GB2263696A - Sealant - Google Patents

Abstract

A sealant composition comprises a cementitious material such as portland cement, a plastics binder such as polyvinylacetate and water in the ratio 1:2:1:1. The sealant is particularly useful for sealing or blocking pipes such as gas pipes.

Description

SEALANT The invention relates to a sealant. It finds particular application in a method and apparatus for relining a pipe such as a domestic gas service pipe, with a new pipe such as a polyethylene pipe. Such method and apparatus is the subject of U.K. Patent Application No. 9003723.5 from which this application has been divided. The invention also finds particular application in methods of permanently blocking domestic gas service pipes, the subject of copending U.K. Patent Application No.

It is often necessary to replace original pipe with new pipe, because of corrosion and other deterioration of the original pipe.

In cases in which the original pipe is buried, removal and replacement is expensive, time consuming and inconvenient, since it necessitates digging up the entire length of original pipe, and interruption of the supply.

To reduce the cost and inconvenience of pipe replacement, techniques have been developed to reline existing pipe in situ. A liner pipe, such as a flexible polyethylene pipe, is inserted into a free end of the original pipe, and fed, if necessary with the aid of a pipe jack, along the original pipe.

In many cases, such as that of a domestic gas supply, this operation, although simpler than pipe replacement, is still complex, since it involves digging, cutting the pipe to be relined to isolate it from the main supply and capping of the cut end.

A typical gas supply is shown in Figure 1. A service pipe 10 is connected at one end to a buried gas main 12, passes through the ground 14, and the wall 16 and the floor 18, of the house and is connected to a tap 20. In Figure 1, the upstream side of the tap is shown unconnected. Normally, it will be connected to a domestic gas meter.

In order to reline the service pipe using current techniques, it must be cut close to its junction 22 with the main 12. This necessitates digging to uncover the junction, and closing off the main supply whilst the service pipe 10 is cut and the main capped.

The tap 20 is then removed, the polyethylene liner pipe inserted into the service pipe and the tap reconnected. The main supply must again be closed off whilst the service pipe 10 is reconnected to the main 12. The operation is time consuming and inconvenient.

A technique for relining pipes, such as gas pipes, which does not involve digging or cutting of pipes and which minimises the risk of leakage is described in U.K. Patent Application No. 9003723.5.

The sealant of the present invention is particularly suited for use in this technique.

In addition to relining existing pipes, it is often necessary to cut off a mains fed supply permanently. A technique which does not involve cutting the service pipe downstream of the main and capping it as described above in the discussion of current relining techniques, is described in the copending U.K. Patent Application No. o The sealant of the present invention is also particularly suited for use in this technique.

It is often desirable to apply plastic to metal pipes to form a gas tight seal as, for example, in the repair of gas service pipes.

According to the invention there is provided a sealant composition comprising: a cementitious material; a plastics binder; and water.

The sealant composition of the invention is particularly useful in the method of relining a service pipe connected at one end to a free main supply, comprising: introducing into the service pipe through a gland in the free end thereof a liner pipe having at its upstream end a double seal which provides a first seal between the liner pipe and the service pipe and a second, breakable, seal over the upstream end of the bore of the liner pipe; locating the double seal in the service pipe at the upstream limit of relining; introducing a sealant into the annular space between the liner pipe and the service pipe; and breaking the breakable seal over the upstream end of the bore of the liner pipe.

A sealant according to the invention is also suitable for use in a method of permanently blocking a pipe, extending between a main and a tap, comprising blocking it by a method comprising: fitting a gland to the downstream side of the tap; introducing a block through the gland, the tap and the pipe and into the main, by means of a flexible rod removably attached to the downstream end of the block; retracting the block to seal it against the internal wall of the pipe immediately downstream of the junction of the pipe with the main; disengaging the flexible rod from the block and withdrawing it through the tap and the gland; removing the gland and filling the pipe with sealant after the block has been placed in it.

The sealant comprises: a cementitious material, such as portland cement; a plastics binder, such as polyvinylacetate; and water.

The preferred proportions by volume of cementitious material: binder: water are 1.2:1:1.

This sealant has excellent pouring properties, and can be poured into the annular space between a gas service pipe and a polyethylene liner pipe to a distance of at least 13m, for example through a sealant head according to the fifth aspect of the invention.

In contrast to currently employed foam sealants, the sealants of the invention are fire resistant. The cost of sealants according to the invention may be as little as a quarter or a fifth of the cost of conventional foam sealants. Waste sealant is easily disposed of, since it contains no toxic components.

The invention will be-further described, by way of example, with reference to the drawings, in which: Figure 1 shows a typical domestic gas supply; Figure 2 shows a side elevation of a preferred plug for insertion through the gland of Figure 4, in a method of relining a service pipe; Figure 3a shows a cross-section through a gland for use in a method of relining a service pipe; Figure 3b shows a plan view of a seal of the gland of Figure 3a; Figure 4 shows a cross-section through a gland for use in a method of relining a service pipe; Figure 5 shows a preferred double seal for use in a method of relining a service pipe; Figure 6 shows, in cross-section, the double seal of Figure 5 sealing a pipe; Figure 7 shows a preferred sealant head for use in a method of relining or permanently blocking a service pipe;; Figure 8 shows a first combined gland/sealant head for use in a method of relining a service pipe; Figure 9 shows a second combined gland/sealant head for use in a method of relining a service pipe; Figure 10a shows a side elevation of the preferred pipe block for reversibly blocking a pipe; Figure lOb shows a downstream (front) and elevation of the block of Figure 10a; Figure 11 shows a longitudinal cross-section through the block of Figures 10a and lOb in position blocking a pipe; Figure 12 shows a sealant head for introducing sealant into a pipe closed by the block of Figures 8 and 9.

The plug 30 of Figure 2 is a single piece of rubber comprising a spine 32 having upstream 34a, middle 34b and downstream 34c circular flanges extending therefrom. The peripheral regions 36a, b, c of the flanges are bevelled, the upstream face of each flange being of smaller diameter than the downstream face.

Figure 2 shows the upstream end of the plug 30 attached, by means of cooperating screw threads, to a flexible rod 38 having at its free end a handle 40.

The flanges 34a, b, c are so dimensioned that they can be introduced into a service pipe 10 through a tap 20 (see Figure 1).

They firstly pass through a gland on the outlet of the tap, which is then opened to allow the plug 30 into the service pipe The flanges 34a, b, c then seal against the inner wall of the service pipe, so that the tap can be removed.

The first embodiment 50 of a gland in Figure 3a comprises a circular cylindrical steel body 52 with internal threads 54 at its lower end for connection to the threaded end of a service pipe 10 (see Figure 1) and external threads 56 at its upper end. The body 52 has a wide portion 58 about a third of the way down, for reception of circular star seals 60a, b, c, d of rubber. A star seal 60 is shown in Figure 3b. It comprises a circular disc of rubber which has six radial slits 62 in it extending toward, but stopping short of, its .edge. Normally, the edges of the slits-62 close to provide a gas tight seal. However, pipes and other equipment can be pushed through the seal 60, deflecting the sectors defined by the slits 62, which then return to the sealing condition.

The sectors will seal against a relatively narrow rod passing through the seal.

The star seals 60a, b, c, d are arranged in the wide portion 58 of the gland 50 in two pairs 60a, b and 60c, d. The pairs of seals are separated by a plastic spacer ring 64.

The gland 50 is provided, upstream of the seals 60a, b, c, d, with a pressure relief valve 66 and a water gauge connection 68, both of which communicate with the interior of the gland 50.

The second embodiment 80 of the gland shown in Figure 4 comprises a circular cylindrical body 82 having a rebated externally threaded neck 84 at its upper end and a wide internally threaded recess 86 at its lower end. An annular flange 88 runs around the inside wall of the body 82 about a third of the way down it.

A cap 90 having a central passage 92 screws onto the neck 84 of the body 82. A first star seal 94a is trapped between the inner face of the cap 90 and the upper face 96 of the body 82. A second star seal 94b rests on the flange 88 in the body 82. A spacer ring 98 maintains the separation of the star seals 94a, b. The two seals 94a, b and the spacer ring 98 may be provided as a single element.

A cylindrical adaptor 100 screws into the recess 86 at the lower end of the body 82 of the gland 80. The inner wall of the adaptor 100 is threaded at its lower end 102 to receive a tap. By employing an adaptor 100 having a suitable dimension at its lower end 102 the gland 80 can be affixed to taps of different diameters.

The body 82 of the gland 80 is provided below the seals 94a, b, with a water gauge connection 104, which communicates with the interior of the gland.

The double seal 110 of Figure 5 is shown inserted into a polyethylene liner pipe 112. The double seal comprises a rubber tube 114, of a diameter to fit snugly in the bore of the liner pipe 112, and which is reinforced by a steel helical spring 116. The spring assists in retaining the downstream end of the tube 114 in the liner pipe 112. It also renders the tube rigid enough to pass over obstacles in the service pipe into which the double seal is inserted whilst maintaining it flexible enough to follow curves in the service pipe.

The upstream end of the tube 114 has an annular nose cone 118 of hard plastic around it. This nose cone, which flares outwardly in the downstream direction, enables the double seal 110 to enter a service pipe easily, and to overcome snags in the pipe.

The nose cone 118 also acts as a shoulder for a first annular sealing flange 120a of rubber around the tube 114, immediately downstream of the nose cone and of greater diameter than the nose cone. A second annular rubber sealing flange 120b is provided around the tube 114 downstream of the first flange, and an annular rubber shoulder of smaller diameter 122 is provided around the tube 114 immediately upstream of the second flange 120b. An annular pipe stop 124 of rubber is provided around the tube 114 downstream of the second flange 120b, against which the liner pipe 112 abuts when the double seal body 110 is inserted in the liner pipe.

The downstream end of the tube 114 is closed by a metal foil seal 126.

In use, the double seal 110, carrying the liner pipe 112 is pushed into a service pipe 10 (see Figure 1) to be relined, through a gland. The double seal 110 is pushed through the pipe until it passes into the main 12. The double seal 110 is then retracted into the service pipe, whereupon the sealing flanges 120a, b are urged over their respective shoulders 118, 122, to seal the annular space between the liner pipe 112 and the service pipe 10, as shown in Figure 6. The bore of the liner pipe 112 is sealed from the main 12 by the metal foil seal 126 over the tube 114 of the double seal 110.

When it is desired to connect the liner pipe 112 to the main 12, a flexible rod with a suitably sharp end is introduced into the liner pipe through a gland, and inserted far enough to break the metal foil seal 126.

In a second preferred embodiment of the double seal, a further metal foil seal is provided across the upstream end of the tube 114, and at least one, preferably two, air bleed holes are provided through the wall of the tube 114 intermediate the pipe stop 124 and the second, downstream, sealing flange 120b. The function of these additional features is discussed below.

Instead of a metal foil seal, the tube 114 may be sealed with a plug, preferably across its upstream end. Most preferably, such a seal is employed in a double seal having the air bleed holes of the second preferred embodiment.

The sealant head 140 of Figure 7, which is shown screwed onto the open end of a gas service pipe 10 lined with a liner pipe 112, comprises a cylindrical body 142 surmounted by a narrower neck section 144. The bottom end 146 of the head 140 is open and threaded on its internal surface, to screw onto the service pipe 10.

The liner pipe 112 extends through the body 142, and the neck 144 is sealed around the liner pipe 112 by an olive 148 around the liner pipe which rests on a flange 150 inside the neck 144. The olive 148 seals against the inside surface of the neck 144 by means of a cap 152 with a central passage, for the liner pipe 112, which screws into the neck 144 of the head 140 and presses onto the olive 148. An externally threaded collar 154 extends around the top of the cap 152 for attachment to a tap.

A hollow side arm 156 for the introduction of sealant extends up and away from the lower end portion of the body 142 of the head 140, and communicates therewith. The free end of the arm 156 is internally threaded to receive either a sealant hose or a plug. The side arm 156 may be provided with a one-way valve, such as a spring loaded ball valve, or a top-hat valve, to prevent sealant from spilling out of the arm when the sealant hose is disconnected from it after use. The body 142 is vented by vent 158.

The first combined gland/sealant head 250, shown in Figure 8, may be used in place of both the gland 50 of Figure 3 and the sealant head 140 of Figure 7. Like reference numerals to those employed in Figures 3 and 7 are used in Figure 8 to indicate like parts.

The gland/sealant head 250, which is shown screwed onto the open end of gas service pipe 10 lined with a liner pipe 112, comprises a cylindrical body 142 surmounted by a separate neck portion 144. The neck portion screws into the mouth 252 of the body 142, which is wider than the body. The bottom end 146 of the gland/head 250 is open and internally threaded to screw onto a service pipe.

When the gland/head 250 is in place and the liner pipe 112 has been introduced into the service pipe 10 as described below, the liner 112 passes through the body 142 and the neck 144 is sealed around the liner pipe by an olive 148 which rests on a flange 150 inside the neck 144. The olive 148 is sealed against the inside surface of the neck 144 by means of a cap 152 having a central passage which screws into the top of the neck 144 and can press the olive 148. The free end of the cap 152 has an external thread 154 for attachment to a tap. The bore of the central passage of the cap 152 is just wide enough at its lower end to accommodate the liner pipe 112, but is narrowed by a pipe stop 254 which the liner pipe 112 abuts.

A hollow side arm 156 for the introduction of sealant extends up and away from the lower end of the body 142 of the gland/head 250, and communicates therewith. The free end of the arm 156 is externally threaded to receive either the hose of a sealant pump or a cap 256. The side arm 156 contains a one-way top-head valve 258, to prevent sealant from spilling out of the arm when the pump hose is disconnected. A retaining ring 260 around the valve 258 is held in a groove 262 around the internal wall of the arm 156 to hold the valve in place.

The neck 144 of the gland/head 280 contains two star seals 60a, c, separated by a spacer ring 58. The lower star seal 60c rests on the shoulder 264 formed by the widening of the body 142 to form the mount 252. The flange 150 of the neck 144 bears upon the upper star seal 60a.

A water gauge connection 68 closed by a screw 26 when not in use is provided in the wall of the body 142 of the gland/head 250.

It will be apparent that the gland/sealant head 250 can perform the functions of both the gland 50 of Figure 3 and the sealant head 140 of Figure 7.

The second combined gland/sealant head 280, shown in Figure 9, functions in a similar manner to the first combined gland/head 250 of Figure 8, and like reference numerals indicate like parts.

The combined gland/head 280, which is shown fitted to a free end of a service pipe 10, comprises a cylindrical body 142 having an open upstream end 282 which fits over the service pipe 10 as far as an internal pipe stop flange 284 in the body 142 allows. The open end 282 is externally threaded, for engagement with a back nut 286 which fits over the service pipe 10 upstream of the gland/head 280.

An olive 288 is compressed between the shoulder 290 of the back nut 286 and the end body 142.

The downstream end of the body i42 of the gland/head 280 is closed by a downstream end wall 292, having an opening 294 for passage of the liner pipe 112. A star seal 296 across the body 142 closes the opening 294.

Immediately upstream of the star seal 296 a side arm 298 opens perpendicularly from the body 142. The free end of the arm 298 is externally thread to receive either the hose of a sealant pump or a cap 256. The side arm 298 has a one-way top-hat valve 258 in it to prevent sealant spilling out of the arm. The valve 258 has a retaining ring 260 around it, held in a groove 262 around the internal wall of the side arm 298. A water gauge connection 68 closed by a screw 266 when not in use is provided in the wall of the body 142 of the gland/head 280.

The plug 30, first 50 and second 80 glands the double seal 110 and the sealant head 140 together form a kit for relining a gas service pipe 10 between a gas main 12 and a tap 20. The first combined gland/sealaning head 250 can replace the first gland 50 and the sealant head 140. The kit is used as follows.

The closed tap 20 is disconnected from the meter.

The gland 80 according to the second embodiment shown in Figure 4 is prepared as follows.

The rod 38 of the plug 30 (see Figure 2) is inserted into the body 82 of the gland 80 through the central passage 92 in the cap 90 of the gland and the two star seals 94a, b. The adaptor 100 of the gland 80 is unscrewed from the body. The rod 38 is screwed onto the downstream end of the plug 30, which is then pulled, by the rod, into the body 82 of the gland 80. The adaptor 100 is rejoined to the body 82.

The prepared gland 80 is screwed onto the free, downstream, side of the tap 20, which is thus sealed. The tap 20 is opened, and the plug 30 is pushed through the tap 20 and into the service pipe 10 by the rod 38. The flanges 34a, b, c on the spine 32 of the plug 30, which are of slightly greater diameter than the internal diameter of the service pipe 10, deform against the internal walls of the service pipe 10 to make a gas tight seal.

The rod 38 is unscrewed from the plug 30 and withdrawn through the tap 20 and the gland 80. A water gauge connected to the water gauge corrector 104 on the gland 80 confirms that the seal has been made. The tap 20, with the gland 80, is unscrewed from the end of the service pipe 10.

The gland 50 according to the first embodiment shown in Figure 3a or the first combined gland/sealant head 250 of the preferred embodiment shown in Figure 8 is screwed onto the end of the service pipe 10. If the combined gland/sealant head is used, its cap 152 is not fitted. The rod 38 of the plug 30 is inserted into the service pipe through the star seals 60a, b, c, d of the gland 50, or the star seals 60a, c of the gland/sealant head 250, and attached to the plug 30. The plug 30 is withdrawn from the service pipe 10 through the gland.

The double seal 110 is inserted into the polyethylene liner pipe 112 (see Figure 5), and fed into the service pipe 10 through the star seals. The sealing flanges 120a, b seal against the inner wall of the service pipe 10. A water gauge is connected to the water gauge connector 68.

The liner pipe 112 and double seal 110 are pushed down the service pipe 10, if necessary with the aid of a pipe jack. When the double seal 110 passes from the service pipe 10 into the gas main 12, the seal between the liner pipe 112 and the service pipe 10 is broken, and gas passes into the annular space between the pipes 10, 112, which is registered on the water gauge.

The double seal 110 is then withdrawn into the mouth of the service pipe 10 by pulling on the liner pipe 112. It seals against the inner walls of the service pipe as described in relation to Figure 6. This is confirmed by the reading on the water gauge.

If the gland 50 has been used, the body 142, olive 148 and cap 152 of the sealant head 140 (see Figure 7) are passed over the liner pipe 112 The body 142 is screwed onto the end of the service pipe 10 The neck 144 of the sealant head 140 is sealed to the liner pipe 112 by screwing in the cap 152 which deforms the olive 148 against the flange 150 in the neck 144 of the head 140.

If the combined gland/sealant head 250 has been used, the olive 148 is passed over the liner pipe 112, which is trimmed to length.

The cap 152 is then screwed into the neck 144 of the combined gland/head 250, deforming the olive 148 to seal against the cap 152 and the liner pipe 112.

The free end of a hose connected at one end to a supply of sealant is screwed into the side arm 156 of the sealant head 140 or gland/head 250. Sealant is introduced into the head, and flows down into the annular space between the service pipe 10 and the liner pipe 112, as far as the downstream flange 124 of the double seal 110. The sealant fills up this annular space, and then the annular space between the liner pipe 112 and the body 142 of the head 140 or combined gland/head 250. When sealant appears at the vent 158 in the head body, the operator knows that the sealant has filled both annular spaces. The hose is then removed from the side arm 156, which is plugged with a threaded plug. The one-way valve in the side arm 156, if provided, prevents sealant from spilling out of the arm.

The sealant of the invention will fill the annular spaces without voids, giving a permanent gas tight seal.

The liner pipe 112 may now be cut flush with the top of the cap 152 of the sealant head 140 if this has been used. The tap 20 and the gland 80 are then fitted to the cap 152, by means of the threads on the collar 154 of the cap cooperating with the threads on the upstream side of the tap.

A seal breaking tool, in the form of a flexible rod having a sharp-end, is introduced into the liner pipe 112 through the gland 80 and the open tap 20. It is inserted down the liner pipe 112 to the metal foil seal 126 on the tube 114 of the double seal 110, and caused to pierce it. This allows gas from the main 12 to pass up the tube 114 of the double seal 110 and into the liner pipe 112.

The seal breaking tool is withdrawn from the liner pipe 112 through the tap 20 and the gland 80. The tap 20 is closed and the gland 80 removed. The tap can be reconnected to the meter.

If the second preferred embodiment of the double seal is used, which includes a further metal foil seal across the upstream end of the tube 114 of the double seal and air bleed holes through the tube 114 intermediate the pipe stop 124 and the second flange 120b of the double, the method is varied as follows.

Before sealant is introduced into the annular space between the liner pipe 112 and the service pipe 10, the downstream seal of the double seal is broken by a seal breaking tool. As sealant is introduced into the annular space, air can pass out of the space into the tube 114 of the double seal, and so be vented to atmosphere. This further ensures that no voids are formed in the sealant in the annular space. The air bleed holes are sealed by the sealant.

The tap 20 and the gland 80 are then fitted as described above, and the connection to the main 12 made by breaking the upstream seal of the double seal.

If the seal across the tube 114 is a plug across its upstream end, the seal breaking tool is a simple flexible rod, which pushes the plug into the main 12. Sealant is introduced as described above, the air bleed holes, if present, acting as described above.

It will be seen that the method and apparatus described, and sealant of the invention allows a pipe to be relined easily and safely, with no need for the pipe to be exposed, and with no danger of leakage.

It may be desired to reline a service pipe not provided with a tap or a threaded free end, for example if access to a gas tap is impracticable, and the service pipe is excavated and cut. In this case, the second combined gland/sealant head 280 is employed, as follows.

The back nut 286 and the olive 288 are fitted over the cut end of the service pipe 10, and the body 142 of the gland/head 280 fitted over the service pipe up to the pipe stop 284. The gland/head 280 is sealed to the service pipe 10 by screwing the back nut 286 onto the upstream end 282 of the body 142, compressing the olive 288. The star seal 296 across the body 142 prevents gas escaping through the opening 294 in the downstream end wall 292 of the gland/head. The liner pipe 112 carrying a double seal 114 at its upstream end is fed through the opening 294 and the star seal 296 into the service pipe, by a pipe jack. When the liner pipe is in position, as indicated by a water gauge connected to the connector 68 on the body 142 of the gland/head 280, sealant is introduced through the side arm 298 as described above for the first combined gland/head 250.

The seal across the upstream end of the liner pipe 112 is broken as described above.

The liner pipe is squeezed off to prevent gas escape while the other part of the service pipe is lined with liner pipe. Another gland/head 280 is fitted to the end of that part of the service pipe, and the annulus filled with sealant through the side arm 298.

The two pipes are connected by conventional electrofusion techniques, and the squeeze off removed, to restore the gas supply to the tap.

The pipe block 170 shown in Figures 10a, 10b, and 11 comprises a central threaded shaft 172 (the threads of which are not shown in Figure 11). A first annular shoulder 174 of steel is mounted on the shaft 172 toward its upstream end. An anchor 176 is mounted on the shaft adjacent to and downstream of the first shoulder. The first shoulder and the anchor are held in place by nuts 178a, b on the shaft.

The anchor 176 is a generally cruciform rubber flange. The four arms 180a, b, c, d of the anchor extend beyond the rim of the first shoulder 174 and are swept back slightly to facilitate insertion of the blockage 170 in a pipe.

On the shaft 172 downstream of the anchor 176 is a second annular steel shoulder 182, the upstream face of which abuts a nut 184 on the shaft 172. On the shaft 172 immediately downstream of the second shoulder 182 is a first annular rubber sealing flange 186 of greater diameter than the second shoulder 182.

A rubber sleeve 188 carrying two spaced apart rubber sealing flanges 190a, b fits over the downstream end of the shaft 172. The downstream end of the sleeve 188 is closed apart from a small central passage 192. The sleeve also carries at its downstream end a metal flange 194, from which extends, in the downstream direction, metal legs 196 supporting a metal ring 198, concentric with the shaft 172 and the sleeve 188.

An insertion rod 200 is attached to the end of the rubber sleeve 188 by a narrow, weakened, end portion 202, which passes through the central passage 192 in the end wall of the sleeve 188 and ends in a disc 204 (see Figure 11), too large to pass through the central hole 192.

In use, the block 170 is introduced into the service pipe 10 to be sealed through a gland and through the tap 20 on the pipe It is pushed by the rod 200 along the service pipe 10 until it passed into the main 112. If the blockage 170 has been introduced through the gland 50 of Figure 30a, a water gauge connected to the water gauge connector 68 of the gland 50 will register this event.

The block 170 is then pulled back into the service pipe 10 with the rod 200, so that it jams in the opening of the service pipe 10, as can be seen from Figure 11. The arms 180a, b, c, d of the anchor 176 are bent upstream over the first shoulder 174 to jam against the internal Ma1l.9f.the pipe 10 to hold the block 170 in place. The sealing flange 186 on the shaft 172 is also bent upstream over the second shoulder 182 and seals against the internal wall of the pipe 10 to provide a gas tight seal. The two flanges 190a, b on the sleeve 188 are also bent upstream to seal against the internal wall of the pipe 10.

Further tension on the insertion rod 200 causes the weak end portion 202 of the rod to break, and the rod is withdrawn from the pipe. The disc 204 which held the rod in the sleeve 188 remains in the sleeve (see Figure 11). The gland is then removed.

If it is desired to remove the block 170 from the pipe, a removal rod carrying at its end a hook is inserted, through a gland and the tap into the pipe. The hook engages with the ring 198 at the downstream end of the block 170, and the block is removed from the pipe 13 through the tap and the gland by pulling on the removal rod. The tap is closed and the gland removed.

If the block is to remain permanently in the pipe, sealant can be poured into the pipe, for example through the sealant head 140 of Figure 7.

The sealant head 220 of Figure 12, which is shown screwed onto the open end of gas service pipe 10 which is blocked by a pipe block (not shown), comprises a cap 222 which has an internally threaded open end 224 for engagement with external threads on the gas service pipe 10. Opposite the open end a hollow arm 226 opens from the cap.

A one-way top-hat valve 228 is provided in the arm. Two retaining rings 234 around the valve 228 located in grooves 236 around the internal wall of the hollow arm 226 to retain the valve. The free end 230 of the arm is externally threaded.

In use, the open end 224 of the cap 222 is screwed tightly onto the open end of the blocked service pipe 10. The closure 232 is unscrewed from the free end 230 öf the hollow arm 226, and replaced by the nozzle of a sealant pump. Sealant is pumped in through the valve 228 to fill the service pipe 10 between the block and the cap.

The sealant pump is removed, and the closure 232 replaced.

Claims (5)

- CLAIMS

1. A sealant composition comprising: a cementitious material; a plastics binder; and water.

2. A sealant compsosition according to claim 1, in which the cementitious material is portland cement.

3. A sealant composition according to claim 1 or 2, in which the plastics binder is polyvinyl acetate

4. A sealant composition according to any preceding claim, in which the proportion by volume of cementitious material:binder:water is about 1.2:1:1.

5. A sealant composition substantially as herein described.