Summarv of the Invention According to the invention, a valve assembly configured to maintain a seal during thermal cycling in a range of predetermined temperatures includes a valve body defining an inlet, an outlet, and a flow passage extending therebetween. A housing including an internal wall defining a shaft bore is connected to the valve body. A moveable fluid control member is disposed in the flow passage for controlling the flow of fluid through the valve body, and an actuating shaft is interconnected with the fluid control member for moving the fluid control member between a first, fluid flow permitting position and a second, fluid flow preventing position.

The actuating shaft extends through the shaft bore with the internal wall of the housing being radially spaced from the actuating shaft to define a sealing cavity therebetween. A seal is located within the sealing cavity for inhibiting fluid flow between the actuating shaft and the housing. The seal is formed of a material that changes size with temperature and includes a plurality of first surfaces. The housing defines a plurality of opposed corresponding surfaces such that sealing contact of the seal with the actuating shaft and the housing is maintained during thermal cycling within the range of predetermined temperatures.

Preferred embodiments of the invention may include one or more of the following additional features. The plurality of first surfaces are formed by contact under pressure of the seal with the plurality of opposed corresponding surfaces of the housing. The seal includes

a primary seal, a secondary seal, and a biaser for loading the primary and secondary seals. The primary seal is formed of the material, e.g., a polytetrafluoroethylene-based material, that changes size with temperature and includes the plurality of first surfaces. The secondary seal is formed of a material, e.g, a graphite-based material, resistant to temperatures above the range of predetermined temperatures such that sealing contact of the secondary seal with the actuating shaft and the housing is substantially maintained at temperatures above the range of predetermined temperatures. The biaser maintains loading of the secondary seal after destruction of the primary seal.

A main seal is located between the valve body and the fluid control member for inhibiting fluid flow therebetween. A body seal is located in a region between the housing and the valve body for inhibiting fluid flow therebetween. The body seal includes a plurality of first surfaces and the housing defines a plurality of opposed corresponding surfaces such that sealing contact of the body seal with the housing and the valve body is maintained during thermal cycling within the range of predetermined temperatures. The plurality of first surfaces are formed by contact under pressure of the body seal with the plurality of opposed corresponding surfaces of the housing.

There is a centering gap between the housing and the valve body. A gap body seal and a seal retainer inhibit fluid flow through the centering gap.

The range of predetermined temperatures is a 300° temperature range (vs. 1000 for a standard valve) within the boundary temperatures of -400F and 4500F.

Advantages of the invention include protection against fugitive emission release from a valve under both thermal cycling conditions and exposure to fire.

Brief Description of the Drawings Fig. 1 is a somewhat diagrammatic illustration of a valve assembly of the invention, taken partially in section; Fig. 2 is a side section view of a housing of the valve assembly of Fig. 1; Fig. 3 is a side section view of a seal assembly disposed within the housing of Fig. 2; Fig. 3A is a side section view, similar to Fig. 3, with the seal assembly shown after exposure to fire; Fig. 4 is an enlarged side section view of region A-A of Fig. 1; Fig. 5 is a side view of a lower packing of the seal assembly of Fig. 3, shown prior to seal loading; and Fig. 5A is a side view of the lower packing of Fig. 5, shown after seal loading.

Descrintion of the Preferred Embodiment Referring to Fig. 1, a quarter-turn valve 10 includes a valve body 12 defining an inlet 14, an outlet 16, and a flow passage 18 extending therebetween. A housing bonnet 30 is mounted to valve body 12 by four bolts 31, two bolts being shown in the figure. A valve stem 20 is connected to, here shown integral with, a fluid control member 22 disposed in flow passage 18.

Fluid control member 22 includes a through channel 24 alignable with flow passage 18 for controlling the flow of fluid through valve body 12. Valve stem 20 further includes an actuating shaft 26 extending within housing 30 and connected to fluid control member 22 for moving the fluid control member between a first, fluid flow permitting position (Fig. 1) in which through channel 24 is aligned with flow passage 18 and a second, fluid flow preventing position (not shown) in which fluid control member 22 has been rotated a quarter turn to place channel 24 out of alignment with flow passage 18.

A sleeve 28 formed from, e.g., an unfilled polytetrafluoroethylene (PTFE) such as virgin PTFE, acts as a bearing surface and as a main valve seal between fluid control member 22 and valve body 12. An upper region 28a of sleeve 28 forms a full circumferential seal with valv body 12 to prevent the passage of fluid axially upward toward valve stem 20. A plug adjuster 52, mounted to housing 30 with bolts 53, is adjustable to produce a desired sealing load on sleeve 28. A packing gland 50, fixedly mounted to housing 30 with bolts 51, produces a desired, predetermined packing load on a valve seal 60, discussed further below.

Referring to Fig. 2, housing 30 has an internal wall 32 defining a shaft bore 34 for receiving actuating shaft 26. Internal wall 32 is radially spaced from actuating shaft 26 to provide sealing cavities 36, 38 located between wall 32 and shaft 26. The cavities 36, 38 are delineated by shoulder 33. A larger diameter region 35 of wall 32 receives packing gland 50. Housing 30 has a shelf area 40 defining one end of cavity 38 and including a plurality of keyed surfaces, e.g., serrations 42. A valve body contacting surface 44 of housing 30 also includes a region of a plurality of keyed surfaces, e.g. serrations 46.

Referring to Figs. 1 and 3, seal assembly 60 for inhibiting fluid flow between shaft 26 and internal wall 32 includes a primary seal 62, formed, e.g., of a chevron-style packing having a lower packing 81 and an upper packing 81a of carbon filled or unfilled PTFE, and v-rings 83 of unfilled PTFE or fluoroelastomer, located within sealing cavity 38; and a secondary seal 64, in the form of, e.g., a flexible graphite based flat seal, located within sealing cavity 36. A stack 66 of non- adjustable Belleville washer-type springs, e.g., three springs, disposed between the primary and secondary seals

62, 64 acts, through follower 68 to load both seals.

Follower 68 is formed, e.g., of a metal compatible with the application fluid and resistant to galling on the surfaces of housing 30 and stem 26; nitronic 60 is a preferred material when used with a stainless steel housing and stem. A leak detection port 67 provided in housing 30 between the primary and secondary seals allows monitoring of primary seal performance.

A seal washer 70 is located between stack 66 and secondary seal 64, and a seal retainer 72 is located on the opposite side of secondary seal 64. Both seal washer 70 and seal retainer 72 are formed, e.g., from a suitable non-galling material such as nitronic 60.

The fixed position of packing gland 50 produces a predetermined axial load on primary seal 62 by compression of the belleville spring washer stack 66 to a preestablished stack height. The predetermined load is a function of the stack height, and of the characteristics and stacking scheme of the belleville springs. This axial compression results in radial compression of primary seal 62 producing a seal between stem 26 and housing 30. Primary seal 62 thus performs the function of a back-up seal to the sealing action of sleeve 28.

The packing gland also axially compresses secondary seal 64 resulting in radial compression of secondary seal 64 producing an additional seal between stem 26 and housing 30. Secondary seal 64 thus performs the function of a back-up seal to the sealing action of primary seal 62.

Referring to Fig. 3A, in use, if valve 10 is subjected to high temperatures, e.g. above about 700°, such as might be encountered during a fire, and the PTFE- based primary seal 62 is consumed by the heat, the follower 68 is displaced, allowing the stack 66 of belleville washers to bear upon shoulder 33 of shaft bore

34, thereby maintaining a positive seal by continued loading of graphite-based secondary seal 64.

Referring to Figs. 4-5A, serrations 42 of shelf area 40 form an impression on a surface 80 of lower packing 81 of primary seal 62 such that, after assembly, the primary seal defines a plurality of opposed keyed surfaces, e.g., serrations 82, disposed in sealing contact with serrations 42 of shelf area 40. These opposed keyed surfaces serve to maintain sealing contact between the primary seal 62 and the opposed shelf surface 40 during thermal cycling, e.g., over a 3000 temperature range within the boundary temperatures of -400F and 4500F; the sealing contact being otherwise lost due to the higher rate of change in size of the PTFE based lower packing relative to the surrounding metal parts during cooling.

Between housing 30 and valve body 12, in the region of housing serrations 46, is located a body seal 84, formed, e.g, of unfilled PTFE. Serrations 46 form impressions in an upper surface 85 of body seal 84 such that, after assembly, the body seal defines a plurality of opposed keyed surfaces, e.g., serrations 86, disposed in sealing contact with serrations 46. As in primary seal 62, this sealing configuration maintains sealing contact during thermal cycling, e.g. over a 300° temperature range within the boundary temperatures of -400F and 4500F.

Adjacent body seal 84, is a second body seal 88, formed, e.g., of flexible graphite, and a body seal retainer 90 formed, preferably, of the same material, e.g., stainless steel, as valve body 12. Body seal retainer 90 acts as an anti-extrusion ring, permitting a gap 91 between valve body 12 and housing 30 while maintaining the seal between the valve body and housing. Gap 91 allows centralization of housing 30 on valve body 12 which properly positions seals 62, 64.

Other embodiments are within the following claims.