It is most obviously seen on steam engines where it regulates the admission of steam into the cylinders. It is also found on internal combustion engines and variously fueled turbines, and in some modern striking clocks
The device shown is from a steam engine. Power is supplied to the governor from the engine's output shaft by (in this instance) a belt or chain (not shown) connected to the lower belt wheel. The governor is connected to a throttle valve that regulates the flow of working fluid (steam) supplying the prime mover (prime mover not shown). As the speed of the prime mover increases, the central spindle of the governor rotates at a faster rate and the kinetic energy of the balls increases. This allows the two masses on lever arms to move outwards and upwards against gravity. If the motion goes far enough, this motion causes the lever arms to pull down on a thrust bearing, which moves a beam linkage, which reduces the aperture of a throttle valve. The rate of working-fluid entering the cylinder is thus reduced and the speed of the prime mover is controlled, preventing over-speeding.
Mechanical stops may be used to limit the range of throttle motion, as seen near the masses in the image at right.
The direction of the lever arm holding the mass will be along the vector sum of the reactive centrifugal force vector and the gravitational force.
