where d = diameter of 1.p. cylinder in inches; D= diameter of driving-wheel in inches; p = mean effective pressure per sq. in., after deductin internal machine friction; hstroke of piston in inches; Z = tractive force required, usually 0.14 to 0.16 of the adhesion. The value of p depends on the relative volume of the two cylinders, and from indicator experiments may be taken as follows: = Horse-power of a Locomotive.-For each cylinder the horsepower is H.P. = pLaN÷ 33,000, in which p = mean effective pressure, L = stroke in feet, a = area of cylinder 4d2, N = number of single strokes per minute, LN'= piston speed, ft. per min. Let M = speed of train in miles per hour, S = length of stroke in inches, and D = diameter of driving-wheel in inches. Then LN = M × 88 × 2SD. Whence for the two cylinders the horse-power is The Size of Locomotive Boilers. (Forney's Catechism of the Locomotive.)-They should be proportioned to the amount of adhesive weight and to the speed at which the locomotive is intended to work. Thus a locomotive with a great deal of weight on the driving-wheels could pull a heavier load, would have a greater cylinder capacity than one with little adhesive weight, would consume more steam, and therefore should have a larger boiler. The weight and dimensions of locomotive boilers are in nearly all cases determined by the limits of weight and space to which they are necessarily confined. It may be stated generally that within these limits a locomotive boiler cannot be made too large. In other words, boilers for locomotives should always be made as large as is possible under the conditions that determine the weight and dimensions of the locomotives. (See also Holmes on the Steam-engine, pp. 371 to 377 and 383 to 389, and the Report ofthe Am. Ry. M. M. Assn. for 1897, pp. 218 to 23.). Holmes gives the following from English practice: Evaporation, 9 to 12 lbs. of water from and at 212°. Ordinary rate of combustion, 65 lbs. per sq. ft. of grate per hour. Heating surface per lb. of coal burnt per hour, 0.9 to 1.5 sq. ft. Qualities Essential for a Free-steaming Locomotive. (From a paper by A. E. Mitchell, read before the N. Y. Railroad Club; Eng'g News, Jan. 24, 1891.)-Square feet of boiler-heating surface for bituminous coal should not be less than 4 times the square of the diameter in inches of a cylinder 1 inch larger than the cylinder to be used. One tenth of this should be in the fire-box. On anthracite locomotives more beatingsurface is required in the fire-box, on account of the larger grate-area required, but the heating-surface of the flues should not be materially decreased. Wootten's Locomotive. (Clark's Steam-engine; see also Jour. Frank. Inst. 1891, and Modern Mechanism, p. 485.)-J. E. Wootten designed and constructed a locomotive boiler for the combustion of anthracite and lignite, though specially for the utilization as fuel of the waste produced in the mining and preparation of anthracite. The special feature of the engine is the fire-box, which is made of great length and breadth, extending clear over the wheels, giving a grate-area of from 64 to 85 sq. ft. The draught diffused over these large areas is so gentle as not to lift the fine particles of the fuel. A number of express-engines having this type of boiler are engaged on the fast trains between Philadelphia and Jersey City. The fire-box shell is 8 ft. 8 in. wide and 10 ft. 5 in. long; the fire-box is 8×91⁄2 ft., making 76 sq. ft. of grate-area. The grate is composed of bars and water-tubes alternately. The regular types of cast-iron shaking grates are also used. The height of the fire-box is only 2 ft. 5 in, above the grate. The grate is terminated by a bridge of fire-brick, beyond which a combustion-chamber, 27 in. long, leads to the flue-tubes, about 184 in number, 134 in. diam. The cylinders a 21 in. diam., with a stroke of 22 inches. The driving-wheels, four-coupled, are 5 ft. 8 in. diam. The engine weighs 44 tons, of which 29 tons are on driving wheels. The heating-surface of the fire-box is 135 sq. ft., that of the flue-tubes is 982 sq. ft.; together, 1117 sq. ft., or 14.7 times the grate-area. Hauling 15 passenger-cars, weighing with passengers 360 tons, at an average speed of 42 miles per hour, over ruling gradients of 1 in 89, the engine consumes 62 lbs. of fuel per mile, or 344 lbs. per sq. ft of grate per hour Grate-surface, Smoke-stacks, and Exhaust-nozzles for Locomotives. (Am. Mach., Jan. 8, 1891.)-For grate-suriace for anthracite coal: Multiply the displacement in cubic feet of one piston during a stroke by 8.5; the product will be the area of the grate in square feet. For bituminous coal: Multiply the displacement in feet of one piston during a stroke by 6%; the product will be the grate-area in square feet for engines with cylinders 12 in. in diameter and upwards. For engines with smaller cylinders the ratio of grate-area to piston-displacement should be 7 to 1, or even more, if the design of the engine will admit this proportion. The grate-areas in the following table have been found by the foregoing rules, and agree very closely with the average practice: Smoke-stacks.-The internal area of the smallest cross-section of the stack should be 1/17 of the area of the grate in soft-coal-burning engines. A. E. Mitchell, Supt. of Motive Power of the N. Y. L. E. & W. R. R., says that recent practice varies from this rule. Some roads use the same size of stack, 131⁄2 in. diam. at throat, for all engines up to 20 in. diam. of cylinder. The area of the orifices in the exhaust-nozzles depends on the quantity and quality of the coal burnt, size of cylinder, construction of stack, and the condition of the outer atmosphere. It is therefore impossible to give rules for computing the exact diameter of the orifices. All that can be done is to give a rule by which an approximate diameter can be found. The exact diameter can only be found by trial. Our experience leads us to believe that the area of each orifice in a double exhaust-nozzle should be equal to 1/400 part of the grate-surface, and for single nozzles 1/200 of the grate-surface. These ratios have been used in finding the diameters of the nozzles given in the following table. The same sizes are often used for either hard or soft coal-burners. Exhaust-nozzles in Locomotive Eoilers.-A committee of the Am. Ry. Master Mechanics' Assn. in 1890 reported that they had, after two years of experiment and research, come to the conclusion that, owing to the great diversity in the relative proportions of cylinders and boilers, together with the difference in the quality of fuel, any rule which does not recognize each and all of these factors would be worthless. The committee was unable to devise any plan to determine the size of the exhaust-nozzle in proportion to any other part of the engine or boiler, and believes that the best practice is for each user of locomotives to adopt a nozzle that will make steam freely and fill the other desired conditions, best determined by an intelligent use of the indicator and a check on the fuel account. The conditions desirable are: That it must create draught enough on the fire to make steam, and at the same time impose the least possible amount of work on the pistons in the shape of back pressure. It should be large enough to produce a nearly uniform blast without lifting or tearing the fire, and be economical in its use of fuel. The Annual Report of the Association for 1896 contains interesting data on this subject. Fire-brick Arches in Locomotive Fire-boxes.-A committee of the Am. Ry. Master Mechanics' Assn. in 1890 reported strongly in favor of the use of brick arches in locomotive fire-boxes. They say: It is the unanimous opinion of all who use bituminous coal and brick arch, that it is most efficient in consuming the various gases composing black smoke, and by impeding and delaying their passage through the tubes, and mingling and subjecting them to the heat of the furnace, greatly lessens the volume ejected, and intensifies combustion, and does not in the least check but rather augments draught, with the consequent saving of fuel and increased steaming capacity that might be expected from such results. This in particular when used in connection with extension front. Size, Weight, Tractive Power, etc., of Different Sizes of Locomotives. (J. G. A. Mever. Modern Locomotive Construction. Am. Mach., Aug. 8, 1885.)-The tractive power should not be more or less than the adhesion. In column 3 of each table the adhesion is given, and since the adhesion and tractive power are expressed by the same number of pounds, these figures are obtained by finding the tractive power of each engine, for this purpose always using the small diameter of driving-wheels given in column 2. The weight on drivers is shown in column 4, which is obtained by multiplying the adhesion by 5 for all classes of engines. Columu 5 gives the weights on the trucks, and these are based upon observations. Thus, the weight on the truck for an eight-wheeled engine is about one half of that placed on the drivers. For Mogul engines we multiply the total weight on drivers by the decimal .2, and the product will be the weight on the truck. For ten-wheeled engines the total weight on the drivers, multiplied by the decimal .32, will be equal to the weight on the truck. And lastly, for consolidation engines, the total weight on drivers multiplied by the decimal .16, will determine the weight on the truck. In column 6 the total weight of each engine is given, which is obtained by adding the weight on the drivers to the weight on the truck. Dividing the EIGHT WHEELED LOCOMOTIVES. TEN-WHEELED ENGINES. adhesion given in column 3 by 7% gives the tons of 2000 lbs. that the engine is capable of hauling on a straight and level track, column 7, at slow speed. The weight of engines given in these tables will be found to agree generally with the actual weights of locomotives recently built, although it must not be expected that these weights will agree in every case with the actual weights, because the different builders do not build the engines alike. The actual weight on trucks for eight-wheeled or ten-wheeled engines will not differ much from those given in the tables, because these weights depend greatly on the difference between the total and rigid wheel-base, and these are not often changed by the different builders. The proportion between the rigid and total wheel-base is generally the same. The rule for finding the tractive power is: Leading American Types of Locomotive for Freight and Passenger Service. 1. The eight-wheel or "American" passenger type, having four coupled driving-wheels and a four-wheeled truck in front. 2. The ten-wheel" type, for mixed traffic, having six coupled drivers and a leading four-wheel truck. 3. The "Mogul" freight type, having six coupled driving-wheels and a pony or two-wheel truck in front. 4. The "Consolidation" type, for heavy freight service, having eight coupled driving-wheels and a pony truck in front. Besides these there is a great variety of types for special conditions of service, as four-wheel and six-wheel switching-engines, without trucks; the Forney type used on elevated railroads, with four coupled wheels under the engine and a four-wheeled rear truck carrying the water-tank and fuel; locomotives for local and suburban service with four coupled driving-wheels, with a two-wheel truck front and rear, or a two-wheel truck front and a four-wheel truck rear, etc. "Decapod" engines for heavy freight service have ten coupled driving-wheels and a two-wheel truck in front. Classification of Locomotives (Penna. R. R. Co., 1900).-Class A, two pairs of drivers and no truck. Class B, three pairs of drivers and no truck. Class C, four pairs of drivers and no truck. Class D, two pairs of drivers and four-wheel truck. Class E, two pairs of drivers, four-wheel truck, and trailing wheels. Class F, three pairs of driving-wheels and twowheel truck. Class G, three pairs of drivers and four-wheel truck. Class H, four pairs of drivers and two-wheel truck. Class A is commonly called a "four-wheeler " B, a six-wheeler "; D, an "eight-wheeler," or " American type; E, "Atlantic" type; F, "Mogul "; G, "ten-wheeler"; H, "Consolidation." Steam-distribution for High-speed Locomotives. (C. H. Quereau, Eng'g News, March 8, 1894.) Balanced Valves.-Mr. Philip Wallis, in 1886, when Engineer of Tests for the C., B. & Q. R. R., reported that while 6 H.P. was required to work unbalanced valves at 40 miles per hour, for the balanced valves 2.2 H.P. only was necessary. Effect of Speed on Average Cylinder-pressure.-Assume that a locomotive has a train in motion, the reverse lever is placed in the running notch, and the track is level; by what is the maximum speed limited? The resistance of the train and the load increase, and the power of the locomotive de.. creases with increasing speed till the resistance and power are equal, when the speed becomes uniform. The power of the engine depends on the average pressure in the cylinders. Even though the cut-off and boiler. pressure remain the same, this pressure decreases as the speed increases; because of the higher piston-speed and more rapid valve-travel the steam has a shorter time in which to enter the cylinders at the higher speed. The following table, from indicator-cards taken from a locomotive at varying speeds, shows the decrease of average pressure with increasing speed: Miles per hour. Calculated. 46 51 51 53 54 57 60 66 224 248 248 258 263 277 292 321 51.5 44.0 47.3 43.0 41.3 42.5 37.3 36.3 46.5 46.5 44.7 43.8 41.6 39.5 35.9 The "average pressure calculated" was figured on the assumption that the mean effective pressure would decrease in the same ratio that the speed increased. The main difference lies in the higher steam-line at the lower speeds, and consequent higher expansion-line, showing that more steam entered the cylinder. The back pressure and compression-lines agree quite closely for all the cards, though they are slightly better for the slower speeds. That the difference is not greater may safely be attributed to the large exhaust-ports, passages, and exhaust tip, which is 5 in. diameter. These are matters of great importance for high speeds.. Boiler-pressure.-Assuming that the train resistance increases as the speed after about 20 miles an hour is reached, that an average of 50 lbs. per sq. in, is the greatest that can be realized in the cylinders of a given engine at 40 miles an hour, and that this pressure furnishes just sufficient power to keep the train at this speed, it follows that, to increase the speed to 50 miles, the mean effective pressure must be increased in the same proportion. To increase the capacity for speed of any locomotive its power must be increased, and at least by as much as the speed is to be increased. One way to accomplish this is to increase the boiler-pressure. That this is generally realized, is shown by the increase in boiler-pressure in the last ten years. For twentythree single-expansion locomotives described in the railway journals this year the steam-pressures are as follows: 3, 160 lbs.; 4, 165 lbs.; 2, 170 lbs.; 13, 180 lbs.; 1, 190 lbs. Valve-travel. An increased average cylinder-pressure may also be obtained by increasing the valve-travel without raising the boiler-pressure, and better results will be obtained by increasing both. The longer travel gives a higher steam-pressure in the cylinders, a later exhaust-opening, later exhaust-closure, and a larger exhaust-opening-all necessary for high speeds and economy. I believe that a 20-in. port and 61⁄2-in. (or even 7-in.) travel could be successfully used for high-speed engines, and that frequently by so doing the cylinders could be economically reduced and the counterbalance lightened. Or, better still, the diameter of the drivers increased, securing lighter counterbalance and better steam-distribution. Size of Drivers.-Economy will increase with increasing diameter of drivers, provided the work at average speed does not necessitate a cut-off longer than one fourth the stroke. The piston-speed of a locomotive with 62-in. drivers at 55 miles per hour is the same as that of one with 68-in. drivers at 61 miles per hour. Steam-ports. The length of steam-ports ranges from 15 in. to 23 in., and has considerable influence on the power, speed, and economy of the locomotive. In cards from similar engines the steam-line of the card from the engine with 23-in. ports is considerably nearer boiler-pressure than that of the card from the engine with 174-in. ports. That the higher steam-line is due to the greater length of steam-port there is little room for doubt. The 23-in. port produced 531 H.P. in an 18-in. cylinder at a cost of 23.5 lbs. of indicated water per I.H.P. per hour. The 174 in. port, 424 H.P., at the rate of 22.9 lbs. of water, in a 19-in. cylinder. Allen Valves.-There is considerable difference of opinion as to the advantage of the Allen ported-valve (See Eng. News, July 6, 1893.) Speed of Railway Trains.-In 1834 the average speed of trains on the Liverpool and Manchester Railway was twenty miles an hour; in 1838 |