PIPE SLEEVES

Abstract: Various constructions of prefabricated sleeve are described for fitting round pipes which are to have brickwork or foundation work in concrete made round the pipe. The sleeve acts to hold the mortar/concrete away from the pipe (12) until it has set, so leaving, after the disintegration of at least components (10) of the sleeve between the outside of the pipe and the outside of the sleeve (2), a hollow void round the pipe, as required by the building regulations. The sleeve may be made of inexpensive materials which can biodegrade in situ, thus avoiding the need to remove them by hand after the mortar/concrete has set. Sleeves may be supplied preassembled, or may be constructed on site, e.g. by folding from a waterproof surfaced fibreboard blank.

Description: PIPE SLEEVES This invention relates to pipe sleeves, by which term is meant devices for covering short lengths of underground pipe work which are to be encased in concrete or brickwork. The sleeve acts as a shutter or other mechanical support for the wet concrete or brickwork comprising a brick and mortar matrix, to hold it spaced from the pipe work while it sets. After the brickwork or concrete has set, most or all of the sleeve is intended to lose its mechanical integrity so that the pipe work and surrounding foundations may move relatively to each other to a limited extent without the pipework being fractured or otherwise damaged. The formation of a space around a pipe which e.g. passes through a concrete foundation wall, is required by the relevant building and constructions regulations in many countries, so that construction workers are used to forming some sort of shuttering about pipework to provide such a space. However, its formation, and then its removal after making the wall (so it does not itself transmit stresses to the pipe) requires skill and can be time-consuming, especially in awkward trench conditions. The present invention aims at providing a sleeve or component thereof which can be placed around a pipe to keep concrete or brickwork spaced from the pipe until it has set, whereafter the sleeve or component degrades naturally to lose its mechanical strength and thus permit relative transverse movement of the pipe and surrounding material, such as the foundation of a building. Accordingly the present invention provides a component for a pipe sleeve intended to embrace a pipe or duct and to function as a form/shutter/mould for later-applied concrete, brickwork or mortar, the component comprising a substantially impermeable part-cylindrical outer member having a series of spacers extending internally therefrom, the outer member having end walls secured thereto or integral therewith to prevent the ingress of wet concrete etc. into the space between the outer member and a pipe or duct in contact therewith, which is adapted to fit together with at least one other like component to form a sleeve completely encircling a length of pipe etc. of external diameter smaller than the internal diameter of the envelope/sleeve defined by the inner ends of the spacers. The basic unit of this invention is a component of which two or more co-operate to form a complete sleeve around a pipe or duct extending for a known or desired cross section, such as to extend across the width of a trench across which the pipes or ducts extend/pass, which trench is intended to be filled at a later date with concrete or brickwork to form a foundation wall or similar structure. In a preferred form of the present invention, a sleeve of any desired length can be made up by connecting several sleeves of unit length together end-to-end. The two or more unit components making up a sleeve may be hinged together to form a pair or set, or may be kept separate from each other until they are to be put into position. When they are in place around a pipe, they are able to transmit to the pipe the pressure applied by the surrounding wet concrete or brickwork without themselves being crushed. As the components later become degraded and crumble, they effectively leave an annular space between the pipe and surrounding concrete. Each component has an outer member of which the surface is substantially impermeable. The outer member is kept away from the pipe by a complex spacer body or by an array of spacers. Even if the outer member is of non- biodegradable plastics material, preferably the spacer is of biodegradable material which loses its mechanical integrity after becoming wet or moist, which can be arranged for deliberately after the concrete or mortar has set. Each component has two end walls to inhibit cement from entering the space between the outer member and the pipe, or to facilitate two components or sleeves being joined together end-to-end. In an alternative pipe sleeve component of the present invention the outer member is of flexible material extending between two relatively-stiff end walls between which an extensible spacer body extends. The spacer takes the form of a corrugated member or bellows of which the folds are deep enough for their inner ends to rest on or be spaced from the pipe around which concrete is to be poured or brickwork assembled with mortar, and with their outer ends secured to the outer member. Because of the bellows construction, not only is the component of adjustable length, but it can also be fitted around a pipe bend. When in place on a pipe, the outer member acts mainly to prevent mortar from intruding to a significant extent into the interior of a component, with the main resistance to crushing being provided by the inner ends of the spacer coming to rest against the pipe and functioning as struts to keep the main bulk of the mortar/concrete spaced from the pipe surface by a distance substantially equal to the depth of the folds in the spacer. The pipe sleeve formed by two or more unit components of the present invention is intended to be fitted on to a pipe which is normally positioned underground. When a length of the pipe is exposed, as during a trenching operation to prepare foundations etc. for a new building, the pipe normally extends from one side of the trench to the other, usually in a straight path which need not be at right angles to the walls of the trench. As many sleeve components are fitted together as is necessary to envelop the exposed pipe surface, with the components being secured together in a manner eliminating any gaps between them into which wet mortar or concrete might flow. When concrete is poured into the trench, as it reaches the sleeved length of pipe it applies hydrostatic forces on the sleeve tending to crush it. This causes the outer surface of the pipe component to act as a form, shutter or mould to keep the concrete spaced from the pipe surface by distance approximately equal to the radial thickness of the sleeve. When the concrete has set, the sleeve may be permitted to degrade naturally, by the ingress of free moisture from the soil forming the walls of the original trench, or free water may be deliberately introduced to assist in the decomposition of the degradable material forming at least the spacers, if not also the end walls and the outer member. The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an end elevation of a first preferred embodiment of a pipe sleeve of the present invention in position on a pipe; Figure 2 is a side elevation of the pipe sleeve shown in Figure 1; Figure 3 is an isometric view of the first preferred embodiment of a pipe sleeve of the present invention partly in position around a pipe; Figure 4 is a view similar to Figure 3 showing the sleeve in a later stage of assembly; Figure 5 is a view, similar to Figure 3 and 4, of a complete pipe sleeve in position ready to -be buried in concrete; Figure 6 is a section through a trench filled with concrete across which a pipe extends and having the otherwise exposed surface of the pipe covered with a pipe sleeve of the present invention; Figure 7 is a plan view showing how incremental and shaped pipe sleeves may be used to cover the surface of a pipe bend; Figure 8 is a diagrammatic isometric view of two alternative pipe sleeve components in an early stage of being put in position around the pipe; Figure 9 is a view similar to Figure 8 but showing a later stage of assembly; Figure 10 is an end elevation of a second embodiment of a pipe sleeve of the present invention in position on a pipe; Figure 11 is an axial section along the lines IX-IX of Figure 8; Figure 12 is a view similar to Figures 10 and 11 of two unit pipe sleeves being assembled together to form a longer pipe sleeve; Figure 13 is a view of the components of Figure 12 secured together to form a two-unit sleeve; Figure 14 is a side elevation of the sleeve of Figure 13 showing its corrugated appearance; Figure 15 is a view similar to Figure 6 but showing the 'bellows-type' sleeves in position; Figure 16 is a plane view of sleeve of Figures 13 and 14 in position on a 90° pipe bend; Figure 17 is a perspective view of a third embodiment of a part of a pipe sleeve of the present invention ; Figure 18 is an end view of the spacing members of the third embodiment; Figure 19 is a plan view of a fourth embodiment of a part of a pipe sleeve of the present invention, and Figure 20 is a end view of the spacing members of the fourth embodiment. Referring first to Figures 1 to 7 of the accompanying drawings, a pipe sleeve 2 shown in Figure 1 consists of two similar components hinged together along a longitudinally-extending edge. Each component is made from fibre board sheeting 4 faced on both sides with a layer of polyethylene to render the board moisture-proof. The board forming the outer member 4 is bent and folded to form virtually a semi-cylinder 6 with internal longitudinal ribs 8. At the angularly-separated ends of the semi-cylinder 6 are integral longitudinal walls 10 which terminate at an inner radial position intended to be spaced by a desired distance from the external surface of the pipe 12 around which the sleeve 2 is to be placed. These end walls 10 act as radial spacers. This may also be the function of the ribs 8 but, in the embodiment illustrated, the ribs 8 are mainly for reinforcement purposes. Positioned internally of the outer member 4 are two circumferential spacers 14 which abut the walls 10 and which are threaded on the ribs 8, being held there either by friction alone or by glue. These spacers 14 are preferably made of fibre board material but without any surface coatings, so that they are not moisture- proof . Two of the adjacent walls 10 on different components are provided with an integral hinge 16 extending along the axis of the sleeve. With this arrangement, the two components forming the sleeve may be opened out sufficiently to be positioned around a pipe from a lateral position, because the sleeve cannot be threaded over the pipe. One of the components has a hooked extension 18 positioned and adapted to engage in an opening in the cylinder 6. The extension 18 is preferably made of a resilient material to permit it to be flexed out of the way when the end walls 10 of the two components remote from the hinge 16 are to be brought into an abutting relationship with each other, at which point the hook on the end of the extension may drop into an opening 20. There may be two or more similar extensions 18 provided on each component. In addition to being spaced at intervals along the length of the sleeve 2, spacers similar to 14 are provided at the axially- separate ends of the sleeve components. These provide end walls 22 which may either abut the ends of the ribs 8 or have cut outs in them to provide mechanical support for the ends of the ribs. The box-like mechanical reinforcement provided by the longitudinal ribs 8 and the circumferential spacers 14 and end walls 22 give the substantially-cylindrical outer surface 4 of the pipe sleeve 2 sufficient mechanical strength to resist the hydrostatic compressive forces applied to the pipe sleeve when immersed in wet concrete as foundations etc. are being poured, and are setting. Figure 3 shows an early stage in the positioning of a pipe sleeve 2 around a pipe 12. This view indicates how projections 24 similar to extensions 18 extend along the axis, said extensions being adapted to engage in apertures 26 in aligned pipe sleeves, in order to permit two or more units of pipe sleeve to be connected together to form a combined sleeve of indefinite length. Figure 4 shows two like pipe sleeves connected together, with one sleeve being completely closed, and the other nearing its fully-closed position. When the latter has been fully closed, the projections 24 are inserted into the openings 26 to latch the two sleeves together end-to- end. When the two components of each sleeve, and when two like sleeves, are connected together by means of the respective projections 18 and 24 engaging the respective openings 20 and 26, the abutting longitudinal walls 10 and end walls 22 are held so closely together that very little, if any, wet concrete may flow into the spaces between the abutting walls. Such webs of concrete, would when set form webs so fragile and brittle as to be easily broken off the parent body of concrete so as to provide no significant resistance to the relative lateral movement of the pipe 12 within the cavity left by decomposition of the pipe sleeve components. Figure 6 shows a concrete filled trench 26 across which extends a pipe 12. A length of pipe 12 was exposed when the trench was excavated. Before the trench was filled with concrete 28, the exposed length of the pipe 12 was covered with as many pipe sleeves of unit length as were required. In Figure 6 two unit pipe sleeves were required, they were joined together end-to-end as shown in Figure 5. Figure 7 shows how an exposed pipe bend may be sleeved with two whole sleeves 2 of unit length. The pipe bend itself is covered with three connection lengths or segments 30 each made by cutting a unit pipe sleeve along two planes inclined at equal angles to the longitudinal axis of the sleeve itself. As the sleeve is made of fibre board, it offers no great resistance to being cut by a suitable implement. The manner in which a sleeve is cut along the inclined planes does not form part of the subject-matter of this invention, and so will not be described herein in any further detail. In order to sleeve a 90° pipe bend each of the planes of a segment 30 subtends an angle of 30°. Because the axial projections 24, and their complementary openings 26, will have been removed, the segments 30 will most conveniently be held together and to their contiguous pipe sleeves by lengths of adhesive tape. Each segment retains its mechanical strength permitting it to resist radial compressive forces applied by the wet cement, with there being little or no axial forces tending to separate the segments 30 from each other and from their adjoining pipe sleeves 2. Alternatively unit pipe sleeve components may be pre-cut at time of manufacture to form the connection lengths 30 required to go round bends. If this method of manufacture is used the projections 24 and openings 26 may be provided on the connection lengths 30. Referring now to Figures 8 and 9, these show the assembly of two components together using an alternative system in place of the tab/slot system shown in Figures 3 to 5. As seen in Figure 8, one edge of each semicylindrical component has two studs 25 and the other two keyhole slots 27. The ends are likewise provided with studs (not shown) or keyhole slots 29. To engage studs 25 in slots 27 the components are moved axially with respect to each other, as shown by the arrows in Figure 9, while if it is desired to enclose a length of pipe longer than the standard component, two or more units each of two components may be mutually engaged end to end using the not shown studs and twisting one pair of components about the axis of the pipe after engaging the not shown studs in keyhole slots 29. In the embodiment of the invention shown in Figures 10 to 16, each pipe sleeve component 31 presents an end wall 32 made of fibre board or like degradable material possessing short-term mechanical strength. In one of each pair of axial-spaced end walls 32 is a keyhole slot 34, while in corresponding positions in the other end wall projects a mushroom-headed stud 36 (Figure 11). Unlike the Figure 1 embodiment, the two components 2 shown in Figure 10 are of identical construction. As shown more clearly in Figure 11, extending between the end walls 32 is a spacer body in the form of a corrugated member 38. The radially-inner end 40 of each corrugation is intended to lie on a cylinder of known internal diameter. The outer end of each corrugation is preferably formed of a hollow-T cross section, so that adjacent corrugations present a substantially part- cylindrical surface with intervening gaps 42. The T- shaped head 44 of each fold is overlaid by a flexible membrane 46 which acts to bridge the gaps 42. The membrane 46 is comprised of a flexible impermeable material such as polyethylene sheeting and is attached to the other constituent parts of the pipe sleeve unit only at the outer radial edge of end walls 32. The flexible member 46 is of sufficient dimensions that the corrugated member 38 is free to be longitudinally extended and compressed from its minimum to its maximum extension enabling it to be fitted in the desired position easily. When the corrugated member 38 is not extended to its maximum extent, the outside of membrane 46 may present the corrugated appearance shown in Figure 14. The membrane 46 is strong enough to resist the intrusion of wet cement into the spaces between adjacent folds of member 38, but the radial compressive forces applied to the sleeve are borne substantially entirely by the heads 44, which are supported by the angled folds of body 38 so that the compressive forces of the wet concrete can be transmitted through the folds to the external surface of pipe 12. Methods of using pipe sleeve components according to this embodiment are shown in Figures 12 to 16. In use a pipe sleeve component 31 is taken, and its two end walls 32 drawn apart the requisite distance. A second pipe sleeve component 31 likewise has its end walls drawn apart the requisite distance. The two components 31 are positioned around the pipe 12 and adhesive tape 33 applied circumferentially about the pipe sleeve 2 to retain the components 31 in position. Further adhesive tape 33 is applied along the longitudinal joins between the two components 31 to render the seams impermeable. If the length of pipe 12 to be covered is greater than the maximum expanded length of a pipe sleeve component 31 then further pipe sleeve units 2 , constructed in the same fashion, may be added and joined together with the slots and studs 34 and 36 respectively. Figure 14 is a view of the two sleeve units so coupled together with their abutting faces shielded by further adhesive tape 33. Figure 15 is a view similar' to Figure 6, showing how the surface of pipe 12 exposed in trench 26 is covered by two or more unit pipe sleeves 2. When used to sleeve a 90° or other pipe bend, as shown in Figure 16, the end walls 32 of one, two or more sleeve units are positioned in planes extending at 90° to the axis of the pipe projecting from the bend itself. This angular orientation of the two end walls 32 cause differential stretching and compression of the spacer body 38 so that the gaps 42 on the inside of the base may be reduced to zero, with the heads 44 of the spacer 38 abutting each other, while on the outside of the bend, the gaps 42 are significantly greater, but not to such an extent that the membrane 46 extending between walls 32 is in any danger of being ruptured or otherwise damaged. It is within the scope of the present invention to use a relatively-stiff plastics material for the outer surface 6 of each pipe sleeve component of the Figure 1 etc. embodiment. The surface 6 may be made of an extrusion of plastics material forming two major surfaces connected together by parallel septa, commercially available under the trade names CORREX or TWINFLUTE. That major surface which is to be on the inside of the pipe sleeve may be interrupted at chosen intervals to give it a degree of flexibility, so that the outer surface of the material may be flexed to form a partial cylinder of substantially cylindrical but more properly of polygonal cross-section. The spacers secured to the interrupted internal face of the plastics board are designed to accommodate this flexure of the board so that they come to extend substantially radially inwardly of the flexed outer surface in like manner to the ribs 8 of the Figure 1 embodiment. According to a third embodiment shown in Figures 17 and 18 the part cylindrical outer member 50 may be formed of a rigid or semi-rigid plastics material skin moulded into shape by a known moulding process. The outer member 50 may also carry stiffening ribs 54 and 56 running longitudinally and circumferentially respectively. Pairs of ribs 56 on the outer member 50 moulding define one or more location slots 58. Location slots 58 are adapted to receive spacers 60. Spacers 60, shown in Figure 18, are comprised of a degradable material, and are configured to have an inner arcuate edge 62 adapted to abut the outer surface of the pipe or duct (not shown) . The spacers 60 may be so configured that two or more spacers 60 completely encircle the pipe or duct. Various configurations are shown in Figure 18. Outer member 50 is provided on both its lateral and end edges with means for attachment to other outer members 50. The means for attachment may be as described in the previous embodiments and will not be described further. An alternative method of fixing would be to use adhesive tape both along the longitudinal and circumferential joins. According to a fourth embodiment of the present invention, shown in Figures 19 and 20, outer member 70, shown in Figure 19, is substantially a cut lamina of impermeable material such as an extruded multicellular plastics sheet commercially available as CORREX or TWINFLUTE. The outer member 70 is comprised of three or more flats 72 and optionally three or more flaps 74. Flaps 74, if present, should not be longer than the minimum distance that the pipe sleeve is required to keep the concrete or brickwork away from the pipe. Flats 72 are separated from each other and from the flaps 34 by hinge portions 76. The hinge portions 76 are formed by known methods suitable for application with the material of the outer member 70. Included in flats 72 are apertures 78 and 80. The spacer member 82, shown in Figure 20, is comprised of a lamina of degradable material. In this embodiment two spacer members 82 are required completely to surround a pipe or duct. Inner radial edges 84 of the space member 82 abut the outer surface of the pipe or duct in use. Outer radial edge 88 is configured to be a series of straight edges 90 running between projections 88. The number and spacing of edges 90 and projections 88 is dependent on the number and circumferential spacing of flats 72 and apertures 78 included in the outer member 70. In use two spacers 82 are placed around a pipe (not shown) with their edges 84 abutting the outside surface of the pipe. The spacers are held in position by appropriate fastening means 92, e.g. pieces of adhesive tape. Pairs of spacers 82 are placed along the length of the pipe to be surrounded at a spacing matching the longitudinal spacing of apertures 78 in the flats 72. Outer member 70 is taken and flaps 74 hinged around hinge portions 76 until they reach a position substantially perpendicular their adjacent flats 72. Flats 72 are placed adjacent to the outer edges 86 of the spacers 82 with apertures 78 and projections 88 adjacent to each other, and flaps 74 extending radially inwards of flats 72. Flats 72 are pushed toward the pipe and projections 88 engage with apertures 78 and edges 90 about flats 72. To retain the outer member 70 in position apertures 80 that are now circumferentially adjacent to each other are joined by a pair of 'U' bend type clips, not shown, and adhesive tape used to substantially waterproof the join. Alternatively adhesive tape may be simply used to retain the outer member 70 in position, and waterproof the join at the same time. It is envisaged that the outer member 70 may be supplied in continuous lengths and the spacer members 82 adapted to fit particular pipe sizes. It may be seen that though the present embodiments describe a method for protecting only a single pipe, the invention in fact makes it possible to protect a number of adjacent pipes. This is particularly possible with the fourth embodiment in which spacers 82 could be adapted to surround two or more adjacent pipes. In that situation an outer member 70 could be supplied in a continuous length, the length of the outer member needed could be calculated, and the required number of flats simply cut off the continuous length. Accordingly, it will thus be seen that the present invention provides pipe sleeves of unit or indefinite length, which may be straight of curved, and which are made of two or more components to permit each pipe sleeve integer to be positioned on a pipe or other duct from a position lateral thereto. When in position, the pipe sleeves possess sufficient radial compressive strength to resist the forces applied to the sleeve when embedded in wet concrete or new brickwork. The radially-extending portions of the sleeves are made of biodegradable material so that after the concrete has been poured and set, or after brickwork made with mortar has set, the pipe sleeves lose their mechanical strength and eventually decompose to leave relatively-clear annular spaces between the originally-sleeved pipes and the surrounding concrete or brickwork.

Claims: CLAIMS 1. A component for a pipe sleeve intended to embrace a pipe or duct and to function as a form/shutter/mould for later-applied concrete, brickwork or mortar, the component comprising a substantially-impermeable substantially part-cylindrical outer member having a series of spacers extending internally therefrom, the outer member having end walls secured thereto or integral therewith to prevent the ingress of wet concrete or mortar into the interior of the component, which is adapted to fit together with at least one other like component to form a sleeve completely encircling a length of pipe etc. of external diameter smaller than the internal diameter of the sleeve of the inner ends of the spacers. 2. A component as claimed in claim 1, in which at least some spacers extend longitudinally of the outer member. 3. A component as claimed in claim 2, including at least one radial spacer extending in parallel with the end walls and secured to the longitudinal spacers. 4. A component as claimed in any preceding claim, in which the outer member has secured to it, or integral with it, two longitudinal walls extending between, and secured to, the end walls. 5. A pipe sleeve comprising at least two components as claimed in claim 4, in which the components are hinged together about the outer edge of the adjacent longitudinal walls. 6. A sleeve as claimed in claim 5, including means for securing together the longitudinal walls and/or the outer members at the ends of the outer members angularly spaced from the hinged walls. 7. A pipe sleeve comprising at least two components as claimed in claim 4, in which the two components are secured together with their longitudinal walls abutting each other. 8. A sleeve as claimed in any of claims 5 to 7, including means for securing two sleeves together end-to-end. 9. A sleeve as claimed in any of claims 6 to 8, in which the securing means takes the form of at least one projection from a component or sleeve and adapted to engage mechanically in a recess in an adjacent surface of a contiguous component or sleeve. 10. A sleeve or component therefor as claimed in any preceding claim, in which the outer member is of fixed length, and is formed from a relatively-stiff sheet material formed into a part-cylinder of arcuate or polygonal cross-section. 11. A sleeve or component as claimed in claim 9, in which the sheet material is of an extruded multichannel hollow plastics board having substantially-impermeable outer surfaces. 12. A sleeve component as claimed in any of claims 1 to 9, in which the outer member is of a flexible material extending between two relatively-stiff end walls, and in which the spacers take the form of a hollow-cylindrical bellows construction of indefinite length. 13. A sleeve comprising at least two components as claimed in claim 12, as dependent from claim 9, in which the securing means takes the form of a mushroom-headed projection adapted to engage in a keyhole-shaped aperture in the opposing component or sleeve. 14. A sleeve comprising at least two sleeves as claimed in any preceding respective claim joined together end-to-end, and including integral flaps adapted to overlie abutting faces to inhibit the intrusion of wet cement between the set surfaces. 15. A component or sleeve as claimed in any preceding claim, in which at least the spacers are formed of a biodegradable material. 16. A component or sleeve as claimed in claim 15, in which the degradable material is of card or some other form of cellulosic fibres. 17. A pipe sleeve element such that two or more elements may be combined to form a sleeve surrounding a length of pipe or duct extending across a trench, the sleeve possessing sufficient radial mechanical strength to resist any hydrostatic or compressive forces resultant from filling the trench with wet concrete; each element having a fixed radial thickness to maintain a fixed minimum radial distance between the pipe or duct and any filling of the trench; wherein the elements comprise, extending in the radial dimension, webs of a material that will degrade and lose its radial mechanical strength when it interacts with water, whereby after filling the trench, the degradation of that material will create an annular void zone about the pipe or duct to allow relative movement between the filling of the trench and the pipe or duct. 18. A pipe sleeve element according to claim 17 comprising at least a substantially impermeable outer member to which one or more spacer members are attached wherein the pipe sleeve elements when combined are configured so that the spacer members extend radially inwards of the outer member. 19. A pipe sleeve element according to claim 17 comprising at least a substantially impermeable outer member adapted to engage with one or more spacer members which when engaged with the outer member extend radially inwards. 20. A pipe sleeve element according to claim 18 or 19, wherein the spacer members are of a degradable material. 21. A pipe sleeve element according to claim 20, wherein the degradation of the spacer members is a result of biodegradability of that material. 22. A pipe sleeve element according to claim 21, wherein the degradation of the spacer members is a result of biodegradability of that material of chemical interaction between that material with water. 23. A pipe sleeve element according to any one of claims 18 to 22 wherein the substantially impermeable outer member is of a known extruded multi-cellular plastics sheet. 24. A pipe sleeve element according to any one of claims 18 to 22 wherein the substantially impermeable outer member is of a plastics coated or waterproofed card.

Inventors: KACZMAREK PETER ANTONY, KAY THOMAS, KACZMAREK, PETER, ANTONY, KAY, THOMAS
Applicants: DUFAYLITE DEV LTD, DUFAYLITE DEVELOPMENTS LIMITED
Application year: 1992
Main classification: F16L5
IPC codes: E02D31, E04G9, E04G15, F16L5