Positive displacement pump having piston and/or liner with vapor deposited polymer surface

Abstract

A metering pump for providing relatively small, precise volumes of fluid is provided. The pump piston and/or the interior of the cylinder has a surface finish exhibiting a roughness average within selected limits and a vapor deposited polymer such as polytetrafluoroethylene. A drive mechanism is provided for simultaneously rotating and reciprocating the piston within a cylindrical chamber. Fluid is thereby drawn into the chamber and expelled. The pump can be employed in a dialysate circuit or other fluidic circuits containing crystal or other residue-forming fluids, obviating the need for pump wash ports.

1 . A metering pump for dispensing small, precise volumes of fluid, comprising: 
 a pump housing;    a chamber within said pump housing, said chamber being bounded by a cylindrical wall within said housing;    a piston having a cylindrical body portion extending within said chamber, said cylindrical body portion of said piston having a cylindrical outer surface and a duct formed therein;    two or more passages extending through said pump housing and communicating with said chamber;    a drive mechanism coupled to said piston for rotating and reciprocating said piston within said chamber;    said outer surface of said cylindrical body portion of said piston including a surface finish exhibiting a roughness average of at least about four microinches and a vapor deposited polymer.    
   
   
       2 . A metering pump as described in  claim 1 , wherein said polymer comprises polytetrafluoroethylene.  
   
   
       3 . A metering pump as described in  claim 1 , wherein said polymer consists essentially of polytetrafluoroethylene.  
   
   
       4 . A metering pump as described in  claim 1 , wherein the total diametrical clearance between said cylindrical outer surface of said piston and said cylindrical wall of said chamber is between about 0.000050 and 0.000100 inches.  
   
   
       5 . A metering pump as described in  claim 1 , wherein said surface finish exhibits a roughness average of at least about eight microinches.  
   
   
       6 . A metering pump as described in  claim 5 , wherein said piston is comprised of a ceramic material and said surface finish exhibits a roughness average of between about eight and sixteen microinches.  
   
   
       7 . A metering pump as described in  claim 5 , wherein said cylindrical wall includes a surface finish exhibiting a roughness average of at least about eight microinches.  
   
   
       8 . A metering pump as described in  claim 7 , wherein said cylindrical wall includes a surface finish exhibiting a roughness average of between about eight and sixteen microinches.  
   
   
       9 . A metering pump as described in  claim 7 , including a seal within said pump housing and engaging said cylindrical body portion of said piston.  
   
   
       10 . A metering pump as described in  claim 9 , including a ceramic liner within said housing, said ceramic liner bounding said chamber.  
   
   
       11 . A piston and cylinder assembly for a metering pump for dispensing small, precise volumes of fluid, comprising: 
 a ceramic piston including a substantially cylindrical outer surface having a surface finish exhibiting a roughness average of at least about four microinches and a duct formed within said surface;    a housing having a ceramic inner surface defining a cylindrical chamber and exhibiting a roughness average of at least about four microinches, said piston extending within said chamber;    inlet and outlet passages extending through said housing; and    a vapor deposited polymer comprising polytetrafluoroethylene on at least one of said substantially cylindrical outer surface of said piston and said inner surface of said housing.    
   
   
       12 . The assembly of  claim 11  wherein the total diametrical clearance between said cylindrical outer surface of said piston and said inner surface of said housing is between about 0.000050 and 0.000100 inches.  
   
   
       13 . The assembly of  claim 11  including a seal mounted to said housing and engaging said cylindrical outer surface of said piston.  
   
   
       14 . The assembly of  claim 11  wherein said surface finish of said piston exhibits a roughness average of at least about eight microinches and said polymer is on said outer surface of said piston.  
   
   
       15 . The assembly of  claim 14  wherein said housing includes a ceramic liner mounted to said housing and defining said ceramic inner surface, first and second openings in said liner communicating, respectively, with said inlet and outlet passages, said ceramic inner surface of said liner including vapor deposited polytetrafluoroethylene.  
   
   
       16 . The assembly of  claim 15  wherein said roughness averages of said outer surface of said piston and said ceramic inner surface are less than about sixteen microinches.  
   
   
       17 . In a circuit comprising one or more fluid supplies, at least one of the fluid supplies containing a fluid forming crystals or other residues upon drying, and a metering pump in fluid communication with one or more of said fluid supplies, said metering pump including a working chamber, a ceramic piston having a cylindrical body portion extending within the working chamber, the cylindrical body portion having a duct formed therein, and a drive mechanism for rotating and reciprocating the piston within the working chamber, the improvement comprising: 
 a single fluid inlet port, said single fluid inlet port communicating with said at least one of the fluid supplies and the working chamber, a fluid outlet port in fluid communication with the working chamber, the cylindrical body portion of the piston having a cylindrical outer surface, substantially all portions of the cylindrical outer surface capable of contacting fluid in the working chamber exhibiting a roughness average of at least about four microinches and a vapor deposited polymer comprising polytetrafluoroethylene.    
   
   
       18 . A circuit as described in  claim 17 , wherein the metering pump includes a cylindrical ceramic surface defining the working chamber, the cylindrical ceramic surface including a surface finish exhibiting a roughness average of at least about four microinches and a vapor deposited polymer comprising polytetrafluoroethylene.  
   
   
       19 . A circuit as described in  claim 17  wherein the ceramic material is selected from the group consisting of alumina and Zirconia.  
   
   
       20 . A circuit as described in  claim 17  wherein the roughness average is less than about sixteen microinches.  
   
   
       21 . A circuit as described in  claim 20  including a dialyzer, the fluid outlet port being in fluid communication with the dialyzer.  
   
   
       22 . In a semiconductor manufacturing system including a fluid supply, a plating cell, a pump for causing fluid to be moved from the fluid supply to the plating cell, the pump including a working chamber bounded by a substantially cylindrical ceramic surface, inlet and outlet ports communicating with the working chamber, a ceramic piston having a cylindrical body portion extending within the working chamber, the cylindrical body having a duct formed therein, and a drive mechanism for rotating and reciprocating the piston within the working chamber, the improvement comprising: 
 the cylindrical body portion of the ceramic piston having a surface exhibiting a roughness average of at least about four microinches and a vapor deposited polymer comprising polytetrafluoroethylene over substantially all areas capable of contacting fluid in the working chamber,    substantially all of the substantially cylindrical ceramic surface bounding the working chamber exhibiting a roughness average of at least about four microinches and a vapor deposited polymer comprising polytetrafluoroethylene.    
   
   
       23 . A system as described in  claim 22  wherein the inlet and outlet ports have inner surfaces comprising a vapor deposited polymer.  
   
   
       24 . A system as described in  claim 22  wherein the surface of the cylindrical body portion of the piston exhibits a roughness average of at least about eight microinches.