LOCOMOTIVE. 388 LOCOMOTIVE. shown by the dotted line in the drawing. The end of the horn then becomes the pivot, and the length of the short arm of the lever is changed to 9V2 inches and of the long arm to about IIM; inclies. The drti pipe is the steam-pipe leading from the throttle valves to the engine cylinders, as shown by Fig. 7. Injectors are used for de- livering feed-water to the boiler. 8ce Injector. The engine or the mechanism for applying the pressure of the steam generated in the boiler to .■Brake Cylinc/er is controlled from the cab by means of a lever known as the reversing lever. Inside the cylinder works the piston. This is a disk-shaped structure of metal, and is made in various ways, but al- ways so as to fit the cylinder steam-tight, and so as to have ample strength to convey the push and pull of the steam to the piston-rod. The piston-rod is circular in secticm and is made of forged steel. It passes through the back cylinder- head by means of a circular orifice packed so as nder FlO. 1.3. DRIVING UHEELa, CONNECTING RODS, AND BRAKE GEAR OF LOCOMOTIVE. Fio. 11. LOCO.IOTIVE THROT- TLE VALVE. the rotation of the driving wheels, con- sists of the cylinders, pistons and piston- rods, connecting-rods and parallel rods, with their attachments and appurtenances. The cylinders are placed one on each side of front end, as shown three parts to each the locomotive near the in Fig. 8. There are cylinder, viz. the cylinder, the steam-chest, and saddle. The saddles of the two cylinders, being bolte<l together, ati'ord a support for the boiler, and in turn rest on the frame, as shown in Fig. 8. The steam-chest on each cylinder re- ceives the steam from the boiler and contains the valve which admits it to the cylinder. Fig. 12 is a longitudinal .section showing the inside of the cylindi'r and steam-chest of a simple locomo- tive. As will l)c seen, there is a steam-port from the chest to each end of the cylimlcr and lictwcen them an exhaust port, h ; the motion of the valve altci'nately opens and closes the steam-ports so as to admit steam first at one end and then at the other end of the cylinder. In the drawing, Fig. 12, steam is shown entering the forward Fig. 12. SECTION of cylinder. end of the cylinder and exhausting from the rear end. The ralre most commonly used is a slide valve of D shape, but piston valves are also em- ployed. A piston valve is shown in the suc- ceeding section on compound locomotives. The sliding motion of the valve is controlled by a device commonly called the valve-gear. Various forms of valre-gear are employed, but the one in most extensive use is the Stephenson link, the operation of which is explained in the article on Steam-Engines. The valve motion to be steam-tight and yet allow for movement to the rod. At its rear end the piston-rod connects with the cross-head, JI, working between the guides G(Fig. 12). In Fig. 1.3 are shown another form of cross-head and guides and also the ar- rangement of the connecting-rod and the side rods for an engine with six drivers. Connecting-rods and side rods are made of forged steel and have I sections. The frame of a locomotive is the platform by which the boiler and engine are supported on the wheels. In America bar frames are nearly al- ways employed. Fig. 14 shows the frame for a heavy freight locomotive. It will be seen that ftW/,2,nj-^ri ^V"?^""/* iSpr,ngM^n.Jr, B<0vmf>cril' Equalizing Bar ■' Fig. 14. frame fob consolidation locomotive. the top and bottom rods of the frame are con- nected by vertical struts known as pedestal- jaws, between which come the boxes of the driv- ing wheels. On the bottoms of the pedestal-jaws are bars or binders known as pedestal-caps. The number of jaws and style of frame are governed mostly by the number of driving wheels. In order to make an engine ride easily and to reduce the shock and concussion on the run- ning gear, the engine is provided with springs placed over each driving box and carried on a saddle which straddles the frame and rests on the <lriving box, as shown by Fig. 14. In order to equalize the weight between drivers there are provided bars between the drivers which are called equalizing bars. Drivinfi wheels are made with cast iron or cast steel centres with a forged steel tire. The usual method of attaching the tire to the cen- tre is to bore the tire slightly smaller than the centre and then expand it by heat until it slips over the centre onto which it shrinks. Driving wheels always have counterbalance weights at- tached on the side opposite the crank-pin to neutralize the shock which an unbalanced wheel gives to the track. As an indication of the quan- tities and quality of the different materials which enter into the construction of a modern heavy locomotive, as described above, the following figures given by W. H. Marshall, superin-
