Centrifugal governor

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A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel (or working fluid) admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions. It uses the principle of proportional control.

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, 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.


James Watt designed his first governor 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 employed for steam engines. James Watt never claimed the centrifugal governor to be an invention of his own. Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. It is therefore a misunderstanding that James Watt is the inventor of this device[1].

A giant statue of Watt's governor stands at Smethwick in the English West Midlands. It is known as the flyball governor.

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, somewhat like a drum brake. This is used in a spring-loaded record player and a spring-loaded telephone dial to limit the speed.

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