A pump assembly includes a pump housing, a stator ring supported within the pump housing, and a pump ring also rotatably supported within the pump housing. The pump ring interfaces with the stator ring to define a plurality of variable volume pressure chambers. A cover plate covers the stator ring and pumping ring within the pump housing. The cover plate is axially displaceable relative to the pump housing and defines a wall of each of the pressure chambers. Pressure within the pressure chambers induces linear movement of the cover plate away from the stator ring and the pump ring.