A typical Proell governor is illustrated in Figure (a) that presents its line diagram. The balls are mounted on the extension of lower arms. The action of this governor is also same to the porter governor where enhance in speed raises sleeve and reduce in speed results in movement of sleeve down. While sleeve moves up opening of valve is decreased and while sleeve moves down opening of it is enhanced. Taking moment regarding instantaneous centre I in Figure (b) for AG being vertical
If AG is not vertical than
The ratio AD /GD is always less than 1. Comparing the equation (12.6) along Eq. (12.4) it is observed that the equilibrium speed is less for Proell governor is less than porter governor for similar mass of sleeve and ball. Hence, for the similar equilibrium speed proell governor needs balls of a smaller mass than that for porter governor. For similar masses, this governor needs smaller change in speed for similar lift of sleeve.
If friction at the sleeve is 'fN', equation (12.6) becomes,