CA2065382A1

CA2065382A1 - Environmental sealing

Info

Publication number: CA2065382A1
Application number: CA 2065382
Authority: CA
Inventors: Donald George Peacock; Jean-Marie Etienne Nolf
Original assignee: Individual
Current assignee: Raychem Ltd
Priority date: 1989-08-25
Filing date: 1990-08-14
Publication date: 1991-02-26
Also published as: WO1991002917A1; BR9007615A; AU6330790A; EP0489084A1; JPH05501906A

Abstract

A method of sealing a substrate (7) which comprises positioning adjacent the substrate a moveable wall (23) and providing a material in communication with the wall, the liquid (11) having a vapour pressure sufficient to maintain the wall in sealing engagement with the substrate.

Description

~09~/02~17 1'Cr/(;n9()/012B3 ~ 1 . 2065382 F.NVIRONMENTAL SEALING

The present invention relates to environmental sealing of substrates such as cables or pipes, particularly within a duct, or a splice caseO This may be done to prevent water~
gas or other contaminant from passing along a duct into a manhole etc, or to protect a cable splice from the environ-ment. The invention will be described primarily in terms of a duct seal, ~which term includes "feedthroughs") but the invention is also applicable to other instances of seaLing, including splice cases, oipe protection and grommets etc.
The reason that a seal (rather than an adhesive bond o no significant thickness) may be required is a disparity in size or shape between the substrate to be sealed and some other object such as a housing within which it lies. For example, a duct may be from several millimetres to several centimetres larger than the cable or other substrate that it carriés, an oval cable may lie within a circular duct, or the installed size of a splice case housing may be larger than the spliced cables within it. Also, when a branch-out between two or more cables is to be sealed it will generally be necessary to convert the concave surface at the crutch region to a convex or straight surface that can be enclosed by, say, half-shells or a dimensionally-recoverable (generally heat-shrinkable) sleeve.
Such seals have usually been formed by the use of a conformable sealing member, ~or example an10-ring, or the use of a mass of sealant or a hot-melt adhesive. Whilst these seals in general work in a satisfactory manner, ~ problems sometimes occur. For example, by their nature, ; conormable sealing members have a low modulus and espe-. ,.,.,, .. ~ , ~ .
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paths may occur if it has not been possible ~o incroduce sufficienc heat into a hot-melt adhesive to melt it. It is for example difficult to introduce heat into a duct.
`i ~Difficulties may also arise due to the materials needed ;for ducts and cahles, which may be incompatible. Cables are often made of polyethylene or lead, and ducts of polyvinyl chloride, steel or cement which may be dirty or crumbly and difficult to clean.
, . , A widely used duct seal, disclosed in GB 1594937 ~Raychem), comprises a hollow body member provided on its inner and~or outer surface with a plurality of spaced apart flanges, each flange extending away rom and around said surface and at least a portion of the flange remote from said surface being deformable, but only at an elevated te~
perature, and at least part of said surface~s) and/or the surface of the flanges having a sealant.thereon.
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EP0179657 (Raychem) discloses a duct seal especially for sealing about four cables which contains a spring which, when operated, radially-expands that part of the duct seal that i~s to seal to the duct. The cables are sealed by heat~
shrink outlets of the duct seal. The spring is operated after heating the part of the duct seal in which it lies.
Heating may so~ten the material of the seal and activate an adhesive.
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EP0152696 (Raychem) disclose~s an as.sembly for sealing an aperture (such as that between a duct and a cable it carries) which comprises a ~lexible envelope that is arranged to be wrapped on itself for insertion into the aperture, the envelope having an opening therein for :' ' :

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receiving an expansible or expanding riller material, for ~xa~ple a curable foam, or expanding the envelope, a con-~ainer containing said expansible filler material, and means arranged to connect the container to the envelope to conduct the filler thereto for erfecting e!xpansion of the envelope, characterized in that an adhesive or sealant is located on or associated with at least part of the outer sur~ace of the envelope. The disclosure of EP0152696 is incorporated herein by reference.
Other patent specifications disclos ng hollow envelopes for sealing include the following. EP0100228 (Raychem) discloses a method forming a seal between at least one elongate object and a surface surrounding the or each object, which comprises:
(a) positioning between the object and the surface a flexible envelope containing a void-filling composition which is capable of undergoing a change from a state of lower viscosity to a state of hi~her viscosity;
(b) deforming at least part of the envelope thereby causing the void-filling composition to conform to the object and to the surface; and (c) causing said change from lower to higher viscosityO
EP0210807 (Raychem) discloses a double-walled ar~icle, two of which may be used one around the other to form a duct seal, in the form of a tube having a small volumé filling of a friction reducing liquid (preferably of high boiling point and low vapour pres~ure) or solid between its two wallsO
The article is able to revolve over a substrate by shear between its two walls to provide environmental or electrical protection.

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,~'0 '~1/()2!)17 1'Cr/(~i~19()/~)12X3 ' ;~ .; , ~ ``' _ 4 _ ` 2065382 GB2006890 (Kraftwerk union) discloses a seal comprising a container formed from resilient plastics sheet and par-tially ~illed with a liquid which is provided between a pro-tective tube in a wall and an insulation layer around a pipe. The contaLner is o~ substantially toroidal shape and permits ~he pipe to move axially and radially whilst main-taining a seal between the insulation layer and the tube.
~ S3038732 (Scott and Bond~ discloses an inflatable seal bushing for sealing a pipeline casing, which comprises a hollow resilient means having an inflated configuration to match the inside surface of said casing and to contact the outside surface of the pipe of said pipeline, means for introducing a fluid into said hollow resilient means to inflate same, and a plurality of angularly disposed, relati-vely solid spacer means integral with said hollow resilient means and transverse thereto for centering and supporting said pipe within said casing, each of said spacer means having a passage therethrough for providing liquid com-munication in the hollow interior of sai~d hollow resilient means.
US2816575 (Stokes) discloses an apparatus for laying a pipe employing inflated annular sealing rings.
US3339011 (Ewers Jr. et al) discloses a pneumatically-sealed cable splice case comprising a longitudinally-split sealable cylindrical casing having means within and adjacent to each of its longitudinal ends to retain and space apar~ a pair of end wall panels each end wall panel including two semi-circular disc portions having rounded outer edges and inner edges including aligned cut-outs therealong.
whereby cables may enter said casing through said aligned cutouts, and inflatable seal means confined between each of said ,~, .

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~. , 029l7 rCr/(i~)n/0l2%3 _ 5 ~ ,2065382 pair of panels of said end walls and having openings aligned with said panel openings, said inflatable means being expan-dable, when so confined, against such cables passed through said end wall openings, characterized in that said end walls are removeable'from the said means to retain them, and said semi-circular disc portions are pivotally pinned to each other with their cut-outs presented together to form said openings of said panels whereby said semi-circular disc portions may be pivo-tally opened apart for placement about said conduits.
An inflatable packing device for insertion between mating surfaces of the hub and spigot ends of a pipe joint is disclosed in GB1077314 (Woodward Iron Company).
A hollow-walled sleeve into which fluid is to be injected for heat-insulation o~ ducts is disclosed in GB1421960 (Commissariat a l'Energie Atomique).
Whilst many of the articles disclosed in the above spe-cification are able to provide satisfactory seals, some problems remain. For example the use of curing or otherwise setting materials may prevent or make difficult subsequent removal of the article, and simple gas pressurization of a seal will generally mean that the article has a short life-time due to leaks or gas-diffusion.
We have now devized a method of sealing, and associated article, that can in certain embodiments avoid these and other problems.
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Thus, the present invention provides: a method of sealing a substrate which compri5es positioning adjacent the substrate a moveable wall and providing a liquid in com-... . .

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The method need not, and in general will not, involve heating. This might be advantageous not merely because an awkward method step is avoided, but also because subsequenG
shrink back on cooling is avoided. The fact that solidi-fication of a sealing material may be, and generally will be~
avoided means that the seal might be more tolerant of move ment during service life, and also might mean that shelf-life before use is not a problem.
Such a method is particularly useful in the cable accessories market where environmental seals might be expected to have life-times comparable to that of the cables to be protected, typically at least twenty years. A seal merely pressurized with a gas would not be satisfactory since, even in the absence of a clear leak, diffusion through the material of its walls over long periods would cause too great a reduction of pressure. Also, a pressure reduction could occur over many years due to creep or the material of the duct and/or cable. By means of the present invention, however, a constant pressure (assuming constant temperature~ can be maintained despite diffusion away of the pressurizin~ vapour. This constant pressure will last until the last drop of liquid has vapourized. If necessary, the seal can be refilled with liquid periodically. Individual seals may be re-filled separately or two or more may be con-nected to a common reservoir of liquid. Removal of the seal may be simply done by releasing the liquid. A low pressure may be preferred if damage to weak cables or ducts is to be avoided over extended periods, whereas a higher pressure may be pre~erred if a more rugged seal is desired.

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We prefer that the liquid and/or vapour thereor is in con~act with the wall, although it need not be and movement the wall may be brought about by mechanical means i~ter connecting the wall and some other object directly agains~c ~nich the vapour pressur~ acts.
The moveable wall ~referably forms at least part oc a -lexible hollow article which preferably contains the ~iquid. It is possible, however, for the liquid to be located in a reservoir remote from the wall and the substrate, and its vapour to be in communication with the ~all by a pipe. This is not at present preferred since we prefer that sealing be achieved by a self-contained ar~icle and that external pipe work be avoided. The article may be supplied with a container containing a certain amaunt of liquid, preferably sufficient for one filling, preferably as a kit-of-parts.
The wall is preferably flexible, and may be stretchable, and thus able to conform to substrates of various sizes and/or of irregular or awkward shape. It may comprise at least three layers, for example one serving to retain the vapour, one to provide mechanical strength for example tensional s~rength against internal pressure, tear-strength or puncture rQsistance and one layer serving to orm a seal to the substrate by accommodating small scale irregularities in the surface of the substrate. To this end the wall may comprise a first layer of metal (or metallized plastics material or metal-coated plastics material) with which the liquid and/or vapour is in contact, and a seco~d strengthening layex such as high density palyethylene, together with a third layer, in direct or indirect face-to-'ace relation with the first layer and positioned between the first layex and the substrate~ The third layer referred ,.: , , . , ~ ~ , .: , . .

~ ' .: :, 1/02~17 PCr/(il3')0/(~1281 06$38'~ - 8 -to above may comprise a deformable material such as a r~bber or other elastomer or a Eoam. Other materials may be used as this third ~ayer, ~or example sealing material.s such as sealants, for example mastics or gels, but we prefer for many uses that no permanent adhesion occurs to the substrate. In general we prefer that the second layer have a hardness of from 35-85, more preferably 40-80, especially 45-75 shore. The various functions referred to above may, however, be provided by fewer layers, where one layer has two or more functions.
The wall may comprise for example a laminate of a metal film and a layer of plastics material either side. Such plastics layers may allow the wall to be heat-welded to itself to make achollow article. Lap bonds, optionally with patches and preferably made that are under shear, rather than peel whan the article is inflated. Such bonds preferably have a significant width for example at least 10 mm, preferably at least 15 mm, to reduce the extent to which liquid can diffuse through the bond and ~hus escape from the envelope. Additional layers may be provided for mechanical strength such as oriented, for example biaxially-oriented or two layers of uniaxially oriented, high density polyethylene such as that known by the trade mark Valeron. A possible structure is as follows; the dimension being merely prererred~
Copolymer 15 - 30 microns Valeron (trade mark) 40 - 160 microns Mylar (trade mark) S - 20 microns Aluminium (as one or more layers) 20 - 80 microns Mylar (trad~ mark) 5 - 20 microns Copolymer 15 - 30 microns This struc-ture may be varied for example by omitting the mylar or using a different material in its place. The :, . , ;

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copolymer should allow heat bonding or welding, and may comprise a hot melt adhesive such as one based on ethylene vinyl acetate. Additionally or alt~rnatively a polyamide based adhesive could be used. The s~ructure preferably has an elongation to break of at least lO~, preferably at least 203. This structure may be used within an envelope for example one comprising a polymer such as an elastomer, such as rubber, optionally reinforced for example with nylon.
Alternatively, it may be laminated to such a polymer, or it may be used alone. The additional material may reduce creep.
In general, it is merely necessary that sealing contact between the wall and the substrate occur along a line that cuts across any potential leak path, although an area of contact of significant width may be preferred. It may be sufficient, therefore, for a sealing article to have a thin strip of rubber, or other third layer as referred to above, that extends over part only of the first layer. The greater size of the first layer may be desirable in order to locate the wall w.th respect to the substrate, or to produce some special effect on pressurlzation.
The layers referred to are preferably thin in order that they be flexible, but in some embodiments the layers ...ay be regarded as nominal layers of an article of signifi-cant thickness.
As mentioned above, the wall preferably forms at least part of a flexible hollow article~ That article preferably comprises a substantially flat (which term includes flat-.
tenable, since the article may be set in a curved~or similarshape) flexible envelope that can be wrapped around an elongate substrate such as a cable to form an annulus which can be deformed by pressure of vapour of the liquid to increase its radial thickness. In this way, an annular gap between a duct and a cable it carries may be sealed.

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The article may be provided with a valve which can allow injection of vapour or liquid but prevents its release. The valve may have means that allows deliberate release of liquid or vapour from the ~rticle since, instead of topping-up the article at regular intervals, it may be desirable to remove the remaining liquid and then refill; in this way one can be sure of a sufficient volume of filling.
The valve is preferably easily accessible when the article is in a duct, or otherwise installed, and it is preferably flush with an external surface o the article, and reached by a nozzle, optionally via a flexible hose, attached to the supply of liquid.
We have found surprising success in.sealing various shapes of substrate using a flat envelope formed simply by bonding or welding together around their edges two rec-tangular sheets of material, one on top of the other.
Nonetheless, for some purposes it may be desirable to pro~
vide a hollow article which has an outwardly facing convex surface for sealing engagement with an internal surface of a duct etc within which the article is positioned. Such a hollow article may alternatively or additionally have an `outwardly-facing concave surface Eor sealing engagement with a cable or other substrate around which the article is posl tioned. Such curved surfaces, which might reduce leak paths through avoidance of wrinkles and allow lower internal pressures to ke used, may be achisved by thermoforming a substantially flat surface or be formed ab initio by mouldin~.

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11- 20~53~2 The article is pre~erably of so called "wrap-around"
~esign, a te~m well-k~own in the cable accessories art ~eaning having the ability to be installed around a cable ~1~hout access to its ends. (Reflerence may be made to GB11;5470 which discloses a wrap-around sleeve.) In order ~hat the embodiment above be wrap-around, we prefer that the concave inwardly facing surface extends to an outwardly facing surface of the article.
The liquid will be chosen according to the particular substrate to be sealed and to the environment within which it is to be used. In general, the liquid is preferably non~
~oxic, non-inflammable, non-corrosive to the substrate and to the article containing it, and also has no deleterious effect on any component of the environment now thought to be at risk. The most important properties of the liquid are its boiling point, and vapour pressures over a range of tem~
peratures. We prefer that its boiling point at atmospheric pressure be less than 10C, more preferable less than 0C, particularly less than -5C, although for some uses it could be up to, say, 15C. Its vapour pressure at 0C is preferably at least 0.25, more preferably at least 0.5, especially at least 0.7 bar guage. We also prefer that the vapour pressure does not exceed 5 bar guage, particularly 4 bar especially 3 bar at 25C more pre~erably at 20C. Such properties may be, and preferably are, achieved with a single liquid and its vapour, although mixtures o~ different components including liquids and gasses such as air may be used. A mixture of a high~vapour pressure liquid and a low vapour pressure may be used to achieve a desired pressure.
Mixtures may however vary in composition with time as one component preferentially evaporates, unless a suitable azeotrope be ~ound. Suitable liquids include fluorocarbons, marketed under the ICI trademark Arcton, such as Arcton 134A

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possibly with Arcton 114. Arcton 134A is CH2FCF3, and Arcton 114 is CHF2-cHF2-';
The invention is ~urther illustratea by the accom-panying drawings, in which:
Figure l shows an envelope into which can be injected a liquid of high vapour pressure;

Figure 2 is an end view of the unexpanded envelope around a cable within a duct;
Figure 3 shows the envelope containing a liquid, and consequentially after expansion;
Figure 4 is a tranverse cross-sectional view of an envelope, showing two different embodiments thereof; and Figures 5 and 6 are end views of further embodiments The envelope of figure 1 comprises opposed sheet-like walls 2,3 of generally rectangular confïguration~ welded or ; bonded together at their edges, optionally with further for example specially shaped,-pieces of material between them as shown at 4. The envelope may be a trapezium as indicated by the dotted lines. One or more walls 2,3 and 4 may be flexible and/or stretchable, and in their rest state, that is before internal pressuri~ation, the walls may be substan-tially planar as illustrated or they may be specially shaped. Such shaping may allow additional expansion and may take the form of corrugations, or may be a more gentle cur-vature to match the substrate to be sealed. The walls may comprise any suitable material, and at least one metal layer such as stainless steel, aluminium or lead is pre-ferred, optionally bonded ~o a plastics film. Metal may be desirable since it can have a very low ability to transmit . ~ ~, ' .

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vapour. Also, tor many uses we prefer that the walls do not stretch, espec1ally in an axial direction with respect to cable and duct. Again, a metal is advantageous, although uniaxially-reinforced plastics, employing axial fibres for example, may be used. The edges 9,9' of the envelope may be tapered to avoid a step at the regions where they overlap when the envelope is installed by wrapping it around a substrate. The envelope is shown with a tube or valve 5 through which the liquid is to be injected. In the drawing, the tube is shown entering through a side wall. It may however simply pass between overlapping layers of the enve-lope that are bonded together as a lap joint. I'he part of the tube that passes between the layers may be at least par-tially flattened so as not unduly to impair the lap bond.
The walls 2 and/or 3 may have a strip of rubber, or gel or other material 6 to help form a seal between the underlying layers containing the liquid and the substrate. Two or more materials of differen~ properties may be used one over the other or side by side. For example a softer material may be held between harder materials either side. Foam coverings to the envelope may be provided having a gap between them filled with gel. The material 6 may avoid leak paths tha~
might otherwise result from the envelope wrinkling. The strip could extend past one end and overlap the other end when the envelope is installed. Preferred materials have a cone penetration value of 100 - 350, more preferably 100 - 300, particularly 150 - 300 ~10-1 mm) according to ASTM D217-68, and preferably an ultimate elongation of at least 100~, particularly at least 200%, especially at least 500% according to ASTM D638-80~ For further details see 4600261. Useful materials may be prepared by gelling a ;; liquid mixture of suitable gel precursor materials such as polyurethane, polysiloxane or styrene alastomeric block copolymers, together with suitable reactive or non-reactive ,, .: . . . .

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; '~,0~ 14 -extenders, for example mineral or vegetable oils. The gel may be contained in the interstices of a material such as an open-cell foam for example in strip form.
In figure 2 the envelope l is wrapped around a telecom-munications or power cable within a duct or an end of a splice case 8. Preferably the annular gap between cable and duct is small, say less than lO ~ measured with the cable at the centre of the duct. Where a larger gap exists, a suitably large envelope may be used, a smaller envelope may be wrapped several times around the cable, or the cable may be built up by wrapping it with for example a rubber tapeO
The envelope may be prestretched around the cable, and held in the wrapped configuration by tape. The envelope is then slid into the duct, either by sliding it along the cable or by moving the cable relative to the duct. A fluid dispen~ser or reservoir lO is then connected to a valve or other inlet on the envelope and fluid ll is injected, qenexally under gravity or the force of its own vapour pressure within reservoir lO.
Where the envelope has a high coef~icient of friction with the cable and/or duct or where the envelope has a material of high coefficient of friction on a surface thereof ~for example a gel or other sealing~material of high tack) that surface may be treated to facilitate sliding with respect to cable and/or duct. For example a gel etc. may have a skin or be coated with a thin film or lubricant, which may be perforate, with a powder such as talc or with small spheres. Where necessary, the coating may be chosen such that contact between gel and cable and/or duct s~ill occurs when the gel is subject to pressure ~hat causes its displacement. In many cases however such contact will not be required, and the high conformability of the gel together WC) 91/0~917 f'Cr/Gf~9()/~Ji ~
- ~5- `; 2~382 with a thin film coating w111 achieve the desired sealing.
~lso. the gel may be coa~ed with a release layer ~hat is -emoved before use.
The fluid inflates or merely deforms the envelope into sealing engagement with the cable and duct thereby forming a seal between them. Liquid may flow from reservoir 10 into the envelope under gravity, and the reservoir 10 may be disconnected when sufficient liquid is in the envelope as shown at 11 in figure 3 either by observing the envelope (for example if it is transparent) or by noting a change in level in the reservoir. The amount of liquid required can be calculated gi~en the rate of vapour transmission through the material of the envelope, and the maximum length of time desired between topping-up.
In some instances the weight of cable, or the force applied to the cable to bend it in the desired direction as it leaves the duct may cause it to lie eccentrically within the duct. The present invention can accommodate a signifi~
cant extent of eccentricity, but where problems are likely to arise a cable support means such as a rigid collar may be positioned around the cable just within the duct.
The fact that pressure is exerted by a fluid might pro-vide significant advantages, because that pressure can be exerted uniformly over the entire surfaces where it is needed, and the uniformity can be maintained inspite of creep of the duct and/or cable and inspite of movement for example of the cable to a position off-centre within the duct; liquid and/or vapour simply moves around the seal as required.
The duct seal may be removed simply by releasing its internal pressure and pulling it out o~ the duct, A handle :

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Figure 4 is an axial section through a duct 8 and duct seal l. The duct seal l is positioned well within the duct to avoid any damaged portion 12. The duct seal has edge portions 13 which are not expansible but serve to align it properly with the duct. The upper and lower sections of the duct seal 1 show respective embodiments. In the lower sec-tion the se~l is a simple envelope as shown in figure l, whereas in the upper section it comprises a plurality of preferably interconnected pockets each of which expands.
The pockets could be shaped by having a greater radius of curvature above and below and a smaller radius left and right as drawn such that pressure deformation was prin-cipally radial rather than axial with respect to cable and ductJ
In the drawing, howe~er, the greater radius of curvature is left and right which might have the effect of reducing the effective radial component of the pressure~ This may be useful if the seal is used with a weak duct.
Figure 5 shows one way in which the invention can deal with more than one cable in a duct. Here each cable lies in a pocket in the duct seal. Such pockets may simply be formed due to the presence of the cables during installa-tion, or the duct seal my be preshaped by moulding or ther-moforming a flat sheet. The seal can be seen to have outwardly-facing concave surfaces 14 for sealing to the cables and an outwardly-facing convex surface 15 for sealing to the duct, In ordei to clarify the terminology, it may be noted that surface 16 is an inwardly-facing surface. The convex surfaces extend to the exterior surface of the article tin this cAse the convex surface 15) allowing the article to be "wrapped-around" the cables.

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, WO91/02917 r'CI'/Cn')0/012~3 , - 17 ~ 5~82 ~ n aLtern~tive to figure S is illustrated in figure 6.
Her~ the pressurizable envelope 1 rnay be thin,, having the general shape of that shown in figure 1 if desired. The cables 7 are built up to a convex shape that substantially fills the duct 8. This may be done by placing the cables 7 in holes that extend through a filling piece 17 of sealing material, preferably a rubber or other elastomer which may be foamed, but in some circumstances may be of the general type that is discLosed in US 460C261 (Raychem), the disclo-sure of which is incorporated herein by reference~ The envelope 1 is pressurized causing the filling piece 17 to be compressed around the cables and causing the space between it and the duct 8 to be sealed. The holes in which the cables 7 are placed may be open as at 18 to an outer surface of the filling piece 17, giving it a "wraparound" nature.
An advantage of preferred embodiments of the invention is that no bonding need occur between the seal and the cables or duct. Not only does this make removal easier but it may be ~egarded as a safety feature. The pressure that the duct seal will retain can be determined according to the nature of the liquid. Thus, if a head of water or other pressure builds up behind the duct seal that is greater than the vapour pressure of the liquid, the duct seal will allow that pressure to be released. ~y contras~, a bonded duct seal may allow dangerous pressures to build up resulting in '' considerable damage when the seal finally fails.
, For'the avoidance of doubt it is noted that the inven-tion provides a method and article for sealing, and a sealed 'article,' particuLarly for cables, employiny a high vapour pressure liquid or solid and/or employing any one or more of the other features referred to herein.

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Claims

1. A method of sealing a substrate which comprises posi-tioning adjacent the substrate a moveable wall and providing a material in communication with the wall, the liquid having a vapour pressure sufficient to main-tain the wall in sealing engagement with the substrate.

2. A method according to claim 1, in which the liquid and/or vapour thereof is in contact with the wall.

3. A method according to claim 1 or 2, in which the wall is flexible.

4. A method according to claim 1,2 or 3, in which the wall is stretchable.

5. A method according to any preceding claim, in which the wall comprises at least two layers.

6. A method according to claim 5, in which the wall comprises a first layer with which the liquid and/or vapour thereof is in contact, and a second layer that provides a seal between the first layer and the substrate.

7. A method according to claim 6, in which the first and second layers are in mutual face-to-face contact.

8. A method according to claim 7, in which the second layer extends over part only of the first layer.

9. A method according to any preceding claim, in which the wall comprises a metal.

10. A method according to claim 6,7 or 8, in which the first layer comprises a metal, and the second layer comprises a material having a hardness of 35-85 shore.

11. A method according to any preceding claim, in which the moveable wall forms at least part of a flexible hollow article containing the liquid.

12. A method according to claim 11, in which the article comprises a substantially flat flexible envelope that can be wrapped around an elongate substrate to form an annulus which can be deformed by pressure of vapour of the liquid to increase its radial thickness.

13. A method according to claim 11, in which the article has a valve through which the liquid can be injected.

14. A method according to claim 13, in which the valve is substantially flush with an external surface of the article.

15. A method according to claim 14, in which the article is substantially non-adhesive on its external surface.

16. A method according to claim 11, in which the hollow article has a outwardly-facing convex surface for sealing engagement with an internal surface of a duct within which the article is positioned.

17. A method according to claim 11 or 16, in which the hollow article has at least one outwardly-facing con-cave surface for sealing engagement with a substrate around which the article is positioned.

18. A method according to claim 16 or 17, in which the con-vex or concave surface is formed by thermoforming a substantially flat surface or is formed ab initio by moulding.

19. A method according to claim 17, in which the concave surface extends to an exterior surface of the article so that the article can be wrapped around a substrate.

20. A method according to ANY preceding claim, in which the liquid has a boiling point at atmospheric pressure of less than 10°C.

21. A method according to claim 20, in which said boiling point is less than 0°C.

22. A method according to claim 21, in which said boiling point is from -25°C to -5°C.

23. A method according to any preceding claim, in which the liquid has a vapour pressure at 0°C of at least 0.25 bar gauge.

24. A method according to any preceding claim, in which the liquid has a vapour pressure at 10°C of at least 0.5 bar gauge.

25. A method according to any preceding claim, in which the liquid has a vapour pressure at 25°C of 0.25-5 bar gauge.

26. A method according to any preceding claim, in which the liquid comprises a mixture of two or more components.

27. A method according to any preceding claim, in which the liquid comprises a fluoro-carbon.

28. A method according to any preceding claim in which the substrate comprises a cable or pipe within a duct, the method comprising positioning a hollow duct seal comprising said wall around the cable or pipe and within the duct, and introducing said liquid into the duct seal such that pressure of vapour of the liquid maintains the wall in sealing engagement with the duct and/or cable or pipe.

29. An article for sealing a substrate which comprises a moveable wall and a liquid in communication with the wall the liquid having a vapour pressure sufficient to maintain the wall in sealing engagement with the substrate.

30. An article according to claim 29, having a wall and/or liquid as defined in any of claims 1-27.

31. A substrate sealed by a method according to any of claims 1-28.

32. A cable sealed within a duct by a method according to any of claims 1-28.