Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Advancing subterranean length of pipe or cable
Reexamination Certificate
2003-04-11
2004-11-30
Shackelford, Heather (Department: 3673)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Advancing subterranean length of pipe or cable
C254S13430R
Reexamination Certificate
active
06824329
ABSTRACT:
A. BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in the field of providing tubular elements generally indicated as ducts, such as e.g. for guiding and protecting cables in the ground. More particularly, it relates to a method and an apparatus for installing a duct around a longitudinal member.
2. Prior Art
A method of the above kind is known from U.S. Pat. No. 5,639,183. The known method is intended for installing a tubular cable-duct around a cable buried in the ground. The method includes steps of freeing a portion of the buried cable from the ground in a forward longitudinal direction of the cable, starting from a free end of the buried cable, and advancing a foremost end and subsequent portions of the cable-duct in the forward longitudinal direction of the cable over the portion of the cable freed from the ground, starting from the free end of the cable. The advancing of the duct is achieved by exerting pulling forces on the free end of the cable by means of a pulling wire passed through the duct via a rearmost end thereof, in combination with the exertion of pushing forces at the rearmost end of the duct. Simultaneously a liquid under pressure may be applied as a kind of drilling liquid, which is fed through the duct from the rearmost to the foremost end of the duct, and which flows out at the foremost end for locally freeing the cable from ground. In this manner, a duct, or a duct consisting of several coupled segments, may be installed underground over a great distance along an existing cable, without much excavation work being required for said purpose. After having been installed, the cable, if so desired, may be pulled out of the duct. An advantage of the known method is that curvy sections are easy to follow, without expensive positioning equipment. Disadvantages, however, are that the duct or duct segment which can be installed in one operation is rather limited in length, and that during operation at first the duct or duct segment has to be laid out above ground in its full length and be provided with a pulling wire of at least the same length. The latter, moreover, makes an installation of a duct directly from a reel, on which it generally will be delivered, impossible. Particularly this aspect makes preparation of the installation process very laborious. Furthermore, a well-sealing T-piece, which is required at the rearmost end of the duct for feeding the liquid under pressure together with passing the pulling wire into the duct, is technically quite troublesome, and in practice will lead to spill of liquid. Finally the known method uses a static pushing force at the rearmost end of the duct(segment). However a considerable part of the pushing force is needed for pushing aside the ground in front of the foremost end of the duct. Since the pushing force available at the foremost end of the duct depends on the loss of force through friction over the length of the duct, the total length of the duct which can be installed with the known method is limited also for this reason.
B. SUMMARY OF THE INVENTION
An object of the invention is to provide a method and an apparatus with which a duct can be installed in the ground, in which the disadvantages of the known techniques discussed above do not occur.
According to a first aspect a method is provided of the kind as indicated above, comprising a step of propelling the duct over a free end and further portions of the longitudinal member. The step of propelling can include, according to this aspect of the invention, a substep of pushing the duct by pushing means which engage locally on and at least partly around an outer surface of the duct in the neighbourhood of, optionally at least at a short distance from the free end of the longitudinal member inside the duct, and a substep of maintaining the free end of the longitudinal member in a substantially fixed position with respect to the pushing means using magnetic means. The magnetic means and the pushing means may be coupled either mechanically or via terra firma, or both. Preferably the magnetic means are electromagnetic means, which preferably include a core member and a solenoid means. A foremost end of the duct is led through the solenoid means. The core member is coupled to the free end of the longitudinal member and then inserted into the foremost end of the duct. Then the duct is pushed further through the solenoid means by the pushing means, and the solenoid means are driven by a current in such a manner that the core member is retained within the attractive range of influence of the solenoid means. In dependency of the kind of magnetic material of the core member the solenoid means may be driven by a direct current or a periodically varying current such as a common alternating current, or any combination thereof, and preferably in a controllable manner. The step of pushing may be carried out by rotating transport means such as caterpillar means. In special cases such as the case in which the longitudinal member is buried in the ground, the method preferably comprises an additional step of feeding a fluid under pressure through the duct, from a rearmost end to the foremost end of the duct, in order to support die propelling step. The duct is preferably supplied from a reel.
According to a second aspect of the invention an apparatus is provided of the kind as indicated above, comprising a duct propelling device which includes pulling means provided with coupling means for a tension-proof coupling to a free end of the longitudinal member, and pushing means for pushing the duct over the free end and further portions of the longitudinal member. The duct propelling device can include, according to the second aspect of the invention, a common housing provided with a duct transit channel. The pulling means include magnetic means provided with a duct transit channel surrounding part and a corresponding core member, preferably a solenoid means and a corresponding core member of a magnetic material, respectively. The pushing means include duct transporting means. The solenoid means and the transporting means have been arranged in the common housing around sections of the duct transit channel. The core member has been provided with coupling means for coupling to the free end of the longitudinal member, and the solenoid means have been arranged for being driven by a current in such a way that during operation the free end of the longitudinal member coupled to the core member is maintainable in a substantially fixed position with respect to the transporting means. In dependency of the kind of magnetic material of the core member the solenoid means have been arranged for being driven by a direct current or a periodically varying current such as a common alternating current, and preferably in a controllable manner. The pushing may be rotating transport means such as caterpillar means. In special cases such as the case in which the longitudinal member is buried in the ground, the apparatus preferably comprises additionally means for feeding a fluid under pressure through the duct, from a rearmost end to the foremost end of the duct, in order to support the operation of the propelling device.
A further object of the invention is to provide a method, with which the propelling step, and preferably also the step of feeding the fluid under pressure are carried out in a more dynamical way, instead of the static way of the known installation technique. In that especially the electromagnetic means are applied advantageously.
According to a third aspect of the invention a method is provided in which the solenoid means are driven by a periodically varying current in such a manner that the core member is alternately attracted and not, at least less strong attracted by the solenoid means. Preferably the core member is of a permanent magnetic material, and the solenoid means are driven by a varying current having a periodically inverting polarity, in such a manner that the core member is periodically attracted and repelled by the solenoid means. In a further preferred
Plumettaz Gerard
Van Bijsterveld Cornelis Casparus
Koninklijke KPN N.V.
Michaelson Peter L.
Michaelson & Associates
Saldano Lisa M
Shackelford Heather
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