Axial vane pump with non-rotating vanes

A vane pump comprising:

• a housing;
• a cam member mounted in the housing for rotation about an axis, the cam member having an annular axial side which defines an undulated cam surface with at least one inlet arc and at least one discharge arc;
• an array of vanes, each having a radially extending contact surface, fixedly mounted in the housing for axial movement parallel to the axis of rotation toward and away from the cam surface, the contact surfaces of the vanes being adapted to respectively engage the cam surface such that rotation of the cam member produces axial movement of the vanes toward and away from the cam member;
• inlet passage means for directing fluid entering the pump into the volume defined between two adjacent vanes when one of the adjacent vanes is traversing an inlet arc;
• discharge passage means for receiving fluid expelled from the volume between two adjacent vanes when one of the adjacent vanes is traversing a discharge arc;
• a spring loaded piston mounted in the housing behind each vane to urge the vane into engagement with the cam surface, the side of the piston remote from the vane being subjected to inlet pressure and the side of the piston adjacent the vane being subjected to the pressure behind the vane;
• and
• means to direct discharge pressure behind each vane, the spring loading on the pistons being such that a discharge pressure achieved at a low pump speed is sufficient to force the pistons away from the vanes, whereby constant flexing of the springs is not encountered during normal operation.