Patent ID: 8297943

Claim:
A rotary positive displacement pump for supplying pressurized working fluid to a driving device, the pump comprising: a control valve comprising a piston moveable in a bore and a biasing spring for biasing the piston to act against a force created by pressurized working fluid from a first outlet port of the pump to reduce output pressure of the pump; and a second outlet port wherein a pressure of the working fluid exiting the second outlet port is greater than a pressure of the working fluid at the first outlet port of the pump and varies with the speed of the pump, the greater pressure working fluid exiting the second outlet port is supplied to the control valve, creating a force which augments and combines with a force of the biasing spring acting on the control valve to counter the force of the pressurized working fluid from the first outlet port acting on the piston, and wherein the entire working fluid output of the second outlet port is supplied to the control valve.