A piston pump includes a piston for increasing and decreasing the volume of a pump chamber formed in a cylinder bore of a cylinder member, by axially reciprocating movement thereof; a suction valve provided in the piston, and opening and closing when the volume of the pump chamber increases and decr
A piston pump includes a piston for increasing and decreasing the volume of a pump chamber formed in a cylinder bore of a cylinder member, by axially reciprocating movement thereof; a suction valve provided in the piston, and opening and closing when the volume of the pump chamber increases and decreases, respectively; and a discharge valve provided at a discharge side of the pump chamber, and opening and closing when the volume of the pump chamber decreases and increases, respectively. A plurality of mutually communicating, axially extending grooves are formed on an outer circumferential portion of the piston located on the pump-chamber side. A cylindrical seat member is fixedly and externally fitted to the piston in a region of the communicating grooves. A valve port and a valve seat of the suction valve are formed at an end portion of the seat member located on the pump-chamber side.
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What is claimed is: 1. A piston pump comprising: a pump housing having a cylinder bore, a suction port, and a discharge port; a piston defining a pump chamber within the cylinder bore, the piston being axially reciprocated so as to increase and decrease a volume of the pump chamber; a suction valve
What is claimed is: 1. A piston pump comprising: a pump housing having a cylinder bore, a suction port, and a discharge port; a piston defining a pump chamber within the cylinder bore, the piston being axially reciprocated so as to increase and decrease a volume of the pump chamber; a suction valve provided at a suction side of the pump chamber, opening when the volume of the pump chamber increases, and closing when the volume decreases; and a discharge valve provided at a discharge side of the pump chamber, opening when the volume of the pump chamber decreases, and closing when the volume increases, wherein a cylindrical seat member is externally fitted in a fixed condition to an end portion of the piston located on a side of the piston toward the pump chamber; a valve port and a valve seat of the suction valve are formed at an end portion of the cylindrical seat member located on the side toward the pump chamber; a plurality of communicating grooves are formed on an outer circumferential portion of the piston located on the side of the piston toward the pump chamber, the communicating grooves extending axially; and a recess is formed at a center portion of an end face of the piston located on the side toward the pump chamber, the recess being coaxial with the piston and opening toward the valve port of the suction valve so that an inner circumference of the recess establishes communication among bottom portions of the communicating grooves at the end face of the piston located on the side toward the pump chamber. 2. A piston pump according to claim 1, wherein an annular flange portion extending radially outward is formed on the seat member; and the flange portion holds an annular seal member interposed between the cylinder bore and the seat member and adapted to seal against the cylinder bore and the seat member. 3. A piston pump according to claim 1, wherein the seat member is a resin-molded part; an annular mounting groove is formed on an outer circumferential portion of the seat member; and the annular seal member interposed between the cylinder bore and the seat member and adapted to seal against the cylinder bore and the seat member is fitted into the mounting groove. 4. A piston pump according to claim 1, wherein the cylinder bore is formed in a cylinder member built into an internal cavity of the pump housing. 5. A piston pump according to claim 2, wherein a guide portion for guiding axial movement of the piston along the cylinder bore is integrally formed on the seat member. 6. A piston pump according to claim 3, wherein a guide portion for guiding axial movement of the piston along the cylinder bore is integrally formed on the seat member. 7. A piston pump according to claim 1, wherein an annular mounting groove is formed on the seat member, a slide ring being fitted into the annular mounting groove in such a manner as to be movable along an axial direction of the piston, the slide ring being axially movable in relation to the piston while synchronizing with increase and decrease in the volume of the pump chamber, and the slide ring serving as a partition between a suction chamber and a discharge chamber provided around an outer circumference of the piston; communication holes are formed in the seat member in order to establish communication between the corresponding communicating grooves and the annular mounting groove; when the volume of the pump chamber increases, the slide ring shuts off communication between the suction chamber and the discharge chamber, fluid is charged into the pump chamber from the discharge chamber via the suction valve, and fluid is charged into the suction chamber through the suction port; and when the volume of the pump chamber decreases, the slide ring establishes communication between the suction chamber and the discharge chamber, and fluid is charged into the discharge chamber from the suction chamber. 8. A piston pump according to claim 7, wherein the seat member comprises a press-shaped part of metal having the valve port and the valve seat, and a resin-molded part connected to the press-shaped part and having the communication holes and the annular mounting groove for the slide ring.
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