Abstract:
A metering pump includes a motor having a motor shaft extending through a drive housing, a carriage assembly disposed around the motor shaft and within the drive housing, a plunger return block mounted to the carriage assembly, a piston disposed along an axis, a carriage bearing disposed on the motor shaft and within the carriage assembly and slidably coupled to the carriage assembly, a cam coupled to the motor shaft to rotate with the motor shaft, and a bearing disposed around the cam to rotate therewith and to contact the stroke adjuster and the plunger return block. The piston also includes a stroke adjuster mounted to the carriage assembly, a plunger having a button-shaped protrusion end, and a drive shaft having a first end connected to the stroke adjuster and a second end having a hook protrusion configured to receive and engage the plunger button-shaped protrusion end.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/155,577 filed on May 1, 2015, and entitled “TWO PIECE PUMP ROD,” the entire contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Companies in the oil and natural gas industry often use metering pumps to transfer fluids in harsh or remote locations. Many such pumps provide precise fluid dispensation by converting rotational motion delivered from a solar or AC grid powered motor to linear reciprocating motion in a piston. During a complete piston stroke, fluid is both drawn into the pump and discharged from the pump at a particular rate depending on piston displacement and rotation cycle time. Frictional forces and side loading acting within these pumps can cause both wear on pump components and operational inefficiency. Wear often decreases the life of these components and results in failure modes requiring downtime for repair. Pump inefficiency can increase demand load on the sources powering the pump. Minimizing component wear and pump inefficiency can thus reduce end-user costs. 
         [0003]    While metering pumps typically drive a piston using a cam, many use either spring or carriage assemblies to return the piston. In spring assemblies, the spring force used to return the piston can act against it during the discharge stroke, causing higher energy penalties and additional wear on the pump head and rotary components. Carriage assemblies, by contrast, can require a number of additional parts to facilitate piston return. Using additional parts often provides more wear points and thus more potential failure modes. 
         [0004]    Metering pump pistons generally reciprocate within a channel. Friction between the piston and the rotary components attached to the motor can impart a slight rotation on the piston. This rotation in turn causes side loading on the parts forming the piston channel. Side loading on these parts decreases the life thereof and can necessitate pump repair. It can also force end-users to purchase more replacement parts. 
       SUMMARY 
       [0005]    In one embodiment, a metering pump includes a motor having a motor shaft extending through a drive housing, a carriage assembly disposed around the motor shaft and within the drive housing, a plunger return block mounted to the carriage assembly, a piston disposed along an axis, a carriage bearing disposed on the motor shaft and within the carriage assembly and slidably coupled to the carriage assembly, a cam coupled to the motor shaft to rotate with the motor shaft, and a bearing disposed around the cam to rotate therewith and to contact the stroke adjuster and the plunger return block. The piston also includes a stroke adjuster mounted to the carriage assembly, a plunger having a button-shaped protrusion end, and a drive shaft having a first end connected to the stroke adjuster and a second end having a hook protrusion configured to receive and engage the plunger button-shaped protrusion end. 
         [0006]    In another embodiment, a method of servicing a metering pump is provided, wherein the metering pump includes a drive housing, a drive shaft, a drive cylinder, a dust cover disposed around the drive cylinder, a pump section that includes a packing nut, a fluid cylinder, and a plunger, and set screws that fasten the drive cylinder to the fluid cylinder. The method includes rotating the dust cover with respect to the drive cylinder, sliding the dust cover toward the drive housing to expose the packing nut, loosening the packing nut, removing the set screws from the drive cylinder, releasing the drive cylinder from the fluid cylinder, disengaging the plunger having a button shaped end from the drive shaft having a hook shaped receiving end, and removing the pump section from the metering pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an isometric view of a metering pump assembly. 
           [0008]      FIG. 2A  is an exploded isometric view one implementation of a metering pump. 
           [0009]      FIG. 2B  is an isometric view of the metering pump shown in  FIG. 2A . 
           [0010]      FIG. 2C  is a front view of the metering pump shown in  FIG. 2A . 
           [0011]      FIG. 2D  is a top plan view of the metering pump shown in  FIG. 2A . 
           [0012]      FIG. 2E  is a bottom plan view of the metering pump shown in  FIG. 2A . 
           [0013]      FIG. 3A  is an isometric cross-sectional view of another implementation of a metering pump. 
           [0014]      FIG. 3B  is a front cross-sectional view of the metering pump shown in  FIG. 3A . 
           [0015]      FIG. 3C  is a bottom plan cross-sectional view of the metering pump shown in  FIG. 3A . 
           [0016]      FIG. 3D  is an enlarged view of metering pump  10  shown in  FIG. 3C . 
           [0017]      FIG. 4A  is an enlarged isometric view of yet another implementation of a metering pump. 
           [0018]      FIG. 4B  is an enlarged front view of the metering pump shown in  FIG. 4A . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is an isometric view of metering pump assembly  2 , which includes tank  4  (which further comprises tank recirculation port  4 R and tank manifold assembly  4 M), power source  6 , pressure relief valve  8 , metering pump  10 , and supply line L. Tank  4  is connected to metering pump  10 . Metering pump  10  is connected to tank  4 , power source  6 , and pressure relief valve  8 . Pressure relief valve  8  is positioned downstream from the outlet of metering pump  10 . Power source  6  provides electrical power to metering pump  10 . Metering pump  10  draws fluid from tank manifold assembly  4 M and then provides the fluid through supply line L to a desired location. Pressure relief valve  8  receives fluid from metering pump  10  and can redirect fluid if the pressure surpasses a threshold. Fluid diverted by pressure relief valve  8  can be recirculated to tank  4  through tank recirculation port  4 R. 
         [0020]      FIG. 2A  is an exploded isometric view of one implementation of metering pump  10 .  FIG. 2B  is an isometric view of metering pump  10  shown in  FIG. 2A .  FIG. 2C  is a front view of metering pump  10  shown in  FIG. 2A .  FIG. 2D  is a top plan view of metering pump  10  shown in  FIG. 2A .  FIG. 2E  is a bottom plan view of metering pump  10  shown in  FIG. 2A .  FIGS. 2A-2E  will be discussed together in the following description. Metering pump  10  includes motor section  12 , drive housing section  14 , pump section  16 , and base section  18 . Motor section  12  includes conduit  20  and motor  22 . Motor  22  further includes junction box  24 , motor housing  26 , and motor shaft  28 . Drive housing section  14  includes drive housing  30  (having first drive housing port  30 A and second drive housing port  30 B), drive guard  32 , carriage bearing  34  (which includes carriage bearing groove  34 G), carriage assembly  36  (which includes carriage assembly inner ridge  36 R), cam  38 , ball bearing  40 , plunger return block  42 , stroke adjuster  44 , drive shaft  46  (which includes drive shaft receiving end  46 R), stroke adjuster nut  48 , sleeve bearing  50 , drive cylinder mating component  52 , drive cylinder  54 , set screws  56 , and dust cover  58 . Pump section  16  includes plunger  60  (which includes plunger button end  60 B), packing nut  62 , backup ring  64 , o-ring  66 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , fluid cylinder  78 , o-ring  80 , valve housing  82 , inlet check valve  84 , and outlet check valve  86 . Base section  18  includes base  90  and base mounting surface  92 . 
         [0021]    Motor section  12  is connected to drive housing section  14 . Drive housing section  14  is connected to motor section  12 , pump section  16 , and base section  18 . Pump section  16  is connected to drive section  14 . Base section  18  is connected to drive housing section  14 . Motor section  12  provides rotational motion to the components in the drive housing section  14 . Drive housing section  14  converts rotational motion from motor section  12  into a linear reciprocating motion to drive pump section  16 . Pump section  16  provides fluid at a desired rate. Base section  18  supports metering pump  10 . 
         [0022]    Regarding motor section  12 , conduit  20  is connected to junction box  24  of motor  22 . Motor housing  26  is connected to drive housing  30 . Motor shaft  28  is positioned to extend along a longitudinal axis of motor  22  and into drive housing  30 . Conduit  20  contains wiring that connects a power source to motor  22 . Junction box  24  protects electrical components of motor  22  and connects to conduit  20 . Motor housing  26  mounts motor section  12  to drive housing  30  of drive housing section  14 . Motor shaft  28  extends and rotates through motor housing  26  into drive housing  30 . Motor  22  imparts rotational motion via motor shaft  28  for conversion into linear reciprocating motion in drive housing section  14 . 
         [0023]    Regarding drive housing section  14 , drive housing  30  is connected to motor housing  26 , drive guard  32 , carriage bearing  34 , drive cylinder mating component  52 , drive cylinder  54 , and mounting surface  92  of base section  18 . Carriage bearing  34  is connected to motor shaft  28 , drive housing  30 , carriage assembly  36 , and cam  38  and is positioned within carriage assembly  36 . Carriage assembly  36  is connected to plunger return block  42  and stroke adjuster  44  and is positioned around carriage bearing  34 . Carriage assembly inner ridge  36 R is positioned within carriage bearing groove  34 G. Cam  38  is connected to motor shaft  28  and is positioned to abut carriage bearing  34 . Ball bearing  40  is connected to and positioned to surround cam  38 . Plunger return block  42  is connected to carriage assembly  36 . Stroke adjuster  44  is connected to carriage assembly  36 , drive shaft  46 , and stroke adjuster nut  48 . Drive shaft  46  is connected to stroke adjuster  44  and plunger  60  and is positioned within sleeve bearing  50 . Stroke adjuster nut  48  is connected to stroke adjuster  44 . The inner radial surface of sleeve bearing  50  abuts drive shaft  46 , while the outer radial surface of sleeve bearing  50  abuts the inner radial surface of drive cylinder mating component  52 . The inner radial surface of drive cylinder mating component  52  abuts the outer radial surface of sleeve bearing  50 , while the outer radial surface of drive cylinder mating component  52  abuts the inner radial surface of drive housing  30  at first drive housing port  30 A. Drive cylinder mating component  52  is also connected to drive cylinder  54 . Drive cylinder  54  is connected to drive housing  30 , drive cylinder mating component  52 , set screws  56 , dust cover  58 , packing nut  62 , and fluid cylinder  78 . Set screws  56  are connected to drive cylinder  54  and fluid cylinder  78  of pump section  16 . Dust cover  58  is positioned around and is connected to drive cylinder  54 . 
         [0024]    Drive housing  30  protects internal components and mounts to motor section  12 , pump section  16 , and base section  18 . Drive housing  30  also connects to drive guard  32 . Drive guard  32  protects and allows access to components within drive housing  30 . Carriage bearing  34  mounts to motor shaft  28  and drive housing  30  and sits within carriage assembly  36 . Carriage bearing  34  restricts the movement of carriage assembly  36  and also provides a bearing surface upon which cam  38  can rotate. Carriage bearing  34  also acts as a second point of contact for carriage assembly  36  in order to maintain horizontal alignment as carriage assembly  36  reciprocates with the movement of stroke adjuster  44 . Carriage assembly  36  connects to stroke adjuster  44  and plunger return block  42  and facilitates the return of drive shaft  46  and plunger  60  once depressed by cam  38  and ball bearing  40 . Cam  38  connects to and rotates with motor shaft  28 . Ball bearing  40  surrounds cam  38  and contacts stroke adjuster  44  as cam  38  rotates, depressing drive shaft  46  and plunger  60 . Plunger return block  42  provides a contact point for ball bearing  40  rotating on cam  38  to return the depressed piston formed in part by stroke adjuster  44 , drive shaft  46  and plunger  60 . Stroke adjuster  44  serves as a first contact point for maintaining the horizontal alignment of carriage assembly  36  in conjunction with the second point of contact provided by carriage bearing  34 . Stroke adjuster  44  also depresses drive shaft  46  and plunger  60  when contacted by ball bearing  40  and cam  38 . Stroke adjuster  44  and stroke adjuster nut  48  allow for control of stroke length. Drive shaft  46  connects to and transfers linear motion to plunger  60 . Sleeve bearing  50  supports and directs the motion of drive shaft  46 . Drive cylinder mating component  52  fastens drive cylinder  54  to drive housing  30 . Set screws  56  secure drive cylinder  54  to fluid cylinder  78 . Dust cover  58  provides a protective barrier over a portion of drive cylinder  54 . 
         [0025]    Regarding pump section  16 , plunger  60  is connected to drive shaft  46 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , and second spacer  76 . Plunger button end  60 B is connected to drive shaft receiving end  46 R. Packing nut  62  is connected to drive cylinder  54 , backup ring  64 , o-ring  66 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , and fluid cylinder  78 . First plunger bearing  68  is connected to plunger  60 , packing nut  62 , and first spacer  70 . The radial inner surface of first plunger bearing  68  abuts the radial outer surface of plunger  60 , while the radial outer surface of first plunger bearing  68  abuts the radial inner surface of packing nut  62 . First spacer  70  is connected to plunger  60 , packing nut  62 , first plunger bearing  68 , and second plunger bearing  72 . The radial inner surface of first spacer  70  abuts the radial outer surface of plunger  60 , while the radial outer surface of first spacer  70  abuts the radial inner surface of packing nut  62 . Second plunger bearing  72  is connected to plunger  60 , packing nut  62 , first spacer  70 , and packing seal  74 . The radial inner surface of second plunger bearing  72  abuts the radial outer surface of plunger  60 , while the radial outer surface of second plunger bearing  72  abuts the radial inner surface of packing nut  62 . Packing seal  74  is connected to plunger  60 , packing nut  62 , second plunger bearing  72 , and second spacer  76 . The radial inner surface of packing seal  74  abuts the radial outer surface of plunger  60 , while the radial outer surface of packing seal  74  abuts the radial inner surface of packing nut  62 . Second spacer  76  is connected to plunger  60 , packing nut  62 , packing seal  74 , and fluid cylinder  78 . The radial inner surface of second spacer  76  abuts the radial outer surface of plunger  60 , while the radial outer surface of second spacer  76  abuts the radial inner surface of packing nut  62 . Fluid cylinder  78  is connected to drive cylinder  54 , packing nut  62 , second spacer  76 , and valve housing  82 . O-ring  80  is connected to fluid cylinder  78 . Valve housing  82  is connected to inlet check valve  84 , outlet check valve  86 , and bleed valve  88 . 
         [0026]    Plunger  60  connects to drive shaft  46  and moves in a linear reciprocating motion therewith. Plunger button end  60 B connects to drive shaft receiving end  46 R. As plunger  60  translates toward valve housing  82 , fluid is pushed through outlet check valve  86 . As plunger is pulled away from valve housing  82  and toward drive housing  30 , fluid is drawn into valve housing  82  through inlet check valve  84 . Packing nut  62 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , and fluid cylinder  78  provide a channel within which plunger  60  reciprocates. Packing nut  62  presses first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , and second spacer  76  together to seal the channel. O-ring  66  and backup ring  64  provide a sealing interface between packing nut  62  and fluid cylinder  78 . O-ring  80  provides a sealing interface between fluid cylinder  78  and valve housing  82 . Bleed valve  88  purges air to facilitate proper fluid flow. 
         [0027]    Regarding base section  18 , base  90  includes a mounting surface  92 . Mounting surface  92  is connected to drive housing  30 . Base  90  mounts to drive housing  30  at mounting surface  92  and provides support for metering pump  10 . 
         [0028]    Metering pump  10  can draw fluid from tank manifold assembly  4 M (shown in  FIG. 1 ) into inlet check valve  84  and then discharge the fluid to supply line L (shown in  FIG. 1 ) through outlet check valve  86 . Fluid is drawn into and discharged from metering pump  10  based on the displacement of the piston formed by stroke adjuster  44 , drive shaft  46 , and plunger  60  and rotation cycle time of motor shaft  28 , cam  38  and ball bearing  40 . Metering pump  10  converts rotational motion from motor shaft  28 , cam  38  and ball bearing  40  into linear reciprocating motion in the piston. Plunger  60  and a portion of drive shaft  46  move linearly within a channel formed by sleeve bearing  50 , drive cylinder mating component  52 , packing nut  62 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , and fluid cylinder  78 . A complete piston stroke includes both suction and discharge strokes. The suction stroke draws fluid into inlet check valve  84  to fill the volume formed by the face of plunger  60 , packing nut  62 , and valve housing  82 . The discharge stroke pushes fluid out through outlet check valve  86  as the face of plunger  60  moves linearly in the direction of valve housing  82  relative to drive housing  30 . 
         [0029]    Motor  22  rotates motor shaft  28 , which in turn rotates cam  38  and ball bearing  40  in drive housing  30 . The eccentric rotation of cam  38  and ball bearing  40  acts to depress and return the piston so that it reciprocates within the channel formed by sleeve bearing  50 , drive cylinder mating component  52 , packing nut  62 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , and fluid cylinder  78 . Carriage assembly  36  attaches to plunger return block  42  and stroke adjuster  44  and facilitates the suction stroke of the piston. Carriage assembly  36 , stroke adjuster  44 , and plunger return block  42  act as a follower for cam  38  and ball bearing  40 . The suction stroke of the piston begins when cam  38  and ball bearing  40  rotate to a position where the larger side of cam  38  is nearest to second drive housing port  30 B, such that ball bearing  40  pushes on plunger return block  42 . Pressing plunger return block  42  drives the carriage assembly  36  toward second drive housing port  30 B along an axis formed along the length of the piston and extending through first drive housing port  30 A and second drive housing port  30 B. This in turn pulls plunger  60  away from valve housing  82  along the same axis, drawing fluid into inlet check valve  84  to fill the volume formed by the face of plunger  60 , packing nut  62 , and valve housing  82 . As cam  38  and ball bearing  40  continue to rotate into a position where the larger portion of cam  38  is nearest drive housing port  30 A, ball bearing  40  pushes on stroke adjuster  44 , depressing the piston formed by stroke adjuster  44 , drive shaft  46 , and plunger  60  and initiating the discharge stroke. Depressing the piston pushes both the piston and carriage assembly  36  toward first drive housing port  30 A along the axis formed along the piston and extending through first drive housing port  30 A and second drive housing port  30 B and dispenses the volume drawn in during the suction stroke through outlet check valve  86 . The continued rotation of motor shaft  28 , cam  38  and ball bearing  40  in turn drives the continued reciprocation of the piston. 
         [0030]    Carriage bearing  34  confers the advantage of providing a second point of contact for maintaining the alignment of carriage assembly  36  along the axis formed by first drive housing port  30 A and second drive housing port  30 B without needing any additional components or structures. Stroke adjuster  44  provides the first point of contact for carriage assembly  36  in aligning carriage assembly  36  along the axis formed along the length of the piston and extending through first drive housing port  30 A and second drive housing port  30 B as it moves between first drive housing port  30 A and second drive housing port  30 B with the rotation of cam  38  and ball bearing  40 . Using carriage bearing  34  as the second point of contact for the alignment of carriage assembly  36  ensures that it does rotate with respect to the axis formed along the length of the piston and extending through first drive housing port  30 A and second drive housing port  30 B. This also limits the rotation of the piston within the channel. In prior art configurations, the use of additional bearings or even a dummy piston is typically required to ensure that a carriage assembly will not rotate. Using additional parts provides more wear points and thus more potential failure modes. Carriage bearing  34 , by contrast, aligns carriage assembly  36  with the axis along the piston without the need for additional parts, reducing possible failure modes and potential repair downtime. 
         [0031]    The coupling and structure of drive shaft receiving end  46 R and plunger button end  60 B confer the advantage of minimizing the side load applied to the channel components such as packing seal  74 , ensuring a longer operating life. The connection of drive shaft receiving end  46 R and plunger button end  60 B is positioned to ensure that it avoids entering sleeve bearing  50  and packing seal  74  during the reciprocation of drive shaft  46  and plunger  60 . In one implementation, plunger button end  60 B has a button shape, while drive shaft receiving end has a corresponding shape, such as a hook, permitting the mating of the two ends. The driveshaft receiving end  46 R and plunger button end  60 B connection provides a degree of freedom of movement between drive shaft  46  and plunger  60  so that any flex or rotation imparted to drive shaft  46  is reduced or eliminated on plunger  60 . As cam  38  and ball bearing  40  rotate into contact with stroke adjuster  44 , ball bearing  40  tends to provide both a force depressing stroke adjuster  44  and drive shaft  46  and an orthogonal force imparting a slight rotation to drive shaft  46 . The orthogonal force is the result of drag friction between stroke adjuster  44  and ball bearing  40  as cam  38  rotates. Rotation of drive shaft  46  can impart a side load downstream on a portion of the channel made up of packing nut  62 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , and second spacer  76 . The degree of freedom in the connection mitigates or eliminates the propagation of the rotation on drive shaft  46 , reducing side loading to the channel components. Reducing the side load on the channel components extends the operating life thereof. In particular, this connection extends the life of packing seal  74  by reducing the potential side loading applied from plunger  60  thereon. In addition, the drive shaft receiving end  46 R and plunger button end  60 B connection also confers the advantage of providing efficient changeover times, minimizing downtime for repair. 
         [0032]    In another embodiment of metering pump  10 , a second piston and pump section, like the piston and pump section  16 , can be added in place of plunger return block  42 . The second piston and second pump section operate like the piston and pump section  16 . 
         [0033]      FIGS. 3A-3D  illustrates another implementation of metering pump  10 .  FIGS. 3A-3D  use similar reference characters to those used in  FIGS. 2A-2E , even though some of the components, such as motor housing  26  and carriage assembly  36 , differ somewhat in structure. A person of ordinary skill in the pertinent art would recognize that components having the same reference numerals perform the same or similar functions.  FIG. 3A  is an isometric cross-sectional view of chemical metering pump  10 .  FIG. 3B  is a front cross-sectional view of metering pump  10  shown in  FIG. 3A .  FIG. 3C  is a bottom plan cross-sectional view of metering pump  10  shown in  FIG. 3A .  FIG. 3D  is an enlarged view of metering pump  10  shown in  FIG. 3C . Metering pump  10  includes motor section  12 , drive housing section  14 , and pump section  16 . Motor section  12  includes motor  22 , junction box  24 , motor housing  26 , and motor shaft  28 . Drive housing section  14  includes drive housing  30  (further comprising first drive housing port  30 A, second drive housing port  30 B, drive housing upper portion  30 U, and drive housing lower portion  30 L), drive guard  32 , carriage bearing  34  (which includes carriage bearing groove  34 G), carriage assembly  36  (which includes carriage assembly inner ridge  36 R), cam  38 , ball bearing  40 , plunger return block  42 , stroke adjuster  44 , drive shaft  46  (which includes drive shaft receiving end  46 R), stroke adjuster nut  48 , sleeve bearing  50 , drive cylinder mating component  52 , drive cylinder  54 , set screws  56 , and dust cover  58 . Pump section  16  includes plunger  60  (which includes plunger button end  60 B), packing nut  62 , backup ring  64 , o-ring  66 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , fluid cylinder  78 , o-ring  80 , valve housing  82 , inlet check valve  84 , and outlet check valve  86 . Also shown in  FIGS. 3A-3D  is axis A. 
         [0034]    Motor housing  26  is connected to drive housing  30 . Motor shaft  28  is positioned to extend along a longitudinal axis of motor  22  and into drive housing  30 . Drive housing  30  is connected to motor housing  26 , drive guard  32 , carriage bearing  34 , drive cylinder mating component  52 , drive cylinder  54 , and mounting surface  92  of base section  18 . Carriage bearing  34  is connected to motor shaft  28 , drive housing  30 , carriage assembly  36 , and cam  38 . Carriage assembly  36  is connected to plunger return block  42  and stroke adjuster  44 . Carriage assembly inner ridge  36 R is positioned within carriage bearing groove  34 G. Cam  38  is connected to motor shaft  28  and is positioned to abut carriage bearing  34 . Ball bearing  40  is connected to and positioned to surround cam  38 . Plunger return block  42  is connected to carriage assembly  36 . Stroke adjuster  44  is connected to carriage assembly  36 , drive shaft  46 , and stroke adjuster nut  48 . Drive shaft  46  is connected to stroke adjuster  44  and plunger  60  and is positioned within sleeve bearing  50 . Stroke adjuster nut  48  is connected to stroke adjuster  44 . The inner radial surface of sleeve bearing  50  abuts drive shaft  46 , while the outer radial surface of sleeve bearing  50  abuts the inner radial surface of drive cylinder mating component  52 . The inner radial surface of drive cylinder mating component  52  abuts the outer radial surface of sleeve bearing  50 , while the outer radial surface of drive cylinder mating component  52  abuts the inner radial surface of drive housing  30  at first drive housing port  30 A. Drive cylinder mating component  52  is also connected to drive cylinder  54 . Drive cylinder  54  is connected to drive housing  30 , drive cylinder mating component  52 , set screws  56 , dust cover  58 , packing nut  62 , and fluid cylinder  78 . Set screws  56  are connected to drive cylinder  54  and fluid cylinder  78  of pump section  16 . Dust cover  58  is positioned around and is connected to drive cylinder  54 . 
         [0035]    Plunger  60  is connected to drive shaft  46 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , and second spacer  76 . Plunger button end  60 B is connected to drive shaft receiving end  46 R. Packing nut  62  is connected to drive cylinder  54 , backup ring  64 , o-ring  66 , first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , packing seal  74 , second spacer  76 , and fluid cylinder  78 . First plunger bearing  68  is connected to plunger  60 , packing nut  62 , and first spacer  70 . The radial inner surface of first plunger bearing  68  abuts the radial outer surface of plunger  60 , while the radial outer surface of first plunger bearing  68  abuts the radial inner surface of packing nut  62 . First spacer  70  is connected to plunger  60 , packing nut  62 , first plunger bearing  68 , and second plunger bearing  72 . The radial inner surface of first spacer  70  abuts the radial outer surface of plunger  60 , while the radial outer surface of first spacer  70  abuts the radial inner surface of packing nut  62 . Second plunger bearing  72  is connected to plunger  60 , packing nut  62 , first spacer  70 , and packing seal  74 . The radial inner surface of second plunger bearing  72  abuts the radial outer surface of plunger  60 , while the radial outer surface of second plunger bearing  72  abuts the radial inner surface of packing nut  62 . Packing seal  74  is connected to plunger  60 , packing nut  62 , second plunger bearing  72 , and second spacer  76 . The radial inner surface of packing seal  74  abuts the radial outer surface of plunger  60 , while the radial outer surface of packing seal  74  abuts the radial inner surface of packing nut  62 . Second spacer  76  is connected to plunger  60 , packing nut  62 , packing seal  74 , and fluid cylinder  78 . The radial inner surface of second spacer  76  abuts the radial outer surface of plunger  60 , while the radial outer surface of second spacer  76  abuts the radial inner surface of packing nut  62 . Fluid cylinder  78  is connected to drive cylinder  54 , packing nut  62 , second spacer  76 , and valve housing  82 . O-ring  80  is connected to fluid cylinder  78 . Valve housing  82  is connected to inlet check valve  84 , outlet check valve  86 , and bleed valve  88 . 
         [0036]    Cam  38  and ball bearing  40  rotate eccentrically with the rotation of motor shaft  28 . Carriage assembly  36 , stroke adjuster  44 , and plunger return block  42  act as a follower for cam  38  and ball bearing  40 . As cam  38  and ball bearing  40  rotate in a circular path to a position where the larger portion of cam  38  is nearest drive housing port  30 A, ball bearing  40  pushes on stroke adjuster  44 , depressing the piston formed by stroke adjuster  44 , drive shaft  46 , and plunger  60 . Depressing this piston in turn dispenses fluid through outlet check valve  86 . As cam  38  and ball bearing  40  rotate to a position where the larger side of cam  38  is nearest to drive housing port  30 B, ball bearing  40  pushes on plunger return block  42 . Pressing plunger return block  42  drives the carriage assembly  36  and thus pulls piston formed by stroke adjuster  44 , drive shaft  46 , and plunger  60  back from the depressed position. Pulling back this piston draws fluid through inlet check valve  84 . 
         [0037]    Carriage bearing  34  sits within carriage assembly  36  and reduces friction for the reciprocating and linear translation of carriage assembly  36  between drive housing ports  30 A and  30  B and along axis A. Carriage assembly inner ridge  36 R couples to and translates along carriage bearing groove  34 G. The coupling of carriage bearing  34  and carriage assembly  36  at the carriage bearing groove  34 G and carriage assembly ridge  36 R interface restricts carriage assembly  36  from traveling in undesirable directions. In particular, the coupling prevents carriage assembly  36  from translating back and forth along the axis extending through motor shaft  28  and drive guard  32  and up and down along the axis extending through drive housing upper portion  30 U and drive housing lower portion  30 L. It also prevents carriage assembly  36  from tilting back and forth between drive guard  32  and where motor section  12  mounts to drive housing  30 . 
         [0038]    Stroke adjuster  44  and carriage bearing  34  ensure the horizontal alignment of carriage assembly  36  with respect to axis A, as shown in  FIG. 3B . Stroke adjuster  44  provides the first point of contact for carriage assembly  36 . Absent a second point of contact, carriage assembly  36  would be free to rotate around and with motor shaft  28  with respect to axis A. Carriage bearing  34  provides a second point of contact to ensure that carriage assembly  36  maintains horizontal alignment. Using carriage bearing  34  as the second point of contact minimizes the number of components needed to align carriage assembly  36 . Placing carriage bearing  34  on motor shaft  28  eliminates the need for incorporating additional aligning features, providing less wear points and possible failure modes. In prior art configurations, additional components, such as a dummy piston or multiple bearings, would be required to align a carriage assembly as it reciprocated. Such additional components provide more wear points and failure modes, which can force end-users to purchase more replacement parts. 
         [0039]    Drive shaft receiving end  46 R connects to plunger button end  60 B, minimizing the side load applied to plunger  60  channel components such as packing seal  74 . The connection is positioned to ensure that it avoids entering sleeve bearing  50  and packing seal  74  during the reciprocation of drive shaft  46  and plunger  60 . As cam  38  and ball bearing  40  rotate into contact with stroke adjuster  44 , ball bearing  40  tends to provide both a force depressing stroke adjuster  44  and drive shaft  46  and an orthogonal force imparting a slight rotation to drive shaft  46 . The orthogonal force is result of drag friction between stroke adjuster  44  and ball bearing  40  as cam  38  rotates. The rotation of drive shaft  46  in turn imparts side load on the channel components. The driveshaft receiving end  46 R and plunger button end  60 B connection provides a degree of freedom between drive shaft  46  and plunger  60  so that any flex or rotation imparted to drive shaft  46  is reduced or eliminated on plunger  60 , minimizing the side loading on first plunger bearing  68 , first spacer  70 , second plunger bearing  72 , and packing seal  74 . Reducing the side load on packing seal  74  increases the life thereof. In addition, the drive shaft receiving end  46 R and plunger button end  60 B connection permits efficient changeover. 
         [0040]      FIG. 4A  is an enlarged isometric view of yet another implementation of metering pump  10 .  FIG. 4B  is an enlarged front view of metering pump  10  shown in  FIG. 4A . Drive housing section  14  includes drive housing  30 , drive guard  32 , drive shaft  46  (which includes drive shaft receiving end  46 R), drive cylinder mating component  52 , drive cylinder  54 , set screws  56 , and dust cover  58 . Pump section  16  includes plunger  60  (which includes plunger button end  60 B), packing nut  62 , and fluid cylinder  78 . Drive housing  30  is connected to drive guard  32 , and drive cylinder mating component  52 . Drive shaft receiving end  46 R of drive shaft  46  is connected to plunger button end  60 B of plunger  60 . Drive cylinder mating component  52  is connected to drive housing  30  and drive cylinder  54 . Drive cylinder  54  is connected to fluid cylinder  78 . Set screws  56  are connected to drive cylinder  54  and fluid cylinder  78 . Dust cover  58  is connected to drive cylinder  54 . 
         [0041]    Plunger  60  can be serviced or replaced quickly without the use of special tools and, in some instances, without removing drive guard  32 . To disconnect plunger  60 , packing nut  62  can be exposed by rotating dust cover  58  and sliding it back toward drive housing  30 . Packing nut  62  can then be loosened. Set screws  56  can then be loosened from drive cylinder  54 , which is fastened to fluid cylinder  78 . Once set screws  56  have been removed, fluid cylinder  78  can be released from drive cylinder  54 . In some embodiments, drive guard  32  can be removed in order to reposition cam  38  (as shown in  FIGS. 2A and 3A ), such that the larger side of cam  38  is aligned with the side being repaired. In other embodiments, cam  38  may not need to be adjusted. Plunger  60  can then be disengaged from drive shaft  46  at the coupling of driveshaft receiving end  46 R and plunger button end  60 B. Decoupling plunger  60  and drive shaft  46  allows for pump section  16  to be removed without needing to access the inside of drive housing  30  or using a special tool to disengage plunger  60  from drive shaft  46 . Plunger  60  can thus be quickly repaired, serviced, or replaced to ensure that the downtime of metering pump  10  is minimized. 
         [0042]    To reconnect a replacement plunger, the replacement plunger button shaped end can be connected to drive shaft receiving end  46 R. The replacement plunger can then be guided into fluid cylinder  78 , as fluid cylinder  78  is guided into drive cylinder  54 . Set screws  56  can then be used to fasten drive cylinder  54  to fluid cylinder  78 . Packing nut  62  can then be tightened. Dust cover  58  can then be pushed forward away from drive housing  30  and then rotated to lock into place. The coupling and structure of drive shaft receiving end  46 R and plunger button end  60 B thus confer the advantage of providing easy and efficient changeover, minimizing downtime for repair. 
         [0043]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.