Patent Publication Number: US-2002011579-A1

Title: Pressure processing a pumpable substance with a flexible membrane

Description:
CROSS REFERENCE TO RELATED APPLICATION  
     [0001] This application is a divisional of U.S. patent application Ser. No. 09/374,649, filed Aug. 13, 1999, now pending, which application is incorporated herein by reference in its entirety. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention relates to methods and devices for pressure processing pumpable substances, such as food or abrasive slurries, using a flexible membrane.  
       [0004] 2. Description of the Related Art  
       [0005] Conventional ultrahigh-pressure fluid systems have been used to pressurize pumpable substances, such as foods and slurries. For example, conventional ultrahigh-pressure systems have been used to improve the quality and longevity of food by subjecting the food to pressures in excess of 10,000 psi. Conventional systems have also been used to pressurize abrasive slurries to ultrahigh-pressure levels. The slurries can then be directed toward a substrate in the form of a liquid jet to cut the substrate or treat the surface of the substrate.  
       [0006] One conventional system includes a high-pressure cylinder with a slidable piston that divides the cylinder into two regions. The pumpable substance is placed in one region while a high-pressure fluid is introduced into the other region, driving the piston against the pumpable substance at a very high pressure. One potential drawback with this system is that as the piston may require specially designed seals to prevent the high-pressure fluid from being transported by the piston into the pumpable substance region. The seals may require periodic monitoring and replacement. Accordingly, it may be desirable to use an improved apparatus for pressurizing a pumpable substance while reducing the likelihood for contact between the pumpable substance and the pressurizing liquid.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] The invention relates to methods and apparatus for pressure processing a pumpable substance, such as a food substance. In one embodiment, the apparatus includes a generally rigid high-pressure vessel having a first opening toward one end, a second opening toward the other end, and an internal vessel wall between the first and second ends. A flexible membrane is disposed within the vessel and has a first membrane opening in fluid communication with the first open end of the vessel and a second membrane opening in fluid communication with the second opening of the vessel. At least a portion of the membrane is movable away from the vessel wall to pressurize a portion of the pumpable substance positioned adjacent to the membrane.  
       [0008] In one embodiment, the second membrane opening can be positioned beneath the first membrane opening so that the pumpable substance can exit the membrane through the second opening under the force of gravity. In another embodiment, valves are coupled to the first and second openings of the high-pressure vessel. In one aspect of this embodiment, the valves can each include a passage having a first portion with a first opening and second portion with a second opening. A piston is sealably positioned in the passage and axially movable within the passage between a closed position with the piston blocking fluid communication between the first and second openings and an open position with the first and second openings being in fluid communication with each other. The pumpable substance can be pumped into the membrane through the first opening, pressurized within the membrane by a high-pressure fluid disposed between the membrane and an inner wall of the vessel, and released from the pressure vessel through the second opening.  
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
     [0009]FIG. 1 is a partially schematic, partial cross-sectional side elevation view of an apparatus having an inlet valve, an outlet valve and a bladder in accordance with an embodiment of the invention.  
     [0010]FIG. 2 is a detailed partial cross-sectional side elevation view of an upper portion of the apparatus of FIG. 1 showing the inlet valve in its open position.  
     [0011]FIG. 3 is a detailed partial cross-sectional side elevation view of the upper portion of the apparatus of FIG. 1 showing the inlet valve in its closed position.  
     [0012]FIG. 4 is a detailed partial cross-sectional side elevation view of the lower portion of the apparatus of FIG. 1 showing the outlet valve in its closed position.  
     [0013]FIG. 5 is a partial cross-sectional side elevation view of the apparatus shown in FIG. 1 having an inlet valve in accordance with another embodiment of the invention.  
     [0014]FIG. 6 is a partial cross-sectional top view of the inlet valve of FIG. 5 shown in its open position.  
     [0015]FIG. 7 is a partial cross-sectional top view of the inlet valve of FIG. 5 shown in its closed position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0016] In general, conventional devices for pressure processing pumpable substances have been directed to high-pressure cylinders having an internal piston and/or having an inlet and outlet for the pumpable substance at one end of the cylinder and an inlet and outlet for the high-pressure fluid at the opposite end of the cylinder. By contrast, one aspect of the present invention includes a high-pressure cylinder having a flexible bladder with an entrance opening for the pumpable substance at one end of the bladder and an exit opening for the pumpable substance at the opposite end of the bladder. Accordingly, in one embodiment, the pumpable substance can be introduced through an inlet port at one end of the cylinder and removed from an outlet port at the opposite end of the cylinder, reducing the likelihood for contamination of the outlet port with unpressurized pumpable substance. The apparatus can also take advantage of gravitational forces to more completely remove the pumpable substance from the pressure vessel. Furthermore, by separating the inlet and outlet ports, each port can be larger, increasing the rate at which the pumpable substance can be moved into and out of the bladder, and increasing the size of pumpable substance constituents that can pass into and out of the bladder.  
     [0017] An apparatus  10  for pressure processing a pumpable substance in accordance with an embodiment of the invention is shown in FIG. 1. The apparatus  10  includes a pressure vessel  12  that receives the pumpable substance from a pumpable substance source  30  and pressurizes the pumpable substance with fluid supplied by a high-pressure fluid source  41 . The pressure vessel  12  can include an open-ended cylinder  13  surrounded by a protective cylindrical shield  14 . Two valve assemblies  20 , shown as an inlet valve assembly  20   a  and an outlet valve assembly  20   b,  cap opposite ends of the cylinder  13 , and are clamped against the cylinder  13  with a yoke  11 . A flexible bladder  50  is coupled between the valve assemblies  20 . The pumpable substance is pumped into the bladder  50  through the inlet valve assembly  20   a,  pressurized by high-pressure fluid entering the cylinder  13  from the high-pressure fluid source  41 , and pumped through the outlet valve assembly  20   b  to a receptacle  80 , as will be discussed in greater detail below.  
     [0018] In one embodiment, the pressure vessel  12  can include a model number 012122 assembly available from Flow International Corporation of Kent, Wash. that includes the cylinder  13 , the yoke  11  and the shield  14 , configured to withstand an internal vessel pressure of at least 100,000 psi. In other embodiments, the pressure vessel  12  can include other cylinders  13  and peripheral components configured to withstand an internal pressure of 100,000 psi or another suitable pressure, depending upon the selected pumpable substance and treatment. Such vessels and components are available from ABB Pressure Systems of Vasteras, Sweden, Autoclave Engineering of Erie, Pa., or Engineered Pressure Systems of Andover, Mass.  
     [0019] The pressure vessel  12  can include a liner  15  adjacent an inner surface of the cylinder  13 . The liner can be formed from stainless steel or other suitable materials that can withstand the high internal pressures within the cylinder  13 . In one embodiment, the liner  15  can be attached to the cylinder  13  by first heating the cylinder  13  so that it expands, then placing the cylinder  13  around the liner  15 , and then cooling the cylinder  13  so that it shrinks tightly around the liner  15 . If the liner  15  later becomes worn or damaged, it can be removed from the cylinder  13  and replaced with a similar liner. An advantage of this arrangement is that cracks that might result from the high pressure within the pressure vessel  12  will tend to form in the liner  15  rather than in the cylinder  13 , and it may be easier and less expensive to replace the liner  15  than the cylinder  13 .  
     [0020]FIG. 2 is an enlarged cross-sectional side elevation view of the upper portion of the apparatus  10  shown in FIG. 1. As shown in FIG. 2, the inlet valve assembly  20   a  fits partially within the cylinder  13  and includes a flow channel  31  having a radial portion  32  in fluid communication with an axial portion  33 . Both the radial portion  32  and the axial portion  33  can be strengthened or reinforced, for example, by passing through these portions a die having a slightly oversized diameter, or by using other known strengthening techniques. An inlet port  27   a  at one end of the radial portion  32  is coupled to the pumpable substance source  30  (FIG. 1). A bladder port  34  at the opposite end of the axial portion  33  is coupled to the bladder  50 . An inlet sealing piston  22   a  moves axially upwardly and downwardly within the axial portion  33  between an open position (shown in FIG. 2) in which the pumpable substance can pass into the bladder  50  and a closed position (discussed in greater detail below with reference to FIG. 3) in which the pumpable substance is sealed within the bladder  50 .  
     [0021] When the inlet valve assembly  20   a  is in its open position, the inlet sealing piston  22   a  is retracted upwardly into a sealing block  23 . An upper piston seal  70   a,  disposed annularly about the inlet sealing piston  22   a,  seals the interface between the inlet sealing piston  22   a  and the axial portion  33  of the flow channel  31  to at least restrict the pumpable substance from passing upwardly along the inlet sealing piston  22   a.  A lower fluid gap  38   a  extends annularly about the inlet sealing piston  22   a,  just above the upper piston seal  70   a,  for collecting and removing pumpable substance that might escape past the upper piston seal  70   a.  Purging fluid can be pumped through an upper inlet port  28   a  and into the lower fluid gap  38   a,  where it can entrain pumpable substance that might be present in the lower fluid gap  38   a.  The purging fluid and entrained pumpable substance can then be removed through an upper exit port  29   a.  In one embodiment, the purging fluid can include water, and in other embodiments the purging fluid can include iodine or other substances that sanitize the surfaces in contact with the purging fluid.  
     [0022] The inlet valve assembly  20   a  further includes a lower seal  70   b  beneath the upper seal  70   a.  When the inlet sealing piston  22   a  is in its open position (as shown in FIG. 2), the lower seal  70   b  is covered with a sleeve  74  that is biased upwardly by a sleeve spring  75 . The sleeve  74  protects the lower seal  70   b  from contact with the pumpable substance. The lower seal  70   b  is exposed and seals against the inlet sealing piston  22   a  when the inlet sealing piston  22   a  is moved to its closed position, as will be discussed in greater detail below.  
     [0023] The inlet sealing piston  22   a  is driven from its open position to its closed position by a driver piston  21  that moves axially within the sealing block  23 . Accordingly, the sealing block  23  includes a driver fluid port  25  that supplies pressurized fluid to the driver piston  21  to move the driver piston and the inlet sealing piston  22   a  together in a downward direction. The sealing block  23  itself can slide laterally along a block rail  24  to secure the inlet sealing piston  22  in the closed position. Accordingly, the sealing block  23  can include an actuator  26  that moves the sealing block  23  laterally back and forth along the block rail  24 .  
     [0024] In operation, the inlet sealing piston  22   a  moves downwardly from its open position to its closed position under the force of the driver piston  21 . As the inlet sealing piston  22   a  moves downwardly, it engages the sleeve  74 , forcing the sleeve downwardly against the resistance provided by the sleeve spring  75 . At this point, both the upper seal  70   a  and the lower seal  70   b  seal against the inlet sealing piston  22   a  and the inlet sealing piston  22   a  blocks communication between the radial portion  32  and the axial portion  33  of the flow channel  31 . The inlet sealing piston  22   a  continues to move in a downward direction until an end cap  35  at the upper end of the inlet sealing piston  22   a  is aligned with a cap engaging surface  36  of the sealing block  23 . The sealing block  23  then slides laterally as indicated by arrow A along the block rail  24  until the end cap  35  engages the cap retaining surface  36 . The inlet sealing piston  22   a  is accordingly secured in its closed position.  
     [0025] To open the valve  20   a,  the sealing block  23  is moved laterally as indicated by arrow B until the driver piston  21  is axially aligned with the inlet sealing piston  22   a.  The sleeve spring  75  then moves the sleeve  74  upwardly, and the sleeve  74  together with pressure from within the bladder  50  drive the inlet sealing piston  22   a  upwardly to its open position.  
     [0026]FIG. 3 is a cross-sectional side elevation view of the inlet valve  20   a  of FIG. 2 shown in the closed position. The inlet sealing piston  22   a  has moved downwardly in the axial portion  33  of the flow channel  31  and the sealing block  23  has moved laterally so that the cap engaging surface  36  engages the end cap  35  to prevent the inlet sealing piston  22   a  from moving in an upward direction. The inlet sealing piston  22   a  has moved the sleeve  74  downwardly so that the lower piston seal  70   b  engages the inlet sealing piston  22   a.  Accordingly, the lower fluid gap  38   a,  now positioned just above the lower piston seal  70   b,  is aligned with a lower inlet port  28   b  and a lower exit port  29   b  to remove pumpable substance from the lower fluid gap  38   a  in a manner generally similar to that discussed above with reference to FIG. 2. An upper fluid gap  38   b  is aligned with the upper inlet port  28   a  and the upper exit port  29   a  to operate in a manner similar to that discussed above with reference to FIG. 2. Accordingly, the inlet valve  20   a  can prevent the pumpable substance from escaping upwardly past the inlet sealing piston  22   a  when the inlet valve  20   a  is in its closed position and the bladder  50  is under pressure.  
     [0027] As shown in FIG. 3, the bladder  50  is attached to the sleeve  74  to receive the pumpable substance through the inlet valve  20   a.  In one embodiment, the bladder  50  includes an elongated tube having an upper opening  54 . The bladder  50  can be formed from rubber, neoprene or any flexible, generally nonporous material. In one embodiment, the bladder  50  can include a medical-grade rubber suitable for use with food products. In another embodiment, the bladder  50  can include an abrasion-resistant rubber or other abrasion resistant material for use with abrasive slurries. In still another embodiment, the bladder  50  can include a laminate of multiple plies bonded together with an adhesive, such as a rubber cement. One advantage of this embodiment is that the bladder  50  can separate the pumpable substance from the high-pressure fluid even if one or more of the plies has a pin hole or other puncture. Another advantage is that the multiple plies can thicken the bladder  50  and provide thermal insulation between the pumpable substance and the high-pressure fluid. Accordingly, hot or cold pumpable substances can be pressure processed in the pressure vessel  12  with a reduced transfer of heat to or from the pumpable substance.  
     [0028] A bladder fitting  51  extends through the upper opening  54  of the bladder  50  and is attached to the bladder  50  with a band  53  or alternatively, with a food-grade adhesive that discourages microorganism growth, or another suitable securing device. The bladder fitting  51  is then coupled to the sleeve  74  with a removable coupling  52 , such as are available from Tri-Clover, Inc., of Kenosha, Wis. In one embodiment, the bladder fitting  51  can be sized to take up a substantial volume within the cylinder  13 , thereby reducing the volume of high-pressure fluid required to pressurize the bladder  50  and reducing the time required to move the high-pressure fluid into and out of the cylinder  13 .  
     [0029]FIG. 4 is a cross-sectional side elevation view of the lower portion of the apparatus  10  shown in FIGS.  1 - 3 . As shown in FIG. 4, the bladder  50  includes a lower opening  55  attached to a bladder fitting  51  which is in turn coupled to a sleeve  74  of the outlet valve assembly  20   b.  In one embodiment, the bladder  50  can be stiffer near the lower opening  55  than near the upper opening  54  (FIG. 3) to prevent the bladder  50  from collapsing on itself near the lower opening  55  when the pumpable substance is removed. In one aspect of this embodiment, the stiffness of the bladder  50  can decrease in a generally uniform manner in an upward direction extending away from the outlet valve assembly  20   b.  In another aspect of this embodiment, the bladder  50  can be made stiffer near the lower opening  55  by increasing the number of plies that form the bladder  50  in this region.  
     [0030] The outlet valve assembly  20   b  includes an outlet sealing piston  22   b,  a driver piston  21  and a sealing block  23 , all of which operate in generally the same manner as was discussed above with reference to the inlet valve assembly  20   a  shown in FIGS. 2 and 3. Accordingly, the outlet valve assembly  20   b  is closed (as shown in FIG. 4) while the pumpable substance is pressurized, and is opened to allow the pressurized pumpable substance to pass out of the bladder  50 .  
     [0031] The outlet valve assembly  20   b  includes a high-pressure port  40  coupled to the high-pressure fluid source  41  (FIG. 1). The high-pressure fluid enters the pressure vessel  12  through the high-pressure port  40  at pressures up to and exceeding 100,000 psi, fills the region between cylinder  13  and the bladder  50 , and pressurizes the contents of the bladder  50 . In one embodiment, the high-pressure fluid can be water. Alternatively, the high-pressure fluid can be sterile citric acid or another sterile solution. In a further aspect of this embodiment, the high-pressure fluid can be selected to include water at an elevated temperature, for example, about 100° F. At such elevated temperatures, the ductility of the metal forming the cylinder  13  can be increased, as determined using a Charpy test or other ductility tests.  
     [0032] After pressurization, the pressurized pumpable substance can be removed through the outlet valve  20   b  by moving the outlet valve  20   b  to its open position and allowing the pumpable substance to pass through a pumpable substance exit port  27   b  to the receptacle  80  (FIG. 1). In one embodiment, the pumpable substance can exit the bladder  50  solely under the force of gravity. In one aspect of this embodiment, the inlet valve  20   a  is opened to a sterile environment at atmospheric pressure to allow the pumpable substance to descend from the bladder  50  under the force of gravity without introducing contaminants to the bladder  50 . In another embodiment, the pumpable substance can be squeezed from the bladder  50  by filling the pressure vessel  12  with a fluid at a relatively low pressure. In one aspect of this embodiment (best seen in FIG. 3), the pressure vessel  12  can include a low pressure valve  60  for transporting the low pressure fluid to and from the cylinder  13 .  
     [0033] The low pressure valve  60  (FIG. 3) can include a fluid passage  62  having a fluid port  61  at one end coupled to a source of the low pressure fluid (not shown). At the opposite end of the fluid passage  62  is a movable sealing ring  66  that can be moved between an open position (shown in FIG. 3) that allows fluid communication between fluid passage  62  and the interior of the cylinder  13 , and a closed position that prevents such fluid communication. In one embodiment, the sealing ring  66  is biased upwardly toward its closed position with a sealing ring spring  67 . The sealing ring  66  can be moved downwardly against the force of the sealing ring spring  67  to its open position by an actuating piston  65 . The actuating piston  65  can be positioned in a gas passage  64  and can move downwardly within the gas passage  64  when gas is supplied through a gas port  63 . To close the fluid passage  62 , the pressure at the gas port  63  is reduced, allowing the sealing ring spring  67  to move the sealing ring  66  and the actuating piston  65  upwardly until the sealing ring seals against the inlet valve assembly  20   a  and closes the fluid passage  62 .  
     [0034] In one embodiment, the fluid passage  62  is one of three fluid passages  62  coupled to the fluid port  61  and spaced 120° apart from each other around the sleeve  74 . Similarly, the gas passage  64  can be one of three gas passages  64  coupled to the gas port  63  and spaced 120° apart from each other around the sleeve  74 . In other embodiments, the low pressure valve  60  can include more or fewer fluid passages  62  and gas passages  64 . An advantage of having a plurality of gas passages  64  is that they more evenly distribute the force applied to the sealing ring  66 , reducing the likelihood that the sealing ring  66  will become cocked or tilted as it moves up and down. An advantage of having a plurality of fluid passages  62  is that the low pressure fluid can be more quickly and uniformly transported into and out of the cylinder  13 . In another embodiment, the outlet valve  20   b  (FIG. 4) can also include a low pressure valve generally similar to the low pressure valve  60  discussed above. An advantage of having two low pressure valves  60  is that the low pressure fluid can be even more quickly transported into and out of the cylinder  13 . A further advantage is that the inlet and outlet valves  20   a,    20   b  can be interchangeable.  
     [0035] Operation of an embodiment of the apparatus  10  is best understood with reference to FIG. 1. Initially, the outlet valve assembly  20   b  is closed by moving the outlet sealing piston  22   b  to its upper position (shown in FIG. 1) and the inlet valve assembly  20   a  is opened by moving the inlet sealing piston  22   a  to its upper position (shown in FIG. 1). The pumpable substance is pumped through the inlet valve assembly  20   a  and into the bladder  50 . The inlet valve assembly  20   a  is then closed by moving the inlet sealing piston  22   a  downwardly and high-pressure fluid is pumped through the high-pressure port  40  of the outlet valve assembly  20   b.  The high-pressure fluid fills the space between the bladder  50  and the liner  15  and biases the bladder  50  inwardly to pressurize the pumpable substance within the bladder  50 . The pumpable substance is then pressurized for a selected period of time.  
     [0036] Turning now to FIG. 3, the low pressure valve  60  is opened by forcing gas through the gas passage  64  to move the actuating piston  65  against the sealing ring  66 . As the sealing ring  66  moves away from the fluid passage  62 , high-pressure fluid escapes through the fluid passage  62  and out through the fluid port  61 . The outlet valve  20   b  (FIG. 1) is then opened and fluid is supplied at low pressure through the low pressure valve  60  to collapse the bladder  50  and force the pressurized pumpable substance out through the outlet valve  20   b.  Once the bladder  50  has collapsed, the apparatus  10  is ready to pressure process a new batch of pumpable substance. After a selected number of pressure cycles, the bladder  50  can be cleaned, for example, by passing through the bladder (in succession) a rinse solution, a caustic solution, hot water, a chemical sterilizer and citric acid.  
     [0037] An advantage of an embodiment of the apparatus  10  shown in FIGS.  1 - 4  is that the bladder  50  can eliminate contact between the pumpable substance and the high-pressure fluid. Accordingly, the likelihood that that pumpable substance will be contaminated with high-pressure fluid (and vice versa) is substantially reduced. A further advantage is that the inlet valve  20   a  is separated by a substantial distance from the outlet valve  20   b,  reducing the likelihood of contaminating the pressurized pumpable substance with unpressurized pumpable substance. Furthermore, by positioning the outlet valve  20   b  beneath the inlet valve  20   a,  the apparatus  10  can take advantage of gravity to remove the pressurized pumpable substance from the vessel  12 . Accordingly, a greater portion of the pumpable substance can be removed from the vessel  12  after pressurization.  
     [0038] Yet another feature of the apparatus  10  is that the flow passages  31  through the valves  20  can have relatively large cross-sectional areas. This is advantageous because it allows the pumpable substance to enter and exit the vessel  13  more quickly. It also allows pumpable substances having chunks or large suspended particles to be more easily directed into and out of the vessel  13 . For example, when the apparatus  10  is used to pressure process chunks of fruit, such as pineapples, the flow passages  31  can have diameters of about one inch. In other embodiments, the flow passages can have other diameters to accommodate chunks of pumpable substance having other dimensions.  
     [0039] Still another advantage is that the movable sleeve  74  can reduce the likelihood of exposing at least one of the piston seals  70   b  to the pumpable substance. Accordingly, the pumpable substance is less likely to become trapped in the piston seal  70   b.  Yet another advantage is that the flow of purging fluid alongside the pistons  22  can further reduce the likelihood of pumpable substance escaping from the vessel  12  when the vessel  12  is under pressure.  
     [0040] In the embodiment discussed above with reference to FIGS.  1 - 4 , the pumpable substance is placed within the bladder  50  and the high-pressure fluid is disposed between the bladder  50  and the inner walls of the cylinder  13 . In another embodiment, the pumpable substance can be positioned between the bladder  50  and the inner walls of the cylinder  13  while the high-pressure fluid is disposed within the bladder  50 . An advantage of placing the pumpable substance in the bladder  50  is that it may be easier to remove the pumpable substance from within the bladder  50  than from between the bladder  50  and the walls of the cylinder  13 .  
     [0041]FIG. 5 is a cross-sectional side elevation view of the upper portion of the apparatus  10  shown in FIG. 1 having an inlet valve  120   a  in accordance with another embodiment of the invention. The inlet valve  120   a  includes a low pressure valve  160  generally similar in appearance and operation to the low pressure valve  60  discussed above with reference to FIG. 3. The inlet valve assembly  120   a  further includes a flow channel  131  having an axial portion  133  connected to a radial portion  132 . One end of the axial portion  133  is closed with a plug  139 , and the other end is coupled to the bladder  50 . As will be discussed in greater detail below, fluid communication between the axial portion  133  and the radial portion  132  can be opened or closed by moving a piston within the radial portion  132 .  
     [0042]FIG. 6 is a top, partial cross-sectional view of the inlet valve  120   a  shown in FIG. 5. As shown in FIG. 6, the inlet valve  120   a  includes a sealing piston  122  that moves laterally within the radial portion  132  of the flow channel  131 . When the sealing piston  122  is in its leftmost position (shown in FIG. 6) the pumpable substance can pass from the radial portion  132  of the flow channel  131  to the axial portion  133  and into the bladder  50  (FIG. 5). When the sealing piston  122  is in its rightmost position (discussed in greater detail below with reference to FIG. 7), the sealing piston  122  prevents fluid communication between radial portion  132  and the axial portion  133 .  
     [0043] The sealing piston  122  is sealed within the radial portion  132  with two piston seal assemblies  170 , shown as a left piston seal assembly  170   a  and a right piston seal assembly  170   b.  The right piston seal assembly  170   b  is covered with a sleeve  174  when the inlet valve is in its open position (as shown in FIG. 6). The sleeve  174  is biased toward the covered position by a sleeve spring  175  when the inlet valve  120   a  is in the open position, in a manner generally similar to that discussed above with reference to the sleeve  74  shown in FIG. 2. The sleeve  174  includes an inlet port  127   a  coupled to the pumpable substance source  30  (FIG. 1) with a flexible conduit  126 . Accordingly, the conduit  126  can maintain the connection between the pumpable substance source  30  and the inlet port  127   a  as the sleeve  174  moves laterally.  
     [0044] The seal assemblies  170  can include a seal  171  that extends between the sealing piston  122  and the walls of the radial portion  132  of the flow channel  131 . The seal assemblies  170  can also include an O-ring  172 , an anti-extrusion ring  173  to prevent the seal  171  from extruding outwardly away from the radial portion  132 , and a backup ring  176  to support the seal  171  and the anti-extrusion ring  173 . This seal assembly arrangement, shown in detail in FIG. 6, can also be used in conjunction with the seals  70   a,    70   b  shown in FIGS.  1 - 4 .  
     [0045] A driver piston  121  connected to one end of the sealing piston  122  drives the sealing piston  122  laterally within the radial portion  132 . The driver piston  121  moves within a driver cylinder  123  which can include two driver fluid ports  125  (shown as a left port  125   a  and a right port  125   b ). When pressurized fluid is supplied to the right port  125   b,  the driver piston  121  and the sealing piston  122  move to the left toward the open position. When pressurized fluid is supplied to the left port  125   a,  the driver piston  121  and the sealing piston  122  move to the right toward the closed position.  
     [0046]FIG. 7 is a top, partial cross-sectional view of the inlet valve assembly  120   a  shown in FIG. 6 with the sealing piston  122  and the driver piston  121  moved to the closed position. As shown in FIG. 7, the sealing piston  122 , when in the closed position, prevents fluid communication between the radial portion  132  and the axial portion  133  of the flow channel  131 . Accordingly, the sealing piston  122  can prevent pumpable substance from escaping from the cylinder  13  when the cylinder is pressurized.  
     [0047] When the sealing piston  122  is in the closed position, it engages the sleeve  174  and moves the sleeve  174  to the right (as seen in FIG. 7) until the sealing piston  122  seals against the right seal assembly  170   b.  Fluid gaps  138  (shown as a left fluid gap  138   a  and a right fluid gap  138   b ) adjacent the sealing piston  122  receive purging fluid from inlet ports  128  (shown as a left inlet port  128   a  and a right inlet port  128   b ) to purge the region adjacent the seals  170 . The purging fluid, with pumpable substance entrained, can be removed through exit ports  129   a  and  129   b  in a manner generally similar to that discussed above with reference to the fluid gaps  38  shown in FIGS. 2 and 3.  
     [0048] From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. For example, the liner  15  can be disposed in a high-pressure vessels that include means other than the bladder  50  for pressurizing the pumpable substance. Accordingly, the invention is not limited except as by the appended claims.