Abstract:
A method of displacing fluid includes pulling a pump displacement member through a suction stroke with a pull, the pull configured to transmit only tensile forces to the fluid displacement member. A working fluid disposed in an internal pressure chamber drive the fluid displacement member through a pumping stroke. The pull is prevented from transmitting any compressive forces to the fluid displacement member, such that the pull does not drive the fluid displacement member through the pumping stroke.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority as a divisional application under 35 U.S.C. § 121 of earlier filed U.S. Non-Provisional application Ser. No. 14/579,618 filed on Dec. 22, 2014, and entitled “Pulseless Positive Displacement Pump and Method of Pulselessly Displacing Fluid,” which claimed priority to U.S. Provisional Application No. 62/022,263 filed on Jul. 9, 2014, and entitled “Mechanically-Driven Diaphragm Pump with Diaphragm Pressure Chamber,” and to U.S. Provisional Application No. 61/937,266 filed on Feb. 7, 2014, and entitled “Mechanically-Driven Diaphragm Pump with Diaphragm Pressure Chamber,” the disclosures of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to positive displacement pumps and more particularly to an internal drive system for positive displacement pumps. 
         [0003]    Positive displacement pumps discharge a process fluid at a selected flow rate. In a typical positive displacement pump, a fluid displacement member, usually a piston or diaphragm, drives the process fluid through the pump. When the fluid displacement member is drawn in, a suction condition is created in the fluid flow path, which draws process fluid into a fluid cavity from the inlet manifold. The fluid displacement member then reverses direction and forces the process fluid out of the fluid cavity through the outlet manifold. 
         [0004]    Air operated double displacement pumps typically employ diaphragms as the fluid displacement members. In an air operated double displacement pump, the two diaphragms are joined by a shaft, and compressed air is the working fluid in the pump. Compressed air is applied to one of two diaphragm chambers, associated with the respective diaphragms. When compressed air is applied to the first diaphragm chamber, the first diaphragm is deflected into the first fluid cavity, which discharges the process fluid from that fluid cavity. Simultaneously, the first diaphragm pulls the shaft, which is connected to the second diaphragm, drawing the second diaphragm in and pulling process fluid into the second fluid cavity. Delivery of compressed air is controlled by an air valve, and the air valve is usually actuated mechanically by the diaphragms. Thus, one diaphragm is pulled in until it causes the actuator to toggle the air valve. Toggling the air valve exhausts the compressed air from the first diaphragm chamber to the atmosphere and introduces fresh compressed air to the second diaphragm chamber, thus causing a reciprocating movement of the respective diaphragms. Alternatively, the first and second fluid displacement members could be pistons instead of diaphragms, and the pump would operate in the same manner. 
         [0005]    Hydraulically driven double displacement pumps utilize hydraulic fluid as the working fluid, which allows the pump to operate at much higher pressures than an air driven pump. In a hydraulically driven double displacement pump, hydraulic fluid drives one fluid displacement member into a pumping stroke, while that fluid displacement member is mechanically attached to the second fluid displacement member and thereby pulls the second fluid displacement member into a suction stroke. The use of hydraulic fluid and pistons enables the pump to operate at higher pressures than an air driven diaphragm pump could achieve. 
         [0006]    Alternatively, double displacement pumps may be mechanically operated, without the use of air or hydraulic fluid. In these cases, the operation of the pump is essentially similar to an air operated double displacement pump, except compressed air is not used to drive the system. Instead, a reciprocating drive is mechanically connected to both the first fluid displacement member and the second fluid displacement member, and the reciprocating drive drives the two fluid displacement members into suction and pumping strokes. 
       SUMMARY 
       [0007]    According to one embodiment of the present invention, a pump includes an inlet manifold, an outlet manifold, a first fluid cavity disposed between the inlet manifold and the outlet manifold, a second fluid cavity disposed between the inlet manifold and the outlet manifold, and an internal pressure chamber. A first fluid displacement member sealingly separates the first fluid cavity from the internal pressure chamber, and a second fluid displacement member sealingly separates the second fluid cavity from the internal pressure chamber. Inlet check valves are disposed between the inlet manifold and the first and second fluid cavities to prevent backflow into the inlet manifold from either fluid cavity. Similarly, outlet check valves are disposed between the fluid cavities and the outlet manifold to prevent backflow from the outlet manifold to either fluid cavity. A piston is disposed within the internal pressure chamber, and the piston has a first pull chamber within a first end of the piston and a second pull chamber within a second end of the piston. The piston also has a slot for engaging a drive. A first pull has a free end and an attachment end, with the free end slidably disposed within the first pull chamber and the attachment end secured to the first fluid displacement member. A second pull has a free end and an attachment end, with the free end slidably disposed within the second pull chamber and the attachment end secured to the second fluid displacement member. 
         [0008]    According to another embodiment, a pump includes an inlet manifold, an outlet manifold, a first fluid cavity disposed between the inlet manifold and the outlet manifold, a second fluid cavity disposed between the inlet manifold and the outlet manifold, and an internal pressure chamber. A first fluid displacement member sealingly separates the first fluid cavity from the internal pressure chamber, and a second fluid displacement member sealingly separates the second fluid cavity from the internal pressure chamber. Inlet check valves are disposed between the inlet manifold and the first and second fluid cavities to prevent backflow into the inlet manifold from either fluid cavity. Similarly, outlet check valves are disposed between the fluid cavities and the outlet manifold to prevent backflow from the outlet manifold to either fluid cavity. A drive extends into the internal pressure chamber, and a hub is disposed on the drive. The hub includes a first attachment portion and a second attachment portion. A first flexible belt connects the first attachment portion to the first fluid displacement member, and a second flexible belt connects the second attachment portion to the second fluid displacement member. 
         [0009]    According to yet another embodiment, a method for operating a pump includes charging an internal pressure chamber with a working fluid. A drive is activated to move a driven member disposed within the internal pressure chamber. The driven member draws either of a first fluid displacement member or a second fluid displacement member into a suction stroke, and the working fluid pushes the other of the first fluid displacement member or the second fluid displacement member into a pumping stroke. Pulsation is eliminated by sequencing the drive such that one fluid displacement member is changing over from a pumping stroke to a suction stroke while the other fluid displacement member is already in a pumping stroke. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a rear perspective view of a pump, drive system, and motor. 
           [0011]      FIG. 2  is an exploded perspective view of a pump, drive system, and drive. 
           [0012]      FIG. 3A  is a cross-sectional view, along section  3 - 3  in  FIG. 1 , showing the connection of pump, drive system, and drive. 
           [0013]      FIG. 3B  is a cross-sectional view, along section  3 - 3  in  FIG. 1 , showing the connection of  FIG. 3A  during an over-pressurization event. 
           [0014]      FIG. 4  is a top, cross-sectional view, along section  4 - 4  in  FIG. 1 , showing the connection of pump, drive system, and drive. 
           [0015]      FIG. 5  is a cross-sectional view, along section  5 - 5  in  FIG. 1 , showing the connection of a pump, a drive system, and a drive. 
           [0016]      FIG. 6  is a cross-sectional view, along section  6 - 6  in  FIG. 1 , showing the connection of a pump, a drive system, and a drive. 
           [0017]      FIG. 7  is a cross-sectional view, along section  7 - 7  in  FIG. 1 , showing the connection of a pump, a drive system, and a drive. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  shows a perspective view of pump  10 , electric drive  12 , and drive system  14 . Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  and outlet check valves  24   a  and  24   b.  Drive system  14  includes housing  26  and piston guide  28 . Housing includes working fluid inlet  30  and drive chamber  32  (best seen in  FIG. 2 ). Electric drive  12  includes motor  34 , gear reduction drive  36 , and drive  38 . 
         [0019]    Fluid covers  20   a  and  20   b  are attached to inlet manifold  16  by fasteners  40 . Inlet check valves  22   a  and  22   b  (shown in  FIG. 2 ) are disposed between inlet manifold  16  and fluid covers  20   a  and  20   b  respectively. Fluid covers  20   a  and  20   b  are similarly attached to outlet manifold  18  by fasteners  40 . Outlet check valves  24   a  and  24   b  (shown in  FIG. 2 ) are disposed between outlet manifold  18  and fluid covers  20   a  and  20   b,  respectively. Housing  26  is secured between fluid covers  20   a  and  20   b  by fasteners  42 . Fluid cavity  44   a  (best seen in  FIG. 3 ) is formed between housing  26  and fluid cover  20   a.  Fluid cavity  44   b  (best seen in  FIG. 3 ) is formed between housing  26  and fluid cover  20   b.    
         [0020]    Motor  34  is attached to and drives gear reduction drive  36 . Gear reduction drive  36  drives drive  38  to actuate pump  10 . Drive  38  is secured within drive chamber  32  by fasteners  46 . 
         [0021]    Housing  26  is filled with a working fluid, either a gas, such as compressed air, or a non-compressible hydraulic fluid, through working fluid inlet  30 . When the working fluid is a non-compressible hydraulic fluid, housing  26  further includes an accumulator for storing a portion of the non-compressible hydraulic fluid during an overpressurization event. As explained in more detail below, drive  38  causes drive system  14  to draw process fluid from inlet manifold  16  into either fluid cavity  44   a  or fluid cavity  44   b.  The working fluid then discharges the process fluid from either fluid cavity  44   a  or fluid cavity  44   b  into outlet manifold  18 . Inlet check valves  22   a  and  22   b  prevent the process fluid from backflowing into inlet manifold  16  while the process fluid is being discharged to outlet manifold  18 . Similarly, outlet check valves  24   a  and  24   b  prevent the process fluid from backflowing into either fluid cavity  44   a  or  44   b  from outlet manifold  18 . 
         [0022]      FIG. 2  is an exploded, perspective view of pump  10 , drive system  14 , and drive  38 . Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  and outlet check valves  24   a  and  24   b.  Inlet check valve  22   a  includes seat  48   a  and check ball  50   a,  and inlet check valve  22   b  includes seat  48   b  and check ball  50   b . Similarly, outlet check valve  24   a  include seat  49   a  and check ball  51   a,  and outlet check valve  24   b  includes seat  49   b  and check ball  51   b . Although inlet check valves  22   a / 22   b  and outlet check valves  24   a / 24   b  are shown as ball check valves, inlet check valves  22   a / 22   b  and outlet check valves  24   a / 24   b  can be any suitable valve for preventing the backflow of process fluid. 
         [0023]    Pump further includes fluid displacement members  52   a  and  52   b.  In the present embodiment, fluid displacement members  52   a  and  52   b  are shown as diaphragms, but fluid displacement members  52   a  and  52   b  could be diaphragms, pistons, or any other suitable device for displacing process fluid. Additionally, while pump  10  is described as a double displacement pump, utilizing dual diaphragms, it is understood that drive system  14  could similarly drive a single displacement pump without any material change. It is also understood that drive system  14  could drive a pump with more than two fluid displacement members. 
         [0024]    Drive system  14  includes housing  26 , piston guide  28 , piston  54 , pulls  56   a  and  56   b,  and face plates  58   a  and  58   b.  Housing  26  includes working fluid inlet  30 , guide opening  60 , annular structure  62 , and bushings  64   a  and  64   b.  Housing  26  defines internal pressure chamber  66 , which contains the working fluid during operation. In the present embodiment, the reciprocating member of drive system  14  is shown as a piston, but it is understood that the reciprocating member of drive system  14  could be any suitable device for creating a reciprocating motion, such as a scotch yoke or any other drive suitable for reciprocating within housing  26 . 
         [0025]    Piston guide  28  includes barrel nut  68  and guide pin  70 . Piston  54  includes pull chamber  72   a  disposed within a first end of piston  54  and pull chamber  72   b  (shown in  FIG. 3A ) disposed within a second end of piston  54 . Piston  54  further includes central slot  74 , axial slot  76 , and openings  78   a  and  78   b  (not shown) for receiving face plate fasteners  80 . Pull  56   a  is identical to pull  56   b  with like numbers indicating like parts. Pull  56   a  includes attachment end  82   a,  free end  84   a,  and pull shaft  86   a  extending between attachment end  82   a  and free end  84   a . Free end  84   a  of pull  56   a  includes flange  85   a.  Face plate  58   a  is identical to face plate  58   b  with like numbers indicating like parts. Face plate  58   a  includes fastener holes  88   a  and pull opening  90   a.  In the present embodiment, fluid displacement member  52   a  includes attachment screw  92   a  and diaphragm  94   a.  Drive  38  includes housing  96 , crank shaft  98 , cam follower  100 , bearing  102 , and bearing  104 . Annular structure  62  includes openings  106  therethrough. 
         [0026]    Inlet manifold  16  is attached to fluid cover  20   a  by fasteners  40 . Inlet check valve  22   a  is disposed between inlet manifold  16  and fluid cover  20   a.  Seat  48   a  of inlet check valve  22   a  sits upon inlet manifold  16 , and check ball  50   a  of inlet check valve  22   a  is disposed between seat  48   a  and fluid cover  20   a.  Similarly, inlet manifold  16  is attached to fluid cover  20   b  by fasteners  40 , and inlet check valve  22   b  is disposed between inlet manifold  16  and fluid cover  20   b.  Outlet manifold  18  is attached to fluid cover  20   a  by fasteners  40 . Outlet check valve  24   a  is disposed between outlet manifold  18  and fluid cover  20   a.  Seat  49   a  of outlet check valve  24   a  sits upon fluid cover  20   a  and check ball  51   a  of outlet check valve  24   a  is disposed between seat  49   a  and outlet manifold  18 . Similarly, outlet manifold  18  is attached to fluid cover  20   b  by fasteners  40 , and outlet check valve  24   b  is disposed between outlet manifold  18  and fluid cover  20   b.    
         [0027]    Fluid cover  20   a  is fixedly attached to housing  26  by fasteners  42 . Fluid displacement member  52   a  is secured between housing  26  and fluid cover  20   a  to define fluid cavity  44   a  and sealingly encloses one end of internal pressure chamber  66 . Fluid cover  20   b  is fixedly attached to housing  26  by fasteners  42 , and fluid displacement member  52   b  is secured between housing  26  and fluid cover  20   b.  Similar to fluid cavity  44   a,  fluid cavity  44   b  is formed by fluid cover  20   b  and fluid displacement member  52   b,  and fluid displacement member  52   b  sealingly encloses a second end of internal pressure chamber  66 . 
         [0028]    Bushings  64   a  and  64   b  are disposed upon annular structure  62 , and piston  54  is disposed within housing  26  and rides upon bushings  64   a  and  64   b.  Barrel nut  68  extends through and is secured within guide opening  60 . Guide pin  70  is fixedly secured to barrel nut  68  and rides within axial slot  76  to prevent piston  54  from rotating about axis A-A. Free end  84   a  of pull  56   a  is slidably disposed within pull chamber  72   a  of piston  54 . Pull shaft  86   a  extends through pull opening  90   a  of face plate  58   a.  Face plate  58   a  is secured to piston  54  by face plate fasteners  80  that extend through openings  88   a  and into fastener holes  78   a  of piston  54 . Pull opening  90   a  is sized such that pull shaft  86   a  can slide through pull opening  90   a  but free end  84   a  is retained within pull chamber  72   a  by flange  85   a  engaging face plate  58   a.  Attachment end  82   a  is secured to attachment screw  92   a  to join fluid displacement member  52   a  to pull  56   a.    
         [0029]    Crank shaft  98  is rotatably mounted within housing  96  by bearing  102  and bearing  104 . Cam follower  100  is affixed to crank shaft  98  such that cam follower  100  extends into housing  26  and engages central slot  74  of piston  54  when drive  38  is mounted to housing  26 . drive  38  is mounted within drive chamber  32  of housing  26  by fasteners  46  extending through housing  96  and into fastener holes  108 . 
         [0030]    Internal pressure chamber  66  is filled with a working fluid, either compressed gas or non-compressible hydraulic fluid, through working fluid inlet  30 . Openings  106  allow the working fluid to flow throughout internal pressure chamber  66  and exert force on both fluid displacement member  52   a  and fluid displacement member  52   b.    
         [0031]    Cam follower  100  reciprocatingly drives piston  54  along axis A-A. When piston  54  is displaced towards fluid displacement member  52   a,  pull  56   b  is pulled in the same direction due to flange  85   b  on free end  84   b  of pull  56   b  engaging face plate  58   b.  Pull  56   b  thereby pulls fluid displacement member  52   b  into a suction stroke. Pulling fluid displacement member  52   b  causes the volume of fluid cavity  44   b  to increase, which draws process fluid into fluid cavity  44   b  from inlet manifold  16 . Outlet check valve  24   b  prevents process fluid from being drawn into fluid cavity  44   b  from outlet manifold  18  during the suction stroke. At the same time that process fluid is being drawn into fluid cavity  44   b,  the charge pressure of the working fluid in internal pressure chamber  66  pushes fluid displacement member  52   a  into fluid cavity  44   a,  causing fluid displacement member  52   a  to begin a pumping stroke. Pushing fluid displacement member  52   a  into fluid cavity  44   a  reduces the volume of fluid cavity  44   a  and causes process fluid to be expelled from fluid cavity  44   a  into outlet manifold  18 . Inlet check valve  22   a  prevents process fluid from being expelled into inlet manifold  16  during a pumping stoke. When cam follower  100  causes piston  54  to reverse direction, fluid displacement member  52   a  is pulled into a suction stroke by pull  56   a,  and fluid displacement member  52   b  is pushed into a pumping stroke by the charge pressure of the working fluid in internal pressure chamber  66 , thereby completing a pumping cycle. 
         [0032]    Pull chambers  72   a  and  72   b  prevent piston  54  from exerting a pushing force on either fluid displacement member  52   a  or  52   b.  If the pressure in the process fluid exceeds the pressure in the working fluid, the working fluid will not be able to push either fluid displacement member  52   a  or  52   b  into a pumping stroke. In that overpressure situation, such as when outlet manifold  18  is blocked, drive  38  will continue to drive piston  54 , but pulls  56   a  and  56   b  will remain in a suction stroke because the pressure of the working fluid is insufficient to cause either fluid displacement member  52   a  or  52   b  to enter a pumping stroke. When piston  54  is displaced towards fluid displacement member  52   a,  pull chamber  72   a  prevents pull  56   a  from exerting any pushing force on fluid displacement member  52   a  by housing pull  56   a  within pull chamber  72   a . Allowing piston  54  to continue to oscillate without pushing either fluid displacement member  52   a  or  52   b  into a pumping stroke allows pump  10  to continue to run when outlet manifold  18  is blocked without causing any harm to the motor or pump. 
         [0033]      FIG. 3A  is a cross-sectional view of pump  10 , drive system  14 , and cam follower  100  during normal operation.  FIG. 3B  is a cross-sectional view of pump  10 , drive system  14 , and cam follower  100  after outlet manifold  18  has been blocked, i.e. the pump  10  has been deadheaded.  FIG. 3A  and  FIG. 3B  will be discussed together. Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  outlet check valves  24   a  and  24   b,  and fluid displacement members  52   a  and  52   b.  Inlet check valve  22   a  includes seat  48   a  and check ball  50   a,  while inlet check valve  22   b  similarly includes seat  48   b  and check ball  50   b.  Outlet check valve  24   a  includes seat  49   a  and check ball  51   a,  and outlet check valve  24   b  includes seat  49   b  and check ball  51   b.  In the present embodiment, fluid displacement member  52   a  includes diaphragm  94   a,  first diaphragm plate  110   a,  second diaphragm plate  112   a , and attachment screw  92   a.  Similarly, fluid displacement member  52   b  includes diaphragm  94   b , first diaphragm plate  110   b,  second diaphragm plate  112   b,  and attachment screw  92   b.    
         [0034]    Drive system  14  includes housing  26 , piston guide  28 , piston  54 , pulls  56   a  and  56   b,  face plates  58   a  and  58   b,  annular structure  62 , and bushings  64   a  and  64   b.  Housing  26  includes guide opening  60  for receiving piston guide  28  therethrough, and housing  26  defines internal pressure chamber  66 . Piston guide  28  includes barrel nut  68  and guide pin  70 . Piston  54  includes pull chambers  72   a  and  72   b,  central slot  74  and axial slot  76 . Pull  56   a  includes attachment end  82   a,  free end  84   a  and pull shaft  86   a  extending between free end  84   a  and attachment end  82   a.  Free end  84   a  includes flange  85   a.  Similarly, pull  56   b  includes attachment end  82   b,  free end  84   b,  and pull shaft  86   b,  and free end  84   b  includes flange  85   b.  Face plate  58   a  includes pull opening  90   a  and face plate  58   b  includes opening  90   b.    
         [0035]    Fluid cover  20   a  is affixed to housing  26 , and fluid displacement member  52   a  is secured between fluid cover  20   a  and housing  26 . Fluid cover  20   a  and fluid displacement member  52   a  define fluid cavity  44   a.  Fluid displacement member  52   a  also sealingly separates fluid cavity  44   a  from internal pressure chamber  66 . Fluid cover  20   b  is affixed to housing  26  opposite fluid cover  20   a.  Fluid displacement member  52   b  is secured between fluid cover  20   b  and housing  26 . Fluid cover  20   b  and fluid displacement member  52   b  define fluid cavity  44   b , and fluid displacement member  52   b  sealingly separates fluid cavity  44   b  from internal pressure chamber  66 . 
         [0036]    Piston  54  rides on bushings  64   a  and  64   b.  Free end  84   a  of pull  56   a  is slidably secured within pull chamber  72   a  of piston  54  by flange  85   a  and face plate  58   a.  Flange  85   a  engages face plate  58   a  and prevents free end  84   a  from exiting pull chamber  72   a.  Pull shaft  86   a  extends through opening  90   a,  and attachment end  82   a  engages attachment screw  92   a.  In this way, attaches fluid displacement member  52   a  to piston  54 . Similarly, free end  84   b  of pull  56   b  is slidably secured within pull chamber  72   b  of piston  54  by flange  85   b  and face plate  58   b.  Pull shaft  86   b  extends through pull opening  90   b,  and attachment end  82   b  engages attachment screw  92   b.    
         [0037]    Cam follower  100  engages central slot  74  of piston  54 . Barrel nut  68  extends through guide opening  60  into internal pressure chamber  66 . Guide pin  70  is attached to the end of barrel nut  68  that projects into internal pressure chamber  66 , and guide pin  70  slidably engages axial slot  76 . 
         [0038]    Inlet manifold  16  is attached to both fluid cover  20   a  and fluid cover  20   b.  Inlet check valve  22   a  is disposed between inlet manifold  16  and fluid cover  20   a,  and inlet check valve  22   b  is disposed between inlet manifold  16  and fluid cover  20   b.  Seat  48   a  rests on inlet manifold  16  and check ball  50   a  is disposed between seat  48   a  and fluid cover  20   a.  Similarly, seat  48   b  rests on inlet manifold  16  and check ball  50   b  is disposed between seat  48   b  and fluid cover  20   b.  In this way, inlet check valves  22   a  and  22   b  are configured to allow process fluid to flow from inlet manifold  16  into either fluid cavity  44   a  and  44   b,  while preventing process fluid from backflowing into inlet manifold  16  from either fluid cavity  44   a  or  44   b.    
         [0039]    Outlet manifold  18  is also attached to both fluid cover  20   a  and fluid cover  20   b . Outlet check valve  24   a  is disposed between outlet manifold  18 , and fluid cover  20   a,  and outlet check valve  24   b  is disposed between outlet manifold  18  and fluid cover  20   b.  Seat  49   a  rests upon fluid cover  20   a  and check ball  51   a  is disposed between seat  49   a  and outlet manifold  18 . Similarly, seat  49   b  rests upon fluid cover  20   b  and check ball  51   b  is disposed between seat  49   b  and outlet manifold  18 . Outlet check valves  24   a  and  24   b  are configured to allow process fluid to flow from fluid cavity  44   a  or  44   b  into outlet manifold  18 , while preventing process fluid from backflowing into either fluid cavity  44   a  or  44   b  from outlet manifold  18 . 
         [0040]    Cam follower  100  reciprocates piston  54  along axis A-A. Piston guide  28  prevents piston  54  from rotating about axis A-A by having guide pin  70  slidably engaged with axial slot  76 . When piston  54  is drawn towards fluid cavity  44   b,  pull  56   a  is also pulled towards fluid cavity  44   b  due to flange  85   a  engaging face plate  58   a.  Pull  56   a  thereby causes fluid displacement member  52   a  to enter a suction stroke due to the attachment of attachment end  82   a  and attachment screw  92   a.  Pulling fluid displacement member  52   a  causes the volume of fluid cavity  44   a  to increase, which draws process fluid through check valve  22   a  and into fluid cavity  44   a  from inlet manifold  16 . Outlet check valve  24   a  prevents process fluid from being drawn into fluid cavity  44   a  from outlet manifold  18  during the suction stroke. 
         [0041]    At the same time that process fluid is being drawn into fluid cavity  44   a,  the working fluid causes fluid displacement member  52   b  to enter a pumping stroke. The working fluid is charged to a higher pressure than that of the process fluid, which allows the working fluid to displace the fluid displacement member  52   a  or  52   b  that is not being drawn into a suction stroke by piston  54 . Pushing fluid displacement member  52   b  into fluid cavity  44   b  reduces the volume of fluid cavity  44   b  and causes process fluid to be expelled from fluid cavity  44   b  through outlet check valve  24   b  and into outlet manifold  18 . Inlet check valve  22   b  prevents process fluid from being expelled into inlet manifold  16  during a pumping stoke. 
         [0042]    When cam follower  100  causes piston  54  to reverse direction and travel towards fluid cavity  44   a,  face plate  58   b  catches flange  85   b  on free end  84   b  of pull  56   b.  Pull  56   b  then pulls fluid displacement member  52   b  into a suction stroke causing process fluid to enter fluid cavity  44   b  through check valve  22   b  from inlet manifold  16 . At the same time, the working fluid now causes fluid displacement member  52   a  to enter a pumping stroke, thereby discharging process fluid from fluid cavity  44   a  through check valve  24   a  and into outlet manifold  18 . 
         [0043]    A constant downstream pressure is produced to eliminate pulsation by sequencing the speed of piston  54  with the pumping stroke caused by the working fluid. To eliminate pulsation, piston  54  is sequenced such that when it begins to pull one of fluid displacement member  52   a  or  52   b  into a suction stroke, the other fluid displacement member  52   a  or  52   b  has already completed its change-over and started a pumping stroke. Sequencing the suction and pumping strokes in this way prevents the drive system  14  from entering a state of rest. 
         [0044]    Referring specifically to  FIG. 3B , pull chamber  72   a  and pull chamber  72   b  of piston  54  allow pump  10  to be deadheaded without causing any damage to the pump  10  or motor  12 . When pump  10  is deadheaded, the process fluid pressure exceeds the working fluid pressure, which prevents the working fluid from pushing either fluid displacement member  52   a  or  52   b  into a pumping stroke. 
         [0045]    During over-pressurization fluid displacement member  52   a  and fluid displacement member  52   b  are retracted into a suction stroke by piston  54 ; however, because the working fluid pressure is insufficient to push the fluid displacement member  52   a  or  52   b  into a pumping stroke, the fluid displacement members  52   a  and  52   b  remain in the suction stroke position. Piston  54  is prevented from mechanically pushing either fluid displacement member  52   a  or  52   b  into a pumping stroke by pull chamber  72   a,  which houses pull  56   a  when the process fluid pressure exceeds the working fluid pressure and piston  54  is driven towards fluid displacement member  52   a,  and pull chamber  72   b,  which houses pull  56   b  when the process fluid pressure exceeds the working fluid pressure and piston  54  is driven towards fluid displacement member  52   b.  Housing pull  56   a  within pull chamber  72   a  and pull  56   b  within pull chamber  72   b  prevents piston  54  from exerting any pushing force on fluid displacement members  52   a  or  52   b , which allows outlet manifold  18  to be blocked without damaging pump  10 . 
         [0046]      FIG. 4  is a top cross-sectional view, along line  4 - 4  of  FIG. 1 , showing the connection of drive system  14  and drive  38 .  FIG. 4  also depicts fluid covers  20   a  and  20   b,  and fluid displacement members  52   a  and  52   b.  Drive system  14  includes housing  26 , piston  54 , pulls  56   a  and  56   b,  face plates  58   a  and  58   b,  and bushings  64   a  and  64   b.  Housing  26  and fluid displacement members  52   a  and  52   b  define internal pressure chamber  66 . Housing  26  includes drive chamber  32  and annular structure  62 . Piston  54  includes pull chambers  72   a  and  72   b  and central slot  74 . Pull  56   a  includes attachment end  82   a,  free end  84   a,  flange  85   a,  and pull shaft  86   a,  while pull  56   b  similarly includes attachment end  82   b,  free end  84   b,  flange  85   b,  and shaft  86   b.  Face plate  58   a  includes pull opening  90   a  and openings  88   a.  Similarly, face plate  58   b  includes pull opening  90   b  and openings  88   b.  In the present embodiment, drive  38  includes housing  96 , crank shaft  98 , cam follower  100 , bearing  102 , and bearing  104 . Crank shaft  98  includes drive shaft chamber  114  and cam follower chamber  116 . 
         [0047]    Fluid cover  20   a  is attached to housing  26  by fasteners  42 . Fluid displacement member  52   a  is secured between fluid cover  20   a  and housing  26 . Fluid cover  20   a  and fluid displacement member  52   a  define fluid cavity  44   a.  Similarly, fluid cover  20   b  is attached to housing  26  by fasteners  42 , and fluid displacement member  52   b  is secured between fluid cover  20   b  and housing  26 . Fluid cover  20   b  and fluid displacement member  52   b  define fluid cavity  44   b.  Housing  26  and fluid displacement members  52   a  and  52   b  define internal pressure chamber  66 . 
         [0048]    In the present embodiment, fluid displacement member  52   a  is shown as a diaphragm and includes diaphragm  94   a,  first diaphragm plate  110   a,  second diaphragm plate  112   a,  and attachment screw  92   a.  Similarly, fluid displacement member  52   b  is shown as a diaphragm and includes diaphragm  94   b,  first diaphragm plate  110   b,  second diaphragm plate  112   b,  and attachment screw  92   b.  While fluid displacement members  52   a  and  52   b  are shown as diaphragms, it is understood that fluid displacement members  52   a  and  52   b  could also be pistons. 
         [0049]    Piston  54  is mounted on bushings  64   a  and  64   b  within internal pressure chamber  66 . Free end  84   a  of pull  56   a  is slidably secured within pull chamber  72   a  by face plate  58   a  and flange  85   a.  Shaft  86   a  extends through opening  90   a,  and attachment end  82   a  engages attachment screw  92   a.  Face plate  58   a  is secured to piston  54  by face plate fasteners  80   a  extending through openings  88   a  and into piston  54 . Similarly, free end  84   b  of pull  56   b  is slidably secured within pull chamber  72   b  by face plate  58   b  and flange  85   b.  Pull shaft  86   b  extends through pull opening  90   b,  and attachment end  82   b  engages attachment screw  92   b.  Face plate  58   b  is attached to piston  54  by face plate fasteners  80   b  extending through openings  88   b  and into piston  54 . 
         [0050]    Drive  38  is mounted within drive chamber  32  of housing  26 . Crank shaft  98  is rotatably mounted within housing  96  by bearing  102  and bearing  104 . Crank shaft  98  is driven by a drive shaft (not shown) that connects to crank shaft  98  at drive shaft chamber  114 . Cam follower  100  is mounted to crank shaft  98  opposite the drive shaft, and cam follower  100  is mounted at cam follower chamber  116 . Cam follower  100  extends into internal pressure chamber  66  and engages central slot  74  of piston  54 . 
         [0051]    Drive  38  is driven by electric motor  12  (shown in  FIG. 1 ), which rotates crank shaft  98  on bearings  102  and  104 . Crank shaft  98  thereby rotates cam follower  100  about axis B-B, and cam follower  100  thus causes piston  54  to reciprocate along axis A-A. Because piston  54  has a predetermined lateral displacement, determined by the rotation of cam follower  100 , the speed of the piston  54  can be sequenced with the pressure of the working fluid to eliminate downstream pulsation. 
         [0052]    When cam follower  100  drives piston  54  towards fluid displacement member  52   b , piston  54  pulls fluid displacement member  52   a  into a suction stroke via pull  56   a.  Flange  85   a  of pull  56   a  engages face plate  58   a  such that piston  54  causes pull  56   a  to also move towards fluid displacement member  52   b,  which causes pull  56   a  to pull fluid displacement member  52   a  into a suction stroke. Pull  56   a  pulls fluid displacement member  52   a  into a suction stroke through attachment end  82   a  being engaged with attachment screw  92   a.  At the same time, the pressurized working fluid within internal pressure chamber  66  pushes fluid displacement member  52   b  into a pumping stroke. 
         [0053]      FIG. 5  is a cross-sectional view, along section  5 - 5  of  FIG. 1 , showing the connection of pump  10 , drive system  214 , and cam follower  100 . Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  outlet check valves  24   a  and  24   b,  and fluid displacement members  52   a  and  52   b.  Inlet check valve  22   a  includes seat  48   a  and check ball  50   a,  while inlet check valve  22   b  includes seat  48   b  and check ball  50   b.  Outlet check valve  24   a  includes seat  49   a  and check ball  51   a,  while outlet check valve  24   b  includes seat  49   b  and check ball  51   b.  In the present embodiment, fluid displacement member  52   a  includes diaphragm  94   a,  first diaphragm plate  110   a,  second diaphragm plate  112   a , and attachment member  216   a.  Similarly, fluid displacement member  52   b  includes diaphragm  94   b,  first diaphragm plate  110   b,  second diaphragm plate  112   b,  and attachment member  216   b . Drive system  214  includes housing  26 , hub  218 , flexible belts  220   a  and  220   b,  and pins  222   a  and  222   b.  Housing  26  defines internal pressure chamber  66 . 
         [0054]    Fluid cover  20   a  is affixed to housing  26 , and fluid displacement member  52   a  is secured between fluid cover  20   a  and housing  26 . Fluid cover  20   a  and fluid displacement member  52   a  define fluid cavity  44   a,  and fluid displacement member  52   a  sealingly separates fluid cavity  44   a  and internal pressure chamber  66 . Fluid cover  20   b  is affixed to housing  26 , and fluid displacement member  52   b  is secured between fluid cover  20   b  and housing  26 . Fluid cover  20   b  and fluid displacement member  52   b  define fluid cavity  44   b,  and fluid displacement member  52   b  sealingly separates fluid cavity  44   b  and internal pressure chamber  66 . Housing  26  includes openings  106  to allow working fluid to flow within internal pressure chamber  66 . 
         [0055]    Hub  218  is press-fit to cam follower  100 . Pin  222   a  projects from a periphery of hub  218  along axis B-B. Similarly, pin  222   b  projects from a periphery of hub  218  along axis B-B and opposite pin  222   a.  Flexible belt  220   a  is attached to pin  222   a  and to attachment member  216   a.  Flexible belt  220   b  is attached to pin  222   b  and to attachment member  216   b.    
         [0056]    Cam follower  100  drives hub  218  along axis A-A. When hub  218  is drawn towards fluid cavity  44   b,  flexible belt  220   a  is also pulled towards fluid cavity  44   b  causing fluid displacement member  52   a  to enter a suction stroke due to the attachment of flexible belt  220   a  to attachment member  216   a  and pin  222   a.  Pulling fluid displacement member  52   a  causes the volume of fluid cavity  44   a  to increase, which draws process fluid through check valve  22   a  and into fluid cavity  44   a  from inlet manifold  16 . Outlet check valve  24   a  prevents process fluid from being drawn into fluid cavity  44   a  from outlet manifold  18  during the suction stroke. 
         [0057]    At the same time that process fluid is being drawn into fluid cavity  44   a,  the working fluid causes fluid displacement member  52   b  to enter a pumping stroke. The working fluid is charged to a higher pressure than that of the process fluid, which allows the working fluid to displace the fluid displacement member  52   a  or  52   b  that is not being drawn into a suction stroke by hub  218 . Pushing fluid displacement member  52   b  into fluid cavity  44   b  reduces the volume of fluid cavity  44   b  and causes process fluid to be expelled from fluid cavity  44   b  through outlet check valve  24   b  and into outlet manifold  18 . Inlet check valve  22   b  prevents process fluid from being expelled into inlet manifold  16  during a pumping stoke. 
         [0058]    When cam follower  100  causes hub  218  to reverse direction and travel towards fluid cavity  44   a  pin  222   b  engages flexible belt  220   b,  and flexible belt  220   b  then pulls fluid displacement member  52   b  into a suction stroke causing process fluid to enter fluid cavity  44   b  from inlet manifold  16 . At the same time, the working fluid now causes fluid displacement member  52   a  to enter a pumping stroke, thereby discharging process fluid from fluid cavity  44   a  through check valve  24   a  and into outlet manifold  18 . 
         [0059]    Flexible belts  220   a  and  220   b  allow outlet manifold  18  of pump  10  to be blocked during the operation of pump  10  without risking damage to pump  10 , drive system  214 , or electric motor  12  (shown in  FIG. 1 ). When outlet manifold  18  is blocked, the pressure in fluid cavity  44   a  and fluid cavity  44   b  equals the pressure of the working fluid in internal pressure chamber  66 . When such an over-pressure situation occurs, hub  218  will draw both fluid displacement member  52   a  and fluid displacement member  52   b  into a suction stroke. However, drive system  214  cannot push either fluid displacement member  52   a  or  52   b  into a pumping stroke because flexible belts  220   a  and  220   b  are not sufficiently rigid to impart a pushing force on either fluid displacement member  52   a  or  52   b.    
         [0060]      FIG. 6  is a cross-sectional view, along section  6 - 6  of  FIG. 1 , showing the connection of pump  10  and drive system  314 . Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  outlet check valves  24   a  and  24   b,  and fluid displacement members  52   a  and  52   b.  Inlet check valve  22   a  includes seat  48   a  and check ball  50   a,  while inlet check valve  22   b  includes seat  48   b  and check ball  50   b.  Outlet check valve  24   a  includes seat  49   a  and check ball  51   a,  while outlet check valve  24   b  includes seat  49   b  and check ball  51   b . In the present embodiment, fluid displacement member  52   a  includes diaphragm  94   a,  first diaphragm plate  110   a,  and second diaphragm plate  112   a,  and attachment screw  92   a.  Similarly, fluid displacement member  52   b  includes diaphragm  94   b,  first diaphragm plate  110   b,  and second diaphragm plate  112   b,  and attachment screw  92   b.    
         [0061]    Drive system  314  includes housing  26 , second housing  316 , piston  318 , and pulls  320   a  and  320   b.  Piston  318  includes reciprocating member  322  and pull housings  324   a  and  324   b . Pull housing  324   a  defines pull chamber  326   a  and includes pull opening  328   a.  Pull housing  324   b  defines pull chamber  326   b  and includes pull opening  328   b.  Pull  320   a  includes attachment end  330   a,  free end  332   a  and pull shaft  334   a  extending between free end  332   a  and attachment end  330   a.  Free end  332   a  includes flange  336   a.  Similarly, pull  320   b  includes attachment end  330   b , free end  332   b,  and pull shaft  334   b  extending between free end  332   b  and attachment end  330   b , and free end  332   b  includes flange  336   b.  Second housing  316  includes pressure chamber  338   a  and pressure chamber  338   b,  aperture  340   a,  aperture  340   b,  first o-ring  342 , second o-ring  344 , and third o-ring  346 . 
         [0062]    Fluid cover  20   a  is affixed to housing  26 , and fluid displacement member  52   a  is secured between fluid cover  20   a  and housing  26 . Fluid cover  20   a  and fluid displacement member  52   a  define fluid cavity  44   a,  and fluid displacement member  52   a  sealingly separates fluid cavity  44   a  and internal pressure chamber  66 . Fluid cover  20   b  is affixed to housing  26 , and fluid displacement member  52   b  is secured between fluid cover  20   b  and housing  26 . Fluid cover  20   b  and fluid displacement member  52   b  define fluid cavity  44   b,  and fluid displacement member  52   b  sealingly separates fluid cavity  44   b  and internal pressure chamber  66 . 
         [0063]    Second housing  316  is disposed within housing  26 . Piston  318  is disposed within second housing  316 . First o-ring  342  is disposed around reciprocating member  322 , and first o-ring  342  and reciprocating member  322  sealingly separate pressure chamber  338   a  and pressure chamber  338   b.  Pull housing  324   a  extends from reciprocating member  322  through aperture  340   a  and into internal pressure chamber  66 . Pull housing  324   b  extends from reciprocating member  322  through aperture  340   b  and into internal pressure chamber  66 . Second o-ring  344  is disposed around pull housing  324   a  at aperture  340   a.  Second o-ring  344  sealingly separates pressure chamber  338   a  from internal pressure chamber  66 . Third o-ring  346  is disposed around pull housing  324   b  at aperture  340   b.  Third o-ring  346  sealingly separates pressure chamber  338   b  from internal pressure chamber  66 . 
         [0064]    Free end  332   a  of pull  320   a  is slidably secured within pull chamber  326   a  by flange  336   a.  Pull shaft  334   a  extends through pull opening  328   a,  and attachment end  330   a  engages attachment screw  92   a.  Similarly, free end  332   b  of pull  320   b  is slidably secured within pull chamber  326   b  by flange  336   b.  Pull shaft  334   b  extends through pull opening  328   b,  and attachment end  330   b  engages attachment screw  92   b.    
         [0065]    Piston  318  is reciprocatingly driven within second housing  316  by alternatingly providing pressurized fluid to pressure chamber  338   a  and pressure chamber  338   b.  The pressurized fluid can be compressed air, non-compressible hydraulic fluid, or any other fluid suitable for driving piston  318 . First o-ring  342  sealingly separates pressure chamber  338   a  and pressure chamber  338   b,  which allows the pressurized fluid to reciprocatingly drive piston  318 . 
         [0066]    When pressurized fluid is provided to pressure chamber  338   a,  second o-ring  344  sealingly separates the pressurized fluid from the working fluid disposed within internal pressure chamber  66 . Similarly, when pressurized fluid is provided to pressure chamber  338   b,  third o-ring  346  sealingly separates the pressurized fluid from the working fluid disposed within internal pressure chamber  66 . 
         [0067]    When pressure chamber  338   a  is pressurized, piston  318  is driven towards fluid displacement member  52   b.  Pull  320   a  is thereby also drawn towards fluid displacement member  52   b  due to flange  336   a  engaging pull housing  324   a.  Pull  320   a  causes fluid displacement member  52   a  to enter into a suction stroke due to the connection between attachment end  330   a  and attachment screw  92   a.  At the same time, the working fluid in internal pressure chamber  66  pushes fluid displacement member  52   b  into a pumping stroke. During this stroke, pull chamber  326   b  prevents piston  318  from pushing fluid displacement member  52   b  into a pumping stroke. 
         [0068]    The stroke is reversed when pressure chamber  338   b  is pressurized, thereby driving piston  318  towards fluid displacement member  52   a.  In this stroke, pull  320   b  is drawn towards fluid displacement member  52   a  due to flange  336   b  engaging pull housing  324   b.  Pull  320   b  causes fluid displacement member  52   b  to enter into a suction stroke due to the connection between attachment end  330   b  and attachment screw  92   b.  While fluid displacement member  52   b  is drawn into a suction stroke, the working fluid in internal pressure chamber  66  pushes fluid displacement member  52   a  into a pumping stroke. Similar to pull chamber  326   b,  pull chamber  326   a  prevents piston  318  from pushing fluid displacement member  52   a  into a pumping stroke. 
         [0069]      FIG. 7  is a cross-sectional view, along section  7 - 7  of  FIG. 1 , showing the connection of pump  10  and drive system  414 . Pump  10  includes inlet manifold  16 , outlet manifold  18 , fluid covers  20   a  and  20   b,  inlet check valves  22   a  and  22   b,  outlet check valves  24   a  and  24   b,  and fluid displacement members  52   a  and  52   b.  Inlet check valve  22   a  includes seat  48   a  and check ball  50   a,  while inlet check valve  22   b  includes seat  48   b  and check ball  50   b.  Outlet check valve  24   a  includes seat  49   a  and check ball  51   a,  while outlet check valve  24   b  includes seat  49   b  and check ball  5  lb. In the present embodiment, fluid displacement member  52   a  includes diaphragm  94   a,  first diaphragm plate  110   a,  and second diaphragm plate  112   a,  and attachment screw  92   a.  Similarly, fluid displacement member  52   b  includes diaphragm  94   b,  first diaphragm plate  110   b,  and second diaphragm plate  112   b,  and attachment screw  92   b.    
         [0070]    Drive system  414  includes housing  26 , second housing  416 , reciprocating member  418 , solenoid  420 , and pulls  422   a  and  422   b.  Reciprocating member  418  includes armature  424  and pull housings  426   a  and  426   b.  Pull housing  426   a  defines pull chamber  428   a  and includes pull opening  430   a.  Pull housing  426   b  defines pull chamber  428   b  and includes pull opening  430   b.  Pull  422   a  includes attachment end  434   a,  free end  436   a,  and pull shaft  438   a  extending between attachment end  434   a  and free end  436   a.  Free end  436   a  includes flange  440   a . Similarly, pull  422   b  includes attachment end  434   b,  free end  436   b,  and pull shaft  438   b  extending between attachment end  434   b  and free end  436   b.  Free end  436   b  includes flange  440   b.    
         [0071]    Fluid cover  20   a  is affixed to housing  26 , and fluid displacement member  52   a  is secured between fluid cover  20   a  and housing  26 . Fluid cover  20   a  and fluid displacement member  52   a  define fluid cavity  44   a,  and fluid displacement member  52   a  sealingly separates fluid cavity  44   a  and internal pressure chamber  66 . Fluid cover  20   b  is affixed to housing  26 , and fluid displacement member  52   b  is secured between fluid cover  20   b  and housing  26 . Fluid cover  20   b  and fluid displacement member  52   b  define fluid cavity  44   b,  and fluid displacement member  52   b  sealingly separates fluid cavity  44   b  and internal pressure chamber  66 . 
         [0072]    Reciprocating member  418  is disposed within solenoid  420 . Pull housing  426   a  is integrally attached to a first end armature  424 , and pull housing  426   b  is integrally attached to a second end of armature  424  opposite pull housing  426   a.  Free end  436   a  of pull  422   a  is slidably secured within pull chamber  428   a  by flange  440   a.  Pull shaft  438   a  extends through pull opening  430   a,  and attachment end  434   a  engages attachment screw  92   a.  Similarly, free end  436   b  of pull  422   b  is slidably secured within pull chamber  428   b  by flange  440   b.  Pull shaft  438   b  extends through pull opening  430   b,  and attachment end  434   b  engages attachment screw  92   b.    
         [0073]    Solenoid  420  reciprocatingly drives armature  424 , which thereby reciprocatingly drives pull housing  426   a  and pull housing  426   b.    
         [0074]    The strokes are reversed by solenoid  420  driving armature  424  in an opposite direction from the initial stroke. In this stroke, pull housing  426   b  engages flange  440   b  of pull  422   b,  and pull  422   b  thereby draws fluid displacement member  52   b  into a suction stroke. At the same time, the working fluid in internal pressure chamber  66  pushes fluid displacement member  52   a  into a pumping stroke. During the pumping stroke of fluid displacement member  52   a,  pull chamber  428   a  prevents pull  422   a  from exerting any pushing force on fluid displacement member  52   a.    
         [0075]    The pump  10  and drive system  14  described herein provide several advantages. Drive system  14  eliminates the need for downstream dampeners or surge suppressors because the drive system  14  provides a pulseless flow of process fluid when piston  54  is sequenced. Downstream pulsation is eliminated because when one fluid displacement member  52   a  or  52   b  is changing over from one stroke, the other fluid displacement member  52   a  or  52   b  is already displacing process fluid. This eliminates any rest within the pump  10 , which eliminates pulsation because fluid is being constantly discharged, at a constant rate. So long as the working fluid pressure remains slightly greater than the process fluid pressure, the drive system  14  is self-regulating and provides a constant downstream flow rate. 
         [0076]    The working fluid pressure determines the maximum process fluid pressures that occur when the downstream flow is blocked or deadheaded. If outlet manifold  18  is blocked, motor  12  can continue to run without damaging motor  12 , drive system  14 , or pump  10 . Pull chambers  72   a  and  72   b  ensure that the drive system  14  will not cause over pressurization, by preventing piston  54  from exerting any pushing force on either fluid displacement member  52   a  or  52   b.  This also eliminates the need for downstream pressure relief valves, because the pump  10  is self-regulating and will not cause an over-pressurization event to occur. This pressure control feature serves as a safety feature and eliminates the possibility of over-pressurization of process fluids, potential pump damage, and excessive motor loads. 
         [0077]    When drive system  14  is used with diaphragm pumps, the drive system  14  provides for equalized balanced forces on the diaphragms, from both the working fluid and the process fluid, which allows for longer diaphragm life and use with higher pressure applications over mechanically-driven diaphragm pumps. Pump  10  also provides better metering and dosing capabilities due to the constant pressure on and shape of fluid displacement members  52   a  and  52   b.    
         [0078]    When compressed air is used as the working fluid, drive system  14  eliminates the possibility of exhaust icing, as can be found in air-driven pumps, because the compressed air in drive system  14  is not exhausted after each stroke. Other exhaust problems are also eliminated, such as safety hazards that arise from exhaust becoming contaminated with process fluids. Additionally, higher energy efficiency can be achieved with drive system  14  because the internal pressure chamber  66  eliminates the need to provide a fresh dose of compressed air during each stroke, as is found in typical air operated pumps. When a non-compressible hydraulic fluid is used as the working fluid drive system  14  eliminates the need for complex hydraulic circuits with multiple compartments, as can be found in typical hydraulically driven pumps. Additionally, drive system  14  eliminates the contamination risk between the process fluid and the working fluid due to the balanced forces on either side of fluid displacement members  52   a  and  52   b.    
         [0079]    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.