LOCOMOTIVE 



3477 



LOCOMOTIVE 



which the pistons slide, and rods connecting the 

 piston with the wheels. The cylinders are car- 

 ried on either side of the engine, near the front. 

 Steam is admitted to them by means of a 

 throttle valve carried in one of the domes on 

 the top of the boiler and operated by means 

 of a lever in the cab. The piston rod slides 

 through a round hole in the back cylinder 

 head, which is packed so as to be steam-tight. 

 Through this rod, power is conveyed to the 

 main driving wheels, and by means of connect- 

 ing side rods to the other driving wheels. 



Types of Steam Locomotives. The two 

 main types of locomotives are those developed 

 by the different needs of passenger and freight 

 service. 



Passenger Service. Passenger service may 

 be divided into through service and local serv- 

 ice. For through service, powerful locomotives 

 of great speed are built to haul from six to 

 fifteen coaches long distances. They are capa- 

 ble of maintaining a speed of seventy-five or 

 eighty miles an hour. Many of them are now 

 constructed with twelve wheels three pairs of 



A MODERN LOCOMOTIVE 



The illustration is that of a locomotive over seventy-five feet long, which weighs 212% tons. A 

 man six feet tall and wearing a silk hat can stand erect in the smaller end of the boiler. A barrel 

 could be placed within one of the cylinders. Fewer than ninety years of development lie between 

 the above monster and the "Rocket" of 1829. 



The working parts of the engine are con- 

 nected by levers with the cab. These are, be- 

 sides the throttle valve already mentioned, the 

 reversing mechanism; the air brakes, which 

 control the brakes of the entire train; the in- 

 jectors, which admit water from the tender to 

 the boiler; the sanding device, which occupies 

 another dome on the engine and conveys sand 

 to the track to prevent the wheels from slip- 

 ping; the whistle and the bell. The engine is 

 often oiled, too, by means of automatic lubri- 

 cators operated from the cab. These lubri- 

 cators provide a continuous flow of oil to parts 

 of the machine where the friction is great. 



driving wheels, two trailing wheels under the 

 cab, and four small wheels for guiding pur- 

 poses. The guiding wheels are attached to the 

 leading truck. The driving wheels on locomo- 

 tives of which speed is required are much 

 larger than those on freight locomotives, so the 

 train may be carried forward farther with each 

 revolution. On locomotives of the so-called 

 Atlantic type and Pacific type, the driving 

 wheels are occasionally eighty inches in diame- 

 ter. Such locomotives may weigh as much as 

 425,000 pounds. For local service, locomotives 

 having much smaller drivewheels and steam 

 capacity are used. 



