Abstract:
An apparatus and method for sealably joining cables to pressure-balanced submersible junction boxes. The apparatus maintains a balanced pressure within the termination chamber; it is field installable, testable, and repairable. The termination chamber is not oil-filled; instead, it is substantially filled with a solid particulate fill material. An apparatus and method for sealably containing the cable&#39;s bitter end within the termination chamber are further provided. The apparatus includes a cable termination assembly having a chamber with a first end including a load bearing cable-attachment to sealably join a cable to the chamber, and a second end including an underwater connector. Within the chamber one or more optical and/or electrical conductors from the cable are terminated to respective one or more attachment points of the connector. The apparatus prohibits cable pistoning into the termination chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of the earlier filing date of U.S. Provisional Application Ser. No. 61/587,800 filed on Jan. 18, 2012 the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the invention generally relate to an apparatus and method for sealably joining cables to pressure-balanced submersible junction boxes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Subsea junction boxes provide protected enclosures for the components housed within them. Components are joined within such enclosures while they are open. The enclosures are then closed and sealed prior to submersion in order to prohibit the intrusion of seawater. There are two broad existing categories of subsea junction boxes. One category comprises a gas-filled compartment in which various components are joined. The compartment pressure remains substantially at one atmosphere. This category of junction box must have very heavy walls and high-pressure seals to withstand the enormous pressure at great depth. In a second existing category of subsea junction boxes, the enclosure in which various components are joined, hereinafter called the termination chamber, is filled with oil that is pressure-balanced to the ambient sea pressure by a compensator. The walls and seals of these pressure-balanced junction boxes can be much less robust than those of the gas-filled junction boxes because there are no high-pressure differentials between the termination chamber and the exterior environment. 
         [0004]    Subsea junction boxes are often used to join two or more subsea cables; or to join one or more cables to underwater connectors, or to other devices; or to join two or more devices without cables. At times they are used as “smart boxes” which join attachment points of a single device, such as an underwater connector or cable, to sensors or other devices within the termination chamber. 
         [0005]    When cables are joined to a junction box sometimes the cable-to-junction-box joint is connectorized, meaning that the cable does not actually penetrate the termination chamber, but instead is joined to it by way of a connector which passes through the termination chamber wall. In other common applications, the cable&#39;s bitter end itself actually penetrates the termination chamber. An underwater cable is essentially a long, thin pressure vessel in which there are voids, such as the interstices between twisted wire strands or between various other cable elements, which are nominally at one atmosphere pressure even when the cable is submerged to great depths. Prior-art termination chambers are typically filled with dielectric oil after the conductors within the chamber are attached to their respective attachment points. Oil is chosen due to the attributes that it is electrically isolative; it is able to evenly transmit the exterior ambient pressure to the interior portions of the chamber volume; and, it can be easily removed for maintenance and repair of the elements within the chamber. The oil pressure within the chamber is possibly very high depending upon its depth in the water. Therefore there can be a large pressure difference between the oil in the termination chamber and the cable interstices. Oil can undesirably flow into interstitial voids in the cable in case of nicks, pinholes, or other small perforations through the conductor jackets or, as described below, through boot seals. 
         [0006]    Boot seals are frequently used to seal cable interfaces from the environment exterior to them. A generic example of a boot seal is shown in  FIG. 4 . Simple jacketed cable  36  in the example has a single, jacketed conductor  37 . A first elastomeric boot-seal sleeve portion  38  is stretched over jacketed cable  36 , and a second smaller elastomeric boot-seal sleeve portion  39  stretches over jacketed conductor  37 . Pressure applied to the exterior of the  FIG. 4  boot seal simply adds to the constrictive pressure of the elastomeric stretch, and enhances the seal between the boot seal and the elements of the cable. Boot seals such as shown in  FIG. 4  are one-way seals. That is, they seal against intrusion of the exterior environment into the interface  40  between cable elements  36  and  37 . But if there is an overpressure within cable interface  40 , such as would occur with pressurized gas, water, or gel within interface  40 , the overpressure could blow the boot seal axially away from the interface, or simply unseat sleeve  38  or  39 . 
         [0007]    Subsea cables are often so large that they cannot be practically transported to a place where they can be terminated in a laboratory-like environment; they must be terminated in the field. Therefore, there is often a need in the offshore industries for cable-to-connector junctions that can be installed, tested, and repaired in the field prior to immersion. Cables for subsea use commonly consist of an exterior jacket which houses a variety of individually jacketed electrical conductors and/or optical fibers within an inner core. The electrical conductors usually consist of stranded wires. In a typical termination process, the cable exterior jacket and core are cut back exposing lengths of the individually jacketed conductors. In the case of a cable carrying optical fibers within tubular conduits, tube-end-seal assemblies such as the example described in U.S. Pat. No. 6,321,021 to Cairns et al. (“the &#39;021 Patent”), the contents of which are included herein by reference, provide sealed barriers between the chamber volume and the interior portion of the fiber-carrying tubular conduits. 
         [0008]    U.S. Pat. No. 5,577,926 to Cox (“the &#39;926 Patent”), the contents of which are incorporated herein by reference, describes a prior art arrangement. In the &#39;926 Patent, a cable is sealably joined mechanically to a junction box whose termination chamber houses the end of the cable core and the exposed conductors. The chamber is filled with dielectric oil. Boot seals are stretched across the joints between the core and the jackets of the exposed lengths of conductors thereby sealing those interfaces to prevent oil from entering the cable. The exposed conductors go further on within the oil chamber to eventually join to other conductors or to the attachment points of connectors or other devices. All joints between the conductors and attachment points are also sealed by boot seals. As a result, there are usually many seals and exposed, jacketed conductors within the oil-filled chamber. When completely installed, a compensator, such as a flexible portion of the chamber wall, allows the pressure within the oil to closely match that of the outside environment. Under pressure any perforations through the boot seals or conductor jackets will cause the chamber oil to be forced into the cable interstices. The chamber walls will then either collapse or rupture, allowing seawater to enter, and creating a catastrophic failure. 
         [0009]    Another failure mode can occur when gel-filled cables are employed. In this mode, as cables are passed over handling devices such as pulleys, the gel can be “milked” toward the oil-filled termination chamber. That can unseat boot seals and result in subsequent failure. Still another failure mode, occurs when a cable is retrieved quickly from great depths. In this case pressurized gas expands within the cable, and seals within the oil-filled chamber can be temporarily or permanently unseated, allowing chamber oil to enter the cable interstices. Failure can also occur when the cable is under axial compression, as can happen during handling. In this case, if not arrested properly, the cable can piston into the oil-filled chamber and destroy the inner works. 
         [0010]    U.S. Pat. No. 6,796,821 to Cairns et al. (“the &#39;821 Patent”), the contents of which are incorporated herein by reference, describes another prior art arrangement. Unlike arrangements prior to it, exemplified by the &#39;926 Patent, the &#39;821 Patent termination has separate first and second termination chambers intended, as discussed in the specification of the &#39;821 Patent, to obviate the aforementioned failure modes by providing an impenetrable barrier between a first chamber, and a second chamber which is filled with oil. The individual cable conductors are terminated in the first chamber to sealed penetrators which pass through the impenetrable barrier and onward into the second, oil-filled, chamber. The &#39;821 Patent discloses three basic embodiments: One with a first chamber filled with a cast, solid material, and maintained at one atmosphere pressure; one with a first chamber filled with a cast, solid material, and pressure compensated with grease to the ambient working pressure; and, one with a first chamber filled entirely with grease and compensated to the ambient working pressure. In all three embodiments the second chamber is oil-filled and pressure compensated to the ambient working pressure. 
         [0011]    In the first two aforementioned embodiments of the &#39;821 Patent termination, once the conductors are terminated to attachment points on the impenetrable barrier the first chamber is filled with a pourable material which cures to a solid. 
         [0012]    In the third aforementioned mentioned &#39;821 Patent embodiment, the first chamber is not filled with solid material, but rather is grease filled; and incorporates a compensator mechanism that balances the pressure within the grease to the ambient working pressure. Therefore, the first chamber in this third embodiment has all of the attributes of the earlier technology comprising only an oil-filled, pressure-balanced termination chamber. 
         [0013]    In early art exemplified by the &#39;926 Patent, cable conductors extending outward from the core were exposed in a single oil-filled termination chamber and therein connected to the attachment points of connectors or other devices. All interfaces presenting potential leak paths of the oil into the cable were sealed with boot seals. The terminations were first completed up to the point of filling the chamber with oil. Next a method such as gas leak testing was employed to find any leaks from the chamber into the cable, or between the chamber and the exterior environment. If leaks were found, the termination could be easily dismantled for repair and retesting. Also at the point prior to oil filling, the quality of electrical and/or optical circuits could be tested, and if necessary, repaired. Even after oil filling, if defects were found in the termination, the oil could be drained, and repairs made. That is not the case with the &#39;821 Patent termination. Once the solid filler is installed into the first chamber, that portion can no longer be non-destructively disassembled for repair, nor can it be leak tested against water ingression. The solid filler embodiments of the &#39;821 Patent are, therefore, not completely testable or repairable in the field. 
         [0014]    It is known to seal leaks in hydraulic and pneumatic systems by adding a mixture of granular and fiber or ribbon material to the fluid or gas. Some examples are given in U.S. Pat. Nos. 8,015,998; 5,755,863; 5,282,895; 4,776,888; and 4,439,561. Such hydraulic and pneumatic systems have relatively large fluid or gas supplies in which stop-leak components are sparsely dispersed. The systems can tolerate a relatively large fluid or gas loss before the dispersed stop-leak components accumulate sufficiently at the leak site to block the leak path. Stop-leak additives are intended to operate in dynamic flow situations wherein the leakage is robust enough to transport the components of the additive quickly to the leak site. 
         [0015]    It might be thought that the addition of stop-leak components to a fluid-filled termination chamber would solve the potential leakage problem. That is not so. Fluid leakage from a subsea junction box in nearly all cases would be far from dynamic. Such systems are typically designed to last decades. Due to the sometimes miniscule rate of fluid migration from the chamber, it can take many years to cause a system failure. In addition, a fluid-filled termination chamber has a very limited supply of fluid, sometimes less than a few hundred cubic centimeters, and no means to replenish the fluid. Therefore the amount of leakage occurring prior to accumulating dispersed stop-leak components at the leak site could easily destroy the integrity of the termination. 
         [0016]    A subsea termination chamber has two fundamental requirements of a fill material: one, that it will transmit the ambient exterior pressure uniformly within the chamber; and two, that it will not escape. Filling the termination chamber with fluid satisfies the first of these requirements, but can fail the second. 
       SUMMARY OF THE INVENTION 
       [0017]    According to embodiments of the invention, a subsea junction box is provided which can be installed, tested, and if necessary, repaired in the field prior to immersion. For simplicity the invented junction box is described herein in terms of a simple but very common termination assembly that joins one subsea cable to one submersible connector. Although the invention is disclosed in those elementary terms, it will be obvious that the invention can be configured for joining a wide variety, size, and number of diverse components. The chosen example contains all of the basic elements and challenges of larger, more complex assemblies. 
         [0018]    Embodiments of the invention maintain a balanced pressure within the termination chamber; it is field installable, testable, and repairable. The termination chamber, according to embodiments of the invention, is not oil-filled; instead, it is substantially filled with a solid particulate fill material. According to embodiments of the invention, there is provided an apparatus and method for sealably containing the cable&#39;s bitter end within the termination chamber. 
         [0019]    Embodiments of the invention include a cable termination assembly having a chamber with a first end including a load bearing cable-attachment to sealably join a cable to the chamber, and a second end including an underwater connector. Within the chamber one or more optical and/or electrical conductors from the cable are terminated to respective one or more attachment points of the connector. Embodiments of the invention prohibit cable pistoning into the termination chamber, while bidirectional gland seals at the interface between the cable core and the exposed lengths of conductors prevent the intrusion of gas, gel, water, or other contaminants from entering the chamber via the cable, and likewise prevent material from the termination chamber from intruding into interfaces of the cable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The details of embodiments of the invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
           [0021]      FIG. 1A  is an axial partially-sectioned view of a subsea junction box configured as a typical cable terminated to an underwater connector. 
           [0022]      FIG. 1B  is a close-up view of a portion of  FIG. 1A . 
           [0023]      FIG. 2  is an exploded view of the posterior portion of the cable termination. 
           [0024]      FIG. 3  is an axial partially-sectioned view of a break-out gland seal. 
           [0025]      FIG. 4  is an axial partially-sectioned view of a prior art boot seal. 
           [0026]      FIG. 5  is a perspective view of the inner chamber wall. 
           [0027]      FIG. 6  is a perspective view of the outer chamber wall. 
           [0028]      FIG. 7  is a perspective view of the inner chamber wall retainer band. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the invention, while eliminating, for purposes of clarity, other elements that may be well known. Those of ordinary skill in the art will recognize that other elements are desirable and/or required in order to implement the invention. However, because such elements are known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The detailed description will be provided herein below with reference to the attached drawings. 
         [0030]    For purposes of the description hereinafter, the terms “upper”, “lower”, “vertical”, “horizontal”, “axial”, “top”, “bottom”, and derivatives thereof shall relate to the invention, as it is oriented in the drawings. However, it is to be understood that the invention may assume various alternative configurations except where expressly specified to the contrary. It is also to be understood that the specific elements illustrated in the drawings and described in the following specification are simply exemplary embodiments of the invention. Therefore, specific dimensions, orientations and other physical characteristics related to the embodiments disclosed herein are not to be considered limiting. 
         [0031]      FIGS. 1A and 1B  illustrate an embodiment of a junction box  1  configured as a simple assembly to terminate one armored cable  2  to one underwater connector  3 . The assembly comprises a cylindrical housing defined by an exterior shell  4  which is closed by a cable union  5  on its posterior end, and by a submersible connector  3  on its anterior end. Cable  2  is a subsea armored cable including an exterior jacket  7  cut back to expose fanned-out armor wires  6 , internal core  8 , one or more jacketed electrical conductors  9  (one of which is shown), and one or more optical fibers  10  (one of which is shown). Elastomeric boot seal  11  acts both as a cable strain relief, and to seal the interface between cable jacket  7  and cable union  5 . Conical seat  12  in cable union  5  accommodates fanned-out armor wires  6 . Cup-shaped housing  13  comprises through-bore  14  that fits closely to the outer surface of cable core  8 , and further comprises rear wall  15  that forms a mechanical barrier between conical seat  12  and the interior of cup-shaped housing  13 . Bore  16  in cable union  5  sealably accommodates cup-shaped housing  13  with o-ring seals  17 . Housing end-cap  18  fits snugly into the anterior end of cup-shaped housing  13 . Engagement threads  19  in the anterior end of cable union  5  engage threads  20  on retainer nut  21 , thereby capturing cup-shaped housing  13  and housing end-cap  18  within bore  16  of cable union  5 . 
         [0032]      FIG. 2  is an exploded view of the mechanical junction between the cable and the termination chamber. Elastomeric gland seal  22  ( FIGS. 2 &amp; 3 ) has a slightly larger diameter than bore  30  of cup-shaped housing  13  into which it is squeeze-fit. Large bore  27  in the posterior portion of gland seal  22  is stretch fit over cable core  8 . Forward wall  28  of bore  27  within gland seal  22  ( FIG. 3 ) cooperates with front face  29  of cable core  8  to arrest the forward motion of the cable core with respect to the gland seal. One or more bores  23  through the anterior end portion of gland seal  22  stretch-fit respectively to the one or more jacketed electrical conductors  9  which pass through them. Similarly, one or more bores  24  stretch fit to the respective one or more optical-fiber conduits  25 , each of the conduits housing one or more optical fibers  10 . Gland seal  22  is slightly shorter axially than the cavity formed by bore  30  of cup-shaped housing  13  and housing end-cap  18 , thereby allowing elastomeric gland seal  22  to elongate axially as it is squeezed radially during insertion. Retainer nut  21  attaches to the anterior portion of cable union  5  through the engagement of housing-nut threads  20  with threads  19  of cable union  5 , thereby fixing cup-shaped housing  13 , gland seal  22 , and housing end-cap  18  within bore  16   a  of the cable union  5 . The rearward motion of captured elements  13 ,  22 , and  18  is limited by shoulder  16   b  of cable union  5 . 
         [0033]    One or more conduits  25  each housing respective one or more optical fibers  10  are sealably terminated by respective one or more feed-through units  26  which may function in a manner similar to the sealed feed-through described in aforementioned U.S. Pat. No. 6,321,021 of Cairns, et al. 
         [0034]    It is to be noted that in embodiments of the invention there are no boot seals on the interfaces between the various elements of cable  2  and the interior of termination chamber  31 ; instead, the sealing of these interfaces is accomplished entirely by gland seal  22 . That is advantageous because boot seals typically have relatively thin walls, and are more easily subject to perforations. Also, mobile elements within the cable such as gas, gel, or intruded water could unseat boot seals. Also, if the pressure of the mobile elements within the cable would exceed the chamber pressure, the boot seals could be unseated. However, these will not unseat gland seal  22 . Therefore, in the construction just described termination chamber  31  is sealed on all levels against the ingress of foreign substances from the cable, and likewise cable  2  is sealed against the intrusion of mobile material from the termination chamber. Gland seal  22  is, therefore, bidirectional as it seals in both directions. 
         [0035]    One or more through-bores  34  of housing end cap  18  fit snugly to the one or more respective jacketed electrical conductors  9 , but do not seal to those conductors. Similarly, one or more through-bores  35  of housing end cap  18  fit snugly to the one or more respective optical fiber conduits  25 , but do not seal to those conduits. Therefore, gland seal  22  is not sealed from termination chamber  31 , and is substantially balanced to the pressure of the termination chamber; which chamber, in turn, is balanced to the ambient pressure of the working environment. There is, therefore, no substantial pressure difference between the cable end portion and either gland seal  22  or termination chamber  31 , and as a result, there are no substantial pressure-related forces urging the cable into chamber  31 . 
         [0036]    There may be other handling forces that urge cable  2  inward toward termination chamber  31 . But due to the solid barrier presented by housing end-cap  18  and housing nut  21 , cable  2  cannot piston into termination chamber  31 . 
         [0037]    As shown in  FIGS. 1A and 1B , conical seat  12  of cable union  5  houses the fanned-out armor wires  6  of cable  2 . Once in place, the cavity formed by conical seat  12  is filled by way of ports  32   a,    32   b  with a pourable epoxy that cures to a solid, thereby gripping the armor wires of cable  2  and prohibiting the axial withdrawal of the cable from cable union  5  even in the presence of high tension. Seal screws  33   a,    33   b  subsequently seal fill ports  32   a,    33   b . Irregularities (not shown) in conical seat  12  prohibit the rotation of cable  12  with respect to cable union  5 . This sort of epoxy-poured strength-termination is old art, well known to those in the field. As pointed out in aforementioned &#39;821 Patent there are many types of submarine cables and many types of existing arrangements to mechanically grip the ends of cables to be terminated. Adaptations to cable union  5  can readily be envisioned to accommodate various other types of cable grips while not diminishing the effectiveness of embodiments of the invention&#39;s sealing and anti-pistoning arrangements. 
         [0038]    The preliminary stages of the termination assembly go as follows: (1) Elements of the mechanical cable junction ( FIG. 2 ) are assembled onto the prepared cable end; (2) conical seat  12  is filled with epoxy, and seal screws  33   a,    33   b  are installed. (3) Stand-off rods  41  (one of which is shown in  FIG. 1A ) are installed to keep the mechanical cable junction ( FIGS. 1A ,  1 B and  2 ) and connector  3  fixed in relative axial and rotational position during the rest of the assembly. (4) One or more jacketed electrical conductors  9  are attached to their respective attachment points (hidden in  FIG. 1A ) and boot seals  43 , similar to the generic example of  FIG. 4 , are installed over the attachment points. (5) One or more optical fibers  10  are attached to their respective one or more attachment points (hidden in  FIG. 1B ) and protective strain relief boots  42  are installed over the attachment points. At this stage of installation, all circuits between the cable and the connector have been completed, and can be preliminarily tested. 
         [0039]    The posterior end of elastomeric inner chamber wall  44  attaches sealably to cable union  5  by the cooperation of inward-facing shoulder  45   a  of the inner chamber wall with cable-union groove  46 , the shoulder being retained within the groove by retainer sleeve  47   a  ( FIGS. 1B and 7 ). The anterior end of inner chamber wall  44  attaches sealably to rearward extension  48  of connector  3  by the cooperation of inward-facing shoulder  45   b  of the inner chamber wall with groove  49  of the rearward extension, shoulder  45   b  being retained within groove  49  by retainer sleeve  47   b  ( FIGS. 1A and 7 ). Tines  64  ( FIG. 7 ) of retainer sleeves  47   a,    47   b  have inward projecting ribs  65  that lock into grooves  66   a,    66   b  ( FIGS. 1B and 1A ) of cable union  5  and rearward extension  48  of connector  3 . Inner chamber wall  44  has a flexible portion which acts a pressure compensator for pressurizing the chamber  31 . Once inner chamber wall  44  has been installed, preliminary low-pressure gas testing of the now-sealed assembly can be performed by introducing gas through one of ports  51   a,    51   b.  After successful preliminary gas testing, inner chamber  31  is filled with fill material  63  via ports  51   a,    51   b,  which are subsequently sealed by respective seal screws  50   a,    50   b.    
         [0040]    Unlike the oil used in prior art arrangements, fill material  63  is composed of a mixture of small, substantially incompressible particles. The fill material can be made from a wide variety and/or mixture of materials with appropriate attributes. According to embodiments of the invention fill material  63  is selected from material having the following characteristics: 
         [0041]    A substantial amount of the fill material will not leak out of the chamber in the event of perforations or defects in the barriers that seal it from the cable interstices; 
         [0042]    The fill material uniformly transmits the external ambient pressure to the innermost reaches of the chamber; 
         [0043]    The fill material is chemically compatible with the other elements which it contacts within the termination chamber, and with seawater; 
         [0044]    The fill material is not soluble or miscible in any fluids with which it comes into contact, including seawater; 
         [0045]    The fill material contains some particles whose size scale is greater than that of the leakage paths. These particles could be small fibers, spheres, ribbons, grains, powder or platelets, for instance, whose size scales are greater than the openings of potential leak paths; 
         [0046]    The fill material does not contain only particles whose size scale is comparable to or larger than those of other termination components such as seals or conductors, because such large particles in the absence of smaller filler particles would cause discreet pressure points on those components. That is particularly important in the case where optical fibers are present. (Single-mode optical fibers typically have a diameter of 125 microns (1 micron=10 −6  meter)). Therefore, the fill material contains a substantial fraction of particles whose size scales are small compared to the smallest diameter of the conductors within the material; 
         [0047]    In the case where there are electrical conductors within the chamber, the fill material is substantially electrically non-conductive; 
         [0048]    The fill material in bulk is at most only slightly compressible; and 
         [0049]    The fill material is easily installable and removable for maintenance and testing. 
         [0050]    Shear strength is an inverse indicator of a material&#39;s ability to flow. The shear strength of particulate material increases with increasing applied pressure causing the material to flow less easily. That in itself is not detrimental to particulate material&#39;s utility as a termination-chamber fill material. Pressure changes affecting subsea termination chambers are not sudden impacts, but instead occur slowly; so as long as the fill material can flow, it will transmit the external pressure into the innermost reaches of the termination chamber. The solid particles used as fill material must on one hand be fine enough so as not to cause pressure points on the other termination components such as optical fibers, and on the other hand must be coarse enough to prevent it from leaking out through perforations or other flaws in the conductor jackets or boot seals. In many circumstances, for example when all potential leak paths are very small, a fill material of one small particle size fulfills these requirements. But in some other applications, it is desirable to have a filler mix containing diverse particle sizes and/or shapes. 
         [0051]    The combination and size of the elements comprising the fill material will therefore vary according to the particular application. Some suggested materials are given in the following example, however many material choices are available that would work equally well. In an application wherein the termination chamber contains both optical fibers and stranded, jacketed electrical conductors the fill material could include, for example: 
         [0052]    A substantial fraction, for example ⅓, of particles such as Boron Nitride powder having equivalent spherical size scales on the order of 1 micron, and providing lubricity at high pressures; 
         [0053]    A substantial fraction, for example ⅓, of particles such as Boron Nitride powder having equivalent spherical size scales on the order of 10 microns, which also provide lubricity at high pressures; and 
         [0054]    A substantial fraction, for example ⅓, of particles such as rigid spheres, for example, glass spheres, having equivalent spherical size scales on the order of 0.5 millimeter (mm) such that the particles are larger than the potential leak paths into the cable. 
         [0055]    The fill mix just described would work in the application wherein the largest leak path from the termination chamber is less than 0.5 mm. For larger leak paths progressively larger particles would have to be added to the mix. Other components added to the mix such as ribbons, flakes, or threads, for instance, would also work in many circumstances. It was noted earlier that termination chambers are typically leak tested with a gas prior to filling. Therefore, undetected leak paths from the chamber are likely to be extremely small and require comparably small particle sizes. 
         [0056]    Every precaution is made to block intrusion of external environmental contamination into termination inner chamber  31 . If a fluid contaminant would accidentally intrude into chamber  31  it might permeate a completely dry fill material, thereby possibly degrading its electrical resistivity. The reliability of the termination can be enhanced by wetting the fill material with an optional benign wetting fluid. Such a benign wetting fluid should be immiscible in the exterior environmental medium, for instance seawater; should be a dielectric; and should be chemically compatible with all substances with which it comes into contact. Polydimethylsiloxane oil is one example of such a fluid. The presence of a benign wetting-fluid fraction, for example 10%, of fill material  63  would retard permeation of the already saturated fill material by an intruding contaminant such as seawater, and therefore would slow deterioration of the fill material&#39;s electrical properties due to the intrusion. Having a fractionally small fluid component of the fill material also aids the lubricity of the mixture, allowing easier flow under high pressure. The fractional portion of fluid within the fill mixture should be such that its entire loss would not be great enough to allow the termination&#39;s pressure balancing means to fail, which in turn would allow the chamber walls to rupture or collapse. 
         [0057]    If there is a small fluid component to the fill material  63 , and if a fluid leak path opened into the cable, fluid would flow into the cable&#39;s interstitial spaces until the fluid pressure within the chamber equilibrated to the cable&#39;s interstitial pressure. That interstitial pressure in most cases would be on the order of one atmosphere, and in all cases would not exceed the ambient external pressure. The particulate portion of the fill material  63  would remain wetted and pressed together at the ambient external pressure, but the fluid within it would no longer be equilibrated to that of the external environment. In the case where fill fluid has leaked out of the chamber and into the cable, having a residual amount that fluid of choice remaining as a wetting agent for the particulate portion of the fill material  63  has some advantages. First, if a second leak path opened up, this time to the external environment, which would be equivalent to a small rupture in the cylinder wall of our analogue example, seawater would enter the chamber. It would leak out of the chamber once again into the cable via the same path from which the fill fluid was lost, but it would be unlikely to completely displace the residual fill fluid; therefore, it would be unlikely to destroy the electrical isolation property of the fill material. Prior art terminations are completely filled with oil, allowing the ambient external pressure to be transmitted throughout the entire chamber volume. The invention&#39;s fill material  63 , which may or may not be wetted, is also able to evenly transmit the exterior ambient pressure to the innermost portions of the chamber volume; and like the oil, it can easily be removed for maintenance and repair of the elements within the chamber. But unlike oil-filled terminations, perforations through the boot seals or conductor jackets will not force any substantial amount of the invention&#39;s chamber fill material into the cable interstices. The chamber walls therefore will not collapse or rupture due to such flaws, and catastrophic failure will not occur. 
         [0058]    As shown in  FIG. 1A , outer chamber elastomeric wall  53  surrounds inner elastomeric chamber wall  44 . The posterior end of outer chamber wall  53  attaches sealably to cable union  5  by the cooperation of inward-facing shoulder  54  of the outer chamber wall with cable-union groove  55 , the shoulder being retained within the groove by exterior shell  4 . The anterior end of outer chamber wall  53  attaches sealably to rearward extension  48  of connector  3  by the cooperation of inward-facing shoulder  57  of outer chamber wall  53  with groove  56  of rearward extension  48 , the shoulder being retained within the groove by exterior shell  4 . Annular volume  52  between outer chamber wall  53  and inner chamber wall  44  is filled with a fill material having the same requirements as fill material  63 . Ribs  59  ( FIG. 5 ) on the exterior surface of inner chamber wall  44  provide axial ventilation paths between inner chamber wall  44  and outer chamber wall  53 . During the final stages of assembly, exterior shell  4 , shown partially cut away in  FIG. 1A , is slid from the rear over the posterior portion of outer chamber wall  53 . Outer chamber-wall shoulder  57  is temporarily unseated from groove  56 , providing an opening through which to fill volume  52 . Once volume  52  is filled, exterior shell  4  is slid far enough forward to capture outer-wall shoulder  57  within groove  56 , but not so far forward as to cover seal screws  50   a,    50   b.  With exterior shell  4  in this position, higher-pressure gas testing of the assembly can be accomplished via ports  51   a,    51   b.  Once testing and filling are complete, exterior shell  4  is slid forward into final position and attached by screws  58  to connector  3  and by similar screws (not shown) to cable union  5 . Seawater (or whatever the exterior environment is) is free to enter the space between exterior shell  4  and outer chamber wall  53  via one or more ports  60  (one of which is shown) through outer shell  4 . As shown in  FIG. 6 , axial ventilation between the interior of exterior shell  4  and outer chamber wall  53  is provided by grooves  61  between lands  62  on the anterior end of outer chamber wall  53 . 
         [0059]    Termination chamber  31  in the invention is well sealed against water intrusion from cable  2 , as well as water intrusion from connector  3 . But in the absence of outer chamber wall  53 , a single perforation of inner chamber wall  44  would permit intrusion of seawater (or whatever the working environment is) into termination chamber  31 . That would not be likely to result in a catastrophic failure, but it is to be avoided if possible. The addition of outer chamber wall  53  with the concomitant creation of annular volume  52  insures that a perforation of either one of outer wall  53  or inner wall  44  would not permit the intrusion of potentially harmful foreign material into termination chamber  31 . Clearly, it would be possible to construct a working termination such as that just described that lacked one or the other of walls  44 ,  53 , but such a device would be more prone to accidental damage and possible contamination as would the previously described two-walled embodiment. 
         [0060]    Although the invention has been described in the context of a simple cable-to-connector junction by way of example only, it will be understood by those skilled in the art that modifications can be made to the disclosed embodiments without departure from the scope or spirit of the invention, which is defined by the appended claims. Accordingly, it is understood that the drawings and the descriptions herein are proffered only to facilitate comprehension of the invention and should not be construed to limit the scope thereof.