Liquid pump

Abstract

A housing of a pump apparatus includes an undivided cavity, an inlet valve through which liquid can enter the cavity, and an outlet valve through which the liquid can exit the cavity. A primary piston is configured to reciprocate in the cavity to draw the liquid into the cavity through the inlet valve during an intake stroke of the piston and discharge the liquid out of the cavity through the outlet valve during a delivery stroke. A reservoir structure is configured to add, to the total volume of the cavity, an extra volume that is a smooth positive function of liquid pressure in the cavity.

1 . A pump apparatus comprising:
 a housing having a cavity, an inlet valve through which liquid can enter the cavity, and an outlet valve through which the liquid can exit the cavity;   a primary piston configured to reciprocate in the cavity to draw tie liquid into the cavity through the inlet valve during an intake stroke of the piston and discharge the liquid out of the cavity through the outlet valve during a delivery stroke of the piston; and   a reservoir structure configured to add, to the total volume of the cavity, an extra volume that is a smooth positive function of liquid pressure in the cavity.   
   
   
       2 . The apparatus of  claim 1  wherein the reservoir structure includes a secondary piston configured to retract by a displacement distance that is a smooth positive function of the liquid pressure. 
   
   
       3 . The apparatus of  claim 2  wherein the extra volume equals the displacement distance times a cross-sectional area of the piston. 
   
   
       4 . The apparatus of  claim 2  wherein the retraction of the secondary piston is along an axis perpendicular to the direction of the reciprocation of the primary piston. 
   
   
       5 . The apparatus of  claim 4  wherein the axis extends through the primary piston at some point during the reciprocation. 
   
   
       6 . The apparatus of  claim 4  wherein the primary piston extends over and beyond the secondary piston at some point during the reciprocation. 
   
   
       7 . The apparatus of  claim 2  further comprising a spring structure against which the liquid pressure acts to retract the secondary piston, with a spring constant that increases with increasing retraction of the secondary piston. 
   
   
       8 . The apparatus of  claim 1  wherein the reservoir structure is configured for all the liquid accumulated in the extra volume during the delivery stroke to be returned to the cavity during the following intake stroke. 
   
   
       9 . The apparatus of  claim 1  wherein the extra volume is located in the primary piston. 
   
   
       10 . The apparatus of  claim 1  wherein the reservoir structure is configured for the amount of the liquid discharged during the delivery stroke to be less than if the extra volume did not exist. 
   
   
       11 . The apparatus of  claim 10  wherein the reservoir structure is configured to render a liquid delivery rate that is inversely related to output pressure of the pump. 
   
   
       12 . The apparatus of  claim 11  wherein the delivery rate is approximately inversely proportional to the output pressure. 
   
   
       13 . The apparatus of  claim 1  further comprising a source of the liquid connected to the inlet valve, and a liquid spray nozzle connected to the outlet valve. 
   
   
       14 . A pump apparatus comprising:
 a housing having a cavity, an inlet valve through which liquid can enter the cavity, and an outlet valve through which the liquid can exit the cavity;   a primary piston configured to reciprocate in the cavity to draw the liquid into the cavity through the inlet valve and discharge the liquid out from the cavity through the outlet valve; and   a cylindrical chamber defined by the housing and communicating with the cavity;   a secondary piston configured to retract within the chamber in response to an increase in liquid pressure in the cavity so as to add an extra volume that, throughout the entire range of retraction of the secondary piston, is limited to the space vacated by the secondary piston as the secondary piston retracts.   
   
   
       15 . The apparatus of  claim 14  configured for all the liquid accumulated in the extra volume during the delivery stroke to be returned to the cavity during the following intake stroke. 
   
   
       16 . The apparatus of  claim 14  wherein the retraction of the secondary piston is along an axis perpendicular to the direction of the reciprocation of the primary piston. 
   
   
       17 . A pump apparatus comprising:
 a housing having a primary chamber, an inlet valve through which liquid can enter the primary chamber, and an outlet valve through which the liquid can exit the primary chamber;   a primary piston configured to reciprocate in the primary chamber to draw the liquid into the primary chamber through the inlet valve during an intake stroke of the piston and discharge the liquid out of the primary chamber through the outlet valve during a delivery stroke of the piston; and   a reservoir volume consisting of a single variable-volume space that is continuously open to the primary chamber and configured to increase in response to an increase in liquid pressure in the primary chamber.   
   
   
       18 . The pump of  claim 17  further comprising a secondary piston configured to vary the volume of the space by retracting in response to the increase in the liquid pressure. 
   
   
       19 . A pump apparatus comprising:
 a housing having a cavity, an inlet valve through which liquid can enter the cavity, and an outlet valve through which the liquid can exit the cavity;   a primary piston configured to reciprocate in the cavity to draw the liquid into the cavity through the inlet valve during an intake stroke of the piston and discharge the liquid out of the cavity through the outlet valve during a delivery stroke of the piston; and   a reservoir structure configured to receive a portion of the liquid from the cavity during the delivery stroke and to return the entire received portion back to the cavity during the following intake stroke.   
   
   
       20 . The apparatus of  claim 19  wherein the reservoir structure is configured to yield a liquid delivery rate that is inversely related to output pressure of the pump.