The Locomotive Of Today

The Engine : Cylinders, Pistons, etc. 67 which is machined up to exactly fit the hole provided in the main frame. An accurate fit is necessary to prevent any movement of the cylinders in the frame plate, the effect of which would be disastrous to the successful running of the engine; substantial cross-stays are requisite for outside cylindered engines owing to the great distance between the centres of the cylinders, often 6-ft. 3-in. After the cylinder castings are set in their places the holes through the flanges and frame plates are reamered out, and bolts, turned a tight clriving fit are put in and screwed up. A gives a cross section through the centre and shows the exhaust passage which terminates in a flanged joint above the cylinder barrel, to this flange one leg of the base of the biast pipe is con- nected. B is a sectional plan showing the piston and piston rod in position, as well as the valve and steam ports. A tail rod prolongation of the piston rod is shown provided with a covering tube attached to the front of the stuffing box cover. Metallic packing of the “Earl” type is shown here for all the rods. C is a view of the steam chest with cover and valve removed exposing the ports; the outline of the casting will be readily followed from this sketch as will also the position of the retaining bolts. D is the front cylinder cover whilst E is the back one which in the case of outside cylinders is usually made separate from the main casting. The cylinder in this case is shown lagged with slieet metal having an intervening air space, but in many cases a cover- ing of wood or asbestos is put on before the cleacling plates are wrappecl round. The front end is also usually finished with a plate filling the inner edge of the flange of the cover. lt is customary in some cases to entirely case the flanges over with dished metal covering caps which impart a very neat appearance to the engine, these caps being held in position by a central nut or the lubricator if such is provided for the cylinders. When the outer cleading is fashioned with a curve to meet the smokebox, it is advisable to place a footstep about midway for the use of the enginemen when passing round the engine. The pistons are usually made of cast iron, wrouglit iron or cast steel, brass being occasionally used. The shape is necessarily determined by the size of the cylinders and the metal employed. For all sizes up to 17 inches, cast iron is most common; for larger, steel or wrought iron are now largely adopted, on account of their g-reater strength, which enables the weight of the head to be materially decreased, this reduction in the weight of the reciprocating parts being a very important consideration, especially on engines designed for