A
variable displacement sliding vane pump comprising a pump body, inlet and outlet ports formed in said pump body, a
drive shaft rotatably mounted in said pump body, a rotor driven by said
drive shaft and co-axially aligned therewith, a plurality of radially extending vanes slidably disposed in said rotor, a pivot disposed in said pump body, a slide pivotally disposed on said pivot in said pump body and having a central axis eccentric to the axis of said rotor, a plurality of fluid chambers defined by said rotor, said vanes, and said slide that are successively connected to said inlet and outlet ports, a spring acting on said slide to urge said slide in one direction, a first chamber and a second chamber, each suitable for receiving a
fluid pressure and each disposed between said pump body and an outer surface of said slide, the first chamber in fluid communication with a pump outlet
discharge pressure, and a valve operable to selectively pressurize and depressurize the second chamber.