Editing Centrifugal governor (section)

==Operation==
[[File:Centrifugal governor and balanced steam valve (New Catechism of the Steam Engine, 1904).jpg|thumb|upright|Cut-away drawing of steam engine speed governor. The valve starts fully open at zero speed, but as the balls rotate and rise, the central [[valve stem]] is forced downward and closes the valve. The drive shaft whose speed is being sensed is top right]]

The devices shown are on steam engines. Power is supplied to the governor from the engine's output shaft by a belt or chain 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 (locomotive)|prime mover]].  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 [[mass]]es 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 the top of this page.

===Non-gravitational regulation===
A limitation of the two-arm, two-ball governor is its reliance on gravity to retract the balls when the governor slows down, and therefore a requirement that the governor stay upright.

Governors can be built that do not use gravitational force, by using a single straight arm with weights on both ends, a center pivot attached to a spinning axle, and a spring that tries to force the weights towards the center of the spinning axle. The two weights on opposite ends of the pivot arm counterbalance any gravitational effects, but both weights use centrifugal force to work against the spring and attempt to rotate the pivot arm towards a perpendicular axis relative to the spinning axle.

Spring-retracted non-gravitational governors are commonly used in [[Single-phase electric power|single-phase]] [[alternating current]] (AC) [[induction motor]]s to turn off the starting [[field coil]] when the motor's rotational speed is high enough. They are also commonly used in [[snowmobile]] and [[all-terrain vehicle]] (ATV) [[continuously variable transmission]]s (CVT), both to engage/disengage vehicle motion and to vary the transmission's pulley diameter ratio in relation to the engine [[revolutions per minute]].