GB2029913A

GB2029913A - Sealing ring assemblies

Info

Publication number: GB2029913A
Application number: GB7924118A
Authority: GB
Original assignee: BESTOBELL SEALS Ltd
Current assignee: BESTOBELL SEALS Ltd
Priority date: 1978-09-11
Filing date: 1979-07-11
Publication date: 1980-03-26
Also published as: GB2029913B

Abstract

A rod or piston sealing assembly comprises a first ring 1 of synthetic rubber, and a second ring 11 of plastics material harder than the synthetic rubber and which fits coaxially with, but is not bonded to, the ring 1. The ring 11 is L-shaped in radial section, having a radially extending arm 12 and an axially extending arm 13, and fits into a rebate 14 in the ring 1. On its inner periphery the assembly has three circumferentially extending sealing lips 9, 18 and 20. The lip 9 is located on the ring 1 adjacent its end face 2. The lip 18 has a diameter greater than that of the lip 9 and is at the free end of the axially extending arm 13. The lip 20 is on the ring 11 and has a diameter greater than that of the lip 18. The free end portion 16 of the arm 13 between the lips 18 and 20 diverges to provide a radial clearance 17. The end face 2 of the ring 1 contains a circumferentially extending recess 6 which faces towards the fluid pressure. <IMAGE>

Description

SPECIFICATION Improvements relating to sealing ring assemblies This invention relates to sealing ring assemblies for forming a sliding seal between two relatively reciprocable members, one of which has a cylindrical surface. The invention may be applied to piston sealing assemblies in which the assembly moves with the piston and its outer periphery forms a sliding seal against the cylinder in which the piston is reciprocated, but primarily the invention is concerned with sealing ring assemblies which are intended to form a seal between a rod, such as a piston rod, and a surrounding housing through which the rod is reciprocated. In this case the assembly is mounted in the housing and the inner periphery of the assembly forms a sliding seal against the cylindrical surface of the rod.

According to the invention, a sealing ring assemblyforforming a sliding seal between two relatively reciprocable members, one of which has a cylindrical surface, comprises a first ring of synthetic rubber and having adjacent one of its ends a first circumferentially extending sealing lip for engaging the member having the cylindrical surface, and a second ring which is of thermoplastic plastics material harder than the synthetic rubber and which fits co-axially into an annular rebate in the first ring from its other end but is not bonded to the first ring, the second ring being L-shaped in radial section with a radially extending arm and an arm which extends axially towards the said one end of the first ring and which has at its free end a second circumferentially extending sealing lip for engaging the member having the cylindrical surface, the first sealing lip projecting radially further from the rest of the assembly than the second sealing lip.

With this arrangement, the assembly in accordance with the invention is single acting in that it is intended to resist pressure applied to it in an axial direction from only one of its ends, that is from the end adjacent the first sealing lip and remote from the second ring. Consequently, in use the assembly is fitted in a groove in one of the relatively reciprocable members so that the sealing lips engage the cylindrical surface of the other member and so that the end of the first ring adjacent the first sealing lip faces towards the pressure which is to be resisted.If a double acting sealing ring assembly is required, which is only likely in the case of piston sealing assemblies, two single acting assemblies may be used, in separate grooves, so that one is operative to resist pressure acting in one axial direction and the other is operative to resist pressure acting in the opposite axial direction.

In the case of piston sealing assemblies the sealing lips will be provided on the radially outer periphery of the assembly, whereas for rod sealing assemblies the sealing lips will be provided on the radially inner periphery. As mentioned earlier, the present invention is in fact primarily concerned with rod sealing assemblies, and when convenient the invention will tend to be described in the context of a rod sealing assembly in the remainder of this specification.

In the case of rod sealing assemblies in accordance with the invention, it is intended that the diameter of the rod with which the assembly is to be used should be greater than the inner diameter of the second sealing lip, that is the lip at the free end of the axially extending arm of the second ring, when the assembly is unstressed. This means that, in use, both this sealing lip and the first sealing lip, which is the lip on the first ring and which in the unstressed state has an inner diameter less than the second lip, will be in a state of tensile hoop stress against the surface of the rod.

Preferably the assembly has a slight radial clearance between a free end portion of the axially extending arm of the second ring and the surrounding portion of the rebate in the first ring. In the case of rod sealing assemblies this radial clearance allows the free end portion of the axially extending arm, which carries the second sealing lip, to deform radially outwards, when the assembly is fitted on a rod, without exerting pressure on the first ring which would tend to reduce the force pressing the first sealing lip against the surface of the rod.

In operation at relatively low pressures, it is the first sealing lip on the first ring which performs the main sealing function of the assembly. At higher pressures however, it is the second sealing lip on the second ring which takes over the main sealing function of the assembly, the second sealing lip being pressed more firmly against the cylindrical surface by the first ring which is placed under axial compression by the pressure against which the assembly is operating. This additional loading of the second sealing lip may be facilitated by providing the end face of the first ring adjacent the first sealing lip with an axially facing circumferentially extending recess into which the fluid under pressure enters during operation of the assembly.In order to ensure that the recess does not become blinded by the end face of the groove in which the assembly is fitted and that the fluid can always enterthe recess, the portion of the end face of the first ring on the side of the recess remote from the first sealing lip (i.e. the side which will be nearer the base of the groove) preferably projects axially further than the portion of the end face on the other side of the recess, i.e. the side nearer the first sealing lip.

In addition to its sealing function, the harder second ring also acts as an anti-extrusion ring, serving to prevent the softer material of the first ring from being forced out of the groove at high operating pressures.

Preferably the assembly in accordance with the invention has a third circumferentially extending sealing lip for engaging the member having the cylindrical surface, this third lip being provided on the axially extending arm of the second ring axially spaced from the second sealing lip at its free end, and the second sealing lip projecting radially further from the rest of the assembly than the third sealing lip. It is intended that, in operation, the third sealing lip should just contact the cylindrical surface of the member against which the first and second lips seal, so that the third sealing lip therefore acts more as a scraper ring which reduces the thickness of the fluid film which in operation adheres to the cylindrical surface.

Preferably the radial thickness of the radially extending arm of the second ring is less than the radial thickness of the first ring, and preferably the second ring fits into the rebate in the first ring so that the end face of the assembly remote from its end face adjacent the first sealing lip is substantially planar, being formed partly by the first ring and partly by the second ring. With this arrangement there will always be a portion of the softer first ring between the second ring. With this arrangement there will always be a portion of the softer first ring between the second ring and the base of the groove in which the assembly is fitted, which facilitates the accommodation of side loadings which are often exerted on the sealing assembly as a result of lateral movements of the rod or piston during its reciprocation.

The sealing assembly in accordance with the invention is extremely simple to manufacture and assemble, and is extremely effective over a wide range of operating pressures. A suitable material for the first ring is nitrile rubber, and a suitable material for the second ring is a thermoplastic polyester elastomer, preferably having a hardness which is between 50 and 65 Shore D.

A preferred example of a rod sealing assembly in accordance with the invention will now be described with reference to the accompanying drawing, which is a radial section through the assembly.

The assembly comprises a sealing ring 1 which is made of nitrile rubber. The ring 1 has axially facing end faces 2 and 3, and radially inner and outer faces 4 and 5 respectively. The end face 2 contains a circumferentially extending U-shaped recess 6, and the portion of the end face 2 radially outwards of the recess 6 projects axially beyond the portion of the end face 2 radially inwards of the recess 6. The inner and outer edges of the ring 1 adjacent the end face 2 are cut away to provide bevelled inner and outer edge faces 7 and 8 respectively, and the inner and outer faces 4 and 5 of the ring 1 are slightly divergent as they approach the end face 2.Consequently, the inner face 4 forms with the bevelled edge face 7 a first radially inwardly projecting circumferentially extending sealing lip 9, and the outer face 5 forms with the bevelled edge face 8 a radially outwardly projecting circumferentiallyextending sealing lip 10.

The assembly also comprises a sealinglanti- extrusion ring 11 which is made of a thermoplastic polyester elastomer harder than the rubber of the ring 1. The ring 11 is L-shaped in radial section, having a radially outwardly extending arm 12 and an axially extending arm 13, and fits coaxially with the ring 1 into a suitably shaped rebate 14 in the end face 3 and the inner face 4 of the ring 1. The end face 3 of the ring 1 radially outwards of the ring 11 lies substantially flush with the end face 15 of the radially extending portion 12 of the ring 11.

The ring 11 is not bonded to the ring 1, but, except for a free end portion 16 of the axially extending arm 13, the radially outer surface of the ring 11 is a close fit in the rebate 14. The free end portion 16 diverges slightly from the rebate 14, from a position approxi mately midway along the arm 13, to provide a slight radial clearance 17 between the free end portion 16 and the surrounding portion of the rebate 14. The extreme free end of the arm 13 projects clear of the inner face 4 of the ring 1 adjacentthe rebate 14 and forms a second radially inwardly projecting circumferentially extending sealing lip 18. The diameter of the second sealing lip 18 is greater than that of the first sealing lip 9 on the ring 1.

At about the position corresponding to the point at which the radially outer surface of the arm 13 begins to diverge from the rebate 14, the radially inner surface of the arm 13 has a radially inwardly projecting rib 19 which forms a third inwardly projecting circumferentially extending sealing lip 20.

The diameter of this third sealing lip 20 is greater than that of the second sealing lip 18.

In use, the sealing assembly is intended to seal around a rod having a diameter approximately equal to that of the third sealing lip 20 on the inner surface of the ring 11, the assembly being fitted in an annular groove in a housing surrounding the rod so that the recessed end face 2 faces towards the pressure which is to be resisted. The outer sealing lip 10 is compressed against the base of the groove, and the inner sealing lips 9 and 18 of the rings 1 and 11 respectively are in tension around the surface of the rod, the free encfportion 16 of the arm 13 carrying the second sealing lip 18 being flexed radially outwards to occupy the radial clearance 17 between the free end portion 16 and the rebate 14.

It will be noted that the axial length of the ring 11 is approximately two thirds of the axial length of the ring 1, and the depth of the recess 6 is approximately one third of the axial length of the ring 1 but measured from the opposite end of the ring. In general it is preferred that the recess 6 and the axially extending arm 13 of the ring 11 should not overlap in the axial direction.

Claims

1. Asealing ring assemblyforforming a sliding seal between two relatively reciprocable members, one of which has a first cylindrical surface, the assembly comprising a first ring of synthetic rubber and having adjacent one of its ends a first circumferentially extending sealing lip for engaging the member having the cylindrical surface, and a second ring which is of thermoplastic plastics material harder than the synthetic rubber and which fits coaxially into an annular rebate in the first ring from its other end but is not bonded to the first ring, the second ring being L-shaped in radial section with a radially extending arm and an arm which extends axially towards the said one end of the first ring and which has at its free end a second circumferentially extending sealing lip for engaging the member having the cylindrical surface, the first sealing lip projecting radially further from the rest of the assembly than the second sealing lip.

2. A sealing ring assembly according to claim 1, in which there is a slight radial clearance between a free end portion of the axially extending arm of the second ring and the surrounding portion of the rebate in the first ring.

3. A sealing ring assembly according to claim 1 or claim 2, which has a third circumferentially extending sealing lip for engaging the member having the cylindrical surface, the third sealing lip being provided on the axially extending arm of the second ring axially spaced from the second sealing lip at the free end of the arm, and the second sealing lip projecting radially further from the rest of the assembly than the third sealing lip.

4. A sealing ring assembly according to any one of the preceding claims, in which the first ring has an axially facing circumferentially extending recess in its end face adjacent the first sealing lip.

5. A sealing ring assembly according to claim 4, in which the portion of the end face of the first ring on the side of the recess remote from the first sealing lip projects axially further than the portion of the end face on the side of the recess nearer the first sealing lip.

6. A sealing ring assembly according to claim 4 or claim 5, in which the recess in the end face of the first ring and the axially extending arm of the second ring do not overlap in the axial direction.

7. A sealing ring assembly according to any one of the preceding claims, in which the radial thickness of the radially extending arm of the second ring is less than the radial thickness of the first ring.

8. A sealing ring assembly according to claim 7, in which the ring fits into the rebate in the first ring so that the end face of the assembly remote from its end face adjacent the first sealing lip is substantially planar, being formed partly by the first ring and partly by the second ring.

9. A sealing ring assembly according to any one of the preceding claims, in which the first ring is made of nitrile rubber.

10. A sealing ring assembly according to any one of the preceding claims, in which the second ring is made of a thermoplastic polyester elastomer.

11. A sealing ring assembly according to claim 10, in which the hardness of the second ring is between 50 and 65 Shore D.

12. A sealing ring assembly according to any one of the preceding claims, in which the second ring, in addition to acting as a sealing ring, in use acts as an anti-extrusion ring for preventing the softer material of the first ring from being extruded between the two members under the action of high operating pressures.

13. A sealing ring assembly according to any one of the preceding claims, which is a rod sealing assembly, the sealing lips being located on the radially inner periphery of the assembly.

14. A sealing ring assembly according to claim 12, or claim 13, forming a sliding seal between a rod which is reciprocated through a housing which surrounds the rod and which has an annular groove in which the sealing ring assembly is seated around the rod, the diameter of the rod being greater than the inner diameters of both the first and second sealing lips, when the assembly is unstressed, so that both the first and second sealing lips are in a state of tensile stress against the surface of the rod.

f5. A sealing ring assembly according to claim 14, in which the diameter of the rod is substantially the same as that of the third sealing lip.

14. A sealing ring assembly according to claim 13, substantially as described with reference to the accompanying drawing.

15. A sealing ring assembly according to claim 13, or claim 14, forming a sliding seal between a rod which is reciprocated through a housing which surrounds the rod and which has an annular groove in which the sealing ring assembly is seated around the rod, the diameter of the rod being greater than the inner diameters of both the first and second sealing lips, when the assembly is unstressed, so that both the first and second sealing lips are in a state of tensile stress against the surface of the rod.

16. A sealing ring assembly according to claim 15 when dependent upon claim 3, in which the diameter of the rod is substantially the same as that of the third sealing lip.

New claims or amendments to claims filed on 25.10.79 Superseded claims 1 -16 New or amended claims:

1. A sealing ring assembly for forming a sliding seal between two relatively reciprocable members, one of which has a cylindrical surface, the assembly comprising a first ring of synthetic rubber and having adjacent one of its ends a first circumferentially extending sealing lip for engaging the member having the cylindrical surface, and a second ring which is of thermoplastic plastics material harder than the synthetic rubber and which fits coaxially into an annular rebate in the first ring from its other end but is not bonded to the first ring, the second ring being L-shaped in radial section with a radially extending arm and an arm which extends axially towards the said one end of the first ring and which has second and third circumferentially extending sealing lips for engaging the member having the cylindrical surface, the second and third sealing lips being axially spaced from each other, and the assembly being arranged so that, in its unstressed condition, the first sealing lip projects radially further from the rest of the assembly than the second sealing lip which, in turn, projects radially further from the rest of the assembly than the third sealing lip.

3. A sealing ring assembly according to any one of the preceding claims, in which the first ring has an axially facing circumferentially extending recess in its end face adjacent the first sealing lip.

4. A sealing ring assembly according to claim 3, in which the portion of the end face of the first ring on the side of the recess remote from the first sealing lip projects axially further than the portion of the end face on the side of the recess nearer the first sealing lip.

5. A sealing ring assembly according to claim 3 or claim 4, in which the recess in the end face of the first ring and the axially extending arm of the second ring do not overlap in the axial direction.

6. A sealing ring assembly according to any one of the preceding claims, in which the radial thickness of the radially extending arm of the second ring is less than the radial thickness of the first ring.

7. A sealing ring assembly according to claim 6, in which the second ring fits into the rebate in the first ring so that the end face of the assembly remote from its end face adjacent the first sealing lip is substantially planar, being formed partly by the first ring and partly by the second ring.

8. A sealing ring assembly according to any one of the preceding claims, in which the first ring is made of nitrile rubber.

9. A sealing ring assembly according to any one of the preceding claims, in which the second ring is made of a thermoplastic polyester elastomer.

10. A sealing ring assembly according to claim 10, in which the hardness of the second ring is between 50 and 65 Shore D.

11. A sealing ring assembly according to any one of the preceding claims, in which the second ring, in addition to acting as a sealing ring, in use acts as an anti-extrusion ring for preventing the softer material of the first ring from being extruded between the two members under the action of high operating pressures.

12. A sealing ring assembly according to any one of the preceding claims, which is a rod sealing assembly, the sealing lips being located on the radially inner periphery of the assembly.

13. A sealing ring assembly according to claim 12, substantially as described with reference to the accompanying drawing.