Gerotor pumps are known for their low cost-to-horsepower ratios and dependability. They are extremely tolerant of contaminants, and provide high efficiencies and quiet operation.
The pump elements include an internal gear, keyed to the shaft, within an external gear. The internal gear has one fewer lobe than the external gear. Volume between the rotating gears increases during the intake portion of each turn, and decreases during the discharge portion.
These pumps are no longer in production. There is only a limited availability of rebuilt units.