Abstract：In order to study internal leakages, especially axial leakage, in an involute internal gear pump with high pressure, the flow in the gap channel between gear rim and pump casing, i.e. the axial leakage, was analyzed, and a simplified geometrical model was established. The pressure distribution along the circumferential direction in this channel was got by performing numerical simulations in Fluent. Based on that, the axial leakage flow rate was calculated, and validated experimentally. It was shown that the axial leakage is significant and it is the main factor that influences the volumetric efficiency of the pump. The flow rate in the axial leakage depends on the tolerance and eccentricity; moreover it increases with increasing clearance, but decreases with increasing eccentricity. In order to make sure the pump can maintain a high volumetric efficiency under a high pressure, the size of the gap between gear rim and pump casing should be controlled strictly in design phase. Meanwhile, the direction of eccentricity should be controlled carefully by figuring out a reasonable design for the radial thrust balance device. As a result, a part of the axial leakage flow rate can be reduced as well by ma-king use of change in eccentricity under a high pressure.
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