Internal gear pumps work on the same principle, but the two interlocking gears have different sizes, one interlocking gear rotates inside the other. The larger gear (rotor) is an internal gear, that is, its teeth protrude inside. Within this range, a smaller external gear is installed eccentrically (idler gear – only drives the rotor). It is designed to interlock with the rotor so that the gear teeth mesh at a certain point. The pinion gear and bushing attached to the pump casing hold the idler in place. A fixed crescent-shaped partition or gasket fills the gap created by the eccentric installation position of the idler and serves as a seal between the inlet and outlet.

When the gears are disengaged from the pump inlet side, they will create an enlarged volume. As the gear continues to rotate against the pump casing and the diaphragm, liquid flows into the cavity and is captured by the gear teeth.

The trapped fluid moves around the sleeve from the inlet to the outlet.

When the teeth of the gear interlock on the discharge side of the pump, the volume decreases and the fluid is forced to discharge under pressure.


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