Abstract:
A liquid level control pump especially well adapted for use in landfill wells is disclosed. The pump makes use of a pump casing, a discharge tube, a control rod, first and second check valves, a float and a pivoting lever assembly for controlling the application of a pressurized fluid from an external pressurized fluid source. In one aspect the float may include a through slot which allows the control rod to pass therethrough and which helps to reduce the chance of the float hanging due to an accumulation of solids between the control rod and the float. In another aspect a removable and replaceable discharge tube sleeve may be included.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a 371 National Phase of International Application PCT/US2015/016040, filed on Feb. 16, 2015, which claims priority from U.S. Provisional Application Ser. No. 62/045,218 filed on Sep. 3, 2014, and U.S. Provisional Application Ser. No. 61/940,691, filed Feb. 17, 2014. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to submersible pumps used in landfill wells for leachate discharge and well liquid level control, and more particularly to a pneumatically driven, automatic pump that is especially resistant to the buildup contaminants on its moving components. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Present landfill leachate and liquid level control pumps typically have metal end plates with four protrusions on the ID on both ends of the pump float to reduce the contact area and thereby reduce stiction forces hindering free movement of the float. Abrasion of the discharge tube surface from the pump float can lead to corrosion and pitting of the discharge tube which in turn can aid in solids adhesion, which increases stiction forces. Stiction is defined as a static friction that must be overcome to enable relative motion of stationary objects initially in contact with each other. Field reports from landfill well sites describe a downward spiral in the discharge tube surface roughness leads to increased susceptibility to corrosion and greater solids adhesion rate and cleaning difficulty. The present rough surface is also an industry standard pipe manufacturing quality, which includes surface pitting. 
     Known pump air control mechanisms include stainless steel “E” clips. The “E” clips&#39; thinness, which is a corrosive attack factor, and susceptibility to subtle damage in disassembly have caused problems requiring replacement in the field. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one aspect the present disclosure relates to a liquid level control pump adapted to be lowered into contact with a fluid collecting with a wellbore, and being in communication with an external pressurized fluid source. The liquid level control pump may comprise a pump casing, a discharge tube, a first check valve, a second check valve, a float, a control rod, and a pivoting lever assembly. The discharge tube is disposed substantially within the pump casing and has a first end and a second end. The discharge tube is operable to receive fluid collecting within an area between the pump casing and an outer surface of the discharge tube. The discharge tube further includes first and second ends. The first check valve is disposed at the first end for controlling a flow of the fluid within the discharge tube to one direction only, that being out from the first end of the discharge tube. The second check valve is disposed at the second end for limiting the flow of fluid to one direction only, that being from the pump casing into the discharge tube at the second end. The source of pressurized fluid is in communication with the pump casing, and the float is arranged coaxially around the discharge tube and movable along the discharge tube towards the first and second ends. The control rod is disposed adjacent the discharge tube and operably associated with the float so as to be lifted by the float as the float moves toward the first end as the area within the pump casing fills with the fluid. The float moves towards the second end as the fluid within the pump casing is pumped out through the discharge tube using a pressurized fluid from the pressurized fluid source. The pivoting lever assembly is operably associated with the float for controlling the application and interruption of the pressurized fluid into the pump casing, to thus control the pumping of the fluid collecting within the pump casing out from the pump casing and into the second end of the discharge tube, towards the first end of the discharge tube. The float includes a through bore and a through slot in communication with the through bore. The through slot permits passage of a portion of the control rod therethrough and operates to permit fluid flow about an entire periphery of the control rod as the float moves up and down adjacent an outer surface of the discharge tube, and relative to the control rod. This reduces or eliminates a buildup of solids between the control rod and the float that could otherwise affect free sliding movement of the float along the discharge tube. 
     In another aspect the present disclosure relates to a liquid level control pump adapted to be lowered into contact with a fluid collecting with a wellbore, and being in communication with an external pressurized fluid source. The liquid level control pump comprises a pump casing, a discharge tube, a first check valve, a second check valve, a control rod, a float, a pivoting lever assembly, and a removable and replaceable discharge tube sleeve. The discharge tube is disposed substantially within the pump casing and has a first end and a second end. The discharge tube is operable to receive fluid collecting within an area between the pump casing and an outer surface of the discharge tube. The discharge tube further includes first and second ends. The first check valve is disposed at the first end for controlling a flow of the fluid within the discharge tube to one direction only, that being out from the first end of the discharge tube. The second check valve is disposed at the second end for limiting the flow of fluid to one direction only, that being from the pump casing into the discharge tube at the second end. The source of pressurized fluid is in communication with the pump casing, and the float is arranged coaxially around the discharge tube and movable parallel to the discharge tube towards and away from the first and second ends. The control rod is disposed adjacent the discharge tube and operably associated with the float so as to be lifted by the float as the float moves toward the first end as the area within the pump casing fills with the fluid. The float then moves towards the second end as the fluid within the pump casing is pumped out through the discharge tube using a pressurized fluid from the pressurized fluid source. The pivoting lever assembly is operably associated with the float for controlling the application and interruption of the pressurized fluid into the pump casing, to thus control the pumping of the fluid collecting within the pump casing out from the pump casing and into the second end of the discharge tube, towards the first end of the discharge tube. The removable and replaceable discharge tube sleeve is disposed over the outer surface of the discharge tube. The float is adapted to move slidably along an outer surface of the discharge tube sleeve. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a partial cross sectional view of a liquid level control pump of the present disclosure positioned in a landfill well at a float lower position; 
         FIG. 2  is a partial cross sectional view of the pump of  FIG. 1  at a float upper position; 
         FIG. 3  is a side elevational view of a pump float of the liquid level control pump of  FIG. 1 ; 
         FIG. 4  is an end elevational view of the pump float of  FIG. 3 ; 
         FIG. 5  is a perspective view of a pump end cap of the liquid level control pump of  FIG. 1 ; 
         FIG. 6  is a front elevational view of the pump end cap of  FIG. 5 ; 
         FIG. 7  is a cross sectional view taken at section  7  of  FIG. 6 ; 
         FIG. 8  is a cross sectional view taken at section  8  of  FIG. 6 ; 
         FIG. 9  is a perspective assembly view of a pivoting lever assembly of the liquid level control pump of  FIG. 1 ; 
         FIG. 10  is a partial cross sectional front elevational view of a pivoting lever portion of the pivoting lever assembly of  FIG. 9 ; 
         FIG. 11  is a partial cross sectional front elevational view of the pivoting lever portion of  FIG. 10 ; 
         FIG. 12  is an end elevational view of a lever poppet bushing of the present disclosure; 
         FIG. 13  is a cross sectional view taken at section  13  of  FIG. 12 ; 
         FIG. 14  is a front elevational view of a housing adapter of the present disclosure; 
         FIG. 15  is a bottom plan view of the housing adapter of  FIG. 14 ; 
         FIG. 16  is a top plan view of the housing adapter of  FIG. 14 ; 
         FIG. 17  is a front cross sectional view taken at section  17  of  FIG. 15 ; 
         FIG. 18  is a rear cross sectional view taken at section  18  of  FIG. 14 ; 
         FIG. 19  is an assembly view of a ball check valve and housing adapter of the present disclosure; 
         FIG. 20  is an elevational view of a replaceable discharge tube sleeve that may be incorporated into the pump of  FIG. 1  by being placed over the discharge tube; 
         FIG. 21  is an end view of the sleeve shown in  FIG. 20  illustrating a plurality of teeth or ridges that may be formed on the inner surface of the sleeve to eliminate play between the sleeve and the discharge tube; 
         FIG. 22  is an enlarged portion of the sleeve of  FIG. 21  showing one example of the shape that the ridges may have, in this example the shape being generally triangular; 
         FIG. 23  shows an example of the ridges of the sleeve having a rectangular shape; and 
         FIG. 24  shows an example of the ridges of the sleeve having a semi-circular shape. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Referring to  FIG. 1 , a liquid level control pump  10  of the present disclosure includes a pump casing  12  which is submerged below an anticipated water level found in a landfill well pipe  14 . Within the pump casing  12  is a discharge tube  16  centrally located in the pump casing  12 . A float  18  is slidably disposed on the outer surface of the discharge tube  16  and can raise and lower as the water level within the landfill well pipe  14  changes. A control rod  20 , positioned external to the discharge tube  16 , is slidably received through the float  18  through each of a first float end cap  22  and a second float end cap  24  positioned at opposite ends of float  18 . 
     After operation of the liquid level control pump  10 , liquid level in the landfill well pipe  14  lowers and the float  18  is positioned in direct contact with a lower float stop  26  fixed to the control rod  20 . Contact between the float  18  and the lower float stop  26  thereafter pulls the control rod  20  downward. An upper float stop  28  is also fixed to an upper location of control rod  20 , whose function will be described in greater detail in reference to  FIG. 2 . A pivoting lever assembly  30  is connected to the control rod  20 , whose position is changed by contact between float  18  and either the lower float stop  26  (as shown) or the upper float stop  28 . At the lower position of float  18  (shown), the pivoting lever assembly  30  is rotated to an orientation which isolates pressurized air in a pressurized air supply tube  32  from entering pump casing  12 . At this lower position of float  18 , a ball  34  defining a portion of a ball check valve is seated against a threaded end  36  of a check valve ball housing  38 . This seated position of ball  34  prevents fluid which has been discharged by operation of liquid level control pump  10  from returning back down into landfill well pipe  14 . A housing adapter  40  is connected to the check valve ball housing  38  and is used to both retain the ball  34  within check valve ball housing  38  and as an adapter for connection to a tubing connector  42 , where fluid discharged by operation of liquid level control pump  10  exits the pump. 
     In the lower position of float  18  (shown), fluid which enters the landfill well pipe  14  flows upward into the pump casing  12  by displacement of a check valve member  44  positioned at a lower end of liquid level control pump  10 . The check valve member  44  displaces away from a valve seat  46 , allowing the inward flow in the direction of flow arrows “A” into pump casing  12 . This inward flow of fluid into pump casing  12  causes the float  18  to upwardly displace in a float upward displacement direction “B”. This upward displacement of float  18  continues until the first float end cap  22  directly contacts the upper float stop  28  and displaces the control rod  20  upward to rotate the pivoting lever assembly  30 . 
     Referring to  FIG. 2 , at the upward displacement position of float  18 , the first float end cap  22  directly contacts upper float stop  28 . After this direct contact occurs with upper float stop  28 , further upward displacement of the float  18  causes the direct displacement of control rod  20  in the upward displacement direction “B”, which rotates the pivoting lever assembly  30  to an opposite orientation from that disclosed with respect to  FIG. 1 . This rotation of pivoting lever assembly  30  displaces a poppet, described in reference to  FIG. 9 , which allows entrance of pressurized air from pressurized air supply tube  32  into the pump casing  12 . The entrance of pressurized air into pump casing  12  forces the liquid within pump casing  12  to close the check valve member  44  and thereby open an entrance path for liquid to flow into the discharge tube  16 , thereafter rising up through discharge tube  16  to upwardly displace the ball  34 , providing a discharge path for liquid through housing adapter  40  and tubing connector  42  via a discharge pipe (not shown) for discharge of the liquid out of the landfill well pipe  14 . Air flow into pump casing  12  continues until the position of float  18  shown in reference to  FIG. 1  is reached again, which thereby rotates the pivoting lever assembly  30 , isolating the pressurized air in pressurized air supply tube  32  from pump casing  12 . This cyclic operation of liquid level control pump  10  continues as long as the fluid level within landfill well pipe  14  is sufficient to raise float  18  into direct contact with upper float stop  28  and as long as pressurized air is available in pressurized air supply tube  32 . Improvements made to the liquid level control pump  10  include design changes which will be described herein with respect to the clearance provided for displacement of float  18  with respect to control rod  20 , modifications to the pivoting lever assembly  30 , and provision of the modified design of housing adapter  40 . 
     Referring to  FIG. 3 , float  18  includes a through bore  48  which is sized to slidably contact the outer wall of discharge tube  16 . According to several aspects, the material of float  18  is selected as a polymeric material to provide the upward force required for displacement of control rod  20 . 
     Referring to  FIG. 4  and again to  FIG. 3 , the through bore  48  of float  18  is centered with respect to a float longitudinal axis  50 . To minimize the frictional contact between control rod  20  and material of float  18 , a through slot  52  is provided, which extends all the way from an outer wall of the float  18  into the through bore  48 . The open design of through slot  52  allows free flow of the liquid of landfill well pipe  14  entirely about the perimeter of control rod  20  for the entire upward and downward displacement of float  18 . Clearance is also provided by a width of the through slot  52  which is sized to be approximately two times a diameter of control rod  20 . This further minimizes the potential for buildup of materials present in the liquid from plating out onto control rod  20  or the surfaces of float  18 , which would increase the frictional resistance to displacement of float  18 . It is noted that through slot  52  is aligned with a slot center axis  54  intersecting with the float longitudinal axis  50 . 
     Referring to  FIG. 5  and again to  FIGS. 1 and 2 , each of the first and second float end caps  22 ,  24  are identical to each other and are installed in oppositely facing directions on the pump casing  12 . Each of the first and second float end caps  22 ,  24  includes a cap body  56  which is washer-like in appearance having a center bore  58 . According to several aspects, a plurality of raised bumpers  60 , each defining a semi-spherical shape, extend inwardly from a bore inner wall  62  of center bore  58 . Each of the raised bumpers  60  are provided to make direct contact with the outer wall of discharge tube  16 . The rounded geometry of the raised bumpers  60 , as well as the use of a minimum quantity of the raised bumpers  60  (according to several aspects four raised bumpers  60  may be provided), minimizes frictional contact with the discharge tube  16 . In addition, a material selected for each of the first and second float end caps  22 ,  24  is a PEEK polymeric material selected due to its low-friction properties and resistance to the materials present in landfill well liquids. Other engineering plastics in addition to PEEK material, such as improved polyamides (nylons) and glass fiber reinforced polyphenylene sulfide (PPS)0 can also be used, each having desirable characteristics for the float end caps such as strength, chemical resistance and wear/abrasion resistance. A control rod receiving aperture  64  is created through cap body  56 , which closely matches an outer diameter of control rod  20 , allowing for sliding contact between the first and second float end caps  22 ,  24  and control rod  20  as the float  18  displaces. 
     Referring to  FIG. 6  and again to  FIGS. 1-2 and 5 , a bumper inner diameter  66  is defined by an innermost rounded surface  68  of each of the multiple raised bumpers  60 . The bumper inner diameter  66  is substantially equal to or larger than a diameter of the discharge tube  16 . According to several aspects, the four raised bumpers  60   a ,  60   b ,  60   c ,  60   d  are each located at approximately 90-degree intervals with respect to each other with one of the raised bumpers  60   b  also axially aligned with control rod receiving aperture  64 . In addition to control rod receiving aperture  64 , first and second fastener apertures  70 ,  72  are also created through the cap body  56 . The first and second fastener apertures  70 ,  72  provide for fastener installation of the first or second float end caps  22 ,  24  at their respective end positions on float  18 . 
     Referring to  FIG. 7  and again to  FIGS. 5-6 , a chamfered edge  74  can be provided with each of the first and second fastener apertures  70 ,  72 . Chamfered edge  74  allows for full recession of a fastener head (not shown) used for installation of the first or second float end caps  22 ,  24 . 
     Referring to  FIG. 8  and again to  FIGS. 5-7 , the geometry of control rod receiving aperture  64  aligns a central axis  65  of the control rod receiving aperture  64  substantially parallel with respect to a central axis  67  of the first and second float end caps  22 ,  24 . 
     Referring to  FIG. 9  and again to  FIGS. 1 and 2 , the pivoting lever assembly  30  is modified in the design of liquid level control pump  10  to reduce the quantity of parts associated with operation of poppets that control the flow of pressurized air into and out of pump casing  12 . The pivoting lever assembly  30  includes each of a first and a second lever half  76 ,  78 , each having a first and second connecting flange  80 ,  82  oppositely extending therefrom. A planar end face  84  is created on each of the first and second connecting flanges  80 ,  82  which abut with the corresponding faces of the opposite half of the pivoting lever assembly  30 . A slot  86  is created between the first and second connecting flanges  80 ,  82 , which provides for the positioning of an insert member  88  which is located substantially at a central position of slot  86 . An elongated slot  90  is provided in each of the first and second lever halves  76 ,  78  to allow for liquid flow past the pivoting lever assembly  30 . 
     A poppet  92  having a needle end  94  is positioned within at least one of the slots  86 . The needle end  94  can be used, for example, to isolate the flow of pressurized air into pump casing  12  from the pressurized air supply tube  32  when the float  18  is not in direct contact with upper float stop  28 . The poppet  92  is connected to one of the first or second lever halves  76 ,  78  using a lever poppet bushing  96  having a bushing rod  98  extending therefrom. The bushing rod  98  is sized to be slidably received through a poppet aperture  100  of poppet  92  and thereafter received in a rod receiving aperture  102  of the insert member  88 , such as insert member  88 ′ (shown). 
     Referring to  FIG. 10  and again to  FIG. 9 , each of the first and second lever halves  76 ,  78  includes an insert aperture  104  which extends inwardly (away) from an end face of slot  86 . An insert outer wall  106  of the insert member  88  is sized to be frictionally coupled against the insert aperture  104  such that a friction fit will retain the insert member  88  within one of the first or second lever halves  76 ,  78 . 
     Referring to  FIG. 11  and again to  FIG. 10 , after insertion of the insert member  88  into the insert aperture  104 , an end face of the insert member  88  is positioned substantially flush with a slot end wall  108  of the slot  86 . 
     Referring to  FIG. 12  and again to  FIGS. 9-11 , the lever poppet bushing  96  includes the bushing rod  98  which is integrally connected to a bushing sleeve  110 . A through aperture  111  created through the bushing sleeve  110  is oriented axially parallel with respect to a longitudinal axis of the bushing rod  98 . For maximum wear life, the material of lever poppet bushing  96  can be a nitride material. 
     Referring to  FIG. 13  and again to  FIG. 12 , the bushing sleeve  110  can be created as a separate part with respect to bushing rod  98  and the two parts fixed together, for example, by welding, adhesive or molding. According to other aspects, the bushing rod  98  and the bushing sleeve  110  can be integrally provided of a single material by machining the geometry of lever poppet bushing  96 . According to several aspects, an inner bore wall of the through aperture  111  extending through bushing sleeve  110  is aligned coplanar with a lower outer surface of the bushing rod  98 . 
     Referring to  FIG. 14  and again to  FIGS. 1-2 , the housing adapter  40  includes a hex head  112  to provide for tool use during installation of the housing adapter onto pump casing  12 . Housing adapter  40  further includes a male threaded shank  114  from which a blade member  116  integrally extends beyond a shank end face  118  at the end of threaded shank  114 . A tubing connection head  120  is provided at an opposite end with respect to threaded shank  114  to provide for connection of a discharge tube or pipe to discharge fluid during operation of liquid level control pump  10 . 
     Referring to  FIG. 15  and again to  FIG. 14 , housing adapter  40  includes a housing bore  122  which is substantially bisected by the blade member  116 . This creates a first and a second bore portion  124 ,  126  of substantially equal size on opposite sides of the blade member  116 . The blade member  116  therefore results in minimal restriction of fluid flow through the housing bore  122 . 
     Referring to  FIG. 16  and again to  FIGS. 14-15 , each of the hex head  112 , tubing connection head  120 , and the housing bore  122  are coaxially aligned with respect to a longitudinal axis of housing adapter  40 . 
     Referring to  FIG. 17  and again to  FIGS. 14-16 , the blade member  116  has a free end defined as a rounded end  128  having, for example, a semispherical shape. Rounded end  128  is provided to minimize the surface area of blade member  116 , which is in direct contact with ball  34  when ball  34  raises to allow discharge of fluid from liquid level control pump  10 . Rounded end  128  increases the service life of ball  34 , while preventing ball  34  from discharging via the housing bore  122  through the discharge pipe. The blade member  116  therefore minimizes fluid flow resistance through the housing bore  122  while simultaneously retaining ball  34 . 
     Referring to  FIG. 18  and again to  FIGS. 14-17 , the blade member  116  is an integral extension of the material of housing adapter  40  outward of the threaded shank  114 . A first and a second blade support leg  130 ,  132  integrally connect the blade member  116  to housing adapter  40 . This extension created by the first and second blade support legs  130 ,  132  also creates a flow window  134  above the blade member  116 , as viewed in reference to  FIG. 18 . Flow window  134  also helps reduce fluid flow resistance through housing adapter  40 . 
     Referring to  FIG. 19  and again to  FIGS. 1-2 and 14-18 , the housing adapter  40  is assembled into the check valve ball housing  38  by threaded insertion of the threaded shank  114  engaging internal threads  136  created in a ball receiving bore  138  of check valve ball housing  38 . The ball  34  is positioned within the ball receiving bore  138  prior to installation of housing adapter  40  such that the blade member  116  prevents release of ball  34 . As previously noted, the rounded end  128  of blade member  116  is provided to minimize the surface area of blade member  116  in direct contact when ball  34  is positioned at its maximum lift location. The check valve ball housing  38  is itself threadably engaged to the pump casing  12  using a housing male thread  140 . 
     The PEEK (polyether ether ketone) plastic, bearing grade float end caps  22 ,  24  are designed to reduce scraping damage to the surface finish of the pump discharge tube  16 , whether the discharge tube  16  is coated or not. The PEEK end caps  22 ,  24  have rounded bumpers  60  extending inwardly from the bore inner wall  62  directed toward the central axis  67  of the end caps  22 ,  24 . The bumpers  60  minimize a surface area of the end caps  22 ,  24  in direct contact with the discharge tube  16 , and thereby help reduce abrasion of the discharge tube surface. This abrasion if not minimized can lead to corrosion and pitting of the discharge tube  16  which in turn can aid in solids adhesion. 
     The pivoting lever assembly  30  on the air control mechanism eliminates the stainless steel “E” clips currently in use for this purpose. The present disclosure pivoting lever assembly  30  design has fewer parts, is easier to assemble and can be retrofitted in the field to existing pumps. 
     The float  18  is provided having the open channel  52  for the control rod  20  to pass-through, rather than the current enclosed channel. The open channel  52  reduces the build-up of solids vs. with the conventional bore design, is easier to clean and makes coatings easier to apply. 
     The float  18  is coated to reduce the adhesion of solids and make them easier to clean off. An epoxy silicone paint is applied to the float  18  which has been found to be effective in reducing adhesion of solids. 
     An improved finish is also provided for the discharge tube  16  to reduce solids adhesion, make cleaning easier and reduce corrosion. The improved surface finish uses centerless grinding followed by electro-polishing for a mirror-bright finish. 
     Referring now to  FIGS. 20-24 , in another embodiment the liquid level control pump  10  may incorporate a discharge tube sleeve (hereinafter simply “sleeve”)  150 . The sleeve  150  forms a tubular component designed to fit over the discharge tube  16  ( FIGS. 1 and 2 ). The sleeve  150  forms a component that may be easily replaced simply by sliding it off from the discharge tube  16  and sliding a new sleeve  150  on over the discharge tube  16 . By incorporating the sleeve  150  and making it readily replaceable, the situation where a buildup of solids on the exterior of the discharge tube  16  might occur can be avoided. Such a condition could impede the smooth, easy sliding motion of the float  18  up and down the discharge tube  16  and potentially cause the float  18  to “hang up” at some intermediate point along its intended path of travel. The sleeve  150  may have a length that extends virtually the entire length of the discharge tube  16 , or a length which is at least sufficiently long to cover that portion of the discharge tube  16  that the float  18  rides along during normal operation of the pump  10 . The sleeve  150  thus functions to provide an exceptionally smooth, low friction surface for the inner surface of the float  18  to ride on. The sleeve  150  may be formed from a bearing grade thermoplastic polymer, for example, but not limited to, polyether ether ketone (PEEK) or Polyphenylene Sulfide (PPS). Other materials such as graphite and/or other lubricants may also be incorporated into its material composition to further reduce friction and/or to help reduce the likelihood of solids buildup on the external surface of the sleeve  150 . 
     An end view of the sleeve  150  is shown in  FIG. 21 . The sleeve  150  may be extruded or formed in any other suitable manner. An inner wall  152  of the sleeve  150  may include a plurality of circumferentially spaced apart teeth or ridges  154 . Preferably the ridges  154  are spaced evenly about the entire circumference of the inner wall  152  of the sleeve  150 .  FIG. 21  shows the ridges  154  spaced about every 30 degrees around the inner wall  152 , but it will be appreciated that a greater or lesser number of ridges  154  may be used, and either a uniform spacing or non-uniform spacing of the ridges  154  can be used. The ridges  154  in this example project about 0.023 inch radially inward, as indicated by dimensional arrows  153  in  FIG. 22 , but again, this dimension could vary significantly. In one example the wall thickness of sleeve  150  is between about 0.030 inch to about 0.060 inch. An inner diameter formed by the ridges  154 , as indicated by dimensional arrow  156  in  FIG. 21 , is preferably just slightly less, for example by 0.010 inch or so, than the outer diameter of the discharge tube  16 . The ridges  154  may bend or deflect slightly as the sleeve  150  is slid onto the discharge tube  16  during assembly of the pump  10 , and thus help to take up the play between the discharge tube  16  and the sleeve  150  and help to maintain the sleeve  150  axially centered about the discharge tube  16 . The outer surface of the discharge tube  16  may also be highly polished to further help resist the buildup of solids thereon. Since the sleeve  150  can be quickly and easily slid on and off the discharge tube  16 , this enables convenient periodic replacement of the sleeve  150  without the need for any special tools or disassembly procedures. It is anticipated that users will find that replacement of the sleeve  150  with a new sleeve may even be easily accomplished in the field. Users may find that establishing a schedule for periodic replacement of the sleeve  150  (e.g., once 6-12 months) may help to ensure that no tangible buildup of solids occurs during use of the pump  10 . 
       FIGS. 23 and 24  show alternative forms of the ridges  154 . The ridges  154   a  in  FIG. 23  are shown as being generally square shaped. The ridges  154   b  in  FIG. 24  are shown as having a rounded, arcuate shape. In both cases the ridges  154   a  and  154   b  are able to flex or deform slightly as the sleeve  150  is inserted onto the discharge tube  16  to eliminate play between the sleeve  154  and the discharge tube  16 . 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.