GB2143596A

GB2143596A - Improvements in and relating to the sealing of electrical cable joints equipment housings or the like

Info

Publication number: GB2143596A
Application number: GB08319497A
Authority: GB
Inventors: Herbert James Calkin Spencer
Original assignee: Telspec Ltd
Current assignee: Telspec Ltd
Priority date: 1983-07-19
Filing date: 1983-07-19
Publication date: 1985-02-13
Also published as: GB8319497D0; GB2143596B

Abstract

A method of forming and testing a fluid tight seal comprises placing a sealing ring (1) between two members (2,3) between which the seal is to be formed, either the sealing ring or the respective members being so shaped and arranged that lines of contact (S1,S2,S3,S4) are formed between the sealing ring and the respective members. Thereby continuous grooves or channels (G1,G2) are formed between the sealing ring (1) and the respective member (2,3). By establishing a pressure difference between the groove or channel (G1,G2) and the ambient atmosphere, the integrity of the seal can be tested by monitoring any fluid flow to or from the closed groove or channel (G1,G2). A single source of fluid pressure may be coupled to both grooves or channels via a union (A) and one or more transverse bores (7) in the sealing ring. <IMAGE>

Description

SPECIFICATION Improvements in and relating to the sealing of electrical cable joints, equipment housings, or the like A common problem when providing electrical cables and equipment housings which are to be located underground is how to ensure that joints between cables and between cables and housings are perfectly sealed against the ingress of water and water vapour. The problem has become more severe since the use of cables with polyethylene sheaths has become widespread. These are more difficult to seal to each other and to housing entry glands than cables with lead sheaths for which conventional plumbing techniques were effective. The standard of integrity of the sealing of cables and housings required is very high because of the large number of seals which can exist in a system. Failure of any one seal can cause failure of the whole system.

Because of the difficulty of making perfect seals it is common practice to apply internal air pressure to both cables and housings. Leaks in them can then be detected by measuring the air flow in a dynamic system orthefall of pressure in a static system.

These techniques are, however, expensive to implement, are not suiable for use with modern filled cables, do not give clear indications of the locations of leaks and are relatively insensitive requiring prolonged monitoring periods to detect small leaks.

Alternative methods of indicating the quality of seals of equipment housing are known in which the sealing members are duplicated in such a way as to enclose an air space between them. The air pressure in this space is raised relative to the atmosphere by an air pump and the pressure then monitored over a period by an air pressure gauge. Because the enclosed air space is smaller in volume than the whole housing the pressure falls more rapidly in the event of a leak than if the whole housing is pressurised and the time necessary to detect small leaks is reduced to a number of hours rather than days.

In accordance with the present invention, a reliable seal which can be tested in a few seconds is obtained by forming a single sealing member and the two cooperating parts in such a way that the sealing member makes contact with each part along two lines between which there are lines of no contact, forming a continuous groove. Bores are provided, in the sealing member and/or the cooperating parts, connecting the grooves to a union at which may be connected a combined source of air pressure and pressure change detector. The efficacy of the seals formed by the lines of contact between the sealing member and the cooperating parts is tested by applying between the union and atmosphere a pressure differential, typically about 6 Ibs per square inch, sealing the union and then monitoring the air pressure.Should any line seal be defective air will flow between the pressure change detector and the atmosphere through the grooves.

Because the volume of air within the grooves is very small, and by designing the pressure change detector to also have a very small internal volume, a small leak will result in a rapid change in air pressure therein. Preferably the volume of the grooves is a few cubic centimetres, depending upon the size of the housing being sealed, and that of the detector less than one cubic centimetre, resulting in a detectable change of pressure occurring in less than five seconds for a very small leak.

A seal in accordance with the invention may be utilised to provide a seal between an electrical cable and an equipment housing.

A known method of connecting a cable to a housing makes use of an entry gland. The cable may first be sealed within the gland by means of the "shrink-down" technique. In this method part of the hole through the gland, which is made from an irradiated material, is initially moulded with an internal diameter less than that of the cable which is to pass through it. The hole is then opened up to a diameter sufficient to accept the cable while the material of the gland is hot and then is cooled down in the enlarged state. Application of heat afterthe cable has been passed through the gland results in the appropriate part of the gland shrinking on the cable to provide a tight fit. The effectiveness of the seal is usually increased by the use of a hot melt adhesive between the cable and the gland.To apply the invention to a seal of this type the seal construction as defined above may be applied between the entry gland and the housing.

The invention is illustrated by way of example in the accompanying drawings, in which: Figures 1 - 4 are respectively sectional elevations of several embodiments of housing seal in accordance with the invention, and Figure 5 is a similar view of a cable gland seal.

Referring to Figure 1 of the drawings, a seal arrangement comprises a resilient rubber ring of circular cross section compressed between the base 2 and the cover 3 of a typical housing. Under compression, sealing contact areas are established along lines perpendicular to the drawing at Sa, S2, S3, and S4. At the same time two V section grooves are formed at G1 and G2. Bore A in the cover provides a connection to G1 at one point. Similarly a bore in the base could provide direct connection to G2 but preferably, as shown, G2 is connected to G, by a cross bore, or bores, 7 in the ring 1 so that both G1 and and G2 are connected to bore A.

Figure 2 shows alternative shapes for the base and cover of the housing which also result in the formation of four sealing areas and two grooves as described.

Figure 3 shows an alternative method of forming the grooves in which the mating surfaces of the base 2 and cover 3 of the housing are flat and the grooves G1 and G2 are preformed in the sealing ring 1.

Figure 4 shows a further alternative construction in which the sealing ring 1 has a circular section and the grooves G1 and G2 are preformed in the mating surfaces of the base 2 and cover 3.

It will be clear that these methods could be used in combination for one seal. Seals of the sections shown may be used for housings with circular or rectangular plan forms.

It will be appreciated that when a seal is effected by the method of the invention two seals are formed in each case. If, however, after the seals have been tested, the union at which the testing device has been connected is left open one of the seals is rendered ineffective. Since the other seal will have been proved to be satisfactory this will be adequate in normal circumstances. If in exceptional circumst andes the added security of two seals in series is desirable this may be realized by sealing the union, either by a screw plug or by a spring loaded valve.

Figure 5 shows how the invention may be applied to a cable gland seal. Sealing areas and grooves are formed as in the housing seal previously described.

The cross-section shown for the sealing ring 1 ensures that the cross bore in it will always register with the grooves formed between a cable gland 4 and a housing 5 providing the entry hole 2. The cable gland 4 is retained in the hole 6 by means of a back nut8 threaded thereon. An alternative method would be to provide two "0" rings in close proximity and to provide access to the limited air space between them. The efficacy of this seal can be tested as previously described. By applying the invention to each cable entry in turn and then to the cover/ -housing joint each seal can be tested and any defective seals rectified so that the security of the complete assembly can be assured.

While in the above descriptions equipment housings have been referred to the housings may actually contain no equipment and then become in effect cable joints. By designing a housing to have a multiplicity of gland entries a number of cables can be jointed together.

Claims

1. A method of forming an annular seal between two members, comprising arranging between respective surfaces of the two members at least one sealing ring, whereby there is formed between each respective surface of each member and said at least one sealing ring a pair of adjacent lines of contact bounding a continuous groove, coupling each said continuous groove to means establishing a fluid pressure differing from the ambient pressure outside said groove, whereby different fluid pressures are established on respective sides of each of said lines of contact, and monitoring any resulting fluid flow to determine the integrity of the seals provided by said lines of contact.

2. A method as claimed in Claim 1, wherein each said member is provided with a V-shaped groove defining said respective surface and said sealing ring is provided with portions of arcuate section for engagement in said grooves whereby each said continuous groove is defined between the base of a said V-shaped groove and the arcuate section of the sealing ring engaging therein.

3. A method as claimed in Claim 1,wherein each said continuous groove is formed in the respective surface of a corresponding one of said members, the cross-section of said groove being small in relation to the cross-section of said sealing ring whereby said lines of contact are formed between the lips of the groove and the sealing ring.

4. A method as claimed in Claim 1, wherein each said continuous groove is formed in the surface of said sealing ring, whereby the lips of said groove form said lines of contact with the respective surface of a corresponding one of said members.

5. A method as claimed in any one of Claims 2 4, wherein each said member is provided with a union for connection to said fluid pressure establishing means, said union being connected to the corresponding continuous groove.

6. A method as claimed in any one of Claims 2 4, wherein one of said members is provided with a union for connection to said fluid pressure establishing means, said union being connected to the corresponding continuous groove, and said sealing ring is provided with at least one transverse bore placing the said continuous grooves in communication with one another.

7. A method as claimed in Claim 6, wherein the said sealing ring is of non-circular cross-section so shaped to fit the respective surfaces of said members that said at least one transverse groove therein is maintained in alignment with said continuous grooves.

8. A method as claimed in Claim 1, substantially as described herein with reference to any one of Figures 1-5 of the accompanying drawings.

9. A seal assembly when formed by the method of any one of Claims 1 - 8.