Low-friction reciprocating pump

Abstract

A reciprocating pump for pumping a fluid, especially for pumping a fluid such as UV ink which is subject to solidification when exposed to frictional forces. The pump has an internal displacement chamber with an inlet, and outlet, and a plunger which is reciprocally movable in the chamber. The plunger reciprocates through an axial passage in the housing at one end of the chamber, the passage being sized to receive the plunger with a clearance fit. First and second seals are positioned in the axial passage. Each seal is annular in shape and extends between the plunger and housing in sealing contact therewith. The pump housing is free from a bearing which contacts the plunger or guides its motion, such that the sealing contacts between the plunger and seals are the only contacts of the plunger in the housing.

1 . A reciprocating pump for pumping a fluid, comprising: 
 a pump housing having an internal displacement chamber with an inlet, and outlet, a longitudinal axis, and opposite ends;    a plunger which is reciprocally movable in the chamber along said axis;    an axial passage in the housing at one end of the chamber through which the plunger axially reciprocates; and    first and second annular seals in the axial passage generally co-axial with the passage and spaced from one another longitudinally of the passage, each seal being sized for sealing contact with the plunger;    wherein the pump housing is free from a bearing which contacts the plunger or guides its motion, wherein the plunger is free from direct engagement with the housing, and wherein said sealing contacts of the plunger with the first and second seals are the only contacts of the plunger in the housing.    
   
   
       2 . A reciprocating pump as set forth in  claim 1  wherein the axial passage comprises an intermediate section between said seals which is sized to receive the plunger therethrough with a clearance fit.  
   
   
       3 . A reciprocating pump as set forth in  claim 2  wherein said intermediate section of the axial passage defines a minimum clearance region for the plunger in the housing.  
   
   
       4 . A reciprocating pump as set forth in  claim 2  wherein the plunger has an outer diameter D 1 , the intermediate section of the axial passage has an internal diameter D 2 , and a ratio of D 2  to D 1  is greater than 1.01.  
   
   
       5 . A reciprocating pump as set forth in  claim 4  wherein D 2  is larger than D 1  by at least about 0.015 inch.  
   
   
       6 . A reciprocating pump as set forth in  claim 2  wherein the plunger has an outer diameter D 1 , the intermediate section of the axial passage has an axial length L 1 , and a ratio of L 1  to D 1  is within a range between 0.5 and 1.0.  
   
   
       7 . A reciprocating pump as set forth in  claim 6  wherein said ratio of L 1  to D 1  is less than 0.8.  
   
   
       8 . A reciprocating pump as set forth in  claim 2  wherein the intermediate section of the axial passage has an axial length L 1  which is less than 1.0 inch.  
   
   
       9 . A reciprocating pump as set forth in  claim 2  wherein the axial passage has internal shoulders at opposite longitudinal ends of said intermediate section, and wherein each of said seals is positioned adjacent a respective shoulder in the axial passage.  
   
   
       10 . A reciprocating pump as set forth in  claim 1  further comprising a threaded nut received in the housing, and wherein the axial passage has an internal shoulder therein, one of said seals being retained at a position adjacent said internal shoulder by the threaded nut.  
   
   
       11 . A reciprocating pump as set forth in  claim 1  wherein each seal has a generally U-shaped cross-section with two opposing legs in respective sealing contact with the plunger and housing.  
   
   
       12 . A reciprocating pump as set forth in  claim 11  wherein said two legs of each seal are asymmetrical.  
   
   
       13 . A reciprocating pump as set forth in  claim 1  wherein the housing comprises a pump head, a cylinder attached to the head, and a gland attached to the head generally opposite the cylinder, and wherein said axial passage is disposed in the gland.  
   
   
       14 . A reciprocating pump as set forth in  claim 1  wherein the pump is a single-acting pump which, during an upstroke, receives fluid through the inlet into the chamber without simultaneous discharge through the outlet, and which, during a downstroke, discharges fluid from the chamber through the outlet.  
   
   
       15 . A reciprocating pump as set forth in  claim 1  further comprising drain comprising an annular groove in the axial passage for draining fluid which is located between the first and second seals.  
   
   
       16 . A reciprocating pump as set forth in  claim 1  in combination with a container for supplying fluid to the inlet of the chamber, and a tube for delivering fluid from the outlet of the chamber to a device requiring fluid, and wherein the tube is free from valves between the outlet and the device.  
   
   
       17 . A reciprocating pump for pumping a fluid, comprising: 
 a pump housing having an internal displacement chamber with an inlet, and outlet, a longitudinal axis, and opposite ends;    a plunger which is reciprocally movable in the chamber along said axis; and    an axial passage in the housing at one end of the chamber through which the plunger axially reciprocates, the axial passage having at least a portion which defines a minimum clearance region for the plunger in the housing;    wherein the minimum clearance region is sized to receive the plunger therethrough with a clearance fit, and wherein the plunger has an outer diameter D 1 , the minimum clearance region has an internal diameter D 2 , and wherein D 2  is larger than D 1  by at least about 0.015 inch.    
   
   
       18 . A reciprocating pump as set forth in  claim 17  wherein a ratio of D 2  to D 1  is greater than 1.01.  
   
   
       19 . A reciprocating pump as set forth in  claim 17  further comprising first and second annular seals positioned in the axial passage generally co-axial with the passage and spaced from one another longitudinally of the passage, each seal being sized for sealing contact with the plunger.  
   
   
       20 . A reciprocating pump for pumping a fluid, comprising: 
 a pump housing having an internal displacement chamber with an inlet, and outlet, a longitudinal axis, and opposite ends;    a plunger which is reciprocally movable in the chamber along said axis; and    an axial passage in the housing at one end of the chamber through which the plunger axially reciprocates, the axial passage having at least a portion which defines a minimum clearance region for the plunger in the housing;    wherein the minimum clearance region of the axial passage has an axial length L 1  which is less than 1.0 inch.    
   
   
       21 . A reciprocating pump as set forth in  claim 20  wherein the plunger has a radial diameter D 1 , and a ratio of L 1  to D 1  is less than 0.8.  
   
   
       22 . A reciprocating pump as set forth in  claim 20  further comprising first and second annular seals positioned in the axial passage generally co-axial with the passage and spaced from one another longitudinally of the passage, each seal being sized for sealing contact with the plunger.  
   
   
       23 . A reciprocating pump for pumping a fluid, comprising: 
 a pump housing having an internal displacement chamber with an inlet, and outlet, a longitudinal axis, and opposite ends, the housing including a pump head, a cylinder attached to the head, and a gland attached to the head generally opposite the cylinder;    a plunger which is reciprocally movable in the chamber along said axis;    an axial passage in the gland through which the plunger axially reciprocates; and    first and second annular seals in the axial passage generally co-axial with the passage and spaced from one another longitudinally of the passage, each seal being sized for sealing contact with the plunger and having a generally U-shaped cross-section with two opposing legs in respective sealing contact with the plunger and housing, wherein said two legs of each seal are asymmetrical;    wherein the axial passage comprises an intermediate section between said seals which is sized to receive the plunger therethrough with a clearance fit;    internal shoulders at opposite longitudinal ends of said intermediate section, each of said seals being positioned adjacent a respective shoulder in the axial passage, at least one of said seals being retained by a threaded nut;    and wherein the pump housing is free from a bearing which contacts the plunger or guides its motion, the plunger being free from direct engagement with the housing, and wherein said sealing contacts of the plunger with the first and second seals are the only contacts of the plunger in the housing.