Abstract:
A seat assembly including preferably telescoping seating elements for use between a gate and a pocket in a gate valve body are disclosed. A seal is provided between the telescoping seating elements that is axially moveable and acts to seal with one or more sloping surfaces disposed on the seating elements. A spring acts to bias the seal towards the sloping surfaces so as to provide an initial seal. The sloping surfaces prevent movement of the seal in one axial direction. As line pressure increases the seal will move against the sloping surfaces with increased force to maintain the seal between the line or valve bore and the bonnet of the valve. A reverse pressure differential across the seal that is greater than the biasing force will cause the seal element to move in the opposite axial direction and bleed off the pressure across it. The seal may be metallic or have metal core with a coating of substantially non-elastic, non-permeable, chemically inert material of the type that is resistant to well bore fluids and other chemicals as well as unaffected by substantial changes in temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to gate valves and, more particularly, to apparatus and methods for a preferably telescoping seat assembly having an axially moveable seal element therebetween. 
     2. Description of the Background 
     Gate valves with telescoping seat assemblies have been in use for some time and have unique advantages. One advantage of this type of seat assembly in particular is the ability to provide a force on the seats that varies due to pressure differentials encountered. In this way, one is assured of a good seal with a wide range of pressure differentials. Another advantage is that friction due to movement of the gate may be kept at a minimum because the seat force applied to the gate may adjust as necessary to maintain the seal. 
     An exemplary type of telescoping valve seat assembly gate valve is shown in U.S. Pat. No. 4,878,651, issued Nov. 7, 1989, to F. W. Meyer, Jr., which is incorporated herein by reference, as a through conduit gate valve apparatus with a valve seat assembly that is field maintainable and which prevents the occurrence of pressure lock. Each valve seat assembly includes a retainer ring fixed in the valve body and a pressure responsive seat ring that seals with the gate member. The seat ring is responsive to fluid pressure in the valve flow passageways for maintaining and enhancing the face seal with the gate and to fluid pressure in the valve chamber for automatically venting the valve chamber to present occurrence of a pressure lock condition. 
     Another telescoping valve seat assembly gate valve is shown in U.S. Pat. No. 5,201,872, issued Apr. 13, 1993, to M. L. Dyer, that discloses a gate valve wherein bore pressure in the body cavity of the valve is isolated in the open and closed position. In the closed position, a double metal sealing barrier is provided across the gate. In the open position, the pressure is isolated from the stem packing and bonnet gasket by the seats on either side of the gate. Formation of hydrates in the body cavity is eliminated, and better retention of body grease is achieved during flow through the valves. Metal-to-metal seal surfaces are developed, thereby eliminating wear on the non-metal components and reducing torque requirements. 
     In some cases, it would be desirable to provide for another method of venting excess pressure in the bonnet. As well, it would be desirable to provide for increased or wider range of temperature operating conditions for a gate valve. In another application, it would be desirable if the downstream seat assembly provided a backup seal if the upstream seat assembly were to fail. Those skilled in the art have long sought and will appreciate the present invention which addresses these and other problems. 
     SUMMARY OF THE INVENTION 
     The present invention provides for a sealing assembly adapted for positioning between the body and the gate of a gate valve. The body defines a flow path therethrough and pockets in which the sealing assembly is positioned. The sealing assemblies on each side of the gate valve are preferably mirror images of each other so that only one is described herein and includes a substantially circular first seat element. As well, a substantially circular second seat element is provided. In one embodiment, the second seat element is telescopingly received with respect to the first seat element such that the first seat element and second seat element are each moveable in an axial direction with respect to the flow path. A sloping surface is provided for at least one of the first seat element or the second seat element. A substantially circular seal element is disposed between the first seat element and the second seat element adjacent to the sloping surface. A biasing spring is provided for biasing the circular seal toward the one axial direction with respect to the flow path for producing an initial seal between the sloping surface and the seal ring. In one embodiment, the circular seal element consists of metal and in another embodiment the circular seal element comprises metal and a coating of material that is non-permeable material substantially without memory that is, in other words, substantially inelastic. The coating is flexible or sufficiently malleable so as to form a seal with the sloping surfaces. If the seal ring consists of metal, then the seal ring is preferably of a different and preferably a softer metal than the sloping surfaces so as to be shaped somewhat for improving the seal therebetween. The seal is mounted for movement in an opposite axial direction in response to a pressure differential across the seal large enough to overcome the force of the biasing spring such that a reverse pressure differential produces flow between the sloping surface(s) and the seal element. 
     It is an object of the present invention to provide an improved seat assembly for a gate valve. 
     It is another object of the present invention to provide a seat assembly that includes a unidirectional seal element. 
     It is yet another object of the present invention to provide a seat assembly that operates at higher temperatures and pressures. 
     It is yet another object of the present invention to provide a seating assembly that will provide a backup downstream seal in case the primary upstream seal fails. 
     A feature of the present invention is an axially moveable sealing element that engages sloping surfaces between two seat elements. 
     Any listed objects, features, and advantages are not intended to limit the invention or claims in any conceivable manner but are intended merely to be informative of some of the objects, features, and advantages of the present invention. In fact, these and yet other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the drawings, the descriptions given herein, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, partially in section, of a gate valve in accord with the present invention; 
     FIG. 2 is an enlarged elevational view, in section, of a portion of a seat assembly with seal element therebetween in accord with the present invention; and 
     FIG. 3 is an enlarged elevational view, in section, of a portion of a seat assembly with a coated seal element therebetween in accord with the present invention. 
    
    
     While the present invention will be described in connection with presently preferred embodiments, it will be understood that it is not intended that the invention is limited to those particular embodiments but the descriptions given herein merely are to provide sufficient information such that one skilled in the art may practice one or more presently preferred embodiments of the invention, in accord with the patent statutes. Thus, the descriptions of the invention provided herein are not intended to limit the invention in any way. On the contrary, it is intended that all alternatives, modifications, and equivalents included within the spirit of the invention and as defined in the appended claims be encompassed as a part of the present invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing, and more particularly to FIG. 1, where a preferred embodiment of gate valve  10 , in accord with the present invention, is illustrated. Gate valve  10  uses two preferably mirror image sets of telescoping seat assemblies such as seat assemblies  100  that have numerous advantages for operation with a gate valve as discussed hereinafter. 
     Gate valve  10  includes a valve body  12  with a removable bonnet or cap portion  13  that provides access to body cavity or gate chamber  14  which is formed within valve body  12  and contains the working gate valve components. Valve body  12  defines flow passageways  16  and  18  which are preferably aligned on a common axis and preferably form a straight through flow path wherein fluid flow is controlled. Depending on design, passageways  16  and  18  are typically designated as upstream and downstream passageways and may require connection in this manner. In a preferred embodiment of the invention, seat assemblies  100  are mirror images of each other and gate valve  10  may be mounted with either passageway  16  or  18  as the upstream passageway. Flanges  20  and  22  may be used to connect gate valve  10  in position although other means can be used for this purpose. 
     Within gate chamber  14  is gate  24  which moves at a right angle with respect to the axis of flow passageways  16  and  18  to thereby open and close gate valve  10 . Preferably gate  24  is mounted so as to be a floating gate thereby allowing some axial movement of gate  24 . This may be effected by leaving the bottom of gate  24  unattached and/or providing linkage to gate  24  that includes a slip joint or the like. Gate  24  is shown in the closed position and is in an open position when gate  24  moves upwardly, as shown in FIG. 1, and laterally with respect to flow passageways  16  and  18  so that gate passageway  26  is lined up with flow passageways  16  and  18 . Thus, when gate  24  is in a downward position as shown in FIG. 1, the valve is closed and when gate  24  is in an upward position, the valve is open. It will be understood that the terms “upper”, “lower”, and the like, refer to the figures and are used for convenience only and that the same components or portions of them may be oriented in different ways in operation, storage, manufacturing, and so forth as known by those skilled in the art. The outer surfaces on gate  24  are preferably polished for sealing purposes as is known to those of skill in the art. Gate  24  is typically operated by some means such as rotation of valve stem  25  within upper housing  27  from the exterior of gate valve  10  to reciprocate gate  24  upwardly and downwardly. Other means for operating gate  24  are known to those of skill in the art. 
     Valve body  12  has formed therein enlarged recesses or pockets  28  that mate with seat assemblies  100  at the juncture of passageways  16  and  18  and chamber  14 . Seat assemblies  100  cooperate with the pockets and gate to form a seal thereby preventing flow past gate  24  when gate  24  is closed. In a preferred embodiment, a metal-to-metal seal between gate  24  and valve seat assemblies  100  is formed as is known to those of skill in the art. The seal between seat assemblies  100  and pockets  28  may be of various types and include multiple seals including metal-to-metal and other types of seals as discussed hereinafter. 
     FIG. 2 discloses one preferred embodiment of seat assemblies  100  in accord with the present invention. It will be understood that the components are showed in substantially conceptual form for ease of understanding and are not intended to represent manufacturing dimensions, sizes, or details. Seating assembly  100  surrounds passageways  16  and  18  and is preferably circular in construction and preferably mounts into cylindrical shaped pockets  28 . First seat element  102  and second seat element  104  are preferably telescopically interconnected such that second seat element  104  is sized to fit within first seat element  102  within receptacle  106  formed within extension  108 . It will be noted that while the seating elements are preferably telescoping with each other, first seat element could be designed to fit within second seat element instead of as shown. Thus, there are no particular restraints on which seat element is interior with respect to the other seat element but in the presently preferred embodiment the seating arrangement is as shown. Surface  110  preferably seals with gate  24  with a metal-to-metal seal. Surface  110  may have various indentations or a designated surface area that may be larger or smaller than other surface area of the seating elements to effect a variable force acting against the gate so that the sealing force that pushes surface  110  against gate  24  is greater than force that would urge the two surfaces apart as is discussed at least in part in the above listed patents. 
     Chamber pressure is available along the top of seat assembly  100 , as shown in FIG. 2, and may enter at  112  into passageway  114  and receptacle  106  between first seat element  102  and second seat element  104 . Receptacle  106  is part of passageway  114 . As well, pressure from the valve passageways  16  and/or  18  may enter at  116  into passageway  114 . It will be understood that chamber pressure acts along upper surfaces  120  of seat assembly  100  and bore pressure acts along lower surfaces  122 . Thus, a differential pressure may typically exist across seal element  118 . 
     Seal element  118  is mounted between first seat element  102  and second seat element  104  within receptacle  106  and is positioned to isolate chamber pressure from line pressure such as pressure in one or both passageways  16  and  18 . Sloping surfaces  124  and  126  define receptacle  106 . Sloping surfaces have a slope that is offset with respect to the axis of passageways  16  and  18 . As well, the slope is not at right angles with respect to the open and closing movement of gate  24 . The angle of each sloping surface  124  and  126  may be different but in the preferred embodiment, are the same. It is possible that only one of the surfaces have a slope so that the opposite surface could be horizontal within the view of FIG. 1-3 or parallel to the axis of passageways  16  and  18 . Sloping surfaces  124  and  126  are positioned opposite of each other. Seal element  118  engages sloping surfaces  124  and  126  to form a seal that isolates valve chamber pressure with bore or line pressure. The angle of each slopping surfaces can vary over a wide range, typically between about zero and about sixty degrees. In one presently preferred embodiment, the angle is about eighteen degrees but that may be changed as desired. As the angle decreases with respect to the axis of passageways  16  and  18 , the sealing force acting on seal element  118  tends to increase due to mechanics of an inclined plane, assuming that the line pressure is greater than the valve chamber pressure. Preferably spring  128  is provided to bias seal ring or seal element  118  axially toward sloping surfaces  124  and  126  in the direction in which the slope of the angles of surfaces decreases thereby producing an initial contact and seal between sloping surfaces  124  and  126  and seal element  118 . Spring  128  may be of various types such as a Belville spring. Spring  128  may include several components, spacers, bushings, rings, and the like as desired to provide an initial seal force against seal element  118 . Spring  128  is preferably circular and surrounds passageways  16  and  18  as does seal element  118  and first and second seat elements  102  and  104 . Thus, preferably spring  128  applies a substantially uniform force around its circular perimeter. 
     Therefore seal element  118  is mounted so as to be moveable axially in the direction of spring  128  or in the direction of decreasing angles of sloping surfaces  124  and  126 . In this way for some applications, seal element  118  may be used to vent pressure from valve chamber  14  into the passageways if the valve chamber pressure is higher than line pressure. This situation may occur if the line pressure is reduced. Other means for venting pressure are discussed in U.S. Pat. No. 4,878,651 that may or may not be used in connection with this feature. As well, additional seal elements such as metal-to-metal seats, metal rings, or seals such as seal  130 , discussed subsequently, may be used along surface  132  between first seat element  102  and second seat element  104 . 
     Seal element  118  is shown with a circular cross-section but may have other shapes such as oval or oblong and the shape may change or be malleable depending on the material of which seal element  118  is made. If seal element  118  is a metal, then it may preferably be a different type of metal as compared with that of sloping surfaces  124  and  126  so that conformance may occur to effect the seal. Thus, seal element  118  is preferably a softer metal, e.g., brass, assuming seal element  118  is comprised wholly of metal. It is undesirable for seal element  118  to be comprised of an elastomeric or permeable material such as is used in O-rings because that will tend to limit the pressure range and temperature operating range of gate valve  10 . 
     FIG. 3 discloses another embodiment  100 A of the present invention wherein seal element  118  is partially metallic with metallic inner core  152  and an outer coating  154  of non-metallic material. The non-metallic material may be a polymer or thermoplastic that has little or no memory such as PEEK (polyetheretherketone), PES (polyethersulfone), PTFE (polytetrafluroroetheylene), and the like. In other words, it is substantially non-elastic but is pliable or flexible enough to act as a good seal material. The selected material should also be non-permeable so as to avoid the problem that many O-rings have of absorbing gasses under pressure and subsequently expanding or exploding when the pressure is released. The non-metallic material should also have a high temperature rating and be resistant to caustic and acidic fluids and other fluids such as those found in oil and gas wells or pipelines. Various materials are available for this purpose. 
     Seal member  130  may be comprised of the same or similar type of material as outer coating  154 . Seal member  130  is a unidirectional seal element and may be used for sealing between seat element  102  and valve body pocket  28 . Additional seals including metal-to-metal seals, unidirectional seals, and the like but preferably not elastic O-ring seals may also be used in place of or in conjunction with seal  130  along pocket seal surface  156  of seat element  102 . 
     In operation, pressure from the line will enter at  116  and act along the surfaces of passageway  114  to produce a force that creates a metal-to-metal seal at the gate along surface  110 . Seal  130  and/or other seals such as metallic rings, additional seals such as seal  130 , or metal-to-metal seals are used to seal with the valve pocket along surface  156 . As discussed previously, seal ring  118  seals between seat elements  102  and  104 . For the case where the valve is closed, and the upstream seating elements leak, the downstream seating elements are preferably designed to provide a backup seal. In this case, line pressure might be in upstream passageway  16  and a reduced or lower pressure may be in downstream passageway  18 . If the upstream seating elements  100  leak, then the line pressure would also enter chamber  14 . Although differential pressure would tend to allow leakage across downstream seating elements including seat element  118 , it may be desirable to have an additional seal along passageway  114  that would be activated, at a minimum, by pressure acting on gate  24  which, as stated previously, is preferably floating to permit some axial movement. The substantially large surface area of gate  24  produces a significant force along surfaces  114  so as produce a seal therein to activate the particular type of seal therein as necessary. As well, one or more seals would act to seal between the valve pocket and the downstream seat element  102 . 
     In summary, the present invention has numerous valuable advantages including extended temperature and pressure applications as well as the possibility to provide venting between the valve chamber and the line, and also the possibility of providing a downstream backup seal in case the primary upstream seal fails. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and it will appreciated by those skilled in the art, that various changes in the size, shape and materials as well as in the details of the illustrated construction or combinations of features of the various actuator elements may be made without departing from the spirit of the invention.