The governor is said to be stable when
1
For each speed within the working range there is only one radius of rotation for the governor ball
2
The equilibrium speed is constant for all radii rotation of the balls within working range
3
There is a slightest increase in speed, the governor balls will fly to this maximum radius.
4
The governor admits either maximum or minimum amount of energy to the engine and will not admit an amount of energy between these two extremes