All About Engines

Fig. 74.—Hartnell governor con- trolling Meyer expansion valve The Modern Reciprocating Engine 123 fixed to the main spindle, and when the balls fly out- wards they lift a collar by which the motion is transmitted to the throttle valve. Used either in this way or in the way to be described, the speed of the engine can be kept constant within per cent. This means that an engine con- structed to run at 200 revolutions per minute would not exceed 202J, nor fall below 197J revo- lutions a minute. But while throttle governing is the simplest, and can O be effected with the smallest governor, in many engines the control is exercised directly upon the valve admitting steam to the cylinder. By alter- ing the cut-off according to the speed of the engine the amount of steam ob- taining admission to the cylinder is regulated with the greatest nicety at the latest possible moment. Fig. 74 shows how this is accomplished with a Hartnell governor and a Meyer expansion valve which has been shown diagram- matically in Fig. 71. The rod of the eccentric which operates this valve