Proell Governor is a different type of governor in which the fly balls are connected to the spindle using an extended arm. The fly balls are mounted on this additional arm. Like the porter governor, proell governor also has central weight which increases the speed of rotation. Proell Governor functions much more accurately than other governors and maintains a constant function without any fluctuation.

Construction :-

Proell Governor has following parts  :- spindle, central weight, arms, extended arms, fly balls and sleeve. The spindle is connected to the engine and its rotation speed increases and decreases with speed of the engine. Spindle has a central load to increase the speed of rotation. Two arms are pivoted at the top of the spindle and these two arms are connected to the extended arms which are connected to the fly balls. The other ends of the two arms which are pivoted to the top of the spindle is connected to the sleeve and moves the sleeve up and down . The sleeve actuates a mechanism which open and close the throttle valve. This sleeve has stoppers in up and bottom to limits its movements.

Working :-

When the load on the engine decreases, the speed of engine increases suddenly and also spindle rotation speed is increased as the spindle is connected to the engine. As the rotation of spindle becomes fast, the arms pivoted to top of spindle also rotates with high speed and the balls move outward due to increased centrifugal forced on the balls. When the balls move outward, the sleeve connected to the arms moves up and actuates a mechanism which closes the throttle valve and decreases the fuel supply which decreases the engine speed. Hence the engine speed is maintained.

On the other hand, when the load on the engine increases, speed of the engine decreases. Since the engine speed decreases, speed of rotation of spindle also decreases and hence the ball rotates at low speed and moves inward due to decrease in centrifugal force. As the balls moves inward, the sleeve moves in downward direction which actuates a mechanism which opens the throttle valve and increases the fuels supply and hence the engine speed increases.
In this way speed is maintained by this governor in both the cases.