(150) Speed Regulation.
On steam tractors a constant speed is maintained by “throttling” the steam, to meet the demands of the load by partially restricting the flow of steam at light loads and opening the inlet at full load. The valve that controls the steam for the different loads is controlled by a “governor” which depends on the centrifugal force exerted by two fly-balls. The balls, or weights are hinged to a revolving spindle, driven by the engine, in such manner that an increase of speed tends to straighten out and revolve in a more nearly horizontal plane. The amount of travel of the balls for a given speed increase, is governed by a spring, which returns them to a vertical position when the speed decreases. By means of a simple system of levers, the valve is closed when the balls fly out, due to an increase of speed, and is opened when the speed decreases, so that the engine will receive the steam at a higher pressure and again build up its speed to normal. As the load fluctuates, the balls are constantly moving up and down, seeking a valve position that will keep the engine at a constant speed.
Speed variation is generally accomplished by increasing or decreasing the tension of the spring that controls the travel of the governor fly balls, and in the majority of engines this may be done without stopping the engine.
Another form of governor used extensively on stationary engines controls the speed by increasing or decreasing the cut-off. Thus with a heavy load the cut-off may occur at ½ the stroke while with a very light load it may be at 1
10 stroke. This is by far the most sensitive and economical form of governor, but on account of the reverse gear it is difficult to apply it on a tractor.