GB2318543A - Dual wall electrofusion coupler - Google Patents

Abstract

A coupling device for connecting end-to-end two adjacent runs of a double pipe in a secondary containment system comprises a thermoplastic moulding providing at either end an inner 14, and an outer 16 cylindrical sleeve for engagement respectively with the end part of the respective inner pipe 10a, 10b, and with the end part of the respective outer pipe 12a, 12b. The sleeves 14 and 16 may be provided with electrical resistance heater windings whereby, after assembly of the pipe joint, the respective windings can be energised to face together the plastics of each said sleeve and the adjacent thermoplastics pipe, thereby effecting a strong and leak-tight connection. The coupling devices may be manufactured by injection moulding using a multi-part injection mould (see Figures 3 and 4, not shown).

Description

DESCRIPTION OF INVENTION Title: "Dual wall electrofusion coupler" THIS INVENTION relates to electrofusion couplers or welding muffs which are used for connection of plastics pipes end to end, or for connection of plastics pipes to branch pipes or various fittings, etc. The invention also relates to a method of manufacturing an electrofusion coupler and apparatus for carrying out the method.

The invention is particularly applicable to electrofusion couplers for use in connection with so-called secondary containment systems utilising plastics pipe lines which comprise, or effectively comprise, concentric inner and outer plastics pipes. Such secondary containment systems are favoured for conveying hazardous or environmentally hostile fluids, the inner pipe normally conveying the fluid in question in the usual way and the outer pipe serving to receive and contain any leakage from the inner pipe. It will be appreciated that once a leak in the inner pipe occurs, the outer pipe represents, in effect, a single containment system. In order that leaks within the inner pipe do not go unnoticed for extended periods of time, sensors may be placed at appropriate locations within the outer pipe, at intervals therealong, to provide to a monitoring facility an indication that a leak has occurred in the inner pipe so that appropriate steps can be taken for replacement or repair.

It is within the scope of the present invention to utilise secondary containment systems in various other ways. For example, the space between the inner and outer pipes may be filled with a non-hazardous fluid at a pressure above that of the fluid conveyed in the inner pipe so that in the event of the inner pipe failing, leakage will occur from the outer pipe to the inner pipe rather than vice versa. Another possibility is for the space between the inner and outer pipes to be filled with a medium adapted to neutralise or otherwise render harmless any liquid leaking from the inner pipe into that space.

A further application of secondary containment systems envisaged by the inventor is in relation to water supplies. Substantial sums of money are spent in treating and purifying water for supply to domestic or industrial premises, to render such water fit for drinking. Most of the water supplied is not used for internal consumption and therefore the major part of the water supplied is, in effect, over-treated. The inventor envisages that it would be possible for water companies to supply both potable and non-potable water to households using pipe lines of the kind used in secondary containment systems, i.e. with an inner pipe within an outer pipe. This would allow, for example, the inner pipe to carry potable water and the outer pipe to carry non-potable water. It would also be possible for the pressures on the outer pipe and in the inner pipe to be different, if appropriate. Because only the potable water would require full purification, water treatment costs would thereby be reduced.

In conventional single containment plastics piping systems, successive lengths of plastics pipe are joined end to end using so-called electrofusion couplers or welding muffs, which typically comprise short plastics sleeves providing sockets at either end having internal diameters of a size to receive the ends of the respective pipes as a close fit and incorporating electrical resistance heating windings whereby two adjoining pipe lengths can be connected end to end by inserting the adjoining pipe ends into such a welding muff or electrofusion coupler from opposite ends of the latter and thereafter passing electric current through the heating winding in order to fuse the internal surfaces of the electrofusion coupler and the adjoining external surfaces of the insertedpipe ends and thereby weld the pipe ends to the electrofusion coupler to form a fluid tight joint.

Hitherto, in constructing secondary containment pipeline systems utilising plastics pipes, the pipe lengths forming the inner plastics pipe have been connected end to end by a first series of electrofusion couplers whilst the pipe lengths forming the outer pipe have been connected end to end by a second series of electrofusion couplers distinct from and separate from those connecting the pipe lengths of the inner pipe. This procedure inevitably involves the threading of the outer pipes and the electrofusion couplers for the outer pipes over the inner pipes and/or the longitudinal displacement of the outer pipes and the electrofusion couplers therefor relative to the inner pipes, and thus involves substantially more labour than the construction of comparable single containment pipe systems by similar techniques. Of course, the longitudinal locations of the joints between the inner pipe ends and the joints between ends of the outer pipe lengths need not be the same (provided that, during pipe line laying, the inner piping precedes the outer).

However, an arrangement in which the inner pipe joints and the outer pipe joints are at different longitudinal positions militates against convenient post-installation repair. In any event, where separate electrofusion couplers are used for the inner and outer pipes, the number of electrofusion operations required is doubled as compared with a comparable single containment piping system. In addition the use of unitary composite pipe stock providing in effect both inner and outer pipes is precluded by the above noted need for relative displacement during assembly.

It is among the objects of the invention to provide a coupler suitable for a double containment plastics piping system which allows joints in a double containment system of the kind referred to to be made more easily than hitherto.

According to one aspect of the invention there is provided a coupling device for use in forming joints in a pipeline system comprising a plurality of piping runs, the coupling device comprising, for each said piping run, a respective socket or hollow spigot for receiving, or extending within, an end of a respective one of two pipe lengths of the respective piping run which meet at the joint, the coupling device providing a fluid communication between the respective pair of sockets for each said run.

Said sockets or hollow spigots are preferably unitary with one another, but may, in certain applications, be capable of limited movement relative to one another.

Preferably the coupling device is intended for a piping system comprising an outer pipe and at least one inner pipe extending within the outer pipe, the coupling device providing respective sockets or spigots for adjoining ends of respective pipe lengths of the outer pipe and, within each of said sockets or spigots for the outer pipe ends, respective sockets or spigots for adjoining ends of respective pipe ends of said inner pipe.

Whilst the coupling device may be adapted to be fixed to the respective pipe ends in any fashion, for example, by adhesive or by friction welding or ultrasonic welding, in preferred embodiments of the invention, intended for pipe lines of thermoplastics, the coupling device is formed of thermoplastics material or includes portions of thermoplastics material affording pipe-engaging surfaces of the coupler and incorporates electrical resistance heater windings through which electrical current can be passed to fuse such thermoplastics and the adjoining regions of inserted thermoplastics pipe ends, thereby to weld the plastics pipe ends to the respective portions of the coupling device.

In preferred embodiments of the invention intended for dual containment piping systems comprising concentric inner and outer pipes, the coupling device preferably comprises a unitary plastics body.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings in which: FIGURE 1A is a schematic view in longitudinal axial section showing a dual containment piping system in the region of a joint therein and further showing a coupling device in accordance with the present invention incorporated in said joint, FIGURE 1B is a perspective view, partly cut away, of the coupling device of Figure 1A before it is installed in a piping system, FIGURES 2A and 2B are respectively views, similar to Figures 1A and 1B, of a joint in a dual containment plastics piping system utilising a variant coupling device, FIGURES 3A, 3C and 3D are schematic views in axial section through part of an apparatus used in the manufacture of a coupling device in accordance with Figures 1A and lB, at successive different positions in said manufacturing process, FIGURE 3B is a schematic view in diametral section through the apparatus on line B-B in Figure 3A, FIGURE 3E is a fragmentary plan view, looking in the direction of arrow E in Figures 3C, to an enlarged scale, FIGURES 4A, 4B, 4C and 4D are views, corresponding to Figures 3A, 3B, 3C and 3D of an apparatus used in the manufacture of the coupling device of Figures 2A and 2B, and, FIGURES 5A and 5B are respectively an elevation view and a perspective view showing terminal arrangements in the inner part of the coupling device of Figures 2A and 2B, at an intermediate stage in manufacture.

Referring to Figures 1A and lB, an electrofusion coupler is shown for use in a plastics piping system comprising an inner pipe line including pipe lines loa and 10b having their adjacent ends connected by the coupler and a concentric outer pipe line including pipe lines 12a and 12k connected in the coupler. The coupler is formed from a fusible thermoplastics material such as polyethylene.

The form of the electrofusion coupler is effectively that of a combination of two conventional electrofusion couplers, arranged concentrically one within the other, the inner one being of a size appropriate to the inner pipes and the outer coupler being of a size appropriate to the outer pipes, with the two electrofusion couplers being connected by bridging pieces extending between the two. Thus, the coupler of Figures 1A and 1B comprises an inner cylindrical sleeve 14 which receives, from its opposite ends, the adjacent ends of pipes 10a and 10b and an outer sleeve 16 which receives from its opposite ends adjacent ends of pipes 12a and 12b. The internal diameter of sleeve 14 is such as to receive the ends of pipes 10a and lob as a close fit and likewise the internal diameter of the outer sleeve 16 is such as to receive the ends of pipes 12a and 12k as a close fit.

Mid-way along the length of the inner sleeve 14, pipe stops 18, which are distributed at intervals around the interior of sleeve 14, project radially inwardly to limit insertion of the pipes 10a and 10b. Bridges 20 integral with sleeves 14 and 16 and distributed at intervals around the periphery of sleeve 14 extend radially across the gap between the inner and outer sleeves and serve to locate the inner sleeve with respect to the outer.

As shown, the bridges 20 are located, like the pipe stops 18, in a diametral plane midway between the ends of sleeve 14 and midway between the ends of sleeve 16. As also shown, the axial length of sleeve 14 is somewhat less than that of sleeve 16. In much the same way as in a conventional electrofusion coupler for single containment plastics pipe systems, the inner sleeve 14 accommodates windings 24 of electrical heating wire which lie close to, or at, the internal surface of sleeve 14 and the outer sleeve 16 accommodates windings 26 of electrical heating wire which lie close to, or at, the internal surface of sleeve 16. The windings of the inner sleeve 14 and outer sleeve 16 are electrically connected with terminal pins 30 projecting from the outer sleeve 16 and shrouded by hollow cylindrical plastics terminal shrouds 32 projecting from and integral with the sleeve 16.

In use, the ends of the inner pipes lOa, lOb, are inserted within respective ends of the inner sleeve 14, the ends of the outer pipes 12a and 12b are inserted within the outer sleeve 16 from opposite ends thereof and the terminal pins 30 are connected to an electrical current source (not shown) which passes electric current through the windings 24, 26 to heat the latter and thus to fuse the plastics material at and adjacent the inner surfaces of the sleeves 14 and 16 and at and adjacent the outer surfaces of pipes 10a, 10b, 12a and 12b, thereby fusing and welding the inserted pipe ends to the respective sleeves of the coupler and forming a secure fluid-tight joint between pipes 10a and lob and between pipes 12a and 12b.

The electrofusion coupler of Figures 2A and 2B, in which parts corresponding to parts in Figures 1A and 1B have like references, differs from that of Figures 1A and 1B in that the sleeve 14 is replaced by a hollow cylindrical body 14a respective opposite ends of which form hollow cylindrical spigots which fit closely within the ends of adjoining inner pipe lengths 10a and 10b, (instead of over the ends of the adjoining inner pipe lengths as in Figure 1A). Electrical resistance heating windings 24a are provided in the hollow spigots formed by sleeve 14a close to the external surfaces of the spigots. There are, of course, no pipe stops within the body 14a. In the arrangement illustrated in Figures 2A and 2B, the outer sleeve and the hollow cylindrical body 14a are connected by a web 40 which extends continuously around the periphery of body 14a, but which has apertures or slots 42 formed therein for fluid flow from the annular space between pipes 10a, 12a to the annular space between pipes 10, 12, the apertures 42 being aligned with these annular spaces. This arrangement is suitable for double containment systems in which the space between the inner and outer pipes is normally empty or accommodates a static fluid, the openings 42 merely serving for the passage of leakage fluid from one section of the pipe line to the next to allow detection of such leakage, or serving to receive leads or the like extending to sensors for detecting such leakage.

Where it is necessary to accommodate a significant flow along the pipe line in the annular space between the inner and outer pipes, the sleeve 14a and the outer sleeve 16 may be connected, as in the arrangement of Figures 1A and lB, by discrete, spaced apart, bridges such as the bridges 20. Conversely, in the arrangement of Figures 1A and lB, the individual bridges 20 may be replaced by a continuous annular web such as the web in Figures 2A and 2B, having apertures 42 therethrough at intervals.

Referring to Figures 3A to 3D a preferred apparatus for manufacture of the coupler of Figures 1A and 1B is illustrated.

The apparatus comprises an inner core comprising a first inner core part 50 and a second inner core part 52 which are aligned axially with one another and which are supported and guided by means not shown so that they can be moved apart and brought together along their mutual longitudinal axes in respective parts of the moulding process as described below. The core parts 50, 52, are hollow to receive an operating cam shaft 54 (see below) which is rotatably mounted in the core part 50 and projects axially therefrom into the core part 52 in the closed position of the mould shown in Figure 3A. A first outer sleeve part 56 fits closely on the periphery of core part 50 and is slidable longitudinally thereon by means not shown and a second outer sleeve part 58 is similarly closely fitting on and slidable axially on the second core part 52 by means not shown. As shown in Figure 3A, with the outer sleeves 56, 58, slid to respective projected positions, opposing ends of the sleeves 56 and 58 meet in the middle of the assembly and define, with one another and with the outer surface of the interengaging ends of the inner core parts 50, 52, a mould space complementary with the sleeve 14 of the coupler of Figures 1A and 1B and with the bridging pieces 20, (spaces for which are provided by aligned notches 60, 62 in the adjoining end surfaces of the sleeves 56, 58). Shown projecting radially into this space, adjacent the axial ends thereof, in Figure 3A, are wire anchoring pins WA2 and WA3, respectively carried by core part 50 and core part 52.

The wire anchoring pins WA2 and WA3 are slidable longitudinally, (i.e. radially with respect to the axis of the core 50, 52), in their respective core parts between radially extended positions, shown in Figure 3A and retracted positions shown in Figure 3D, by respective cam followers 51, 53, connected with the wire anchoring pins and mounted within the core parts 50, 52 respectively, for diametral sliding movement. The cam followers 51, 53 have oval apertures therethrough (as shown in Figure 3B), through which an eccentric cylindrical bar, forming the operative part of cam shaft 54, extends, the apertures in the cam followers 51, 53 cooperating with the surface of the eccentric bar whereby the anchoring pins WA2 and WA3 may be moved between their extended and extracted positions by rotation of the cam shaft 54 in the core parts 50, 52.

Likewise, terminal support pins TSP1 and TSP4 extend radially through the outer sleeves 56 and 58 respectively and are slidable radially between projected and retracted positions by means of similar cam followers 55, 57 similarly cooperating with the cam shaft 54. The pins TSP1 and TSP4, however, are slidable longitudinally (i.e. along the axis of the core parts 50, 52), with their respective sleeves 56, 58 and their respective followers 55, 57 and to this end pins TSP1 and TSP4 extend through elongate slots 59, 61 in the core parts 56, 58. The terminal support pins are designed to receive respective end portions of resistance heating wire windings and to receive split ends of terminal pins 30. The terminal pin receiving arrangement is not described in greater detail here but may be substantially as described in International Patent Application PCT/GB95/00720, published as W095/26873.

The method of manufacture of the coupler of Figures 1A and 1B using the apparatus of Figures 3A to 3D is as follows: (a) With the outer core sleeves 56, 58 retracted and both terminal support pins and both wire anchoring pins in their outwardly projected positions a resistance wire is staked to terminal support pin TSP1, using the technique described in W095/26873.

(b) The wire is wound tightly around outer core sleeve 56 by rotation of the assembly shown in Figures 3A to 3D about its axis and then enters a tapered groove 63 (Figure 3E) in the end of outer core sleeve 56 (in the inner end of one of the notches 60 which partially define bridges 20), which tapered groove 63 grips the wire, retaining the tension already applied to the wire.

(c) The winding is then continued down to inner core 50 and passes into wire anchor pin WA2 into a tapered groove in the end of the pin to be gripped thereby.

(d) The wire is then wound in a pre-defined pattern across the inner cores 50 and 52 and is secured in a further tapered groove in the end of the other wire anchor pin WA3, to be gripped by the edges of that groove, whereby the wound wire extending between the pins WA2 and WA3 is held in appropriate tension.

(e) The wire beyond pin WA3 is extended into a further tapered groove similar to groove 63, similarly provided in the end of outer core sleeve 58, and which likewise grips the wire firmly by a wedging action.

(f) The wire is then wound around outer core sleeve 58, and is secured, in terminal support pin TSP4 to a further terminal in that support pin, using the method described in W095/26873.

(g) With the wire now firmly secured to the pins WA2, WA3, to the tapered grooves 63 in sleeves 56, 58 and to the terminals in terminal support pins TSP1 and TSP4, the outer sleeves 56, 58 are moved towards one another until their adjacent ends abut, as shown in Figure 3A, and the sleeves 56, 58 are locked in this position. The longitudinal spacing between the tapered groove 63 in each sleeve 56, 58, and the adjacent wire anchoring pin WA2 or WA3 in the position illustrated in Figure 3C in which the sleeves 56, 58 are fully withdrawn from each other, is equal to or greater than in the position illustrated in Figure 3A in which the sleeves 56, 58 have been advanced into engagement with each other, so that in this position the portion of wire extending between each wire attachment pin and the adjacent groove 63 is not tensioned but extends in a slack condition through the mould cavity defined between cores 50, 52 and sleeves 56, 58.

(h) The complete core assembly is now positioned in a plastics injection mould (not shown) which provides a mould cavity around the adjacent ends of sleeves 56, 58 and the terminal support pins TSP1, TSP4 of a shape complementary with the desired form of sleeve 16 communicating with the inner cavity via the slots 31. Mould inserts, not shown, are extended into the outer mould cavity to cooperate with the terminal support pins TSP1 and TSP4 and the terminal pins supported therein and to define cavity parts for the terminal shrouds. Molten plastics is then injected into the mould to form the electrofusion coupler.

(i) After solidification of the plastics, the core assembly and moulding thereon are removed from the mould and the cam shaft 54 is rotated causing the terminal support pins TSP1 and TSP4 and wire anchor pins WA2, WA3 to be retracted radially inwardly from the peripheral surfaces of the sleeves 56, 58 and the cores 50, 52 respectively.

The inward retraction of the wire anchoring pins WA2, WA3, pulls from the tapering grooves in the latter the wire previously wedged therein and now securely retained by the moulded plastics.

(j) The cores 50, 52 can now be separated axially from one another and from the moulded electrofusion coupler, and the sleeves 56, 58 likewise separated axially from one another and from the coupler. Such axial separation of the cores and sleeves 56, 58 from the coupler also pulls from the grooves 63 the wire previously wedged therein (and largely retained by the moulded plastics).

(k) Both core parts 50, 52 are then pushed back together, the cam shaft 54 rotated to push the terminal support pins and wire anchor pins to their outwardly projected positions with the sleeves 56, 58 being in their retracted position so that the apparatus is again in the position shown in Figure 3B ready for a repetition of the process described above, for manufacture of the next electrofusion coupler.

Referring to Figures 4A to 4D, the apparatus used for the manufacture of the electrofusion coupler of Figures 2A and 2B differs from that of Figures 3A to 3E principally in the omission of wire anchoring pins WA2, WA 3. Parts corresponding to parts in Figures 3A to 3E have the same references. Where, as in Figures 2A and 2B, the coupler is to have a continuous web 40 therearound, the sleeves 56, 58 will, of course, meet only in discrete projections adapted to form the slots 42. This difference, however, is not shown in Figures 4A to 4D.

Figures 4A, 4C and 4D like Figures 3A, 3C and 3D represent the main core assembly in the three main stages of manufacture of the coupler. Thus, in Figure 4C, the outer core sleeves are retracted, ready for initial tube moulding and winding. In Figure 4A, the outer core sleeves are in their advanced positions, closest to one another, ready for encapsulation with plastics. Figure 4D shows the core assembly fully separated for extraction of the moulded electrofusion coupler.

(a) The process is similar to that described with reference to Figures 3A to 3E but differs in that, before any wire winding, a plastics tube, indicated in phantom at 14a in Figure 4C, and shown to a larger scale, in elevation and perspective respectively, in Figures 5A and 5B, is first moulded around the inner cores 50 and 52. This plastics tube or sleeve, forming component 14a of the finished coupler, has grooves formed in its outer periphery to receive an electrical resistance heater wire. The component 14a is moulded within a split mould (not shown), herein referred to as the inner sleeve mould, engaged around the core parts 50, 52, whilst the sleeves 56, 58 are in the retracted positions shown in Figure 4C, (although, as explained below, during such moulding, the pins TSP1 and TSP4 are in their retracted position, rather than the extended positions shown in Figure 4C). The grooves on the outer periphery of component 14a may be formed by a heated embossing tool, not shown, after the component 14a has been moulded between sleeves 56, 58 and cores 50, 52 or may be moulded with such grooves in the split mould referred to.

Figures 5A and 5B illustrate this component 14a in plan and in perspective, respectively, to an enlarged scale and without the mould parts. As shown in Figure 5A and 5B, the component 14a has, at its middle, a circumferential flange 71 which will form the web 40 in the finished coupler. The component 14a has terminal pegs 70 projecting radially therefrom (for example, as shown, disposed in a gap in the flange 71). The terminal pegs 70 may be of plastics, e.g. moulded integrally with component 14a or may be metal pegs inserted prior to (or after) moulding of component l4a. With the apparatus in the condition shown in Figure 4C and the sleeves 56, 58 still retracted, a resistance wire is laid into the groove and is secured at its mid-point to the central peg 70 and at its ends to the pegs 70 on either side of the central peg. Any convenient fixing method may be used. For example, the wire may be extended into tapering slots in the pegs 70 and wedged therein.

(b) Respective ends of two further pieces of resistance wire are similarly fixed firmly to posts in the two outer pegs 70 in electrical contact with the ends of the winding on part 14a. By way of example, such electrical connection may be ensured by fitting metal caps or sleeves over the pegs after the wires have been attached thereto. It would be possible, instead of terminating the wire winding around part 14a on pegs 70 and attaching separate wires to pegs 70 for winding around the outer sleeves, to use a single length of wire. However, in practice, such an arrangement is less conveniently managed than the preferred one.

(c) The outer sleeves 56, 58 are then both moved into their positions closest to one another and are locked in position. The two further lengths of resistance wire referred to are led through the gap between adjacent ends of sleeves 56, 58 which receives the web 40 and pegs 70.

In a variant, the further resistance wires and/or terminal caps or sleeves must be applied to pegs 70 before the sleeves 56, 58 have been brought together.

(d) The wire now protruding from between the two outer sleeves is located in tapered grooves (not shown) in the opposing faces of the outer cores, such grooves corresponding to groove 63 in Figure 3E.

(e) The wire is wound around the respective outer sleeves 56, 58 and terminated at the terminal support pins TSP 1 and 2 to which terminal pins are fitted using the method of W095/26873.

(f) The complete core assembly is now positioned in the cavity of an injection mould which, just as described with reference to Figures 3A to 3E, defines with the sleeves 56, 58, the form of the outer sleeve part 16 of the coupler.

Molten plastics is then injected into this cavity. During this moulding step the outer sleeve 16 may become welded to the portions of flange 71 exposed between the sleeves 56, 58, and in any case encapsulates the flange 71 preventing longitudinal separation of the inner and outer parts of the coupler, and the pegs 70 and the wires extending thereto are encapsulated in plastics.

(g) After removing the combined core assembly and moulding from the injection mould the cam shaft 54 is rotated causing the cams and terminal support pins TSPl and TSP4 to retract from the peripheral surfaces of the sleeves 56, 58 and thus from the internal surface of the sleeve 16.

(h) The sleeves 56, 58 and the core parts 50, 52 can now be separated axially from one another and from the moulded coupler, allowing easy extraction of the coupler.

(i) The core parts 50, 52 are then pushed back together, the outer sleeves being retained in their retracted positions. The cam actuator is not rotated and the terminal support pins are left in their retracted positions for safety.

(j) The complete core assembly is now positioned in the inner sleeve mould and the next inner form part 14a only is moulded in plastics, as described above.

(k) On removal of the core assembly and part 14a from the inner sleeve mould, the cam shaft 54 is rotated to push the terminal support pins to their extended positions, allowing the winding phase of the process to start again.

Claims (14)

1. A coupling device for use in forming joints in a pipeline system comprising a plurality of piping runs or fittings, the coupling device comprising, for each said piping run, a respective socket or hollow spigot for receiving, or extending within, an end of a respective one of two pipe lengths of the respective piping run which meet at the joint, the coupling device providing a fluid communication between the respective pair of sockets for each said run.

2. A coupling device according to claim 1 wherein said sockets or hollow spigots are unitary with one another.

3. A coupling device according to claim 1 or claim 2 suitable a piping system comprising an outer pipe and at least one inner pipe extending within the outer pipe, the coupling device providing respective sockets or spigots for adjoining ends of respective pipe lengths of the outer pipe and, within each of said sockets or spigots for the outer pipe ends, respective sockets or spigots for adjoining ends of respective pipe ends of said inner pipe.

4. A coupling device according to any preceding claim which is formed of thermoplastics material or includes portions of thermoplastics material affording pipe-engaging surfaces of the coupler and incorporates electrical resistance heater windings through which electrical current can be passed to fuse such thermoplastic and the adjoining regions of inserted thermoplastics pipe ends, thereby to weld the plastics pipe ends to the respective portions of the coupling device.

5. Apparatus for use in forming a coupler in accordance with claim 3 by moulding, including a mould core comprising a first core part and a second core part separable axially from one another, and respective sleeve part slidable axially on each core part, and an outer mould adapted to receive the assembly comprising said core parts and said sleeves, whereby a cavity for a hollow cylindrical body defining said sockets or spigots for respective pipe ends of said inner pipe can be defined between said first and second core parts and said sleeve parts and a cavity for a hollow cylindrical body defining said sockets or spigots for respective pipe ends of said outer pipe can be defined around said sleeve parts within the outer mould.

6. A method of forming a coupler according to claim 3, using apparatus in accordance with claim 5, including placing said first and second core parts together with said sleeve parts retracted from one another, securing one end of an electrical resistance wire to first temporary retaining means on one of said sleeve parts, forming a first winding part over said one sleeve part, securing the other end of said first winding part to second temporary retaining means on said one sleeve part, extending the wire longitudinally to third temporary retaining means on said core, winding a second winding part on said core from said third temporary retaining means to fourth temporary retaining means on said core, extending said wire longitudinally to fifth temporary retaining means on the other said sleeve, winding a third winding part on said other sleeve, securing the other end of said winding means to sixth temporary retaining means, bringing said sleeves together axially to define a first mould cavity between said core parts and said sleeves, and placing this assembly within a mould to define a second mould cavity, connected with the first between the mould and said sleeves, injecting molten plastics material into the mould to fill said cavities and extracting the moulded coupler whilst or after disengaging said temporary retaining means from the wire.

7. A method of forming a coupler according to claim 3, using apparatus in accordance with claim 5 including placing said first and second core parts together, moulding an inner hollow spigot part in plastics around said core part, winding an electrical resistance heater wire around said inner hollow spigot part and securing the ends of the winding to terminals on said inner hollow spigot part at the middle thereof, securing further ends of electrical resistance heater wires to said terminals, before or after bringing said sleeves towards one another around the wound inner part, winding said further electrical resistance heater wires over said sleeves, securing said further wires temporarily with respect to said sleeves, placing the assembly within an injection mould and moulding an outer sleeve around said sleeves so as to fuse with exposed regions of said inner sleeve, and subsequently extracting the coupler and core assembly from the mould and said sleeves and core parts from the coupler.

8. An electrofusion coupler substantially as hereinbefore described with reference to and as shown in Figures 1A and 1B of the accompanying drawings.

9. An electrofusion coupler substantially as hereinbefore described with reference to and as shown in Figures 2A and 2B of the accompanying drawings.

10. Apparatus for use in manufacture of an electrofusion coupler, substantially as hereinbefore described with reference to and as shown in Figures 3A to 3E of the accompanying drawings.

11. Apparatus for use in manufacture of an electrofusion coupler, substantially as hereinbefore described with reference to and as shown in Figures 4A to 4D of the accompanying drawings.

12. A method of making an electrofusion coupler, substantially as hereinbefore described with reference to Figures 3A to 3E of the accompanying drawings.

13. A method of making an electrofusion coupler, substantially as hereinbefore described with reference to Figures 4A to 4D of the accompanying drawings.

14. Any novel feature or combination of features disclosed herein.