and steam turbines and internal-combustion engines, where fuel furnishes the
energy to the machine, the governor regulates the flow of fuel. To control
the speed of a hydraulic turbine generator, a governor can alter the water
flow by opening and closing gates and valves. Another type of mechanical
governor, used to regulate the speed of aircraft engines, varies the pitch of
the propeller blades attached to the engine.
common type of mechanical governor operates by means of the forces of inertia
(the resistance to change or motion) that arise from longitudinal or rotary
motion. For example, when a spring-loaded mechanical governor is rotated, the
flyweights, or flyballs, are flung outward by centrifugal force (see
Centripetal Force). At a given speed, the flyweights are in an equilibrium
position and the spring is partially compressed. An increase in speed causes
the flyweights to rise as they pull farther out from the axis of rotation.
This causes a further compression of the spring. The spring sets up a control
force that may close a valve or in some other way decrease the energy input
to the machine. As a result, the speed of the machine decreases, at which
point the flyweights begin to fall. Then, the spring becomes less compressed
and valve is opened once again.