GB2171485A

GB2171485A - Mole or pig

Info

Publication number: GB2171485A
Application number: GB08505093A
Authority: GB
Inventors: Geoffrey Ingles Mood
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1985-02-27
Filing date: 1985-02-27
Publication date: 1986-08-28
Also published as: GB8505093D0; GB8511646D0

Abstract

The apparatus comprises a vehicle 1 for self-propelled passage along a cable 2 extending along the bore of the existing pipeline or duct. The vehicle 1 has a rearward end 3 to which, in use, a replacement pipe 4 or electric cable is clamped, an optional forward end in the form of a cone 6 adapted to engage and fracture the internal wall of the existing pipeline and a cylindrical body portion 5 between the forward end 6 and the rearward end 3 to form a bore through the fractured pipeline for the passage of the replacement pipeline 4 therethrough. The vehicle 1 has a pair of cable gripping members 7 and 8, which are relatively movable to each other and in tandem can cause the vehicle 1 to move along the cable 2 in a step- wise manner by alternately causing one member to slide along the cable 2 in a forward direction while causing the other member to grip the cable 2. The forward cable gripping member 8 on forward movement actuates a movable portion 40 of the conical forward end 6 to pivot outwardly to engage and fracture the wall of the existing pipeline. <IMAGE>

Description

SPECIFICATION Apparatus for towing an elongate member along the interior of a length of pipeline The present invention relates to apparatus for towing an elongate member along the interior of a length of pipeline and particularly though not exclusively the invention relates to apparatus designed to permit the replacement of an existing pipeline such as a gas, water or sewer main with a replacement pipeline.

According to one aspect of the present invention, there is provided apparatus for towing an elongate member along the interior of a length of pipeline, the apparatus comprising a vehicle for self-propelled passage through the pipeline along an elongate guide adapted to extend along the interior of the length of pipeline, the vehicle having a rearward end to which, in use, the elongate member is releasably secured and a pair of guide gripping members spaced from each other and adapted releasably to grip the guide, the members being otherwise movable relative to each other and the arrangement being such that the vehicle can move along the guide in a step Wise manner by alternately causing one member to move in a forward direction along the guide while causing the other member to grip the guide.

An embodiment of the invention will now be described with reference to the drawings in which: Figures 1A and 18 comprise a longitudinal section through the apparatus with Fig. 1A comprising a rear portion of the apparatus and Fig. 1B the front portion of the apparatus.

Figure 2 is an enlarged perspective view of the cable gripping member shown in Fig. 1A, only a longitudinal section of the member being shown for the purposes of clarity.

Figure 3 shows an arrangement for clamping a cable at one end of a pipeline and Fig. 4 shows an hydraulic circuit for use with the apparatus.

The apparatus shown--in Figs. 1A and 1B is adapted for in situ replacement of an existing pipeline by a tubular replacement member (ie.

a replacement pipeline), the apparatus in use serving to engage and fracture the internal wall of the existing pipeline and forming a bore through the fractured pipeline whilst towing the replacement pipeline through the bore so formed.

Referring to Figs. 1A and 1B the apparatus comprises a vehicle or traction unit 1 which is adapted for self propulsion along an elongate guide in the form of a cable 2 which in use extends through the bore of the existing pipeline (not shown).

The vehicle 1 has a rearward end 3 to which in use a tubular replacement pipeline 4 is detachably secured, a body portion 5 intermediate the forward and rearward ends of the vehicle 1 for forming a bore in the fractured pipeline for the passage of the replacement pipeline 4 and a forward end 6 adapted to engage the internal wall of the existing pipeline to fracture it.

The vehicle 1 also houses a pair of cable gripping members 7 and 8 by means of which, in use, the vehicle 1 is enabled to move along the cable 2 in a step-wise manner.

The body portion 5 of the vehicle 1 is cylindrical and houses the rearward one 7 of the two cable gripping members. The body portion 5 also houses a double-acting piston cylinder assembly 9 by means of which the vehicle 1 is propelled along the pipeline and as will be shown by means of which power is provided to fracture the internal wall of the pipeline.

The forward end 6 of the vehicle 1 tapers forwardly in the shape of a cone to a nose 10 which forms the forward extremity of the vehicle 1. The conical forward end 6 of the vehicle 1 houses the forward one 8 of the two cable gripping members. The forward one 8 of the members serves not only to assist in propulsion of the vehicle 1 forwards but also actuates a movable portion of the forward end 6 to engage and fracture the wall of the existing pipeline as will be described subsequently.

Referring to Fig. 1A the rear end 3 of the vehicle 1 comprises an assembly for clamping the replacement pipeline 4 to the vehicle 1.

The assembly comprises a member 11 of generally tubular structure over a rear portion 12 of which one end of the replacement pipeline 4 fits, in use, and a split collar type clamp 13 for clamping the pipeline 4 to the member 11.

The rear portion 12 of the member 11 has a section 14 whose diameter is slightly greater than the rest of the rear portion 12 so that the replacement pipeline 4 which will be of generally flexible plastics type material such as PVC or the like can be force fitted thereover. Once in position on the rear portion 12 of the member 11, the replacement pipeline 4 can be clamped to the member 11 by the split collar 13 whose halves are bolted together by bolts 14 in the usual manner.

The front portion 15 of the member 11 forms a neck which projects into the rear end 16 of the vehicle body portion 6 by way of an aperture in a back plate 17 of the body portion 5. A shoulder 18 formed between the neck 15 and rear portion 12 of the tubular member 11 seats within a recess in the back plate 17 and the member 11 is secured to the plate 17. Housed within the neck portion 15 of the tubular member 11 is a frame 19 for supporting the rearward one 7 of the two cable gripping members.

Referring now to Figs. 1A and 4 the rearward one 7 of the two cable gripping members comprises a rectangular block 20 which is provided with an internal recess 21 to house a slidable wedge 22. The wedge 22 is urged by a spring 23 from a position where the lower surface 24 of the wedge 22 and the lower surface 25 of the recess 21 are spaced apart as shown in Fig. 2 to a position where the surfaces 24 and 25 are at least in close proximity as shown in Fig. 1A. In this position the cable 2 is gripped immovably between the surface 24 of the wedge 22 and the surface 25 of the recess 21. The surfaces 24 and 25 have corresponding grooves 26 and 27 to accommodate the cable 2.

The wedge 22 has an uppermost surface 28 which slopes downwardly in a forward direction, this surface 28 engaging with and, in use, sliding along a corresponding uppermost surface 29 of the recess 21, the surface 29 also sloping downwardly in a forward direction.

The frame 19 for supporting the gripping member 7 has a pair of spaced legs 30 and 31 which are secured to the neck portion 15 of the tubular member 11 and which project forwardly to support the block 20 to which they are secured. The frame 19 has a back plate 32 between which and the slidable wedge 22, the spring 23 is supported to bias the wedge 22 in a forward direction. The back plate 32 has a central aperture to permit passage of the cable 2 therethrough.

In use, the block 11 is movable synchronously in the same direction of movement as the body portion 5 of the vehicle 1 and therefore the vehicle 1 as a whole while the wedge 22 will tend to try and move in a direction opposite to that in which the body portion 5 of the vehicle 1(it. the vehicle as a whole) itself is moving. Consequently on forward movement of the body portion 5 the wedge 22 will tend to move backwards against the spring bias so that the wedge 22 will release its grip from the cable 2. However, any tendency of the body portion 5 to move backwards will be resisted by the wedge 22 moving forwards to grip the cable 2.

Referring to Fig. 1B, the forward end 6 of the vehicle 1 comprises a conical head and has a movable uppermost portion 40 and a fixed lowermost portion 41, the uppermost portion 40 being in the general shape of a half cone with the lowermost portion 41 including a corresponding half conical section 42 adjoining the nose 10 of the head 6 on one side and adjoining on the other side a cylindrical rear section 43 which is secured to the front end of the body portion 5.

Located within the conical end 6 of the vehicle 1 is the more forward one 8 of the two cable gripping members. This member 8 comprises a main wedge block 44 and a minor wedge block 45 situated within a recess 46 in the body of the block 44.

The main wedge block 44 has a recess 47 formed in its lowermost surface 48, the recess 47 forming a channel to receive the uppermost surface 49 of a step 50 extending upwardly from the inner wall of the lowermost conical portion 41. This arrangement permits the block 44 to slide in a direction parallel to the axis of the vehicle 1, the uppermost surface 49 of the step 50 actually having a plane extending parallel to the axis of the vehicle 1.

The movable uppermost portion 40 of the vehicle head 6 sits loosely upon the main wedge block 44 with its front tip 51 engaging in a suitable recess in the nose 10 of the head 6 but otherwise the portion 40 is not attached to lowermost portion 41 of the head 6. The portion 40 has a step 52 extending radially inwardly from its inner surface, the step 52 having a lowermost surface 53 received in a recess 54 in the uppermost wall 55 of the main wedge block 44, this wall 55 sloping downwardly in a forward direction.

The recess 54 forms a channel to guide the movement of the portion 40 which on forward movement of the main wedge block 44 is caused to be lifted by the wedge block 44 and to move radially outwardly. Rearward or return movement of the block 44 causes the portion 40 to be set down and therefore to retract radially inwardly to the at-rest position shown in Fig. 1B.

The conical vehicle head 6 is formed with a pair of pipeline engaging blades 56 on diametrically opposed sides of the head 6 whereby to engage and fracture the wall of the existing pipeline, the blades 56 extending along the surface of the head 6 between the rear of the head 6 and the nose portion 10, each portion 40,41 of the head 6 being formed with a blade 56.

The rear face 57 of the main wedge block 44 is secured to the shaft 58 of a piston 59 forming part of the double-acting piston cylinder assembly 9, the piston 59 serving to impart forward and return motion to the wedge block 44.

The piston 59 comprises the shaft 58, which is in the form of a tube to permit the cable 2 to pass therethrough, and a body 60 located within the cylinder 61 of the assembly 9.

The cylinder 61 itself is contained within the cylindrical body portion 5 of the vehicle 1 and has a front wall 62 received in a recess formed between the rear end of the conical vehicle head 6 and the cylindrical wall 63 of the vehicle body portion 6. As will be seen from Fig. 1B the front wall 62 of the cylinder 61 abuts against an apertured plate 64 forming the rear wall of the conical head 6.

The piston body 60 is disposed midway along the length of the shaft 58 and comprises an annular gasket 65 of flexible material forming a seal against the internal wall of the cylindrical body 66 of the cylinder 60. The gasket 65 is mounted within a recess formed between two flanges 67 and 68 extending ra dially outwardly from the piston shaft 58.

The piston body 60 divides the cylinder 61 into two compartments 69 and 70, each of which is connected to hydraulic power lines 71 and 72 adapted to impart the forward and return motion to the piston 59 in a manner to be described with reference to Fig. 4.

The wedge block 44 is as will be seen from Fig. 1B secured to that portion 73 of the piston shaft 58 which is disposed forwardly of the piston body 60. The piston shaft portion 73 extends through an aperture in the front wall of the cylinder 61 and through the apertured back plate 64 of the conical head 6.

That portion 74 of the piston shaft 58 which is disposed rearwardly of the piston body 60 extends through an aperture in the rear wall 75 of the cylinder 61. It will be appreciated that appropriate seals are provided between the piston shaft 58 and the cylinder walls 62 and 75.

The minor wedge block 45 is arranged to operate in a manner similar to that previously described for the slidable wedge 22 housed in the rectangular block 20 (Fig. 1A). The wedge 45 is slidable under the action of a spring 76 from a position where the lower surface 77 of the wedge 45 and the lower surface 78 of the recess 46 in the body of the main block 44 are spaced apart to the position where the surfaces 77 and 70 are at least in close proximity as shown in Fig. 1B.

In this position the cable 2 is gripped immovably between the surface 77 of the wedge 45 and the lower surface 78 of the recess 46. The surfaces 77 and 78 have corresponding grooves to accommodate the cable 2.

As with the cable gripping assembly 7 shown in Fig. 1A the wedge 45 has an upper surface 79 which slopes downwardly in a forward direction and which, in use, engages with and slides along the corresponding uppermost surface 80 of the recess 46, this surface 80 also sloping downwardly in a forward direction. The spring 76 is disposed between the back wall 81 of the recess 46 and the back wall 82 of the wedge 45 to bias the wedge 45 in a forward direction. It will be seen that the main wedge 44 has a throughgoing bore communicating with the recess 46 on either side to permit passage of the cable 2 through the block 44. The body of the wedge 44 is also provided with three throughgoing apertures 82 to reduce its overall weight. The nose 10 of the conical portion 6 is also provided with an aperture 83 to permit the cable 2 to pass therethrough.

A forward stroke of the piston 59 causes the main wedge 44 to slid forward on the step 50 of the head portion 41. This causes the movable head portion 40 to move outwardly. This will cause the blade 56 on the portion 40 in use to engage and fracture the wall of the existing pipeline (not shown).

A return stroke of the piston 59 will retract the main wedge 44 and cause the movable head portion 40 to move inwardly to retract the head portion 40.

The minor wedge 45 will tend to try to move in a direction opposite to that of the major wedge 44. Consequently on forward movement of the major wedge 44 the minor wedge 45 will tend to move backwards against the spring bias so that the minor wedge 45 will release its grip from the cable 2. However, return motion of the major wedge 44 will tend to cause the minor wedge 45 to move forwards to grip the cable 2 and prevent any further return movement of the major wedge 44. The major wedge 44 will however return to a sufficient extent to retract the movable head portion 40.

To impart forward movement to the piston 59 the left-hand compartment 69 (as viewed) of the cylinder 61 is supplied with hydraulic fluid under pressure and to cause the piston body 60 to move in the right-hand direction as viewed. This causes the forward gripping member 8 to slide forwardly along the cable 2. At the same time there is a counter force on the cylinder 61 tending to move the remainder of the vehicle 1 rearwardly. However, such rearward movement is arrested by the gripping member 7 (Fig. 1A) gripping the cable 2 in the manner previously described.

To impart return movement to the piston 59, the right-hand compartment 70 of the cylinder 61 is supplied with hydraulic fluid under pressure to cause the piston body 60 to move in the left-hand direction as viewed.

This causes the forward gripping member 8 to slide backwards to grip the cable 2. At the same time the remainder of the vehicle 1 is caused to move forwards with the gripping member 7 (Fig. 1A) released from the cable 2 as previously described.

To sum up therefore on forward strokes of the piston 59, the movable head portion 40 moves radially outwardly to fracture the wall of the existing pipeline while the vehicle 1 is at rest. On return strokes of the piston 59 the movable head portion 40 is retracted at the same time as the vehicle 1 moves along the cable 2 towing the replacement pipeline into place within the fractured pipeline. The vehicle 1 therefore proceeds along the cable 2 in a step-wise manner by the forward movement of one gripping member along the cable whilst the other member is gripping the cable.

To use the vehicle for the replacement of an existing pipeline by a new pipeline, it is first necessary to expose the opposite ends of the pipeline to be replaced. Where the pipeline is below ground it will be necessary to excavate to gain access to each end of the existing pipeline.

The vehicle is then located at one end of, and with its front end pointing towards, the existing pipeline. One end of the cable is threaded through the existing pipeline, through the vehicle itself and finally through the replacement pipeline. The replacement pipeline is then clamped to the rear end of the vehicle as previously described with reference to Fig.

1A. Next, the end of the cable at the near end of the replacement pipeline is clamped in the manner shown in Fig. 3. In this case a stake 90 is driven firmly into the ground and the cable 2 is clamped securely to the stake 90 by means of the clamp 92. Finally, the end of the cable adjacent to the far end of the existing pipeline is also clamped to a frame (not shown) braced against the wall of the excavation pit. The cable is now held at both ends and operations can begin.

The apparatus is caused to move along the cable 2 in a step-wise sequence. Between each period when the vehicle is at rest, the movable portion 40 of the head 6 is actuated to enable the blade 56 to engage and fracture the wall of the existing pipeline. Where the internal diameter of the existing pipeline is smaller than the outer diameter of the vehicle body portion 5, the blades 56 of the head portion 6 of the vehicle 1 will be engaging the wall of the pipeline at all times so that in this case the pipeline will be fractured both by actuation of the movable head portion 40 and by simple movement of the vehicle through the existing pipeline. Where the internal diameter of the existing pipeline is the same as the other diameter of the vehicle body portion 5, pipeline wall fracture will depend on actuation of the movable head portion 40.As the vehicle 1 proceeds through the fractured pipeline, the cylindrical body 6 will form a bore through the pipeline for the passage of the replacement pipeline through the fractured pipeline.

When the vehicle 1 has reached the far end of the existing pipeline, it is allowed to emerge therefrom and is then removed from the replacement pipeline 4 now forming an insitu replacement for the existing pipeline. Next the cable 2 is released from the clamps at either end and is withdrawn from both the vehicle 1 and the replacement pipeline 4. The stake and bracing frame are withdrawn and after connecting the replacement pipeline to adjoining pipelines as necessary the excavations are backfilled.

Referring to Fig. 4 a suitable hydraulic circuit is shown for providing automatic cycling of the piston/cylinder assembly 9. Where appropriate the same reference numerals are used here as have been used in Fig. 1B.

The circuit includes a fluid reservoir 101 having a fluid supply line 102 for supplying fluid to a spool valve 103 by means of a pump 104 and for receiving fluid from the spool valve 103 by a return line 105. The circuit also includes fluid supply and return lines 71 and 72 extending between the spool valve 103 and the piston/cylinder assembly 9, the line 71 terminating in compartent 69 of the cylinder 61 and the other line 72 terminating in compartment 70 of the cylinder 61.

The spool valve 103 includes a reversing valve 106 for reversing fluid flow between the lines 71 and 72. The reversing valve 106 moves between the positions 107 and 108 to reverse the flow. The spool valve 103 also includes two actuating valves 109 and 110 wherein the valve 109 causes the reversing valve 106 to change from the position 108 to the position 107 and the valve 110 causing the reversing valve 106 to change back from the position 107 to the position 108. A further actuating valve 111 short circuits the flow when the fluid pressure exceeds a preset value. The actuating valves 109 and 110 are arranged to cause reversal at different preset fluid pressures which are lower than that at which the valve 111 is caused to operate.

A non-return valve 112 includes a flow restrictor and serves to enable a small amount of the hydraulic fluid in line 71 to return to line 72 and thence to the reservoir 101 on forward strokes of the piston only. This allows the fluid to circulate back to the reservoir via a cooler (not shown).

When the reversing valve 106 is in position 108, fluid flows from the reservoir 101 and line 102 to line 71 and into compartment 69.

In this case the piston 59 is caused to be moved forwardly (to the right as shown) and the cylinder 61 rearwardly (to the left). This causes the movable head portion to move radially outwards while the vehicle is caused to be arrested. Any fluid in compartment 70 then discharges into the reservoir 101 by lines 72 and 105.

When the reversing valve 106 is in position 107, fluid flows from the reservoir 101 and line 102 to line 72 and into compartment 70.

In this case the piston 59 is caused to move rearwardly (to the left as shown) and the cylinder 61 forwardly (to the right). This causes the movable head portion to retract and the vehicle to move forward.

The apparatus described is suitable for use in the replacement of any pipelines of breakable material such as cast iron, steel, some types of synthetic resin, ceramic and clay. The apparatus is therefore suitable for the replacement of gas and water mains which are usually of cast iron or steel and sewer pipes and mains which are usually of clay or ceramic.

The most usual replacement pipeline material will be a flexible synthetic resin such as PVC or polyethylene.

It will be appreciated that the apparatus can merely be used as a vehicle to convey an elongate member such as an electric cable along a pipeline such as a suitable underground duct. In this case of course, the pipel ine fracturing head can be dispensed with and the design of the vehicle can be greatly simplified.

Claims

1. Apparatus for towing an elongate member along the interior of a length of pipeline, the apparatus comprising a vehicle for selfpropelled passage through the pipeline along an elongate guide adapted to extend along the interior of the length of pipeline, the vehicle having a rearward end to which, in use, the elongate member is releasably secured and a pair of guide gripping members spaced from each other and adapted releasably to grip the guide, the members being otherwise movable relative to each other and the arrangement being such that the vehicle can move along the guide in a step-wise manner by alternately causing one member to move in a forward direction along the guide while causing the other member to grip the guide.

2. Apparatus as claimed in claim 1 in which the vehicle has a forward end adapted to engage and fracture the wall of the pipeline as the vehicle moves therethrough and a body portion intermediate the forward and rearward ends for forming a bore in the pipeline for the passage of an elongate tubular member through the pipeline to provide in situ replacement of the pipeline, the tubular member, in use, being releasably secured to the rearward end of the vehicle.

3. Apparatus as claimed in claim 2 in which the forward end of the vehicle tapers radially inwardly from a point adjacent to the body portion of the vehicle to a nose which forms the forward extremity of the vehicle, the forward end being provided with at least one blade for engaging and fracturing the wall of the pipeline.

4. Apparatus as claimed in claim 3 in which at least a portion of the forward end is retractably movable radially outwardly from the axis of the vehicle and is provided with at least one blade so that radially outward movement of the portion can cause the blade to engage and fracture the wall of the pipeline.

5. Apparatus as claimed in claim 4 in which a forward one of the two guide gripping members is capable of a limited backward movement along the guide and is engageable with the radially retractable portion of the forward end in such a manner that forward movement of the member causes the portion to move radially outwardly and backward movement of the member causes the portion to retract.

6. Apparatus as claimed in claim 5 in which the forward one of the two guide gripping members is movable along the guide independently of the vehicle body.

7. Apparatus as claimed in claim 5 or claim 6 in which movement of the guide gripping members is provided by a doubleacting piston cylinder device, the piston of which is secured to the forward one of the two members and the cylinder of which is secured to the body of the vehicle, the rearward one of the members also being secured to the body of the vehicle.

8. Apparatus as claimed in any of the preceding claims in which the guide is a cable which extends through the pipeline.

9. Apparatus substantially as hereinbefore described with reference to the drawings.