The Locomotive Of Today

The Engine : Pistons, Piston Rings. 69 high speed. Ihey are mad© with a thicksned. boss, through which the end of the piston rod passes, the hole being usually tapered and recessed slightly at the largest end for the reception of a shoulder turned on the rod; the taper . is generally about i in 8, the rod being sometimes ground in, but generally siæply turned to the same tapsr as the hole, a good fit with from to | of an inch “ draw,” and it is then pulled home to the shoulder by means of a nut placed on the screwed end of the rod, the nut is often octagonal to occupy less space. Wlien. the nut is fa.st, a, hole is drillsd tliroug^h it and the rod for the reception of a rivet or taper pin, the ends of which are hammered into countersinks, preventing the nut from slacking loose in working-. Instead of the rivetted pin, the end of the rod may be rivetted over to secure the nut; in either case it is generally necessary to split the nut for removal. The rim of the piston is widsned. and turned up to A inch less in diameter than the cylinder, and has a recess or recesses turned in it for the reception of one or more rings, one being- used for small pistons, and two or three for larger ones. A, Fig. 14, shows a piston used for cylinders from 17 to i8| inches in diameter. It is made of cast iron, but if Steel were used the disc might be made thinner. It is turned to take two rings. B is one intended for three rings, and may be in either of the above metals. C is a piston for mueh smaller cylinders, and has one ring only. The advantages of having more than one ring are—less liability of the steam passing, and greater flexibility, as one ring- being- necessarily stiffer, has a mueh greater tendency to cut the cylinder. The rings can be made in cast-iron, Steel or brass, the first being the metal by far the most commonly employed. A barrel of the necessary diameter, and about one foot long- is cast, and then turned to ^-in. larger in diameter than the cylinders which the rings are to fit, and the pieces wide enough to form rings are turned off with a parting tool; two holes are drilled at a distance of about i^~in. apart, and the piece between them removed. The rings can then be sprung- into the cylinder a good fit, they are kept from turning on the piston by pins screwed into it, but these are not exaetly in the same place for both rings, so that should steam pass one ring it is not likely to get by the next; the ends, too, are also kept away from the ports in which they might catch. When Steel or brass is used it is often made in bars of the required section, and the rings are bent to shape, the joints being simply cut across diagonally and butted together. The first- named metal is used for very hard cylinders, and the latter for soft ones.