Plunger pump

Abstract

A plunger pump includes a pump body, a pump head attached to a tip end portion of the pump body, the pump head including a pump chamber, an inlet path and an outlet path, a plunger that slides in an axial direction along the inner wall of the pump chamber, and a ring-shaped plunger seal for preventing fluid leakage from the pump chamber to the pump body. The plunger seal is arranged between the pump chamber and the pump body with a front surface facing the pump chamber and a back surface facing the pump body, includes a penetration hole from the front surface to the back surface, and holds the plunger in a slidable manner with the inner wall of the penetration hole. The plunger seal includes a ring-shaped hollow portion surrounding the penetration hole, the hollow portion communicating with a back surface side of the plunger seal and not communicating with a front surface side of the plunger seal. An elastic member for expanding the hollow portion in a radial direction of the plunger by an elastic force is provided inside the hollow portion.

The invention claimed is: 
     
         1 . A plunger pump comprising:
 a pump body;   a pump head attached to a tip end portion of the pump body, the pump head including a pump chamber, and an inlet path and an outlet path communicating with the pump chamber;   a plunger whose base end is held inside the pump body and whose tip end is inserted into the pump chamber, the plunger being adapted to slide in an axial direction along an inner wall of the pump chamber; and   a ring-shaped plunger seal arranged between the pump chamber and the pump body with a front surface facing the pump chamber and a back surface facing the pump body, the plunger seal including a penetration hole from the front surface to the back surface, and holding the plunger in a slidable manner with an inner wall of the penetration hole and preventing fluid leakage from the pump chamber to the pump body,   wherein the plunger seal includes a ring-shaped hollow portion surrounding the penetration hole, the hollow portion communicating with a back surface side of the plunger seal and not communicating with a front surface side of the plunger seal, and an elastic member for expanding the hollow portion in a radial direction of the plunger by an elastic force is provided inside the hollow portion, and   wherein a metal member is not provided at a position that comes into contact, at the front surface side of the plunger seal, with fluid that is delivered.   
     
     
         2 . The plunger pump according to  claim 1 , wherein the elastic member has a ring shape surrounding the penetration hole along a ring shape of the hollow portion. 
     
     
         3 . The plunger pump according to  claim 2 , wherein the elastic member is a coil spring that is curved into a ring shape. 
     
     
         4 . The plunger pump according to  claim 1 , further comprising:
 a ring-shaped pressure space communicating with the front surface side of the plunger seal, the pressure space being adapted to press the plunger seal in the radial direction of the plunger by a pressure caused by entering of the fluid which has been delivered.   
     
     
         5 . The plunger pump according to  claim 4 , wherein the pressure space is provided inside the plunger seal, and is adapted to expand in the radial direction of the plunger with an increase in an internal pressure of the pressure space and to press the plunger seal against the plunger and an inner wall surface of the pump head. 
     
     
         6 . The plunger pump according to  claim 4 , wherein the pressure space is a gap provided between an outer surface of the plunger seal and an inner wall surface of the pump head.