Abstract:
A seal assembly for a fluid pressure control device includes a guide element having a scaling surface and a first guide surface. A throttling element assembly includes a throttling element positionable within a fluid flow path, the assembly defines a mating surface adapted to seal with the sealing surface, and a second guide surface sized to slidingly engage the first guide surface. A relief void is formed in at least one of the guide element and the throttling element assembly adjacent the first and second guide surfaces to receive loose solid material, to thereby prevent disruption of the seal formed between the sealing surface and the mating surface.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present application is a divisional application of co-pending U.S. patent application Ser. No. 10/985,305, filed Nov. 10, 2004, the entire contents of which are hereby incorporated herein by reference. 
     
    
     FIELD OF THE DISCLOSURE  
       [0002]     The present disclosure generally relates to fluid pressure control devices and, more particularly, to assemblies for sealing between sliding components used in such devices,  
       BACKGROUND OF THE DISCLOSURE  
       [0003]     Fluid pressure control devices, such as control valves at-d regulators, are commonly used to control the flow characteristics of a fluid. A typical device includes a valve body defining an inlet, an outlet, and a fluid flow path extending between the inlet and the outlet. A valve seat is coupled to the valve body and defines an orifice through which the flow path travels. A throttling element, such as a plug, is moveable relative to the valve seat thereby to control fluid flow through the orifice. In a sliding-stem fluid control device, the throttling element is coupled to a stem extending outside the valve body, which in turn is coupled to an actuator for positioning the throttling element relative to the valve seat.  
         [0004]     Sliding stem fluid control devices often require components for guiding the throttling element assembly with respect to the valve seat. In particular, it is desirable to guide the linear movement of the throttling element assembly so that it is concentric with the bonnet, packing bore, cage, seat ring, or other component coupled to the valve body. Close guiding of the stem and/or plug tip also maintains maximum lateral stability to resist vibration and fatigue failures, Accordingly, components which guide movement of the throttling element often include guide surfaces that slide against one another.  
         [0005]     Rubbing and sliding of guide components in fluid control devices may cause material from the valve components to become free due to wear, galling, or other causes. The non-corrosive materials used for some applications are particularly susceptible to galling. Galling and other wear phenomena can cause movement and transfer of component material along the contact path. The loose material may degrade or disrupt sealed engagements within the fluid control device, such as the primary seal between a throttling element and seat, a secondary seal between a throttling element and cage, or a stem packing seal between a stem and packing assembly, to name a few.  
         [0006]     Conventional approaches to reduce galling typically employ the use of dissimilar materials for the components which contact one another. This practice can result in higher cost materials and assembly, and may limit use of the device in certain applications. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a side elevation view, in cross-section, of a fluid control device having a relief void positioned adjacent the contact surface between a plug and seat;  
         [0008]      FIG. 2  is an enlarged view of a detail of  FIG. 1  illustrating the relief void;  
         [0009]      FIG. 3  is a side elevation view, in cross-section, of a second embodiment of a fluid control device having a relief void positioned between a plug and cage;  
         [0010]      FIG. 4  is an enlarged view of a detail of  FIG. 3  illustrating the relief void; and  
         [0011]      FIG. 5  is a side elevation view, in cross-section, of a further embodiment of a fluid control device having a relief void positioned adjacent the stem and packing assembly.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     A seal assembly for a fluid control device is disclosed which includes a relief void for reducing the deleterious affects of galling or other wear damage to sealed contact areas within the device. The relief void provides a space into which material, typically metal material, from components in contact may collect, thereby preventing the material from entering areas intended for sealed contact. For example, the relief void may be positioned adjacent the sealed contact area between a plug and valve seat, between a plug and cage, or between a stem and packing assembly. While these exemplary embodiments are described in greater detail below, it will be appreciated that the relief void may be located in other areas within a fluid control device that would benefit from the benefits taught herein.  
         [0013]      FIGS. 1 and 2  illustrate a sliding-stem, single port, unbalanced plug control valve  10  having a valve body  12  defining an inlet  14  and an outlet  16 , wherein the valve  10  controls fluid flow from the inlet  14  to the outlet  16 . A valve seat  18  is coupled to the valve body  12  and defines an orifice  20  through which the flow path passes. In the illustrated embodiment, the valve seat  18  is coupled to the valve body  12  by a threaded engagement, however other known coupling methods may be used. An upper portion of the valve seat  18  is formed with a sealing surface  22 , which has a frostoconical shape in the exemplary embodiment. A lower portion of the valve seat  18  is formed with a cylindrical interior surface  24 .  
         [0014]     A throttling element assembly  26  is inserted through a top port  28  of the valve body to control fluid flow through the valve seat orifice  20 . The throttling element assembly  26  includes a throttling element, such as plug  30 , coupled to a stern  32 . The plug  30  includes a mating surface  34  that is shaped to complement the valve seat sealing surface  22 , SO that the mating surface  34  sealingly engages the sealing surface  22  to form a primary seal when the plug  30  is in the closed position, as illustrated in the  FIG. 2 . The plug  32  also includes a cylindrical exterior surface  36  sized to slidingly engage the valve seat interior surface  24 . In this embodiment, the interior surface  24  of the valve seat  18  and the exterior surface  36  of the plug  30  provide first and second guide surfaces which direct the plug mating surface  34  toward the valve seat sealing sur:face  22  as the throttling element assembly  26  moves to the closed position.  
         [0015]     In the embodiment illustrated in  FIG. 1 , the plug  30  further includes flow characterizing legs  38  extending downwardly from the exterior surface  36 . The legs  38  are shaped to form gaps  40  therebetween, thereby to obtain desired flow characteristics when the throttling element assembly  26  is only partially open, as is well known in the art. It will be appreciated that other types of plugs, with and without flow characterizing legs, may be used without departing from the scope of the present disclosure.  
         [0016]     The stem  32  extends from a top surface of the plug  30  and through the valve body top port  28 . A free end  42  of the stem  32  is adapted for coupling to an actuator (not shown) which provides a motive force to the throttling element assembly  26 .  
         [0017]     A bonnet assembly  43  is coupled to the valve body  12  to enclose the top port  28  and to seal with the stem  32 . The bonnet assembly  42  includes a bonnet  44  releasibly coupled to the body  12 , such as by fasteners. The bonnet  44  has an inner bore  48  defining a packing chamber  50  and a neck  52 . The neck  52  may slidingly engage the stem  32  to provide additional guidance to the throttling element assembly  26  during movement, as discussed in greater detail below with reference to the embodiment of  FIG. 5 . A packing assembly  54  may be inserted into the packing chamber  50  to seal between the valve stem  32  and the bonnet inner bore  48  to prevent leakage of fluid therethrough.  
         [0018]     A relief void  56  is formed in the valve seat  18  to reduce the risk of freed material, such as from galling, from entering the primary seal area. As illustrated in  FIGS. 1 and 2 , the relief void  56  is formed as a generally annular groove which creates a gap between the plug exterior surface  36  and the valve seat interior surface  24 . The void  56  has a volume sufficient to receive material from the plug  30 , the valve seat  18 , or other component that may be loosened or otherwise transferred during operation of the throttling element assembly  26 .  
         [0019]     In the exemplary embodiment the relief void  56  is positioned between the primary seal formed by the sealing surface  22  and mating surface  34  and the guide surfaces provided by the plug exterior surface  36  and the valve seat interior surface  24 . Accordingly, material freed by galling, wear, or other causes, which will typically originate in the area of the guide surfaces, will collect in the relief void  56 , thereby avoiding disruption of the primary seal. Material deposited in the relief void  56  may be subsequently removed by process fluid flow or may remain in the relief void indefinitely. While the exemplary embodiment shows the relief void  56  positioned immediately adjacent the primary seal, it will be appreciated that the relief void  56  may have other locations, as long as it is proximate either the guide surfaces or the sealing surfaces. Furthermore, while the relief void  56  is shown as formed in the valve seat  18 , it may additionally or alternatively be provided in the plug  30 . Accordingly, the same or similar materials may be used for the valve seat  18  and plug  30 , such as  316  Stainless Steel,  304 L Stainless Steel, Stainless Steel Alloy  20 , or the like.  
         [0020]      FIGS. 3 and 4  illustrate an alternative embodiment of the seal assembly incorporated into a valve  110  having a cage-style trim and balanced valve plug. The valve  110  includes a valve body  112  defining an inlet  114  and an outlet  116 , wherein the valve controls fluid flow from the inlet  114  to the outlet  116 . A valve seat  118  is coupled to the body  112  and defines an orifice  120  through which the flow path passes. Again, while the valve seat  118  is illustrated as being coupled to the valve body  112  by a threaded engagement, other known types of couplings may be used. The valve seat  118  includes a sealing surface  122 .  
         [0021]     A throttling element assembly  126  and a cage  160  are inserted through a top port  128  of the valve body  112  to control fluid flow through the valve seat orifice  120 . The cage  160  includes a flange  162  that is coupled to and substantially closes off the body top port  128 . A cylindrical wall  164  extends downwardly from the flange  162  and has a bottom edge  166  that is spaced from the valve seat  118  when assembled, thereby to allow fluid flow therebetween. The cylindrical wall  164  further defines an interior surface  168 . The cage  160  also includes a boss  170  having a center bore  172  formed therein. The center bore  172  is substantially concentric with the interior surface  168  and defines a packing chamber  150  and a neck  152 .  
         [0022]     The throttling element assembly  126  includes a throttling element moveable within the fluid flow path. The throttling element, such as a plug  130 , is coupled to a stem  132  which extends from a top surface of the plug  130  and through the valve body top portion  128 . A free end  142  of the stem  132  is adapted for coupling to an actuator (not shown) which provides a motive force to the throttling element assembly  126 . A bottom portion of the plug  130  includes a mating surface  134  that is shaped to complement the valve seat sealing surface  122 , so that the mating surface  134  sealingly engages the sealing surface  122  to form a primary seal when the plug  130  is in the closed position. The plug  132  also includes a balance port  133  which allows fluid to flow into an upper chamber  135  defined by the cage  160  and an upper surface of the plug  130 .  
         [0023]     The plug  130  includes a guide ring  137  defining an exterior surface  136  sized to slidingly engage the cage interior surface  168 . In this embodiment, both the guide ring  137  and the cage interior surface  168  are cylindrical to provide first and second guide surfaces adapted to direct the plug mating surface  134  toward the valve seat sealing surface  122  as the throttling element assembly  126  moves the closed position.  
         [0024]     The plug  130  also includes a seal ring  139  for preventing fluid leakage through a secondary flow path between the cage  160  and plug  130 . The seal ring  139  is also generally cylindrical and defines a second mating surface  141  sized to slidingly engage and seal with the cage interior surface  168 . The seal ring  139  may be formed of a material that adequately seals with the metal cage material while allowing sliding along the cage interior surface  168 . Possible materials include a fluoropolymer resin, such as the TEFLON® product marketed by DuPont, a graphite material or nitrile rubber.  
         [0025]     A first relief void  156  is formed in the plug  130  to reduce the risk free material from entering the secondary seal area of contact between the seal ring  139  and the cage interior surface  168 . As best illustrated in  FIG. 4 , the relief void  156  is formed by an intermediate recessed portion  158  of the plug  130 . The intermediate recessed portion  158  creates a generally annular groove having a volume sufficient to receive material from either the plug  130 , the cage  160 , or other valve components that may be loosened or otherwise transferred during operation of the throttling element assembly  126 . In the illustrated embodiment, the first relief void  156  is positioned between the guide ring and the seal ring, however the alternative locations noted above with respect to the embodiment of  FIGS. 1 and 2  may also be used.  
         [0026]     To further protect the sealed contact between the seal ring  139  and the cage interior surface  168 , a second relief void  190  may also be provided. As illustrated in FIGS,  3  and  4 , the second relief void  190  is formed by a top portion  192  of the plug  130  having a reduced diameter. As with the first relief void  156 , the second relief void  190  creates a gap between the plug  130  and the cage interior surface I  16  which may receive material Freed by galling, wear, or other causes.  
         [0027]     An additional embodiment of a seal assembly for use in a fluid control device is illustrated in  FIG. 5 , which shows an enlarged elevation view, in cross-section, of a sealed contact between a packing assembly  210  and a stem  211 , The stem  211  is part of a throttling element assembly including a throttling element (not shown). A bonnet  212 , which may be coupled to a valve body (not shown), includes a center bore  214  sized to receive the valve stem  211 . The center bore  214  defines a packing chamber  218 , a neck  220 , and a receptacle  222 . The packing assembly  210  maybe inserted into the packing chamber  218  to seal between the valve stem  211  and the inner bore  214 , thereby to prevent leakage of fluid therebetween.  
         [0028]     The illustrated packing assembly  210  includes a V-ring  230 , a male adaptor  232 , a female adaptor  234 , upper and lower anti-extrusion rings  236 , and a packing box ring  238 , however, other known packing box components may be used without departing from the present disclosure. In operation, the packing assembly  210  is compressed so that an interior mating surface  240  of the V ring  230  sealingly engages an exterior sealing surface  242  of the stem  211 . Material for the V ring  230  is selected so that it provides a good seal with the stem while allowing the stem to slide.  
         [0029]     A bearing ring  246  is inserted into the receptacle  222  for further guiding the stem  211  during travel. As such, the bearing ring  246  includes an interior surface  248  that closely fits an exterior surface of the stem  211 , yet allows the stem to slide. Accordingly, the interior surface  248  and stem exterior surface provide guide surfaces for directing sliding movement of the throttling element assembly,  
         [0030]     A relief void  250  is formed adjacent the interior surface  248  for receiving loosened material, thereby reducing the risk of degrading the packing assembly/stem seal. The relief void  250  is formed as an enlarged diameter portion of the interior surface  248 , which creates an annular groove. The groove defines a gap between the bearing ring interior surface  248  and the stem exterior surface having a volume sufficient to receive valve material loosened during operation. In this embodiment, the relief void  250  is positioned immediately adjacent the guiding surfaces defined by the bearing ring interior surface  248  and the stem exterior surface, which are slightly spaced from the sealed contact between the packing assembly and stem.  
         [0031]     The foregoing detailed description has been given for clearness and understanding only, and no unnecessary limitations should be understood therefrom, as modifications would be obvious to those skilled in the art.