The Piston and Rods. The pistons of locomotives vary greatly in details of construction but the general idea is the same in all cases. Since the pistons receive all the power the locomotive delivers, they must be strongly constructed and steam tight. All pistons consist of a metal disk mounted on a piston rod which has grooves on the outer edges for properly holding the packing rings. The pistons are commonly made of cast iron, but where great strength is required, steel is now being used. Fig. 79 illustrates the present tendency in design. The cylindrical plate is made of cast-steel and the packing rings, two in number, are made of cast iron. The packing rings are of the snap ring type and are free to move in the grooves.
As can be seen, the rim is widened near the bottom in order to provide a greater wearing surface. Fig. 79 also clearly shows the method used in fastening the piston to the piston rod. The piston rod is made of steel and has a tapered end which fits into the cross-head where it is secured by a tapered key. The crosshead fit is made accurate by careful grinding. The crosshead key should likewise be carefully fitted.
Table of Contents; Page 110; Page 112; Index