Patent Publication Number: US-11035477-B2

Title: Knife gate valve liner

Description:
RELATED APPLICATIONS 
     This application is a divisional of co-pending U.S. patent application Ser. No. 16/210,880, filed on Dec. 5, 2018, which is a divisional of U.S. patent application Ser. No. 15/171,918, filed on Jun. 2, 2016, which claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 62/170,602 filed on Jun. 3, 2015, and to U.S. Provisional Patent Application No. 62/190,099 filed on Jul. 8, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Gate valves or knife gate valves are used to control the flow of fluid, such as process fluid, in a pipeline. These valves include a housing having a fluid passageway and a moveable gate for opening or closing the fluid passageway. The gate is configured to slide within a liner located within the housing. In an open position, the gate is moved to allow flow through the fluid passageway between inlet and outlet ports of the valve. In a closed position, the gate is moved to close the fluid passageway and inhibit flow. The liner is usually one-piece and completely lines the inside of the valve. One-piece liners prevent the metal portion of the valve body from wearing through. For “cast in place” liners, once these liners wear out, the valve is usually thrown away. 
     SUMMARY OF THE INVENTION 
     Some embodiments of the invention provide a housing assembly for a knife gate valve. The housing assembly includes a valve body assembly that defines a passageway having an axis and having a first body and a second body, each having a flange recessed portion that extends toward the axis and defines a flange recess surface that is recessed axially relative to a flange surface. Each of the flange recess surfaces includes a first flange surface portion, a second flange surface portion, and a raised flange bead arranged between the first flange surface portion and the second flange surface portion. The first flange surface portion and the second flange surface portion being coplanar and extending in a direction that is transverse to the axis. The housing assembly further includes a one-piece liner arranged between the first body and the second body and having a first liner flanged portion that forms a first liner recess and a second liner flanged portion that forms a second liner flanged portion. The first liner recess receives the flange recessed portion of the first body so that the first liner flanged portion extends around the flange recessed portion of the first body to bring the raised flange bead of the first body into engagement with the first liner flanged portion. The second liner recess receives the flange recessed portion of the second body so that the second liner flanged portion extends around the flange recessed portion of the second body to bring the raised flange bead of the second body into engagement with the second liner flanged portion. 
     Some embodiments of the invention provide a housing assembly for a knife gate valve. The housing assembly includes a valve body assembly that defines a passageway having an axis and having a first body and a second body, each of the first body and the second body includes a flange surface and a flange recessed portion that protrudes radially inward relative to the flange surface. Each flange recess portion includes a first flange surface portion, a second flange surface portion, and a raised flange bead arranged between the first flange surface portion and the second flange surface portion. The housing assembly further includes a one-piece liner arranged between the first body and the second body and defining a gate slot. The one-piece liner includes a first liner bore surface, a first liner flange, a second liner bore, and a second liner flange. The gate slot extends along a first gate surface in engagement with the first body and a second gate surface in engagement with the second body. The first liner bore surface extends axially away from the first gate surface and the first liner flange extends from the first liner bore surface radially away from the axis, opposite the first gate surface, to define a first liner recess that receives the flange recessed portion of the first body to bring the first liner flange into engagement with the raised flange bead of the first body. The second liner bore surface extends axially away from the second gate surface and the second liner flange extends from the second liner bore surface radially away from the axis, opposite the second gate surface, to define a second liner recess that receives the flange recessed portion of the second body to bring the first liner flange into engagement with the raised flange bead of the second body. 
     Some embodiments of the invention provide a housing assembly for a knife gate valve. The housing assembly includes a valve body assembly that defines a passageway having an axis and having a first body and a second body each having a flange recessed portion that extends toward the axis and that defines a flange recess surface that is recessed axially relative to a flange surface. Each flange recess surface includes a first flange surface portion, a second flange surface portion, and a raised flange bead arranged between the first flange surface portion and the second flange surface portion. The housing assembly further includes a one-piece liner arranged between the first body and the second body and including a first liner bore surface, a first liner flange, a second liner bore surface, and a second liner flange. The first liner flange extends at least partially along and in engagement with the first flange surface portion, the raised flange bead, and the second flange surface portion of the first body. a radial gap is formed between a distal end of the first liner flange and a radially-inner edge of the flange surface of the first body. The second liner flange extends at least partially along and in engagement with the first flange surface portion, the raised flange bead, and the second flange surface portion of the second body. A radial gap is formed between a distal end of the second liner flange and a radially-inner edge of the flange surface of the second body. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a knife gate valve according to one embodiment of the invention. 
         FIG. 2  is a front view of the knife gate valve of  FIG. 1 . 
         FIG. 3  is an exploded perspective view of a valve body assembly and a gate of the knife gate valve of  FIG. 1 . 
         FIG. 4  is a cross-sectional view of the knife gate valve of  FIG. 3  taken along line  4 - 4  with the gate in a first position. 
         FIG. 5  is a cross-sectional view of the knife gate valve of  FIG. 1  taken along line  5 - 5 . 
         FIG. 6  is a front view of a portion of a liner of the knife gate valve of  FIG. 1  according to one embodiment of the invention. 
         FIG. 7  is a graph illustrating a relationship between a percent decrease from a maximum protrusion height H max  and distance along a first and second radial sealing bead of a liner of the knife gate valve of  FIG. 1  according to one embodiment of the invention. 
         FIG. 8  is a front view of a portion of a liner of the knife gate valve of  FIG. 1  according to another embodiment of the invention. 
         FIG. 9  is a graph illustrating a relationship between a percent decrease from a maximum protrusion height H max  and distance along a first and second radial sealing bead of a liner of the knife gate valve of  FIG. 1  according to another embodiment of the invention. 
         FIG. 10  is a cross-sectional view of the knife gate valve of  FIG. 3  taken along line  4 - 4  with the gate in a first position. 
         FIG. 11  is a cross-sectional view of the knife gate valve of  FIG. 3  taken along line  4 - 4  with the gate in a second position. 
         FIG. 12  is a cross-sectional view illustrating a pipe coupled to the knife gate valve of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
       FIG. 1  illustrates a knife gate valve  10  according to one embodiment of the invention. The knife gate valve  10  includes a valve body assembly  14 , a gland assembly  18  and a gate actuation mechanism  22 . The valve body assembly  14  includes a first body half  26   a,  a second body half  26   b  symmetrical to the first body half  26   a,  and a liner  30  arranged between the first body half  26   a  and the second body half  26   b.  The valve body assembly  14  defines a passageway  34  having an axis  38  along which process fluid can flow bi-directionally. 
     The first and second body halves  26   a,    26   b  are symmetric, and the following description of the first body half  26   a  also applies to the second body half  26   b.  The first body half  26   a  and the second body half  26   b  include similar features which are identified with like reference numerals and distinguished by the suffix “a” and “b” in the figures. As shown in  FIG. 3 , the first body half  26   a  includes a plurality of joining apertures  42   a,  a flange portion  46   a , and a gland portion  50   a.  The plurality of joining apertures  42   a  are each arranged to align with a corresponding joining aperture  42   b  on the second body half  26   b.  The joining apertures  42   a,    42   b  are each configured to receive a fastening element  54  (see  FIG. 1 ) for joining the first body half  26   a  and the second body half  26   b.  In one embodiment, the fastening elements  54  are bolts secured by nuts. The first body half  26   a  and the second body half  26   b  are fabricated from a metal material, such as iron, stainless steel, or other ferrous or non-ferrous alloys. 
     As shown in  FIG. 4 , the flange portion  46   a  of the first body half  26   a  includes a flange surface  58   a  and a flange recessed portion  62   a  protruding radially inward towards axis  38  relative to the flange surface  58   a.  The flange surface  58   a  includes a plurality of flange apertures  66   a  (see  FIG. 2 ) arranged radially around the flange surface  58   a,  which enables first body half  26   a  to couple to a pipe (not shown) through which the process fluid flows. The flange recessed portion  62   a  defines a valve bore B v  and a flange recess surface  74   a  arranged substantially parallel to and recessed from the flange surface  58   a.  The flange recess surface  74   a  includes a first flange surface portion  75   a,  a second flange surface portion  76   a,  and a raised flange bead  78   a  arranged between the first flange surface portion  75   a  and the second flange surface portion  76   a  that protrudes from the flange recess surface  74   a.  The first flange surface portion  75   a  and the second flange surface portion  75   b  are coplanar and arranged substantially perpendicular to the axis  38 . The raised flange bead  78   a  is arranged radially around the flange recess surface  74   a  and defines a substantially rectangular shape. In other embodiments, the raised flange bead  78   a  can define a substantially round shape, a substantially triangular shape, a substantially polygonal shape, or another suitable shape. 
     As shown in  FIG. 3 , the gland portion  50   a  of the first body half  26   a  includes a male gland follower  82   a  and a mounting surface  86   a  extending axially outward from the male gland follower  82   a.  The male gland follower  82   a  defines a conforming recess  90   a  which is configured to receive a portion of the liner  30 . The mounting surface  86   a  includes a plurality of mounting apertures  92   a  for attaching the gland assembly  18  and the gate actuation mechanism  22  (as shown in  FIGS. 1 and 2 ). 
     As also shown in  FIG. 3 , the liner  30  is a one-piece liner formed as a single piece of material and is configured to be received between the first body half  26   a  and the second body half  26   b.  In some embodiments, the liner  30  is fabricated from a polymeric material, such as polyurethane, that has a high resistance to abrasive and/or corrosive process flows. The liner  30  includes a first cylindrical portion  94   a,  a second cylindrical portion  94   b  symmetrical to the first cylindrical portion  94   a,  an upwardly extending chest portion  98 , and a gate slot  102 . Similar to the first body half  26   a  and the second body half  26   b,  the first cylindrical portion  94   a  and the second cylindrical portion  94   b  are symmetrical, and the following description of the first cylindrical portion  94   a  also applies to the second cylindrical portion  94   b.  Additionally, the first cylindrical portion  94   a  and the second cylindrical portion  94   b  include similar features which are identified with like reference numerals and distinguished by the suffix “a” and “b” in the figures. 
     As shown in  FIG. 4 , the first cylindrical portion  94   a  includes a liner bore surface  110   a  extending away from the gate slot  102  and a liner flange  114   a  extending substantially perpendicularly from the liner bore surface  110   a.  The liner bore surface  110   a  defines a liner bore BL. The liner bore surface  110   a  and the liner flange  114   a  combine to form a liner recess  116   a  which is configured to receive the flange recessed portion  62   a  of the first body half  26   a  and place the liner flange  114   a  into engagement with the flange recess surface  74   a.    
     As shown in  FIG. 4 , the upwardly extending chest portion  98  extends from the first cylindrical portion  94   a  and the second cylindrical portion  94   b  to a liner top flange  122  (see  FIG. 3 ). The chest portion  98  is configured to be received within the conforming recesses  90   a ,  90   b  and the liner top flange  122  is configured to engage the male gland followers  82   a,    82   b,  as shown in  FIG. 3 . 
     As further shown in  FIG. 4 , the gate slot  102  slidably receives a gate  126  of the knife gate valve  10 . The gate slot  102  extends through the liner  30  from the liner top flange  122  (see  FIG. 3 ) to a gate recess  130  arranged at the bottom of the liner  30  between the first and second cylindrical portions  94   a,    94   b  in a direction perpendicular to the axis  38 . The illustrated gate slot  102  defines a substantially rectangular shape to conform to the geometry of the gate  126 . In other embodiments, the gate slot  102  can define another shape to conform to another geometry of the gate  126  to provide bi-directional flow. 
     As shown in  FIG. 5 , the gate slot  102  includes a top sealing bead  132  arranged adjacent to the liner top flange  122 , a first radial sealing bead  134   a  arranged adjacent to the liner bore surface  110   a  on a first longitudinal surface  138   a  of the gate slot  102 , and a second radial sealing bead  134   b  (see  FIG. 4 ) arranged adjacent to the liner bore surface  110   b  on a second longitudinal surface  138   b  of the gate slot  102 . The first radial sealing bead  134   a  is symmetric to the second radial sealing bead  134   b,  and therefore, the following description of the first radial sealing bead  134   a  on the first longitudinal surface  138   a  also applies to the second radial sealing bead  134   b  on the second longitudinal surface  138   b.    
     As shown in  FIG. 4 , first radial sealing bead  134   a  protrudes from and is arranged radially around the first longitudinal surface  138   a.  A distance that the first radial sealing bead  134   a  protrudes from the first longitudinal surface  138   a  is defined as a protrusion height. In one embodiment, the first radial sealing bead  134   a  defines a varying protrusion height that includes a maximum protrusion height H max  at a top  140   a  of the first radial sealing bead  134   a,  a height H c  at centerline  144  (see  FIG. 5 ), and a minimum height H min  at a bottom  148   a  of the first radial sealing bead  134   a.  The varying protrusion height of the first radial sealing bead  134   a  is described with reference to a percent decrease from H max  defined by Equation 1 below: 
     
       
         
           
             
               
                 
                   
                     % 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       DecreasefromH 
                       max 
                     
                   
                   = 
                   
                     
                       
                         
                           H 
                           max 
                         
                         - 
                         
                           H 
                           d 
                         
                       
                       
                         H 
                         max 
                       
                     
                     * 
                     1 
                     ⁢ 
                     0 
                     ⁢ 
                     0 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where H d  is the protrusion height at a distance d along the first radial sealing bead  134   a  from the top  140   a  to the bottom  148   a  of the first radial sealing bead  134   a.    
     As shown in  FIGS. 6 and 7 , the protrusion height initially remains constant at H max  and then begins to decrease at a location approximately fifteen degrees below the centerline  144 . At the location approximately 15 degrees below the centerline  144 , the protrusion height of the first radial sealing bead  134   a  starts to decrease substantially linearly to between approximately seventy-five percent and fifty percent from H max . The protrusion height reaches H min  at the bottom  148   a  of the first radial sealing bead  134   a.  In one embodiment, the minimum protrusion height H min  has decreased approximately fifty-five percent from H max . 
     As shown in  FIGS. 8 and 9 , in another embodiment, the protrusion height initially remains constant at H max  and then begins to decrease at a location approximately fifteen degrees below the centerline  144 . The protrusion height decreases substantially linearly from H max  at the location approximately 15 degrees below the centerline  144  to H min  at a location approximately sixty-five degrees below the centerline  144 . In one embodiment, the protrusion height of the first radial sealing bead  134   a  decreases between approximately seventy-five percent and one hundred percent from H max . In another embodiment, the protrusion height of the first radial sealing bead  134   a  decreases approximately one hundred percent from H max . 
     In some embodiments, the relationship between the percent decrease in the protrusion height from H max  and the distance along the first radial sealing bead  134   a  can fall between the relationships shown in  FIGS. 7 and 9 . For example, the minimum protrusion height H min  can be reached at a location between approximately sixty-five degrees below the centerline  144  and the bottom  148   a,  and decrease between approximately fifty percent and one hundred percent from H max . In one embodiment, the protrusion height can decrease from H max  starting above the centerline  144 . 
     Although the profiles of the percent decrease in the protrusion height from H max  as a function of the distance along the first radial sealing bead  134   a,  as shown in  FIGS. 7 and 9 , illustrate the protrusion height decreasing substantially linearly with distance, the protrusion height can alternatively define a step change or a non-linear relationship, as a function of distance along the first radial sealing bead  134   a.  Additionally, the profiles discussed above are only exemplary and other ranges and slopes/profiles of decreased bead height are contemplated. The invention generally provides a bead height that decreases in any manner between a top and a bottom of the first radial sealing bead  134   a.    
     As shown in  FIG. 3 , the gland assembly  18  includes a gland box  152  attached to the mounting surfaces  86   a,    86   b  of the first and second body halves  26   a,    26   b  via fastening elements  154  (removed from  FIG. 2  for clarity, see  FIG. 1 ) inserted through gland mounting apertures  156  and into the mounting apertures  92   a,    92   b.  The gland box  152  is configured to enclose one or more layers of packing  160  and compress the packing  160  against the liner top flange  122  which seals the liner top flange  122  between the male gland followers  82   a,    82   b  and the packing  160 . The gland box  152  and the packing  160  each include a gland slot  164  which is aligned with the gate slot  102  in the liner  30  and is configured to slidably receive the gate  126 . 
     As shown in  FIG. 1 , the gate actuation mechanism  22  is coupled to the gate  126  and attached to the mounting surfaces  86   a,    86   b  of the first and second body halves  26   a,    26   b.  The gate actuation mechanism  22  is configured to actuate the gate  126  between a first or open position (as shown in  FIG. 10 ) where the gate  126  does not block any of the passageway  34  and process fluid is allowed to flow through the passageway  34  and a second or closed position (as shown in  FIG. 11 ) where the gate  126  blocks the passageway  34  and process fluid is inhibited from flowing through the passageway  34 . In some embodiments, the gate actuation mechanism  22  is an electronic actuator. In other embodiments, the gate actuation mechanism  22  can be a pneumatic actuator, a hand wheel and a threaded rod, or a lever. 
     As shown in  FIG. 12 , the knife gate valve  10  is assembled by installing the liner  30  onto the first body half  26   a  by first manipulating the liner flange  114   a  through the smaller diameter of the valve bore B v  defined by the flange recessed portion  62   a.  Once the liner flange  114   a  is manipulated through the flange recessed portion  62   a,  it is then expanded to position the flange recessed portion  62   a  within the liner recess  116   a  and place the liner flange  114   a  into engagement with the raised flange bead  78   a  on the flange recess surface  74   a.  With the flange recessed portion  62   a  positioned within the liner recess  116   a,  the chest portion  98  is also positioned within the conforming recess  90   a  and the liner top flange  122  is placed into engagement with the male gland follower  82   a.  In one embodiment, the liner  30  can be fabricated from polyurethane which provides the liner  30  with the flexibility to be manipulated through the valve bore B v  and the rigidity to not permanently deform during the manipulation through the valve bore B v . 
     A similar process is used to install the liner  30  onto the second body half  26   b,  as the second body half  26   b  and the second cylindrical portion  94   b  are symmetrical to the first body half  26   a  and the first cylindrical portion  94   a,  respectively. Once the liner  30  is installed onto both the first and second body halves  26   a,    26   b,  the liner  30  is arranged between the first and second body halves  26   a,    26   b  and the fastening elements  54  are installed through the joining apertures  42   a,    42   b  and tightened to join the first body half  26   a  and the second body half  26   b . This completes assembly of the valve body assembly  14  and the gland assembly  18  is then installed onto the valve body assembly  14  by first placing the packing  160  on the liner top flange  122  so that the gland slot  164  aligns with the gate slot  102 . The gland box  152  is then installed over the packing  160  and the gate  126  is installed through the gland slot  164  and the gate slot  102 . Once the gate  126  is installed, the fastening elements  154  are positioned, as shown in  FIG. 1 , then inserted though the gland mounting apertures  156  and into the corresponding mounting apertures  92   a,    92   b  and then tightened to compress the packing  160  against the gate  126  and seal the liner top flange  122  between the packing  160  and the male gland followers  82   a,    82   b.    
     As shown in  FIG. 1 , the gate actuation mechanism  22  is then coupled to the gate  126  and attached to the first and second valve body halves  26   a  and  26   b  via rods  168  received within the corresponding mounting apertures  92   a,    92   b.  The rods  168  provide enough clearance between the gate actuation mechanism  22  and the mounting surfaces  86   a,    86   b  so that the gate  126  can actuate between the open position and the closed position. 
     As shown in  FIG. 12 , a pipe  174  is coupled to the first body half  26   a  using a pipe flange  176 . The pipe flange  176  is fastened to the flange surface  58   a  via the plurality of flange apertures  66   a  (see  FIG. 1 ). In some embodiments, the pipe flange  176  arrangement is a “slip on flange.” The pipe flange  176  defines a pipe flange bore B p  that is greater in diameter than the liner bore B L . The liner flange  114   a  is not supported all the way to the liner bore B L  by the pipe flange  176 . In other words, due to the design of slip on flanges, a portion of the liner flange  114   a  is not in contact with the pipe flange  176 . Typically, knife gate valves with replaceable liners are not able to seal properly with a slip on flange. 
     As also shown in  FIG. 12 , once the pipe flange  176  is fastened to the flange surface  58   a,  the pipe flange  176  compresses the liner flange  114   a  against the flange recess surface  74   a  and the raised flange bead  78   a.  The raised flange bead  78   a  provides a localized area of higher compression (e.g., a line contact seal) which prevents the liner flange  114   a  from moving and forms an integral seal between the liner flange  114   a  and the flange recess surface  74   a.  The pipe flange  176  compresses the liner flange  114   a  substantially perpendicularly against the first flange surface portion  75   a,  the second flange surface portion  76   a,  and the raised flange bead  78   a  of the flange recess surface  74   a.  As the first flange surface portion  75   a  and the second flange surface portion  76   a  are coplanar and arranged substantially perpendicular to the axis  38 . This aids in inhibiting the liner flange  114   a  from creeping, or moving, under load from the pipe flange  176  or the process fluid. In addition to enabling the knife gate valve  10  to be operable with a slip on flange, the raised flange bead  78   a  eliminates the need for a separate gasket to be placed between the pipe flange  176  and the flange surface  58   a.    
     Another pipe can be coupled to the second body half  26   b  using another pipe flange to allow process fluid to be carried after flowing through the passageway  34 . Additionally, the second body half  26   b  and the second cylindrical portion  94   b  are symmetrical to the first body half  26   a  and the first cylindrical portion  94   a,  respectively. Therefore, the preceding description also applies to the second body half  26   b  and the second cylindrical portion  94   b  of the liner  30 . Furthermore, the first body half  26   a  and the second body half  26   b  are capable of coupling to other, non-slip on pipe flanges that define a pipe bore B p  that is less than or equal to the liner bore B v . 
     As shown in  FIG. 4 , during operation, the process fluid imparts a differential pressure across the gate  126  of the knife gate valve  10  when the gate  126  is in the closed position. The differential pressure across the gate  126  causes the gate  126  to seal against either the first radial sealing bead  134   a  or the second radial sealing bead  134   b,  depending on the direction force provided by the differential pressure, preventing process fluid from leaking past or along the gate  126 . As the differential pressure across the gate  126  increases, the gate  126  can deflect. For example, the gate  126  can engage the top  140   a  of the first radial sealing bead  134   a  and deflect to engage the bottom  148   b  of the second radial sealing bead  134   b.  Since the gate  126  is supported by the chest portion  98  of the liner  30 , deflection of the gate  126  is typically at a maximum towards the bottom  148   a,    148   b  of the first and second radial sealing beads  134   a,    134   b.    
     The first and second radial sealing beads  134   a,    134   b  define a decreasing protrusion height from a maximum protrusion height H max  at the top  140   a,    140   b  of the first and second radial sealing beads  134   a,    134   b  to a minimum protrusion height H min  at the bottom  148   a,    148   b  of the first and second radial sealing beads  134   a,    134   b.  The varying height of the first and second radial sealing beads  134   a,    134   b  enable the liner  30  to use the deflection of the gate  126  to increase sealing with increased differential pressure. This is achieved because the first and second radial sealing beads  134   a,    134   b  define a maximum protrusion height H max  where deflection of the gate  126  is at a minimum and define a minimum protrusion height H min  where deflection of the gate  126  is at a maximum. 
     Simultaneously, the varying height of the first and second radial sealing beads  134   a ,  134   b  maintains a minimum valve closing force while deflection of the gate  126  increases with increased differential pressure. The valve closing force is the force necessary to move the gate  126  from the open position to the closed position. When the gate  126  is moving towards the closed position, and the differential pressure causes the gate  126  to deflect, a leading edge  172  of the gate  126  must overcome the protrusion height at the bottom  148   a,    148   b  of the first radial sealing bead  134   a  or the second radial sealing bead  134   b,  depending on the direction of the deflection of the gate  126 , to reach the closed position. The protrusion height at the bottom  148   a,    148   b  of the first and second radial sealing beads  134   a,    134   b  is the minimum protrusion height H min  which minimizes the valve closing force and still provides an effective seal. 
     An integral seal is formed between the liner flanges  114   a,    114   b  and the flange recess surfaces  74   a,    74   b  and the liner top flange  122  is sealed between the packing  160  and the male gland followers  82   a,    82   b.  These seals enable the liner  30  to completely isolate the valve body halves  26   a,    26   b  from process fluid flowing through the passageway  34 . This protects the valve body halves  26   a,    26   b  from coming into contact with the process fluid which can be highly abrasive and/or corrosive, and enables the knife gate valve  10  to be reused while only requiring the liner  30  to be replaced as the process fluid begins to wear the liner  30  down. 
     The symmetry defined by the first and second body halves  26   a,    26   b,  the first and second cylindrical portions  94   a,    94   b,  and the first and second radial sealing beads  134   a,    134   b  enables the knife gate valve  10  to achieve bi-directional sealing in either flow direction (i.e., from the first body half  26   a  towards the second body half  26   b  or from the second body half  26   b  towards the first body half  26   a ). 
     It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. 
     Various features and advantages of the invention are set forth in the following claims.