Abstract:
A positive displacement pump includes two fluid flow paths, two center sections with a common fluid valve, a changeover valve, and three fluid displacement members. Each center section contains a diaphragm shaft, and the two sections are separated by the third diaphragm. In low-pressure mode the pump operates as a typical positive displacement pump with pumping fluid sup plied to one center section and the changeover valve allowing the fluid to freely circulate within the second center section. In high-pressure mode, the changeover valve is switched and the changeover valve allows the common fluid valve to supply pumping fluid to both center sections to drive the fluid displacement members therein, which generates a higher outlet fluid pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/915,874 filed on Dec. 13, 2013, and entitled “High Pressure AODD pump with High to Low Change Over Valve,” the disclosure of which is incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to positive displacement pumps, and more particularly to a high-pressure to low-pressure changeover valve for a positive displacement pump. 
         [0003]    A standard air operated diaphragm pump (AODD) utilizes a single housing, dual diaphragms, and compressed gas to drive a process fluid through the pump. In an AODD, two fluid displacement members, typically diaphragms, are joined by a shaft, and compressed gas is the working fluid in the pump. Compressed gas is applied to one of two pumping chambers, associated with the respective diaphragms. When compressed air is applied to the first pumping chamber, the first diaphragm is deflected into the first fluid cavity, which discharges the process fluid from that fluid cavity. Simultaneously, the first diaphragm pulls the shaft, which is connected to the second diaphragm, drawing the second diaphragm in and pulling process fluid into the second fluid cavity. Delivery of compressed gas is controlled by a valve, and the valve is usually actuated mechanically by the diaphragms. Thus, one diaphragm is pulled in until it causes the actuator to toggle the valve. Toggling the valve exhausts the compressed gas from the first pumping chamber and introduces fresh compressed gas to the second pumping 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. 
         [0004]    A high-pressure AODD operates similar to a typical AODD, but it has an additional diaphragm and two additional pumping chambers. In a high-pressure AODD, a second housing is attached to the first housing, with a central diaphragm disposed between the two housings. A high-pressure AODD has four pumping chambers and three diaphragms. During a first stroke compressed gas drives the first diaphragm and the central diaphragm towards the first fluid chamber, providing twice the output pressure of a standard AODD. On the reverse stroke, compressed gas drives the second diaphragm and the central diaphragm towards the second fluid chamber. 
       SUMMARY 
       [0005]    According to one embodiment of the present invention, a double displacement pump includes a first fluid cavity, a second fluid cavity, a primary pump, a secondary pump, a first fluid displacement member sealingly enclosing an end of the primary pump, a second fluid displacement member sealingly enclosing an end of the secondary pump, and a central fluid displacement member sealingly disposed between the primary pump and the secondary pump. The primary pump has a primary pumping chamber, a secondary pumping chamber, a first pilot valve disposed within the first pumping chamber, and a second pilot valve disposed within the second pumping chamber. The secondary pump has a third pumping chamber and a fourth pumping chamber. A connecting rod connects the first fluid displacement member, the second fluid displacement member, and the central fluid displacement member. A primary air inlet is mounted to the primary pump, and a secondary air inlet is mounted to the secondary pump. A changeover valve is attached to the primary air inlet. The changeover valve prevents pumping fluid from flowing to the third pumping chamber and the fourth pumping chamber when the double displacement pump is in a low-pressure mode, and the changeover valve allows pumping fluid to flow to third pumping chamber and the fourth pumping chamber when the double displacement pump is in a high-pressure mode. 
         [0006]    According to another embodiment of the present invention, a changeover valve includes a housing, a first manifold opening through the housing, a second manifold opening through the housing, and a changeover disk disposed within the housing. The changeover disk includes a first face, a second face, a first fluid flowpath extending between the first face and the second face, and a second fluid flowpath blocking flow between the first face and the second face. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a changeover valve. 
           [0008]      FIG. 2A  is an exploded view of a changeover valve in a low-pressure position. 
           [0009]      FIG. 2B  is an exploded view of a changeover valve in a high-pressure position. 
           [0010]      FIG. 3  is a cross-sectional view of a high pressure positive displacement pump. 
           [0011]      FIG. 4A  is a cross-sectional view of a high pressure positive displacement pump and changeover valve, with the positive displacement pump in a low-pressure mode. 
           [0012]      FIG. 4B  is a cross-sectional view of a high pressure positive displacement pump and changeover valve, with the positive displacement pump in a high-pressure mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  shows a perspective view of changeover valve  10 , primary manifold  12 , and handle  14 . Changeover valve  10  includes housing  16 , first manifold opening  18 , second manifold opening  20 , slot  22 , and openings  24 . Primary manifold  12  includes first slot  30 , second slot  32 , and exhaust slot  34 . 
         [0014]    Changeover valve  10  is secured to primary manifold  12  by bolts  36  extending through openings  24  in housing  16  and into primary manifold  12 . Handle  14  extends through slot  22  and engages changeover disk  38  (best seen in  FIG. 2 ). When handle  14  is in a first position, as shown, changeover disk  38  prevents compressed air from flowing from primary manifold  12  through either first manifold opening  18  or second manifold opening  20 , thus keeping the pump in a low-pressure mode. To switch changeover valve  10  from a low-pressure position to a high-pressure position, handle  14  is slid along slot  22  to second position (shown in dashed lines). In the second position, changeover disk  38  is aligned such that changeover disk  38  allows compressed air to flow from primary manifold  12  through first manifold opening  18  and second manifold opening  20 . 
         [0015]      FIG. 2A  is an exploded perspective view of changeover valve  10 , primary manifold  12 , and handle  14  with changeover valve  10  in a low-pressure position.  FIG. 2B  is an exploded perspective view of changeover valve  10 , primary manifold  12  and handle  14  with changeover valve  10  in a high-pressure position.  FIGS. 2A and 2B  will be discussed together. Changeover valve  10  includes housing  16 , first manifold opening  18 , second manifold opening  20 , slot  22 , openings  24 , changeover disk  38 , o-rings  40   a,    40   b,    40   c,  and  40   d,  and o-ring  42 . Changeover disk  38  includes first face  44 , second face  46 , two high-pressure flowpaths  48   a  and  48   b  extending from first face  44  to second face  46 , and circulatory flowpath  52  within first face  44 . Changeover disk  38  also includes grooves  54  disposed on first face  44  around the circumference of both high-pressure flowpaths  48   a  and  48   b.  Additionally, changeover disk includes groove  58  disposed around circulatory flowpath  52 . 
         [0016]    Primary manifold  12  includes bolt holes  60 , first high-pressure port  62 , and second high-pressure port  64 . Primary manifold  12  also includes groove  66  disposed around the circumference of high-pressure port  62 , and groove  68  disposed around the circumference of second high-pressure port  64 . Primary manifold  12  includes first slot  30 , second slot  32 , and exhaust slot  34 . 
         [0017]    Changeover valve  10  is secured to primary manifold  12  by bolts  36  extending through openings  24  and into bolt holes  60 . Changeover disk  38  is rotatably disposed within housing  16  with second face  46  adjacent primary manifold  12 . O-ring  40   a  is seated within groove  54 . O-ring  40   b  is seated within groove  56 . O-ring  42  is seated within groove  58 . Additionally o-ring  40   c  is seated within groove  66  and o-ring  40   d  is seated within groove  68 . Handle  14  extends through slot  22  and engages changeover disk  38 . 
         [0018]    Changeover valve  10  allows double displacement pump  70  (shown in  FIG. 3 ) to selectively operate in either a low-pressure mode or a high-pressure mode. Referring specifically to  FIG. 2A , in the low-pressure mode circulatory flowpath  52  is aligned with first manifold opening  18  and second manifold opening  20 . In the low-pressure mode, changeover disk  38  prevents pumping fluid from being pumped from first high-pressure port  62  through first manifold opening  18 . Changeover disk  38  also prevents pumping fluid from being pumped form second high-pressure port  64  through second manifold opening  20 . 
         [0019]    Referring specifically to  FIG. 2B , changeover disk  38  is shown in the high-pressure mode. To switch from low-pressure mode to high-pressure mode, handle  14  is moved along slot  22  and rotates changeover disk  38  to a high-pressure position. In the high-pressure position, changeover disk  38  is arranged such that high-pressure flowpath  48   a  is aligned with first high-pressure port  62  and first manifold opening  18 . In this way, high-pressure flowpath  48   a  provides a flowpath through which pumping fluid can be pumped from primary manifold  12  through first manifold opening  18 . Similarly, high-pressure flowpath  48   b  is aligned with second high-pressure port  64  and second manifold opening  20 . Thus, high-pressure flowpath  48   b  also provides a flowpath through which pumping fluid can be pumped from primary manifold  12  through second manifold opening  20 . 
         [0020]      FIG. 3  is a cross-sectional view of high pressure positive displacement pump  70 , primary manifold  12 , secondary manifold  72 , and fluid valve  74 . High pressure positive displacement pump  70  includes inlet manifold  76 , outlet manifold  78 , fluid covers  80   a  and  80   b,  inlet check valves  82   a  and  82   b,  outlet check valves  84   a  and  84   b,  primary pump  86  and secondary pump  88 , first fluid displacement member  90 , second fluid displacement member  92 , and central fluid displacement member  93 . Primary pump  86  includes first pumping chamber  94 , second pumping chamber  96 , primary connecting rod  98 , pilot valves  100   a  and  100   b,  first pumping fluid flowpath  102 , second pumping fluid flowpath  104 , and exhaust flowpath  106 . Secondary pump  88  includes third pumping chamber  108 , fourth pumping chamber  110 , plugs  112   a  and  112   b,  third pumping fluid flowpath  114 , fourth pumping fluid flowpath  116 , and secondary connecting rod  118 . 
         [0021]    Primary manifold  12  includes first high-pressure port  62 , second high-pressure port  64 , first pumping fluid flowpath  102 , second pumping fluid flowpath  104 , and exhaust flowpath  106 . Valve plate  26  includes first slot  30 , second slot  32 , and exhaust slot  34 . Secondary manifold  72  includes third pumping fluid flowpath  114 , fourth pumping fluid flowpath  116 , third high-pressure port  120 , and fourth high-pressure port  122 . Fluid valve  74  includes housing  124 , piston  126 , valve plate  26 , and cup  128 . 
         [0022]    First fluid displacement member  90  includes first set screw  130 , first diaphragm  132 , and first diaphragm plate  134 . Second fluid displacement member  92  includes second set screw  136 , second diaphragm  138 , and second diaphragm plate  140 . Central fluid displacement member  93 , includes third set screw  142 , central diaphragm  144 , third diaphragm plate  146 , and fourth diaphragm plate  148 . 
         [0023]    Inlet manifold  76  is attached to fluid cover  80   a  and fluid cover  80   b.  Inlet check valve  82   a  is disposed between inlet manifold  76  and fluid cover  80   a,  and inlet check valve  82   b  is disposed between inlet manifold  76  and fluid cover  80   b.  Similarly, outlet manifold  78  is attached to fluid cover  80   a  and fluid cover  80   b.  Outlet check valve  84   a  is disposed between outlet manifold  78  and fluid cover  80   a,  and outlet check valve  84   b  is disposed between outlet manifold  78  and fluid cover  80   b.  First fluid displacement member  90  is disposed between fluid cover  80   a  and primary pump  86 . First fluid displacement member  90  and fluid cover  80   a  define fluid cavity  150   a.  First fluid displacement member  90  sealingly encloses first pumping chamber  94 . Second fluid displacement member  92  is disposed between fluid cover  80   b  and secondary pump  88 . Second fluid displacement member  92  and fluid cover  80   b  define fluid cavity  150   b.  Second fluid displacement  92  sealingly encloses third pumping chamber  108 . Primary pump  86  is attached to secondary pump  88  with central fluid displacement member  93  disposed between primary pump  86  and secondary pump  88 . Central fluid displacement member  93  sealingly separates second pumping chamber  96  and fourth pumping chamber  110 . 
         [0024]    Primary manifold  12  is attached to primary pump  86 . Housing  124  is mounted to primary manifold  12 . Secondary manifold  72  is attached to secondary pump  88 . Valve plate  26  is disposed on primary manifold  12  and between housing  124  and primary manifold  12 . Valve plate  26  is disposed such that first slot  30  is aligned with first pumping fluid flowpath  102 , second slot  32  is aligned with second pumping fluid flowpath  104 , and exhaust slot  34  is aligned with exhaust flowpath  106 . First pumping fluid flowpath  102  extends through primary pump  86  and primary manifold  12  such that first pumping chamber  94  is in fluid communication with fluid valve  74 . Similarly, second pumping fluid flowpath  104  extends through primary pump  86  and primary manifold  12  such that second pumping chamber  96  is in fluid communication with fluid valve  74 . 
         [0025]    Piston  126  is slidingly disposed within housing  124 . Cup  128  is attached to piston  126 , and cup  128  is adjacent to valve plate  26 . As piston  126  reciprocates within housing  124 , cup  128  slides along valve plate  26 . Cup  128  provides a connection between either first pumping fluid flowpath  102  or second pumping fluid flowpath  104  and exhaust flowpath  106 . Fluid valve  74  allows pumping fluid to altematingly flow through first pumping fluid flowpath  102  and first high-pressure port  62  or second pumping fluid flowpath  104  and second high-pressure port  64 . 
         [0026]    Diaphragm  132  sealingly separates first pumping chamber  94  from a process fluid flowing through pump  70 . First diaphragm plate  134  is disposed on first diaphragm  132  and within first pumping chamber  94 . First set screw  130  extends through first diaphragm plate  134  and into diaphragm  132 , and first set screw  130  is attached to primary connecting rod  98 . Similarly, second diaphragm  138  sealingly separates third pumping chamber  108  from a process fluid flowing through pump  70 . Second diaphragm plate  140  is disposed on diaphragm  138  facing second pumping chamber  108 . Second set screw  136  extends through second diaphragm plate  140  and into second diaphragm  138 , and second set screw  136  is attached to secondary connecting rod  118 . Central diaphragm  144  sealingly separates second pumping chamber  96  and fourth pumping chamber  110 . Third diaphragm plate  146  is disposed on central diaphragm  144  and within second pumping chamber  96 . Fourth diaphragm plate  148  is disposed on central diaphragm  144  within fourth pumping chamber  110 . Third set screw  142  extends through third diaphragm plate  146 , central diaphragm  144 , and fourth diaphragm plate  148 . Third set screw  142  is attached to primary connecting rod  98  and secondary connecting rod  118 . 
         [0027]    Pumping fluid, usually a compressed gas, is provided to fluid valve  74  by an external compressor (not shown). While pumping fluid is described as a compressed gas, it is understood that pumping fluid may be any fluid suitable for driving first fluid displacement member  90 , second fluid displacement member  92 , and central fluid displacement member  93 , such as non-compressible hydraulic fluid. When pump  70  is in a low-pressure mode, pumping fluid alternatively flows through first pumping fluid flowpath  102  and charges first pumping chamber  94  and through second pumping fluid flowpath  104  and charges second pumping chamber  96 . During a first stroke, first pumping chamber  94  is filled with pumping fluid, first fluid displacement member  90  is displaced into fluid cavity  150   a.  Displacing first fluid displacement member  90  into fluid cavity  150   a  decreases the volume of fluid cavity  150   a,  which causes process fluid to be discharged from fluid cavity  150   a  through outlet manifold  78 . At the same time, primary connecting rod  98  pulls central fluid displacement member  93  thereby causing the volume of second pumping chamber  96  to decrease. Pumping fluid is exhausted from second pumping chamber  96  through second pumping fluid flowpath  104 , cup  128 , and exhaust flowpath  106 . When first fluid displacement member  90  is fully displaced, third diaphragm plate  146  contacts pilot valve  100   b,  which causes piston  126  to reciprocate within housing  124  such that cup  128  now forms an exhaust circuit with first pumping fluid flowpath  102  and exhaust flowpath  106 . 
         [0028]    During a second stroke, second pumping chamber  96  is filled with a pumping fluid. The pumping fluid pushes central fluid displacement member  93  into fourth pumping chamber  110 , and second fluid displacement member  92  is driven into fluid cavity  150   b  by central fluid displacement member  93  and secondary connecting rod  118 . This causes fluid cavity  150   b  to decrease in volume, which discharges process fluid from fluid cavity  150   b  through outlet manifold  78 . 
         [0029]    Similar to the first stroke, primary connecting rod  98  pulls first fluid displacement member  90  into first pumping chamber  94  thereby simultaneously decreasing the volume of first pumping chamber  94  and increasing the volume of fluid cavity  150   a.  Decreasing the volume of first pumping chamber  94  exhausts pumping fluid from first pumping chamber  94  through first pumping fluid flowpath  102 , cup  128 , and exhaust flowpath  106 . Increasing the volume of fluid cavity  150   a  draws process fluid into fluid cavity  150   a  from inlet manifold  76 . When central fluid displacement member  93  is fully displaced, first diaphragm plate  134  contacts pilot valve  100   a,  which causes piston  126  to reciprocate within housing  124  such that cup  128  now forms an exhaust circuit with second pumping flowpath  104  and exhaust flowpath  106 . 
         [0030]      FIG. 4A  is a cross-sectional view of changeover valve  10 , primary manifold  12 , secondary manifold  72 , fluid valve  74 , first pumping fluid manifold  152 , and second pumping fluid manifold  154  with changeover valve  10  in a low-pressure position.  FIG. 4B  is a cross-sectional view of changeover valve  10 , primary manifold  12 , secondary manifold  72 , fluid valve  74 , first pumping fluid manifold  152 , and second pumping fluid manifold  154  with changeover valve  10  in a high-pressure position.  FIG. 4A  and  FIG. 4B  will be discussed together. Changeover valve  10  includes housing  16 , first manifold opening  18 , second manifold opening  20 , openings  24 , and changeover disk  38 . Changeover disk  38  includes first face  44 , second face  46 , high-pressure flowpaths  48   a  and  48   b  extending from first face  44  to second face  46 , and circulatory flowpath  52  within first face  44 . 
         [0031]    Primary manifold  12  includes bolt holes  60 , first high-pressure port  62 , second high-pressure port  64 , first pumping fluid flowpath  102 , second pumping fluid flowpath  104 , and exhaust flowpath  106 . Valve plate  26  includes first slot  30 , second slot  32 , and exhaust slot  34 . Secondary manifold  72  includes third high-pressure port  120  and fourth high-pressure port  122 . Fluid valve  74  includes housing  124 , piston  126 , valve plate  26 , and cup  128 . 
         [0032]    Changeover valve  10  is mounted to primary manifold  12  by bolts  36  extending through openings  24  and into bolt holes  60 . Changeover disk  38  is rotatably disposed within housing  16  with second face  46  adjacent primary manifold  12 . First pumping fluid manifold  152  is attached to first manifold opening  18  and fourth high-pressure port  122 . Second pumping fluid manifold  154  is attached to second manifold opening  20  and third high-pressure port  120 . 
         [0033]    Primary manifold  12  is attached to primary pump  86 . Housing  124  of fluid valve  74  is mounted to primary manifold  12 . Secondary manifold  72  is attached to secondary pump  88 . Valve plate  26  is disposed on primary manifold  12  and between housing  124  and primary manifold  12 . Valve plate  26  is disposed such that first slot  30  is aligned with first pumping fluid flowpath  102 , second slot  32  is aligned with second pumping fluid flowpath  104 , and exhaust slot  34  is aligned with exhaust flowpath  106 . 
         [0034]    Piston  126  is slidingly disposed within housing  124 . Cup  128  is attached to piston  126 , and cup  128  is adjacent to valve plate  26 . As piston  126  reciprocates within housing  124 , cup  128  slides along valve plate  26 . Cup  128  provides a connection between either first pumping fluid flowpath  102  or second pumping fluid flowpath  104  and exhaust flowpath  106 . Fluid valve  74  allows pumping fluid to altematingly flow through first pumping fluid flowpath  102  and first high-pressure port  62  or second pumping fluid flowpath  104  and second high-pressure port  64 . 
         [0035]    Referring specifically to  FIG. 4A , when changeover valve is in a low-pressure position, circulatory flowpath  52  is in fluid communication with both first manifold opening  18  and second manifold opening  20 . Additionally, second face  46  sealingly covers both first high-pressure port  54  and second high-pressure port  56 . As described above, in a low-pressure mode, pumping fluid alternatively flows through first pumping fluid flowpath  102  and charges first pumping chamber  94  (shown in  FIG. 3 ) and through second pumping fluid flowpath  104  and charges second pumping chamber  96  (shown in  FIG. 3 ). During the low-pressure mode, when first pumping chamber  94  is charged, primary connecting rod  98  (shown in  FIG. 3 ) pulls central fluid displacement member  93  (shown in  FIG. 3 ) into second pumping chamber  96 , and secondary connecting rod  118  (shown in  FIG. 3 ) pulls second fluid displacement member  92  (shown in  FIG. 3 ) into third pumping chamber  108  (shown in  FIG. 3 ). When the volume of third pumping chamber  108  decreases, any pumping fluid contained in third pumping chamber  108  flows through second pumping fluid manifold  154 , through circulatory flowpath  52 , through first pumping fluid manifold  152 , and into fourth pumping chamber  110  (shown in  FIG. 3 ). 
         [0036]    On the reverse stroke, second pumping chamber  96  is charged, and the pumping fluid pushed central fluid displacement member  93  into fourth pumping chamber  110 , and secondary connecting rod thereby pushes second fluid displacement member  92  into fluid cavity  150   b,  thereby decreasing the volume of fourth pumping chamber  110  and increasing the volume of third pumping chamber  93 . During this stroke, pumping fluid contained in fourth pumping chamber  110  flows through first pumping fluid manifold  152 , through circulatory flowpath  52 , through second pumping fluid manifold  154 , and into third pumping chamber  108 . 
         [0037]    While pump  70  is in a low-pressure mode, no process fluid is being provided to third pumping chamber  108  or fourth pumping chamber  110 . During the low-pressure mode, any pumping fluid contained in secondary pump  88  circulates between third pumping chamber  108  and fourth pumping chamber  110  through first pumping fluid manifold  152 , second pumping fluid manifold  154 , and circulatory flowpath  52 . 
         [0038]    Referring specifically to  FIG. 4B , when changeover valve  10  is rotated to a high-pressure position, high-pressure flowpath  48   a  is aligned with first high-pressure port  62  and first manifold opening  18 , and high-pressure flowpath  48   b  is aligned with second high-pressure port  64  and second manifold opening  20 . In a high-pressure mode, pumping fluid flows through first pumping fluid flowpath  102  and first pumping fluid manifold  152  to charge both first pumping chamber  94  and fourth pumping chamber  110 . First pumping chamber  94  is charged by the pumping fluid flowing though first pumping fluid flowpath  102 , and fourth pressure chamber  110  is charged by the pumping fluid flowing to fourth pressure chamber  110  through first high-pressure port  62 , high-pressure flowpath  48   a,  first manifold opening  18 , first pumping fluid manifold  152 , and fourth high-pressure port  122 . 
         [0039]    Pumping fluid is exhausted from third pumping chamber  108  via third high-pressure port  120 , second pumping fluid manifold  154 , second manifold opening  20 , second high-pressure flowpath  48   b,  second high-pressure port  64 , second pumping fluid flowpath  104 , cup  128 , and exhaust flowpath  106 . Simultaneously, pumping fluid is also exhausted from second pumping chamber  96  through second pumping fluid flowpath  104 , cup  128 , and exhaust flowpath  106 . 
         [0040]    Similar to the low-pressure mode, the stroke changes over when first fluid displacement member  90  is fully displaced. When first fluid displacement member  90  is fully displaced, third diaphragm plate  144  contacts pilot valve  100   b,  which causes piston  126  to reciprocate within housing  124  such that cup  128  now operatively connects first pumping fluid flowpath  102  and exhaust flowpath  106 . The changeover valve  10  described herein provides several advantages. 
         [0041]    Changeover valve  10  allows pump  70  to operate in a low-pressure mode, which gives the pump a standard 1:1 outlet pressure to inlet pressure ratio. When the changeover valve  10  is shifted to a high-pressure position, the outlet pressure to inlet pressure ratio becomes 2:1. The ability to change from low-pressure mode to high-pressure mode enables the user to run the pump  70  at the low-pressure setting which gives the benefits of lower pumping fluid consumption. The changeover valve  10  allows the user to switch to a high-pressure mode by shifting a single valve when applications demand increased fluid pressure. The high-pressure mode allows for process fluid pressures higher than available inlet fluid pressures. 
         [0042]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.