All About Engines

The Modern Reciprocating Engine 129 the valve chamber. The end inside the chamber is forked and rests just in a groove on the valve spindle When the outer end, which is turned upwards, is piessed down the valve rises, and when it is released the valve falls to its seating again. What is required, then, is some means of pressing down the outer end of this lever during part of each revolution of the crankshaft. . Look again at Fig. 78. The shaft runs parallel with the cylinder and is driven by toothed wheels from the crankshaft at the same speed. On this shaft are two eccentrics for the admission valves and two cams for the exhaust valves. It will be clear rom the diagram how the exhaust valve is worked rom the cam, lever and rod pointing downwards and to the right. The rod pointing upwards to the right is pinned to a short lever which works at its other end on the same pin as the lever which lifts the valve. To this short lever is pinned a small bell-crank lever which is supported in a way shown in b, Fig. 79, so that one leg hangs over the end of the lever which lifts the valve. As the shaft turns, then, this bell-crank lever rises and falls, at each fall lifting the admission valve which it serves. Now, continuing to look at Fig. 79, there is a new shaft close to the valve chamber, and on this shaft is an arm, c, which holds up the hori- zontal arm of the bell-crank lever. This shaft is turned round a little to right or left, and the arm holding up the bell-crank rises or falls, according to the speed of the governor. If the speed increases J