[737]. Spring friction grip wheels.
[738]. Intermittent reversible feed motion. The pinion is of leather, and drives the segment till it runs out of gear; when the machine is reversed it travels an equal distance the opposite way.
Section 41.—GOVERNING AND REGULATING SPEED, POWER, &c.
[739]. Is a device for varying the opening of a main valve (connected to rod A) by the pressure on the small piston, which moves it against the tension of a spring.
[740], [741], [742], & [743]. Types of centrifugal governors, of which numerous varieties are in use.
Pumping engines may be governed by allowing the pressure of water in the rising main to accumulate in a stand pipe or equivalent device until it stops the engine by excess of pressure. To prevent such an engine running away a catch is used, kept open by the pressure of water; when the pressure falls below a certain point the catch is released and closes the throttle valve.
Steam engines may also be safeguarded in the same way by a catch which is released and closes the throttle valve when the governor becomes fully expanded.
[744]. Screw and nut device, to control the travel of any machine, such as a lift, by reversing the belt or throwing out a catch after any specified number of revolutions, the travel being adjusted by the stop nuts.
[745]. The cataract is one of the oldest governing devices. It consists essentially of a vessel which is filled with water by one stroke of the engine, and empties itself through an adjustable orifice during the return stroke, the valve motion being prevented from reversing till the water is all discharged.