High-pressure flexible seat valve trim

Abstract: The valve trim includes a flexible metal seat with a lip portion (28) which flexes outwardly upon sealing contact with a valve plug seating surface (14). A deformable seal (20) mounted in the seat is prevented from substantial outward movement by a rigid metal seal retainer (42) and is squeezed inwardly around the plug seating surface as the seat lip portion flexes outwardly.

Description: FIELD OF THE INVENTION This invention relates to fluid valves and more particularly to fluid sealing apparatus in fluid valves for providing a reliable shutoff of high pressure fluid. BACKGROUND OF THE INVENTION In many applications, such as in power plants, high temperature boiler feedwater systems require fluid valves having reliable valve fluid sealing components (i.e., valve trim) which is required to provide a tight fluid shutoff for long periods of time. Special problems arise in such environments in view of the high pressures and the high temperatures which can range from about 250° to about 450° Fahrenheit (121° to about 232° Celsius). Presently available valves for such environments include complex shaped valve trim components which lead to costly manufacturing and time consuming and costly replacement during normal valve maintenance. Typically, fluid valves employ metal-to-metal seating for all general applications over a wide range of pressure drops and temperatures, and metal-to-TFE (tetrafluoroethylene) seating for more stringent shutoff requirements. An example of such a standard and optional seating is available in a design ES valve body made by Fisher Controls International, Inc. This commercially available fluid valve includes a valve trim having a valve plug seating against a seal ring formed of tetrafluoroethylene (TFE) which is located in a metal seal ring housing and held in place by a metal disk retainer. While such a configuration is acceptable for most conditions, it is desired to provide a fluid valve with improved valve trim components for reliable use under stringent high pressure and high temperature conditions. In US-A-3 809 362 there is described an improved valve trim for high pressure fluid valve use, wherein a deformable plastic insert seat ring is mounted on a seat ring housing and held in place by a seat ring retainer. The seat ring retainer includes a series of inwardly and outwardly formed surfaces facing opposite similarly shaped seat ring housing surfaces, and with the deformable plastic seat ring having a similar series of surfaces and located between the retainer and the housing. During valve closing, the valve plug compresses the deformable seat ring to stress the ring above the yield point and cause it to act like a liquid to enable the seat ring to deform and displace so as to establish a plastic-to-metal hydrostatic seal. US-A-3 027 911 discloses a safety relief valve comprising a valve plug with an outwardly extending plug seating surface, a deformable, resilient seal ring and a seal ring housing located axially in line with said valve plug, said seal ring housing having an annular cavity for receiving said deformable, resilient seal, said cavity being formed by a flexible metal seat which comprises a flexible metal lip protruding from the seat ring housing. The resilient seal ring is arranged in the movable plug/plug guide assembly. During valve closing , the flexible metal lip contacts the valve seating surface and the seat flexes the flexible metal lip inwardly to cause the resilient seal ring to flow outwardly and contact the valve seating surface to form a plastic compression seal. In this valve, the plug and the plug guide must be threadably engaged and properly adjusted to deform the annular seal ring e.g. to the shape shown in Figure 3. It is desired to provide a fluid valve having a valve trim which is capable of reliable operation under high pressure, high temperature conditions. It is also desired to provide such a valve trim which is more easily manufactured and at less cost than presently available units and which can be more easily and readily maintained during normal valve maintenance. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a fluid valve as defined in the claims. The valve includes a valve plug with an outwardly extending plug seating surface, a deformable seal ring of resilient material, a seal ring housing with a flexible metal seat for holding the deformable seal ring, and a metal seal retainer surrounding the flexible metal seat and the seal. The seal retainer has a closely matching contour to the seal ring so as to hold the seal ring tightly in place and so that as the valve plug closes and engages the flexible metal seat, one portion of the metal seat flexes radially outwardly to squeeze the deformable seal inwardly against the valve plug. Outward movement of the seal during flexing of the rigid metal seat is prevented by the closely matching contour of the metal seal retainer. This valve trim has the capability to produce a tight seal on assembly with no adjustment being required. The seal relaxes when the valve plug is opened and is squeezed inwardly against the valve plug to form a leak tight seal around the perimeter of the valve plug as the valve plug contacts the flexible metal seat. The plastic seal is preferably made of carbon-filled TFE, which allows repeated valve closings at temperatures up to 450° Fahrenheit (232° Celsius). A significantly advantageous feature of the present invention is that the fluid valve, and particularly the valve trim components are readily manufactured, assembled, and can easily be replaced during maintenance. In particular, during assembly of the valve trim, the deformable plastic seal is merely inserted into the flexible metal seat and the seal retainer placed in position to surround both the seal and the flexible metal seat without any adjustment of the position of the components. BRIEF DESCRIPTION OF THE DRAWINGS The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the several figures and in which: Figure 1 is an expanded view illustrating a preferred embodiment of a set of valve trim components for a fluid valve in accordance with the principles of the present invention; and Figure 2 is a fragmentary sectional view of a valve including the assembled valve trim components as shown in Figure 1. DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a set of valve trim components 10 for a high pressure fluid valve in accordance with an embodiment of the present invention. A valve plug 12 includes an outwardly extending plug seating surface 14. A seal ring housing 16 includes a flexible metal seat 18 at an axial end of the housing for containing a deformable seal 20 formed of a resilient material such as an elastomer, rubber, synthetic resin polymer, etc. For high pressure applications it is preferred that seal 20 be formed of TFE or other synthetic resin polymer material. The flexible metal seat includes a cavity 22 which is formed and defined between an outer axially extending wall 24 and an inner axially extending wall 26. Wall 26 includes an extension portion projecting beyond cavity 22 and outer wall 24, and which extension portion ends in a thin, lip portion end 28. Wall 26 and lip portion end 28 are formed so that upon seating contact by valve plug seating surface 14, as shown in Figure 2, the lip portion will be flexed outwardly. It is preferred that the lip portion end has a small radius to define an arcuate surface 29 which contacts valve plug seating surface 14. Deformable seal 20 has a portion 30 adapted to fit within cavity 22, an outer trim portion 32 which extends slightly over an end 34 of outer wall 24; an inner portion 36 which extends slightly over lip portion end 28; and an contoured portion 40 which projects beyond cavity 22 and is adjacent to lip portion end 28. A rigid metal seal retainer 42 is adapted to surround the flexible metal seat and the deformable seal. In particular, retainer inner surface 44 is shaped similar to and closely matches the contour of seal ring housing surface 46, and retainer arcuate surface 48 is shaped similar to and closely matches the similar arcuate contour of outer surface 50 of the deformable seal. In addition, the closely matched contour surfaces of the retainer, seal and housing are formed with close dimensional tolerances so that there is a relatively snug fit between these components. Thus, with reference to Figure 2, it can be seen that when seal 20 is placed in the flexible metal seat 18, the seal retainer holds the seal in place with a closely matching contour when seal retainer bottom surface 52 abuttingly contacts a ledge 54 of the seal ring housing. O-ring 56 may be provided if desired as an additional seal between retainer 42 and housing 16. In operation, during closing of the valve, plug 12 is moved towards seal ring housing 16 so that plug seating surface 14 seatingly engages in metal-to-metal sealing contact with flexible lip 28. As the valve plug closes against the metal lip, the lip flexes, thereby squeezing against the seal 20. However, in view of the closely matched contour between seal retainer 42 and the seal 20, seal 20 cannot move outwardly and instead is squeezed inwardly against valve plug seating surface 14. This provides a leak tight seal around the perimeter of the valve plug. Upon opening of the valve, plug 12 is moved away from the flexible metal seat and the seal relaxes. The deformable seal 20 preferably is made of carbon-filled TFE, so as to allow repeated closings of the valve at temperatures up to 450° Fahrenheit (232° Celsius). Other grades of plastic material could be substituted for different temperature requirements and fluids. It is to be understood that while the present invention has been described for use in high pressure valves, where the valve trim is required to provide tight shutoff for long periods of time, the invention may also be used on less demanding situations involving lower pressure differentials and lower temperatures such as gasses or chemicals. In addition, while the present invention has been illustrated for use in a sliding stem valve, the valve trim itself can also be used in a rotary valve. As an example, the valve trim of the present invention could be adapted for use in a rotary type valve with an off-centered shaft that can rotate a valve plug into the trim seal, instead of merely sliding across the valve opening as in a normal ball valve configuration. The valve plug seating surface thus may be rotated into a flexible metal seat containing a deformable seal rigidly held in place by a surrounding metal seal retainer. A small seat portion may be flexed outwardly to squeeze the deformable seal inwardly against the rotary valve seating surface. The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

Claims: A fluid valve for high pressure applications including a valve plug (12) with an outwardly extending plug seating surface (14), a deformable, resilient seal ring (20) and a seal ring housing (16) located axially in line with said valve plug, said seal ring housing having a cavity (22) for receiving said deformable, resilient seal ring (20), said cavity (22) being formed in a flexible metal seat (18), characterized in that: said seal ring housing cavity (22) is arranged at an axial end of said seal ring housing (16) and in that said flexible metal seat (18) includes an inner wall (26) projecting axially contiguous with and extending beyond said cavity (22) and ending in a lip portion end (28) for seating engagement contact with said valve plug seating surface (14); said axially extending inner wall (26) and lip portion end (28) being dimensioned for flexible radial outward action upon urging of said valve plug seating surface (14) during seating engagement contact thereof; said deformable, resilient seal ring (20) is adapted to fill said cavity (22) and including a seal portion (40) contoured to be axially disposed adjacent to said lip portion end (28) of said flexible metal seat (18); a rigid metal seal retainer (42) is provided axially alignable with said valve plug (12) and said seal ring housing (16) and surrounding said flexible metal seat (18) and said seal ring (20); said rigid metal seal retainer (42) including an interior portion (44) having a surface contour (48) substantially similar to the surface contour (50) of said contoured seal portion (40) to enable said contoured seal portion (40) to be squeezingly urged inwardly against said valve plug seating surface (14) in response to said flexible radial outward action of said inner wall (26) and lip portion end (28) during seating engagement by said valve plug seating surface. The fluid valve of claim 1, wherein the metal seal retainer interior portion (44) and said contoured seal portion (40) having a substantially similar surface contour (48,50) also are formed with close dimensional tolerances. The fluid valve of claim 1 or 2, wherein said deformable seal ring (20) is formed of TFE or other synthetic resin polymer material. The fluid valve of any of claims 1 - 3, wherein said deformable seal ring (20) includes an inner rim portion (36) which extends over said lip portion end (28) of said inner wall (26). The fluid valve of any of claims 1 - 4, wherein said flexible metal seat (18) further includes an outer axially extending wall (24) opposite said inner wall (26) to define said cavity (22) there-between. The fluid valve of claim 5, wherein said inner wall (26) extends beyond said outer wall (24) in axial direction. The fluid valve of any of claims 5 - 6, wherein said deformable seal ring (20) includes an outer rim portion (32) which extends over said outer wall (24). The fluid valve of any of claims 1 - 7, wherein said lip portion end (28) includes an arcuate surface (29) for seating engagement contact with said valve plug seating surface (14). The fluid valve of any of claims 1 - 8, wherein said metal seal retainer interior portion (44) and said contoured seal portion (40) are formed with matching arcuate surface contours (48,50).

Inventors: DAVIS JAMES RUSSELL, DAVIS, JAMES RUSSELL
Applicants: FISHER CONTROLS INT, FISHER CONTROLS INTERNATIONAL, INC.
Application year: 1989
Main classification: F16K1
IPC codes: F16J15, F16K1