GB2141201A

GB2141201A - Pipe-cleaning pull through

Info

Publication number: GB2141201A
Application number: GB08315741A
Authority: GB
Inventors: Gerard Bagnall
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1983-06-08
Filing date: 1983-06-08
Publication date: 1984-12-12
Also published as: GB8315741D0; GB2141201B

Abstract

The pull-through comprises a first element 1, a second element 2, which is releasably engageable with the first element, and a magnetic propulsion unit 3 for the second element 2. The first element 1 comprises a pair of rubber discs 5,6 which are mounted on the ends of a central spindle 7 to sweep the pipe. The second element 2 is attached to a rope 24 by which the pull-through can be pulled through the main 4 and has a catch 32 at the other end to provide the releasable engagement with the rear end of the first element 1. The second element 2 also has a pair of diametrically opposed magnets 44 and 45 mounted on the peripheral surface of its body 25. These enable the second element 2 to be propelled along the main 4 towards the first element 1 when a hand-held magnetic propulsion unit 3 is moved along the external wall of the main 4 towards the first element 1. The magnet 49 in the unit 3 attracts one of those in the second element 2. When the second element 2 reaches the first element 1, the elements 1,2 engage enabling them to be pulled in the opposite direction by the rope 24 to clean out the main 4. <IMAGE>

Description

SPECIFICATION Pull-through The present invention relates to so called "pullthroughs" which are used extensively in the laying of gas distribution mains to clean out the mains while they are being constructed and before they are put into service.

Conventional cast iron gas mains are laid as pipes in a newly dug trench with each pipe being con nected to the section which has just been laid until eventually the main is complete. During the main laying, detritus such as earth, sand and gravel may accidentally enter the main or may be deliberately introduced in the form of bricks, stones and other debris by vandals if the main is left unattended for any period before the trench is filled in. This detritus may present a significant obstacle to the free flow of gas through the main when in service and must therefore be removed.

Traditionally this detritus is removed by means of a so-called "pull-through". As its name suggests it is pulled through the newly laid main from one end and out through the other by means of a hawser or rope to which it is attached thereby sweeping the detritus away from the internal wall of the main.

One conventional type of pull-through comprises two flexible rubber discs to act as sweepers, the discs being mounted at each end of a central spindle.

A pulling rope is attached to the spindle so as to enable the pull-through to be pulled through the main.

In use, the pull-through is placed in the first pipe of the main being laid. One end of the pipe is then capped off and sealed with a cap containing a screwed plug which can be removed to prevent movement of the pull-through being hampered by suction. This prevents the accidental or deliberate ingress of detritus into the pipe through that end of the pipe. The rope is then passed out of the outer end of the pipe and the pull-through is pulled up to, not beyond, the other end of the pipe thereby removing from that pipe any detritus.

Just before the next pipe is connected to the first pipe, the rope is passed through the next pipe which is then connected to the fist pipe. The pull-through is then pulled up to but not beyond the mouth of the next pipe. This process is repeated as further pipes are added until finally the pull-through is removed from the last pipe to be connected.

During the last five years or so, it has increasingly been the practice to use polyethylene pipes rather than cast iron pipes and indeed it is almost certain that eventually all new mains will be of polyethylene rather than cast iron.

As with cast iron mains, the polyethylene mains comprise several pipes connected together. However, the polyethylene pipes are joined together by a heat fusion technique which makes it impossible to use the conventional pull-through to clear away any detritus in the main.

In this heat fusion technique, a steel disc is heated by eddy currents to a temperature at which it will melt the polyethylene. The disc is then located between the adjoining ends of two adjacent pipes and after a small end region of the pipes has been melted by the heated disc, the ends are pressed together to form a butt weld connection between the pipes. The same technique is used to produce a socket-jointed polyethylene pipe.

Clearly, the use of butt-welding precludes the use of a conventional pull-through since the rope could not be passed through the newly attached pipe immediately prior to fusion jointing without prevent ing jointing of the adjoining pipes.

In some mains laying operations it is the practice to join several pipes together on the ground above the trench before connecting them to the last pipe in the trench by the butt-jointing technique. The main so formed on the surface is usually at least twenty metres long. Furthermore it has not been found possible to gain access either to the pull-through itself or to its rope by way of the open end of the newly attached pipe because in general the pipes are too long. It is therefore an object of the present invention to provide a pull-through which overcomes the above disadvantages.

According to the present invention therefore, there is provided a pull-through for sweeping detritus away from the internal wall of a main of nonmagnetic material when the pull-through to which, in use, a hawser is attached, is pulled by means of the hawser from a point near a first end of the main towards and out of a second end of the main, the pull-through comprising two elements which are releasably engageable with each other there being a first element which includes means for sweeping away detritus from the internal wall of the main and which is for location near the first end of the main and a second element to which, in use, the hawser is attached and which is movable along the main from the second end into engagement with the first element following which the pull-through may be pulled by the hawser along and out of the main, the second element being movable along the main towards the first element by means of a magnet which is movable along the external wall of the main towards the first element.

In one embodiment of the invention, the elements are provided with complementary latching means to enable the elements to releaseably engage each other.

An embodiment of the invention will now be particularly described with reference to the drawings in which: Figure 1A shows a plan view in section of a first element of the pull-through which in the drawing is positioned near one end of a polyethylene main, Figure 1B shows a side view in section of a second element of the pull-through shown positioned near the other end of the same main as appears in Figure 1 A together with a magnetic propulsion unit for the second element and Figure 2 is a section through the second element along the line ll-ll of Figure 1 B.

Referring to the drawings, the pull-through comprises a first element 1, a second element 2 which is releasably engageable with the first element and a magnetic propulsion unit 3 for propelling the second element 2 through the main 4 towards the first element 1.

The first element 1, which is similar to a conventional pull-through, comprises a sweeping device having a pair of rubber discs 5,6 which are mounted on the ends of a central spindle 7 between pairs of disc-clamping plates 8 and 9 and 10 and 11. The diameter of the plates 8 to 11 is less than that of the discs 5 and 6 so that peripheral portions 12 and 13 of the discs 5 and 6 extend radially outwardly beyond the plates 8 to 11 to engage flexibly with any detritus in the main 4 and sweep it along the main 4 towards thefarend 14 of the main 4.

The inner plates 9 and 10 of each pair engage with washers 15 and 16 mounted rigidly on the spindle to prevent inward movement ofthe plates 9 and 10 along the spindle. The outer plates 8 and 11 of each pair are held against their respective rubber discs 5 and 6 by means of nuts 17 and 18 which are connected to the spindle 7 by threaded end portions 19 and 20 of that member. The rubber discs 5 and 6 are thereby clamped securely between their respective plates.

Secured to the face of the outer plate 8 are the arms 21 and 22 of a generally C shaped member 23 which forms one part of means whereby the second element 2 can be releasably latched to the sweeping device 1.

The second element 2 forms a device for carrying the hawser in the form of a rope 24 by which the pull-through can be pulled through the main 4.

Referring to Figures 1 B and 2, the second element comprises a generally hollow body 25 having a generally cylindrical central section 26 lying between two frusto-conical end sections 27 and 28. The walls of the frusto-conical end sections 27 and 28 curve inwardly towards and adjoin circular end portions 29 and 30.

Secured to one end portion 29 of the body 25 is a curved bar 31 to which in use the rope 24 is tied.

Secured to the other end portion 30 of the body 25 is a catch 32 which forms the other part of the latch for engaging the elements 1 and 2. The catch 32 is similar to those used to close garden gates and comprises a hook 33 which pivots on a pin 34 between two spaced catch plates 35 (only one shown in Figure 1B).

The plates 35 are formed with a recess 36 to receive the locking pin 37 mounted between the arms 21 and 22 of the C-shaped member 23 of the element 1. When the hook 33, which in Figure 1 B is shown in the closed position, engages the locking pin 37, the hook 33 lifts to let the pin 37 enter the recess 36. The hook 33 then drops to retain the pin 37 releasably within the recess 36.

The catch 32 is provided with a base plate 38 on which the catch plates 35 are mounted to enable the catch 32 to be secured to the end portion 30 of the body 25. To this end, the base plate 38 and the end portions 29 and 30 of the body 25 are apertured to permit a securing bolt 39 to extend through the body 25 as shown in Figure 1 B. The aperture in the base plate 38 is located between the catch plates 35 and the bolt head 40 engages the plate 38 after the bolt 39 has passed through it. The other end 41 of the bolt 39 is threaded and after passing through the aperture in the end portion 29 is secured thereto by the nut 42 and washer 43. In this way the catch 32 is securely clamped to the end portion 30.

Two diametrically opposite insert magnets 44 and 45 are located within recesses 46 and 47 provided in the outer surface of the cylindrical body section 26.

These magnets 44 and 45 are made of an appropri ate rare earth material. So as not to interfere with the magnetic field formed by these magnets, the body 25 of second element 2 is constructed of a suitable lightweight non-magnetic material such as plastics.

There is also provided a magnetic propulsion unit 3 for use externally on the main 4 and therefore externally of the second element 2 to propel the second element 2 along the main 4. The unit 3 is designed to be hand-held for movement along the external wall of the main 4 and comprises a plate 48 in which is located an appropriate rare earth magnet 49 within a recess 50 in the lower face of the plate 48.

The plate 48 is formed with a curved handle 51 and the plate 48 and handle 51 may be made of a similar material to the body 25 of the second element 2. The magnet 49 in the unit 3 and those magnets 44 and 45 in the body 25 of the second element 2 are so arranged that the magnet 49 attracts either of the magnets 44 and 45.

The diameter of the two rubber discs 5 and 6 is arranged to be as close as possible to the internal diameter of the main 4 so that the discs 5 and 6 engage and remove as much as possible of any detritus in the main 4. Since the discs are of rubber and are flexible they can easily slide over any protruberances in the main 4 such as the internal butt fusion joints 52 and 53 shown in Figures 1A and 1B.

On the other hand, the body 25 of the second element 2 is arranged to have a diameter whose maximum value (across the cylindrical central section 26) is somewhat smaller than the internal diameter of the main 4. This enables the element 2 to be propelled freely along the main 4 over any detritus which may otherwise block its path.

In one method of use of the pull-through, the completed main is laid in its trench and the first element 1 is inserted through one end to a position close to that end but in front of the first butt fusion joint. The second element 2 is then located in the other end of the main with one of its two magnets upwards. After fusion of the joints between pipes is completed the magnetic propulsion unit 3 is then moved along the outer wall ofthe now completed main towards the first element 1. Because of the magnetic attraction between the magnet in the propulsion unit 3 and the corresponding magnet in the second element 2, the second element 2 is also caused to move in this direction towing the rope 24 behind it. Naturally the rope 24 should be of sufficient length so that some protrudes from the other end of the main after the second element 2 has been latched to the first element 1. When the catch 32 engages the locking pin 37, the hook 33 is lifted and then drops to locate the pin 37 between the catch plates 35 and the hook 33. The pull-through device now formed is pulled by the rope 24 in the reverse direction to that in which the second element 2 was moving to withdraw the assembly from the main. As this occurs the detritus is conveyed in this direction by the discs 5 and 6 of the pull-through and is removed from the other end of the main with the withdrawal of the assembly. The first element 1 can then be released from the second element 2 for further use.

While the first element 1 has been described as comprising rubber discs 5 and 6 to provide means for sweeping away detritus it could instead comprise flexible brushes orthe like for sweeping away the detritus.

Claims

1. A pull-through for sweeping detritus away from the internal wall of a main of non-magnetic material when the pull-through to which, in use, a hawser is attached, is pulled by means of the hawser from a point near a first end of the main towards and out of a second end of the main, the pull-through comprising two elements which are releasably engageable with other, there being a first element which includes means for sweeping away detritus from the internal wall of the main and which is for location near the first end of the main and a second element to which, in use, the hawser is attached and which is movable along the main from the second end into engagement with the first element following which the pull-through may be pulled by the hawser along and out of the main, the second element being movable along the main towards the first element by means of a magnet which is movable along the external wall of the main towards the first element.

2. A pull-through as claimed in Claim 1 in which the elements are provided with complementary latching means to enable the elements to releasably engage each other.

3. A pull-through substantially as hereinbefore described with reference to the accompanying drawings.