Patent Publication Number: US-2006006359-A1

Title: Low distortion seat ring assemblies for fluid valves

Description:
FIELD OF THE DISCLOSURE  
      The present disclosure relates generally to fluid valves and, more specifically, to low distortion seat ring assemblies for use with fluid valves.  
     BACKGROUND  
      Process control systems often employ fluid valves, such as rotary valves (e.g., ball valves, butterfly valves, etc.) and/or sliding stem valves such as, for example, globe valves to control the flow of process fluids. In general, the trim used within known sliding stem valves includes a seat ring, a gasket for sealing between the seat ring and the valve body, a closure member (e.g., a plug), and a cage, which may guide the movement of the closure member, provide a desired flow characteristic, reduce flow induced noise or turbulence, inhibit cavitation, etc.  
      In operation, the closure member may be moved linearly via a valve stem toward or away from the seat ring to vary an amount of fluid flowing through the valve. To close the valve and prevent the flow of fluid through the valve, the closure member or plug is driven against the seat ring. To achieve a tight shut off, the sealing surfaces of the seat ring and closure member must be substantially free of distortion.  
      In many known sliding stem valves such as globe valves, the seat ring is configured to be bolted to the valve body. However, when the seat ring is installed in the valve body and the bolts are tightened, the seat ring is often distorted in a manner that compromises the ability of the closure member to seal against the seat ring. For example, the seat ring may be distorted to have a non-circular opening or out-of-round characteristic and/or may otherwise become misaligned or improperly shaped with respect to the closure member.  
      To correct the seat ring distortions that occur when the seat ring is bolted to a valve body, the seat ring may be machined after it is installed within the valve body to restore its ability to seal against the closure member. However, once the seat ring has been machined in this manner, the seat ring and valve body become a matched set, thereby precluding subsequent field replacement or maintenance of the valve trim. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded assembly view of a known seat ring assembly.  
       FIG. 2  is a cross sectional view of the known seat ring assembly shown in  FIG. 1 .  
       FIG. 3  is an exploded assembly view of an example low distortion seat ring assembly.  
       FIG. 4  is an assembly view of the example seat ring assembly shown in  FIG. 4 .  
       FIG. 5  is a cross sectional view of the example seat ring assembly shown in  FIGS. 3 and 4 .  
       FIG. 6  is a cross sectional view of another example seat ring assembly.  
       FIGS. 7-9  are example multi-piece retainers that may be used with the example seat ring assemblies described herein.  
       FIG. 10  is an example fluid valve within which the example seat ring assemblies described herein may be used.  
     SUMMARY  
      In one example embodiment, a seat ring assembly for use with a fluid valve includes a seat ring having an outer circumferential surface and a shoulder extending about at least a portion of the outer circumferential surface. The shoulder includes a first surface configured to form a seal against a valve body and a second surface substantially opposite the first surface. The seat ring assembly also includes a seat ring retainer configured to be attached to the valve body and to apply a force to the second surface to hold the first surface to form the seal against the valve body.  
      In another example embodiment, a seat ring assembly includes a substantially cylindrical member having a first end configured to seal against a valve closure member and a second end configured to form a seal with a valve body. The seat ring assembly also includes a retainer configured to be attached to the valve body and to apply a force to an outer surface of the substantially cylindrical member to hold the first end of the substantially cylindrical member to form a sealed engagement with the valve body.  
      In yet another embodiment, a seat ring assembly includes a seat ring and a seat retainer configured to fasten the seat ring to a valve body to impart substantially no distortion to seat ring in a fastened condition.  
      In still another embodiment, a method of reducing distortion imparted to a seat ring when fastening the seat ring to a valve body includes placing the seat ring within the valve body, engaging a seat ring retainer with the seat ring, and bolting the seat ring retainer to the valve body to fasten the seat ring to the valve body without imparting substantial distortion to the seat ring.  
    
    
     DETAILED DESCRIPTION  
      The example low distortion seat ring assemblies described herein use a seat ring portion or structure and a retainer portion or structure to hold the seat ring portion or structure in a sealed engagement with a valve body. In contrast to known seat ring assemblies, the example seat ring assemblies described herein are configured so that a seat ring retainer applies a sealing force to a structure associated with an outer surface of the seat ring that is opposite and substantially aligned with a sealing surface and/or gasket associated with the seat ring. As a result of the manner in which the example seat ring retainers apply compressive force to the seat ring, distortion of the seat ring following its installation within the valve body is substantially reduced or eliminated, thereby eliminating the need to perform a secondary machining operation on the seat ring and enabling subsequent field replacement and maintenance of the seat ring assembly.  
      Before turning to a discussion of the example low distortion seat ring assemblies mentioned above, a description of an example known seat ring assembly is provided below in connection with  FIGS. 1 and 2 .  FIG. 1  depicts an exploded assembly view of an example seat ring assembly  100 . As shown in  FIG. 1 , a valve body  102  (only a portion of which is shown for clarity) includes a plurality of threaded apertures  104 . A seat ring  106 , which is of unitary construction, includes a plurality of passages  108  that correspond to the threaded apertures  104 . Cap bolts  110  pass through the passages  108  to threadably engage with the apertures  104  to fasten, fix or attach the seat ring  106  to the valve body  102 . A spiral gasket  112  is compressed between a sealing surface  114  of the valve body  102  and the seat ring  106  to form a seal therebetween. A cage (not shown) may be disposed on the seat ring  106  in a conventional manner.  
       FIG. 2  is cross sectional view of the example known seat ring assembly  100  shown in  FIG. 1 . As can be seen in  FIG. 2 , the cap bolts  110  pass through a portion of the seat ring  106  that is radially spaced from the portion of the seat ring  106  that contacts the gasket  112 . In addition, to ensure that the gasket  112  is compressed between the seat ring  106  and the valve body  102 , the sealing surface  114  is configured (e.g., is recessed) so that prior to installation of the seat ring  106 , an upper surface of the gasket  112  extends above a surface  118  of the valve body  102  (e.g., prior to its compression, the gasket  112  has a thickness that exceeds the depth of the recessed surface  114 ). When the seat ring  106  is bolted to the valve body  102 , the gasket  112  is compressed via a portion of the seat ring  106  that is spaced radially inwardly from (i.e., is not substantially aligned with) the cap bolts  110 , which imparts a bending moment to the seat ring  106  about the gasket  112 . The bending moment imparted to the seat ring  106  can result in a distortion of the seat ring  106 , which may prevent the seat ring  106  from sealing against a closure member such as a plug (not shown) unless a secondary machining operation is performed on the seat ring  106 .  
      In addition, the spiral gasket  112  is typically used with the example known seat ring assembly  100  of  FIGS. 1 and 2  to maintain tension in the cap bolts  110  to inhibit or prevent loosening of the cap bolts  110  and a loss of the seal between the gasket  112 , the valve body  102 , and the seat ring  106 . However, such spiral gaskets are relatively costly and have unpredictable compression characteristics, which further aggravate the above-noted seat ring distortion problems.  
       FIG. 3  is an exploded view of an example low distortion seat ring assembly  300  according to one embodiment. The example seat ring assembly  300  includes a valve body  302  (only a portion of which is shown for clarity), a flat sheet gasket  304 , a seat ring  306 , a seat ring retainer  308 , and threaded fasteners  310 .  
      As depicted in the example assembly  300  of  FIG. 3 , the valve body  302  includes a plurality of circumferentially spaced apertures  314 , which may be threaded to engage with the threaded fasteners  310 , and a sealing surface  316  that may be recessed relative to a surface  318  and configured to form a seal with the gasket  304  and the seat ring  306 . While the gasket  304  is depicted as being a flat sheet gasket, other suitable types of gaskets could be used instead.  
      As shown, the seat ring  306  is a substantially cylindrical member that has a first end  320  configured to seal against the gasket  304  and the sealing surface  316  of the valve body  302 . The seat ring  306  has a second end  322  that is configured to seal against a closure member such as a plug (not shown). The seat ring  306  also includes a structure such as, for example, a shoulder  324  that extends about at least a portion of an outer circumferential surface  326  of the seat ring  306 . The shoulder  324  is configured to engage with the seat ring retainer  308  to hold the first end  320  of the seat ring  306  to form a seal or in a sealed engagement with the valve body  302 .  
      The seat ring retainer  308  is substantially ring-shaped and includes a plurality of apertures or passages  328  through which the fasteners  310  pass to engage with the threaded apertures  314  to attach the seat ring retainer  308  and the seat ring  306  to the valve body  302 .  FIG. 4  depicts an assembled view of the example seat ring assembly  300  of  FIG. 3 .  
       FIG. 5  is cross sectional view of the example seat ring assembly  300  of  FIGS. 3 and 4 . As can be seen in  FIG. 5 , the shoulder  324  of the seat ring  306  has a first surface  330  that engages the gasket  304  (most clearly shown in  FIG. 3 ) to form a seal against the valve body  302 . The shoulder  324  has a second surface  332  substantially opposite and substantially aligned with the first surface  330 . When the seat ring  306  and seat ring retainer  308  are fixed, fastened or attached to the valve body  302  by tightening the threaded fasteners  310  into the apertures  314 , an inner circumferential portion  334  of the seat ring retainer  308  drives against the second surface  332  of the shoulder  324 . The ability of the seat ring retainer  308  to move relative to the seat ring  306  (e.g., pivotally) during installation of the seat ring  306  and the seat ring retainer  308  results in substantially all of the force applied to the seat ring  306  via the surface  332  to be substantially opposite or aligned with the surface  330 , the gasket  304 , and the surface  316 .  
      The seat ring retainer  308  may also include a circumferential chamfered portion  336  that may facilitate relative movement (e.g., rotation, rocking, pivoting, etc.) of the retainer  308  toward the shoulder  324  of the seat ring  306 . Such movement of the retainer  308  relative to the seat ring  306  may facilitate the sealing force applied by the retainer  308  to the seat ring to be substantially aligned with and opposite the gasket  314 . In contrast to the known seat ring assembly  100  shown in  FIG. 1 , and as a result of the manner in which the seat retainer  308  applies force to and holds the seat ring  306 , substantially no bending moment or distortion is imparted to the seat ring  306 . The substantial elimination of the above-mentioned bending moment and seat ring distortion can eliminate need to perform a secondary machining operation after the seat trim has been installed and enables subsequent field replacement or maintenance of the seat ring  306 .  
       FIG. 6  is a seat ring assembly  600  according to another embodiment. The seat ring assembly  600  is similar in many respects to the seat ring assembly  300  and includes a valve body  602  (partially shown), a seat ring  604 , a gasket  606  (e.g., a flat sheet gasket), a retainer  608 , and a plurality of threaded fasteners  610 . In contrast to the valve body  302  of the seat ring assembly  300 , the valve body  602  includes a structure such as a shoulder  614  that is configured to receive and support an outer circumferential surface of the retainer  608 .  
      When the retainer  608  and seat ring  604  are bolted or otherwise attached to the valve body  602  via the threaded fasteners  610 , an inner circumferential portion  616  of the retainer  608  applies force to a first surface  618  of a shoulder  620 , which extends about at least a portion of an outer circumferential surface  622  of the seat ring  604 . The force applied to the first surface  618  holds a second surface  624  against the gasket  606  to form a seal against the valve body  602 .  
      The ability of the retainer  608  to move (e.g., pivot about the shoulder  614 ) relative to the seat ring  604  during installation of the seat ring  604  and the retainer  608  enables the force applied to the shoulder  620  of the sealing ring  604  to be substantially opposite and aligned with the gasket  606 . As a result, substantially no bending moment and, thus, substantially no distortion is imparted to the seat ring  604  when the seat ring  604  is installed within the valve body  602 .  
       FIGS. 7, 8  and  9  depict example seat ring retainers having multiple sections or segments. In particular,  FIG. 7  depicts a two-piece retainer,  FIG. 8  depicts a four-piece retainer, and  FIG. 9  depicts a twelve-piece retainer, which provides a retainer section or segment for each threaded fastener used. The multi-piece retainers shown in  FIGS. 7-9  may be used to implement the retainers  308  and  608  described above. The multi-piece retainers shown in  FIGS. 7-9  may be advantageously used in applications where the inner diameter of the valve opening (e.g., the opening of the upper portion of the valve body to which a bonnet may be attached) is smaller than the outer diameter of the assembled seat ring retainer. In this case, the multiple pieces of the retainer can be separately passed through the valve opening and assembled within the valve body.  
       FIG. 10  is an example of a globe valve  1000  within which the example seat ring assemblies described herein may be used. The example valve  1000  includes a seat ring assembly  1002  that is fixed to a body  1004  of the valve  1000  generally as described herein. However, it should be understood that the example seat ring assemblies described herein may be more generally applicable to other types of fluid valves as well.  
      Although certain apparatus have been described herein, the scope of coverage of this patent is not limited thereto. To the contrary, this patent covers all embodiments fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.