A peculiar form of engine ([Fig. 126]) has been designed by Forney, in which the whole weight of engine, tender, coal, and water, is carried by one frame and on one set of wheels, the permanent weight falling on the driving-wheels and the variable load on the truck. These engines have also a comparatively short wheel-base and high pulling-power. The lightest tank-engines of the first class mentioned weigh 8 or 10 tons; but engines much lighter than these, even, are built for mines, where they are sent into the galleries to bring out the coal-laden wagons. The heaviest engines of this class attain weights of 20 or 30 tons. The heaviest engine yet constructed in the United States is said to be one in use on the Philadelphia & Reading Railroad, having a weight of about 100,000 pounds, which is carried on 12 driving-wheels.
Fig. 127.—British Express Engine.
Fig. 128.—The Baldwin Locomotive. Section.
A locomotive has two steam-cylinders, either side by side within the frame, and immediately beneath the forward end of the boiler, or on each side and exterior to the frame. The engines are non-condensing, and of the simplest possible construction. The whole machine is carried upon strong but flexible steel springs. The steam-pressure is usually more than 100 pounds. The pulling-power is generally about one-fifth the weight under most favorable conditions, and becomes as low as one-tenth on wet rails. The fuel employed is wood in new countries, coke in bituminous coal districts, and anthracite coal in the eastern part of the United States. The general arrangement and the proportions of locomotives differ somewhat in different localities. In [Fig. 127], a British express-engine, O is the boiler, N the fire-box, X the grate, G the smoke-box, and P the chimney. S is a spring and R a lever safety-valve, T is the whistle, L the throttle or regulator valve, E the steam-cylinder, and W the driving-wheel. The force-pump, B C, is driven from the cross-head, D. The frame is the base of the whole system, and all other parts are firmly secured to it. The boiler is made fast at one end, and provision is made for its expansion when heated. Adhesion is secured by throwing a proper proportion of the weight upon the driving-wheel, W. This is from about 6,000 pounds on standard freight-engines, having several pairs of drivers, to 10,000 pounds on passenger-engines, per axle. The peculiarities of the American type ([Fig. 128]) are the truck, I J, or bogie, supporting the forward part of the engine, the system of equalizers, or beams which distribute the weight of the machine equally over the several axles, and minor differences of detail. The cab or house, r, protecting the engine-driver and fireman, is an American device, which is gradually coming into use abroad also. The American locomotive is distinguished by its flexibility and ease of action upon even roughly-laid roads. In the sketch, which shows a standard American engine in section, A B is the boiler, C one of the steam-cylinders, D the piston, E the cross-head, connected to the crank-shaft, F, by the connecting-rod, G H the driving-wheels, I J the truck-wheels, carrying the truck, K L; N N is the fire-box, O O the tubes, of which but four are shown. The steam-pipe, R S, leads the steam to the valve-chest, T, in which is seen the valve, moved by the valve-gear, U V, and the link, W. The link is raised or depressed by a lever, X, moved from the cab. The safety-valve is seen at the top of the dome, at Y, and the spring-balance by which the load is adjusted is shown at Z. At a is the cone-shaped exhaust-pipe, by which a good draught is secured. The attachments b, c, d, e, f, g—whistle, steam-gauge, sand-box, bell, head-light, and “cow-catcher”—are nearly all peculiar, either in construction or location, to the American locomotive. The cost of passenger-locomotives of ordinary size is about $12,000; heavier engines sometimes cost $20,000. The locomotive is usually furnished with a tender, which carries its fuel and water. The standard passenger-engine on the Pennsylvania Railroad has four driving-wheels, 51∕2 feet diameter; steam-cylinders, 17 inches diameter and 2 feet stroke; grate-surface 151∕2 square feet, and heating-surface 1,058 square feet. It weighs 63,100 pounds, of which 39,000 pounds are on the drivers and 24,100 on the truck. The freight-engine has six driving-wheels, 545∕8 inches in diameter. The steam-cylinders are 18 inches in diameter, stroke 22 inches, grate-surface 14.8 square feet, heating-surface 1,096 feet. It weighs 68,500 pounds, of which 48,000 are on the drivers and 20,500 on the truck. The former takes a train of five cars up an average grade of 90 feet to the mile. The latter is attached to a train of 11 cars. On a grade of 50 feet to the mile, the former takes 7 and the latter 17 cars. Tank-engines for very heavy work, such as on grades of 320 feet to the mile, which are found on some of the mountain lines of road, are made with five pairs of driving-wheels, and with no truck. The steam-cylinders are 201∕8 inches in diameter, 2 feet stroke; grate-area, 153∕4 feet; heating-surface, 1,380 feet; weight with tank full, and full supply of wood, 112,000 pounds; average weight, 108,000 pounds. Such an engine has hauled 110 tons up this grade at the speed of 5 miles an hour, the steam-pressure being 145 pounds. The adhesion was about 23 per cent. of the weight.
