Patent Publication Number: US-11022106-B2

Title: High-pressure positive displacement plunger pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to U.S. Provisional Application No. 62/615,115 filed on Jan. 9, 2018, and entitled “HIGH PRESSURE POSITIVE DISPLACEMENT PLUNGER PUMP,” the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     This disclosure relates to positive displacement pumps and more particularly to an internal drive system and displacement mechanism for positive displacement pumps. 
     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. 
     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 supplied to one of two diaphragm chambers, associated with the respective diaphragms. When compressed air is supplied 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. The compressed air that had previously driven the second diaphragm is typically exhausted to the atmosphere. 
     The delivery of compressed air is controlled by an air valve, and the air valve is usually mechanically actuated 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. 
     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. 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 hydraulic fluid is typically exhausted back to the hydraulic circuit as the fluid displacement members are pulled through the suction stroke. The use of hydraulic fluid and pistons enables the pump to operate at higher pressures than those achievable by an air driven diaphragm pump. 
     Alternatively, double diaphragm 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 
     According to one aspect of the present disclosure, a pump for pumping a process fluid includes a housing defining an internal pressure chamber, the internal pressure chamber configured to contain a working fluid; a reciprocating member disposed within the internal pressure chamber; a fluid displacement component having a first surface and a second surface, the first surface configured to contact the working fluid and the second surface configured to contact the process fluid, wherein the fluid displacement component is configured such that pressure exerted on the first surface by the working fluid moves the second surface in a first direction towards the process fluid to expel the process fluid downstream, and wherein the area of the first surface is greater than the area of the second surface; and a pull extending between the reciprocating member and the fluid displacement component, the pull mechanically transferring a pulling force from the reciprocating member to the fluid displacement component to move the fluid displacement component in a second direction that is the opposite of the first direction, wherein the pull does not mechanically transfer a pushing force from the reciprocating member to the fluid displacement component when the reciprocating member moves in the first direction. 
     According to another aspect of the present disclosure, a pump for pumping a process fluid includes a housing defining an internal pressure chamber, the internal pressure chamber configured to contain a working fluid; a reciprocating member; a fluid displacement component having a first surface and a second surface, the first surface configured to contact the working fluid and the second surface configured to contact the process fluid, wherein the fluid displacement component is configured such that pressure exerted on the first surface by the working fluid moves the second surface in a first direction to expel the process fluid, and wherein the area of the first surface is greater than the area of the second surface; and a pull that links the reciprocating member to the fluid displacement component, the pull mechanically transferring a pulling force from the reciprocating member to the fluid displacement component to move the fluid displacement component in a second direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a rear perspective view of a pump, drive system, and motor. 
         FIG. 2A  is an exploded perspective view of the pump, drive system, and drive of  FIG. 1 . 
         FIG. 2B  is a cross-sectional view, taken along line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a second pump. 
         FIG. 4  is a cross-sectional view of a third pump. 
         FIG. 5  is a cross-sectional view of a piston and pulls. 
         FIG. 6  is a cross-sectional view taken along line  2 - 2  in  FIG. 1 . 
         FIG. 7  is a cross-sectional view of a fourth pump. 
         FIG. 8  is a cross-sectional view of a fifth pump. 
     
    
    
     DETAILED DESCRIPTION 
       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 ,  20   b ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; and outlet check valves  26   a ,  26   b . Drive system  14  includes housing  28  and piston guide  30 . Housing  28  includes working fluid inlet  32 . Electric drive  12  includes motor  34 , gear reduction  36 , and drive  38 . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d.    
     Housing  28  defines an internal drive chamber that at least partially accommodates drive  38  of electric drive  12 . Fluid covers  20   a  and  20   b  are attached to housing  28  by fasteners  40   a . End covers  22   a ,  22   b  are attached, respectively, to fluid covers  20   a ,  20   b  by fasteners  40   b  extending through end covers  22   a ,  22   b  into fluid covers  20   a ,  20   b . Fasteners  40   a  and fasteners  40   b  can be any desired fastener suitable for connecting various components together for operation. For example, fasteners  40   a  and fasteners  40   b  can each be threaded bolts, but it is understood that any other desired type of fastener can be utilized. Elbows  19   a ,  19   b  provide a flowpath between outlet manifold  18  and end covers  22   a ,  22   b , respectively. Elbows  19   c ,  19   d , respectively, provide flowpaths between inlet manifold  16  and end covers  22   a ,  22   b . While outlet manifold  18  is described as including elbows  19   a ,  19   b  and inlet manifold  16  is described as including elbows  19   c ,  19   d , it is understood that outlet manifold  18  and inlet manifold  16  can include any suitable structure for providing flowpaths into and out of end covers  22   a ,  22   b . It is further understood, that elbows  19   a ,  19   b  and elbows  19   c ,  19   d  can be separate from or integrated into outlet manifold  18  and inlet manifold  16 , respectively. 
     Inlet check valves  24   a ,  24   b  (shown in  FIG. 2 ) are disposed between inlet manifold  16  and end covers  22   a ,  22   b , respectively. Outlet check valves  26   a ,  26   b  are disposed between outlet manifold  18  and end covers  22   a ,  22   b , respectively. Inlet check valves  24   a ,  24   b , and outlet check valves  26   a ,  26   b  are oriented to manage the flow of process fluid from inlet manifold  16  to outlet manifold  18 . Inlet check valves  24   a ,  24   b , and outlet check valves  26   a ,  26   b  prevent retrograde flow of process fluid from outlet manifold  18  to inlet manifold  16 . 
     Motor  34  is attached to and drives gear reduction drive  38 . Gear reduction drive  38  includes internal gearing (not shown) configured to reduce the output speed of motor  34  to a desired driving speed for drive  38 . Gear reduction drive  38  powers drive  38  to cause the pumping of pump  10 . Drive  38  is secured to housing  28  and extends at least partially into a drive chamber defined by housing  28 . 
     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  may further include an accumulator (not shown) 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 of the two flowpaths through end covers  22   a ,  22   b . The working fluid in housing  26  causes a fluid displacement member internal to pump  10  to discharge the process fluid from either flowpath though end covers  22   a ,  22   b  to outlet manifold  18 . Inlet check valves  24   a ,  24   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  26   a ,  26   b  prevent the process fluid from backflowing into either flowpath from outlet manifold  18  as the process fluid is drawn into the flowpaths from inlet manifold  16 . 
       FIG. 2A  is an exploded, perspective view of pump  10 .  FIG. 2B  is a cross-sectional view of pump  10  taken along line  2 - 2  in  FIG. 1 .  FIGS. 2A and 2B  will be discussed together. Pump  10  includes inlet manifold  16 ; outlet manifold  18 ; fluid covers  20   a ,  20   b ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; bushings  42   a ,  42   b ; fluid displacement components  44   a ,  44   b ; outer cylinders  46   a ,  46   b ; collars  48   a ,  48   b ; and sealing rings  50   a ,  50   b . Drive system  14  includes housing  28 ; piston guide  30 ; piston  52 ; pulls  54   a ,  54   b ; and face plates  56   a ,  56   b . Housing  28  includes working fluid inlet  32  and guide opening  58 . Housing  28  defines internal pressure chamber  60 . Piston guide  30  includes barrel nut  62  and guide pin  64 . Piston  52  includes pull chambers  66   a ,  66   b ; central slot  68 ; and axial slot  70 . Fluid covers  20   a ,  20   b  include, respectively, ports  72   a ,  72   b . Fluid displacement components  44   a ,  44   b  include, respectively, diaphragms  74   a ,  74   b ; inner plates  76   a ,  76   b ; outer plates  78   a ,  78   b ; plungers  80   a ,  80   b ; attachment members  82   a ,  82   b . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d . Drive  38  of electric drive  12  ( FIG. 1 ) is shown. As shown in  FIG. 2B , drive  38  includes drive shaft  84  and cam follower  86 . 
     A left-right directional convention is indicated on  FIG. 2B . “Inner” as used herein refers to being closer to the axis of drive shaft  84  and/or cam follower  86  while “outer” as used herein refers to being further away from the axis of drive shaft  84  and/or the follower  86  along pump axis A-A in either the left or right direction. 
     Housing  28  is disposed between fluid cover  20   a  and fluid cover  20   b . Outer cylinder  46   a  extends between and is retained between fluid cover  20   a  and end cover  22   a . Outer cylinder  46   b  extends between and is retained between fluid cover  20   b  and end cover  22   b . Inlet manifold  16  is configured to provide process fluid to pumping chambers  90   a ,  90   b  ( FIG. 2B ) within end covers  22   a ,  22   b . Elbow  19   c  extends to end cover  22   a , and elbow  19   d  extends to end cover  22   b . Inlet check valve  24   a  is disposed between end cover  22   a  and elbow  19   c . Inlet check valve  24   b  is disposed between end cover  22   b  and elbow  19   d . Inlet check valves  24   a ,  24   b  allow the process fluid to flow into end covers  22   a ,  22   b , while preventing the process fluid from backflowing out of end covers  22   a ,  22   b  to inlet manifold  16 . While inlet check valves  24   a ,  24   b  are shown as ball and seat-type check valves, it is understood that any suitable valve for preventing backflow of the process fluid can be utilized. 
     Outlet manifold  18  is configured to receive process fluid from pumping chambers  90   a ,  90   b . Elbow  19   a  extends from end cover  22   a , and elbow  19   b  extends from end cover  22   b . Outlet check valve  26   a  is disposed between end cover  22   a  and elbow  19   a . Outlet check valve  26   b  is disposed between end cover  22   b  and elbow  19   b . Outlet check valves  26   a ,  26   b  allow the process fluid to flow out of end covers  22   a ,  22   b , while preventing the process fluid from backflowing into end covers  22   a ,  22   b  from outlet manifold  18 . While outlet check valves  26   a ,  26   b  are shown as ball and seat-type check valves, it is understood that any suitable valve for preventing backflow of the process fluid can be utilized. 
     Piston  52  is disposed within housing  28  and is configured to be driven in a reciprocating manner along pump axis A-A by drive  38 . Drive shaft  84  is powered by electric drive  12  ( FIG. 1 ). Cam follower  86  extends from drive shaft  84  into central slot  68  of piston  52  to drive the reciprocation of piston  52 . Cam follower  86  engages the walls defining central slot  68  of piston  52 . Bushings  42   a ,  42   b  are disposed within and supported by housing  28 . Piston  52  is disposed within, and rides on, bushings  42   a ,  42   b , which restrict piston  52  to lateral (left and right) motion. As shown, cam follower  86  is offset from the axial center of the drive shaft  84  such that cam follower  86  orbits the axis of drive shaft  84 , instead of merely rotating about its own axis. Due to cam follower  86  being located within vertically orientated central slot  68  of piston  52 , cam follower  86  does not push piston  52  up or down. Instead, cam follower  86  forces piston  52  to reciprocate laterally left and right along pump axis A-A. While pump  10  is described as including piston  52 , it is understood that any desired type of reciprocating member can be utilized, which may include, but is not limited to, a scotch yoke or other reciprocating drive. 
     Piston guide  30  extends through housing  28  and is configured to prevent piston  52  from rotating about piston axis A-A. Barrel nut  62  extends through guide opening  58 , and guide pin  64  is connected to barrel nut  62 . As shown, guide pin  64  rides within axial slot  70  of piston  52  to prevent piston  52  from rotating about piston axis A-A. Piston guide  28  thereby ensures that the motion of piston  52  is limited to reciprocation along piston axis A-A. 
     Piston  52  includes pull chamber  66   a  disposed within a first end of piston  52  and pull chamber  66   b  disposed within a second, opposite end of piston  52 . Face plates  56   a ,  56   b  are disposed at opposite ends of piston  52  and cap pull chambers  66   a ,  66   b . Face plates  56   a ,  56   b  are configured to retain pulls  54   a ,  54   b , within pull chambers  66   a ,  66   b  of piston  52 . Face plates  56   a ,  56   b  include fastener openings to facilitate connection with piston  52 . Any desired fastener, such as a bolt, can extend through the fastener openings into piston  52  to secure face plates  56   a ,  56   b  to piston  52 . Pulls  54   a ,  54   b  extend out of pull chambers  66   a ,  66   b  through the openings in face plates  56   a ,  56   b.    
     Pump  10  includes fluid displacement components  44   a ,  44   b . In the present embodiment, fluid displacement components  44   a ,  44   b  are shown to include diaphragms  74   a ,  74   b , respectively. It is understood, however, that fluid displacement components  44   a ,  44   b  can omit diaphragms or other illustrated components. Fluid displacement components  44   a ,  44   b  can be or contain pistons or any other suitable component for displacing process fluid. Additionally, while pump  10  is described as a double displacement pump, utilizing dual fluid displacement components  44   a ,  44   b , it is understood that a single fluid displacement component may be used in a pump (e.g., with only one diaphragm or piston). As such, various examples of pump  10  can be single-displacement or double-displacement pumps. 
     Fluid covers  20   a ,  20   b  are secured to opposite ends of housing  28  by fasteners  40   a  extending through fluid covers  20   a ,  20   b  into housing  28 . Ports  72   a ,  72   b  extend through fluid covers and fluidly connect outer chambers  88   a ,  88   b , which are defined by diaphragms  74   a ,  74   b  and fluid covers  20   a ,  20   b , with the atmosphere. Diaphragm  74   a  is secured between housing  28  and fluid cover  20   a  to define and seal, in part, internal pressure chamber  60 . Similarly, diaphragm  74   b  is secured between housing  28  and end cover fluid cover  20   b  to define and seal, in part, internal pressure chamber  60 . Diaphragms  74   a ,  74   b  are configured to flex and spring back to a nominal shape. For example, diaphragms  74   a ,  74   b  can be elastic disks. Diaphragms  74   a ,  74   b  are sandwiched between inner plates  76   a ,  76   b  and outer plates  78   a ,  78   b . Inner plates  76   a ,  76   b  are disposed on a side of diaphragms  74   a ,  74   b  facing internal pressure chamber  60 . Outer plates  78   a ,  78   b  are disposed on a side of diaphragms  74   a ,  74   b  facing outer chambers  88   a ,  88   b.    
     Diaphragm  74   a  defines, in part, two chambers: internal pressure chamber  60  and outer chamber  88   a . Diaphragm  74   b  also defines, in part, two chambers: internal pressure chamber  60   a  and outer chamber  88   b . Internal pressure chamber  60  is defined by housing  28  and diaphragms  74   a ,  74   b . Outer chambers  88   a ,  88   b  are further defined in part by fluid covers  20   a ,  20   b . The volume of outer chambers  88   a ,  88   b  changes inversely with a change in the volume of internal pressure chamber  60  due to the movement of the diaphragms  74   a ,  74   b . For example, when diaphragm  74   a  is pushed rightward the volume in outer chamber  88   a  becomes smaller. Such change in volume in outer chamber  88   a  could increase the pressure within the outer chamber  88   a , thereby increasing a countervailing force pushing diaphragm  74   a  leftward against the force generated by the fluid charge in internal pressure chamber  60 . Likewise, leftward movement of diaphragm  74   a  could create a suction or vacuum condition in outer chamber  88   a . However, ports  72   a ,  72   b  provide vent paths for outer chambers  88   a ,  88   b  to prevent overpressure or vacuum conditions from developing in outer chambers  88   a ,  88   b  during pumping, which conditions can cause inefficient pumping. 
     In some examples, outer chambers  88   a ,  88   b  can be sealed to prevent fluid from escaping outer chambers  88   a ,  88   b . In such an example, outer chambers  88   a ,  88   b  can be charged with a fluid (gas or liquid), the presence of which may prevent process fluid or working fluid from escaping into and through the outer chambers  88   a ,  88   b . The charge fluid in outer chambers  88   a ,  88   b  can thereby prevents contamination of the process fluid or working fluid in the event of seal failure. 
     Plungers  80   a ,  80   b  extend from outer plates  78   a ,  78   b , through outer cylinders  46   a ,  46   b , and into pumping chambers  90   a ,  90   b . Diaphragms  74   a ,  74   b  are attached to plungers  80   a ,  80   b  by attachment members  82   a ,  82   b . Attachment members  82   a ,  82   b  can connect diaphragms  74   a ,  74   b  and plungers  80   a ,  80   b  in any desired manner. For example, attachment members  82   a ,  82   b  can threadedly engage the central holes in plungers  80   a ,  80   b  and pulls  54   a ,  54   b , sandwiching and securing inner plates  76   a ,  76   b ; the central portions of diaphragms  74   a ,  74   b ; and outer plates  78   a ,  78   b  therebetween. As such, pull  54   a , attachment member  82   a , diaphragm  74   a , inner plate  76   a , outer plate  78   a , and plunger  80   a  are attached as an assembly and move together. Similarly, pull  54   b , attachment member  82   b , diaphragm  74   b , inner plate  76   b , outer plate  78   b , and plunger  80   b  are attached as an assembly and move together. While attachment members  82   a ,  82   b  are used to connect the central portions of diaphragms  74   a ,  74   b  with plungers  80   a ,  80   b , it is understood that plungers  80   a ,  80   b  can be connected to diaphragms  74   a ,  74   b  in any desired manner. For example, outer plates  78   a ,  78   b  can be partially or wholly embedded in the material that forms diaphragms  74   a ,  74   b , and plungers  80   a ,  80   b  can be connected (e.g., adhered, welded, bolted, or threadedly attached) to outer plates  78   a ,  78   b . In another example, plungers  80   a ,  80   b  are at least partially embedded in the material that forms diaphragms  74   a ,  74   b , thereby omitting outer plates  78   a ,  78   b . In another example, plungers  80   a ,  80   b  and outer plates  78   a ,  78   b  are integrally formed as a single part. 
     Fasteners  40   b  extend through end covers  22   a ,  22   b  and into fluid covers  20   a ,  20   b , clamping outer cylinders  46   a ,  46   b  therebetween. Plungers  80   a ,  80   b  extend into pumping chambers  90   a ,  90   b  through outer cylinders  46   a ,  46   b . Pumping chambers  90   a ,  90   b  are formed between end covers  22   a ,  22   b  and plungers  80   a ,  80   b . Plungers  80   a ,  80   b  are configured to slide within outer cylinders  46   a ,  46   b  and into and out of pumping chambers  90   a ,  90   b . The diameter of the outer circumference of plungers  80   a ,  80   b  is slightly less than the diameter of the inner circumference of outer cylinders  46   a ,  46   b . As such, the outer circumferential surface of plungers  80   a ,  80   b  interfaces with the inner circumferential surface of outer cylinders  46   a ,  46   b . These surfaces can be dimensioned to move relative to each other but also seal between themselves. Likewise, the inner surfaces of the inside entrances to end covers  22   a ,  22   b  are cylindrical and interface with the outer circumferential surface of plungers  80   a ,  80   b  to limit or prevent leakage of process fluid past the interface of plungers  80   a ,  80   b  and end covers  22   a ,  22   b.    
     Collars  48   a ,  48   b  are disposed adjacent the inner sides of end covers  22   a ,  22   b . Collars  48   a ,  48   b  receive an outer end of outer cylinders  46   a ,  46   b . Sealing rings  50   a ,  50   b  are disposed between collars  48   a ,  48   b  and end covers  22   a ,  22   b . Sealing rings  50   a ,  50   b  extend around and interface with an outer edge of plungers  80   a ,  80   b . Sealing rings  50   a ,  50   b  seal circumferentially about plungers  80   a ,  80   b  to prevent process fluid within pumping chambers  90   a ,  90   b  from escaping along the periphery of the plungers  80   a ,  80   b . Likewise, sealing rings  50   a ,  50   b  can prevent working fluid that has escaped from internal pressure chamber  60  (or from another source) from entering pumping chambers  90   a ,  90   b  and contaminating the process fluid. While pump  10  is described as including outer cylinders  46   a ,  46   b  and collars  48   a ,  48   b , it is understood that end covers  22   a ,  22   b  can directly abut fluid covers  20   a ,  20   b . In such an example, sealing rings  50   a ,  50   b  can be retained between fluid covers  20   a ,  20   b  and end covers  22   a ,  22   b.    
     Internal pressure chamber  60  is configured to be charged with a working fluid during operation of pump  10 . The working fluid is either a gas, such as compressed air, or a non-compressible hydraulic fluid. The output pressure from pump  10  is set by charging the working fluid in internal pressure chamber  60  to a desired operational pressure. The working fluid is configured to drive each fluid displacement component  44   a ,  44   b  through a pumping stroke, where plungers  80   a ,  80   b  are driven into pumping chambers  90   a ,  90   b  to reduce the volume of pumping chambers  90   a ,  90   b  and drive the process fluid downstream out of pumping chambers  90   a ,  90   b  to outlet manifold  18 . Piston  52  is configured to draw each fluid displacement component  44   a ,  44   b  through a suction stroke, where plungers  80   a ,  80   b  are pulled out of pumping chambers  90   a ,  90   b  to increase the volume of pumping chambers  90   a ,  90   b  and draw the process fluid upstream into pumping chambers  90   a ,  90   b  from inlet manifold  16 . 
     During operation, drive shaft  84  rotates about its axis and causes orbital movement of cam follower  86  about driveshaft axis D-D (shown in  FIG. 1 ). Cam follower  86  drives the oscillation of piston  52  along piston axis A-A. Pulls  54   a ,  54   b  facilitate mechanical pulling of fluid displacement components  44   a ,  44   b  during suction strokes, but not pushing on fluid displacement components  44   a ,  44   b  during pumping strokes. Pulls  54   a ,  54   b  and piston  52  are configured such that pulls  54   a ,  54   b  are unable to exert sufficient pressure on fluid displacement components  44   a ,  44   b  to cause fluid displacement components  44   a ,  44   b  to proceed through a pumping stroke. While pump  10  is shown as including pulls  54   a ,  54   b , it is understood that any desired intermediate component capable of pulling in tension but not pushing in compression can connect piston  52  to fluid displacement components  44   a ,  44   b.    
     Pulls  54   a ,  54   b  are slidably disposed within pull chambers  66   a ,  66   b . Each pull  54   a ,  54   b  has a main body that extends through the pull opening in face plate  56   a ,  56   b . The respective ends of pulls  54   a ,  54   b  disposed within pull chambers  66   a ,  66   b  are flanged, such that the flanged end of each pull  54   a ,  54   b  has a wider diameter than the main body portion of each pull  54   a ,  54   b . While the diameters of pulls  54   a ,  54   b  along the main bodies are small enough to slide through the central openings of face plates  56   a ,  56   b , the diameter of the flanged ends of pulls  54   a ,  54   b  are too large to fit through the central openings of face plates  56   a ,  56   b.    
     Face plates  56   a ,  56   b  are configured to engage the flanged ends of pulls  54   a ,  54   b  to facilitate the suction stoke of each fluid displacement components  44   a ,  44   b . Piston  52  is thereby capable of pulling pulls  54   a ,  54   b , and thus fluid displacement components  44   a ,  44   b , inward through a suction stroke, but is incapable of pushing fluid displacement components  44   a ,  44   b  outward through a pumping stroke. Pull chambers  66   a ,  66   b  are dimensioned such that pulls  54   a ,  54   b  simply slide further into pull chambers  66   a ,  66   b  as piston  52  moves toward fluid displacement components  44   a ,  44   b.    
     Piston  52  is driven leftward and rightward along piston axis A-A by cam follower  86 . As piston  52  moves leftward, piston  52  pulls, by way of face plate  56   a , pull  54   a  to the left. Piston  52  thereby pulls fluid displacement component  44   a  to the left due to the connection of pull  54   a  and fluid displacement component  44   a . However, the flanged end of pull  54   a  can move within pull chamber  66   a , so when piston  52  reaches the end of the leftward travel and reverses to rightward travel, the flanged end of pull  54   a  can slide relative to piston  52  within pull chamber  66   a . As such, piston  52  is prevented from pushing on pull  54   a  as piston  52  moves rightward. Piston  52  thereby does not drive fluid displacement component  44   a  rightward through a pumping stroke. Instead, what moves fluid displacement component  44   a  rightward is the charge pressure of the working fluid within internal pressure chamber  60  pushing on the inner side of the fluid displacement component  44   a , and specifically on inner plate  76   a  and the diaphragm  74   a.    
     Inward movement, to the left, of fluid displacement component  44   a , due to the connection of fluid displacement component  44   a  with piston  52  via pull  54   a  and face plate  56   a , partially withdraws the outer end of plunger  80   a  from pumping chamber  90   a  within end cover  22   a . Such movement increases the available volume within the pumping chamber  90   a , creating a suction condition that opens inlet check valve  24   a  and draws the process fluid from inlet manifold  16  into pumping chamber  90   a  past inlet check valve  24   a . The suction condition also causes outlet check valve  26   a  to close, thereby preventing retrograde flow of process fluid from outlet manifold  18  into pumping chamber  90   a.    
     As piston  52  travels leftward the charge pressure of the working fluid within internal pressure chamber  60  drives fluid displacement component  44   b  leftward through a pumping stroke. Piston  52  does not mechanically force fluid displacement component  44   b  to move leftward (outward) because the inner flanged end of pull  54   b  slides within pull chamber  66   b , preventing piston  52  from pushing on pull  54   b . Instead, the charge pressure of the working fluid in internal pressure chamber  60  pushes fluid displacement component  44   b , and specifically diaphragm  74   b  and inner plate  76   b , thereby forcing plunger  80   b  further into pumping chamber  90   b . Forcing plunger  80   b  into pumping chamber  90   b  reduces the available volume within pumping chamber  90   b , increasing the pressure within pumping chamber  90   b . The increased pressure causes outlet check valve  26   b  to open and drives the process fluid downstream out of pumping chamber  90   b  through outlet check valve  26   b . The process fluid flows out of pumping chamber  90   b  into outlet manifold  18 . The increased pressure in pumping chamber  90   b  due to the advancement of plunger  80   b  also causes inlet check valve  24   b  to close, thereby preventing retrograde flow of process fluid from pumping chamber  90   b  upstream past inlet check valve  24   b.    
     After piston  52  reaches the furthest extent of its leftward movement, piston  52  reverses course and is driven rightward by cam follower  86 . As discussed above, the charge pressure of the working fluid drives fluid displacement component  44   a  through a pumping stroke as piston  52  moves rightward, and piston  52  pulls fluid displacement component  44   b  through a suction stroke as piston  52  moves rightward. 
     As piston  52  moves rightward, piston  52  pulls pull  54   b , by way of face plate  56   b , to the right. Piston  52  thereby pulls fluid displacement component  44   b  to the right, causing fluid displacement component  44   b  to proceed through a suction stroke. However, the flanged end of pull  54   b  can move within pull chamber  66   b . As such, when piston  52  reaches the end of its rightward travel and reverses to leftward travel, the flanged end of pull  54   b  can slide relative to piston  52  within pull chamber  66   b , and piston  52  is prevented from pushing on pull  54   b  as piston  52  moves leftward. Piston  52  thereby does not drive fluid displacement component  44   b  leftward through a pumping stroke. Instead, the charge pressure within internal pressure chamber  60  pushing on the inner side of the fluid displacement component  44   b , and specifically on inner plate  76   b  and the diaphragm  74   b , moves fluid displacement component  44   b  leftward through a pumping stroke. 
     Inward movement, to the right, of fluid displacement component  44   b , due to the connection of fluid displacement component  44   b  and piston  52  via pull  54   b  and face plate  56   b , partially withdraws the outer end of plunger  80   b  from pumping chamber  90   b  within end cover  22   b . Such movement increases the available volume within the pumping chamber  90   b , creating a suction condition that opens inlet check valve  24   b  and draws the process fluid from inlet manifold  16  into pumping chamber  90   b  past inlet check valve  24   b . The suction condition also causes outlet check valve  26   b  to close, thereby preventing retrograde flow of process fluid from outlet manifold  18  into pumping chamber  90   b.    
     As piston  52  travels rightward the charge pressure of the working fluid within internal pressure chamber  60  drives fluid displacement component  44   a  rightward through a pumping stroke. Piston  52  does not mechanically force fluid displacement component  44   a  to move rightward (outward) because the inner flange end of pull  84   a  slides within pull chamber  66   a . Instead, it is the charge pressure of the working fluid in internal pressure chamber  60  that pushes fluid displacement component  44   a , and specifically diaphragm  74   a  and inner plate  76   a , forcing plunger  80   a  further into pumping chamber  90   a . Forcing plunger  80   a  into pumping chamber  90   a  reduces the available volume within pumping chamber  90   a , increasing the pressure within pumping chamber  90   a , thereby causing outlet check valve  26   a  to open and driving the process fluid downstream out of pumping chamber  90   a  through outlet check valve  26 . The process fluid flows out of pumping chamber  90   a  into outlet manifold  18 . The increased pressure in pumping chamber  90   a  due to the advancement of plunger  80   a  causes inlet check valve  24   a  to close, thereby preventing retrograde flow of process fluid from pumping chamber  90   a  upstream past inlet check valve  24   a.    
     Fluid displacement components  44   a ,  44   b  are thereby mechanically pulled through their respective suction strokes, but are not mechanically pushed during their respective pumping strokes. Instead, the charge pressure of the working fluid within internal pressure chamber pushes, either pneumatically or hydraulically, on the inner side of fluid displacement components  44   a ,  44   b  to drive fluid displacement components  44   a ,  44   b  through their respective pumping strokes. 
     Pump  10  and the alternating use of piston  52  to mechanically pull, but not mechanically push, the fluid displacement components  44   a ,  44   b  during the suction stroke, and use of a charge of pressurized fluid within internal pressure chamber  60  to pneumatically or hydraulically push, but not pull, fluid displacement components  44   a ,  44   b  during the pumping stroke provides significant advantages. Piston  52  is prevented from exerting an uncompromising mechanical pushing force on either fluid displacement component  44   a ,  44   b , which would otherwise risk dramatically spiking the pressure within the process fluid, particularly when an outlet for the process fluid is suddenly shutoff or otherwise blocked (known as a deadhead condition). In some embodiments of the present disclosure, all of the pressure placed on the process fluid by pump  10  is generated by the charge of the pressurized working fluid within internal pressure chamber  60 . 
     If the pressure in the process fluid exceeds the pressure in the working fluid, then fluid displacement components  44   a ,  44   b  will not be pushed through a pumping stroke, thus avoiding a spike in process fluid pressure. In the deadhead condition, drive  38  will continue to drive the oscillation of piston  52 , but pulls  54   a ,  54   b  and fluid displacement components  44   a ,  44   b  will remain in a retracted (suction stroke) position over one or multiple reciprocation cycles of piston  52 . Fluid displacement components  44   a ,  44   b  remain in the retracted position because the working fluid pressure is insufficient to push fluid displacement components  44   a ,  44   b , through a pumping stroke. One or both of fluid displacement components  44   a ,  44   b , will be remain in the retracted position until the downstream pressure of the process fluid decreases to a level below the working fluid pressure, such that the working fluid pressure can cause fluid displacement components  44   a ,  44   b  to enter their respective pumping strokes. Allowing piston  52  to continue to oscillate without pushing either fluid displacement component  44   a ,  44   b  into a pumping stroke allows pump  10  to continue to run during the deadhead condition without causing any harm to the motor or pump. As piston  54  continues to oscillate, pulls  54   a ,  54   b  will simply slide within pull chambers  66   a ,  66   b  without imparting the pushing force to fluid displacement components  44   a ,  44   b  necessary to initiate the pumping stroke. Allowing pump  10  to continue to run prevents undesired wear to components of pump  10  that can occur due to repeated start up and shut down. In addition, allowing pump  10  to continue to run increases the efficiency of the pumping operation, as the user is not required to stop and start pump  10  whenever the user desired to close the outlet. Moreover, damage to various components of pump  10  is avoided, as electric drive  12  ( FIG. 1 ) and drive  14  will not experience unexpected resistance during the deadhead, as pulls  54   a ,  54   b  simply slide within pull chambers  66   a ,  66   b  instead of transmitting forces to piston  52  from fluid displacement members  44   a ,  44   b.    
     Another benefit, in some embodiments, is a reduction or elimination of downstream pulsation of the process fluid. A constant downstream pressure can be produced by pump  10  to eliminate pulsation by sequencing the speed of piston  52  with the pumping stroke caused by the working fluid. Sequencing the suction and pumping strokes can prevent drive system  14  from entering a state of rest where one fluid displacement member  44   a ,  44   b  completes a pumping stroke prior to piston  52  reversing course along pump axis A-A. 
     Piston  52  is sequenced by setting the speed of oscillation and/or the pressure of the working fluid such that when piston  52  begins to pull one fluid displacement component  44   a ,  44   b  into a suction stroke prior to that fluid displacement component  44   a ,  44   b  completing a pumping stroke. This is possible because piston  52  can pull one fluid displacement component  44   a ,  44   b  through a suction stroke faster than the working fluid charge pressure can drive the other fluid displacement component  44   a ,  44   b  through an entire pumping stroke. The difference in speed can be achieved due to the different causes of pulling (mechanical) and pushing (fluid). Therefore, at least one fluid displacement component  44   a ,  44   b  is always moving in a pumping stroke, which eliminates pulsation because process fluid is constantly discharged to outlet manifold  18  at a constant rate. 
     Moreover, pump  10  can generate higher output pressures in the process fluid than the charge pressure of the working fluid. The respective surface areas of fluid displacement components  44   a ,  44   b  on which the working fluid directly contacts and pushes are larger than the respective surface areas of fluid displacement components  44   a ,  44   b  that directly contact and push on the process fluid. 
     More specific to the illustrated embodiment, the diameter of the inner parts of fluid displacement components  44   a ,  44   b  that contact and are pushed upon by the working fluid (e.g., defined by diaphragms  74   a ,  74   b  and inner plates  76   a ,  76   b ) is larger than the diameter of the outer end faces of plungers  80   a ,  80   b  that contact and push upon the process fluid. Therefore, while the lateral travel of the working fluid-contacting surface and the process fluid-contacting surface of fluid displacement components  44   a ,  44   b  are the same, the displacements of the working fluid and the process fluid will be different for every stroke due to the difference in diameters and overall fluid-contacting surface areas. The displacement of process fluid by the outer ends of plungers  80   a ,  80   b  is smaller for each stroke as compared to the displacement of working fluid, but the pressure generated in the process fluid is greater than the pressure of the working fluid acting on fluid displacement components  44   a ,  44   b . This generates higher process fluid pressure within pumping chambers  90   a ,  90   b . The process fluid pressure is higher even than the working fluid pressure in internal pressure chamber  60 . Therefore, the pumping pressure developed in pumping chambers  90   a ,  90   b  and further downstream due to the pumping strokes of fluid displacement components  44   a ,  44   b  can be higher than the working fluid pressure that acts upon and pushes fluid displacement components  44   a ,  44   b . The pressure multiplication provides a more compact pump  10 , as pump  10  can provide higher pumping pressures in a more compact arrangement due to the variations in surface area. Moreover, pump  10  has increased efficiency, as less energy is required to charge the working fluid to achieve the desired output pressure. 
     High pressure output of process fluid is beneficial in various applications of fluid handling, such as for dispensing or spraying viscous fluid. Embodiments of the present disclosure extend the output pressure from pump  10  above the supply pressure while still allowing the downstream outlet of pump  10  to be shutoff or otherwise deadheaded without concern of spiking pressure or damaging pump  10 . For example, the user may only have a 100 PSI compressor available for generating the initial charge of working fluid within internal pressure chamber  60 . The mechanical advantage gained by fluid displacement components  44   a ,  44   b  having different sized working/process fluid contacting surfaces, and therefore different working/process fluid displacements, allows the output pressure of process fluid to be significantly higher than 100 PSI. Moreover, the user&#39;s application may further require frequent starting and stopping of process fluid dispenses, which results in frequent deadheading of the fluid. Pulls  54   a ,  54   b  avoid pressure spikes and prevent pump  10  from suffering damage that can otherwise result from frequent starting and stopping of process fluid dispenses. Pulls  54   a ,  54   b  house within pull chambers  66   a ,  66   b  and prevent piston  52  from pushing on fluid displacement components  44   a ,  44   b , while facilitating piston  52  pulling fluid displacement components  44   a ,  44   b.    
     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 internal pressure chamber  60  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 components  44   a ,  44   b.    
       FIG. 3  is a cross-sectional view of pump  100 . Pump  100  includes end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; bushings  42   a ,  42   b ; outer cylinders  46   a ,  46   b ; collars  48   a ,  48   b ; sealing rings  50   a ,  50   b ; drive cylinders  92   a ,  92   b ; fluid covers  120   a ,  120   b ; and fluid displacement components  144   a ,  144   b . Drive system  14  includes housing  28 ; piston guide  30 ; piston  52 ; pulls  54   a ,  54   b ; and face plates  56   a ,  56   b . Housing  28  includes guide opening  58  and defines internal pressure chamber  60 . Piston guide  30  includes barrel nut  62  and guide pin  64 . Piston  52  includes pull chambers  66   a ,  66   b ; central slot  68 ; and axial slot  70 . Fluid covers  120   a ,  120   b  include, respectively, ports  72   a ,  72   b . Fluid displacement components  144   a ,  144   b  include, respectively, plungers  80   a ,  80   b ; attachment members  82   a ,  82   b ; and drive pistons  94   a ,  94   b . Drive pistons  94   a ,  94   b  include piston grooves  96   a ,  96   b  and piston rings  98   a ,  98   b . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d . Drive shaft  84  and cam follower  86  of drive  38  are shown. 
     Housing  28  defines internal pressure chamber  60 . Bushings  42   a ,  42   b  are disposed within housing. Piston  52  is disposed within housing  28  and supported by bushings  42   a ,  42   b . Cam follower  86  extends into central slot  68  of piston  52  and is configured to drive oscillation of piston  52  along piston axis A-A. Piston guide  30  extends through housing  28  and engages axial slot  70  of piston  52  to prevent piston  52  from rotating about piston axis A-A. Barrel nut  68  extends through guide opening  60 , and guide pin  70  is connected to barrel nut  68 . As shown, guide pin  70  rides within axial slot  76  of piston  52  to prevent piston  52  from rotating about piston axis A-A. 
     Piston  52  includes pull chamber  72   a  disposed within a first end of piston  52  and pull chamber  72   b  disposed within a second, opposite end of piston  52 . Face plates  56   a ,  56   b  are disposed at opposite ends of piston  52  and cap pull chambers  66   a ,  66   b . Face plates  56   a ,  56   b  are configured to retain pulls  54   a ,  54   b , within pull chambers  66   a ,  66   b  of piston  52 . Face plates  56   a ,  56   b  include fastener openings to facilitate connection with piston  52 . Any desired fastener, such as a bolt, can extend through the fastener openings into piston  52  to secure face plates  56   a ,  56   b  to piston  52 . Pulls  86   a ,  86   b  extend out of pull chambers  72   a ,  72   b  through openings in face plates  56   a ,  56   b.    
     Drive cylinders  92   a ,  92   b  are disposed between housing  28  and fluid covers  120   a ,  120   b . Fluid covers  120   a ,  120   b  are attached to housing  28  by fasteners (not shown) extending through fluid covers  120   a ,  120   b  into housing  28 . Outer cylinders  46   a ,  46   b  are disposed between fluid covers  120   a ,  120   b  and end covers  22   a ,  22   b . End covers  22   a ,  22   b  are attached to fluid covers  120   a ,  120   b  by fasteners (not shown) extending through end covers  22   a ,  22   b  into fluid covers  120   a ,  120   b . Collars  48   a ,  48   b  are disposed adjacent the inner sides of end covers  22   a ,  22   b . Collars  48   a ,  48   b  receive an outer end of outer cylinders  46   a ,  46   b . Sealing rings  50   a ,  50   b  are disposed between collars  48   a ,  48   b  and end covers  22   a ,  22   b . Sealing rings  50   a ,  50   b  extend around and interface with an outer edge of plungers  80   a ,  80   b.    
     Fluid displacement components  144   a ,  144   b  are configured to draw process fluid into pumping chambers  90   a ,  90   b  during suction strokes and to drive process fluid downstream out of pumping chambers  90   a ,  90   b  during pumping strokes. Drive pistons  94   a ,  94   b  are disposed within drive cylinders  92   a ,  92   b . Drive piston  94   a  defines, in part, two chambers: internal pressure chamber  60  and outer chamber  88   a . Drive piston  94   b  similarly defines, in part, two chambers: internal pressure chamber and outer chamber  88   b . Internal pressure chamber  60  is defined by housing  28  and drive pistons  94   a ,  94   b . Outer chambers  88   a ,  88   b  are further defined in part by fluid covers  120   a ,  120   b . The volume of outer chambers  88   a ,  88   b  changes inversely with a change in the volume of internal pressure chamber  60  due to the movement of the drive pistons  94   a ,  94   b . Ports  72   a ,  72   b  extend through fluid covers  120   a ,  120   b , respectively, to connect outer chambers  88   a ,  88   b  to the atmosphere and prevent overpressurization and/or vacuum conditions from forming in outer chambers  88   a ,  88   b.    
     Piston grooves  96   a ,  96   b  extend circumferentially about drive pistons  94   a ,  94   b . Piston rings  98   a ,  98   b  are disposed in piston grooves  96   a ,  96   b  and are configured to interface with and seal against an inner circumferential surface of drive cylinders  92   a ,  92   b . Piston rings  98   a ,  98   b  fluidly isolate internal pressure chamber  60  from outer chambers  88   a ,  88   b . Piston rings  98   a ,  98   b  form a dynamic seal with the inner surface of drive cylinders  92   a ,  92   b  as drive pistons  94   a ,  94   b  oscillate within drive cylinders  92   a ,  92   b  during operation. 
     Plungers  80   a ,  80   b  extend from drive pistons  94   a ,  94   b  and into pumping chambers  90   a ,  90   b . Plungers  80   a ,  80   b  extend through outer cylinders  46   a ,  46   b . Pull  54   a , drive piston  94   a , and plunger  80   a  are connected to move as an assembly. Similarly, pull  54   b , drive piston  94   b , and plunger  80   b  are connected to move as an assembly. Attachment members  82   a ,  82   b  extend through drive pistons  94   a ,  94   b  and into pulls  54   a ,  54   b  and plungers  80   a ,  80   b . In some examples, the openings in each of pulls  54   a ,  54   b ; drive pistons  94   a ,  94   b ; and plungers  80   a ,  80   b  are threaded to engage with threaded attachment members  82   a ,  82   b . It is understood, however, that pulls  54   a ,  54   b ; drive pistons  94   a ,  94   b ; and plungers  80   a ,  80   b  can be interconnected in any desired manner. In one example, drive pistons  94   a ,  94   b  and plungers  80   a ,  80   b  are integrally formed as a single component. As such, fluid displacement components  144   a ,  144   b  can be single-piece, dual-diameter pistons. 
     The operation of pump  100 ′ is similar to the operation of pump  100  ( FIGS. 2A-2B ), except the working fluid acts on drive pistons  94   a ,  94   b  instead of diaphragms  74   a ,  74   b  ( FIGS. 2A-2B ). As piston  52  is driven rightward by cam follower  86 , piston  52  pulls fluid displacement component  144   b  to the right due to the connection of pull  54   b  and fluid displacement component  144   b . Pulling fluid displacement component  144   b  to the right retracts plunger  80   b  from fluid cavity  90   b  creating suction and drawing the process fluid into fluid cavity  90   b  through inlet valve  24   b.    
     As piston  52  moves rightward, the charge pressure of the working fluid in internal pressure chamber  60  drives fluid displacement component  144   a  rightward. The rightward movement of fluid displacement component  144   a  causes plunger  80   a  to proceed into fluid cavity  90   a , thereby decreasing the volume of fluid cavity  90   a  and driving the process fluid out of fluid cavity  90   a  through outlet check valve  26   a.    
     The charge pressure acts on the inner faces of drive piston  94   a  to cause the rightward movement of fluid displacement component  144   a . The diameter D 1  of drive piston  94   a  is larger than the diameter D 2  of plunger  80   a . As such, the area of drive piston  94   a  acted on by the working fluid is larger than the area of plunger  80   a  acting on the process fluid. The force exerted on drive piston  94   a  by the working fluid is the same as the force exerted on the process fluid by plunger  80   a , due to the rigid connection between drive piston  94   a  and plunger  80   a . Because the forces are the same, the pressure differential between the working fluid and the process fluid is the inverse of the area differential between the inner face of drive piston  94   a  and the outer face of plunger  80   a . Force (F) is related to surface area (A) and pressure (P) according to the following equation:
 
F=PA
 
As such, assuming that the working fluid has a charge pressure of about 100 psi, that driving piston  94   a  has a diameter of about 2 in, and that plunger  80   a  has a diameter of about 1 in. The output pressure of the process fluid generated by fluid displacement component  144   a  is thus about 400 psi. The diameters D 1  and D 2  can be dimensioned according to any desired ratio to provide the desired output pressure based on the set charge pressure.
 
     After piston  52  has shifted rightward, cam follower  86  causes piston  52  to reverse direction and move leftward. Face plate  56   a  engages the flanged end of pull  54   a , and piston  52  begins to pull fluid displacement component  144   a  through a suction stroke. Plunger  80   a  is withdrawn from pumping chamber  90   a , creating suction in pumping chamber  90   a  and drawing the process fluid into pumping chamber  90   a  through inlet valve  24   a.    
     As piston  94   a  pulls fluid displacement component  144   a  through a suction stroke, the charge pressure of the working fluid pushes fluid displacement component  144   a  through a pumping stroke. The charge pressure acts on the inner face of drive piston  94   b  to push fluid displacement component  144   b  through the pumping stroke. Plunger  80   b  is driven into pumping chamber  90   b  by drive piston  94   b , thereby decreasing the volume in pumping chamber  90   b  and driving the process fluid downstream from pumping chamber  90   b  through outlet valve  26   b . Fluid displacement component  144   b  provides a force multiplication similar to fluid displacement component  144   a.    
     Pump  100  provides significant advantages. The working fluid in internal pressure chamber  60  acts on the inner faces of drive pistons  94   a ,  94   b  to drive fluid displacement components  144   a ,  144   b  through respective pumping strokes. Drive pistons  94   a ,  94   b  reciprocate within drive cylinders  92   a ,  92   b  and remain rigid during pumping. Because drive pistons  94   a ,  94   b  are rigid, the full area of drive pistons  94   a ,  94   b  are able to transmit the full force from the working fluid to plungers  80   a ,  80   b  across the full displacement distance of fluid displacement components  144   a ,  144   b . Drive pistons  94   a ,  94   b  thereby provide consistent force multiplication to plungers  80   a ,  80   b  throughout the displacement of fluid displacement components  144   a ,  144   b . The force multiplication provided by fluid displacement components  144   a ,  144   b  provides for a greater pressure output from a more compact pump  100 . The more compact pump arrangement is less costly to manufacture, easier for the end user to use and store, and more energy efficient. 
     In addition, the reciprocation of piston  52  can be sequenced to provide pulseless downstream flow. To achieve the pulseless flow, the speed of piston  52  is set such that piston  52  begins to pull fluid displacement components  144   a ,  144   b  into suction strokes prior to that fluid displacement component  144   a ,  144   b  completing its pumping stroke. As such, at least one fluid displacement component  144   a ,  144   b  is always proceeding through a pumping stroke and providing the process fluid downstream. The process fluid is pumped out of each pumping chamber  90   a ,  90   b  and provided to outlet manifold  18  at the same pressure because each fluid displacement component  144   a ,  144   b  is driven by the same charge pressure of the working fluid. 
       FIG. 4  is a cross-sectional view of pump  200 . Pump  200  includes inlet manifold  16 ; outlet manifold  18 ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; outer cylinders  46   a ,  46   b ; collars  48   a ,  48   b ; sealing rings  50   a ,  50   b ; fluid covers  220   a ,  220   b ; and fluid displacement components  244   a ,  244   b . Drive system  114  includes housing  128 , solenoid  202 , armature  204 , and pulls  154   a ,  154   b . Housing  128  defines internal pressure chamber  60 . Fluid covers  220   a ,  220   b  include, respectively, ports  72   a ,  72   b . Fluid displacement components  244   a ,  244   b  include inner portion  206   a ,  206   b  and outer portion  208   a ,  208   b . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d.    
     Pump  200  is similar to pump  10  ( FIGS. 2A-2B ) and pump  100  ( FIG. 3 ), except pump  200  is electrically driven. In addition, pulls  154   a ,  154   b  are bands instead of shafts having flanged and attachment ends. Housing  28  defines internal pressure chamber  60 . Solenoid  202  is supported by housing  28  and is electrically connected to a power source. The power source can be external to pump  10 , such motor  34  ( FIG. 1 ) or an electric cord configured to connect to the electric grid, or internal to pump  10 , such as a battery mounted in housing  28 . However, with solenoid  202  supported by housing  28 , drive system  14  can be considered as having the power source of drive system  14  integrated into housing  28  and internal pressure chamber  60 . 
     Armature  204  is disposed within and configured to be driven by solenoid  202 . Armature  204  is connected to fluid displacement components  44   a ,  44   b  by pulls  154   a ,  154   b . Pulls  154   a ,  154   b  are attached to armature  204  and to inner portions  206   a ,  206   b  of fluid displacement components  244   a ,  244   b . In the example shown, pulls  154   a ,  154   b  include flexible members, such as plastic, rubber, or elastic bands that pull in tension but do not meaningfully push in compression. Instead, in compression, pulls  154   a ,  154   b  are configured to bend so as to not transfer a compressive or pushing force to fluid displacement components  244   a ,  244   b . Pulls  154   a ,  154   b  can be secured to armature  204  and fluid displacement components  244   a ,  244   b  in any desired manner. For example, inner portion  206   a ,  206   b  can include a groove and a cross-bore, with the end of the band forming pull  154   a ,  154   b  inserted into the groove and a set pin or cotter pin inserted into the cross-bore to retain the end of the band. In another example, pulls  154   a ,  154   b  can be integrally molded to one of fluid displacement components  244   a ,  244   b  or armature  204 . Pulls  154   a ,  154   b  can also be attached to armature  204  in any desired manner, such as by pins. 
     While pump  10  is described as including pulls  154   a ,  154   b , it is understood that armature  204  and fluid displacement components  244   a ,  244   b  can be connected in any desired manner. For example, armature  204  can include pull chambers, similar to pull chambers  66   a ,  66   b  ( FIGS. 2B-3 ), extending into opposite ends of armature  204 . Pulls  54   a ,  54   b  ( FIGS. 2B-3 ) can then extend from the pull chambers and be connected to fluid displacement components  244   a ,  244   b  in any desired manner, such as by attachment members  82   a ,  82   b  ( FIGS. 2B-3 ). 
     Solenoid  202  and armature  204  are of any suitable configuration for causing armature  204  to reciprocate along pump axis A-A. Solenoid  202  can be either a single-acting solenoid, such that solenoid  202  drives armature  204  in a single direction and a spring drives armature  204  in the other direction, or a double-acting solenoid, such that solenoid  202  drives armature  204  in both the left and right directions. In examples where solenoid  202  is double-acting, armature  204  can be a permanent magnet such that reversing the polarity through solenoid  202  drives the reciprocation of armature  204 . In examples where solenoid  202  is single-acting, solenoid  202  can be configured to drive armature  204  in a first direction and a spring (not shown) can be configured to drive armature  204  in a second, opposite direction. For example, solenoid  202  can be configured to pull armature  204  leftward, causing armature  204  to pull fluid displacement component  44   a  through a suction stroke. The spring can be configured to push armature  204  rightward, causing armature  204  to pull fluid displacement component  44   b  through a suction stroke. It is understood that solenoid  202  can pull armature  204  rightward and the spring can push armature leftward. 
     Outer portions  208   a ,  208   b  and inner portions  206   a ,  206   b  of fluid displacement components  244   a ,  244   b  are integrally formed. Outer portions  208   a ,  208   b  extends from inner portions  206   a ,  206   b  through outer cylinder  46   a ,  46   b  and into fluid cavity  90   a ,  90   b . Inner portion  206   a ,  206   b  is surrounded by a bore within fluid cover  220   a ,  220   b . Is some examples, fluid covers  220   a ,  220   b  are formed from multiple components, such as inner cover portions  221   a ,  221   b  and outer cover portions  223   a ,  223   b . In other examples, fluid covers  220   a ,  220   b  can be formed from a single part. For example, each fluid cover  220   a ,  220   b  can include outer cover portion  223   a ,  223   b  that is bolted to the central portion of housing  128 , and inner cover portions  221   a ,  221   b  that define the bore within which inner portions  206   a ,  206   b  of fluid displacement components  244   a ,  244   b  reciprocate. Outer cover portions  223   a ,  223   b  and inner cover portions  221   a ,  221   b  can be formed of different materials. For example, outer cover portions  223   a ,  223   b  can be metallic, and inner cover portions  221   a ,  221   b  can be formed from a material suitable for sealing directly or indirectly with inner portions  206   a ,  206   b . In one example, inner cover portions  221   a ,  221   b  of each fluid cover  220   a ,  220   b  can be formed from an elastomer. In another example, inner portions  206   a ,  206   b  can each include a circumferential groove and a seal (similar to grooves  96   a ,  96   b  and rings  98   a ,  98   b  shown in  FIG. 3 ), and the seal can seal against inner cover portions  221   a ,  221   b  of each fluid cover  220   a ,  220   b.    
     Inner portion  206   a  defines, in part, two chambers: internal pressure chamber  60  and outer chamber  88   a . Inner portion  206   b  defines, in part, two chambers: internal pressure chamber  60  and outer chamber  88   b . Internal pressure chamber  60  is defined by housing  28  and inner portions  206   a ,  206   b . Outer chambers  88   a ,  88   b  are further defined in part by fluid covers  220   a ,  220   b . Inner portions  206   a ,  206   b  seal against the bores in fluid covers  220   a ,  220   b  to prevent the working fluid from leaking out of internal pressure chamber  60  into outer chambers  88   a ,  88   b . Ports  72   a ,  72   b  provide vent path between outer chambers  88   a ,  88   b  and the atmosphere. 
     The operation of pump  200  is similar to the operation of pump  10  ( FIGS. 2A-2B ) and pump  100  ( FIG. 3 ), except the working fluid acts on fluid displacement components  244   a ,  244   b  and reciprocation is caused by solenoid  202  and armature  204 . A charge is provided to solenoid  202  to cause displacement of armature  204  along pump axis A-A. As armature  204  moves rightward, armature  204  pulls fluid displacement component  244   b  to the right due to pull  154   b  connecting armature  204  and fluid displacement component  244   b . Pulling fluid displacement component  44   b  retracts outer portion  208   b  from pumping cavity  90   b , creating suction and drawing the process fluid into pumping cavity  90   b  through inlet valve  24   b.    
     As armature  204  moves rightward, the charge pressure of the working fluid in internal pressure chamber  60  drives fluid displacement component  244   a  rightward. The rightward movement of fluid displacement component  244   a  causes outer portion  208   a  to move into pumping cavity  90   a , thereby decreasing the volume of pumping cavity  90   a  and driving the process fluid out of pumping cavity  90   a  through outlet check valve  26   a . The working fluid acts on inner portion  206   a  to drive fluid displacement component  244   a . In the example shown, inner portion  206   a  has a larger diameter than outer portion  208   a , and as such fluid displacement component  244   a  provides a force multiplication between the charge pressure of the working fluid and the output pressure of the process fluid. 
     After armature  204  has shifted rightward, armature  204  reverses direction and moves leftward. As discussed above, the leftward movement can be caused by a spring when the charge is removed from solenoid  202 , by a reversal of the polarity of the charge to solenoid  202 , or by any other suitable mechanism or method. Pull  154   a  connects armature  204  and fluid displacement component  44   a , and pull  154   a  pulls fluid displacement component  44   a  through a suction stroke. Outer portion  208   a  is withdrawn from pumping chamber  90   a , creating suction in pumping chamber  90   a  and drawing the process fluid into pumping chamber  90   a  through inlet valve  24   a.    
     As armature  204   a  pulls fluid displacement component  44   a  through a suction stroke, the charge pressure of the working fluid pushes fluid displacement component  44   b  through a pumping stroke. The charge pressure acts on inner portion  206   b  to push fluid displacement component  44   b  through the pumping stroke. Outer portion  208   b  is driven into pumping chamber  90   b  by inner portion  206   b , thereby decreasing the volume in pumping chamber  90   b  and driving the process fluid downstream from pumping chamber  90   b  through outlet valve  26   b . Fluid displacement component  244   b  provides a force multiplication similar to fluid displacement component  244   a.    
     Pump  200  provides significant advantages. The electric driving components, solenoid  202  and armature  204 , are disposed within housing  28  and internal pressure chamber  60 , which provides for a compact, self-contained pump. Fluid displacement components  244   a ,  244   b  provide force multiplication between the charge pressure within internal pressure chamber  60  and the output pressure of the process fluid due to the differing diameters of inner portions  206   a ,  206   b  and outer portions  208   a ,  208   b . Armature  204  pulls fluid displacement components  244   a ,  244   b  through suction strokes but is prevented from pushing fluid displacement components  244   a ,  244   b  through pumping strokes by pulls  154   a ,  154   b . Instead, the working fluid pushes fluid displacement components  244   a ,  244   b  through the pumping strokes. As such, the strokes of fluid displacement components  244   a ,  244   b  can be sequenced to eliminate downstream pulsation. In addition, pump  10  can be deadheaded without damaging any components, as pulls  154   a ,  154   b  do not transfer compressive, pumping forces to fluid displacement components  244   a ,  244   b.    
     As shown, different drive mechanisms, reciprocating members, pulls, and fluid displacement components are possible, and embodiments consistent with this disclosure are not limited to the particular embodiments or options disclosed herein. While electrically driven motors and pistons have been disclosed herein, an air or hydraulically driven piston or other reciprocating member could be used instead of or in combination with any fluid displacement component of any embodiment herein. 
       FIG. 5  is a cross-sectional view of piston  52  and pulls  254   a ,  254   b . Piston  52  includes face plates  56   a ,  56   b ; pull chambers  66   a ,  66   b ; central slot  68 ; and axial slot  70 . Pulls  254   a ,  254   b  include inner sections  256   a ,  256   b  and outer sections  258   a ,  258   b . Inner sections  256   a ,  256   b  include first outer flanges  260   a ,  260   b ; first shafts  262   a ,  262   b ; and first inner flanges  264   a ,  264   b . Outer sections  258   a ,  258   b  include second outer flanges  266   a ,  266   b ; second shafts  268   a ,  268   b ; and attachment bores  270   a ,  270   b.    
     Piston  52  is configured to reciprocate within a housing, such as housing  28  ( FIGS. 1-3 ), to pull fluid displacement components, such as fluid displacement components  44   a ,  44   b  ( FIGS. 2A-2B ), fluid displacement components  144   a ,  144   b  ( FIG. 3 ), and fluid displacement components  244   a ,  244   b  ( FIG. 4 ), through suction strokes. Face plates  56   a ,  56   b  are attached to opposite ends of piston  52  and enclose pull chambers  66   a ,  66   b . Pulls  54   a ,  54   b  are configured to transmit tensile forces but not compressive forces, such that piston  52  can pull the fluid displacement components via pulls  254   a ,  254   b , but cannot push the fluid displacement components via pulls  254   a ,  254   b.    
     Inner sections  256   a ,  256   b  are at least partially retained within pull chambers  66   a ,  66   b  by face plates  56   a ,  56   b . First outer flanges  260   a ,  260   b  project from first shafts  262   a ,  262   b  and are disposed within pull chambers  66   a ,  66   b . First shafts  262   a ,  262   b  extend through openings in face plates  56   a ,  56   b  and are configured to slide within the openings in face plates  56   a ,  56   b . First outer flanges  260   a ,  260   b  are wider than the openings through face plates  56   a ,  56   b  such that first outer flanges  260   a ,  260   b  cannot pass through the openings. Instead, first outer flanges  260   a ,  260   b  engage the inner sides of face plates  56   a ,  56   b.    
     First inner flanges  264   a ,  264   b  of inner sections  256   a ,  256   b  project into a bore through the end of inner sections  256   a ,  256   b  disposed opposite first outer flanges  260   a ,  260   b . Outer sections  258   a ,  258   b  are configured to slide within inner sections  256   a ,  256   b . Second shafts  268   a ,  268   b  extend through the bore defined by first inner flanges  264   a ,  264   b . Second outer flanges  266   a ,  266   b  are configured to engage first inner flanges  264   a ,  264   b  to prevent outer sections  258   a ,  258   b  from sliding out of inner sections  256   a ,  256   b . Attachment bores  270   a ,  270   b  are configured to receive attachment members  82  ( FIGS. 2A-3 ) to connect pulls  54   a ,  54   b  to the fluid displacement members. 
     During operation, outer members  258   a ,  258   b  are configured to house within inner members  256   a ,  256   b , and inner members  256   a ,  256   b  are configured to house within pull chambers  66   a ,  66   b  to prevent piston  52  from pushing the fluid displacement members. As such, pulls  54   a ,  54   b  are configured to telescope during operation. While pulls  54   a ,  54   b  are each shown as including two members that are slidable, it is understood that pulls  54   a ,  54   b  can include as many or as few slidable members as desired. Pulls  54   a ,  54   b  including multiple slidable members configured to telescope reduces the depth required for pull chambers  66   a ,  66   b  to house pulls  54   a ,  54   b . The more compact pull chambers  66   a ,  66   b  reduces the footprint of the pump and provides for a more compact pump. 
       FIG. 6  is a cross-sectional view of pump  10 . Pump  10  includes inlet manifold  16 ; outlet manifold  18 ; fluid covers  20   a ,  20   b ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; bushings  42   a ,  42   b ; fluid displacement components  44   a ,  44   b ; outer cylinders  46   a ,  36   b ; collars  48   a ,  48   b ; and sealing rings  50   a ,  50   b . Drive system  14  includes housing  28 ; piston guide  30 ; piston  52 ; pulls  54   a ,  54   b ; face plates  56   a ,  56   b , and plugs  99   a ,  99   b . Housing  28  includes working fluid inlet  32  and guide opening  58 . Housing  28  defines internal pressure chamber  60 . Piston guide  30  includes barrel nut  62  and guide pin  64 . Piston  52  includes pull chambers  66   a ,  66   b ; central slot  68 ; and axial slot  70 . Fluid covers  20   a ,  20   b  include, respectively, ports  72   a ,  72   b . Fluid displacement components  44   a ,  44   b  include, respectively, diaphragms  74   a ,  74   b ; plungers  80   a ,  80   b ; attachment members  82   a ,  82   b . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d . Drive shaft  84  and cam follower  86  of drive  38  are shown. 
     Pump  10  shown in  FIG. 6  is the same as pump  10  shown in  FIG. 2B , except pump  10  shown in  FIG. 6  includes plugs  99   a ,  99   b . Plugs  99   a ,  99   b  are disposed in pull chambers  66   a ,  66   b  and are configured to prevent pulls  54   a ,  54   b  from sliding within pull chambers  66   a ,  66   b . Instead, plugs  99   a ,  99   b  allow piston  52  to transmit compressive, pushing forces to fluid displacement components  44   a ,  44   b  such that piston  52  can drive fluid displacement components  44   a ,  44   b  through pumping strokes in addition to suction strokes. As such, plugs  99   a ,  99   b  enable pump  10  to be easily converted between mechanical/fluid operating mode and a mechanical/mechanical operating mode. In the mechanical/fluid operating mode fluid displacement components  44   a ,  44   b  are mechanically pulled through their respective suction strokes and are driven through respective pumping strokes by the charge pressure of the working fluid disposed in internal pressure chamber  60 . In the mechanical/mechanical operating mode, fluid displacement components  44   a ,  44   b  are mechanically pulled through their respective suction strokes and are also mechanically driven through their respective pumping strokes. When operating in the mechanical/mechanical operating mode, internal pressure chamber  60  does not require a charge of working fluid, as piston  52  drives fluid displacement components  44   a ,  44   b  through the pumping strokes. 
     To convert pump  10  to the mechanical/mechanical operating mode, the user removes face plates  56   a ,  56   b  and pulls  54   a ,  54   b , from piston  52  and drops plugs  99   a ,  99   b  into pull chambers  66   a ,  66   b . Face plates  56   a ,  56   b  and pulls  54   a ,  54   b  can then be reinstalled on piston  52 . 
     In some examples, pump  10  includes a pressure switch (not shown) connected to drive system  14 . The pressure switch can be configured to switch off drive system  14  based on a sensed pressure reaching or exceeding a threshold. For example, pressure switch can be configured to sense the pressure in pumping chambers  90   a ,  90   b  and/or in outlet manifold  18 . In the event pump  10  is deadheaded, the pressure will spike in either pumping chambers  90   a ,  90   b  and/or outlet manifold  18  as drive  38  causes reciprocation of piston  52 . The spike in pressure will trip the pressure switch, causing the pressure switch to deactivate drive  38  while pump  10  is deadheaded. In some examples, the user can reactivate pump  10  after downstream flow is returned. In other examples, the pressure switch can be configured to sense the drop in the process fluid pressure, indicating that downstream flow has returned, and can reactivate pump  10  based on that drop in process fluid pressure. 
     Pump  10  provides significant advantages. Pump  10  is convertible between the mechanical/fluid operating mode and the mechanical/mechanical operating mode, thereby providing a wide range of pumping options to the end user. The end user can operate in the mechanical/mechanical mode when high downstream pressures are desired or working fluid is unavailable. The end user can operate in the mechanical/fluid operating mode to eliminate downstream pulsation and allow pump  10  to continue operating when deadheaded. 
       FIG. 7  is a cross-sectional view of pump  300 . Pump  300  includes inlet manifold  16 ; outlet manifold  18 ; fluid covers  20   a ,  20   b ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; bushings  42   a ,  42   b ; outer cylinders  46   a ,  46   b ; collars  48   a ,  48   b ; sealing rings  50   a ,  50   b ; fluid displacement components  344   a ,  344   b . Drive system  314  includes housing  28 , piston guide  30 , and piston  352 . Housing  28  includes guide opening  58 . Piston guide  30  includes barrel nut  62  and guide pin  64 . Piston  352  includes central slot  368  and axial slot  370 . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d . Drive shaft  84  and cam follower  86  of drive  38  are shown. 
     Housing  28  is disposed between fluid covers  20   a ,  20   b . Outer cylinders  46   a ,  46   b  are disposed between fluid covers  20   a ,  20   b  and end covers  22   a ,  22   b . Inlet manifold  16  is configured to provide process fluid to pumping chambers  90   a ,  90   b  within end covers  22   a ,  22   b . Inlet check valves  24   a ,  24   b  are disposed between inlet manifold  16  and end covers  22   a ,  22   b . Outlet manifold  18  is configured to receive process fluid from pumping chambers  90   a ,  90   b . Outlet check valves  26   a ,  26   b  are disposed between end covers  22   a ,  22   b  and outlet manifold  18 . 
     Bushings  42   a ,  42   b  are disposed within housing  28  and configured to support piston  352 . Piston  352  is disposed within bushings  42   a ,  42   b  and is configured to reciprocate along pump axis A-A. Piston guide  30  prevent piston  352  from rotating about pump axis A-A. Barrel nut  62  is disposed in guide opening  58 , and guide pin  64  is connected to barrel nut  62  and extends into and engages axial slot  370 . Fluid displacement component  344   a  extends from a first side of piston  352 , through outer cylinder  46   a , and into pumping chamber  90   a  within end cover  22   a . Fluid displacement component  344   b  extends from a second side of piston  352 , through outer cylinder  46   b , and into pumping chamber  90   b  within end cover  22   b . As shown, fluid displacement components  344   a ,  344   b  are integrally formed with piston  352 . It is understood, however, that fluid displacement components  344   a ,  344   b  can be formed separately from piston  352  and joined with piston  352  in any desired manner, such as by a fastener similar to attachment members  82   a ,  82   b  ( FIGS. 2A-3 ). 
     Fluid displacement components  344   a ,  344   b  and piston  352  are configured to reciprocate as a single assembly. Piston  352  is configured to drive fluid displacement components  344   a ,  344   b  through both their respective suctions strokes and pumping strokes. During a suction stroke, piston  352  retracts fluid displacement component  344   a ,  344   b  from fluid cavity  90   a ,  90   b  to increase a volume of fluid cavity  90   a ,  90   b , creating suction in fluid cavity  90   a ,  90   b  and drawing process fluid into fluid cavity  90   a ,  90   b  through inlet valve  24   a ,  24   b . During a pumping stroke, piston  352  drives fluid displacement component  344   a ,  344   b  into fluid cavity  90   a ,  90   b  to decrease a volume of fluid cavity  90   a ,  90   b  and drive the process fluid out of fluid cavity  90   a ,  90   b  through outlet valve  26   a ,  26   b.    
     While pump  300  is shown as including fluid displacement components  344   a ,  344   b , it is understood that pump  300  can include any fluid displacement member suitable for displacing the fluid within pumping chambers  90   a ,  90   b . In one example, pump  300  can include fluid displacement components  44   a ,  44   b  (best seen in  FIG. 2B ), with diaphragms  74   a ,  74   b  (best seen in  FIG. 2B ) rigidly connected to piston  352  such that piston  352  drives fluid displacement components  44   a ,  44   b  through both suction and pumping strokes. In other examples, pump  300  can include fluid displacement components  144   a ,  144   b  ( FIG. 3 ) or fluid displacement components  244   a ,  244   b  ( FIG. 4 ) rigidly connected to piston  352  such that piston  352  drives fluid displacement components  144   a ,  144   b  or fluid displacement components  244   a ,  244   b  through both suction and pumping strokes. 
     Pump  300  provides significant advantages. Drive system  314  mechanically drives fluid displacement components  344   a ,  344   b  through both suction and pumping strokes. Mechanically driving fluid displacement components  344   a ,  344   b  provides increased efficiency by eliminating working fluids. As such, pump  300  can be utilized at locations where compressed air and/or hydraulic fluid is not readily available. In addition, fluid displacement components  344   a ,  344   b  being configured as pistons allows pump  300  to generate higher pumping pressures as compared to mechanically-driven diaphragms. 
       FIG. 8  is a cross-sectional view of pump  400 . Pump  400  includes inlet manifold  16 ; outlet manifold  18 ; end covers  22   a ,  22   b ; inlet check valves  24   a ,  24   b ; outlet check valves  26   a ,  26   b ; outer cylinders  46   a ,  46   b ; collars  48   a ,  48   b ; sealing rings  50   a ,  50   b ; fluid covers  220   a ,  220   b ; and fluid displacement components  444   a ,  444   b . Drive system  414  includes housing  128 , solenoid  202 , armature  204 , and intermediate members  446   a ,  446   b . Outlet manifold  18  includes elbows  19   a ,  19   b . Inlet manifold  16  includes elbows  19   c ,  19   d.    
     Pump  400  shown in  FIG. 8  is substantially similar to pump  200  shown in  FIG. 4 , except pump  400  shown in  FIG. 8  includes armature  204  that is rigidly connected to fluid displacement components  444   a ,  444   b  by intermediate members  446   a ,  446   b . Fluid displacement components  444   a ,  444   b  are substantially similar to fluid displacement components  244   a ,  244   b . Armature  204  is rigidly connected to fluid displacement components  444   a ,  444   b  such that armature  204  drives fluid displacement components  444   a ,  444   b  through both the suction and pumping strokes. Intermediate members  446   a ,  446   b  can be any desired component capable of transmitting forces both in tension and in compression. For example, intermediate members  446   a ,  446   b  can be threaded members configured to engage with threaded bores on both armature  204  and fluid displacement components  444   a ,  444   b . In other examples, intermediate members  446   a ,  446   b  can be pinned to armature  204  and fluid dispensing components  444   a ,  444   b ; can be formed integrally with one or both of fluid dispensing components  444   a ,  444   b  and armature  204 ; or can provide a rigid connection in any other manner suitable for transmitting both compressive and tensile forces between armature  204  and fluid displacement components  444   a ,  444   b.    
     Solenoid  202  is configured to drive armature  204  along pump axis A-A to cause armature  204  to drive fluid displacement components  444   a ,  444   b  through the suction and pumping strokes. The current supplied to solenoid  202  is configured to prevent overpressurization in the event that pump  400  is deadheaded during operation. The current is sufficient to drive armature  204 . However, when pumping chambers  90   a ,  90   b  are pressurized during the deadhead event, the process fluid pressure acts on fluid displacement components  444   a ,  444   b  and resists movement of armature  204  and overcomes the driving force provided by solenoid  202 . As such, the output pressure capable of being produced by pump  400  is dependent on the current powering solenoid  202  and the surface area of fluid displacement component  444   a ,  444   b  impacting the process fluid. 
     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.