Gear pump or motor with bypass throttle passage to prevent cavitation

A gear pump or motor comprising a housing having a chamber bounded by a circumferential wall and two opposite end walls;

• a high pressure channel extending through said circumferential wall and having an inner end communicating with said chamber;
• a low pressure channel extending opposite said high pressure channel through said circumferential wall and likewise communicating at an inner end with said chamber;
• a pair of meshing external gears mounted in said chamber for rotation about axially parallel shafts, each of said gears having two opposite axial end faces, the flanks of the gear teeth of the two gears engaging each other between the inner ends of said channels along lines and forming between the engaging lines interstices increasing in the region of the inner end of said low pressure channel and decreasing in the region of the inner end of said high pressure channel;
• means mounting said shafts for rotation an engaging said opposite end faces of said gears;
• and a throttle passage in one of said mounting means having an inlet end in a region of said chamber which is under high pressure and an outlet end in the region of an interstice increasing in volume during rotation of the gears and which is sealed off by the engaging flanks from said high and low pressure channels.