GB2074971A - Guiding a draw cable during cable-pulling operations - Google Patents

Abstract

A method of drawing a supply cable through a duct by means of a draw cable and a winch, includes the use of a flexible incompressible sheath 1 through which the draw cable is passed, and which is attached at one end to a prop located along the draw cable and at the other end to the winch frame. As the draw cable is tensioned by the winch, the pull on the winch frame is balanced by the compressive force developed in the sheath since it is trapped between the winch frame and the prop. The preferred form of the flexible incompressible sheath consists of a plurality of vertebra-like metal bobbins 2 with complementary hemispherical end faces and each having an axial channel 6 the bobbins being enclosed in a flexible hose 3 having end fittings 4, 5 suitable for plugging the sheath into a socket. The flexibility of the sheath permits the operation of the draw cable with a curved lie, and the sheath will transmit a compressive force without distortion since it is not compressible. <IMAGE>

Description

SPECIFICATION Method and apparatus for propping a cable winch during cable-pulling operations The invention relates to a method and apparatus for propping a cable winch during cable-pulling operations, and especially but not exclusively to a method and apparatus for propping a cable winch used for drawing a supply cable through a duct.

Supply cables, such as electricity supply cables and telephone cables, are generally installed in underground ducts, the installation operation requiring the supply cables to be drawn through the ducts. The installation of a supply cable in a duct is facilitated by the use of a powered winch mounted on a vehicle, and the use of a draw cable on the winch for pulling the supply cable. Since most cable ducts are located away from roadways, the vehicle must be suitably positioned on the roadway and the draw cable guided between the duct and the vehicle-mounted winch.

The operation of drawing a cable through a duct by means of a powered winch at present involves the use of large blocks or turning wheels for guiding the draw cable from the duct to the vehicle-mounted winch. The winch is anchored by its firm attachment to the vehicle which in turn depends on its brakes to hold it in position. The maximum winch pull available is of the order of several thousand pounds force.

The operation of a cable-pulling winch from a vehicle which is held by its brakes imposes considerable load on the vehicle chassis, suspension and brakes. The stress on the vehicle may be reduced by the use of a stabiliser jack which provides a rigid support for the chassis, but the stabiliser jack represents an additional item of equipment and consequently additional costs. If a stabiliser jack is not used, and no steps are taken to increase the damping of the vehicle suspension, there is a tendency for the vehicle to oscillate up and down, which leads to surging in the pull on the winch cable. Surging is undesirable, the best results being obtained from a steady pull on the winch cable and the service cable.

It is an object of the present invention to provide a method of drawing a cable through a duct, and apparatus for performing the method, which simplifies the task of absorbing the reaction to the pull of the winch cable.

According to the invention, a method of drawing a service cable through a duct by means of a draw cable and a winch includes the use of a flexible incompressible support adapted to fit on to the draw cable and so arranged in the vicinity of the winch that, in operation, an equal and opposite force to the tension of the draw cable is applied to the winch by the flexible support.

The method of drawing a service cable through a duct by means of a draw cable and a winch may include the use of a flexible incompressible sheath adapted to fit around the draw cable and arranged to be attached to the winch frame and to a prop located at a point along the draw cable.

The use of a flexible incompressible support which is attached to the draw cable during a cable-drawing operation ensures that the necessary reaction to the winch rope tension is provided by means of the flexible support at or near the entry point of the winch rope on to the winch, and the support cannot be compressed and become distorted. The prop may be a cabling stand or a manhole frame which, in a cable-drawing operation, will be located at road level and arranged to guide the draw cable downwards towards a duct which lies below road level.

Apparatus for guiding a draw cable during a cable-laying operation includes a sheath adapted to enclose the draw cable and to resist longitudinal compression.

In one form of the invention, the sheath is arranged to form a flexible backbone for the draw cable, the sheath having a longitudinal tunnel for accommodating the draw cable without gripping it, the sheath including a plurality of vertebra-like members adapted to transmit a compressive force, and a terminating member at each end.

The sheath may be constructed as a plurality of hardened steel bobbins with complementary hemispherical end faces enclosed in a length of flexible hose with hardened steel end fittings.

An example of a guide according to the invention and a method of employing it in a cablelaying operation will now be described by way of example only and with reference to the accompanying drawings in which: Fig. 1 shows a longitudinal cross-section of a guide according to the invention, Fig. 2 is a diagrammatic representation of a flexible cable guide according to the invention installed between a vehicle-mounted winch and a cabling stand, and Fig. 3 is a diagrammatic plan view of the arrangement of Fig. 2.

Referring to Fig. 1 , a flexible cable guide 1 consists of a chain of hardened steel bobbins, such as 2A, which are enclosed in a length of flexible hose 3 and trapped within the hose 3 by means of hardened steel fittings 4, 5 at each end. The bobbins are required to withstand a compressive force equal to the maximum winch pull available.

Each bobbin, such as 2A, is of generally cylindrical form, and has one hemispherical convex end face and a complementary hemispherical concave end face. This bobbin shape permits the end to end connection of a plurality of bobbins which are then displaceable angularly with respect to each other while contact between adjacent mating faces is maintained, each convex face being placed adjacent to a concave face in the chain of bobbins. It will be appreciated that several alternative forms of bobbins may be used to achieve the result of a flexible spine adapted to resist compression. For example, the end faces may be the complementary inner and outer surfaces, respectively, of any part of a sphere. There may be two forms of bobbin employed, one form having a pair of convex end faces and the other form having a pair of complementary concave end faces.

Where two forms of bobbin are employed, they may consist of a spherical ball and a cylindricai bobbin having concave end faces complementary to the ball, respectively. The two forms of bobbin may be made of different materials. However, in a preferred form of the invention, the bobbins are identical and are made of the same material.

Each bobbin, such as 2A, is provided with an axial channel 6 of generally circular transverse cross-section, and the fittings blocking the ends of the cable guide 1 also have a channel each, so that the cable guide 1 has a centrally located axial duct running from end to end. The axial channel in each bobbin need not have a circular transverse cross-section, any channel shape which will accommodate a winch rope without giving rise to clamping of the rope being suitable, and the channel need not be axially located within the bobbin. However, an axially located channel of circular transverse cross-section is to be preferred.

The fitting 4 is provided with a circumferential groove 7, which lies within the hose when the fitting 4 is in position on the hose 3, the fitting 4 being retained at the end of the hose 3 with the aid of a clamp 9 which encircles the hose 3 in the region of the groove 7 to cause the hose 3 to grip the fitting 4 in the vicinity of the grooves 7. The fitting 5 has a similar groove 8, and is held in position with the aid of a clamp 10.

The fitting 4 is of generally cylindrical form with a stepped outer profile, the step in the profile being due to an increase in the diameter of the fitting 4 from a diameter corresponding to the bore of the hose 3, to a diameter corresponding to the outer diameter of the hose 3. The end face of the smaller diameter portion of the fitting 4 has a concave hemispherical surface which is complentary to the convex hemispherical surface of the bobbin 2A on which it bears. The fitting 5 is generally of the same form as the fitting 4 with the exception that the fitting 5 has a convex hemispherical end face on its smaller diameter portion which bears on a bobbin 2Z which has its concave hemispherical face in contact with the fitting 5. The larger diameter portions of the fittings 4, 5 are identical and are adapted to fit into a socket or the like provided in a winch, for example.

The material of the flexible hose 3 may be rubber or any synthetic material having similar properties. The main function of the hose 3 is to resist separation of the components of the flexible guide 1 when a tensile force is exerted on the guide. A tensile force may be exerted during handling of the cable guide 1 in positioning it for a cable-pulling operation, for example, by pulling it along. The flexible hose 3 is also intended to provide some protection from the ingress of water and other foreign matter which may come into contact with the flexible guide 1 during cable drawing operations.

In the illustration of Fig. 2, a draw cable 21 used for pulling a supply cable through a duct 22 is passed through the longitudinal channel present in the flexible guide 1, one end of the flexible guide 1 is plugged into a housing on the winch 23 on to which the draw cable will be wound, and the other end of the flexible cable is plugged into a similar housing on a cabling stand 24 located over a manhole 25 into which the draw cable passes.

The draw cable passes over a top turning wheel 26 mounted on the cabling stand 24 to change the lie of the draw cable from a generally horizontal attitude to a generally vertical attitude.

When a pull is exerted on the draw cable 21 by the winch, the equal and opposite reaction on the winch is transmitted to the flexible guide 1 by virtue of its attachment to the winch frame, and the reaction is transmitted along the flexible guide 1 to the cabling stand 24 to push it in a direction opposite to the pull of the draw cable with an equal force to the tension in the draw cable with an equal force to the tension in the draw cable. The resuit is that the only force exerted by the draw cable 21 on the cabling stand 24 is a downward force and there is no resultant force on the cable winch 23 and the vehicle on which it is mounted.

Use of the cable sheath may also be applied to the taking-up and stowage part of a cable-pulling operation. The use of the cable sheath in the taking-up and stowage part of the operation is achieved by having the winch arranged as two separate units so as to separate the pulling capstan or bull wheels from the take-up reel, positioning the pulling capstan or bull wheels near the rear of the vehicle for best pulling effect, and positioning the take-up reel at the most convenient cable stowage position. A separate take-up sheath is then used to transfer the cable from the pulling capstan or bull wheels at low tension to the take-up reel. There is no need to mount the reels rigidly with respect to each other since the use of the cable sheath affects reactioncancellation.

Claims (4)

1. A method of drawing a supply cable or the like through a duct by means of a draw cable and winch, including the use of a flexible incompressible support adapted to fit on to the draw cable and so arranged in the vicinity of the winch that, in operation, an equal and opposite force to the tension of the draw cable is applied to the winch by the flexible support.

2. A method of drawing a supply cable or the like through a duct, as claimed in claim 1, including the use of a flexible incompressible sheath adapted to fit around the draw cable and arranged to be attached to the winch frame and to a prop located at a point along the draw cable.

3. A flexible support for a draw cable or the like, the support having a longitudinal tunnel adapted to accommodate the draw cable without gripping it, and including a plurality of vertebra-like members arranged to resist compression and a terminating member at each end.

4. A flexible support for a draw cable or the like, as claimed in claim 3, wherein the vertebra-like members are a plurality of metal bobbins with complementary hemispherical end faces, and the flexible support includes a length of flexible hose enclosing the vertebra-like members.