Abstract:
A valve assembly comprising a valve body defining a fluid passage with a seat member positioned adjacent the fluid passage. A gate, having a leading edge, is supported in the valve body and is moveable relative to the fluid passage along a given axis between an open position and a closed positioned wherein the gate sealingly engages the seat member. The seat member includes a portion whose tangent is perpendicular to the given axis. At least a portion of the gate leading edge that is laterally aligned with the portion of the seat member whose tangent is perpendicular to the given axis may extend at an obtuse angle relative to the given axis. The gate leading edge may be configured such that any portion of the leading edge contacting a respective portion of the seat member is non-parallel to a tangent of that portion of the seat member.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to valves, more particularly knife gate valves. 
         [0002]    Knife gate valves are well known in the art for use in a variety of applications in a broad range of industries, including but not limited to, pulp &amp; paper, chemical, petroleum refining, mining, iron and steel manufacture, waste water, power generation, food and beverage, and marine applications. In particular, knife gate valves are advantageous for use in non-abrasive and abrasive slurry applications and for large diameter water applications. The use of elastomeric valve seats are known to be particularly helpful for applications having high solids or prone to scaling. 
         [0003]    One advantage of knife gate valves is the ability to cut through slurries, scale, and surface build ups. Another advantage is the unobstructed flow path, which not only provides high flow capacity, but also allows large objects to safely pass through the valve. Small face-to-face dimensions reduce the weight of the valve and facilitate piping design. Knife gate valves are typically available in sizes as small as 2″ diameter to specially fabricated valves exceeding 100″ in diameter. 
         [0004]    Disadvantages of knife gate valves of this type may include pinch of the valve seats between the gate and the valve housing as the gate penetrates the seat. Damage to the seat may also occur if the gate has been tapered to a sharp edge or has burrs or other defects which may catch the seat. Additionally, if the gate has been deflected downstream by the hydrodynamic forces of the flowing media, it may be even more likely to catch on the downstream seat. 
       SUMMARY OF THE INVENTION 
       [0005]    In one aspect, the present invention provides a valve assembly comprising a valve body defining a fluid passage with a seat member positioned adjacent the fluid passage. A gate, having a leading edge, is supported in the valve body and is moveable relative to the fluid passage along a given axis between an open position and a closed positioned wherein the gate sealingly engages the seat member. The seat member includes a portion whose tangent is perpendicular to the given axis. At least a portion of the gate leading edge that is laterally aligned with the portion of the seat member whose tangent is perpendicular to the given axis extends at an obtuse angle relative to the given axis. 
         [0006]    In another aspect, the present invention provides a valve assembly comprising a valve body defining a fluid passage with a seat member positioned adjacent the fluid passage. A gate, having a leading edge, is supported in the valve body and is moveable relative to the fluid passage along a given axis between an open position and a closed positioned wherein the gate sealingly engages the seat member. The gate leading edge is configured such that any portion of the leading edge contacting a respective portion of the seat member is non-parallel to a tangent of that portion of the seat member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1A  is a plan view of an exemplary valve incorporating an embodiment of the present invention. 
           [0008]      FIG. 2  is a cross-sectional view of the valve of  FIG. 2 , taken across line  2 - 2  in  FIG. 1 . 
           [0009]      FIG. 3  is an exploded perspective view of the valve of  FIG. 1 . 
           [0010]      FIG. 4  is a perspective view of a leading edge of the gate in accordance with an embodiment of the present invention. 
           [0011]      FIG. 5  is a front elevation view of the gate of  FIG. 4 . 
           [0012]      FIG. 6  is a front elevation view of the gate of  FIG. 4  relative to an exemplary seat. 
           [0013]      FIG. 7  is a perspective view of a leading edge of the gate in accordance with an alternative embodiment of the present invention. 
           [0014]      FIG. 8  is a front elevation view of the gate of  FIG. 7 . 
           [0015]      FIG. 9  is a front elevation view of the gate of  FIG. 7  relative to an exemplary seat. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
         [0017]    Referring to  FIGS. 1-3 , an exemplary knife gate valve  10  incorporating an exemplary embodiment of the present invention is shown. The valve  10  described herein is exemplary only and the invention is not limited to such. The valve  10  in accordance with the present invention may have various housing structures, sealing assemblies and actuating assemblies. Accordingly, the invention is not limited to valves having any particular components except those specifically recited in the claims. 
         [0018]    Exemplary valve  10  comprises two body halves  12  and  14 , and two liners  87 . Spacers  88  separate the liners to define a gate channel through which gate  16  slides to open or close pathway  18  through the orifices  13  in the valve body. Mounted on top of the body halves  12  and  14  are yoke halves  20  and  22 . The body halves are typically connected to the yoke halves with yoke hold down bolts  24  and fasteners  26 . A yoke hub  28 , connected to the yoke halves with hub hold down bolts  30  and fasteners  26 , sits atop the yoke halves and provides a platform for handwheel  32 . The invention is not limited to handwheel actuators, however, as removal of the hub allows the use of other types of actuators, such as but not limited to pneumatic, hydraulic, electric or bevel gear actuators. 
         [0019]    Handwheel  32  turns drive nut assembly  36 , which turns the threaded stem  34 . Wave spring  44 , retaining washer  45 , and retaining nut  46  fix the drive nut assembly  36  to the handwheel  32 . Wave spring  44  keeps the handwheel in tension and prevents it from shaking off in high vibration applications. At the end of stem  34  is gate clamp  38  which is attached to gate  16  with bolts  40 . As the threaded stem  34  turns the gate clamp  38  either travels up or down along the axis of the stem  34 . A lockout pin  48  is provided for insertion in any of lockout holes  49  in the yoke and/or gate to mechanically prevent the valve from being opened or closed (depending upon the location of the gate when pinned) pursuant to common industry safety procedures. Additional components, not shown or shown but not discussed, may also be present. 
         [0020]    Elastomer seats  90  each have an inner face  94  and an outer face  96 . Inner face  94  is the face adjacent gate  16  and comprises a substantially flat portion  98 . Inner faces  94  are in contact with each other when the gate is removed, thus creating a continuous rubber lining for the media flow-path  90  and with enough compressive force to create a tight seal. 
         [0021]    Referring to  FIGS. 4-6 , a gate  16  in accordance with a first embodiment of the invention will be described. The gate  16  includes a leading edge  50  extending between its opposed sides  51 . The leading edge  50  is illustrated with a tapered knife edge  53 , but it may have other configurations. As illustrated in  FIG. 5 , at least a portion  57  of the leading edge  50  extends at an angle Ø relative to the centerline of the gate  16 . In the present embodiment, the entire leading edge  50  between the sides defines the angled portion  57 , however, the angled portion of the leading edge  50  may extend less than the entire width, as described with respect to the embodiment illustrated in  FIGS. 7-9 . Angle Ø is desirably in the range of approximately 95 degrees to 135 degrees measured from the centerline toward the trailing side  56  of the leading edge  50 . The leading edge  50  may be angled such that the right side defines the trailing side  56  as illustrated, or it may be reversed such that the left side defines the trailing side. The angle Ø is not limited to 95 degrees to 135 degrees, but may be greater or less than such angle. Furthermore, the angle of the leading edge  50  does not have to be consistent as illustrated, but may vary across the width. 
         [0022]    Referring to  FIG. 6 , it is shown that the tangent T 2  to the portion  93  of the seat  90  at the very bottom thereof is perpendicular to the direction of travel D of the gate  16 , i.e. parallel to the gate&#39;s centerline. This portion  93  of the seat  90  having its tangent T 2  perpendicular to the direction of travel D is most prone to pinching. Accordingly, at least the portion  55  of the gate leading edge  50  that is laterally aligned with the portion  93  of the seat member  90  whose tangent is perpendicular to the direction of travel extends at an obtuse angle relative to the centerline. 
         [0023]    As further shown in  FIG. 6 , a portion  52  of the leading edge will contact the seat  90  along the port  99  as the gate  16  is moved toward the closed position. While not as likely, there is also a chance that the seat  90  may be pinched or damaged anywhere along where this portion  52  of the leading edge contacts it. Accordingly, it is desirable that across this portion  52 , the leading edge  50  is non-parallel to a tangent of that portion of the seat member  90  which the leading edge will contact. As illustrated in  FIG. 6 , the leading edge  50  is non-parallel to any of the respective tangents T 1 , T 2 , T 3  which the leading edge  50  will contact, but instead is at an angle a with respect thereto. This relationship is generally achieved by maintaining the portion  52  at an obtuse angle Ø relative to the centerline, however, other configurations and relationships may be utilized. 
         [0024]    In each of these configurations, the gate  16  always presents the leading edge  50  to the point of contact where it penetrates the seat  90  at an angle other than perpendicular to the direction of travel. Because the gate  16  is moving in a direction skewed form the normal to the point of contact, static friction is more quickly overcome between the gate  16  and the seat  90 , reducing the likelihood of catching, rolling or pinching the seat  90 . 
         [0025]    Referring to  FIGS. 7-9 , a gate  16 ′ in accordance with another embodiment of the invention will be described. The gate  16 ′ is similar to the previous embodiment and includes a leading edge  50 ′ extending between its opposed sides  51 . The leading edge  50 ′ is illustrated with a tapered knife edge  53 , but it may have other configurations. As illustrated in  FIG. 8 , at least a portion  57  of the leading edge  50 ′ extends at an angle Ø relative to the centerline of the gate  16 ′. In the present embodiment, the angled portion  57  does not extend completely between the sides  51  of the gate  16 ′, but instead have portions  54  along each side  51  which extend perpendicular to the centerline of the gate  16 ′. These portions  54  extend outward of the portion  52  of the leading edge that will contact the seat  90  along the port  99  as the gate  16  is moved toward the closed position. Again, angle Ø is desirably in the range of approximately 95 degrees to 135 degrees measured from the centerline toward the trailing side  56  of the leading edge  50 . Since the angled portion  57  does not extend across the entire width of the gate  16 ′, the leading edge  50 ′ may have a reduced height compared to the previous embodiment. Again, the leading edge  50 ′ may be angled such that the right side defines the trailing side  56  as illustrated, or it may be reversed such that the left side defines the trailing side. The angle Ø is not limited to 95 degrees to 135 degrees, but may be greater or less than such angle. Furthermore, the angle of the leading edge  50 ′ does not have to be consistent as illustrated, but may vary across the width of the angled portion  57 . 
         [0026]    Referring to  FIG. 9 , it is shown that the tangent T 2  to the portion  93  of the seat  90  at the very bottom thereof is perpendicular to the direction of travel D of the gate  16 , i.e. parallel to the gate&#39;s centerline. This portion  93  of the seat  90  having its tangent T 2  perpendicular to the direction of travel D is most prone to pinching. Accordingly, at least the portion  55  of the gate leading edge  50 ′ that is laterally aligned with the portion  93  of the seat member  90  whose tangent is perpendicular to the direction of travel extends at an obtuse angle Ø relative to the centerline. 
         [0027]    As further shown in  FIG. 9 , a portion  52  of the leading edge  50 ″ will contact the seat  90  along the port  99  as the gate  16  is moved toward the closed position. It is desirable that across this portion  52 , the leading edge  50 ′ is non-parallel to a tangent of that portion of the seat member  90  which the leading edge will contact. As illustrated in  FIG. 9 , the leading edge  50 ′ is non-parallel to any of the respective tangents T 1 , T 2 , T 3  which the leading edge  50 ′ will contact, but instead is at an angle α with respect thereto. This relationship is generally achieved by maintaining the portion  52  at an obtuse angle Ø relative to the centerline, however, other configurations and relationships may be utilized. 
         [0028]    In each of these configurations, the gate  16 ′ always presents the leading edge  50 ′ to the point of contact where it penetrates the seat  90  at an angle other than perpendicular to the direction of travel. Because the gate  16 ′ is moving in a direction skewed form the normal to the point of contact, static friction is more quickly overcome between the gate  16 ′ and the seat  90 , reducing the likelihood of catching, rolling or pinching the seat  90 . The portions  54  do not contact the seat  90  along the port  90 , but instead generally remain in continuous contact with the seat member  90  and are not prone to pinching and the like. 
         [0029]    Although shown in two embodiments that include a plurality of desirable features, embodiments comprising fewer than all of these features may also be constructed, including any combination of the elements described herein. Accordingly, the invention is not limited only to the embodiment shown. Although ideal for use in slurry service, it should be understood that valves having the features described and claimed herein may be used in any kind of fluid handling service, where the term “fluid” is interpreted broadly, to include gas, liquid, solids, or any combination thereof. 
         [0030]    While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.