Pipes and tubular conduits – Combined
Patent
1990-12-19
1994-10-25
Bryant, III, James E.
Pipes and tubular conduits
Combined
138110, 138137, 138140, 138177, 138178, 174121A, 385109, 428913, 428921, F16L 5700
Patent
active
053580117
DESCRIPTION:
BRIEF SUMMARY
This invention relates to transmission lines and especially to the ducts in which transmission lines are installed.
Transmission lines are generally installed in ducts both for in-building and external locations. These ducts serve to protect the lines and to route a plurality of lines in an ordered manner. In the case of optical fibre transmission line packages these can be installed in the duct by a process known as fibre blowing in which the package is advanced through the duct by a fluid such as compressed gas. Currently it is customary to provide ducts suitable for blown installations in bundles of seven, with six ducts disposed around a central seventh duct, and for an outer casing to be provided over the bundle. Each duct usually houses a single optical fibre transmission line package. In the event that fewer than seven of the ducts are required they remain empty or a smaller bundle of ducts is provided. Bundles of 1, 2, 4, or 19 ducts are also available. If it is necessary to connect one, or some, of the lines from a bundle to a branch it is necessary to break the outer sheathing and locate the correct duct, which may not always be easily accessible if it is in the middle or far side of the bundle. The breakage of the outer casing can also create problems if it provides fire protection because it is then necessary to reconnect a suitable fire resistant sheathing in the area of the breakout. In practice this means that a breakout connection assembly is required. In order to achieve maximum distances along which fibre package can be blown it is necessary to have a duct that exhibits satisfactory characteristics in terms of internal surface finish and elasticity. For blowing performance slip enhanced medium density polyethylene (MDPE) is preferred although high density polyethylene (HDPE) may also be used. In some instances assemblies such as a bundle of seven ducts are too stiff especially when HDPE is used and also some grades of HDPE suffer from environmental stress cracking and thus are unsatisfactory alone for long term installations.
The present invention is directed towards providing an alternative duct assembly.
Accordingly the present invention provides a duct assembly for transmission lines comprising a tubular member having an inner layer of a material having a suitable inner surface for fibre blowing installation and an outer fire retardant layer.
Preferably the assembly comprises a plurality of said tubular members disposed side by side and longitudinally interconnected by webs to form a ribbon.
A second aspect of the invention provides a duct assembly for transmission lines comprising a plurality of tubular members each tubular member being longitudinally joined to at least one other of the tubular members.
In a preferred embodiment the tubular members each comprise inner and outer layers, and the members are joined by webs formed integrally with the outer layer.
Preferably the outer layer comprises a fire retardant material known as Megolon and the inner layer comprises high density polyethylene, carbon doped high density polyethylene, slip enhanced medium density polyethylene or polyether imide.
A further aspect of the invention provides a method of making a transmission line duct, the method comprising forming an inner layer and extruding an outer layer over the inner layer.
The inner and outer layers may be coextruded or the outer layer may be serially extruded over a previously formed inner layer, preferably in in a single process.
The invention is now described by way of example with reference to the accompanying drawings in which:
FIG. 1 is an isometric view of a preferred embodiment of the invention;
FIG. 2 is a cross sectional view of the embodiment of FIG. 1, and
FIG. 3 is an isometric view illustrating a breakout arrangement with an embodiment of the invention.
Referring to the drawings a preferred embodiment is shown in which four individual ducts 1 are formed interconnected in a web or ribbon in a single extrusion process. The number and size of the ducts 1 and their spacing
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Barker Philip A.
Bates Roger J.
Cook Clifford F.
Stockton David J.
British Telecommunications public limited company
Bryant III James E.
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