GB2152621A

GB2152621A - A method of threading an elongate flexible element through an elongate passage

Info

Publication number: GB2152621A
Application number: GB08400381A
Authority: GB
Inventors: John Edmund Dawe
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-09
Filing date: 1984-01-09
Publication date: 1985-08-07
Also published as: GB8400381D0

Abstract

String (2) is threaded through a pipe or conduit (1) by attaching it to a pig (3) and drawing the pig (3) through the conduit (1) by suction. The suction is applied by a pump (4). The string (2) may be a leader for an electric or fibre optic cable. The pig (3) may comprise a spring loaded scissor linkage (Fig. 4 not shown) or discs having spring loaded balls or wheels (Fig. 5 not shown). A membrane or diaphragm (11, Figs. 4,5) is employed. <IMAGE>

Description

SPECIFICATION A method of threading an elongate flexible element through an elongate passage This invention relates to a method of threading an elongate flexible element through an elongate passage, for example threading string through pipes laid under the ground and which are awkward to reach, the string being used as a leader to pull wire or cable through the pipe.

It is often necessary either to thread cable or wire through a pipe fixed in an awkward position, or to provide prethreaded pipe. Previously cable or wire has been threaded through a pipe by pushing a relatively stiff but flexible leader through the pipe from one end, and then attaching the cable tothe leader so that the cable can be pulled into the pipe.

Alternatively, the leader is used to thread a string into the pipe, and the string is then used to pull the cable into the pipe. This technique is unsatisfactory where the pipe is long or has sharp bends.

According to the present invention, there is provided a method of threading an elongate flexible element through an elongate passage, the method comprising attaching the element to a carrier, inserting the carrier into one end of the passage and reducing the pressure in the passage between the carrier and the other end of the passage so that the carrier is caused to move, with the element, through the pasage.

According to another aspect of the present invention there is provided a carrier for use in the method defined in the preceding paragraph, the carrier comprising a radially expandable body for resilient engagement with the wall of the passage, means being provided on the body for attachment to the elongate flexible element.

In a preferred embodiment, the carrier comprises two substantially identical arrangements, each arrangement having one or more pair of elongate members, each one of the or each pair being pivoted with respect to the other of each pair at a point spaced from each end of each elongate member, one end of each elongate member having a rotating element for running along the wall of the passage, the elongate members of the or each pair being inerconnected by resilient means which act to bias respective rotating elements apart from each other, wherein each arrangement is mounted on a common link, one of the arrangements being provided with a flexible membrane to restrict or prevent air flow past the carrier in the lengthwise direction of the passage.

For a better understanding of the present invention, and to show how it maybe carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:~ Figure 1 illustrates a method of threading string into a relatively straight length of pipe; Figure 2 illustrates a method of threading string into a coil of pipe; Figure 3 illustrates one way of varying the vacuum applied to the interior of the pipe; Figure 4 illustrates one embodiment of a carrier for use in the methods represented in Figs. 1 to 3; and Figure 5 illustrates another embodiment of a carrier.

Fig. 1 shows a length of pipe 1 into which, for example, fibre optic cable or electric cable is to be inserted. In order to provide a leader for the cable, string from a coil 2 is first threaded through the pipe 1. A carrier 3 is attached to one end of the string 2 and is inserted into the one end 1 a of the pipe 1. A vacuum pump 4 is then connected to the other end 1 b of the pipe 1 to create a vacuum in the pipe 1 which draws the carrier 3 along the pipe 1. Some air flow will occur between the carrier 3 and the wall of the pipe 1. This air flow will tend to keep the carrier 3 away from the wall of the pipe 1, so reducing frictional resistance to the travel of the carrier 3. A gas permeable obstruction, for example a piece of gauze 5, is placed near the end 1 b of the pipe 1 to prevent the carrier 3 from being sucked into the vacuum pump 4.

In Fig. 2, the method illustrated is applied to a coil 2 of string. In Fig. 2, the reference numerals used correspond to those used in Fig. 1 for the same parts.

In some cases, particularly when long pipes are to be threaded, shutters 6 may be used as illustrated in Fig. 3. The shutters 6 can be moved towards and away from each other as illustrated by arrows A. In use, the shutters 6 would be closed while air is drawn from the pipe 1. The shutters 6 would then be opened, allowing a rush of air to enter the pipe 1 to drive the carrier 3 along. This process could be repeated several times to carry the carrier 3 from one end of the pipe to the other.

Using this technique. a relatively small vacuum pump can be used.

An embodiment of a suitable carrier 3 is shown in Fig. 4. This carrier comprises two substantially identical "scissor" arrangements 7. Each "scissor" arrangement 7 has two elongate members 8 pivoted to each other and to a link 10 at point 9. One end of the carrier is provided with a flexible membrane or diaphragm 11. The inner ends of the two elongate members 8 of each arrangement 7 are interconnected by a respective spring 12 to bias these ends apart from each other. The members 8 have rotating members 12, such as wheels or balls which run on the inside of the pipe 1. The carrier shown in Fig. 4 can be used with pipes of different diameters, or where a pipe has a diameter which varies along its length.

The "scissor" arrangement 7 may have more than one pair of elongate members 8, according to the diameter of the pipe.

Another embodiment of a carrier is shown in Fig. 5. In this embodiment, a plurality of discs 14 (two of which are illustrated in Fig.

5) are attached to a common link 10. The discs 14 are provided with respective passageways 15 for receiving a plunger 16 bearing at its inner end a spring 12 and at its outer end a rotating member 13. The carrier is provided with a flexible diaphragm 11.

It wil be appreciated that, once the string 2 has been inserted into the pipe 1, it can be connected to an electric cable or fibre optic cable to draw the cable into the pipe.

The method of the present invention is particularly useful for threading a pipe which is laid under concrete and which has several bends, or pipe which is otherwise awkward to thread.

Claims

1. A method of threading an elongate flexible element through an elongate passage, the method comprising attaching the element to a carrier, inserting the carrier into one end of the passage and reducing the pressure in the passage between the carrier and the other end of the passage so that the carrier is caused to move, with the element, through the passage.

2. A method as claimed in claim 1, in which entry of air into the said one end of the passage is restricted or prevented during pressure reduction, free entry of air subsequently being permitted to move the carrier through the passage.

3. A method as claimed in claim 1 or 2, in which the passage comprises a conduit for electrical wiring.

4. A method as claimed in claim 3, in which the elongate flexible element comprises a leader for an electrical cable.

5. A method as claimed in any one of the preceding claims, in which the elongate flexible element is string.

6. A method of threading an elongate flexible element through an elongate passage as claimed in claim 1 and substantially as described herein.

7. A carrier for use in a method in accordance with any one of the preceding claims, the carrier comprising a radially expandable body for resilient engagement with the wall of the passage, means being provided on the body for attachment to the elongate flexible element.

8. A carrier as claimed in claim 7, in which two substantially identical arrangements are mounted on a common link, each arrangement comprising one or more pairs of elongate members, one end of each member having a rotating element for engagement with the wall of the passage, resilient means being provided which biasses the respective rotating elements apart from each other.

9. A carrier as claimed in claim 8, in which the elongate members of each pair are pivotally interconnected at a position away from their ends.

10. A carrier as claimed in claim 8, in which the elongate members of each pair are slidably connected to the common link for movement apart from each other.

11. A carrier as claimed in any one of claims 8 to 10, in which a flexible membrane is provided on one of the arrangements for restricting or preventing air flow past the carrier.

12. A carrier for use in a method in accordance with claim 1, substantially as described herein with reference to, and as shown in, Figs. 4 and 5 of the accompanying drawings.