CONDUIT SEAL FOR HAZARDOUS ENVIRONMENTS

Abstract: A sealing assembly for a non-circular conduit - such as an oval spare cable entry on a joint enclosure (1) - is suitable for use within a zone 1 hazardous environment, for example a sewer. The sealing assembly comprises: (i) a longitudinally compressible rubber sealing member (11) having a shape and dimensions corresponding to those of the conduit; and (ii) a first flange (17) which is electrically conductive and is shaped, dimensioned and positioned such that (a) it covers a major part of the surface of the rubber sealing member (11) and (b), in use, it is in contact with the hazardous environment. The first flange (17) can be moved relative to another member (for example using one or more bolts) to urge the sealing member (11) against the said other member to compress the rubber sealing member (11) longitudinally, causing it to be urged into sealing engagement with the conduit.

Description: CONDUIT SEAL FOR HAZARDOUS ENVIRONMENTS The present invention relates to a sealing system within a conduit, such as a tubular passageway, for use in hazardous environments, and to a method for sealing a conduit for use in a hazardous environment . Hazardous environments are areas in which the atmosphere may become explosive. Explosive atmosphere is defined as a mixture of ignitable substances in the form of gases, vapours or mixtures with air under atmospheric conditions in critically mixed ratios such that excessive high temperature, arcs or sparks may cause an explosion. According to Elex V, DIN VDE 0165-1991, endangered areas are classified into zones, according to the probability of the existence of a dangerous explosion prone atmosphere. The present invention is directed to use within so-called "zone 1" hazardous environments. A zone 1 explosive atmosphere is, according to Elex V, DIN VDE 0165-1991, a zone in which an explosive mixture can occur during normal operation. Examples of zone 1 hazardous environments include sewers, petrochemical plants and pipelines, and petrol stations. It has been proposed to use the existing infrastructure of sewers as passageways for carrying cables, for example communications or power cables. As described above, the environment within a sewer network is classified as a "zone 1" environment. In general objects to be used in zone 1 hazardous environments must satisfy the criteria set out in European Standard EN 50014:1997. In particular, it is important that any objects that are to be used within such an environment are designed such that under normal conditions of use, maintenance and cleaning , danger of ignition due to electrostatic charges is avoided, thereby avoiding possible explosions. Also the objects should be designed so that the maximum surface temperature shall not exceed a specified temperature, usually being the ignition temperature of any gasses, fluids or solids present. The value of the specified maximum temperature depends on the exact nature of the environment, and for zone 1 hazardous environments varies between 85°C and 450°C. Furthermore objects used within a zone 1 hazardous environment must be UV resistant, chemically inert, and resistant to flexing even at temperatures above 85°C. Cables known today include optical cables or copper core cables, both for communications purposes, electrical power cables, and composite cables including both optical fibres and copper conductors . Whatever the system, the usual network configurations include joint enclosures at various points in the network. The joint enclosures include means for joining, terminating, splitting, tapping etc. of the cable, in a manner well known to the man skilled in the art. The joint enclosures are typically in the form of a box shaped housing, with cable outlets for entry and exit of cables. Typically the cable outlets are tubular, and circular or oval in cross-section, but they may be rectangular or of other appropriate shapes. Circular cross- section outlets typically receive individual cables, and oval outlets typically receive a cable loop from which a tap is to be taken without cutting the cable, so that two separate outlets cannot be used. Usually there will be a plurality of outlets, typically four to twelve. Commonly not all of the outlets will be used in the initial set-up of the cable system, and some of the outlets will be left unoccupied, so that these are available for introduction of cables where future modifications of the network are desired. It is therefore necessary that these unoccupied outlets are blocked and sealed to prevent access of any contaminants into the cable joint enclosure. Where the cable joint enclosure is to be used within a zone 1 hazardous environment it is important that the means for effecting the blocking and sealing of any initially unused cable outlets satisfies the criteria required for apparatus to be used in such a hazardous environment. This is easy for circular conduits: for example, they can be sealed with plugs in screw-threaded engagement with them, provided that the dimensions of the threaded parts meet the prescribed requirements for preventing the passage of flame or hot gas through between the parts. It is not easy if the conduit is non-circular, and the best available current practice requires the use of a correspondingly shaped cap secured and sealed in place with a heat-shrink member that may need additional protection for some hazardous environments (e.g. in the case of a sewer environment to prevent damage by rodents) and has to be cut away and discarded if it is desired to re-open the conduit, either permanently or temporarily. The present invention defines a sealing assembly for use when the conduit to be sealed is non-circular, and a method for sealing a non-circular conduit, both for use within a zone 1 hazardous environment. The invention is therefore suitable for use, inter alia, in sealing the unused conduits from a cable joint enclosure to be used in a zone 1 hazardous environment such as a sewer system. Where cable networks are to be positioned within an existing conduit system, the positioning is generally such that the cable joint enclosures are easily accessed. For, example, where cable networks are to be introduced into an existing sewer system, the joint enclosures are usually arranged immediately beneath man-holes for easy access. FR2758017A is representative of many known arrangements for making a seal around a cable, pipe or other member passing through a round opening in which a resilient ring is compressed axially between two rigid rings. Such a construction is clearly uneconomic for use in making a blank closure for a circular opening, and would not be considered by experts in relation to the design of a seal with no cable passing through it. A first aspect of the present invention provides sealing assembly in a conduit comprising: (i)a longitudinally compressible rubber sealing member; and (ii) a first flange which is electrically conductive, covers a major part of the surface of the rubber sealing member and when in use is in contact with the hazardous environment wherein the first flange can be moved relative to another member to urge the sealing member against the said other member to compress the rubber sealing member longitudinally, causing it to be urged into sealing engagement with the conduit, characterised in tha t the assembly is for use within a zone 1 hazardous environment, the conduit is non-circular and the rubber sealing member and the first flange are of corresponding non-circular shape and dimensions . A second aspect of the invention provides a method of sealing a conduit comprising: (i) positioning a longitudinally compressible rubber sealing member in engagement with the conduit, and positioning a first flange, which is electrically conductive, covers a major part of the surface of the rubber sealing member and in use, is in contact with the hazardous environment; (ii) moving the first flange relative to another member to urge the sealing member against the said other member to compress the rubber sealing member longitudinally, causing it to be urged into sealing engagement with the conduit; and (iii) inserting the conduit and installed sealing system into the hazardous environment chara cterised in tha t the assembly is for use within a zone 1 hazardous environment, the conduit is non-circular and the rubber sealing member and the first flange are of corresponding non-circular shape and dimensions . As used herein, the phrase "longitudinally compressible", means that the sealing member is compressible in the direction substantially parallel to the axis of the conduit . All preferred features for the sealing system of the present invention also apply to the method of the present invention. The invention is primarily intended for making blank closures, that is closures with no cable pipe or other member passing through them. Preferably the said other member is a second flange positioned such that the rubber sealing member *is between the first and second flanges inside the conduit, and in such case the shape and dimensions of the rubber sealing member will normally closely approximate the internal shape and dimensions of the conduit. The flanges may be in direct contact with the sealing member, or there may be other intervening members. Preferably one or each of the first and second flanges is substantially planar. In this embodiment, with the sealing member positioned within the conduit, longitudinal compression of the sealing member causes it to increase in its transverse dimension, and thereby be urged into sealing engagement with the inner surface of the conduit. In another embodiment the said other member is the end face of the conduit, and in this alternative construction the shape and dimensions of the rubber sealing member preferably closely approximate the external shape and dimensions of the conduit. According to both aspects of the present invention, the sealing member comprises compressible rubber, preferably EPDM. While this material is well suited to perform the required sealing function, the exposure of polymeric or rubber surfaces to zone 1 hazardous environments is not desirable, since they tend to build up electrostatic charge, and there is a consequent risk of ignition and possible explosion. In some hazardous environments, they may also be susceptible to damage by exposure to fluids from the environment (e.g. sewer gases or petroleum vapours) According to the present invention, this problem is minimised by the provision of a first substantially planar flange which is electrically conductive, and is positioned so that it, rather than the rubber sealing member, is exposed to the hazardous environment. This is achieved by ensuring that the first flange covers a major part of the surface of the rubber sealing member. In a preferred embodiment one major surface of the flange is in contact with the rubber sealing member and the other major surface of the flange is in contact with the hazardous environment. The first flange is preferably electrically conductive to the extent that it has an insulation resistance that does not exceed IGohm at (23+2) °C and (50 + 5)% relative humidity as measured in accordance with 23.4.7.8 of European Standard EN 50014:1997. Preferably the first flange comprises a metal. A particularly preferred metal is steel, especially a stainless steel. Other metals that could be used include aluminium, cast steel, galvanised steel, gunmetal and brass. As an alternative to a metal, a polymeric material with an appropriate conductivity could be used. The electrically conductive first flange is arranged to separate the rubber sealing member from the hazardous environment. To this end, the first flange covers a major part of the surface of the rubber sealing member. It preferably covers at least 80% of the surface of the rubber sealing member. More preferably the first flange covers at least 90%, especially preferably 95% of the surface of the rubber sealing member. Preferably the first flange covers a sufficient part of the surface of the sealing member such that any length of surface of the sealing member that is exposed to the hazardous environment in use, measured radially of the conduit, is shorter than 1cm. The term "radially of the conduit" means in a direction from the axis of the conduit to the outer surface of the conduit. It applies regardless of the cross-sectional shape of the conduit, which may be, for example, oval, rectangular, or any other suitable shape. These arrangements mean that the possibility of electrostatic charges building up on the insulating surface of the rubber sealing member is substantially avoided. Preferably the amount of exposed rubber sealing member is not sufficient to retain enough energy to create a spark. Notwithstanding these precautions, it may be desirable in some cases for the rubber sealing member itself to be loaded with carbon or other suitable filler to make it electrically conductive. In those embodiments in which the first flange passes across the top of the conduit to seal it, it could in addition pass down the outer surface of the conduit, in the form of an end-cap. In preferred assemblies and methods of the invention, the conduit also comprises a metal. The metals, and the conductive polymeric material, described as preferred for the first flange are also suitable for the material of the conduit. In one preferred embodiment the system also comprises a joint enclosure in the form of a housing, preferably a metal housing, and the said conduit forms a cable outlet from the housing of the joint enclosure. Preferably the housing comprises a plurality of cable outlets. These may be any shape in cross-section, especially circular oval or rectangular in cross-section, but the invention relates only to the sealing of those which are non- circular. Conveniently the sealing of the conduit is effected outside of the hazardous environment, and then the sealed conduit introduced into the hazardous environment. For example, for a sewer system, the conduit, (for example a joint enclosure with a number of sealed conduits, and other conduits containing cables) is sealed above ground level, and then introduced into the sewer through a manhole, preferably leaving enough slack in the cables to allow it to be withdrawn if required for modification or servicing. In accordance with requirements for hazardous environments, the electrically conductive flange will be earthed [grounded] . This ensures that there is no potential difference between the flange and the conduit, which must also be earthed, usually through a housing to which it is typically attached. This arrangement again minimises the possibility of sparking, and consequent potential ignition and explosion. Preferably the sealing member has one or more apertures, and the second flange also comprises apertures, in register with those in the sealing member for passage of a corresponding number of bolts (but no other apertures) . In a preferred form of the invention, the first flange itself forms the head of a bolt (or of more than one bolt), which pass(es) through the aperture (s) in the sealing member and in the second flange, the assembly additionally comprising one or more nutsfor screw-threaded engagement with the stem(s), so that the nuts can be tightened to urge the first and second flanges towards each other. Mechanical arrangements other than a nut and bolt which could be passed through the apertures in the sealing member and second flange, and tightened could also be used, and would be apparent to the man skilled in the art. In preferred embodiments of the invention, the seal assembly comprises two or more stacked compressible sealing members, separated by one or more substantially rigid spacers. The spacers may be polymeric or of metal or any other suitable material, since they are not exposed to the hazardous environment. Instead, one single sealing member may be used. The sealing members may be formed in any suitable way, for example by moulding or stamping. The seal assembly preferably also comprises means to prevent over-compression of the sealing members. In accordance with preferred mechanical engineering practice, the compression limiting means is preferably arranged to prevent compression of the sealing member (s) beyond their Shore compression limit. The compression limiting means preferably comprises a substantially rigid member positioned between the first and second flanges. It extends only part of the distance between the first and second flanges prior to compression of the sealing member. As the flanges are urged towards each other, they abut against opposite ends of the rigid compression limiting member and further relative movement between the first and second flanges is substantially prevented. Thus over-compression of the sealing members is substantially prevented. Where the assembly comprises two or more apertured sealing members and corresponding apertured spacers therebetween, the compression limiting means preferably comprises a substantially rigid sleeve which fits within the apertures. The present invention will now be further described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of a cable joint enclosure having a plurality of circular cross-sectioned tubular cable outlets and one oval one projecting therefrom; Figure 2 is a longitudinal sectional view through the oval outlet of the enclosure of Figure 1, showing a sealing assembly according to the present invention; and Figure 3 is a plan view of the sealing assembly of Figure 2. Figure 1 shows a stainless steel joint enclosure 1 which may contain, for example, optical fibre organiser trays and/or electronic boards (not shown) . The metal enclosure 1 comprises body portion 3 and a lid 5 which can be separated to access the interior of the enclosure for forming O 00/38290 10 connections and the like. Six cable outlets 7, 8 that are generally circular in cross-section and one cable outlet 9 that is generally oval in cross-section project from the lid 5 of the cable joint enclosure 1. The oval outlet 9 is to be closed by a sealing assembly according to the invention, as described in more detail with reference to the remaining figures. Some of the circular cross-section outlets 7 are open for receipt of cables, and others may be sealed in any conventional manner, say by screw-threaded plugs or caps. Typically each outlet 7,8,9 projects from the housing 1 by a distance of about 30 cm. Figures 2 and 3 show a sealing assembly according to the present invention, within the oval cross-section cable outlet 9 of Figure 1. The sealing system comprises three longitudinally compressible EPDM sealing members 11, separated from each other by two substantially rigid polymeric spacers 13. Each of the sealing members 11 and polymeric spacers 13 is substantially the same oval shape and size as the internal cross-sectional shape of the conduit 9, but the clearances to the rigid members may be a little larger than that to the rubber sealing members, even in the unstressed (as-manufactured) condition. There are two apertures in each member 11 and spacer 13, the apertures being in register with each other. Stainless steel bolts 19 are welded to a first stainless steel flange 17 which is assembled in contact with the and almost covers surface of the outermost EPDM sealing member 11 of the system and is thus exposed to the hazardous environment. The stems of the bolts 19 pass through the apertures in the sealing members 17 and spacers 13. A washer 21 is positioned adjacent the sealing member 11 furthest from the head 15 of bolt 17. This washer 21 forms the second flange according to the present invention, and is substantially planar. A nut 23 is provided for each bolt adjacent washer 21, and this can be tightened against a screw thread on the stem of the bolt 19 in order to urge the first flange 17 and the second flange 21 (the washer) towards each other, and consequently to cause the sealing members to expand radially into contact with the inner surface of conduit 8. A rigid compression-limiting sleeve 24, made of Nylon 66, extends around stem of each bolt 19, part way only between the flange 17 and the washer 21 (the second flange) . The length of the sleeves 24 is chosen to prevent compression of the sealing members 11 beyond their Shore compression limit, the flanges 17 and 21 abutting opposite ends of the compression limiting sleeve 24 before the compression limit of the sealing members is reached. The sealing members 11 are shown in their compressed state in Figure 2. An earthing lug 25 is also electrically connected to one of the bolts 19 by means of a second nut 27. The earthing lug 25 ensures that there is no potential difference between the bolt 17 and the conduit 8 and remainder of housing 1. Any potential difference would be potentially dangerous when the system is installed in a zone 1 hazardous environment since it could result in sparking. A star washer 29 is also included to ensure good electrical contact and good vibration resistance. As shown in the arrangement of Figure 1, the metal flange 17 of bolt 15 covers most of the surface of the adjacent EPDM sealing member 11. Therefore the possibility of static charge build up on the surface of the insulating sealing member 11, and the possibility of consequent ignition and explosion, is substantially avoided.

Claims: Claims : 1. A sealing assembly in a conduit comprising: (i) a longitudinally compressible rubber sealing member; and (ii) a first flange which is electrically conductive, covers a major part of the surface of the rubber sealing member and in use is in contact with the hazardous environment; wherein the first flange can be moved relative to another member to urge the sealing member against the said other member to compress the rubber sealing member longitudinally, causing it to be urged into sealing engagement with the conduit, characterised in tha t the assembly is for use in a zone 1 hazardous environment, the conduit is non-circular and the rubber sealing member and the first flange are of corresponding non- circular shape and dimensions. 2. A sealing assembly according to claim 1, wherein the said other member is a second flange positioned such that the rubber sealing member is between the first and second flanges. 3. A sealing assembly according to claim 1 or 2, wherein the first flange is substantially planar. 4. A sealing assembly according to claim 2, or claim 3 when dependant on claim 2, wherein the second flange is substantially planar. 5. A sealing assembly according to any preceding claim, wherein the sealing member is positioned within the conduit, and longitudinal compression of the sealing member causes it to increase in its transverse dimension, and thereby be urged into sealing engagement with the inner surface of the conduit. 6. A sealing assembly according to claim 1 wherein the said other member is provided by the end face of the conduit. 7. A sealing assembly according to any preceding claim , wherein the first flange comprises a metal, preferably stainless steel. 8. A sealing assembly according to any preceding claim, wherein the conduit comprises a metal, preferably stainless steel. 9. A sealing assembly according to any preceding claim, wherein the first flange covers at least 80% of the surface area of the rubber sealing member after the sealing member has been compressed into sealing engagement with the conduit. 10. A sealing assembly according to any preceding claim, wherein the first flange covers a sufficient part of the surface of the sealing such that any length of surface of the sealing member that is exposed to the hazardous environment in use, measured radially of the conduit, is shorter than 1cm. 11. A sealing assembly according to claim 2, wherein the sealing member and the second flange each have at least one aperture in register with each other and wherein the first flange forms the head of at least one bolt, which passes through the apertures in the sealing member and in the second flange, the system additionally comprising a nut for the or each bolt which can be tightened to urge the first and second flanges towards each other. 12. A sealing assembly according to any preceding claim, comprising two or more stacked compressible sealing members, separated by substantially rigid spacers. 13. A sealing assembly according to any preceding claim, additionally comprising a compression limiting member, to limit the extent of compression of the sealing member (s) . 14. A sealing assembly according to claim 13, wherein the said other member comprises a second flange, and wherein the compression limiting member is positioned between the first and second flanges, and extends only part of the distance between the first and second flanges. 15. A sealing assembly according to any preceding claim, wherein the conduit is a cable outlet from a cable joint enclosure, which outlet is to be temporarily blocked. 16 A sealing assembly according to any preceding claim, sealed to a conduit by compression of the sealing member and installed in a zone 1 hazardous environment. 17 A sealing assembly according to claim 16 in which the zone 1 hazardous environment is a sewer system. 18. A method of sealing a conduit comprising: (i) positioning a longitudinally compressible rubber sealing member in engagement with the conduit, and positioning a first flange, which is electrically conductive, covers a major part of the surface of the rubber sealing member and in use, it is in contact with the hazardous environment; (ii) moving the first flange relative to another member to urge the sealing member against the said other member to compress the rubber sealing member longitudinally, causing it to be urged into sealing engagement with the conduit; and (iii) inserting the conduit and installed sealing system into the hazardous environment, characterised in tha t the assembly is for use in a zone 1 hazardous environment, the conduit is non-circular and the rubber sealing member and first flange are of corresponding non-circular shape and dimensions. 19. A sealing assembly substantially as described with reference to the drawings . 20. A method of sealing a conduit, which is to be installed in a zone 1 hazardous environment, substantially as described with reference to the drawings.

Inventors: BLACKHALL EDWARD, BLACKHALL, EDWARD
Applicants: BLACKHALL EDWARD, CORNING COMMUNICATIONS LTD, BLACKHALL, EDWARD, CORNING COMMUNICATIONS LIMITED
Application year: 1999
Main classification: H02G15
IPC codes: F16J15, F16L55, H02G1, H02G3, H02G9, H02G15, H05K5