GB2340899A

GB2340899A - Protection of a lip seal

Info

Publication number: GB2340899A
Application number: GB9917979A
Authority: GB
Inventors: Michael Jones; Andrew John Iddeson
Original assignee: Fluorocarbon Co
Current assignee: Saint Gobain Performance Plastics Corp
Priority date: 1998-08-06
Filing date: 1999-07-31
Publication date: 2000-03-01
Anticipated expiration: 2019-07-31
Also published as: GB9817012D0; GB9917979D0; GB2340899B

Abstract

A spring energised annular lip seal with a jacket (21) of polymeric material. The jacket has a cross-section including a channel portion (22) and peripheral sealing lips (24), to contact the surfaces to be sealed. An annular spring (23) is seated in the channel portion to support the sealing lips. In use, the spring, which is oversized for the channel is compressed, the cross-section becomes elliptical and protrudes from the channel, thereby protecting the sealing lips from damage. The jacket may be produced from virgin PTFE, polyamide or polyurethane with or without fillers or additives such as carbon, graphite, bronze, glass, molybdenum or combinations of these. The spring can be made from a resilient elastomeric material or helically wound flat metal strip or ribbon, where the metal may be stainless steel, nickel-chromium alloy, or cobalt-nickel-chromium-molybdenum alloy. The resilient elastomeric spring my be formed from ethylene, propylene, fluoroelastomer, nitrile rubber, polychloroprene or silicone rubber.

Description

U101006UK 2340899 SEALING DEN7C This invention relates to a scaling

device. It is particularly concerned with annular spring gised seals for hydraulic and fluid handling equipment such as cylinders, valves and energ 0 pumps.

Polymeric materials such as polytetrafluoroethylene (ptfe) are used extensively to manufacture annular seals, because they possess a combination of desirable properties such as resilience, low friction and resistance to wear and abrasion.

Sealing may be required between coaxial parts, for example, a piston and cylinder wh6-re relative movement is axial, or a shaft and housing where relative movement is rotational.

c Alternatively static seals may be required between parts which do not move relative to each other, to prevent fluid leakage between them. Face seals may also be required between mating surfaces.

In the type of seal with which the invention is concerned, a jacket of polymeric material such as ptfe is provided with a pair of sealing lips which press against the matin,(,,,, surfaces to be scaled. Such seals are primarily single-acting, with fluid pressure being applied to 0 1:7 only one side of the seal. For double-acting seals, where fluid pressure will be applied at both sides of the seal, two pairs of lips are provided at opposite ends of the seal, or two single-actine, seals are provided back to back.

W CP Primary scaling is achieved by the interference of the peripheral lips of the seal and the matin. surfaces. However, the effectiveness of such primary sealing is influenced by the resilience of the polymeric material and its tendency to relax or creep, thereby reducing W the radial loading between the lip and the mating surface. In addition, many polymeric materials used for such seals have relatively higher levels of thermal ex ansion and 0 p contraction than the mating metallic or other parts. Differential expansion or contraction will reduce the interference or contact pressure between the peripheral sealing lips and the 0 mating surfaces, giving rise to risk of leakage. This is particularly apparent when the fluid W => LPOW06UK 2 pressure is low.

To compensate for potential primary sealing, failure, it is- known. to "enerc,,ise" the peripheral lips of a seal with a spring member. The spring member, which can be metallic or of resilient elastomeric materig serves to support the seal and exert radial pressure on the lips to provide a secondary sealing force. However, this secondary sealing force alone cannot provide sealing if the lips of the seal are damaged.

1 1 Damage can occur during, assembly of the seal, particularly in equipment allowing only limited access. Damag p ge can also take lace in service. For example, a double-acting seal may be moved axially by excess pressure on one side of the seal, causing the periphe-r-al sealing lips at the other side to be crushed. The seal then becomes ineffective when the direction of pressure is reversed. In a single-acting seal, a sudden back-pressure created downstream of the seal may force the single-acting seal backwards, again giving rise to lip damage.

1 It is an object of the present invention to provide a spring energised seal which overcomes or reduces these problems.

According, to the invention there is provided a spring energised annular seal comprising 1 1 _n ajacket of polymeric material of annular shape overall and having a cross section including a channel portion provided with peripheral sealing lips adapted to contact matingr, members to be sealed., and an associated energising spring of annular shape overall seated in the channel portion of the jacket to support the peripheral sealing lips; wherein the energising spring protrudes from the channel portion between the peripheral sealing lips to protect the lips from damage.

The energising spring may comprise a metal spring or a resilient elastomeric spring, t> c 0 11:1 1 In a preferred embodiment, the energising spring is a helically wound metal spring, which 0 C-1) LP01006UK 3 may be of flat metal strip or ribbon.

The cross-section of the helically wound sprinj,:, may be slightly oversize for the channel portion, so that the cross-section of the spring becomes elliptical on assembly with the 3 jacket, with the longer axis of the ellipse so orientated as to protrude from the channel portion.

According to the intended use of the seal, in particular the expected pressure and 0 temperature range of use and the chemical environment, different materials may be selected for the jacket and for the energising spring. The polymeric jacket may be of ly C virgin ptfe or may use such fillers as carbon, graphite, bronze, glass or molybdenui-n -6r combinations of these. Alternatively, the material of the jacket may be based on polyamide or polyurethane, again with or without fillers or additives.

Metal energising springs may be of various grades of stainless steel, nickel-chromium 1 0 0 0 alloy, or cob alt-nickel-chromium-molybdenu m alloy, depending particularly on the chemical environment in which the seals are to be used. Elastomeric rubber energising g springs may be of ethylene propylene, fluoroelastomer, nitrile rubber, polychloroprene or 1 silicone rubber.

The invention also provides a fluid handling apparatus comprising a pair of components 0 0 having mating surfaces and a spring energised annular seal as set out above disposed between the components of the pair, Seals embodying the invention will now be described in more detail with reference to the accompanying drawings, in which:- Z 0 FIGURE 1 is a sectional view through a trunnion-mounted ball valve suitable for lowtemperature, high pressure fluid handling systems and illustrating the mode of use of spring energised seals.

LP01006UK 4 FIGURE is a sectional view through a mechanical face seal assembly, of a type used in reffigeration compressors for example; FIGURE 3 is an enlarged view of part of Figure 2 showing a face seal embodying the invention; FIGURE illustrates the face seal in more detail in a free condition; FIGURE illustrates the protective function of a face seal in an assembled condition,- FIGURE 6 illustrates a double-acting coil spring energised seal in a free condition C 0 MCITRE illustrates a double-acting, coil spring energised seal in an assembled condition, in use under pressure.

Referring to Figure 1, a trunnion-mounted ball valve 10 is shown, suitable for low- Z. 1 temperature, high pressure fluid handling systems. The valve 10 is shown open, allowing fluid to pass along the pipeline 11. A ball 12 is rotatable on a trunnion arrangement 13, 0 C to prevent the ball 12 being forced down-stream by pressure in the pipeline 11.

0 The trunnion-mounted ball valve is typical of applications in which spring-energised seals 0 are used. A number of metal coil-spring energised seals are shown in the drawing, for 1 0 CP example a double acting carder seal 14, a face seal 15 and a single- acting radial stem seal 16.

Figure 2 shows an annular mechanical face seal 17 of a type used in refrigeration 1 1 compressors, which is a single-acting seal, sealing, between two members 18 and 19 which 0 C> may undergo relative movement in the axial direction 20. As seen in Figure 3 on an enlarged scale, the seal 17 comprises a jacket 21 of polymeric material such as virgin or filled ptfe, which includes a channel cross-section portion 22 adapted to house an energising spring 23. The jacket 21 has a pair of peripheral sealing lips 24 which are an 0 C W C LP01006UK 5 interference fit with the walls 18a and 19a of the members 18 and 19. The energising C spring 23 is seated within the channel portion 22 and protrudes slightly fiom the channel betweeg the peripheral sealing lips 24. The arrangement - can- be seep in more detail in Figures 4 and 5.

r) Figure 4 shows the spring energised seal 17 in a relaxed condition, assembled prior to use. The helically wound metal strip spring 23 is seen to be normally of circular cross-section and to protrude slightly at 25 beyond the free ends of the lips 24. The small distance of I projection is indicated at d in Figure 4.

The spring pushes the bps outwardly at 26, to provide sealing surfaces adapted to bear on the walls I 8a and 19a in use.

In Figure 5, the seal 17 is shown in use having been inserted between the members 18 and 19. The wall 19a is ramped to assist in assembly of the seal between the members. The portions 26 of the lips 24 are a tight interference fit with the surfaces 18a and 19a and the seal is compressed. The spring is therefore extruded further from the channel portion 22 and becomes compressed into a generally elliptical shape, with the long axis of the ellipse I aligned so as to protrude from the channel by an amount D, greater than th distance d of Figure 4.

In use, or during assembly, if the members IS and 19 approach each other too closely, the first contact is made between the protruding part 25 of the spring and the facing surface l8b of member 18, rather than between the delicate elastomeric material of the peripheral lips 24 and the surface l8b, which would be the case with a standard spring-energised seal. The spring 2') carries the load and distributes it at the base of the channel 22. The lips 24 remain undamaged while the spring 23 protects them.

Figures 6 and 7 illustrate a double-acting seat 27, which may comprise a pair of singleacting seals back to back as shown, or may have a double. acket 28 moulded in one piece.

=> J A channel cross-section portion 29, 30 is provided at each end of the jacket 28 and LPO 1006UK 6 receives a respective oversized hefically coded strip metal energising spring 31, 32. Again g the springs protrude from the channels by a small distance d in the relaxed condition of the seal,and the peripheral lips 33, 34 are pushed outwardly by the springs to provide sealing surfaces.

In Figure 7, the seal is in place in apparatus in which fluid under high pressure enters a seal chamber 35 between members at inlet 36. The righthand end of the seal 27 has arrows 37 to indicate the supporting or energising function of the spring 32. At the left-hand end W W of the seal, contact has been made at 3) 8 between the protruding portion of the spring 3 1 and the end wall of the chamber 3 5. The spring 3) 1 carries the force load back to the channel portion 29 and prevents the lips 3 3_) from contacting the end wall of the chamber, which miaht result in damaae.

Z:- 0 It will be appreciated that the seal is symmetrical and, when pressurised fluid enters the seal chamber 35 from the other end, via inlet 39, the operation is the same, but reversed end for end.

Although the invention has been described with reference to seals energised by helical metal springs, the same principles can be applied to seals energised by resilien elastomeric 1 g 1:1 g. t springs.

1 According to the intended use of the seal, in particular the expected pressure and temperature range of use and the chemical environment, different materials may be W selected for the jacket and for the energising spring. The polymeric jacket may be of W virgin ptfe or may use such fillers as carbon, graphite, bronze, glass or molybdenum or combinations of these. Alternatively, the material of the jacket may be based on a polyamide or polyurethane, with or without fillers or additives.

Metal energising springs may be of various grades of stainless steel, nickel-chromiurn alloy, or cobalt-nickel-chromium-molybdenum alloy, depending particularly on the 0 chemical environment in which the seals are to be used. Elastomeric rubber energising 1 1 LPO 1006UK 7 springs may be of ethylene propylene, fluoroelastomer, nitrile rubber, polychloroprene or silicone rubber.

P1006UK. 8

Claims

1. A sphng energised annular seal comprising a jacket of polymeric material of annular 0 shape overall and having a cross section including a channel portion provided with peripheral sealing lips adapted to contact mating members to be sealed; and an associated energising spring of annular shape overall seated in the channel portion of the jacket to support the peripheral sealing lips; wherein the energising spring protrudes from the channel portion between the peripheral sealing lips to protect the lips from damage.

2. A seal as claimed in claim 1 in which the energising spring comprises a metal spring or a resilient elastomeric spring.

3. A seal as claimed in claim 1 or 2 in which the energising spring comprises a helically wound metal spring of flat metal strip or ribbon.

C1

4. A spring as claimed in claim 3 in which the cross-section of the helically wound spring is slightly oversize for the channel portion, so that the cross-section of the spring becomes elliptical on assembly with the jacket, with the longer axis of the ellipse so orientated as to protrude from the channel portion.

5. A seal as claimed in any one of claims 1 to 4 in which the material of the polymeric jacket comprises virgin ptfe, with or without such fillers as carbon, graphite, bronze, 0 glass or molybdenum or combinations of these.

6. A seal as claimed in any one of claims 1 to 4 in which the material of the jacket comprises polyamide or polyurethane, with or without fillers or additives.

P 1006UK. 9

7. A seal as claimed in any one of claims 2 to 6 in which the metal energising springs are of various grades of stainless steel, nickel-chromium alloy, or cobalt- nickel-chromium molybdenum alloy, depending particularly on the chemical environment in which the seals are to be used.

8. A seal as claimed in any one of claims 2 to 6 in which the resilient elastomeric energising spring comprises ethylene propylene, fluoroelastomer, nitrile rubber, tn 0 polychloroprene or silicone rubber.

9. A fluid handling apparatus comprising a pair of components having mating surfaCes and a spring energised annular seal as claimed in claim 1 disposed between the components of the pair.

10. A spring energised annular seal substantially as herein described with reference to and t> as illustrated in the accompanying drawings.