Pre-pressurization pump liner for vane pump

A vane pump comprising:

• a vane liner body defining an inner bore for providing a cam surface, a rotor having a rotational axis and carrying vanes in contact with said cam surface;
• said cam surface having a suction opening formed through the body at one circumferential extent, and having a discharge opening through the body at a distinct circumferential extent;
• and
• a pre-pressurization opening extending through said body at a location upstream of an upstream end of said discharge opening, but spaced by at least 90 degrees from a downstream end of said suction opening.

A vane pump comprising:

• a vane liner body defining an inner bore for providing a cam surface, a rotor having a rotational axis and carrying N vanes in contact with said cam surface;
• said cam surface having a suction opening formed through the body at one circumferential extent, and having a discharge opening through the body at a distinct circumferential extent;
• and
• a pre-pressurization opening extending through said body at a location upstream of an upstream end of said discharge opening, but spaced by at least X degrees from a downstream end of said suction opening, and wherein X equals 360/N.