The Locomotive Of Today

The Engine : Tail Rods, Slide Bars. 73 I here are numerous other methods of packing piston rods, but the principles involved are generally as already described. The valve spindles have stuffing- box.es which may be the same as those for the piston rods,, but generally with metallic packing they are simplified by leaving out the arrangements introduced for securing flexibility, not being so likely to get •out of truth. With large cylinders the piston rods are often carried through the front cover, the tail rod thus formed being intended to assist in carrying the weight of the piston and save wear of the bottom of the cylinder. Valve spindles are treated in a similar manner, and an advantage may be claimed for this practice that it is possible to fix the valve centrally over the ports by means of the giands if by chance the back spinclle gets broken inside the steam chest. Of the frames proper we shall deal later, when describing the carrying gear of the locomotive. The motion or “spectacle” plate extends across between the frames __ of engines with inside cylinders at a point about 4 feet behind them, forming a transverse stay and a means of attachment for the slide bars and various parts of the motion. It may be built up of plate, strengthened with angles, or, as is more usual in new engines, cast in Steel with suitable lugs on it for fixing the slide bars, etc., to. The slide bars are intended to keep the movement of the piston rod in a straight line, as the crosshead is fixed to the end of the piston rod to which the small end of the connecting rod is attached, and which would be continually forced up- wards when the engine was working forwards, or downwards when the engine was reversed; this, if permitted, would be fatal to the piston rods. There may be either one, two, three or four of these slide bars to each crosshead, according to the fancy of the designer. When one is used it is usually made in wrought iron, about 3-in. thick by 6-in. wide for 18-in. cylinders, case-hardened and afterwards ground to shape, or it may be of Steel; it is fixed above the piston rod, and the crosshead encloses it. When two are provided, one is placed above and one below the piston rod, and the crosshead works between them ; they may be in either of above metals or of cast iron. Three are used on some engines doing most of their work in one direction; the top bar is of cast iron made wide to allow a good surface for the slide, and the two lower ones—one on each side—support the crosshead when the en- gine is running’ backwards. Four bars are arranged, two above and two below, and the crosshead works between a slide block on either side running- between two bars ; any of above metals