LOCOMOTIVE. 387 LOCOMOTIVE. against the diaplira^m iilatc and are deflected downward or pass through the m-llinf; and out of the stack which is located direct!}' ahove the ex- haust nozzle. The exhauxt nozzle is the nozzle- like casting which terminates the exhaust-steam pipes from the cylinders. The successive cjiin- FlU. 8. 8ECT10.NAL ELEVATION OF FUOXT EXD OF A LOCO- MOTIVE. derfuls of steam pass up through it and out of the stack above in a succession of forcible blasts which entrain the gases in the smoke-box and carry them out of the stack, thus producing a partial vacuum in the smoke-box and conse- quently a suction or draught on the fire. The snwkcstack of a modern locomotive is usually open from top to bottom. In the older forms of locomotives the "diamond stack' was always used, and it is still employed under special couditions. aogqp Fig. 9. LOCOMOTIVE safety valve. Among the necessary fittings of a locomotive boiler besides those already described are safe- ty valve, whistle, steam-gauge, water-gauge, blower, throttle valve, dry pipe, and injectors. The locations of several of these fittings on the boiler are shown by Fig. 7. Safety valves for locomotives are of the pop type, and two are always employed, giving an aggregate area of opening of about 1 square inch to each 2 square feet of grate surface. Fig. 9 is a section through a safety valve. The valve u rests upon the seat 6 and is held in place by the pressure of the spiral spring d bearing down on the spindle e. The pressure of this spring is i-cgulatcd by screwing the collar e up and down. Outside of the valve-seat there is a projection / beneath which a. groove g is cut in the casing. When the valve lifts this groove is filled with steam which presses against the portion of the valve outside of the seat, and by liius increasing the efl'ecti^e area of the valve, causes it to rise higher and remain open longer than it would witliout this device. The adjustment of the valve is so made that it will allow steam to escape until the pressure in the boiler is 4 pounds below the normal. The perforated casing or muffler h breaks the escaping steam into nu- merous single jets and thus reduces the noise of the escaping steam. The ichistle consists of a, bell (A, Fig. 10) closed at the top and sharpened at the lower edge. By opening the valve shown the steam escapes through the narrow circular orifice B, and, enter- ing the bell, sets up vibrations which cause the 'whistle.' The t<me is controlled by the size of the bell and the pressure of the steam, being lower the larger the bell is, and louder the greater the steam pressure is. Chime whistles are commonly used, and they consist usually of a bell having three compart- ments, tuned respectively to the first, third, and fifth of the mu- sical scale. The bloicer consists of a pipe leading from the cab to tlie stack into which it turns up- ward so that by opening a valve a jet of steam is sent up through the stack and gives tj <lraught on the fire when the locomotive is stand- ing still and when, consequently, the exhaust is not acting as previously described. The throttle valve in general use is a double- seated poppet valve, shown in section by Fig. 11. As will be seen, there are two valves, a and 6, attached to a single stem. The upper valve, a, is the larger, and the lower valve. 6, is of such diameter that it will pass through the upper valve- seat. The steam, therefore, exerts a pressure on the lower face of b and on the upper face of «, so that the valve is partly balanced, but the valve a being larger than the valve 6. the down- ward pressure is the greater and tends to keep the valve closed. Considerable force is required to raise the valve against this pressure, and in order that this may be e.xcrted so as to task the strength as little as practicable, the lever ar- rangement shown is employed. The rod c from the cab is attached to the bell-crank d. and this in turn is attached to the valve-stem E. The point of the bell-crank is provided with a slotted hole. At the start of the pull the length of the lever arm is about 2V» inches, while the long arm is 91/2 inches. After the valve has been lifted from its seat and is free from the excess of pressure on a, the projecting horn A on the back of the bell-crank conies in contact with the bracket B, and the crank takes the position FlO. 10. LOCOMO- TIVE WHISTLE.
