The present invention relates to the sealing of a clearance between a host pipe and a liner pipe.

It is known to line host pipes with liner pipes to replace or repair the host pipe because the host pipe is already defective in some way or may become defective and fluid may be leaking from it or be about to leak from it.

Where the host pipe is a gas carrying service pipe supplying gas from an external main to a building such as a dwelling, the liner pipe is normally of plastic eg polyethylene and the service pipe of steel .

To replace the service pipe, the liner pipe is fed into a downstream (in the sense of the direction of gas flow) end of the service pipe into and then along the service pipe until the desired length of service pipe has been replaced. To permit the easy passage of the liner pipe into and along the service pipe the external diameter of the liner pipe and the internal diameter of the service pipe are chosen so that there is a clearance between the pipes.

A so-called "nose-cone" is connected to the leading end of the liner pipe before it is fed into the service pipe. This is a

tubular member of the plastics material which in use, may be adhered to or force fitted onto the leading end of the liner pipe. The nose-cone is provided with at least one vane or fin radially directed outwardly from the body of the member. The vane or vanes are flexible and, in use, engage the internal wall of host pipe to provide a seal or barrier to the flow of gas along the clearance from the upstream to the downstream end of the clearance both while the liner pipe is being fed into the host pipe as well as after the feeding step has been completed.

The nose-cone is also provided with a frangible means to block the bore of the nose-cone while it and the liner pipe are being fed into and along the service pipe. This temporarily prevents gas entering the liner pipe.

The frangible means may take the form of a frangible membrane or a push-out or pop-out stopper or plug. When the liner pipe is in place the membrane is ruptured and/or removed or the stopper pushed out to permit gas to enter the liner pipe.

Then a sealant is introduced into the clearance to form a further seal in the clearance. The sealant may be a two-part anaerobic sealant which while fluid is injected into the clearance and then sets or hardens after a delay.

A full description of a typical service pipe replacement technique is described in UK Published Patent Application No. 2227071A together with a typical nose-cone.

Another method and nose-cone is described in UK Published Patent Application No. 2275901A.

The sealant used in the two documents referred to above is relatively expensive and a significant amount of it must be used to ensure a gas-tight seal.

It is therefore an object of the present invention to seal the clearance between a host pipe and a liner pipe in a less expensive manner than is described in the above documents .

According to one aspect of the present invention, there is provided apparatus for sealing a clearance between a host pipe and a liner pipe which, in use, is fed into the host pipe, the apparatus comprising a tubular element for connection to or forming a leading end of the liner pipe and a compressible seal which is adapted when compressed longitudinally to expand radially and which, in use, is mounted on the element, the arrangement being such that the seal moves freely with the element in the direction of feeding of the liner pipe but when the liner pipe is retracted counter to the direction of feeding further seal movement is arrested and the seal is compressed longitudinally by the element so that the seal

expands radially to engage the internal wall of the host pipe and seal the clearance.

According to another aspect of the present invention, there is provided a method for sealing a clearance between a host pipe and a liner pipe which, in use, is fed into the host pipe, the method comprising, after the liner pipe has been fed into the host pipe, causing a compressible seal mounted on a leading end of the liner pipe to be compressed longitudinally so that the seal expands radially to engage the internal wall of the host pipe and seal the clearance.

Preferably the seal is annular in shape.

The seal may be porous and may also be in the form of a sponge possibly of foam plastic or the like.

A sealant is suitably provided in liquid form for application to the seal, the sealant, in use, on being applied to the seal permeating the pores of the seal before the seal is fed into the host pipe and then setting after a time which allows the seal to be fed into the host pipe, compressed and expanded radially into engagement with the internal wall of the host pipe.

The sealant maybe a two part sealant conveniently of the anaerobic kind which sets some time after the components have

been mixed, the time of setting being variable dependent on the initial proportion of the components .

Preferably the tubular element is provided with first and second stop means between which, in use, the seal is compressed.

The first of the stop means is suitably located forwardly of the second stop means which is slidably mounted on the element and is adapted, in use, to move with the element in the direction of feeding of the liner pipe but is also adapted to grip the internal wall of the host pipe and remain stationary during the rearward movement of the liner pipe when this is retracted so that the seal is compressed between the two stop means .

Conveniently the first stop means is a nose-cone for connection to the leading end of the tubular element.

The nose-cone may be similar to any of those referred to in the introduction.

An embodiment of the invention will now be particularly described with reference to the accompanying drawings in which: -

Figures 1 to 3 are longitudinal sections through the host pipe and liner pipes and the sealing apparatus at various stages of the sealing method.

Referring to Figure 1 which is the position immediately before the liner pipe 1 is inserted into the host pipe, in this case a gas service pipe 2, the sealing apparatus comprises a tubular element 3 which in use, is connected at its rear end 4 to the leading end 5 of the liner pipe 1, a compressible annular seal 6 which fits over the element 3, a nose-cone 7 fitted to the leading end 8 of the element 3 and an annular stop means or member 9 also fitting over the element 3 and lying between the liner pipe 1 and the service pipe 2.

The tubular element 3 is a plastics tube of, say, polyethylene. It is or may be a moulding produced with an annular flange 10 acting as a stop means or stop member adjacent its rear end for purposes to be described.

The annular seal 4 is of a compressible porous material such as a foamed plastic. It is dimensioned to form a close fit over the tube 3.

The nose-cone 5 is of conventional design and comprises a moulded polyethylene stub tube 11 the rear end 12 of which is dimensioned to form a close fit in the bore of the tube 3. Circumventing the outer wall of the front end 13 of the nose-

cone 5 are five annular vanes or fins 14 to 18, the diameter of the vanes increasing in a direction away from the nose-cone 5. The front end 13 of the nose-cone 5 is closed by a removable plug or puncturable membrane 19 to temporarily block the bore of the liner pipe 1 to the flow of gas.

The annular stop member 9 is of a resilient material eg rubber and is a slide fit on the tube 3. Its purpose will also be described subsequently.

Also located as a slide fit on the tube 3 is a further stop means or member 20, comprising a moulded polyethylene stub tube 21 circumventing the outer wall of which are five annular vanes or fins 22 to 26, the diameter of the vanes increasing in a direction away from the nose-cone 5. Once again the purpose of the stop means 20 will be described subsequently.

To assemble the apparatus, firstly the rear end 4 of the tube 3 is fitted into the leading end 8 of the liner pipe 1 which end 8 engages the stop member 10. Then a clamping ring 27 is threaded over the liner pipe 1 until this ring 27 too engages the stop 10, the ring 27 being dimensioned to compress the liner pipe 1 against the tube 3 and provide a secure connection therebetween.

Next, the stop member 9 is fitted over the leading end 8 of the liner pipe 1 and is slid along the liner pipe 1 towards the stop member 10. Then the stop member 20 is fitted over

the leading end 8 of the liner pipe 1 and is slid along the liner pipe 1 towards the stop member 9.

Following this stop, the annular seal 6 is fitted over the leading end 8 of the liner pipe 1 and is slid along the liner pipe 1 towards the stop member 20.

Finally the rear end 12 of the nose-cone 5 is fitted into the bore of the liner pipe 1 at its leading end 8. The outer wall of the rear end 12 of the nose-cone 5 is coated with a strong adhesive such as an anaerobic glue to ensure the nose-cone 5 is securely attached to the liner pipe 1.

Just before the sealing apparatus in inserted into the liner pipe 1, a two part liquid hardenable sealant mix such as a two part anaerobic sealant mix is applied to the annular seal 4 in such a way that the seal 6 is completely saturated in the sealant .

The assembly of the liner pipe 1 and sealing apparatus is then inserted into the service pipe 2 as shown in Figure 2. The assembly may be pushed through a gland (not shown) connected to the service pipe 2 until the nose-cone 5 enters the external main (not shown) and is then retracted back into the service pipe 2 in the well known manner.

At this point (Figure 3) the stop members 9 and 20 lock in position in the service pipe 2 by gripping the internal wall

of the pipe 1 while the liner pipe 1 itself, the annular seal 4 and the nose-cone 5 continue to move rearwardly to compress the seal 4 between the nose-cone 5 and the stop member 20 to cause the seal to expand radially into engagement with the internal wall of the service pipe 2.

The stop member 20 also acts as a barrier to the sealant in the seal 6 so as not to allow sealant from the seal 6 to contaminate the stop member 9 whereby members 20 and 9 slip or slide thereby reducing the compression of member 6 resulting in a potential leakage track.

The apparatus is left in position at this point until the sealant has cured and the apparatus is now firmly secured to the inner wall of the service pipe 2 to seal the clearance between the pipes 1 and 2.

A rod (not shown) is passed along the bore of the pipe 1 as is well known to engage and cause the plug to pop out or to pierce or puncture the membrane to permit gas to flow into the liner pipe 1.