Patent ID: 7371053

Claim:
A two-stage hydraulic pump comprising: a rotor having an axis of rotation and a plurality of slots each radially extending from a circumference of said rotor toward said axis of rotation; a plurality of pumping members each slidably disposed in a different one of said plurality of slots to thereby define a pumping volume therebetween; a ring member disposed radially outwardly of said rotor and contacting said pumping members during a rotation of said rotor to permit outward movement of each of said pumping members during an inlet stroke of the pump to increase said pumping volume and inward movement of each of said pumping members during a discharge stroke of the pump to decrease said pumping volume; the pump having two discharge ports each at least partially coextensive with said rotor, one radially inward of said plurality of slots and the other radially outward adjacent said ring, said two discharge ports communicating with a discharge passage, and two inlet ports each at least partially coextensive with said rotor, one radially inward of said slots and the other radially outward adjacent said ring; a valve for providing fluid communication between said discharge passage and one of said inlet ports while disconnecting said inlet ports during a low flow arrangement and interconnecting said inlet ports during a high flow arrangement; wherein a 180 degree rotation of said rotor from a bottom dead center position to a top dead center position defines said inlet stroke, and a 180 degree rotation of said rotor from said top dead center position to said bottom dead center position defines said discharge stroke.