Patent ID: 6974312

Claim:
A pumping element for a hydraulic pump, comprising: a cylinder forming a compression chamber and having a discharge port; a piston having a pressure surface, a spill port, and a passageway connecting the pressure surface with the spill port, the piston disposed in the cylinder for reciprocal movement between a first position and a second position, the pressure surface of the piston being adapted to increase the pressure of a fluid disposed in the compression chamber as the piston moves between the first position and the second position, the pressurized fluid flowing through the discharge port of the cylinder; and a metering sleeve disposed around the piston and configured to selectively cover the spill port as the piston reciprocates between the first and second positions, the metering sleeve having a groove being adapted for fluid communication with the spill port as the piston reciprocates between the first and second positions, wherein the metering sleeve includes a plurality of grooves configured to communicate with the spill port as the piston reciprocates between the first and second positions.