The Locomotive Of Today

THE LOCOMOTIVE OF TO-DAY. 63 Section II.—THE ENGINE. HAVING explained the construction and details of the boiler, and shown how the steam is generated, we take next in order the mechanism by means of which the energy of the steam is transformed into useful work; this, in the case of a locomotive, is the propulsion of itself and the load to which it is attached. Primarily the engine consists of cylinders into which the steam is admitted, thereby moving the pistons, whose recipro- cating motion is transformed through the medium of the piston and connecting’ rods into a rotary one at the crank axle, pro- pelling the engine either backwards or forwards as required. There being usually two cylinders, there are correspondingly two cranks, to each of which one of the pistons is connected. These cranks are arranged at right an gies, so that when one is at the end of its stroke and doing no useful work, the other is working at its best advantage. To actuate the valves, distributing the supply of steam to the cylinders, a “motion ’ is required which admits steam alternately to either side of the pistons, and allows . steam on the opposite side to discharge through the biast pipe to the atmosphere. Owing to the work that a locomotive has to do, it is absolutely necessary that the “motion” should be rever- sible, to enable the engine to travel in either direction; the various descriptions of this will be detailed later. The cylinders are the heart of the machine, and are usually fitted at the front of the engine, either between the frames, when the engine is called “inside cylindered,’ or on the outside of the frames, when it is known as “outside cylindered. ’ The first is most common in Britain, whilst the latter is larg'ely adopted on the Continent, and is universal in America. The advan- tages claimed for the cylinders between the frames, are, greater rigidity to the whole structure as they act as a frame stay, and the motion being transmitted between the frames, the engine is inclined to be steaclier, further the width over all may be less; the disadvantages are, the cranked axle and the difficulty of getting large cylinders in without cramping the steam chest. For the outside cylinders the great accessi- bility of all parts is an important argument. The size of the cylinders depends on the work for which the engine is designed, and it will range from 8-in. diameter by 10-in. stroke to 20-in. diameter by 26-in. stroke ; almost every size between these are to be met with, as well as examples smaller and larger. The metal employed is cast