Abstract:
A plunger pump including an airtight bellows surrounding a portion of a drive shaft to protect the drive shaft and associated seals and/or bearings from harmful fluids that are being pumped. No counter-pressure fluid exists inside the bellows, other than air, and the bellows is sufficiently rigid to withstand the pressure of the pumped fluid without collapsing. The interior of the bellows is in fluid communication with the atmosphere, negating the need for a reservoir to accommodate varying quantities of counter-pressure fluid as the pump operates.

Description:
BACKGROUND  
       [0001]     The present invention relates to a plunger pump in which the interior of the bellows structure is substantially at atmospheric pressure.  
         [0002]     U.S. Pat. No. 4,436,494 teaches a plunger pump having a bellows surrounding a plunger. The bellows is constructed of flourine plastics and the like. When the pump operates, the bellows extends and contracts within the housing of the pump, and separates the fluid to be pumped from the plunger. To offset the pressure exerted on the outer surface of the bellows by the fluid being pumped through the pump, the bellows is filled with a liquid such as oil and the like. The extension and contraction of the bellows changes the volume within the bellows, which either forces oil out of the bellows or draws oil into the bellows. Variations in the volume in the bellows is matched with a variation of volume in a liquid filled portion of an upper case portion due to the simultaneous movements of a socket constituting a part of the plunger.  
       SUMMARY  
       [0003]     The present invention provides an improvement over the plunger pump disclosed in U.S. Pat. No. 4,436,494. The prior art bellows is constructed of a material that does not have predictable fatigue characteristics. Maintenance is made difficult by the unpredictable failure of the prior art bellows. Also, should there be a failure of the prior art bellows, there is a risk of contamination of the fluid being pumped with the oil in the bellows. The present invention utilizes a plunger pump having a bellows that communicates with atmospheric air and is not filled with oil. This enables a plunger pump to be constructed without a variable volume accumulator to handle oil displaced from the inside of the bellows during operation.  
         [0004]     In one embodiment, the invention provides a pump comprising a housing defining an inner cavity and having an inlet port, an outlet port, and a bellows port. A first valve permits one-way flow of fluid into the inner cavity through the inlet port. A drive rod is supported for reciprocal movement within the inner cavity. A bellows within the inner cavity surrounds a portion of the drive rod, and extends and contracts in response to the reciprocal movement of the drive rod. A second valve is interconnected with the drive rod for reciprocal movement within the inner cavity and permits one-way flow of fluid from a first side of the second valve to a second side of the second valve. The inner cavity is divided into an inlet portion on the first side of the second valve, an outlet portion between the second side of the second valve and an outer surface of the bellows, and an atmospheric portion within the bellows. The inlet port is adapted for communication between the inlet portion and a source of fluid to be pumped, the outlet port is adapted for communication between the outlet portion and a receptacle for pumped fluid, and the bellows port is adapted for communication between the atmospheric portion and the atmosphere. The bellows is substantially airtight and separates the outlet portion of the inner cavity from the atmospheric portion. Air is drawn into and displaced from the atmospheric portion of the inner cavity in response to respective extension and contraction of the bellows.  
         [0005]     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view of a pump embodying the invention.  
         [0007]      FIG. 2  is a cross-section view of the pump in first working position.  
         [0008]      FIG. 3  is a cross-section view of the pump in a second working position. 
     
    
     DETAILED DESCRIPTION  
       [0009]     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings, respectively. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
         [0010]      FIG. 1  illustrates a plunger pump  10  that includes a housing  12 . The housing  12  includes a cylindrical side wall  14  and top and bottom flanges,  16 ,  18 , respectively. The top flange  16  is adapted to have a prime mover  17  mounted to it. The prime mover  17  may be, for example, a motor operating under the influence of compressed air. In other embodiments and constructions, the prime mover may be of a type that operates under the influence of electricity, internal combustion, or another motive force. The bottom flange  18  is adapted to be mounted to a wiper  19  that is positioned within a container of fluid to be pumped by the pump  10 . For example, the wiper  19  may be positioned within a container of UV/EB ink. The bottom flange  18  surrounds an aperture  21  defined by the wiper  19 . The aperture  21  places an inlet port  20  in fluid communication with the fluid to be pumped. The size of the wiper  19  matches the size of the container of fluid being pumped. The wiper  19  extends across the container and forms a fluid-tight sliding seal with the inside surface of the container. The housing  12  also includes an outlet port  22  near the top of the side wall  14 , and a bellows port  24  in the top flange  16 .  
         [0011]     With reference to  FIGS. 2 and 3 , a plunger assembly  26  extends through the housing  12  and includes a primer shaft  28  extending through the inlet port  20 , an intermediate shaft  30 , a coupler  32 , and a drive shaft  34  extending through the bellows port  24 . The drive shaft  34  and intermediate shaft  30  thread into the coupler  32 , and the primer shaft  28  threads into an enlarged end  36  of the intermediate shaft  30 . The primer shaft  28  and drive shaft  34  are partially supported for reciprocating movement by bearing  40 . A bellows  42  surrounds a portion of the drive shaft  34  extending into the housing  12  and is airtightly sealed to an enlarged-diameter end  44  of the coupler  32  at one end and to the top flange  16  at the other end.  
         [0012]     A first check valve  46  is disposed on the primer shaft  28  and a second check valve  48  is disposed on the intermediate shaft  30 . Both of the first and second valves  46 ,  48 , are one-way valves that, in the illustrated embodiment, permit the flow of fluid only upwardly through the pump  10 . A valve stop  50  is mounted to the bottom flange  18 , and the first check valve  46  is movable between abutment with the valve stop  50  (as in  FIG. 2 ) and abutment with the inlet port  20  (as in  FIG. 3 ). When the first check valve  46  is in abutment with the inlet port  20 , it acts as a bearing to support the primer shaft  28 . The enlarged end  36  of the intermediate shaft  30  includes a generally conical surface  52 . The second check valve  48  is slidable along the intermediate shaft  30  into abutment with the conical surface  52  (as in  FIG. 2 ) and abutment with the enlarged-diameter end  44  of the coupler  32  (as in  FIG. 3 ).  
         [0013]     The housing  12  defines an inner cavity that is divided into three portions: an inlet portion  54  on one side of the second check valve  48 , an outlet portion  56  on the other side of the second check valve  48  and around the outside of the bellows  42 , and an atmospheric portion  58  within the bellows  42 . The inlet portion  54  communicates with the container of fluid through the inlet port  20  and through the aperture  21  in the wiper  19 , the outlet portion  56  communicates with a receptacle into which the fluid is pumped through the outlet port  22 , and the atmospheric portion  58  communicates with the atmosphere through the bellows port  24 .  
         [0014]     In operation, an external downward force is applied to the pump  10 . The downward force may come from a hydraulic cylinder, one or more biasing members, or any other mechanism capable of applying constant controllable force to the entire pump  10 . The downward force will force the wiper  19  into the container of fluid. Since the wiper  19  extends across the container and forms a fluid-tight sliding seal with the inner surface of the container of fluid, fluid rises through the aperture  21  to the inlet port  20 . In some embodiments, the bottom flange  18  is coupled to a source of fluid under sufficient pressure that the fluid is forced to the inlet port  20  without having to use a wiper  19 .  
         [0015]     Also during operation, the prime mover  17  is interconnected with an end of the drive shaft  34  and causes cyclical reciprocation of the plunger assembly  26 . On the upward stroke (i.e. movement of the plunger assembly  26  from the position illustrated in  FIG. 3  to the position illustrated in  FIG. 2 ), suction is created within the inlet portion  54  when the second valve  48  is moved upward within the housing  12  under the influence of the intermediate rod  30 . The suction raises the first valve  46  into abutment against the valve stop  50 , and draws fluid into the inlet portion  54  from the container of fluid. A primer button  60  is secured to a free end of the primer shaft  28  to feed fluid into the inlet portion  54  during the first few strokes of pump  10  operation when there is insufficient suction to draw the fluid in. During this upward stroke, any fluid in the outlet portion  56  is forced out of the outlet port  22  into the receptacle for the fluid. The arrows in  FIG. 2  illustrate fluid movement during this upward stroke.  
         [0016]     On the downward stroke (i.e., movement of the plunger assembly  26  from the position illustrated in  FIG. 2  to the position illustrated in  FIG. 3 ), the first valve  46  is forced down by fluid pressure in the inlet portion  54  and blocks the inlet port  20 . The second valve  48  rides up the intermediate shaft  30  and abuts the enlarged end  44  of the coupler  32 . Fluid in the inlet portion  54  is forced into the outlet portion  56  through the second valve  48  as the drive shaft  34  continues to force the second valve  48  down. Due to the expanding volume occupied by the bellows  42 , the volume of fluid entering the outlet portion  56  is greater than the volume of the outlet portion  56 . This forces some of the fluid entering the outlet portion  56  to flow through the outlet port  22  into the receptacle for the fluid. Fluid flow during the downward stroke is illustrated with arrows in  FIG. 3 .  
         [0017]     When in abutment with the bottom flange  18 , the first check valve  46  blocks the inlet port  20  to prevent the flow of fluid out of the inlet port  20 . However, when the first check valve  46  lifts off the bottom flange  18  and abuts the valve stop  50 , a flow path  62  for fluid from the container of fluid into the inlet portion  54  of the inner cavity of the housing  12  is opened. When the second valve  48  abuts the conical surface  52  of the intermediate shaft  30 , it prevents the flow of fluid from the outlet portion  56  of the inner cavity into the inlet portion  54 . However, when the second valve  48  lifts off the conical surface  52 , it opens a flow path  64  around an end  36  of the intermediate shaft  30 , through the second check valve  48 , and into the outlet  56  portion of the inner cavity.  
         [0018]     During operation, the bellows  42  extends and contracts as the prime mover  17  inserts and retracts the drive shaft  34  with respect to the housing  12 . Because the interior of the bellows  42  (i.e., the atmospheric portion  58  of the inner cavity of the housing  12 ) communicates with the atmosphere through the bearing  40  in the bellows port  24 , any air drawn into or displaced from the atmospheric portion  58  is sucked in from or exhausted to the atmosphere. No separate accumulator or other device is required to hold fluid displaced from the interior of the bellows  42 . Also, should the bellows  42  develop small cracks but continue to pump fluid out of the outlet  22  (albeit less efficiently), there is no fluid (other than air) in the bellows  42  that would leak into and contaminate the pumped fluid prior to discovery of the flaw in the bellows  42 .  
         [0019]     The bellows  42  is constructed of a material that has sufficient rigidity to maintain its shape while forcing fluid into and out of the outlet portion  56 , but that has sufficient flexibility to be formed into a bellows  42  shape. The material should be chemically non-reactive with the fluids being pumped. Also, the material should have fatigue characteristics that enable its cycles to failure to be accurately predicted, so the bellows  42  can be replaced prior to failure. One example of a material that may be used for the bellows  42  is stainless steel.  
         [0020]     Various features of the embodiments are set forth in the following claims.