Hydraulic pump

摘要

A hydraulic pump (20) is provided, having a pumping element (26) and including a cylinder (46) forming a compression chamber (48) and having a discharge port (49). A piston (32) having a pressure surface (70), a spill port (72), and a passageway (74) connecting the pressure surface (70) with the spill port (72) is disposed in the cylinder (46) for reciprocal movement between a first position and a second position. The pressure surface (70) of the piston (32) is adapted to increase the pressure of a fluid disposed in the compression chamber (48) as the piston (32) moves between the first position and the second position. The pressurized fluid flows through the discharge port (49) of the cylinder (32). A metering sleeve (34) is disposed around the piston (32) and is configured to selectively cover the spill port (72) as the piston (32) reciprocates between the first and second positions. The metering sleeve (34) has a groove (84) that is adapted for fluid communication with the spill port (72) as the piston (32) reciprocates between the first and second positions. <IMAGE>