TWO-STAGE POSITIVE DISPLACEMENT PUMP

摘要

A positive displacement pump comprising a first pumping gear arranged in engagement with second and third pumping gears thereby establishing primary and secondary pump stages; each pump stage being adapted to displace fluid from a low pressure port to a high pressure port, regulator valve means communicating with the high pressure port of each pump for establishing a controlled bypass between said high pressure ports and low pressure fluid supply circuit and a feed-back circuit connecting the inlet side of the secondary pumping stage to the outlet side of said regulator valve means whereby a pressure buildup occurs on said inlet side thereby rendering the secondary pump stage inactive when the driven speed of said pumping gears exceeds a predetermined value, both pumps being active during operation at low speeds and the secondary pump being rendered inactive during operation at high speeds.