Piston type small discharge pump

Abstract

The present invention provides a piston type small discharge pump capable of reducing a dead volume and effects of unbalanced load to the piston shaft, and being self-priming. The fluid taken through a inlet port is introduced into a cylinder portion via a flat type check valve, and discharged into a discharge port through a discharge hole and a check valve as a piston moves up and down. A flat type check valve is provided in the vicinity of a bottom dead center of the piston and a spring for biasing the piston upwardly is provided outside the cylinder portion, thus reducing the dead volume.

1 . A piston type small discharge pump characterized in that a spring for biasing a piston towards a top dead center is provided outside a cylinder.  
     
     
         2 . The piston type small discharge pump as claimed in  claim 1 , wherein a flat type check valve is disposed in the vicinity of the bottom dead center of the piston so as to reduce a dead volume at the bottom dead center.  
     
     
         3 . The piston type small discharge pump as claimed in  claim 1 , wherein there are provided an internal recycling passage where an outlet side of a check valve disposed at an outlet side of the cylinder is communicated with an inlet portion side of a check valve at an inlet portion side of the cylinder, and a flow rate adjusting valve at said internal recycling passage.  
     
     
         4 . The piston type small discharge pump as claimed in  claim 3 , wherein there is provided a flow rate adjusting valve at a discharge port side.  
     
     
         5 . The piston type small discharge pump as claimed in  claim 4 , wherein a check valve is provided at said internal recycling passage.  
     
     
         6 . The piston type small discharge pump as claimed in  claim 1 , wherein there is provided either or both an outer diameter reduced portion where the outer diameter is reduced at a lower portion of the piston and an inner diameter increased portion where the inner diameter is increased at a lower portion of the cylinder.  
     
     
         7 . The piston type small discharge pump as claimed in any one of  claims 1  to  6 , wherein an envelope of a cam portion, mounted in the middle of a rotary shaft, for driving a piston is defined not to extend beyond an outer shape of the rotary shaft.  
     
     
         8 . The piston type small discharge pump as claimed in  claim 7 , wherein an intermediate member which substantially does not move as the cam portion rotates is interposed between the cam portion and a top of the piston driven by the cam portion.  
     
     
         9 . The piston type small discharge pump as claimed in  claim 8 , wherein the cam portion is column-shaped and eccentric of the central axis of the rotary shaft.