The Locomotive Of Today

The Locomotive of To-day. Section I.—THE BOILER. ÄLLHOUGH not the most economical steam generator, the modern locomotive boiler possesses numerous advantages. It is a quick steam producer for its size and weight, can be readily forced when occasion demands, and in shape is admirably adapted for its particular purpose. It is, however, expensive, and many attempts have been made to substitute a less c.ostly construction, but although some of these have been partially successful, the faet remains that the improved boiler of the “Rocket,” of Rainhill farne, is the acceptecl model for the locomotive boiler of to-day. It may be described as an internally fired horizontal multitubular boiler, consisting essentially of four main portions:—Ihe inner firebox, the outer firebox or shell, the barrel containing the tubes, and the smokebox. Referring now to our illustration, Fig. i, at one end of the boiler, in the inner firebox the fire is placed and the heated gases from it are conducted through a number of tubes or flues arranged in the barrel, and around which the water to be raised into steam circulates, to the smokebox at the other end, and thence to the chimney. With the number of tubes employed, usually from 200 to 250, it will be seen that the heating surface in contact with the water is very large, but even then to make sufficient steam to keep the engine supplied it is necessary to urge the fire artificially to inerease the rate of combustion. To do this the exhaust steam escaping from the engine cylinders is utilised. It is emitted from a so-called “ biast pipe ” below the base of the chimney, and almost any desireel intensity of draught can be obtained by contracting this outlet for the exhaust steam. Every stroke of the piston sends a discharge of steam through this “ biast pipe ” up the chimney, with- drawing a percentage of the contents of the smokebox with it, and leaving a partial'vaeuum in that chamber, and it is to destroy this that atmospheric air rushes through the fire from beneath producing the rapid combustion desired. Passing now to the construction of the boiler, the inner firebox first demands attention. In the early Bury locomotives this was