Patent Publication Number: US-2023141287-A1

Title: Fluid pump with pressure relief path

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This International application claims priority from U.S. Provisional Patent Application No. 63/000,914 filed Mar. 27, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to liquid pumping systems, wherein one liquid is pumped or fed into the stream of another liquid. More particularly, the present invention relates to a liquid pump with a liquid reservoir and modified pressure relief slot to minimize leaking. 
     There are situations in which it is necessary to inject or feed one liquid into the stream of another liquid. Some liquid pumping systems require an occasional injection of liquid while others need a more continuous feed of the liquid. Still others might require a combination of the two. For purposes of this disclosure, it is understood that the term “feed” will include inject. 
     One such common application is in the field of water treatment wherein certain chemicals, such as chlorinating solutions, fluorination chemicals and other liquids, are fed into the water stream at a point prior to its delivery for end use by consumers. It is important to maintain certain percentage levels of these added liquids in order to assure adequate functionality without exceeding predetermined concentrations which could be objectionable or even harmful to the consumer. 
     A variety of apparatus is available in the industry to perform this chemical feed task. Such apparatus typically takes the form of a pump, wherein pump speed and chemical feed rate is controlled by well known electronic means which employs chemical concentration detection means and provides voltage or current signal output for use by the pump drive system to adjust its feed rate. This system operates in a closed loop fashion to maintain a relatively stable concentration of the desired chemical in the water stream. 
     Pumps used to inject chlorinating solutions, such as Sodium Hypochlorite (NaOCl), into a pressurized water stream frequently encounter problems associated with crystallization of the NaOCl. Although crystallization, with its tendency to lock parts, has been previously considered in various pump designs, the abrasive nature of these crystals was not thoroughly considered. 
     Positive displacement pumps having a ceramic piston and a liner are often plagued with consequential problems arising from such abrasive crystals. During normal pump operation, the piston will rotate and reciprocate in and out of the pump head. Upon outward movement of the piston, suitably designed sealing elements will wipe the piston surface to minimize dragging of any pumped liquid out of the pump head. This squeegee action of the seals is not, however, perfect. Some liquid is always present as a film on the exposed piston surface. 
     This primary difficulty occurs most often in those installations where the NaOCl injection pump does not run continuously. In such applications, the pump might run for as little as one (1) hour and then be allowed to sit idle for the next twenty-three (23) hours. If the piston is partially or fully withdrawn from its mating pump head during such idle time, the previously described NaOCl film will dry, resulting in hard, abrasive crystals forming on the piston surface. At this point, the piston surface can be likened to a nail file with a fine abrasive. 
     When the pump next begins to run, the piston having the newly formed abrasive surface will travel past the seal elements on its way into the pump head. This has been found to prematurely wear the seal elements such that they gradually lose the ability to perform their squeegee action on the piston. This in turn leads to an increase in crystallization during idle time and ultimate failure of the seal. 
     Once seals have been sufficiently worn, additional problems arise during idle time. NaOCl injection pumps of the type being addressed typically utilize a slight negative pressure of approximately 1-2 psig on the inlet port to preclude leakage of NaOCl out of the pump head during idle times. Pumps of the prior art typically include a pressure relief slot, also known as a “scavenger slot,” to provide for such negative pressure. However, the combination of a worn seal with a pressure relief slot allows the negative pressure to aspirate air into the pump head. This air flow will gradually lead to evaporation of NaOCl liquid within the pump head such that crystallization will cause the piston to lock and be unmovable when the pump is later energized. 
     Design of the pump drive mechanism can be such as to assure full piston insertion into the pump head during idle time but such mechanisms add considerably to complexity, size and cost. 
     Previous attempts to address the problem of the prior art have been attempted. For example, as shown in U.S. Pat. No. 9,261,085, a slot is cut on the inside of a liner from the inlet port up to the top of the liner where there is an annular liquid reservoir. This allows the liquid to travel down the slot preventing the cavity from filling up. 
     An internal groove version has also been developed as another solution to the problem. A slot is formed on the inner diameter of the liner and starts at the inlet port but does not go up to the top of the liner. Instead an annular liquid reservoir is made inside the liner bore located between the port and the top of the liner. The slot is made up to the groove and provides the same pressure relief. 
     However, these designs require a larger overall clearance between the piston and liner, an open path between the inlet port and top of the liner and difficulty in measuring the clearance of the piston/liner set. 
     Therefore, it would be desirable to provide an effective solution to the crystallization and leakage problems described above, with minimum cost and without increasing size or complexity of the pump. More particularly, it would be desirable to provide a simply designed pump with provisions for reducing leakage at the seal and piston interface and that relieves using a relatively thin walled liner. 
     SUMMARY 
     The present disclosure provides a liquid pump including a pump housing having an interior sidewall forming an interior. The housing has an inlet port and an outlet port. A liner is disposed in the interior and has opposed transverse openings in line with the inlet and outlet ports. The liner has a central longitudinally extending bore. A pump piston is axially and rotatably slidable within the liner longitudinal bore for pumping the liquid from the inlet port to the outlet port. A seal assembly is secured to the pump housing adjacent to an upper end of the liner. The seal assembly including a seal body, an upper end of the piston extending though the seal assembly and in sealing engagement with the seal body. The seal assembly and liner upper end form a cavity there between. An upper end of the piston extending though the seal assembly and in sealing engagement with the seal body, the seal body and liner upper end forming a cavity there between. The housing having a passageway providing a fluid communication between the cavity and the inlet port. 
     The present disclosure also provides a liquid pump including a pump housing defining a central longitudinal bore. A transverse bore communicates with the central bore for conveying a liquid through the pump housing. A pump piston is axially and rotatably slidable disposed within the central longitudinal bore for pumping the liquid through the transverse bore. The piston and housing define a cavity therebetween and the housing includes a passageway in fluid communication with the cavity and the inlet port. 
     The disclosure further provides a method for reducing leakage of a liquid pump including the steps of:
         creating a negative pressure at an inlet of a pump housing of the pump with a piston axially movable within a liner disposed in a central bore of the pump housing;   creating a positive pressure at an outlet of the pump housing with the piston; and   transferring fluid from a cavity formed in the pump housing to and from the inlet via a passageway formed in the pump housing extending between the inlet and the cavity.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is cross-sectional view of first embodiment of fluid pump. 
         FIG.  1 A  is a perspective view of a fluid pump of the present disclosure. 
         FIG.  2    is a detail cross-sectional view taken from  FIG.  1   . 
         FIG.  3    is a top plan view of the pump embodiment of  FIG.  1   . 
         FIG.  4    is a cross-sectional view of the pump in a base assembly. 
         FIG.  5    is a cross-sectional view of the pump housing with a liner. 
         FIG.  6    is a cross-sectional view of the pump housing with the liner removed. 
         FIG.  7    is cross-sectional view of second embodiment of a fluid pump. 
         FIG.  8    is a detail cross-sectional view taken from  FIG.  7   . 
         FIG.  9    is a top plan view of the pump embodiment of  FIG.  7   . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS.  1  to  6   , a fluid pump  10  generally includes a pump housing  12  and a piston  14  disposed within. The pump housing  12  has an inlet port  16 , an outlet port  18 . The inlet  16  and outlet  18  ports are connectable to fluid conduits (not shown) operably connected to the ports for supplying fluid to and carrying fluid away from the pump  10 . The pump housing defines a cylindrical chamber  20  in fluid communication with the inlet and outlet ports  16  and  18 . The chamber  20  has a sidewall  22  extending between an enclosed bottom end  24  and an open upper end  26 . The sidewall  22  has a surface  25  that is exposed to and defines the housing chamber  20 . 
     Received in the cylindrical chamber  20  is a ceramic piston liner  28  having a central longitudinally extending bore  30  and a transverse bore  32  communicating with the longitudinal bore. The transverse bore  32  includes opposed transverse openings including an inlet portion  34  fluidly communicating with the outlet port  18  of the pump housing so that a liquid, such as a chlorine solution, can be pumped from the inlet port, through the liner, to the outlet port in a manner as will be described below. 
     With reference to  FIG.  4   , the pump  10  may be disposed in a base assembly  42  which is covered by a cap  40 . The piston  14  is operably secured to a motor (not shown) which actuates the piston  14 . The housing  12  may include a threaded portion  44  to which a sleeve  46  is threadingly engaged. The sleeve  46  provides a uniform mounting surface when the pump housing  12  is mounted in the base assembly  42 . 
     The piston  14  is axially and rotatably slidable within the central longitudinal bore  30  of the piston liner  28 . A clearance space  48  exists between the piston and the liner&#39;s central bore  30  in order to permit the piston  14  to move smoothly relative to the line liner. This clearance  48  is very small and may be approximately 0.000100″. One end of the piston  14  forms a stem  50  that extends out of pump housing open end  26 . The opposite end of the piston is formed with a relieved portion  52 . As described above, the relieved portion  52  is designed to direct fluid into and out of the pump  10 . 
     With particular reference to  FIGS.  1  and  2   , a seal assembly  54  is provided at the open end  26  of the pump housing  12  to seal the piston  14  and the housing chamber  20  and to maintain the fluid within the pump housing  12 . The seal assembly  54  is secured at the open end  26  of the pump housing  12  by a rigid holder  62 . The seal assembly  54  includes a seal body  56  and an elastomeric biasing member  58  which may be in the form of an O-ring. The seal assembly  54  has a central opening  60  to receive the piston stem  50 . The seal body  56  includes an outer flange  61  which is held between the holder  62  and a washer  64 . The washer  64  has a central opening  65  and is disposed between the seal outer flange  61  and the housing upper end  74  for supporting the seal body  56 . The seal body  56  also includes an annular recess  63  for receiving the biasing member  58 . The annularly inner-most portion of the seal body is a flexible wall  67  having an end forming a lip seal  69 . The biasing member  58  has a diameter larger that the recess  63 . Thus when the biasing member  58  is pushed into the recess  63 , the biasing member  58  urges the lip seal  69  radially inwardly such that the lip seal  69  sealingly engages the piston  14 . 
     With reference to  FIG.  4   , the base assembly  42  includes abutment surfaces  66  which engage the holder  62  and thus secure the seal assembly, piston  14  and pump housing  12  together when the cap  40  is secured to the base assembly  42 . 
     A cavity  70  is formed between a liner upper end  72  and the seal assembly  54 . The liner upper end  72  is disposed below a housing upper end  74 . This creates a space which contributes to the volume of the cavity  70 . The washer central opening  65  also creates space contributing to the volume of the cavity  70 . 
     In operation, a motor (not shown) drives the piston  14  to both axially translate and rotate within the liner longitudinal bore  30  to draw liquid into the transverse bore  32  from the inlet port  16  to the outlet port  18 . The piston  14  is drawn back as required to take in the desired volume of liquid into the bore  30  of the pump liner  28 , thereby producing a negative pressure within the inlet portion  34  of the liner transverse bore  32 , which draws in liquid from the inlet port  16 . The piston  14  is then rotated to align the relieved portion  52  with the outlet port  18  of the pump housing. The piston is then driven forward the required distance to create a positive pressure to force liquid into the outlet port via the outlet portion  36  of the transverse bore  32  to produce the desired discharge flow. 
     During operation, fluid may migrate into the clearance  48 . Eventually the fluid fills the clearance  48  and reaches the top of the liner  28 . The fluid will then pool in the cavity  70 . Once the cavity  70  is filled, any extra fluid seeping from the clearance  48  will begin to build pressure in the cavity  70 . If this pressure is not relieved, the fluid could start to slip past the seal assembly  54  as the piston  14  moves in and out of the liner  28 . 
     In order to relive the fluid pressure and prevent leakage, a pressure relief passageway  80  is provided to permit the fluid collected in the cavity to be drained therefrom. The passageway provides a fluid communication between the cavity  70  and the input port  16 . The passageway  80  may be disposed on the housing chamber sidewall  22  that extends from the inlet port  16  to the cavity  70 . 
     As shown in  FIGS.  1 - 6   , in one embodiment the pressure relief passageway  80  may be a channel  82  formed in the housing sidewall surface  25 . The channel  82  may be in the form of a groove that is open along its length and exposed to the clearance between the liner and the housing sidewall surface  25 . The channel  82  has a top end terminating at the top end of the housing where it is open to the cavity  70 . The channel has a lower end  86  which opens to the inlet port  16 . Therefore, fluid will flow from the cavity  70  back into the inlet port  16  and through the pump  10  upon operation of the piston. The channel  82  may be formed, for example, by cutting or molding a groove in the housing inner sidewall. Fluid collected in the cavity  70  will flow through the channel  82  into the inlet port  16  due to the pressure differential between the cavity and the inlet port  16  as the piston  14  is actuated. 
     An alternative embodiment is shown in  FIGS.  7  to  9   . The elements of the pump  10  are similar to the embodiment shown in  FIGS.  1 - 6   , except that the pressure relief passageway  80  may a duct  88  formed within the housing sidewall  22 . The duct  88  may be formed by drilling a through hole in the sidewall  22 . The duct  88  is enclosed along its length and open at an opposed first end  90  and second end  92 . The duct first end  90  is disposed at the top edge of the housing sidewall and communicates with the cavity  70 . The washer  64  may include a notch  94  extending from the central opening  65  to provide a clearance for the duct first end  90 . The duct second end  92  is open to and communicates with the inlet port. Thus, a passageway  80  is formed between the cavity and inlet port. By including the passageway in the value housing, the liner wall thickness can be made thinner then if the passageway were formed in the liner. Fluid collected in the cavity  70  will flow through the duct  88  into the inlet port  16  due to the pressure differential between the cavity  70  and the inlet port  16  created by the moving piston  14 . 
     In one exemplary application, the pump  10  of the present disclosure may be used to inject chlorinating solutions, such as Sodium Hypochlorite (NaOCl), into a pressurized water stream frequently encounter problems associated with crystallization of the NaOCl. However, it is contemplated that the pump  10  can be used in any application in which a fluid is to be transported in a controlled manner. 
     Although preferred embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various other changes and modifications may be affected herein by one skilled in the art without departing from the scope or spirit of the invention, and that it is intended to claim all such changes and modifications that fall within the scope of the invention.