Patent ID: 8496445

Claim:
A pump system for supplying pressurized working fluid to a device with working fluid pressure requirements that vary with the operating speed of the device, the system comprising: a variable displacement pump operated by the device such that the pump operating speed is dependent upon the device operating speed, the pump including a moveable control member where the position of the control member determines a displacement of the pump; a regulating valve including an inlet port in fluid communication with an output of the pump, a first outlet port in fluid communication with a reservoir of working fluid and a second outlet port in fluid communication with the control member of the pump, the regulating valve further including a biased reciprocating spool that moves in response to pump output pressure, a first chamber in communication with a first portion of the spool, and a second chamber in communication with a second portion of the spool, the regulating valve being operable in a first mode where the spool is located at a first position to provide fluid communication between the second outlet port, the control member and the reservoir, a second mode where the spool is located at a second position isolating the control member of the pump from the second outlet port and the reservoir, and a third mode where the spool is located at a third position to provide fluid communication between the inlet port and the second outlet port, wherein the first chamber is in receipt of pressurized fluid from the output of the pump to generate a first force which urges the spool to move against the bias; and a control valve to switch between providing fluid communication between the second chamber and the output of the pump and providing fluid communication between the second chamber and the reservoir, wherein pressurized fluid in the second chamber generates a second force acting with the first force to urge the spool against the bias, the control valve being operable to alter output pressure of the pump between a first equilibrium pressure and a higher second equilibrium pressure.