GB2144190A - Coupling pipes - Google Patents

Abstract

A seal 5 for a spigot and socket pipe joint consists of an elastomeric seal ring 6 united with a retaining ring or sleeve 7 of injection moulded plastics which is initially interference-fitted in the pipe socket 3 or on the pipe spigot 2. The seal ring and retaining sleeve are united by being cast or moulded together or by a weld. <IMAGE>

Description

SPECIFICATION Coupling pipes This invention relates to coupling elements for drainage pipes and the like made of clay, cement, asbestos, and other mineral materials. The invention is particularly applicable to clayware pipes.

Clay drainage pipes with socket or bell ends are commonly provided with elastomer seals. Various types of seal are known. They must be capable of receiving a spigot pipe end relatively easily on site without any appreciable risk of the socket being burst as the spigot is inserted, and must accommodate tolerances of the pipe spigot and socket and provide water tightness despite possible relative movement of the pipes under vertical shear loading.

One form of seal comprises a rolling seal ring, that is, a ring of substantially circular cross section which rolls between the surfaces of the pipe spigot and socket as the latter is inserted in the socket.

Such rings can be designed to cater for the pipe tolerances together with the limitations imposed by jointability (or socket bursting) at one extreme, and movement under vertical shear load (water tightness) at the other. However the seal rings have relatively large ring chord sections even if the tolerances are kept close, and therefore the rings are relatively large and costly. The need to supply, store and fit the ring as a separate component is inconvenient.

Alternatively the seal ring can be located in a preformed groove but this requires very close tolerances, for example by grinding the pipe ends or providing fairings. Because the ring has to be seated in the groove to prevent dislodgement, the ring is again relatively large and costly.

Sliding seal rings have been very successful for coupling plastics pipes, or for coupling clay pipes using a plastics coupling sleeve, but hitherto have not been successfully applied to clay pipe sockets because they require to be fastened in place for example by glueing, and jointability is more difficult than with a rolling ring unless pipe tolerances are small.

We have now found that a pipe socket can be fitted with a sliding seal ring in a convenient and effective manner, if the seal ring is united with a stiff retaining sleeve or ring, preferably of plastics material, and the resulting unitary assembly is fitted in the pipe socket, preferably with an interference or force fit.

In an analogous manner, a sliding seal ring can be fitted to the exterior surface of a pipe spigot.

If the tolerances of the pipe diameter and circu larity are sufficiently small, the retaining member can have a simple substantially cylindrical surface yet nevertheless achieve a satisfactory fit, prefera bly an interference fit, with the pipe surface. Suita bly close tolerances can be achieved by modern pipe-making methods for example the roller kiln process described in our British Patent Specification No. 2021743. Alternatively or in addition, a surface of adequate circularity and dimensional accuracy to receive the unitary assembly can be obtained by grinding or cutting the pipe for example using a diamond cutter.The additional manufacturing cost due to this operation is more than outweighed by the fact that the seal assembly can be manufactured simply and cheaply and can be fitted to the pipe by a simple mechanical fit, so that the finished pipe with its sliding seal is comparable or cheaper in cost and superior in convenience compared with existing products using rolling seal rings, seal rings held in grooves, or seal rings fixed by adhesives.

For use under less onerous conditions, e.g. domestic pressures of about 3m. rather than 20m.

which is often specified, a wider tolerance of, say, 5mum. can be acceptable with seals of the invention. In this case, grinding or cutting of the pipe ends will not usually be needed, as modern pipemaking methods achieve such tolerances with little difficulty.

The seal ring and retaining member can be united in various ways. For example, an elastomer seal ring and a thermoplastic retaining member can be united by cast;ng or moulding one onto the other, for example by successively moulding the two components in a common injection mould, or moulding the two components simultaneously in a common mould by injecting the respective different materials into different regions of the mould cavity. Techniques for directly uniting rubber and plastics members by injection moulding are disclosed in our British Patent Specifications Nos.

1477074 and 1572099.

Alternatively, the plastics retaining member, and a rubber seal ring, may be initially moulded as separate components, and then heated and brought together under pressure to form a direct bond or weld, for example using a polyolefine retaining member and an EPDM seal ring.

The present invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows in section a clay pipe socket fitted with a seal assembly according to the invention, and Figure 2 shows an alternative seal assembly.

Figure 1 shows a bell or socket end 3 of a first clay pipe 1 and an adjacent spigot end of a second clay pipe 2. The clay pipes have been made by the process described in our British Patent Specification No. 2021743 and as a result the external surface of the pipe spigot end is accurately circular and of close dimensional tolerances, typically 2 m.m. for a pipe of diameter 100 m.m. The outer end part of the pipe socket is of comparable accuracy and tolerance internally, either by virtue of the manufacturing process or as a result of machining, typically to a tolerance of 1 m.m. on a 100 m.m.

pipe In the illustrated arrangement, the pipe socket is shown as having an internal rebate formed by such machining.

The socket contains a sliding seal assembly 5 which consists of an elastomeric sealing ring 6 united with a plastics retaining sleeve 7. In one convenient embodiment, the plastics sleeve is of injection moulded polypropylene and the sealing ring is of injection moulded EPDM, and these two components are directly bonded by a moulding or welding process as outlined above.

The seal ring may have any convenient shape. In the illustrated embodiment, its cross section is similar to our Hepsleve seal ring, comprising a main body part 8which rests against the internal surface of the socket, and an inner sealing lip 9 which engages and is deflected by the inserted pipe spigot to form a seal under compression.

The plastics retaining sleeve 7 is a simple cylindrical sleeve with a locating flange 10 at its outer end which abuts on the end of the pipe socket to ensure that the seal ring is located in the correct position within the socket: The sealing assembly consisting of the seal ring and retaining sleeve is prefabricated, and then rammed or otherwise inserted into the pipe socket to form preferably an interference fit between the external surface of the retaining sleeve and the internal surface of the pipe socket. The seal ring itself is not clamped against the socket, being held only by the end of the retaining sleeve, and is therefore free to move as required to accommodate itself to the pipe socket and inserted spigot.

The production and fitting of the seal assembly can be substantially or entirely automatic. Because substantially the whole of the volume of elastomer is operative as a seal, the amount of relatively expensive elastomer used can be minimised. Because the seal assembly is a unitary element which can be factory-fitted, problems arising from the provision of separate sealing rings to be fitted on site are eliminated and the making of a pipe joint is simplified.Unlike a rolling or a groove-fitted seal ring, the seal ring in the assembly according to the present invention can be designed to have the most effective cross section for ensuring sealing together with easy jointing, particularly as the plastics sleeve prevents over-compression of the seal' the thickness of the plastics sleeve limits radial compression of the seal e.g. due to vertical or lateral relative movement of the pipes and therefore the risk of leakage due to such movement is much reduced.

Figure 2 shows an alternative seal assembly in which the seal ring additionally has an axial skirt which extends along the outer side of the retaining sleeve 7 in order to increase the area of bonding between these two components. Alternatively such a skirt may extend along the inner surface of the retaining sleeve. In the assembly illustrated in Figure 2, the skirt will bear against and form at least part of the interference fit with the socket. Alternatively, the retaining sleeve may be rebated so that the stress of the interference fit is taken at least partly by direct contact by the socket surface and that part of the sleeve surface which is of greater diameter, the skirt of the sealing ring being accommodated in the rebate of the sleeve.

The strength of the bond between the sealing ring and retaining sleeve can also be increased by having the end part of the sleeve embedded within the material of the sealing ring, or conversely by having the material of the sealing ring extend into a groove or holes provided in the end of the sleeve.

An interference fit is preferred between the seal assembly and the pipe, but is not essential: the seal assembly can be a relatively loose fit (but should not fall out during handling), as it will be held securely in place by the compression of the seal ring when the spigot and socket are coupled together.

Claims (11)

1. A seal for spigot and socket pipe joints, comprising a sliding seal ring united with a stiff annular retaining member, adapted to be fitted in a socket or on a pipe spigot end.

2. A seal as claimed in claim 1 in which the retaining member is a sleeve or ring of plastics material.

3. A seal as claimed in claim 1 or 2 in which the retaining member has a substantially cylindrical surface for engaging the surface of the socket or spigot.

4. A seal as claimed in claim 1, 2 or 3 in which the seal ring and retaining member are united by casting or moulding one onto the other.

5. A seal as claimed in claim 1, 2 or 3 in which the seal ring and retaining member are united by a thermal band or weld.

6. A pipe seal as claimed in any preceding claim in which the retaining member has a radially projecting locating element axially spaced from the seal ring.

7. A pipe seal substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

8. A pipe spigot or socket, having fitted thereon or therein a seal as claimed in any of the preceding claims.

9. A pipe spigot or socket as claimed in claim 8 in which the seal is an interference fit on the spigot or in the socket.

10. A pipe spigot or socket as claimed in claim 9 in which the interference fit is substantially solely between the remaining member and the spigot or socket.

11. A spigot and socket pipe joint sealed by a seal as claimed in any of claims 1 to 10.