Abstract:
A gate valve assembly having a body, a gate, a stem, and a backseat for sealing between the stem and the body. The backseat is an annular member with a complementary surface on its inside that fits over a spherically shaped section of the stem; thus allowing the backseat to rotate and pivot with respect to the stem. An outer surface of the backseat is beveled for sealingly engaging a stem passage formed through the body. A flex member is provided that is for sealing a surface adjacent the backseat. The flex member can form a seal between the backseat member and the stem or between an annular retainer and the backseat.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention relates generally to a valve assembly. More specifically, the invention relates to a backseat assembly for a gate valve assembly that is pivotable with respect to a stem of the gate valve assembly. 
         [0003]    2. Description of Prior Art 
         [0004]    Gate valves typically have a body with a cavity intersected by a flow passage. A gate moves in the cavity between a closed position, blocking flow through the flow passage and an open position that allows flow through the passage. A stem is usually included for moving the gate that engages the gate, and when rotated, causes the movement of the gate. The stem extends through a stem passage in the body of the gate valve. Stem seals seal between the stem and the stem passage, preventing leakage of pressure from the cavity. 
         [0005]    Gate valves sometimes include a backseat feature for sealing between a valve stem and valve bonnet so that packing in the valve assembly can be changed. Backseats are typically made up of complimentary profiled surfaces in the stem and valve bonnet that when urged together isolate pressure communication along the stem. Backseats are generally energized by the pressure in the flow through the valve exerting a force on a bottom surface of the valve stem and urging together the profiled surfaces in the stem and bonnet. 
       SUMMARY OF THE INVENTION 
       [0006]    Provided herein is an example of a gate valve assembly that includes a body with an inner cavity. A neck opening is formed through the body that has a conically shaped portion intersecting the cavity. This example of the gate valve assembly also includes a stem that projects into the neck opening in the body and having an end in the cavity that is coupled to an end of a gate. A profile circumscribes a portion of the stem that has a radius that changes along a length of the stem. A ring like backseat member is on the profile, that can rotate and pivot with respect to the stem. The backseat member has an inner surface complementary to an outer surface of the profile. An outer surface on the backseat member has a portion shaped complementary to the conically shaped portion of the neck opening. Thus when the stem is urged in a direction that wedges the backseat member between the profile and the neck portion, a seal is formed between the stem and neck opening. An annular retainer is optionally mounted around the stem and positioned adjacent a lower surface of the backseat member to define a resilient sealing interface between the retainer and backseat member, so that when the stem tilts from an aligned position to an unaligned position, the sealing interface is maintained in the unaligned position. The retainer includes a body, a furrow formed in an outer radial surface of the body that defines a spring like flex element that projects radially outward from the body and that biases against the lower surface of the backseat member to form a sealing interface. An o-ring is provided in a space between an upper end of the body and a lower end of the profile. A recess may be formed along the inner surface of the backseat member along with an elongated flex leg that depends from an interface between the recess and inner surface, where the flex leg biases against the profile. In an example, the gate valve assembly further includes an annular retainer circumscribing the stem adjacent a lower end of the profile and a soft metal inlay on an upper surface of the retainer that contacts a lower surface of the backseat member that forms a sealing interface. Optionally, the flex leg forms a sealing interface when biased against the profile that is maintained with rotation and tilting of the stem with respect to the backseat member. In one example, the profile has a spherical type curvature. 
         [0007]    Also described herein is a gate valve assembly that is made up of a body with an inner cavity, a stem passage in the body having a conically shaped opening that is adjacent the cavity, an elongated cylindrically shaped stem that extends from within the cavity and into the stem passage, a profile circumscribing a portion of the stem having a curved outer surface that resembles a portion of a sphere, an annular backseat member having an inner surface formed complementary to the curved outer surface of the profile and an outer surface that is in selective sealing engagement with the conically shaped opening, and a spring like member that forms a sealing interface adjacent a surface of the backseat member when the outer surface of the backseat member is in sealing engagement with the conically shaped opening. The spring like member can be a flex leg disposed on the inner surface of the backseat member and that is selectively biased against the profile. A recess may be formed in the backseat member, where the recess extends radially outward a distance from the inner surface and substantially parallel with the inner surface to define the flex leg. In one optional embodiment, the gate valve assembly further includes an annular retainer circumscribing the stem and having a soft metal inlay on an upper surface that sealingly engages a lower surface of the backseat member. The spring like member may be a flex element that resiliently maintains a sealing interface on a lower surface of the backseat member. The flex element may optionally be part of an annular retainer that circumscribes the stem adjacent a lower end of the profile and wherein a metal o-ring is disposed in sealing contact between an inner surface of the annular retainer and an outer circumference of the stem. 
         [0008]    Another example embodiment of a gate valve assembly disclosed herein includes a body with an inner cavity, a stem passage in the body having a conically shaped opening that is adjacent the cavity, a stem assembly comprising an elongated cylindrically shaped stem that extends from within the cavity and into the stem passage, a profile circumscribing a portion of the stem having a curved outer surface, and an annular retainer circumscribing the stem adjacent a lower end of the profile. This embodiment of the gate valve assembly includes an annular backseat member circumscribing a portion of the profile that provides a means for providing a seal between the stem and stem passage and that maintains the seal when the stem is tilted into an unaligned position. A spring like member may be includes that forms a sealing interface adjacent a surface of the backseat member when the outer surface of the backseat member is in sealing engagement with the conically shaped opening. In an example, the backseat member has an inner surface formed complementary to the curved outer surface of the profile. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a side partial sectional view of an example embodiment of a valve assembly having a backseat stem seal in accordance with the present invention. 
           [0011]      FIG. 2  is a side sectional view of an example of the backseat stem seal of  FIG. 1  between a stem and a bonnet and in an unsealed position in accordance with the present disclosure. 
           [0012]      FIG. 3  is a side sectional view of an example of the backseat stem seal of  FIG. 1  between a stem and a bonnet and in a sealed position in accordance with the present disclosure. 
           [0013]      FIG. 4  is a side sectional view of the example of  FIG. 3  with the stem misaligned in accordance with the present disclosure. 
           [0014]      FIG. 5  is a side sectional view of an alternate embodiment of the backseat stem seal between a stem and bonnet of  FIG. 3  in accordance with the present invention. 
           [0015]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
         [0017]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
         [0018]    Referring to  FIG. 1 , gate valve  11  is of a type typically used in oilfield applications for controlling well fluid flow. Valve  11  has a body  13 , which may be a single piece or multiple pieces as shown. Body  13  has a central gate cavity  15  having aligned inlet and outlet ports (not shown) for the flow of fluid through valve  11 . Gate  17  strokes within gate cavity  15  and may be a single slab or a two-slab type. Gate  17  has an aperture  19  that aligns with the inlet and outlet ports (not shown) of valve  11  in the open position. Gate  17  blocks flow when in the closed position, which is the position shown in  FIG. 1 . 
         [0019]    A stem  21  connects to gate  17  for moving gate  17  between the open and closed positions. Generally, in gate valves, there are two types of stems, one of which translates axially when rotated, referred to as a rising stem, and another that remains axially stationary when rotated, referred to as a non-rising stem. In this embodiment, stem  21  is a non-rising type. Stem  21  extends through a stem passage  22  into cavity  15 , stem passage  22  being in fluid communication with cavity  15 . Stem  21  engages a threaded nut  23  in gate  17  that translates rotational motion of stem  21  into axial movement of gate  17 . When gate  17  moves upward to the open position, a lower portion of stem  21  will be located in a cavity  24  in gate  17 . 
         [0020]    Body  13  includes a bonnet  25 , which is an upper housing that bolts to the upper end of body  13 . Bonnet  25  forms the upper end of gate cavity  15  and has a neck  26  through which stem passage  22  extends. Stem seals  27  in stem passage  22  seal around stem  21  to prevent leakage of pressurized fluid from gate cavity  15 . Stem seals  27  may be of a variety of types. 
         [0021]    A variety of devices may be used to impart rotational motion to stem  21 , including hydraulic, electrical and manual. In this example, a roll pin  29  connects the upper end of stem  21  to a bearing carrier  31 . An optional bearing carrier  31  has upper and lower bearings  33 ,  35  for accommodating axial thrust imposed on stem  21  due to pressure in gate cavity  15 . Smaller valves, particularly those having lower pressure ratings, may not require thrust bearings  33 ,  35 . Bearing carrier  31  mounts rotatably within a stationary collar  37 . Collar  37  secures by threads to the upper end of bonnet neck  26 . 
         [0022]    A gear box  39  mounts to collar  37  in this embodiment. Gear box  39  has an output shaft  41  that extends into a polygonal receptacle in bearing carrier  31 . A hand wheel  43  connects to the input of gear box  39 . Gear box  39  provides a mechanical advantage to the rotation of hand wheel  43 . Gear box  39  is optional and many gate valves, particularly those of smaller size and lower pressure ratings, do not utilize a gear box. 
         [0023]    A backseat seal assembly  45  locates at junction of stem passage  22  with the upper end of gate cavity  15 . Backseat seal assembly  45  is normally in an unsealed condition, which allows any pressure in gate cavity  15  to communicate to stem seals  27 . In the event of leakage of stem seals  27 , the operator can actuate backseat seal assembly  45  to seal the pressure in gate cavity  15 . Once the pressure in gate cavity  15  is relieved, the operator can replace stem seals  27 . 
         [0024]      FIG. 2  is a detailed side sectional view of an example of a portion of the gate valve assembly  11  of  FIG. 1  that illustrates the backseat seal assembly  45  in an expanded view. The backseat seal assembly  45  of  FIG. 2  is illustrated as having an annular backseat member  47  with lower and upper surfaces  49 ,  51  that are substantially normal to an axis A X  of the stem  21 . The outer radial periphery of the backseat member  47  includes a lower portion that is substantially parallel with the axis A X  and extends upward from an outer edge of the lower surface  49 . At an upper end of the lower portion  53 , the outer radial periphery of the backseat member  47  bevels radially inward to define an upper portion  55  shown having a surface that extends at an angle oblique to the axis A X . Distal from the lower portion  53 , the upper portion  55  terminates at an outer radial end of the upper surface  51 . Further illustrated in the example of  FIG. 2  is that the lower end of the stem passage  22  flares radially outward to define an opening  56  shown intersecting with the cavity  15 . The sides of the opening  56  define a sealing surface  57  that has a slope approximately complementary to the slope of the upper portion  55 . 
         [0025]    An inner surface  59  of the backseat member  47  of  FIG. 2  is curved with respect to its axis; and where the curvature is complementary to a profile  61  shown formed on an outer circumference of the stem  21 . In one example embodiment, the profile  61  resembles a portion of a sphere, so that when engaged with the profile  61 , the backseat member  47  can rotate at least partially about the stem  21 . Moreover, the corresponding configurations of the inner surface  59  and profile  61  allow pivoting of the backseat member  47  with respect to the stem  21 . 
         [0026]    An annular retainer  63  is further included in the example of the backseat seal assembly  45  of  FIG. 2 . In the example of  FIG. 2 , the retainer  63  includes a ring-like body  65  that mounts on an outer surface of the stem  21  disposed adjacent to and below the lower surface  49 . A furrow  66  is provided on an outer radial surface of the body  65  set axially downward from an upper surface of the body  65 . The presence of the furrow  66  defines a cantilever like flex element  67  on the upper surface of the body  65  and along its outer periphery. In one example the flex element  67  is in biasing engagement with the lower surface  49  of the backseat member  47  and defines a sealing interface between the retainer  63  and backseat member  47 . The lower end of the profile  61  juts radially inward and to define a transition  69  that in cross-section forms a  90  degree angle. A metal O-ring  71  is shown provided on an outer surface of the stem  21  and adjacent the transition  69 . A rectangular groove on an inner radial surface of the body  65  provides an open space for the O-ring  71 . Thus, a sealing means is provided by the O-ring  71  and flex element  67  for blocking pressure communication on a path between the backseat member  47  and stem  21 . 
         [0027]    A snap ring  73  may optionally be included with the backseat seal assembly  45 . A groove  75  is shown formed circumferentially around the stem  21  and axially just above the profile  61 . The presence of the snap ring  71  can help contain the respective axial positions of the backseat element  47  and snap ring  21 . 
         [0028]    Referring now to  FIG. 3 , an example is shown of energizing the backseat seal assembly  45  against the bonnet  25  thereby blocking pressure communication through the stem passage  22 . More specifically, a section of the upper portion  55  is shown contacting the sealing surface  57  thereby defining a sealing interface between the backseat member  47  and bonnet  25 . As illustrated in the example of  FIG. 3 , the respective surfaces of the upper portion  55  and sealing surface  57  lie in planes that are disposed at angles to one another. In the example of  FIG. 3 , a lower section of the upper portion  55  engages the sealing surface  57  while a section of the upper portion proximate the upper surface  51  remains spaced apart from the sealing surface  57 . Upwardly urging the stem  21  so the upper portion  55  and sealing surface  57  become engaged results in a force urging the lower surface  49  and flex element  67  into contact thereby enhancing the sealing functions between the retainer  63  and backseat element  47 . 
         [0029]    An advantage of the backseat seal assembly  45  enclosed herein is illustrated in side sectional view in  FIG. 4 . As shown, the stem  21  has tilted coaxial to axis A S , which is at an angle θ with respect to the axis A X  of the valve assembly  11 . However, the complementary curved surfaces respectively of the inner surface  59  and profile  61  allow the pivoting action between the stem  21  and backseat member  47  to take place without compromising the sealing ability of the backseat seal assembly  45 . More specifically, sealing interfaces are maintained between the upper portion  55  and sealing surface  57 , the retainer  63  and backseat member  47 , and retainer  63  and stem  21 . Maintaining the sealing interface between the retainer  63  and flex member  47  when the stem  21  tilts is due at least in part to the spring-like action of the flex element  67 , which allows compression of the flex element  67  on one side (schematically represented on the right side of  FIG. 4 ) and axial movement of the portion of the flex leg  67  upward where the body  65  has angled downward from the tilt of the stem  21 . A left side of FIG.  4  illustrates a relaxed flex element  67  that continues to maintain a sealing surface against the lower surface  49  of the backseat element  47 . Also, because the retaining element  63  is mounted to the stem  21 , the O-ring  71  remains in place against the stem  21  to continue sealing along the outer surface of the stem  21 . Accordingly, misalignment of stems may be accommodated with use of the design and method described herein while yet still achieving successful backseat sealing within a gate valve. 
         [0030]      FIG. 5  is a side sectional view of an alternate example embodiment of a backseat seal assembly  45 A for use between a stem  21  and bonnet  25  of a valve assembly. The backseat element  47 A of  FIG. 5  is shown having a recess  77  formed along its inner surface  59 A. The recess  77  extends radially outward from the inner surface  59 A and has a portion that runs parallel to the inner surface  59 A but set back radially outward therefrom. This portion of the recess  77  defines a flex leg  79  that forms a portion of the inner surface  59 A and responds similar to a cantilever member. Strategically forming of the flex leg  79  provides a force from the leg  79  that is directed radially inward onto an outer surface of the profile  61  and forms a sealing interface between the backseat member  47 A and stem  21 . Also optionally, the retaining element  68 A is shown having a body  65 A whose cross-section is substantially rectangular and wherein the retaining element  63 A mounts circumferentially around the stem  21  adjacent a lower end of the profile  61 . Optionally, included on an upper surface of the body  65 A is an inlay  81  that may be formed from a metal softer than the metal of the backseat member  47 A. Similar to the embodiments of  FIGS. 2 through 4 , the embodiment of the backseat seal assembly  45 A of  FIG. 5  can maintain sealing in the stem passage  22  even in conditions when the stem  21  is tilted as illustrated in  FIG. 4 . In one example, the soft metal inlay  81  provides a resilient body that can allow for the tilting movement while maintaining a sealing function. 
         [0031]    If leakage past the stem seals  27  is detected, the backseat seal assembly  45  can be energized ( FIG. 2 ) to block pressure communication between the cavity  14  and above the opening  56 . In an example, energizing the backseat seal assembly  45  can be done by releasing the set screw and unscrewing collar  37  from bonnet neck  26  a selected distance. The pressure in gate cavity  15  causes stem  21  and backseat member  47  ( FIG. 2 ) to move upward an increment until the upper portion  55  and sealing surface  57  contact each other and deflect to form a metal-to-metal seal. The stem seals  27  can be replaced with pressure in the cavity  15  being isolated. Normally, the pressure in gate cavity  15  is first relieved before removing stem seals  27  ( FIG. 1 ). After replacing the stem seals  27 , the collar  37  is retightened that pushes stem  21  downward to the position shown in  FIG. 2 . This sets the upper portion  55  away and out of contact with the sealing surface  57 . 
         [0032]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. cm What is claimed is: