Positive displacement pump systems

Abstract

To minimize the power absorbed by a positive displacement pump system used where the requirement for pressure fluid varies inversely with the pump speed, notably in automobiles, the system provides two separate delivery passages 61, 62 for the pumped fluid and a discharge passage 66 into which the fluid from the delivery passage is passed under the control of a valve means 70, 71, the valve means commencing to operate on one (62) of the two delivered flows at lower speeds to by-pass a proportion of said one flow to an overspill 79, while the fluid not bypassed is added to the flow from the other delivery passage being passed to the discharge passage. The said proportion is increased in a manner to maintain the pressure drop across a discharge orifice in the discharge passage 66 at a constant value, and as the pump speed increases further the valve means commences to by-pass also an increasing proportion of the flow from said other delivery passage 61 to the overspill to maintain the said pressure drop constant. The increase in area of communication between the second delivery passage and overspill is greater than the increase in area of communication between the first delivery passage and overspill. In this way, the final regulation is carried out on a smaller quantity of fluid and less fluid is pumped to the highest pressure in the system.

Dependencies are inferred from the claim text.