The Locomotive Of Today

32 The Boiler: Blast Pip es, Petticoat Pipes. so that its size can be varied by opening or closing these flaps by means of suitable rods and levers. As will be seen, how- ever, the shape of the escaping steam will be different for each variation. This form of pipe is shown at F. Another method is to have the outlet of the pipe made serrated by vertical cuts, a ring- is made to revolve on the top of this, having on its internal diameter similar nicks ; thus, when the ring- is turned so that its teeth coincide with the teeth on the pipe the outlet is largest, and when the teeth of one covers the gaps of the other the outlet is smallest. This also is open "to the objection stated above. A novel arrangement of exhaust pipe and chimney is adopted on the P. L. M. Railway, France. It is remarked that the internal portion of the cone of steam issuing from an ordinary biast pipe is not utilised, but passes away as a wasted power, and in order to use it the diameter of the chimney is in this case made much larger with a copper cone up the centre over the exhaust pipe, small at the bottom, swelling out towards the middle, and reducing again at the top, thus the area through which the exhaust steam has to pass is about the same as that of an ordinary tapering chimney, although here the chimney itself is made parallel. When the steam leaves the biast pipe it strikes the bottom of the cone and spreads and filis the annulus between the cone and chimney. It is claimed that this secures a much steadier and softer draught on the fire. On referring to the drawing F, which shows this device in section, it will be seen that there is a pipe provided by which steam can be admitted at will to the lower part of the cone, which has a ring of holes around it, thus forming a blower. It should be observed that all the nuts that are used for holding down the biast pipe should be made of brass, and form caps to protect the ends of the studs from the corroding action of the steam and burnt gases ; on referring to A these- nuts will be seen. In America it has been the practice to make the biast pipe very short, and above it, up to the chimney base, provide “ petticoat ” pipes, sometimes one, and in many cases four or five, as they are saicl to give a more equable draught over the whole tube area. Ihis has now become a common practice here with the high pitched boilers now in vogue, and their consequent very short chimneys. It is a faet, well known to enginemen, that any obstruction placed in the biast pipe will materially add to the draught on the fire, and this knowledge has been made use of in the case of bad steaming engines by placing a bolt across the pipe