value rdfl. which moves on the arc of a curve shown by OAV instead of on a straight radial line. Then let OV, ON, OM, etc., denote a series of consecutive positions of the curve OAV, at differential angular intervals 6.6. Then for the actual curved path ABCD substitute the broken line path made up of a series of arcs each rd0 in length, and the series of differential bits of the curve OAV as shown. Then at the limit the record of any inte- grating or averaging instrument will be the same, whether the tracing point is carried along the curve or along the broken line as shown. Then suppose an integrating instru- ment, as shown in Figs. 93 and 94, is applied to such a diagram, and let the tracing-point P be carried along the zig-zag path. The record of the wheel will be made up of two parts: 1. That due to the circular arcs rd# and representing by summation the of/r 2. That due to the differential por- tions of the arc OAV. Now it is clear that if the diagram extends all the way around from A through BCD to A again the differential elements of the curve OAV may be considered as existing in pairs, and that for every element traversed in the outward direction there will be an equal element traversed in the inward direction. PQ and ST denote the members of such a pair. The record for such a pair will therefore disappear in the summation; that is, for all the pairs, and also for the diagram as a whole. In such a case, therefore, part " 2 " above be- comes zero and the record of the wheel for the entire diagram consists simply of / rd0. This reasoning is seen to be entirely general and independent of the character of the path OAV, and hence must be true whether it be the arc of a circle, a straight line or any other path. • In case the curve occupies only part of the revolution, as ABC, then it is clear that in going from A to C the record will involve the two parts, " 1 " and " 2 " above, and that the latter will remain included in the final result and will represent the summation of the record due to the elements of OAV between A and C. This obviously will be the value of / rd(9 for the arc GC and it will be canceled by carrying the tracing-point of the instrument back from C to G. This method of reasoning is inde- Fig. 95. — Theoretical Curves for Bristol-Durand Instrument. MEASUREMENT OF AREAS 91 pendent of the extent of the arc and is therefore equally true for an entire revolution, even when the diagram does not end at the same radial dis- tance, as at the beginning. In such cases it is necessary only to trace along the arc OAV so as to " close " the curve, thus canceling part " 2 " above and finding directly the value of / rd0 for a whole revolution. In all cases the correction for part " 2 " of the record is made by tracing from the terminal point of the curve along the path, representing no change of time to a point lying in a circumference passing through the initial point. This may be stated in other words by saying that to eliminate part " 2 " of the record the tracing-point must start and finish at the same distance from the center, and if the diagram is not of the kind to satisfy this condition then the necessary portion of a path of zero change of time must be used to supplement- the diagram. This discus- sion is independent also of the nature of the curve OAV. It may be stated, however, that when OAV becomes a straight line the value of the correction becomes zero. CHAPTER V ENGINE INDICATORS AND REDUCING MOTIONS The engine indicator is simply an instrument showing by graphic diagrams the variations of the pressure in the engine cylinder of steam, gas, air, or whatever the working substance may be. Before James Watt invented the engine indicator (about 1814) he had already used a steam Fig. 97. — Watt's Original Steam Engine Indicator (Type of 1814). Fig. 98. — Section of Watt's Indicator. pressure gage on the cylinder of his engine, and since the movement of the piston in the early steam engines was very slow, he was able to observe with his eyes how the pressure varied during a stroke of the piston. In modern engines the movement of the piston is so rapid, how- ever, that a recording instrument is absolutely necessary. 92 ENGINE INDICATORS AND REDUCING MOTIONS 93 Watt's indicator is illustrated in Figs. 97 and 98. It consists of a cylinder CC (Fig. 98) in which the piston P is moved against the resistance of the spring S by steam pressure from the engine cylinder, this pressure being exerted, of course, -on the lower side of the piston. A pencil at- tached to the upper end of the piston rod traces on a sheet of paper a diagram DD, of which the height on any ordinate is proportional to the pressure. The paper is moved back and forth on a slide by a string E moved in conformity with the piston. The instrument was of great service to Watt in perfecting his steam engines. In the modern indi- cators, of which a few of the best known makes are to be described, there are many improvements over the instrument used by Watt. Thompson Indicator. Of the engine indicators now in general use the Thompson is the oldest and best known. Fig. 99 shows one view of this instrument and Fig. 100 shows the corresponding sectional drawing. Thompson Indicator. It consists in essential parts of a piston 8 (Fig. 100) moving in a cylin- der 4. This piston is rigidly connected to the rod 12, which passes up through the cap 2. The motion of the piston rod 12 is transferred to the pencil 23 by means of suitable links designed to make the pencil move parallel to but usually four times as far as the piston 8. The maximum pressure of the pencil on the paper used for the diagram is adjusted by the thread and set-screw on the handle attached to the bracket X. 94 POWER PLANT TESTING The method of changing the springs in the various common forms of engine indicators should be well understood by everyone likely to be called on to " indicate " engines. When the work of changing springs is done clumsily or carelessly, a great deal of time is often wasted by the whole party engaged in the test. The method to be fol- lowed in changing springs of a Thompson indicator may be stated briefly as follows: The milled-edged cap 2 should first be unscrewed from the top of the cylinder containing the spring and piston. This cap, together with the sleeve and bracket X carrying the pencil lever and linkages, the piston rod, and the piston, can then be lifted from the main body of the indicator. By unscrew- ing the small milled-headecl screw 19 connecting the piston rod with the pencil arm the spring can then be unscrewed, first from the cap 2 and finally from the piston 8. By exactly reversing the operation another spring can be put in the place of the one removed. Changing springs in this instrument is a simple operation. No wrenches or other tools are required. Care should be taken, of course, to screw up the spring firmly against both the cap and the piston. Probably one-half the troubles with indicators in operation arise from loose springs, although not so often, probably, with Thompson indicators as with some other types. The height of the pencil can be adjusted by turning the screw- head 19 up or down on the piston rod. As a general rule, the spring selected for an indicator should be of such a scale that the largest diagram to be taken will not be more than If inches high; that is, if the maximum pressure will be about 140 pounds, a spring with a scale of 80 pounds per square inch should be selected. Instruction books going with indicators have usually tables showing the spring recommended for a given maximum pressure. Gener- ally a higher card is permissible for light springs and slow engine speeds than for stiff springs and high speeds. The tension of the spring 31 in- side the drum carrying the paper for the diagram is varied by loosening Fig. 100. — Section of Thompson Indicator. ENGINE INDICATORS AND REDUCING MOTIONS 95 the thumb nut and turning the large milled cap until the proper adjust- ment is secured. 1 Crosby Indicators. For high-speed engines and for accurate results the Crosby indicator has long been a favorite with engineers. This in- dicator is illustrated in Figs. 101 and 102. It consists of a piston 8 moving in the cylinder 4, and is connected by means of the piston rod 10 and the link 14 to the pencil lever 16. All of the pencil mechanism (arranged to move the pencil point 23 in a straight line parallel to the Fig. 101. — Typical Crosby Indicator. motion of the piston 8) is supported by the links 13 and 15 on the sleeve 3. The indicator spring is fastened at its lower end to the piston by a ball-joint and at its upper end it is screwed into the cap 2. The method of attachment of the springs to the piston by means of the ball-joint is shown more in detail in Fig. 103. In this indicator the spring is changed by first unscrewing the milled 1 Unless there is a very good reason for a change in the tension of the spring in the drum it should not be altered. Particularly in indicators which have been used a long time the pin holding the spring in place is likely to be much worn, so that if adjusted often the spring may get loose, and then there is usually considerable difficulty in get- ting it again into its proper position. 96 POWER PLANT TESTING cap 2, then this cap, the sleeve 3, the piston rod 10, and the connected parts can be removed from the cylinder 4. By unscrewing the spring by hand from the cap, which, of course, must be prevented from turn- ing, and also from the screw on the swivel head 12, the piston, the spring and the hollow piston rod 10 are detached from the other parts. A socket-wrench of the special form provided in every indicator box of this make is to be slipped over the piston rod to engage with the small nut shown (at 10) in Fig. 102 at the lower end of the piston rod. Then the Fig. 102. — Section of Crosby Indicator. piston rod is readily unscrewed from the piston and at the same time the spring is released from its attachment to the piston. Now with the pis- ton rod still in the socket of the wrench, slip the spring to be used over the piston rod until the head of the spring rests in the concave end of the rod. To do this, the wrench must be held upright, and then if the piston is inverted, or, in other words, if it is held so that the end screw- ing into the piston rod points downward, the piston rod is ready to be screwed into the piston, so that the transverse wire of the spring pass- ing through the bead will be held firmly in the slotted portion of the ENGINE INDICATORS AND REDUCING MOTIONS 99 changed when the thumbscrew at the top of the central spindle has been unscrewed. In Fig. 105 a slightly different outside-spring arrangement is shown. It is distinguished particularly from Fig. 104 in having the indicator spring in compression instead of being in tension as in most other outside- spring types. The obvious advantages of the designs having the springs in tension are that springs can be changed much more readily than in other types; and that it is practically impossible if the springs and piston are well made for the spring to buckle over and bind the piston as happens frequently in all types having the spring in compression. The weakness of the designs having the spring in tension is in requiring a very long and slender piston rod which, being in compression, may have a ten- dency to buckle over and produce vari- able errors. As regards temperature effects, one arrangement is about as good as the other. Star Brass Indicator — Navy Pattern. The indicator called the " Navy Pattern," manufactured by the Star Brass Co., is shown in Fig. 106. In general principles of construction it is like the Crosby in- dicator illustrated in Fig. 104. The most essential difference is in the type of straight-line parallel motion for the pencil lever. It will be observed that this is practically the same as that used in the Thompson indicator (Fig. 99). Tabor Indicator. 1 In the form in which it is now manufactured the Tabor indicator, Fig. 107, differs from indicators like the Crosby par- ticularly in the means employed for producing a straight-line parallel motion for the pencil. In this device a roller is attached to the pencil lever and is arranged to move in curved slots on the inside of the rectan- gular box-shaped part shown in the figure. As regards the point of flexibility in the mechanism, this is not be- tween the spring and the piston, but, more like the Thompson, is in the ball and socket joint between the piston and the piston rod. Details of this construction are shown in Fig. 108. The principal precaution to observe in the use of this indicator is to Fig. 105. — " Compression " Type of Outside Spring Indicator. Ashcroft Mfg. Co., Liberty Street, N. Y. 100 POWER PLANT TESTING Fig. 106. — Star Brass Indicator — Navy Pattern. Fig. 107. — Tabor Indicator. ENGINE INDICATORS AND REDUCING MOTIONS 101 be certain at all times that the roller on the pencil lever moves freely in the curved slots. Outside spring types of this indicator are also made. To Change the Spring. The cylinder cap must be first unscrewed, and then this cap, together with the piston, spring, and connected parts can be lifted from the cylinder of the indicator. By removing the small screw under the piston the latter can be unscrewed from the lower end of Fig. 108. — Section of a Tabor Indicator. the spring. The other end of the spring can then be unscrewed from the cylinder cap. Another spring is put. into the indicator by slipping it over the piston rod with the end stamped T uppermost, screwing this end into the cylinder cap and screwing the piston to the lower end. The pencil mechanism must be moved downward until the piston rod enters the piston and the square shoulder enters the corresponding square socket in the piston. In this last operation care must be taken that the rod is firmly and accurately in the hole, and then the screw at the bottom of the piston should be firmly applied. 102 POWER PLANT TESTING 3RL Section of Trill Indicator. To Change the Tension of the Spring in the Drum. The drum itself is first removed. Then after loosening the knurled nut on the central shaft and after the drum carriage has been lifted clear of the stops, the carriage can be turned in the required direction to secure the necessary tension and it can then be replaced by lowering into the stops. Care must be taken also that a firm grasp on the drum carriage is not lost, otherwise the spring will become uncoiled and probably also detached. Fig. 109 shows a section of a Trill outside-spring indicator. 1 In principle it is very much the same as the one shown in Fig. 105. Im- portant parts are labeled with their proper names, which should be studied. Bachelder Indicator. 2 Fig. no illustrates an engine indicator which is in many essential parts entirely different from all the types already described. It is so simple in construction that scarcely any description is necessary. The most radical difference is, however, in the form of spring used. This is a flat bar and is arranged with a movable fulcrum which can be adjusted to change the scale of the spring. Although a wide range is obtainable in this way, it has been found unsatisfactory to attempt to use a single spring for all the ranges from the highest pres- sures to low vacuums. On this account at least two springs, one for high and the other for low pressures, are usually supplied. On account of its heavy parts it is not suitable for high speeds. Springs are changed by first removing the taper screw shown at the extreme right-hand side in the figure, and then after unscrewing a cir- cular cap on the side of the cylinder the pin connecting the spring to the piston rod can be withdrawn with a small pliers or similar instru- ment. Usually before the spring can be withdrawn the thumbscrew attached to the movable fulcrum must be loosened. In the ordinary operation of the instrument the piston is not removed. 3 1 Trill Indicator Co., Corry, Pa. 2 Richard Thompson & Co., 126 Liberty Street, New York. 3 When the spring is calibrated, the piston should be taken out so that a little cylinder oil can be put on it. It is not so necessary for this type when in use on a steam engine, as the oil in the steam will usually provide sufficient lubrication ex- cept when the steam is superheated. ENGINE INDICATORS AND REDUCING MOTIONS 103 The principal difficulty with indicators of this type is that, there is always some uncertainty about getting the fulcrum set at exactly the right point. Also if the fulcrum slides easily it may shift during a test. The only safe way is to examine the setting of the fulcrum frequently throughout all tests. The spring on the drum is conical in form and is adjusted in practi- cally the same way as in the Crosby indicator. Fig. 110. — Bachelder Indicator. Precautions for Care of an Indicator. Unless an engine indicator is well taken care of, very soon it will be in a condition in which no reliance can be placed on results obtained with it. That the necessary precautions should be taken is all the more important, because it is one of the most expensive as well as the most delicate instruments used by an engineer in his ordinary practice. The following precautions are particularly important: 1. Before an indicator is used all the working parts, especially the piston, should be carefully cleaned. Then after a spring suitable for the pressure has been attached in its proper position and a little cylinder oil has been smeared in a thin coat on the working surface of the piston, the parts should be replaced. Moving parts of the pencil mechanism should be oiled occasionally with watchmaker's or porpoise oil. It is a very good practice, especially when comparatively new indicators are being used on long tests, to take out the piston of the indicator fre- 104 POWER PLANT TESTING quently and smear it with cylinder oil. For lubricating this piston it is a little better to use a comparatively thin cylinder oil of high flash test (like gas-engine oil) than one that is very viscous. 2. Adjust the screw on the handle provided for moving the pencil so that when the pencil is sharp the application of the usual pressure on the handle will give a very fine line. 3. Adjust the length of the indicator cord so that the drum will be neither too loose nor too tight; or in other words, so that the drum will not strike either of the stops when the engine is operating. On a small engine this is most easily tested by observing the diagram when the engine is on each of the dead-centers. If the diagram is either too long or too short the drum will not be moved the required distance, and the indicator diagram will be correspondingly too short and therefore inac- curate. The cord used should be selected with care. It must be of such a quality as not to be stretched appreciably by the forces to which it is subjected. For accurate work and on long-stroke engines fine an- nealed steel or phosphor-bronze wire, or indicator cord wit'h a wire core, 1 should be used. The length of the cord should be adjusted very care- fully and fastened securely so that it will not slip or stretch so as to bring the drum up against one of the stops, making the diagrams too short. This effect can^usually be detected by the clicking sound of the drum striking the stop, if there is not too much noise in the room. The experi- enced engineer, however, will by force of habit invariably put his finger now and then during a test on the top of the drum or on the side of the bracket supporting it to determine whether its operation is satis- factory. Another way to determine a faulty adjustment on the usual crank-shaft type of engine 2 is to measure the lengths of the indicator diagrams. If the cord stretches the diagrams will be variable in length. 4. The atmospheric line should always be taken preferably after the diagram has been made. It is drawn, of course, when the indicator cock is closed. By this order of procedure in tests, the diagram can be more easily taken exactly " on the signal." The length of the diagram must alvays be measured on the atmospheric line or on a line parallel to it. The indicator cock should be kept closed and the cord to the reducing motion should be unhooked except when a diagram is to be taken. When the cord is unhooked the drum should not be permitted to snap back against the stop. By observing these precautions the useful life of an indicator can be much prolonged. 1 This indicator cord with a wire core which is guaranteed not to stretch in ordinary use can be obtained from the Athletic Store, State College, Pa. It is the most satis- factory indicator cord obtainable. 2 In an engine without a crank-shaft like a direct-acting steam pump the length of the stroke and consequently of the indicator diagram is likely to be quite variable. ENGINE INDICATORS AND REDUCING MOTIONS 105 5. Immediately after a diagram has been taken it should be removed from the drum and examined. If there are unusual irregularities in the lines, unaccountable differences in the areas or in the lengths of different cards, the facts should be noted and the best efforts should be made to remedy the faults. Irregularities are usually due to stretch- ing of the indicator cord, grit on the piston, lost motion in the working parts (usually inside the indicator cylinder) or excessive friction caused by overheating of the piston, particularly when used on gas engines. To correct these faults concerning the piston it must be removed from the cylinder and should then be carefully cleaned and again lubricated with cylinder oil. Before putting the piston and connected parts back into the indicator cylinder it' should be observed whether or not all the parts are connected firmly and without lost motion. 1 6. After a test, the indicator should be removed immediately from the engine, protecting the hands with waste or thick gloves to prevent burns. All the parts, especially those in the cylinder, should be thor- oughly cleaned and then put together again without the spring, which should be put away with the other springs in a box provided for the indi- cator. An indicator should never be handled by taking hold of the drum, as usually it is fastened to the indicator by only a loose slip joint, and this comes off easily. 7. Before opening the indicator cock to take the first diagram in a test, examine the indicator carefully to see that piston, spring and pencil mechanism are attached securely. A good method is to take hold of the end of the pencil lever near the pencil-point and try to move it up and down. If there is no lost motion observable and the pencil-point seems to be at about the right height for drawing the atmospheric line, it may be assumed that the indicator has been assembled properly. Otherwise it will be observed immediately by this test if the indicator has been put on the engine without inserting a spring, or if the milled nut at the top of the indicator cylinder has not been firmly screwed down. Observe also whether the " union " nut attaching the indicator to the cock is held by at least three or four good threads. Otherwise if this nut slacks 1 One of the causes of errors in results obtained with indicators not so readily de- tected is due to the pencil motion not being parallel to that of the piston in the indica- tor. A simple test for this 'is to draw an atmospheric line on a card placed on the drum. The card should be at least as wide as the height of the drum. Then after taking out the spring raise the pencil to the full height of the card by pressing lightly on the piston. This operation should be repeated several times at several points along the length of the card. To secure the best accuracy it is desirable to "block" the drum in each position. If the lines drawn are exactly perpendicular to the atmos- pheric lines there is no error in the pencil mechanism. If the test for perpendicularity is made by a triangle and straight edge, it should be done with the triangle first lying on one side and then on the other, to eliminate any inaccuracy in it. Often the triangles used by engineers are very inaccurate. 106 POWER PLANT TESTING back a little the whole indicator may be thrown by the f orce 1 of the steam pressure against the ceiling of the room. More indicators are worn out and broken by careless assembling than in any other way. 8. One of the best ways to put an indicator card on the drum is to first bend over one of the short edges of the card on a line about a quarter inch from the end and place this end with the line of bending snugly against the top of the longer clip on the drum. Then lap the card around the drum and insert the other end of the card into the upper end of the shorter clip. The card should then be pushed down to the stops in the clips, being careful however to keep it tight and straight, so that there will be no wrinkles. Finally to prevent the card from shifting on the drum, the end of the card under the shorter clip should be bent over carefully and firmly. SPECIAL TYPES OF ENGINE INDICATORS Cooley-Hill Continuous Indicator. For many purposes of investiga- tion it is very important to have continuous records showing the varia- tions of the cycles in the operation of an engine. Many devices have been used for this purpose, but as the motion was taken from the crank shaft there was no simple relation between points on these diagrams and the corresponding points in the stroke of the engine. Furthermore, because of the difficult relation, such cards could not be measured with a planimeter. Similar apparatus for the same purpose operated by an electric motor were open to the same objection. To overcome these difficulties a continuous indicator was developed in which the motion was proportional at every instant to the movement of the piston. With a diagram obtained with this instrument it is not difficult to determine the dead-center following release, and the conventional indicator card for an engine is then readily obtained by turning the diagram for the complete cycle back on itself by folding the card or ribbon at this dead- center. If transparent paper is used, the complete diagram can be seen with all the points in their true relative positions as regards the move- ment of the piston. The indicated horse power can then be readily cal- culated with the aid of a planimeter. This continuous indicator is illustrated in Fig. in. The indicator cylinder C, the piston, and the pencil motion may be of any standard make, as the collar M, for attach- ing the drum mechanism, is adjustable in size so that it can be fitted to indicator cylinders of different diameters. By this arrangement only one drum motion need be provided for using this indicator motion on a number of types of indicators such as would be required for use with steam engines, gas engines, high-pressure air compressors, ammonia compressors, etc. In this apparatus the drum D moves forward a given amount with every stroke of the engine. The indicator cord S is con- ENGINE INDICATORS AND REDUCING MOTIONS 107 nected to the indicator reducing motion and is driven by being connected in the usual way to the cross-head of the engine. The mechanism operating the drum motion is illustrated in Fig. ma. It consists essentially of two miter wheels B and C, meshing with a similar wheel E, to which the pulley W, carrying the indicator cord, is attached. At the top of the wheel B and at the bottom of C are so-called silent Fig. 111. — Coolev-Hill Continuous Indicator. ratchet clutches a, a, each of which operates in only one direction to grip the collars concentric with the wheels B and C. Only one of these collars is shown in the figure. Both are rigidly attached to the central spindle J, carrying the indicator drum D (Fig. in). For example: This central spindle is gripped by the ratchets a, a in the wheel B, during the " for- ward" stroke of the engine, and is released during the " backward" stroke. The ratchet in the wheel C, on the other hand, grips this same spindle during the "backward" stroke and releases on the "forward" stroke. 108 POWER PLANT TESTING In this way the drum D is constantly moved on the spindle J in the same direction. Neither of the wheels B nor C is directly attached to the cen- tral spindle, and they can move it only when they move in the direction in which they grip their ratchets a, a, engaging in the grooves g, g. The miter wheels B and C are con- nected to each other by means of a spiral spring enclosed in the casing D. This serves the function of the ordi- nary drum spring in the usual type of indicator for bringing the drum and cord back when the cross-head moves toward the indicator. Optical Indicators. The usual types of indicators operating with a piston are not suitable for engines running at much over 400 revolutions per minute. For higher speeds optical indicators are used. These operate by the deflection of a beam of light from a mirror, the deflection being proportional at any in- stant to the pressure. When such a device is used on an engine successive indicator diagrams can be readily ob- served and compared by marking with a pencil the reflection upon a ground- glass plate, and if a photographic sensi- tive plate is exposed to the beam of light in the place of the ground glass, a permanent impression can be taken, showing at any instant the operation of the engine. Optical indicators are prac- tically the only kind that can be used successfully for indicating the action of modern high-speed automobile engines. Every well-equipped automobile testing plant should be provided with one of these instru- ments. One of the simplest and best apparatus of this kind is illus- trated in Fig. 112. The indicator is shown in the picture vertically above and connected to the head of the engine. Steam pressure is communi- cated to the instrument through the usual type of indicator cock sup- porting it. A system of levers shown (a simple reducing motion) serves for reducing the length of the stroke of the engine to a suitable size for such a small instrument. A glass mirror moved about a vertical axis by the motion transmitted from the cross-head and about a horizontal axis by the pressure in the engine cylinder reflects a beam of light from Fig. Ilia. — Details of Cooley-Hill Indicator. ENGINE INDICATORS AND REDUCING MOTIONS 109 a lamp upon a sheet of paper so that the indicator diagram can be traced. Details of the essential parts of this instrument are shown in Fig. 112a. Through the indicator cock the pressure in the engine cylinder is com- Fig. 112. — Perry's Optical Indicator. This pressure tilts the mir- municated to the cored passages marked A, A. ror B, attached to the thin steel diaphragm D. When, there- fore, the mirror is still, a ray of reflected light will be seen as a bright spot on the screen; but when moved both by the pres- sure and the motion of the cross-head the conventional in- dicator diagram is traced. It is very interesting to watch the rapid change of shape of such diagrams as load, speed, pressure, cut-off, etc., are changed. With such an instru- ment these interesting phenom- ena in engine operation can be illustrated on a ceiling to a large class of students. Fig. 112a. — Essential Parts of Perry's Optical Indicator. 110 POWER PLANT TESTING Another type of optical indicator intended particularly for high-speed automobile engines is shown in Fig. 113. In this instrument the move- ment of the beam of light is produced by reflection from a small mirror M arranged to move in two distinct planes at right angles to each other. In one plane the movement of the piston is accurately reproduced, and in the other plane the movement is proportional to the pressure. Either of these movements or deflections of the mirror, taken alone, would cause the reflected beam of light to trace on the ground-glass plate a straight line; that due to the pressure being arranged to produce a straight verti- cal line and that due to the motion of the piston a straight horizontal line. But obviously the two movements taken together trace a diagram Ground Glass Plate Fig. 113. — Section of a "Manograph" Optical Indicator. indicating at any instant the pressure in the engine cylinder for the cor- responding position of the piston. A flexible shaft, attached at one end to the crank shaft of the engine, moves the disk A and with it the crank C, as well as the small lever L attached to it. The free end of this lever is arranged to turn the mirror M about a vertical axis by means of the small strut a, while the pressure exerted on the diaphragm D, as trans- mitted from the engine cylinder by the pipe P, moves the mirror about a horizontal axis by means of the strut b. In this apparatus the dia- phragm takes the place of the piston and spring in the ordinary type of indicator. These diaphragms, like those used in pressure gages (see page 11), can be made of such thickness that a diagram of satisfactory size can be obtained for high or low pressures. When the diaphragms are care- fully calibrated, a reasonable degree of accuracy can be expected. The ENGINE INDICATORS AND REDUCING MOTIONS 111 l^J relative motions of the mirror in the two planes are set in phase by ad- justing the milled screw S, operating a small worm wheel serving for changing the angular position of the crank disk A, to make the move- ment of the mirror about the vertical axis correspond with that due to the pressure. There are various methods for determining the proper adjustment for correct " phase rela- tion," but the simplest is to break the ignition circuit on the cylinder to be indicated when the engine is operating. The compression curve will then prac- tically coincide with the expansion line when the adjustment is correct. The principle of operation is shown more clearly in the diagrammatic sketch of Fig. 114. Parts are indicated by the same letters as for Fig. 113. Fig. 115 shows the apparatus as it would be set up for indicating an engine. A dia- gram taken from a gasoline automobile engine is shown in Fig. 116. The Hopkinson optical indicator is shown very clearly in Fig. 117. It is essentially similar to the manograph, except that it has a piston F instead of a diaphragm and a direct type of reducing motion is used as shown in Fig. 117a. The long tubes connecting the " manograph " type with the engine cylinder are very likely to introduce considerable errors. The time lag between the pressure in the cylinder and that at the diaphragm is very Line Diagram of "Mano- graph." Acetylene Ground -Top of Tripod Stand Fig. 115. — "Manograph" Ready for Attachment to Engine. appreciable at high speed. This error is largely eliminated by adjusting the cyclic relations so that the compression curve observed when the spark is cut off is in phase with the expansion line. But the long tube also throttles very considerably the pressures of the gases and in- creases the effective clearance of the cylinder. To eliminate these diffi- culties an ingenious gear device is inserted between the engine shaft 112 POWER PLANT TESTING and the small crank R. By this means the crank R can be retarded behind the engine crank by any phase difference that is necessary. This retard- ation varies, however, with the speed of the engine and the adjustment Fig. 116. — Indicator Card taken from a High-speed Automobile Engine with an Optical Indicator. Fig. 117. — Hopkinson's Optical Indicator. must be made every time the speed is changed in order to get accurate diagrams. Calibration of Indicator Springs. The pistons of engine indicators are invariably made of a very definite area, usually one-half square inch ; and it is possible to calibrate the deflection of the springs with respect ENGINE INDICATORS AND REDUCING MOTIONS 113 to this area, so that a certain definite pressure per square inch 1 in the cylinder will correspond to a definite deformation of the springs. In English units the pressure on the piston in pounds per square inch cor- responding to a movement of the indicator pencil on the diagram of one inch is called the scale 2 of the spring. Indicator springs should always be calibrated by the makers. The calibration should be made when they are in the indicator in which they are to be used. Short Brass Slecvo Soldered to WIro 1 Screwed wilh 2 Clamping Nuts String to Crosahcad or Pump Rod Le?er Pkotled ~" " Fig. 117a. — Reducing Motion for Hopkinson's Indicator. Cooley Apparatus for the Calibration of Indicator Springs. An ap- paratus similar to the one designed by Professor M. E. Cooley is very generally used for the calibration of indicator springs. One of the latest and more elaborate forms of this instrument is shown in Fig. 118. In its essential parts this apparatus consists of a small cylinder C, sup- ported on a bracket B, a connection I at the top of this cylinder for the attachment of the indicator to be tested, and a stuffing-box or gland at the bottom of the cylinder into which a plunger-piston P is fitted. The lower end of this plunger rests on a sensitive platform scales. Any pressure in the cylinder C can therefore be weighed. Steam may be admitted to the cylinder through a pipe E, and is exhausted through the pipe A. By adjusting the globe valves on the pipes A and E any pressure desired can be secured in the cylinder C, and this same pressure is, of course, exerted both on the piston of the indicator above and on the plunger P below. This plunger is usually made with an area of one-half square inch. For a plunger of this area, then, if for a given pressure the scales balance at 10 pounds, the pressure in the cylinder C, and on the piston of the indicator, is 20 pounds per square inch. To eliminate friction 3 1 Indicators are always designed to relieve the pressure above the piston due to leakage around it, so that on this side there is always atmospheric pressure. 2 Instead of "scale" the word "number" is often used. That is, a spring of which the scale is 40 pounds would be called "No. 40." 3 The operation of the apparatus is usually much improved by pouring, just before the steam valves are opened, a few drops of cylinder oil into the cylinder C through I to lubricate the plunger. 114 POWER PLANT TESTING as much as possible, the plunger P should be kept spinning when obser- vations are being taken. For this purpose a hand wheel K with con- siderable mass, for its " fly-wheel " effect, is provided on the shaft of the plunger. A more uniform motion of the plunger is obtained, however, by having the hand wheel grooved to take a small belt to be driven by an electric motor M. The plunger is supported usually on a ball-bearing joint set in a low pedestal L. By connecting a pipe E to a suitable manifold or similar fitting, to which are attached three separate pipes supplying respectively steam, air, and water under pressure, an indicator can be tested with varying Fig. 118. — Apparatus for Calibrating Indicator Springs. pressures under the actual conditions in service; that is, when used for steam, air or water. American engineers always prefer making calibra- tions of indicators under conditions as nearly as possible those pertain- ing to their ordinary use. The Power Test Committee of the A.S.M.E. recommends also the following procedure: To bring the conditions approximately at least to those of the working indicator, the steam should be admitted to the indicator in as short a time as practicable for each of the pressures tried, and then the indicator cock should be closed and the steam ex- hausted before another pressure is tried. By this means the parts are heated and cooled as under working conditions. For each required pressure open and close the in- dicator cock a number of times in quick succession, then quickly draw the line for the ENGINE INDICATORS AND REDUCING MOTIONS 115 desired record, observing at the same instant the "reading" of the standard used for comparison. A corresponding atmospheric line is to be taken immediately after each pressure line. Indicator springs for gas and oil engines should also be calibrated with the indica- tor in as nearly the same condition as to temperature as exists when it is in use. A simple way of heating recommended is to subject it to steam pressure just before cali- bration. Compressed air is a suitable fluid for the actual calibration, being preferred to steam as it brings the conditions as nearly as possible to those of practice when the indicator is in actual use in gas or oil engines. In Europe an apparatus like Fig. 119 is used a great deal. It is essen- tially the same as the dead-weight gage testers described on page 17, except that there is a connection for an indi- cator. Pressure is applied by loading weights on the platform P resting on the plunger. In this apparatus the gage G serves merely as a means of checking and avoiding mistakes. American engineers object to this method be- cause the calibration is made when the indi- cator is under nothing like the conditions of service, at least as regards temperature. Many engineers calibrate their indicators by compar- Fig. 119. — Dead-weight ing them with a good test-gage which has been Tester for Indicator Springs, carefully calibrated with a dead-weight tester. The gage and indicator are put on the same pipe carrying high-pressure steam. The movement of the pencil of the indicator is carefully ob- served, and compared with the reading of the gage. This latter is the method suggested by the Power Test Committee of the A.S.M.E. in their report in Nov., 1912. A simpler form of the Cooley apparatus intended for the so-called " dry method " of testing is shown in Fig. 120. A suitable fitting for receiving the indicator I is supported on the bracket B. The legs of this bracket span over a sensitive platform scales S. A small rod R rests at its lower end on a small pedestal standing on the platform of the scales S. On the top of this rod there is a cap supported on a small conical bearing to give some flexibility. This cap is made to fit easily into the lower side of the piston in the indicator. The indicator itself is attached to the top of the hand wheel W. Then when the hand wheel is screwed downward the indicator comes down with it and compresses the indicator spring. At the same time a pressure is exerted on the rod R which can be balanced on the scale beam. When a force is ap- plied to compress the spring in the indicator, the magnitude of the force can be determined by weighing the pressure on the scales. If the area of the piston in the indicator is one-half square inch, then twice the weight on the scales is the pressure exerted in pounds per square 116 POWER PLANT TESTING inch. Heat can be applied to the indicator by passing steam through a rubber or flexible copper tube wrapped around the cylinder. 1 Method for Calibration of Springs. After cleaning the internal parts of the indicator, inserting the spring to be calibrated, and oiling the piston with cylinder oil, the indicator is to be attached to the indicator cock on the calibrating apparatus. Before putting the card on the in- Fig. 120. — Apparatus for "Dry" Method of Indicator Testing. 1 Some engineers, particularly in Germany, advocate that an indicator should be slightly jarred just before each calibration line is drawn, intending that this jarring is equivalent to the vibrations which an indicator receives when in service on an engine. Since, however, readings are taken with both increasing and decreasing pressures it is doubtful whether this additional work is necessary on an apparatus like Fig. 118. If on the other hand a dead-weight tester like Fig. 119 or the method of comparison with a test gage (page 115) is used, tapping both the indicator and the gage is probably very advisable. ENGINE INDICATORS AND REDUCING MOTIONS 117 dicator drum on which the record is to be made, two approximately parallel and vertical lines should be drawn on it about one-half inch apart, similar to the lines AB and CD in Fig. 121. Meanwhile the indi- cator should be thoroughly warmed if a calibration with steam pressure is to be made. Then with the indicator cock and the valve on the steam pipe E (Fig. 118) closed and the exhaust pipe A open, draw the first calibration line on the card. This should be made by setting the pencil point at D, and then by pulling the cord attached to the drum draw a line crossing the vertical line AB. With springs of which the scale is 40 pounds or less, a similar record should be made for incre- ments of every 5 pounds per square inch change in pressure, while for higher scales the increments may be made 10 pounds. If with in- Na^j?__ Hnur /. '.TC6rd to Indicator 1 i \ r® f— *\ ~™ y !=£ K ooo v oy 1 Piston and pencil indicators are made by the H. Maihak Aktiengessellschaft which give accurate diagrams at from 500 to 600 r.p.m. 142 POWER PLANT TESTING Where p = mean effective pressure on the piston, pounds per square inch; 1 = length of stroke in feet; a = net area of piston in square inches; 1 n = number of revolutions per minute. Of the terms of this equation only one, the mean effective pressure, is obtained from the indicator cards. If we consider now only one end of the cylinder, the steam does work on the piston during a " forward " stroke, and, on the other hand, the piston does work on the steam on the " return " stroke. Hence to get the mean effective pressure for a stroke the average pressure during the return stroke must be subtracted from the average pressure on the " forward " stroke; and this is obviously the same as the average length of all the ordinates intercepted between the upper and lower lines of the indicator diagram multiplied by the scale of the spring. Usually the mean effective pressure is found by means of planimeters, the use of which for this purpose was explained on pages 75 to 86. An engineer should, however, know how to calculate the mean effec- tive pressure of an indicator di- agram with reasonable accuracy without the use of such in- struments. In such cases the method of ordinates is very con- venient. With suitable drafts- man's triangles 2 draw ordinates perpendicular to the atmos- pheric line at both ends of the diagram as shown in Fig. 165. Lay off on the edge AB of a piece of smooth flat paper, a scale of ten equal divisions so chosen that the total length of the ten divisions is a little greater than the length of any of the indicator diagrams. This scale should then be placed ob- liquely across the diagram to be measured, so that the beginning and end of the scale will be located on the ordinates at the ends of the dia- gram. Now mark the diagram opposite the divisions of the scale with fine points, and at the middle of each of these divisions draw ordinates across the breadth of the diagram. The sum of the lengths of these 1 In all piston engines the area of the piston rod must be subtracted from the area of the piston on the side where the rod reduces the area effective for the action of the steam or other working substance. 2 Triangles to be used for this purpose should be tested for accuracy by setting on a straight edge and drawing a vertical line. Then turn over the triangle and observe whether the line drawn coincides with the edge of the triangle. Fig. 165. Diagram illustrating Method of* Mean Ordinates. ENGINE INDICATORS AND REDUCING MOTIONS 143 ordinates divided by ten gives the value of the mean ordinate, 1 and this when multiplied by the true scale of the spring gives the mean effective pressure. Some time can be saved in summing the ordinates if they are transferred with dividers one after the other to the edge of the strip of paper. The total length laid off divided by ten is then the mean ordinate. The Engine Constant for Indicated Horse Power. In the use of equation (25), page 141, where . , plan i.h.p. = - , 33>ooo' considerable time can usually be saved when calculating engine tests if- the terms r^— > (26) called the engine constant which always remains constant for each end of the cylinder, are first computed carefully and then used as constants throughout the calculations. In other words, the indicated horse power is found for each end of the cylinder by taking the product of the terms, Engine Constant X p X n. Indicated Horse Power of Rotary Engines. Fig. 166 shows by a simple diagram a typical rotary engine. The steam inlet is at I and Fig. 166. — Diagram of Typical "Rotary" Engine. the exhaust is at E. A sliding blade P, corresponding to a piston, moves back and forth through the rotor R, as the latter revolves. In the figure P is shown at the point of cut-off, the dotted shading indicating the full charge of steam. Equation (25) can be written, 2 pn 33,000 volume swept through by piston f — j-^— '■ j 1 Methods of calculating areas of irregular figures are given on page 74. The area divided by the length gives the mean ordinate. 2 In equation (25) 1 is in feet and a in square inches. The volume in cubic inches must therefore be divided by 12 to permit substitution in the equation. 144 POWER PLANT TESTING A hole should be tapped through the casing near the top for the attach- ment of an indicator to determine the mean effective pressure (p) through- out the cycle. This hole can also be used to determine, by filling with water, the maximum volume in the cycle (method explained on page 293) , and these data together with the number of revolutions per minute (n) serve "or calculating with considerable accuracy the indicated horse power. The steam consumption per i.h.p. per hour for all types of such engines, if well made and when new, is about 100 to 125 pounds. It is difficult to take up wear in such engines, so that after use for a short time much steam leaks through without doing work. Speed Counters. Some kind of mechanical counter is ordinarily used for determining the speed of engines and of other machinery with re- volving shafts. For the usual services in testing, a hand speed counter Fig. 169. — Starrett's Differential Speed Counter. (Fig. 1 69) is considered most reliable. 1 It is generally applicable, inex- pensive, and accurate, so that every engineer should have one. For slow-speed engines some type of fixed counter (Fig. 170) is fre- Fig. 170. — Integrating Engine Counter. quently provided for attachment to the gage board in the engine-room. For gas engines operating by a " hit and miss " method of governing such fixed integrating counters are used in many places for counting the 1 Starrett's hand counters are generally preferred both in America and abroad. ENGINE INDICATORS AND REDUCING MOTIONS 145 number of explosions. Actually the number of times the gas valve opens is counted. The greatest trouble with counters of this type is that they will sometimes " stick " even at the normal speeds of stationary engines. Schaeffer & Budenburg make a pointer and dial revolution counter (Fig. 171) which is suitable for observing high speeds. Tachometers, operated centrifugally (Figs. 172 and 173) or by the vibrating reed method (Figs. 174 and 175) are not accurate enough for the determination of indicated or brake horse power. They can be used conveniently, however, for observing roughly variations in the speed of steam turbines or electric generators when no accurate results are to be calculated from the observations. The vibrating reed type operates by being placed on the frame of the machine and the reed Fig. 171. - Belt-driven Speed Counter. "G^ Fig. 172. — Hand Type of Centrifugal Tachometer. Fig. 173. — Sleeve and Weights in Centrifugal Tachometers. which is most nearly in synchronism with the vibration of the machine indicates by its excessive vibration the speed on a calibrated scale. Belted tachometers because of the added uncertainty regarding the slip of the belt are particularly unreliable. Fig. 174. — Details of Vibrating Reed Tachometer. Electro-magnetic tachometers depend for their operation on the inten- sity of the magnetic drag due to flux generated which is proportional to the speed. They are simple in construction, but rather delicate for commercial service and the temperature correction is usually difficult to compensate. 146 POWER PLANT TESTING Fluid tachometers are essentially small centrifugal pumps discharging a colored liquid (usually alcohol colored red) into a vertical glass dis- charge pipe. The blades of the wheel are radial so that the instrument registers the same when running in either direction. The greater the speed the higher the liquid will stand in the tube. Since the height to Fig. 175. — Commercial Form of Vibrating Reed Tachometer. which the liquid will be forced in the tube varies approximately as the square of the speed of the wheel, the upper part of these tubes has a very much more open scale than near the bottom where accurate observations are difficult. Speeds less than 300 or 400 r.p.m. cannot be satisfactorily observed with such instruments. CHAPTER VI MEASUREMENT OF POWER — DYNAMOMETERS A dynamometer, according to its derivation, is an instrument for measuring force or " power." These are of two kinds: 1. Those absorbing the power by friction and dissipating it as heat. 2. Those transmitting or passing on the power they measure, thus wasting only a small part in friction. Absorption Dynamometers (Prony Brakes). Of the class of dyna- mometers in which the power received is all absorbed in friction, the type generally used is called a Prony brake, named for Rev. John Prony, who many years ago developed a device of this kind for measuring power. 1 One of the simplest forms is shown in Fig. 180. It consists of a lever A, from which a weight w is suspended from one end, and a block B, supported on a revolving drum or pulley, is at- tached to the other end. A strap to which wooden cleats are fastened is held in place and tightened by the thumb-nuts N, N. When the friction on the strap and block just balances the weight w, the lever arm A is horizontal and the apparatus is in adjustment. Stops, marked S S, are provided so as to limit the movement of the lever arm. When the brake is adjusted or " balanced," the work done in a given time in producing the friction (the power absorbed) is measured by the weight moved multiplied by the distance it would pass through in that time if free to move. Then if, r = length of brake arm in feet. 2 n = revolutions of the shaft per minute. w = weight on the brake arm in pounds. • Brake Horse Power (b.h.p.) =— .27) 1 Strictly speaking, a brake of this kind does not provide means for directly measur- ing power, as, for example, horse power, because the element of time is not indicated. In other words, it measures the tangential force, of which a couple (torque) in linear- weight units, such as foot-pounds, can be computed. 2 The length of the brake arm is measured by the perpendicular distance from the line of action of the weight w to the center of the wheel. When the arm A is horizontal, as in Fig. 180, the length of the brake arm is usually measured by the horizontal dis- tance from P to a line passing through the center of rotation perpendicular to the arm. 147 148 POWER PLANT TESTING In equation (27) the fraction is a constant quantity for a given 33,ooo brake and is called the brake constant. When a brake like the one in Fig. 180 is used the effective weight of the brake itself as weighed at the point P must be added to the weight w. According to Bach suitable dimensions for a brake of this type are given by bd = ■ * ■- where d is the diameter of the brake pulley in inches, b is the breadth of the brake blocks in inches (usually about 1.5 times the diameter of the shaft), b.h.p. is the brake horse power to be absorbed, k is § for air cooling, and varies from 2.5 to 5 for water cool- ing as the speed increases. 1 Steel Band Fig. 180. — Simple Prony Brake. A very common variation of the Prony brake is illustrated in Fig. 181. The block B in the preceding figure is replaced by a series of narrow cleats of maple or oak. Rotation being in the opposite direction from that in Fig. 180, the knife-edge at E on the arm A will now press on the pedestal T, and the weight w can be determined by weighing the pressure on a platform- scales S. Since the scales receive not only the pressure due to the force producing friction, but also that due to the weights of the brake and of the pedestal, these weights must be determined and are to be subtracted from all of the readings of the scales to obtain the net weight w for sub- stitution in equation (27). Weight of the brake and the pedestal, called the, zero reading, must be obtained with the brake strap slack, so that the block B will rest as lightly as possible on the pulley. With small engines this zero reading is obtained most accurately by observing the weights on the scales when the brake pulley is turned around by hand first in one direction and then in the other. In this way we obtain for both the brake and pedestal, with rotation in one direction the weight plus the friction due to their own weight, and with rotation in the other direction the same weight minus the same friction. Half the sum of 1 For information regarding the designing of Prony brakes for absorbing large powers the reader is referred to Engine and Boiler Trials, by R. H. Thurston, pages 260-279. MEASUREMENT OF POWER — DYNAMOMETERS 149 the two readings is, therefore, the weight corresponding to the pressure on the scales due to gravity alone. With large engines it is sometimes difficult to turn them uniformly by hand, so that the zero reading must be obtained by some other method. This is done usually in practice by placing a very small rod on D (Figs. 180 and 181) ver- =^ I Fig. 181. — Prony Brake with Platform Scales. tically over the center of the shaft. Then if the strap is loose and due care is observed, the pressure on the scales can be obtained with sufficient accuracy without rotation. The cleats are attached to the bands by wood screws inserted from the outside and countersunk into the bands. Screws used for attaching the cleats to the upper block are inserted through the cleats and countersunk into the wood. At least \ "Rough and Ready" Prony Brake. inch spaces should be left between the cleats to permit air circulation. In all such constructions for dynamometers screws and nails should not touch the rubbing surface as they are likely to cause the friction to be variable and the sound produced is objectionable. Many designers cut grooves into the inside surface of a few of the cleats. These grooves are to be filled with thick grease for lubrication. A similar arrangement to Fig. 181 is shown in Fig. 182, showing maple 150 POWER PLANT TESTING Fig. 183 cleats screwed to a leather belt. A piece of old belting is ordinarily used for this purpose so that by this method a very inexpensive Prony brake can be made quickly in any power plant. It has also the important advantage over the two preceding types in that it is readily adjust- able to different sizes of pulleys. Washers should be provided for the heads of the screws used to attach the cleats to the belt. If the inside surface of the pulley can be satisfactorily cooled by water the rubbing surface of the cleats need be not more than five square inches per brake horse power at peripheral velocities not over 2,000 feet per minute. For a velocity of 5,000 feet per minute about 10 square inches per brake horse power should be allowed. Another form of Prony brake is illustrated in Fig. 183, called a strap brake. It is made up merely of a band of steel or leather or of strands of rope placed over or wrapped around a suitable pulley. 1 In this case weights must be suspended from both sides of the brake wheel or pulley. In the case of the strap brake, Fig. 183, the net pull, corresponding to the weight w, in equation (27), page 147, is Wi — w 2 . Now the same relation would hold if, as is often done, a spring balance is fastened to the floor on say the left-hand side; the pull registered by the spring balance would then be W1, 2 and the net pull is, as before, Wi — w 2 . 1 It is desirable to use for Pony brakes pulleys of which the section of the face is a double " U," like Fig. 184. The outside rims are for keeping the brake in position on the pulley and those on the inside for receiving a small stream of water played upon the inside of the pulley. This stream of water by its evaporation will assist materially to dissipate the heat generated. Such brakes are often operated with pipes arranged to discharge water into the pulley and another pipe to carry it away. This is an ex- cellent system provided the latter pipe is used only to carry away a little overflow, but if so much water is used that there is practically no " steaming," the inside rim of the pulley will fill up with water to be spattered around in every direction as well as over the face of the pulley, where it is particularly objectionable, as it produces variable friction. 2 To the pull (wi) must be added, however, the weight of any hooks placed be- tween the end of the strap or rope and the spring balance; and if the balance is for any reason suspended in the inverted Dosition the weight of the balance itself must also be added. MEASUREMENT OF POWER — DYNAMOMETERS 151 Brake horse power is calculated then by equation (27), substituting for w the net pull Wi — w 2 , so that 2 7rrn (wi — w 2 ) (b.h.p.) (28) 33,000 where r is the radius of the pulley plus half the thickness of the strap, in feet, and n is the number of revolutions per minute. This type of strap brake is very accurate and sensitive, but is suitable only for low powers. About the same friction surface must be allowed as for wooden blocks in Bach's formula. I : Fig. 184. — Special Pulley for Brakes. Rope brakes, 1 like the one shown in Fig. 185, are much used for " com- mercial testing " of engines, as they are easily portable or can be made quickly at a small expense from materials always at hand. Moreover, they are self-adjusting, so that accurate fitting is not required. One of this type consists of a rope doubled around a pulley or fly-wheel on the shaft transmitting the power to be measured. As the friction at the rim of the pulley increases, the tendency will be to lift up the weight Wi. The effect will be to reduce the tension in the end of the rope overhead connected to the spring balance and thus prevent a tendency to further increase of the friction. Several U-shaped distance pieces of wood, preferably maple, are provided to prevent the rope from slipping off the pulley and to keep the parts of the rope sepa- rated. These distance pieces should be attached to the rope by soft iron or copper belt lacing, drawn in from the outside of the wooden pieces 1 Sir William Thomson (Lord Kelvin) invented in 1872 the first rope brake of which we have any record. Although he utilized this device as a friction brake, it was not used by him as a dynamometer. 152 POWER PLANT TESTING through the center of the rope, instead of being fastened with screws or nails on the inside, which will heat to a high temperature and then char the rope. Sometimes such fastenings when of hard metal will cut grooves into the surface of the pulley. In this arrangement the spring balance must be supported from some point overhead. An anchoring rope or safety stop securely attached to the weight w x should be provided to prevent the weights going over the wrong way Fig. 185. — Rope Brake. when starting or stopping an engine in case the valve is not very well set. Its weight or the weight of that part suspended from the weights must be included in Wi. Similarly the weight of the rope between the spring balance and the point where it touches the pulley should be de- ducted from the readings of the spring balance in accurate work. Spring balances require frequent and very careful calibrations. A modifica- cation of practically the same rope brake is shown in Fig. 186, where the rope is fastened at the top and bottom to a frame resting on a plat- form scales. MEASUREMENT OF POWER — DYNAMOMETERS 153 Equation (28) is used also for calculating the brake horse power for a rope brake, except that r becomes the radius of the pulley or brake wheel plus half the diameter of the rope. All in feet. Rope brakes are best arranged with the rope placed on the pulley double as in the figures so as to form a loop for supporting the weights. A brake made in this way of double f-inch rope and provided with six cleats each of about ten square inches of rubbing surface will absorb fifty horse power if the pulley carrying the brake is about three feet in diameter, and the speed is not over 300 revolutions per minute. For absorbing smaller powers half-inch rope with 4 cleats can be used. Fig. 186. — Rope Brake with Standard. Manilla or cotton rope is generally preferred. By steeping the rope in a mixture of deflocculated graphite and melted tallow its frictional prop- erties are improved. Water- jacketed Bands. A very good method of putting a brake on a wide wooden pulley is shown in Fig. 187. Outside of the steel band is a similar band of rubber and canvas. Canvas and steel bands are riveted along the edges, making the space between the canvas and steel a water- tight compartment. Connections are made with the water supply and drain at the ends of the brake strap by means of flexible hose, and a cur- rent of water is kept circulating round the wheel, quickly removing the heat generated by friction. The brake strap may be of almost any width, 20 inches being that used by Professor Goss. The face of the pulley must be cylindrical and not rounded, and any inequalities in the face should be made good 154 POWER PLANT TESTING before proceeding to use it. Especially is this the case at the joint in split pulleys, and if any space between the halves is left at all, this should be filled with glued wooden plugs. The thickness of a steel band used on a pulley 24 inches in diameter was No. 12 gage. A layer of rub- ber should be inserted at the joints between the canvas and steel band, so as to ensure a good joint, and special cast-iron ends are usually riv- eted to the brakestrap and fitted with water connections. Fig. 187. — Water-jacketed Band for Brake. A somewhat similar brake has been used at the Pennsylvania State College, consisting of a flat strap with both sides made of copper. It is applied to the fly-wheel, much in the same manner as the Prony brake. The ends are coupled together by an adjustable screw. The pressure of the brake strap on the wheel is produced and regulated by water flowing through the tube, much in the same way as in the Alden dynamometer (page 155). If the wheel surface is maintained in a well-lubricated con- dition, the wear of the copper tube is inappreciable. In a modified form of this brake a thin metallic band is interposed between the copper tube and the wheel, and consequently no wear of the tube takes place. Fan Brakes or Dynamometers. For determining the power of high- speed engines a dynamometer consisting of two flat fan blades arranged Fig. 188. —Fan Brake. to be attached to the engine shaft is very convenient. Power is ab- sorbed by the " fan " action of the plates on the surrounding air. MEASUREMENT OF POWER — DYNAMOMETERS 155 Tr / 65 1 i / / GO i ii / / • 10 J H B ;uh:s ztt Ui / •> fi n // tt II ii / " V // U- II 7/ 01 ^/s/il Ui II / / R r 1 zr ' hit / ZL 77 ~7zm' ~N- zz ///// lU- Kz 7 ^ / , Zp '//, /-■ ^ y 1U £&. 50" d — SSsSp-~ R.^.M. Amount of power absorbed by fan blades depends (1) on the size of the blades, (2) their distance from the center of rotation, and (3) on ap- proximately the cube of the number of revolutions per minute. Fig. 1 88 shows a somewhat elaborate testing-base for automobile and marine engines. The engine is connected by means of a universal coupling C to the shaft S to which the fan blades E are attached. The frame Q is for supporting the engine. A tachometer J is used to indi- cate the approximate speed. The fan is shown enclosed in a glass frame-work M to prevent the air currents from other engines, etc., from interference with the discharge of air from the fan blades. Fig. 189 shows typical calibration curves for the fan in Fig. 188. Fans for this purpose are usually calibrated by at- taching them to a variable-speed elec- tric motor of which the efficiency curve is known. For appropriate work a fan built as shown in the figure can be used for testing and even without the casing M the curves will show satis- factory values of power with a prob- able error of less than three per cent. The blades are ten inches wide in the radial direction, fourteen inches wide in the axial direction, and § inch thick. Numbers on the curves indicate inches from the center of the shaft to the middle of the blades. This distance can be varied by shifting the bolts. The speed to be used in accurate calculations should be taken on a high-speed engine with a good hand- counter. Alden Brake. An entirely different type of absorption dynamometer is the Alden brake, illustrated in Fig. 190. In this apparatus the rubbing surfaces producing the friction neces- sary for absorbing the power are separated by a film of oil, and the heat generated is carried off by a stream of water circulating as indi- cated by arrows. It consists of a disk of cast iron A, which is connected to the shaft S, transmitting the power. This disk revolves between two thin copper plates E, E, fastened together at their outer edges to form a shallow cylinder which is filled with a bath of heavy (cylinder) oil. Water under pressure is discharged into the chamber adjoining the copper plates and any increase in pressure causes the copper plates to press toward the cast-iron plate A with more force. The friction of the thin film of oil between these copper and iron plates tends to turn those of copper, but as they are rigidly connected to the outside casing C carrying the brake arm P, the tendency to turn can be determined by 2C0 400 000 800 1000 1200 1400 1000 1S00 Kesulting Curves from on Actual Calibration of a Fan Dynamometer Fig. 189. — Curves for Fan "Brake in Fig. 188, with 10" X 14" Blades. 156 POWER PLANT TESTING weighing as with a Prony brake. To maintain the moment of resistance constant under all circumstances the pressure and consequently the flow of water into the casing is automatically regulated by a cylindrical valve V, which becomes partially closed if the brake arm moves above a certain horizontal position. This valve is shown in section in Fig. 191. The end at W is connected to the water main and the other end Y to the brake casing by means of a right-angled bend R (Fig. 190). Water enter- ing by the pipe W passes through the ports N and then through the ports H into the pipe Y. Now a small angular movement of the pipe Fig. 190. — Alden Brake. W, relative to the pipe Y, will open or close the ports H and thus reg- ulate the supply of water. These ports are very narrow, so that a very small angular motion is sufficient to close them. By making the outer casing of the valve of rubber it is found to be sufficiently flexible to permit moving the valves and at the same time it offers very little resistance to the movement of the casing. Reynolds-Froude Dynamometer. Professor Osborn Reynolds has designed a modification of the Froude brake which is shown in section in Figs. 192 and 193. This device has a very large capacity for absorb- ing power. One of these brakes with a single rotor only 30 inches in diameter will absorb 700 horse power at 200 revolutions per minute. MEASUREMENT OF POWER— DYNAMOMETERS 157 Fig. 191. — Regulating Valve in Alden Brake. M L ;x /yi £# ^ tkUQ- j i ^ ^yZy ?h5 i T i b^ n vj Fig. 192. — Reynolds-Froude Dynamometer. " M Fig. 193. — Reynolds-Froude Dynamometer Shown Dia- grammatically. Water is supplied to the apparatus through the flexible pipe marked E (a rubber hose is very satisfactory) from which it passes in the direction of the arrows into the space H, (Fig. 193), then into the centers of the vortices through the holes J (shown dotted) which are drilled 158 POWER PLANT TESTING through the walls of the pockets. From these pockets the water passes between the rotor and the casing into the space M from which it dis- charges through the discharge outlet D into the drain. If any air collects in the center of the vortices it can escape through the holes I in the pocket walls in the casing into the cored channel L and the air outlet pipe O. If any water comes through these passages with the air it is carried off through a funnel and pipe emptying into the main discharge pipe D. The brake horse power (b.h.p.) for this dynamometer is expressed on a very conservative rating by the equation b.h.p. To^ n2dD > where n is the number of revolutions per minute and d is the diameter of the rotor in inches. Water Brakes. Power can also be absorbed by moving in water a rotor similar to those in steam turbines. Such an apparatus is called a turbine water brake. A good example is shown in Figs. 194 and 195. Fig. 194. — Westinghouse Water Brake. It is the type used by the Westinghouse Machine Company of Pitts- burg for testing the power of large steam turbines. It consists of a rotor R, mounted on a shaft S, S, of which one end is arranged to be connected directly by means of a coupling to the shaft of the turbine or engine to be tested. This rotor revolves within a closed casing Z, supported on the journals J, J, through which the shaft passes. Around the periphery of the rotor there is a series of rows of vanes which when revolving tend MEASUREMENT OF POWER — DYNAMOMETERS 159 to give to any water contained in the casing a rotary motion. Between every two rows of vanes on the rotor there is fitted a row of stationary vanes attached to the inside of the casing. This arrangement is illus- trated diagrammatically in Fig. 195, where the cross-hatched sections represent the stationary vanes and the " solid " sections the moving vanes. The tendency of the moving vanes to produce this rotary motion of the water is, as it were, resisted by the stationary ones, and this action develops a very large amount of heating, due to fluid friction in a manner analogous to the operation of a Prony brake or any other absorption dynamometer. As a result of this friction a force is developed tending to turn the casing in the direction of motion of the rotor. The casing, however, is prevented from turning by a radial arm bearing down on a platform scales. The intensity of this tendency to turn can be regulated as in the Alden brake (page 155) by adjusting the valves controlling the flow of water through the casing. The vanes on the rotor are of the 8-3 fT eaa ^ eza VT era fZ r w r $k~-%;-WM-fc ■% fc £ £ ^.m^ n c £ - £ Fig. 195. — Vanes of Westinghouse Water Brake. same kind as used in steam turbines and have the function of imparting a high velocity to the water flowing through them in an axial direction. Water enters the casing through the inlet pipes C, C (Fig. 194), discharg- ing a stream from both sides of the casing toward the central portion of the rotor. At the middle of the periphery of the rotor there are a number of slots or ports A, A, A, A through which the water discharges to the right and left, passing first through a broad central row of stationary vanes shown in Fig. 195. Escaping from these vanes it is picked up by the rows of moving vanes on each side, which give it a high velocity and, in turn, discharge it into the adjacent rows of stationary vanes where the velocity just acquired is checked, and so on across the face of the rotor, the moving vanes adding velocity only to be lost in the next row of sta- tionary vanes. From the last rows of moving vanes the water is dis- charged into semicircular passages B, B', which direct the flow of water into the center of the rotor when the cycle is repeated. The water brake illustrated here was designed for high powers, so that a number of rows of vanes was necessary. For small powers of, for example, from 200 to 160 POWER PLANT TESTING Fig. d d 196. — Simple Water Brake. 500 horse power, not more than two rows of moving vanes with the corresponding number of stationary vanes would be required. 1 Power absorbed by a water brake is calculated in the same way as for an ordinary Prony or rope brake. In the operation of the brake the water is quickly raised to the boiling- point and a considerable portion evaporates, carrying off as steam very large quantities of heat. Vents for the escape of this steam are indi- cated by D and D' in the fig- ure, showing the cross-section of the brake. Unless consid- erably more water, however, was admitted to the casing than was required to replace that lost by evaporation, the action of the brake would be more or less irregular, so that an excess of water is supplied and there is a constant dis- charge of hot water through the passages marked E and E'. Another type of water brake is shown in Figs. 196 and 197 which is also used for testing engines and turbines. 2 The revolving paddle wheel or " runner " R is designed to run in very close clearance with the serrated rim piece P. The outer casing is rigidly attached to the lever arm A made of such a length as to facilitate rapid calculation. A little roller or wheel W on the end of this arm rests upon the plat- form scales used to weigh the load. Water is admitted through a flexible hose connection at the opening I and from there enters the interior of the wheel. When the wheel is revolving this water is thrown out by centrifugal force through small holes drilled in the rim, entering into the outer teeth spaces. In this passage of the 1 To calculate the resistance of such vanes see " The Steam Turbine," by the author, pages 115-125. 2 A very satisfactory water brake is also made by the Michigan Motor Specialties Co., Woodbridge Street, Detroit. It has an extensive sale for automobile testing. Fi<; Section of Brake shown in Fig. 196. MEASUREMENT OF POWER — DYNAMOMETERS 161 water a considerable fluid resistance is produced. The water finally es- capes after passing through this tortuous passage through the close clear- ance around the outside of the wheel and discharges through the pipes connected at D. Webb's " Viscous" Dynamometer, Fig. 198, consists of a number of flat steel plates Pi (circular saw blanks are excellent) fastened to a hub H which is keyed to the driving shaft S. Between these plates on the shaft are other plates P 2 rigidly attached to the casing C. When a liquid is put into the casing the rotating plates Pi tend to carry it around with them by the action of viscosity, and the turn- ing moment of the shaft S is commu- nicated to the fixed plates P 2 and to the casing. The casing is supported on pedestals E provided with ball- bearings. The turning moment on the casing is balanced by weights placed on a horizontal arm as ar- ranged for the Alden dynamometer (Fig. 190) or may be set up so as to press on a platform scale as in Fig. 181. The latter method is probably the better. Water is most commonly used as the liquid. It enters through the funnel F near the center of the casing and leaves at the discharge pipe D. A flow of liquid is maintained which carries away the heat generated. The power absorbed varies as the cube of the speed and the fifth power of the diameter. The frictional or " viscous " resistance can therefore be varied by adjusting the depth of the water in the casing. Usually a number of holes are made in both sets of plates through which water can pass to the discharge con- nection without having the casing filled to the tips of the fixed disks before overflowing to the next compartment. The quantity of water in the casing can be regulated by both the inlet and discharge valves. It is generally best to adjust both valves at the same time for large variations in load. Viscosity of the water decreases somewhat with rise of temperature of the water. Professor Webb has also arranged in some of his designs to supply the water through a hollow shaft and regulate the supply by a piston valve to be adjusted axially to supply a varying number of compart- ments. Fig. 198. Webb's "Viscous" Dyna- mometer. 162 POWER PLANT TESTING Regulation is accomplished not only by varying the radial depth of the water but also by changing the number of compartments containing water. In this latter arrangement no holes are required in the fixed or stationary plates to permit draining. Discharge connections are pro- vided for each compartment so that there are as many drain pipes as compartments. The dynamometer starts easily and without load so that it is better suited for use on steam turbines than those of the Alden and Froude types. The steel plates are the only parts subjected to high centrifugal stress and they are strong enough for all practicable speeds. This apparatus is not large for the power absorbed. One of these dynamometers provided with two disks, each two feet in diameter, absorbed 180 brake horse power when running at 2500 revolutions per minute with a radial depth of three inches of water, and with one inch of radial depth of water 60 horse power can be absorbed. Brake horse power (b.h.p.) absorbed by each rotating plate is approximately b.h.p. n 3 (r 2 5 - ri 5 ) 130,000,000 where n is the revolutions per minute, r 2 is the radius of the moving plate in feet and r x is the inner radius of the annular ring of water in the casing. Dynamos (Electric Generators and Motors) as Power Dynamometers. One of the most convenient means for measuring the power of high- speed engines and turbines is to con- nect an electric generator to the main shaft as in Fig. 199. Then if the effi- ciency of the generator is known at the particular speed and output at which it is to be operated, a very ac- curate method of measuring the power of the engine or of any other type of motor becomes readily available. The output of the generator should be de- termined by observations of the volts and amperes with carefully calibrated portable instruments. Remembering that for direct-current generators volts times amperes gives watts and that 746 watts are equivalent to one horse power, then if e.h.p. is the horsepower output of the generator we have ^ Fig. 199. — Electric Generator used as Power Dynamometer. e.h.p. volts X amperes 746 MEASUREMENT OF POWER — DYNAMOMETERS 163 It is not unusual to hear this result called the " Electrical " horse power of the engine or turbine. 1 The actual horse power delivered to the generator is, of course, the brake horse power, and into this result the efficiency of the generator enters. Thus, for direct- (or continuous) current generators , volts X amperes * p ' 746 X efficiency of generator * The load on the generator should be maintained uniform by absorb- ing the electrical output in lamp or wire resistances for small powers but for larger powers a water resistance or rheostat is generally used. Electrodes are generally made of \- to ^-inch iron or steel plates, allow- ing about 1 square inch per ampere. As a rule electric motors are very serviceable in mechanical engineer- ing laboratories as power dynamometers. The efficiency is easily ob- tained, the usual method being to determine an efficiency curve for varying power inputs by a Prony brake test. This efficiency is Efficiency of motor = ' , e.h.p. where e.h.p. is the " electrical " horse power input, as measured with voltmeters and ammeters. If then a pump, air compressor, ventilating fan or a similar machine is to be tested by the electrical method, it should be direct-connected to the shaft of the motor, and its efficiency E will be u.h.p. E = e.h.p. X efficiency of motor' where u.h.p. is the useful work done by the machine, in horse power. This last method serves also as a convenient method for obtaining the efficiency of generators, since by connecting it directly to the shaft of a motor previously " calibrated " (for efficiency) the electrical out- put of the generator and the input to the motor are readily deter- mined. When a so-called variable-speed motor is used as a dynamometer, its efficiency must be determined at the particular speed and power at which it will operate when driving the machine to be tested. Eddy-current Brakes 2 are built with a number of electro-magnets and one or more copper disks. Either the coils or the copper disks may be 1 When an alternating-current generator is used the power factor must also be measured with a suitable instrument. In this case, the actual e.h.p. is (volts X amperes X power factor) -5- 746. 2 For more information regarding the design of this type see "Eddy-current Brakes" in Journ. Inst. E. E., (London) vol. 35, (1904-5). 164 POWER PLANT TESTING rotated with the shaft while the other is held stationary. Eddy cur- rents generated by rotation with the electro-magnets excited produce a resistance of which the moment is measured by a lever arm and scales as with similar forms of dynamometers. Transmission Dynamometers. Instruments of this type are used to measure the amount of power transmitted without absorbing any more power than is absolutely needed to move the dynamometer. Goss Belt Dynamometer. One of the simplest forms of transmission dynamometers, designed by Professor W. F. M. Goss, is illustrated in Fig. 200 by a line drawing. Being so simple in construction, it can readily be made in any factory or workshop with the materials available. It is essentially a differential lever measur- ing the difference in tension between the two sides of a belt. This lever is pivoted at the point D and to it are attached the shafts carrying the pul- leys A and B. Weight hangers are at- tached to the ends of the beam. The beam and hanger must be balanced to be in the horizontal position, that is, in the position of equilibrium when the belt is not moving. Power trans- mitted is measured by the product of the speed of the belt and the differ- ence in belt tension between the two sides of the dynamometer. The force tending to raise the left- hand end of the lever is to be twice the tension ti of the tight side of the belt, while that raising the right- hand side is twice the tension t 2 in the slack side of the belt. These tensions on the two sides of the lever can be measured by weights Wi and w 2 suspended from the hangers. The force tending to rotate the lever is therefore twice the difference in tension on the two sides of the belt 2 (ti — t 2 ) and this force acts with a leverage AD = DB = r, when these two arms are made equal. If now the distance from the pivot D to the point of support of the weight Wi is made twice AD = 2 r, and if the weight Wi is made equal to the difference in the tensions it will balance the lever. For these conditions, taking moments about D, Wi X 2 r — 2 tir + 2 t 2 r = o, 2 Wi = 2 (ti — t 2 ), Wi = ti - t 2 . 2ji ^ Fig. 200. — Goss Belt Dynamometer. MEASUREMENT OF POWER — DYNAMOMETERS 165 Now in any transmission system the difference in the tension of a belt or a rope on the two sides of a driven pulley multiplied by its speed is a measure of its power. If, then, d is the diameter of the driven pulley C, plus the thickness of the belt or rope in feet, n is the number of revolutions per minute of this pulley, and Wi is the weight in pounds on the left-hand side required to balance the lever; when power is transmitted, then, Horse power transmitted = l (20) 33,ooo To reduce the vibrations of the apparatus a dash-pot is connected to the right-hand side. To prevent excessive movement of the lever when unbalanced, stops are placed above and below the lever on the left- jiand side. Another form much used for mill purposes and fan testing is the belt dynamometer, shown in Fig. 201. The driving pulley is A and the driven pulley is B. The connecting belt passes over the pulleys C and D. Fig. 201. — Compact Belt Dynamometer. These two pulleys are mounted on the frame of the dynamometer carry- ing a scale beam A, all of which turns on the center of support. The dif- ference in the total stress on the two sides of the belt is computed by multi- plying the net weight on the beam by the equivalent leverage, the latter being found by dividing the length of the beam by the distance from the center of support to the centers of pulleys C or D. Differential Dynamometers. The apparatus illustrated in Fig. 202 is typical of a number of dynamometers indicating by means of a differ- ential lever operated by gearing, the amount of power transmitted. 1 This is a very common form of transmission dynamometer. Power is received from the motor (or engine) by the shaft A, which is connected only indirectly by means of gears to the shaft A' opposite, which trans- mits the power to the work. To the adjoining ends of these shafts bevel wheels B and D are attached. The lever L turns on an axis concentric with the shafts A and A', in a plane perpendicular to them. It carries 1 Similar forms of differential dynamometers are known as White's, King's and Bachelder's. The first instrument of this kind, it is stated, was invented by Samuel White in 1780. These dynamometers are sometimes called epicyclic, signifying "wheels traveling around a circle or around another wheel." 166 POWER PLANT TESTING bevel wheels C and Ci, gearing with B and D, through which the power is transmitted. There is a tendency then for the left-hand end of L to go downward and for the right-hand end to rise. If, furthermore, the lever L were permitted to revolve, no work would be transmitted from B to D, and therefore D would remain stationary. As these gears are usually proportioned so that B revolves with half as many revolutions in a given time as L, a force applied at B at a given radius from the center will balance a weight twice as large at the same radius on the lever L. Weight Shaft to Work. Fig. 202. — Typical Differential Lever Dynamometer. Then the moment of the force applied to the lever L to balance it must be twice as great as the moment of the force transmitted from either C or Ci to D. That is, the sum of the moments applied to C and Ci must equal the moment applied to B. If, therefore, 1 is the length (feet) of the arm at which the weight w (pounds) is applied, and n is the number of revolutions per minute of the shaft A, then the power transmitted PER MINUTE = (foot-pounds), (30) and Horse power (h.p.) = xlnw 33,000 (3i) MEASUREMENT OF POWER — DYNAMOMETERS 167 Now if the lever L is to be prevented from turning about its axis, a couple will be required which is twice the driving couple being trans- mitted. If, then, a weight of w pounds sliding on L as shown in the figure is placed at a distance 1 feet from the axis, so that the lever remains horizontal, the driving couple can be determined; and when the revolu- tions of the shaft A are known, the power can be found. A dash-pot D is usually attached to the differential lever L to reduce vibrations. This dash-pot should always be kept filled with glycerine or good clean oil. If the dash-pot is sticky consistent results cannot be expected. A Webber Differential Transmission Dynamometer as made commer- cially is illustrated in Fig. 203. The scale on the lever arm of this instru- Fig. 203. — Webber Differential Transmission Dynamometer. ment is graduated into 100 divisions and a bell is provided which rings at every 100 revolutions. Since the horse power transmitted in one -n-lnw revolution per minute is equation (31), then the horse power 33,000' corresponding to one division on the scale per 100 revolutions per minute is also for a perfect calibration. 33,000 168 POWER PLANT TESTING It is interesting to observe that if we let v = the vertical force acting at C and Ci; p = the vertical pressure between the teeth at each point of contact; d = distance from the center of the rotation to C and Ci; 1 = the distance from the same center to the weight w. Then from the foregoing discussion it should be clear that 2 v = 4 p and wl = 2 vd = 4 pd. If r is the effective pitch radius of the driving gear wheel B, ri is the radius of the small bevel wheels, and the force pro- ducing the turning movement in the shaft A is represented by f , we have, fr = 2 pri, and , 2pri wlri ' f = -r = idr (32) If we know the number of revolutions, then the space passed through by the force f can be calculated, and the work in foot-pounds is the prod- uct of the force times the distance passed through. The units given above are of course respectively in feet and pounds. About ten horse power can be transmitted and measured by one of these instruments having wheels B and D about ten inches in diameter, when operating at 800 revolutions per minute. 1 Wear on the gears and noise becomes excessive at higher power and speed. Calibration of a Differential Dynamometer. 1. Examine the dash- pot and observe whether the piston moves freely in the cylinder, par- ticularly without " sticking." After the apparatus has been well oiled the position of the poise to make the lever arm horizontal should be observed for " no load." If this is not at zero then all the readings on the scale must be corrected by the amount of this zero reading. 2. At each of the speeds required make a preliminary run without load and observe the reading of the poise when the lever is balanced. 3. Attach a Prony brake to the shaft from which the power is to be transmitted and observe for a series of loads and speeds the readings of the poise on the dynamometer lever. 4. For each speed plot a curve with theoretical foot-pounds per minute by equation (30) as abscissas and actual foot-pounds per minute as determined by the Prony brake as ordinates. Emerson Power Scales. . Another very satisfactory instrument for the measuring of power transmitted by shafting is known as the Emer- son Power Scales. It is illustrated in Fig. 204. It consists of a pulley C keyed to the shaft. To this pulley C a wheel B is connected loosely by studs EE projecting between and bearing against its spokes. The pressure exerted on these studs is proportional 1 S. S. and W. O. Webber, Trans. Am. Soc. M. E., vol. 4, page 227. MEASUREMENT OF POWER — DYNAMOMETERS 169 to the power transmitted by means of the pulley C, and this pressure is transmitted by a system of levers LL and bell-cranks MM to a sleeve A connected to a " weighing lever " W. The sleeve slides loosely on the main shaft. The amount of the pressure exerted on the studs is indicated for small values by a pointer P, moving over a graduated scale F. For pressures beyond the limits of the graduated scale weights are placed on the scale pan N. A dash-pot D is pro- vided to prevent excessive vi- brations and make the pointer " dead-beat." The scale F is calibrated to read the pressure (force) exerted by the torque of the pulleys C on the studs E in pounds. The work or "power" is calculated, therefore, by taking the product of this force times the distance moved through. If d is the diametral distance between the centers of the studs in feet, n the revolutions per minute and w the read- ing of the scales, then, , xdnw Horse power 1 = . 33,000 — Emerson Power Scales. (33) A speed counter is attached to the apparatus for counting the num- ber of revolutions. This apparatus is made by the Florence- Machine Co., Florence, Mass. Flather's Hydraulic Transmission Dynamometers. A form of trans- mission dynamometer which is operated by hydraulic pressure is shown in Fig. 205. The power shaft is keyed to the boss of a pulley B with two or more arms carrying hydraulic cylinders R. Projecting ends or studs from these cylinders bear upon the arms of a loose pulley A on the same shaft. The torque imparted by the driving belt to the loose pulley A is thus transmitted to the shaft S through the liquid, and the resulting pressure is conveyed by radial pipes U to the hollow central shaft, and then to a pressure gage G. The hollow shaft is always filled Compare with (31) for differential dynamometers, page 166. 170 POWER PLANT TESTING with oil. In the figure an engine indicator I is shown attached to the hollow shaft for recording the pressure. The loose pulley A drives the tight pulley B through its pistons which press on the oil in the cylinders carried by the tight pulley. By means of a worm drive the drum of the indicator receives its motion from the central shaft S. Figs. 206 and 207 show more in detail the construction of the hydraulic cylinders on the pulley B. Fig. 208 shows typical indicator diagrams from this Fig. 205. — Flather's Hydraulic Transmission Dynamometer. apparatus. Both were taken from a dynamometer connected to a mining drill. The first was taken when the drill was sharp, the second when it was dull. Among the advantages claimed are: (1) its simplicity, (2) that it is not appreciably affected by the velocity of the shafting, (3) that no countershaft is required, (4) by connecting it to a recording gage a con- tinuous diagram of the load can be obtained. Torsion or Shaft Dynamometers. When a shaft is subjected to a twisting moment an angular twist is produced which is proportional to MEASUREMENT OF POWER — DYNAMOMETERS 171 Fig. 206. — Diagram Showing Pulleys, Pistons, and Shaft of Flather's Dynamometer. Fig. 207. — Details of Pistons and Cylinders in Flather's Dynamometer. -At^iff^ ^\/Y /VA/ V/ r/ K Fig. 208. — Indicator Diagrams from Flather's Dynamometer Attached to a Mining Drill. 172 POWER PLANT TESTING that moment. Thus if 6 is the angle of twist produced by a twisting moment T in inch-pounds and if n is r.p.m., then 2 xTn b.h.p. = — . 12 X 33jQoo Torsion meters, shown in Figs. 209, 210, 211 and 212, although ap- plicable to large as well as small powers, have their most important ap- plications for measuring shaft horse power of marine turbines and engines. A Shaft Dynamometer consists essentially of a long metal tube en- circling the shaft and fastened to it at one end, but free at the other and is maintained in alignment by adjustable rollers; two radial arms, one attached to the shaft and the other to the free end of the tube, which rotate a slight amount with reference to each other, according to the twist of the enclosed length of shaft; and a set of levers which multiply this rotative movement and at the same time convert it into linear motion, which is transmitted to a sleeve and collar mounted, upon the shaft and sliding thereon. These parts all revolve with the shaft. An independent indicating apparatus is provided, which is mounted on a stationary frame, and the sliding movements of the rotat- ing collar is transmitted through it to an index hand. The torsional strain is determined from the reading of the accompanying scale, which is graduated to millimeters. The zero reading is found by disconnecting the propeller and turning the shaft at a slow speed, first in one direction and then in the other, observing the indication in both cases, and fixing the point of zero strain at the mean of the two. When it is impracticable to disconnect the propeller the readings may be taken when the vessel is drifting under her own headway after shutting off steam. The calibration of the instru- ment, which can best be done when the shaft is in the shop before installation, is carried on by securing the shaft in a fixed position, and ap- plying a torsional strain by means of weights at the end of a lever at- tached beyond the dynamometer, taking readings with a number of different weights. The horse power shown by the dynamometer is determined by mul- tiplying the reading of the instrument expressed in millimeters by the number of revolutions of the shaft per minute, and by a constant de- termined from the calibration. The constant is an expression for the horse power corresponding to a speed of one revolution per minute and a reading of one millimeter. A shaft dynamometer requires very delicate adjustment as such instru- ments used on large steam turbines and engines requiring a shaft of com- paratively large size, require a movement at the end of the two arms of only one hundredth of an inch to produce a change of 500 horse power in the load being transmitted. MEASUREMENT OF POWER — DYNAMOMETERS 173 Fig. 209. — Spring Dynamometer. Fig. 210. — Mechanically Operated Shaft Dynamometer. Electro-Magnet Telephone Handwheel N p^- / Receiver with Scale Fig. 211. — Electrically Operated Shaft Dynamometer. Fig. 212. — Shaft Dynamometer with Optical Means of Observation. 174 POWER PLANT TESTING Kenerson Torsion Dynamometer 1 (Figs. 213 and 214) consists essen- tially of a divided shaft with a flanged coupling rigidly fastened to each of the adjoining ends. These io Gage, fl fl T T E Jj. flanges are only loosely con- nected by stud bolts and "latches." The latter are twisted by the power impressed so that their ends are forced against a pressure plate. The pressure against this plate is a measure of the power trans- mitted. Ball-bearing races attached to a diaphragm covering an oil chamber communicate this pressure or thrust to a chamber in which the pressure is indicated by a Bourdon gage. Readings must be corrected for static head if the gage is placed above or below the couplings. The accelerometer shown in Fig. 215 is used a great deal in automobile testing. From the indications of this instrument in terms of acceleration 213. — Kenerson Dynamometer. Fig. 214. — Parts of Kenerson Dynamometer. the power developed can be computed. 2 This instrument is designed on the principle that a pendulum hung on a moving body will be in a vertical position when at rest and moving uniformly. In the figure D is a copper disk pivoted on a rotating vertical axis, M is a magnet for dampening the move- ment of this disk, and G shows two gear wheels of equal diameter, one fastened to the axis supporting the disk and the other on a separate axis carrying the needle N. A coil spring brings the needle back to zero. One side of the disk D is heavier than the FlG - 215.— Acceler- other, so that when the acceleration takes place in 1 Transactions American Society of Mechanical Engineers, vol. 31 (1909), pages 171 to 179. 2 Internal Combustion Engineering, (London), Oct. 2, 1912, and Engineering, Sept. 16, 1910. .Direction cf Motion MEASUREMENT OF POWER — DYNAMOMETERS 175 the direction of the arrow the heavier side tends to lag behind, causing a movement of the gears and the needle. If F is the total resistance in pounds per ton at N miles per hour and W is the weight of the vehicle in tons, then brake horse power equals F X W X N divided by a constant. CHAPTER VII FLOW OF FLUIDS The flow of fluids will be discussed under these heads : 1. The flow of air. 2. The flow of steam. 3. The flow of water. The Flow of Air. When subjected to only a.low pressure, air and many other gases are usually measured by a gas meter, of which there are many types sold commercially. There are, however, two general types: (1) "wet" and (2) "dry.". The former is by far the more reliable and should be always used in preference to a " dry " meter when it can be obtained. " Wet " meters receive their name from the water seal main- tained in them. This seal must be always kept at a constant level, de- termined by calibration, and before using such a meter in a test one should always observe whether the water level is at the standard mark. If it is not, then water must be added or withdrawn as the case may be. A section of a" wet " meter is shown in Fig. 220. It consists of a rotor somewhat resembling a paddle wheel revolving on a horizontal axis in an enclosed cylindrical casing partly filled with water. Fig. 221 illus- trates a typical apparatus of this kind, with four compartments A, B, C and D. When air or any gas flows 1 into one of the chambers of the meter it accumulates over the surface of the water and by its pressure raises the chamber until it is filled. During rotation, by means of the water seal the central ports a, b, c and d are opened and closed. When these are open gas from the pipe at the gas inlet is admitted to the compartments out of the water. Discharge ports a', b', c' and d' through which the gas passes to the discharge pipe are also opened and closed by the water seal. If the drum revolves freely no gas can pass through the meter without producing the required move- ment of the recording mechanism, because the admission and discharge ports will not be open simultaneously in any compartment. Even the smallest rates of flow are accurately measured. Rotation is due to the difference in water level, as shown in the figure, between the two sides when the meter is operating. In the figure gas is being admitted on the left-hand side so that the pressure on that side will be slightly greater 1 The nature or specific gravity of the gas is not important, as gas meters are cali- brated to record volumes, usually cubic feet. 176 FLOW OF FLUIDS 177 than on the right, causing the water level to be higher and making a greater weight on the right-hand side than on the left. On account of the Fig. 220. — Typical "Wet" Gas Meter. difficulty in making the admission and discharge ports of the rotor of suffi- cient size the admission ports are usually placed at one end and the dis- Gas Enters Fig. 221. — Diagram of "Wet " Gas Meter. Fig. 222. — Rotor of " Wet " Gas Meter. charge ports at the other, as illustrated in Fig. 222, the flow of gas being shown by the arrows. In the assembled view (Fig. 220) the gas enters at the dry-well, V, passes through the drum and out at the front end, then 178 POWER PLANT TESTING over the drum between it and the case to the outlet. 1 In this way the drum is made to revolve to the left by the pressure on the surface of the water below and the slanted partition C above, forming an ever-increas- ing pyramidal space between the surface of the water and the plane of the slanted partition. Fluctuations of pressure or of velocity cause errors only when great enough to produce a sufficient surging of the water, so that the water sealing on the valves may at times be prevented. If the flow is inter- mittent as in the suction pipe of gas engines and compressors a pressure regulator must be provided. A rubber bag is used as a regulator when the gas is under pressure and a diving bell hung on springs for suction gas. " Dry " Gas Meters are used for the usual " house metering " of gas. They are not nearly so accurate as the " wet " types, but can be used more conveniently because they are not dependent on a constantly maintained water level. In simplest terms such meters consist of two chambers separated by a vertical partition, each chamber containing an interior measuring receiver having a flexible shell. Gas is admitted to these measuring receivers alternately by means of slide valves actuated automatically. The reciprocating movement of alternately filling and emptying these receivers operates the counting mechanism. " Wet " meters are usually very accurate, while " dry " meters are not " supposed to be instruments of great accuracy." Pitot Tube for Measurement of Air. Probably the most accurate method of measuring air in large volumes is by means of a Pitot tube. A standard instrument of this kind designed for the measurement of air by the American Blower Company is shown in Fig. 223. It consists simply of two concentric brass tubes, a small one A being placed inside of a larger one B, as illustrated in detail in Fig. 224. These tubes are arranged so that each has a separate connection, as at A' and B'. The lower end of the small tube is open at A, while the outside and larger tube is tapered and closed; but approximately midway along its horizontal portion, as shown in the figure, there are two holes on each side. 2 These holes should be not much more than /„ inch in di- ameter. The Taylor Pitot tube was formerly much used. It differs essentially from the one shown in the figures by having a short slot 2| inches long and T V inch wide on each side. At high velocities these slots cause 1 More frequently the outlet for the gas is on the top of the casing than at the back as shown in the figure. 2 The holes for static pressure are shown here at the top and bottom. In practice these holes are usually placed at the sides of the tube as in this location they are less likely to become filled with dust and refuse. FLOW OF FLUIDS 179 eddies 1 and the static pressure observed will be too high. Taylor tubes being 13 inches long compared with 4| inches for the ABC types are much more clumsy and liable to breakage in handling. When the instrument is used it is placed so that the opening at A points against the direction of flow and receives the full effect of the pressure due to the velocity of flow. The side openings in B are subjected to only Fig 223. — " American Blower Co Standard Pitot Tube. Fig. 224. — Section of Pitot Tube. the static pressure. For convenience let p = velocity pressure and s = static pressure. For example, the difference in the levels in the manom- eter, a, Fig. 226, is therefore that due to (p + s) — s, or simply p, the velocity pressure. Another type of Pitot tube much used and known as Burnham's is shown in Fig. 225. It is made up of two tubes A and B. Tube A is for obtaining the total pressure and in principle is not different from those already described. The static tube B is unique. It is open at the end and is pointed downward. On the side toward the direc- tion of flow it is beveled at an angle of about 45 degrees. Neither the Taylor nor the Burnham types are satisfactory for measuring velocities above 6,000 to 8,000 feet per minute, while the ABC type is accurate for very high velocities. The latter type is the one recommended by the Power Test Committee of the A.S.M.E. (see Journal, Nov., 1912, page 1831). Pitot tubes are usually connected to manometers or preferably to sensitive draft gages, showing the pressure in small fractions of an inch of water. When the end of the Pitot tube at A' is connected to the left-hand end of a draft gage, like those in the figures on page 182, and the end at B' is attached to the right-hand end, the instrument acts as a differential gage and the difference between the reading when thus con- nected and its zero reading is the pressure in inches of water corre- 1 This inaccuracy of the Taylor type of tube can be remedied by soldering neatly a sheet of fine brass gauze over the slots. For results of tests with the Taylor tube see Trans. A.S.M.E., vol. 33 (1911), pages 1137-1173. Fig. 225. — Burnham's Pitot Tube. 180 POWER PLANT TESTING sponding to the velocity alone; that is (p + s) — s. If, as before, we call the velocity pressure F in inches of water, and if h is the height or " head " in feet of an equivalent column of air producing the same pressure, then the velocity of the air v in feet per minute is v = 60 V2 gh, where g is the force of gravity (32.2), and wt. of a cu.;f t. of water 1 h = -^X 12 wt. of a cu. ft. of air 62.3 p 5.196 p 12 X wt. cu. ft. air wt. cu. ft. air' Y = I W w t.cu P ft.air (34) In the following table the weight is given of dry air and also the weight of air completely saturated with moisture (100 per cent humidity). The data given are at atmospheric pressure (14.7 pounds per square inch) and the temperature given is that indicated by the " dry " thermometer. By interpolating between these tables, the weight of air for any temperature and degree of saturation is easily obtained. Remembering also that the weight per cubic foot is directly proportional to the absolute pressure, the weight for any pressure is readily de- termined. Tables for determining the percentage of saturation by means of wet- and dry-bulb thermometers are given on page 368. For many engineering calculations relating to tests of fans and blowers it is accurate enough to interpolate between columns (3) and (4) to allow for humidity. For work requiring greater accuracy use the curve sheets given on pages 1006 and 1007 in the Transactions of A.S.M.E., vol. 33. Observe that the numbers on the curved lines on page 1006 should be marked per cent instead of degrees. To determine the volume of air flowing through a circular duct, the average velocity is most accurately obtained by dividing the cross- section of the duct or pipe into 5 or 10 imaginary annular rings of equal area. Each of these rings is then again divided into two others of equal area. Observations for a given flow are then made by shifting the Pitot tube rapidly along a diameter and taking readings with the tip of the tube at each of these last points of subdivision, called " stations." Average velocities and flows are then readily obtained from these observations. This is sometimes known as the " ten point " method. For a pipe of radius r, divided into five annular rings, the " stations " 1 The weight of a cubic foot of water at about "room" temperature (about 70 deg. Fahr.) is about 62.3 pounds. FLOW OF FLUIDS 181 PROPERTIES OF AIR.* Weight of Specific Volume, Cu. Ft. Weight of Water Vapor per Pound Specific Volume, Cu. Ft. Temp, by Dry Bulb, Water Vapor per Pound per Lb. Temp, by Dry Bulb, Deg. F. per Lb. Deg. F. Pure Air, Lbs. Dry Air. 100% Satu- Pure Air, Dry Air. 100% Satu- rated Air. Lbs. rated Air. (1) (2) (3) (4) (1) (2) (3) (4) .0009 11.588 11.603 74 .0179 13.449 13.593 10 .0016 11.795 11.820 76 .0192 13.499 13.654 20 .0024 12.051 12.091 78 .0206 13.549 13.715 32 .0038 12.388 12.414 80 .0220 13.600 13.777 34 .0041 12.439 12.469 82 .0235 13.650 13.841 36 .0044 12.489 12.523 84 .0252 13.701 13.906 38 .0047 12.539 12.576 86 .0269 13.752 13.971 40 .0051 12.590 12.629 88 .0288 13.801 14.038 42 .0055 12.640 12.682 90 .0307 13.852 14.106 44 .0060 12.692. 12.736 92 .0328 13.903 14.173 46 .0065 12.741 12.791 94 .0350 13.954 14.241 48 .0070 12.792 12.846 96 .0374 14.004 14.310 50 .0076 12.842 12.901 98 .0399 14.055 14.382 52 .0082 12.893 12.957 100 .0424 14.106 14.455 54 .0088 12.944 13.012 105 .0500 14.232 14.643 56 .0094 12.993 13.068 110 .0586 14.358 14.840 58 .0100 13.044 13.124 115 .0687 14.484 15.050 60 .0108 13.095 13.180 120 .0804 14.611 15.272 62 .0117 13.146 13.240 125 .0941 14.736 15.509 64 .0126 13.196 13.298 130 .1102 14.863 15.761 66 .0135 13.246 13.354 135 .1293 14.959 16.032 68 .0145 13.298 13.413 140 .1515 15.116 16.325 70 .0156 13.348 13.471 145 .1782 15.242 16.643 72 .0167 13.398 13.532 150 .2100 15.368 16.993 1 W. H. Carrier in the Transactions of A.S.M.E., vol. 33 (1911) pages 1005-1136. These table are generally considered more reliable than any other available data. The tables of the U. S. Weather Bureau are in error because they were computed on the assumption that saturated air is a perfect gas. The fallacy is particularly observable at high temperatures. or points of observation would be at the following distances from the center: (1) 0.316 r; (2) 0.548 r; (3) 0.707 r; (4) 0.837 r; (5) 0.949 r. When the Burnham Pitot tube is used readings are taken usually in only one position. This position giving the average velocity is stated to be at a distance of T 8 o of the actual internal radius from the center of the pipe. Ducts of square or rectangular section are usually divided up simi- larly into a series of elementary squares or rectangles. Figs. 226 and 227 show the methods of connecting a Pitot tube to manometers for observing velocities when the pressure is above or below atmospheric. The usual case is where the pressure is greater than atmospheric, and the cases where it is less are most often in the suction line of a ventilating fan. In Fig. 227 positions of "stations " (a, b, c, and d) are 182 POWER PLANT TESTING marked on a board to assist in taking observations. Measurements of velocity with a Pitot tube should not be attempted if there is not at least 15 feet of straight pipe in the direction in which the tube is pointed. This precaution is necessary to avoid the effect of eddies in the pipe. For Pressures above Atmospheric For Pressures less than Atmospheric Fig. 226. Fig. 227. Arrangement of Connections for Pitot Tube Measurements. Anemometers. A very convenient and simple method for measuring directly the volume of the air, or any gases, is by using an instrument called an anemometer. This instrument, Fig. 228, consists in its essen- tial parts of a light vane wheel like a screw-propeller having either flat or lightly curved vanes mounted on slender arms. The wheel must be made very light in weight, must be accurately balanced, and should move easily in its bearings. By its own motion it operates a counting me- chanism attached to its shaft which indicates velocities in feet. Readings of the counter are taken at the be- ginning and end of a suitable lapse of time, usually \ to 1 minute. Such instruments must be placed with the axis of rotation in the direction of the flow of air or gas. They have upper and lower velocity limits be- yond which they should not be used. The lower limit cannot be defined as it will depend on the precautions taken in manufacture and in use to eliminate friction. As regards the higher limit, it will usually depend on the size of the wheel, large wheels being less suitable than smaller ones for high velocities. Practically none should be used for velocities higher than 1,000 feet per minute. 228. — A Typical Anemometer for Measuring Velocity of Air. FLOW OF FLUIDS 183 A calibration chart must always be provided for such instruments and the calibration should be frequently checked at several points within its velocity limits. Methods of Calibrating Anemometers, Pitot Tubes, and Gas Meters. Probably the best method of calibrating anemometers is to compare their readings with the actual measurements of air discharged from a gasometer or gas-holder like Fig. 229. It consists of a tank A for holding water or other liquid into which the "bell" B is raised and lowered. The piping as shown is arranged with a three-way cock (see page 139), but for accurate work separate inlet and dis- charge pipes should be provided. The weight W is to counterbalance the weight of the bell. This method of counterbalancing if used without a means for correction would cause a change of pressure of the gas in the holder as the bell ascends or descends, due to a variation of depth of immersion. As a means to correct this, a compensating weight w is suspended from a cord wrapping over a can C. Observations required to determine volume of gas are (1) pressure (usu- ally read with a water manometer M) (2) tem- perature; and (3) movement of the bell in a given time. In order to get the temperature of the gas in the bell accurately the temperature of the liquid should be as nearly as possible the same as that of the gas. Movement of the bell is usually read directly with the help of a suitable scale and some form of sighting device to insure accuracy in reading the scale. Gasometers may be calibrated by calculation or by actual tests, pref- erably on the displacement of water. When the method of calculation is used, measurements of the diameter should be made at several points on the circumference to allow for possible lack of symmetry. Large gasometers such as are installed at gas works are also fre- quently used to calibrate Pitot tubes; and gas meters are invariably calibrated by comparison with a gasometer. Gas meters may also be calibrated by any apparatus suitable for the displacement of the gas as it is withdrawn by water or other suitable liquid. It is very necessary, of course, that when the weighings are made the pressure and temperature of the gas be accurately deter- mined. Anemometers are suitable only for low velocities (from about 50 to 1500 feet per minute) and Pitot tubes in general are best adapted to Fig. 229. — Gasometer. 184 POWER PLANT TESTING velocities from 300 to 3000 feet per minute, but instruments like the "A. B. C." type (Fig. 223) designed to avoid eddies around the "static " openings are satisfactory up to 6000 feet per minute. In order to use an anemometer successfully all the gas to be measured must be passed through openings of suitable size in which the instru- ment can be placed. These openings should each have an area of about 15 square inches (if the anemometer is about 2| inches in diam- eter) so that the resistance interposed by the instrument will be negligible. A very common method of calibrating anemometers and Pitot tubes is by mounting them on the end of a long and light rod arranged to be revolved about a central point. The readings of the instrument are compared with its computed velocity. Other methods of calibration under more nearly " working conditions " are generally considered better, as the method of swinging about a central point makes the instrument read too high on account of the eddies produced. " The standard of reference for calibrating Pitot tubes, anemometers, etc., is the gasometer, 1 and if the instrument used cannot be calibrated by actual measurement, the constants employed should be those ob- tained from a similar instrument which has been calibrated by actual reference to a gasometer measurement." (Report of Power Test Com- mittee, A.S.M.E, Nov., 1912.) Flow of Air through an Orifice. Air under comparatively high pres- sures is usually measured in practice by means of pressure and tempera- Fig. 230. — Measuring Flow of Air through an Orifice. ture observations made on the two sides of a sharp-edged orifice in a diaphragm. Fig. 230 illustrates the method with two pressure gages on opposite sides of the orifice and a thermometer for obtaining the tem- 1 It is very difficult to get a uniform temperature in a gasometer so that the vol- ume of gas discharging from the outlet may be different by 2 or 3 per cent from that in- dicated by the scale on the gasometer. When accurate work is to be done a better method to use is the displacement of water as measured by its weight in a vessel of heavy sheet metal. The walls of the vessel should be heavy to prevent rapid radiation to the surrounding air. A long thermometer should be used which should be inside the vessel itself and may be read through a peep-hole. If the vessel is of heavy glass the conditions will be still better. FLOW OF FLUIDS 185 perature ti at the initial or higher pressure p x . The flow of air w, in pounds per second, may then be calculated by Fliegner's formulas. w = .530 X a * ■ when p x is greater than 2 p 2 (45) vTi w = 1.060 X a y T when pi is less than 2 p 2 , . . (46) where a is the area of the orifice in square inches, Ti is the absolute initial temperature in degrees Fahrenheit at the absolute pressure p L in the " reservoir or high-pressure side " and p 2 is the absolute discharge pres- sure, both in pounds per square inch. When the discharge from the orifice is directly into the atmosphere, p 2 is obviously barometric pressure. For small pressures it is often desirable to substitute manometers for pressure gages. One leg of a U-tube manometer can be connected to the high-pressure side of the orifice and the other leg to the low-pressure side. Many engineers insert valves or cocks between the manometer and the pipe in which the pressure is to be observed for the purpose of " dampening " oscillations. This practice is not to be recommended as there is always the possibility that the pressure is being throttled. 1 A better method is to use a U-tube made with a restricted area at the bend between the two legs. This will reduce oscillations and not affect the accuracy of the observations. Discharge from compressors and the air supply for gas engines are frequently measured by orifice methods. When pi — p 2 is small compared with pi, the simple law of discharge 2 of fluids can be used as follows: w = -£- V2 g X 144 (Pi - P2) s, (47) 144 1 Report of Power Test Committee, Journal A.S.M.E., Nov., 1912, page 1695. 2 If the density is fairly constant, 144 Pi , Vl 2 _ 144 P2 Vo 2 ■ i ' — t" > S 2 g S 2g where Vi is the velocity in feet per second in the "approach" to the orifice and v is the velocity in the orifice itself. Since Vi should be very small compared with Vo, V 144 (pi - P2) 2g S Vo=\/ : 2 g X 144 (Pi - Pa) fa Vo s , . / 2 g X 144 (P i - P2) w = = fas V , 144 V s •w= — V2 g X 144 (pi - P2) s. 144 186 POWER PLANT TESTING where w is the weight in pounds discharged per second, a is the area of smallest section of orifice in square inches, the pressures pi and p 2 are in pounds per square inch, f is a coefficient from experiments, g is the accel- eration due to gravity (32.2), and s is the unit weight of the gas meas- ured, in pounds per cubic foot, for the average of the initial and final conditions of temperature and pressure (Table of weight of air on page 181). If the difference in pressure is measured in inches of water h with a manometer then 144 (pi — p 2 ) = - — — X h, (lbs. per sq. ft.) ^y 2ghs X-~, (lbs. per sec), where 62.4 is the weight of a cubic feet of water (density) at usual "room" temperatures. This equation can also be transformed so that a table of the weight of air is not needed, since by elementary thermodynamics 144 pv = 53.3 T, where v is the volume in cubic feet of one pound of air or other gas and T is the absolute temperature in degrees Fahrenheit. Since v is the reciprocal of s, then s = 144 p -f- 53.3 f , and i7~~ I w = .2opfay/^ (48) Here p and T should be the values obtained by averaging the initial and final pressures and temperatures. Great care should be exercised in obtaining correct temperatures. When equation (47) is used, for accu- rate work, corrections of s for humidity must be made. 1 For measurements made with orifices with a well-rounded entrance and a smooth bore so that there is practically no contraction of the jet the coefficient f in equations (47) and (48) may be taken as 0.98. In the rounding portion of the entrance to such a nozzle the largest diameter must be at least twice the diameter of the smallest section. For circular orifices with sharp corners Professor Dalby 2 in reporting very recent experiments stated that the coefficient for his sharp-edged orifices in a thin plate of various sizes from 1 inch to 5 inches in diameter was in all cases approximately .60; and these data agree very well with those published by Durley. 3 1 Tables of humidity are given on page 368. 2 Engineering (London), Sept. 9, 1910, page 380, and Ashcroft in Proc. Institution of Civil Engineers, vol. 173, page 289. 3 Transactions American Society of Mechanical Engineers, vol. 27 (1905), page 193. FLOW OF FLUIDS 187 When p 2 -j- pi = .99 the values obtained with this coefficient are in error less than § per cent; and when p2-^Pi = .93 the error is less than 2 per cent. Flow of Air Measured by Cooling. This method depends on taking from the air an amount of heat 1 which can be measured and then computing from the heat units absorbed, the difference in temperature, and specific heat of the air, its weight and volume. 2 The arrangement of the apparatus is shown in Fig. 231. A coil of pipes C, of which the cooling surface is as equally as possible distributed over the section of the duct D, D', carrying the air to be measured, is used to absorb heat by circulating water through it. Thermometers are arranged so that the temperatures of the air and of the water can be observed, and a S 11 I 4J 1 f Fig. 231. — Measuring Flow of Air by Cooling. platform scales is shown for obtaining the weight of water. Using the symbols ti and t 2 for the initial and final temperatures of the air in de- grees Fahrenheit, t' and t" for the temperatures of the water entering and leaving in degrees Fahrenheit, w a = weight of air passing through duct in pounds per second, w === weight of water collected in pounds per second, and .2375 = specific heat of the air at constant pressure and at temperatures not much above " atmospheric," then the heat absorbed by the water per second is w (t" — t' ), B.t.u. and this equals the heat lost by the air, or .2375 w a (ti — t 2 ), and therefore w (t"-t') 4.2 1 1 Wo - w > = i-M-%) (5I) In accurate laboratory tests the humidity of the air entering the com- pressor should be measured in order to reduce this weight of air to the corresponding equivalent volume at atmospheric pressure and temper- ature. Principal errors in this method are due to difficulty in measuring the average temperature in the receiver. Whenever practicable the final pressure should be maintained in the receiver at the end of the test until the final temperature is fairly constant. FLOW OF FLUIDS 189 The above method is often reversed by discharging air at high pres- sure from a receiver. Constant discharge pressure is maintained by throttling with a valve. Measurement of Air by Chemical Analysis. Quantity of air supplied for combustion in boilers and other furnaces can be determined from the analysis of the products of combustion by the formulas given on pages 251 and 281. Venturi Meters (see page 199) are also used successfully for measur- ing large volumes of gas as in tests of gas producers/ etc. The Flow of Steam through Nozzles and Orifices. The flow of the steam from an orifice or nozzle has a very definite critical value when the final pressure is approximately 0.58 of the initial pressure. When the final pressure is less than this critical value the flow is expressed very accurately by the following empirical formula, based on the experi- ments of Professors Emswiler and Fessenden. Using the following symbols : pi = initial absolute pressure of the steam in pounds per square inch; p 2 = final absolute pressure of steam in pounds per square inch; a = area of the smallest section of the nozzle or orifice in square inches. Then the weight of the dry saturated steam discharged in pounds per second is approximately, 2 w = ^ when p 2 is less than 0.58 pi (52) Now since in the theoretical formulas the weight discharged is inversely proportional to the square root of the specific volume v, or w is propor- tional toy— the formula above corrected for initial quality x of the steam is w = — ^— — 7- when p 2 is less than 0.58 pi. . . (54) 60.5 v x When the steam is superheated the specific volume is considerably increased, and for this condition the author has found 'that the follow- ing equation gives very satisfactory results, 3 Ihf Ji W 60.5 (1 + .00065 d) ' {55) 1 Trans. A.S.M.E., vol. 28, page 483 and vol. 29, page 952. See also Bulletin No. 76, Builder's Iron Foundry, Providence, R. I. 2 A somewhat simpler formula, known as Napier's formula, which is accurate enough for most calculations, is the following: Pi a w = — when p 2 is less than 0.58 pi. (53) 70 3 For a more extended discussion of the flow of steam see The Steam Turbine, by the author, pages 52-57. 190 POWER PLANT TESTING when, as before, po is less than 0.58 pi and where d is the number of degrees (Fahrenheit) of superheat. When the final pressure p 2 is greater than 0.58 p x , the formulas must be modified to correspond to the reduced flow observed by inserting a coefficient K as a factor in the right-hand member of the equations. Values of this coefficient are most conveniently obtained from the curve in Fig. 232, which was plotted from the experimental results obtained by Professor Rateau. Formulas (52) to (55) are for the flow through nozzles with smooth walls, being well rounded at the entrance and the length along the axis 1.0 0.9 $> » a 0.8 .1*; •5 r° .2 ^ 0.7 a < °> fj « 8> f/ y IS °-4 / / |1" / / CURVES FOR DISCHARGE OF STEAM MAINLY WHEN FINAL PRESSURE IS O (3 / ?E / GREATER THAN 58% OF INITIAL PRESSU 0.1 f Fig. 232. — Rateau's Curve for Flow of Steam giving Values of the Coefficient K. at least three times the length of the shortest side or diameter. If the nozzles are of approximately rectangular section they must be made without well-defined edges; in other words the cross-section must show well-rounded corners. Orifice Measurements of the flow of steam are particularly recom- mended by some engineers for ascertaining the steam consumption of the " auxiliaries " in a power plant. This method commends itself particularly because of its simplicity and accuracy. It is best applied by inserting a plate J inch thick with an orifice one inch in diameter, with square edges, at its center, between the two halves of a pair of flanges on the pipe through which the steam passes. Accurately cali- brated steam gages are required on each side of the orifice to determine the loss of pressure. The weight of steam for the various differences of pressure may be determined by arranging the apparatus so that the FLOW OF FLUIDS 191 steam passing through the orifice will be discharged into a tank of water placed on a platform scales. The flow through this orifice in pounds of dry saturated steam per hour when the discharge pressure at the orifice is 100 pounds by the gage is given by the following table: 1 Pressure, Drop, Lbs. per Sq. In. Flow of Dry Steam per Hour, Lbs. Pressure, Drop, Lbs. per Sq. In. Flow of Dry Steam per Hour, Lbs. 2 1 2 3 4 430 615 930 1200 1400 5 10 15 20 1560 2180 2640 3050 The Flow of Steam. Pitot Tube Meters are represented at their best in one of the types made by the General Electric Co. A nozzle plug (Fig. 233) is inserted into the steam pipe and in this plug there are two sets of holes each communicating with a separate tube starting from the end of the plug. These pipes are connected separately to the unions in Fig. 234, showing the apparatus. The " leading " set of holes is subjected to velocity plus static pressure, while the trailing holes are subjected to velocity less static pressure only. The principles of operation are therefore the same as for the measurement of air by the Pitot tube Leading Set Fig. 233. — Nozzle Plug for Steam Meter. (see page 178). The part actuating the recorder consists of two cups connected by a hollow tube forming an elongated U-shaped vessel which is filled with mercury. This vessel is balanced on knife-edges. The cups are connected by flexible steel tubing to the unions shown at the top of the figure which are to be joined to pipes running to the nozzle plug. In the operation of the instrument the excess of pressure in the leading holes of the nozzle plug causes the mercury to shift its level and stand higher in the cup connected to the trailing holes. As a result of this unbalancing of weights the whole vessel will swing on the knife edges untii equilibrium is again established. A clock and drum device is provided for recording on charts the movement of the mercury vessel on its knife edges. Charts are graduated in pounds of steam per hour. Correction for variation of flow on account of fluctua- 1 Journal A.S.M.E., Nov. 1912, page 1693. 192 POWER PLANT TESTING tion of pressure is automatic. This correction device is simply a Bour- don tube of a pressure gage connected to the recording device so that as the curvature of the tube changes to correspond with the pressure it shifts a small weight intended to adjust the pen. When superheated Balancing Weight Pressure and Temp. Correction Weight Fig. 234. —Steam Meter of Pitot Tube Type. steam is being measured temperature correction must be made by shift- ing the same weight by hand. The Burnham Steam Meter is one of the simplest types, and is serviceable only as an indicating instrument for " rough" measurements. The difference in level between the tip of the Pitot tube and the water in a gage glass is proportional to the flow of steam. The Pitot Tube used is shown in Fig. 225. The Orifice Steam Meter (Fig. 236) requires the insertion into the steam pipe of a special flanged fitting F in which there is an orifice as shown. Pressure difference between the two tubes ti and t 2 located in this flange (produced by veloc- ity) is measured by a differential mercury manom- eter. Without changing the orifice the apparatus is not adapted to a large range in the rate of flow. The spiral coils d and c 2 are inserted for maintaining by condensation constant water Fig. 236. —Orifice Steam Meter. FLOW OF FLUIDS 193 levels in each of the legs of the manometer, irrespective of variations of pressure. A variation of the orifice method has been applied very successfully on steam turbines of the few-stage type like the Curtis. The area of the nozzles between the second and third stages, and often also between the first and second stages, is invariable with the load if there is no over- load by-pass valve. The pressure drop is always great enough when steam is supplied at boiler pressure to make Napier's formula (page 189) for the flow of steam applicable; that is, the weight of dry saturated steam passing through these nozzles of constant area is proportional to the pressure on the " inlet " side. If the area of the nozzles in one of these stages is known where the steam is approximately dry and satu- rated, and an ordinary recording pressure gage is attached to indicate the pressure on the " inlet " side of the nozzles, the weight of steam can be determined much more accurately than with any of the other auto- matic devices yet devised. If desired the chart of the recording gage can be readily graduated by a skillful draftsman to indicate directly pounds of dry steam. If the steam is superheated a correction curve can be readily made by applying the formula (55). Float Steam Meters are designed so that a float, usually a disk or a cone, moves against a constant resistance in a passage in which the un- restricted area for the flow of steam varies with the height of the float. This principle is applied in the St. John and Sargent meters in each of which there is a conical float connected to the registering device showing the rate of flow. In the St. John meter (Fig. 237) the float V rises with increased flow, carrying with it the arm N connected to the registering device. Accuracy of steam meters is usually not greater than ± 5 per cent. Prices of steam meters: " G. E." Pitot tube $85 to $165 for indicating types, $260 to $270 for recording types (General Eleetric Co., Sche- nectady, N. Y.); St. John Recorder $250 for 2- inch pipe, $550 for 6-inch pipe (G. C. St. John, New York); Sargent $200 for 2-inch pipe, $450 for 6-inch pipe (Pittsburg Supply Co., Pittsburg, Pa.). The Flow of Water. When the quantity of water to be measured is not too large it is most accurately determined by weighing in tanks placed on scales, or by direct measurement of volume in calibrated tanks or barrels. Sometimes it is impracticable to weigh or measure the Fig. 237.— St. John Steam Meter. 194 POWER PLANT TESTING volume of the water directly, particularly when it must be measured under pressure. For measurements in pipes up to 2 or 3 inches in diameter a water meter is generally used. A great many types of water meters are sold commercially and not very many are accurate, so that it is absolutely necessary to calibrate them at least before and after a test, under the same conditions of tem- perature, pressure, and rate of flow. In many plants where meters are used constantly, suitable con- Dial nections are made to the dis- charge from the meter, so that at any time the flow through it can be diverted into a tank in which it can be measured by volume or weighed. One of the best types of water meters is illustrated in Fig. 238. This belongs to the class operating with a " pulsa- ting diaphragm." The inclined shaft S on this diaphragm trav- eling around in contact with the peg P on the plate B moves the counting mechanism through intermediate gears. This diaphragm in the Thom- son-Lambert meter (Fig. 239) is made of hard rubber reinforced with a steel plate, making it much more durable than those made without reinforcing. As the side cham- bers are alternately filled and emptied, the diaphragm is moved up and down with a kind of " pulsating " motion and operates the recording mechanism. The diaphragm divides the measuring chamber into two compartments of equal volume. While one of these is filling the other is emptying. For general purposes this type is probably used more than any other, and for a fairly constant flow is quite accurate; but because of leakage it is not accurate for rates of flow that at times have very low values. Piston Water Meter. The piston type of water meter (Fig. 240) is also used frequently. It belongs to the type operating in a cylin- der by a reciprocating piston which is driven backward and forward by the pressure of the water. In this device there are two pistons side by side. Water is admitted alternately at each end by a slide valve A moving on seats in the plate S, just above the bottom casting containing the inlet and outlet chambers. These valves are moved by 238. — Pulsating Diaphragm Water Meter. FLOW OF FLUIDS 195 Fig. 239. — Thomson-Lambert Water Meter. Fig. 240. — Piston Water Meter. contact with the inner faces of the plunger heads near the end of the travel and move them over at the proper time. The lever L is moved back and forth by one of the plungers to operate the counting mecha- nism. The cored passages in the bottom casting are too complicated to 196 POWER PLANT TESTING Water Meter Operated by Velocity. be shown clearly. The plungers at the end of their travel strike against the rubber bumpers R, which are provided to reduce the shock. Meters actuated by the velocity of water are particularly suitable for measuring large quantities at low pressure. Fig. 241 shows an example of this class. Water flows into the wheel I after entering and passing through the screen S as shown by the arrows. Guide vanes deflect the water hori- zontally and radially outward from the center into the discharge passage A. The wheel when it revolves moves the counting mechanism G above. Objections to such meters are that they are very unreliable for small flows because of the friction of the parts, and an appreciable flow is required to start them. Friction is an important element in meters of this type, but they are not injured by moderately hot water. The readings of a water meter are usually in cubic feet. A water meter is essentially a water motor adapted for operating the gearing connected to the counting mechanism. Frequent calibrations of water meters are necessary because they are likely to become more or less clogged with dirt and refuse. The read- ings are also affected by the temperature, head, and quantity of water flowing, as well as by the amount of air carried in the water. A meter should always be calibrated at least at two or three rates of flow, as it scarcely ever happens that the conditions of the test are so uniform that the meter will be used only for a certain predetermined rate of flow. 1 Willcox Water Meter. Automatic measuring devices are often used for determining the weight of condensed steam in engine tests or the weight of feed water in boiler trials. The Willcox meter 2 is a most satis- factory apparatus of this kind. It consists of a tank (Fig. 242) divided by a partition P into two compartments A and B, one above the other. The upper compartment A receives the inflow of water and the lower one B serves for measuring. Projecting into the lower compartment is a U-shaped discharge pipe C, which is always water-sealed. The upper end of the discharge pipe is covered by a bell float F, which is permitted a short, up-and-down movement. In the upper compartment there is a 1 Calibration curves are usually plotted with meter readings as abscissas and actual volumes as ordinates. A curve should be plotted for each of the several rates of flow if they are different. Curves of meter readings (abscissas) and correction factors (ordinates) are also useful. 2 Willcox Engineering Co., Saginaw, Mich. FLOW OF FLUIDS 197 short standpipe S, which is simply a hollow cylinder open at the top and bottom. The bell float F and the standpipe S are connected rigidly by a vertical rod (Fig. 243) so that they move together as one piece, and this is the only moving part in the apparatus. The lower end of this standpipe has a corrugated face, and when it is down in its lowest posi- tion its corrugated face rests on a soft seat or ring surrounding a circular opening in the partition P. This seat is made of a rubber composition which is not injured by boiling water. The apparatus can be used, therefore, with either hot or cold water without risk. Counter M Gage Glass Stand Pipe Fig. 242. — Willcox Water Weigher (by Volume). Fig. 243. — Bell Float. In the operation of the apparatus, when the standpipe S is down on its seat, water entering through the side inlet accumulates in the upper compartment A until it overflows the top of the standpipe. The water then flows down through the hollow standpipe into the lower compartment until there is a sufficient amount to seal the lower edge of the bell float F. Then as more water accumulates the bell float rises, lifting the standpipe S from its seat and the water in the upper compartment flows down into the lower one until the volume is that of a " unit charge " for the apparatus, when the " tripping " device dis- charges the water through the discharge pipe C. The " tripping " is accomplished by a " trip " pipe T, which is normally water-sealed, but which becomes unsealed when a " unit charge " has accumulated. While the water is accumulating in the lower compartment B the water in the left-hand leg of the " trip " pipe T is being slowly pushed down 198 POWER PLANT TESTING because of the increasing pressure of the air under the bell float F, due to the increase of head of water, and a. corresponding amount of water spills over the upper end of the right-hand leg R of the " trip " pipe into the discharge pipe C. Due to this action the water level in T is lowered until it reaches the bend in the lower end of the " trip " pipe. Under these conditions the water column in R exactly balances the head of water in the lower compartment B and the air entrapped in the float valve F has a function similar to that of a scale beam, balancing on one side the head of water in the tank and on the other side the head of the standard water-column in R, which of course is always constant. At the instant this balance is secured a very small amount of water added in the lower compartment and the corresponding additional spill from R will destroy this equilibrium. Then the air compressed in the bell float F and the upper part of the discharge pipe breaks the water seal in R by suddenly discharging all the water in it. When the air pressure in the bell float F is thus reduced it drops down, carrying down with it the standpipe S in the upper compartment A. In this last operation the air is moved from the interior of the bell float F, and water flowing in to replace it will spill over the top of the discharge pipe C and will flow out at the other end until the lower chamber is emptied of the " unit charge." At this time the standpipe S becomes seated, due to the pressure of the water above the bell float and to the downward suction of the syphon. Thus the standpipe is held tightly upon its seat only at the instant when tightness is required; that is, while the " unit charge " is being discharged. After the standpipe has seated water again accumulates in the upper compartment A and the cycle of oper- ations is repeated. A mechanical counter shown at the side of the apparatus is connected to a ball float inside the lower compartment and registers the number of times the apparatus is tripped. An automatic device of this kind is easily calibrated by weighing several " unit charges," and it can then be used with, as great a degree of accuracy as can be expected with rapid weighings in tanks on platform scales. It may be expected to weigh hot or cold water with a maximum error of not more than one per cent for the conditions of calibration. ♦ Leinert (Worthington) Weigher. The apparatus shown in Fig. 244 is one of the few devices made which actually weighs the liquid to be measured. It can therefore be used for liquids of widely varying den- sity without making corrections. It consists of a pair of open tanks supported on trunnions with knife-edge bearings (K) in such a way that when empty they assume the normal position as shown in the figure. After a certain quantity of liquid has entered the tank the counter- balancing effect of the lead weights in the casing W is overcome and the FLOW OF FLUIDS 199 tank tips over and the contents are siphoned out through the pipe P. By this tipping action the trough H receiving the liquid from the sup- ply pipe I is switched from the full to the empty tank, and at the same time the counter C is operated to register the number of times the tanks have been filled. Since weight is the method of measure- ment the record is independent of the temperature of the liquid; but there is always a very small vari- ation of weight with the rate of flow. The weight per charge can be adjusted by changing the number of weights in the casing W 1 , Venturi Meter. An arrange- ment of piping in which there is a gradual narrowing of the section to a minimum followed by a more gradual enlargement was invented by Mr. Clemens Herschel for measuring the flow of water. This apparatus is called a venturi meter and is shown in Fig. 245. Piesometer tubes (manometers) are arranged to indicate the pressure at the sections shown. Pressures at these sections will be denoted respectively by p m and p„. Fig. 244. — Tilting Tank Water Weigher. Pipes to Manometer J:£2==^=21= uu^** ==! Fig. 245. — Herschel's Venturi Meter. From Bernouilli's theorem 2 it follows that the relation between the pressure in pounds per square foot and the velocities in feet per second at the two sections v m and v„ of a stream flowing through such a closed horizontal channel is given by + 51 = + 2g (56) 1 Henry R. Worthington, 115 Broadway, New York, and Holden & Brooke, London. 2 See Jamieson's Applied Mechanics, vol. 2, page 458. 200 POWER PLANT TESTING where 5 is the density of the water in pounds per cubic foot. If a repre- sents the area of a section in square feet, the volume of water flowing through any section, (cubic feet per second), is ,v m = a„v„ = a„ / 2 gfo»-P» ) (57) With suitable manometers or with gages the pressures p m and p„ can be obtained, and since all other quantities can be represented by a constant k, we have Volume per Unit of Time = k (p m — p n ) . * . . . . (58) As usually made the venturi tube is merely a pipe which tapers from each end towards the throat, which is usually lined with 'hard bronze to secure a smooth bore and has a diameter of from \ to \ that of the pipe line. Its total length is about eight times the diameter of the pipe. In the commercial forms of this apparatus near the inlet or up-stream end and also at the throat are annular chambers encircling the tube, which communicate with the interior by numerous small vent holes. When no water is flowing in the venturi tube the pressure will be the same in these two annular chambers; but when there is a flow of water through it the throat pressure becomes less than the up-stream pressure. The difference between the two is proportional to the square of the velocity of the water. A recording device 1 has been arranged, consisting essentially of a large U-tube serving the same function as the one in the figure filled with mercury, supporting in each leg an iron float. These floats have toothed racks connected to their upper ends which engage with pinions on the same horizontal shaft with a cam. A small wheel supporting the recording pencil rides on the perimeter of this cam, which is ar- ranged so that the wheel rides on the greatest eccentricity of the cam and consequently the recording pencil will indicate on the chart the greatest flow when the rack is at its maximum height. The pipes connecting the U-tube with the venturi meter should always be full of water. Air cocks are provided for removing air that may accumulate in pockets. 2 Since the flow is proportional to the square root of the difference of pressure a complicated cam device is required to permit the charts of the recorder to be made with equal divisions. The General Electric Flow Meter (see page 191) is also sometimes applied for measuring the flow of water in pipes. 1 Builder's Iron Foundry, Providence, R. I. 2 For more detailed discussion and tests see Herschel's papers in Trans. American Society of Civil Engineers, Nov., 1887 and Jan. 1888; also Power, Jan. 23, 1912. FLOW OF FLUIDS 201 Flow of Water through Orifices and Nozzles. Theoretically the veloc- ity of flowing water under any pressure is the same as the velocity at- tained by a body falling freely through a distance equal to that head (h) as in Fig. 247. Furthermore this statement would be the same even if the water had no free surface, provided, however, the pressure at the orifice was that due to a head h. If then there is no loss of head due to friction and eddies formed by the water passing through the orifice the velocity of discharge, v in feet per second, is v = vTgh, (59) where g 1 is the acceleration due to gravity and h is the head over the center of the orifice in feet. Fig. 247. — Discharge of Water from an Orifice. If a is the area of the cross-section of the orifice in square feet, q is the quantity or volume of water discharged in cubic feet per second, and assuming the stream is of the same cross-sectional area as the orifice, then q = aV2lh (60) Since the actual flow is less than the theoretical in most cases, and con- siderably less when the discharge is from a hole with sharp edges in a thin plate, a more general form may be written by inserting a suitable coefficient 2 of discharge k, then, q = ka V2gh (61) 1 The value of g is approximately 32.2, so that equation (59) can be simplified into v = 8.02 Vh. 2 This coefficient is often called the coefficient of contraction. 202 POWER PLANT TESTING For an orifice located in the side or bottom of a tank, consisting of a circular opening in a thin metal plate with a smooth sharp edge, the value of the coefficient k may be taken as 0.6 for all practical purposes. (See Report Power Test Committee of A.S.M.E. in Journal, Nov., 1912, page 1829, and Hamilton Smith, Jr's, Hydraulics.) Calibration of Orifices and Nozzles. Water under a constant pressure is often measured by observations of the flow through either orifices or short nozzles which have been carefully calibrated. The apparatus re- quired for this calibration consists usually of a suitably arranged stand- pipe to which the orifice or nozzle can be attached so that a given head of water can be maintained 1 and barrels on scales (or a tank calibrated for volumes) to receive the water discharged. A pressure of one pound per square inch is equivalent to a head of water at 62 degrees Fahrenheit of 27.72 inches, or 2.31 feet. A normal atmospheric pressure (14.7 pounds per square inch) is therefore equiv- alent to a head of 33.96 feet of water. Then for a given pressure or head the quantity of water discharged in a given time is readily obtained and the coefficient of discharge can be computed by substituting the values of quantity of discharge q, the head h, and the area a, in formula (61). Data and results should be tabulated in the form given below. The relative roughness of the edge of the orifice or of the inside surface of the nozzle should be recorded. FLOW OF WATER Flow of water through a Date Observers Form of orifice or nozzle Formula Diameter, feet (Sketch) Area, square feet No. of Reading. Head in Feet. Time in Seconds. Total Pounds or Cu. Feet. Pounds per Second. Cu. Feet per Second. Coefficient of Discharge (k). Remarks. Average 1 In many places a suitable pressure tank is not available, and in such cases the cali- bration can be made by attaching the orifices or nozzles to pipes carrying water under pressure. The readings of the pressure gage can be reduced to the equivalent head in feet, to which must be added, if the center of the gage is higher than the orifice or nozzle, the distance in feet from the center of the nozzle to the center of the gage. FLOW OF FLUIDS 203 Curves. Curves should be plotted for each orifice or nozzle with head in feet for abscissas and (1) the discharge (cubic feet per second) and (2) the coefficient of discharge for ordinates. Flow of Water over Weirs. When large quantities of water are to be measured, then orifices are unsuitable and it is customary to pass the whole body of water over a weir or gage notch. This consists of a board placed across the stream so that all the water must pass over it. The length of the notch is usually made less than the width of the stream to give definite conditions. This is accomplished most easily by sawing the notch out of a long board and beveling the edges. A typical arrangement for measuring the head of water on a weir is illustrated in Fig. 248. The head must be determined with great accuracy, and this is done usually by means of a hook-gage, Fig. 249, and a suitable machinist's or carpenter's level. Fig. 248. — A Weir for Measuring Water. Fig. 249.— A Hook Gage. The hook-gage consists of a sharp-pointed hook H, attached to a vernier scale V, intended to measure very accurately the amount the hook is moved. Before taking an observation the hook must first be submerged and then raised slowly till the point just breaks the surface of the water. The correct height of the surface is obtained at the in- stant when the point of the hook pierces it. The head h of the water flowing over the weir (Fig. 248) is obtained by setting by means of a straight-edge SE and the level L the point of the hook at the same level as the crest of the weir. The height observed in this position is called the zero head. It is to be subtracted from all other readings to get the head of water flowing. The hook-gage must be placed in such a position on the upstream side of the weir where the surface has no 204 POWER PLANT TESTING appreciable velocity and where there is very little disturbance due to eddies. In terms of the following symbols, q = quantity or volume of water discharged in cubic feet per second; h = the head in feet on weir measured in still water; b = breadth of the weir in feet; n = the number of contractions; k = coefficient of discharge. q = 2/3 kh % (b — 0.1 nh) Wg ..... (62) This is the well-known Francis formula for a rectangular notch. The ordinary rectangular notch has two contractions, one at each side of the crest. Triangular notches in weirs are sometimes used. One of these in the form of a right-angled isosceles triangle is shown in Fig. 250. It has the advantage of giving the same form of stream what- Fig. 250. — Weir with a Triangular Notch. ever the size of the notch or the height of water passing through. It is, therefore, particularly suitable for measuring a flow of water which is somewhat variable The quantity of water discharged over a triangular weir or notch is q = 4/15 kbh% V2g. (63) When the angle is 90 degrees, b = 2 h and q = 4.26 kh % . . . Also when the angle is 60 degrees, b = 2 h tan 30 and q = 2.47 kh%. . . . (64) . • • (65) FLOW OF FLUIDS 205 3. Weir Meters. A weir or notch will measure any quantity of water if made of a suitable size. Rectangular weirs are generally used for large quantities and notches of various shapes for small quantities. For accurate work the head on the crest is measured with a hook-gage but in many cases a float is used. The instrument used for measuring the head should not be less than two feet from the crest and preferably farther away. The distance of the crest from the bottom of the weir tank should be not less than three times the average head. For a weir with two contractions the width of the tank should be not less than three times the width of the weir. To maintain the surface free from ripples baffle plates, preferably of perforated sheet metal, should be located between the supply pipe and the instrument for measuring the head. Lea's Recorder 1 for V-notch Weirs is successfully used in many services for measuring water. Water level is measured by a sheet- metal float usually about 12 inches in diameter which is attached to the vertical shaft S of the recorder in Fig. 251. On the upper end of this shaft is a rack R meshing with a pinion on the left-hand end of the horizontal shaft carrying the drum D which has on its curved surface a spiral band over which a trailing- arm F is fitted. The] curvature of the spiral band has been made to conform to a logarithmic curve so that increments of movement of the trailing-arm are proportional to the quantity of water flowing, and not to the up and down movement of the float. The trailer F is connected to the pen-arm P, making a record on the paper drum C. These charts will therefore have equally spaced ordinates and the area under the curve traced on them is proportional to the quantity of water flowing in a given time. Mover's Recorder (Fig. 252) consists of a weir tank T into which water discharges through the supply pipe S. A float F is located un- der the recorder R. The vertical shaft of the float, held in line by small ball-bearing guides, is connected to the pen point P directly, without any intervening gears or linkages. Baffle plates B are placed between the supply-pipe and the float to eliminate ripples and steady the float. The notch N follows almost exactly the theoretical lines for a flow pro- 1 Yarnall-Waring Co., Chestnut Hill, Pa. Fig. 251. — Lea's Recorder. 206 POWER PLANT TESTING Fig. 252. — Moyer's Recording Weir. portional to the head, accurate allowances being made also for end contractions. Radial ordinates traced by the pen point P are there- fore proportional to the rate of flow. By measuring these charts with a Bristol-Durland averager for circular charts (see page 87) the quantity of water flowing in a given time can be accurately obtained. The charts are graduated in pounds of water per hour jinstead of cubic feet. This is made possible by the au- tomatic temperature correc- tion of this apparatus. For a given weight of flow as the temperature increases or decreases the head in- creases or decreases corres- pondingly and vice versa; but at the same time the displacement of the float in- creases as the water becomes, lighter by reason of being hotter. These two influences therefore counterbalance, making the weight discharged in a given time proportional to the ordi- nates of the curve traced by the pen of the recorder. This apparatus is accu- rate to | per cent for temperature cor- rection. An automatic float valve is provided for shutting off the water supply to pre- vent overflowing. Lea's Recorder indicates also pounds per hour, but because the movement of the float is not proportional to the head the automatic correction for temperature is only an approximation. No weir device is very accurate for very low rates of flow. Any mistake made in determining h will produce a larger percentage error in the results with the rectangular and triangular notches than with an orifice. Where great accuracy is desired and the quantity of water to be handled is not too large, an orifice calibrated Fig. 253. — Best Kind of Orifice for Engine Tests. FLOW OF FLUIDS 207 and used in the bottom of the tank as shown in Fig. 253 is to be pre- ferred to measurements with a weir. This remark is particularly appli- cable in connection with the measurements of cooling (circulating) water in tests of large steam engines and turbines. Calibration Data Sheets. Use the same form for data as given for calibration of orifices or nozzles on page 202. Curves should be plotted with heads for abscissas and (1) the discharge (cubic feet per second) and (2) the coefficient of discharge for ordinates. Weighing Liquids in Tanks. In order to weigh liquids under a con- tinuous' flow two tanks, usually made of sheet metal, are generally used. Each tank is placed on a scales and the liquid is alternately discharged into each. The discharge pipe is usually arranged so that it is movable from one tank to* the other by turning on a screw thread. At the side of each tank near the bottom a so-called " quick opening " valve or cock is provided for rapidly emptying the tanks. These discharge valves should be large, because the more rapidly the tanks can be emptied the greater the quantity of water the arrangement will handle. 1 When only one platform scales is available an arrangement like that shown in Fig. 254 can be used efficiently. The larger tank is placed on the scales and the smaller one is supported on a platform or bench at such a height that it can be readily discharged into the larger tank. During the operation of weighing and emptying the larger tank, the liquid is discharging into the smaller one; and when the discharge is again directed into the larger tank the valve or cock on the smaller one is opened so that its contents will be included in the next weighing of the larger tank. For weighing feed-water in boiler tests the reverse of this arrange- ment is frequently applied. There are as before two tanks or barrels, of these the one more elevated is on a platform scales, and the attendant doing the weighing empties weighed quantities of water into the lower tank as needed to supply the feed-pump. In the lower tank the water level must be the same level at the end as at the beginning of a test. 2 -In cases where the flow is absolutely constant as in the discharge of water from nozzles or orifices with a constant head a tank may be filled at intervals, observing accurately the time for filling with a stop-watch and weighing each time. The average of several such determinations gives a fairly accurate result. 1 The discharge can be increased by attaching a short pipe to the discharge side of the valve which by reducing the contraction increases the flow. 2 For determining these levels in the tank a water-gage glass is very convenient. If, however, there is no gage glass on the tank marks can be made with a knife-scratch or by painting a line on the inside of the tank. 208 POWER PLANT TESTING Liquids are also often measured instead of weighed in calibrated tanks. In every case the temperature of the liquid must then be ob- served. In some cases the tanks have graduated scales at the side of a glass water gage from which the volume of water can be observed; or again there is only a single mark up to which the tank is to be filled each time. Establishing the exact level for a large surface is not an easy matter and to make this method more accurate the marks up to which the tank is to be filled are preferably put on a portion of the tank at the top which has been made considerably smaller in size than the rest of the tank. It is a very poor method to fill tanks up to the rim on account of the variableness of the meniscus which may vary from various causes. ife J^Quick Jt pT\ Opening" LJ-\J- m Fig. 254. — Weighing Device. Fig. 255. — "Double" Tank. Actual weights corresponding to measurements of volume are always varying with the temperature of both the liquid and of the tank or collecting vessel. It is therefore necessary in every case to determine by actual tests the weight corresponding to the volume of a tank for a given liquid at various temperatures and apply a calibration curve for temperature variations to all measurements. Calibrations should be made also with the inside wetted surface in as nearly the same condition as it will be after each emptying in a test. An ingenious method of measuring the flow of a liquid is illustrated in Fig. 255. It shows a tank separated by a partition into two parts. The partition is not quite as high as the sides of the tank. In oper- ation one of the halves is filled up to the top of the partition, permitting any excess to flow over into the other half. Then the supply pipe is swung over to the second half which is filling while the first half is being emptied. The tanks must be emptied, of course, more rapidly than they are filled. FLOW OF FLUIDS 209 In order to make easier the supervision and checking of tests it is desirable that as nearly as possible equal quantities should be weighed or measured as the case may be. Automatic scales provided with a continuously operating controlling device have been successfully developed. The poise on the weighing- beam is set in motion when the article to be weighed is put on the scales and when the beam shows it is balanced it stops automatically. The weight is usually registered by means of a counting device but a printing recorder can also be used. CHAPTER VIII CALORIFIC VALUE OF FUELS — SOLID, LIQUID AND GAS Calorific power is a term applied to the quantity of heat generated by the complete combustion of a definite quantity of fuel. In order to insure rapid and complete combustion the fuel is preferably burned in an atmosphere of oxygen under pressure. This calorific power of fuels is expressed in the English system as British thermal units per pound, and in the metric system as calories per kilogram. In fuel calorimetry it is always assumed in engineering calcula- tions that at about the usual " room " temperatures the specific heat of water is constant, so that the weight of reasonably pure or distilled water in pounds times the change in temperature in degrees Fahrenheit is the heat change in British thermal units (B.t.u.). Similarly the weight of water in kilograms times the change of temperature in Centi- grade degrees is the heat change in kilogram-calories (French) or Warme Einheiten (German). For conversion constants see page 29. The quantity of heat generated by combustion is measured by the rise in temperature of a given weight of water in a calorimeter of which the cooling effect or water equivalent k has been determined, and the temperature of any gas escaping has been reduced to that of the room. Now if W/ = weight of the fuel in pounds, w w = weight of the water in pounds, k = water equivalent 1 of the calorimeter, in pounds, ti = initial temperature of water, degrees Fahrenheit, t 2 = final temperature of water, degrees Fahrenheit, Q = total heat generated, B.t.u. 1 Water equivalent is used to express the heat-absorbing effect of the calorimeter as equivalent to that of a weight of water. This may be found (1) as for calorime- ters used for determining the quality of steam by the hot-water method (see page 72) (2) by taking the sum of the products of the weights and specific heats of the various parts of the calorimeter (see Calorific Power of Fuels, by H. Poole, pages 14 and 15), or (3) by comparing the results obtained with those that should have been secured, if there had been no absorption of heat, by the combustion in oxygen gas of some substance of which the heat value is known; as, for example, pure sucrose, carbon, napthalene, or benzoic acid. Samples of the materials of which the heat value has been worked out very accurately may be obtained together with a certificate at a very small ex- pense from the U. S. Bureau of Standards, Washington, D. C. The standard sample 210 CALORIFIC VALUE OF FUELS 211 H = (68) then the calorific value H per pound of fuel in British thermal units is Q _ (w B + k) (t 2 - ti) W/ W/ Corrections for Radiation can be practically eliminated by having the temperature of the water in the calorimeter before ignition as much below the " room " temperature as the final temperature is above. Bomb Calorimeters. Formerly the calorimeters used for burning fuels in an atmosphere of oxygen were arranged for combustion at con- stant pressure, but since it was found that more reliable results could be obtained generally with apparatus maintaining a constant volume, the former type is not now much used. When the combustion takes place at constant volume, the vessel receiving the charge of fuel and oxygen must be designed to withstand a great pressure, and therefore on account of the massive construction required the vessel is called a bomb calorimeter. The essential part of such a calorimeter is the strong steel vessel or bomb simi- lar to Fig. 256. It consists essentially of a steel shell S having a capacity of about 50 cubic inches and capable of resisting with safety a pressure of about 750 pounds per square inch. This shell is usually provided with a coat of enamel or a lining of platinum or nickel on the inside and is nickel- plated on the outside. The coating or lining on the inside is intended to resist corrosion and oxi- dizing action during the combustion. The advan- tage of the nickel lining over the coat of enamel is that when it is worn out or broken it can readily be replaced and at much less expense than the en- amel. The shell is closed at the top by an iron cover or cap which is to be made tight by screwing down on a lead washer with considerable force, using a long wrench. At the top of this cover or cap there is a conical seated valve, which is screwed in through the gland and stuffing- box G, by attaching a wrench at P. The valve and its seat are made of good nickel, as this metal is not easily oxidized. A wire electrode B, which is well insulated from the cover, extends into the shell and con- should be made into a pellet (see page 216) weighing about 1.5 grams which imme- diately after weighing should be put into the calorimeter and burned in commer- cially pure oxygen gas at about 400 pounds per square inch. After correction for radiation (see page 214) the discrepancy in the heat balance is the product of the re- quired water equivalent (pounds) and the observed temperature range. Detailed directions for very accurate determinations are given in Circular No. 11, of U. S. Bureau of Standards. ^VV^^vVxVX^ Fig. 256.— Section of Bomb Calorimeter. 212 POWER PLANT TESTING ducts the electric current for firing the charge of fuel, which is placed ©n a platinum dish or crucible supported by another wire A, attached to the cover on the inside. Usually one gram of finely powdered coal which will pass through a sieve having 100 meshes to the inch (" 10,000 meshes to the square inch ") is put into the dish to make a test for calorific value. 1 A small iron wire (which was previously weighed) is then suspended over the dish between the electrode and the wire support for the dish. The cover should then be screwed on with a long wrench, the shell itself being held in a vise. The complete Mahler apparatus 2 is shown in Fig. 257, showing the cylinder of oxygen O, the pressure gage M, the calorimeter vessel D. The end of the conical-seated valve (Fig. 256) is: Fig. 257. — Complete Mahler Apparatus. attached by means of pipe connections, preferably flexible, to the union U and to the valve W, which because of the high pressure should be opened slowly and carefully, and allow sufficient oxygen to pass into the bomb to provide a considerable excess above that actually required. 1 The Power Test Committee of A.S.M.E. recommended that the sample should be " air dried" (see page 232); and that a similar "air dried" sample should be tested for moisture, so that the final result may be based on heat value per pound dry coal. Many chemists and engineers prefer to use a sample of coal powdered "as received" and determine the heat value per pound "as received." The latter method does not give as accurate results as the former, but slightly reduces the time required for making the calorific determination. 2 The Mahler type of calorimeter is recognized as the most complete and accurate apparatus of its kind. Where the engineer does not have this instrument or some other reliable calorimeter of similar construction, the heat units can be determined by sending samples to a testing laboratory where such instruments are used." — Report of Power Test Committee of A.S.M.E. in Journal, Nov., 1912, page 1698. CALORIFIC VALVE OF FUELS 213 The' pipes for connecting the bomb to the oxygen cylinder should connect also with a pressure gage as shown, so that the pressure in the bomb can be regulated. For the combustion of coal a sufficient volume of oxygen is admitted to Mahler bombs of the usual size to make the pressure in the bomb from 350 to 375 pounds per square inch. Now close the valve on the oxygen cylinder and the conical-seated valve on the bomb, removing also the connections between the bomb and the oxygen cylin- der. Oxygen should be admitted to the bomb slowly, because if acci- dentally the oxygen be allowed to go in a little too rapidly, some of the sample of coal will be blown out of the dish and will probably not be burned. The bomb should then be placed in the calorimeter vessel D, which should be filled with a quantity of water previously weighed (at least about five pounds) to fill it to about the level indicated in the figure. Place the calorimeter thermometer T into the vessel, being careful that the end will not be touched and broken by the stirrer or other parts, and then after agitating the water for a few minutes to establish a uniform temperature, the observations can begin. The temperature should be very carefully observed for five minutes and recorded minute by minute, to determine the rate of variation of temper- ature before combustion. Then the electric circuit should be made and the combustion will, of course, begin immediately; but some little time will be required for the transmission of the heat generated to this water. Now take the temperature at the end of a half minute after making the electric circuit, and continue observing the temperature every half minute until it reaches its maximum value and begins to fall off regularly. Continue the observations for five minutes more to determine the rate of the fall of the temperature. The stirrer should be worked continuously but not too rapidly throughout the test, being careful, however, that the thermometer is not broken. When the observations have been finished, the conical-seated valve should be opened first to relieve the pressure and then the cover or cap can be unscrewed and removed. 1 • The method described for the use of the Mahler bomb calorimeter can be applied also for determinations of calorific value of liquid fuels. Heavy oils can be weighed directly in the platinum dish or crucible, but light oils which are easily vaporized must be put into specially prepared glass bulbs which are broken to allow access of the oxygen, 1 Some engineers wash out the inside of the bomb with a little distilled, water to collect the nitric and sulphuric acids formed. Usually, however, this correction for acids is not made, as the heat liberated in the formation of the acids is usually less than one-third of one per cent, which, of course, would be subtracted from the calorific value obtained. If the reader is interested he will find the method explained with the necessary data in the Calorific Power of Fuels, by H. Poole, page 62. 214 POWER PLANT TESTING just before the cover is put on the bomb. If sufficient oxygen is pro- vided in every case there will be complete combustion in the calorimeter with no other refuse than the cinders remaining. A specimen calculation is given below: Weights, — coal, .0030 lb.; 1 water in calorimeter, 4.85 lbs.; water equivalent of bomb, etc., 1.10 lbs. Weight of iron wire, .0002 lb. Preliminary Observations. Beginning 60.23° F., 3 minutes, 60.26° F., 1 minute, 60.24° F., 4 minutes, 60.27° F., 2 minutes, 60.25° F., 5 minutes, 60.28° F. „ , , . .. , , . .. 60.28-60.23 mo ' Rate of variation before combustion a = = = .01 F. 5 Observations during Combustion. 6 minutes, 65.45° F., 7 minutes, 67.29° F., 8 minutes, 67.38° F., max. 2 Observations after Maximum was reached. 9 minutes, 67.34° F., 12 minutes, 67.28° F., 10 minutes, 67.32° F., 13 minutes, 67.27° F. 11 minutes, 67.30° F., t, . , . • .. - + • 67.38 - 67.27 AOOO _ Kate of variation alter maximum a m = = = .022 h . 5 The rate of variation of temperature before combustion was for cool- ing the water and that after combustion was for a loss of temperature by the water. Evidently, then, the two rates are opposed in effect and the true average rate of variation is a „ = ~ - 01 + - 022 = _j_ -006 o F per minute> Three minutes (5-6, 6-7, and 7-8) were required for complete com- bustion or for the water to reach the maximum temperature. Total cooling correction to be added to the observed rise in temperature is, therefore, 3 X .006 = .018° F. 1 The coal had been warmed for one hour at a temperature of from 240 to 280 degrees Fahrenheit before weighing, in a crucible over a Bunsen burner or an alcohol lamp to drive off the moisture. In the best modern practice determinations are made on the basis of dry coal. 2 Some engineers make a curve of temperatures (ordinates) and time (abscissas) and use for the final temperatures in the calculations the value from the curve, when the part of the curve representing the cooling becomes a straight line. The difference in numerical values by the two methods is usually very slight. CALORIFIC VALUE OF FUELS 215 The total rise as corrected is 7.10 + .018 = 7.118° F. The quantity of heat generated is, therefore, Q = (4.85 + 1.10) X 7.118 = 42.35 (B.t.u.) for .0030 lb. of coal: and from this result &* - _:_t:: ._: y////////?////z/z/////s//, a MS/MS/M/ft Fig. 258. — Atwater's Fuel Calorimeter. Fig. 259. — Emerson's Fuel Calorimeter. must be subtracted the heat of combustion of the iron wire .0002 X 3000 1 or 0.60 B.t.u. The net value of the heat generated from the coal is, therefore, 42.35 - .60 = 41.75 B.t.u. A modification of the Mahler bomb calorimeter has been designed 1 The calorific value of pure iron is about 3000 B.t.u. per pound, and iron wire No. 34 B. & S. gage one inch long will generate in combustion .63 B.t.u. This is the size of wire generally used in calorimeter work. 216 POWER PLANT TESTING 2LX a '!£. by Atwater, 1 Fig. 258, and another by Emerson, Fig. 259. The former consists of the shell of the bomb A, the cap C screwed on numerous threads to the shell, and holding down the cover B. Into the vertical neck of this cover a screw E, holding another screw F, is fitted and is to rmmj. p-™i be turned down tightly, a lead washer serving ^ ^ . as " packing." A small passage for the ad- mission of oxygen from G is opened and closed as required by turning the screw F operating a needle-valve. A wire H of platinum or other non-oxidizable metal passes through the cover B and is insulated from it by a collar of hard rubber. Another wire rod I is attached to the lower side of the cover and electrical con- nection is made between the two wires H and I by a small iron wire stretched between them. A platinum crucible provided for receiving the fuel is supported by a " screw " ring. Ball bearings of hard steel are sometimes placed between the cover and the cap to reduce fric- tion when screwing down. Holes located in the sides of the cap are for the attachment of a long spanner wrench when turning down the cap. A hand-stirring device S is used for agitating the water in the vessel Q. The usual arrangement of the oxygen tank, pressure gage and tubing for charging a bomb calorimeter is illustrated in Fig. 260. A pellet press for compressing samples of fuel into a suitable size to burn in the crucible of this calorimeter is shown in Fig. 261. Fig. 259 shows another form of bomb calorimeter (Emerson) of which the Mahler is typical. It consists of a nearly spherical shell S, divided into two parts which are screwed together by the ring R. Powdered fuel is placed in the cm- cible C and is ignited electrically FiG m _ A pdIet Pregs for Compress . by the current passing through the ing Samples of Fuel. water in the vessel Q from the terminal at A, then through an insulated contact point P in the bottom of the calorimeter to a small platinum or iron wire in the crucible C, which becomes heated by the passage of the current to a white heat, 1 Atwater, Bulletin No. 21, U. S. Dept. of Agriculture. Fig. 260. — Apparatus for Charging a Bomb Calo- rimeter with Oxygen. CALORIFIC VALVE OF FUELS 217 igniting the fuel. One end of this small wire is fastened to make elec- trical contact with the lining of the calorimeter, which in turn is con- nected electrically with the plug and terminal at B. The outer vessel O is to be filled with water to the top. The stirring device consists of small propellers F, on a vertical shaft operated by a small electric motor M. Fig. 262. - Typical Parr Calo- rimeter. Fig. 263. — Parr Bomb for Hot Tube Ignition. Fig. 264. — Parr Bomb for Elec- trical Ignition. Parr Calorimeter. It is not always convenient to secure a supply of oxygen under pressure for use in a Mahler bomb, and consequently another type of fuel calorimeter, known as Parr's using a chemical (sodium peroxide) as the source of oxygen, has found considerable use, especially for relative determinations in power plants. The results obtained can scarcely be depended on to be as accurate as determina- 218 POWER PLANT TESTING tions with one of the bomb type. 1 Fig. 262 illustrates a simple form of Parr calorimeter. Sectional views of the two kinds of calorimeter vessels used are shown in Figs. 263 and 264. In the former the ignition is accomplished by dropping a hot wire through the neck into the shell A of the calorimeter. The cover is attached to the shell by means of a threaded nut F. A charge for the bomb consists of about .002 to .004 pound of pulverized coal from which the moisture has been driven off by warming for about an hour at a temperature of about 240 to 280 degrees Parr Calorimeter with Motor Stirring Device. Fahrenheit, and eighteen times as much by weight of sodium peroxide, which supplies the oxygen needed for combustion. Reactions pro- duced by combustion are complex as the products of combustion C0 2 , H 2 0, S0 2 , S0 3 , etc., combine with some of the Na 2 2 or Na 2 to form Na 2 C0 3 , NaOH, Na 2 S0 4 , etc. The charge should be well mixed 1 As regards the accuracy of the determinations very much depends on the chemi- cal purity and dryness of the sodium peroxide. If it is absolutely pure and the apparatus is handled with skill, it is easily possible to get results comparable with the bomb types. CALORIFIC VALUE OF FUELS 219 by shaking the shell after the cover has been securely fastened. The cover must be attached very securely by turning up the nut with a long wrench while the shell is held in a vise or in some similar manner, because there is a violent explosion when ignition takes place. When the hot wire (Fig. 263) is put into the tube in the long neck L, the cap R at the top must be struck quickly with a mallet in order to open the valve M, which opens inward into the shell and permits the wire to fall through before it cools. To be certain of obtaining a good result the wire should be heated almost to a white heat, and the coal should preferably be put into the shell after the sodium peroxide. The rise of the mercury in the thermometer will indicate when an explosion has occurred. The calorimeter is provided usually with wings or small propeller blades for agitating the water in the vessel O. The small pulley P (Fig. 262) shown at the top of the neck is used for turning the calorimeter bodily in the water when supported on the pivot F, shown at the bottom of the figure. The water equivalent of the calorimeter is determined in the same way as for other fuel calorimeters. Fig. 265 shows the Parr calorimeter as designed for electrical ignition and with a stirring device operated by an electric motor. Allowance must be made in the calculations for the heat generated by the chemical reactions of the sodium peroxide, which for the proportions given for a charge is approximately 27 per cent of the heat generated. Example Illustrating Calorific Determination with Parr Calorimeter. Weight of powdered coal .00401b., containing 1.3 per cent moisture, and 6.7 per cent ash. Weight of sodium peroxide .072 lb. Weight of water 7.160 lbs. Water equivalent of bomb 0.253 lb. Total equivalent weight of water 7.413 lbs. Temperature rise 10.2°F. Total heat generated, 7.413X10.2 = 75.61 B.t.u. Heat due to combustion of Iron Wire (see page 215) 1.11 B.t.u. Heat due to coal alone, (75.61 - 1.11) (1.00 - .27) = 54.39 B.t.u. Heat value per lb. coal as fired, ^a>- 13,598 B.t.u. Heat value per lb. dry coal, 13,598 , n _„„ t-. , "igr- 18,780 B.tu. Heat value per lb. combustible, 13,780 ., . «<->/-> t-« i -^3- = 14,780 B.t.u. 220 POWER PLANT TESTING Carpenter's Calorimeter. There are few calorimeters in which the oxygen is supplied at constant pressure which are altogether successful. One of the best forms of an apparatus of this kind has been designed by Carpenter, especially for coal determinations. With this apparatus no thermometers are needed, as the rise in temperature is measured by the expansion of the mass of water surrounding the combustion chamber. This apparatus is shown in Fig. 266. It consists of a combustion chamber 15, provided with a removable bottom 17, through which the tube 23, supplying the oxygen, passes into the combustion chamber. Electric current for ignition is con- ducted through the wires 26 and 27. The removable bottom sup- ports also the asbestos cup or crucible 22, used for holding the sample of coal to be burned. Just beneath the crucibles a silver mir- ror 38 is provided to " deflect " the heat. The plug containing the wires and the oxygen pipe 23 is made of alternate layers of asbestos and vul- canite. Products of combustion leave the combustion chamber through a spiral tube, the parts of which are marked 28, 29, 30, and 31, into the small vessel 39, at- tached to the outer casing of the instrument, and are finally dis- charged into the air from a small hole 41 in the side of the vessel. The pressure in the chamber 39 is indicated by a manometer gage 40. The inner casing of the instrument 1, containing the water for absorb- ing the heat generated, is nickel- plated and highly polished to re- duce radiation as much as possible. An open glass water gage 10 passes through the casings and extends below the water level. This water gage, with the scale attached to it, replaces the thermometer used in other calorimeters for measuring the rise in temperature. The scale is graduated to read inches, and it is calibrated usually by burning coke in the calorimeter, and determining thus the rise of the water level for a determinable weight of pure carbon. A calibration curve is usually supplied with the instrument. By mov- Fig. 266. — Carpenter's Calorimeter. CALORIFIC VALUE OF FUELS 221 ing the diaphragm 12, by means of the screw 14, the water level can be regulated, as well as the " zero " level in the glass water gage 10. A funnel 37 is provided for filling the instrument, and by inverting it, this funnel can be used also for draining. The instrument holds 5 pounds of water, and 2 grams of coal is the amount taken usually for a charge, requiring about twenty minutes for complete combustion of powdered coal. The asbestos cup 22 should be heated in the flame of a Bunsen burner before it is weighed. The charge of dried coal should then be put into it and weighed again. The difference will be the weight of the coal used. Now put the charge into the combustion chamber 15, place the platinum ignition wire above the coal, connect wires 26 and 27 to the battery, and as soon as the heat generated causes the level of the water to rise in the glass water gage 10, open the valve in the pipe discharging oxygen into tube 23, and then by pulling down the platinum wires to touch the contents of the crucible, the coal will be kindled. At the same time the reading of the glass scale opposite the gage glass 10 must be observed and recorded. Progress of the com- bustion can be observed through the glasses 33, 34, and 36, arranged vertically over each other for this purpose. As soon as the combustion is complete observe the time and the reading of the scale opposite the glass water gage 10. The difference between this last reading and the one taken at the beginning of the test is called the " actual " scale read- ing. The Correction for Radiation is made by observing the reading of the scale of the water gage after the oxygen has been shut off, for a length of time equal to that required for the combustion. The difference between this reading and the " actual " reading is to be added to the " actual " reading to obtain the corrected reading. By weighing the asbestos cup after the test is finished and subtracting from this weight that obtained previously for its weight empty, the weight of ash is determined. In order that Carpenter's calorimeter may give determinations of heat values that are at all accurate, all the air must be removed from the water used, as the presence of air 1 will affect the relative level of the water in the gage glass for a given rise in temperature. The oxygen must also be supplied at a constant pressure, maintaining the pressure indicated by the manometer gage at the value for which the calorimeter was calibrated. Most calibration curves are made for a pressure of about 10 inches of water. The apparatus can be made to give good comparative results when operated carefully and " according to direc- tions," but the general experience has been that calorimeters of this 1 About two inches of kerosene oil are usually put into the glass water gage to prevent air from coming in contact with the water. 222 POWER PLANT TESTING type give values that are from one to two per cent too low compared with results with a bomb calorimeter due to incomplete combustion. In general, the statement is often made that coal calorimeters intended for combustion at constant pressure will usually give nothing more than " faint approximations " to correct results. When making calorific determinations of coal the distinction must be carefully made between results obtained per unit weight of combustible or per unit weight of coal (including moisture and ash). Junkers' Calorimeter for Liquids and Gases. An apparatus for de- termining the calorific value of gases is shown in Fig. 267 and Fig. 268. The gas flowing in a pipe at the left (Fig. 267) passes through the meter A, then through the regulator B, and is burned in a type of Bunsen burner C in the lower part of the calorimeter. This instrument consists of a cylindrical copper vessel through which water is con- stantly circulating. The gases from the Bunsen flame in the calorimeter pass up through the hollow central portion of the instrument and near the top are deflected downward through Fig. 267,-Junkers' Calorimeter with Auxiliary a S roU P ° f Sma11 tubeS ranged Apparatus. m an annular ring between the outside and inside walls of the calorimeter. 1 Around these tubes water is kept circulating continuously to absorb the heat generated by burning the gas tested. After leaving these tubes the products of combustion discharge first into a chamber 31 (Fig. 268) and then into the air through the flue D. In order to keep the flow of water as regular as possible it is brought from the supply pipe G into a small reservoir in which the water is kept at a constant level (constant head) by means of an overflow pipe H. The water supplied to the calorimeter passes down through the pipe 6, through a valve at I, and discharges at K, running into a vessel in which it is weighed. A graduated tube Q (Fig. 267) is provided to collect the 1 A modification of Junkers' calorimeter is made by the American Meter Company of New York and Philadelphia. In principle it is exactly the same as the one described, but is much improved in mechanical construction, the greatest advantage being that the nest of small tubes can be readily removed for repairs. In the original design removal for repairs is difficult if not almost impossible. The "American" type is used exclusively by the U. S. Bureau of Standards, which is a sufficient guarantee of reliability. CALORIFIC VALUE OF FUELS 223 moisture from the steam that is condensed. The condensed steam col- lects in the combustion chamber 31 and escapes through the tube 35. A thermometer N, in a cup near the valve I, indicates the temperature of the water entering the calorimeter, and one at M shows the temper- ature of the water leaving. The temperature of the products of com- bustion (burned gases) is indicated by the thermometer O in the gas flue. The calorimeter is provided with an air jacket and is covered with sheets of copper, nickel plated and highly- polished so that the radiation loss is consid- ered negligible. If, then, the flow of water and the rate of burning the gas are regulated so that the temperature of the products of combustion as indicated by the thermometer at O is the same as the temperature of the air surrounding the calorimeter, practically all the heat generated by the burning gas is absorbed by the water. The rise in temper- ature of the water is observed by reading the thermometers at N and M. Now if the temperatures of the water at the inlet and the discharge have been ob- served and the weight of the water flowing has been determined while, for example, a cubic foot of gas has been burned, then the difference in temperature in degrees Fahren- heit times the weight of water in pounds gives the heat value in British thermal units per cubic foot of gas. This is called the higher heat value of the gas. Results of calorific determinations of a gas should be stated in a report as calculated as heat units per cubic foot of gas for the stand- ard conditions of pressure and temperature. The American Society of Mechanical Engi- neers has favored the adoption 1 of 30 inches of mercury pressure (14.7 lbs. per sq. in.) and 62 degrees Fahrenheit, while chemists and European engineers use as standard 29.92 inches (760 mm.) of mercury pressure and 32 degrees Fahrenheit (0 degrees Centigrade). This conversion can be readily made because the volume of the gas is directly proportional to the temperature and inversely to the pressure. For some calculations relating to the efficiency of heat engines it is desirable to know the number of heat units representing the calorific 1 Journal A.S.M.E., Nov., 1912, pages 1795-1801. Fig. 268. — Section of Junkers' Calorimeter. 224 POWER PLANT TESTING value of the gas when the steam formed in. the combustion is not con- densed but is carried off with the products of combustion as is the case in practice. To determine this value, sometimes called the "lower" heat value of the gas, the latent heat at atmospheric pressure of the amount of condensed steam collected in the Junkers calorimeter must be subtracted from the value obtained by multiplying together the rise in temperature and the weight of water used. This correction is usually about five to ten per cent, having usually the smaller value for producer gases with high percentages of CO. When thermal efficiencies of gas. engines are calculated, it should al- ways be clearly stated whether the " higher " or the " lower " heat value of the gas has been used. In all the codes of the American Society of Mechanical Engineers the " higher " heat value has the preference, but this is not by any means the generally accepted practice. This apparatus, although it operates by a constant pressure method, gives very satisfactory determinations. Radiation loss is small and is neglected. Since tests with this apparatus are started when all parts are already heated normally, no water equivalent is to be taken into account. If the temperature of the discharge gases is not the same as that of the air supplied the results will be in error but the amount of this correction (see page 252, footnote) and the method of computing it is uncertain. For this reason the temperature of the discharge gases should be regulated most carefully and not more than two or thres degrees Fahrenheit difference should be permitted between the tem- perature of these gases and that of the air supplied. Often it is neces- sary to open the windows of laboratory rooms to secure the proper temperatures. Temperatures of the water should be practically con- stant before a test is started. As the Junkers calorimeter is ordinarily operated it does not determine accurately the "higher" heating value even if all the precautions stated have been observed. It is because an excess of moisture above that which came in with the air goes off in the discharged gases. The only way to eliminate this error is to supply gas and air that are saturated with moisture. The calorimeter will then give the true " higher " heating value, because all the moisture resulting from the combustion of hydro- gen will be condensed, and will give up its latent heat. When a wet-gas meter is used it may be assumed that the gas is saturated as it comes to the apparatus. The obvious way to eliminate this error is to supply air which is also saturated. A convenient design is to connect the closed top of a cylindrical vessel about two feet high and five inches in diameter by a one-inch rubber tube to the bottom of the calorimeter, which, ex- cept for the opening for this tube, has been made air-tight. The cylinder is provided with a water-waste cock at the bottom. Several trays CALORIFIC VALUE OF FUELS 225 covered with coke are placed inside the cylinder which is perforated with a number of half-inch holes around the perimeter near the bottom for the admission of air. A water-jet discharges from the top of the cylinder and the water trickles down over the coke as the air enters at the bottom and passes up to the air-pipe leading to the calorimeter. By this method air is thoroughly saturated and not only more accurate but also much more consistent results for the " higher " heat values are obtained. Obviously this humidity correction has no effect at least in the theory of combustion on the " lower " heat values, as they are calculated for the condition when all the water vapor due to combustion leaves in the discharged gases. This is one reason why many engineers prefer to base calculations of thermal efficiency on the " lower " heat values. The error due to humidity can, however, be calculated approximately and the results correspondingly corrected. Moisture carried in the air can be determined by a wet- and dry-bulb thermometer (see page 368) and then assuming the discharged gases and the gas burned are saturated, the excess of condensation carried away in the discharged gases are readily calculated since their weight can be determined by a laborious calcu- lation involving the computation of the weight of air supplied which must be obtained from the analysis of the products of combustion (discharged gases). For making determinations of the calorific value of suction producer gas where the working gas pressure is less than atmospheric, a good method is to collect a sample with an aspirator and collecting bottle as explained for sampling flue gas (see page 236). Producer gas and other gases of low heating value can be mixed with a little air and burned in a simple metal tube, covered over at the end with a piece of fine gauze to prevent firing back into the mixing chamber. The mixture formed should preferably be non-explosive. The author has made continuous recording gas calorimeters using a simple pipe burner and positive pressure blowers (similar in design to those on page 366). One blower for measuring the gas is of about one- sixth the capacity of the larger one for measuring the air. Both blowers being driven by a single electric motor will always deliver gas and air in a constant ratio, provided pressure and temperatures of gas and air are maintained at about the values at which the instrument was calibrated. Calorific value of the gas is then proportional to the difference in temperature between the air and gas entering and the tem- perature of the discharged gases. A differential recording thermometer with the chart graduated in heat units per cubic foot of gas as determined by comparison with a Junkers calorimeter gives a continuous record of heat values of the gas. An apparatus of this kind is very useful in a. 226 POWER PLANT TESTING producer gas plant in showing the quality of gas produced and the rel- ative care observed in the operation of the producers. Exercise. Calorific Value of Gas. One cubic foot of coal gas at an absolute pressure of 28.9 inches of mercury and at 70 degrees Fahren- heit when burned in a Junkers calorimeter raised the temperature of 8.36 lbs. of water from 57.7 to 121.4 degrees Fahrenheit. Weight of condensation (water) collected due to combustion was .056 lb. Abso- lute atmospheric pressure 14.2 lbs. per sq. in. and corresponding latent heat of steam from tables = 971.5 B.t.u. per pound. " Higher " Heat Value at " Room " Conditions, B.t.u. per cu. ft. = (121.4 - 57.7) X 8.36 = 532.5. " Lower " Heat Value at " Room " Conditions, B.t.u. per cu. ft. = 532.5 - (971.5 X .056) = 478.2. Volume of Same Gas at Standard Conditions (30 in. mercury press, and 62 degrees Fahrenheit) = 1X28.9X522 An . n ,, 30X530 =°- 949c "- ft - " Higher " Heat Value at Standard Conditions, B.t.u., per cu. ft. = 532.5 .949 562. Lower Heat Value at Standard Conditions, B.t.u. per cu. ft. = 478.2 _.. w = 504 - Fig. 269 shows a balance and lamp attachments for a Junkers calorim- eter set up for determining the heat value of liquid fuels like gasoline, kerosene, crude oil, etc. The heat gen- erated is measured in the same way as when gas is burned and the weight of oil used is determined by weighing on the balance to which the lamp L is at- tached. This lamp is provided with a " regenerative " burner B with a long stem as shown. A small hand pump P is arranged for attachment to the valve V to put the oil in the bowl of the lamp under a pressure of about ten pounds per square inch. This air pres- sure forces the oil up the stem and through a coil of metal tubing which lies above the flame and is heated by it and gasified. The gaseous fuel escapes as a jet through a minute orifice where it should burn with a Fig. 269. — Balance and Lamp for Burning Oils in Junkers Calori- meter. CALORIFIC VALUE OF FUELS 227 blue flame indicating perfect combustion. When using oils heavier than gasoline the regenerator coil must be heated by burning alcohol in the cup shown in the figure just below the burner B. When combustion is not complete as is always the case when the flame is started soot ac- cumulates on the coil and is likely to choke the orifice of the burner. A piece of fine piano wire should always be at hand for cleaning the orifice. Calorific Values from Chemical Analysis. Dulong stated a long time ago that the heat generated by burning any fuel was equal to the sum of the " possible heats " generated by its component elements, less that portion of the hydrogen which combined with the oxygen in the fuel to form water. When hydrogen and oxygen exist together in a compound in the proper proportions to form water, the combination of these ele- ments has no effect on the calorific value of the compound. Now the calorific value of a pound of carbon is 14,600 B.t.u. and of a pound of hydrogen is 62,000 B.t.u., so that by Dulong's formula, the calorific value of a pound of fuel x would be stated, using these values, as x = 14,600 C + 62,000 ( H — -^ J + 4,000 S, . . . (69) where C, H, O and S are respectively the weights of the carbon, hydro- gen, oxygen and sulphur in a pound of fuel. A similar formula known as that of the Verein deutscher Ingenieure expressed in units and terms used in Dulong's, but corrected for w per cent of moisture is given as follows: x = 14,400 C + 62,000 (H — -^-J + 4,500 S — 1,100 w. . (70) Formulas given above are all for the " higher " heat values corre- sponding to those obtained with a bomb calorimeter. The last formula (70) expressed for " lower " heat value is: x = 14,400 C + 52,000 (H — -g J — 1,100 w. . . . (71) As the result of testing forty-four different kinds of coal with his bomb- calorimeter Mahler developed the following formula, using the same symbols used in Dulong's, x = 200.5 C + 675 H - 5,400. ..... (72) Using this latter formula Lord and Haas 1 computed the calorific values for a series of 40 Pennsylvania and Ohio coals' which they had analyzed and found that the maximum differences between the calculated results and the determinations with a bomb calorimeter were from 2.0 to — 1.8 1 Trans. American Inst, of Mining Engineers, Feb., 1897. 228 POWER PLANT TESTING \ X V. ^\ ^ t 10 15 20 25 30 35 Percent Volatile Matter "as Rec'd" Fig. 270. — Curve for Determin- ing Calorific Value of Coal. per cent. With fuels like coke, charcoal, and anthracite coal, in which the content of volatile matter is small, the calorific values calculated from an accurate analysis are usually in very close agreement with accurate calori- meter tests, but with coals having more than 20 per cent of volatile matter there is likely to be considerable error. A formula which is as accurate as any of those given above is based on the results of the proximate analysis. In this formula, known as Goutal's, 1 c = per cent fixed carbon in coal " as re- ceived." v = per cent volatile matter in coal " as received." a = constant from the curve in Fig. 270, then, x = 147.6 c + w. . (73) Proximate Analysis of Coal. For all tests in which an analysis of the coal or its calorific value is to be determined, it is very necessary that the sample to be tested be selected with the greatest care. The method generally adopted for obtaining a fair sample is known as " quartering," as explained in the Rules for Conducting Boiler Tests adopted by the American Society of Mechanical Engineers. (See page 231.) The utmost care must be taken that the amount of moisture in the sample received for analysis is the same as that in the original condition, or more specifically in a boiler test, at the time when the coal used in the test was weighed. For this reason samples of coal should be trans- ported and stored in air-tight preserving jars or similar vessels. It is not unusual, moreover, to find that coal containing 10 per cent of mois- ture will lose as much as 2 or 3 per cent of its moisture in the process of careless sampling, crushing, resampling, etc., while if it is allowable to remain exposed to atmospheric conditions for a considerable time in a warm room as much more may be lost by evaporation. Crushing, sampling, and weighing should always be done as rapidly as possible. Only during recent years has the proper importance of correct sampling of coal for analysis been understood. Particularly in run-of-mine coal, that is, coal as mined without crushing or screening, the careful selection of coal for the sample as regards size is also very important. If the sam- pling has not been done so as to get coal that is representative, certainly the analysis can be of no value. Proportionate amounts should be 1 Wisconsin Engineer, Dec, 1911. CALORIFIC VALUE OF FUELS 229 taken of both large and small sizes as well as of the fine dust. In the best engineering practice to-day at least 200 pounds of coal is collected for the process of sampling for the analysis. This amount of coal is to be broken up on a clean floor by any convenient means to a size of about | inch diameter, then thoroughly mixed and spread out on a flat circular pile. This pile is then " quartered," and opposite quarters are discarded. The remainder is now further broken up to about | inch diameter and the mixing, quartering and discarding is continued until from five to ten pounds remains. This is to be put into a glass jar or a tin can that can be made air-tight. The sealing should be carefully done, to prevent any deterioration of the sample in transportation to the laboratory where the analysis is to be made. In the laboratory the coal should be emptied from the jar or can and crushed to a fineness of about a 20-mesh sieve (20 meshes to the inch). The crushed coal is thoroughly mixed and a small portion, about 2 or 3 ounces, is put into an air-tight bottle and is to be used for the analysis. The rest is put back into the jar or can and sealed. It is to be retained for possible use in check tests. Proximate analysis of coal consists in determining the moisture, volatile matter, fixed carbon, ash and sulphur. Methods for these determinations are more or less empirical and vary slightly, so that in a report the authorship of the methods used should be stated. The methods most generally accepted by progressive engineers are those defined by the American Chemical Society, 1 and are in common use both in this country and in England. 2 Moisture and ash determinations are most important because they are non-combustible are detrimental constituents, the moisture requiring the wasting of heat for its evaporation into steam and the ash when present in large amounts is often likely to form clinker in poorly designed or badly operated furnaces and is also expensive to dispose of. Sulphur determinations are important only when the furnaces are not suitable for the combustion of coal containing one or two per cent of sulphur. Fur- naces are readily designed for burning coals having from four to five per cent of sulphur without clinkering the ash. Methods of the American Chemical Society are as follows : — 1. Moisture. Weigh in a covered crucible about four grams (about | oz.) of the coal passing through a 20-mesh sieve that was prepared for analysis as described above. This should be done as quickly as possible to avoid loss of moisture to the air. Remove the cover and heat in an oven for an hour at a temperature of from 220 to 230 degrees Fahrenheit. At the end of the hour replace the cover on the crucible, remove it from 1 Journal of American Chemical Society, vol. 21 (1899). 2 The Testing of Motive Power Engines, by R. Royds (London, 1911), page 293. 230 [POWER PLANT TESTING the oven and place it in a desiccator to cool. 1 When the crucible and the coal it contains are at nearly the same temperature they should be weighed. Again remove the cover and heat as before in the oven for a half hour longer. If the weight has remained constant no more heating is necessary and the difference between the first and last weigh- ings is the moisture in the coal. 2. Volatile Matter. Weigh about one gram Q$ oz.) of the " 20- mesh " crushed coal prepared for analysis in a platinum crucible weigh- ing from 20 to 30 grams (f to 1 oz.) 2 having a closely fitting cover. Support the covered crucible on a chemist's triangle of nichrome steel or of platinum which should be about 3 to 3| inches above the top of a good Bunsen burner. Heat the covered crucible for seven minutes in the full flame of the burner which should be at least eight inches high when unobstructed. Cool the crucible in a desiccator and then weigh carefully. The loss is the sum of the volatile matter plus the moisture. The room in which the test for volatile matter is made should be free from drafts which might cause a variation in the intensity of the flame. 3 3. Fixed Carbon and Ash. The crucible without the cover and the residue from the preceding test are now intensely heated with a Bunsen flame or with an air-blast lamp until all the carbon has been burned, and the weight of crucible and contents becomes constant. The use of the air- blast lamp in place of the Bunsen burner for this last determination will very much reduce the time required. The contents of the crucible may be stirred slightly with a platinum wire to break up the ash which should 1 While the sample is cooling there is the possibility that it may absorb moisture from the air unless it is placed in a desiccator until cool. It is difficult to get accurately the weight of hot bodies on account of the air currents produced. 2 The capacity of the crucible should be about three times the volume of the coal to allow for its expansion in coking. 3 It is not at all unusual for persons making tests on the same sample of coal to dis- agree as to the volatile content. This is because not all chemists and engineers will use the same type of burner, and if they are in different places they may have gas of widely different heat value. To overcome these difficulties the author has made electric furnaces consisting of a single resistance coil of nichrome wire calibrated for an im- pressed wattage to give a temperature of from 850 to 900 degrees Fahrenheit in a plati- num crucible placed in its core. In five minutes after the electric current is applied to the coil a constant and maximum temperature is reached and the covered platinum crucible is then inserted to be heated for seven minutes. Weighings are made as with the regular method. Results show remarkably close agreement, and are independent of variable gas supplies. Porcelain crucibles should never be substituted for platinum crucibles for accurate work as the porcelain requires a longer time to attain a constant temperature and therefore the duration of the application of the maximum temperature may not be the same as with one of platinum. CALORIFIC VALUE OF FUELS 231 become a powdery mass when combustion is complete. Combustion is assisted by inclining the crucible on the triangle during this test so as to admit air more freely for oxidation. After cooling in a desiccator make a final weighing. The difference between this weight and that of the crucible without cover when empty is the ash. Weight of fixed carbon is obtained by subtracting the sum of the weights of moisture, volatile matter and ash from the original weight of the sample of coal tested. Weighings should be made with chemical scales sensitive to TJJ \ o of the amount weighed. Two determinations of the complete proximate analysis should be made of each sample and the results should check within half of one per cent of the weight of the coal. In a report record with the regular data whether in the volatile test the coal coked into a single spongy mass or whether it remained granular. A. S. M. E. Methods. Methods proposed for poximate analysis of coal by the Power Test Committee of the American Society of Me- chanical Engineers vary somewhat from the above. The following important items should be cited: 1. In tests where firing is done by hand select a representative shovel- ful from each barrow-load as it is drawn from the pile and store the samples in a cool place in a tightly covered metal receptacle. When all the coal has thus been sampled, break up the lumps, thoroughly mix the whole quantity, and finally reduce it by the process of repeated crushing, quartering and discarding opposite quarters to a sample weighing about 5 pounds, the largest pieces being about the size of a pea. From this sample two one-quart air-tight glass fruit jars, or other air-tight vessels, are to be promptly filled and preserved for sub- sequent determinations of moisture, calorific value and chemical com- position. These operations should be conducted where the air is cool and free from drafts. When in the process of quartering and discarding the sample lot of coal has been reduced to about 100 pounds, a portion weighing say from 15 to 20 pounds should be withdrawn for the purpose of immediate moisture determination. This is placed in a shallow iron pan and dried on the hot iron boiler flue for at least 12 hours, being weighed before and after drying on scales reading to quarter ounces. The moisture thus determined is approximately reliable for anthra- cite and semi-bituminous coals, but not for coals containing much inherent moisture. For such coals, and for all absolutely reliable determinations, the method to be pursued is as follows: Take one of the samples contained in the glass jars and subject it to a thorough air-drying, by spreading it in a thin layer and exposing it for several hours to the atmosphere of a warm room, weighing it before and 232 POWER PLANT TESTING after, thereby determining the quantity of surface moisture it contains. Then crush the whole of it by running it through an ordinary coffee mill or other suitable crusher adjusted so as to produce somewhat coarse grains (less than T V inch), thoroughly mix the crushed sample, select from it a portion of from 10 to 50 grams, 1 weigh it in a balance which will easily show a variation as small as 1 part in 1000, and dry it for one hour in an air or sand bath at a temperature between 240 and 280 de- grees Fahrenheit. Weigh it and record the loss, then heat and weigh again until the minimum weight has been reached. The difference between the original and the minimum weight is the moisture in the air- dried coal. The sum of the moisture thus found and that of the surface moisture is the total moisture. To determine volatile matter place one gram of air-dried powdered coal in the crucible and cover it with a loose platinum plate. Heat 3^ minutes in the flame 2 of the Bunsen burner, and continue the heat- ing for 3| minutes longer in the flame of the blast lamp. Cool down, 3 ' remove the cover, and weigh the residue. The loss in weight repre- sents the combined volatile matter and moisture. Subtracting the moisture, the weight of volatile matter alone is determined. To ascertain the ash expose the residue in the crucible to the blast lamp until it is completely burned, using a stream of oxygen if desired to hasten the process. The residue left is the ash. The difference between the residue left after the expulsion of the vola- tile matter and the ash is the fixed carbon. To determine sulphur by Eschka's method, which is the one com- monly used, heat 1 gram of coal mixed with 1 gram of magnesium oxide and ^ gram of sodium carbonate for 1 hour, using an alcohol lamp. After cooling mix with 1 gram of ammonium nitrate and heat the mixture 10 minutes; then dissolve in 200 cc. of water, heat and reduce by evapora- tion to 150 cc, acidify with hydrochloric acid and filter. Add barium chloride to the filtrate and determine the sulphur by calculation from the quantity and composition of the barium thereby precipitated. The carbon and hydrogen are obtained by the use of the combustion apparatus. One-half gram of the pulverized air-dried coal is placed in a porcelain "boat," which is introduced between the copper roll of oxi- dized copper gauze and the copper oxide within the glass combustion tube. After the coal and the entire contents within have been thor- oughly dried out by a sufficient preliminary heating, aided by a current of dry air, the furnace is set to work and the coal burned by first passing 1 About i ounce to 2 ounces. 2 Height of flame is not specified. It could be stated that it should be in the hottest part of flame as in some coal specifications. 3 Cool in a desiccator. CALORIFIC VALUE OF FUELS 233 air through the tube and finally oxygen. The products of combustion are to be passed through potash bulbs and a chloride of calcium tube. The carbon dioxide produced by the combustion of the carbon is absorbed by the potash, and the water formed by the combustion of hydrogen, together with that due to the moisture in the air-dried coal, is taken up by the chloride of calcium. The quantity of carbon is determined by weighing the bulbs before and after, thereby obtaining the weight of the carbon dioxide produced, and then calculating the weight of carbon from the known composition of the dioxide. Likewise, the quantity of hydrogen is determined by weighing the calcium tube before and after, which, after deducting the moisture in the air-dried coal, gives the amount of water produced, and, dividing by 9, the amount of hydrogen. The ultimate analysis of coal for sulphur, pure carbon and hydrogen, as will be seen from the above description, requires the use of so much chemical apparatus, and at best it is so complicated, that it is not likely to be done except in a fully equipped chemical laboratory. It should not be undertaken by one who is not entirely familiar with all the details of the work. Hydrogen from Proximate Analysis. Professor L. S. Marks 1 has de- veloped an empirical formula for the determination of the hydrogen in coal from the proximate analysis. In this formula V is the per cent by weight of volatile matter in the combustible part; that is, coal less the sum of moisture and ash, and H is similarly the per cent by weight of hydrogen in combustible, then, 7-35 H = V(^ + 10 .013 Purchasing Coal by Calorific Value (" B. t. u's ") and Analysis. Every year there are more power plants purchasing their coal on the basis of analysis and calorific value. It may be generally assumed that shipments of coal coming from the same mine at different times will not vary a great deal in the composition of combustible. Moisture and ash may however vary considerably and every large shipment, pref- erably every car-load should be tested at least for moisture and ash content as a check to determine whether the specifications are being fulfilled. At frequent intervals particularly when ash or moisture determinations indicate a doubtful quality, samples should be sent to some laboratory for a complete analysis. For only the moisture and ash determinations no special equipment is needed. If moderately large weights are used, a fairly accurate " counter " or even a good plat- form scales may be used for weighing; and aside from this only a few sheet metal or tin pans, one or two thermometers, and several Bunsen 1 Power, Dec, 1908. 234 POWER PLANT TESTING burners and porcelain crucibles are absolutely required. 1 Besides the scales for weighing the equipment needed can be purchased for ten dollars. For a drying box almost any kind of a discarded galvanized iron or tin vessel can be used. There should be a small hole in the top for the insertion of a thermometer. To burn coal to ash with Bunsen burners requires the application of heat for a great many hours. Instead of providing air pressure for a blast lamp some engineers prefer to buy oxygen in tanks 2 and burn the coal rapidly in a pure oxygen atmosphere. 1 For a more complete discussion of the sampling and analysis of coal as well as criticisms of sample specifications, see Bulletin No. 5, The Pennsylvania Engineering Experiment Station, State College, Pa. (Free distribution.) 2 Linde Air Products Co., Buffalo, N. Y., with distributing stations in several large cities. CHAPTER IX FLUE GAS ANALYSIS Flue Gas Analysis. The analysis of flue gases in connection with tests of steam boilers gives a valuable means for determining the relative value of different methods of firing and of different types of furnaces. Errors in the analysis of flue gases are most often due to the inability to secure an average sample of the gases in the different parts of a flue or chimney. The composition is likely to vary considerably even during short intervals, and it is therefore desirable to adopt some method of sampling which will permit collecting the sample slowly and continu- ously for a considerable period. A very simple and convenient sampling apparatus is shown in Fig. 275. The sample of gas 1 is taken from the flue or chimney through the pipe P shown at the top of the figure. This pipe extends well into the flue and has usually a long slot cut into its side so that presumably a better sample of gas can be taken than if it were taken at the end of the pipe. The pipe outside the flue is connected by means of a short rub- ber tube to the sampling bottle. A valve V should be put as near as possible to the end of such pipes, so that they can be closed up when the sampling bottle is removed for analysis. If the pipe cannot be closed, the suction in the flue will draw air into the pipe and fill it so that when again connecting up the sampling bottle all this air must be removed before a true sam- ple can be taken. The sampling bottle is preferably one with a wide neck, closed with a rubber stopper through which two glass tubes pass into the bottle, one reaching nearly to the bottom and the other en- tering only a little below the stopper. Tube B can be connected to an aspirator or ejector, or any similar device producing a suction, and there will be a steady flow of gas through the bottle. If still another short tube like B is put into the stopper it can be used for the attachment of gas analysis apparatus, making a very satisfactory arrangement, and it is then unnecessary to disconnect the sampling bottle from the pipe. Small aspirators or ejectors (Fig. 276) operating on the principle of 1 For further discussion of sampling of the gas see " Boiler Code — Location of In- struments," page 272. 235 Fig. 275.— Gas Sam- pling Bottle. 236 POWER PLANT TESTING an injector with a small stream of water which entrains the gases is very convenient for collecting samples continuously. A slightly different design made of pipe fittings is shown in Fig. 277. a | ter Water enters through a vertical nozzle N and in discharging as a jet at high velocity entrains air or gas drawn in through the side opening and the mixture of atomized water and air is dis- charged with considerable velocity through the forcing tube F at the bottom. If an aspirator is not available, the sampling bottle and the tube B may be filled with mercury. Then by gradually siphoning the mer- cury from the bottle the flue gases will be drawn in. By adjusting the valve V the rate of flow of the gases into the bottle can be regulated. Mer- cury is too heavy to use in a very large sam- pling bottle so that water is often used instead, with the disadvantage, however, that the water will probably absorb some of the constituents of the gas. On this account very little water should be left in the bottle with the sample of gas. If the water is saturated with gases, as it will be from long use, this precaution is not so essential. Sampling and collecting bottles should have rubber rather then cork stoppers, because cork is too porous. 1 The sampling bottle and the tubes must be com- pletely filled with the liquid before beginning to take the sample by the method of displacing water, because any air left in them will remain in the bottle and will be mixed with the sample of the gas. If the end of the stopper going into the bottle is made slightly conical it will be easier to avoid entrapping bubbles of air at the top of the bottle when inserting the stopper. This type of sampling bottle when filled with liquid can be used also very conveniently by re- versing the connections of its tubes; that is, by attaching the long tube to the pipe entering the flue, and then turning the bottle upside down. The liquid will then run out through the shorter tube and the gas will be drawn in to fill the bottle. Discharge Fig. 276. — Water-jet As- pirator or Ejector. Bushing Fig. 277. made of Pipe Fit- tings. 1 A good way to cut holes in rubber stoppers for tubes is with the ordinary drills used for metal work, using a drill considerably larger than the hole required. FLUE GAS ANALYSIS 237 A portion of the gas can be removed from the sampling bottle into the measuring burette or tube required for making the analysis of the flue gas by connecting the short tube of the sampling bottle to the burette or to some other part of the gas analysis apparatus as may be required. If now the rubber tube connected to the longer tube of the sampling bottle when disconnected is put into a pail well filled with water, then as the gas is withdrawn from the bottle, water will be drawn from the pail to dis- place it. One of the advantages of this sampling apparatus is that it can be easily made from the materials obtainable in almost any town or village. A two-quart preserving jar with a rubber stopper to fit and tubes of glass, brass or iron can be used to make up a very good apparatus. Fig. 278 shows a sampling device used extensively in England. It consists of an iron tube T of f -inch-iron pipe open only at the end in the flue. The end is located carefully how- ever in English practice so that it lies well into the current of the gases. The pipe T is connected to a vessel M about two feet in diameter. The bottom is connected to another vessel of about the same size which is open at the top to the atmosphere. Samples for analysis are taken from the small bottle A. Vessels M and N are provided to prevent stag- nation of the gases in the pipes. Rubber tubing is used in only very short lengths because it is said to be more or less porous to C0 2 . When the test is started the bottle A is full of mercury, cock C is closed, and D is open just enough to permit a slow flow of mercury into B. When a new test is to be started the mercury in B is poured into C and A is filled and slowly emptied as before. Since there is nearly always a great variation in the composition of the gases in the various parts of a flue or chimney it is not very likely that a tube open at the end and having a long slit like the one described in the preceding paragraphs will give a " fair " sample. Obviously most of the gas will enter the slot in that portion of its length nearest the collecting apparatus. Another device often used for a sampling tube consists of a horizontal pipe into which a number of branch tubes are fitted. These branch tubes are arranged so that the openings at their ends will take samples from the different parts of the flue or chim- ney in which they are placed. Sometimes these branch pipes are also slotted or are perforated with small holes drilled into their walls. Fig. 279 shows an arrangement of sampling tubes for collecting flue V/*« Fig. 278. — English Gas Sampling Apparatus. 238 POWER PLANT TESTING gas recommended by the American Society of Mechanical Engineers in the code of 1899. It consists of a series of standard one-fourth inch pipes, all open and otherwise alike at the ends and of equal lengths. Each pipe is to be placed with one end in a shallow air-tight box or receiver made of sheet iron. It is convenient usually to make the depth of this sheet-iron box about the same as that of a course of bricks. These tubes should be arranged so that the open ends will be at points well distributed over the area of the flue which in the figure is marked A. The other ends, which are also open, are to be enclosed in the receiver B. The receiver is connected by four tubes C, C with a mixing box D. The flue gases drawn from it should be well mixed and should represent an average sample from the flue or chimney from which they are taken. Tests have shown that two such sampling devices placed in the same flue one above the other about a foot apart, will furnish samples of the flue gases showing the same composition when analyzed. There are several reasons why this apparatus having for a number of years the approval of the national societies was scarcely ever used. First, it is very expensive costing about $25 for each installation, and second, it is difficult to keep air-tight in large sizes. The recent recommendation of the Power Test Committee is that a single tube be used having perforations " extending the whole length of the part " immersed ", and pointing toward the current of gas, the collective area of the perfora- tions being less than the area of the pipe." Many American engineers of repute prefer a single pipe open only at the end like the one in Fig. 278, and observe extreme care in its location to get an average sample. A very convenient type of sampling bottle is shown in Fig. 280. It consists of a bottle with an opening at the bottom (tubulated), and is provided with a stopper at the mouth through which a glass funnel F and a tube are passed. The bottle contains water and light oil, and when it is filled there will be a layer of about 4 inches of the oil over the water. The tube O at the top is to be connected to the sampling tubes in the flue and the sample is taken in by opening the valve in this tube and also the one at the bottom of the bottle. The water drains off at the bottom and is replaced by the sample of gas. The glass funnel is used for pouring water into the bottle and in this way expelling the gas needed for analysis. The gas is thus made to pass out through the same tube through which it is drawn in. Another type of sampling apparatus used by many engineers consists of two galvanized-iron tanks, each about 2 feet high, and about 5 inches in diameter. On the side of each of these tanks and close to the bottom a valve is attached by soldering. These two valves are connected by a piece of heavy rubber tubing. One of the tanks is closed at the top, and a small stopcock or valve is attached to the cover. The other tank is FLUE GAS ANALYSIS 239 open at the top. The apparatus is used for collecting gas by filling to " overflowing " the tank with the closed top with water from the other tank by raising the latter so that the level of the water in it is above that of the water in the closed tank. By means of rubber tubing the stopcock or valve on the closed tank is then connected to the sampling tubes in the chimney or flues. Meanwhile the open tank is held at such an elevation that the water will not run back into it and create a vacuum in the closed tank. After this connection has been made the stopcock and valves are to be opened again, so that when the open tank is placed below the level of the closed one, the water will flow into the open tank Fig. 279. — A.S.M.E. Arrangement of Sam- pling Tubes for Flue Gas. Fig. 280. — Another Type fo Sampling Bottle. and fill the other one with gas. This operation should be repeated several times before the sample is carried away to be analyzed, so that there can be no doubt that none of the air in the sampling tubes en- tered the sample to be analyzed. This water can be used over and over again, and when it has become saturated with gas it is practically as good as mercury for use in collecting the gases. When a sample of flue gas is taken from the flue at a considerable distance from the furnace it is likely to become mixed with air leaking through the brickwork of the boiler setting, and the analysis will not show the true relations between the volumes of the so-called flue gases and the excess of air. To prevent as much as possible this leakage of air the joints in the masonry must be examined and repaired if neces- sary and the sample must be taken as near as possible to the fire, bear- 240 POWER PLANT TESTING ing in mind, however, that they must be drawn very slowly from the hot flue in order that they will be cooled down gradually to avoid dis- sociation. For hot gases an earthenware collecting vessel may be used if a glass bottle is likely to be broken. If dissociation occurs in the sample the analysis may show results entirely different from the true composition of the gas in the flue. It is also difficult to prevent the entrance of air into a flue through the bearings of dampers, and when- ever it is possible the sample of flue gas should be obtained between the furnace and the damper. At high temperatures sampling tubes of other metals than platinum 1 or nickel are not quite satisfactory, since by their oxidation they abstract the oxygen from the gases passing through them. Apparatus for the Analysis of Flue Gases. Samples of flue gases con- tain in varying amounts carbon dioxide (carbonic acid), oxygen, carbon monoxide, nitrogen, unburned hydrocarbons, and occasionally some free hydrogen. For the data which an engineer usually requires it is not necessary to determine by direct analysis more than three of these; carbon dioxide, C0 2 , oxygen, 2 , and carbon monoxide, CO. The determination of CO with the facilities and the portable apparatus ordinarily available in engineering laboratories is often somewhat doubtful. Some authorities state that there is rarely more than a trace of CO to be found in the gases from combustion in the ordinary types of furnaces. When more than one per cent of CO is shown by the analysis and the CO2 determination is not over 14 per cent, it may usually be assumed that a large part of what is taken to be CO is oxygen which was not absorbed by the proper reagent. * In the following table a set of analyses of flue gases is shown. The determinations were made by Scheurer-Kestner with coal from Ron- champ. Other analyses of flue gases may be checked by a comparison with this table. Thus when the analysis shows about 8.2 per cent C0 2 , the sum of the percentages of C0 2 and 2 will probably be between 19 and 20. PERCENTAGE COMPOSITION OF FLUE GAS co 2 o 2 CO N Hydrocarbons. 8.2 11.3 .2 79.8 .5 10.8 9.0 .2 79.7 .3 12,9 5.5 .2 80.3 1.1 13.4 4.4 .2 80.2 1.8 14.6 2.8 .3 80.6 1.7 1 Porcelain and annealed glass are sampling tubes for very hot flues. satisfactory materials to use for making FLUE GAS ANALYSIS 241 In the portable apparatus used by engineers for the analysis of flue gases a separate pipette or treating tube is provided for each reagent, and the chemicals used are of greater strength than the reagents used by some chemists. The following reagents give satisfactory results in a portable apparatus : (1) For absorbing C0 2 a solution of one part of potassic hydrate or caustic potash (KOH) dissolved in two parts by weight of water is generally used. (2) For absorbing O2 either an alkaline solution of pyrogallic acid 1 or sticks of phosphorus are employed. The alkaline solution of pyrogallic acid is prepared by mixing together preferably in the absorption pipette or treating tube, to prevent access of air, 5 grams of pyrogallic acid powder and 100 cubic centimeters of potassic hydrate (KOH) solution prepared as explained above. To make the absorption more rapid some engineers use a solution very much stronger in pyrogallic. This is not good practice as stronger solutions are likely to evolve CO in the presence of oxygen. Phosphorus is more rapid in its action than the pyrogallate, but has the disadvantage of being difficult to use as it must be handled under water. (3) For absorbing carbon monoxide a hydrochloric acid solution of cuprous chloride is used. This is prepared by dissolving about 10 grams of cupric oxide in from 100 to 200 cubic centimeters of concentrated hydrochloric acid. This solution must be allowed to remain in a bottle tightly closed and well filled with copper wire or gauze, until the cupric chloride is reduced to cuprous chloride. In this latter state the liquid will be colorless. Exposure to the air produces a brown color, indicating the cupric state. After a time these reagents must be replaced by new solutions. The potassic hydrate solution may be used until each volume has absorbed forty volumes of C0 2 . Pyrogallic acid solution deteriorates rapidly and each volume should be expected to absorb only one or two volumes of 2 . Cuprous chloride will absorb an equal volume of CO. Portable devices for the analysis of flue gases are generally known as " Orsat " apparatus. Of these there are various types. The one devised by Fisher, shown in Fig. 281, has been used extensively. It consists of a measuring-tube M surrounded by a water-jacket, and set of absorption pipettes, A, B, C, each filled with a reagent. Each of these pipettes (Fig. 282) consists of two glass vessels connected by a U-shaped glass tube at the bottom. One end of these pipettes is joined by means of a short piece of rubber tubing to a glass yoke T, which is designed for 1 When the temperature is lower than about 55 degrees Fahrenheit this reagent does not give satisfactory results. 242 POWER PLANT TESTING attachment at one end to a tube leading to the sampling-bottle and at the other end to the measuring-tube. A water bottle W is connected by a flexible rubber tube P to the bottom of the measuring tube. Before a sample of gas is taken into the apparatus for analysis certain adjustments must be made. In the first place, the reagents in the pipettes must all be brought to a standard level at some arbitrary point, usually indicated by a scratch on the glass tube just below the short rubber tube connecting it to the manifold yoke. This adjustment is Fig. 281. — Fisher's "Orsat" Apparatus. Fig. 282. — Pipette of Fisher'; "Orsat" Apparatus. accomplished by opening, one at a time, the valves at the tops of the pipette and removing the air (or the gas as the case may be) from it by lowering the water level in the measuring tube. The position of the water bottle determines, of course, the level of the water in the measuring tube. When all the air and gases remaining from a previous test have been expelled from the apparatus by filling the measuring tube and the tubes comprising the yoke with water, one of the tubes in the sampling bottle should be connected to the apparatus at e and by opening the FLUE GAS ANALYSIS 243 valve in the yoke at that end and lowering gradually the level of the water in the measuring tube M,a sample is obtained for analysis. This sample must be measured by the scale on the measuring tube at atmos- pheric pressure 1 to the nearest tenth of a cubic centimeter. 2 After the measurement has been made and recorded if the cock in the tube lead- ing to the absorption pipette containing the reagent for absorbing C0 2 is opened and then the water bottle is raised, all of the measured sample of gas can be forced over into the pipette. The reagent acts more rapidly on the gas if the water bottle is raised and lowered a few times. This movement of the water in the measuring tube agitates the gas and also the reagent and exposes more of the gas to the direct action of the absorbent. To increase the surface over which the reagents can act, the pipettes are filled with small glass tubes. When the gas has been in the first pipette for about a minute, it should be drawn back into the meas- uring tube with the level of the reagent brought back to the mark where it was originally, and the cock should be closed. The pressure of the gas is again made atmospheric and its volume measured. Now repeat this operation until two or three measurements are obtained which are alike, showing that all the C0 2 has been absorbed. Then the cock on the tube leading to the pipette containing the absorbent for oxygen can be opened, the gas forced over, and measured several times until a constant volume is observed. Finally the gas is passed into the third pipette for absorbing CO, repeating the operation of measuring as with the other pipettes. The absorption of oxygen will usually require considerably more time than for the determinations of the carbonic acid (C0 2 ) and the carbon- monoxide (CO), so that it is unnecessary to make a measurement of the gas until after the gas has been exposed for about three minutes to the reagent. Soft rubber bulbs or bags (see Fig. 282) should be attached by means of glass tubes to the corks shown in the pipettes on the farther side in Fig. 281 and are provided to protect the reagents from absorbing oxygen from the air. Both pyrogallic acid and cuprous chloride will absorb oxygen from atmospheric air, so that the access of fresh air must be prevented. The rubber bags are useful also for the purpose of pro- ducing alternately, with the pressure of the hand, suction and pressure for agitating the reagents. Allen-Moyer Gas Apparatus. A form of flue gas apparatus particu- larly suitable for portable use, and in which renewals of broken parts can be cheaply and easily made, is illustrated in Fig. 283. This appa- 1 The pressure of the gas is " atmospheric" when the water bottle is held so that the water in it and that in the measuring tube are at the same level. 2 The scales of practically all measuring tubes used for gas analysis apparatus are graduated in cubic centimeters. 244 POWER PLANT TESTING ratus, designed by Professor John R. Allen and the author, 1 is also particularly suitable for the use of engineers because the pipettes con- taining the reagents can be removed from the apparatus very easily for changing solutions. They can be emptied, refilled, and replaced in a very short time. The absorption pipettes (Fig. 284) are made simply of two glass test-tubes, the smaller one inside the larger one. The small test-tube is held inverted, and has a very small glass "capillary" tube fused into its closed end. The outer tube is closed at the top by a rubber stopper through which the capillary portion of the inner tube passes. Very small glass tubes are placed in the inner test-tube to increase the h Fig. 283. — Allen-Moyer Gas Apparatus. Fig. 284. — Absorption Pipette of Allen-Moyer Gas Apparatus. surface for the action of the reagent. The complete pipette is held in place by means of a hard-rubber disk supported on brass screws. The level of the reagent in the pipette is established when the air in the inner tube is drawn out and the level of the liquid rises to a mark on the glass capillary tubes. In the usual forms of the Orsat apparatus the pipettes invariably become leaky at the stopper provided for emptying. In the Allen-Moyer apparatus there is no opportunity for such leakage. When the sample of the gas is passed through the capillary tube into the inner test-tube, the reagent is displaced and raises the level in the outer test-tube. Similarly when the gas is passed back into the measur- ing tube the level falls in the outer tube, rises in the inner one, and is 1 Made by Bausch & Lomb Co., Rochester, N. Y. FLUE GAS ANALYSIS 245 brought back to the original level at the mark on the capillary tube. Otherwise the method of operation is the same as described for Fischer's apparatus (Fig. 281). In this apparatus the measuring tube M and water bottle W are of the conventional type. The yoke is also similar, although usually made of hard rubber to avoid breaking it in transportation. It has also spring pinchcocks instead of ground-glass cocks. When glass cocks are used by inexperienced persons all sorts of difficulties are likely to result, as it often happens that they are not pressed into their seats tightly enough to prevent the loss of gas or the entrance of air. Sometimes the glass cocks will be put into their seats so tightly that it is impossible to move them without breaking. These difficulties, although met often enough in laboratory work, are still more frequently observed in practice. It sometimes happens that, when a, b or c are open, and the pinch- cock on the tube between M and W is closed, the reagent in A, B or C fails, due not to a leak, as is usually supposed, but to the weight of the column of the reagent expanding the gas. In case any of the reagent in A or B be drawn over into the measuring tube and into the water, the analysis is not spoiled but may be continued by flushing out the tubes with water through d or e, or the addition of a little hydrochloric acid to the water in W will neutralize the hydrate or pyrogallate and the washing may be postponed until convenient. To remove pipettes A, B or C when necessary to renew the reagents, disconnect the gas bags and the rubber tube which connects the glass capillary and rubber capillary tubes, loosen the supporting screw and lift the pipette out. The rubber stopper may now be removed and solu- tions changed. Gases should be cooled well in the sampling bottle before beginning the analysis, because such gases change ¥ ^ T of their volume for a varia- tion of one degree Fahrenheit, or a change of 1 per cent in volume for 4.91 degrees. As an example, if the actual percentage of C0 2 is 10, and during the time required for analysis the temperature changed 4.91 degrees Fahrenheit, then there will have been a shrinkage of a vol- ume of one per cent due to temperature, and the apparent volume of CO2 will be eleven instead of ten. Producer Gas Analysis. For the analysis of producer and city illuminating gases which are more complex than the flue gases from coal furnaces the Hempel apparatus is generally used. Typical parts of the apparatus are shown in Figs. 285 and 286. It is slightly more difficult to operate and must be handled with greater care than a simpler portable apparatus arranged for flue gas analysis. . Essential parts of the apparatus are shown in Fig. 285. They are the leveling tube L, a measuring burette B, and an absorption pipette P. 246 POWER PLANT TESTING In the operation of the apparatus the pinchcocks Ci and C 2 are opened and water which has been thoroughly saturated with the kind of gas to be analyzed is poured into the leveling tube until both tubes are about half full. Now raise the leveling tube L so that the water from it flows into the burette B, making it entirely full. The pinchcock Ci should now be closed and connect the rubber capillary tubing at the pinchcock to the pipe from which the gas for analysis is to be taken. After connecting to the gas pipe again open the pinchcock Ci and draw a little more than 100 cubic centimeters of gas into the burette. Allow the apparatus to stand a minute in this position to per- mit the water clinging to the sides of the burette to drain. Now close the pinch- cock Ci and by raising the leveling tube compress the gas in the burette until the meniscus stands at the 100 cubic centi- meter mark, close the pinchcock C 2 on the lower length of rubber tubing and open the pinchcock Ci at the top of the burette momentarily to release the pres- sure in it. During this adjustment hold the leveling tube so that the surface of the water in it is on the same level as in the burette. There will be exactly 100 cubic centimeters of gas in the burette at atmospheric pressure if, when the pinchcock Ci is opened, the meniscus remains at the 100 mark. If, however, the meniscus shifts from the 100 mark, the adjust- ment will have to be repeated. Constituents of the gas must be absorbed in the following order: (1) carbon dioxide (C0 2 ) with potassium hydrate (KOH) 1 or sodium hydrate (NaOH) ; (2) " illuminant hydrocar- bons " (ethylene C2H2, and benzine C 6 H 6 in combination) with saturated bromine water 2 or fuming sulphuric 1 These reagents are the same as used in the flue gas apparatus. 2 Power Test Committee of A.S.M.E. specified bromine water for the hydrocarbons and NaOH for CO2. NaOH is cheaper than KOH but the latter is the more rapid absorbent. Fig. 285. — Hempel Gas Apparatus. Fig. 286. — Explosion Pipette. FLUE GAS ANALYSIS 247 acid; (3) oxygen (0 2 ) with caustic pyrogallic acid; (4) carbon monoxide (CO) with cuprous chloride; (5) marsh gas or methane (CH 4 ), hydrogen (H 2 ) and nitrogen (N 2 ). A pipette must be provided for each of the reagents and those for pyrogallic acid and cuprous chloride which absorb oxygen must be pro- vided with water seals. Both ends of the pipette for fuming sul- phuric acid must be kept closed except when an absorption is being made. After the sample has been collected in the burette the latter is at- tached to an absorption pipette as shown in Fig. 285 by a short piece of bent glass capillary tubing. Before this attachment is made the glass capillary should be filled with water by means of a medicine dropper, so as to avoid the error of entrapping air in this tubing. The pinch- cock Ci should now be open and by raising the leveling tube all the gas should be forced over into the pipette until the water from the burette fills the glass capillary connecting tube. Now close the pinchcock Ci and shake the pipette lightly to give the gas the best sort of contact with the absorption reagent. After shaking for two or three minutes the gas should be drawn back into the burette by lowering the leveling tube until the solution from the pipette fills the connecting capillary tube when the pinchcock Ci should be closed. The surfaces of the water in the leveling tube and in the burette should now be brought to the same level. The reading on the scale observed after draining the burette for two minutes as read at the bottom of meniscus should be recorded. The process must be repeated as in the operation of an apparatus for flue gas analysis until the reading is constant. In this way by the use of the proper pipettes all the constituents of the gas to be analyzed, with the exception of H 2 and CH 4 , are determined. Explosion Tests. For determining hydrogen and marsh gas (CH 4 ) combustion tests are made in a pipette like Fig. 286 which is made par- ticularly strong for exploding gases over mercury. In the upper portion of the pipette A there are two very fine platinum wires which are fused into the glass from opposite sides. When the spark from an induction coil is made to pass through the air gap between the two wires the explosive mixture contained is ignited. The explosion takes place with consider- able force so that extreme precautions should be taken to observe that the glass cock C and a very strong screw type of pinchcock at the end of the capillary tube U are very firmly closed. It is also very desirable to hold a wire screen about a foot square between the operator and the pipette when the spark is made and the explosion occurs. Procedure for the explosion pipette is as follows: Measure about 15 cubic centimeters (call this m) of the n cubic centimeters of gas remaining after the absorption of CO by the cuprous chloride and put 248 POWER PLANT TESTING the gas remaining in the burette into the pipette for absorbing CO. Now transfer these 15 cubic centimeters to the explosion pipette and immediately thereafter measure about 85 cubic centimeters of air and add this to the gas in the explosion pipette. Then after closing both cocks very carefully and tightly and shaking lightly to insure a good mixture, close the electric circuit momentarily through the induction coil to cause the explosion. After the explosion, and allowing a little time for cooling, measure the gas in the burette. Then pass the same gas into the C0 2 pipette, measure the absorption of CO2 in the burette, call this V cubic centimeters, and finally pass the remainder into the 2 pipette and deter- mine the volume of oxygen remaining. In the explosion the following reactions took place: 2H 2 + 2 = 2H 2 0. CH 4 + 20 2 = C0 2 + 2H 2 0. / If y is the number of cubic centimeters of oxygen absorbed after the explosion, then since there are 20.8 per cent of oxygen by volume in air, and if x cubic centimeters of air were used to make the explosive mixture, the oxygen supplied is 0.208 x, and the oxygen used in the explosion is 0.208 x — y. Assuming the water is all condensed and has practically no volume, the equations above show as regards volumes, Contraction of volume of gas (z) = § H 2 + 2 CH 4 . . . . (85) Oxygen used (0.208 x - y) = \ H 2 + 2 CH 4 (86) C0 2 formed (v) = CH 4 . Subtracting equation (86) from (85), z — [0.208 x — y] = H 2 (in m cu. cm. of " residual " gas), and total H 2 in original sample = — \z — [0.208 x — y]\. Similarly CH 4 in m cubic centimeters of " residual " gas is the absorption nv of C0 2 (v) and the total CH 4 in original sample is — ■ . Volume of nitrogen N can then be obtained by subtracting the sum of all the constituents now determined from the original volume of the sample of gas. Calculation of nitrogen content is, however, a good check on the accuracy of the analysis. Thus if, as above, x cubic centimeters of air were mixed with the m cubic centimeters of " residual " gas for the explosion test, then 0.208 x was oxygen and (x — 0.208 x) was nitrogen. After the C0 2 and 2 were absorbed from the products of the explosion there were say w cubic centimeters of nitrogen remaining, so that the m cubic centimeters of "residual " gas contained w — (x — 0.208 x) of nitrogen. Nitrogen content of the original sample is therefore - [w - x(l - 0.208)]. FLUE GAS ANALYSIS 249 Results of the analysis should be tabulated and the accuracy as regards the " nitrogen check " stated clearly. Coefficient of Dilution. The coefficient of dilution is the ratio of the volume of the air supplied to the volume theoretically necessary to provide the oxygen required for combustion. It will now be shown how this coefficient can be calculated from an analysis of the flue gases. Oxygen when combining with carbon to form carbon dioxide pro- duces a volume equal to itself, thus, C + 2 = C0 2 , (74) and in forming carbon monoxide produces twice the volume 2 C + 2 = 2 CO (75) Now if we use symbols to designate the percentages by volume of the gases in a sample of flue gas as follows: a is the percentage by volume CO2, b is the percentage by volume 2 , c is the percentage by volume CO, d is the percentage by volume N 2 (nitrogen). Then the volume occupied by the free oxygen in the air before com- bining with the carbon was a + b + \ c per cent, while that required for complete combustion is obviously a + c per cent. The coefficient of dilution 1 is therefore, *-W- <*» 1 This coefficient is variously defined so that in stating a result the method of com- putation should be given. Many engineers write it thus: a +b + \ c x = ' a + \c where the denominator as given is the air required for the kind of combustion as indi- cated by the analysis. Another method sometimes used is based on the nitrogen content. Practically all the nitrogen indicated by the analysis is due to the total air supplied, and using d for the percentage of nitrogen we can write for the nitrogen which was a part of that used for combustion, approximately, d - 11 (& - I c), d and x = j W7Z TV d - Ir (& - i c) This last formula is not as accurate as any of the others, giving usually results about 10 per cent too low. A better method than the last, based on the fact that the air supplied contains 20.8 per cent by volume of oxygen, is stated thus, _ 20.8 X ~ 20.8 - b ' 250 POWER PLANT TESTING In a little different form the reactions given in the last paragraph may be stated (1) for carbon burned to C0 2 , 2 C + 2 2 = 2 C0 2 , (77) (solid) (2 vols.) (2 vols.) 24 64 88 and (2) for carbon burned to CO, 2 C + 2 = 2 CO (78) (solid) (1 vol.) (2 vols.) 24 32 56 The ratio of the theoretical volume of the carbon burned to C0 2 , to the volume burned to CO is the same as the ratio of the volume of C0 2 in the products of combustion is to the volume of CO. Further since the ratio of volumes of the carbon vapor is obviously the same as the ratio of the corresponding weights, we may say that in a mixture of gases the ratio of the weight of carbon required to produce the C0 2 to the weight needed for the CO is equal to the ratio of the volume of C0 2 in the mixture to the volume of CO. The atomic weights of carbon and oxygen" show (equation (77)) that the volume of oxygen is 2| (64/24) times as heavy as an equal volume of carbon vapor. It follows then that for burning one pound of carbon to C0 2 , 2f pounds of oxygen are required. The other reaction (78) show- ing the combination of carbon and oxygen to form CO shows with the same reasoning that If pounds of oxygen are required to burn one pound of carbon to CO. In the general case we are considering and using symbols a and c re- spectively as before to represent the volumes of C0 2 and of CO in the flue gases, then the weight of the carbon burned to C0 2 is to the weight burned to CO as a is to c and if represents the weight of carbon a ~\~ c burned to C0 2 and the weight burned to CO, then the weight of a -\- c oxygen required per pound of carbon is 2§ ( — ~— J + i| f — — J and the weight of air 1 per pound of carbon is in pounds, K-r-cHfe)] m 100 r_ If z is the percentage by weight of carbon in the coal then the weight of air in pounds per pound of coal is 100 z I 1 Weight of air may be checked with Peabody's and Jacobus' equations (86, 87, and 88), pages 281 and 283. K-f>*(aT-c)] <» FLUE GAS ANALYSIS 251 Volumetric analyses of the flue gases can be used also to calculate the weight of the products of combustion (flue gases) per pound of coal burned and also the heat units lost in these gases. For this calculation the relations of the molecular weights are important. Molecular weight of C0 2 = 44; 2 = 32; CO = 28; N 2 = 28; C = 12. Now in a sample of x pounds of flue gases in which the percentages by volume are represented by the symbols a, b, c, d, the relative per- centages by weights of the constituents will be nr . 44 a _ 32 6 __ 28 c AT 28 d , ., , ,, C0 2 = ; 2 = ; CO = ; JN 2 = ; and we can write further x x x x Weight of carbon burned to C0 2 in x pounds of gas = \\ X 44 a = 12 a. Weight of carbon burned to CO in x pounds of gas = $f X 28 c = 12 c. Total weight of carbon burned in x pounds of gas = 12 (a + c). Total weight of carbon burned per pound of gas = 12 • Total weight of gas generated per pound of carbon = -^ — — - - • i.Z \Cb -\- c) Of this total weight of gas as expressed by the last equation the con- stituents are distributed in percentages by weight as follows : Weight of C0 2 in samples per pound carbon burned, 44 ax w\ 12 x (a + c)' co 2 tea ~ Wl ~ 12 (a + c) 2 32 6 W2 12 (a + c) CO 28 c Ws 12 (a + c) N 2 28 c? or we may write lb.; 14 ya -|- c) and similarly, lb. lb. 12 (a + c) lb ' Total weight of gases w g per pound of coal burned, if there is z per cent 1 of carbon in the coal, is in pounds z (44 a + 32 b + 28 c + 28 d) , Q , w '~ 12 (a + c) 100 (8l) Now if we represent by t f and t a the temperatures respectively in degrees Fahrenheit of the gases in the flue and of the air entering the 1 It may be assumed for very approximate values that z = 1 — y where y is the per cent of ash and moisture in the coal. 252 POWER PLANT TESTING furnace, then the heat lost in the flue gases Q g per pound of coal is, inserting values of specific heats, 1 Q g = —^(.217 W! + .217 w 2 + .245^3 + .244 Wi ) (t, - t a ). The total heat generated Qo by the more or less incomplete com- bustion of one pound of coal when there are a and c percentages by volume respectively of C0 2 and CO in the flue gas is Qo = ^(— ^xi4,600 + -4-xMooWt.u.), • • ( 82 ) 100 \a + c a + c / since the heat of combustion of carbon when burned to C0 2 is approxi- mately 14,600 and when burned to CO is about 4400 B.t.u. Finally, if Q p is the heat from perfect combustion or the " calorific " value in B.t.u. of a pound of coal, then the efficiency of the furnace 2 = ~ . The percentage of heat from perfect combustion lost in the flue Q g gases = jf> Recording Apparatus for Determining C0 2 . A typical apparatus for making a continuous record of the percentage by volume of carbon dioxide in gases is shown in Fig. 287. 3 The gas is taken to the instrument from the side flue or last combustion chamber of each boiler or furnace to the inlet pipe D and is drawn through the machine by a special water aspirator Q, fixed to the top of the instrument by means of the standard T. After actuating the aspirator Q, a portion of the water flows to the small tank L, which serves as a pressure regulator, and is provided with an overflow tube R. From this tank the water enters the. tube H in a fine stream, which is adjusted by the cock S and gradually fills the vessel K. This vessel consists of an upper and a lower compartment, the two being in communication through a tube erected in the upper chamber and reaching nearly to the top. Water, which enters this vessel K through the tube H, gradually fills the upper chamber and thus compresses the air contained in it. This pressure is transmitted to the lower compartment through the communication tube mentioned above, and acts upon the mixture of glycerine and water with which this is filled, driving it out into the calibrated tube C. When the rising liquid in C has reached the inlet and outlet to this vessel, no more gas can enter 1 This method of finding the heat escaping in the flue gases may be used to correct determinations made with the Junkers calorimeter (page 224) when the products of combustion are discharged at a temperature different from that of the room. 2 For the calculation of related quantities see "Heat Balance " (A.S.M.E. Rules), pages 280 and 281. 3 Sarco Engineering Co., West Street, N. Y. FLUE GAS ANALYSIS 253 the calibrated tube and the aspirator will now draw the gas through the seal F. Before the liquid can close the central tube in C, the gas must over- come the slight resistance offered by the elastic bag P, and is thereby forced to assume atmospheric pressure. When the liquid has sealed the lower open end of this central tube, exactly 100 cubic centimeters of flue gas are trapped off in the outer vessel C and its companion tube, under atmospheric pressure. As the liquid rises, the gas is forced through the thin tube Z into the vessel A, which is filled with a solution of caustic potash for ab- sorbing carbon dioxide. The gas remaining gradually displaces the potash solution in A, sending it up into the vessel B. This has an outer jacket filled with glycerine and supports a float N. Through the center of this float reaches a thin tube, through which the air in B is kept at atmospheric pressure. The float is suspended from the pen gear M by a silk cord and counterbalanced by the weight X. The liquid in B forces a portion of the air through the central tube in the float, and then raises the latter, causing the pen lever to swing upward, carrying the pen Y with it. The mechanism is so calibrated and ad- justed that the pen will travel to the top, or zero line, on the chart when only atmospheric air is passing through the machine, and nothing is absorbed by the potash in A. When there is any carbon dioxide in the gas it is absorbed by the potash in A, and not so much of this liquid would be forced up into the vessel B. The float would not then cause the pen to travel up so high on the chart, in proportion to the amount of C0 2 absorbed. " Precision " Simmance-Abady C0 2 Recorder 1 (Fig. 288) is a most satisfactory instrument, being at the same time simple and accurate. Through the valve V a continuous flow of water is maintained into the chamber k, with an overflow through o. Some of this water flows through E into the tank A and the float F rises with the water level. As it rises the cylinder d falls since they are joined by a cord c. When F is at the top of its stroke it raises a valve stem S, trips the valve and 1 Precision Instrument Co., Detroit. — Recording C0 2 Apparatus. 254 POWER PLANT TESTING causes the water in A to be siphoned out through the tube g. This lowering of the water level permits the float F to be lowered and at the same time raises the cylinder d, making a partial vacuum under it. Chimney gases are thus drawn from the flues into this bell through a supply pipe P. The water discharged from the tube g into the cup U when it overcomes the counterweight W, closes the valve h in the pipe P, and entraps a fixed volume of gas below d. In the meantime water has been continuously flowing into A, causing F to rise again and d to drop as before. As d goes down the entrapped flue gas is forced by means of the small pipes shown through the KOH solution in M and then into the " recorder " chamber R which is also water sealed by a cylinder j. Displacement of the cylinder j will be less in proportion to the volume of gas (C0 2 ) absorbed. The elevation to which j rises is indicated on a scale N graduated in per cent of C0 2; and a very simple record- ing device not shown in the figure regis- ters on a chart corresponding values. Samples are analyzed and records made every three minutes. A branch of the gas pipe P goes to Q where it enters a small water aspirator supplied with water from the pipe V which is continuously exhausting gas from the flues so that the sample entering the instrument shows its true analysis when it was taken. Uehling's C0 2 Recorder or " Composimeter m is shown diagram- matically in Fig. 289. The gas to be analyzed is drawn through the two apertures at A and B by a constant suction produced by an aspirator. If these apertures are kept at the same temperature, the suction or partial vacuum in the chamber between the two apertures will remain constant so long as all the gas passes through both apertures ; if, however, part of the gas be taken away or absorbed in the space between the apertures the vacuum will increase in proportion to the amount of gas absorbed. It is evident that if a manometer or light vacuum gage be connected with this chamber, the amount of gas absorbed will be indi- cated by the vacuum reading. The diagram shows the more important parts of the instrument. Gas is drawn from the last pass or uptake of the boiler by means of the 1 Uehling Instrument Co., Passaic, N. J. Fig. 288. — "Precision' corder. C0 2 Re- FLUE GAS ANALYSIS 255 To CO? "Recorder Absorption Chamber A aspirator through a preliminary filter located at the boiler, then through a second filter on the instrument as shown, and finally it passes through aperture A, the absorption chamber, and aperture B, to the aspirator, where it leaves the instrument with the exhaust steam. The C0 2 is completely absorbed by the caustic solution as the gas flows through the absorption cham- ber located between apertures A and B. Its volume will be reduced which causes a change in the tension (par- tial vacuum) of the gas between the two apertures. This tension varies with the percentage of C0 2 contained in the gas, and is indicated by a water column at the instrument, and by a recording vacuum gage gradu- ated to read percentages of C0 2 . Another apparatus for making con- tinuous determinations of C0 2 in flue gases is shown in Fig. 290. Gas from the boiler flue enters at M, passes through an excelsior filter where dust is removed, and then goes on through tubes leading it through glass vessels containing cotton wool and calcium chloride. After being cleaned and dried it passes in the direction of the arrows through the valve B into the weighing apparatus. On account of the greater specific gravity of C0 2 the larger the percentage of this gas the greater the tendency will be to pull downward the vessel G so that the pointer S on the balance can be adjusted to make the scale over which it travels indicate the per- centage of C0 2 . For such a method of determination, obviously, the gas must be clean and dry. The cleaning is done by the excelsior and wool filters and the drying is done by the calcium chloride. Smoke Determinations. The method most generally used to de« termine the density of smoke is with a Ringelmann chart, which is shown in reduced scale in Fig. 291. Cards ruled like those shown, but covering a much larger area, are placed in a horizontal row about 50 feet from the observer and in line with the chimney, together with plain white and black cards. The observer glances rapidly from the chimney to the cards and judges which one corresponds most nearly with the color of the smoke. The lines in cards 1 to 4 are respectively 1, 2.3, 3.7 and 5.5 millimeters thick and the spaces are 9, 7.7, 6.3, and 4.5 millimeters. Gas "Composi- 256 POWER PLANT TESTING c h M pg From Boiler Flue Fig. 290. — C0 2 "Weighing" Apparatus (Econometer), A soot collecting method is sometimes used. It is applied by sus- pending by a wire from the top of the flue a plate f-inch wide and 24 inches long. The hole through which the plate is inserted is kept covered at other times. This plate is temporarily withdrawn every two hours and the collection of soot removed and weighed. ■ ■ ■ ■ n ■ ■ ■ ■ ■ ■ No.3 ~No.l No.2 Fig. 291. — Ringelmann Smoke Chart. No.4 In another apparatus adopted by the Chicago Commerce Association a continuous sample of gas is drawn from the chimney by means of a special Pitot tube and exhauster. Solid particles in the gas collected are entrapped in a filter. The collecting tube is so arranged that the rate of flow through the apparatus is the same as that through the FLUE GAS ANALYSIS 257 chimney, so that when applied to chimneys of different areas the weight of soot, etc., collected is a measure of the density of the smoke. Eddy Smoke Recorder 1 is one of the few devices for automatically recording the density of smoke. The apparatus consists in its latest form of a steam ejector which draws a continuous flow of gas from the chimney and discharges it through a nozzle against a paper-covered drum revolved by a clock mechanism. The soot in the smoke makes its own record on the chart. 1 Hamler-Eddy Co., Chicago. CHAPTER X INSTRUCTIONS REGARDING REPORTS OF TESTS IN GENERAL 1 Object. Ascertain the specific object of the test, and keep this in view not only in the work of preparation, but also during the progress of the test, and do not let it be obscured by devoting too close attention to matters of minor importance. Whatever the object of the test may be, accuracy and reliability must underlie the work from beginning to end. If questions of fulfillment of contract are involved, there should be a clear understanding between all the parties, preferably in writing, as to the operating conditions which should obtain during the trial, and as to the methods of testing to be followed, unless these are already ex- pressed in the contract itself. Among the many objects of performance tests, the following may be noted: Determination of capacity and efficiency, and how these compare with stand- ard or guaranteed results. Comparison of different conditions or methods of operation. Determination of the cause of either inferior or superior results. Comparison of different kinds of fuel. Determination of the effect of changes of design or proportion upon capacity or efficiency, etc. Dimensions. Measure the dimensions of the principal parts of the apparatus to be tested, so far as they bear on the objects in view, or determine these from correct working drawings. Notice the general features of the same, both exterior and interior, and make sketches, if needed, to show unusual points of design. The dimensions of the heating surfaces of boilers and superheaters to be found are those of surfaces in contact with the fire or hot gases. 2 The submerged surfaces in boilers at the mean water level should be considered as water-heating surfaces, and other surfaces which are exposed to the gases as superheating surfaces. In the case of condensers, feedwater heaters, and the like, the outside surfaces are to be taken. In reheaters and steam jackets, the surfaces to be considered are those exposed to the steam of lower pressure. The dimensions of engine cylinders should be taken when they are cold, and, 1 Report of Committee on Power Tests, Journal of American Society of Mechanical Engineers, Nov., 1912. 2 Heating surface in fire-tube boilers is therefore calculated on the basis of the in- side diameter of the tubes. 258 REPORTS OF TESTS IN GENERAL 259 if extreme accuracy is required, as in scientific investigations, corrections should be applied to conform to the mean working temperature. If the cylinders are much worn, the average diameter should be found. Clearance of the cylinders may be determined approximately from working drawings of the engine. For accurate work, when practicable, the clearance should be determined by the water measurement method. (See page 293.) Examination of Plant. Make a thorough examination of the physical condition of all parts of the plant or apparatus which concern the object in view, and record the conditions found, together with any points in the matter of operation which bear thereon. Boiler Leakage. In boilers, for example, examine for leakage of tubes and riveted or other metal joints. Note the condition of brick furnaces, grates and baffles. Examine brick walls and cleaning doors for air leaks, either by shutting the damper and observing the escaping smoke 1 or by candle-flame test. Determine the condition of heating surfaces with reference to exterior deposits of soot and interior deposits of mud or scale. See that the steam main or header is so arranged that condensed and entrained water cannot flow back into the boiler. Ascertain the interior condition of all steam, air, gas, or water cylinders and the condition of their pistons, and of water plungers and impellers, together with the valves and valve-seats belonging thereto. Locate vacuum leaks in ex- haust piping, condenser, packings, etc., using vacuum gage or candle-flame test. Examine steam, air, gas, or water piping, traps, drip valves, blow-off cocks, safety valves, relief valves, heaters, etc., and make sure that they do not leak. Determine the condition of the blading, nozzles, and valves in steam turbines, and of buckets, guides and draft-tubes in water turbines. If the object of the test is to determine the highest efficiency or ca- pacity obtainable, any physical defects, or defects of operation, tending to make the result unfavorable should first be remedied ; all fouled parts being cleaned, and the whole put in first-class condition. If, on the other hand, the object is to ascertain the performance under existing conditions, no such preparation is either required or desired. General Precautions against Leakage. In steam tests make sure that there is no leakage through blow-offs, drips, etc., or any steam or water connections of the plant or apparatus undergoing test, which would in any way affect the results. All such connections should be blanked off, or satisfactory assurance should be obtained that there is leakage neither out nor in. This is a most important matter, and no assurance should be considered satisfactory unless it is susceptible of absolute demon- stration. Apparatus and Instruments. Select the apparatus and instruments specified in the Code of Rules 2 applying to the test in hand, locate and install the same, and complete the preparations for the work in view. 1 Test for air leaks in the setting by firing a few shovelsful of smoky fuel and by immediately closing the damper, observing the escape of smoke through the crevices. 2 Various codes are given in this book, beginning on page 269. 260 POWER PLANT TESTING The arrangement and location of the testing appliances in every case must be left to the judgment and ingenuity of the engineer in charge, the details being largely dependent upon locality and surroundings. One guiding rule, however, should always be kept in view, viz., see that the apparatus and instruments are substantially reliable, and arrange them in such a way as to obtain correct data. A summary is given below, embracing the entire list of apparatus and instruments referred to in the various Codes, with descriptions of their leading features, methods of application and use, and, where needed, methods of calibration. (a) Weighing Scales. For determining the weight of coal, oil, water, etc., ordinary platform scales serve every purpose. Too much dependence, however, should not be placed upon their reliability without first calibrating them by the use of standard weights, and carefully examining the knife-edges, bearing plates, and ring suspensions, to see that they are all in good order. Other scales required in connection with test work are small scales for weigh- ing coal-samples used in drying, and laboratory scales for analysis and calorific determinations pertaining to fuels. Such scales should be sensitive to 1/1000 of the quantity weighed. For testing locomotives and some classes of marine boilers, where room is lacking, sacks or bags are sometimes required to facilitate the handling of coal, the sacks being previously weighed at the time of filling. (a) Leakage. It is not always necessary to blank off a connecting pipe to make sure that there is no leakage through it. If satisfactory assurance can be had that there is no chance for leakage, this is sufficient. For example, where a straightway valve is used for cutting off a connecting pipe, and this valve has double seats with a hole in the bottom be- tween them, this being provided with a plug or pet cock, assurance of the tightness of the valve when closed can be had by removing the plug or opening the cock. Like- wise, if there is an open drip pipe attached to an unused or empty section of pipe beyond the valve, the fact that no water escapes here is sufficient evidence of the tight- ness of the valve. The main thing is to have positive evidence in regard to the tight- ness of the connections, such as may be obtained by the means suggested above; but where no positive evidence can be obtained, or where the leakage that occurs cannot be measured, it is of the utmost importance that the connections should be broken and blanked off. Leakage of relief valves which are not tight, drips from traps, separators, etc., and leakage of tubes in the feed-water heater must all be guarded against or measured and allowed for. It is well, as an additional precaution, to test the tightness of the feed-water pipes and apparatus concerned in the measurement of the water by running the pump at a slow speed for, say, fifteen minutes, having first shut the feed valves at the boilers and making sure they are tight. Leakage will be revealed by disappearance of water from the supply tank. In making this test a gage should be placed on the pump discharge to guard against undue or dangerous pressure. (b) Water-glass Tests of Leakage. To determine the leakage of steam and water from a boiler and steam pipes, etc., the water-glass method may be satisfactorily employed. This consists of shutting off REPORTS OF TESTS IN GENERAL 261 all the feed valves (which must be known to be tight) and the main feed valve, thereby stopping absolutely the entrance or exit of water at the feed pipes to the boiler; then maintaining the steam pressure (by means of a very slow fire) at a fixed point, which is approximately that of the working pressure, and observing the rate at which the water falls in the gage glasses. It is well, in this test, as in other work of this char- acter, to make observations every ten minutes, and to continue them for such length of time that the differences between successive readings attain a constant rate. In many cases the conditions will have become constant at the expiration of fifteen min- utes from the time of shutting the valves, and thereafter the fall of water due to leak- age of steam and water become approximately constant. It is usually sufficient, after this time, to continue the test for two hours, thereby obtaining a number of half-hourly periods. When this test is finished, the quantity of leakage is ascertained by calcu- lating the volume of water winch has disappeared, using the area of the water level and the depth shown on the glass, making due allowance for the weight of one cubic foot of water at the observed pressure. The water columns should not be blown down during the time a water-glass test is going on, nor for a period of at least one hour before it begins. If there is opportunity for condensation to occur and collect in the steam pipe dur- ing the leakage test, the quantity should be determined as closely as desirable, and properly allowed for. (c) Piston Rod and Valve Rod Leakage. In making an engine test where the steam consumption is determined from the amount of water discharged from a surface condenser, leakage of the piston rods and valve rods should be guarded against; for if these are excessive the test is of little use, as the leakage consists partly of steam that has already done work in the cylinder and of water condensed from the steam when in contact with the cylinder. If such leak- age cannot be prevented, some allowance should be made for the quantity thus lost. The weight of water as shown at the condenser must be increased by the quantity allowed for this leakage. MISCELLANEOUS INSTRUCTIONS The person in charge of a test should have the aid of a sufficient number of assistants, so that he may be free to give special attention to any part of the work whenever and wherever it may be required. He should make sure that the instruments and testing apparatus con- tinually give reliable indications, and that the readings are correctly recorded. He should also keep in view, at all points, the operation of the plant or part of the plant under test and see that the operating con- ditions determined on are maintained and that nothing occurs, either by accident or design, to vitiate the data. This last precaution is especially needed in guarantee tests. Before a test is undertaken, it is important that the boiler, engine, or other apparatus concerned, shall have been in operation a sufficient length of time to attain working temperatures and proper operating conditions throughout, so that the results of the test may express the true working performance. 262 POWER PLANT TESTING It would, for example, be manifestly improper to start a test for determining the maximum efficiency of an externally fired boiler with brick setting, until the boiler had been at work a sufficient number of days to dry out thoroughly and heat the brick work to its working temperature; and likewise improper to be- gin an engine test for determining the performance under certain prearranged conditions until those conditions had become established by a suitable prelimi- nary run. An exception should be noted where the object of the test is to obtain the working performance, including the effect of preliminary heating in which case all the conditions should conform to those of regular service. In preparation for a test to demonstrate maximum efficiency, it is desirable to run preliminary tests for the purpose of determining the most advantageous conditions. In all tests in which the object is to determine the performance un- der conditions of maximum efficiency, or where it is desired to ascertain the effect of predetermined conditions of operation, all such conditions which have an appreciable effect upon the efficiency should be main- tained as nearly uniform during the trial as the limitations of practical work will permit. In a stationary steam plant, for example, where maximum efficiency is the object in view, there should be uniformity in such matters as steam pressure, times of firing, quantity of coal supplied at each firing, thickness of fire, and in other firing operations; also in the rate of supplying the feed-water, in the load on the engine or tur- bine, and in the operating conditions throughout. On the other hand, if the object of the test is to determine the performance under working conditions, no attempt at uniformity is either desired or required unless this uniformity corresponds to the regular practice and when this is the object the usual working conditions should prevail throughout the trial. A log of the data should be entered in notebooks or on blank sheets suitably prepared in advance. This should be done in such manner that the test may be divided into hourly periods, or if necessary, periods of less duration, and the leading data obtained for any one or more periods as desired, thereby showing the degree of uniformity obtained. •' The readings of the various instruments and apparatus concerned in the test other than those showing quantities of consumption (such as fuel, water, and gas) should be taken at intervals not exceeding half an hour and entered in the log. Whenever the indications fluctuate, the intervals should be reduced according to the extent of the fluctuation. In the case of smoke observations, for example, it is often necessary to take observations every minute, or still oftener, continuing these through- out the period covering the range of variations. Make a memorandum of every event connected with the progress of a test, however unnecessary at the time it may appear. A record should REPORTS OF TESTS IN GENERAL 263 be made of the exact time of every such occurrence and the time of tak- ing every weight and every observation. For the purpose of identi- fication the signature of the observer and the date should be affixed to each log sheet or record. In the simple matter of weighing coal by the barrow-load, or weighing water by the tank-full, which is required in many tests, a series of marks, or tallies, should never be trusted. The time each load is weighed or emptied should be recorded. The weighing of coal should not be dele- gated to unreliable assistants, and whenever practicable, one or more men should be assigned solely to this work. The same may be said with regard to the weighing of feedwater. To show the uniformity of the data at a glance the whole log of the trial should be plotted on a chart, using horizontal distances to represent times of observation, and vertical distances on suitable scales to repre- sent various data as recorded. Such a chart showing the log of a boiler test is illustrated in Fig. 296, page 268. It is very heplful to plot the leading data on such a chart while the test is in progress. Report of a test should present all the leading facts bearing on the design, dimensions, condition, and operation of the apparatus tested, and should include a description of any other apparatus and auxiliaries concerned, together with such sketches as may be needed for a clear understanding of all points under consideration. It should state clearly the object and character of the test, the methods followed, the conditions maintained, and the conclusions reached, closing with a tabular summary of the principal data and results. . The standard units on which to base the various measures of capacity and the standard forms of expressing efficiency and economy to which the codes apply are as follows: STANDARD UNITS OF CAPACITY a Boilers 1 f One pound of water evaporated into dry steam 1 from and at 212 deg. F. per hour. (One indicated horse power developed in the main cylinders i.h.p. One brake horse power delivered by the main shaft b.h.p. c Steam Turbines f One brake horse power delivered by the main I shaft b.h.p. 1 A subsidiary unit which may be used for stationary boilers is a " Boiler Horse Power," or 34| pounds of water evaporated from and at 212 deg. F. per hour, i.e., from water at 212 deg. F. into steam at the same temperature. Electrical engineers have suggested a unit termed " Myriawatt," which differs but little from boiler horse power when expressed in B.t.u. per hour. 264 POWER PLANT TESTING driven generators) Pumping Machinery. kw.-hr. 1 One kilowatt-hour delivered at the busbar, 1 not \ I including exciter output 2 One gallon of water discharged to the force main in 24 hours. One gallon of water discharged per min 3 gal. per min. One water horse power delivered to the force main, based on the total head including suction / Air Machinery g Locomotives. . Gas Produce Gas and Oil Engines . w.h.p. F. and 30-in.' cu. ft. air h.p. i.h.p. One cu. ft. of air at 62 barometer ; One air horse power One indicated horse power developed in the main cylinders One dynamometer horse power delivered to the draw-bar dyn. h.p. h Gas Producers One pound of dry fuel consumed per hour (One brake horse power delivered by the main ( shaft b.h.p. . w , . ( One brake horse power delivered by the main 7 W aterwneels { i ^ , i i J I shaft b.h.p. STANDARDS OF EFFICIENCY AND ECONOMY a Boilers. 6 Reciprocating Steam Engines c Steam Turbines . d Turbo-generators, (including engine- driven generators) . . Relation between B.t.u. absorbed by boiler coal fired and calorific value of 1 lb. coal, of boiler furnace and grate.) Relation between B.t.u. absorbed by boiler, combustible burned and calorific value of bustible. (Efficiency of boiler and furnace.) '(1) B.t.u. per i.h.p.-hr. (2) B.t.u. per brake h.p.-hr. (3) Thermal efficiency ratio referred to i.h.p. (4) Thermal efficiency ratio referred to b.h.p. (5) Lbs. of dry steam per. i.h.p.-hr. (6) Lbs. of dry steam per b.h.p.-hr. '(1) B.t.u. per b.h.p.-hr. (2) Thermal efficiency ratio. (3) Lbs. of dry steam per b.h.p.-hr. (1) B.t.u. per kw.-hr. (2) Thermal efficiency ratio. (3) Lbs. of dry steam per kw.-hr. per lb. of (Efficiency per lb. of 1 lb. com- 1 It is assumed that the drop in voltage between generator terminals and switch- board is not over one-half of one per cent. 2 If the exciter current is taken from an outside source the kw. thus supplied are to be deducted from the total output. 3 This unit applies to small pumps and some classes of large-sized pumps. 4 30-in. barometer is referred to a temperature of 62 deg. F.; or 29.92-in. referred to 32 deg. F. (see page 223). REPORTS OF TESTS IN GENERAL 265 Pumping Engines . / Air Machinery . (1) Ft.-lbs. of work per million B.t.u. (2) Ft.-lbs. of work per 1000 lbs. dry steam. (3) Ft.-lbs. of work per 100 lbs. dry fuel. '(1) B.t.u. per net air h.p. per hr. (2) Lbs. of dry steam per net air h.p. per hr. (3) Lbs. of dry steam per 1000 cu. ft. of free air com- pressed to 100 lbs. gage pressure reduced to atmospheric temperature. Locomotives . h Gas Producers. i Gas and Oil Engines . j Waterwheels k Steam Power Plants. I Electric Power Plants . . - m Pumping Engine Plants Lbs. of dry fuel per i.h.p.-hr. Lbs. of dry fuel per dyn. h.p.-hr. Lbs. of dry steam per i.h.p.-hr. Lbs. of dry steam per dyn. h.p.-hr. Lbs. of dry fuel per ton-mile. Relation between B.t.u. of the gas output per lb. of fuel charged and calorific value of 1 lb. of fuel. (1) B.t.u. per brake h.p.-hr. (2) Thermal efficiency ratio referred to b.h.p. (3) Lbs. of dry fuel per b. h.p.-hr. (4) Cu. ft. of gas per b. h.p.-hr. | Relation between brake h.p. and potential h.p. of total water used. r (1) Lbs. of dry fuel per i.h.p.-hr., main engine. (2) Lbs. of dry fuel per i.h.p.-hr., auxiliaries. (3) Lbs. of dry fuel per i.h.p.-hr., whole plant. (4) Lbs. of dry steam per i.h.p.-hr., main engine. (5) Lbs. of dry steam per i.h.p.-hr., auxiliaries. (6) Lbs. of dry steam per i.h.p.-hr., whole plant. "(1) Lbs. of dry fuel per kw.-hr., main engine or turbine. (2) Lbs. of dry fuel per kw.-hr., auxiliaries. (3) Lbs. of dry fuel per kw.-hr., whole plant. (4) Lbs. of dry steam per kw.-hr., main engine or turbine. (5) Lbs. of dry steam per kw.-hr., auxiliaries. (6) Lbs. of dry steam per kw.-hr., whole plant. (1) Ft.-lbs. of work per million B.t.u. (2) Ft.-lbs. of work per 100 lbs. dry fuel. (3) Ft.-lbs. of work per 1000 lbs. dry steam. ( (1) Lbs. of dry fuel per brake h.p.-hr. I (2) Cu. ft. of gas per b. h.p.-hr. The i.h.p. and b.h.p. in this table refer to that of the main engine, turbine, or waterwheel, and the kw. to the current measured at the busbar, not including exciter current. (See second footnote, page 264.) Contracts for power plant apparatus should specify the leading dimensions of the apparatus and its rated capacity, expressed in the units given in the table. If a specific guarantee of capacity is made, either working capacity or maximum capacity, the operating condi- tions under which the guarantee is to be met should be clearly set forth, such, for example, as steam pressure, speed, vacuum, quality of fuel, force of draft, etc. Likewise if a contract contains a guarantee of economy all the conditions should be fully specified. n Gas Power Plants. 266 POWER PLANT TESTING Commercial Ratings. The commercial rating of capacity determined on for power plant apparatus, whether for the purpose of contracts, for sale, or otherwise, should be such that a sufficient reserve capacity beyond the rating is available to meet the contingencies of practical operation; such contingencies, for example, as the loss of steam pressure and capacity due to cleaning fires, inferior coal, oversight of the attendants, sudden de- mand for an unusual output of steam or power, etc. To secure this end, the following requirements should be met: (a) Boilers. The reserve capacity of a boiler should be at least one-third of the commercial rating, when using coal which is regarded as a standard where the boiler is located, the fire being crowded, and the draft between the damper and the boiler being at least ^-in. water column (draft gage) . A sufficient amount of grate surface should be provided in such a boiler to develop the rated capacity with the coal and draft named without crowding the fire. (b) Reciprocating Steam Engines and Steam Turbines. The reserve capacity of a steam engine or steam turbine at a stipulated steam pressure should be such as to allow a drop of at least 15 per cent in the pressure without material reduction in the normal speed at its rated capacity or load. It should also allow an over- load at the specified pressure amounting to at least 25 per cent of the rated power. (c) Pumping Engines. The reserve capacity of a pumping engine should be such as to permit a drop in the steam pressure of at least 15 per cent without sensible reduction in the quantity of water discharged at its rated capacity, and to al- low an increase in power sufficient to discharge 20 per cent more water than the rated amount. (d) Gas Producers. The reserve capacity of a gas producer should be such that when forced it will burn in a given time 20 per cent more coal of the quality agreed upon than the rated capacity. (e) Gas and Oil Engine^. The reserve capacity of an internal-combustion engine should be such that when supplied with gas of the kind and quality which it is designed to use, it should develop at least 20 per cent more power than the com- mercial rating. (/) Water wheels. The reserve capacity of a waterwheel should be at least 10 per cent more than the commercial rating at the specified head, the buckets in the wheel being clean and the flow of water unobstructed. CHAPTER XI BOILER TESTING Tests of steam boilers are made to determine usually the following principal results: (1) Quantity of steam evaporated or furnished per hour. (2) Efficiency as a heat user, or weight of water evaporated per pound of combustible (fuel less moisture and ash). (3) Weight of water evaporated per hour per square foot of water- heating surface. (4) Weight of fuel burned per hour per square foot of grate surface. Leakages of any kind are always a lurking enemy for those engaged in any kind of accurate testing, and work with boilers is no exception. Poor results with boilers are due more often to air leakage than to any other fault. Air entering the setting and flues instead of the furnace does not assist combustion, but, on the contrary, absorbs from the hot gases a quantity of heat which otherwise might pass through the boiler- heating surfaces into the water in the boiler. When the object of a series of tests is, for example, to compare one kind of coal with another, or one type of grate or mechanical stoker with another, the losses due to air leakage would not be of much consequence in what are only comparative results; but if a boiler is to give the best possible efficiency and capacity, air leaks must be stopped. In practice the importance of closing air leaks in the boiler setting is forcefully presented when patented devices for fuel saving are installed in boiler plants. Important economies in many cases are guaranteed if the new device is adopted, and then the claims of the agent are made good by instructing his workmen to go over the boiler, closing up all cracks in the setting through which cold air could enter, and at the same time covering the outside surface of the setting with a coating impervious to air. By such means the owner of the plant pays a high price for results that could have been obtained much more cheaply. The first of the principal objects of a boiler test stated above is to determine its capacity " rating." 1 The unit of capacity most generally 1 When the steam supply is small or if, for any reason, the noise due to escaping steam from the calorimeters used is objectionable, a calorimeter may be shut off some- times between readings. The length of time the calorimeter is in operation must then be carefully noted in order to determine the weight of steam lost through it by cal- 267 268 POWER PLANT TESTING used in steam boiler practice is the " boiler " horse power. Now this term horse power has two very distinct meanings in engineering practice. Usually it is taken to mean the rate of doing work or the work done in a definite period of time. In this sense it means, as in the case of engines, turbines, waterwheels, etc., 33,000 foot-pounds per minute. 1 In the case of a steam boiler, however, where the work done must be measured by the conversion of water into steam, a horse power is taken as the evaporation of 30 pounds of water at a temperature of 100 degrees Fahrenheit into steam at 70 pounds pressure above the . atmosphere. When this unit was adopted it was considered that 30 pounds per hour was approximately the requirement per indicated horse power of an m mmm wM Fig. 296. — Graphical Chart of a Boiler Trial. average engine. The Committee on Boiler Tests of the American Society of Mechanical Engineers have adopted what is in effect the same unit, stating it, however, somewhat differently — that a boiler horse power is equivalent to evaporating 34.5 pounds of steam per hour from feed- water temperature of 212 degrees Fahrenheit into steam at the same temperature. According to the latest steam tables this is equivalent to approximately 33,480 B.t.u. per hour, or 558 B.t.u. per minute. Unit of Evaporation. For reducing the results of the boiler tests to a common standard the term " unit of evaporation " is used. It is the heat required to evaporate a pound of water from and at 212 degrees culating the flow through its orifice (see page 189). The flow of steam, however, through the calorimeter must always be started before observations of the temperatures are to be taken in order to get constant conditions. 1 This unit of horse power was adopted by James Watt, who considered it equiva- lent to the work done by a good London draft horse. BOILER TESTING 269 Fahrenheit, 1 which according to standard steam tables is approximately- equivalent to 970.4 B.t.u. 2 Graphical Log Sheets of boiler tests similar to the one shown in Fig. 296 are very serviceable for checking the observations when made during the test as the data are taken. In the report of a test it shows also the relative irregularity or regularity of the conditions affecting the results. Standard Methods for Boiler Trials. The American Society of Mechanical Engineers has adopted rules for conducting boiler trials which are generally accepted in America and are also considered with favor in England. 3 These rules are so complete that they will be given here with practically no abridgment. 4 RULES FOR CONDUCTING EVAPORATIVE TESTS OF BOILERS A.S.M.E. CODE OF 1912 (general Procedure. Determine the object, take the dimensions, note the physical conditions, examine for leakages, install the testing appliance, etc., as pointed out in the general instructions given on pages 258 to 266, and make preparations for the test accordingly. Fuel. Determine the character of fuel to be used. 5 For tests of maximum efficiency or capacity of the boiler to compare with other boilers, the coal should be of some kind which is commercially regarded as a standard for the locality where the test is made. In the Eastern States the standards thus regarded for semi-bituminous coals are Pocahontas (Va. and W. Va.) and New River (W. Va.); for anthracite coals those of the No. 1 buckwheat size, fresh-mined, containing not over 13 per cent ash by analysis; and for bituminous coals, Youghiogheny and Pittsburg coals. In some sections east of the Allegheny Mountains the semi-bituminous Clear- field (Pa.) and Cumberland (Md.) are also considered as standards. These coals when of good quality possess the essentials of excellence, adaptability to various kinds of furnaces, grates, boilers, and methods of firing required, be- sides being widely distributed and generally accessible in the Eastern market. There are no special grades of coal mined in the Western States which are widely and generally considered as standards for testing purposes; the best coal obtainable in any particular locality being regarded as the standard of compari- son. A coal selected for maximum efficiency and capacity tests should be the best of its class, and especially free from slagging and unusual clinker- forming impurities. 1 See also Equivalent Evaporation defined in same units, page 275. 2 Marks and Davis' Steam Tables and Diagrams, see also Peabody's Steam Tables. 3 Engines and Boilers by W. W. F. Pullen, pages 466-475. 4 Journal of American Society of Mechanical Engineers, vol. 34, pages 1693-1872. 5 This code relates primarily to tests made with coal. For reference to oil and gas fuel tests see page 276. 270 POWER PLANT TESTING The size of the coal, especially where it is of the anthracite class, should be determined by screening a suitable sample. Screens for Sizing Coal. The dimensions of screen openings to be used for sizing anthracite coals are given in the following table, the sizes in each case being the opening through which the specified grade will pass, and that over which it will be carried without passing through. The openings referred to are circular. ANTHRACITE COAL SIZES Name. Diameter of Opening through or over which Coal will pass, ins. Name. Diameter of Opening through or over which Coal will pass, ins. Through. Over. Through. Over. 4§ If 1 3j 2^ If f T5 No. 1 Buckwheat No. 2 Buckwheat No. 3 Buckwheat Culm 9 16 A s 1 6 3 32 A * Stove Pea The sizes and grades of bituminous and semi-bituminous coals vary so much according to kind and locality that there are no standards of size for these coals which are generally recognized. Bituminous coals in the Eastern States may be graded and sized as follows : (a) Run of mine coal; the unscreened coal taken from the mine. (b) Lump coal; that which passes over a bar-screen with openings 1| in. wide. (c) Nut coal; that which passes through a bar-screen with 1^-in. openings and over one with f-in. openings. (d) Slack coal; that which passes through a bar-screen with f-in. openings. Bituminous coals in the Western States may be graded and sized as follows: (a) Run of mine coal; the unscreened coal taken from the mine. (b) Lump coal; divided into 6-in., 3-in. and lj-in. lump, according to the diameter of the circular openings over which the respective grades pass; also 6 by 3 lump and 3 by 1| lump, according as the coal passes through a circular opening hav- ing the diameter of the larger figure and over that of the smaller diameter. (c) Nut coal; divided into 3-in. steam nut, which passes through an opening 3-in. diameter and over lj-in. diameter opening; lj-in. nut, which passes through a lf-in. diameter opening and over a f-in. diameter opening; f-in. nut, which passes through a f-in. diameter opening and over a f-in. diameter opening. (d) Screenings; that which passes through a lj-in. diameter opening. Apparatus and Instruments. for boiler tests are: The apparatus and instruments required (a) Platform scales for weighing coal and ashes. (6) Graduated scales attached to the water glasses. BOILER TESTING 271 (c) Tanks and platform scales for weighing water (or water meters calibrated in place). (d) Pressure gages, thermometers, and draft gages. (e) Calorimeters for determining the calorific value of fuel and the quality of steam. (J) Furnace pyrometers. (g) Gas analyzing apparatus. Full directions regarding the use and calibration of the above-men- tioned appliances are given in the preceding chapters. Location of Instruments, (a) The feedwater thermometer should be placed in a thermometer well inserted in the feed pipe. Except in cases where an injector is used 1 the point selected should be as near as practicable to the boiler. Where an in- jector is employed, and the water is weighed or measured before it is supplied thereto, the well should be placed on the suction side of the injector, and the injector should receive steam through a short covered pipe connected directly to the boiler under test. If the steam is taken from some other source and it is of different pressure and different quality from that of the boiler under test, correction should be made for such differ- ence, and especially for any excessive moisture thus introduced into the feedwater. When the temperature of the water changes between the injector and boiler, as by the use of a heater or by excessive radiation, the temperature at which the water not only enters and leaves the injector, but that also at which it enters the boiler, should also be taken. In that case, the weight to be used is that of the water leaving the in- jector, computed from the heat units if not directly measured and the temperature, that of the water entering the boiler. The weight of condensed steam to be added to the weight of water entering the injector, to obtain that leaving the injector, may be computed by multiplying the weight entering by the proportion h-i — h 3 ' in which hi = heat units per pound of water entering injector. h 2 = heat units per pound of steam entering injector. h s = heat units per pound of water leaving injector. (b) The location of the steam calorimeter and steam thermometer should be as close to the boiler as possible. (c) Draft gages should be attached to each boiler between the hand damper and the boiler, and as near the damper as practicable. In the case of a plant containing a number of boilers, a gage should also be attached to the main flue between the regu- lating damper and the boiler plant. It is desirable also to have gages connected to the furnace or furnaces of the boilers, and in cases of forced blast, to the ashpits and blower ducts. If there is an economizer in the flue a gage should be connected to the flue at each end of this apparatus. The same draft gage may be used for all the points. 1 In feeding a boiler undergoing test with an injector taking steam from another boiler, or from the main steam pipe from several boilers, the evaporative results may be modified by a difference in the quality of the steam from such source compared with that supplied by the boiler being tested, and in some cases the connection to the in- jector may act as a drip for the main steam pipe. If it is known that the steam from the main pipe is of the same pressure and quality as that furnished by the boiler under- going the test, the steam may be taken from such main pipe. 272 POWER PLANT TESTING noted, provided suitable pipes are run from the gage to each, arranged so as to be readily connected to any of these points at will. (d) The flue thermometer should be located where it will show the average tem- perature of the whole body of gas. For an extremely large flue the thermometer may be placed in an oil pot of small diameter, which is suspended in the flue, and the ther- mometer lifted partially out of the oil when the temperature is read. (e) Samples for flue gas analysis should be drawn from the region near the center of the main body of escaping gases, and the point selected should be one where there is no chance for air leakage into the flue, which could affect the average quality. In a round or square flue having an area of not more than one-eighth of the grate surface, the sampling pipe may be introduced horizontally at a central point, or preferably a little higher than the central point, and the pipe should contain perforations extending the whole length of the part immersed and pointing toward the current of gas, the collective area of the perforations being less than the area of the pipe. Duration. The duration of tests to determine the efficiency of a hand- fired boiler, should be 10 hours of continuous running, or such time as may be required to burn a total of 250 pounds of coal per square foot of grate. In the case of a boiler using a mechanical stoker, the duration, where practicable, should be at least 24 hours. If the. stoker is of a type that permits the quantity and condition of the fuel bed at beginning and end of the test to be accurately estimated, the duration may be reduced to 10 hours, or such time as may be required to burn the above noted total of 250 pounds per square foot. In commercial tests where the service requires continuous operation night and day, with frequent shifts of firemen, the duration of the test, whether the boilers are hand-fired or stoker-fired, should be at least 24 hours. Likewise in commercial tests, either of a single boiler or of a plant of several boilers, which operate regu- larly a certain number of hours and during the balance of the day the fires are banked, the duration should not be less than 24 hours. The duration of tests to determine the maximum evaporative capacity of a boiler, without determining the efficiency, should not be less than three hours. Starting and Stopping. The conditions regarding the temperature of the furnace and boiler, the quantity and quality of the live coal and ash on the grates, the water level, and the steam pressure, should be as nearly as possible the same at the end as at the beginning of the test. To secure the desired equality of conditions with hand-fired boilers, the following method should be employed: The furnace being well heated by a preliminary run, burn the fire low, and thor- oughly clean it, leaving enough live coal spread evenly over the grate (say from two to four inches) 1 to serve as a foundation for the new fire. Note quickly (1) the thickness of the coal bed as nearly as it can be estimated or measured; also 1 1 to 2 inches for small anthracite coals. BOILER TESTING 273 (2) the water level, 1 (3) the steam pressure, and (4) the time, and record the latter as the starting time. (5) Fresh coal should then be fired from that weighed for the test, (6) the ashpit should be thoroughly cleaned, and the regular work of the test proceeded with. Before the end of the test the fire should again be burned low and cleaned in such a manner as to (1) leave the same amount of live coal on the grate as at the start. When this condition is reached, observe quickly (2) the water level, 1 (3) the steam pressure, and (4) the time, and record the latter as the stopping time. If the water level is not the same as at the beginning (5) a correction . should be made by computation, rather than by feeding additional water after the final readings are taken. Finally (6) remove the ashes and refuse from the ashpit. In a plant containing several boilers where it is not practicable to clean them simultaneously, the fires should be cleaned one after the other as rapidly as may be, and each one after cleaning charged with enough coal to maintain a thin fire in good working condition. After the last fire is cleaned and in working con- dition, burn all the fires low (say 4 to 6 in.), note quickly the thickness of each, also the water levels, steam pressure, and time, which last is taken as the start- ing time. Likewise when the time arrives for closing the test, the fires should be quickly cleaned one by one, and when this work is completed they should all be burned low the same as at the start, and the various observations made as noted. In the case of a large boiler having several furnace doors requiring the fire to be cleaned in sections one after the other, the above directions pertaining to starting and stopping in a plant of several boilers may be followed. To obtain the desired equality of conditions of the fire when a mechani- cal stoker other] than a chain grate is used, the procedure should be modified where practicable as follows: Regulate the coal feed so as to burn the fire to the low condition required for clean- ing. Shut off the coal-feeding mechanism and fill the hoppers level full. Clean the ash or dump plate, note quickly the depth and condition of the coal on the grate, the water level, 1 the steam pressure, and the time, and record the latter as the starting time. Then start the coal-feeding mechanism, clean the ashpit, and proceed with the regular work of the test. When the time arrives for the close of the test, shut off the coal-feeding mecha- nism, fill the hoppers and burn the fire to the same low point as at the beginning. When this condition is reached, note the water level, the steam pressure, and the time, and record the latter as the stopping time. Finally clean the ash plate and remove the ashes. In the case of chain grate stokers, the desired operating conditions should be maintained for half an hour before starting a test and for a like period before its close, the height of the throat plate and the speed of the grate being the same during both of these periods. The coal should be weighed and delivered to the firemen in portions sufficient for one hour's run, thereby ascertaining the degree of uniformity of firing. An ample supply of coal should be maintained at all times, but the quantity on 1 Do not blow the water-glass column for at least one hour before these readings are taken. An erroneous indication may otherwise be caused by a change of tempera- ture and density of the water within the column and connecting pipe. 274 POWER PLANT TESTING the floor at the end of each hour should be as small as practicable, so that the same may be readily estimated and deducted from the total weight. The records should be such as to ascertain also the consumption of feedwater each hour, and thereby determine the degree of uniformity of evaporation. Ashes and Refuse. The ashes and refuse withdrawn from the furnace and ashpit during the progress of the test and at its close should be weighed so far as possible in a dry state. If wet the amount of moisture should be ascertained and allowed for, a sample being taken and dried for this purpose. This sample may serve also for analysis and the deter- mination of unburned carbon and fusing temperature. Analyses of Flue Gases. For approximate determinations of the com- position of the flue gases, a portable type of apparatus should be em- ployed. If momentary samples are obtained the analyses should be made as frequently as possible, say every 15 to 30 minutes, depending on the skill of the operator, noting at the time the sample is drawn the furnace and firing conditions. If the sample drawn is a continuous one, the intervals may be made longer. Smoke Observations. In tests of bituminous coals requiring a deter- mination of the amount of smoke produced, observations should be made regularly throughout the trial at intervals of five minutes (or if neces- sary every minute), noting at the same time the furnace and firing conditions. Calculation of Results. The methods to be followed in expressing and calculating those results which are not self-evident are explained as follows : (a) Efficiency. The "efficiency of boiler, furnace and grate " is the relation be- tween the heat absorbed per pound of coal fired, and the calorific value of one pound of coal. The "efficiency of boiler and furnace" is the relation between the heat ab- sorbed per pound of combustible burned, and the calorific value of one pound of combustible. This expression of efficiency furnishes a means for comparing one boiler and furnace with another, when the losses of unburned coal due to grates, cleanings, etc., are eliminated. The " combustible burned" is determined by subtracting from the weight of coal supplied to the boiler, the moisture in the coal, the weight of ash and un- burned coal withdrawn from the furnace and ashpit, and the weight of dust, soot, and refuse, if any, withdrawn from the tubes, flues, and combustion cham- bers, including ash carried away in the gases, if any, determined from the analyses of coal and ash. The " combustible " used for determining the calorific value is the weight of coal less the moisture and ash found by analysis. The " heat absorbed " per pound of coal, or combustible is calculated by multiplying the equivalent evaporation from and at 212 degrees per pound of coal or combustible by 970.4. (b) Corrections for Moisture in Steam. When the percentage is less than 2 per cent it is sufficient merely to deduct the percentage from the weight of water fed. If BOILER TESTING 275 the percentage is greater than 2 per cent or if extreme accuracy is required, the factor of correction equals X + P^4 (85) (H - q 2 ) in which X is the quality of the steam (one minus the decimal representing the percentage of moisture), P the proportion of moisture, 1 qi the total heat of water at the temperature of the steam, q 2 the total heat of the feed water, and H the total heat of saturated steam of the given temperature. (c) Correction for live steam, if any, used for aiding Combustion. If live steam is admitted into the furnace or ashpit for producing blast, injecting fuel, or aid- ing combustion, it is to be deducted from the total evaporation, and the net evaporation used in the various calculations. (d) Equivalent Evaporation. The equivalent evaporation from and at 212 deg. is obtained by multiplying the weight of water evaporated, corrected for moisture in steam, by the "factor of evaporation." The latter equals H-g 2 970.4 ' in which H and q 2 are respectively the total heat of saturated steam and of the feedwater entering the boiler. When the steam is superheated, the total heat of the steam is that of saturated steam plus the product of the number of degrees of superheating by the specific heat of the steam. Unless otherwise provided, a combined boiler and superheater should be treated as one unit, and the equivalent of the work done by the superheater should be included in the evaporative work of the boiler. (e) Heat Balance. The " heat balance," or approximate distribution of the calorific value of the coal or combustible among the several items of heat utilized and heat lost, should be obtained in cases where the flue gases have been analyzed and a complete analysis made of the coal. The loss due to moisture in the coal is found by multiplying the difference between the total heat of one pound of superheated steam at the temperature of the escaping gases and the temperature of the air in the boiler room, by the weight of moisture in a pound of coal. The loss due to moisture formed by the burning of hydrogen is obtained by multiplying the total heat of one pound of superheated steam at the temper- ature of the escaping gases, calculated from the temperature of the air in the boiler room, by the proportion of the hydrogen, determined from the analysis of the coal, and multiplying the result by 9. The loss due to heat carried away in the dry gases is found by multiplying the weight of gas per pound of coal or combustible by the elevation of tem- perature of the gases above the temperature of the boiler room, and by the specific heat of the gases (0.24). The weight of gas referred to is obtained by finding the weight of dry gas per pound of carbon burned, using the formula 11CQ 2 +8Q+7(C0+N) /Q ^ 3 ( C0 2 + CO) ' (86) ' PagG 281 ' in which C0 2 , CO, O, and N are expressed in percentages by volume, and mul- tiplying this result by the proportion borne by the carbon burned to the whole amount of coal or combustible as determined from the results of the analysis of the coal, asli and refuse. 1 Proportion of moisture is the ratio of the percentage of moisture in the steam to 100. 276 POWER PLANT TESTING The loss due to incomplete combustion of carbon is found by first obtaining the proportion borne by the carbon monoxide in the gases to the sum of the carbon monoxide and carbon dioxide, and then multiplying this proportion by the proportion of carbon in the coal or combustible, and finally multiplying the product by 10,150, which is the number of heat units generated by burning to carbon dioxide one pound of carbon contained in carbon monoxide. The loss due to combustible matter in the ash and refuse is found by multi- plying the proportion that this combustible bears to the whole amount of coal or combustible, by its calorific value per pound. For most purposes it is sufficient to assume the combustible to be 14,600 B.t.u. per pound, the same as that of carbon. The loss due to moisture in the air is determined by multiplying the weight of such moisture per pound of coal or combustible by the elevation of temper- ature of the flue gases above the temperature of the boiler room and by 0.47. The weight of moisture is found by multiplying the weight of air per pound of coal or combustible by the moisture in one pound of air determined from read- ings of the wet- and dry-bulb thermometer. (/) Total Heat of Combustion of Coal, by Analysis. The total heat of combustion may be computed from the results of the ultimate analysis by using the formula -9 14,600 C + 62,000 H - - + 4000 S, (69), page 227, in which C, H, O, and S refer to the proportions of carbon, hydrogen, oxygen and sulphur, respectively. (g) Air for Combustion. The quantity of air used may be calculated by the formulae: , , • , , , ' h 3.032 N Pounds of air per pound of carbon = — — — , CO2 -\- CO in which N, CO2 and CO are the percentages of dry gas obtained by analysis, and Lbs. of air per lb. of coal = lbs. air per lb. C X per cent C in the coal. The ratio of the air supply to that theoretically required for complete com- . ■ . N bustion is ■ Compare with formulas on page 249. Tests with Oil and Gas Fuels. Tests of boilers using oil or gas for fuel should accord with the rules here given, excepting as they are varied to conform to the particular characteristics of the fuel. The duration in such cases may be reduced, and the " flying " method of starting and stopping employed. The table of data and results should contain items stating character of furnace and burner, quality and composition of oil or gas, temperature of oil, pressure of steam used for vaporizing and quantity of steam used for both vaporizing and for heating. TABLE 1. DATA AND RESULTS OF EVAPORATIVE TEST — SHORT FORM CODE OF 1912 (1) Test of boiler located at to determine conducted by (2) Kind of furnace (3) Grate surface sq. ft. BOILER TESTING 277 (4) Water-heating surface 1 sq. ft. (5) Superheat ing surface 1 sq. ft. (6) Date (7) Duration hrs. (8) Kind and size of coal '. Average Pressures, Temperatures, etc. (9) Steam pressure by gage lbs. per sq. in. (9a) Absolute steam pressure lbs. per sq. in. (10) Temperature of feedwater entering boiler deg. F. (11) Temperature of escaping gases leaving boiler deg. F. (12) Force of draft between damper and boiler ins. water (13) Percentage of moisture in steam, or number deg. of superheating (per cent or deg. F.) Total Quantities (14) Weight of coal as fired 2 lbs. (15) Percentage of moisture in coal per cent (16) Total weight of dry coal consumed lbs. (17) Total ash and refuse lbs. (18) Percentage of ash and refuse in dry coal per cent (19) Total weight of water fed to the boiler 3 lbs. (20) Total water evaporated, corrected for moisture in steam lbs. (21) Total equivalent evaporation from and at 212 deg. F lbs. Hourly Quantities and Rates (22) Dry coal consumed per hour lbs. (23) Dry coal per sq. ft. of grate surface per hour lbs. (24) Water evaporated per hour corrected for quality of steam lbs. (25) Equivalent evaporation per hour from and at 212 deg. F lbs. (26) Equivalent evaporation per hour from and at 212 deg. F. per sq. ft. of water- heating surface lbs. Capacity and Economy Results (27) Evaporation per hour from and at 212 deg. F. (same as Line 25) lbs. (28) Boiler horse power developed (Item 27 -r 34|) :.:,... .bl.h.p. (29) Rated capacity, in evaporation from and at 212 deg. F. per hour. ......... .lbs. (30) Rated boiler horse power bl.h.p. (31) Percentage of rated capacity developed. per cent (32) Water fed per lb. of coal fired (Item 19 + Item 14) . . lbs. (33) Water evaporated per lb. of dry coal (Item 20 -f- Item 16) ...:...... lbs. (34) Equivalent evaporation from and at 212 deg. F. per lb. of dry coal (Item 21 -5- Item 16) .'. lbs. (35) Equivalent evaporation from and at 212 deg. F. per lb. of combustible [Item 21 -=- (Item 16 - Item 17)] >.lf. - lbs. 1 See page 258 for definition of heating surfaces. 2 The term "as fired" means actual condition including moisture, corrected for estimated difference in weight of coal on the grate at beginning and end of test. 3 Corrected for inequality of water level and steam pressure at beginning and end of test. 278 POWER PLANT TESTING Efficiency (36) Calorific value of 1 lb. of dry coal B.t.u. (37) Calorific value of 1 lb. of combustible B.t.u. (38) Efficiency of boiler, furnace and grate 100 X — — = — per cent L Item 36 J f Item 35 X 970. 4~| (39) Efficiency of boiler and furnace 100 X per cent |_ Item 37 J Cost of Evaporation (40) Cost of coal per ton of ... . lbs. delivered in boiler room dollars (41) Cost of coal required for evaporating 1000 lbs. of water from and at 212 deg., dollars TABLE 2. DATA AND RESULTS OF EVAPORATIVE TEST — COMPLETE FORM, CODE OF 1912 (1) Test of boiler located at to determine conducted by Dimensions, Proportions, etc. (2) Number and kind of boilers (3) Kind of furnace (4) Grate surface width length area sq. ft. (5) Approximate width of air spaces in grate ins. (6) Proportion of air space to whole grate surface . per cent (7) Water-heating surface sq. ft. (8) Superheating surface sq. ft. (9) Ratio of water-heating surface to grate surface , to 1 (10) Ratio of minimum draft area to grate surface 1 to (11) Date (12) Duration hrs. (13) Kind of coal (14) Size of coal Average Pressures, Temperatures, Quality of Steam, etc. s (15) Steam pressure by gage lbs. per sq. in. (16) Barometric pressure ins. mercury = lbs. per sq. in. (16a) Absolute steam pressure lbs. per sq. in. (17) Force of draft at dampers of individual boilers ins. water (18) Force of draft in main flue near boilers ins. water (19) Force of draft in main flue between economizer and chimney ins. water (20) Force of draft in furnaces ins. water (21) Force of blast in ashpits ins. water (22) State of weather (23) Temperature of external air deg. F. (24) Temperature of fireroom deg. F. (25) Temperature of steam deg. F. (26) Normal temperature of saturated steam deg. F. (27) Temperature of feedwater entering flue heater or economizer deg. F. (28) Temperature of feedwater leaving heater or economizer and entering boilers deg. F, BOILER TESTING 279 (29) Temperature of gases leaving boilers deg. F. (30) Temperature of gases leaving economizer deg. F. (31) Percentage of moisture in steam per cent (32) Number of degrees of superheating deg. F. (33) Quality of steam (dry steam = unity) Total Quantities (34) Weight of coal as fired 1 lbs. (35) Percentage of moisture in coal per cent (36) Total weight of dry coal consumed lbs. (37) Total ash and refuse lbs. (38) Total combustible consumed (Line 36 — Line 37) lbs. (39) Percentage of ash and refuse in dry coal per cent (40) Total weight of water fed to boiler 2 lbs. (41) Total water evaporated corrected for moisture in steam lbs. (42) Factor of evaporation, based on temperature of water entering boilers (43) Total equivalent evaporation from and at 212 deg. F. lbs. Hourly Quantities and Rates (44) Dry coal consumed per hour lbs. (45) Combustible consumed per hour lbs. (46) Dry coal per sq. ft. of grate surface per hour lbs. (47) Water evaporated per hour, corrected for quality of steam lbs. (48) Equivalent evaporation per hour from and at 212 deg. 3 F lbs. (49) Equivalent evaporation per hour and at 212 deg. F. per sq. ft. of water-heat- ing surface 2 lbs. Proximate Analysis op Coal (50) Fixed carbon per cent (51) Volatile matter per cent (52) Moisture per cent (53) Ash per cent 100 per cent (54) Sulphur, separately determined . per cent Ultimate Analysis of Dry Coal (55) Carbon (C) per cent (56) Hydrogen (H) per cent (57) Oxygen (O) per cent (58) Nitrogen (N) per cent (59) Sulphur (S) per cent (60) Ash per cent 100 per cent (61) Moisture in sample of coal as received per cent 1 The term "as fired" means actual condition including moisture, corrected for difference in weight of coal on grate at beginning and end of test. 2 Corrected for inequality of water level and steam pressure at beginning and end of test. 3 The symbol U.E. meaning "units of evaporation" (see page 268) may be sub- stituted for the expression, equivalent water evaporated into dry steam from and at 212 deg. Fahrenheit. 280 POWER PLANT TESTING Analysis of Ash and Refuse (62) Carbon per cent (63) Earthy matter per cent (64) Temperature of fusion of ash deg. F. Calorific Value (65) Calorific value of 1 lb. of dry coal by calorimeter B.t.u. (66) Calorific value of 1 lb. of combustible by calorimeter B.t.u. (67) Calorific value of 1 lb. of dry coal by analysis B.t.u. (68) Calorific value of 1 lb. of combustible by analysis B.t.u. Capacity, Economy Results and Efficien'cy (69) Evaporation per hour from and at 212 deg. F. (same as Line 48) lbs. (70) Boiler horse power developed (Line 69 -5- 34|) bl.h.p. (71) Rated capacity per hour, from and at 212 deg. F lbs. (72) Rated boiler horse power bl.h.p. (73) Percentage of rated capacity developed per cent (74) Water fed per lb. of coal (Item 40 -^ Item 34) lbs. (75) Water evaporated per lb. of dry coal (Item 41 -r- Item 36) lbs. (76) Equivalent evaporation from and at 212 deg. F. per lb. of coal fired (Item 43 -e- Item 34) lbs. (77) Equivalent evaporation from and at 212 deg. F. per lb. of dry coal (Item 43 -v- Item 36) lbs. (78) Equivalent evaporation from and at 212 deg. F. per lb. of combustible (Item 43 -v- Item 38) lbs. T Item 77 X 970.4] s 100 X ; per cent |_ Item 65 J (80) Efficiency of boiler and furnace 100 X — L Item 66 J (79) Efficiency of boiler, furnace, and grate 100 X Item di> J 5 X 970.41 .per cent Cost of Evaporation (81) Cost of coal per ton of .... lbs. delivered in boiler room dollars (82) Cost of coal required for evaporating 1000 lbs. of water under observed conditions dollars (83) Cost of coal required for evaporating 1000 lbs. of water from and at 212 deg. F dollars Smoke Data (84) Percentage of smoke as observed per cent (85) Weight of soot per hour obtained from smoke meter Methods of Firing (86) Kind of firing, whether spreading, alternate, or coking (87) Average thickness of fire ins. (88) Average intervals between firings for each furnace during time when fires are in normal condition min. (89) Average interval between times of leveling or breaking up min. BOILER TESTING 281 Analysis of Dky Gases by Volume (90) Carbon dioxide (C0 2 ) per cent (91) Oxygen (O) per cent (92) Carbon monoxide (CO) per cent (93) Hydrogen and hydrocarbons per cent (94) Nitrogen, by difference (N) per cent 100 per cent HEAT BALANCE BASED ON DRY COAL AND COMBUSTIBLE Dry Coal as Fired. Combustible Burned. B.t.u. Per Cent. B.t.u. Per Cent. (95) Heat absorbed by the boiler (Line 77 or 78 X 970.4) (96) Loss due to evaporation of moisture in coal (page 275) (97) Loss due to heat carried away by steam formed by the (102) Loss due to unconsumed hydrogen and hydrocarbons, to (103) Total calorific value of 1 lb. of dry coal or combustible 100 COMPUTATION OF THE WEIGHT OF THE CHIMNEY GASES FROM THE ANALYSIS BY VOLUME OF THE DRY GAS Two methods of calculating from the analysis by volume of the dry chimney gases the number of pounds of dry chimney gases per pound of carbon, or the weight of air supplied per pound of carbon, have been given by different writers. These may be expressed in the shape of formulas as follows: 1 1 CO, + 8 O + 7 (CO + N) (A) Pounds dry gasper pound C = (B) Pounds air per pound C = 5.1 3 (C0 2 + CO) 2(C0 2 + O) + CO (87) C0 2 + CO • ' " in which C0 2 , 2 , CO and N are percentages by volume of the gases. Formula A may be^derived from the method of computation given in Mr. R. S. Hale's paper on " Flue-Gas Analyses," Transactions American Society of Mechanical Engineers, vol. 18, page 902, and formula B from the method given in Peabody's and Miller's " Treatise on Steam Boilers." Both are based on the principle that the density, relatively to hydrogen, of an elementary gas (O and N) is proportional to its atomic weight, and that of a compound gas (CO and C0 2 ) to one-half its molecular weight. Both formulas are very nearly accurate when pure carbon is the fuel burned, but formula B is inaccurate when the fuel contains hydrogen, for the reason that the portion of the oxygen of the air supply which is re- 282 POWER PLANT TESTING quired to burn the hydrogen is contained in the chimney gas as water vapor and does not appear in the analysis of the dry gas. The following calculations of a supposed case of combustion of hydrog- enous fuel illustrates the accuracy of formula A and the inaccuracy of formula B. Assume that the coal has the following analysis: C, 66.50; H, 4.55; 0, 8.40; N, 1.00; water, 10.00; ash and sulphur, 9.55— total, 100. Assume that one-tenth of the C is burned to CO, and nine-tenths to CO2; that the air supply is 20 per cent in excess of that required for this combustion; that the air contains 1 per cent by weight of moisture; and that the S in the coal may be considered as part of the ash. We then have the following summary of results of the combustion of 100 pounds of coal: from Air. N=OXI5- Total Air. C0 2 . CO. H 2 0. 59.85 lbs. C toC0 2 X2f 159.60 8.87 28.00 534.31 29.70 93.74 693.91 38.57 121.74 219.45 6.65 " CtoCOxH 3.50 " HtoH 2 Ox8 15.52 3L50 196.47 39.29 657.75 "loo" 131.55 854.22 170.84 1.05 " H to H 2 ( 8.40 " HtoHoOj 10.00 " Water 1.00 " N 9.45 10.00 9.55 " Ash and S 100.00 Excess of air 20 per cent. 1025.06 Moisture in air 1 per cent. 10.25 Total wt. gases, 1125.76 lbs.= Total dry gases, 1064.56 lbs. Per Cent Total dry gases, by weight, Total dry gases, by volume, 39.29 3.69 3.508 790.30 N 74.24 80.656 219.45 C0 2 20.61 14.252 15.52 CO 1.546 1.584 61.20 Total gases 1125.76 + ash and S 9.55 = 1135.31 lbs. total products. Total air 1025.06 + moisture in air 10.25 + coal 100 = 1135.31 lbs. Dry gas per lb. coal 10.6456; per lb. carbon = 10.6456 -=- .665 = 16.008 Dry air per lb. coal 10.2506; per lb. carbon = 10.2506 + .665 = 15.414 Computation of the weight of dry gas and of air per lb. carbon. Formula A: Dry gas per lb. C = Formula B: 14.252 X 11 + 3.508 X 8 + 82.240 X 7 Air per pound C = 5.1 3 (14.252 + 1.584) 2 (14.252 + 3.508) + 1584 = 16.008 pounds. 13.589 pounds. 14.252 + 1.584 The error in the last result is 15.414 - 13.589 = 1.825 pounds. Professor D. S. Jacobus gives another formula for the air per pound of carbon, in which the error of formula 87 is almost entirely avoided. BOILER TESTING 283 It is Formula C: Air per pound C = ^C^FCO) * °- 77 ' ° r 0.33 (C0 2 + 00) ' (88) in which N, C0 2 , and CO are the percentages by volume of these gases. Making the computation from the data of the above analysis, we have : Air per pound C = ^ ^^ 1.584) = 15 " 434 P ° Unds ' the true value being 15.414 pounds. CHAPTER XII STEAM ENGINE TESTING Most important of the tests made of nearly all classes of machinery is that for mechanical effic ency; meaning the comparison of the useful work performed with the amount of work theoretically possible to obtain with a perfect machine. In other words, in an engine the mechanical efficiency, E m , is the ratio of the brake horse power to the indicated horse power, or _ b.h.p. i.n.p. STEAM ENGINE TESTING TESTS FOR MECHANICAL EFFICIENCY AND FRICTION Test made by (89) Date Description of engine tested Tare of Brake lbs. Length of brake arm feet . Engine and Brake Constants (see pages 143 and 148) No. of Read- Time. Weight on Brake, lbs. R.P.M. Areas of Indicator, Cards, sq. ins. Indicated Horse Power. Brake Horse Power. Fric- tion Horse Power. Mech. Effic. ing. Gross. Net. Head End. Crank End. Head End. Crank End. Total. The difference between the indicated horse power and the brake horse power is called the friction horse power. In many cases with very large engines, it is not readily possible to obtain the brake horse power directly, and in such cases it is customary to obtain approxi- mately the horse power lost in friction from a so-called " friction indicator diagram," obtained from the areas of indicator diagrams when the only work done is that required to overcome its own friction, or in common parlance, when the engine is " running light." The brake horse power is then taken to be the difference between the indicated horse power 284 STEAM ENGINE TESTING 285 and the friction horse power. Such a determination of friction horse power and of mechanical efficiency by calculation cannot be considered very accurate, because the friction of an engine increases slightly with increasing loads. Observed and calculated data of mechanical efficiency may be tabu- lated as shown in table on page 284. Valve Setting (Slide Valve Engines). In order that steam may be used economically in an engine, it is necessary that the valve be set care- fully and accurately, so that when an indicator card is taken the diagram obtained will be as nearly as possible like the ideal. Adjustment of a slide valve on an engine is accomplished in two different ways, with differ- ent effects: (1) By moving the valve on its stem; (2) By adjusting the eccentric. Typical slide valves are shown in Figs. 297 and 298. Exhaust Lap _^f L*. I ' -=* ^ Exhaust Lap Steam Lap J Exhaust Port Ordinary D-slide Valve in Mid-position. f s 4 ■ Exhaust LapjwJ Steam Lap H Exhaust Lap Fig. 298. — Piston Type of Slide Valve in Mid-position. To Set the Valve for Equal Leads. The first step in setting a valve is to place the engine on dead-center and adjust the angle between the crank and eccentric so that the valve opens the port leading to the cylinder a slight amount. The width of the opening should be measured and recorded as a preliminary value of the lead on that end, 1 — suppose 1 It is assumed of course that corresponding dimensions of the ports are the same at the two ends of the valve seat. 286 POWER PLANT TESTING for example it is | inch. Then the engine should be placed on the opposite dead-center and the port opening on that end measured and recorded as the preliminary value of the lead on that end, suppose it is T V inch. There is then a difference in lead on the two ends of T V inch. The valve must be moved on its stem a distance equal to half the difference, or -^ inch. This movement of the valve will be in a direction away from the port having the smaller opening. By the method described the two leads of the valve will be made the same; in other words, the distance the valve uncovers the steam ports when the engine is on the dead-center will be the same at both ends of the cylinder. But while the leads are equal they are not necessarily the required amount and it remains to set the eccentric to give the leads de- sired. Place the engine once more accurately on dead-center 1 and after loosening the eccentric move it on the shaft so as to change the lead to the amount desired. As a final check, after securing the eccentric, the engine can be placed on the other dead-center to see that the lead is correct. 2 To set the valve for equal cut-offs, the valve is first set on its stem so that the travel will be the same on both sides of the mid-position as explained at the bottom of this page to make its movement symmetrical with the ports. Now an adjustment of the eccentric must be made so that steam will be cut off at each end of the cylinder when the piston has moved the same distances or the same per cent of the stroke from the two ends. To perform this adjustment mark on the cross-head as accurately as possible the limits of the stroke, and set the cross-head at the per cent of the stroke for cut-off appearing to be most suitable for the conditions of load. Move the eccentric on the shaft in the direction 1 An engine can be put on dead-center quite accurately by the " method of tram- mels." When the engine is just a little off the center to be determined, make small scratch-marks opposite each other both on the cross-head and on one of the guides. Now set a pair of dividers or trammels with one end resting on the bedplate of the en- gine, its foundation, or some convenient stationary object near the fly-wheel, and with the other end mark a point on the fly-wheel. The engine should then be moved over or beyond the dead-center until the marks made on the cross-head and on the guide come together again. With the dividers set with the points the same distance apart as before again put a mark on the fly-wheel. Then if the engine is turned back so that the end of the dividers used to mark on the fly-wheel is at a point half way between the two marks, it will be set quite accurately on the dead-center required. In all these adjustments care must be taken to turn the engine each time in the same direction with respect to the dead-center so that the lost motion or back lash is taken up in the same direction. The engine must be placed accurately on center because when the crank is near the dead-center the eccentric is in such a position that a slight movement of the shaft causes considerable movement of the valve. 2 This method applies only explicitly to a valve like the one in Fig. 297, which takes steam on the " outside." When the valve takes steam on the inside (Fig. 298) the eccentric must be moved in the opposite direction. STEAM ENGINE TESTING 287 in which the engine is to run until it can be seen that the valve would be just closing the steam port at the end of the cylinder from which the piston is moving. Fasten the eccentric securely in this position and turn the engine over to observe whether the valve will be just closing the other steam port when the piston has moved the same distance, measured on the cross-head, from the other end of the cylinder. If the setting is not correct, the error should be halved, correcting for one half the error by moving the valve on the stem and for the other half by moving the eccentric on the shaft. This operation, which is a " cut and try" process, must be repeated until the required setting is secured. Methods similar to those described are preferred usually for the accu- rate setting of the slide valves of slow- and medium-speed engines. High-speed engines as well as slow-speed engines of the Corliss type have their valves set usually on the basis of the information secured Cut Off Compression Atmospheric Line Fig. 299. — Indicator Diagram Illustrating the Point of Cut-off. from indicator diagrams taken on the engines, showing approximately the " timing " of the events of the stroke. To set a slide valve successfully by the " indicator " method, the valve and ports should be measured to determine the " lap " dimensions and port openings indicated in Fig. 297 page 285, as well as the valve travel. With these data a Zeuner 1 valve diagram should be constructed, showing a good steam distribution for assumed lead or cut-off. Then construct the theoretical indicator card from the Zeuner diagram and adjust the setting of the valve on the stem and the eccentric on the shaft until a close approxi- mation to the theoretical card is obtained. In this adjustment the first thing to be done is to equalize the travel of the valve by locating it on its stem so that the travel will be the same on both sides of its mid- position. Use a spring in the indicator light enough to give a diagram about 1£ 1 It is beyond the scope of this book to take up a discussion of valve diagrams. The theory and construction of the Zeuner diagram are given in nearly all books on the steam engine. Bilgram valve diagrams, although excellent for designers, are not as good as the Zeuner diagram for valve setting requirements. 288 POWER PLANT TESTING inches high so that events of the stroke, — admission, cut-off, release, and compression, will be shown as clearly as possible. Sometimes it is difficult to determine these events on a diagram on account of the curves gradually running into each other without the point separating the different curves being clearly defined. A good method for such cases is to produce along their regular trend both of the curves of which the intersection is re- quired and take for the intersection the point where these curves cross each other. The method is illustrated on an indicator card in Fig. 299 showing the point of cut-off. In a slide-valve engine it is not possible to set the valve to secure at the same time equal cut-offs and equal leads. Ideal and imperfect indicator diagrams taken from slide-valve and Corliss engines are shown in Fig. 300. A little study of such diagrams may help to solve many difficulties in valve setting. Setting Corliss Valves. A brief description 1 of the essential parts of the valve gear of a Corliss engine will assist in obtaining a clearer con- ception of the subject. In Figs. 301 and 302 similar letters of refer- ence indicate the same parts of the mechanism. Fig. 301 shows all the essential parts of the valve gear. The steam valves work in the chambers S, S and the exhaust valves work in the chambers E, E. The double-armed levers AC, AC work loosely on the hubs of the valve-stem brackets and the lever arms B, B ; the former are connected to the wrist plate W by the rods M, M; the levers B, B are keyed to the valve stems V, V, and are also connected by the rods O, O to the dashpots D, D. The double-armed levers carry at their outer ends C, C hardened steel catch plates, which engage with arms B, B, making the two arms B and C work in unison until steam is to be cut off; at this point another set of levers H, H, connected by the cam rods G, G to the governor, come into play, causing the catch plates to release the arms B, B, the outer ends of which are then pulled downward by the weight of the dashpot plunger, causing the steam valves to rotate on their axes and thus cut off steam. These are the essential features of the Corliss gear, although the design of the mechanism is greatly modified by different builders. The exhaust valve arms F are connected to the wrist plate by the rods N, N, and it is seen that all the valves receive their motion from the wrist plate; the latter receives its motion from the hook rod I; this rod is generally attached to a rocker arm, not shown; to this arm the eccentric rod is also attached. The carrier arm is usually placed about midway between the wrist plate and eccentric, and in the center of its travel stands in a vertical position. 1 This description is mainly from American Machinist, vol. 18, page 391. For clear- ness the article is considered unusually good. STEAM ENGINE TESTING 289 290 POWER PLANT TESTING The setting of the valves is not a difficult matter when, on the wrist plate, its support, valves and cylinder, the customary marks have been placed for finding the relative positions of wrist plate and valves. Now referring to Fig. 302, when the back bonnets of the valve chambers have been taken off, there will be found a mark or line a on the end of each valve s, s, coinciding with the working or opening edges of each valve; another line b will be found on each face of the steam valve chamber coin- ciding with the working edge of the valve, and the line h, on the face of each exhaust valve chamber, coincides with the working edge of the Fig. 301. — Corliss Valve Gear. exhaust port. On the hub of the wrist plate will be found a line d, coinciding with the center line d, k; lastly, there are three lines f, c, f, on the hub of the wrist-plate support, placed in such a way that when the line d coincides with the line c, the wrist plate will stand exactly in the center of its motion, and when the line d coincides with either of the lines f, f, the wrist plate will be at one of the extreme ends u or v of its travel. It should be noticed that since the lines f , e, f are drawn on the periphery of the hub of the wrist-plate support, and the line d is drawn on the periph- ery of the wrist-plate hub, these lines cannot stand in a vertical line, as shown. This way of showing them has been adopted simply for the purpose of making the matter plain. In setting the valves the first step will be to set the wrist plate in its STEAM ENGINE TESTING 291 central position, so that lines c and d will coincide, and fasten the wrist plate in this position by placing a piece of paper between it and the washer L on its supporting pin. Now set the steam valves so that they will have a slight amount of lap, that is to say, the lines a, a must have moved a little beyond the lines b, b ; the amount of this lap depends much on individual preference and experience; it ranges from T V to \ inch for small engines, and from \ to T %- inch for comparatively large engines. This lap is obtained by lengthening or shortening the rods M, M by means of the adjusting nuts. Now by lengthening or shortening the rods N, N and by moving the adjusting nuts, place the exhaust valves e, e, in a position so that the working edges will just open the exhaust ports, or, in other words, place the lines g and h nearly in line with each other. Some engineers prefer a slight amount of lap, others prefer a slight opening of the exhaust ports Fig. 302. — Diagram of a Corliss Valve Mechanism. when the valves are in this position; under these conditions the lines g and h cannot be in line, but will stand apart, as indicated in the diagram. The distance between these lines will, of course, be equal to the desired amount of opening. For small engines it is about T V inch, and for larger engines may be increased to T 3 g inch, but in any case the amount of this opening should be less than the lap of the steam valves, otherwise there will be danger of steam blowing through without doing work. The paper between the wrist plate and the washer on the supporting pin should now be taken out, so that the wrist plate connected to the valves can be swung on its pin. The next step will be to give some attention to the rocker arm. Set this arm in a vertical position by means of a plumb-line, and connect the eccentric rod to it, then turn the eccentric around on the shaft, and see that the extreme points of travel are at equal distances from the plumb- line. To secure this a little adjustment in the stub end of the eccentric 292 POWER PLANT TESTING rod may be necessary. Now connect the hook rod I to its pin on the wrist plate, and again turn the eccentric around on the shaft, and thus determine the extreme points of travel of the wrist plate. If all parts have been correctly adjusted, the line d will coincide with the lines f, f at the extreme points of travel; if this is not the case, the hook rod will have to be adjusted at its stub end so as to obtain the desired eqaalized motion of the wrist plate. The next step will be to set the valves correctly with respect to the position of the crank. To do so the lengths of the rods M, M, N and N must not be changed, but the following procedure should be followed : Place the crank on one of its dead-centers, and turn the eccentric loosely on the shaft in the direction in which the engine is to run, until the steam valve nearest to the piston shows an opening or lead of £% to § inch, according to size of engine, the smaller lead, of course, being adopted for small engines. After the proper lead has been given to this valve, secure the eccentric, and turn the shaft with eccentric in the same direction in which the engine is to run until the crank is on the opposite dead-center, and notice if the opening or lead at this end of the cylinder is the same as on the other steam valve; if not, shorten or lengthen slightly, as may be necessary, the connection between wrist plate and eccentric. Much adjustment in the length of these connections is not permissible without resetting the valves with reference to the wrist plate. The only thing which now remains to be done is to adjust the cam rods, G, G. To do this, secure the governor balls in their highest position, and disconnect the hook rod from wrist pin. Lengthen or shorten the cam rods G, G, so as to bring the detachment apparatus into action, swing the wrist plate back and forward and make such adjustments in the rods G, G, as to permit the steam valves to be released when the steam port has been opened about | inch. This adjustment is for the purpose of keeping the engine under the control of the governor, in case, for some reason or another, the load on the engine is suddenly thrown off. After this adjust- ment the governor balls should be placed in their lowest position, in which the releasing gear should not detach the steam valves, but allow the steam to follow nearly full stroke. Sometimes the releasing gear is constructed in such a manner as to close the steam valves automatically, in case the belt leading to the governor should be broken, or the load on the engine suddenly thrown off. In cases of this kind the governor balls need not be placed in their highest position, but should be placed in their lowest position, and the wrist plate moved to either end of its extreme travel. The steam port opposite this end of travel of wrist plate will then be wide open. Now adjust the corresponding cam rod so that the releasing gear is nearly on the point of releasing the valve; then move the wrist plate to other end of its extreme travel, and adjust the other cam rod in STEAM ENGINE TESTING 293 the same manner. To prove the correctness of the cut-off adjustment, raise the governor balls to about a position where they would be when at work, or to a medium height, and block them there; then, with the con- nection made between the eccentric and the wrist plate, turn the engine shaft slowly in the direction in which it is to run, and when the valve is released measure upon the slide the distance through which the cross- head has moved from its extreme position. Continue to turn the shaft in the same direction, and when the other valve is released, measure the distance through which the cross-head has moved from its extreme position, and if the cut-off is equalized, these two distances will be equal to each other. If they are not, adjust the length of the cam rods until the points of cut-off are at equal distances from the beginning of the stroke. Replace the back bonnets and see that all connections have been properly made, which will complete the setting of the valves. Wherever convenient, it is desirable that an indicator be applied to the engine when at work, and the setting of the valves tested. If necessary, they should be readjusted for the best possible condition for economical work. Clearance Determination of an Engine. This test is made usually to determine the clearance volume of a steam or a gas engine. It is some- times important to know the clearance volume of an engine, as it materi- ally affects the expansion curve of the engine. If it is too large it causes an excessive loss in the engine. The clearance volume is also necessary if a theoretical expansion curve is to be constructed. The engine is first set on dead-center with the piston at the head end of the cylinder. This is done by the " method of trammels " (see foot- note, page 286) . Then the steam chest cover and valve are to be removed and a rubber gasket under a block of wood is placed over both steam-port openings in the valve seat and bolted on. Usually candle wicking must be packed around the piston to stop excessive leakage. For this purpose the cylinder head must be removed and again replaced. Two vessels filled with clean water should be provided and weighed. The clearance space is to be filled from one vessel, the time required being taken. As soon as the space is filled the first vessel is removed and the space is kept filled with water from the other vessel for five minutes. The vessels are then again weighed and the water used from each of them determined. The average rate of leakage while filling the space is usually assumed to be one-half the rate of leakage when full of water as during the leakage test. If W\ = weight in pounds to fill the clearance space; t minutes = the time required to fill the clearance space; and w 2 = the weight of water in pounds necessary to keep it full for one minute, then the leakage during filling is approximately «/ = fx*,; 294 POWER PLANT TESTING and the clearance = {w\ — w') in pounds of water which can be readily reduced to cubic inches. The clearance for the crank end is found in the same general way as for the head end. Most engines have small holes at the top of the cylinder at each end (for double-acting engines) which lead into the clearance space. Holes which are covered by the piston on the dead-center would obviously be of no value. All water must of course be drained from each end before filling. Removing the cylinder head for packing the piston is the best method for observing with certainty that there is no water in the head end- The drip pipes in the cylinder can usually be relied on to remove water from the crank end. Determinations should be repeated several times, and the average value is to be used in calculations. RULES FOR CONDUCTING TESTS OF RECIPROCATING EN- GINES. A.S.M.E. CODE of 1912 1 Determine the object, take the dimensions, note the physical conditions not only of the engine but of all parts of the plant that are concerned in the determinations, examine for leakages, install the testing appliances, etc., as pointed out in the general instructions given on pages 258 to 263, and prepare for the test accordingly. The apparatus and instruments required for a simple performance test of a steam engine, in which the steam consumption is determined by feed- water measurement, are: (a) Tanks and platform scales for weighing water (or water meters calibrated in place). (b) Graduated scales attached to the water glasses of the boilers. (c) Pressure gages, vacuum gages, and thermometers. (d) A steam calorimeter. (e) A barometer. (/) Steam engine indicators. ig) A planimeter. (h) A speed measuring device. (i) A dynamometer for measuring the power developed. Directions regarding the use and calibration of these appliances are given in the preceding chapters. The determination of the heat and steam consumption of an engine by feedwater test requires the measurement of the various supplies of water fed to the boiler; that of the water discharged by separators and drips not returned to the boiler, and that of water and steam which escapes by leakage of the boiler and piping; all of these last being deducted from the total feedwater measured. 1 Journal of A.S.M.E., Nov., 1912. STEAM ENGINE TESTING 295 Where a surface condenser is provided and the steam consumption is determined from the water discharged by the air pump, no such measurement of drips and leakage is required, but assurance must be had that all the steam passing into the cylinders finds, its way into the condenser. If the condenser leaks the de- fects causing it should be remedied, or suitable correction made for the leakage. To ascertain the consumption of heat, the various feed temperatures are taken and heat calculations made accordingly. If the conditions imposed by the particular method adopted for carrying on the test depart from the usual practice, as for example where a colder supply of feedwater is used than the ordinary supply, a preliminary or subsequent run should be made to ascertain the temperatures which obtain under the usual working conditions, and the heat measurements obtained under the test- conditions appropriately corrected for such departures. The steam consumed by steam-driven auxiliaries which are required for the operation of the engine should be included in the total steam from which the heat consumption is calculated and the quantity of steam thus used should be determined and reported. Duration. A test for heat or steam consumption, with substantially constant load, should be continued for such time as may be necessary to obtain a number of successive hourly records, during which the results are reasonably uniform. For a test involving the measurement of feed- water for this purpose, five hours is sufficient duration. Where a surface condenser is used, and the measurement is that of the water discharged by the air pump, the duration may be somewhat shorter. In this case, successive half-hour records may be compared and the time corre- spondingly reduced. When the load varies widely at different times of the day, the duration should be such as to cover the entire period of variation. The preliminary or subsequent trial for determining the working temperatures on a heat test, where the temperatures obtained under the test conditions depart from the usual temperatures, should be of such duration as may be required to secure working results. Starting and Stopping. The engine and appurtenances having been set to work and thoroughly heated under the prescribed conditions of test, except in case where the object is to obtain the performance under working conditions, note the water levels in the boilers and feed reservoir, take the time and consider this the starting time. Then begin the measurements and observations and carry them forward until the end of the period determined on. When this time arrives, the water levels and steam pressure should be brought as near as practicable to the same points as at the start. This being done, again note the time and consider it the stopping time of the test. If there are dif- ferences in the water levels, proper corrections are to be applied. 296 POWER PLANT TESTING Where a surface condenser is used, the collection of water discharged by the air pump begins at the starting time, and the water is thereafter measured or weighed until the end of the test, no observations of the boilers being required. Care should be taken in cases where the activity of combustion in the boiler furnaces affects the height of water in the gage glasses that the same conditions of fire and drafts are operating at the end as at the beginning. For this reason it is best to start and stop a test without interfering with the regularity of the oper- ation of the feed pump, provided the latter can be regulated to run so as to supply the feed water at a uniform rate. In some cases where the supply of feed- water is irregular, as, for example, where an injector is used of a larger capacity than is required, the supply of feedwater should be temporarily shut off. Suitable care should be observed in noting the average height of the water in the glasses, taking sufficient time to satisfactorily judge of the full extent of the fluctuation of the water line, and thereby its mean position. Records. A set of indicator diagrams should be obtained at intervals of 10 or 20 minutes, and at more frequent intervals if the nature of the test makes it necessary. Mark on each card the cylinder and the end on which it was taken, also the time of day. Record on one card of each set the readings of the pressure gages concerned, taken at the same time. These records should subsequently be entered on the general log, together with the areas, pressures, lengths, etc., measured from the diagrams, when these are worked up. CALCULATION OF RESULTS (a) Dry Steam. The quantity of dry steam consumed when there is no superheating is determined by deducting the moisture found by calorimeter test from the total amount of feedwater (the latter being corrected for leakages) or from the amount of air-pump discharge, as the case may be. When there is superheating the dry steam is found by multiplying the weight of superheated steam by the factor , C v {T-t) 1 + —^ (90) H - q 2 in which C p = specific heat at constant pressure of superheated steam at observed pressure and temperature. T = temperature of superheated steam. t = temperature of saturated steam. H = total heat of saturated steam at the observed pressure. q 2 = total heat of feedwater. (b) Heat Consumption. The number of heat units consumed by the engine is found by multiplying the weight of feedwater consumed, corrected for leakages, by the total heat of the steam above the working feed temperature, and multiplying the product by a factor of correction expressing the quality of the steam. If the steam contains moisture, this factor equals * + P ? 5p- ! , <*> H -qt STEAM ENGINE TESTING 297 in which x is the quality of the steam (one minus the decimal representing the percentage of moisture), P the proportion of moisture, qi the total heat of water at the temperature of the steam, q^ the total heat of the feedwater, and H the total heat of saturated steam at the observed pressure. If the steam is superheated, the factor is that given above under (a) Dry- Steam. If there are a number of sources of feedwater supply, the corresponding heat units should be determined for each supply and the various quantities added together. The British standard of heat consumption is based on a feedwater temper- ature assumed to be that of the temperature of saturated steam corresponding to the observed back pressure (whether this is above or below the atmosphere), plus the temperature due to heat derived from jacket or reheated drips. It does not include the heat consumed by any auxiliaries, except jackets and re- heaters. (c) Indicated Horse Power. In a single double-acting cylinder the indicated horse power is found by using the formula PLA N 33,000 in which P represents the average mean effective pressure in pounds per sq. in. measured from the indicator diagrams, L the length of stroke in ft., A the area of the piston less one-half the area of the piston rod, or the mean area of the rod if it passes through both cylinder heads, in sq. in., and N the number of single strokes of the engine per minute. Where extreme accuracy is required, the power developed by each side of the piston may be determined and the results added together. (d) Brake Horse Power. The brake horse power is found by multiplying the net weight on the brake arm (the gross weight minus the weight when the brake is entirely free) in pounds, the circumference of the circle passing through the bearing point at the end of the brake arm, in ft., and the number of revolutions of the brake shaft per minute; and dividing the product by 33,000. (e) Electrical Horse Power. The electrical horse power for a direct-connected gen- erator is found by dividing the output at the bus-bar, expressed in kilowatts, by the decimal 0.746. For alternating-current systems the net output is to be used, being the total output less that consumed for excitation. 1 (J) Efficiency. The efficiency is expressed by the thermal efficiency ratio, which is found by dividing the quantity 2545 by the number of heat units consumed per h.p.-hr., either indicated or brake. (g) Steam accounted for by Indicator Diagrams. The steam accounted for, ex- pressed in pounds per i.h.p. per hour, may readily be found by using the formula 2 ^^ [(C + E)W C -(H + E) W h ], (92) m.e.p. in which m.e.p. = mean effective pressure, lbs. per sq. in. C = proportion of stroke completed at cut-off or release. E — proportion of clearance. H = proportion of stroke uncompleted at compression. W c = weight of 1 cu. ft. steam at cut-off or release pressure. Wh = weight of 1 cu. ft. steam at compression pressure. 1 Calculation of electrical output is explained on pages 323 and 324. 2 Compare with equation (98) page 312. 298 POWER PLANT TESTING The points of cut-off release and compression, referred to are indicated in Fig. 299. In multiple expansion engines the mean effective pressure to be used in the above formula is the combined m.e.p. referred to the cylinder under consideration. In a compound engine the combined m.e.p. for the h.p. (high-pressure) cylinder is the sum of the actual m.e.p. of the h.p. cylinder and that of the l.p. (low- pressure) cylinder multiplied by the cylinder ratio. Likewise the combined m.e.p. for the l.p. cylinder is the sum of the actual m.e.p. of the l.p. cylinder and the m.e.p. of the h.p. cylinder divided by the cylinder ratio. (h) Cut-off and Ratio of Expansion. To find the percentage of cut-off, or what may best be termed the " commercial cut-off," the following rule should be observed: Through the point of maximum pressure during admission draw a line parallel to the atmospheric line. Through a point on the expansion line, where the cut-off is complete, draw a hyperbolic curve. The intersection of these two lines is the point of commercial cut-off, and the proportion of cut-off is found by dividing the length measured on the diagram up to this point by the total length. To find the ratio of expansion divide the volume corresponding to the piston displacement, including clearance, by the volume of the steam at the commer- cial cut-off, including clearance. In a multiple expansion engine the ratio of expansion is found by dividing the volume of the l.p. cylinder, including clearance, by the volume of the h.p. cylinder at the commercial cut-off, including clearance. TABLE 1. DATA AND RESULTS OF HEAT AND FEED WATER TESTS OF STEAM ENGINE, SHORT FORM, CODE OF 1912 (1) Test of engine located at to determine conducted by (2) Type and class of engine and auxiliaries 1st Cyl. 2d Cyl. 3d Cyl. (3) Dimensions of main engine: (a) Diameter of cylinder ins (b) Stroke of piston ft (c) Diameter of piston rod each end ins (d) Average clearance per cent (e) Cylinder ratio (/) Horse power constant for 1 lb. m.e.p. and 1 r.p.m (4) Dimensions and type of auxiliaries . (5) Date (6) Duration hrs. Average Pressures and Temperatures (7) Pressure in steam pipe near throttle by gage lbs. per sq. in. (7a) Absolute pressure in steam pipe near throttle lbs. per sq. in. (8) Barometric pressure of atmosphere in ins. of mercury (9) Pressure in receivers by gage lbs. per sq. in. (10) Vacuum in condenser in ins. of mercury (11) Pressure in jackets and reheaters by gage lbs. per sq. in. (11a) Temperature of steam near throttle deg. F. STEAM ENGINE TESTING 299 (lib) Temperature of steam in steam chest deg. F. (12) Temperature of main supply of feedwater deg. F. (13) Temperature of additional supplies of feedwater deg. F. Total Quantities (14) Total water fed to boilers from main source of supply lbs. (15) Total water fed from additional supplies lbs. (16) Total water fed to boilers from all sources lbs. (17) Moisture in steam or superheating near throttle per cent or deg. F. (18) Factor of correction for quality of steam (19) Total dry steam consumed for all purposes lbs. Hourly Quantities (20) Water fed from main source of supply lbs. (21) Water fed from additional supplies lbs. (22) Total water fed to boilers per hour lbs. (23) Total dry steam consumed per hour lbs. (24) Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant lbs. (25) Net dry steam consumed per hour by engine and auxiliaries lbs. (26) Net dry steam consumed per hour: (a) By engine alone lbs. (6) By auxiliaries lbs. Heat Data (27) Heat units per lb. of dry steam, based on temperature of Line 12 B.t.u. (28) Heat units per lb. of dry steam, based on temperature of Line 13 B.t.u. (29) Heat units consumed per hour, main supply of feed B.t.u. (30) Heat units consumed per hour, additional supplies of feed B.t.u. (31) Total heat units consumed per hour for all purposes B.t.u. (32) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. (33) Net heat units consumed per hour: (a) By engine and auxiliaries B.t.u. (b) By engine alone B.t.u. (c) By auxiliaries B.t.u. Indicator Diagrams 1st Cyl. 2d Cyl. 3d Cyl. (34) Commercial cut-off in per cent of stroke (35) Initial pressure in lbs. per sq. in. above atmosphere (36)^Back pressure at lowest point above or below atmos- phere in lbs. per sq. in (37) Mean effective pressure in lbs. per sq. in (38) Steam accounted for by indicator in lbs. per i.h.p. per hour: (a) Near cut-off (b) Near release Speed (39) Revolutions per minute rev. (40) Piston speed in ft. per min ft. 300 POWER PLANT TESTING Power (41) Indicated horse power developed by main engine cylinders: 1st cylinder i.h.p. 2d cylinder i.h.p. 3d cylinder whole engine i.h.p. Whole engine i.h.p. (42) Brake horse power b.h.p. Economy Results (43) Heat units consumed by engine and auxiliaries per hour: (a) Per indicated horse power B.t.u. (6) Per brake horse power B.t.u. (44) Dry steam consumed per indicated horse power per hour: (a) By engine and auxiliaries lbs. (b) By main engine alone lbs. (c) By auxiliaries lbs. (45) Dry steam consumed per brake horse power per hour: , (a) By engine and auxiliaries lbs. (6) By main engine alone lbs. (c) By auxiliaries lbs. (46) Percentage of steam used by main-engine cylinders accounted for by in- dicator diagrams: (a) Near cut-off per cent (b) Near release per cent (47) Sample Diagrams TABLE 2. DATA AND RESULTS OF STEAM-ENGINE TEST— COMPLETE V FORM, CODE OF 1912 (1) Test of engine located at to determine conducted by (2) Type of engine (simple, compound, or other multiple expansion; condensing or non-condensing) (3) Class of engine (mill, marine, electric, etc.) (4) Rated power of engine (5) Name of builders (6) Number and arrangement of cylinders of engine; how lagged; type of con- denser (7) Type of valves (8) Type of boiler (9) Kind and type of auxiliaries (air pump, circulating pump, feed pump; jackets, heaters, etc.) IstCyl. 2dCyl. 3d Cyl. (10) Dimensions of engine: (a) Single or double acting (6) Cylinder dimensions: Bore, ins Stroke, ft Diameter of piston rod, ins Diameter of tail rod, ins STEAM ENGINE TESTING 301 (c) Clearance in per cent of volume displaced by- piston per stroke: Head-end, per cent Crank-end, per cent Average, per cent (d) Surface in sq. ft. (average) : Barrel of cylinder, sq. ft Cylinder heads, sq. ft Clearance and ports, sq. ft Ends of piston, sq. ft (c) Jacket surfaces or internal surfaces of cylinder heated by jackets, in sq. ft.: Barrel of cylinder, sq. ft Cylinder heads, sq. ft Clearance and ports, sq. ft Receiver jackets, sq. ft (g) Horse power constant for 1 lb. m.e.p. and 1 r.p.m (11) Dimensions of boilers: (a) Number (b) Total grate surface sq. ft. (c) Total water heating surface sq. ft. (d) Total steam heating surface sq. ft. (12) Dimensions of auxiliaries: (a) Air pump <-. (b) Circulating pump (c) Feed pumps (d) Heaters (13) Dimensions of condenser (14) Dimensions of electric or other machinery driven by engine (15) Date (16) Duration hrs. Average Pressures and Temperatures (17) Steam pressure at boiler by gage lbs. per sq. in. (18) Steam pipe pressure near throttle, by gage lbs. per sq. in. (19) Barometric pressure of atmosphere in lbs. per sq. in (20) Pressure in first receiver by gage lbs. per sq. in. (21) Pressure in second receiver by gage lbs. per sq. in. (22) Vacuum in condenser: (a) In ins. of mercury ins. (b) Corresponding absolute pressure lbs. per sq. in. (23) Pressure in steam jacket by gage lbs. per sq. in. (24) Pressure in reheater by gage lbs. per sq. in. (24a) Temperature of steam at boiler deg. F. (24b) Temperature of steam near throttle deg. F. (24c) Temperature of steam in steam chest deg. F. (25) Superheat in steam leaving first receiver deg. F. (26) Superheat in steam leaving second receiver deg. F. (27) Temperature of main supply of feedwater to boilers deg. F. (28) Temperature of additional supplies of feedwater deg. F. 302 POWER PLANT TESTING (29) Ideal feedwater temperature corresponding to the pressure of the steam in the exhaust pipe, allowance being made for heat derived from jacket or reheater drips (British Standard) deg. F. (30) Temperature of injection or circulating water entering condenser deg. F. (31) Temperature of injection or circulating water leaving condenser deg. F. (32) Temperature of air in engine room deg. F. Total Quantities (33) Water fed to boilers from main source of supply lbs. (34) Water fed from additional supplies lbs. (35) Total water fed to boilers from all sources lbs. (36) Moisture in steam or superheating near throttle per cent or deg. F. (37) Factor of correction for quality of steam, dry steam being unity (38) Total dry steam consumed for all purposes Hourly Quantities (39) Water fed from main source of supply lbs. (40) Water fed from additional supplies lbs. (41) Total water fed to boilers per hour lbs. (42) Total dry steam consumed per hour lbs. (43) Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant lbs. (44) Net dry steam consumed per hour by engine and auxiliaries lbs. (45) Dry steam consumed per hour: (a) Main engine alone \ lbs. (6) Jackets and reheaters lbs. (c) Air pump lbs. (d) Circulating pump '. lbs. (e) Feedwater pump lbs. (/) Other auxiliaries lbs. (46) Injection or circulating water supplied condenser per hour cu. ft. Heat Data (47) Heat units per pound of dry steam, based on temperature of Line 27 B.t.u. (48) Heat units per pound of dry steam, based on temperature of Line 28 B.t.u. (49) Heat units consumed per hour, main supply of feed B.t.u. (50) Heat units consumed per hour, additional supplies of feed B.t.u. (51) Total heat units consumed per hour for all purposes .B.t.u. (52) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. (53) Net heat units consumed per hour: (a) By engine and auxiliaries B.t.u. (b) By engine alone B.t.u. (c) By auxiliaries •. B.t.u. (54) Heat units consumed per hour by the engine alone, reckoned from tem- perature given in Line 29 (British Standard) B.t.u. Indicator Diagrams 1st Cyl. 2d Cyl. 3d Cyl. (55) Commercial cut-off in per cent of stroke (56) Initial pressure in lbs. per sq. in. above atmosphere (57) Back-pressure at mid-stroke above or below atmos- phere in lbs. per sq. in STEAM ENGINE TESTING 303 (58) Mean effective pressure in lbs. per sq. in (59) Equivalent mean effective pressure in lbs. per sq. in.: (a) Referred to first cylinder (6) Referred to second cylinder (c) Referred to third cylinder (60) Pressures and percentages used in computing the steam accounted for by the indicator diagrams, measured to points on the expansion and com- pression curves: Pressure above zero in lbs. per sq. in. : (a) Near cut-off , (6) Near release (c) Near beginning of compression Percentage of stroke at points where pressures are measured: (d) Near cut-off (e) Near release (/) Near beginning of compression . . . . (61) Aggregate m.e.p. in lbs. per sq. in. referred to each cylinder given in heading (62) Mean back pressure above zero, lbs. per sq. in (63) Steam accounted for in lbs. per indicated horse power per hour: (a) Near cut-off (6) Near release (64) Ratio of expansion (65) Mean effective pressure of ideal diagram 1 lbs. per sq. in. (66) Diagram factor 1 Speed (67) Revolutions per minute (68) Piston speed per minute ft. (69) Variation of speed between no load and full load r.p.m. (70) Fluctuation of speed on suddenly changing from full load to no load, meas- ured by the increase in the revolutions due to the change r.p.m. Power (71) Indicated horse power developed by main engine: 1st cylinder i.h.p. 2d cylinder i.h.p. 3d cylinder i.h.p. Whole engine i.h.p. (72) Brake horse power b.h.p. (73) Friction i.h.p. by diagrams, no load on engine, computed for average speed, .i.h.p. (74) Difference between Lines 71 and 72 h.p. (75) Percentage of i.h.p. of main engine lost in friction per cent (76) Power developed by auxiliaries 2 i.h.p. 1 See Journal of A.S.M.E., Nov., 1912, page 1861. 2 These are not included in the power developed by the main engine. 304 POWER PLANT TESTING Economy Results (77) Heat units consumed per indicated horse power per hour: 1 (a) By engine and auxiliaries B.t.u. (b) By engine alone B.t.u. (78) Heat units consumed per brake horse power per hour: , (a) By engine and auxiliaries B.t.u. (6) By engine alone B.t.u. (79) Heat units consumed by engine per hour, corresponding to ideal temperature of feedwater given in Line 29, per indicated horse power (British Standard) B.t.u. (80) Dry steam consumed per i.h.p. per hour: (a) By engine and auxiliaries lbs. (b) By main engine alone lbs. (c) By auxiliaries lbs. (81) Dry steam consumed per brake h.p. per hour: (a) By engine and auxiliaries lbs. (6) By main engine alone lbs. (c) By auxiliaries lbs. (82) Percentage of steam used by main engine cylinders accounted for by indi- cator diagrams: 1st Cyl. 2d Cyl. 3d Cyl. (a) Near cut-off '. (b) Near release Efficiency Results (83) Thermal efficiency ratio for engine and auxiliaries: (a) Per indicated horse power per cent (6) Per brake horse power per cent (84) Thermal efficiency ratio for engine alone: (a) Per indicated horse power per cent (6) Per brake horse power per cent (85) Ratio of economy of engine to that of an ideal engine working with the Rankine cycle (see page 308) per cent Work Done per Heat Unit (86) Ft.-lbs. of net work per B.t.u. consumed by engine and auxiliaries (1,980,000 -=- Line 78a) ft.-lbs. Note. Both the Short Form and Complete Form here given refer to a steam engine used for general service. For an engine driving an electric generator the form should be enlarged to include the electrical data, embracing the average voltage, number of amperes in each phase, number of watts, number of watt hours, average power factor, etc. ; and the economy results based on the electrical output embracing the heat units and steam consumed per electric h.p. per hour and per kw.-hr., together with the efficiency of the generator. See table for Steam Turbine Code, pages 325 to 328. Likewise, in a marine engine having a shaft dynamometer, the form should include the data obtained from this instrument, in which case the brake h.p. becomes the shaft h.p. 1 The h.p. on which the economy and efficiency results are based are those of the main engine given in Line 71. STEAM ENGINE TESTING 305 Surface condensers are usually perferred for accurate engine tests because the steam used by the engine can be determined directly by weighing or measuring the condensed steam. A surface condenser is essentially a vessel of considerable size in which there are a great many brass tubes. It is usually designed so that exhaust steam passes on its way through the condenser into contact with the outside surface of these tubes while cold water for condensing the steam circulates inside the tubes. Steam condensed in this way accumulates in the bottom of the condenser and is removed by an air pump used for producing a vacu- um, or by gravity if the pressure in the condenser is atmospheric, as it will be if the engine is operating " non-condensing," that is, without a vacuum. It is very essential, however, that surface condensers be tested for leakage, preferably before and after every important test is made; and the leakage should be determined with the same vacuum in the condenser as there is when it is used in the engine test. Probably the best method to determine the amount of condenser leakage is to pass cooling water through the tubes at the normal rate of flow, maintaining at the same time with the air pump the required vacuum. Then the amount of water removed by the air pump is the leakage of circulating water through the tubes into the steam space. Under normal operating conditions there would be no leakage of steam into the circulating water, because the water will be at a higher pressure than the steam. If only a test is to be made to determine whether or not there is any leakage in the condenser, the test most generally applied is to close all connections to the condenser and observe whether a vacuum once established can be maintained a reasonably long time. A more rapid test applicable, however, only where salt water is used for cooling, is to test the condensed steam several times during a test by adding a little silver nitrate to a small amount of the condensed steam. If there is no appreciable precipitate 1 it may be assumed that the condenser does not leak. Som'e of the important considerations to be observed in an accurate engine test will now be given as stated in the rules adopted by the Ameri- can Society of Mechanical Engineers. Discussion of Thermal Efficiency. The ratio of the heat converted into work to the heat supplied to the engine is called the thermal efficiency. The first of these quantities is calculated from the indicated horse power and the latter from the weight and total heat per pound of the steam supplied. The only uncertainty arises as to the proper base from which to calculate. The total heat of steam given in steam tables is calculated from 32 degrees Fahrenheit, but it is obvious if this base is adopted the 1 The white precipitate formed with the salt in sea water is of course silver chloride, thus, AgN0 3 + NaCl = AgCl + NaN0 3 . 306 POWER PLANT TESTING engine may be charged with more than its share of heat. If, for ex- ample, the exhaust steam from the engine passes through a feedwater heater and the engine returns the condensed steam to the boiler as feedwater at say 150 degrees Fahrenheit, then there will be 150 — 32, or 118 B.t.u. in every pound of steam passing continually from the engine to the boiler and from the boiler back to the engine without doing any work. More accurately, then, the thermal efficiency of an engine (E t ) should be stated as e, = 5^Q/ ( 93 ) where Q u and Q f are the heat equivalents respectively of the useful work and of the engine friction, while Q„ should be denned as the net heat supplied to the engine. From this discussion it follows that the more efficient the feedwater heater the higher the efficiency of the engine will be, and if an efficient heater is not used there is no reason for charging a loss to the engine. Obviously the limit to the amount of heat returnable to the boiler by means of a heater is the amount of heat in the exhaust steam, and this limit can be nearly ap- proached under actual practical conditions. It is, therefore, very reason- able that the " datum " for the calculation of the heat supplied to the engine should be the heat of the liquid corresponding to the temperature of the steam in the exhaust pipe from the engine. All this applies, of course, equally well to engines whether operating condensing or non- condensing. In other words, the net heat supplied to the engine is the total heat of the steam entering the engine, less the heat of the liquid at the temperature of the engine exhaust. The temperature of the exhaust must be taken by a thermometer in a suitable thermometer cup placed in the exhaust pipe close to the engine; and, similarly, the temperature and quality of the steam supplied to the engine must be determined by thermometers and a steam calorimeter placed close to, but on the boiler side of, the engine throttle valve. Fig. 303 shows diagrammatically the heat distribution and various losses in a steam plant, and gives approximate percentage values of the losses. Engine Performance Expressed in British Thermal Units. A method which is rapidly gaining in favor among practical engineers is to express the performance of a steam engine or turbine by the number B.t.u. supplied per indicated horse power per minute, the heat units supplied per minute being determined, as explained in the preceding paragraphs; that is, the total heat in the steam entering at the throttle less the heat of the liquid at the temperature of the exhaust. Hirn's Analysis. For certain scientific investigations it is useful to make a heat analysis of the indicator diagram, to show the interchange of heat from steam to cylinder walls, etc., which is going on within the STEAM ENGINE TESTING 307 308 POWER PLANT TESTING cylinder. This is unnecessary for commercial tests. Years ago deduc- tions from such an analysis were considered to be of considerable impor- tance to designers; but, lately, such data are considered of very doubtful importance. Ratio of Economy of an Engine to that of an Ideal Engine. The cycle of the ideal engine recommended for obtaining this ratio is that which was adopted by the Committee appointed by the Civil Engineers of London, to consider and report a standard thermal efficiency for steam engines. This engine is one which follows the Rankine cycle where steam at a con- stant pressure is admitted into a cylinder having no clearance, and after the point of cut-off is expanded adiabatically to the back-pressure. In obtaining the economy of this engine the feed-water is assumed to be returned to the boiler at the exhaust temperature (Fig. 304). — >■ Volume Fig. 304. — Indicator Diagram for the Ideal Rankine Cycle. The ratio of the economy of an engine to that of the ideal engine is obtained by dividing the heat consumption per indicated horse power per minute for the ideal engine (called the " theoretical water-rate ") by that of the actual engine. Engine Performance Compared with the Rankine Cycle. In order to know how much the efficiency of an engine can be improved it is most desirable to compare the actual thermal efficiency, with the highest pos- sible efficiency. For steam engines the standard cycle for comparison is now generally taken as the Rankine cycle, 1 in which the operation of the engine is assumed to be perfect; that is, without clearance in the cylinder, initial condensation, leakage or radiation. The indicator dia- gram for the Rankine cycle is represented by Fig. 304. The steam is assumed to be supplied to the engine cylinder at constant pressure until the point of cut-off, after which it is expanded adiabatically down to the 1 Years ago it was not unusual to make this comparison with the efficiency of the Carnot cycle as a basis. This efficiency of a heat engine, it will be remembered, is ex- pressed by the ratio of 7\ — T 2 to 7\ where 2\ is the absolute initial temperature and T% is the absolute final temperature. STEAM ENGINE TESTING 309 back pressure at which the engine is operated on the return stroke when the exhaust steam is swept out of the cylinder and returned as feed-water to the boiler at the temperature of the exhaust. The same Rankine cycle represented in Fig. 304 when shown by a so-called entropy-temperature diagram can be made simpler both for analysis and calculations. This other kind of diagram, the details of which are somewhat more difficult to understand, is universally used by steam turbine engineers and has for the problem in hand particular advantages. In this diagram, any sur- face represents accurately to given scales a quantity of heat. Absolute temperatures (T) are the ordinates, and entropies 1 () are the abscissas. Specific Heat of Superheated Steam. In modern practice super- heated steam often enters our calculations. The specific heat of steam a \ L , .66 \ \ \ \ \ \ .64 V \ \ \ V \ \ \ { .62 \ V \ V \ \ \ V , s \ V \ \ \ \ \ N .58 / \ S s v s \\ s s, S S 1 \ s \ \ \ / \ \ N Lb! / s \ V \ 5.8 r.2 / 2i ' Pl70.4 / -113.0 " .50 / . 85.2 .48 -J t / 42 200 350 700 750 Fig. 305. 350 400 450 500 550 6C Temperature" P Mean Values of Specific Heat (C p ) of Superheated Steam Integrated from Knoblauch and Jacob's Data. varies with the temperature and pressure as shown in Figs. 305 and 306, giving values of the mean and the true specific heat at constant pressure (Cp), as determined by Knoblauch and Jakob. 2 1 Entropy, which Perry calls the " ghostly quantity," has no real physical significance, so that complete definition is not possible. If dQ is a small amount of heat added to a body and T is the absolute temperature at which the heat is added, then the change in entropy of that body is dQ/T, or d— dQ/T. Entropy of saturated steam above the entropy of water at the freezing point is easily calculated. For saturated steam at any pressure, then 4> = xr/T + 6, where x is the quality of the steam, r is the heat of vaporization, T is the absolute temperature, and 6 is the entropy of the liquid (water). 2 Zeit. Verein deutscher Ingenieure, Jan. 5, 1907. Values of mean specific heat are taken from Mechanical Engineer, July, 1907, and Professor A. M. Greene's paper in Proc. American Society of Mechanical Engineers, May, 1907. 310 POWER PLANT TESTING True specific heat represents the ratio of the amount of heat to be added to a given weight of steam at some particular condition of tem- perature and pressure to raise the temperature one degree to that re- quired to raise the temperature of water at maximum density one degree. The mean specific heat is almost invariably used in steam engine and turbine calculations. 0.90 200 250 Temperature °C. Fig. 306. — Values of the "True" Specific Heat of Superheated Steam. Approximate Steam Consumption Calculated from an Indicator Diagram. It is often very convenient to be able to calculate the approxi- mate steam consumption of a steam engine from the data obtainable from an indicator card, the size of the piston, the stroke, and the speed. Using a double-acting, engine, the following symbols 1 may be used: 1 Compare with Power, September, 1893. STEAM ENGINE TESTING 311 p = mean effective pressure, pounds per square inch from indicator diagram. 1 = length of the stroke of the engine in feet. a = area of the piston in square inches. b = percentage of clearance to the length of the stroke. c = percentage of stroke at any point in the expansion line. 1 n = number of revolutions per minute; and 120 n = number of strokes per hour. w = weight of a cubic foot of steam having a pressure as shown by the indicator diagram corresponding to that at the point in the expansion line selected for c, pounds. w' = weight of a cubic foot of steam corresponding to the pressure at the "" end of compression, pounds. . -^" . — la (b + c) Then the number of cubic feet per stroke = — ■— {- in the clearance 144(100) and piston displacement volumes (at c). Weight of steam per stroke, pounds = -, ~ (04) 144 (100) v ^ y Volume of the clearance, cubic feet = 144 (100) Weight of steam in clearance, pounds remaining in the cylinder = law'(b) t , 144(100)*' Approximate net weight of steam used per stroke law (b + c) law' (b) la r/ , . , , n , N = —, x 7-^A = [(b + c) w - bw']. . (95) 144(100) 144(100) 14,400 J y ^ OJ Approximate weight of steam from diagram per hour = i2onla _ bw , } 14,400 lK y Indicated horse power for a double-acting engine = ^- n (97) 33,000 1 In other words this is the percentage of the entire stroke which has been swept through by the piston corresponding to the point in the expansion curve selected for measurements. It is preferable, however, to take this point not very far from the point of cut-off, since the assumption must be made that the product of pressure times volume in the expansion curve is constant, which is, of course, not accurate, and the error becomes greater as the expansion increases. 312 POWER PLANT TESTING Steam consumption per indicated horse power 1 is (96) divided by (97) or 137.5 [(b+c)w-bw' (98) Compare this with formula (92) page 297. The difference between the theoretical steam consumption calculated by the formula and the actual consumption as determined by tests represents steam " not accounted for by the indicator," due to cylin- der condensation, leakage through ports, radiation, etc. If the steam supplied to the engine is very wet, corrections for this moisture should be made in the value of w. Willans Law. One of the most serviceable checks that can be applied to engine tests is plotting the Willans line of total steam consump- tion per hour. Curve sheets illustrating this as plotted from actual tests by Barra- clough and Marks 2 are shown in Fig. 307. It will be ob- served that the points repre- senting the weight of steam used per hour when plotted for the horse power corre- sponding are on a straight line. In other words Willans law is usually stated thus: " With a fixed cut-off and a throttling governor the total steam used by the engine per hour at different loads can be represented by a straight line upon a mean effective pressure base or upon a horse- power base." - It will be shown also in the following paragraphs how, theoretically, this relation holds for an engine operating at a fixed cut- off and with a throttling governor and that the total steam used per hour is proportional to the mean effective pressure and also to the horse power developed. 1 A method of determining steam consumption by means of logarithmic curves of indicator diagrams by J. P. Clayton is described in Bulletin No. 65 of Engineering Ex- periment Station of University of Illinois and in abridged form in Journal of A.S.M.E., April, 1912. 2 Proceedings Institution of Civil Engineers, vol. 120, page 323. 7uo r u 7 £ .V 7 7 7 -/ ^A- 1? ->- 7 A * 1 - * -.el ^ 1 ^- -S -;< 200 . ' IV ^ + Qs* Fig. 10 20 30 Indicated Horse Power 307. — "Willans" Lines for an Engine with a Throttling Governor. Pi STEAM ENGINE TESTING 313 If we assume that the expansion curve is hyperbolic, which is usually near the truth, then the mean " forward " pressure given by an indicator diagram is 1 f±^} (9.) where pi is the initial pressure of the steam and r is the ratio of expansion. With a throttling governor r is of course constant. The terms in the parenthesis can then be represented by a constant c and the mean forward pressure p/ then can be written as piC. Volume of steam used per hour for a double-acting engine can be expressed in cubic feet as 120 (nV), where n is the number of revolutions per minute and V is the volume of steam admitted to the cylinder per stroke. Now if we use the symbol Vi for the specific volume, that is, the volume in cubic feet of a pound of steam at the pressure pi, and assuming for a small range of pressures that piVi = a constant k, then we can write, if W is the weight of steam used per hour in pounds, = 120 (nV) _ 120 (nV Pl ) Vi k v ' Now with a throttling governor and constant cut-off all these quantities are constant except pi, and writing a constant z for the term ~ — - we have W = zpi, but it was shown above that the mean forward pres- sure p/ = cpi, so that W = z — • So that the curve representing this equation is a straight line and passes through the origin of coordinates. If, however, we use the mean effective pressure instead of the mean forward pressure, then m.e.p. = p/ - p6, where p& is the mean " back " or exhaust pressure: In these last terms then W = - (m.e.p. + p&) (101) This last equation may be stated as W = a constant X m.e.p. + another constant which, when plotted to a scale of mean effective pres- sure for abscissas and weight of steam used per hour for ordinates, is also a straight line, intersecting the axis of ordinates above the origin at a distance corresponding to the steam consumption per hour at no load. Since the indicated horse power (i.h.p.) is proportional to mean effective pressure, a straight line will result when the steam consumption and indicated horse power are plotted; and the same holds true also 1 Compare with Perry's " Steam Engine," page 286. 314 POWER PLANT TESTING when steam consumption is plotted with brake horse power (b.h.p.) instead of indicated horse power. Curves Showing Results of Tests Graphically. One of the best checks of an engine test is to plot the principal observations graphically as the test proceeds. This is particularly important as regards the total weight of steam used per hour. For a series of tests each made with a different load the points plotted with horse power (either indicated or brake) as abscissas and total steam per hour as ordinates should lie along a straight line, known as the Willans line. This statement applies accurately only for engines operating with a throttling governor at, of course, constant speed, but is generally applicable to steam turbine tests, irrespective of the type of governor. CHAPTER XIII TESTING STEAM TURBINES AND TURBO-GENERATORS Testing Steam Turbines. 1 In every power plant the means should be available for making tests of the steam equipment to determine the steam consumption. Usually tests are made to determine how nearly the performance of a turbine approaches the conditions for which it was designed. The results obtained from tests of a turbine are to show usually the steam consumption required to develop a unit of power in a unit of time, as, for example, a horse power^or a kilowatt-hour. In such tests a number of observations must be made regarding the condition of the steam in the passage through the turbine and of the per- formance of the turbine as a machine. To get a good idea of what these observations mean, it may be profitable to follow the steam as it passes through the turbine. The steam comes from the boilers through the main steam pipe and the valves of the turbine to the nozzles or stationary blades as the case may be. It then passes through the blades and finally escapes through the exhaust pipe to the condenser. It is preferable to have a surface condenser for tests, so that the exhaust steam can be weighed. The weighing is preferably done in large tanks mounted on platform scales. Methods for Testing. The important observations to be made in steam turbine tests are: 1. Pressure of the steam supplied to the turbine. 2. Speed of rotation of the turbine shaft, usually taken in revolutions per minute. 3. Measurement of power with a Prony or a water brake, if the power at the turbine shaft is desired; or with electrical instruments (ammeters, voltmeters, and wattmeters), if the power is measured by the output of an electric generator. 4. Weight, or measurement by volume, of the condensed steam dis- charged from the condenser. Unless a surface condenser is used it is very 1 Tests of the turbines alone in a modern station may be only a rough indication of the over-all economy of the plant. Recently steam turbines were installed in a large power plant where they replaced steam engines of an excellent make. Tests of the turbines and of the engines made without considering the losses in the rest of the plant showed very little gain in efficiency by this change, although it was found that the fuel consumption was reduced twenty per cent. Parts of this chapter and the chapter following are taken from the author's work on "The Steam Turbine" (John Wiley & Sons, New York). 315 316 POWER PLANT TESTING difficult to obtain the amount of steam used by the turbine. All leakages from pipes, pumps, and valves, which are a part of the steam which has gone through the turbine, must be added to the weight of the condensed steam. The accuracy of a test often depends a great deal on how ac- curately leaks have been provided against, or measured when they occur. 5. Temperature of the steam as it enters the turbine. 1 6. Vacuum or back-pressure in the exhaust pipe of the turbine. All gages, electrical instruments, and thermometers should be carefully calibrated before and after each test, so that observations can be corrected for any errors. The zero readings of Prony and water brakes for measur- ing power should be carefully observed and corrected to eliminate the friction of the apparatus with no load. Unless all these precautions are taken the difficulties in getting reliable tests of turbines are greatly increased. In all cases tests should be continued for several hours with absolutely constant conditions if the tests are to be of value. The most valuable test of a steam turbine or of a reciprocat- ing steam engine is made when varying only the load; that is, with pressures, superheat, and speed constant. When the steam consumption is then plotted against fractions of full load, a water-rate curve is obtained. For such a curve a series of tests] are needed, each for some fraction of full load; and in each separate test the power as well as all the other conditions must be held con- stant. Another important test of the performance of a steam turbine is made by varying both the speed and the power and keeping the other conditions constant. The observations of speed and power from such a test give a power parabola as illustrated in Fig. 308. This curve shows at what speed the turbine gives the greatest output. 1 The most satisfactory tests of turbines are made with steam slightly superheated rather than wet. When steam is very wet (more than about 4 per cent moisture for ordinary pressures) the determination of the quality is difficult. There is also a danger that steam showing only a few degrees of superheat by the reading of the thermometer is actually wet. The high temperature is due in such cases to heating from eddies around the thermometer case or in steam pockets near it. ^.50 -0^ "^ g..45 A- -\ > & a 3 400 &35 *\i 30 1*25 •v /^ % O M 300 "^ ^ \ % 26 \ M V M 25 | 24 3 23 1 22 p. I 21 §20 | 19 sl8 <.-^ \ %<% \ en a basis of kilowatts output should be net; that is, the power required for excitation should be substracted from 1 Usually the nozzles discharging the steam into the second stage of the turbine are always open, so that the total area is always constant. If, therefore, the areas of the smallest sections of these nozzles are measured and the pressure is observed in the first stage, the weight can be calculated with a considerable degree of accuracy by using the formula for the flow of steam on page 189. STEAM TURBINES AND TURBO-GENERATORS 321 the generator output. If, however, the generator is self-exciting the net output can be measured directly at the terminals of the machine. " Guarantee '' tests of steam engines and turbines should be made under conditions as nearly as possible the same as that for which the turbine was designed. Different machines will have different correction factors for varying conditions of pressure, superheat, vacuum, etc., so that water rates corrected for large variations are always likely to be more or less inaccurate. This is particularly true in respect to vacuum corrections. Some turbines will give a very good efficiency with a low vacuum, but at a high vacuum because of an insufficiently large steam space the efficiency will be low. Heat Unit Basis of Efficiency A thermal efficiency can be calculated readily by determining what percentage the heat equivalent of the work is of the heat " used by the turbine," assumed to be the difference between the total heat in the steam at the initial conditions and the heat of the liquid in the condensed steam at the temperature of the exhaust. By this method the full-load test of a Westinghouse-Parsons turbine reported by F. P. Sheldon & Co., will be calculated from the data given in an official report. In order to make the results of such calculations of steam turbine tests comparable with the usual heat unit computations of reciprocating steam engine tests the results are often expressed in terms of indicated or "internal " horse power. It was assumed the mechanical efficiency of a reciprocating engine of about the same capacity at this load was about 93.3 per cent. THERMAL EFFICIENCY OF A 400-KILOWATT STEAM TURBINE Brake horse power 660 Corresponding indicated or " internal " horse power of a reciprocating engine = 708 & .933 Total steam used per hour, pounds 9169 Steam used per " internal " horse power per hour, pounds 12.96 Steam used per " internal " horse power per minute, pounds 0.216 Steam pressure, pounds per square inch, absolute 166 . 9 Superheat, degrees Fahrenheit 2.9 Vacuum, referred to 30 inches barometer, inches 28 .04 Temperature of condensed steam, degrees Fahrenheit (at .96 pound per square inch absolute pressure) = 100 . 6 Total heat contents of one pound of dry saturated steam at the initial pres- sure, B.t.u 1193.9 Heat equivalent of superheat in one pound of steam, B.t.u. (C p from Fig. 305, page 309) . 1.9 322 POWER PLANT TESTING Total heat contents of one pound of superheated steam, B.t.u 1195.8 Heat of liquid in condensed steam, B.t.u 68 . 6 Heat used in turbine per pound steam, B.t.u 1127.2 Heat used in turbine per " internal " horse power per minute, B.t.u (1127.2 L X 0.216) 243 .5 33 000 Heat equivalent of one horse power per minute, B.t.u. = — ' 42.42 Thermal efficiency, per cent (42.42 -r- 243.5) 17.4 CALCULATION OF EFFICIENCY (SHAFT AND BUCKET) OF A STEAM TURBINE GENERATOR COMPARED WITH THE RANKINE CYCLE. 1. " Electrical " kilowatts. 2. R.P.M. 3. Steam per hour (corrected for moisture). 4. Water rate per " electrical " kilowatt, pounds per hour. (3) -5- (1). 5. PR, loss in generator, kilowatts. 6. Rotation loss of generator alone, kilowatts. 7. Rotation loss of wheel and generator, kilowatts. 8. " Shaft " kilowatts. (1) + (5) + (6). 9. " Bucket » kilowatts. (1) + (5) + (7). 10. Water rate per " shaft " kilowatt, pounds per hour. 11. Water rate per " bucket " kilowatt, pounds per hour. 12. Steam-chest pressure, pounds per square inch, absolute. 13. Exhaust pressure, pounds per square inch absolute. 14. Available energy, B.t.u. 44200 15. Theoretical water rate, pounds per kilowatt hour, B.t.u. = — — — — — • Avail. En. (14) 16. "Shaft" efficiency = (15) -i- (10). 17. "Bucket" efficiency = (15) -*- (11). Notes. — For calculating rotation loss of a new design, stage pressures are of course used. Steam per hour is usually calculated from the area of the nozzles in the first stage if the governor is not operating. For a speed-torque test the flow of steam is constant and kw. for determining items (8) and (9) are read from this curve I kw. = X r.p.m. \ r.p.m. The speed output curve (Fig. 308, page 316) is very useful to engineers to determine if a turbine is running at its best speed. If the corresponding curves of steam consumption per kilowatt output (usually called water rate per kilowatt) and efficiency curves are calculated according to the above form a great deal of information is obtained about the operation and economy of a turbine. The torque line in Fig. 308 is always drawn straight, just as a " Willans line." A curve of total steam consumption is usually a straight line for the normal operating limits of a turbine, but usually becomes curved when a by-pass valve opens on overload, or when the turbine is over its capacity so that the pressures are not normal in the stages. STEAM TURBINES AND TURBO-GENERATORS 323 The torque line shows why a turbine engine is not adaptable to auto- mobiles. The starting torque of a small commercial turbine is not large, so that starting would be difficult with a small wheel, and reversing and speed reduction would be as difficult as with a gasoline engine. The reciprocating steam engine as well as the gasoline engine has, there- fore, advantages over the steam turbine for this service. Electrical Output of Turbine Generators. Measurement of Direct Current. Careful engineers will not ordinarily use the instruments on the switchboard of a power station for measuring the electrical output of & generator, because, unless exceptional precautions have been taken to avoid " stray " magnetic fields and the instruments have been calibrated in place under operating conditions with a sufficient interval of time between observations of current (amperes) at different loads so that the shunts of the ammeters will reach a constant temperature for the particular value of current flowing there may be considerable error in the observations. Switchboard voltmeters are usually satisfactory if they are carefully calibrated; but the shunts of the type of ammeters ordinarily used have approximately only 60 millivolts drop, so that the indicating part of the ammeter must be almost entirely a circuit of copper wire. It is for this reason that such instruments are likely to be affected considerably by varying room temperatures, and with some shunt arrangements they are susceptible to errors, also from variations in the value of the circuit itself. For accurate measure- ments, it is therefore best to use only the portable types of indicating ammeters having shunts of 200 millivolts 1 drop. In these latter instru- ments the indicating part is made up largely of resistance wires having practically no temperature coefficient. Portable voltmeters are also to be preferred to those on the switchboards. Unless standard shunts of 200 millivolts drop as provided for good port- able ammeters are used the influence of " stray " magnetic fields must be guarded against. When on the other hand switchboard instruments are used, such influences must be investigated and arrangements must be devised so that " stray " fields will not affect the measurements. The influence of very weak magnetic fields can be eliminated from the final results by turning the instruments between successive readings. Obser- vations of current (amperes) made with the switchboard type of instru- ments are also often in error due to thermo-electric effects producing a small electromotive force sufficient, however, to alter the readings of the millivoltmeter. The error due to this cause can be observed by reading the millivoltmeter at the close of the test immediately after the 1 This value for the drop in shunts is an arbitrary value selected by a number of makers of electrical instruments because it gives the best compensation of all the tem- perature errors. See General Electric Review, February, 1911. 324 POWER PLANT TESTING current has been shut off in the main circuit. It should be, of course, the object of the observer to take this reading before the shunts and leads have cooled appreciably. If there is an error due to this cause there will be a small positive or negative deflection of the needle from the correct zero, which should be applied as a correction to all the observations of current. Measurement of Alternating Current. The same general precautions outlined above for direct-current instruments must be observed in the use of those for alternating current. Although steady magnetic fields are not often a cause of much trouble, it happens often, particularly in the case of large generators, that there are large magnetic fields in- fluencing the measuring instruments, which have the same frequency as that of the current measured. To eliminate the effect of such " stray " fields shielded types of instruments should be used. Only with the most expert handling can accurate results be expected when unshielded instruments are used. For measuring large values of alternating current, instrument transformers are generally used. These should be of the precision type and should be sent to a standardizing laboratory before and after a series of tests to be calibrated, and a certificate of accuracy should be obtained. The transformers should be calibrated at as nearly as possible the values of the current to be measured in the tests. Whenever it is possible tests of generators should be made with a non- inductive load, water rheostats being usually the most satisfactory apparatus for providing such a load. At least tests should be made under conditions giving a low power factor, so that there can be no error in the readings of the instruments due to phase displacements in the in- strument transformers. With a purely non-inductive load the readings of the ammeters and the voltmeters can be used to check the wattmeters. Although the readings of the wattmeters should be taken as the correct value of the output the apparent power as indicated by the ammeters and voltmeters should agree with the wattmeter readings within one per cent. If a non-inductive load cannot be secured the switchboard am- meters and voltmeters will be satisfactory for readings to indicate whether or not the load on the circuits is properly balanced. Watt-hour meters are not usually satisfactory for the accuracy expected in most tests, and the use of these instruments should be generally avoided. It is only in the case where tests must be made under extremely variable service conditions, where it is difficult to obtain a true average from the readings of indicating instruments, that a watt-hour meter, either for direct or for alternating current, may sometimes give more accurate results than the portable indicating types of instruments. Whenever watt-hour meters are used in tests they should be checked in place STEAM TURBINES AND TURBO-GENERATORS 325 for a series of constant loads at the frequency, voltage, etc., which are to be used in the test. Single-phase indicating instruments are to be preferred for measure- ments of polyphase current to the standard types of so-called polyphase instruments. The reason for this preference is that the indications of a polyphase instrument are produced by two influences from separate phases of the current in such manner that a correction cannot be applied to obtain true values unless the division of the load is determined by the use of single-phase instruments. Obviously, then, if it is necessary to have single-phase instruments in the separate circuits, it is desirable to have them of the precision type, and polyphase instruments are not needed. RULES FOR CONDUCTING TESTS OF STEAM TURBINES AND TURBO-GENERATORS. A.S.M.E. CODE OF 1912 Determine the object, take the dimensions, note the physical conditions not only of the turbine but of the entire plant concerned, examine for leakages, install the testing appliances, etc., as pointed out in the general instructions given on pages 258 to 263 and prepare for the test accordingly. The apparatus and instruments required for a simple performance test of a steam turbine or turbo-generator, in which the steam consumption is determined by feedwater measurement, are: (a) Tanks and platform scales for weighing water (or water meters calibrated in place). (&) Graduated scales attached to the water glasses of the boilers. (c) Pressure gages, vacuum gages, and thermometers. (d) A steam calorimeter. (e) A barometer. (J) A tachometer or other speed-measuring apparatus. (g) A friction brake or dynamometer. (h) Volt meters, ammeters, wattmeters, and watt-hour meters for the electrical measurements in the case of a turbo-generator. The determination of the heat and steam consumption of a turbine or turbo-generator should conform to the same methods as those described in the Steam Engine Code, pages 294 to 304. The steam consumed by steam-driven auxiliaries required for the operation of a turbine should be included in the total steam from which the heat consumption is calculated the same as in the case of the steam engine. Determine what the operating conditions should be to conform to the object in view and see that they prevail throughout the trial. The rules pertaining to the subjects Duration, Starting and Stopping, Records, and Calculation of Results, are identically the same as those 326 POWER PLANT TESTING given under the respective headings in the Steam Engine Code, pages 294 to 298 with the single exception of the matter relating to indicator diagrams and results computed therefrom; and reference may be made to that code for the directions required in these particulars. DATA AND RESULTS OF STEAM TURBINE OR TURBO-GENERATOR TESTS (1) Test of turbine located at to determine conducted by (2) Type of turbine and class of service (3) Type of generator, kind of current, etc (4) Rated power of turbine (5) Type of boiler (6) Kind and type of auxiliaries (air pumps, circulating pumps, feed pumps, etc.) (7) Dimensions of turbine or turbo-generator (8) Dimensions of boilers (9) Dimensions of auxiliaries (10) Dimensions of condenser (11) Date (12) Duration hrs. Average Pressures and Temperatures (13) Steam pipe pressure near throttle, by gage lbs. per sq. in. (13a) Absolute steam pipe pressure near throttle lbs. per sq. in # (14) Steam chest pressure by gage lbs. per sq. in. (14a) Absolute steam chest pressure lbs. per sq. in. (15) Barometric pressure of atmosphere in ins. mercury = lbs. per sq. in. (16) Vacuum in condenser: (a) In inches of mercury ins. (6) Corresponding absolute pressure lbs. per sq. in. (17) Exhaust chamber pressure (absolute) lbs. per sq. in. (17a) Temperature in steam pipe near throttle deg. F. (17b) Temperature in steam chest deg. F. (18) Temperature of main supply of feedwater to boilers . deg. F. (19) Temperature of additional supplies of feedwater deg. F. (20) Temperature of injection or circulating water entering condenser deg. F. (21) Temperature of injection or circulating water leaving condenser deg. F. Total Quantities (22) Water fed to boilers from main source of supply lbs. (23) Water fed from additional supplies lbs. (24) Total water fed to boilers from all sources lbs. (25) Moisture in steam or superheating near throttle per cent or deg. F. (26) Factor of correction for quality of steam, dry steam being unity (27) Total dry steam consumed for all purposes lbs. Hourly Quantities (28) Water fed from main source of supply lbs. (29) Water fed from additional supplies lbs. STEAM TURBINES AND TURBO-GENERATORS 327 (30) Total water fed to boilers per hour lbs (31) Total dry steam consumed per hour lbs (32) Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant lbs (33) Net dry steam consumed per hour lbs (34) Dry steam consumed per hour : (a) By turbine lbs (b) By auxiliaries lbs (35) Injection or circulating water supplied condensers per hour cu. ft Heat Data (36) Heat units per pound of dry steam, based on temperature of Line 18 B.t.u. (37) Heat units per pound of dry steam, based on temperature of Line 19 B.t.u. (38) Heat units consumed per hour, main supply of feed B.t.u. (39) Heat units consumed per hour, additional supplies of feed B.t.u. (40) Total heat units consumed per hour for all purposes B.t.u. (41) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. (42) Heat units consumed per hour: (a) By turbine and auxiliaries B.t.u. (b) By turbine alone B.t.u. (c) By auxiliaries B.t.u. Electrical Data (43) Average volts, each phase volts (44) Average amperes, each phase amperes (45) Average kilowatts, first meter kw. (46) Average kilowatts, second meter kw. (47) Total kilowatt output kw. (48) Power factor (49) Output consumed by exciter kw. (50) Net kilowatt output kw. Speed (51) Revolutions per minute (52) Variation of speed between no load and full load r.p.m. (53) Fluctuation of speed on suddenly changing from full load to no load, measured by the increase in the revolutions due to the change r.p.m. Power (54) Brake horse power b.h.p. (55) Electrical horse power e.h.p. Economy Results (56) Heat units consumed by turbine and auxiliaries per brake h.p.-hr B.t.u. (57) Dry steam consumed per brake h.p.-hr. : (a) By turbine and auxiliaries lbs. (b) By turbine alone lbs. (c) By auxiliaries lbs. (58) Dry steam consumed per kw.-hr. : (a) By turbine and auxiliaries lbs. (b) By turbine alone lbs. (c) By auxiliaries lbs. 328 POWER PLANT TESTING Efficiency Results (59) Thermal efficiency ratio per brake horse power per cent (60) Ratio of economy of turbine to that of an ideal turbine working with the Rankine cycle Work Done per Heat Unit (61) Ft.-lbs. of net work per B.t.u. consumed by turbine and auxiliaries (1,980,000 -=- Line 56) , , ft.-lbs. CHAPTER XIV METHODS OF CORRECTING STEAM TURBINE AND ENGINE TESTS TO STANDARD CONDITIONS Standard Conditions for Turbine and Engine Tests. If tests of steam turbines and engines could be always made at some standard vacuum, superheat and admission pressure, then turbines and engines of the same size and of the same type could be readily compared, and an engineer could determine without any calculations which of two turbines or engines was more economical for at least these standard conditions. But steam turbines and engines even of the same make are not often designed and operated at any standard conditions, so that a direct comparison of steam consumptions has usually no significance. It will be shown now how good comparisons of different tests can be made by a little calculation involving the reducing of the results obtained for varying conditions to assumed standard conditions. The method given here is that generally used by manufacturers for comparing different tests on the same turbine or engine (a " checking " process) or on different types to determine the relative performance. To illustrate the method by an application, a comparatively simple test will first be discussed. Practical Example. Corrections for Full-load Tests. The curve in Fig. 309 shows the steam consumption for varying loads obtained from 35 Ho a* 35 cs m 20 15 40 1G0 Fig. 309. 80 100 120 140 Output of Generator in Kilowatts Water Rate Curve of a Typical 125-Kilowatt Steam Turbine. Output.) (Generator tests of a 125-kilowatt steam turbine operating at 27.5 inches vacuum, 50 degrees Fahrenheit superheat, and 175 pounds per square inch abso- 329 330 POWER PLANT TESTING lute admission pressure (at the nozzles). It is desired to find the equiv- alent steam consumption at 28 inches vacuum, degrees Fahrenheit superheat, and 165 pounds per square inch absolute admission pressure for comparison with the " guarantee tests " (Fig. 310) of a steam engine of about the same capacity operating at the latter conditions of vacuum, 53 \ \ \ 35 \B \ ^ • F^ __ --" 20 A. Steam Consumption of Engine 15 of Steam Turbine. 60 80 100 120 140 Output of Generator in Kilowatts Fig. 310. ■ Comparative Water Rate Curves of a Reciprocating Steam Engine and a Steam Turbine. (Both with Standard Generators.) superheat and pressure. The manufacturers of the steam turbine have provided the curves in Figs. 311, 312, and 313, showing the change of economy with varying vacuum, superheat and pressure. With the help of these correction curves, the steam consumption of the turbine can be 2 I 1 2 J 2 4: 2 5 2 6 2 7 2 3 ) fl 30 n 25 O S Pi J320 Vacuum Incnes of Mercury Fig. 311. — Vacuum Correction Curve for a 125-Kilowatt Steam Turbine. reduced to the conditions of the engine tests. Fig. 311 shows that between 27 and 28 inches vacuum a difference of 1 inch changes the steam consumption 1.0 pound. Fig. 312 shows a change of 2.0 pounds per 100 degrees Fahrenheit superheat, and from Fig. 313 we observe a change of 5.0 pounds in the steam consumption for 100 pounds difference in CORRECTING STEAM TURBINE AND ENGINE TESTS 331 admission pressure. Compared with the engine tests the steam turbine was operated at .5 inch lower vacuum, 50 degrees Fahrenheit higher superheat, and 10 pounds higher pressure. At the conditions of the engine tests, then, the steam consumption of the steam turbine should be reduced .5 pound to give the equivalent at 28 inches vacuum, but is increased 1.0 pound to correspond to degrees Fahrenheit superheat, and 2h 20 15 10 2 i E i Sup 1 erh 00 3at- 1 Deg 30 s.F 140 ahr. 160 180 200 Fig. 312. — Superheat Correction Curve for a 125-Kilowatt Steam Turbine. .5 pound more to bring it to 165 pounds absolute admission pressure. The full-load steam consumption for the steam turbine at the conditions required for the comparison is, therefore, 24.5 — .5 + 1.0 + .5, or 25.5 pounds. 1 Persons who are not very familiar with the method of making these corrections will be likely to make mistakes by not knowing whether a .2 §25 §M20 I! 15 10 130 140 150 160 Steam Pressure -Lbs. Per 170 180 . In. Abs. Fig. 313. — Pressure Correction Curve for a 125-Kilowatt Steam Turbine. correction is to be added or subtracted. A little thinking before writing down the result should, however, prevent such errors. When the per- 1 The corrected steam consumption is found to be nearly the same as that which the three correction curves show for the same conditions, that is, about 25.0 pounds. If there had been a difference of more than about 5 per cent between the corrected steam consumption and that of the correction curves for the same conditions, the " ratio " method as explained on page 332 for fractional loads should have been used also for full load. 332 POWER PLANT TESTING formance at a given vacuum is to be corrected to a condition of higher vacuum, the correction must be subtracted, because obviously the steam consumption is reduced by operating at a higher vacuum. When the steam consumption with superheated steam is to be determined in its equivalent of dry saturated steam (0 degrees superheat) the correction must be added because with lower superheat there is less heat energy in the steam and consequently there is a larger consumption. Usual correc- tions for differences in admission pressure are not large; but it is well established that the economy is improved by increasing the pressure. Corrections for Fractional Loads. It is the general experience of steam turbine manufacturers that full-load correction curves, if used by the following " ratio " or percentage method, can be used for correcting fractional or overloads. This statement applies at least without appreci- able error from half to one and a half load, and is the only practicable method for quarter load as well. 1 Stated in a few words, it is assumed then that the steam consumption at fractional loads is changed by the same percentage as at full load for an inch of vacuum, a degree of super- heat, or a pound pressure. It will now be shown how this method applies to the correction of the steam consumption of the turbine at fractional loads. Now according to the curve in Fig. 311, the steam consumption at 27.5 inches (25.6 pounds) must obviously be multiplied by the ratio 2 25 7^-3 , of which the numerator is the steam consumption at 28 inches and the denominator at 27.5 inches, to get the equivalent consumption at 28 inches vacuum. This reasoning establishes the proper method for making corrections; that is, that the base for the percentage (denomina- tor of the fraction) must be the steam consumption at the condition to which the correction is to be applied. 3 Similarly the correction ratio to change the consumption at 50 degrees Fahrenheit superheat to degrees 25.0 Fahrenheit is ttt-f: , and to correct 175 pounds pressure to 165 pounds the 24 8 ratio is -^-^ . Data and calculated results obtained by this method may then be tabulated as follows: 1 A very exhaustive investigation of this has been made by T. Stevens and H. M. Hobart, which is reported in Engineering, March 2, 1906. 2 Assuming that this short length of the curve may be taken for a straight line with- out appreciable error. 3 In nearly all books touching this subject so important to the practical, consulting, or sales engineer, the alternative method of taking the steam consumption at the re- quired conditions as the base for the percentage calculation is implied. By such a method percentage correction curves derived from straight lines like Figs. 208 and 209 would be straight lines and, in application, give absurd results. Actually such per- centage corrections will fall on curves. CORRECTING STEAM TURBINE AND ENGINE TESTS 333 Conditions of Test. Required Conditions. Correction Ratio. Percentage Correction. 27.5 50. 175. 28 165 25.0 25.6 25.0 24.0 24.8 24.3 -2.34%i +4.17% +2.06% +3.89% Admission pressure, pounds absolute 25 1 Steps in the calculations are omitted in the table, thus — — ■ = .9766 or 97.66 per 25.6 cent making the correction 100 — 97.66 or 2.34 per cent. It may seem unreasonable to the reader that these percentages are calculated to three figures when the third figure of the values of steam consumption is doubtful. In practice, however, the rul- ing of the curve sheets must be much finer and to larger scale so that the curves can be read more accurately. The signs +- and — are used in the percentage column to indicate whether the correction will increase or decrease the steam consumption. " Net correction " is the algebraic sum of the quantities in the last column. . The following table gives the results of applying the above " net cor- rection " to fractional loads. \ Load 31.3 kw. J Load 62.5 kw. jLoad 93.8 kw. J Load 125 kw. f Load 156.3 kw. Steam consumption from test (Fig. 309) 31.2 + 1.2 32.4 26.9 +1.1 28.0 25.2 + 1.0 26.2 24.5 +1.0 25.5 23.6 Net correction + 3.89% +0.9 Corrected steam consumption 24.5 Curve B in Fig. 310 shows the corrected curve of steam consumption for the steam turbine as plotted from the above table. By thus com- bining, on the same curve sheet, curves A and B as in this figure, the points of better economy of the turbine are readily understood. Results of economy tests of various turbines are of very little value for comparison when the steam consumptions or " water rates " are given for all sorts of conditions. With the assistance, however, of curves like those shown in Figs. 311, 312 and 313, if they are representative of the type and size of turbine tested, it is.possible to make valuable comparisons between two or more different turbines. Some very recent data of Curtis and Westinghouse-Parsons turbines are given below, together with suitable corrections adopted by the manufacturers for similar machines. The following test of a Westinghouse-Parsons turbine, rated at 7500 kilowatts, was taken at Waterside Station No. 2 of the New York Edison 334 POWER PLANT TESTING 7500-KILOWATT WESTINGHOUSE-PARSONS TURBINE, WATER-SIDE STATION NO. 2; NEW YORK EDISON COMPANY Corrected to Correction per cent. 1 8 750 177.5 27.3 95.7 9830.5 15. 15 2 Average steam pressure, pounds gage Average vacuum, ins. (referred to 30 in. barom.) 179 28.5 100 -0.15 -3.36 -0.29 Average load on generator, kilowatts -3.80 Corrected steam consumption, pounds per kilowatt- 14.57 1 The following corrections were given by the manufacturers and accepted by the purchaser as representative of this type and size of turbine: Pressure correction .1 per cent for 1 pound. Vacuum correction 3.5 per cent for 1 inch. Superheat correction 7.0 per cent for 100 degrees Fah- renheit. 2 This is 7| per cent better than the manufacturer's guarantee. from Electric Journal, November, 1907, page 658. 9000-KILOWATT CURTIS TURBINE, FISK STREET STATION, COM- MONWEALTH ELECTRIC COMPANY, CHICAGO Corrected to Correction per cent. 1 750 179 29.55 116 8070 13.0 179 28.5 100 .0 Average vacuum, inches (referred to 30 in. barom.). . + 12.39 -j- 1.28 Steam consumption, pounds per kilowatt-hour +13.67 Corrected steam consumption, pounds per kilowatt- 14.77 1 The following percentage corrections were used: Superheat corrections 8 per cent for 100 degrees Fahrenheit. Vacuum correction 8 per cent for 1 inch from curve in Fig. 314. f Pressure correction hot given. J G. E. Bulletin, No. 4531. Co., and a comparison is made with a test of a five-stage 9000-kilowatt Curtis turbine at the Fisk Street Station of the Commonwealth Electric Company of Chicago. As no pressure correction is given for the Curtis machine, the New York Edison test is corrected to the pressure at which the other machine was operated (179 pounds per square inch gage). Approximately an average vacuum for the two tests is taken for the CORRECTING STEAM TURBINE AND ENGINE TESTS 335 standard, and 100 degrees Fahrenheit superheat is used for comparing the superheats. These assumed standard conditions make the corrections for each turbine comparatively small. When two tests are to be com- pared, by far the more intelligent results are obtained if each is cor- rected to the average conditions of the two tests, rather than correcting one test to the conditions of the other. There is always a chance for various errors when large corrections must be made. These results show a difference of only .20 pound in the corrected steam consumption, so that for exactly the same conditions these two machines would probably give approximately the same economy. Each turbine is doubtless best for the special conditions for which it was designed. These results are equivalent to respectively 9.58 pounds and 9.72 pounds per indicated horse power, assuming 97 per cent as the efficiency of the generator and 91 per cent as the mechanical efficiency of a large Corliss engine according to figures given by Scott. 1 From experience with other similar turbines it seems as if the vacuum corrections given are too low for each turbine. The correction for the Curtis turbine was obtained „ from the curve in Fig. 314, as given between 27 and 28 inches, while it was used be- tween 28.5 and 29.5 inches, where the curve of steam consumption most likely slopes somewhat as shown by the dotted line in the fig- ure, which was derived from the percentage change of the theoretical steam consump- tion calculated from the available energy. The cor- rection of 2.7 per cent per inch of vacuum for the Westinghouse-Parsons turbine is probably too low also, although the percentage correction would not be nearly as large as for the Curtis. If both of these corrections are too low, the effect of increasing them would be to increase the corrected steam con- sumption of the Curtis turbine and reduce that of the Westinghouse- Parsons. 1 Electric Journal, July, 1907. It is stated also, in this article that the vacuum correction of a Westinghouse-Parsons turbine is 3.5 per cent per inch between 28 and 28.5 inches. Jude states that the vacuum correction for Parsons turbines is 5 to 6 per cent per inch. V s \ 23 24 25 26 27 28 29 Vacuum Inches of Mercury Fig. 314. — Typical Vacuum Correction Curve for a 5000-Kilowatt Impulse Turbine. CHAPTER XV TESTS OF COMPLETE STEAM POWER PLANTS A. S. M. E. Code of 1912. These rules are intended to apply to commercial tests of a complete plant to determine the number of pounds of fuel consumed per unit of work done in a unit of time. For tests of the component parts of a complete plant, such as boilers, engines, turbines, etc., rules may- be found in the respective Codes on the preceding pages applying to such cases. Read the general instructions given on pages 258 to 263. Take the dimensions, note the physical conditions, examine for leakages, install the testing appliances, etc., as there pointed out, and prepare for the test accordingly. Fuel. Determine the character of the fuel to be used according to the object in view. For further particulars reference may be made to the Boiler Code, page 269. Apparatus and Instruments. The apparatus and instruments re- quired for a simple performance test of a steam plant are : (a) Platform scales for weighing coal and ashes. (b) Coal calorimeter. (c) Steam engine indicators. (d) A speed-measuring apparatus. (e) Electrical instruments for determining the output of an electric plant. If the test involves the determination of boiler performance, and engine or turbine performances, additional instruments should be used as pointed out in the respective Codes referring to such tests. Duration. The duration of a plant test should be not less than one day of 24 hours, and preferably a full week of seven days, including Sunday. In cases where the engine or turbine is in operation only a part of the day, the duration on which the results are computed should be considered the length of time that the engine or turbine is in opera- tion at its working speed. Starting and Stopping. In a plant operating continuously, day and night, the times fixed for starting and stopping should follow the regular periods of cleaning the fires. The fires should be quickly cleaned and 336 TESTS OF COMPLETE STEAM POWER PLANTS 337 then burned low, say to a thickness of 4 inches. When this condition is reached the time should be noted as the starting time, and the thickness of each coal bed observed, as also the water levels and the steam pressure. Fresh coal should then be fired from that weighed for the test, the ashpits thoroughly cleaned, and the regular work of the test proceeded with. At the close of the test, following a regular cleaning, the fires should again be burned low, and when their condition has become the same as that observed at the beginning, the water levels and steam pressure also being the same, the time is observed and this time taken as the stopping time. If the water levels and steam pressure are not the same as at the beginning a suitable correction should be made by computation. The ashes and refuse are then hauled from the ashpits. In a plant running only a part of the day, and during the remainder of the day the fires are banked, the time selected for the beginning and end of the test should be that following the close of the day's run, when the fires have been burned low preparatory to cleaning and banking. The amount of live coal left on the grates under these circumstances is estimated at the beginning of the test, and the fires brought to the same condition, as near as may be, at the close of the test the next day. If the two quantities differ, a suitable correction is made in the weight of coal fired, as found by calculation. Records. The general data should be recorded as pointed out on page 296, under the head of Records. Half-hourly readings of the various instruments concerned are usually sufficient, excepting where there are wide fluctuations. A set of indicator diagrams should be obtained at intervals of 20 minutes, and at more frequent intervals if the nature of the test makes it necessary. Mark on each card the cylinder and the end on which it was taken, also the time of the day. Record on one card of each set the readings of the pressure gages con- cerned, taken at the same time. These records should subsequently be entered on the general log, together with the areas, pressures, lengths, etc., measured from the diagrams, when these are worked up. Sampling and Drying Coal. During the progress of the test the coal should be regularly sampled for the purpose of analysis and deter- mination of moisture. Ashes and Refuse. The ashes and refuse withdrawn from the furnace and ashpit during the progress of the test and at its close should be weighed in a dry state, and, if desired, a representative sample should be obtained for proximate analysis and the determination of the amount of unburned carbon which it contains. 338 POWER PLANT TESTING DATA AND RESULTS OF COMPLETE STEAM POWER PLANT TEST (1) Test of plant located at to determine conducted by (2) Type of engine or turbine and class of service ( (3) Rated power of engine or turbine (4) Type of boilers (5) Kind and type of auxiliaries (air pump, circulating pump and feed pump; jackets, heaters, etc.) (6) Dimensions of engine or turbine (7) Dimensions of boilers (8) Dimensions of auxiliaries (9) Dimensions of condenser (10) Date (11) Duration hrs. (12) Length of time engine or turbine was in motion with throttle open hrs. (13) Length of time engine or turbine was running at normal speed hrs. (14) Kind of coal (15) Size of coal Average Pressures and Temperatures (16) Steam pressure at boiler by gage lbs. per sq. in. (17) Steam pipe pressure near throttle, by gage lbs. per sq. in. (18) Barometric pressure of atmosphere in in. of mercury (19) Pressure in receiver by gage lbs. per sq. in. (20) Vacuum in condenser ins- (20a) Temperature of steam near throttle deg. F. (21) Number of degrees of superheating, if any, near throttle deg. F. (22) Temperature of feedwater entering boilers deg. F. Total Quantities, Time, Etc. (23) Total coal as fired 1 lbs. (24) Moisture in coal per cent (25) Total dry coal consumed lbs. (26) Ash and refuse lbs. (27) Percentage of ash and refuse to dry coal per cent (28) Calorific value by calorimeter test per lb. of dry coal B.t.u. (29) Cost of coal per ton of lbs dollars Hourly Quantities (30) Dry coal consumed per hour, based on duration of running period ... .... lbs. Indicator Diagrams (31) Mean effective pressure in lbs. per sq. in Electrical Data (32) Total electrical output kw.-hr. (33) Electrical output per hour kw. 1 Where an independent superheater is used, this includes coal burned in the super- heater. See also footnote page 277. TESTS OF COMPLETE STEAM POWER PLANTS 339 (34) Output consumed by exciter kw. (35) Net electrical output per hour kw. (36) Average volts each phase volts (37) Average amperes each phase amperes (38) Power factor Speed (39) Revolutions per minute Power (40) Indicated horse power developed by main engine: First cylinder i.h.p. Second cylinder i.h.p. Whole engine i.h.p. (41) Net electrical horse power e.h.p. Economy Results (42) Dry coal consumed per i.h.p. per hour lbs. (43) Dry coal consumed per kw.-hr lbs. (44) Cost of coal per i.h.p. per hour cents (45) Cost of coal per kw.-hr '. cents " Plant " as used in this report should include the entire equipment of the steam plant producing power; that is, the main cylinder or cylinders, the steam jackets and reheaters, the air, circulating and boiler-feed pumps if steam driven, and any other machinery driven by steam re- quired for the operation of the engine. That the engine plant should be charged with the steam used by all the auxiliary machinery in determining the plant economy is necessary because the steam consumption of the engine is finally benefited, or at least it should be, by the heat they return to the system. It is, of course, now the general practice in commercially operated plants to pass the exhaust steam from auxiliaries operated non- condensing through a feedwater heater, thus carrying back to the boiler a great deal of the heat. When a plant is operating non-condensing, discharging the steam into the atmosphere, or with a jet condenser, the steam consumption of the engine cannot be determined by weighing or measuring the steam used as can be done when a surface condenser is used. The method followed in this case is to determine the steam used by the weight of water supplied to the boiler, assuming, of course, that all the steam from the boiler or boilers used goes to the engine tested. It can usually be arranged for a test of one of the engines in a large plant that one or more boilers can be segregated or cut off in the piping connections so that these boilers alone supply the engine. When, however, this method is to be used it is necessary to determine by a separate test the leakage of the boiler and of the piping from the boiler to the throttle valve of the engine. This leak- 340 POWER PLANT TESTING age is, of course, the amount of feed-water pumped into the boiler to keep the level in the water gage constant without taking away any more steam than is lost in this way. When determining this leakage, the pressure in the boiler must be maintained the same as that at which steam is to be supplied to the engine for its test. The feed-water pumped into the boiler supplying the engine less the boiler and pipe leakage will be the net amount of steam used by the engine. CHAPTER XVI GAS AND OIL ENGINE AND PRODUCER TESTING The testing of internal combustion engines of the reciprocating type operating with gas, gasoline, kerosene, and alcohol does not differ essen- tially in the important details from steam engine practice already explained in Chapter XII. Indicator diagrams can be utilized to show the inner workings in the engine cylinder, giving a record of the pressure, " timing " of the valves and ignition for the operation of the engine through a cycle. 1 Brake horse power is measured with a Prony brake or any other type of dynamometer permitting the determination with facility of the power of the engine. If with a Prony brake or similar device then the brake horse power is expressed by the usual formula b.h.p. = , (104) 33)Ooo' v *' where 1 is the length of the brake-arm in feet, n is the number of revolu- tions per minute, and w is the net weight indicated by the scales on the brake. Similarly the indicated horse power is given by the usual formula for a single-acting steam engine (page 143) except that the number of explosions must be used in calculations instead of the number of revolu- tions, thus, . , plan e , . l.h.p. = -£ , (105) 33>ooo' where p is the mean effective pressure in pounds per square inch measured from the indicator diagram, 1 is the length of the stroke in feet, a is the area of the piston in square inches, and n e is the number of explosions per minute, then Mechanical Efficiency = ^-^- (106) Certain important precautions should be observed when taking indicator diagrams, so that a reasonable degree of accuracy may be expected from the results of tests. In the first place the connections 1 In what is called usually a four-cycle engine there are four piston strokes — one each for suction, compression, expansion, and exhaust, corresponding to two revolu- tions of the crank shaft for a complete cycle, while in a so-called two-cycle engine, two strokes of the piston make a complete cycle — corresponding to one revolution of the crank-shaft. In the latter case suction and compression are combined in one stroke and expansion and exhaust in another. 341 342 POWER PLANT TESTING between the indicator and the combustion chamber should be as short as possible. It is much more important that in an internal-combustion engine the volume by which the combustion chamber (clearance) is increased by the indicator connections should be small in comparison to the volume of the engine cylinder than in a steam engine; because by increasing the clearance volume, obviously, the pressure resulting from compression is reduced as well as the pressure due to the explosion. It is in this way that large indicators and indicator connections may cause Fig. 315. — Crosby Gas Engine Indicator. a considerable reduction in the thermal efficiency of an engine, that is, reducing the efficiency of the transformation of heat energy into work. Tests of gas engines as made commercially have usually three objects in view: (1) Brake horse power. (2) Indicated horse power. (3) Gas or oil consumption per horse power per hour. Many types of gasoline engines, particularly those designed for the automobile service, operate at such high speeds that the indicated horse power cannot be obtained with accuracy. In many other kinds of en- gines classed in this group the mechanical efficiency is very low. It is GAS AND OIL ENGINE AND PRODUCER TESTING 343 for these reasons that such engines are rated by the useful or brake horse power instead of by the indicated horse power, as with steam engines. Brake horse power is therefore the prime criterion by which the per- formance of these engines is expressed. Ordinary types of steam engine indicators, moreover, are not very satisfactory for testing gas engines, and many engineers prefer to use one of the type shown in the accompanying illustration, Fig. 315. It differs essentially from steam engine indicators of the same type in having in the lower part of the main " barrel," a cylinder of smaller diameter than the one just above it, containing the spring. This smaller cylinder takes a piston of only half the area of the standard size. By this means the scale of the spring ordinarily used is doubled and the shock on the small rods and levers of the pencil motion is only half as great, thus making the liability to breakage and the cost of repairs for such indicators very much less than when a piston of the standard size is used. Measurement of the Fuel Used. For tests of gas engines the gas used is usually measured by means of a gas meter. A so-called " wet " meter (page 177) is always to be preferred, but if a carefully calibrated dry meter is used very good results can be obtained and it is accurate enough for commercial tests. For gasoline, kerosene and other oil engines the amount of fuel used is preferably determined by direct weighing. The author has found the automatic indicating scales of the pendulum type 1 now generally used by grocers and meat dealers to be most satisfactory. By this means the weight of the oil remaining in the " supply " vessel can be observed regularly throughout a test just as with a gas meter, so that irregularities in operation can be immediately observed. The vessel containing the oil used by the engine when placed on a scales must be connected to the carbureter or the pump, as the case may be, with a very flexible metallic tube made without rubber insertion. 2 If an indicat- ing scales is not available a very small platform or grocers' beam scales can be used satisfactorily, although if the weight of fuel oil is desired at regular intervals throughout a test some little time is required to balance the poise. Another method very commonly applied, however, is to use a cylindrical vessel of small diameter provided with a gage glass in which the level of the liquid can be observed. Such a vessel can be calibrated to determine the weight or volume of oil per inch of height measured on the gage glass. 1 Very satisfactory scales for this purpose are made by the Toledo Scale Co., of Toledo, Ohio. Similar scales of the spring type are not recommended, because neces- sarily some of the vibrations of the engine will be transmitted to the scales and. the in- dications of the pointer will not be as accurate as they should be. 2 Tubes of this kind are made by the Pennsylvania Flexible Metallic Tubing Co., Philadelphia. 344 POWER PLANT TESTING 150: .140 .9120 8,110- Observations taken for a test of a gas or oil engine are in general much more uniform than the corresponding data taken in a steam engine trial. For this reason gas engine tests in particular can be made of much shorter duration than upon a steam engine for the same degree of accu- racy. For both gas and oil engines the points plotted on a scale of brake horse power for abscissas and fuel used per unit of time for ordinates will fall along a straight line, similar and resembling the Willans line for steam engines and steam turbines (see page 312). A typical set of curves of the results of a test of a gas engine is shown in Fig. 316. Brake horse power is taken for the abscissas, as should always be done for gas and oil engine tests and gas used per hour, to its corresponding scale of ordinates, is given by the top curve. Other curves show the gas used per brake horse power per hour and per indi- cated horse power per hour, the indi- cated horse power, the mechanical efficiency, the number of explosions per minute, the revolutions per minute and the thermal efficiency (heat equivalent of the brake horse power 1 divided by heat supplied). If the engine is one using gas generated from coal in a producer, the test should cover a long enough period of time to determine with accuracy the coal used in the gas producer ; such a test should be of at least twenty- four hours' duration, and in most cases it should preferably extend over several days. Gas bags should be placed between the meter and the engine to di- minish the variations of pressure, and these should be of a size propor- tionate to the quantity used. Where a meter is employed to measure the air used by an engine, a receiver with a flexible diaphragm should be placed between the engine and the meter. The temperature and pressure of the gas should be measured, as also the barometric pressure and tem- perature of the atmosphere. 1 Most engineers consider the thermal efficiency calculated on the basis of brake horse power more important than that based on indicated power because, particularly for high-speed engines, indicators are not very reliable. j : :: ::z:: :::::: ...zt ........ - tZZZZ-Z ----- -Z :EEE ztt~zz _L1U ^ : :: . cm TTT «/ |¥:::::?::::::::: ±zW :::2 ::::::: :; ?3h :fe:::!!:::i6 ''W. IWMllPfflip ±±izz-"2iz z\M& |i 5 jJJfiaijaflXj-- — r^-'&m 1 ----- Wf+- 4 7T/T^ Z/ " Tif~-^\7 L Tllir ^WJmtfflil ■H "TV §f ":::: P flffp iipiSl V 3 ual-Efi oiemW n 1 r-f :^^i s i:::: : ffiffPffl Fig. 316. — Typical Economy, Speed, Horse Power, and Efficiency Curves of a Five Horse Power Gas Engine. GAS AND OIL ENGINE AND PRODUCER TESTING 345 RULES FOR CONDUCTING TESTS OF GAS AND OIL ENGINES. A.S.M.E. CODE OF 1912. Determine the object, take the dimensions, note the physical condition of the engine and its appurtenances, install the testing appliances, etc., as explained in the general instructions given on pages 258 to 263, and make preparations for the test accordingly. Apparatus and instruments required for simple performance tests of gas and oil engines are: (a) Tanks and platform scales for weighing oil. (b) A calorimeter for determining the heat of combustion of oil. (c) A gas meter or other apparatus for measuring gas. (d) A gas calorimeter. (e) Pressure gages and thermometers. (/) Gas engine indicators. (g) A planimeter. (h) A speed-measuring apparatus. (i) Gas analyzing apparatus. (j) Scales and tanks for weighing or a water meter for measuring jacket water. (k) A dynamometer. Duration. The test of a gas or oil engine with substantially constant load should be continued for such time as may be necessary to obtain a number of successive records covering periods of half an hour or less during which the results are found to be uniform. In such cases a duration of from three to five hours is sufficient for all practical purposes. 1 Starting and Stopping. The engine having been set to work under the prescribed conditions and thoroughly heated (except in cases where the object is to obtain the performance under working conditions), the test is begun at a certain predetermined time by commencing to weigh the oil, or measure the gas, as the case may be, and take other data concerned; after which the regular measurements and observations are carried forward until the end. When the stopping time arrives the test is closed by simply taking the final readings. Calorific Tests and Analyses. The quality of the oil or gas should be determined by calorific tests and analyses made on representative samples. CALCULATION OF RESULTS (a) Heat Consumption. The number of heat units consumed by the engine is found by multiplying the heat units per lb. of oil or per cu. ft. of gas (higher value), as determined by calorimeter test, by the total weight of oil in lbs. or volume of gas in cu. ft. consumed during the trial. 1 For tests of maximum power for high-speed engines, it is often impracticable to run tests for a total duration of more than an hour. — Author. 346 POWER PLANT TESTING (b) Horse Power and Efficiency. The indicated horse power, brake horse power, and efficiency are computed by the same methods as those explained in the Steam Engine Code, on pages 296 to 298, to which reference may be made. (c) Heat Balance. The various quantities showing the distribution of heat in the heat balance given in Table 2, page 348, are computed in the following manner: The heat converted into work per i.h.p.-hr. (2545 B.t.u.) is found by dividing the work representing 1 h.p., or 1,980,000 ft.-lbs., per hour by the number of ft.-lbs. representing 1 B.t.u., or 778. The heat rejected in the cooling water is obtained by multiplying the weight of water supplied by the number of degrees rise of temperature, and dividing the product by the indicated horse power. The heat rejected in the dry exhaust gases per i.h.p.-hr. is found by multiply- ing the weight of these gases per i.h.p.-hr. by the sensible heat of the gas reckoned from the temperature of the air in the room and by its specific heat. The weight of the dry gases per i.h.p.-hr. may be found by multiplying the weight of dry gas per lb. of carbon, using the formula: 11C0 2 + 8Q + 7(C0 + N) 3 (C0 2 + CO) (I ° 7) in which C0 2 , CO, O, and N are expressed in percentages by volume, by the proportion borne by the carbon in the total fuel (either gas or oil), and by the weight of fuel per i.h.p.-hr. The heat lost in the moisture formed by the burning of hydrogen in the gas is found by multiplying the total heat of 1 lb. of superheated steam at the tem- perature of the gas, reckoning from the temperature of the air in the room, by the proportion of the hydrogen in the fuel as determined from the analysis, and multiplying the result by 9. The heat lost through incomplete combustion is obtained by analyzing the exhaust gases and computing the heat of the unburned products which would have been produced by their combustion. TABLE 1. DATA AND RESULTS OF GAS OR OIL ENGINE TEST — SHORT FORM. CODE OF 1912 (1) Test of engine, located at to determine conducted by (2) Type and class of engine and number of cycles (3) Dimensions: (a) Single or double acting (6) Diameter of cylinders ins. (c) Stroke of pistons ft. (d) Diameter of piston rods ins. (e) Compression space or clearance per cent (/) H.p. constant for 1 lb. m.e.p. and 1 r.p.m (4) Rated capacity (5) Date (6) Duration hrs. (7) Kind of gas (8) Kind of oil (9) Physical properties of oil (specific gravity, burning point, and flashing point) GAS AND OIL ENGINE AND PRODUCER TESTING 347 Average Pressures and Temperatures (10) Pressure of gas near meter ins. water (11) Barometric pressure ins. mercury = lbs. per sq. in. (12) Temperature of cooling water: (a) Inlet deg. F. (b) Outlet deg. F. (13) Temperature of gas near meter deg. F. (14) Temperature of air deg. F. (15) Temperature of exhaust gases deg. F. Total Quantities (16) Gas or oil consumed cu. ft. or lbs. (17) Cooling water supplied to jackets lbs. (18) Calorific value of gas per cu. ft., or of oil per lb., by calorimeter test (higher value) B.t.u. Hourly Quantities (19) Gas or oil consumed per hour cu. ft. or lbs. (20) Cooling water supplied to jackets per hour lbs. Indicator Diagrams (21) Maximum pressure lbs. per sq. in. (22) Mean effective pressure lbs. per sq. in. Speed and Explosions (23) Revolutions per minute (24) Average number of explosions per minute . Power (25) Indicated horse power i.h.p. (26) Brake horse power b.h.p. (27) Friction horse power by difference Line 25 — Line 26 fr. h.p. (28) Friction horse power by friction diagrams fr. h.p. (29) Percentage of indicated horse power lost in friction (Line 27) per cent Economy Results (30) Heat units consumed by engine per hour 1 : (a) Per indicated horse power B.t.u. (b) Per brake horse power B.t.u. (31) Pounds of oil or cubic feet of gas consumed per hour: (a) Per indicated horse power cu. ft. or lbs. (&) Per brake horse power cu. ft. or lbs. Sample Diagrams Note. For an engine driving an electric generator the form may be enlarged to in- clude electrical data in the manner given in the Steam Turbine Code, page 327. 1 If these results in the case of a gas engine are based on the "lower value" of the heat units, that fact should be so stated. 348 POWER PLANT TESTING TABLE 2. DATA AND RESULTS OF GAS OR OIL ENGINE TEST — COM- PLETE FORM. CODE OF 1912 (1) Test of engine, located at to determine conducted by (2) Type of engine, whether oil or gas (3) Class of engine (mill, marine, motor for vehicle, pumping, or other) (4) Number of revolutions for one cycle, and class of cycle (5) Method of ignition (6) Name of builders (7) Dimensions: (a) Class of cylinder, whether working or compressing (b) Vertical or horizontal (c) Single or double acting (d) Diameter of cylinders ins. (e) Stroke of pistons ft. (/) Diameter of piston rods ins. (g) Compression space or clearance, . . cu. in = . . per cent of piston displacement (Ji) H.p. constant for 1 lb. m.e.p. and 1 r.p.m (8) Rated capacity (9) Date (10) Duration hrs. (11) Kind of oil (12) Physical properties of oil (specific gravity, burning point, flashing point) (13) Kind of gas Average Pressures and Temperatures (14) Pressure of gas near meter ins. water (15) Barometric pressure ins. mercury = lbs. per sq. in. (16) Temperature of cooling water: (a) Inlet deg. F. ■(6) Outlet deg. F. (17) Temperature of gas near meter deg. F. (18) Temperature of air: (a) By dry-bulb thermometer deg. F. (b) By wet-bulb thermometer deg. F. (19) Temperature of exhaust gases deg. F. Total Quantities (20) Gas or oil consumed cu. ft. or lbs. (21) Air supplied in cu. ft cu. ft. (22) Cooling water supplied to jackets lbs. (23) Calorific value of oil per lb., or of gas per cu. ft., by calorimeter test (higher value) B.t.u. Hourly Quantities (24) Gas or oil consumed per hour cu. ft. or lbs. (25) Cooling water supplied per hour lbs. GAS AND OIL ENGINE AND PRODUCER TESTING 349 Analysis of Oil (26) Carbon (C) per cent (27) Hydrogen (H) per cent (28) Oxygen (O) per cent (29) Sulphur (S) per cent (30) Moisture per cent 100 per cent Analysis op Gas by Volume (31) Carbon dioxide (C0 2 ) per cent (32) Carbon monoxide (CO) per cent (33) Oxygen (O) '. per cent (34) Hydrogen (H) per cent (35) Marsh gas (CH 4 ) per cent (36) Olefiant gas (C 2 H 4 ) per cent (37) Nitrogen (N by difference) per cent 100 per cent Indicator Diagrams (40) Pressure in lb. per sq. in. above atmosphere: (a) Maximum pressure lbs. per sq. in. (6) Pressure at beginning of stroke lbs. per sq. in. (c) Pressure at end of expansion lbs. per sq. in. (d) Exhaust pressure at lowest point lbs. per sq. in. (41) Mean effective pressure in lbs. per sq. in Speed and Explosions (42) Revolutions per minute (43) Average number of explosions per minute (44) Variation of speed between no load and full load r.p.m. (45) Fluctuation of speed on suddenly changing from full load to no load measured by the increase in the revolutions due to the change Power (46) Indicated horse power i.h.p- (47) Brake horse power b.h.p- (48) Friction horse power by difference (Line 46 = Line 47) fr. h.p. (49) Friction horse power by friction diagrams fr. h.p. (50) Percentage of indicated horse power lost in friction (Line 48) per cent Economy Results (51) Heat units consumed by engine per hour 1 : (a) Per indicated horse power B.t.u. (b) Per brake horse power B.t.u. (52) Pounds of oil or cubic feet of gas consumed per hour: (a) Per indicated horse power cu. f t. or lbs. (6) Per brake horse power cu. ft. or lbs. 1 If these results, in the case of a gas engine, are based on the "lower" value op the heat units, that fact should be so stated. See page 224. 350 POWER PLANT TESTING Efficiency (53) Thermal efficiency ratio: (a) Per indicated horse power per cent (6) Per brake horse power per cent Work Done Per Heat Unit (54) Ft.-lbs. of net work per B.t.u. consumed (1,980,000 -^ Line 516) ft.-lbs. Heat Balance Based on B.t.tj. per i.h.p. per Hour B.t.u. Per Cent (55) Heat converted into work " 2545 (56) Heat rejected in cooling water (57) Heat rejected in the exhaust gases (58) Heat lost due to moisture formed by burning of hydrogen (59) Heat lost by incomplete combustion (60) Heat unaccounted for, including radiation (61) Total heat consumed per i.h.p. per hour, same as Line 51a Sample Diagrams Note. For an engine driving an electric generator, the form may be enlarged to include electrical data in the manner given in the Steam Turbine Code, page 327. Indicator Diagrams of the Suction Stroke of a Gas or Oil Engine. With the ordinary stiff spring used for measuring the horse power of gas and oil engines, very little information regarding the action of the valves during the suction stroke is obtainable from the indicator diagram. For this reason the events in the suction stroke must be obtained with a com- paratively light spring, which must be protected, however, from injury when subjected to the excessive pressure of the explosion stroke by inserting a suitable stop of some kind to prevent undue compression of Fig. 317. — "Light Spring" Indicator Diagram of a Gas Engine the spring. The device usually adopted is to slip a small brass tube over the piston rod of the indicator to act as a distance piece. Another method, also satisfactory, is to fit a short but very thin brass tube over the outside of the spring, but of such a diameter that it will pass easily inside the cylinder of the indicator and rest freely on the top of the piston. A " light-spring " diagram is shown in Fig. 317, which was taken from an engine giving an ordinary diagram like Fig. 318. In Fig. 317 the lower horizontal line is the atmospheric line and the upper horizontal line GAS AND OIL ENGINE AND PRODUCER TESTING 351 is traced by the pencil of the indicator, during the compression and explosion strokes, showing the effect of the stop. The wavy line S shows the exhaust stroke, and the slightly curved line E is the suction. The diagram shows that there was a partial vacuum throughout the suction stroke and for a part of the exhaust stroke, the latter effect being due doubtless to the inertia of the gases in the exhaust pipe. Fig. 318. — Normal Indicator Diagram of a Gas Engine. In the three figures following very interesting indicator diagrams of gas engines due to Pullen are illustrated. Figs. 319 and 320 show explosions during the suction stroke, generally called explosions in the air pipe, for the reason that since the air valve is then open the explosion occurred probably in the air pipe. In Fig. 319 the effect of the explosion is shown in the indicator diagram by the hump near the atmospheric line near the middle of the stroke, while in Fig. 320 the explosion occurred near the Fig. 319. — Indicator Diagram of a Gas Engine Showing Explosion in Air Pipe. end of the stroke. Explosions in the air pipe are sometimes attributed to there being too weak a mixture (too little rich gas) in the cylinder, caus- ing very slow burning instead of a sharp explosion. Under these condi- tions combustion will not be complete at the end of the working stroke, and this slow burning goes on through the exhaust stroke. Then when the exhaust valve closes, some of this smouldering gas remains in the clearance space, which, when mixed with the new charge during the 352 POWER PLANT TESTING next suction stroke, forms a combustible mixture which is easily exploded. Explosions of this nature are generally spoken of as " back-firing." In Fig. 320 the explosion occurred near the end of the suction stroke at x, and the air valve has closed before the pressure has had time to fall to atmospheric. On this account the compression line c is much higher than it would be under normal conditions as shown by b. Since no Fig. 320. — Abnormal Gas Engine Diagrams. explosion takes place at the proper time, the curve d corresponding to the working stroke lies just below this abnormal compression line. No less interesting are the diagrams illustrated in Fig. 321, showing the effect of pre-ignition on the indicator diagram of a gas engine. Here in two of the diagrams shown the ignition occurred too early or before the end of the compression stroke. Under these conditions there is Fig. 321. Indicator Diagrams of a Gas Engine Illustrating the Effect of "Timing" (from Pre-ignition to Slow Burning). usually a heavy thumping noise in the engine cylinder, and the engine will not develop as much power as there would be if ignition were "timed" a little later. This effect may be caused in poorly designed engines by some small metal projection or web in the clearance space becoming hot enough to ignite the charge before the ignition device operates. On the other hand, the point of ignition may have been advanced too far by inexperienced persons. GAS AND OIL ENGINE AND PRODUCER TESTING 353 Fuels for Gas and Oil Engines. The ordinary type of gas engine is generally operated with either illuminating gas or natural gas. Since, however, natural gas occurs only in limited areas its use is very much restricted. Blast-furnace gas is used in iron works for operating engines with the waste gases from the blast furnaces. The gas from coke- ovens, also a waste gas, is now being used to some extent in the gas engines of power plants in the coke regions. Of the various kinds of so-called fuel gases producer gas is for the average engineer by far the most important. Anthracite coal is more easily converted into pro- ducer gas than any other fuel, although bituminous coals are now also used. The apparatus used for generating producer gas is called in tech- nical language a producer. There are in common use two types of pro- ducers for converting solid fuel into a permanent fuel gas. In one type the air or the steam (or both together) that is required for the operation of the producer is forced under pressure, produced usually by a blower, through the bed of solid fuel. In the other type of producer the air and water are drawn through the bed of fuel either by the suction of the engine itself, or by the suction of an auxiliary " exhauster." Gas is made at a more or less uniform rate in a pressure producer while it operates and the gas is stored in tanks, generally of comparatively small capacity, from which it is drawn to meet the varying needs of the engine. A suc- tion producer operating without an auxiliary " exhauster " is not pro- vided with a storage tank, but the gas is generated at the rate demanded by the needs of the engine. Producer Gas. The most common method for making producer gas to be used in engines is to admit both air and steam (or water vapor) simulta- neously and continuously to the incandescent fuel bed. Another method is to burn the fuel for a time with air alone ; that is, without any steam, until the fuel bed becomes highly incandescent, and then shut off the supply of air and pass steam or water vapor into the fuel until its temperature becomes so low that very little gas is formed and the air must be used again with the steam supply shut off. The producer continues in opera- tion by alternating the admission of air and steam to the fuel bed. The former of these two methods is the one most generally used. Suction Gas Producer. Anthracite coal is the most satisfactory fuel for suction gas producers, some preferring " chestnut " size, while others get the most satisfactory operation with the " pea " size if the coal supplied is clean. A producer or generator for such fuel is illustrated in Fig. 322. Capacity and Efficiency of Gas Producers. The important result to be determined from tests of a gas producer is the ratio of the heat value of the gas produced (in B.t.u.) to the heat value in the same units of the fuel used and the mechanical or electrical energy required 354 POWER PLANT TESTING in producing the gas. The capacity or the rate at which gas can be produced is also important, since a high rate of gasification means lower initial costs of the plant. In reports of tests of gas producers it should be clearly stated whether the higher or the lower heat value of the gas has been used in the calculations. There is no accepted rule as to whether the higher or the lower heat value should be used in guarantees, so that the one to be used must be clearly stated. Probably the best method of stating guarantees is to give the amount (volume) of gas at a standard temperature and pressure and the heat value (higher or lower as preferred) per unit volume (usually a cubic foot) that a producer and its accessories will deliver from a stated weight of coal, of which the heat value per Fig. 322. — Suction Gas Producer and Engine pound is also given. Mechanical, electrical, or other energy received from outside sources must also be taken into account. In the speci- fications for guarantees it should be stated that the loss of unburned fuel in the ash is to be charged as fuel used by the producer. RULES FOR CONDUCTING TESTS OF GAS PRODUCERS. A.S.M.E. CODE OF 1912 Object and Preparations Determine the object, take the dimensions, and note the physical condition of the producer and its appurtenances. Fuel. 1 Determine the character of the fuel to be used. If an untried fuel is selected and a test-producer is available, make a preliminary trial of the fuel in this apparatus and ascertain its working characteristics and the proper methods of handling it. 1 This code is primarily intended for producers using coal. If other fuel such as wood or oil, is burned, the rules may be modified accordingly. GAS AND OIL ENGINE AND PRODUCER TESTING 355 In tests of maximum efficiency and capacity of a producer for com- parison with other producers, the fuel should be some kind of coal which is commercially regarded as a standard for such use in the locality where the test is made. The coal selected for such tests should be the best of its class and free from unusual slag-forming impurities. Apparatus and Instruments. The apparatus and instruments re- quired for producer tests are: (a) Platform scales for weighing coal and ashes. (&) A coal calorimeter. (c) A gas calorimeter. (d) Gas analyzing apparatus and appliances for determining tar and soot. (e) A gas meter, pitot tube, or other suitable apparatus for measuring the gas out- put. (/) A manometer or pressure gage. (g ) Water meters for measuring feed and scrubber water, and steam meters for measuring steam used by the apparatus. (h) Thermometers. The location of the pitot tube, if used, should be in the delivery pipe at a point near the producer or just beyond the scrubber, or at both points, according to the use made of the gas, either for fuel or power, and other requirements. Duration. The duration of both efficiency and capacity tests of a producer, with the exceptions noted below, should be such that the total consumption of fuel is at least ten times the weight of the fuel contained in the producer when in normal operation, estimating this weight in the case of coal at 45 lb. per cu. ft. In cases like down-draft producers which require the fuel bed to be entirely removed and rebuilt at regular intervals, and in producers where a complete cleaning and renewal occurs before the total consumption above stipulated has been reached, the duration should be that of the regular commercial operating cycle, or the time elapsing between two successive renewals of the fuel bed. Starting and Stopping. The conditions regarding the temperature of the producer and its contents, and the quantity and quality of the latter, should be as nearly as possible the same at the end as at the beginning of the trial. To secure the desired equality of conditions, the starting and stopping should occur at times of regular cleanings, and they should be preceded for a period of not less than 10 hours by the same regular working conditions as those characterizing the test as a whole. The operations of starting and stopping should then be carried on as follows: (a) Up-draft Suction Producers. Remove the ash and clinkers from the grate and the lower part of the furnace space, taking care that the crust or closely-united layer which supports the coal above is not unduly disturbed. Then break open the crust and allow the mass to drop into the space left vacant. Introduce a 356 POWER PLANT TESTING poker rod through the poke holes in the upper head and stir up the coal within, thereby causing it to settle and fill the remaining spaces. As a final step, quickly replenish the producer with coal, leaving the hopper level-full, take the time, and consider this the starting time. Then clean the ash pit, and thereafter proceed with the regular work of the test, using weighed coal. When the time arrives for bringing the trial to a close, the cleaning operations described above are repeated, ending with fining the hopper, taking the time, and considering this the stopping time; finally hauling the ashes and refuse from the ashpit. (b) Up-draft Pressure Producers. Remove the ashes until the top of the ash bed is lowered to the normal working point, say six inches above the blast-hood. Introduce the poker-rod and break down any bridge or crust that may have formed, at the same time closing up the channels that run through the fuel bed, thereby making the bed homogeneous. Then replenish the producer with coal, fill the hopper level-full, take the time, and consider this the starting time. Thereafter proceed with the regular work of the test, using weighed coal. When the time approaches for closing the test, the operations above described are repeated, ending with replenishing the producer and filling the hopper with weighed coal, taking the time, and considering this the stopping time. The ashes and refuse finally removed are to be dried before weighing, or a sample should be taken and the moisture, as determined therefrom, allowed for. (c) Down-draft Pressure Producer. Thoroughly clean the producer of its entire contents. Introduce a weighed supply of coke or coal, start the fire and build up the fuel bed to its working condition, using weighed coal. When this point is reached, take the time, and consider this the starting time. Thereafter pro- ceed with the regular work of the test. When the time approaches for closing the test, burn the fuel bed as low as practicable to prepare for cleaning, stop the exhauster, note the time, and con- sider this the stopping time. Then completely empty the producer, quench the fire remaining in the live coals, separate and weigh the coke and ash, and deduct the weight of the former from that of the coke as charged. Finally dry the ash and refuse, or take a sample and allow for the moisture determined therefrom. The directions pertaining to Records, Sampling and Drying Coal, Ashes and Refuse, Calorific Tests and Analyses of Coal, are practically the same as those given under the corresponding headings in the Boiler Code, pages 269 and 276. Calorific Tests and Analyses of Gas Output. The quality of the gas should be determined by calorific tests and analyses, continuous samples for this purpose being taken from the delivery pipe at a point near the producer and at other points as may be needed. The calorific test should be made with the Junker calorimeter, or its equivalent. Unless otherwise required the " higher value " should be employed in calculating the results of the test. For an approximate determination of the composition of the gas, a modified type of Orsat ap- paratus may be used, and for complete determinations, the Hempel ap- paratus or its equivalent. The frequency with which these determinations should be made depends on the uniformity of the output, but the inter- GAS AND OIL ENGINE AND PRODUCER TESTING 357 vals, where practicable, should not be more than one-half hour, the time taken for collecting each sample being not less than one-half hour. CALCULATION OF RESULTS (a) Total Volume of Gas Delivered. The volume of gas (cu. ft.) found by pitot tube measurement is determined by multiplying the area of the delivery pipe in sq. ft. at the tube by the velocity of the gas in ft. per minute, and the product by the duration of the trial in minutes. The equivalent volume at atmospheric pressure (30 in. barometer) and temperature of 62 deg. Fahr. is obtained by the usual method of thermodynamics as explained on page 226. (6) Net Volume of Gas Delivered. The net volume of gas delivered is found by sub- tracting from the total volume the equivalent volume of gas required for fur- nishing steam drawn from an outside source, if any, or for furnishing power used for any purpose concerned in the operation of the producer and its auxiliaries. (c) Weight of Gas. The weight of dry gas delivered is found by multiplying the volume in cu. ft., reduced to 62 deg. and 30 in. barometer, given in Table 2, page 360, Line 21, by the weight per cu. ft. of gas given in Table 2, Line 77. The weight of the gas per cu. ft. is determined by multiplying the percentage of each component gas as found by analysis (see Lines 55 to 63, Table 2, page 361) by its weight in lb. per cu. ft., at -62 deg. and 30 in., barometer as given in the following table, and dividing the sum of the products by 100. C0 2 0.1116 CH 4 0.0428 CO 0.0736 Q>H 4 0.0737 2 0.0842 S0 2 0.1638 Ho 0.0053 H 2 S 0.0868 N 2 0.0740 (d) Moisture in Gas Leaving Producer. The percentage of moisture in the gas is found by passing a measured sample of the gas through a chloride of calcium tube and weighing the amount of moisture absorbed. (e) Percentage of Tar and Soot in Gas. The percentage of tar and soot is found by comparing the total weight determined, including that collected from the vari- ous tar drips with the total weight of dry fuel used. (/) Efficiency. The efficiency is the relation between the calorific value of the gas per lb. of fuel charged, or combustible burned, and the calorific value of 1 lb. of fuel or combustible. The former is ascertained by multiplying the B.t.u. per cu. ft. of gas as determined by the calorimeter test (higher value) by the cu. ft. of gas delivered, and dividing the product by the total weight of fuel charged or combustible burned. The "combustible burned" is determined by subtracting from the weight of coal charged the moisture in the coal and the ash and refuse, including un- burned coal which is withdrawn from the producer or ash-pit during the progress of the trial. The "combustible" used for determining the calorific value is the weight of the coal less the moisture and ash found by analysis. The efficiency of "conversion and cleaning" in the above calculation is found by using the total volume of gas delivered. The "efficiency of the plant" is found by using the net volume of gas delivered. (g) Heat Balance. The various quantities showing the distribution of heat in the heat balance given in Table 2, page 361, are computed in the following manner: 358 POWER PLANT TESTING The heat contained in the dry gas is found by multiplying the cubic feet of gas at 62 deg. and 30 in. barometer per lb. of dry coal by the calorific value of 1 cu. ft. of gas at 62 deg. and 30 in. barometer (higher value). The heat carried away by the scrubber is obtained by multiplying the weight of water fed to the scrubber by the number of degrees rise of temperature, and dividing the product by the total weight of dry coal consumed. The heat contained in the moisture leaving the producer is found by mul- tiplying the total weight of dry gas by the proportion of moisture in the gas leaving the producer and by the total heat of 1 lb. of superheated steam at the temperature of the gas leaving the producer reckoned from the temperature of the air in the room, and dividing the product by the weight of dry coal con- sumed. Chart. In trials having for an object the determination and exposition of the complete performance from beginning to end, the entire log of readings and data should be plotted on a chart and represented graphi- cally. (See Fig. 296, page 268.) TABLE 1. DATA AND RESULTS OF GAS PRODUCER TEST — SHORT FORM. CODE OF 1912 (1) Test of producer located at . . : to determine conducted by (2) Type of producer (3) Rated capacity of producer (4) Date (5) Duration , hrs. (6) Kind of coal 1 and where mined (7) Size of coal Average Pressures, Temperatures, Etc. (8) Steam pressure in vaporizer by gage lbs. per sq. in. (9) Gas pressure in delivery main at point where gas is measured ins. water (10) Temperature of feedwater deg. F. (11) Temperature of gas in delivery main near producer deg. F. (12) Temperature of gas in delivery main at point where gas is measured deg. F. (13) Force of blast or draft in ashpit ins. water Total Quantities (14) Weight of coal as charged lbs. (15) Percentage of moisture in coal per cent (16) Total weight of dry coal consumed lbs. (17) Total ash and refuse lbs. (18) Percentage of ash and refuse in dry coal per cent (19) Total cu. ft. of gas as measured cu. ft. (20) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer cu. ft. (21) Net cu. ft. of gas at 62 deg. F. and 30 in. 2 barometer cu. ft. (22) Total water fed to vaporizer lbs. (23) Total water supplied to scrubber lbs. 1 If other fuel than coal is used the lines may be changed to read accordingly. 2 After deducting equivalent gas required for auxiliaries. GAS AND OIL ENGINE AND PRODUCER TESTING 359 Hourly Quantities (24) Dry coal consumed per hour lbs. (25) Dry coal per sq. ft. of main fuel bed per hour lbs. (26) Total cu. ft. of gas delivered per hour cu. ft. (27) Total cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. (28) Net cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. Economy Results (29) Total cu. ft. of gas delivered per lb. of dry coal (Line 13 -5- Line 10) cu. ft. (30) Equivalent total gas at 62 deg. F. and 30 in. barometer per lb. of dry coal. .cu. ft. (31) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal 1 . . . .cu. ft. (32) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of combustible. cu. ft. Efficiency 2 (33) Calorific value of dry coal per lb B.t.u. (34) Calorific value of combustible per lb B.t.u. (35) Calorific value of gas per cu. ft. (higher value) B.t.u. (36) Efficiency of producer based on coal per cent (37) Efficiency of producer based on combustible per cent Cost of Production (38) Cost of coal per ton of .... lbs. delivered dollars (39) Cost of coal required for producing 10,000 net cu. ft. of gas at 02 deg. F. and 30 in. barometer dollars (40) Cost of coal required for producing one million B.t.u. in the gas dollars TABLE 2. DATA AND RESULTS OF GAS PRODUCER TEST — COMPLETE FORM. CODE OF 1912 (1) Test of producer located at to determine conducted by Dimensions (2) Outside diameter of producer ft. (3) Height of producer ft. (4) Inside diameter of producer ft. (5) Diameter of grate ft. (6) Area of grate sq. ft. (7) Percentage of air space in grate per cent (8) Area of fuel bed (at maximum diameter) sq. ft. (9) Area of water-heating surface in vaporizer sq. ft. (10) Rated capacity of producer in lbs. of coal per hour lbs. (11) Date (12) Duration hrs. (13) Kind of coal 3 and where mined (14) Size of coal 1 After deducting equivalent gas required for auxiliaries. 2 If the efficiency is based on the "lower value" of the heat units in the gas the fact should be so stated. 3 If other fuel than coal is used the lines may be changed to read accordingly. 360 POWER PLANT TESTING Average Pressures, Temperatures, Etc. (15) Steam pressure in vaporizer by gage lbs. per sq. in. (16) Gas pressure in main at point where gas is measured ins. water (17) Force of blast or draft in ashpit ins. water (18) Barometric pressure . ins. mercury (19) Temperature of feedwater entering vaporizer deg. F. (20) Temperature of gas in main near producer deg. F. (21) Temperature of gas in main at point where gas is measured deg. F. (22) Temperature of air in room deg. F. (23) Temperature of water entering scrubber deg. F. (24) Temperature of water leaving scrubber deg. F. (25) Weight of dry gas per cu. ft. reduced to 62 deg. F. and 30 in. barometer lbs. Total Quantities (26) Weight of coal as fired lbs. (27) Percentage of moisture in coal per cent (28) Total weight of dry coal consumed lbs. (29) Total ash and refuse lbs. (30) Percentage of ash and refuse in dry coal per cent (31) Total number of cu. ft. of gas as measured cu. ft. (32) Equivalent cu. ft. of gas at temperature of 62 deg. F. and pressure of atmos- phere of 30 in. barometer cu. ft. (33) Net cu. ft. of gas at 62 deg. F. and 30 in. 1 barometer cu. ft. (34) Total weight of dry gas lbs. (35) Percentage of moisture in gas leaving producer per cent (36) Percentage of tar and soot in gas referred to total fuel per cent (37) Total water fed to vaporizer : lbs. (38) Total water evaporated in vaporizer lbs. (39) Total weight of steam supplied to producer lbs. (40) Total weight of water fed to scrubber lbs. Hourly Quantities (41) Dry coal consumed per hour lbs. (42) Dry coal consumed per hour per sq. ft. of grate lbs. (43) Dry coal consumed per hour per sq. ft. of main fuel bed lbs. (44) Total cu. ft. of gas delivered per hour (Line 20 -f- Line 17) cu. ft. (45) Total cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. (46) Net cu. ft. of gas delivered per hour at 62 deg. F. and 30 in. barometer. . . .cu. ft. (47) Weight of dry gas per hour lbs. (48) Water fed per hour to vaporizer lbs. (49) Water evaporated per hour in vaporizer lbs. (50) Steam supplied to producer per hour lbs. (51) Water fed to scrubber per hour •. .lbs. Proximate Analysis of Coal (52) Fixed carbon per cent (53) Volatile matter per cent 1 After deducting equivalent gas required for auxiliaries. GAS AND OIL ENGINE AND PRODUCER TESTING 361 (54) Moisture per cent (55) Ash per cent 100 per cent (56) Sulphur, separately determined per cent Ultimate Analysis op Dry Coal (57) Carbon (C) per cent (58) Hydrogen (H 2 ) per cent (59) Oxygen (0 2 ) per cent (60) Nitrogen (N 2 ) per cent (61) Sulphur (S) per cent (62) Ash per cent 100 per cent (63) Moisture in sample of coal as received per cent Analysis op Ash and Refuse (64) Carbon per cent (65) Earthy matter per cent Analysis op Gas by Volume 1 (66) Carbon dioxide (C0 2 ) per cent (67) Carbon monoxide (CO) per cent (68) Oxygen (0 2 ) per cent (69) Hydrogen (H 2 ) per cent (70) Marsh gas (CH 2 ) per cent (71) Olefiant gas (C 2 H 4 ) per cent (72) Sulphur dioxide (S0 2 ) per cent (73) Hydrogen sulphide (H 2 S) per cent (74) Nitrogen (N 2 by difference) per cent 100 per cent Calorific Values by Calorimeter (75) Calorific value of dry coal per lb B.t.u. (76) Calorific value of combustible per lb B.t.u. (77) Calorific value of gas per cu. ft. at 62 deg. F. and 30 in. barometer (higher value) B.t.u. Economy Results (78) Total cu. ft. of gas as measured, per pound of dry coal consumed cu. ft. (79) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal . cu. ft. (80) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of com- bustible cu. ft. (81) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal. . . . cu. ft. (82) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of combustible, .cu. ft. 1 Sample of gases should be collected at producer outlet before the gases pass through the scrubber as some of the carbon dioxide and hydrocarbons are absorbed in the scrubbers. 362 POWER PLANT TESTING Efficiency 1 (83) Efficiency of producer based on coal: (a) Conversion and cleaning per cent (6) Plant per cent (84) Efficiency of producer based on combustible: (a) Conversion and cleaning per cent (b) Plant per cent Cost of Production (85) Cost of coal per ton of ... . lbs., delivered dollars (86) Cost of coal required for producing 10,000 net cu. ft. of gas at 62 deg. F. and 30 in. barometer .• dollars (87) Cost of coal for producing 1,000,000 B.t.u dollars Heat Balance Based on 1 Lb. of Dry Coal B.t.u. Per cent (88) Heat contained in dry gas (89) Heat carried away by scrubber (90) Heat contained in moisture leaving producer (91) Heat unaccounted for, including radiation, — difference be- tween the sum of Lines 88, 89, and 90 and Line 92 (92) Total calorific value of 1 lb. of dry coal, same as Line 75 RULES FOR CONDUCTING TESTS OF COMPLETE GAS POWER PLANTS. A.S.M.E. CODE OF 1912 Object and preparations The usual object of testing a complete gas power plant, embracing producer, engine, and appurtenances, is the determination of its com- mercial performance, i.e., the number of pounds of fuel consumed per unit of work done in a unit of time, and the rules given in this code apply to tests having that object. For directions pertaining to tests of the producer and engine individually, reference may be made to the Producer and Gas Engine Codes, pages 345 and 354. Determine the character of the fuel to be used. The duration of a gas producer plant test should conform to that of the producer alone, rules pertaining to'which may be found in the Gas Producer Code. In cases where the engine is in operation only a part of the day, the hourly consumption of coal from which the economy results are com- puted should be the total coal burned in the producer divided by the number of hours that the engine is in operation at its working speed. The rules for starting and stopping a complete plant test are governed by those required for starting and stopping the test of the producer, which are those given in the Producer Code, page 355. 1 If the efficiency is based on the "lower value" of the heat units in the gas, the fact should be so stated. GAS AND OIL ENGINE AND PRODUCER TESTING 363 DATA AND RESULTS OF TEST OF COMPLETE GAS POWER PLANT. CODE OF 1912 (1) Test of gas power plant at to determine conducted by (2) Type and dimensions of producers (3) Rated capacity of producers (4) Total area of main fuel bed at maximum diameter sq. ft. (5) Type and dimensions of engine (6) Rated power of engine (7) Date (8) Duration hrs. (9) Kind of coal (10) Size of coal Average Pressures and Temperatures (11) Pressure of gas near throttle valve ins. water (12) Barometric pressure ins. water (13) Temperature of cooling water leaving engine deg. F. (14) Temperature of air in room deg. F. Total Quantities (15) Weight of coal as charged lbs. (16) Percentage of moisture in coal per cent (17) Total weight of dry coal consumed lbs. (18) Total ash and refuse lbs. (19) Percentage of ash and refuse in dry coal per cent (20) Calorific value of 1 lb. of dry coal by calorimeter test B.t.u. (21) Cost of coal per ton of .... lbs dollars Hourly Quantities (22) Dry coal consumed per hour lbs. (23) Dry coal per sq. ft. of main fuel bed per hour lbs. Indicator Diagrams (24) Mean effective pressure in lbs. per sq. in Speed and Explosions (25) Revolutions per minute (26) Number of explosions per minute Power (27) Indicated horse power developed by engine i.h.p. Economy Results (28) Dry coal consumed per i.h.p. per hour lbs. (29) Cost of coal per i.h.p. per hour dollars (30) Heat units consumed per i.h.p. per hour (Line 20 X Line 28) B.t.u. Note. For an engine driving an electric generator, the form may be enlarged to include electrical data in the manner given in the code for Complete Steam Power Plants, page 336. CHAPTER XVII TESTING OF VENTILATING FANS OR BLOWERS AND AIR COMPRESSORS Centrifugal Fans are used almost exclusively when large volumes of air are to be handled at a comparatively small pressure. Such a fan consists essentially of a number of plates, either flat or curved, attached to radial arms springing from a central hub through which the driving shaft passes, as in the " spider " type shown in Fig. 325, or the blades may be attached to a conical plate as in Fig. 326. Fans resembling either of these two designs are known commercially as the " standard " type. The " width " of the blades is, in most cases, parallel to the shaft. Fig. 325. Fig "Standard" Types of Ventilating Fans. The work performed by a centrifugal type of fan is equal to the resist- ance times the velocity of flow. Since, however, the fan resistances are proportional to the square of the velocity, 1 the work done is proportional to the cube of the velocity. Disk or Propeller Fans are best illustrated by the so-called " electric " fans so commonly used in offices, shops and dwellings. Fans of this type are usually of a very light construction with the vanes arranged as in a screw propeller for a ship. In many cases fans of this type are not provided with casings, so that it is more difficult to make velocity measurements than with centrifugal fans. Turbine or " Sirocco " fans have an impeller or fan wheel of the " squirrel-cage " type, as illustrated in Fig. 327. Fans of this type can be designed to give very high efficiencies. This is due primarily to two characteristic features adopted in these designs. By the use 1 See Professor Rateau's articles in Revue de Mecanique vol. 1, pages 629-837. 364 TESTING OF VENTILATING FANS OR BLOWERS 365 of very short blades a very large intake space for the suction is pro- vided which is practically unobstructed, thus giving a very free " suction." The other important feature of this fan is that the air leaves the blades at a higher velocity than that at which the tips of the blades are moving. The importance of this re- sult is shown by a compari- son of Figs. 328 and 329. The former illustrates the type of blading in a turbine or " Sirocco " fan and shows graphically by a velocity diagram, constructed like a parallelogram of forces, the velocity of the tips of the blades V&, the velocity of radial flow in the blades V r and the absolute velocity of the discharge V a , which is the velocity of the air with respect to the stationary casing. It will be observed FlG . 327. — Turbine Type (Sirocco) Fan. that in Fig. 328, V a is nearly 50 per cent greater than the velocity of the tips V & , while in Fig. 329, representing the corresponding velocities for a standard type of fan, the Fig. 328. — Velocity Diagram for a Turbine Fan. Fig. 329. — Velocity Diagram for a "Standard" Fan. absolute velocity of the discharge V a is actually considerably less than the speed of the tips of the blades. Increased velocity is accomplished in a type of fan like Fig. 328, not only by the curvature of the tips of the blades but also to some extent by making the blades somewhat concave 366 POWER PLANT TESTING Fig. 330. — Typical Positive Pressure Blower. with the inner ends (toward the center) practically radial. By this method of designing the outer edges of the blades have a smaller space between them than the inner edges. This has the effect of reducing the area on the discharge side of the blades and consequently the velocity of the air is increased. Positive Pressure Blowers are used principally for blast furnaces and smelters where a higher pressure is needed than can be efficiently obtained with a centrifugal fan. A section showing the rotors and casing of one of the blowers is shown in Fig. 330. It is often called Boot's blower. The effi- ciency of a blower of this type depends on the accuracy of the fitting of the two rotors, A and B, both with respect to each other and to the casing. It is for this reason that when new the efficiency is high, but after being in service for several years the bearings and the surfaces of the rotors will become worn, so that there is considerable leakage and consequent loss of efficiency. Tests of Ventilating Fans or Blowers are made usually by a very simple method; that is, by determining the necessary data for calcu- lating efficiency by measuring the work done by the fan " on the air " in giving velocity, and the power required to drive the fan alone, ex- cluding bearing friction. The fan is preferably operated by an electric motor, of which the efficiency can be readily determined by a Prony brake test. The power required to overcome the bearing friction of the shaft of the fan may well be first determined by measuring the power input 1 (kilowatts) for a series of speeds when the keys fastening the fan to its shaft have been removed and the fan itself has been " blocked " in its casing or, still better, has been removed from the shaft. After attaching the fan again to the shaft the input to the motor and the work done by the fan " on the air" should be determined for various speeds. Then obviously the ratio of the work done by the fan divided by the power required to drive it after correction for the efficiency 2 of the motor and bearing friction is the actual efficiency of the fan. In general terms this may be stated as follows : 1 For normal operation "friction work" is, for machinery in general, proportional to the speed. 2 Motor efficiency must be necessarily determined for the conditions of each test; that is, for the same kilowatts and speed as for each test. TESTING OF VENTILATING FANS OR BLOWERS 367 f = input to motor to drive motor and shaft of fan in bearings, kilowatts ; i = input to motor to drive motor and fan, in kilowatts; e = efficiency of motor for motor input of i kilowatts and at speed of test; e' = efficiency of motor for motor input of f kilowatts and at speed of test. Then if i n is the net work in horse power to drive fan alone, i„ = z~ ' (108) 0.746 ^ If the fan to be tested is direct-connected to a steam engine, the test is usually made by measuring the indicated horse power of the engine at the various speeds and also with the fan disconnected for no load. If it is possible to do so the fan should be removed from the shaft for the no-load test to determine bearing friction. ■ The work done by the fan " on the air" is most readily calculated by the same method used to calculate the efficiency of hydraulic pumps (see page 408), that is, by multiplying the number of pounds of air delivered per unit of time by the head in feet of air corresponding to the discharge pressure. This product is obviously in terms of work in foot-pounds per unit of time, and dividing by 33,000 the corresponding horse power is obtained. Using the following symbols, the same results may be expressed, however, by the product of " pressure times volume " as follows : v = velocity of air in feet per second; h = head in feet of air necessary to produce a velocity of v feet per second, or, = water pressure p in inches observed with a manometer, produced by the velocity of the air times the ratio of wt. of a cubic foot of water wt. of a cubic foot of air 1 \/ p X 62.3 2 £ wt. cu. ft. air for test (109) and V m = velocity in feet per minute is (taking 2 g = 64.3) V m = 1096.4%/— , , p . , — — — . . . . (no) Vwt. cu. ft. air for test 1 Weight of air taken for calculation must be that corresponding to the total pres- sure in the discharge pipe, the temperature and the humidity. For tables of weight of air see pages 180 and 181, also Kent's "Mechanical Engineers' Pocket-Book," 8th edition, pages 583-588, and "Calculating and Testing Ventilating Systems," issued by U. S. Navy Department, Washington. 368 POWER PLANT TESTING Now the velocity in feet per minute V m multiplied by the area of the section at which the velocity was observed, gives cubic feet C of air discharged per minute, and if P is the total pressure (static + velocity) in pounds per square foot then we have for j the " air horse power " or the work done by the fan " on the air." CP j = 33^oo' t 1 ") and efficiency of fan E, is j _ CP E = 33,ooo (112) Velocity measurements are usually made with a Pitot tube consisting essentially as shown in Figs. 224 to 225, page 179, of two tubes with openings at the end, arranged so that one of them " faces " in the direction of flow and the other extends in a radial direction. The former is subjected to the sum of the velocity and static pressures, while the latter receives only the static pressure. The following table of relative humidity for determinations with a wet- and a dry-bulb thermometer, Fig. 331, or the sling psychrometer, Fig. 332, as used by the U. S. Weather Bureau: TABLE OF RELATIVE HUMIDITY, PER CENT Dry Ther- mometer Deg. F. Difference between the Dry and Wet Thermometers, Deg. F. 4 5 6 7 9 10 11 12 13 14 15 16 17 IS 19 20 21 22 23 21 Relative Humidity, Saturation being 100. (Barometer = 30 ins.) A sling psychrometer is much more accurate than the stationary wet- and dry-bulb type. It should be revolved at about 150 revolutions per minute. By using the above table the weight of a cubic foot of air for any degree of saturation and temperature can be easily calculated from the tables of the weight of dry air and ioo per cent saturated air as given on page 181. Anemometers are also frequently used for velocity measurements of air, but they are not generally so reliable as good Pitot tubes. Since, TESTING OF VENTILATING FAN$ OR BLOWERS 369 however, the observations can be taken directly in feet per minute these instruments are used for nearly all work where no great accuracy is expected. An example showing the method of calculation for j ; the work done by the fan " on the air," may assist in making the method of calculation clearer. A series of Pitot-tube measurements taken at ten different places in the cross-section of an air duct shows that the " velocity " pressure was .795 and the total pressure 1.09 inches of water. The observations of barometric pressure and temperatures by wet- and dry-bulb thermom- eters, together with the " total " pressure given above, served to deter- Fig.] 331. —Wet- and Dry-Bulb Thermom- eters. Fig. 332. — Sling Psychrometer. (Wet- and Dry-Bulb Thermom- eters arranged for Rotation.) mine the density or the weight of a cubic foot of air at the conditions of the test. Barometric pressure was 39.40 inches of mercury and tem- peratures of wet- and dry-bulb thermometers were respectively 54 and 71 degrees Fahrenheit. According to the tables of the properties of air (see footnote, page 181) this was .07449 pound per cubic foot. Velocity of the air V m in feet per minute is, therefore, V m - 1096.4 = 3625 feet per minute. V .07449 The diameter of the pipe was 10 inches, of which the area is 0.545 square foot. Cubic feet air discharged per minute (C) are 3625 X 0.545 or 1978. The total pressure P is the " total " pressure 1 in pounds per 1 In this expression 13.6 is the specific gravity of mercury, .491 is a factor for chang- ing inches of mercury at room temperature to pounds per square inch, and 144 is used to change pounds per square inch to pounds per square foot. 370 POWER PLANT TESTING square foot or ' ) .491 X 144 or 5.66. Work done by the fan " on the air " is, then, 1978 X 5.66 J = 33,000 = °' 34 h ° rSe p0Wer ' Efficiency tests should be made with the fan operating under the discharge pressure for which it was designed or for which] the guarantee was made, as the case may be. The efficiency of the fan may be consider- ably higher with a lower discharge pressure than when connected up in a ventilating system where the discharge pressure is comparatively high. Testing Ventilating Systems. When tests are to be made of ventilat- ing systems precautions should be taken in the examination of all ducts and piping to see that they are clear of all lumber, rubbish, etc., and that the dampers are properly set. The tests consist usually in measuring in each system the " static " and the " total " pressures with a Pitot tube with all louvers open. These tests should be made with the fan running at high, low and three or four intermediate speeds. All the results should be checked by plotting a curve with revolutions per minute for abscissas and cubic feet of air delivered per minute for ordinates. This curve should be approximately a straight line passing through the origin if all the louvers have remained open throughout the tests. On the same abscissas curves of pressure for ordinates will also be of advantage in showing the consistency of observations. The location selected for the testing slot to be used for inserting the Pitot tube in the mains should be as near as possible to the fan; preferably no branches, however small, should run off between the fan and the testing slots in the mains. Fur- thermore the testing slots should not be near turns and bends and par- ticularly no turns or elbows should be immediately ahead of a slot, that is, in the direction toward the fan. These testing slots should be covered when not in use. In the U. S. Navy Department the standard conditions adopted for testing ventilating fans and air-supply mains are a pressure of 5 pounds per square foot in the moving air at the discharge outlet from the fan and a velocity of 2000 feet per minute. Air at the standard conditions is to be at 70 degrees Fahrenheit and a relative humidity of 70 per cent. Under these standard conditions a cubic foot of air weighs .07465 pound. The pressure of 5 pounds is equivalent to a pressure head of 67 feet of standard density air. A velocity of 2000 feet per minute corresponds to a velocity head of 17.27 feet. Total head against which the air is delivered to the supply mains for the standard conditions is then 84.27 feet, making a very satisfactory combination of velocity and pressure head, approaching as it does the maximum possible delivery for this pressure head. TESTING OF VENTILATING FANS OR BLOWERS 371 Corrections for Losses of Total Head in Ducts. There is always some loss of total head along a duct or pipe due to friction. As a result there is a smaller delivery than that given for standard conditions. Using the following symbols: h/ = loss of head in feet due to friction; f = coefficient of friction = .00008 in piping of good construction; 1 = length of duct in feet ; d = diameter of duct in feet; V m = velocity of flow through duct in feet per minute. h ' = n,25o"foood (II3) If V m = 2000 then h f = .3556 -r. Loss of head in a square duct is usually assumed to be the same as for a round one; but for a duct of rectangular section of which the short side is b and the long side is nb, the formula above becomes, using 1 and V m as before, 1 4- n 1 V 2 h/ = i-±-?x£x— -^ (114) n b 22,500,000 With the help of these formulas when the size of the main ducts and the discharge in cubic feet per minute at each outlet are known, the head at each outlet as compared with the standard total head of 84.27 feet can be calculated. As a " rough and ready " rule it is often stated that for a loss of one foot of head there is a loss of six-tenths per cent delivery (cubic feet per minute). Testing Air Compressors. The various types of machines for com- pressing air are usually operated either by a steam engine or by an electric motor. Power delivered to the compressors by the engine or motor is therefore measured by one of the methods already outlined for ventilating fans. Air compressors, particularly of the reciprocating type, are designed, as a rule, for operation at considerably higher pressures than would be suitable for ventilating fans, and the volume delivered must usually be measured in a comparatively small pipe. Air at high pressure is generally measured by calculating the flow through an orifice in a receiver or one of the other methods described on pages 185 to 188. Foot-pounds of work " done on the air " per second; and this product divided by the net power required to drive the compressor is the " net " mechanical efficiency. (See also bottom page 373.) In an air compressor in which the air cylinder is direct-connected to the steam cylinder the net power required to drive the compressor is determined by finding the indicated horse power of the air cylinder and adding the friction in the air cylinder, which in many cases can be as- 372 POWER PLANT TESTING sumed to be half the difference between the indicated horse power as measured in the steam and air cylinders. For use on air compressors operating at high pressures special indicators are made. One of the best is made by the Crosby Steam Gage and Valve Co., Boston, Mass., and is illustrated in Fig. 333. It is similar in design to the gas engine indicator illustrated in Fig. 315, page 342, except that the piston in the lower Fig. 333. — Crosby High-pressure Indicator (Ordnance Type). cylinder of the indicator is very small, only one-fortieth of a square inch in area. This indicator can therefore be readily used for pressures as high as 10,000 pounds per square inch. RULES FOR CONDUCTING TESTS OF STEAM-DRIVEN COM- PRESSORS, BLOWERS AND FANS 1 A.S.M.E. CODE OF 1912 If the air end of a compressor is of the reciprocating type, indicator dia- grams should be regularly taken from this end as well as from the steam end. The rules pertaining to dry steam, heat consumption, and indicated horse power of the steam end, are identically the same as those given 1 In the case of air machinery driven by some other prime mover than a steam engine or turbine, the code may be modified to meet the particular requirements. TESTING OF VENTILATING FANS OR BLOWERS 373 on pages 296 and 297 of the Steam Engine Code, and reference may be made to that code for the necessary directions in these particulars. TESTING OF VENTILATING FANS OR BLOWERS AND AIR COMPRESSORS (a) Air Horse Power. The gross work done at the air end of a reciprocating machine expressed in horse power, is found by multiplying together the net area of the air piston in sq. in., the mean effective air pressure in lb. per sq. in. as determined from indicator diagrams, the length of the stroke in ft., and the number of single strokes per minute; and dividing their product by 33,000. The net work at the air end of either reciprocating or rotary machines, ex- pressed in ft.-lb. per minute, is found by multiplying the corrected volume of the compressed air in cu. ft. discharged into the main delivery pipe per minute, by the impact or total pressure in lb. per sq. ft. and by the hyperbolic logarithm of the ratio of the total pressure to the atmospheric pressure (all pressures be- ing absolute pressures). The net air horse power is found by dividing the product by 33,000. The corrected volume of the compressed air may be found by multiplying the sectional area of the delivery main in sq. ft. by the mean velocity in ft. per minute as determined by pitot tube or other measurement, and reducing the result to atmospheric temperature by multiplying by the proportion. 460 + t 460 + T in which t is the temperature of the air supplied to the machine and T the tem- perature of the air in the delivery main. (b) Capacity. The capacity is the number of cu. ft. of air discharged through the delivery main per minute, as determined by gasometer, tank or other mode of measurement, reduced to the equivalent free air at the atmospheric tempera- ture and pressure. The correction for pressure is made by multiplying by the P 2 proportion — in which Pi is the atmospheric pressure and P 2 the total pressure Pi in the main (absolute pressures), and the correction for temperature as above. The capacity may also be expressed in the number of cu. ft. of compressed air discharged per minute at a given pressure above the atmosphere reduced to the atmospheric temperature. (c) Miscellaneous. For methods of calculating results pertaining especially to the performance of the steam-end of a reciprocating air-pumping machine, reference may be made to the Steam Engine Code. The "efficiency of compression" in a reciprocating machine is determined by first ascertaining the net work at the air end given above under the heading, (a) "Air Horse Power," and then dividing the net work thus found by the gross work given under the same heading. The " mechanical efficiency " of a reciprocating machine is determined by dividing the gross air horse power at the air end by the indicated horse power at the steam end, or by the horse power delivered by the belt or motor in the case of other means of driving. DATA AND RESULTS OF TEST OF AIR MACHINERY. CODE OF 1912 (1) Test of located at to determine conducted by (2) Type of machinery 374 POWER PLANT TESTING (3) Rated capacity in cu. ft. of free air per minute (4) Rated capacity in cu. ft. of air discharged per minute at 100 lbs. per sq. in. above atmosphere, reduced to the atmospheric temperature cu. ft. (5) Type of boilers (6) Type of auxiliaries : (7) Dimensions of engine or turbine at steam end (8) Dimensions of cylinders or blowers at air end (9) Dimensions of boilers (10) Dimensions of auxiliaries (11) Dimensions of condenser (12) Date (13) Duration hrs. Average Pressures and Temperatures (14) Steam pressure at boiler by gage • lbs. per sq. in. (15) Steam pipe pressure near throttle, by gage lbs. per sq. in. (16) Barometric pressure of atmosphere. . . .ins. of mercury = lbs. per sq. in. (17) Pressure in receiver by gage lbs. per sq. in. (18) Vacuum in condenser in ins. of mercury (19) Pressure in delivery main by gage (impact pressure) . . . •. . .lbs. per sq. in. (20) Total head, expressed in ft ft. (21) Temperature of main supply of feedwater to boilers deg. F. (22) Temperature of additional supplies of feedwater deg. F. (23) Temperature of air in engine room or air supplied to machine deg. F. (24) Temperature by wet-bulb thermometer deg. F. (25) Temperature of air in delivery main deg. F. Total Quantities (26) Water fed to boilers from main source of supply lbs. (27) Water fed from additional supplies lbs. (28) Total water fed to boilers from all sources lbs. (29) Moisture in steam or superheating near throttle per cent or deg. F. (30) Factor of correction for quality of steam, dry steam being unity (31) Total dry steam consumed for all purposes lbs. (32) Total cu. ft. of compressed air delivered as measured cu. ft. (33) Total cu. ft. of compressed air delivered reduced to atmospheric temperature and pressure cu. ft. (34) Total weight of air delivered lbs. Hourly Quantities (35) Water fed from main source of supply lbs. (36) Water fed from additional supplies ; . . . lbs. (37) Total water fed to boilers per hour lbs. (38) Total dry steam consumed per hour lbs. (39) Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant lbs. (40) Net dry steam consumed per hour lbs. (41) Dry steam consumed per hour: (a) By main engine or turbine lbs. (6) By auxiliaries ; lbs. TESTING OF VENTILATING FANS OR BLOWERS 375 (42) Cu. ft. of compressed air delivered per hour as measured cu. ft. (43) Cu. ft. of compressed air delivered per hour reduced to atmospheric tem- perature cu. ft. (44) Cu. ft. of compressed air delivered per hour reduced to atmospheric temper- ature and pressure cu. f t. (45) Weight of air delivered per hour lbs. Heat Data (46) Heat units per lb. of dry steam based on temperature Line 21 B.t.u. (47) Heat units per lb. of dry steam based on temperature Line 22 B.t.u. (48) Heat units consumed per hour based on main supply of feed B.t.u. (49) Heat units consumed per hour based on additional supplies of feed B.t.u. (50) Total heat units consumed per hour for all purposes B.t.u. (51) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. (52) Net heat units consumed per hour B.t.u. (53) Heat units consumed per hour : (a) By engine or turbine alone B.t.u. (6) By auxiliaries B.t.u. Indicator Diagrams (54) Mean effective pressure in steam cylinders lbs. per sq. in. (55) Mean effective pressure in air cylinders lbs. per sq, in. Speed and Stroke (56) Revolutions per minute (57) Number of single strokes per minute Power (58) Indicated horse power developed at steam end of reciprocating machine i.h.p. (59) Gross air horse power as indicated in air cylinders of reciprocating ma- chine air h.p. (60) Net air horse power as computed from Line 43 . air h.p. (61) Friction of reciprocating machine (Line 58 — Line 59) fr. h.p. (62) Percentage of i.h.p. lost in friction of machine per cent Economy Results, Steam End op Engine-driven Machines (63) Heat units consumed per i.h.p. per hour: (a) By engine or turbine and auxiliaries B.t.u. (b) By engine or turbine alone B.t.u. (c) By auxiliaries B.t.u. (64) Dry steam consumed per i.h.p. per hour 1 : (a) By engine or turbine and auxiliaries lbs. (6) By engine or turbine alone lbs. (c) By auxiliaries lbs. Economy Results, Air Delivered (65) Heat units consumed per hour per net air h.p. of Line 60: (a) By engine or turbine and auxiliaries B.t.u. (6) By engine or turbine alone B.t.u. (c) By auxiliaries B.t.u. 1 The i.h.p. on which these economy results are based is that of the main engine given in Line 58. 376 POWER PLANT TESTING (66) Dry steam consumed per hour per net h.p. of Line 60: (a) By engine or turbine and auxiliaries lbs. (b) By engine or turbine alone lbs. (c) By auxiliaries lbs. Efficiency Results (67) Thermal efficiency ratio for engine alone: (a) Per i.h.p., steam end (2545 -~- Line 636) per cent (6) Per net air h.p., air delivery (2545 -e- Line 656) per cent Work Done Per Heat Unit (68) Ft.-lbs. of net work per B.t.u. consumed by engine or turbine and auxiliaries (1,980,000 -r- Line 65a) ft.-lbs. Capacity (69) Cu. ft. of compressed air delivered per minute as measured cu. ft. (70) Cu. ft. of compressed air delivered per minute, reduced to atmospheric temperature cu. ft. (71) Cu. ft. of compressed air delivered per minute at 100 lbs. pressure, reduced to atmospheric temperature cu. ft. (72) Cu. ft. of compressed air delivered per minute reduced to atmospheric tem- perature and pressure (free air) * cu. ft. Miscellaneous Results Steam-driven Reciprocating Machine (73) Efficiency of compression (Line 60 4- Line 59 X 100) per cent (74) Mechanical efficiency of machine (Line 59 -r Line 58 X 100) per cent (75) Volumetric efficiency (Line 72 -f- 1st Compr. Displ. X 100) per cent Note. In the case of air compressors having more than one stage and in those hav- ing intercoolers, additional data should be given covering pressures and temperatures in the different stages, the quantity of water used for cooling and temperatures of the air and water entering and leaving the cooler. CHAPTER XVIII TESTING OF REFRIGERATION PLANTS Refrigerating machines present a most interesting example of the conversion of heat energy. In the simplest forms these machines consist of a compressor driven by a steam engine, or other motive power, serving to compress a gas or vapor as the case may be. This gas or vapor is then passed under pressure through a surface condenser, where the cooling water absorbs the heat generated in the work of compression and then passes into an expanding vessel into which it discharges at a very low temperature. Now in order to vaporize any liquid, it is necessary to maintain a continual application of heat in order to bring about this physical change. To convert a unit weight of liquid to a unit weight of vapor at the same pressure the heat required is always a constant quantity for the same liquid. Thus, as a familiar example, to convert a pound of water at " atmospheric " pressure and 212 degrees Fahrenheit into steam at the same pressure and temperature requires the application of 970 B.t.u.; and conversely, to condense a pound of steam at this same pressure and temperature, it is necessary to abstract 970 B.t.u. by contact with a cold body. Steam as the working medium in a refrigerating machine would, of course, be impracticable, because the lowest tempera- ture resulting from actual condensation in a workable plant would be very much above the freezing point of water; but there are a number of liquids which have a very much lower boiling point than water. Of these ammonia (NH 3 ), carbon dioxide (C0 2 ), and sulphurous dioxide (S0 2 ) are successfully used for purposes of refrigeration. The use of all these depends on the absorption of their latent heat in their conversion from a vapor or gas to the liquid condition. In practice the refrigerating medium most commonly used is anhydrous ammonia, although carbon dioxide is also frequently employed. The latter is preferred usually where ammonia gas might be dangerous or otherwise objectionable. In the simplest form of refrigerating plant the necessary machinery consists of (1) a compressor to raise the gas to the necessary pressure; (2) a surface condenser to absorb by means of cooling water the heat generated by the mechanical work of compression; and (3) an expanding or evaporating vessel where the liquid is reevaporated into a gas and, of course, absorbs heat in the operation. A very simple refrigerating machine is shown in Fig. 334. It consists of the compressor C discharg- 377 378 POWER PLANT TESTING ing gas under pressure 1 through the pipe P into the condensing coil D, consisting in this simple apparatus of a coil of pipe in a tank through which the cooling water circulates. An expanding valve V serves for reducing the pressure and evaporating the liquid coming from D. The expanding vessel or evaporator E consists of a coil of pipe immersed in a tank containing the liquid to be cooled. Drops of liquid accumulate in the bottom coils of the condenser D, to be discharged through the expanding valve V into the evaporator E. Since the compressor receives its supply of gas from the evaporator, the pressure in the latter must be less than in the condenser. On this account, then, the liquid after expanding will begin to boil and will absorb heat from the surrounding liquid in its transformation into a gas. In such a process the tempera- ture of the cooling liquid may become very low. The refrigerating liquid IBM Fig. 334. — Typical Refrigerating Apparatus. in the evaporator will be entirely gasified or vaporized and returns finally to the compressor C in this state through the suction pipe S, thus com- pleting the cycle of operations. After this brief explanation of the principles of the operation of a refrigerating machine we can take up a brief discussion of the thermal processes as regards the interchangeability of heat and work. Using the symbol r for the latent heat of vaporization of the refrigerating medium in B.t.u. per pound, h for the heat imparted by compression in the same units, 2 w for the weight in pounds of the gas or vapor entering the com- 1 In order to liquefy any gas or vapor, obviously it is necessary to bring the mole- cules closer together, and this can be accomplished either by increasing the pressure or decreasing the temperature or by both. 2 The ratio - is often called the coefficient of efficiency of the refrigerating medium. h TESTING OF REFRIGERATION PLANTS 379 pressor in a given time, then, neglecting external losses, wr will represent the heat abstracted in the evaporator and h + wr is the heat given to the cooling liquid in the condenser. In the practical operation of a refrigerating plant the evaporator is maintained at a very low temperature, and some heat must necessarily be given to it by the refrigerating medium itself, since it enters the evaporator, in comparison, in a moderately warm condition. Now if the difference in temperature between the condenser and the evaporator is t degrees Fahrenheit, a pound of refrigerating medium will give to the evaporator st B.t.u., if s is the specific heat of the refrigerating medium; and further if w' is the weight of this medium in pounds passing into the evaporator in a given time then the heat abstracted from the evaporator by the cooling liquid is wr — y — w'st, where y is the heat in B.t.u. lost by radiation. The term w'st is comparatively small in practical machines. If there is no leakage then, of course, w' will be the same as w. Anhydrous ammonia is most commonly used as the refrigerating medium. It is preferable to many other fluids because of its compara- tively high latent heat 1 and low pressure of vaporization. Carbon dioxide (C0 2 ), commercially known as carbonic acid, is a color- less gas without odor when pure, and is furthermore quite innocuous and has practically no injurious effect on animal tissues. It is injurious only when the proportion of it in air becomes so large that there remains an insufficient amount of oxygen. On this account, therefore, it is much safer and suitable as a refrigerating medium than ammonia. This gas can be readily liquefied either by lowering its temperature or by increasing the pressure. At ordinarily low temperatures it can only remain in the liquid state when under considerable pressure. When the pressure is removed, the heat absorbed from surrounding bodies assists in the rapid evaporation of the liquid and these bodies become correspondingly colder by this loss of heat. Carbon dioxide is used only to a limited extent, but it is found par- ticularly desirable on shipboard because of the compactness of the compressor that it requires and its inoffensive character when a leak occurs. A typical commercial refrigerating plant for making ice and operating with a horizontal ammonia compressor is shown in Fig. 335. The same descriptive letters used in Fig. 334 serve again for marking the im- portant parts. The efficiency of a refrigerating machine depends upon the difference 1 The latent heat of vaporization of ammonia is 555 B.t.u. at a temperature of zero degrees Fahrenheit, while that of carbon dioxide is only 123. The corresponding absolute pressures at the same temperature are 30 pounds per square inch for ammonia and 310 for carbon dioxide. 380 POWER PLANT TESTING between the extremes of temperature, but unlike heat engines, it has the greatest efficiency when the range of temperatures is small and when the final temperature is high. When a change of volume of a saturated vapor is made under constant pressure in the presence of an excess of the liquid, the temperature remains constant. In this case the addition or absorption of heat to produce the change of volume causes an increase or decrease in the amount of the liquid mixed with the vapor. Vapors, even when satu- rated, if no longer in contact with their liquids, having heat added either by compression, by mechanical force or from an external source of heat, will behave practically like permanent gases and will become superheated. On this account refrigerating machines using liquefiable COMPLETE ICE MAKING PLANT Fig. 335. — Refrigerating Plant with Ammonia Compressor. gas will give results differing according to the conditions of operation, depending primarily upon the state of the gas; that is, whether it remains constantly saturated or is superheated during a part of the cycle. Some ammonia plants are operated with an excess of liquid present during compression so that superheating is prevented. This is known in prac- tice as the " wet " or " cold " system of compression. Density op Ammonia Vapor At temp. deg. C At temp. deg. F Density, lb. per cu. ft -10 -5 5 10 15 . (approx.) . . 14 23 32 41 50 59 cu. ft . 0.6492 .6429 .6364 .6298 .6230 .6160 20 Ledoux found Latent Heat op Evaporation op Ammonia he = 555.5 - .613 T - 0.000219 T 2 (in B.t.u. and degrees F.) h e = 583.33 - .5499 T - 0.0001173 T 2 (in B.t.u. and degrees F.). TESTING OF REFRIGERATION PLANTS 381 For experimental values at different temperatures determined by Professor Denton, see Transactions American Society Mechanical En- voi. 12, page 356. For calculated values, see vol. 10, page 646. Specific Heat and Available Latent Heat of Hot Ammonia Latent heat at 15.67 lbs. per sq. in. gage press, and degrees F. = 550.5 B.t.u. Specific heat = 1.096 - 0.0012 T (degrees). Values at 15.67 lbs. per sq in. Gage Pressure (Lucre) Temperature of Liquid Supply, Deg. F. Specific Heat of Liquid. Correction for Cooling, B.T.U. Available Latent Heat for Saturated Vapor, B.T.U. per lb. 5 1.090 5.45 550.05 10 1.084 10.84 544.66 15 1.078 16.17 539.33 20 1.072 21.44 534.06 25 1.066 26.65 528.85 30 1.060 31.80 523.70 35 1.054 36.89 518.61 40 1.048 41.92 513.68 45 1.042 46.89 508.61 50 1.036 51.80 503.70 55 1.030 56.65 498.85 60 1.024 61.44 494.06 65 1.018 66.17 489.33 70 1.012 70.84 484.66 75 1.006 75.45 480 05 80 1.000 80.00 475.50 85 .994 84.49 471.01 90 .988 88.92 466.58 95 .982 93.29 462.21 100 .976 97.60 457.90 The latent heat of saturated ammonia vapor as given by Lucke must be corrected in three ways : (1) For the temperature of the liquid, which must be cooled from its initial temperature to the temperature corresponding to the suction or back-pressure; (2) for wetness of the vapor, for which the correction is 5.555 B.t.u. for each per cent of mois- ture; (3) for superheat of vapor in case it leaves the expansion coil (evaporator) at a higher temperature than that corresponding to the pres- sure. This last correction is additive and is approximately the number of degrees of superheat times the specific heat of superheated ammonia gas taken as 0.508. Leakages of ammonia gas are very objectionable and may be dan- gerous. One of the most convenient and reliable means for locating a small leak is to burn a little sulphur at the end of a stick of wood about fifteen inches long. Where the sulphur fumes come into contact with the ammonia gas a white vapor is observed. 382 POWER PLANT TESTING Units of Refrigeration and Capacity. A practical way to express the performance of a refrigerating plant is found by using as a basis the amount of fuel consumed and the " ice-melting " capacity 1 of the plant. If we use the following symbols: R = refrigeration of "ice-melting" capacity per pound of fuel, in pounds; w& = pounds of brine circulated per hour, pounds; s 6 = specific heat of brine; ti = temperature of brine entering expansion coils, deg. F.; t 2 = temperature of brine leaving expansion coils, deg. F. ; w f = fuel used per hour, pounds; R= w„s t (t 2 -t,) 144 W/ v °' and the capacity C of a machine in tons, of 2000 pounds, of refrigeration or ice-melting per 24 hours is c= 2 4 W 6 S 6 (t 2 -t 1 ) 144 X 2000 Ice-making Capacity is usually defined as half the refrigerating capa- city as given by (116). The above are the " practical " units used in ordinary commercial tests. When, however, facilities are provided for determining the weight of refrigerating medium (ammonia, etc.) a more accurate method of calculation is as follows, using: c = refrigerating effect per lb. (ammonia, etc.) in B.t.u.; s = specific heat of liquid (ammonia, etc.); s g = specific heat of gas at constant pressure ( = 0.508 for ammonia) ; t s = temperature of saturated gas in evaporating coils, deg. F. (from tables) ; t e = temperature of liquid at expansion valve, deg. F.; t a = temperature of gas (actual) leaving evaporating coils, deg. F.; r, = latent heat of vaporization at temperature t s ; then c =T S -s (t e - t s ) +s ff (t a - t s ) (117) and by this method, capacity of refrigeration, C is C' = -^^, (118) 288,000' 1 Ice-melting capacity is a term applied to represent the cold produced in an in- sulated bath of brine, measured by the latent heat of fusion of ice, which is 144 B.t.u. per pound. More accurately it is the heat required to melt a pound of ice at 32 de- grees Fahrenheit to water at the same temperature. The capacity of a machine in pounds or tons of "ice-melting" or of "refrigeration" does not mean that the ma- chine would make that amount of ice; but that the cold produced is equivalent to the melting of the weight of ice to water. TESTING OF REFRIGERATION PLANTS 383 when W is weight of refrigerating medium (ammonia, etc.) circulated per 24 hours in pounds. As calculated by equations (117) and (118) refrigeration units are not comparable for different conditions of operation, and a standard of pressure has come to be quite generally accepted, these being 185 lbs. per sq. in. gage 1 pressure at the discharge of the compressor and 15.67 lbs. also by gage and dry saturated gas at the suction. Equivalent refrigerating effect and equivalent tons of refrigeration at these standard conditions are readily calculated from equations (117) and (118), where the last term in (117), representing superheat, becomes zero. Volumetric Efficiency. The ratio of the actual volume of refrigerating medium, discharged from the compressor to that calculated from the piston displacement is called the volumetric efficiency. The following formula deduced from Voorhees 2 gives in most practical cases the volu- metric efficiency E„ of an ammonia compressor with a remarkable degree of accuracy: E _(t 1Z1 ito) (iig) 1330 where ti is the theoretical temperature of the gas after compression, t is the temperature of the gas delivered to the compressor. Here to can be calculated from the general equation for adiabatic compression where ti + 460 = (to + 460) f^Y' 24 ("9) Here pi and p are the absolute pressures of the gas corresponding re- spectively to the temperatures ti and to. The actual temperature of the gas discharged from the compressor will be usually considerably, some- times from 50 to 60 degrees Fahrenheit less than the theoretical. Lucke 3 has deduced the following formula for the indicated horse power of compressor (i.h.p.) required per ton of refrigerating capacity, expressed in the following symbols: p = the mean effective pressure in compressor in lbs. per square inch; 1 = the length of the stroke in feet; a = the area of the piston in square inches; n = the number of compressions per minute; E„ = the volumetric efficiency, as defined above; w c = the weight of a cubic foot of ammonia vapor at the back pressure as it exists in the cylinder when compression begins; v c is the latent heat of vaporization available for refrigeration at suction pressure (see table 1 Since gage pressures are used it is obvious our methods of calculation for refriger- ating machinery are not on a sound scientific basis. 2 "Ice and Refrigeration" (1902). 3 Proceedings American Society of Refrigerating Engineers (1908). 384 POWER PLANT TESTING page 381); 288,000 = the B.t.u. equivalent to one ton of refrigeration per twenty-four hours, that is, 2000 X 144. Then, plan *•"*•- UB.nw.xffx 60X24 ( " 0) 144 X 288,000 •%*l ™ Theoretical Efficiency of Refrigerating Machines. The maximum theoretical efficiency E TO of a refrigerating machine is expressed by the ratio, Em= TT^T" ' * * (I22) where Ti is the highest and T is the lowest absolute temperature of the refrigerating medium. Heat Balance. The heat balance for the cycle of operation may be calculated as follows: The liquid enters the brine coils at a temperature of t e ; first: this temperature must be lowered to t a the temperature of saturation. Under ideal conditions (without losses) the heat added to the brine by this lowering of the temperature of the liquid is s(t e — t s ) per pound of liquid. Second, the liquid is vaporized and takes, the latent heat of the ammonia r s per pound of liquid from the brine. Third, if the temperature of the gas leaving the coils is superheated then this heat re- ceived by the gas from the brine in addition to'the above will be s ff (t a — t s ) B.t.u. per pound of ammonia. Then the total heat Hi (B.t.u.) received by the ammonia per pound in passing through the brine coils will be (under ideal conditions — no losses), using symbols as on page 382, Hi = r a - s(t e - t s ) + s g (ta - t s ). [Same as (117)-] This will also represent the amount of heat taken from the brine tank per pound of ammonia circulated. Heat received in passing from the brine tank to the compressor in B.t.u. per pound of ammonia gas circulated, where ti is the temperature of the gas at the compressor before entering, deg. F., H 2 = S ff (tl - ta). Heat Received in Passing through Suction Valves. The gas in passing through the suction valves of the compressor is superheated due to the friction and throttling when coming in contact with the hot metal in the cylinder. The temperature t 2 at the beginning of compression can be determined approximately as follows: t,-.t. + £x«.6-t I + £j? 1 when d is the diameter of the compressor in inches. Then heat added in the valves H 3 = s„(t 2 — ti) per pound of ammonia circulated. TESTING OF REFRIGERATION PLANTS 385 Heat due to Compression. The work done as shown by the indicator card will represent the heat added to the gas by the compressor. The work done on the gas is represented by the total work shown by the indicator cards to be taken from all the cylinders W k , which is in B.t.u. per pound of ammonia. Total Heat Added. Total heat added to the ammonia per pound of liquid flowing through the cycle will be H = Hi + H 2 + H 3 + W*. Heat by Jacket Water. The water flowing through the jackets of the compressor cylinder removes some heat from the ammonia gas, which is, H 4 = W](ts — U) where Wi is weight of jacket water circulated in same time as one pound of ammonia, also t 5 and t 4 are respectively temperatures of water leaving and entering, deg. F. Heat Absorbed by Ammonia Condenser: H 5 = r c + s ff (t 3 — t c ) in B.t.u. per pound of liquid. Where t c = temperature of condensed liquid in ammonia receiver, deg. F., r c = the corresponding latent heat, and t 3 = temperature of gas as discharged from the compressor. Heat absorbed by condensing water w 2 (t 7 — t 6 ) should equal the above when w 2 is weight of condensing water used while one pound of ammonia is circulated, also t 7 and t 6 are the temperatures of water leaving and entering, deg. F. Heat Balance. Heat added = heat absorbed + radiation (R). H x + H 2 + H 3 + H w = H 4 + H 5 + R (123) Mechanical Efficiency. The mechanical efficiency of the machine will be the ratio between the work done in the compressor cylinder to that done in the steam cylinder. tv/t i_ -ru* i.h.p. compressor , . Mech. Eff. = — t^- —. ■ (124) i.h.p. engine Ammonia Absorption Refrigerating Machines. Another class of refrigerating apparatus, operating by what is known as the absorption system, has been installed in some places. It consists of a generator containing a concentrated solution of ammonia in water. This generator is heated usually by means of a coil of pipes taking live steam from a boiler, although frequently the exhaust steam from engines is utilized to advantage. In this system a weak ammonia vapor passes first into an " analyzer " where some of the water is separated from the ammonia vapor and then into a " rectifier," where the concentrated vapor is cooled, precipitating still more water, and then discharges into the condenser coils. The lower coils of the condenser are connected to the upper part of the " cooler " or brine tank. An absorption chamber is provided which is filled with a weak solution of ammonia, and this 386 POWER PLANT TESTING chamber is also connected with the cooling tank. The absorption chamber communicates with generator by two tubes, one going to the bottom of the generator from the top of the chamber, and the other from the bottom of the chamber to the top of the generator. In the latter pipe line, a pump is located to force the liquid from the absorption cham- ber, where the pressure is about atmospheric, to the generator, where the pressure is from 100 to 200 pounds per square inch. In the operation of this apparatus the ammonia and water in the generator are first heated by the coil of steam pipes, and as the ammonia is freed from the solution the pressure rises. When this pressure attains that of saturated vapor at the temperature of the condenser it becomes liquefied, condensing also a small amount of steam. A suitable expansion valve regulates the flow of the liquefied gas into the refrigerating coils in the cooler. As it escapes into these coils it expands and is again vapor- ized, absorbing heat from the liquid or gas required to be cooled. Just as rapidly as vaporization goes on the gas is absorbed by the weak solution in the absorbing chamber. The heat in the generator has the effect of separating a strong from a weak solution, the greater concentration being in the upper part. The weaker portion of the solution is con- veyed by the pipe entering the top of the absorption chamber. The satisfactory operation of this apparatus depends upon careful adjust- ments and regulation of the flow of gas and liquid, controlling in this way the temperature in the cooler. Testing of Refrigerating Plants. The primary object of a test of a re- frigerating apparatus is to compare the refrigerating effect with the heat equivalent of the mechanical work and of the cooling of the water or brine. The making of ice is not satisfactory for accurate results in a test. The range of temperature should not be greater than necessary to secure accuracy in the thermometer readings. The brine should be measured or weighed in suitable tanks as for the condensed steam in engine tests. One of the most important precautions to be observed is to determine accurately the specific heat of the brine for the temperature range of the test. Small differences in its concentration and composition may produce a considerable variation in results. When a compressor and steam engine are coupled directly together on the same shaft a direct measurement of the power required for the compresser is not obtain- able. By measuring the horse power of the engine running without doing any work in the compressor — that is, operating it " empty " — and by comparing the differences in power between the steam engine and compressor for wide variations of condenser pressure, the effective horse power required to drive the refrigerating machine can be determined with some degree of accuracy. TESTING OF REFRIGERATION PLANTS 387 The following data sheet is used in parts by Denton 1 : 1. Average high ammonia pressure above atmosphere 2. Average back ammonia pressure above atmosphere 3. Average temperature brine inlet 4. Average temperature brine outlet 5. Average range of temperature 6. Lbs. of brine circulated per minute 6a. Specific heat of brine 7. Average temperature condensing water at inlet 8. Average temperature condensing water at outlet 9. Average range of temperature 10. Lbs. water circulated per minute through condenser 11. Lbs. water per minute through jacket 12. Range of temperature in jackets 13. Lbs. ammonia circulated per minute 14. Probable temperature of liquid ammonia entrance to brine-tank 15. Temperature ammonia corresponding to average back pressure 16. Average temperature of gas leaving brine tank 17. Temperature of gas entering compressor 18. Average temperature of gas leaving compressor 19. Average temperature of gas entering condenser 20. Temperature due to condensing pressure 21. Heat given ammonia: By brine per B.t.u. per minute By compressor, B.t.u. per minute By atmosphere, B.t.u. per minute 22. Total heat received by ammonia, B.t.u. per minute 23. Heat taken from ammonia: By condenser, B.t.u. per minute By jackets, B.t.u. per minute By atmosphere, B.t.u. per minute 24. Total heat rejected by ammonia, B.t.u. per minute 25. Difference of heat received and rejected, B.t.u. per minute 26. Per cent of work of compression removed by jackets 27. Average revolutions per minute 28. Mean effective pressure steam cylinder, lbs. per square in 29. Mean effective pressure ammonia cylinder, lbs. per square in 30. Average H.P. steam cylinder 31. Average H.P. ammonia cylinder 32. Friction in per cent of steam H.P 33. Total cooling water, gallons per minute, per ton ice-melting capacity per 24 hours . 34. Tons ice-melting capacity per 24 hours 35. Lbs. ice-refrigeration effect per lb. coal at 3 lbs. per H.P. hour 36. Cost coal per ton of ice-refrigerating effect at $4 per ton 37. Cost water per ton of ice-refrigerating effect at $1 per 1000 cu. ft. per 24 hours. . . 38. Total cost of 1 ton ice-refrigeration effect 39. Refrigeration effect per I. H.P. in compress, cyl., B.t.u. per minute 40. Refrigeration effect per I. H.P. in steam, cyl., B.t.u. per minute 41. Refrigeration effect per pound of steam, B.t.u. per minute 1 Transactions American Society of Mechanical Engineers, Vol. 12, page 356. 388 POWER PLANT TESTING Another form for data and results, including a heat balance is as follows : RESULTS OF REFRIGERATING PLANT TESTS General 1. Date of test located at 2. Object of test 3. Duration of test 4. Type of machine 5. Dimensions: 6. Diam. of ammonia cyl diam. steam cyl 7. Stroke of compressor stroke of steam engine . . . 8. Diam. of piston rod comp. cyl diam. piston rod steam cyl 9. Average Temperatures of Ammonia: Leaving machine. . . . entering machine 10. Leaving condenser .... entering expansion coils 11. Leaving expansion coils 12. Average temperatures of water: 13. Entering ammonia condenser .... leaving ammonia cond 14. Entering compressor jackets .... leaving comp. jackets : 15. General temperatures: All temperature in degrees 16. Room .... outside air .... brine 17. Pressures: (Lbs. per sq. inch absolute.) 18. Steam .... discharge, ammonia .... suction ammonia 19. Atmospheric 20. Weights: (pounds.) 21. Ammonia used .... jacket water .... ammonia condenser 22. Ammonia per hour .... jacket water per hour 23. Ammonia condensed per hr ammonia per 24 hrs 24. Jacket water per 24 hrs ammonia cond. per 24 hrs 25. Scale of spring, ammonia cylinder lbs. per sq. in. 26. Scale of spring, engine cylinder r.p.m. 27. Average i.h.p. per hour (steam cylinder) 28. Average i.h.p. per hour (ammonia comp.) 29. Condition of gas leaving machine deg. F. sup. 30. Condition of gas at beginning of compression deg. F. sup. 31. Condition of gas entering machine deg. F. sup. 32. Refrigerating effect, actual, per lb. ammonia B.t.u. 33. Tons of refrigeration, actual 34. Ice-making capacity, actual (line 33 -f- 2) tons 35. Mechanical efficiency per cent 36. Equivalent refrigerating effect based on standard conditions (seepage383) B.t.u. per lb. 37. Equivalent tons of refrigeration based on standard conditions (see page 382) 38. Ice-making capacity based on standard conditions tons 39. Per cent rating obtained 40. Volumetric efficiency (see page 383) per cent 41. Heat balance (see pages 384) CHAPTER XIX TESTING OF HOT-AIR ENGINES Hot-air Engines of the conventional type are reciprocating " piston " engines which are operated by the alternate expansion and contraction of a charge of air. This alternate expansion and contraction is pro- duced by heating and cooling. Engines of this kind now in use are found most often in country places, where they are used for pumping water. Usually coal is burned for fuel; but sometimes gas is used, particularly in the natural-gas districts. Rider Hot-air Engine. The most successful engine of this kind is made by the Rider-Erics- son Engine Company of New York. This engine, illustrated in Fig. 336, consists of a com- pression cylinder C and a power cylinder P, each provided with a separate piston. These two cyl- inders are connected together by a rectangular passage R contain- ing a large number of thin metal- lic plates and forming what is called in engines of this type the regenerator. This regenerator has for its function the alternate abstracting and returning to the air of a quantity of heat. Air leaking out is replaced by a fresh supply admitted through the check valve V, which opens inward, provided with a water-jacket. The cycle of operations in this engine consists of a compression stroke when the piston in the compression cylinder C compresses the cold C- Compression Cylinder p -Power Cylinder E- Cooler H -Heater R- Regenerator II -Cranks set at about 100° JJ-Connecting Rods L-Check Valve M-Pump Primer T— Water Jacket, to protect packing fromjieat U-Pump Fig. 336. — Hot-air Engine. The compression cylinder C is 390 POWER PLANT TESTING air from which the heat has been abstracted by its passage through the regenerator R, and then by the simultaneous advancing upward move- ment of the piston in the power cylinder P the air passes again through the regenerator and also through the heater H without appreciable change of volume. As a result the addition of heat increases the pres- sure of the air and when it enters the power cylinder P it pushes the piston upward to the end of its stroke. This upward movement of the power piston in the last half of its stroke carries with it the piston in the com- pression cylinder C, which is on the same shaft but set at an angle of 90 degrees, so that the two pistons do not reach the ends of their strokes together. Now as the charge of air cools the pressure falls, so that the piston in the power cylinder falls and in the last half of this stroke carries downward with it the piston in the compression cylinder and again starts compressing the charge of air. As the heated air passed through the regenerator plates on its way to the compression cylinder the greater portion of the heat it contained was left in them to be ab- stracted on the return movement to be used again for increasing the temperature of the charge. In Fig. 336 a water pump U is shown at the left-hand side of the engine. Besides being used for supplying a water system it pumps the cooling water needed for the water-jacket T and the cooler E. Tests of Hot-air Engines do not differ in the important details from tests of steam and gas engines. The indicated horse power is obtained by attaching engine indicators to both the power and the working cylinders and the net indicated horse power is the difference between that for the power and that for the compression cylinders. A Prony brake or similar device attached to the main shaft for absorbing the power can be used to determine the useful or brake horse power and the ratio of the brake to the indicated horse power is the mechanical efficiency. For testing such engine to determine the efficiencies and economy it is preferable to use gas or oil for fuel instead of coal, because of the obvious advantages in the determination of fuel consumption. Thermodynamic efficiency is the ratio of the range of temperature to the initial absolute temperature of the air in the power cylinder. Temperatures not determinable by direct measurement may be calcu- lated from the pressures and the specific volumes by the general formula for perfect gases, T = pv/R, (122) where R for air is 53.21. CHAPTER XX TESTS OF HOISTS, BELTS AND FRICTION WHEELS Efficiency of Hoists. An efficiency test of a hoist is made by deter- mining the ratio between the work done in lifting the load to that applied to the hand chain. Stated briefly, this determination is made by raising slowly a known weight, observing at the same time by means of a spring balance fastened to the hand chain, the pull or force required to keep the load moving after it has been started. The method is, of course, the same for determining the efficiency of a rope hoist, except that some special provision must be made for attaching the hook of the spring balance to the rope. Allowance must also be made, of course, for the number of times the power is multiplied, that is, the relative velocity value. Differential Hoists. Differential hoists (Fig. 337) are a little more complicated than the ordinary chain or rope hoist. In this apparatus, as shown in the standard books on the theory of mechanism, the velocity ratio is expressed according to the dimensions in the figure by 2R1 * , r7^r 2 (I23) It is difficult, however, to measure accurately the radius of these wheels on account of the irregular surface made for gripping the links. Now since the circumferences of these wheels are proportional to the radii, the velocity ratio may be determined by count- ing the number of link-pockets in each of the wheels, and its value will be given by the ratio of twice the number of link-pockets in the larger wheel divided by the difference between the number of link-pockets in the larger and the smaller wheels. In some other types of hoists where this method is not applicable and the diameters cannot be readily measured, the velocity ratio can be determined by tying a piece of string on a link of the " load " chain or rope, as the case may be, oppo- site some fixed part of the hoist and mark ir the same way a point on the chain or rope to which the pull is appliec Now when the "load" chain has been moved a measured distance, /he corresponding move- 391 Fig. 337. — Differ- ential Hoist. 392 POWER PLANT TESTING ment of the point of application can be measured. Several observations should be made to eliminate probable errors in the measurements. Velocity ratio is usually expressed by making the second member of the ratio unity, thus 13 : 1, 4 : 1, etc. The force required to move the hand chain by the spring balance multiplied by the velocity ratio is the work " put into " the hoist, while the weight lifted is proportional to the work done. Efficiency is then the work done divided by the work " put in," or in the terms above is the weight lifted divided by the product of the pull on the hand chain times the velocity ratio. 1 On account of the great friction at starting the reading of the spring balance should be made when constant after starting by hand. Determinations should also be made when the load is being lowered, but these results should not be averaged with those for raising the load because a hoist is generally used only for raising loads. Determination of Tension in Belts and Rope Drives. Tests are often required to determine the power transmitted by belts and ropes for specified conditions of load, speed, tension, and the coefficient of friction between these and the pulleys on which they run. Suitable apparatus for such tests consists of a device with which the belts or ropes can be operated with different tensions. Usually the load is not increased be- yond the limit producing 3 per cent slip. 2 The initial tension in the belt or rope should be measured when at rest. Testing of Belts. For determining the qualities of belts as regards power transmission and the coefficient of friction belt tests are desirable. _^X 3 Sometimes belts or pulleys of different mate- rials are to be compared, while again tests may be required to determine the effect of belt dressings. The apparatus to be described is simple in construction and inexpensive. It consists essentially of two pulleys on the ends of a universal coupling. One of these pulleys is driven by a variable speed motor to which ^ ooo nn j ™ it is belted. The other is set up on the frame Fig. 338. — Belt and Rope . i . ,. , Testing Apparatus. shown m Fig. 338 suspended on a knife-edge bearing at O so that the end at S is free to move in a vertical plane and any horizontal tension in a belt placed on it produces a proportional r ressure on a scales at S. This pulley shown in the figure is the driver f :>r another pulley attached to shafting about 1 If the spring balance is us< d in the inverted position, its weight must be added to the pull. Also the weight o the scale pans used for supporting the weights must be added. 2 Slip in belts or ropes is rat > of the difference between the revolutions of the driver and the follower divided by th revolutions of the driver, each taken, of course, for the same time unit. TESTS OF HOISTS, BELTS AND FRICTION WHEELS 393 25 feet away in fixed bearings and is attached to a Prony brake. This last shaft is adjustable in its bearings so that the tension in the belt can be varied. Let Ti = tension in tight side of belt, lbs.; T 2 = tension in slack side of belt, lbs.; W = pressure on scales at S, lbs; then (T 1 + T 2 )a=Wb or Ti + T 2 = — (124) a When power is being transmitted by the belt and absorbed by the Prony brake we have, since the power transmitted is proportional to the difference of tension, by moments wR + T 2 r = Tir, and then Ti-T 2 =^, (125) where w = net weight on brake, lbs.; R = length of brake arm, ft.; r = radius of driven pulley, ft. Combining (124) and (125) Wb wR Ti= a 2 r (126) WbwR „, a r (127) These last equations give the total tensions Ti and T 2 which are usually reduced to pounds per inch of width of the belt. The coefficient of friction (f) between the belt and the pulley is given in books on Mechanics as logsr • • (128) 0.434 C where c is the arc of contact of the belt on the pulley in inches divided by the radius of the pulley in inches. Belts will be stretched more on the tight than on the slack side and this unequal stretching causes a difference in velocity, or per unit of time, a difference between the length of belt on the driving and driven pulleys. This difference is called the creek or slip of the belt. If r' is the radius and N' the r.p.m. of the driving pulley, while r is the radius and N is the r.p.m. of the driven pulley then the difference in velocity is 2 7rr'N' — 2 71-rN. This is because the length of belting coming on a 394 . POWER PLANT TESTING pulley in a unit of time is equal to its peripheral speed. Slip or creek is expressed usually as a percentage of the speed of the driver so that r'N' — rN Percentage slip or creek = ^ — (129) Efficiency of Transmission = Delivered Horse Power 4- Horse Power Input. Tests of Friction Wheels. The apparatus frequently used for deter- mining the coefficient of friction between friction wheels consists of a pair of pulleys, one of them at least usually made of some soft metal like aluminum or a fibrous material like straw fiber, leather fiber or paper. This driver runs on a follower generally of some other material. Power delivered to the " follower " shaft is absorbed by the Prony brake. A bell-crank lever to which weights can be attached is used to hold or press the two pulleys together. The coefficient of friction as determined by such an apparatus is the ratio of the tangential pull to the total normal pressure. If the coefficient of friction is represented by f , and other symbols are used as follows : ri = the effective brake arm in inches; x 355.- Bucket of an Impulse Water efficiency curve of the motor for vary- Wheel, ing power. Tests of Impulse Water Wheels. Impulse wheels used to operate with water under pressure consist usually of a series of buckets attached to 1 For more detailed testing of centrifugal pumps see "Centrifugal Pumps," by Lowenstein and Crissey (D. Van Nostrand Co., 1911). 420 POWER PLANT TESTING Fig. 356. — Typical Impulse Water Wheel. Fig. 357. — Water Jet Discharging at High Pressure from the Nozzle of an Impulse Wheel. HYDRAULIC MACHINERY 421 the periphery of a disk or wheel. The buckets are usually divided by a central rib so that two " pockets " are formed (Fig. 355). The curves for each of the divisions of the bucket are designed to turn the direction of the impinging steam without shock. Fig. 356 shows a typical impulse wheel. Impulse wheels are designed to operate most efficiently with high heads. It is, therefore, impracticable to measure the head directly in feet, but it is done usually by measuring the pressure near the nozzle N with a gage. When the center of the gage is at a higher level than the center of the nozzle discharging on the wheel, then this difference in level must be added to the head calculated from the gage pressure to determine the total head under which the wheel is operating. Power developed is measured usually by a Prony brake connected to the shaft Fig. 358. — Buckets and Jet of a Pelton Wheel. S. In all tests where a large quantity of water is used, the temperature of the water should be recorded and the weight corresponding should be used. A view of the jet discharged from one of these nozzles is given in Fig. 357. The type of impulse wheel most in use commercially is called the Pelton, of which typical buckets and the engaging jet of water are shown in Fig. 358. Laboratory tests for a given head are usually run when varying both the load and speed. Make the first test with the load on the Prony brake as light as possible consistent with fairly steady operation of the wheel, and then take a series of tests increasing the load in increments to reduce the speed about 100 revolutions per minute in each succeeding test. Duration of test at each speed should be from twenty to thirty minutes with observations taken every two minutes. The following form may be used for tests: 422 POWER PLANT TESTING Test op Impulse Wheel General Data: 1. Date : 2. Name of wheel and nominal horse power 3. Kind of bucket 4. No. of buckets 5. Angle of buckets 6. Diameter of bucket wheel, inches 7. Area of nozzle and delivery pipe, sq. ins 8. Coefficient of discharge for type of nozzle 9. Diameter of brake wheel, inches . 10.. Length of brake arm, inches 11. Tare of brake, lbs 12. Duration of test 13. Average temperature of water, deg. F 14. Average pressure by gage at wheel, lbs. per sq. in 15. Average head at wheel in feet 1 16. Quantity of water for total run in pounds 17. Quantity of water in pounds per minute 18. Cubic feet of water per minute 19. Foot-pounds of work per minute calculated from (15) and (17) 20. r.p.m 21. Net weight on brake, lbs 22. Horse power as measured by brake 23. Over-all efficiency of motor, per cent (22) -h (19) X 33,000 Curves. Plot a curve for each head with speed for abscissas and efficiency per cent for ordinates, also curves for the ratio of the velocity of the periphery of the wheel v p to the theoretical velocity due to the head v«; that is, v p /v t for abscissas and the maximum horse power developed for ordinates. 2 Tests of Water Turbines. A typical reaction turbine is shown in Fig. 359» The power is transmitted by the main shaft and the smaller shaft is used for controlling the gates regulating the quantity of water passing through the wheel. For testing a Prony brake can be placed directly on the vertical shaft. In some respects a rope brake is most suitable, as one end can be attached to a spring balance and the other end can be led over a pulley, and will thus support weights on a vertical hanger. It is preferable to have the lower web of the brake-wheel solid, that is, without arms, so that it will retain the cooling water, which should be arranged to flow into it at the rate required. Power supplied is determined by the weight of water used and by the head under which the wheel operates. These quantities are deter- 1 Corrected for vertical distance from the center of the gage to the center of the nozzle. 2 Plot curves showing effect of head on efficiency if several tests are run at differ- ent heads. HYDRAULIC MACHINERY 423 mined in the same general way as for a test of an impulse wheel, already described, except in the case of a reaction turbine, where the housing or casing in which the wheel is placed is always completely filled with water. With this arrangement the turbine receives not only the effect due to the pressure-head, measured from the level in the head-race to the center of the wheel, but also that due to the suction head, measured from the center of the wheel to the level in the tailrace. Data can be recorded in a form similar to that for tests on impulse wheels. Typical Reaction Water Turbine.' Curves. Plot a curve for each gate opening at a constant head with speed for abscissas and efficiency per cent for ordinates. Air Lifts. Pumping water by compressed air has had in recent years extensive application. There are several methods in use, but the most successful is that using air expansively for raising water as shown diagram- matically in Fig. 360, called the " Air lift." It consists of a delivery- pipe D set down into the well and a smaller pipe for compressed air 424 POWER PLANT TESTING having a nozzle N at the end and entering the discharge pipe as shown. It is a more usual construction to admit the air to the discharge pipe through holes from an annular chamber encircling it, but the method of operation is practically the same as shown. Water is raised by the buoyancy of the air. Let hi be the depth of sub- mersion of the delivery pipe measured to the point where the air enters, and h 2 be the total lift measured from the same point. Pressure of air at the place of entrance must be theoretically equal to the pressure corresponding to the head of mixed water and air above it in D. This pressure decreases, however, as the air rises and expands so that at the top of D the pressure is little above atmospheric. Work required of the compressor varies with the difference between the depth of submersion of the delivery pipe hi com- pared with the net lift h 2 — hi. The pres- sure required is then comparatively high and the efficiency low. On the other hand, a very small submergence necessitates a relatively large quantity of air to produce the required velocity, so that again the efficiency is low. Maximum efficiency, usually about 50 per cent, is obtained when the net head h 2 — hi is from 15 to 30 feet. At 150 feet the efficiency is scarcely ever as much as 20 per cent. The following quantities should be determined in a test: (1) horse power of air compressor ; (2) volume of free air (see page 376, line 72) compressed; (3) weight of water pumped; (4) net lift (h 2 — hi); (5) efficiency, which is the ratio of the work equivalent of lifting the water to the work done in compressing the air, both in foot-pound units. Tests of Hydraulic Rams. A section of a typical hydraulic ram is shown in Fig. 362. It consists of an air chamber H, to which is connected the discharge pipe I. There is a check valve G opening into the air chamber from the lower chamber A into which water is brought by the pipe S. There is a waste valve at B. This valve is weighted and opens inward. By means of a nut J on the stem of this valve the lift or amount of opening of the valve can be regulated. When water is supplied to the ram, it escapes through the waste valve B with a velocity corresponding approximately to that due to the head under which the water is supplied. The effect of this velocity head is to reduce the pressure on the upper side Fig. 360. — Air Lift. HYDRAULIC MACHINERY 425 of the valve so that it becomes unbalanced and closes suddenly. Then the momentum of the column of water in the pipe S becomes sufficient to open the valve G, and will discharge some water into the discharge pipe I against a considerable head. As soon as the pressures become equalized the valve G closes, the waste valve B opens and water from the supply pipe is again " wasted." This alternate action is produced with regularity, and as a result the water in the supply pipe acquires a certain " backward and forward " wave-motion. As the rule is generally stated, the length of the supply pipe leading from the reservoir to the ram must be at least five times the head. This length is necessary to secure some resistance to this " backward and forward " wave-motion. A small air chamber shown at P, with a check-valve C opening inward to supply air, Fig. 362. — Section of a Simple Hydraulic Ram. is provided in many of these rams, as it improves the efficiency. The rate of opening of the waste valve or the number of pulsations in a given time can be varied by changing the weight on its stem. This apparatus is tested usually by measuring the supply and the discharge heads, the weight of water discharged through the delivery pipe Wi and that passing through the waste valve w 2 in pounds per minute. Then the available energy in the water is (wi + w 2 )h s , where h s is the supply head; and the useful work is Wih d , where h d is the discharge head, 1 then, Efficiency = 7 — * lhd . . , (131) (wi + w 2 ) h s and the capacity Q in gallons per twenty-four hours is Q = 1440 w x q, where q is the fraction of a gallon of water in a pound. Satisfactory runs of twenty minutes' duration can usually be made, each run being made 1 Both the supply and the discharge heads must be measured, of course, from the same datum or "zero" level. 426 POWER PLANT TESTING with a different lift or " stroke " of the waste valve B. Observations of the heads should be taken every five minutes if they are variable, and weighing as often as necessary, depending on the size of the tanks used. The effect on the efficiency of increasing the lift or " stroke " of the waste valve from one-eighth inch by increments of one-eighth inch is very interesting. Curves. Plot curves with length of " stroke " as abscissas and take for ordinates: (1) Efficiency; (2) Capacity in gallons per twenty-four hours; • (3) Strokes per minute. Fig. 363 shows a slightly different form of ram, as made commercially. The principle of operation is, however, the same as the one in Fig. 362. Letters used for marking the parts are the same in the two figures. Tests of Pulsometers. A type of steam pump called a pulsometer is illustrated in section in Fig. 365. In the form shown here it consists of Fig. 363. — Commercial Type of Hydraulic Ram. Fig. 365. — Steam Pulsometer. two chambers AA, joined by tapering necks into which a ball C is fitted so as to move in the direction of the least pressure between seats in these tapering passages. The chambers AA, on opposite sides, are connected by means of check or clack valves EE with the " induction " chamber D. Water is delivered through the passage H, which is connected "to the chambers through the valves G. Between the chambers is also a vacuum HYDRAULIC MACHINERY 427 chamber J, connecting them, with the " induction " chamber D. Small air valves, moving inward, supply air to the chambers AA by opening when the pressure is less than atmospheric. Its operation is explained briefly as follows: Starting with the left-hand chamber full of water and with a vacuum in the right-hand chamber, this latter chamber will fill with water which by its momentum due to rushing in suddenly, pushes back the valve C toward the left. Now during this time steam has entered the left-hand chamber to the left of the valve C (before it has shifted) and by exerting a pressure on the surface of the water it forces it through the check valve G, first into the delivery passage H and then into the air chamber J. Then the steam in this left-hand chamber con- denses in contact with the cold water and forms a vacuum, permitting the repetition of this cycle of events, except that the operations in the two chambers are reversed. Since all the steam used is condensed and discharged with the water lifted, the analysis of the operations in a pulsometer are similar to those in the familiar types of injectors, except that the steam acts in the pulsometer by pressure instead of by impact as in the injector. Using the following symbols: w a = weight of dry steam, pounds; w„, = weight of water lifted, pounds; ti = temperature of the water supply, deg. Fahr.; t 2 = temperature of the water delivered, deg. Fahr.; r = the latent head of evaporation of the steam in B.t.u.; t 8 = the temperature of the steam, deg. Fahr.; hi = the suction head, feet; h 2 = the delivery head, feet; hi + h 2 = the total head, feet, then w 8 (t 8 - t 2 + r) = w w (f 2 - ti) (132) The heat equivalent of the mechanical work done is in B.t.u., r^g (w»hi + (w. + w„) hi), and the heat expended is in B.t.u., w 8 (t s - t 2 + r), and Thennal Efficiency - £££ I*?* . • • (US) And if we neglect the work done in lifting the condensed steam, Efficiency = ^±^j d34) 428 POWER PLANT TESTING Curves. Plot with discharge pressures for abscissas curves with both thermal efficiency and capacity (gallons or pounds of water per twenty- four hours) as ordinates. Tests of Injectors. The injector is known particularly in stationary service as the device used for pumping water into the boiler when the ' feed-pump fails. One of the various forms of injectors sold commercially is shown in Fig. 366. The steam supply, the suc- tion or water supply, the delivery or discharge, and the overflow are marked clearly. Method of Operating Injec- tors. The method to be given, although applicable particularly to the ones described, is, how- ever, more or less generally ap- plicable to all makes. Open wide both the steam- and water-sup- ply (suction) valves. Then close the water-supply (suction) valve slowly until the overflow ceases. Regulate the rate of delivery by closing the water-supply (suc- tion) valve. Before testing an injector or indeed even before trying to operate a new injector, inspect the pipe fittings and particularly the valves on the water-supply pipe to observe whether they are tight. It is not at all unusual to find that the valve is not air-tight, and for this reason it is a very good prac- tice to put always some new wicking in the space for packing around the stem of the valve on the water-supply pipe; and turn up the cap over the packing tightly. Method of Testing. For the testing of injectors the arrangement of apparatus consists usually of two barrels supported on platform scales, or carefully calibrated tanks fitted with gage glasses. During a test the injector draws water from one barrel or tank and discharges it into the other. A test of an injector must be made, of course, with established conditions; that is, with a flying start. This may be accomplished by having the injector draw water from the supply tank, but discharge water through a by-pass connection on the discharge pipe until the test is to begin. For this preliminary operation of the injector the level in the supply tank can be maintained very closely, at any point marked by — Single Tube Steam Injector. HYDRAULIC MACHINERY 429 manipulating a " quick-opening " valve. When the test is to begin, close as quickly as possible this valve on the pipe discharging into the supply tank and turn the discharge from the by-pass into the delivery tank. To make this adjustment all the valves to be operated should be of the " quick-opening " type. The pressure against which the injector is to operate is secured by throttling the discharge pipe by means of a globe or an angle valve placed between the injector and the by-pass on the discharge pipe. The quick-opening valve would not be satisfactory. The suction head is measured from the middle of the injector to the average level of the water in the supply tank. The discharge head is obtained by adding to the head in feet corresponding to the pressure indicated by the gage the distance in feet from the center of the gage to a horizontal line through the middle of the injector. The temperatures of the water in the supply and delivery pipes must be observed. The injector is stopped at the end of the test by closing the steam valve. The following form, similar to the one used at Purdue University, is very complete. Notes explaining the calculations required are given above : Test of an Injector Make of injector Date Number Size of connections: steam in. dia.; water in. dia.; discharge in. dia.; area of discharge ( = a) sq. in. Diameter (minimum) of lifting tube in.; forcing tube in. a. Duration of test b. Steam pressure (average) pounds gage, p s c. Delivery pressure (average) pounds gage, p 2 d. Maximum pressure against which injector will discharge, p max e. Suction-head (average), feet, hi /. Delivery-head (average), feet, h 2 g. Temperature of supply (average) fa h. Temperature of delivery (average) fa i. Pounds water supplied per hour, w w j. Pounds water and steam delivered per hour, w m k. Cubic feet of water delivered per hour, Q 1. Wet steam per hour, w s ( = w m — w w ) m. Dry steam per hour, w' s ( = xw s ) n. Water delivered per pound wet steam, pounds ( = w w -f- w s ) o. Water delivered per pound dry steam, pounds ( = w w -f- w' s ) p. Velocity of discharge, feet per second, v ( = 144 Q -f- 3600 a) q. Energy delivered, raising injection water, B.t.u. per hour r. Energy delivered, heating injection water, B.t.u. per hour s. Energy delivered, velocity of discharge, B.t.u. per hour t. Total energy delivered, B.t.u. per hour u. Energy supplied, B.t.u. per hour v. Thermal efficiency as a boiler-feed apparatus w. Thermal efficiency as a pump 430 POWER PLANT TESTING x. Horse power y. Dry steam per horse power per hour, pounds The energy of raising injection water = [w w (hi -+- h 2 ) + w g h 2 ] -f- 778 B.t.u. per hour. The energy of heating injection water = w w (q 2 — qi) where qi and q 2 correspond to h and U B.t.u. per hour. The energy of discharge = w m v 2 -f- (2 g X 778) B.t.u. per hour. The total energy delivered = item q + item r + item s. The energy supplied = w s (xr s + q s — q 2 )i where r 3 and g s correspond to p 8 , and g 2 corresponds to t 2 . x = quality of steam. item t The thermal efficiency as a boiler feed apparatus = 100 X . ■ . itemu item q + item s The thermal efficiency as a pump = 100 X : — • item u rp, , Ww (h + h 2 ) + w s h 2 ^ 1 he horse power = (135) P 60 X 33,000 V *° The dry steam per horse power per hour = w 8 ' -J- item x. m , 1,000,000 + item p The pump duty = : item t 1,000,000 [w w (h + h 2 ) + w 8 h 2 ] 778w s (xr 3 +q a - q2 ) " " (I3 The weight of steam found by direct weighing may be checked, by calculating (assuming radiation loss negligible) a " heat balance " in which this weight will be the only unknown, thus for this condition, i r v 2 ~\ w s (xr s +q s -q 2 ) = ==g \w w (h 1 +h 2 )+w.h2+(w w + w,) ^-\ +w w (q 2 - qi), or, approximately, wjh 1 + h 2 + 778 ( ff , - ffl ) + ~ 1 778 (xr 3 + q a -q 2 )-h 2 ' ' ' ' ^ 37; CHAPTER XXIII TESTING THE STRENGTH OF MATERIALS Machines for Testing the Strength of Materials consist, in general, of (1) a power system for producing in the specimen tested the required stresses, and (2) a weighing system to determine the amount- of force applied. In the usual form of testing machine the load is applied to the specimen through a train of gears and screws operated either by power or by hand, depending, of course, largely on the capacity. The stress is measured by balancing the force exerted on the specimen by a poise adjusted at the end of a system of levers just as weight is determined with a platform scales. The general principle of most machines for testing materials is illustrated in a simple form in the apparatus for calibrating indicator springs, Fig. 120, page 116. In this case the power is applied to the hand wheel, which exerts two forces equal but opposite in direc- tion, one compressing the spring in the indicator and the other pressing on the platform of the scales. A diagrammatic view of a typical machine for testing materials in tension and compression is shown in Fig. 370. It consists essentially of a table T, to which the upper " head " A is rigidly attached by means of the vertical bars DD. Heavy vertical screws SS, carrying the lower cross-head B, are moved up or down by the system of gears GG. Moving the cross-head B downward puts a tensile stress on a test specimen s if it is attached firmly to both the upper " head " A and to the cross-head B. The force applied to the specimen is transmitted by the bars DD to the weighing table T, which rests on the first weighing lever M, having a fulcrum at F. The load on the table T is applied to the lever M at the middle of the table. The long arm of. this lever is connected by means of a short link to a second lever N, and this again is connected to the short arm of the lever Q at the other end of which the weighing poise P is to be balanced. The position of the poise on this last lever (scale beam) indicates the force applied to the specimen s. Fig. 371 is a remarkably good illustration for showing the parts of a standard testing machine and for explaining its operation. Vertical screws SS, connected by gearing to the power system, move the cross- head B up or down according to the direction of motion. The speed of these screws is controlled and their motion reversed by manipulation of the levers marked li, 1 2 , and 1 3 . The vertical columns supporting the upper " head " A are bolted to the table T, which rests on the system 431 432 POWER PLANT TESTING Fig. 370. — Diagram of a Simple Machine for Testing the Strength of Materials. Fig. 371. — Standard Testing Machine. TESTING THE STRENGTH OF MATERIALS 433 of levers M, N, and Q. The poise P is moved on the lever or scale- beam Q by means of a cord connected to the hand wheel W. The levers are balanced " to zero " by means of the counterpoise C. To prevent the sudden jarring of the machine when the load is released by the breaking of a specimen, vertical rods fastened to the base pass up loosely through holes in the table T, at its four corners, and on their ends large " check-nuts " are screwed. When the machine is in use these nuts must be loose, otherwise they will cause a pressure on the table causing the indication of the scale-beam to be greater than the weight due to the load on the specimen. Small testing machines with a capacity not exceeding 50,000 pounds are made to operate by hydraulic pressure. In this type of machine the movable head applying the load to the specimen is moved by the pressure on a piston in a hydraulic cylinder. This hydraulic pressure is produced usually in a small hand-operated pump at the side of the machine. Oil is generally used for the working medium. In order to return the oil to the pump from the cylinder, when the pressure is to be released, a small check valve controlled by a lever or a screw is usually provided. Machines operating hydraulically are not satisfactory for large loads, because the leakage from the cylinder is likely to be ex- cessive. When a specimen is to be tested in tension its upper end is fastened into the wedges or " jaws " in the upper " head " and its lower end is similarly gripped in the lower or movable cross-head. For tests in compression the specimen is placed between the movable cross-head and the table. Transverse loads can be applied to long wooden or metal beams with the machine shown in Fig. 371, by placing the beam between the supports or abutments UU', and applying the load by means of the movable cross-head B. Usually a special fitting with a blunt but " definable " edge to localize the load is inserted into the cross- head B for such tests. Extensometers. Some of the physical properties of materials are determined by the rate of deformation of the specimen as the stress is applied. To measure the deformation some very accurate instru- ments have been devised, one of which is shown in Fig. 372. It consists essentially of a pair of clamps CC, fitted with sharp-pointed thumb- screws for attaching them to the specimen SS. Two rods B and B', fitted to the upper clamp on opposite sides of the specimen, are pro- vided at their lower ends with adjustable points to be screwed up or down by means of the small milled wheels W and W. Opposite these rods and fastened to the lower clamp are two micrometer screws, usually graduated to ten-thousandths of an inch, for measuring the elongation of the specimen. Electrical connections are made, as shown, with a 434 POWER PLANT TESTING battery and a bell. As the specimen stretches out the contact points at P and P' are moved apart and the distance the micrometer screws are raised measures the elongation. With the help of the bell it is possible to make, for all observations, uniformly light con- tacts. Deflectometer. A very simple device for measuring the deflection of beams is shown in Fig. 373, consisting of a plate P sup- ported upon a steel bar attached to the end supports UU\ Deflections can be meas- ured with this apparatus with the aid of ordinary " inside " calipers, micrometer cal- ipers, or with a special deflectometer. This instrument illustrated in Fig. 374, is often used to measure the deflection of wooden and metal beams subjected to transverse stress. It can also be used with success to measure the contraction of short specimens in compression. Physical Properties of Materials Defined. The elastic limit is a more or less definite value of the unit stress beyond which, as the stress is increased, the increase in deformation is greater relatively than the increase in stress; and further, at this point, the deformations produced will not disappear entirely when the stress is removed. Per- manent set or "set" is used to represent the lasting deformations pro- duced by stresses greater than the elastic limit. Fig. 372. — Extensometer. 3^? Fig. 373. — Simple Device for Measuring the Deflection of Beams. Modulus of Elasticity is a term used to express the ratio of the unit stress to the deformation per unit of length 1 accompanying that stress, within the elastic limit. For example, if f is the stress in pounds per square inch within the elastic limit and s is the accompanying defor- 1 This unit deformation is often called the unit elongation for slender test-pieces, and more generally the strain. TESTING THE STRENGTH OF MATERIALS 435 mation per inch of length in inches, then the modulus of elasticity, in pounds per square inch, is E = f/s (140) The total stress under which a body fails is called its ultimate strength ; and the corresponding unit stress is called the ultimate unit strength, or, for short, simply the ultimate strength. The ratio of the total elongation of a body to its original length is called the percentage of elongation. It is obviously the same as the term unit deformation. For calculations of percentage of elongation measurements are taken, according to convention, between two gage marks usually 8 inches apart. This percentage of elongation is a measure of the ductility of the material tested. The ratio of the smallest area after rupture to the original area is called the " reduction of cross-section." Fig. 374. — Deflectometer. Resilience, often called the modulus of resilience, is a term used to represent the potential energy stored in a body; or, from another viewpoint, it is the amount of work that can be done by the body when relieved from a state of stress. More specifically, however, it is taken to mean in practice the work, in foot-pounds, done on a cubic inch of a material in stressing it to the elastic limit. For any value of the load the resilience is equal to the product of half the stress in pounds per square inch at the elastic limit times the distortion (usually the elonga- tion) of the test-piece in feet per inch of length up to the elastic limit, the latter term being the space passed through. Values of resilience calculated as thus defined may be checked by comparing with the square of the unit stress at the elastic limit divided by 24 times the value of the modulus of elasticity (E). Forms of Test-pieces for Tension Tests. Specimens for testing should be prepared with a great deal of care. Standard form for tests of flat bars 1 as well as for " coupons " cut from plates and structural shapes in tension is shown in Fig. 375. On such test-pieces marks one inch apart are usually made between the limits of the so-called gage length 1 Adopted by American Society for Testing Material (1909). 436 POWER PLANT TESTING which is generally 8 inches. A standard scale similar to the one in Fig. 377 is of great assistance in marking a test-piece. At the left- hand end a percentage scale is shown from which the percentage of Parallel Section- not less than 9" "~ About VL^fiJtf' Radius LJ_L 1 ■W-H W Lbijrat %'' Piece to be same thickness as plate Fig. 375. — Standard Flat Bar for Tension Tests. elongation, in a length of 8 inches, can be read directly. For testing round bars a shape shown in Fig. 376 is sometimes used, making the middle portion f inch in diameter. A special test piece of circular section only two inches long between the fillets where it is J inch in diameter Not less than 1 to 3 mad. Fig. 376. — Round Bar sometimes used for Tension Tests. is more generally recommended. The enlarged ends are f inch in diameter and have screw threads turned on them. Machine work on specimens for testing should be done carefully, so that the material is not torn or weakened in other ways. If there is 40 S illinlimlim 8 7 e 5 4 3 2 1 jvi^jvr\jvj\jvr\J Fig. 377. — Scale for Marking Test-pieces. any flaw, marked irregularity or other defect in the material, the test- piece should be rejected. After a test-piece has been " necked " and broken as shown in Fig. 378, the accurate measurement of the elonga- tion is sometimes difficult. One method is to measure the elongation A 1 a 3 4 5 6 7 Fig. 378. — Test-piece after Rupture. from the point of rupture toward each end. In materials in which the " necking " effect is very marked the measured amount of elongation will vary according to the distance of the fracture from the gage marks TESTING THE STRENGTH OF MATERIALS 437 A and B. If the fracture is midway between these marks then nearly all the elongation will be between these marks ; but if the fracture is near one of the gage marks then a great deal of the elongation will fall outside of the marks, so that the measured elongation is too small. To correct for these discrepancies mentioned, a so-called " equivalent elongation " may be calculated by the following method: Assume that the standard test-piece, Fig. 375, has been divided originally into 8 equal spaces between the gage marks A and B, and that the nearest number of spaces between the points of fracture (Fig. 378) and the nearer gage mark is 3. The method may be stated that if the length between gage marks has been divided into x equal spaces and y is the nearest number of these spaces on the shorter portion between the point of rupture and the gage mark, then mark two points M and N on the longer portion, which are y and 1/2 x spaces, respectively, from the fracture. Place the two portions of the specimen as closely together as possible and measure from the gage mark in the short portion to the mark M. This distance, added to double the distance from M to N, gives the required total length after rupture. In this way the elongation of the " standard " length (x spaces) will be obtained, as if the fracture had occurred midway between the gage marks. To illustrate by the figure, there are 3 spaces on the shorter portion between the point of rupture and the gage mark B. The term y as defined above is therefore 3. Then the total length to be compared with the original is to be measured on the broken test-piece from 2 to B, corresponding to 6 spaces, plus twice the distance from 1 to 2, corresponding to the remaining 2 spaces to be accounted for. Specifications are often made to require that the fracture shall be within the " middle third of the length." Detailed Method for Tension Tests. A standard test-piece to be tested in tension should be without flaws or cracks, and furthermore the material should be monogeneous. Before putting it into the testing machine it should be carefully measured. With a scriber scratch the marks indicating one-inch divisions should be made with the " laying- off " gage. (Fig. 377.) Very light punch marks may then be made at each of the division marks accurately along the axis of the bar. 1 At each of these punch marks the diameter of the cross-section should be carefully measured with a micrometer caliper to thousandths of an inch. The outside punch marks, called the " gage marks," are often made a little heavier than the others, so that if an extensometer of the type illustrated 1 Punch marks can be made accurately along the axis of a round bar by putting them at the "scratch" marks made with a scriber an inch apart along the length of the test-piece on the reflection of a "beam of light" on the bright surface of the test- piece. 438 POWER PLANT TESTING in Fig. 372 is used, one of the thumbscrews supporting the clamps at each end can be set accurately but lightly into these marks. In this position the extensometer will measure accurately the elongation of the specimen between the gage marks. The testing machine to be used should then be balanced by adjusting the counterpoise provided for this purpose. It should be observed also that the " check-nuts " rest loosely on the table. As the load is increased, however, these nuts should be screwed down a little from time to time so that if the load is suddenly removed when the test-piece breaks, or should happen to slip out of the jaws or wedges holding it in place, the jar on the machine will be very much relieved. After balancing the machine the test-piece should be placed carefully and vertically between the " jaws " or wedges in both the upper and lower heads, and the extensometer should be put in position if one is to be used. Start the machine at a low rate of speed until a load of about 1000 to 2000 pounds is indicated before taking any measurements of elongation. This first load is applied for the purpose of permitting the test-piece to assume a true central position, to allow for some slight slipping of the test-piece in the jaws before it becomes firmly gripped, and also to allow for possible irregularity in the adjustment of the extens- ometer or similar auxiliary apparatus. After this light load has been reached, during which time, doubtless for the kind of materials ordinarily tested, there will have been only a very small elongation, the load should be applied continuously and uniformly until the test-piece breaks, stop- ping only long enough, at the required intervals, to make the necessary observations of elongation and change of shape of the cross-section when " necking " begins. Increments of load are usually determined by taking one-tenth 1 the product obtained by multiplying the approximate esti- mated elastic limit of the material in pounds per square inch by the area of the cross-section in square inches. Near the elastic limit it is often found desirable to take observations at intervals of 500 pounds up to the yield point, where suddenly the rate of elongation increases very rapidly. By taking these observations at very close intervals at the elastic limit, data are secured which make the curves to be plotted much more satisfactory. In a standard test the stress, that is, the load, must never be decreased any appreciable amount when it is intended to apply still larger loads. A stress once applied must be maintained or increased continuously until the end of the test. Extensometers or other apparatus of delicate construction used for measuring the elongation should be removed 1 In practice the increments of load in commercial tests are often one-half or one- third of the load at the elastic limit. For laboratory investigations it is not unusual to make the increments as small as one-twentieth of this load. TESTING THE STRENGTH OF MATERIALS 439 from the test-piece before the specimen is broken. It is customary to take off such apparatuses just after the elastic limit is reached, although, as a rule, they can be left in place relatively longer for materials that are ductile than for those that are hard and brittle. Micrometers used on extensometers provided with electrical connections are to be set for readings on one side at a time, advancing the screw device until the bell rings, indicating that the contact has been made. Then turn it back just enough to stop the ringing of the bell, and advance the screw on the other side until the bell rings again. After also turning back the microm- eter screws just enough to stop the ringing, observations should be taken on both micrometers. Considerable time can be saved if, while these observations are being taken, the attendant having charge of the machine is meanwhile slowly advancing the load. The scale beam should be kept " floating " at all times during a test. Never run the balancing poise out on the scale beam beyond the point necessary to balance the beam. If the scale beam is carefully kept " floating " a point will be observed at from 50 to 75 per cent of the maximum load where the scale beam will fall, indicating apparently that it has been advanced too far. This point is called the yield point. It is defined as the stress at which the rate of elongation suddenly and rapidly increases. Beyond the elastic limit, when the extensometer has been removed, the rate of elongation can be measured with considerable accuracy by means of a large machinist's dividers, with the points set accurately on the " gage marks " at the ends of the standard length. The load when rupture occurs is not usually the maximum. When, therefore, considerable "necking" effect is observed, the poise on the. scale beam should be watched closely and when the maximum load has been reached, indicated by the falling of the scale beam, this weight should be quickly observed and recorded and then the poise should be brought back to follow the decreasing load. It will be observed that this part of the work is very interesting if it is done carefully. After the test-piece has been broken, stop the machine, remove the test-piece, clean and return the jaws or wedges to their proper places, and leave the machine in good order. The broken ends of the test-piece should be joined carefully and the length between each of the marks which were originally one inch apart should be measured. Check the sum of these lengths with the over-all length between the gage marks. With a micrometer, or preferably a vernier caliper, measure as accurately as possible the diameter of the smallest area at the fracture. The fracture should be carefully exam- ined to observe whether it is fibrous, granular or crystalline; whether coarse, fine or " silky;" whether cup-shaped, half-cup, or irregular in shape. 440 POWER PLANT TESTING Curves and Calculations. Plot a curve with elongation per inch of length (" strain ") as abscissas and stress in pounds per square inch as ordinates. This is the familiar " stress-strain " diagram. Determine from the data obtained the modulus of elasticity (E), 1 the elastic limit, the maximum stress, the ultimate stress, per cent elongation in 8 inches, percentage elongation in 2 inches at the fracture, and per- centage reduction in area at the fracture. Plot a curve of elongation per inch, using for abscissas 2 the original length in inches and for ordinates the elongations measured for each inch between the gage marks. Report op Tension Tests 1. Date and names of observers 2. Material to be tested — specification 3. Makers and brand of material 4. Length between principal punch marks, before test 5. Length between principal punch marks, after test 6. Average width of test-piece, before test (6 readings) 7. Average width of test-piece, after test (6 readings) 8. Average thickness of test-piece, before test (9 readings) 9. Average thickness of test-piece after test (6 readings) Readings to be taken, for observations 10 and 11 for increments of 2000 lbs. on scale beam until an elongation of 0.40 in. is obtained between readings and then by increments of 1000 lbs. until elongation of 0.03 in. is obtained between readings, and finally by 500 lbs. until piece nears point of maximum strength, when readings should be taken as frequently as possible, keeping beam balanced all the time. 10. Total pull in pounds as shown by the machine 11. Corresponding total elongation in piece in inches 12. Yield point, pounds total (elastic limit) 13. Maximum load, pounds total 14. Breaking load, pounds total • 15. Character of fracture, description and sketch The following results are to be computed: 16. Original cross-section, sq. in 17. Final cross-section, sq. in 18. Reduction in area in sq. in., and in per cent of original area 19. Final elongation, total and per cent 20. Stress (pounds per square inch of original area) at elastic limit, maximum load and breaking load. y_ J The modulus of elasticity can be determined also from the " stress-strain " dia- gram by calculating the value of the tangent for the angle between a line drawn through the origin parallel to the straight part of " stress-strain " curve, reading the scales of coordinates, of course, in the units of stress and elongation marked on the diagram. It is obvious that the value of the tangent of the angle in this case is the unit stress divided by the unit elongation, which is, by definition, the modulus of elasticity. 2 If on the curve sheet the " inch marks" on the test-piece are indicated by equal divisions on the scale of abscissas, then the points showing elongation for each inch should be plotted midway between the division lines indicating the position of the " inch marks." TESTING THE STRENGTH OF MATERIALS 441 Tests in Compression. When a specimen of which the length is less than five times the smallest dimension is subjected to a load producing compression, it fails usually by crushing. Longer specimens fail usually by bending toward the side of least resistance. Two general classes of materials are frequently tested in compression: (1) Brittle materials, like brick, stone, wood, cement, cast iron, etc., which fail usually by shearing, and (2) plastic materials, like soft steel, wrought iron, copper, etc., which fail usually by a " flowing " of the metal. Because of the difficulty in measuring the deformations of short specimens of the plastic materials, and because the elastic limit in tension is invariably practically the same as in compression, these plastic materials are not often subjected to compressive loads. Methods to be explained here apply, therefore, par- ticularly to materials like wood, brick, stone, and cast iron. Detailed Method for Compression Tests of Short Test-pieces. Speci- mens of stone, cement, wood, or brick, of which the length is less than five times the smallest dimension, are usually provided in forms approximately cubes, although brick and wood are as often tested in the form of parallelo- pipeds similar to ordinary commercial bricks. Bearing surfaces, of specimens of stone, brick and cement should be made as nearly flat and parallel as possible, and should then be covered with a thin layer of plaster of Paris. Sized paper in thin sheets should be placed on the bearing surfaces between the specimen and the plaster to prevent the absorption of water from the latter. In order to have the plaster set in a true surface the specimen is placed between the " heads " of the testing machine for about ten minutes after the movable cross-head (B, Fig. 371) has been lowered to press lightly on the plaster. For tests in compression the test-piece is placed on the table T and the load is applied by lowering the movable cross-head B. Dimensions of test-pieces must be carefully measured and recorded before they are put into the testing machine; and, if any of them require the' application of plaster of Paris, then the measurements must be made before the plaster is put on. After balancing the testing machine by means of the counterweight with the test-piece on the table, apply the load continuously until the specimen is fractured; or in the case of plastic materials until the deformation is quite noticeable. In general conduct the test in the same way as for tension, 1 except that the specimen is 1 Measurements of the amount of compression (shortening) of the test-piece can- not be made directly, but must be made between points on the heads of the testing machine. If there is likely to be much yielding of the parts of the machine, the mov- ing head should be lowered until its steel "compression plate" presses on the correspond- ing steel block on the table or lower platform with a force of about 1000 pounds. Now measure with micrometers the distance between the points on the two heads used for compression measurements, first with the load of 1000 pounds and then with additional increments of 1000 pounds up to considerably above the breaking load of the material 442 POWER PLANT TESTING compressed instead of being stretched. If the material tested is cast iron or even hard stone or brick, precautions must be taken to protect persons near the machine from flying fragments. If the specimen begins to spall or flake off before it breaks down, the load corresponding as well as similar information should be recorded and placed in the tabulated report under " Remarks." Usually the specimen breaks down suddenly and the interior cone or pyramid in stone, brick, cement and cast iron will be plainly seen if the load has been " fairly " applied. In the case of tests of wood, this phenomenon will not be observed, but the lines of cleavage will usually show clearly a constant angle of shearing. Detailed Method of Compression Tests of Long Pieces (Columns). When the length of a specimen to be tested in compression is greater than, at the most, ten times its least dimension, it fails invariably by bending toward the side of least resistance. The condition of the ends of such test-pieces should be as nearly as possible either fixed or per- fectly free to turn. Either condition is, however, difficult to obtain. For test-pieces from 15 to 20 inches long usually an extensometer may be connected up to read the compression or shortening of the test-piece, if it is desired. 1 The observations will be taken in the same general way as for tension tests except that now the micrometer screws on the exten- someter will approach each other, so that these screws must be turned back after taking a measurement by an amount greater than the compression that will be produced by the next increment of load. Report on Compression Tests 1. Date and names of observers 2. Kind of material 3. Average thickness of test-piece (4 readings), inches 4. Average width of test-piece (4 readings), inches The machine is to be started and kept running continuously until fracture takes place, the beam being kept balanced carefully all the time. Readings are to be taken, and calculations made therefrom as follows: In making these tests wood and brick will be used and two pieces of each kind are to be tested, with each kind of stress. to be tested. From these data a correction curve should be plotted with which to cor- rect the deflections observed when the specimen is tested. When blocks of wood are to be tested in compression, readings of the micrometers should not be taken until a pressure of from 500 to 1000 pounds per square inch has been applied. This load will be required to crush the rough fibers. 1 The lateral deflection along the neutral plane is sometimes determined by stretch- ing a fine wire along the length of the specimen parallel to the neutral axis. TESTING THE STRENGTH OF MATERIALS 443 White Pine. Yellow Pine. 1 2 1 2 * 2 Scale reading in pounds at time of fracture. Cross-section from items 3 and 4, square Breaking stress lbs. per square inch for Average breaking stress for each kind of Modulus of elasticity, lbs. per square inch. . . Sketches, Curves and Calculations. Sketch the character of the fracture for each specimen tested, indicating, for wood, the direction of Fig. 379. — Machine for Transverse Tests. the grain. Previously, the original shape of the specimen should have been sketched and dimensioned, 444 POWER PLANT TESTING Calculate the maximum unit stress. If the material was suitable for the measurement of compression, plot " stress-strain " diagrams, and calculate the modulus of elasticity. Transverse Bending Tests. The most .common test by transverse or cross-bending is that of a beam usually of either wood or steel, of which the coefficient of elasticity and the " elastic curve " are desired. Deflec- tions of such beams give the data needed. Such tests may be made with a testing machine like the one shown in Fig. 371, which is provided with supporting abutments marked in the figure UU', and by inserting into the movable head the attachment for applying the load along a line across the beam rather than on a comparatively large area as in the tests already described when the load was applied directly by the flat surface of the cross-head B. Special transverse testing machines are, however, some- times available. A machine of this kind is illustrated in Fig. 379. In the Case of a wooden beam to be tested by loading at the middle, a fine steel wire should be stretched between two pins located as accu- rately as possible above the points of support and on the line of inter- section of the neutral plane with the side of the beam. The wire should be fastened to one of these pins and allowed to hang over the other, being kept taut by means of a weight attached to the free end, Fig. 380. -- - u I] u Fig. 380. — Device for Measuring the Deflection of a Wooden Beam. A steel scale, preferably highly polished so that it will show the image of the wire, should be attached in any suitable way to the side of the beam, so that the edge along which the scale readings to be observed are marked will be exactly half-way between the two supports. The beam must be protected from indentation by the knife-edges by small bearing plates. The load should be applied centrally in increments to give approximately 5^ inch deflections to the elastic limit, and beyond to give deflections of approximately ^ inch If it can be done succes- sively, the deflections should be read without stopping the test; unless, of course, the permanent set is to be determined, when after each incre- ment, the beam must be released from its load. Curves and Calculations. Plot a curve taking the load applied in pounds for abscissas and deflections in inches for ordinates. Sketch the character of the fracture. TESTING THE STRENGTH OF MATERIALS 445 Calculate the modulus of elasticity, 1 the modulus of rupture, and the stress in the outer fiber at the elastic limit from the curve. Torsion Tests are made to determine the strength of a material to resist twisting forces. A typical machine for such tests is illustrated in Fig. 381. It consists in its essential parts of the frame FF', the " jaw " heads A and B for gripping the rod R to be tested, and the system of weighing levers on which the poise P is balanced. The load is applied to the rod R by power through the gears shown connected to the head B. Fig. 381. — Torsion Testing Machine. The power is applied by means of the pulley and gears shown at the right-hand side, or may be applied by hand power by turning hand wheels. With hand power usually more satisfactory results can be obtained than with power applied mechanically, because the rate of twisting can be more closely regulated. The amount of twist or the 1 The modulus of elasticity is calculated by the formula E=^ (-4-) 48 dl The modulus of rupture from . w M lc U = — - , (142) 4 1 and the stress in the outer fiber at the elastic limit by w e lc . . fe=— ~, (143) 4 1 when w e = load at the elastic limit in pounds per square inch; w u = load at the point of rupture in pounds per square inch; 1 = length of beam (span) in inches; d = deflection in inches; c = distance from the neutral axis to the outer fiber in inches; I = moment of inertia, inch (4th power) units. 446 POWER PLANT TESTING angular deformation is indicated by index-arms connected to opposite ends of the test-piece. 1 An autographic torsion testing machine operated by hand power by means of the crank is sometimes used. The movement of the crank tends to rotate the test-piece which at the opposite end of the machine is fastened to a pendulum carrying a heavy bob. The resistance of the pendulum and its weight measure the power applied, which is equal to the length of the lever arm times the sine of the angle of inclination times the constant weight of the bob. Tests are made usually by increasing the twisting moment by incre- ments of about 200 inch-pounds, 1 measuring for each increment the torsion angle. Curves and Calculations. Plot a curve, using torsion angle for abscissas and twisting moment for ordinates. Calculate from this curve the unit stresses 2 (shearing) at the elastic limit, at the point of rupture, and also the maximum value of stress. Determine the torsion angle at the elastic limit and at the point of rupture, the helix angles, 3 and the modulus of elasticity for torsion. 4 Impact Tests. Materials are tested by impact, usually by striking a test-piece with a weight allowed to fall upon it. Metals used in the manufacture of machinery and in railroad construction where it is likely to be subjected to shocks and blows are in many cases tested to determine the effect of the impact due to a blow. Some testing machines for such tests are made like a pile-driver with 1 If tests are made of large sections of high-grade material, like, for example, a shaft of nickel steel for a students' class, it is expensive to break many specimens, so that for this reason the twisting moment producing a maximum stress just inside the elastic limit is computed before making the test, and this value is not to be exceeded. 2 The unit stress is calculated with the formula: M/f, = V c, or f s = Mc/I p , (144) where M is the torsional moment in inch-pounds, c is distance in inches from the neutral axis to the extreme fiber, and I p is the polar moment of inertia. When c = r (the radius) as in the case of a cylindrical test-piece, I p = \ xt 4 . 3 Torsion produces a peculiar arrangement of the outer fibers in the form of helices, as observed in broken test-pieces. Each one of these fibers makes an angle with its original position equal to its angular distortion a. Any particle on the surface is also moved through an angle /?, having its vertex in the axis and in a plane perpendicular to the axis. Now if we neglect the functions of small angles, we can write approxi- mately la = r/3, where 1 is the effective length of the test-piece and r is the radius. The helix-angle a = r/3/1. 4 The modulus of elasticity in torsion (" modulus of rigidity "), E a = f s 4- a, as above, then E « = ^ (I45) TESTING THE STRENGTH OF MATERIALS 447 the weight dropping vertically from a sort of gallows upon the test- piece. A more common form, however, of such machines consists of a pendulum provided with a heavy bob intended for delivering a blow on the middle of a test-piece in the shape of a bar, preferably" of a rect- angular section, held on two knife-edge supports attached to a heavy bedplate. Such machines are particularly designed for comparative tests of cast iron. They are provided with an arc concentric with the movement of the bob of the pendulum, graduated to read the verti- cal fall of the bob in feet. A tripping device is attached to the side of the graduated arc for permitting the bob to be supported and then dropped from any height within the limits of the machine. Since the deflection is very small, a device is usually supplied for magnifying it, and by means of a pencil-point traveling over a chart an autographic record is made of the deflections for each blow delivered by the bob. With such instruments the rebound of the test-piece and its permanent set must be carefully excluded from the measured deflection. One way to do this is to draw a " zero line " with the test-piece in place but before a blow is struck. Deflections and permanent set will then be measured on one side of this line and " rebounds " on the other. To determine the center load to be applied that will be equivalent to the impact, the following symbols are used : Let Wi = weight of the bob in pounds; h = the vertical distance it falls, in feet; W2 = the equivalent maximum center load, in pounds and d = the deflection in feet, then w x h = \ w 2 d, 2Wih . ,. w 2 =— ^— (146) With this valve of w 2 the usual properties of the material may be calcu- lated by formulas (141), (142) and (143), page 445. Cement Tests. Cements are tested usually for (1) fineness; (2) time required for " setting " ; (3) tensile strength; (4) specific gravity; (5) sound- ness or freedom from cracks after setting; (6) crushing strength; and (7) toughness or ability to resist blows. Tests for crushing strength (com- pression) are usually made by crushing cubical blocks in a testing machine designed for general tension and compression tests (see page 432). For tensile tests, however, special machines, designed particularly for testing cement, are generally used. Because of the nature of the material it is absolutely necessary that the power be applied in the line of the axis of the test-piece and also with steadiness and in increments as uniform as possible. There is a standard size and shape for test- pieces of cement, and they must be made in a certain prescribed way 448 POWER PLANT TESTING Fig. 385. — Standard Cement Briquette. in order that different tests may be compared. The standard briquette for testing (one square inch section) is shown in Fig. 385. The strength of the briquettes is affected by the time allowed for hardening, the amount of water used, and by the method of mix- ing the cement. Power is applied in the automatic cement-testing machine in Fig. 387, by shot dropped from a cylindrical hopper into a pail supported on a scales. The briquette of cement being tested is held between two shackles or "holders" con- nected to a hand wheel used to regulate the distance between the shackles. When a briquette breaks the scale beam drops, and closes automatically a valve, stop- ping the delivery of shot into the pail. The operation of the machine may be described briefly as follows: Hang the hopper on the hook as shown and put enough shot into it to balance the coun- terpoise. Now put the briquette into the shackles and adjust the hand wheel so that the scale beam will rise nearly to the stop. When the valve is opened shot will begin to fall into the pail. The delivery of the shot into the pail should be slow. When the briquette has broken, the scale beam has dropped and the valve has been closed. The weight of shot collected in the pail shows the number of pounds required to break the briquette. A non-automatic type of cement-testing machine is illustrated in Fig. 388. In this machine the power is applied by moving a hand wheel operating by means of a screw the system of levers transmitting the load to the briquette in the shackles. The tension produced by this load may obviously be balanced by weights applied to the scale beam above. In order to secure a very uniform and slow movement of the poise it is carried along the scale beam by a cord moved by a small crank. In applying the load the hand wheel should be moved as slowly and uni- formly as possible to avoid a jerking motion. In the figure one of the standard briquette moulds, and a tray used for immersing the briquettes in water after they have set are shown. Fig. 389 shows the proper position of the briquette in the supporting shackles. Test of Cement for Fineness is made by determining the amount by weight of a given sample that will not pass through sieves with meshes of a standard size. The American Society of Civil Engineers recommends the use of sieves of 2500, 5476 and 10,000 meshes per square inch. Sieves TESTING THE STRENGTH OF MATERIALS 449 with approximately these meshings are known as Nos. 50, 80, and 100; that is, they have this number of meshes to the linear inch. A weighed sample of cement is first passed through a No. 50 sieve and the weight of that remaining in the sieve is recorded. That passing through is then put into the next sieve (No. 80) and the residue in this sieve is likewise weighed, while that passing through goes to the finest sieve (No. 100). Fig. 387. — Automatic Cement Testing Machine. Results of this test for fineness are expressed by the percentages that the various residues remaining in the sieves are of the original weight of the sample. Unless cement is ground as fine as flour it has very little " binding power." The coarse particles are nearly as inert for " cementing " as sand. Throughout America generally the following methods for testing cement adopted by the American Society of Civil Engineers in 1903 and 1904 and revised in January, 1909, are used; 450 POWER PLANT TESTING Selection of Sample. The selection of the sample for testing is a detail that must be left to the discretion of the engineer ; the number and the quantity to be taken from each package will depend largely on the importance of the work, the number of tests to be made and the facilities for making them. Fig. 388. — Hand-operated Cement Testing Machine. The sample shall be a fair average of the contents of the package ; it is recommended that, where conditions permit, one barrel in every ten be sampled. Samples should be passed through a sieve having twenty meshes per linear inch, in order to break up lumps and remove foreign material; this is also a very effective method for mixing them together in order to obtain an average. Method of Sampling. Cement in barrels should be sampled through a hole made in the center of one of the staves, midway between the heads, TESTING THE STRENGTH OF MATERIALS 451 or in the head, by means of an auger or a sampling iron similar to that used by sugar inspectors. If in bags, it should be taken from surface to center. Chemical Analysis. As a method to be followed for the analysis of cement, that proposed by the Committee on Uniformity in the Analysis of Materials for the Portland Cement Industry, of the New York Section of the Society for Chemical Industry, and published in Engineering News, Vol. 50, p. 60, 1903, is recommended. Specific Gravity. The specific gravity of cement is lowered by adult- eration and hydration; but the adulteration must be in considerable quantity to affect the results appreciably. Inasmuch as the differences in specific gravity are usually very small, great care must be exercised in making the determination. The determination of specific gravity is most conveniently made with Le Chatelier's apparatus. This consists of a flask (D), Fig. 390, of 120 cu. cm. (7.32 cu. in.) capacity, the neck of which is about 20 cm. bW Fig. 389. — Briquette in Shackles. Fig. 390. — Le Chatelier'i Specific Gravity Flask. (7.87 in.) long; in the middle of this neck is a bulb (C), above and below which are two marks (F) and (E); the volume between these marks is 20 cu. cm. (1.22 cu. in.) The neck has a diameter of about 9 mm. (0.35 in.), and is graduated into tenths of cubic centimeters above the mark (F). Benzine (62° Baume naphtha), or kerosene free from water, should be used in making the determination. Specific gravity can be determined in two ways : (1) The flask is filled with either of these liquids to the lower mark (E), and 64 grams (2.25 oz.) of powder, cooled to the temperature of the liquid, is gradually introduced through the funnel (B) [the stem of which extends into the flask to the top of the bulb (C)], until the upper mark 452 POWER PLANT TESTING (F) is reached. The difference in weight between the cement remaining and the original quantity (64 g.) is the weight which has displaced 20 cu. cm. (2) The whole quantity of the powder is introduced, and the level of the liquid rises to some division of the graduated neck. This reading plus 20 cu. cm. is the volume displaced by 64 g. of the powder. The specific gravity is then obtained from the formula: q -f, n •+ _ Weight of Cement, in grams Displaced Volume, in cubic centimeters The flask during the operation is kept immersed in water in a jar (A), in order to avoid variations in the temperature of the liquid. The results should agree within 0.01. The determination of specific gravity should be made on the cement as received;, and, should it fall below 3.10, a second determination should be made on the sample ignited at a low red heat. A convenient method for cleaning the apparatus is as follows: The flask is inverted over a large vessel, preferably a glass jar, and shaken vertically until the liquid starts to flow freely; it is then held still in a ver- tical position until empty; the remaining traces of cement can be re- moved in a similar manner by pouring into the flask a small quantity of clean liquid and repeating the operation. Fineness. It is generally accepted that the coarser particles in cement are practically inert, and it is only the extremely fine powder that possesses adhesive or cementing qualities. The more finely cement is pulverized, all other conditions being the same, the more sand it will carry and produce a mortar of a given strength. The degree of final pulverization which the cement receives at the place of manufacture is ascertained by measuring the residue retained on certain sieves. Those known as the No. 100 and No. 200 sieves are recommended for this purpose. The sieves should be circular, about 20 cm. (7.87 in.) in diameter, 6 cm. (2.36 in.) high, and provided with a pan 5 cm. (1.97 in.) deep, and a cover. The wire cloth should be of brass wire having the following diameters: No. 100, 0.0045 in.; No. 200, 0.0024 in. This cloth should be mounted on the frames without distortion; the mesh should be regular in spacing and be within the following limits: No. 100, 96 to 100 meshes to the linear inch; No. 200, 188 to 200 meshes to the linear inch. Fifty grams (1.76 oz.) or 100 grams (3.52 oz.) should be used for the test, and dried at a temperature of 100 deg. Cent. (212 deg. Fahr.) prior to sieving. The thoroughly dried and coarsely screened sample is weighed and placed on the No. 200 sieve, which, with pan and cover attached, is held in one hand in a slightly inclined position, and moved forward TESTING THE STRENGTH OF MATERIALS 453 and backward, at the same time striking the side gently with the palm of the other hand, at the rate of about 200 strokes per minute. The operation is continued until not more than one-tenth of 1 per cent passes through after one minute of continuous sieving. The residue is weighed, then placed on the No. 100 sieve and the operation repeated. The work may be expedited by placing in the sieve a small quantity of steel shot. The results should be reported to the nearest tenth of 1 per cent. Normal Consistency. The use of a proper percentage of water in making the pastes 1 from which pats, tests of setting, and briquettes are made, is exceedingly important, and affects vitally the results ob- tained. The determination consists in measuring the amount of water required to reduce the cement to a given state of plasticity, or to what is usually designated as the normal consistency. Method, Vicat Needle Apparatus. — This consists of a frame (K), Fig. 391, bearing a movable rod (L), with the cap (A) at one end, and at the other a cylinder 1 cm. (0.39 in.) in diam- eter, the cap, rod and cylinder weighing 300 grams (10.58 oz.). The rod, which can be held in any desired position by a screw (F) carries an indicator, which moves over a scale (graduated to centimeters) attached to the frame (K). The paste is held by a conical, hard-rubber ring (I), 7 cm. (2.76 in.) in diam- eter at the base, 4 cm. (1.57 in.) high, resting on a glass plate (J), about 10 cm. (3.94 in.) square. In making the determination the same quan- tity of cement as will be subsequently used for each batch in making the briquettes, but not less than 500 grams, is kneaded into a paste, as described, and quickly formed into a ball with the hands, completing the operation by tossing it six times from one hand to the other, maintained 6 inches apart; the ball is then pressed into the rubber ring, through the larger opening, smoothed off, and placed (on its large end) on a glass plate and the smaller end smoothed off with a trowel; the paste, confined in the ring, resting on the plate, is placed under the rod bearing the cylinder, which is brought in contact with the surface and quickly released. The paste is of normal consist- ency when the cylinder penetrates to a point in the mass 10 mm. (0.39 in.) 1 The term " paste " is used in this report to designate a mixture of cement and water, and the word " mortar " a mixture of cement, sand and water. 391. —Vicat Needle Apparatus. 454 POWER PLANT TESTING below the top of the ring. Great care must be taken to fill the ring exactly to the top. Trial pastes are made with varying percentages of water until the correct consistency is obtained. The Committee has recommended, as normal, a paste, the consistency of which is rather wet, because it believes that variations in the amount of compression to which the briquette is subjected in moulding are likely to be less with such a paste. Having determined in this manner the proper percentage of water required to produce a paste of normal consistency, the proper percentage required for the mortars is obtained from an empirical for- mula. The subject proves to be a very difficult one, and although the committee has given it much study, it is not yet prepared to make a definite recommendation. The Committee inserts the following table : PERCENTAGE OF WATER FOR STANDARD MIXTURES Neat 1 to 1 lto2 1 to 3 lto4 1 to 5 Neat 1 tol lto 2 lto 3 lto 4 1 to 5 18 12.0 10.0 9.0 8.4 8.0 33 17.0 13.3 11.5 10.4 9.6 19 12.3 10.2 9.2 8.5 8.1 34 17.3 13.6 11.7 10.5 9.7 20 • 12.7 10.4 9.3 8.7 8.2 35 17.7 13.8 11.8 10.7 9.9 21 13.0 10.7 9.5 8.8 8.3 36 18.0 14.0 12.0 10.8 10.0 22 13.3 10.9 9.7 8.9 8.4 37 18.3 14.2 12.2 10.9 10.1 23 13.7 11.1 9.8 9.1 8.5 38 18.7 14.4 12.3 11.1 10.2 24 14.0 11.3 10.0 9.2 8.6 39 19.0 14.7 12.5 11. 2' 10.3 25 14.3 11.6 10.2 9.3 8.8 40 19.3 14.9 12.7 11.3 10.4 26 14.7 11.8 10.3 9.5 8.9 41 19.7 15.1 12.8 11.5 10.5 27 15.0 12.0 10.5 9.6 9.0 42 20.0 15.3 13.0 11.6 10.6 28 15.3 12.2 10.7 9.7 9.1 43 20.3 15.6 13.2 11.7 10.7 29 15.7 12.5 10.8 9.9 9.2 44 20.7 15.8 13.3 11.9 10.8 30 16.0 12.7 11.0 10.0 9.3 45 21.0 16.0 13.5 12.0 11.0 31 16.3 12.9 11.2 10.1 9.4 46 21.3 16.1 13.7 12.1 11.1 32 16.7 13.1 11.3 10.3 9.5 lto 1 lto 2 lto 3 lto 4 lto 5 t 500 500 33 66 3 3 250 750 200 800 167 833 Time of Setting. The object of this test is to determine the time which elapses from the moment water is added until the paste ceases to be fluid and plastic (called the " initial set "), and also the time re- quired for it to acquire a certain degree of hardness (called the " final " or "hard set"). The former of these is the more important since, with the commencement of setting, the process of crystallization or hardening is said to begin. As a disturbance of this process may produce a loss of strength, it is desirable to complete the operation of mixing and moulding or incorporating the mortar into the work before the cement begins to set. It is usual to measure arbitrarily the beginning and end TESTING THE STRENGTH OF MATERIALS 455 of the setting by the penetration of weighted wires of given diameters. For this purpose the Vicat Needle, Fig. 391, should be used. In making the test, a paste of normal consistency is moulded and placed under the rod (L), bearing the cap (A) at one end and the needle (H), 1 mm. (0.039 in.) in diameter, at the other, weighing 300 grams (10.58 oz.). The needle is then carefully brought in contact with the surface of the paste and quickly released. The setting is said to have commenced when the needle ceases to pass a point 5 mm. (0.20 in.) above the upper surface of the glass plate, and is said to have terminated the moment the needle does not sink visibly into the mass. Test-pieces should be stored in moist air during the test; this is accomplished by placing them on a rack over water contained in a pan and covered with a damp cloth, the cloth to be kept away from them by means of a wire screen; or they may be stored in a moist box or closet. Care should be taken to keep the needle clean, as the collection of cement on the sides of the needle retards the penetra- tion, while cement on the point reduces the area and tends to increase the penetration. The determination of the time of setting is only approx- imate, being materially affected by the temperature of the mixing water, the temperature and humidity of the air during the test, the percentage of water used, and the amount of molding the paste receives. Standard Sand. The Committee recognizes the grave objections to the standard quartz now generally used, especially on account of its high percentage of voids, the difficulty of compacting in the moulds, and its lack of uniformity; it has spent much time in investigating the various natural sands which appeared to be available and suit- able for use. For the present, the Committee recommends the natural sand from Ottawa, 111., screened to pass a sieve having 20 meshes per linear inch and retained on a sieve having 30 meshes per linear inch; the wires to have diameters of 0.0165 and 0.0112 in., respectively, i.e., half the width of the opening in each case. Sand having passed the No. 20 sieve shall be considered standard when not more than 1 per cent passes a No. 30 sieve after one minute's continuous sifting of a 500 g. sample. 1 Form of Briquette. While the form of the briquette recommended by a former Committee of the Society is not wholly satisfactory, this Committee is not prepared to suggest any change, other than rounding off the corners by curves of |-in. radius, Fig. 383. Molds. The molds should be made of brass, bronze, or some equally non-corrodible material, having sufficient metal in the sides to prevent 1 The Sandusky Portland Cement Company, of Sandusky, Ohio, has agreed to undertake the preparation of this sand, and to furnish it at a price only sufficient to cover the actual cost of preparation. 456 POWER PLANT TESTING spreading during molding. Gang molds, which permit molding a number of briquettes at one time, are preferred by many to single molds, since the greater quantity of mortar that can be mixed tends to produce greater uniformity in the results. The type shown in Fig. 393 is recom- mended. The molds should be wiped with an oily cloth before using. J\ '/z^^j Fig. 393.— Briquette Mold. Mixing. All proportions should be stated by weight; the quantity of water to be used should be stated as a percentage of the dry material. The metric system is recommended because of the convenient relation of the gramme and the cubic centimeter. The temperature of the room and the mixing water should be as near 21 deg. Cent. (70 deg. Fahr.) as it is practicable to maintain it. The sand and cement should be thoroughly mixed dry. The mixing should be done on some non-absorbing surface, preferably plate glass. If the mixing must be done on an absorbing surface it should be thoroughly dampened prior to use. The quantity of material to be mixed at one time depends on the number of test pieces to be made; about 1000 grams (35.28 oz.) makes a convenient quantity to mix, especially by hand methods. The material is weighed and placed on the mixing table, and a crater formed in the center, into which the proper percentage of clean water is poured; the material on the outer edge is turned into the crater by the aid of a trowel. As soon as the water has been absorbed, which should not require more than one minute, the operation is completed by vigorously kneading with the hands for an additional one and a half minutes, the process being similar to that used in kneading dough. During the operation of mixing, the hands should be protected by gloves, preferably of rubber. Molding. Having worked the paste or the mortar consistency it is at once placed in the molds by hand. The molds should be rilled im- mediately after the mixing is completed, the material pressed in firmly with the fingers and smoothed off with a trowel without mechanical ramming; the material should, be heaped up on the upper surface of the mold, and, in smoothing off, the trowel should be drawn over the mold in such a manner as to exert a moderate pressure on the excess material. The mold should be turned over and the operation repeated. A check upon the uniformity of the mixing and molding is afforded by weighing the briquettes just prior to immersion, or upon removal TESTING THE STRENGTH OF MATERIALS 457 from the moist closet. Briquettes which vary in weight more than 3 per cent from the average should not be tested. Storage of Test-pieces. During the first twenty-four hours after molding, the test-pieces should be kept in moist air to prevent them from drying out. A moist closet or chamber is so easily devised that the use of the damp cloth should be abandoned if possible. Covering the test-pieces with a damp cloth is objectionable, as commonly used, be- cause the cloth may dry out unequally, and, in consequence, the test- pieces are not all maintained under the same condition. Where a moist closet is not available, a cloth may be used and kept uniformly wet by immersing the ends in water. It should be kept from direct contact with the test-pieces by means of a wire screen or some similar arrange- ment. A moist closet consists of a soapstone or slate box, or a metal- lined wooden box — the lining being covered with felt and this felt kept wet. The bottom of the box is so constructed as to hold water, and the sides are provided with cleats for holding glass shelves on which to place the briquettes. Care should be taken to keep the air in the closet uniformly moist. After twenty-four hours in moist air, the test-pieces for longer periods of time should be immersed in water maintained as near 21 deg. Cent. (70 deg. Fahr.) as practicable; they may be stored in tanks or pans, which should be of non-corrodible material. Tensile Strength. The tests may be made on any standard machine. A solid metal clip, as shown in Fig. 389 (page 451), is recommended. This clip is to be used without cushioning at the points of contact with the test specimen. The bearing at each point of contact should be J in. wide, and the distance between the center of contact on the same clip should be 1| in. Test pieces should be broken as soon as they are removed from the water. Care should be observed in centering the briquettes in the testing machine, as cross-strains, produced by improper centering, tend to lower the breaking strength. The load should not be applied too suddenly, as it may produce vibration, the shock from which often breaks the briquette before the ultimate strength is reached. Care must be taken that the clips and the sides of the briquette be clean and free from grains of sand or dirt, which would prevent a good bearing. The load should be applied at the rate of 600 lbs. per min. The average of the briquettes of each sample tested should be taken as the test, excluding any results which are manifestly faulty. Constancy of Volume. The object is to develop those qualities which tend to destroy the strength and durability of a cement. As it is highly essential to determine such qualities at once, tests of this character are for the most part made in a very short time, and are known, therefore, as accelerated tests. Failure is revealed by cracking, checking, swelling, or disintegration, or all of these phenomena. A cement which remains 458 POWER PLANT TESTING perfectly sound is said to be of constant volume. Tests for constancy of volume are divided into two classes: (JL) normal tests, or those made in either air or water maintained at about 21 deg. Cent. (70 deg. Fahr.), and (2) accelerated tests, or those made in air, steam, or water at a temperature of 45 deg. Cent. (115 deg. Fahr.) and upward. The test-pieces should be allowed to remain 24 hours in moist air before immersion in water or steam, or preservation in air. For these tests pats, about 7| cm. (2.95 in.) in diameter, 1| cm. (0.49 in.) thick at the center, and tapering to a thin edge, should be made upon a clean glass plate [about 10 cm. (3.94 in.; square], from cement paste of normal consistency. Normal Test. A pat is immersed in water maintained as near 21 deg. Cent. (70 deg. Fahr.) as possible for 28 days, and observed at intervals. A similar pat, after 24 hours in moist air, is maintained in air at ordinary temperature and observed at intervals. Data regarding tests of neat cement and mortar briquettes may be tabulated in a form similar to the following: FORM FOR CEMENT TESTS 1. Date, and names of observers. 2. Name and kind of cement. 3. Makers and location of plant. 4. Distinguishing mark on briquettes. 5. Date of mixing and time. 6. Temperature of room at time of mixing, deg. F. 7. Temperature of water at time of mixing, deg. F. 8. Conditions of setting: as to time briquettes were left iu dampened : 9. Activity of the cement or time of initial and final setting. 1 10. Fineness of grinding. before immersion, etc. Kind of Briquette. Composition of Briquettes. Per Cent of Cement . Per Cent of Water . . Per Cent of Cement. Per Cent of Water.. Per Cent of Sand.... No. of Briquettes. 12 3 4 Time of test. Breaking strength, lbs. Appearance of fracture — give sketch of each here. Temp, of room at time of test. deg. F. 28 Day. 7 Day. 28 Day 1 2 3 4 5 • 7 S In reporting the results of these experiments it is important that the effect of different percentages of water sand, etc., and time of immersion, be fully discussed. See pages 454 and 455. TESTING THE STRENGTH OF MATERIALS 459 Accelerated Test. A pat is exposed in any convenient way in an at- mosphere of steam, above boiling water, in a loosely closed vessel, 1 for 5 hours. To pass these tests satisfactorily, the pats should remain firm and hard, and show no signs of cracking, distortion or disintegration. Should the pat leave the plate, distortion may be detected best with a straight-edge applied to the surface which was in contact with the plate. 1 The apparatus recommended for this test is shown with a dimensioned drawing in Proc. A.S.C.E., vol. 35, No. 2 (1909). CHAPTER XXIV OUTLINES OF SUGGESTED TESTS i. Calibration and Adjustment of Pressure Gage. Reference, pages 7-22. Apparatus. Dead weight gage tester, standard weights, and gage to be tested. Method. Take readings at intervals of 5 lbs. per sq. in., up and down. Spin platform and weights to eliminate friction. Remove the indicating needle with special jack and take off dial. Sketch parts in interior of gage. Reset needle to read correctly in part of scale most used. 1 Attach needle firmly. Repeat readings up and down for new calibration. Report. Explain methods of adjustment. Tabulate as on page 21. Curves. 2 (See page 22.) Draw curves only for final condition of gage. 2. Calibration and Adjustment of Vacuum Gage. Reference, pages 22-24 and 236. Apparatus. Mercury U-tube, aspirator (ejector) or air pump, and gage to be tested. Method. Take readings at intervals of 2 in. vacuum, up and down. If there is water or other impurity on mercury column correction must be made. (Reset needle if so instructed.) Report. Explain details of method used. Tabulate as on page 21, omitting second column and writing " ins. vac. " for "pressure, lbs. per sq. in." Curves. Similar to instructions for test No. 1. 3. Thermometer Calibration for Range Above 212 F. Reference, pages 29-39. Apparatus. Steam gage used in test No. 1, thermometers (a standard high-reading thermometer is sometimes used to check the results), barometer and steam tables (pages 468-470). Method. Read thermometer being tested (and " standard " if one is used) at intervals of approximately 5 lbs. per sq. in. on the gage calibrated in test No. 1. Be sure the steam is not superheated and allow at least 5 min. after final adjustments of valves before readings are taken. Report. Sketch with a simple line drawing the interior of apparatus used with neces- sary piping connections. Tabulate as on page 37. Calculate " stem " corrections when necessary. Curves. (See page 36.) " True " temperatures are from steam tables. 4. Use and Calibration of a Planimeter. Reference, pages 74-87, 141. Apparatus. Polar planimeter, large compass, scale, and micrometer. Method. 1. Measure length of tracing-arm from pivot to tracing-point and diameter of rolling or graduated wheel to check accuracy for reading areas in sq. in. 1 2. Calculate length of tracing-arm so that one revolution of graduated wheel will indicate 8 sq. in. 3. Find area of zero circle by at least two methods (see pages 77, 80). 4. Determine average error in per cent of instrument by first measuring and then calculating the area of circles of 1, 2, and 3 in. diameter (see page 87, footnote). 1 If other instructions are not given assume two-thirds maximum graduation of dial. 2 Arrangement of coordinates for curves is throughout to make them most applicable for use; that is, in the use of a curve the given quantity should be read on the scale of abscissas and the value to be found will then be obtained from the scale of ordinates. 460 OUTLINE OF SUGGESTED TESTS 461 Measure each area three times and take average. Mark percentage error + if instru- ment reads too small and — if too large. 5. Determine indicated horse power for an indicator card. Scale of indicator spring = 40 lbs. per sq. in. (i.e., No. 40 spring); area of piston •= 66 sq in.; length of stroke = lft.; andr.p.m. = 200. Report. Record data, method of measurements, and calculations. Tabulate results. 5. Calibration of Indicator Springs in Compression. Reference, pages 92-106, 112-120, 136-144. Read Precautions for Care of Indicator, pages 103-106. Apparatus. Indicator, set of springs, and indicator spring tester. Method. 1. Test perpendicularity of motion of pencil-point to atmospheric line. (Footnote, page 105.) 2. Obtain at least two good calibration cards for each spring similar to Fig. 121, for increasing and decreasing pressures. Obviously unless the cards obtained for a spring are alike, the work is not successful. Take increments of 5 lbs. per sq. in. for all springs up to and including the " 40 lb." spring. For springs of higher scale take increments of 10 lbs. per sq. in. Lines of maximum pressure on calibration card should be about If ins. above the atmospheric line. When a plunger type of tester is used, that is, similar in principle to Fig. 118, the diameter of the plunger must be measured with a micrometer and the relation accurately calculated between the weight and the unit pressure applied to the indicator in lbs. per sq. in. Examine at least two types of indicators. Insert the spring and study the adjustment of the height of the pencil. When work with an indicator is finished, always remove the " piston " spring and thoroughly clean all parts, inside and outside. Report. Tabulate and draw curves as directed on page 119. Calculate the true scale of spring from the average of four equidistant points on this curve. Explain calculations. Discuss any discrepancies in data. If a " 40-lb." spring has been calibrated, assume this was used in obtaining the indi- cator card used in test No. 4, and calculate the corrected indicated horse power. 5a. Calibration of Indicator Springs in Tension (for use with Vacuum). Reference, pages 118, 119. Apparatus. Indicator, springs, and special tester. Method and report same as for test No. 5. 6. Study of Reducing Motions. Reference, pages 121-138. Apparatus. Steel scale and drawing instruments. Method and Report. Examine reducing motions in laboratory. Design an accurate device for an engine as designated by instructor. 7. Calorimeter Tests, Use and Comparison. Reference, pages 55-73. Apparatus. Separating calorimeter, glass beaker (or graduate), pail with cover having a hole for insertion of hose for condensing steam, platform scales, watch, throt- tling calorimeter, thermometers, steam pressure gage, barometer and monkey wrench. Method. Calibrate steam gage,. Connect the separating and throttling calorimeters by means of standard sampling nipples (see page 56) to the same vertical steam pipe where they will both take steam of the same quality. Allow steam to blow through both calorimeters until the temperatures in the throttling type have reached a maximum value and the other has become thoroughly heated and enough water has collected to bring the level in the water gage glass up to, or a little above, the zero on the scale. Make the condensing pail about two-thirds full of water. Obtain this weight of water by weighings. When all conditions are satisfactory, put the hose through which steam has been discharging from the separating calorimeter into the hole in the cover of the pail, and at the same time observe reading of scale of water gage. Read temperatures 462 POWER PLANT TESTING and pressures every three minutes. Run the test until an appreciable volume of steam discharges from the hole in the cover of the pail. Then throw steam tube out of pail and read the level in the water gage. Again weigh pail and contents. Calibrate the scale of the water gage by removing and weighing water from the separating calorimeter between any two levels within the limits of the scale. Make one test at each of four steam pressures above 60 lbs. per sq. in. gage as designated by instructor. Calculate the quality of steam roughly by the charts on pages 59 or 61 during the progress of the tests and immediately check with data from separating calorimeter. Report. Tabulate all observed and calculated data. Sketch and describe fully the calorimeters used. State in detail all operations in performing test. Discuss relative accuracy of results. 8. Test of Platform Scales. Apparatus. Platform scales to be tested, 12 in. steel scale, graduated to —^ in. and standard 50- or 100-lb. weights. Method. Platform scales are probably used more in engineering work about a power plant than any other measuring device, and usually young engineers do not very well understand their operation. They consist essentially of a device by which a load is applied to a system of levers, of long and short arms, arranged so that a load on the platform can be balanced by weights applied at the end of a final lever called the beam, or by shifting a poise along the length of this latter lever. Essentially it is like the weighing device shown in Fig. 370. This weighing beam is usually placed on an upright post at one end of the platform. 1. Take off the platform and measure the length of all the lever arms between knife- edges to the nearest y^ in. Draw simple line sketch showing all arms and lengths. 2. Observe the means provided to adjust the beam to read zero. 3. Observe sensitiveness of scales by finding range through which poise can be shifted without appreciably disturbing the balance. 4. Calibrate the scales after assembling by placing standard weights on the platform and observing the reading on the beam when balanced. After calibration shift scales around roughly and observe result by a recalibration. Test also by placing loads in middle of platform as a scales should be used, and then at any of the sides. Report. 1. Plot results of the calibration with observed weights as abscissas and standard weights as ordinates. 2. Discuss effect of rough handling on the calibration, and whether an accurate calibration of a scales made before shipping can be considered absolutely reliable later. Explain effect of non-central loading on the platform. 3. From the measured lever arms calculate the weight of poise for two different positions on the beam. 4. Calculate the weight of a poise for an additional beam which would indicate readings to to the smallest division on the beam of this scale. (Note that the additional weight of the extra beam could be balanced by a larger adjusting counterweight.) 9. Oil Tests : Viscosity, Flash and Burning Points, and Specific Gravity. Reference, pages 395-404. Apparatus. Viscosimeter, flash tester, hydrometer, 2 thermometers, 2 glass gradu- ates, Bunsen burner, matches, wax tapers, test-tube, and watch. Method. 1. Determine flash and burning points of oil in flash tester, with top closed for flash point and open for burning point. To check, use at least two samples of the same kind of oil. Never use a second time a sample that has been heated. Why? Determine the chill point of the oil if ice is available. 2. With the orifice of viscosimeter and inner cup thoroughly cleaned determine the time required for 50 cu. cm. of water at " room " temperature to flow through this OUTLINE OF SUGGESTED TESTS 463 orifice, starting from the level of the tip of the hook-gage. Make 3 tests and take average. Determine similarly the time required for 50 cu. cm. of the oil at temperatures of 80, 110, 140 and 170° F. to flow through the same orifice when starting at the same level. 3. Determine the specific gravity of the oil in both the Baume and the " specific gravity " scales at about 80°, 100°, 120°, and 140° F. (Avoid pouring hot oils into cold glass vessels as they are likely to be broken.) Report. Tabulate results of the various tests. Plot (1) temperatures as abscissas and viscosities as ordinates, (2) temperatures as abscissas and specific gravity as ordi- nates, both curves having the same abscissass on the same sheet. Discuss suitableness or unsuitableness of this oil for various services. io. Oil Tests (Cont'd) : Coefficient of Friction and Temperature Rise of Bearings. Reference, pages 404-405. Apparatus. Pendulum oil-tester, thermometer, wooden strut with knife-edge at end, sensitive platform scales, spirit level, and steel scale graduated to T £ ff in. Method. Support the pendulum in a horizontal position (as determined by a spirit level) on a strut, provided with a knife-edge at the bottom where it rests on a platform scales. Determine the weight of the pendulum alone in this position. Measure also the effective length of the lever arm from the center of the journal to a vertical line through the knife-edge. Repeat weighing and measurement of length of arm for several points along the pendulum. Remove the pendulum and determine its weight accurately. Measure the length (1) and diameter (d) of the journal so as to calculate W'R the projected area 21d of the bearing surface. Compute the constant , and by setting the pendulum at various angles determine whether the scale is correctly gradu- ated. In order to get satisfactory results the bearing and shaft must be perfectly clean and smooth. Calibrate spring in pendulum. Operate the machine at constant speed with pressures of 50, 100, 150 and 200 lbs. per sq. in. on the bearing. Record the arc of deflection, temperatures of bearing and of room, speed, and rate of oil feed (usually 3 drops per minute). Report. Plot curves of bearing pressure (lbs. per sq. in.) as abscissas and coefficient? of friction and temperatures as ordinates. Calculate velocity of rubbing faces in ft. per min. In machines arranged like ordinary shop bearings where all the load is on the bottom half of the bearing this velocity ia calculated on the basis of only half the circumference. Discuss possible errors in the data as shown by the curves. ii. Proximate Analysis of Coal. Reference, pages 228-234. Apparatus. Crucibles, Bunsen burners, matches, coal crusher, mortar and pestle, 20-mesh sieve, 2 air-tight bottles, drying oven, air-blast lamp (or an equivalent), rubber tubing, watch, desiccator, and " chemical " balance sensitive to 1 part in 1000 of amount weighed. Method. That of Am. Chem. Soc. (pages 229-231) or of A.S.M.E. (pages 231-233) as directed by instructor. Inquire about location of mine from which coal was taken. Make duplicate determinations to check values of moisture and volatile matter. Report. Record all data. Determine percentages of moisture, volatile matter, fixed carbon and ash in coal " as received." Also percentages of volatile matter, fixed carbon and ash in dry coal. Discuss results by comparing with analyses of coals from same district as given in mechanical engineers hand-books, etc. 12. Calorific Value of Coal. Reference, pages 210-222. A. Apparatus. Bomb calorimeter with platinum crucible, mortar and pestle, 100- mesh sieve, oxygen tank with pipe connections to fit threads on bomb, accurate 464 POWER PLANT TESTING calorimeter, thermometer, pail, 1 scales for weighing water, fine iron wire for ignition, " chemical " balance sensitive to 15V0 gram, briquet ting machine, 2 monkey wrench and calorimeter spanner. B. Apparatus. Same as " A " except Parr calorimeter is used instead of bomb type, and absolutely pure sodium peroxide is used instead of oxygen gas. Method. See pages 210-215 for " A " and pages 217-219 for " B." Make at least two determinations. Report for " A " or " B." Describe apparatus used and procedure in detail. Calcu- late heating value of coal tested in B.t.u. per lb. " as received," also heating value per lb. dry coal and per lb. combustible in same units. Record all data. Discuss results by comparing with heating value of coals from same district as given in mechanical engineer's hand-books, etc. 13. Calorific Value of Gas. Reference, pages 222-227. Apparatus. Junkers' calorimeter (with gas burner), 2 calorimeter thermometers, 2 ordinary thermometers, 2 glass graduates, large pail, platform scales, '" wet " gas meter, gas regulator, glass U-tube for gas pressure, barometer, and rubber tubing. Method. See pages 223-226. Read thermometers every two minutes. Make at least two determinations which should check within 1 per cent. Report. Tabulate all observations. Explain calculations. Determine " higher " and " lower " heating values of the gas per cu. ft. (1) at condi- tions of test and (2) at standard conditions (see pages 223). Sketch apparatus used. Discuss possible errors in method. 14. Calorific Value of Oil. Reference, pages 222-227. Apparatus. Junkers' calorimeter (with oil lamp and chemical balance for its attach- ment) and hydrometer. Otherwise same as for test No. 13. Method. See pages 226-227. Collect water from calorimeter during time required for burning exactly 50 grams of oil. Determine specific gravity of oil used. Make at least two determinations. Report. Tabulate all observations. Calculate " higher " and " lower " heating values per lb. of oil. Discuss results by comparing with data given in books on gas and oil engines or in mechanical engineer's hand-books. 15. Analysis of Flue Gas. Reference, pages 235-252, 281-283. Apparatus for sampling and chemical absorption of gases as directed by instructor. Method. See pages 235-245. Make at least two analyses from the same sample of gas which should check throughout within T V per cent. Report. Tabulate data and results (calculated as percentages). From the average results of the analysis calculate number of lbs. air required to burn (1) a lb. of carbon and (2) a lb. of dry coal, assuming the dry coal contains 83 per cent carbon, 3 per cent hydrogen, 4 per cent oxygen and 10 per cent earthy matter. 16. Study of Brakes. Reference, pages 147-163. Apparatus. Steel scale, calipers, and drawing instruments. Method and Report. Design prony brake of type stated by instructor for absorbing b.h.p. at. . .r.p.m. Show calculations for diameter at root of thread of tightening bolt, and for determining capacity of scales required to take the pressure of the brake. Calcu- late also weight of water required per hour for cooling the brake, assuming 10 per cent of heat dissipated by radiation. Answer the following questions: 1. If water were shut off from the brake what damage would result? 1 Instead of the pail and scales a large glass graduate is often used to measure the water in cu. cm. 2 Briquetting the coal is not required by A.S.M.E. recommendations. OUTLINE OF SUGGESTED TESTS 465 2. Why is it a very bad practice to stop the engine with the full load on the brake? 3. Why should a safety-cord be attached to the arm of the brake? 4. What is the effect of putting oil on the rim of the brake pulley? Of putting on water? If there is any doubt as to the proper answers, run an engine with a Prony brake attached to find out by experience. 17. Calibration of a Transmission Dynamometer. Reference, pages 164-174. Apparatus. Dynamometer and its weights steel scale, hand speed counter and watch. Method. Measure length of lever arms. Observe condition of dash-pot as explained on page 168. Remove the brake from its pulley and make a series of runs; that is, without load at various speeds and observe the corresponding readings of instrument. Attach the brake to its pulley and make a series of tests at three different speeds with net loads on the brake for each speed of approximately (1) . . . (2). . .(3) . . ., and (4) . . .lbs. Determine " zero " load or tare of brake, lbs., and length of brake arm, ft. For each test record: (1) Gross brake load, lbs., (2) net brake load, lbs., (3) reading of dynamometer (theoretically, lbs.), (4) r.p.m., and (5) names of observers. Report. Examine construction of dynamometer and sketch arrangement of lever arms (and gears, if any). For each speed calculate ft.-lbs. per minute corresponding to readings of dynamometer and plot curve with these as abscissas and ft.-lbs. by brake as ordinates. Plot also curve for each speed of reading of dynamometer as abscissas and net brake load, lbs. as ordinates. (For Flather's and Morin's dynamometers plot height of autographic diagram, ins. as abscissas with ft.-lbs. by brake as ordinates.) 18. Belting Tests. Reference, pages 392-394. Apparatus. Belt tester, steel tape, 2 hand speed counters, watch, calibrated scales for weighing, and 3 ft. scale for lengths. Method. See pages 392-394. Determine " zero " load or tare on each scale. Adjust the distance between driving and driven pulleys when at rest so that there is initial tension in belt of 25 lbs. per in. of width. Run tests at a given constant speed of the driver at varying loads until the belt begins to slip. Make about five runs for this value of initial belt tension. Each test should be of at least 5 min. duration during which time both speed counters should be read continuously. Observe for each test also average brake load, lbs. and tension reading, lbs. Make similar sets of runs with initial belt tensions of 50 and 75 lbs. per in. of width. Measure diameter of either driving or the driven pulleys (inches) and also arc of contact of belt on this pulley (inches). Calculate ratio of arc in inches to radius in inches. Measure length, width and thickness of belt. Report. Calculate slip of belt, coefficient of friction, b.h.p., and efficiency of trans- mission. For each value of initial tension plot b.h.p. as abscissas and as ordinates (1) slip (per cent) and (2) coefficient of friction. Also initial tension of belt as abscissas and b.h.p. as ordinates. Discuss results in their application to shop practice. 19. Test of Hoists. Reference, pages 391-392. Apparatus. Hoists to be tested, spring balance, scale with graduations marked very plainly. Method. Same pages as reference. Report. Sketch hoists used. On the same curve sheet plot for each hoist a curve of load lifted (lbs.) as abscissas and efficiency as ordinates. 20. Mechanical Efficiency Test of Steam Engine. Determinations of Indicated and Brake Horse Power. Reference, pages 136-142, 147, 150, 284. Apparatus. Steam engine indicators, steam pressure gage, prony or rope brake, hand speed counter, watch, scale about 3 ft. long, platform scales and planimeter, cans of cylinder and engine oils. 466 POWER PLANT TESTING Method. Put spring in indicator, oil its piston with cylinder oil and the joints of pencil motion with porpoise or similar light oil. Adjust indicator parts so that there is no lost motion in pencil mechanism. Attach firmly to engine cylinder. Adjust cord so that it will have normal tension when engine is turned over both dead centers. Fill engine cylinder lubricator with cylinder oil and all oil cups with engine oil. Adjust feed of all oiling devices. Measure effective brake arm and " zero " load or tare of brake (see pages 148-151). Vary net load on brake by increments of 50 lbs. up to maximum engine will carry without slowing down. Run each test for 12 min., taking all indicator cards and read- ings of r.p.m. and gross brake reading, lbs. every 3 min. Measure as many indicator cards as possible while test is in progress and compare at least a few values of indicated with brake h.p. before test is finished. This is done to check the accuracy of the work. Always clean the engine and shut off the lubricator and oil cups when finishing a test. Calculate engine and brake constants (see pages 143 and 148). Report. Tabulate data and calculated results as on page 284. Examine and sketch the reducing motion. Explain whether or not it gives an accurate reduction. Plot with i.h.p. as abscissas the following as ordinates: (1) b.h.p., (2) mech. effic. (per cent), (3) r.p.m. and (4) friction h. p. If friction horse power has not constant values discuss reasons. 21. Setting of Plain D-slide Valve on Steam Engine. Reference, pages 285-288, 289. Apparatus. Steel scale, monkey wrench, trammels or large machinist's dividers, chalk, drawing-board and instruments and indicators. Method. See pages 285-287. Remove steam chest cover and valve from its stem. Measure face of valve and ports. Make dimensioned drawing like Fig. 297 (page 285) and Zeuner valve diagram. 1 Adjust laps and eccentric as explained in reference. Replace steam-chest cover. Attach indicators and take diagrams. Compare with ideal diagram obtained from the Zeuner drawing. If indicator diagrams are not satisfactory make the adjustments needed. Report. Explain in detail procedure. Discuss each step in making adjustments. 22. Setting of Corliss Valve on Steam Engine. Reference, pages 288-293. Apparatus. Monkey wrenches, steel scale, plumb bob and line and indicators. Method. Adjust (1) wrist plate, (2) all reach-rods for given laps, (3) rocker. Put engine on dead center and set eccentric for a given lead. Readjust reach-rods. Take indicator cards and readjust valves. 23. Volumetric Clearance of Engine. Reference, pages 293-294. Apparatus. Pails with cocks near the bottom, rubber tubing, funnels, small platform scales for weighing water in pails, trammels, chalk, monkey wrench, watch, wooden blocks to cover parts of engine and rubber packing. Method. Remove steam-chest cover and cover ports with blocks on top of rubber packing. Set engine on dead-center (see page 286, footnote). Continue procedure as in reference above. 24. Boiler Test. Reference, pages 258-283. Apparatus. Steam gage, draft gage, barometer, watch, wrenches, steam calorimeter (with manometer if needed), thermometers with maximum graduation below 240° F. for (1) external air, (2) boiler room, (3) feed-water entering boiler 2 and (4) make-up water; above 240° F. for (1) temperature of steam at steam nozzle (discharge from boiler) and (2) steam calorimeter, platform scales for (1) coal, (2) ashes and (3) feed- 1 See treatises on Steam Engines. Zeuner diagrams are most useful for valve setting and Bilgram diagrams and best for designing. 2 For plants operating with an economizer a thermometer for higher temperatures would be required. OUTLINE OF SUGGESTED TESTS 467 water, large tanks for feed-water, standard weights, thermo-couple for flue temperature, flue gas apparatus for sampling and analyzing, jars or cans for samples of coal and ash, means for marking level of water in gage glass, large closed cans for accumulating samples of coal and ashes. Method. See reference. Calibrate gage and thermometers. Plot a graphical log as test proceeds (see page 268). Run boiler leakage test for 3 hrs. at normal boiler pressure (see page 339) before regular boiler test begins. Report. Tabulate all data. Use A.S.M.E. " short " or " long " form as directed by- instructor. 25. For Economy Tests of Steam Engines, Steam Turbines, Complete Steam Power Plants, Gas Engines, Oil Engines, Gas Producers, as well as Pump Tests, Injector Tests, Air Compressor Tests, Air Lift Tests, Ventilating Fan Test, and Refrigerating Plant Tests. See detailed instructions and A. S. M. E. codes, pages 294-314, 317-328, (329-335), 336-340, 345-363,372-376, 386-388, 409-424, 428-430. 26. Tests of the Strength of Materials of Construction. See Chapter XXIII for detailed methods and reports. APPENDIX Two sets of tables which the author has found useful for " rough and ready " calculations are given on the following pages. Table I is a short table of the more important properties of saturated steam. This table has been taken with permission from Allen and Bursley's Heat Engines. Table II gives for various common substances the specific gravity, density (weight per cubic foot) , specific heat and coefficients of expansion per degree Fahrenheit, both linear and volumetric. Coefficient of volumetric expansion is three times the linear coefficient of expansion. TABLE I Properties op Saturated Steam english units Abs. Pres- sure, Pounds per Sq. In. Tempera- ture, De- grees F. Heat of the Liquid. Latent Heat of Evapora- tion. Total Heat of Steam. Specific Vol- ume, Cu. Ft. per Pound. Density, Pounds per Cu. Ft. Abs. Pres- sure. Pounds per Sq. In. V t q or h rovL H v l V V .0886 32 1072.6 1072.6 3301.0 .000303 .0886 .2562 60 28.1 1057.4 1085.5 1207.5 .000828 .2562 .5056 80 48.1 1046.6 1094.7 635.4 .001573 .5056 1 101.8 69.8 1034.6 1104.4 333.00 .00300 1 2 126.1 94.1 1021.4 1115.5 173.30 .00577 2 3 141.5 109.5 1012.3 1121.8 118.50 .00845 3 4 153.0 120.9 1005.6 1126.5 90.50 .01106 4 5 162.3 130.2 1000.2 1130.4 73.33 .01364 5 6 170.1 138.0 995.7 1133.7 61.89 .01616 6 7 176.8 144.8 991.6 1136.4 53.58 .01867 7 8 182.9 150.8 988.0 1138.8 47.27 .02115 8 468 APPENDIX 469 Properties op Saturated Steam — Continued ENGLISH UNITS Abs. Pres- sure, Pounds per Sq. In. Tempera- ture, De- grees F. Heat of the Liquid. Latent Heat of Evapora- tion. Total Heat of Steam. Specific Vol- ume, Cu. Ft. per Pound. Density, Pounds per Cu. Ft. Abs. Pres- sure, Pounds per Sq. In. V t q or A r or L H V l P 9 188.3 156.3 984.8 1141.1 42.36 .02361 9 10 193.2 161.2 981.7 1142.9 38.38 .02606 10 11 197.7 165.8 978.9 1144.7 35.10 .02849 11 12 202.0 170.0 976.3 1146.3 32.38 .03089 12 13 205.9 173.9 973.9 1147.8 30.04 .03329 13 14 209.6 177.6 971.6 1149.2 28.02 .03568 14 14.7 212.0 180.1 970.0 1150.1 26.79 .03733 14.7 15 213.0 181.1 969.4 1150.5 26.27 .03806 15 16 216.3 184.5 967.3 1151.8 24.77 .04042 16 17 219.4 187.7 965.3 1153.0 23.38 .04277 17 18 222.4 190.6 963.4 1154.0 22.16 .04512 18 19 225.2 193.5 961.5 1155.0 21.07 .04746 19 20 228.0 196.2 959.7 1155.9 20.08. .04980 20 21 230.6 198.9 958.0 1156.9 19.18 .05213 21 22 233.1 201.4 956.4 1157.8 18.37 .05445 22 23 235.5 203.9 954.8 1158.7 17.62 .05676 23 24 237.8 206.2 953.2 1159.4 16.93 .05907 24 25 240.1 208.5 951.7 1160.2 16.30 .0614 25 26 242.2 210.7 950.3 1161.0 15.71 .0636 26 27 244.4 212.8 948.9 1161.7 15.18 .0659 27 28 246.4 214.9 947.5 1162.4 14.67 .0682 28 29 248.4 217.0 946.1 1163.1 14.19 .0705 29 30 250.3 218.9 944.8 1163.7 13.74 .0728 30 31 252.2 220.8 943.5 1164.3 13.32 .0751 31 32 254.1 222.7 942.2 1164.9 12.93 .0773 32 33 255.8 224.5 941.0 1165.5 12.57 .0795 33 34 257.6 226.3 939.8 1166.1 12.22 .0818 34 35 259.3 228.0 938.6 1166.6 11.89 .0841 35 36 261.0 229.7 937.4 1167.1 11.58 .0863 36 37 262.6 231.4 936.3 1167.7 11.29 .0886 37 38 264.2 233.0 935.2 1168.2 11.01 .0908 38 39 265.8 234.6 934.1 1168.7 10.74 .0931 39 40 267.3 236.2 933.0 1169.2 10.49 .0953 40 41 268.7 237.7 931.9 1169.6 10.25 .0976 41 42 270.2 239.2 930.9 1170.1 10.02 .0998 42 43 271.7 240.6 929.9 1170.5 9.80 .1020 43 44 273.1 242.1 928.9 1171.0 9.59 .1043 44 45 274.5 243.5 927.9 1171.4 9.39 .1065 45 . 46 275.8 244.9 926.9 1171.8 9.20 .1087 46 47 277.2 246.2 926.0 1172.2 9.02 .1109 47 48 278.5 247.6 925.0 1172.6 8.84 .1131 48 49 279.8 248.9 924.1 1173.0 8.67 .1153 49 50 281.0 250.2 923.2 1173.4 8.51 .1175 - 50 51 282.3 251.5 922.3 1173.8 8.35 .1197 51 52 283.5 252,8 921.4 1174.2 8.20 .1219 52 53 284.7 254.0 920.5 1174.5 8.05 .1241 53 54 285.9 255.2 919.6 1174.8 7.91 .1263 54 55 287.1 256.4 918.7 1175.1 7.78 .1285 55 56 288.2 257.6 917.9 1175.5 7.65 .1307 56 57 289.4 258.8 917.1 1175.9 7.52 .1329 57 58 290.5 259.9 916.2 1176.1 7.40 .1351 58 59 291.6 261.1 915.4 1176.5 7.28 .1373 59 60 . 292.7 262.2 914.6 1176.8 7.17 .1394 60 61 293.8 263.3 913.8 1177.1 7.06 .1416 61 470 POWER PLANT TESTING Properties of Saturated Steam — Continued ENGLISH UNITS Abs. Pres- sure, Pounds per Sq. In. Tempera- ture, De- grees F. Heat of the Liquid. Latent Heat of Evapora- tion. Total Heat of Steam. Specific Vol- ume, Cu. Ft. per Pound. Density, Pounds per Cu. Ft. Abs. Pres- sure, Pounds per Sq. In. V t gor h . V or L H * V V 62 294.9 264.4 913.0 1177.4 6.95 .1438 62 63 295.9 265.5 912.2 1177.7 6.85 .1460 63 64 297.0 266.5 911.5 1178.0 6.75 .1482 64 65 298.0 267.6 910.7 1178.3 6.65 .1503 65 66 299.0 268.6 910.0 1178.6 6.56 .1525 66 67 300.0 269.7 909.2 1178.9 6.47 .1547 67 68 301.0 270.7 908.4 1179.1 6.38 .1569 68 69 302.0 271.7 907.7 1179.4 6.29 .1591 69 70 302.9 272.7 906.9 1179.6 6.20 .1612 70 71 303.9 273.7 906.2 1179.9 6.12 .1634 71 72 304.8 274.6 905.5 - 1180.1 6.04 .1656 72 73 305.8 275.6 904.8 1180.4 5.96 .1678 73 74 306.7 276.6 904.1 1180.7 5.89 .1699 74 75 307.6 277.5 903.4 1180.9 5.81 .1721 75 76 308.5 278.5 902.7 1181.2 5.74 .1743 76 77 309.4 279.4 902.1 1181.5 5.67 .1764 77 78 310.3 280.3 901.4 1181.7 5.60 .1786 78 79 311.2 281.2 900.7 1181.9 5.54 .1808 79 80 312.0 282.1 900.1 1182.2 5.47 .1829 80 81 312.9 283.0 899.4 1182.4 5.41 .1851 81 82 313.8 283.8 898.8 1182.6 5.34 .1873 82 83 314.6 284.7 898.1 1182.8 5.28 .1894 83 84 315.4 285.6 897.5 1183.1 5.22 .1915 84 85 316.3 286.4 896.9 1183.3 5.16 .1937 85 86 317.1 287.3 896.2 1183.5 5.10 .1959 86 87 317.9 288.1 895.6 1183.7 5.05 .1980 87 88 318.7 288.9 895.0 1183.9 5.00 .2002 88 . 89 319.5 289.8 894.3 1184.1 4.94 .2024 89 90 320.3 290.6 893.7 1184.3 4.89 .2045 90 91 321.1 291.4 893.1 1184.5 4.84 .2066 91 92 321.8 292.2 892.5 1184.7 4.79 .2088 92 93 322.6 293.0 891.9 1184.9 4.74 .2110 93 94 323.4 293.8 891.3 1185.1 4.69 .2131 94 95 324.1 294.5 890.7 1185.2 4.65 .2152 95 96 324.9 295.3 890.1 1185.4 4.60 .2173 96 97 325.6 296.1 889.5 1185.6 4.56 .2194 97 98 326.4 296.8 889.0 1185.8 4.51 .2215 98 99 327.1 297.6 888.4 1186.0 4.47 .2237 99 100 327.8 298.4 887.8 1186.2 4.430 .2257 100 101 328.6 299.1 887.2 1186.3 4.389 .2278 101 102 329.3 299.8 886.7 1186.5 4.349 .2299 102 103 330.0 300.6 886.1 1186.7 4.309 .2321 103 104 330.7 301.3 885.6 1186.9 4.270 .2342 104 105 331.4 302.0 885.0 1187.0 4.231 .2364 105 106 332.0 302.7 884.5 1187.2 4.193 .2385 106 107 332.7 303.4 883.9 1187.3 4.156 .2407 107 108 333.4 304.1 883.4 1187.5 4.119 .2428 108 109 334.1 304.8 882.8 1187.6 4.082 .2450 109 110 334.8 305.5 882.3 1187.8 4.047 .2472 110 111 335.4 306.2 881.8 1188.0 4.012 .2493 111 112 336.1 306.9 881.2 1188.1 3.977 .2514 112 113 336.8 307.6 880.7 1188.3 3.944 .2535 113 114 337.4 308.3 880.2 1188.5 3.911 .2557 114 114.7 337.9 308.8 879.8 1188.6 3.888 .2572 114.7 APPENDIX 471 Properties of Saturated Steam english units Continued Abs. Pres- sure, Pounds per Sq. In. Tempera- ture, De- grees F. Heat of the Liquid. Latent Heat of Evapora- tion. Total Heat of Steam. Specific Vol- ume, Cu. Ft. per Pound. Density, Pounds per Cu. Ft. Abs. Pres- sure, Pounds per Sq. In. V t qorl ror L H V l V V 115 338.1 309.0 879.7 1188.7 3.878 .2578 115 - 116 338.7 309.6 879.2 1188.8 3.846 .2600 116 117 339.4 310.3 878.7 1189.0 3.815 .2621 117 118 340.0 311.0 878.2 1189.2 3.748 .2642 118 119 340.6 311.7 877.6 1189.3 3.754 .2663 119 120 341.3 312.3 877.1 1189.4 3.725 .2684 120 121 341.9 313.0 876.6 1189.6 3.696 .2706 121 122 342.5 313.6 876.1 1189.7 3.667 .2727 122 123 343.2 314.3 875.6 1189.9 3.638 .2749 123 124 343.8 314.9 875.1 1190.0 3.610 .2770 124 125 344.4 315.5 874.6 1190.1 3.582 .2792 125 126 345.0 316.2 874.1 1190.3 3.555 .2813 126 127 345.6 316.8 873.7 1190.5 3.529 .2834 127 128 346.2 317.4 873.2 1190.6 3.503 .2855 128 129 346.8 318.0 872.7 1190.7 3.477 .2876 '129 130 347.4 318.6 872.2 1190.8 3.452 .2897 130 131 348.0 319.3 871.7 1191.0 3.427 .2918 131 132 348.5 319.9 871.2 1191.1 3.402 .2939 132 133 349.1 320.5 870.8 1191.3 3.378 .2960 133 134 349.7 321.0 870.4 1191.4 3.354 .2981 134 135 350.3 321.6 869.9 1191.5 3.331 .3002 135 136 350.8 322.2 869.4 1191.6 3.308 .3023 136 137 351.4 322.8 868.9 1191.7 3.285 .3044 137 138 352.0 323.4 868.4 1191.8 3.263 .3065 138 139 352.5 324.0 868.0 1192.0 3.241 .3086 139 140 353.1 324.5 867.6 1192.1 3.219 .3107 140 141 353.6 325.1 867.1 1192.2 3.198 .3128 141 142 354 ,2 325.7 866.6 1192.3 3.176 .3149 142 143 354.7 326.3 866.2 1192.5 3.155 .3170 143 144 355.3 326.8 865.8 1192.6 3.134 .3191 144 145 355.8 327.4 865.3 1192.7 3.113 .3212 145 146 356.3 327.9 864.9 1192.8 3.093 .3233 146 147 356.9 328.5 864.4 1192.9 3.073 .3254 147 148 357.4 329.0 864.0 1193.0 3.053 .3275 148 149 357.9 329.6 863.5 1193.1 3.033 .3297 149 150 358.5 330.1 863.1 1193.2 3.013 .3319 150 152 359.5 331.2 862.3 1193.5 2.975 .3361 152 154 360.5 332.3 861.4 1193.7 2.939 .3403 154 156 361.6 333.4 860.5 1193.9 2.903 .3445 156 158 362.6 334.4 859.7 1194.1 2.868 .3487 158 160 363.6 335.5 858.8 1194.3 2.834 .3529 160 162 364.6 336.6 858.0 1194.6 2.801 .3570 162 164 365.6 337.6 857.2 1194.8 2.768 .3613 164 166 366.5 338.6 856.4 1195.0 2.736 .3655 166 168 367.5 339.6 855.5 1195.1 2.705 .3697 168 170 368.5 340.6 854.7 1195.3 2.674 .3739 170 172 369.4 341.6 853.9 1195.5 2.644 .3782 172 174 370.4 342.5 853.1 1195.6 2.615 .3824 174 176 371.3 343.5 852.3 1195.8 2.587 .3865 176 178 372.2 344.5 851.5 1196.0 2.560 .3907 178 180 373.1 345.4 850.8 1196.2 2.532 .3949 180 182 374.0 346.4 850.0 1196.4 2.506 .3990 182 184 374.9 347.4 849.3 1196.7 2.480 .4032 184 186 375.8 348.3 848.5 1196.8 2.455 .4074 186 472 POWER PLANT TESTING Properties of Saturated Steam — Concluded ENGLISH UNITS Abs. Pres- sure, Pound, per Sq. In. Tempera- ture, De- grees F. Heat of the Liquid. Latent Heat of Evapora- tion. Total Heat of Steam. Specific Vol- ume, Cu. Ft. per Pound. Density Pound3 per Cu. Ft. Abs. Pres- sure, Pounds per Sq. In. V t q or h rot L H V i V 188 376.7 349.2 847.7 1196.9 2.430 .4115 188 190 377.6 350.1 847.0 1197.1 2.406 .4157 190 192 378.5 351.0 846.2 1197.2 2.381 .4200 192 194 379.3 351.9 845.5 1197.4 2.358 .4242 194 196 380.2 352.8 844.8 1197.6 2.335 .4284 196 198 381.0 353.7 844.0 1197.7 2.312 .4326 198 200 381.9 354.6 843.3 1197.9 2.289 .4370 200 202 382.7 355.5 842.6 1198.1 2.268 .4411 202 204 383.5 356.4 841.9 1198.3 2.246 .4452 204 206 384.4 357.2 841.2 1198.4 2.226 .4493 206 208 385.2 358.1 840.5 1198.6 2.206 .4534 208 210 386.0 358.9 839.8 1198.7 2.186 .4575 210 212 386.8 359.8 839.1 1198.9 2.166 .4618 212 214 387.6 360.6 838.4 1199.0 2.147 .4660 214 216 388.4 361.4 837.7 1199.1 2.127 .4700 216 218 389.1 362.3 837.0 1199.3 2.108 .4744 218 220 389.9 363.1 836.4 1199.5 2.090 .4787 220 222 390.7 363.9 835.7 1199.6 2.072 .4829 222 224 391.5 364.7 835.0 1199.7 2.054 .4870 224 226 392.2 365.5 834.3 1199.8 2.037 .4910 226 228 393.0 366.3 833.7 1200.0 2.020 .4950 228 230 393.8 367.1 833.0 1200.1 2.003 .4992 230 232 394.5 367.9 832.3 1200.2 1.987 .503 232 234 395.2 368.6 831.7 1200.3 1.970 .507 234 236 396.0 369.4- 831.0 1200.4 1.954 .511 236 238 396.7 370.2 830.4 1200.6 1.938 .516 238 240 397.4 371.0 829.8 1200.8 1.923 .520 240 242 398.2 371.7 829.2 1200.9 1.907 .524 242 244 398.9 372.5 828.5 1201.0 1.892 .528 244 246 399.6 373.3 827.8 1201.1 1.877 .532 246 248 400.3 374.0 827.2 1201.2 1.862 .537 248 250 401.1 374.7 826.6 1201.3 1.848 .541 250 275 409.6 383.7 819.0 1202.7 1.684 .594 275 300 417.5 392.0 811.8 1203.8 1.547 .647" 300 350 431.9 407.4 798.5 1205.9 1.330 .750 350 APPENDIX 473 TABLE II Properties of Common Substances Specif Grav- ity. Weight per Cubic Foot, Lbs. Weight of One Cubic Inch, Lb. Specifi. Heat. Coefficient of Expan- sion per Deg. F. Volu- metric. Aluminum Bismuth Boxwood, along or across grain. Brass Cement Copper Coal (anthracite) Coke Gasoline Glass Gold... Ice (at 32° F.) Iron (cast) Iron (wrought) Lead Limestone Mercury (at32°F.) Nickel Pine (white), along grain Pine (white), across grain Platinum Porcelain Oak, along grain Silver Steel Tin Zinc 2.60 9.82 161 613 .095 .353 8.10 2.24 8.79 1.43 1.00 .68 2.89 19.26 .92 7.5 7.74 11.35 3.16 13.60 8.90 .55 503 140 545 88. 62. 42. 180. 1200 57. 465 582 708 197 849 547 .293 .083 .318 .058 .037 .105 .697 .033 .271 .280 .411 .114 .492 .321 .020 21.5 1342 .779 10.47 7.83 7.29 7.19 653 486 452 445 .379 .292 .264 .260 .212 .031 .094 .20 .097 .241 .203 .000011 .000008 .000002 .00001 .000008 .000009 .000033 .000024 .000006 .00003 .000024 .000028 .198 .032 .504 .130 .110 .031 .217 .033 .109 .65 .000005 .000008 .000014 .000024 .000006 .000007 .000016 .000018 .000021 .000048 .032 .056 .116 .056 .095 .000033 .000007 .0000025 .000020 .000005 .000002 .000003 .000011 .000007 .000012 .000016 .000100 .000020 .000008 .000080 .000015 .000006 .000009 .000033 .000020 .000035 .000048 TABLE III Metric Conversion Table Millimeters X .03937 = inches. Millimeters -5- 25.4 = inches. Centimeters X .3937 = inches. Centimeters -v- 2.54 = inches. Meters X 39.37 = inches. (Act of Congress.) Meters X 3.281 = feet. Meters X 1.094 = yards. Kilometers X .6214 = miles. Kilometers + 1.6093 = miles. Kilometers X 3280.8 = feet. Square Millimeters X .00155 = sq. inches. Square Millimeters -f- 645.2 = sq. inches. Square Centimeters X -155 = sq. inches. Square Centimeters -f- 6.452 = sq. inches. Square Meters X 10.764 = sq. feet. Square Kilometers X 247.1 = acres. Hectare X 2.471 = acres. Cubic Centimeters -f- 16.387 = cubic inches. Cubic Meters X 35.314 = cubic feet. 474 POWER PLANT TESTING Cubic Meters X 1.308 = cubic yards. Cubic Meters X 264.2 = gallons (231 cu. in.) Liters X 61.023 = cubic in. (Act of Congress.) Liters X .2642 = gallons (231 cu. in.) Liters -5- 3.785 = gallons (231 cu. in.) Liters 4- 28.317 = cubic feet. Hectoliters X 3.531 = cubic feet. Hectoliters X 2.838 = bushels (2150.42 cu. in.) Hectoliters X .1308 = cubic yards. Hectoliters X 26.42 = gallons (231 cu. in.) Grams X 15.432 = grains (Act of Congress.) Grams X 981. = dynes. Grams -r- 28.35 = ounces avoirdupois. Grains -r- 15.432 = grams. Grains 4- 7000 = pounds. Joule X .7373 = foot pounds. Kilograms X 2.2046 = pounds. Kilograms X 35.27 = ounces avoirdupois. Kilograms -r- 907.2 = tons (2,000 lbs.) Kilogr. per sq. cent. X 14.223 = lbs. per sq. in. Kilogrammeters X 7.233 = foot lbs. Kilo per sq. Meter X .672 = lbs. per sq. foot. Kilo per Cu. Meter X .0624 = lbs. per cu. ft. Kilowatts X 1.34 = Horse Power. Watts -T- 746. = Horse Power. Watts X .7373 = foot pounds per second. Calorie X 3.968 = B.t.u. Cheval vapeur X .9863 = Horse Power. (Centigrade X 1.8) + 32 = degree Fahrenheit. Franc X .193 = Dollars. Gravity Paris = 980.94 centimeters per sec. = 32.17 feet per TABLE IV The Equivalents op Ounces, per Square Inch, in Inches of Height op Columns op Water and Mercury 27.71 inches of water and 2.04 inches of mercury equal one pound per square inch at atmospheric pressure and 62° F. Temperature. Mercury is 13.58 times as heavy as water. Ounces. Inches of Water. Inches of Mercury. Ounces. Inches of Water. Inches of Mercury. .146 0.25 .018 7 12.12 .892 .292 0.51 .037 8 13.85 1.019 .438 0.76 .055 9 15.59 1.148 .584 1.01 .074 10 17.32 1.275 1 1.73 .127 11 19.05 1.402 2 3.46 .255 12 20.78 1.529 3 5.20 .382 13 22.52 1.658 4 6.93 .510 14 24.25 1.785 5 8.66 .637 15 25.98 1.913 6 10.39 .765 16 27.71 2.036 INDEX PAGE Absolute Pressure Gages 6 Absorption Refrigerating Machines 385 Accelerometer 174 Air Compressors, Testing of 371-376 Air Engines , 389 Air, Flow of 176 "Air" Horse Power 368, 373 Air Pump 23 Air, Velocity and Volume of 180, 369 Air Supplied to Furnace, Determination of, from Flue Gases 250, 281 Alden Brake Dynamometer 155 Allen-Moyer Gas Apparatus 243 Alternating Current, Measurement of 317, 324 Ammonia, Leakage of 381 , Properties of, Tables 380-381 " Refrigerating Plants 377 Amsler Planimeter 76 Analysis of Coal, Proximate 328-333, 463 Analysis of Flue Gases 235, 464 Analysis of Fue Gases, Typical Examples of 240 Anemometers 182 Aneroid Barometers 6 Areas, Measurement of 74 Ash in Fuel, Determination of 230 Aspirator 236 Atwater's Fuel Calorimeter " 216 Averager (Planimeter), Ansler 75-81 " , Coffin 81-85 Bachelder Indicator 102-103 Back-firing Indicator Diagrams 352 Balance-sheet of Gas Engine . . . 350 Balance-sheet of Gas Producer 362 Balance-sheet of Boiler 275, 281, 282 Balance-sheet of Steam Engine or Steam Turbine 320 Barometers 4 " , Corrections for 5 Barraclough & Mark's Engine Tests 312 Baume Scale of Specific Gravity 397 Belts,Testing Tension in 392, 465 Bending (Transverse) Tests 444 Blowers, Testing of 364-371 Boiler Balance-sheet 275, 281, 282 475 476 INDEX PAGE Boiler Efficiency 274, 278 Boiler Feed-pumps, Testing of 410-417 Boiler Feed-water, Measurements of, in Tests 273, 319 Boiler Heat Balance 275, 281, 282 Boiler Horse Power : 263, 268 Boiler Summary Sheets 276-281 Boiler Test Graphical Log Sheet 268 Boiler Testing: Datum Lines of Water and Fire in Tests 272, 273 Boiler Testing, Principal Objects of 267 Boiler Testing, Rules for (A.S.M.E.) 269-281 Bourdon Pressure Gage, Theory of 7-8 Bourdon Pressure Gage with Steel Tube 10 Brake Dynamometers 147-164, 464 Brake Horse Power 147 Brake Pulley, Design for 151 Briquettes of Neat Cement for Testing 447 Bristol-Durand Integrator for Circular Diagrams 87-91 Brumbo's Pulley 126 Burning Point of Oils, How Tested 402, 462 Calibration of Pressure Gages 15-22, 460 " Vacuum " ■ 22, 460 Indicator Springs 112-120, 461 " Thermo-Electric Thermometers and Pyrometers 45 " Mercury Thermometers 29-37, 460 Calorific Value of Fuel, Determination of 210, 463 Calorific Value of Gas 222, 464 Calorimeter, Barrel (for Steam) 70 , Bomb (for Fuels) 211 , Combined Separating and Throttling 65-69 , Condensing (Steam) 70 , Calibration of 73, 461 , Electric 69 , Fuel 211-227, 463 , Junkers 222-227, 464 , Separating (Steam) 63-65 , Throttling 55-63 , Wire-drawing (or Throttling) 55-63 Charts, for Determining Moisture in Steam 59, 61 Nipples ' 56, 57, 60, 66 Capillary Corrections for Mercury 3 Carbonic Acid (C0 2 ), Apparatus for Determining 240-245, 252 Carbonic Acid Refrigerating Machine 379 Cement Tests 447 Centrifugal Fans,Testing of 364-371 " Pumps, Testing of 419 Chemical Analysis of Fuels to Determine Calorific Value 227 Chill Point of Oils 403 Chimney Gases, Weight of, Calculated from Analysis 251, 281 Clearance of an Engine Cylinder, Determination of 293 Coal Analysis, Proximate 228-233 Coal, Calorific Value of, from Analysis 227 INDEX 477 PAGE Coals Recommended for Standard Boiler Trials (A.S.M.E.) 269, 270 Coal Testing: Proximate Analysis 228, 233, 463 Coal Calorimeters 211-222, 463 Coefficient of Dilution 249 " Discharge for Orifices 186, 189, 191, 202 " " " Weirs 204 " " Expansion of Mercury 21 Coefficients of Expansion of Various Substances Appendix " " Friction of Friction Wheels 394 " " " " Oils and Bearings 404, 463 Coffin Planimeter 81-85 Columns, Testing of 442 Combined Separating and Throttling Calorimeters 65-69 Commercial Steam Engine Testing 295 " Turbine Testing 317 Composimeter 255 Compound Gages 12 Compression Tests of Materials 441-442 Compressors, Air, Testing of 371-376 " , Ammonia, Testing of 382-385 Condensers, Testing of 305 Continuous Indicator 106 Conversion of Pressures 7 " Temperatures and Heat Units 29 Cooley-Hill Continuous Indicator 106 Cooley Indicator Spring Tester 113-120 Cooley Stroke Measuring Counter 412 Corliss Engine Diagrams, Normal and Abnormal 289 Corliss Engine-Valve setting 288-293 Correcting Steam Engine and Steam Turbine Tests to Standard Conditions . 329-340 Correction Curves for a Steam Turbine 329-339 Correction for Stem Exposure of Mercury Thermometers 36-39 Crosby Indicator 95-99 Cups, Thermometer .....:... 30-31 Curve, Hyperbolic as Applied to Indicator Diagram 298 " , Typical "Error" 22 Curves for Determinations of Moisture in Steam 59, 61 Cut-off, How Determined 288, 298 Dead-center to Set Engine On 286 Dead-weight Gage Testers 17-19 Deflectometers 434 Density of Water at Different Temperatures 7 " " Ammonia (Liquid) 380 " " Substances, Table of Appendix Diagram Factor of Engines 303 Diaphragm Gages 11 Differential Dynamometer, Calibration of 168 Gages 12 Direct Current, Measurement of 323 Draft Gages 24-27 Drum Motion Testers 120-122 478 INDEX PAGE Ducts, Loss of Velocity in 371 " , Measuring Velocity of Air in ." 180,369 Durand-Bristol Integrator 87 Duty of a Steam Pump 414 Dynamometer, Alden 155 " , Differential 165 " , Dynamo 162 " , Emerson "Scales" 168 " , Fan 154 , Flather 169 " , Hints on Management 150 " , Kenerson's 174 " , Rope and Strap 150-153 , Torsion 172-175 , Water Brake 155-162 " , Webber Transmission 167, 465 Dynamos as Dynamometers 162 Eccentric, Setting of, Effect on Indicator Diagram 289 Econometer 256 Economy of Steam Engine Compared with Ideal 308 Eddy Current Brakes 163 Efficiency of Steam Boiler 274,278 " " Fans or Blowers 368,373,376 " " Gas Engine 341,346,350 " " Gas Producer 357,359 " " Refrigerating Machines 384,385 " " Steam Engines, Thermal 305 " " " Turbines, Thermal 322 " Compared with Rankine Cycle 322 Ejector for Flue Gases 236 Elastic Limit Defined 434 Electric Dynamometers 162,163 Electrical Measurement of Power 323 " Instruments, Precautions to be Observed 324 " Pyrometers 41-45 Emerson Fuel Calorimeter 216 " Power Scales 168 Engine and Boiler Tests (Combined) 336-340 Engine Lubricators 405 Entropy Defined 309 Entropy-temperature Diagram 309 Error Curve, Typical 22 Extensometer 433 Fan Dynamometers 154-155 Fans, Ventilating 364 Feed-water, Measurement of 193-209 " Thermometer and Gage 53 Feed Pumps, Testing of 408,410 Flashing Point of Oil, How Determined 400-403, 462 Flather's Dynamometer 169 INDEX 479 PAGE Fliegner's Formula 185 Flow of Air 176-189, 369 Steam 189-193 Water 193-209 Flue Gas Analysis 235, 464 Flue Gas, Determination of Air Supply from 250, 281, 283 Flue Gases, Loss of Heat in 252, 281 , Weight of 251, 281, 282 Form for Report of Boiler Test 276 " " Gas Engine Test 346 Steam Engine Test 298 " " " Pump Test 415 " Turbine Test 325 Francis Formula for Weirs 204 Friction Brakes and Dynamometers 147-164 " Horse Power 284 Wheels, Tests of 394 Fuel: Calculation of Heating Value 214, 219, 226, 228 Fuel Calorimeters 211-227 Fuel for Gas and Oil Engines, Measurement of 176, 343 Fuels, Calorific Value of 210 Fuel Testing 210-234 Gages, Bourdon 7,8 , Calibration of 15-22, 460 , Diaphragm 11 , Draft 24-27 , Pressure 7-15 , Recording 12-15 , Vacuum 2, 12 Gage Notch 203, 204 Gage Testers 17-19 Gas, Calorific Value of 222 " , Measurement of 176-189 Gas Engine Balance Sheet 350 , Efficiency of 341, 350 " Fuel, Measurement 343 " Indicator Diagrams: Normal, "Suction," etc 350, 351 " showing "Timing" of Ignition 352 Gas Fuels 353, 464 " Meters 176 " Producers 353 Gasoline, Measurement of 343 Goss Dynamometer 164 Goss' Experiments on Indicator Connections 139 "Guarantee" Tests 321 Head at a Pump (Suction, Discharge, Total), Defined 409, 414 Heat Balance of Boiler 281 Gas Engine 350 " " Producer 362 " Refrigerating Plant 384 480 INDEX PAGE Heat Units, Conversion of 29 Heating Value of Fuels Calculated from Analysis 227 " " by Experiment 211-227 Heat Unit Basis of Engine Testing 296, 306 Hempel Gas Apparatus 245-248 Hirn's Analysis 306 Hoists, Efficiency of 391, 465 Hook Gage 203 Hopkinson's Optical Indicator 112 Horse Power, Boiler 263, 268 , Brake 147, 465 , Indicated 136, 141, 284, 341, 465 Hot-air Engine, Testing of 389 Humidity of Air 368 Hydraulic Machinery, Testing of 408 Hydraulic Motors, Testing of 419 Rams, Testing of 424 Hydrostatic Pressure on Gages 11 Hyperbolic Curve Applied to Engine Indicator Diagrams 298 Ice Making Capacity 382 Ice Melting Capacity 382 Impellers of Fans 364 Impulse Water Wheels 424 Indicated Horse Power, Calculation of 136, 141, 284, 341, 465 " " Engine Constant 143 Indicator, Bachelder 102 , Care of 103 , Continuous 106 , Crosby 95 , Crosby Gas Engine 342 , High-pressure (Ordnance) 372 , Optical 108 , "Star Brass" 99 , Tabor- 99 , Thompson 93 , Watt 92 Indicator Diagrams, Analysis of 136-141 " , Calculation of Steam Consumption from 297, 304, 310, 312 " from Flather's Dynamometer 170-171 of Gas and Oil Engines 350-352 " showing Back Firing 352 " of Suction Stroke 350 " Taken with Light Spring Attachment 350 Indicator Drum Testing Apparatus 120-122 Spring Testing " 112-120 " , Calibration of 112, 460 Injector, Method of Operating 428 Testing 428 " Test, Form for Report on 429 " Used in Boiler Testing, Correction Applied to Feed- Water 271 Integating Instruments, Durand-Bristol 87 INDEX 481 PAGE Integrating Instruments, Planimeters 75-91 "Internal" Horse Power 321 Junkers Gas Calorimeter 222-227, 464 Kenerson's Torsion Dynamometer , 174 Latent Heat of Ammonia 381 Steam, Table of Appendix Leakage Test of a Boiler 259, 319, 339 of Steam in Tests 260, 305 Light Spring Indicator Diagrams of Suction Stroke of Gas Engine 350 Log Form for Indicator Spring Test 119 " for Mechanical Efficiency Test of Engine 284 " for Pressure Gage Test 21 " for Thermometer Calibration 34, 37 Losses of Head in Ducts 371 Low Pressure Gages 22 Lower Heat Value of Gas 224-226 Lubricators, Engine 405-407 Lubricants, Tests of 395-407 Mahler Bomb Calorimeter 21 1-214 Machines for Testing Strength of Materials 431-450 Manograph 110-112 Manometers 1-4 Mean Ordinate, Determination of 80, 83, 142 " Effective Pressure by Coffin Planimeter -83 Mechanical Pyrometer 45 Efficiency 284, 341, 371, 385, 465 Mercury Columns, Cleaning of 7 " " , Corrections for 3 " , and Equivalent Pressure per Unit Area 7 " Column for Calibrating Gages 19-23 " Expansion of 21 and Appendix " Thermometers 28 Metallic Pyrometers 45 Meter, Gas 176-178 " , Venturi 199 Metric Conversion Table 471 Modulus of Elasticity 434 Moisture in Coal 229, 232 " " Steam (by Charts) , 58-61 " " " , Determination of 55 Moulds for Cement Briquettes 448-450 Napier's Formula 189 Oil Engines, Measurement of Fuel for '. 343 Oils, Tests of 395-407, 462 "Orsat" Apparatus 241-245 Optical Indicators 108-113 Optical Pyrometers 50 482 INDEX PAGE Pantograph Reducing Motion for Indicators 121, 124, 127 Parallel Rule for Dividing Diagrams 142 Parr Calorimeters 217 Pendulum Reducing Motions 125 Permanent "Set" Defined 434 Perry Optical Indicator 108-109 Pitot Tubes 178-182 Planimeter, Amsler 76 , Calibration of 86, 460 , Coffin 81 " , Polar, Theory of 76 " , Roller 85 Platform Scales 260, 462 Pneumatic Pyrometers 46 Polar Planimeter 75 Positive Pressure Blowers 366 Power, Measurement of 147 Power Scales, Emerson 168 Pressure (lbs. per square inch) and Equivalent Head of Water or of Air 7, 474 Pressure and Temperature of Steam, Table of Appendix Pressure Type of Gas Producer 353 Pressure Gages 7-16 " , for Measuring Draft 24 " , Calibration of 15-23 " , Recording' 12-15 Pressure Gage Tester, Dead-weight 17 Pressure Scales, Crosby" 18, 19 Prony Brake 147, 464 Proximate Analysis of Coal 228-233, 463 Pulsometer, Testing of 426 Pump, Centrifugal, Testing of 419 Pumping Engine Trials 413-419 Pumps, Effective Head at (footnote) 409 " , Testing of Feed 411 Pyrometer, Calibration of 45 Calorimeter 51 " Cones 52 " , Electric Resistance 44 " , Mechanical 45 " , Mercury 40, 46, 53 , Optical 50 " , Radiation 47-50 , Recording 39-41, 47 " , Thermo-electric 41-44 Quality of Steam, How Calculated 58, 68, 70, 72 " Determined from Charts 59, 61 Radiation Loss in Calorimeters 64, 67, 68, 211, 214, 221 Rankine Cycle Steam Engines and Turbines 304, 308, 322 Ratings of Capacity, Commercial 266 Ratio of Expansion 298 INDEX 483 PAGE Reaction Water Turbines 422 Recording C0 2 Apparatus 252-255 " Gages 12-15 " Thermometers 37-41 " Pyrometers 37-41, 47 Reducing Motions for Indicators 121-136, 461 Refrigerating Plants 377 " Capacity 382 Report of Boiler Test, Forms For 276 " Gas Engine Test, Forms for 346 " Steam Engine Test, Forms for 298 " " Turbine Test, Forms for 325 Resilience 435 Revolution Counters 144 Rider Hot Air Engine 389 Rope Brake 151, 464 " , Hints on Management of (footnote) 150 Rope Drives, Tension in 392 Rotary Engine, Indicated h. p 143 Rules for Boiler Testing (A.S.M.E.) 269 Gas Engine Testing (A.S.M.E.) 345 Steam Engine Testing (A.S.M.E.) 294 " Turbine Testing (A.S.M.E.) 325 Sampling Bottle for Flue Gases 235-240 Sampling Coal 228, 231 Tubes for Flue Gas (A.S.M.E.) 238, 272 Scales -for Weighing Fuel 260, 462 Seger Pyrometer Cones 51 Separating Calorimeter 63 " Set" (Permanent) Defined 434 Shaft Dynamometers 172, 175 Simpson's Rule for Areas 74 Siphons for Steam Gages 9-10 Sirocco Fans 364 Slip in Pumps 409, 413 Smallwood's Drum Motion Tester 121-122 Smoke Observations 225, 274 Specific Gravity Determinations 395, 451 Specific Gravities of Various Substances, Table of Appendix Specific Heat of Ammonia 381 " " Various Substances, Table of Appendix " " Superheated Steam 309, 310 " Volume of Steam Appendix Speed Counters 144, 146 Speed-output Curves 316, 322 Spring Tester, Indicator 112-120 Standard Conditions for Ventilating Fans(U. S. Navy) 370 " " Engine and Turbine Tests 329 " " Gases 223, 226, 357 Steam, Flow of 189 Steam Calorimeters 55-73, 461 484 INDEX PAGE Steam Consumption Calculated from Indicator Diagram 297, 304 ,310, 312 " Determined from Feed-water 296, 319, 339 when using Surface Condenser 295, 305 " Calculated from Heat Balance 319, 320 " Engine Lubricators 405 " " Testing, Rules for 294 " " Thermal Efficiency of 305 Steam Measurement (Meters, etc.) 189-193 " , Tables of Properties of 34, 468 Stem Exposure of Thermometers, Correction for 36-39 Stroke-measuring Counter 412 Suction Gas Producer, Testing of 353 " Stroke Diagrams of a Gas Engine 350 " Head of Pump, Measurement of with Gage (footnote) 409 Superheated Ammonia 381 " Steam, Flow of 189 " " , Specific Heat of 309 Surface Condensers, Testing of 305 Tabor Indicator 99 Tachometers 145 Temperature, Measurement of 28 " Scales, Conversion of 29 Tension Tests of Materials 435, 437 Testing Boilers 267 " Gas Engines 341 " Hydraulic Motors 419-426 " Impulse Water Wheels 419 " Refrigerating Machines 377 " Steam Engines 284, 294 " " Pumps 413 " Turbines 315 " Strength of Materials 431 " Ventilating Fans and Blowers 364 " Water Turbines 422 Test-pieces, Standard Shapes and Sizes for 436,448 Theoretical Water Rate 322 Thermal Efficiency of a Gas Engine 350 " " Steam Engine 297, 304, 305 " " " Turbine 322, 328 Thermo-electric Pyrometers and Thermometers 41-44 Thermometer, Alcohol 29 " and Pressure Gage Combined 53 , Calibration of 29, 31-37, 460 " Correction for Stem Exposure 36-39 for Flue Gases 28, 41-54 " for High Temperatures 28, 46 , Mercury 28-38, 40, 46, 53 " , Recording 39-41 " with Mercury Well for Steam Pipes 53-54 " , Regraduating of (footnote) 28 ' , Standard 31 INDEX 485 PAGE Thermometer, Thermo-electric 41-44 Wells 30-31 , Wet and Dry Bulb 368-369 Thompson Indicator 93-94 Throttling Calorimeters 55 Timing of Ignition 352 Torque (footnote) 147 of Steam Turbine 322 Torsion Dynamometers 172-175 Total Heat of Saturated Steam, Table of Appendix " " Superheated Steam 296 Trammels, Method of, for Setting Engine on Dead Center (footnote) 286 Transmission Dynamometers 164-175, 465 Transverse Bending Tests 444 Turbine Dynamometer, Westinghouse 158 Two-fluid Manometers (Draft Gages) : 26-27 Ultimate Strength Defined 435 U-tube Manometers 1-4, 6, 24, 26 Vacuum Gages, 2, 12 on Suction Pipes of Pumps (footnote) 409 Valve Setting, D-slide and Piston Types ■. 285-288 Corliss Type 288-293 Velocity of Air 178-183, 367 Ventilating Fans 364-367 R ; ij " Systems, Testing of 366 Venturi Water Meter 199 Vicat Needle 453 Viscosity 398, 462 Volatile Matter in Coal 230, 232 Volume of Air Discharged by a Blower ' 368 " of a Pound of Steam, Table of Appendix Volumetric Efficiency of Refrigerating Machine 383 Water Brakes 155-162 " Cooled Brake Pulley 150-151 " Equivalent of Calorimeters 72, 210 " Flow through Circular Orifice or Nozzle 201-203 " Friction Djmamometer, Westinghouse 158-161 " Measurement of by Weir 203-207 " , Measuring Tank, Continuous 196-198, 207-209 " Meters 193-206 " Meter, Venturi 199 " Rate Curve 316 " Rate, Theoretical ' 322 " Seals for Pressure Gages 9-10 " Turbines 422 " , Weight of at Different Temperatures 7 " Wheels, Testing of *. 419 Watt's Indicator 92-93 Weak Spring Indicator Diagrams 350 486 INDEX PAGE Webber's Transmission Dynamometer 167 Webb's Viscous Dynamometer 161-162 Weighing Machine for Water 196-199, 205 Weight of Air Required to Burn a Pound of Fuel 250, 281-283 Weight of Air, Table of 181 " Chimney Gases 251, 281 " Flue Gases 251, 281 " a Cubic Foot of Steam, Table of Appendix " Various Substances, Table of Appendix " Water at Different Temperatures 7 Wells, Thermometer 30-31 Westinghouse Water Brakes 158-161 Wet and Dry Bulb Thermometer for Humidity 368-369 Willans Law 312 " Lines ; . • 313-315 Willcox Water Weigher 196 Wire-drawing Calorimeters (Throttling) 55