The Locomotive Of Today

The Engine : Cylinders, Ports. 65 irön of best selected close-grained quality, and as hard as can be worked. In the illustration, Fig 13, several views ofa pair of inside cylinders of common form are shown. They are suitable for all classes of engines requiring them not larger than 18-in. diameter. The steam chest is placed between the two cylinders, which has made it customary to cast them in two portions, to facilitate the machining of the ports; the two halves benig then accurately faced up and bolted together. Improvements in the machine tools employed have, however,. made it possible now to cast the cylinders of this design in one piece, thus obviating the necessity for a troublesome steam joint between them. At A and B a pair of cylinders is shown, the channels by which the steam gets to the chest are best seen at A. It will be noted that the passage branches out and supplies steam to both ends of the steam chest simultaneously, this is most necessary on this type of cylinder as the valves and.their buckles take so much room ; if steam were only allowed to enter at one end the other port would be insufficiently supplied and give the engine a weak beat. The exhaust outlet is shown at the centre, and above it the biast pipe stands. At B the other cylinder is shown in sectional plan with the slide valve in mid-position, so that the shape of the ports and covers may be seen, with the valve; the face on which the slide works is raised about |-in. above the surrounding metal to allow for wear and, if necessary, refacing. The metal forming the cylinder barrel is made thick enough to allow of more than one re-boring, as wear takes place unequally, the barrel being worn more opposite the ports, especially at the front end, and then allowing steam to pass the piston when the engine is commencing its stroke. At either end the bore is enlarged or recessed so that the piston wears no shoulder at the finishing points of its stroke. The covers are made to follow the contour of the piston, so that too much steam shall not be imprisoned there. The distance between the cover and the piston is termed the “clearance,” and is usually f-in. at the front end and J-in. at the back end ; this allows for wear and tear and the expansion of the piston rod. The metal employed for the front cover is usually cast iron, but steel both cast and stamped is sometimes used. The back cover containing the stuffing box is always cast iron. The faces for the cover joints are carefully scraped up true and then made tight with thin red lead and boiled oil. In tightening the joint the nuts should not be screwecl full up on one side before some pressure is applied opposite or the joint will not be tightened up all round. 5