A variable displacement vane pump

A variable displacement vane pump (1), e.g. for providing power assistance to a vehicle steering system (47), comprises a cam ring (3) which is movable between minimum and maximum operating positions, and a pressure relief and flow control valve arrangement (29) having a flow control orifice and a hydraulic liquid feedback circuit. When power assistance is not required the cam ring (3) is in a minimum position and the pump (1) operates in a standby output mode to provide a pilot hydraulic liquid flow via orifices 44 and 24, line 45 and steering control valve 46 to keep the hydraulic system served by the pump (1) in a charged condition. When power assistance is required the cam ring (3) is moved with the use of a back pressure to the maximum position and the pump (1) operates in a maximum output mode to provide a maximum hydraulic liquid flow. The flow control valve (30) is moved against spring (43) by the pressure differential created across orifice (24) when the flow reaches a predetermined level to release excess flow to spill port (42). Excess pressure is relieved to spill port (42) by the automatic opening of relief valve (34).