A centrifugal governor controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions.

It is most obviously seen on steam engines where it regulates the admission of steam into the cylinder(s). It is also found on internal combustion engines and variously fueled turbines.

The device shown is from a steam engine. It connected to a throttle valve and to the prime mover (not shown). The action of the governor is dependent on centrifugal force. As the speed of the prime mover increases, the central spindle of the governor rotates at a faster rate and the two masses move outwards, this motion is translated by the series of rods and arms to the throttle valve reducing its aperture. The rate of steam entering the cylinder is thus reduced and the speed of the prime mover falls. If the speed of the prime mover falls the reverse effect occurs and the throttle valve opens further.

The first governor was designed by James Watt in 1788 following a suggestion from his business partner Matthew Boulton. It was a conical pendulum governor and one of the final series of innovations Watt had developed for steam engines.

Another kind of centrifugal governor consists of a pair of masses on a spindle inside a cylinder, the masses or the cylinder being coated with pads. This is used in a spring-loaded record player and a spring-loaded telephone dial to limit the speed.

A similar form of power control can be achieved using a flywheel.