VALVE MEMBER

Abstract: A valve member (E) for a shut-off valve has a stem tip seal (F) and is adapted for selective movement axially towards and away from an associated valve seat (76). A generally cylindrical sleeve (80) is carried by the valve member (E) and has an end defining an outer annular seal surface (91) adapted for cooperative sealing engagement with the seat (76). Mounted centrally within the sleeve (80) for limited axial movement is a rigid cylindrical body (88) that defines an inner annular seal surface (90) adapted for engagement with the seat (76) at a location radially inwardly of the outer annular seal surface. Formed between the sleeve (80) and the rigid body (88) is an annular chamber (96) which opens axially inwardly from a narrow slot (94) located between the inner annular seal surface (90) and the outer annular seal surface (91). A mass of resilient packing material (97) substantially fills the chamber (96) and extends axially outwardly of the slot (94) to define a medial annular seal surface (103). Means are associated with the rigid body (88) for generating pressure on the packing material (97) when the body is forced axially towards the valve member (E). In addition, the inner annular seal surface (90) is configured to engage the seat (76) prior to engagement by either the medial annular seal surface (103) or the outer annular seal surface (91).

Description: The present invention relates to valves and more particularly, to a valve member having an improved stem tip seal. The invention is especially suited for use in a particular diaphragm type shut-off valve and will be described with reference thereto; however, the invention is capable of broader application and could be used in a variety of different valves. Typically, shut-off valves employ a valve member having a stem tip comprising a relatively soft, resilient material mounted on the end of the valve stem for sealing cooperation with a metal valve seat. A variety of different resilient materials mounted to the stem in different ways have been used in the prior art While many of the prior art proposals have performed adequately, seal breakdown, blowout, and chipping and nibbling have been ongoing problems. In addition, certain materials having highly desirable properties, such as high lubricity and resistance to attack by chemicals and high temperature, often produce cold flow and extrusion problems when used as stem tips seals. Accordingly, there has been an ongoing need for a stem tip seal which overcomes the noted problems while allowing a variety of seal materials to be used safely and effectively. One object of the invention is the provision of a stem seal assembly which significantly increases the life of the seals while preventing blowout, cold flow, and the like. A further object of the invention is the provision of a stem tip seal assembly which effectively confines the resilient seal material when the valve member is in both an open and closed position. In accordance with the present invention, there is provided a stem seal assembly for a shut-off valve which includes a valve member mounted for selective movement towards and away from an associated valve seat and a stem tip seal which includes a generally cylindrical sleeve carried by the valve member and having an end defining an outer annular seal surface adapted for cooperative sealing engagement with the associated valve seat, a generally cylindrical rigid body mounted centrally within the sleeve for limited axial movement and defining an inner annular seal surface adapted for engagement with the associated valve seat at a location radially inwardly of the outer annular seal surface, the cylindrical sleeve and the rigid body cooperating to define an annular chamber which opens axially inwardly from a narrow slot located between the inner annular seal surface and the outer annular surface, and a mass of resilient packing material substantially filling the chamber and extending axially outwardly of the slot to define a medial annular seal surface, means being associated with the rigid body for generating pressure on the packing material when the body is forced axially toward the valve member, and the inner annular seal surface being configured to engage the associated seat prior to engagement by the medial inner seal surface and the outer seal surfaces as the valve member is moved towards the seat. In accordance with another aspect of the invention, the outer seal surface is configured to make generally line contact with the associated seat after the inner and medial seal surfaces have engaged the seat. According to another aspect of the invention, the sleeve has an inner wall configuration such that pressure generated in the packing attempts to move the outer seal surface axially towards the associated seat. Because the inner seal surface is located annularly inwardly of the resilient packing and, further, because it makes sealing contact with the seat prior to engagement between the packing and the seat, the packing is brought into engagement with the seat only after substantially all flow through the seat has ceased. Additionally, the force acting from the seat against the rigid body causes the packing to be pressurized and move outwardly of the narrow slot into sealing engagement with the seat. This pressure also causes the outer sealing surface to be held in position relative to the packing and when the outer sealing surface engages the seat the packing is trapped in the slot in firm engagement with the seat. The relationship between the inner rigid body and the outer sleeve ensures that the resilient packing is totally enclosed to protect it while also preventing it from being extruded or cold flowing. In addition, as the valve is opened, the pressure on the packing is released so that the packing does not extrude or cold flow out of the narrow annular slot. The invention is further described, by way of example, with reference to the accompanying drawings in which:- Fig. 1 is a cross-sectional view of a diaphragm type shut-off valve incorporating a stem tip seal formed in accordance with the present invention; Fig. 2 is a greatly enlarged cross-sectional view of the stem tip and seat area of the valve of Fig. 1; and, Figs. 3 to 5 are partial cross-sectional views showing the stem tip seal and its relation to the associated valve seat at various points in a closing cycle of the valve. Referring now to the drawings, Fig. 1 shows a shut-­ off valve assembly of the general type described in GB-A-2137738. The primary difference between the valve shown in Fig. 1 and that described in the afore­ mentioned GB-A-2137738 is with respect to the stem seal assembly which will subsequently be described in detail. The valve of Fig. 1 comprises a valve body A having a bonnet member B connected thereto by a bonnet nut C. The bonnet nut C and the body A are interconnected by threads 12. Additionally, cooperating shoulders 14 are formed between the bonnet nut C and the bonnet B such that, upon tightening of bonnet nut C, the bonnet B is moved axially towards the body A. A diaphragm D is securely clamped between the upper end of body A and the lower face of bonnet B. The diaphragm D is preferably, sealingly clamped between the body and bonnet by cooperating clamp faces more fully described in GB-A-2137738. Extending axially inwardly from the upper end of valve body A is a cylindrical bore 20 having a slightly larger outer end diameter at 22 and a reduced inner end diameter indicated generally at location 24. Inlet and outlet ports or openings 26, 28 connect from the exterior of body A through suitable passages with portion 24 of bore 20, as shown. Fluid inlet and outlet lines (not shown) can be connected to the inlet and outlet 26, 28, respectively, by any convenient known means. Positioned centrally in bore 20 is an axially movable valve member E which has an enlarged head portion 30 slidably guided in the larger diameter portion 22 of bore 20. The outer axial end of head 30 faces towards diaphragm D and has a generally spherical configuration. The radially outer periphery of the head 30 is generally hexagonal so that only the corners thereof are guided from the walls of the bore portion 22. Carried at the lower end of valve member E is a stem tip seal assembly F. As shown, a cylindrical outer surface 32 of assembly F is guided through a guide washer 34 having a cylindrical outer surface closely received in bore 20 and resting on the shoulder between the central portion of bore 20 and the smaller diameter inner end portion 24. Positioned between the guide washer 34 and the enlarged diameter head portion 30 of valve member E is a coil spring 36. The coil spring 36 acts to maintain a continuous upward bias on the valve member E to maintain the spherical upper surface of enlarged head 30 constantly in engagement with the diaphragm D. Selective operation of the valve member E in a direction axially of the bore 20 is provided by an operating stem 40 which extends axially through the bonnet to a position outwardly thereof. Cooperating external and internal threads 42 between stem member 40 and bonnet member B serve to impart axial movement to stem member 40 upon rotational movement thereof relative to the bonnet. An enlarged head 44 on the lower end of stem 40 carries a button 46 formed of plastic or other suitable material. The lower face of button 46 is convex and engages the diaphragm D on the opposite side thereof from the enlarged head 30 of valve member E. Connected at the upper end of stem 40 by splines 50 is an operating member 52 carrying an outwardly extending handle member 54. Operating member 52 is secured to the end of stem 40 by a nut 56 and a lock washer 58. A cover plate 60 snaps into a circular recess in the top of operating member 52 in a known manner. Associated with the operating member 52 and extending downwardly therefrom is a stop pin 64 which is received in an arcuate groove 66 formed in the upper end of bonnet B. Groove 66 is sized to limit the total range of movement of the operating member 52. Also associated with the operating member 52 and carried at the upper end of the bonnet B is an indicating ring or sleeve member 68 which cooperates with suitable indicia or a pointer carried on operating member 52 to give a visual indication of the position of the valve. In addition, bonnet B is provided with a panel nut member 70 which can be used for mounting the valve through a suitable panel opening (not shown). As mentioned earlier, the apparatus thus far described is shown and described is shown and described in great detail in GB-A-2137738. Of importance to the present invention is, however, the arrangement of the stem tip seal assembly F. As best shown in Fig. 2, the stem tip seal assembly F is carried at the reduced diameter lower end portion 74 of valve member E and is arranged to sealingly cooperate with an annular seat 76 defined by the bottom wall of portion 24 of bore 20 circumferentially about an axial inlet passage 78. Passage 78 of bore 20 is connected, as shown in Fig. 1, with the inlet port 26. In the embodiment under consideration, the assembly F includes an outer, imperforate cylindrical sleeve-­ like member 80 which is closely but slidably received on the lower end of valve member E. Preferably, sleeve 80 is formed of metal, such as stainless steel, and is retained on member E by a pair of tabs 82 which are deformed over the outwardly extending shoulder 84. Positioned centrally of the sleeve member 80 and axially aligned with valve member E and the seat area 76 is a relatively rigid insert body 88 having a circular lower face 90 of a maximum diameter slightly greater than the diameter of passage 78 and slightly less than the inner diameter of the lower end of sleeve 80. Thus, as illustrated, the insert member 88, in combination with the sleeve 80, defines a narrow slot 94 which extends circumferentially of the lower end face of the seal assembly F. The slot 94 opens inwardly to a chamber 96 defined by the lower end face 98 of of stem E, the inner wall of sleeve 80 and the outer side and top surfaces of insert 88. The chamber 96 is totally filled with a suitable resilient, elastomeric packing or seal material 97, such as polytetrafluoroethylene or the like. For reasons which will subsequently become apparent, the lower portion of the internal wall of sleeve member 80 is provided with a series of steps or serrations 100 which are arranged to cause the chamber 96 to have a gradually decreasing diameter in a direction towards the seat 76. The outer surface of the insert member 88 is similarly provided with reversely oriented serrations or shoulder portions 102. To assemble the tip assembly thus far described, the seal material 97 is preformed into a generally cup shape with its outer surface shaped to conform to the steps or serrations 100 of sleeve 80 and its inner diameter sized to the maximum diameter of insert 88. The cup shaped mass of packing or seal material 97 is then slid into sleeve 80 from its upper end and the sleeve and seal assembly are slid onto the lower end of valve member E to generally the position shown. Thereafter, the insert 88 is slid axially into position in the seal material 97. With the insert in position, a substantial axial force is applied to end face 90 of insert 88. As is apparent, with the arrangement thus far described, forces acting axially against lower face 90 of insert 88 generate pressure within the packing mass 97. This causes the packing to mould about the insert 80 and to tend to move downwardly through annular slot 94. Additionally, the internal pressures acting against the sleeve member 80 produce a resultant force tending to move sleeve 80 downwardly on valve member E. When the packing has been suitably pressurized and moulded about the insert 88, the tabs 82 of sleeve 80 are bent or deformed over the shoulder 84 and the tip assembly is in its assembled, operative condition. Referring to Fig. 3, the stem tip seal assembly F is shown in an open position vertically spaced from the seat surface 76. Preferably, the seat surface 76 has a generally conical configuration and forms an angle alpha of approximately 7 1/2° relative to a plane perpendicular to the axis 106 of the seal assembly F. The lower face 90 of the insert F forms an outer annular seal surface and preferably has a conical configuration which lies at an angle alpha relative to a plane perpendicular to axis 106. Angle alpha is preferably also approximately 7 1/2° so that the surface 90 is generally parallel to the seat surface 76. The lower end surface (91) of sleeve member 80 forms an inner annular seal surface and also has a generally conical configuration and lies at an angle beta which is preferably approximately 15° relative to the plane perpendicular to axis 106. As the stem tip seal assembly F is moved axially towards seat 76, engagement between the seat 76 and the seal assembly first takes place in a narrow annular band 101 between the insert 88 and the seat (76). Preferably, the band 101 has a width W in the range of 0.050 inch (1.27mm) or less. With continued downward movement of valve member E, the sealing pressure along band 101 increases and the pressure within the resilient mass 97 in chamber 96 is increased, causing the seal material to extend through slot 94 into engagement with seat 76 in a narrow annular band 103 about the insert 88. Preferably, the insert 88 and the sleeve 80 are sized such that this band has a width in the range of approximately 0.010 inch (0.254mm) to 0.020 inch (0.508mm). With continued downward pressure on valve member E, and the generation of increased pressure within the packing material in chamber 96, the sealing pressure between the seat 76 and the narrow band 103 produced by slot 94 and forming a medial annular seal surface continues to increase and the sleeve 80 finally makes line contact as shown in Fig. 5 and indicated by the point 105. This line contact is complete about the outer periphery of the narrow band 103 of resilient seal material extending through slot 94. The seal material is thus totally confined between the insert member 88 and the sleeve 80, while engaging the seat 76 with substantial force. The relationship between the insert 88 and the sleeve 80 thus totally confines the packing material 97 and prevents it from cold flowing even though it is contacting seat 76 with a relatively high sealing pressure.

Claims: 1. A valve member for a shut-off valve, the valve member (E) being adapted for selective movement axially towards and away from an associated circular valve seat (76) and being provided with a stem tip seal (F), characterised in that the stem tip seal comprises a generally cylindrical sleeve (80) carried by said valve member (E) and having an end defining an outer annular seal surface adapted for cooperative sealing engagement with the associated valve seat (76), a generally cylindrical rigid body (88) situated axially within said sleeve (80) for limited axial movement and defining an inner annular seal surface (90) adapted for engagement with the associated valve seat (76) at a location radially inwardly of said outer annular seal surface and a mass of resilient packing material (97) substantially filling an annular chamber (96) formed between said sleeve and said rigid body, said chamber opening axially inwardly from a narrow annular slot (94) located between said inner annular seal surface (90) and the outer annular seal surface and said packing material (97) extending axially outwardly of said slot to define a medial annular seal surface, the arrangement being such that pressure on said packing material (97) is generated when said body is forced axially towards said valve member and said inner annular seal surface (90) being configured to engage the associated seat (76) prior to engagement by said medial annular seal surface (103) and said outer annular seal surface (91) as said valve member is moved towards the seat. 2. A valve member according to claim 1, wherein said medial annular seal surface is configured to make contact with the associated seat along a narrow annular band (103). 3. A valve member according to Claim 1 or 2 wherein said outer annular seal surface (97) is configured to make generally line contact (105) with the said associated seat (76). 4. A valve member according to claim 1, 2 or 3, wherein said seal surface (90, 91) have a generally conical configuration. 5. A valve member according to any of claims 1 to 4, wherein said sleeve (80) is mounted for limited axial movement relative to said valve member (E). 6. A valve member according to claim 5, wherein said sleeve (80) has an inner wall configuration such that pressure generated in said packing (97) acts to attempt to move said outer annular seal surface (91) axially towards the associated seat (76). 7. A valve member according to claim 5, wherein said chamber has a generally increasing cross-sectional area axially inwardly of said slot (94). 8. A valve member according to claim 5, wherein said packing material (97) fully encloses said rigid body (88) axially inwardly of said slot (94), and wherein the radial exterior of said body has an axial series of circumferential grooves (102). 9. A valve member according to claim 8, wherein the interior of said sleeve (80) has an axial series of circumferential grooves (100) facing the circumferential grooves (102) on said body. 10. A valve member according to any of claims 5 to 8, including means (82) for limiting the axial outward movement of said sleeve (80). 11. A valve member for a shut-off valve, the valve member (E) being adapted for selective movement axially towards and away from an associated circular valve seat (76) and being provided with a stem tip seal (F), characterised in that the stem tip seal (F) comprises a rigid sleeve member (80) mounted on said valve member (F) and having an axial end defining an outer annular seal surface (97) adapted for cooperative engagement with the associated valve seat (76), a mass of resilient packing material (97) within said sleeve (80), and a rigid body (88) located centrally within said packing material (97) and defining an inner annular seal surface (90) facing axially outwardly for cooperation with the associated seat (76) at a location radially inwardly of said outer annular seal surface (97), means being associated with said rigid body (88) for generating pressure within said packing material (97) when pressure is applied to said rigid body (88) in an axial direction towards said valve member (E) and said outer and inner annular seal surfaces (91, 90) being configured to cause said inner annular seal surface (90) to engage the associated seat (76) prior to said outer seal surface (91) when said valve member (E) is moved towards said associated seat (76). 12. A valve member according to claim 11, wherein said inner annular seal surface (103) and said outer annular seal surface (91) define a narrow annular slot (94) therebetween through which a portion of said packing material (97) can extend to define a medial annular seal surface (103) adapted to cooperate with the associated seat (76). 13. A valve member according to claim 12, wherein said inner and medial annular seal surfaces have a generally conical configuration. 14. A valve member according to claim 13, wherein said outer seal surface has a generally conical configuration. 15. A valve member according to any of claims 11 to 14, wherein said inner annular seal surface (90) and said outer seal surface (91) are both inclined in a radial direction at different angles relative to one another. 16. A valve member according to any of claims 1 to 10 or any of claims 12 to 15, wherein said inner and medial annular seal surfaces each have a width in the range of 0.050 inch (0.127mm) or less.

Inventors: SCHEFFEL, GARY WILLIAM
Applicants: NUPRO COMPANY
Application year: 1987
Main classification: F16K1
IPC codes: F16K1