The pumping mechanism consists of two elements: an inner rotor and outer stator. The inner element always has one less tooth than the outer. The volume of the "missing tooth" multiplied by the number of driver teeth determines the volume of fluid pumped at each revolution (cubic displacement per revolution). The number of teeth may vary -- depending on such design considerations as volume to be pumped, speed, and available pump envelope--but the inner element always has one less tooth than the outer.

As the toothed elements (mounted on fixed centers but eccentric to each other) turn, the chamber between the teeth of the inner and outer elements gradually increases in size through approximately 180° of each revolution until it reaches its maximum size-- equivalent to the full volume of the "missing tooth."

During this initial half of the cycle, the gradually enlarging chamber is exposed to the suction port creating a partial vacuum into which the liquid flows. During the subsequent 180° of the revolution, the chamber gradually decreases in size as the teeth mesh and the liquid is forced out the discharge port.

See Anamation