GB2388648A

GB2388648A - Attaching an elastomeric seal to a valve closure member

Info

Publication number: GB2388648A
Application number: GB0306351A
Authority: GB
Inventors: Otto Varga; Clive Dingley
Original assignee: Seetru Ltd
Current assignee: Seetru Ltd
Priority date: 2002-03-22
Filing date: 2003-03-20
Publication date: 2003-11-19
Anticipated expiration: 2023-03-20
Also published as: GB0306351D0; GB2388648B; DE10312967A1; ITMI20030537A1; GB0206767D0

Abstract

A valve sealing arrangement 1, such as a safety valve for use with refrigeration media, includes a plunger 2, or a disc secured to the plunger by means of screw thread or pin, and provided with a recess 6 in which an elastomeric seal 8 is chemically bonded such as by being moulded, cured and bonded. The seal 8 may be of annular shape having a bead 9 which protrudes beyond the sealing face 10 of the plunger 10, deforming inwardly upon contact with the valve seat 9 to provide a hydrostatic self sealing action. The seal 8 may have a feather edge 12 to prevent seepage behind the seal 8. Alternatively, the seal 8 may have an elastomeric film 22 integral with the bead 9 to prevent seepage behind the seal 8.

Description

IMPROVEMENTS IN OR RELATING TO

VALVE SEALING ARRANGEMENTS

10001] This invention concerns improvements in or relating to valve 5 sealing arrangements and has particular although not exclusive reference to such arrangements of use with refrigeration media.

100021 Soft seal arrangements for use in safety valves are well established and have proved to be capable of service on high pressure duty in a l0 reliable and leakproof manner. The present Applicant has developed a considerable number of seal elements over many years and they all share the characteristic that the seal element is a separate elastomeric component which is inserted into the safety valve plunger or disc and which develops in use a highly efficient sealing function in the interaction 15 between the safety valve seat and the safety valve plunger or disc. The expressions 'plunger' and 'disc' relate to the same component which is the normally spring-loaded closing component providing the safety valve action. As used herein the said expressions are interchangeable.

20 100031The design of the elastomeric component is such that it will not be dislodged during the safety valve action and remain firmly fitted in its recess throughout valve action.

[00041 However, a problem has been found to arise in service with 25 refrigeration media, such as Freon R22 and other mainly Fluorine-based refrigeration thermodynamic fluids. These media are very searching and are predisposed to permeate through the molecular structure of the elastomeric seal element. In particular, the media can enter the elastomer mass during the high pressure cycle and subsequently during the low 30 pressure phase, which occurs in many refrigeration systems, it can escape from the elastomer mass and cause fissures in it and lead to severe

leaking. Also, the refrigeration medium can pass through the seals and accumulate between them and the metallic valve plunger or disc material.

When this occurs it is possible for the seal to be forced out of its socket or for the seal to be torn when the medium escapes into the valve space 5 during a low pressure part of the refrigeration cycle.

[OOOS1 An object of the invention is to obviate this problem and provide an improved sealing arrangement impervious to highly searching refrigeration media.

10006] It is a further object of the present invention to provide a valve sealing arrangement with the capacity to display a sensitive hydrostatic self sealing action.

15 [0007] According to the invention a valve sealing arrangement includes an elastomeric seal chemically bonded to a valve plunger, the seal in use being co-operable with a valve seat.

100081 Conveniently the valve plunger of the valve sealing arrangement is 20 recessed to accommodate the seal which is moulded and bonded therein.

The recess may in section be rectilinear, curvilinear or arcuate.

100091 Preferably the seal is formed with a rim portion which protrudes to some extent from the face of the plunger in order to make initial 25 contact in use with the valve seat, the seal being bonded into the recess circumferentially and onto the base of the recess.

100101 The seal may be formed with a base having a rim portion, the base being constituted by a thin film of elastomer extending across the recess 30 and bonded thereto. The rim portion is bonded to the recess at its periphery. In use the film of elastomer serves to prevent any access of l

( the pressure medium to the back of the seal at any point. The rim provides the sealing function of the arrangement. This embodiment of sealing arrangement is suitable for valves of a relatively small size, for example of not more than 2cm diameter.

lOOIll For larger valves in view of the expense of elastomers, especially Men fluorinated compounds are involved an alternative configuration is provided and is of annular form fitting into and bonded within the recess which comprises a circular groove in the [ace of the plunger. The 10 relatively inner face of the plunger, extending inwardly of the groove, may be coincident with the level of the outer face, which extends outwardly of the groove. Alternatively the inner face may be lower or higher than the outer face dependent upon the required fluid action it is desired to create during operation of the valve plunger.

lOO 121 The circular groove may exceed the radial dimension of the elastomeric seal which may of L-shaped section with a relatively wide and somewhat bulbous upright rim, which is adapted to perform in the manner hereinbefore described. The foot of the seal may be of relatively thin 20 section of elastomer covering the base of the groove. In this embodiment in use the pressure medium may enter the groove space when the plunger is in the closed position in relation to the valve seat with which it is in contact. In this manner the fluid may exert radial pressure onto the sealing rim as described earlier in relation to seal arrangements employed 25 for smaller diameter valves.

100131 The face of the plunger is intended to make direct metal-to-metal contact with the valve seat, the seal in practice being sufficiently compressed to allow such contact generally under the action of a spring, 30 particularly in safety valves.

4] The seal of the present invention being moulded and bonded within the recess of the valve plunger is constrained radially outwards, but not in an inwardly direction and is thus able to distend to some extent into the cavity space of the recess. Accordingly pressure medium will in 5 use fill the cavity bounded by the seal rim and will act radially outward against the rim to provide a hydrostatic self-sealing force on the seal crown against the face of the plunger. The seal crown although bonded into the recess acts as part of an 'O' ring and will provide the well- known self-sealing action associated with 'O' rings.

100151 In alternative embodiments the thin film may be dispensed to leave the base of the recess or the groove uncovered. In this case the seal is in the form of an annulus provided with a feather edge foot sealed against the base of the recess or groove at a relatively small distance from the 15 sealing rim or bead. In these embodiments it is the feather edge foot that prevents ingress of pressure medium to the rear face of the seal. In all other respects the rim or bead functions in the same way as previously described, and relies on the hydrostatic action or the bead acted upon by the pressure medium.

[00161 As intimated supra the sealing arrangement requires metalto-

metal contact as between the plunger and the seat circumjacent the bonded seal. In this connection the plunger may be configured in any convenient manner to assist in the operation of the valve in terms of its opening and 25 closure within pressure limits as prescribed by the Safety Valve Standards. Such configuration outside the sealing area of the plunger has aerodynamic and/or hydrodynamic significance to the flow characteristics of the pressure medium through the valve whereby it will function efficiently and effectively within the time limits prescribed by the 30 Standards.

( 10017] It will be appreciated that the sealing arrangement of the present invention requires the valve plunger to be placed in the mould in which the elastomeric material is to be cured and bonded. Since with some valve sizes, the plungers are often quite deep it within the scope of the 5 present invention to provide a separate disc element of suitable material, for example metal or a plastics material, the element being significantly - shallower than the plunger per se. The element carries the bonded seal and is then secured to the plunger. Accordingly a relatively small or thinner element is required to be inserted into an elastomer mould and 10 accordingly production of the sealing element is improved.

100181 The securement of the disc element carrying the seal may be effected in a number of ways. For example the disc element may screw fixed to the plunger, push or press fitted, or retained by a thimble or 15 shroud member on the plunger. Since the disc element in practice will always be forced against the plunger as such by fluid pressure a particularly easy way of fitting is to provide a central pin or spigot for the plunger over which the disc element may and held together by a simple press fit. The pin or spigot may be in the form of a proprietary 20 hollow rolled spring element for positive location in the plunger and the disc element. This assembly facilitates assembly and reduces costs.

Furthermore, the ease with which the integers may be dismountable one from the other affords replacement possibilities whereby the disc element carrying the seal may be exchanged after use for new one as necessary or 25 the maintenance procedure dictates.

1001 9l The present invention also concerns a safety valve incorporating the valve sealing arrangement disclosed herein.

100201 By way of example only, two embodiments of the valve sealing arrangement according to the invention are described below with reference to the accompanying drawings in which: 5 100211 Figure I is a cross sectional view of a first embodiment in a first initial sealing position; 100221 Figure 2 is a cross sectional view of the first embodiment shown in Figure 1 in a final sealing position; 0023] Figure 3 is a cross sectional view of a second embodiment in a first initial sealing position; and 100241 Figure 4 is a cross sectional view of the second embodiment 15 shown in Figure 3 in a final sealing position.

100251 Referring first to Figures 1 and 2 a valve sealing arrangement is shown generally at 1 and includes a plunger 2 provided at its sealing end 4 with a recess 6 of rectilinear form in cross section. An annular 20 elastomeric seal 8 is moulded and bonded into the recess 6 at its base and its circumferential wall, and the seal 8 protrudes to some extent beyond the sealing face 10 of the plunger 2 in the form of a bead 9. At the junction between the recess 6 and the seal 8 there is provided a feather edge foot 12 which effectively prevents seepage of the pressure fluid 25 passing across the valve face 10 behind the seal 8. The sealing face 10 of the plunger 2 is defined by a shoulder 14 circumscribing the recess 6.

[00261 The plunger 2 is arranged axially with respect to the body of a safety valve (not shown) and its sealing face 10 is aligned with the valve 30 seat 16 formed on a central boss 18 having a through bore 20 for the passage of a pressure medium.

10027] As will be seen from Figure l when the valve plunger 2 approaches and is initial sealing contact with the seat 16, the seal 8 gently contacts the seat 8 with the seal beginning to deform inwardly into the 5 recess 6 thereby providing a sensitive hydrostatic sealing action. Upon completion of its closing stroke the plunger 2 moves such that its sealing face lO is intimate metal-to-metal contact with the seat 16, the seal being further deformed into the recess 6 to give a very good seal that is substantially impenetrable by searching fluids such as those employed in to refrigeration circuitry. This combination of impermeability and sensitive of contact as between the seal and the valve seat voids the problems associated with conventional safety valves.

100281 Referring now to Figures 3 and 4, like parts have been given like 15 numerals of reference. It will be observed that the seal 8 of the second embodiment is of a different form in that in addition to the bead 9 there is provided an elastomeric film 22 extending across and bonded to the base of the recess 6, the film 22 being integral with the bead 9 of the seal but being of smaller gauge. The provision of this film 22 is especially useful 20 for safety valves of relatively smaller size and serves to prevent the penetration of the pressure medium behind the seal.

Claims

1. A valve sealing arrangement including an elastomeric seal chemically bonded to a valve plunger, the seal in use being co-operable with a 5 valve seat.

2. An arrangement according to Claim 1 in which the valve plunger of

the valve sealing arrangement is recessed to accommodate the seal which is moulded and bonded therein.

3. An arrangement according to Claim 1 or 2 in which the seal is formed with a rim portion which protrudes to some extent from the sealing face of the plunger in order to make initial contact in use with the valve seat.

4. An arrangement according to Claim 3 in which in use after the said initial contact, the plunger face comes into metal-to-metal contact with the valve seat circumjacent the seal.

20

5. An arrangement according to Claim 4 in which in use during full closure of the valve the seal is distended inwardly and the fluid pressure medium exerts a force outwardly thereby in combination providing an effective hydrostatic seal preventing seepage.

25

6. An arrangement according to any one of the preceding claims in which the seal may be formed with a base having a rim portion, the base being constituted by a thin film of elastomer extending across the recess and bonded thereto.

30

7. An arrangement according to any one of the preceding Claims 3 to 6 in which the rim portion has a bead.

(

8. An arrangement according to any one of the preceding claims in which the recess is in the form of a circular groove in the sealing face of the plunger, the seal being moulded and bonded into the groove.

9. An arrangement according to Claim 8 in which the seal is moulded and bonded into the groove with one rim portion thereof being bonded to the circumferential wall of the groove, and a foot part thereof being bonded to the base of the groove.

10. An arrangement according to Claim 9 in which the rim portion is spaced from the other bounding wall of the groove.

11. An arrangement according to Claim 9 or 10 in which the foot has a 15 feather edge for the purpose of providing a seal to prevent pressure medium seepage behind the seal between the seal and the groove.

12. An arrangement according to any one of the preceding claims in which the recess is of rectilinear, curvilinear or arcuate form.

13. An arrangement according to Claim 8 and any claim dependent thereon in which the sealing face of the plunger within the area circumscribed by the groove is coplanar with that face of the plunger outside said area.

14. An arrangement according to Claim 8 and any one of Claims 9 to 11 as dependent on Claim 8 in which the seal ing face of the plunger within the area circumscribed by the groove is proud of that face of the plunger outside said area.

(

15. An arrangement according to Claim 8 and any one of Claims 9 to 11 as dependent on Claim 8 in which the sealing face of the plunger within the area circumscribed by the groove is below that of that face of the plunger outside said area.

16. An arrangement according to any one of the preceding claims in which the plunger is provided with a disc element securable thereto and carrying the seal moulded and bonded thereto.

10

17. An arrangement according to Claim 16 in which the disc element is recessed and the seal is accommodated therein.

18. An arrangement according to Claim 16 or 17 in which the disc element is detachably securable to the plunger.

19. An arrangement according to Claim 18 in which the disc element is provided with a screw mounting.

20. An arrangement according to Claim 18 in which the disc element and 20 the plunger are securable by means of a pin, the element being a push fit on the pin.

21. An arrangement according to Claim 20 in which the pin is hollow and sprung.

22. A valve sealing arrangement substantially as hereinbefore described with reference to Figures 1 and 2, and 3 and 4 of the accompanying drawings. 30

23. A safety valve incorporating a valve sealing arrangement as claimed in any one of the preceding claims.