Pulling element for installing a cable in a duct and ducting system comprising such pulling element

Abstract: For the purpose of installing, by means of compressed air, cables in a ducting system comprising successively first ducts and second ducts with a different, greater diameter, the invention provides a pulling element with a body of which an end can be connected to a cable to be installed, which body consists at least of a first part which is provided with flexible members suitable for sealing engagement with the inner wall of the first duct, which first part is provided at the other end with a coupling member, and a second part, comprising a central longitudinal opening, flexible members provided on the second part, which are suitable for sealing engagement with the inner wall of the second duct, and coupling means capable of cooperating with the coupling member of the first part so as to couple the two parts when the first part reaches the transition between the first and the second duct.

Description: This invention relates to a pulling element with a body having an end which is connectable to a cable to be installed in a duct and having another end, the body being provided round about with flexible members intended for sealing engagement with the inner wall of such a duct. Such a pulling element for the purpose of installing cables, in particular telecommunication cables, in a duct is known from British patent application 2,152,621. In the method described in that application, a reduced pressure is created at one end of the duct, and the pulling element having attached thereto the cable or a leader for a cable to be installed is inserted into the duct at the other end thereof. As a result of the pressure difference created, the pulling element is displaced through the duct and thus the cable or the leader is installed in the duct. In the known pulling element, the flexible members serve to ensure that also when the diameter of the duct varies, the flexible members are in engagement with the inner wall of the duct at all times, because otherwise the reduced pressure at the front of the pulling element would have no effect or too little effect. Variation in the diameter of the duct can occur not only with a duct having an irregular inner diameter, but also at the transition from a duct with a first diameter to a duct with a second, different diameter. A drawback of the known pulling element is that the diameter variations that can be accommodated with it are relatively small, because these are determined by the maximum travel of coil springs. Accordingly, the object of the invention is to provide a pulling element suitable for use in a ducting system in which duct diameters can differ greatly and in which the installation proceeds from a duct or ducts with a first inner diameter into ducts with a second, greater inner diameter, and optionally even into ducts with a still greater inner diameter. To that end, the invention provides a pulling element of the above-mentioned type, characterized in that the body of the pulling element consists at least of a first part, which is provided with flexible members suitable for engagement with the inner wall of a duct with a first inner diameter, which first part is provided at the other end with a coupling member, and a second part, comprising a central longitudinal opening, flexible members provided on the second part, which are suitable for engagement with the inner wall of a duct with a second inner diameter, which is greater than the first inner diameter, and coupling means capable of cooperating with the coupling member of the first part so as to actively couple the two parts when the first part of the body of the pulling element, during the installation of a cable, comes within the proximity of the second part of the body of the pulling element. According to the invention, a coupling between the first and the second part of the pulling element can be effected in a mechanical manner or by means of magnetic force. The invention is based on the insight that for an optimum installation of cables in ducts with different inner diameters increasing in the installing direction, it is advantageous to build up the pulling element from two or more parts each optimally adapted to the inner diameter of the relevant duct, whereby the first part of the pulling element, after the installation of a cable in the duct or ducts with the first diameter, couples with the second part of the pulling element, which is ready at the beginning of the length of duct having the second, greater diameter. The second part of the pulling element can be placed at the beginning of the length of duct with the second diameter at the time when the installation of the cable is to take place, for instance by detaching at that point the coupling piece connecting the duct with the first diameter to the duct with the second diameter. Preferably, however, the second part of the pulling element is already fitted at the location of the coupling between a duct with a first diameter and a duct with a second diameter when the ducting system is being installed or completed, so that installation can subsequently take place without further digging work and the like. It is noted that JP-A-5260622 discloses a pulling element for a cable, which consists of a body with a first part and a second part, which parts are permanently coupled to each other. The first and the second part are provided with flexible members which are expandable under fluid pressure, which members are in engagement with the inner wall of the duct in which the cable is installed. The first part of the body comprises a piston and the second part a hydraulic cylinder, so that the first part can be moved relative to the second part. By alternately expanding the flexible members and clamping them against the duct wall and extending or retracting the piston relative to the cylinder, the pulling element can be moved through the duct by small steps, which is particularly favourable when installing cables in a vertical duct. This publication does not mention a pulling element with two parts that are separate until the moment of coupling during operation, nor any successive ducts with different diameters. Accordingly, according to a second aspect, the invention relates to a ducting system for cables, in particular telecommunication cables, consisting of a first length of duct with a first diameter and a second length of duct with a second, greater diameter, there being provided a coupling piece for connecting the end of the first length of duct to the beginning of the second length of duct, characterized in that in the coupling piece or in the initial portion of the second length of duct a pulling element is arranged, comprising a body with a longitudinal opening, flexible members attached to the body, which are in engagement with the portion of the inner wall of the coupling piece that has substantially the same diameter as the second length of duct or with the inner wall of the second length of duct itself, and coupling means arranged on the end of the body proximal to the first length of duct. According to a third aspect, the invention relates to a coupling piece for coupling a duct with a first diameter and a duct with a second, greater diameter, there being provided in the portion of the coupling piece intended for receiving the duct with the second diameter a pulling element comprising a body with a longitudinal opening, flexible members attached to the body, which are in engagement with the portion of the inner wall of the coupling piece that has substantially the same dimension as the inner diameter of the second duct, and coupling means which are arranged on the end of the body proximal to the portion of the coupling piece intended for receiving the first duct. In the following, the invention will be further described on the basis of an exemplary embodiment, with reference to the drawing, wherein: Fig. 1 is a cross section of a first embodiment of the pulling element according to the invention, placed in a coupling piece connecting two ducts of different diameters; Fig. 2 is a similar cross section to Fig. 1, but now of a second embodiment of the pulling element; and Fig. 3 is a similar cross section to Fig. 1, but now of a third embodiment of the pulling element. In the figures, equal parts are denoted by equal reference numerals. Figs. 1, 2 and 3 show an end portion of a first duct 1, which forms part of a first length of duct with a first inner diameter d, and an initial portion of a second duct 2, which forms part of a second length of duct with a second inner diameter D, with D > d. The end portion of duct 1 and the initial portion of duct 2 are coupled by means of a coupling piece 3, which at one end has an inner diameter substantially equal to the outer diameter d + 2w of the duct 1, and at the other end has an inner diameter substantially equal to the outer diameter D + 2W of the duct 2, where w is the wall thickness of the duct 1 and W is the wall thickness of the duct 2. For the purpose of a proper airtight and moisture-proof joint with the ducts 1 and 2, O-rings 4 and 5, respectively, are provided on the inside of the coupling piece 3. Reference numeral 6 denotes an end of a cable, in particular a telecommunication cable, and more particularly a telecommunication cable with optical glass fibers, to be installed in a ducting system of which ducts 1 and 2 form a part. The end 6 is connected to the body 8 of a pulling element 7 so as to be resistant to tensile strain. The body, in a manner known per se, is provided with flexible members 9 in some form, which abut against the inner wall of the duct 1, in order that if a source of fluid under pressure, for instance a source of compressed air, is connected to the other end, not shown, of duct 1, the pulling element 7 is propelled through the duct as a result of the pressure of the fluid. Such a pulling element 7 is generally known from, for instance, EP-A-0,445,858 and can be completely closed in cross section but can also be provided with openings through which a part of the fluid can pass, as explained in the aforementioned European patent application. According to the invention, the pulling element 7 constitutes a first part of a pulling element consisting of two parts, and the forward end - viewed in the direction of insertion of the cable end 6 - of the body 8 of the pulling element part 7 is provided with a coupling member 10. In the exemplary embodiment according to Fig. 1, the coupling member consists of a part of a magnetic coupling, and in the embodiment according to Figs. 2 and 3 it consists of a part of a mechanical coupling. Further, according to the invention, in the portion of the coupling piece 3 connecting to the initial portion of the duct 2, a second pulling element part 11 is arranged, with a body 12 and flexible members 13, which abut against the inner wall of the duct 2 and fulfil the same function as the flexible members 9 of the pulling element part 7 in the duct 1. The body 12 is provided with coupling means 14 capable of cooperating with the coupling member 10 at the end of the pulling element part 7. In Fig. 1 the coupling member 10 is an element of ferromagnetic material or a magnetic element and the coupling means 14 consist of a magnetic element or a ferromagnetic material, at least one of the elements 10 and 14 being a magnetic element. The element 14 and the body 12 of the pulling element part 11 have a central opening. For an airtight joint between the elements 10 and 14, the element 14 can be provided with a recess 14', into which element 10 fits, and optionally with a rubber O-ring 15 to optimize the seal. In Fig. 2 the coupling member 10 consists of an extension 8' of the body 8, which fits within the coupling means 14, which consist of the central opening in the body 12 of the pulling element part 11. To couple the two pulling element parts 7 and 11 permanently, the end 8' is provided with a hook 10', of such length that the hook-shaped end 10'' of the hook 10' projects beyond the forward end of the opening in the body 12 of the pulling element part 11 when the body 8 of the pulling element part 7 rests against the proximal end of the body 12 of the pulling element part 11. For a good seal between the element 11 and the central opening, this last can be provided with an O-ring 16. In Fig. 3 the coupling member 10 consists of an extension of the body 8 of the pulling element part 7, having at the end thereof a barb in the form of a flexible member 10', for instance a rubber disc, which closes off the central opening as it passes therethrough and, after passing therethrough, forms a stop at the forward end of the body 12, which stop seals the central opening 14 as soon as the compressed air pressure strikes the second pulling element part. When inserting a cable into a ducting system consisting (inter alia) of the ducts 1 and 2, as described, for instance a source of compressed air is connected to the end of the duct 1 that is not shown, so that the pulling element part 7, as a result of the compressed air pressure, is moved through the duct 1 and thus installs the cable end 6 and hence a cable in the duct. The air cushion that is built up in front of the pulling element part 7 can escape via the central opening in the body 12 of the pulling element part 11. When the pulling element part 7 reaches the end of duct 1, the coupling member 10 engages the coupling means 14, whereby either a magnetic coupling or a mechanical coupling between the two pulling element parts is produced, and the central opening 19 in the body 12 is closed off, so that the pulling element part 11 can take over the function of the pulling element part 7 to guide the cable end 6 through the duct 2. To avoid the pulling element part 11 leaving its position prematurely, that is, before the coupling has been realized, it is possible to provide on the inside of the coupling piece 3 a cam-shaped ridge 17 which can only be passed by the flexible members 13 as a result of the air pressure built up after the coupling. In the embodiment according to Fig. 3, to avoid the pulling element part 11 being displaced too early as a result of the flexible member 10' closing off the central opening of the body, that is, before the coupling has been effected, the coupling should be completed before the pulling element part 7 leaves the duct 1 and the air pressure strikes the pulling element part 11. To that end, the pulling element part 11 can, for instance, be placed against a cam-shaped ridge 18 on the inside of the coupling piece. Finally, it is noted that the body 12 of the second pulling element part can be provided with an air passage in such a manner that it is maintained also after the coupling with the first part, thereby to realize for the second portion of the length of duct a semi-open pulling element with the advantages described in EP-A-0,445,858. As described, the pulling element according to the invention is particularly suitable for use in installing cables in ducting lines comprising ducts with more than one duct diameter, increasing in the installing direction. Such transitions from a first duct diameter to a second, greater duct diameter can, for instance, occur between two different sections of a telecommunications network, for instance because one section was laid at a later time than the other section. With the passage of time, often smaller duct diameters are installed because: a need arises for a greater concentration of cores in the network to be installed; the cable diameters become smaller, for instance due to the transition from copper cable to glass fiber cable; improvements in the art enable an increasingly higher degree of miniaturization. It will be clear to those skilled in the art that within the scope of the invention different variations of the pulling element parts 7 and 11, which likewise embody the concept underlying the invention, are possible. In addition, it will be clear that the pulling element can consist of more than two parts, each having a cross section adapted to a specific duct diameter, thereby enabling a cable to be installed by means of air pressure in a ducting line comprising ducts having more than two different, successively greater duct diameters.

Claims: A pulling element (7, 11) with a body (8, 12) having an end which is connectable to a cable (6) to be installed in a duct and having another end, the body being provided round about with flexible members (9, 13) intended for sealing engagement with the inner wall of such a duct, characterized in that the body of the pulling element consists at least of a first part, which is provided with flexible members (9) suitable for engagement with the inner wall of a duct (1) with a first inner diameter (d), which first part is provided at the other end with a coupling member (10), and a second part, comprising a central longitudinal opening (19), flexible members (13) provided on the second part, which are suitable for engagement with the inner wall of a duct (2) with a second inner diameter (D), which is greater than the first inner diameter, and coupling means (14) capable of cooperating with the coupling member (10) of the first part so as to actively couple the two parts when the first part of the body (8) of the pulling element, during the installation of a cable (6), comes within the proximity of the second part of the body (12) of the pulling element. A pulling element according to claim 1, characterized in that the coupling member (10) and the coupling means (14) form a magnetic coupling. A pulling element according to claim 2, characterized in that the coupling member (10) consists of a ferromagnetic material or of magnetic material and that the coupling means (14) likewise consist of a ferromagnetic or of a magnetic material, at least one of the two consisting of a magnetic material. A pulling element according to claim 1, characterized in that the coupling member (10) and the coupling means (14) form a mechanical coupling. A pulling element according to claim 4, characterized in that the coupling member (10) consists of a hook-shaped extension (10") of the body (8) of the first part of the pulling element, which upon coupling engages via the opening (19) in the body (12) of the second part of the pulling element the forward end thereof. A pulling element according to claim 4, characterized in that the coupling member (10) consists of an extension of the body (8) of the first part of the pulling element, having at the end thereof a flexible disc-shaped member (10') which upon coupling engages via the opening (19) in the body (12) of the second part of the pulling element the forward end thereof. A pulling element according to any one of claims 1-6, characterized in that means (14', 16) are provided for airtightly sealing the coupling after it has been effected. A pulling element according to any one of claims 1-6, characterized in that the first part of the body of the pulling element is provided with a longitudinal opening. A pulling element according to any one of claims 1-6, characterized in that means are arranged for providing in the pulling element an air passage when the first part and the second part of the body are coupled. A ducting system for cables, in particular telecommunication cables, consisting of a first length of duct (1) with a first diameter (d) and a second length of duct (2) with a second, greater diameter (D), there being provided a coupling piece (3) for connecting the end of the first length of duct to the beginning of the second length of duct (2), characterized in that in the coupling piece (3) or in the initial portion of the second length of duct a pulling element (7, 11) is arranged, comprising a body (12) with a longitudinal opening (19), flexible members (13) attached to the body, which are in engagement with the portion of the inner wall of the coupling piece (3) that has substantially the same diameter as the second length of duct (2) or with the inner wall of the second length of duct (2) itself, and coupling means (14) arranged on the end of the body (12) proximal to the first length of duct (1). A coupling piece (3) for coupling a duct (1) with a first diameter (d) and a duct (2) with a second, greater diameter (D), there being provided in the portion of the coupling piece (3) intended for receiving the duct (2) with the second diameter a pulling element (7, 11) comprising a body (12) with a longitudinal opening (19), flexible members (13) attached to the body (12), which are in engagement with the portion of the inner wall of the coupling piece (3) that has substantially the same dimension as the inner diameter of the second duct (2), and coupling means (14) which are arranged on the end of the body proximal to the portion of the coupling piece (3) that is intended for receiving the first duct (1).

Inventors: GRIFFIOEN WILLEM, GRIFFIOEN, WILLEM
Applicants: KONINKL KPN NV, KONINKLIJKE KPN N.V.
Application year: 1997
Main classification: H02G1
IPC codes: F16L1, G02B6, H02G1