Sealing gland

A gland seal comprises a plurality of sealing plates (24, 28, 30) sealingly received in a bore (12). Each pair of adjacent plates define between them a sealing channel (42). The channels are linked by elongate slots (41) in the plates to define a generally helical path. The channels are filled with a sealant through a filling hole (54) at one end of its respective channel.

FIELD OF THE INVENTION 
This invention relates to sealing glands. 
BACKGROUND OF THE INVENTION 
There are many applications in which a flexible elongate element such as a 
line or conduit requires sealing at an interface between two environments 
between which there is a high pressure differential. The boundary may be 
constituted by a bulkhead at which the sealing must be performed. The 
element may, for example, be an optical fibre for monitoring conditions on 
one side of the boundary. Another example is a fine tube used for 
capillary sampling of material on one side of the boundary. 
It is particularly important to provide highly reliable seals for such 
elements at interfaces in many different applications, for example the 
chemical and food processing and nuclear industries, in which the 
consequences of leakage of fluid past the seal can be severe. 
Another field in which the reliability of seals is very important is that 
of undersea telecommunication elements, for example optical fibres, in 
which stretches of telecommunication cable are interrupted by repeaters at 
which the signal in the fibres is boosted. The seal between the fibre and 
the repeater housing must be designed to withstand the extreme pressures 
at considerable depths for a projected life time of 25 years or more. 
Sealing glands are known for undersea optical communication fibres which 
comprise a metallised fibre soldered into a cylindrical body screwed into 
a bulkhead flange and also an electrode embedded in insulating ceramics 
also screwed into bulk head flange for power feed connections. In both 
cases the gland assembly comes as a unit with approximately 1 meter 
lengths of fibre sealed in place which are spliced to the fibres of the 
incoming cable, on one side, and to the receiving fibres inside the 
repeater housing, on the other. 
In both cases, the gland comprises a tubular arrangement extending out of 
the housing in line with the cable. The radial thickness of the 
arrangement is considerable in comparison with the cable to be sealed in 
order for it to be strong enough to withstand the pressures at depth. It 
is also made long enough in order to provide sufficient sealing contact 
between the sealing material and both the cable and the housing. Both of 
these factors have to be taken into account when designing the housing and 
can necessitate a more bulky housing shape than would otherwise be the 
case. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a less bulky yet still 
reliable seal than known seals. 
It is also an object of the invention to provide a versatile seal the 
components of which it is possible to vary to suit a particular 
application. 
According to the present invention there is provided a gland seal for 
sealing a flexible elongate element passing through an aperture in a 
boundary, the seal comprising a set of sealing plates, each adjacent pair 
of plates defining at least one sealing channel between them, each plate 
having an aperture through which, in use, the line to be sealed extends 
into the associated sealing channel, the line being sealingly engaged in 
the channel to inhibit the passage of fluid therethrough. 
The seal provided by the assemblage of plates can be applied to existing 
elements without the need for it to be formed as a sealed unit and 
attached, i.e. spliced, to the ends of elements an either side of the 
boundary. 
The channels defined between the assemblage of plates may be packed out 
with different sealants according to the application in which the gland is 
used. Furthermore, different sealants can be used between adjacent plates 
in the same gland in order to address differing sealing requirements on 
either side of the seal. 
Alternatively, the plates may be resilient and sealingly engage the line to 
define the sealing channel. 
The channels defined in the plates are preferably disposed substantially 
normally to the path of the line passing through the boundary to which the 
seal is attached. In this case, the assembly is also particularly compact. 
The present invention can be put into practice in several ways one of which 
will now be described by way of example with reference to the accompanying 
drawings in which:

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to the drawings, a seal 10 is secured within an aperture 12 
formed in a repeater housing through which the components of a cable, 
comprising optical fibres 14 and various electrical command and wires 16, 
pass from a subsea environment generally to the left in FIG. 1, into the 
sealed environment of the housing containing the electronic repeater 
circuitry. 
The part of the cable illustrated in FIG. 1 is only the terminating end 
portion 18 which is secured to the cable itself to enable it to be mounted 
on the seal. In terminating the cable, the optical fibres are separated 
from the command wires before they reach the seal. 
The gland comprises a main boss plate 20 on the seaward side, consisting of 
an annular collar 22 having a radially outwardly extending flange 24 at 
the seaward end of the boss plate 20. Thus, the boss plate 20 has an 
annular boss portion 26 extending into the repeater from the flange 24. 
The flange abuts a lead sealing washer 25 located on an annular ledge in 
the bulkhead defining the aperture 12. 
One or more (in this case two) gland plates 28, 30 are received on the boss 
portion 26. These are held in place by a packing ring 32, also received on 
the boss portion 26, comprising an annular flange 33 which mates with the 
repeater-side plate 30. 
The packing ring 32 extends away from the plates 28, 30 in the form of a 
short co-axial sleeve section that is formed with a radially inwardly 
extending collar 34 which extends over the end of the boss portion 26. The 
packing ring 32 is secured to the end of the boss portion 26 by bolts, 
thus urging the plates towards the flange 24. 
In order to seal between the mated faces of the plates, the repeater-side 
mating face of each plate is formed with a radially outer circular recess 
36 which, together with the adjacent seaward-side mating face, forms a 
square section channel in which a O-ring seal 40 is located. 
Each of the mating faces formed with the channel 38 is also formed with a 
radially inner recess 36' defining a square section channel with the 
adjacent seaward-side mating face. 
Each plate 20, 28, 30 is also formed with a sealing channel along which the 
fibre passing into the repeater housing runs. From the seaward-side, the 
fibre enters an arcuate slot 41 in the flange 24. The slot 41 guides the 
fibre into a first circular sealing channel defined by a groove 42 in the 
flange 24 and the adjacent flat mating face of the neighboring plate 28. 
The angle of entry of the fibre through the slot is acute with respect to 
the direction normal to the cross-section depicted in FIG. 1. This allows 
the fibre to assume the pattern of the groove with the minimum of stress 
induced by bending. 
The shape and extent of the slot 41 and groove 42 are best illustrated in 
FIG. 3. The slot 41 covers an arc of about 25 degrees. The fibres then 
follow a 270 degree circular path along the groove 42 up to a point about 
90 degrees from the end of the slot. 
A similar slot 41a in adjacent plate 28 is in registry with the end of the 
groove 42. Thus, the fibre passes from the groove 42 through the slot 41a 
into a similar groove 42a in the adjacent plate 28 at a similarly acute 
angle. 
The fibre follows the 270 degree circular path in the plate 28 and enters a 
further slot 41b in the next adjacent plate 30 which is angularly shifted 
by a further 45 degrees. In order to ensure that the plates are correctly 
angularly relatively positioned, each one may be provided with a locating 
pin or other detent which engages a hole or other recess in the adjacent 
plate. 
The detail of the slots and grooves are shown in FIG. 2. Here, it will be 
noted that each disassembled plate is rotated by 45 degrees with respect 
to adjacent plates in order that the slots clearly can be seen. When 
assembled, each plate is offset by 45 degrees from its neighbor in order 
that the slots register with the end of an adjacent groove. After the 
fibre has passed around the sealing channel defined by the groove 42b in 
the plate 30, it exits through a similar slot 44 in the packing ring 32. 
The slots are elongate to provide a smooth, transition between one channel 
and another in order that the bending stresses in the fibre are as small 
as possible. 
The boss plate 20 is formed with a central bore 46 having a screw thread on 
its internal wall. In order to seal the bore a sealing plate 48 is mounted 
on the terminating end 18 of the cable. The sealing plate may be made of 
glass, ceramic or some other insulating material. Conveniently, it may be 
moulded with the command wires in place in order to provide a particularly 
sound seal. When no command wires are to pass through, a steel blanking is 
used in place of the sealing plate 48. 
A sealing O-ring 50 is located within a square-section channel between the 
sealing plate and the boss plate 20. As the terminated end of the cable is 
tightened in the bore, the O-ring 50 seals between the sealing plate 48 
and the boss plate 20. Alternatively, the bore could be sealed using any 
other sealing arrangement, such as a flanged face on the end 18 of the 
terminated cable mating with a similar face on the boss plate. 
The sealing channel in each plate is filled with a sealing material. Each 
channel may be filled with a different material in accordance with the 
requirements dictated by the environments to be sealed from one another 
and/or the fibre or other line passing through the seal. For example, the 
channel in the first plate may have a chemically inert sealant buffer 
which protects a silicon rubber sealant and/or a solid sealant, such as 
epoxy, in the next channels. Another suitable sealant is viscous material, 
such as polyisobutadene. It will be appreciated that the seal is designed 
to be complete. However, for searching gases, such as helium and hydrogen, 
a leak rate within acceptable limits of, say 10.sup.-9 cc/sec/atmosphere 
is tolerated. As a practical matter a leak rate of this sort still 
constitutes a seal and the word "seal" is intended to embrace this. 
To fill each sealing channel, each plate is provided with a cross-bore 
drilled filling hole 54 at one end of its channel and a similar riser 56 
at the other end. The assembly can be assembled and filled with sealant 
once assembled to ensure an adequate seal is created around the fibre that 
will not be disturbed by subsequent relative movement between the parts. 
Typical materials for the sealant are epoxy, silicon rubber or a high 
viscosity material. Before the fibre, or bunch of fibres, is threaded 
along the channels it may be pre-coated with sealant. Additional sealant 
can be injected after the seal is assembled. Once the sealant has been 
injected the filling holes 54 and risers 56 are closed off using grub 
screws threadedly received in the holes. 
In certain applications the boss plate 20 may not be required to have a 
bore, in which case the seal is required of the plates alone. 
Suitable materials for the boss plate and plates are bronze, brass, steel- 
or copper-based alloys. However, the choice of material will be dictated, 
to a large extent, by the application to which the seal is put. 
The invention provides a versatile seal which can have one or more plates 
to define any number of channels. The boss plate 20 may also be separated 
into two separate components, namely the boss and a plate similar to those 
plates 28 and 30. The number of plates which can be used is limited only 
by the size of the boss portion 26. By winding &the fibre to be sealed in 
an effectively helical fashion the length of sealing engagement is made 
extensive in a compact space. 
It will be apparent to the skilled person that the sealing arrangement of 
the present invention finds application in many different fields where a 
versatile and compact seal is required for an elongate flexible element 
across a boundary between environments having a high pressure differential 
between them.