Patent ID: 8011906

Claim:
A piston pump comprising: a housing having a pump chamber for compressing a fluid, a suction port from which the fluid is drawn, and a discharge port for discharging the compressed fluid; a piston located in the housing to reciprocate in an axial direction, the piston having a circular groove portion on its outer periphery; a pump mechanism for changing a volume of the pump chamber to move the piston such that the fluid drawn from the suction port is compressed in the pump chamber and is discharged from the discharge port; and a feed mechanism that has a feed ring attached to the circular groove portion of the piston to be slaved with a movement of the piston, a feed chamber defined between the feed ring and the housing, and a valve portion for opening and closing an inlet passage of the feed chamber by contacting the piston to the feed ring and separating the piston from the feed ring, wherein: the feed mechanism is located in a suction passage from the suction port to the pump chamber; the feed ring has an inner peripheral surface that is spaced from an outer peripheral surface of the piston at the groove portion to form a part of the suction passage; the valve portion is closed in a suction stroke to reduce a volume of the feed chamber so as to pressure-feed the fluid in the feed chamber to the pump chamber; the piston has a flange portion protruding radially outwardly; the inner peripheral surface of the feed ring has an inner-diameter enlarged portion extending radially outwardly to have an enlarged passage portion between the inner peripheral surface of the feed ring and the outer peripheral surface of the piston; the valve portion is constructed of an end portion of the inner diameter enlarged portion of the feed ring and the flange portion; wherein the suction passage has first and second paths from a position of the valve portion to the feed chamber; the first path is a passage passing through an interior of the piston; and the second path is located between the piston and the feed ring in parallel with the first path relative to a flow of the fluid.