Pump with bypass valve

摘要

A pump includes a housing having at least a first pumping chamber, an inlet, an inlet passage leading from the inlet to the pumping chamber, an outlet and an outlet passage leading from the pumping chamber to the outlet. A first pumping member is movable in the pumping chamber on an intake stroke whereby fluid from the inlet passage is drawn into the pumping chamber and on a discharge stroke whereby fluid in the pumping chamber is discharged into the outlet passage. A drive is provided for moving the pumping member on the intake and discharge strokes. A bypass passage leads from a location in the outlet passage to a location in the inlet passage. A bypass valve is provided and is movable in response to the pressure from the outlet passage and substantially independent of the pressure from the inlet passage between an open position in which fluid flows through the bypass passage and a closed position in which fluid is prevented from flowing through the bypass passage. Having a bypass valve movable only in response to the pressure from the outlet passage enhances the reliability and consistency of bypass valve operation.