Plunger pump device

Abstract

A plunger pump device includes a housing defining a compression chamber, a plunger slidably accommodated in the housing and exposed to the compression chamber at one end, a drive cam for reciprocating the plunger, a discharge valve connected to the compression chamber, an intake valve connected to the compression chamber, and a low-pressure reservoir for accommodating fluid with a predetermined pressure or more connected to the compression chamber through the intake valve. Even if the intake valve is in a closed position, a small amount of the fluid is discharged from the compression chamber into the low-pressure reservoir side through a slit formed on the intake valve. The small amount of the fluid discharged through the slit is accommodated in a capacity space under a small pressure.

What is claimed is:  
     
         1 . A plunger pump device comprising: 
 a housing defining a compression chamber;    a plunger slidably accommodated in the housing and exposed to the compression chamber at one end;    a drive means for reciprocating the plunger;    a discharge valve connected to the compression chamber;    an intake valve connected to the compression chamber;    a low-pressure reservoir for accommodating fluid with a predetermined pressure or more connected to the compression chamber through the intake valve;    a discharge permitting means for permitting a small amount of the fluid to be discharged from the compression chamber into the low-pressure reservoir side even if the intake valve is in a closed position; and    a capacity means including a capacity space for accommodating the small amount of the fluid discharged from the discharge permitting means and for accommodating the fluid under a small pressure less than the predetermined pressure.    
     
     
         2 . The plunger pump device according to  claim 1 , wherein the intake valve includes a valve seat and a valve portion always biased to be seated on the valve seat, and a slit is formed on at least either one of the valve portion or the valve seat for configuring the discharge permitting means.  
     
     
         3 . The plunger pump device according to  claim 1 , wherein the plunger is slidably accommodated in the housing through a seal member for permitting the small amount of the fluid to be discharged from the compression chamber, and the discharge permitting means is configured by the seal member.  
     
     
         4 . The plunger pump device according to  claim 1 , wherein the low-pressure reservoir includes a cylinder connected to the compression chamber through the intake valve, a piston slidably accommodated in the cylinder and forming a fluid chamber for accommodating the fluid in the cylinder, and a biasing means for biasing the piston in a direction in which the volume of the fluid chamber is reduced.  
     
     
         5 . The plunger pump device according to  claim 4 , wherein the piston is formed with a concave portion being covered by a diaphragm member on a surface of the piston exposed to the fluid chamber.  
     
     
         6 . The plunger pump device according to  claim 5 , wherein the capacity space of the capacity means is configured by an expanded space formed in the fluid chamber when.; the diaphragm member is deformed inside the concave portion.  
     
     
         7 . The plunger pump device according to  claim 5 , wherein the diaphragm member is integrally formed with the piston.  
     
     
         8  The plunger pump device according to  claim 4 , wherein an annular groove is formed on an outer periphery of the piston and an annular elastic member is inserted into the annular groove for forming a predetermined space therebetween in a sliding direction of the piston.  
     
     
         9 . The plunger pump device according to  claim 8 , wherein the capacity space of the capacity means is configured by an expanded space formed between the annular elastic member and the annular groove when the annular elastic member is deformed.  
     
     
         10 . The plunger pump device according to  claim 4 , wherein a reverse biasing means is provided for biasing the piston in a reverse direction to a biasing force of the biasing means.  
     
     
         11 . The plunger pump device according to  claim 10 , wherein the capacity space of the capacity means is configured by an expanded space in the fluid chamber being expanded by adjusting the biasing force of the reverse biasing means relative to that of the biasing means.  
     
     
         12 . The plunger pump device according to  claim 10 , wherein the reverse biasing means is an elastic member disposed between the piston and the cylinder.  
     
     
         13 . A plunger pump device according to  claim 1 , wherein the capacity means includes a sub-cylinder formed at the piston for communicating to the fluid chamber, a sub-piston slidably accommodated in the sub-cylinder and forming a sub-fluid chamber for accommodating the fluid in the sub-cylinder, and a sub-biasing means for biasing the sub-piston in a direction in which the volume of the sub-fluid chamber is reduced.  
     
     
         14 . The plunger pump device according to  claim 1 , wherein the capacity means includes a sub-cylinder formed at the housing for communicating to the fluid chamber, a sub-piston slidably accommodated in the sub-cylinder and forming a sub-fluid chamber for accommodating the fluid in the sub-cylinder, and a sub-biasing means for biasing the sub-piston in the direction in which the volume of the sub-fluid chamber is reduced.  
     
     
         15 . The plunger pump device according to  claim 3 , wherein the seal member is provided between a first annular groove and the compression chamber and inserted into a second annular groove so as to form a small space therebetween for permitting the small amount of the fluid to be discharged from the compression chamber.  
     
     
         16 . The plunger pump device according to  claim 15 , wherein a hydraulic passage is formed between the seal member and the second annular groove for permitting the small amount of the fluid to be discharged from the compression chamber under a compressed condition thereof.  
     
     
         17 . The plunger pump device according to  claim 15 , wherein a seal member is provided between the drive cam and the first annular groove.