The governor is used to control the speed at which steam flows from the boiler into the piston cylinder. Power from the engine turns the shaft of the governor. As the shaft turns, the ball-shaped weights move out and up as they spin. As the speed of the engine increases, the weights move up the shaft until they close the connected steam valve. This reduces the amount of steam in the piston cylinder, which in turn slows down the engine. The weights then slow down and move down the shaft, until they are low enough to open the connection to the steam valve again.
