Pig for installing a cable in a conduit

A pig for installing a cable in a conduit, in which it comprises a body and a seal intended to follow the internal surface of the conduit, the body comprising a radially elastic tubular part on which the seal is mounted, and a support part fixed to or integral with the tubular part, the support part having a guide surface intended to guide the pig in the conduit, the diameter of the guide surface being slightly less than the maximum diameter of the seal, so that the support part radially deforms the tubular part when the pig passes through deformed parts of the conduit.

BACKGROUND OF THE INVENTION

The present invention relates to the technical field of cable installations, for example optical fibre or electrical, inside buried and/or submerged installation conduits. The term “cables” must also be taken to mean tubes or the like for conveying power, fluids and electrical, light or other signals. The term “cable” also concerns low, medium and high power electrical cables, single or three-phase.

Various methods are known for installing cables within conduits. These methods are defined below.

“Pulling” means that the cable is attached by its end to a sling already installed in the conduit. This sling is attached to the drum of a winch which winds the latter and enables the cable to be installed in the conduit, by sliding the cable within the said conduit.

“Pulling-pushing” means simultaneous drawing and pushing with the use of means for pushing the cable at its entry into the conduit, in order to reduce the traction forces on the cable head and to increase the installation distance. Means of driving the cable towards the half-way mark can also be provided.

“Blowing” means that the installation conduit is put under pressure, by means of a fluid, between the cable supply means and a fluidtight pig attached to the head of the cable. The pressure prevailing inside the conduit thus moves the pig, pulling on the cable head. The pressurisation is generally effected with air.

“Blowing-pushing” means the use of means for pushing the cable at its entry into the conduit, associated with the means used in the so-called “blowing” method. There also, an increase in the cable installation distance is obtained.

“Floating-pushing” and/or “carrying-pushing” means a technique in which a fluid, generally air or water, is injected into the conduit at a speed greater than the speed of movement of the cable, and it is the friction of the fluid on the external sheath of the cable which exerts the traction force. In this installation technique, the static pressure of the air or of the liquid inside the conduit has the effect of pushing the cable out of the conduit.

In certain “pulling-pushing” techniques, water is also injected into the conduit. The traction force comes from a pig fixed to the head end of the cable on which the pressure of water injected into the conduit is exerted. For this purpose, the pig is provided with one or more seals.

One of the advantages of the techniques of injecting water or other liquids is the reduction of the bearing force of the cable against the internal wall of the conduit due to the buoyancy and consequently the friction forces. The installation distance is however limited by the maximum permissible water pressure, which is determined by the maximum pressure which can be applied to the pig.

Because of the radii of curvature in the conduit, and the deformation in an oval shape of the profiles of the conduits, existing pigs are provided with a juxtaposed series of flexible rubber lips in a conical shape or in the form of disks. These flexible lips have the great disadvantage of not withstanding a very high pressure not normally exceeding a few bar, so that the pulling force of the pig is relatively limited.

In the light of these drawbacks, one aim of the invention is to provide a pig for installing cables in conduits which makes it possible to increase the cable installation distance, that is to say the length of the cable which can be inserted in a conduit.

It is advantageous to provide a cable installation pig able to be used in installation techniques in which a liquid, for example water, is injected into the cable conduit.

It is also advantageous to provide a pig for installing cables in a conduit which is reliable and economical and which reduces or even eliminates leakages of liquid.

It is advantageous to provide a cable installation pig which can also be used for extracting a cable from a conduit.

Aims of the invention are achieved by a pig for installing cables.

SUMMARY OF THE INVENTION

In the present invention, a pig for installing a cable in a conduit comprises a body and a seal intended to follow the internal surface of the conduit, the body comprising a radially elastic tubular part on which the seal is mounted, and a support part fixed to or integral with the tubular part, the support part having a guide surface intended to guide the pig in the conduit, the diameter of the guide surface being slightly less than the maximum diameter of the seal, so that the support part radially deforms the tubular part when the pig passes through deformed parts of the conduit. The support part also acts as an axial support for the seal.

Advantageously, the fact that the axial support of the seal has a diameter approaching an outside diameter of the seal makes it possible to avoid problems of reversal of the lips of the seal and therefore to withstand higher pressures, whilst allowing radial deformation of the seal, by mounting it on an elastic tubular part which adapts to the deformations of the conduit through the support parts.

The support parts can be in the form of teeth extending radially from the tubular part of the body. These parts can be formed integrally with the body from a material offering low drag coefficients, such as certain plastics of the POM, nylon or Teflon type. The body can also comprise a radial wall partially or completely closing off one end of the tubular part, this wall serving on the one hand to stabilise the body and on the other hand to block the transfer of fluids. In order to limit the hydrostatic pressure within the body, a calibrated valve in the form of a pressure reducer can be mounted in the body, in particular in the radial wall. Advantageously, one or more radial orifices for injecting a certain quantity of water downstream of the seal are formed in the body in order to lubricate and cool the lip of the seal.

It is advantageously possible to mount two or more bodies in axial tandem so as to avoid pressure drops when there are irregularities in the conduit, for example when passing a coupling between two conduit ends.

In such a configuration, radial orifices in communication with the pressure reducer are disposed between two seals, which makes it possible to distribute the pressure between the successive seals as well as the differential pressure between the inside of the tubular part of the body and the outside. Assembling several bodies and corresponding seals also makes it possible to withstand higher water injection pressures in the conduit and therefore to increase the installation distance.

Guidance elements can be mounted at each axial end of the body or of the plurality of bodies, the whole for example fixed by fixing means comprising for example a central fixing spindle to which it is also possible to fix a ring or hook or other attachment element for attaching the end of the cable head.

The guidance elements can advantageously be provided with elastic elements, such as elastic fingers disposed on the periphery of the element, for the purpose of adapting to the deformation of the conduit.

The guidance element at the head can advantageously be provided with a conical or essentially conical receptacle for positioning it on the cable ferrule when the pig is used for extracting the cable from a conduit.

Several pigs comprise at least a body, a seal, a guide means and a pressure reducer and can be coupled by articulated fixing means.

Other advantageous characteristics and aspects of the invention will also emerge from the detailed description given below, with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures, more particularly toFIGS. 1 to 3, a pig for installing a cable in a conduit comprises a body2, a seal3, front and rear guidance elements4,5, means6of fixing the various parts of the pig, and an attachment member7for attaching the pig to one end of a cable to be installed in a conduit. A ferrule (not shown) is mounted on the end of the cable, the ferrule comprising a complementary attachment member.

The body2comprises a radially elastic tubular part9, a radial walled part10at least partially closing off one end of the tubular part9, with the exception of the passages for the fixing means6as well as orifices and cavities for receiving a valve or a pressure reducer. The wall part10on the one hand separates the internal cavity11of the body from the outside12and on the other hand stabilises and stiffens the body and enables it to be connected to other bodies and/or to the guidance elements4,5. The tubular part is, in this embodiment, essentially in the form of a hollow cylinder having a relatively thin wall in order to be radially elastic for reasons which will be understood better in the following description.

The body2also comprises a rigid support part13which extends from the tubular part9and which serves as an axial support for the seal3. In this embodiment, the seal support part13is in the form of teeth extending so as to be integral with the tube part9in a radial direction, and provided with a peripheral guide surface14having a diameter slightly less than the diameter of the conduit in which the pig is intended to be inserted, and therefore slightly less than the maximum diameter of the seal3.

The guide surface14therefore serves on the one hand to centre and guide the pig and in particular the seal13on the pig in the conduit and on the other hand to form a rigid axial support for the seal which is preferably a lip seal, for example in the shape of a V, in order to withstand high pressures. When passing a deformed part of a conduit8, as shown inFIG. 2, the peripheral guide surfaces14of the seal support parts13come into abutment against the internal surface of the conduit where the diameter is reduced and elastically deform the part of the tube9on which they are mounted. The peripheral guide surface14is preferably made from a material having a low coefficient of friction in order to reduce the friction forces acting on the pig.

When the tubular part9deforms, the seal3mounted on the tubular part follows the deformation and provides a good seal between the internal surface of the conduit and the body. This design makes it possible in particular to use a seal, such as a lip seal, adapted to high-pressure uses, for example pressures of around35bar, which will substantially increase the length of the cable which can be inserted in a conduit.

In order to lubricate and cool the lips15of the seal3, small radial orifices16pass through the tubular part9and/or the seal support parts14, thus forming a passage for the water from the internal cavity11to the external space12of the body. The number and diameter of the orifices, for example 4 to 8 in number on the periphery of the body, are adapted to supply sufficient water for cooling and lubrication of the joint without for all that causing a significant pressure drop. It is also possible to supply the cooling and lubrication water for the seals3through a valve or pressure reducer18, for example mounted in a cavity in the wall part10of the body, this pressure reducer18having an inlet communicating with the internal cavity11of the body and an outlet17communicating with the external space12. Where the pressure reducer16is mounted between two seals3,3′ on respective bodies2,2′, as shown inFIG. 3orFIG. 6, it serves to reduce the differential pressure between the external space12,12′,12″ and the internal cavity11,11′,11″ of the bodies. This makes it possible in particular to distribute the thrust load on the two seals3,3′,3″.

In the embodiment inFIG. 3, the bodies3′,3are essentially identical, but it is possible to mount bodies in opposition as shown inFIG. 6, where the radial walls10′,10′ of the bodies2′ and respectively2″ are pressed against one another.

The mounting in opposition according to the embodiment inFIG. 6makes it possible to increase the distance between the seals3′,3″ and the support parts13′,13″, which can improve the guidance as well as the impermeability of the pig seals.

The pig fixing means6can comprise a central spindle19disposed along the central axis of the pig and axially compressing the front and rear guidance elements4,5as well as the bodies2,2′,2″ through sleeves20mounted coaxially around the central spindle19. The sleeves20serve to ensure that the open end21,21′,21″ of the tubular part of the body9is free so as to allow its elastic movement. The length of the sleeves20is therefore designed so as to leave a certain clearance between the open end21,21′,21″ of the tubular part and the adjacent element, that is to say an end guidance element4,5or the wall10′ of the adjacent body.

The front and rear guidance elements4,5are advantageously provided with elastic fingers22disposed on the periphery and being slightly inclined in order to give an essentially conical shape to the guidance elements. The elastic fingers22on the one hand centre the pig in the conduit and on the other hand prevent the pig from becoming attached to the inside of the conduit, in particular with irregularities or discontinuities due for example to the connection of ends of the conduit or to a damaged surface. The elastic fingers also enable the guidance elements to adapt to the internal profile of the conduit.

The front guidance element4is advantageously provided with a receptacle with an essentially conical shape or having another splayed shape on its front face in order to house and centre a ferrule mounted on a cable which is to be extracted from a conduit. The pig can thus not only be used for pulling a cable when it is installed in a conduit but also for pushing a cable when it is extracted from a conduit. The centring of the cable ferrule in the splayed front face23of the guidance element prevents problems of jamming of the pig in the conduit, in particular when taking bends in the conduit.