US 2838596 A
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Inventar S. G. FOORD 2% llorey June O, 1958 s. G. FOORD GLANDs FOR ENTRY oF SUBMARINE CABLES INT0 REPEATER HOUSINGS Filed Jun 2s, 1954 ggg/? United States Patent O FOR ENTRY F SUBMARINE CABLES INTO REPEATER HOUSINGS Stanley George Foord, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware GLANDS This invention relates to moisture tight seals for an electrical conductor passing through a bulkhead separating a comparatively low pressure chamber from a region of much higher pressure.
The invention is particularly, but not exclusively, applicable to the provision of such a seal through a bulkhead separating deep sea pressure from a chamber containing a repeater for a submarine cable.
The submarine cable connected to such a repeater normally consists of a central conductor surrounded by waterproof plastic insulating material such as high molecular weight polythene.
It has previously been proposed to lead an insulated submarine cable conductor into a chamber containing re peater apparatus through a plug of insulating material similar to that of the cable insulation. Organic insulating materials such as polythene, however, allow of the slow diffusion of water vapour under high hydraulic pressures. This is found not to be harmful as regards the submarine cable conductor itself but the presence of water vapour within a housing containing repeater apparatus cannot be tolerated. Consequently it is necessary to provide hermetic sealing means to supplement the mass of polythene, and it is also necessary to provide means for preventing the mass of polythene being extruded, under the high pressure dihference, into the repeater housing. This has previously been done by providing a ceramic plug seating against conical surfaces of a passage through the bulkhead and provided with a central bore for passage of the conductor.
ln order to seal the conductor in this passage it has been proposed to provide central and outer metallic sleeves encircling the conductor, said sleeves having tapered outer and inner surfaces respectively cooperating with and cemented to correspondingly tapered inner and outer surfaces of an intermediate ceramic sleeve to provide a nonyielding water proof support for the mass of polythene.
ln my copending application No. 1614/53 there has been described and claimed a moisture tight seal of the kind above set forth comprising an insulating bushing of quartz, ceramic or vitreous material sealed into a passage through the bulkhead and provided with a central bore into which the conductor has been drawn in such manner that a portion of said conductor has been reduced in diameter by the drawing process until the conductor lits tightly in said bore.
The bush was provided with an external conical surface pressed into a complementarily shaped seating in said bulkhead with an intervening layer of metal soft enough to flow under the high pressure, which pressure maintains the bushing in its seating.
It is the object of the present invention to provide a form of moisture tight seal which is economic in manufacture and simple to assemble and in which the number and extent of surfaces needing to be accurately ground to shape is reduced to a minimum.
According to the present invention a moisture tight seal for an electrical conductor passing through a bulk` head separating a comparatively low pressure chamber from a region of much higher pressure comprises an insulating bushing of hard insulating material provided with a central bore and fitting within a passage through said bulkhead, sealing means sealing said low pressure chamber against entry of moisture between said bushing and the walls of said passage, a metal rod passing through said central bore and having integral therewith an enlarged head placed on the high pressure end of said bore and having a surface soldered to a metallised surface on the end of said insulating bushing surrounding the aperture of said central bore.
An embodiment of the invention will now be described with reference to the accompanying drawing which shows in cross-section a moisture tight seal for a housing containing repeater apparatus for a submarine cable.
The cable to be terminated at the repeater, which cable may be a tail cable jointed to the submarine cable proper comprises a central conductor 1 surrounded by a plastic insulating material 2 such as polythene.
The bulkhead 3 isolates 'the low pressure chamber in which the repeater equipment is contained from the outside of the repeater housing which in service is under full hydrostatic pressure. An insulating bushing 4 made of a suitable hard material such as a ceramic, glass or quartz is provided of which the larger part is a cylindrical sliding t in an aperture in the bulkhead 3. This insulating bushing is also provided with what is well known as un i-ring 5 seated in a groove in the bushing 4.
The inner conductor 1 of the external cable is sweated as shown at 7 to the head S of a rod 5 which passes through an axial cylindrical aperture in the insulating bushing 4 and is designed to be a sliding t therein. The construction is therefore extremely simple as no carefully shaped conical tapering bores are involved. The shaped head S of the inner conductor 6 has a flat surface which is soldered to the corresponding metallised surface of the bushing as shown at 9. lt can be seen that this soldered seal at 9 will be under heavy pressure in service and therefore that the solder at 9 will spread and improve the humidity tightness of the seal. During the soldering of the head 3 to the metallised surface of the bushing 4 pressure is brought to bear by tightening up the thumb nut 1i) on the end of the shank of the inner conductor member 6.
As regards the outer penetration path, that is to say, the pc'h along the outside of the insulating bushing 4 this is completely sealed with a soft metal seal l1 which may be made of any of the softer metals such as lead, silver, copper or aluminium. The pressure on the soft metal exceeds the external hydrostatic pressure by an amount depending on the internal and external diameters of the ring Suitably the pressure in the seal may be made to be about twice the external hydrostatic pressure. Under these conditions the soft metal will creep into any small interstices and provide a' completely moisture proof seal. The bedding of the seal shown in the drawing is a sloping surface, but could be a plane surface at right angles to the axis of the insulating bushing 4. A sloping surface is however to be preferred, since the maximum shear stress set up in the bushing is thereby reduced.
A plastic moulding l?. of the same material as the cable insulation, for example, polythene, is injection moulded around the end of the cable insulation 2 with which it forms a bond, and also around the upper portion of the bush 4, and is extended to form a diaphragm l5. The upper surface of the bulkhead as shown is provided with a dish shaped recess 13 the central portion i4 of which is deeper than the rim portion.
The whole cable assembly comprising the bushing 4 with rod 6 and plastic moulding 12 is inserted into the bulkhead until the O-ring 5 just disappears from view. The central portion 14 of the recess in the surface of aeaasae the bulkhead is iilled with viscous liquid whilst hot. This liquid may be a viscous polyisobutylene (with or without additions such as wax or polythene) which provides a liquid seal and a breathing means for the diaphragm, 15.
`When this liquid has cooled suiciently the whole assembly is pressed firmly down until the soft metal ring 11 is in compression, trapped air and surplus liquid in the space 14 being thereby squeezed out under the diaphragm 15. The assembly is secured in position by a circlip 16, after which a metal clamping ring 17 is secured in position over the edge of the diaphragm 15 by means of small screws (not shown).
When the full hydrostatic pressure is applied the whole assembly is forced down on the soft metal seal il. The diaphragm 15 is somewhat flexible and does not impede this downward movement. The O-ring prevents any liquid being forced down to the seal 11 before it is made completely effective bythe high hydrostatic pressure.
It will be noted that the sealing means shown are such that the whole bulkhead assembly can be completely fabricated in the factory, or on site. Moreover entry of water between the bushing 4 and the bulkhead is prevented even at low pressures, e. g. Whilst the housing is being lowered to the bottom of the sea bed. Furthermore extreme accuracy of fitting is unnecessary; the few accurate parts required involving only simple turning or grinding for fabrication.
While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.
What I claim is:
1. A moisture-tight seal for an electrical conductor passing through a bulkhead separating a comparatively low pressure chamber from a region of much higher 4 pressure, comprising an insulating bushing of hard iusulating material provided with a central bore and fitting within a passage through said bulkhead, sealing means sealing said low pressure chamber against entry of moisture between said `bushing and the walls of said passage, a metal rod passing through said central bore and having integral therewith an enlarged head joined to an external conductor, the head being placed on the high pressure end of said bore and abutting an end of said bushing, Va recess in the face of said bulkhead on the sideV subjected to high pressure, a viscousliquid filling said recess, a mass of plastic insulating material surrounding said enlarged head and its joint with said conductor, a diaphragm integral with said mass of plastic insulating material, and means clamping said diaphragm against the surface of said viscousrliquid filling said recess.
2. A moisture-tight seal as claimed in claim 1, in which the surface of said enlarged head which abuts said bushing is soldered to a metallised surface on the end of said bushing.
3. A moisture tight seal as claimed in'claim 1 in which said bushing is a cylindrical fit in said passage and the sealing means between the said bushing and the walls of said passage comprises a soft metalV seal effected by the higher pressure.
4. A moisture tight seal as claimed in claim 3 in which an O-ring seal is also provided around said bushing.
References Cited in the le of this patent UNITED STATES PATENTS 2,282,106 Underwood May 5, 1942 2,356,831 De Monte et al .Aug. 29, 1944 2,668,187 Van Wald et al Feb. 2, 1954 2,718,543 Lidderdale Sept. 20, 1955 FOREIGN PATENTS 1,011,551 France Apr. 2, 1952