GB2425365A

GB2425365A - Seal for cable gland assembly and tool therefor

Info

Publication number: GB2425365A
Application number: GB0508232A
Authority: GB
Inventors: John Robert Scott Conway
Original assignee: BRITISH ENGINES Ltd
Current assignee: BRITISH ENGINES Ltd
Priority date: 2005-04-23
Filing date: 2005-04-23
Publication date: 2006-10-25
Also published as: GB0508232D0; WO2006114587A1

Abstract

A seal 52, for a cable gland assembly particularly for use with cables carrying optical fibres, has a first sealing part 58 adapted to seal around a first portion of one or more cables. The first sealing part has a first displacement part 62 for applying an inwardly directed displacement force to at least part of the first portion of the cables. The seal also includes a second sealing part 60 adapted to seal around a second portion of the or each cable. The seal further includes an abutment surface 74 extending between said first and second sealing parts, the abutment surface being adapted to engage a junction between the first and second portions. A tool 120, for assisting in the locating of a gland assembly seal onto a cable with a plurality of internal sheaths, comprises a base portion 122 and a plurality of pins 124 therein matching the arrangement of internal sheaths within an external sheath of the cable.

Description

CABLE GLAND ASSEMBLY AND SEAL THEREFOR

The present invention relates to a cable glad assembly and to a seal for a cable gland assembly and relates particularly, but not exclusively, to a cable gland and seal for use with optical fibre cable ducts. The invention also relates to a too] for assisting in the installation of the seal and gland on an optical fibre cable duct.

It is well known for ducts, in the form of thermoplastic moulded tubes to be used for housing optical fibres and optical fibre cables. Typically a bundle of ducts are surrounded by an outer sheath and optical. fibres or optical fibre cables are b]own along one or more of the ducts after the ducts have been installed.

It is also well known, in connection with electrical cables, to use a cable gland to provide a seal at the junction between a cable and its entry into a device such as a junction box. However, such cable glands utilise a large compressive force to LLain the cable within the gland. An example of such a gland is shown in Figures 1 and 2 which show a gland 10 having a cable 12 extending therethrough.

The cable 12 has an external sheath 14 which surrounds a plurality of sheathed wires 16. nIhe gland 10 has three components a seal 18 and two housings portions 20, 22.

The seal 18 engages the external sheath 14 and has an inclined surface 24 which engages inclined surface 26 of second housing 22. The first housing has an end surface 28 which presses against end surface 30 of seal 18. An externally mounted thread 32 on housing 20 engages an internally mounted thread 34 on second housing 22. When first housing 20 is rotated relative to second housing 22 the end surface 28 causes seal 18 to be pushed such that inclined surface 24 slides over inclined surface 26 causing a radially inward compression force to be appl.ed to cable 14. First housing portion 20 is rotated sufficiently so that cable 12 is strongly gripped by seal 18 preventing the ingress of water and allowing the cable 12 to be securely c]amped within gland 10.

Where optical fibre cables are used such a clamping force is unsuitable since a compressive force may alter the optical properties of a fibre optic cable and may even cause damage to the optical fibres.

Preferred embodiments of the present invention seek to overcome problems with the prior art, including, but not restricted to, those set out above.

According to an aspect of the present invention there is provided a seal for a cable gland assembly, the sea].

comprising: - first sealing means adapted to substantially seal around at least one first portion of at least one cable, the sealing means having first displacement means for applying at least one inwardly directed displacement force to at least part of said first portion; second sealing means adapted to substantially seal around at least one second portion of the or each said cable; and at least one abutment surface extending between said first and second sealing means and adapted to engage a junction between at least one first portion and at least one second portion.

By providing a seal for a gland assembly the seal having two sealing means, one of which has a compression force exerted upon it, and an abutment surface extending between them, the advantage is provided that a substantially waterproof seal for a gland for a fibre optic cable can be provided without the risk of damaging the cables or altering their optical properties. In particular, by providing the second sealing means which most typically extends around inner sheaths or ducts, which are themselves surrounded by an outer sheath, this provides additional sealing following the compression seal of the first sealing means. It is also sufficient to prevent water, which may have leaked into the device to which the gland is attached, from extending back up the cable along the outside of the inner sheaths but within the outer sheath. Such water ingress within the external sheath is of a particular problem since if this water were to freeze the damage caused from the expansion of the frozen water to the ducts and sheath can result in damage to the optical fibre cables such as breakage of indI.vdual optical fibres. When the seal is used with a cable gland, the first sealing means, which acts on the external sheath of the cable and applies the inwardly directed displacement force, wii.l most typically be located on the external side of a device into which a cable g]and and cable are extending whilst the secondary sealing means, around the internal sheaths of the cable are within the device. The first seaUng means, with the addition of the dsp1acement means, provides sufficient sealing to substantially prevent water ingress from the outside of the device. If the device is exposed to external weather condiLions, then the splashing effect of rain or, if installed on a ship, the splashing effect of spray, this water can act as though it were under increased pressure and therefore the displacement force or compression applied by the first sealing rings around the external sheath is required to prevent water from passing between the external.

sheath and first sealing means. Inside the device there should be no water at all, although it is possible that very small quantities could get in, for example as humidity or when a sealed door in the device is opened in order to gain access to the device. Such small quantities of water do not exert significant pressure on the second sealing means and therefore do not require the compression force to be applied to them. Overall it. is the combined sealing actions of the first sealing means with its compression means, the second sealing means and the abutment surface which allow an adequate seal to be provided without the need for a high compressive force to be applied to the external sheath.

The first sealing means may comprise at least one first aperture having at least one first internal surtace adapted to engage at least one external surface of at least one first sheath of the or each said cable.

The second sealing means may comprise at least one second aperture having at least one second internal surface adapted to engage at least one external surface of at least one second sheath of the or each said cable.

The first displacement means may comprise at least one first inclined surface extending between external surfaces of sai.d first and second sealing means.

In a preferred embodiment at least one abutment surface is adapted Lo engage at least one cut end of said first sheath.

tn another preferred embodiment at least one abutment surface is substantially perpendicular to at least one firsL internal surface and/or at least one second internal surface.

The seal. may comprise at least one thermoplastic material and may be moulded in a single piece.

According to another aspect of the present invention, there is provided a cable gland assembly comprising:- a seal as defined above; first seal engaging means having second displacement means adapted to cause said first displacement means to apply said displacement force to the or each cable; second seal engaging means for maintaining said first and second compression means in mutual engagement; and retaining means allowing the first and second seal engaging devices move relative to each other and then be retained in a position thereby substantially sealing the or each cable in the gland assembly.

in a preferred embodiment retaining means comprises mutually engaging threads located on at least one said seal engaging device and at least one said second sealing device.

The assembly may further comprise at least one stop for limiting the engagement of said mutually engaging threads and thereby limit the displacement force applied to the first portion of the seal.

By providing a stop for limiting the movement of the threaded portions of the gland assembly, the advantage is provided that the displacement force applied by the first sealing means of the seal can be precisely limited, thereby ensuring that the gland assembly does not cause damage to the optical fibres and optical fibre assembly.

The second displacement means may comprise at least one second inclined surface adapted to engage said first inclined surface.

According to a further aspect of the present invention, there is provided a tool for assisting in the locating of a gland assembly seal onto a cable having a p].urai.ity of internal sheaths, the tool comprising:- a base portion; and a plurality of pins located in said base portion and attached to said base portion in a arrangement substantially matching the arrangement of internal sheaths within an external sheath of a cable.

By providing a tool with a base portion into which a plurality of pins are attached in an arrangement matching the arrangement of internal sheaths within a cable, the advantage is provided that where an external, sheath contains many internal sheaths, for example an external sheath may typically have seven internal sheaths within it, these internal sheaths can be easily located within the seven apertures of the second sealing portion. This provides the further advantage that the second sealing portion can therefore be sufficiently tightly located around the external sheath to provide a close interference fit without making it excessively difficult for the operator to locate the seal on the internal sheaths.

In a preferred embodiment said pins are retained in loose attachment to said base portion By attaching the pins in loose attachment to the base the advantage is provide that the pins are more easily ].ocating in the ducts of the cable.

In a preferred embodiment said pins are tapered away from said base portion.

Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:- Figure 1 is a partial. sectional view of a cable gland

assembly of the prior art;

Figure 2 is a perspective view of a cable gland assembly

of the prior art;

Figure 3 is an end view of a cable gland assembly of the present invention; Figure 4 is a sectional view along the line A-A of Figure 3; Figure 5 is a partial sectional view of a cable gland assembly of Figure 3; Figures 6 and 7 are partial sectional views of a cable gland assembly of Figure 3 during a process of installation of a cable; Figure 8 is a side view of the cable gland assembly of Figure 3 during a process of installation of a cable; Figure 9 is a perspective view of the gland assembly of Figure 3 with a cable installed; Figure 10 is an end view of another cable gland assembly of the present invention; Figure 11 is a sectional view of the cable gland assembly of Figure 10 along the H.ne AA; Figure 12 is an end view of a cable gland assembly of the present invention; Figure 13 is a sectional view of the cable gland assembly of Figure 12 along the].ine A-A; Figure 14 is an end view of a seal of the present invention; Figure 15 is a sectional view of the seal of Figure 14 along the line A-A; Figure 16 is an enlarged portion of Figure 15; Figure 17 is a partial sectional view of a cable gland assembly of the present invention; Figures 18 and 19 are partial sectional views of a cable gland assembly and associated insertion tool of the present invention; Figure 20 is a side view of a cable gland assembly and cable gland partially installed therein; and Figure 21 is a perspective view of the cable gland assembly of Figure 17 with cable installed.

Referring to Figures 3 and 4, a cable gland assembly 50 has a seal 52, a first seal engaging means in the form of an entry housing 54 and a second seal engaging means, in the form of actuating element 56. The seal has a first sealing means 58 and a second sealing means 60. The first sealing means 58 has a first displacement means or inclined surface 62 and a first aperture 64 having an internal surface 66.

The second sealing means 60 has a pair of second apertures 68 which have internal surfaces 70. The second internal surfaces have sLight]y tapering portions 72 which assist in allowing the internal sheaths of the cable installed therein to extend into aperture 68. An abutment surface 74 extends between internal surfaces 66 and 70 of first and second apertures 64 and 68.

In use, the seal 52 is located wiLhiri an enLry housing 54 which has an inclined surface 76 which is adapted to engage inclined surface 62 on seal 52. An externally threaded portion 78 engages with an internally threaded portion on a device, such as a junction box (not shown), into which the cable gland extends. A hexagonal tool engaging surface is used to form a tight seal between the entry housing 54 and the device (not shown) . An internally threaded portion 82 is provided on entry housing 54 and engages an externally threaded portion 84 of actuating element 56. A hexagonal tool engaging surface 86 allows the actuating element 56 to be moved along internal thread 82 of entry housing 54. An end surface 88 of actuating element 56 engages an end surface 90 of seal 52.

The cable gland assembly 50 is designed for use with a cable 92 which has a pair of internal ducts or sheaths 94 which are surrounded by an external sheath 96. The internal ducts 94 have external surfaces 98 which engage internal surfaces 70 of second apertures 68. The external sheath 96 has an external surface 100 which is adapted to engage internal surface 66 of first aperture 64. The external sheath has a cut end which exposes an end surface 102 which engages abutment surface 74. The cut surface 102 of external sheath 96 has an approximately oval shape resulting from a tight fit of the external sheath 96 around internal ducts 94.

In use, the entry housing 54 is attached to a device (not shown) such as a junction box by engaging thread 78 with a respective internal thread on the device. A cable 92 for optical fibres is cut to the required length and the external sheath 96 is cut so as to reveal a short length of internal ducts 94. The internal ducts 94 are inserted through first aperture 64 in seal 52 and through second apertures 68. The slightly tapered portions 72 allow easy alignment of the internal ducts 94 with second apertures 86. The seal 52 is slid along internal ducts 94 so that external sheath 96 extends within first aperture 64. The external surface 100 of sheath 96 engages internal surface 66 of first aperture 64 providing a good interference fit. Similarly, the external surfaces 98 of internal ducts 94 engage internal surfaces 70 of second aperture 68 with a good interference fit. The seal 52 is then introduced into entry housing 54 so that the inclined surface 62 on seal 52 is engaged with inclined surface 76 of entry housing 54.

The external thread 84 of actuating element 56 is then engaged with internal thread 82 of entry housing 54. Upon rotation of actuating element 56, end surfaces 88 and 90 of actuating element 56 and seal 52 become engaged. Upon further rotation, actuating element 56 pushes seal 52 in direction D. This causes slight movement of inclined surface 62 of seal 52 over inclined surface 76 of entry housing 54. Such movement causes an inwardly directed displacement of at least part of the first dealing portion 58 thus applying a compression force radially inwardly to external sheath 96. The amount of displacement and therefore of compression force that is applied can be limited by limiting the movement of actuating element 56 by providing entry housing 54 and actuating element 56 with stop surfaces 104 and 106. Further compression of the seal 52 is prevented by stop surfaces 104 and 106 becoming engaged, thereby preventing any further movement of actuating element 56 along internal thread 82.

Referring to Figures 10 to 21, in which parts in common with Figures 3 to 9 are denoted with like referenced numerals increased by 100. The most significant difference between the gland assembly 50 and gland assembly 150 is the number of internal ducts 194 which extend through second apertures 168 in seal 152. In the examples shown in Figures 10 - 21, a bundle of seven internal ducts 194 are surrounded by an external sheath 196. The main difference between the seals shown in Figures 10 and 11 and those in Figures 12 to 16 is that the seal in Figures 10 and 11 is for use with a partially hexagonally shaped fibre optic cable bundle, whereas that in Figures 12 to 16 is for use with a cable having a circular crosssection. The partially hexagonal cross-section of the outer sheath, seen in Figures 10 and 11, results from the outer sheath being tightly formed around the seven internal ducts by material of approximately uniform thickness. The outer sheath in the cable of Figures 12 to 16 is moulded so as to have a circular cross-section. As a result the seal in Figures 10 and 11 has an internal profile of the first aperture which is partially hexagonally shaped so a to match the profile of the outer sheath of the cable and provide a close interference fit. Similari.y the internal profile of the first aperture in Figures 12 to 16 is circular in cross-section.

In order to assist in the insertion of seven ducts 194 into seven dpertures 168, a tool 120 is provided. The tool has a base portion 122 into which seven tapered pins 124 are loosely fixed in an arrangement approximately the same as the arrangement of the ducts in the cable 192. The loose attachment of the tapered pins to the base allows their tapered ends, those furthest away from base 122 to move transverse to their axes whilst they are held within base 122.

Referring to Figure 18, the gland assembly 150 works n substantially the same manner as the gland assembly 50.

However, the tool 120 s used to assist in the loading of the seven ducts 194 into the seven apertures 168 in seal 152.

The pins 24 of tool 120 are inserted through the entry housing and into the apertures 168 of seal 152. The loose attachment of tapered pins 124 in base 122 means that if the seal 152 is not introduced in perfect alignment with pins 124, the pins are able to move transverse to their axes in order to enter apertures 168.

Referring to Figure 19, the seven ducts 194 are then introduced onto pins 124. Once positioned, the ducts 194 can be threaded along pins 124 so as to enter the apertures 168.

Once the ducts 194 are within ducts 168, the tool 120 can be removed and the actuating element]58 threaded onto entry housing 154.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

Claims 1. A seal for a cable gland assembly, the seal comprising:- first

sealing means adapted to substantially seal around aL least one first portion of at least one cable, the sealing means having first displicemerit means for applying at least one inwardly directed displacement force to at least part of said first portion; second sealing means adapted to substantially seal around at least one second portion of the or each said cable; and at least one abutment surface extendi.ng between said first and second sealing means and adapted to engage a junction between at least one first portion and at least one second portion.
2. A seal according to claim 1, wherein said first sealing means comprises at least one first aperture having at least one first internal surface adapted to engage at least one external surface of at least one first sheath of the or each said cable.
3. A seal according to claim 1 or 2, wherein sai.d second sealing means comprises at least one second aperture having at least one second internal surface adapted to engage at least one external surface of at least one second sheath of the or each said cable.
4. A seal according Lo any one of the preceding claims, wherein said first displacement means comprises at least one first inclined surface extending between external surfaces of said first and second sealing means.
5. A seal according to any one of the preceding claims, wherein at least one abutment surface is adapted to engage at least one cut end of said first sheath.
6. A seal according to any one of the preceding claims, wherein at least one abuLment surface is substantially perpendicular to at least one first internal surface and/or at least one second internal surface.
7. A seal according to any one of the preceding claims comprising at least one thermoplastic material.
8. A seal according to claim 7, wherein said seal is moulded in a single piece.
9. A seal for a cable gland assembly substantially as hereinbefore described with reference to the accompanying drawings.
10. A cable gland assembly comprising:- a seal according to any one of the preceding claims; first seal engaging means having second displacement means adapted to cause said first displacement means to apply said displacement force to the or each cable; second seal engaging means for maintaining said first and second compression means in mutual engagement; and ( retaining means allowing the first and second seal engaging devices move relative to each other and then be retained in a position thereby substantially sealing the or each cable in the gland assembly.
11. An assembly according to claim 10, wherein said retaining means comprises mutually engaging threads located on at least one said seal. engaging device and at least one said second sealing device.
12. An assembly according to claim 11, further comprising at least one stop for limiting the engagement of said mutually engaging threads and thereby limit the displacement force applied to the first portion of the seal.
13. An assembly according to any one of claims 10 to 12, wherein said second displacement means comprises at least one second inclined surface adapted to engage said first inclined surface.
14. A gland assembly substantially as here inbefore described with reference to he &ccompariyirig drawings.
15. A tool for assisting in the locating of a gland assembly seal onto a cable having a plurality of internal sheaths, the tool comprising:- a base portion; and a plurality of pins located in said base portion and attached to said base portion in a arrangement substantia]]y matching the arrangement of internal sheaths within an external sheath of a cable. 1'
16. A tool according to claim 15, wherein said pins are retained i.n loose attachment to said base portion.
17. A tool according to claim 15 or 16, wherein said pins are tapered away from said base porLion.
18. A too] for assisting in the locating of a gland assembly seal onto a cable having a plurality of internal sheaths substantially as hereinbefore described with reference to he accompanying drawings.