Abstract:
Reciprocating pumps are disclosed. Particularly, reciprocating pumps including pressure chambers and fluid chambers defined by flexible members are disclosed. The volume of the pressure chambers and fluid chamber may be controlled using a piston driven by the flow of a control fluid to a pressure chamber and associated piston chamber. The flow of the control fluid may be directed to a first pressure chamber and associated piston chamber or a second pressure chamber and associated piston chamber. A pneumatically driven switch or an electrically driven switch may direct the flow of control fluid. The electrically driven switch may be controlled with a timer, a pressure sensor, or an optical sensor. The reciprocating pump requires minimal modification to permit the use of a pneumatic switch or electrical switch.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a reciprocating pump which may be pneumatically or electronically shifted. 
         [0003]    2. State of the Art 
         [0004]    Numerous industries and many applications utilize reciprocating pumps, particularly in the fluid industry. Reciprocating fluid pumps may include two fluid chambers. Each fluid chamber may include an associated pumping means, such as a piston, bellows, or diaphragm, which may be driven such that when one fluid chamber is being compressed to expel fluid, the other fluid chamber is expanded to receive fluid. The pumping means may include two pressure chambers, which alternate being filled with pressurized air and exhausting pressurized air. A reciprocating spool valve may operate the pumping means, shifting the pressurized air flow from one pressure chamber to the other as the pumping means reaches the end of a pumping stroke. A valve spool element in the spool valve may shift between two positions. The first position may supply pressurized air to the pressure chamber of one side of the pump while simultaneously exhausting the air from the pressure chamber on the other side of the pump. The shifting of the valve spool element simply alternates this pressurized air/exhaust between pressure chambers, driving the pumping means, thereby creating the reciprocating pumping action of the pump. 
         [0005]    The valve spool element may be shifted mechanically, electronically, or pneumatically. A conventional, mechanically shifted reciprocating pump is described in U.S. Pat. No. 4,902,206 to Nakazawa et al. A system of rods and actuating means may drive the spool valve element to the opposite position each time the pumping means reaches the end of its pumping stroke, causing a new pumping stroke to begin. Pressurized air is thus supplied to alternating pressure chambers. 
         [0006]    A conventional electronically actuated switching valve is described in U.S. Pat. No. 4,736,773 to Perry et al. An electronically actuated solenoid exhaust valve including pressure pilots on either side of a valve spool may be operable to cause a pressure drop in one pressure pilot on one side of the valve spool, causing the valve spool to change position. 
         [0007]    A conventional pump which uses solenoids to regulate the supply of pressurized air between pressure chambers is described in U.S. Pat. No. 6,079,959 to Kingsford et al. Pressurized air may be injected into a pressure chamber, or the supply of pressurized air to a pressure chamber may be terminated when a fiber optic sensor senses the desired travel of a piston driving the pressure chamber. 
         [0008]    A conventional pump having a pneumatically activated switching mechanism is described in U.S. Pat. No. 6,874,997 to Wantanabe et al. The switching mechanism of Wantanabe includes a rod having a bore formed in the axial direction extending from the base end to the tip. The bore has a top portion communicating with holes formed in the sidewalls. The holes in the sidewalls communicate with holes in a cylindrical case housing the rod when the rod is positioned in certain locations within the cylindrical case, namely near the end of a pump stroke. Pilot air or control fluid may pass through the bore within the rod, through the holes in the sidewall of the rod and the holes in the cylindrical case, and travel to a valve spool, causing the valve spool to change position, thereby switching the flow of pressurized air from one pressure chamber to the other. However, the bore and hole within the rod are difficult and expensive to manufacture, and lower the strength of the rod. 
         [0009]    It may be desirable in some instances to use a pneumatic or mechanically actuated switching mechanism, while an electronically activated switching mechanism may be desirable in other applications. For example, electrical switching of the spool valve may be prohibited in some situations because of the potential for spark and fire hazards generally associated with electric (i.e., spark generating) switching devices. 
         [0010]    A pump manufacturer may need to carry numerous parts to supply pneumatic, mechanical, and electronically controlled reciprocating pumps in order to meet the needs of different customers. Therefore, it would be advantageous to provide a pump system which requires only slight modification to be driven electronically or pneumatically. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    One embodiment of the present invention provides a reciprocating pump having a first pressure chamber at least partially defined by a first flexible member and a second pressure chamber opposing the first pressure chamber at least partially defined by a second flexible member. A first shift piston may drive the first flexible member. The first shift piston may comprise an elongated member including a first end portion having a first cross-sectional area and a central portion having a second cross-sectional area greater than the first cross-sectional area. 
         [0012]    In addition, a second shift piston may be included for driving the second flexible member. The second shift piston may comprise an elongated member including a first end portion having a first cross-sectional area and a central portion having a second cross-sectional area greater than the first cross-sectional area. A connecting member may effect reciprocating movement of the first flexible member and the second flexible member as the first pressure chamber and the second pressure chamber are alternately filled with control fluid. The supply of control fluid may be shifted from the first pressure chamber to the second pressure chamber with a pneumatically shifted spool valve. Alternatively, the spool valve may be electronically shifted. The electronic shifting may be actuated using a signal from an optical sensor. The shift piston may include a first portion bordered with contrasting color portions for sensing by the optical sensor. In other embodiments of the present invention, the electronic shifting may be actuated using a pressure sensor or a timer. 
         [0013]    In another aspect of the present invention, a method of driving a reciprocating pump includes providing a housing having a first pressure chamber and a second pressure chamber disposed therein, wherein the first pressure chamber is at least partially defined by a first flexible member and the second pressure chamber is at least partially defined by a second flexible member. The first pressure chamber may be filled with a control fluid, thus increasing the volume of the first pressure chamber. A first piston chamber may be filled with the control fluid, thus pressing a first shift piston at least partially housed within the first piston chamber against the first flexible member. Displacing the first shift piston creates a shift conduit between an outside surface of the first shift piston and an inside surface of the first piston chamber. A first shift line in communication with the shift conduit and the first piston chamber may be filled with the control fluid. Displacing the first shift piston eliminates communication between the first piston chamber and the first shift line. 
         [0014]    Displacing the first shift piston may be toward the first flexible member, and at least a portion of the first flexible member may be simultaneously displaced. Control fluid may be expelled from the second pressure chamber while simultaneously filling the first pressure chamber with the control fluid. Shifting a shuttle valve with a force generated by the flow of the control fluid from the first shift line will switch the flow of control fluid from the first pressure chamber to the second pressure chamber. Optionally, a pressure switch in communication with the first shift line may be signaled when the first shift line fills with control fluid. The flow of control fluid between the first pressure chamber and the second pressure chamber may be controlled with the pressure switch. In another embodiment, the displacement of the first shift piston may be optically sensed with an optical sensor, and the flow of control fluid between the first pressure chamber and the second pressure chamber may be controlled with a control switch in communication with the optical sensor. 
         [0015]    Another embodiment of a reciprocating pump may include a body defining a first fluid chamber and a first pressure chamber separated with a first flexible member and a second fluid chamber and a second pressure chamber separated with a second flexible member. A shaft may connect the first flexible member and the second flexible member. A switching mechanism may alternately supply control fluid to the first pressure chamber and the second pressure chamber, the first flexible member and the second flexible member displacing with the supplied control fluid. A first shift piston configured for displacement with the first flexible member may be driven by the supplied control fluid. The first shift piston may comprise an elongated member including a first end portion having a first cross-sectional area and a central portion having a second cross-sectional area greater than the first cross-sectional area. Likewise, a second shift piston may be configured for displacement with the second flexible member, driven by the supplied control fluid. The second shift piston may comprise an elongated member including a first end portion having a first cross-sectional area and a central portion having a second cross-sectional area greater than the first cross-sectional area. A first shift line may be in communication with the supplied control fluid when the first end portion of the first shift piston is adjacent thereto and isolated from the supplied control fluid when the central portion of the first shift piston is adjacent thereto. A second shift line may be in communication with the supplied control fluid when the first end portion of the second shift piston is adjacent thereto and isolated from the supplied control fluid when the central portion of the second shift piston is adjacent thereto. 
         [0016]    The switching mechanism of the reciprocating pump may be actuated by the supplied control fluid in the first shift line and the second shift line. Alternatively, the switching mechanism of the reciprocating pump may be actuated by a pressure sensor configured to detect the supplied control fluid in the first shift line and the second shift line. In yet another alternative, the switching mechanism may be actuated by an optical sensor configured to detect a first position and a second position of the first shift piston. Optionally, the switching mechanism may be actuated by an optical sensor configured to detect a first position of the first shift piston and a first position of the second shift piston, or with a timer. 
         [0017]    In yet another aspect of the present invention, a system of reciprocating pumps may comprise a control pump having a reciprocating shift piston with at least three bands of contrasting colors, an optical sensor configured to detect at least a first position, a second position, and a third position of the reciprocating shift piston, a shifting system in communication with the optical sensor, the shifting system configured to shift the supply of a control fluid from a first side of the control pump to a second side of the control pump, and a second pump controllable by the shifting system, the control fluid being alternately supplied to a first side of the second pump and a second side of the second pump from the shifting system. 
         [0018]    Other features and advantages of the present invention will become apparent to those of skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    The foregoing and other advantages of the present invention will become apparent upon review of the following detailed description and drawings in which: 
           [0020]      FIG. 1  shows a pneumatically actuated reciprocating pump according to the present invention; 
           [0021]      FIG. 2  shows the pneumatically actuated reciprocating pump of  FIG. 1  in another phase of a pump cycle; 
           [0022]      FIG. 3  shows a shift valve of the present invention in the phase of the pump cycle of  FIG. 2 ; 
           [0023]      FIG. 4  shows the shift valve of  FIG. 3  in the phase of a pump cycle of  FIG. 1 ; 
           [0024]      FIGS. 5A-5F  show close-up views of a shift mechanism according to the present invention in different phases of a pump cycle; 
           [0025]      FIG. 6  illustrates an optically controlled reciprocating pump according to the present invention; 
           [0026]      FIG. 7A  depicts another optically controlled reciprocating pump according to the present invention; 
           [0027]      FIG. 7B  shows a close-up view of the shift piston of the reciprocating pump of  FIG. 7A ; 
           [0028]      FIG. 8A  shows another embodiment of a reciprocating pump according to the present invention; 
           [0029]      FIG. 8B  shows a variation of the reciprocating pump of  8 A; 
           [0030]      FIG. 9  shows yet another embodiment of a reciprocating pump according to the present invention; 
           [0031]      FIG. 10A  shows an outside view of the shift valve of  FIGS. 3 and 4 ; 
           [0032]      FIG. 10B  shows an outside view of a reciprocating pump according to the present invention; 
           [0033]      FIG. 11  shows a cross-sectional view of a reciprocating pump according to the present invention with a shuttle valve built in; 
           [0034]      FIG. 12  shows an outside view of a reciprocating pump according to the present invention; and 
           [0035]      FIG. 13  shows a system of multiple reciprocating pumps of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    The shift piston according to the present invention may be used in a variety of reciprocating pump applications. The shift piston may be used with a pneumatically actuated spool valve or an electronically actuated spool valve controlled using fiber optics, pressure sensors, or a timer. Reciprocating pumps having mechanisms other than a spool valve, also known as a shuttle valve, for switching the flow of control fluid from one pressure chamber to another are also within the scope of the present invention. The shift piston may also be used in a reciprocating pump having stroke monitoring capabilities. 
         [0037]    A first embodiment of reciprocating pump  100  including a shift piston according to the present invention is depicted in  FIG. 1 . The pump  100  is generally symmetrically configured along a line  25  extending through the midpoint of a housing  50  thereof. The reciprocating pump  100  includes a fluid inlet port  110  and a fluid outlet port  120 . The fluid inlet port  110  and fluid outlet port  120  may be in communication with a first fluid chamber  130  and a second fluid chamber  140 . At the start position depicted in  FIG. 1 , fluid may be drawn into the first fluid chamber  130  through the fluid inlet port  110  and expelled from the second fluid chamber  140  through the fluid outlet port  120 . The fluid inlet and outlet ports may be operable by one-way valves, also known as check valves. One suitable example of a check valve is a ball valve, which may prevent mixing of the fluid being drawn into the reciprocating pump  100  and the fluid being expelled from the reciprocating pump  100 . 
         [0038]    The volume of the first fluid chamber  130  may be controlled by a first flexible member  160 . The first flexible member  160  may comprise, for example a diaphragm or a bellows which forms a first pressure chamber  150 . The term “flexible member” applies to members constructed entirely of flexible material, as well as members having rigid portions as well as flexible portions, such as the bellows depicted in  FIG. 1 . Any member or combination of members capable of forming an expandable and contractable chamber is within the scope of the present invention. 
         [0039]    A flow of a control fluid, for example pressurized air, into the first pressure chamber  150  as shown in  FIG. 2  may cause the first pressure chamber  150  to expand, and the first flexible member  160  to move rightward, reducing the volume of the first fluid chamber  130  and forcing the fluid out the fluid outlet port  120 . Likewise, a second flexible member  180  forming a second pressure chamber  170  may control the volume of a second fluid chamber  140 . The first flexible member  160  and the second flexible member  180  may be fixed relative to one another with a shaft  400 . As the first flexible member  160  is forced rightward by the flow of control fluid into the first pressure chamber  150 , the second flexible member  180  may be pushed rightward by the shaft  400 . The volume of the second fluid chamber  140  may increase, and the volume of the second pressure chamber  170  may decrease. Thus, fluid may be drawn into the second fluid chamber  140  through the fluid inlet port  110 . 
         [0040]      FIG. 1  depicts the pump  100  in a start position for a return stroke. Return is used for clarity in the description; however, it will be understood that the reciprocating pump may begin operation at any phase of any stroke. In a return stroke, fluid may be discharged from the second fluid chamber  140  through the fluid outlet port  120  and drawn into the first fluid chamber  130  through the fluid inlet port  110 . A flow of control fluid into the second pressure chamber  170  may cause the second pressure chamber  170  to expand, and the second flexible member  180  to move leftward, reducing the volume of the second fluid chamber  140  and forcing the fluid out of the fluid outlet port  120 . As the second flexible member  180  is forced leftward by the flow of control fluid into the second pressure chamber  170 , the first flexible member  160  may be pushed leftward by the shaft  400 . The volume of the first fluid chamber  130  may increase, and the volume of the first pressure chamber  150  may decrease. Thus, fluid may be drawn into the first fluid chamber  130  through the fluid inlet port  110 . 
         [0041]    In operation, the volume of the first pressure chamber  150  may be increased by control fluid entering from a first supply line  190  through a first primary supply port  200  as shown in  FIG. 2 . Control fluid from the first supply line  190  may also enter a first piston chamber  210  through a first secondary supply port  220 . The control fluid within the first piston chamber  210  may force a first shift piston  230  against a surface  165  of the first flexible member  160  facing the first pressure chamber  150 . Control fluid entering the first pressure chamber  150  and the first piston chamber  210  forces the first shift piston  230  and the first flexible member  160  to displace to the right, increasing the volume of the first pressure chamber  150  and decreasing the volume of the first fluid chamber  130 . 
         [0042]    The first flexible member  160  and the second flexible member  180  may be fixed relative to one another with a shaft  400 . The first flexible member  160  and the second flexible member  180  may be attached to the shaft  400 , such that both a pushing and a pulling force on either flexible member may be translated through the shaft  400 . Alternatively, the first flexible member  160  and the second flexible member  180  may merely abut the ends of the shaft  400 , such that a pushing force may be translated from one flexible member to the other via the shaft  400 . Thus, the first and second flexible members  160 ,  180  may be easily removed if the respective first or second housing end portion  60 ,  70  is removed. As the first flexible member  160  is forced rightward by the control fluid, the shaft  400  is displaced rightward, and the second flexible member  180  is pushed rightward by the shaft  400 . The volume of the second fluid chamber  140  increases, and the volume of the second pressure chamber  170  decreases. Control fluid within the second pressure chamber  170  is forced out of a second primary supply port  320 . 
         [0043]    At the end of a stroke, the control fluid must feed into the pressure chamber of the other side of the pump in order to initiate the next stroke. A spool valve  260  may shift the supply of control fluid from the first supply line  190  to the second supply line  390 . The spool valve  260  includes a shuttle spool  250  therein. The position of the shuttle spool  250 , and thus the supply of control fluid, may be shifted by a blast of control fluid or other methods such as electronic actuation. 
         [0044]      FIG. 3  depicts a close-up view of the spool valve  260  in a first position, the first position being the position of the phase of operation depicted in  FIG. 2 . Control fluid may be supplied to the first supply line  190 , and the second supply line  390  may be in communication with a second exhaust port  490 . Control fluid may be provided by a control fluid source, such as a pressurized air source (not shown) through air supply port  270 . The air supply port  270  may communicate with the first supply line  190  through a conduit  280   b  in the spool valve  260 . The spool valve  260  includes three conduits  280   a ,  280   b ,  280   c . Each conduit may comprise a gap positioned between an inner wall of the shuttle valve housing and a portion of the substantially cylindrical shuttle spool  250  with a lesser cross-sectional area. With the shuttle spool  250  in the first position, the first conduit  280   a  may be in communication with a first exhaust line  290 . The second conduit  280   b  may provide communication between the air supply port  270  and the first supply line  190 . The third conduit  280   c  may provide communication between the second supply line  390  and a second exhaust port  490 . Thus, referring back to  FIG. 2 , the control fluid may be supplied through the first supply line  190  to fill the first pressure chamber  150 . Simultaneously, air may be exhausted from the second pressure chamber  170  through the second supply line  390  to the second exhaust port  490 . 
         [0045]    With the shuttle spool  250  in a second position, as shown in  FIG. 4 , the first conduit  280   a  provides communication between the first supply line  190  and the first exhaust line  290 . The second conduit  280   b  provides communication between the between the air supply port  270  and the second supply line  390 . The third conduit  280   c  may communicate only with the second exhaust port  490 . Thus, referring back to  FIG. 1 , control fluid may be supplied through the second supply line  390  to fill the second pressure chamber  170 . Simultaneously, air may be exhausted from the first pressure chamber  150  through the first supply line  190 . 
         [0046]    The shuttle spool  250  may be shifted by a blast of control fluid through either a first shift line  240  or a second shift line  340 . The blast of control fluid may be provided at a longitudinal end of the shuttle spool  250 , which may displace the shuttle spool  250  in a longitudinal direction, shifting the communication positions of the conduits  280   a ,  280   b ,  280   c  from the first position to the second position. Turning to  FIGS. 5A through 5F , the first shift piston  230  may control the delivery of control fluid to the first shift line  240 .  FIGS. 5A through 5D  illustrate close-up views of the first shift piston  230  and first piston chamber  210  in different phases of a pump cycle. 
         [0047]    As previously described, when the first pressure chamber  150  is filled with control fluid, the control fluid may also enter the first piston chamber  210  through a first secondary supply port  220 . The control fluid within the first piston chamber  210  may force the first shift piston  230  against a surface  165  of the first flexible member  160 . As the control fluid enters the first pressure chamber  150  and the first piston chamber  210 , the first shift piston  230  and the first flexible member  160  displace to the right. Referring now to  FIG. 5A , a close-up view of the first shift piston  230  midway through a stroke to the right, direction A, the first shift piston  230  includes a shift portion  230   a  having a cross-sectional area less than a cross-sectional area of a central portion  230   b  of the first shift piston  230 . The cross-sectional area of the central portion  230   b  may be substantially the same as the cross-sectional area of the inside of the first piston chamber  210 , providing a seal between the first piston chamber  210  and the central portion of the first shift piston  230 . The cross-sectional area of the shift portion  230   a  of the first shift piston  230  may be less than the cross-sectional area of the inside of the first piston chamber  210 , which may provide a shift conduit  210   a  between the inside surface of the first piston chamber  210  and the outside surface of the shift portion  230   a  of the shift piston  230 , similar to the conduits created by the shuttle spool  250 . The shift conduit  210   a  is in communication with a main chamber  212  of the first piston chamber  210 , the main chamber  212  being the portion distal from the first flexible member, and always in communication with the first supply line  190 , through the first secondary supply port  220 . 
         [0048]    The shift conduit  210   a  may provide access to the first shift line  240  when the first shift piston  230  is displaced to the rightmost position as shown in  FIG. 5B , at the end of a stroke, with the first pressure chamber  150  expanded, and the fluid expelled from the first fluid chamber  130 . Thus, communication between the first piston chamber  210  and the first shift line  240  is provided at the end of a stroke. The control fluid within the first piston chamber  210  may travel through the first shift line  240  and provide a blast of control fluid within the spool valve  260 , shifting the shuttle spool  250  from the first position depicted in  FIG. 3  to the second position depicted in  FIG. 4 . The blast of control fluid may be provided at a longitudinal end of the shuttle spool  250 , which may displace the shuttle spool  250  in a longitudinal direction, shifting the communication positions of the conduits  280   a ,  280   b ,  280   c  from the first position ( FIGS. 2 and 3 ) to the second position ( FIGS. 1 and 4 ). Thus, the flow of control fluid is switched from the first supply line  190 , filling the first pressure chamber  150 , as shown in  FIG. 2 , to the second supply line  390 , filling the second pressure chamber  170 , as shown in  FIG. 1 . 
         [0049]    The first shift piston  230  may be configured as an elongated cylinder with the shift portion  230   a  on a first end, the central portion  230   b  with a diameter sufficient to create a seal within the first piston chamber  210 , and a vent portion  230   c  on a second end.  FIG. 5E  depicts a cross-sectional view of the first shift piston  230 , taken along line  5 E of  FIG. 5D . The cross-section of the shift portion  230   a  and the vent portion  230   c  of the first shift piston  230  depicted in  FIG. 5E  are circular. Thus, the first shift piston  230  comprises three cylindrical sections, arranged longitudinally end-to-end, about the same longitudinal axis, line x-x in  FIG. 5D . The shift portion  230   a  may have the smallest diameter, with the vent portion  230   c  having a larger diameter than the shift portion  230   a , yet a smaller diameter than the central portion  230   b . A shift portion  230   a  having a diameter larger than the diameter of the vent portion  230   c  is also within the scope of the present invention. 
         [0050]    In addition to creating the shift conduit  210   a , the shift portion  230   a  having a diameter smaller than the diameter of the central portion  230   b  also provides a pushing surface  231  (see  FIG. 5A ) on the longitudinal end of the central portion  230   b , surrounding the shift portion  230   a . The pushing surface  231  may be acted on by the control fluid within the first piston chamber  210 . As the control fluid fills the first piston chamber  210 , the increased pressure against the pushing surface  231  will force the first shift piston  230  to the right, in the direction of arrow A. 
         [0051]    It may be desirable for the shift portion  230   a  to have a diameter smaller than the diameter of the vent portion  230   c . If the pushing surface  231  has a greater area than an opposing surface  232  on the central portion  230   b , surrounding the vent portion  230   c , the force of any control fluid within the first piston chamber  210  on the pushing surface  231  will be greater than the force of the control fluid within the first pressure chamber  150  on the opposing surface  232 . Thus, the first shift piston  230  will be forced into the first pressure chamber  150  and against the first flexible member  160  as control fluid fills the first piston chamber  210  and the first pressure chamber  150 . 
         [0052]    The first shift piston  230  and the first piston chamber  210  may be formed of, for example, ceramic, and the outside diameter of the central portion  230   b  may be just smaller than the inside diameter of the first piston chamber. With a tight tolerance, an additional gasket will not be needed to form a seal between the first shift piston central portion  230   b  and the first piston chamber  210 . It will be understood that a shift piston including a seal is also within the scope of the present invention. Air, or control fluid, may provide a bearing between the first shift piston central portion  230   b  and the first piston chamber  210 , enabling the first shift piston  230  to reciprocate with minimum friction, and without wearing down either part. Likewise, the vent portion  230   c  of the first shift piston  230  may reciprocate within the portion of the first piston chamber  210  adjacent to the first pressure chamber  150 , forming a seal to prevent control fluid from traveling between the vent conduit  210   c  (described hereinbelow) and the first pressure chamber  150 . The vent portion  230   c  need not have a circular cross-section, as further described hereinbelow, however the outside perimeter of the vent portion  230   c  may be just smaller than the inside perimeter of the surrounding portion of the first piston chamber  210 . Thus, control fluid may provide a bearing therebetween. 
         [0053]      FIG. 5F  depicts an alternative embodiment of the shift piston cross-section. In the embodiment depicted in  FIG. 5F , the cross-section of the shift portion  230   a ′ and the vent portion  230   c ′ of the first shift piston  230 ′ are not circular, rather the shift portion  230   a ′ and the vent portion  230   c ′ with lesser cross-sectional areas are shown as portions of the elongated cylinder having a non-circular cross section. The shift portion  230   a ′ may be flattened to form a conduit for control fluid between the first piston chamber and the shift portion  230   a ′ of the shift piston  230 ′. The flattened portion may comprise opposing planar surfaces  232 ,  234  as shown in  FIG. 5F . Opposing arcing portions of the first shift piston  230 ′ may be truncated to form the flattened portions, or opposing planar surfaces  232 ,  234 . Thus the shift conduit  210   a ′ may be two parallel conduits within the first piston chamber  210 , on opposing sides of the shift portion  230   a ′ of the first shift piston  230 ′. Alternatively, only one arcing portion of the first shift piston  230 ′ may be truncated, with a single shift conduit  210   a ′ formed against one planar surface of the shift piston  230 ′. 
         [0054]    It is also within the scope of the present invention for the shift conduit  210   a ′ to be formed with a concave or convex surface on the shift portion  230   a ′ of the first shift piston  230 ′. Any shape or volume of the shift portion  230   a  is within the scope of the present invention, provided the first piston chamber  210  is not filled, and a shift conduit  210   a  is formed between the shift portion  230   a  and the first piston chamber  210 . In addition, it is within the scope of the present invention for the first piston chamber  210  and the first shift piston  230  to have a cross-section which is not circular, provided the central portion  230   b  of the first shift piston  230  may create a seal with the first piston chamber  210  and the shift portion  230   a  of the first shift piston  230  enables a shift conduit  210   a  between the inside surface of the first piston chamber and the outside surface of the first shift piston  230 . The shift piston may be made of one or more of a ceramic, plastic, polymeric materials, composites, metal, and metal alloys, for example. 
         [0055]    The second end of the first shift piston  230  may include the vent portion  230   c . The cross-sectional area of the vent portion  230   c  may be less than the cross-sectional area of the central portion  230   b  and the first piston chamber  210 . The vent portion  230   c  may be housed in a distal portion of the first piston chamber  210 , proximate to the first flexible member  160 . A vent conduit  210   c  is formed between the first piston chamber  210  and the vent portion  230   c  of the first shift piston  230 . The vent conduit  210   c  within the first piston chamber  210  may be vented to the exterior of the pump through a vent port  215  and a vent line  217  in a pump housing end cap  60 . As the first shift piston  230  displaces toward the right, as shown in  FIG. 5A , the central portion  230   b , or end cap, which has substantially the same cross-section as the interior of the first piston chamber  210 , may force air from the vent conduit  210   c  within the first piston chamber  210  through the vent port  215  and the vent line  217 .  FIG. 5B  depicts the first shift piston  230  in a later phase of a rightward stroke, with the shift piston  230  displaced to the right, and the volume of the vent conduit  210   c  of the first piston chamber substantially filled with the central portion  230   b  of the first shift piston  230 . 
         [0056]    As the pump begins the return stoke, with the shuttle spool  250  in the second position as shown in  FIG. 4 , control fluid may enter the second pressure chamber  170  and the second piston chamber  310 . (see  FIG. 1 ) The second shift piston  330  may be forced to the left by the control fluid in the second piston chamber  310 . A vent conduit within the second piston chamber  310  may be vented to the exterior of the pump through a vent port and a vent line  317  in the second end portion  70 . As the second shift piston  330  displaces to the left, a central body portion, which has substantially the same diameter as the interior of the second piston chamber, may force air from the vent conduit of the second piston chamber  310  through the vent port and the vent line  317 . Referring now to the first side of the pump, depicted on the left side in  FIG. 1 , and in an enlarged view in  FIG. 5C , the first shift piston  230  is forced to the left, direction C, by the surface  165  of the first flexible member  160 . The vent portion  230   c  of the first shift piston  230  provides the vent conduit  210   c  within the first piston chamber  210  in open communication with the vent port  215  and vent line  217 . 
         [0057]      FIG. 5C  depicts the first shift piston  230  mid-stroke, with the first fluid chamber  130  being filled with fluid and the control fluid within the first pressure chamber  150  being expelled. The first shift piston  230  is traveling to the left, in the direction of arrow C. Air from the exterior of the pump housing may be vacuumed into the vent conduit  210   c  of the first piston chamber  210 . Air within the main chamber  212  of the first piston chamber  210  may be expelled through the secondary port  220  to the first supply line  190 . As the first flexible member  160  is displaced to the left, air is also expelled to the first supply line  190  from the first pressure chamber  150  through the first primary supply port  200 .  FIG. 5D  depicts the first shift piston  230  displaced to the leftmost position, at the end of a stroke, with the first pressure chamber  150  contracted, and the first fluid chamber  130  filled. 
         [0058]    As the first shift piston  230  is displaced to the left, in the direction of arrows C and D in  FIGS. 5C and 5D , the first shift conduit  210   a  is also displaced to the left, and communication between the first shift conduit  210   a  and the first shift line  240  is closed. The central portion  230   b  of the first shift piston  230  fills the portion of the first shift conduit  210   a  with access to the first shift line  240 , eliminating the flow of control fluid from the main chamber  212  into the first shift line  240 . Thus, the first shift piston  230  enables control fluid to pass through the first shift conduit  210   a  and fill the first shift line  240  at the end of each stroke to the right, when the first pressure chamber is filled, then during the return stroke, the flow of the control fluid to the first shift line  240  is cut off by the central portion of the first shift piston  230 . Likewise, the second shift piston  330  enables control fluid to pass through a shift conduit in the second piston chamber and fill the second shift line  340  at the end of each stroke to the left, when the second pressure chamber is filled, then during the following stroke, the flow of the control fluid to the second shift line  340  is cut off by the central portion of the second shift piston. 
         [0059]    The first shift piston  230  is forced against the surface  165  of the first flexible member  160  facing the first pressure chamber  150  by the control fluid within the first piston chamber  210 . The first shift piston  230  may abut the surface  165  of the first flexible member  160  without being attached thereto, and be held in place by the pressure of the control fluid within the first piston chamber  210 . Alternatively, the first shift piston  230  may be affixed to the first flexible member  160 , for example with a threaded connection between the end of the first shift piston  230  and the first flexible member. Likewise, the second shift piston  330  may be attached to the second flexible member  180 , or may merely abut a surface thereof. 
         [0060]    In a second embodiment of the present invention, illustrated in  FIG. 6 , a reciprocating pump  500  may use an electronic shuttle valve or other switching mechanism  550  for switching the flow of control fluid from one pressure chamber to another. The first and second supply lines  190 ,  390  are not depicted in  FIG. 6  for simplicity. A pair of sensors  510   a ,  510   b  may optically detect the end of each stroke. The reciprocating pump  500  may draw fluid in through an input port  110 , and discharge fluid through an outlet port  120 . The first flexible member  160  and second flexible member  180  may be displaced in a reciprocating fashion, as control fluid fills a first pressure chamber  150  and simultaneously exhausts from a second pressure chamber  170 . The first shift piston  230  may travel within the first piston chamber  210 , displacing to the right as the first pressure chamber  150  is filled with control fluid, and displacing to the left as the air is exhausted. As the reciprocating pump  500  reaches the end of a stroke, the first shift piston  230  will pass by the first sensor  510   a . The first sensor  510   a  may comprise a pair of fiber optic sensors disposed through a conduit  560  in the pump housing end cap  60 . The conduit  560  in the housing terminates at the main chamber  212  of the first piston chamber  210  and is in optical communication therewith. The sensor  510   a  may detect the presence of the first shift piston  230  within the main chamber  212  of the first piston chamber  210 , signifying the end of a stroke.  FIG. 5D  depicts the first shift piston  230  within the main chamber  212  of the first piston chamber  210 . The sensor  510   b  may likewise detect the end of a stroke to the right, with the second shift piston  310  within the main chamber  312  of the second piston chamber  310 . 
         [0061]    A signal may be transmitted to a controller for a switching mechanism  550 , for example an electronically activated shuttle valve, to switch the flow of control fluid from one side of the pump to the other at the end of each stroke. The components of the previously described pneumatically actuated reciprocating pump  100  and the optically actuated reciprocating pump  500  may be identical, with the exception of the conduit  560  in the first pump housing end portion  60  and the conduit  570  in the second pump housing end cap  70  for the optical sensors  510   a ,  510   b.    
         [0062]    In a third embodiment of the present invention, illustrated in  FIGS. 7A-7B , a reciprocating pump  600  includes a sensor  510   a  on the first side of the pump  600 , aligned with the distal portion of the first piston chamber  610 . The first shift piston  630 , depicted in  FIG. 7B  includes longitudinally adjacent contrasting color portions  632 ,  634 ,  635  around the perimeter of one end thereof. The contrasting color portions may be different shades, detectable by an optical sensor. The first shift piston  630  may comprise an elongated member, and an outside contrasting color portion  632  may comprise a distal end thereof. A central contrasting color portion  635  may be a different shade around the perimeter of the first shift piston  630 , adjacent to the central contrasting color portion  635 . An inner contrasting color portion  634  may be located adjacent to the central contrasting color portion  635 , and is the contrasting color portion farthest from the longitudinal end of the first shift piston  630 . Outside contrasting color portion  632  and inner contrasting color portion  634  may be a matching shade, while central contrasting color portion  635  disposed longitudinally therebetween may comprise another shade. The sensor  510   a  may include a pair of fiber optic sensors positioned side-by-side to detect the passage of the first shift piston  630 . The outside contrasting color portion  632  passing under the sensor  510   a  may indicate the end of a first stroke of the reciprocating pump, such as the position of the first shift piston  230  depicted in  FIG. 5D . The inner contrasting color portion  634  passing under the sensor  510   a  may indicate the end of a second stroke of the reciprocating pump, such as the position depicted in  FIG. 5B . As either the outside or the inner contrasting color portion  632 ,  634  is sensed, a signal may be transmitted to a controller for a switching mechanism  550 , for example an electronically activated shuttle valve, to switch the flow of control fluid from one side of the pump to the other. 
         [0063]    The outside and the inner contrasting color portions  632 ,  634  may comprise, by way of example, black perfluoroalkoxy fluorocarbon resin disposed about the first shift piston  630 . The longitudinally adjacent contrasting color portions  632 ,  634 ,  635  may be formed integrally with the first shift piston  630 , or the longitudinally adjacent contrasting color portions  632 ,  634 ,  635  may comprise a cap, which may be an interference fit about the shift portion  630   a  of the first shift piston  630 . 
         [0064]    Returning to  FIG. 7A , a extended cap  601 , which may be formed of a translucent material, may be provided to extend the length of the first piston chamber. Thus, the length of the first shift piston  230  may be increased to accommodate the longitudinally adjacent contrasting color portions  632 ,  634 ,  635 , and still have room to reciprocate within the first piston chamber  210 . The extended cap  601  may be threaded to removably mate with the housing end portion  60 , and may be translucent to enable an optical pathway therethrough for the sensor  510   a.    
         [0065]    In a fourth embodiment of the present invention, illustrated in  FIG. 8A , a reciprocating pump  700  may have a pressure sensor  710   a ,  710   b  on each side of the pump to detect the end of a stroke and send a signal to an electronic shuttle. A first pressure sensor  710   a  may be mounted at the first shift line  240  to detect an increase in pressure at the end of a rightward stroke when the first shift piston is displaced to the right.  FIG. 8  shows a reciprocating pump  700  partially through a stroke; however a close-up view of the first shift piston displaced to the right at the end of a stroke is shown in  FIG. 5B . While  FIG. 5B  depicts a previously described embodiment of the present invention, the reciprocating movement of the shift pistons  230 ,  330  during each stroke may be replicated in each embodiment. At the end of a stroke expelling fluid from the first fluid chamber  130 , the first piston chamber  210  is filled with control fluid, and in communication with the first shift conduit  210   a  and the first shift line  240 . The increase in pressure within the first shift line  240  as it fills with control fluid may be detected by the first pressure sensor  710   a.    
         [0066]    A second pressure sensor  710   b  may be mounted at the second shift line  340  for detection of the end of a stroke to the left, expelling fluid from the second fluid chamber  140 . As the end of a stroke is detected by either the first or the second pressure sensor  710   a ,  710   b , a signal may be transmitted to a controller for a switching mechanism  550 , for example an electronically activated shuttle valve, to switch the flow of control fluid from one side of the pump to the other. 
         [0067]    A pressure sensor  710   a ,  710   b  may comprise, for example a diaphragm having strain gages mounted thereon. A pressure switch, for example a solid-state pressure switch may be useful. The solid-state pressure switch may comprise a polysilicon strain gauge in communication with an ASIC (Application Specific Integrated Circuit) to provide thermal compensated pressure sensing. The sensing results may be used to actuate a solid-state relay or transistor switch such as a piezoelectric transistor. One example of a suitable pressure switch is the DP2-41N digital vacuum and pressure sensor available from SUNX of Kasugai, Japan. 
         [0068]      FIG. 8B  depicts a variation of the fourth embodiment of the present invention. The reciprocating pump  700 ′ may have pressure sensors  710   a ′,  710   b ′ located remotely from the pump to detect the end of each stroke and send a signal to an electronic shuttle. Tubing  711   a ,  711   b  may connect the first shift line  240  and the second shift line  340  with the remote pressure sensors  710   a ′,  710   b ′. The remote pressure sensors  710   a ′,  710   b ′ may signal the switching mechanism  550  at the end of each stroke. 
         [0069]    In a fifth embodiment of the present invention, depicted in  FIG. 9 , a reciprocating pump  800  does not include stroke detection means. Rather, a timer  850  may be used to switch the flow of control fluid from one side of the pump to the other. The timer  850  may send the control fluid to each side for a predetermined length of time. That is, the timer  850  may send the control fluid through the first supply line  190 , filling the first pressure chamber  150  until the predetermined time has been reached, then the timer may switch the flow of control fluid to the second supply line  390 , filling the second pressure chamber  170 . The switching mechanism may be built into the timer  850 , or the switching mechanism may be located remotely from the timer  850 . The timer  850  may be useful to adjust the stroke length, thereby monitoring the fluid output. For example, by using the timer  850  to shorten the time of each stroke, and thus the stroke cycle, the fluid chambers  130 ,  140  will not completely fill and empty with each stroke. The fluid output may thus be lessened. Optional conduits  560  in the end caps  60 ′,  70 ′ provide a conduit for optional optical sensors to perform cycle counting for pump monitoring. The pump speed may also be monitored. 
         [0070]    In the event that the timer is not properly calibrated to switch the control fluid from one side to the other at the end of a stroke, the reciprocating pump may be vented to bleed the excess control fluid at the end of a stroke. If the excess control fluid is not vented, and for example, the first pressure chamber  150  continues to fill with control fluid at the end of the stroke, the first flexible member  160  may balloon and tear to release the excess control fluid. Referring back to  FIG. 1 , the portions of the first shift line  240  and the second shift line  340  in communication with the first shift chamber  210  and second shift chamber  310 , and passing through the first housing end portion  60  and the second housing end portion  70 , respectively, may be included in the reciprocating pump  800  depicted in  FIG. 9 . The portions of the first shift line  240  and the second shift line  340  through the housing end portions may provide vents at the end of each stroke. Referring to  FIG. 5B , at the end of a stroke to the right, if the control fluid continues to enter the pump through the first supply line  190 , the excess control fluid may enter the first piston chamber  210  through the first secondary supply port  220 . Because it is the end of the stroke, the first shift piston  230  is displaced to the right, and open communication is provided between the first shift chamber  210 , the shift conduit  210   a , and the first shift line  240 . The excess control fluid may thus vent through the first shift line  240 , which may be open to the outside atmosphere. 
         [0071]    A view of a housing  960  for a switching mechanism, for example a spool valve, is shown in  FIG. 10A . A view of a housing  950  for a reciprocating pump  900  of the present invention is shown in  FIG. 10B . A first port  910  and a second port  920  within the switching mechanism housing  960  may enable communication with pressure sensors  710   a ′ and  710   b ′, as shown in  FIG. 8B . The housing  960  may enable the switching mechanism to be located remotely from the body of the reciprocating pump  900 . 
         [0072]    Turning to  FIG. 10B , the housing  950  may include a central portion  50  housing the first fluid chamber  130  and the second fluid chamber  140 . A first housing end portion  60  may include the first piston chamber  210  therein, and may be threaded to removably attach to the central housing portion  50 . A second housing end portion  70  may include the second piston chamber  310  therein, and may be threaded to removably attach to the central housing portion  50 . Other methods of attaching the first and second housing end portions  60 ,  70  and the central housing portion  50  are within the scope of the present invention. For example, the housing portions  50 ,  60 ,  70  may be permanently attached with resin or epoxy, a weld, or the housing portions may have tight tolerances, and be friction fitted together. 
         [0073]    The central housing portion  50  may be generally cylindrical, and may be formed from plastic, polymeric materials, composites, metal, and metal alloys for example. The central housing portion  50  may be annular, forming the first fluid chamber  130  and the second fluid chamber  140  therein. The first end portion  60  may include the first piston chamber  210  therein, and include a threaded inner circumference  62  to engage with threads  52  on the circumference of the pump housing central portion  50  (see  FIG. 2 ). A second end portion  70  may include the second piston chamber  310  therein, and include a threaded inner circumference to engage with threads on the circumference of the pump housing central portion  50 . 
         [0074]    A seventh embodiment of the present invention is depicted in  FIG. 11 . A reciprocating pump  1000  includes a spool valve  1050  housed within a second end cap  70 ″ of the reciprocating pump  1000 . Conduits (not shown) within the housing of the pump may provide passage for the control fluid supply lines, which are depicted outside the pump housing in  FIGS. 1 and 2 . Including the spool valve  1050  within the pump housing, specifically within an end cap of the housing, enables the length of the fluid supply lines to be minimized, and the reciprocating pump may be transported more efficiently.  FIG. 11  depicts a pump configured for the use of an optical sensor  510   a , however a reciprocating pump having any actuating mechanism for the spool valve  1050  housed within the primary pump housing is within the scope of the present invention. For example, the pump may be shifted pneumatically, and the reciprocating pump  1000  may not include an optical sensor  510   a . In yet another example, the pump may be shifted pneumatically and the optical sensor may be useful for purposes such as pump monitoring. 
         [0075]      FIG. 11  depicts an optional truncated second shift piston  330 ′. The truncated second shift piston  330 ′ does not include a shift portion. Referring back to  FIG. 5A , the shift portion  230   a  is the portion of the first shift piston  230  extending into the main chamber  212  of the first piston chamber  210 . Turning back to  FIG. 11 , the stroke detection means for the reciprocating pump  1000  is the optical sensor  510   a , which detects the position of the first shift piston  230 . The second shift piston  330 ′ does not require a shift portion, as the position thereof is not being detected. The second piston chamber  310 ′ may thus be shorter than the second piston chamber  310  of the reciprocating pump  100  shown in  FIG. 1 . This may provide additional space within the second end cap  70 ″ for the spool valve  1050 . It will be understood by one skilled in the art that a truncated piston may be useful as both the first and the second shift piston in a reciprocating pump having pneumatic actuating means, as depicted in  FIGS. 1 and 2 , as well as reciprocating pumps having pressure sensors for stroke detection, as depicted in  FIGS. 8A and 8B , and reciprocating pumps having a timer, as depicted in  FIG. 9 . Use of a truncated piston may be useful to enable use of a shorter end cap, and thus the length of the entire pump may be shortened. 
         [0076]    In an eighth embodiment of the present invention, depicted in  FIG. 12 , a reciprocating pump  1100  including a spool valve  1050  in the head of the reciprocating pump  1000  is configured for the use of pressure switches for detection of the end of a stroke. Ports  1150   a ,  1150   b  in the end cap  60 ″ enable connection with the pressure switches. The pressure switches may be useful for pump monitoring, and one or two pressure switches may be used. A pressure switch on only one side of the pump may be sufficient for pump monitoring. Monitoring of the reciprocating pump  1000  may be useful, as the pump running faster or slower may be indicative of problems. For example, the pump may run faster if there is a hole in the bellows, or slow down if a filter backs up. The fluid inlet port  110  and the fluid outlet port  120  through the pump housing central portion  50 ′ are shown. The pump housing central portion  50 ′ is depicted with a rectangular cross-section; however, a cross-section of any geometrical configuration is within the scope of the present invention. 
         [0077]      FIG. 13  illustrates a system  1200  of multiple reciprocating pumps having a shifting system  1205  controlled by the movement of one control pump  1220  of the multiple reciprocating pumps. The system  1200  of multiple reciprocating pumps is integrated with staggered cycles, enabling reduced fluid surge in the system. When the control pump  1220  is at the end of a stroke as shown, a second pump  1230  may be at the pumping/exhaust cycle point in the cycle. At the end of the stroke, the control pump  1220  is not expelling fluid from the outlet port  120 A. At this time, the second pump  1230  is mid-stroke, and is expelling fluid from the outlet port  120 B. 
         [0078]    The control pump  1220  includes an optical sensor  1210  in communication with a shifting mechanism  1250  of the shifting system  1200 , and a first shift piston  1223  including at least three shaded bands  1224 ,  1225 ,  1226 . When the optical sensor  1210  detects the first shaded band  1224 , the shifting system  1205  may switch the control fluid for the control pump  1220  from a first side to a second side. This may momentarily pause the flow from the control pump outlet port  120 A; however the second pump  1230  will be mid-stroke, and steady flow from the second pump outlet port  120 B will be maintained. When the second shaded band  1225  is detected, the control fluid for the second pump  1230  may be switched from a first side to a second side. This may momentarily pause the flow from the second pump outlet port  120 B; however the control pump  1220  will be mid-stroke, and steady flow from the control pump outlet port  120 A will be maintained. When the third shaded band  1226  is detected, the control fluid for the control pump  1220  may be switched from a second side to a first side, and the shift piston  1223  will change directions. Steady flow from the second pump outlet port  120 B will cover the pause from the control pump outlet port  120 A. When the second shaded band  1225  is detected again, the control fluid for the second pump  1230  may be switched from the second side to the first side, and so on. Thus a more constant and uniform fluid flow from the multiple reciprocating pumps  1200  is enabled. It will be understood that a system of more than two reciprocating pumps with staggered cycles is within the scope of the present invention, with an additional shaded band added to the shift piston  1223  for each additional reciprocating pump. 
         [0079]    Although specific embodiments have been shown by way of example in the drawings and have been described in detail herein, the invention may be susceptible to various modifications, combinations, and alternative forms. Therefore, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, combinations, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.