The Locomotive Of Today

The Boiler: Blast Pipe. 29 through a ring of holes forming the blower, which will be referred to later on. In designing a blast pipe care should be taken to make it so that the cone of escaping steam just enters the lower end of the barrel of the chimney, and not strike the base of the chimney or the top of the smokebox wrapper plate, as by doing this the draught on the fire is greatly impaired; the distance from the top of the biast nozzle to the base of the chimney will therefbre depend on their relative sizes. Varying opinions exist as to the cross section of the pipe, and also as to its form at the upper part, but it would seem advantageous to secure as easy a passage for the exhaust steam as possible from the cylinder ports to the top of the pipe, and therefore all awkward bends should be eliminated. The outlet should be exactly central, with the centre line of the chimney for the last foot of its length. Some designers make the last i^-in. of the bore parallel as at A, Fig. 6. Others will only have J-in. parallel, and some bring the taper of the pipe up to the top, with very little, if any, parallel at all, as at B. A con- tracted orifice is a frequent cause of back pressure in the cylinders, but sometimes the exhaust steam from one cylinder passing over and interfering with that from the other will cause equal trouble, and to overcome this many engines have two exhaust orifices, one for each cylinder, the pipe having two flanges and made “ breeches ” shape, with legs joined at the top and terminating in a single nozzle. American builders make the exhaust steam from each cylinder entirely free from this interference by providing each cylinder with an inde- pendent pipe and separate nozzles; the disadvantage of this arrangement is that it does not give an orifice exactly central with the chimney. Ordinary biast pipes at each stroke of the piston discharge a cone of steam through the chimney. This steam is sur- rounded by the products of combustion which are withdrawn from the smokebox by the velocity of the steam, but nozzles are made which collect the gases both inside and outside the ex- hauststeam. Thesearevariouslytermed “vortex,” “expansion” pipes, etc., and are cast to a shape which discharges the exhaust through an annular outlet, drawing the gases from the lower tubes through the centre of it. This design is claimed to give a more regular draught over the tube area than the ordinary pipe. C shows the Adams’ form of vortex biast pipe in section Another device discharges the exhaust in a hollow ring, but the centre is occupied by the waste steam from the ejector for the vacuum brakes, which is thus assurecl of being exactly air with the chimney centre line.