Abstract:
A method of sealing a cable penetration includes assembling a cable seal and inserting the cable seal into a cable penetration. Assembling the cable seal includes adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket, and positioning a secondary elastic seal over the heat-shrinkable tubing. An example of a secondary elastic seal could be O-rings. A cap or other means provides the outer sealing surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/297,671, filed Dec. 8, 2005, now issued as U.S. Pat. No. 7,232,955, which is hereby incorporated by reference and is assigned to assignee of the present invention. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to methods and apparatus for assembling cable seals. 
     Many known industrial facilities have a variety of cable systems used to conduct electrical and electronic signals between field apparatus and non-field apparatus. Some examples of field apparatus are pressure data transmitters and valve position drive motors. Some examples of non-field apparatus include power sources and control system cabinets located in areas such as control rooms and offices. Some examples of cable uses are to transmit data to and from a variety of field apparatus and non-field apparatus, transmit electronic directives to field apparatus from non-field apparatus and to provide electrical power to apparatus regardless of location. 
     Many known cable systems include data and power cables that are typically routed through open passages of apparatus, the open passages often referred to as cable penetrations. The cable penetrations typically have seals to maintain the integrity of the cable jackets and to mitigate the potential for vapor ingression into the associated instrumentation/electronics region of the apparatus. The aforementioned seals may also be used in circumstances where separating differing environmental conditions between an electronic device and the cable penetration is not as important as simply providing for a cable support mechanism for facilitating cable routing, for example, cable tray ingress and egress, building wall penetrations and cable vault risers. 
     Many facilities have operating environments that include humidity levels that may exceed 50% relative humidity and temperature levels that may exceed 66° Celsius (C.) (150° Fahrenheit (F.)) for extended periods of time. Some facilities may also have apparatus positioned such that a potential for exposure to steam or other vapors may be present. In the aforementioned environmental circumstances, the outer jackets of the cables may experience cold flow, i.e., a time dependent strain (or deformation) of the cable jacket resulting from stress, and allow a subsequent vapor ingression into the associated instrumentation/electronics region of the apparatus. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of sealing a cable penetration is provided. The method includes assembling a cable seal and inserting the cable seal into a cable penetration. Assembling the cable seal includes adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket, and positioning a secondary elastic seal over the heat-shrinkable tubing. An example of a secondary elastic seal could be O-rings. A cap or other means provides the outer sealing surface. 
     In another aspect, a cable seal is provided. The cable seal includes at least one cable having an FEP outer jacket. The seal also includes at least a portion of a predetermined length of a heat-shrinkable tubing that is inserted over at least a portion of the cable outer jacket. The seal further includes a cap having at least one sealing surface. The cap is inserted over at least a portion of the heat-shrinkable tubing. The seal also includes at least one elastic member. The member includes at least one sealing surface and is inserted over at least a portion of the heat-shrinkable tubing. 
     In a further aspect, a cable penetration sealing system is provided. The system includes a cable seal for a cable and at least one apparatus. The seal includes a predetermined length of a heat-shrinkable tubing, a cap, and at least one elastic member. The cable includes an FEP outer jacket. The tubing is inserted over at least a portion of the cable outer jacket. The cap includes at least one sealing surface and the cap is inserted over at least a portion of the heat-shrinkable tubing. The elastic member includes at least one sealing surface and is inserted over at least a portion of the heat-shrinkable tubing. The apparatus includes at least one cable penetration and the cable penetration is configured to receive the seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary illustration of an exemplary cable seal; and 
         FIG. 2  is an enlarged view of the cable seal shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a fragmentary illustration of an exemplary cable seal  200 . Seal  200  is integral to an apparatus  202 . In the exemplary embodiment, apparatus  202  is a proximity probe (sometimes referred to as an eddy current probe and/or a displacement transducer). Alternatively, apparatus  202  may be, but not be limited to, an electrical current transducer, a resistance temperature detector (RTD), or any other industrial field instrument. Also alternatively, apparatus  202  may be any object having a cable penetration, including a wall, cable tray side member, and a bracket assembly. Apparatus  202  is often used to measure bearing (not shown in  FIG. 1 ) vibration on large machines, such as turbines, as a function of the relative movement between the bearing and the journal. As the relative position between the bearing and journal varies, an electrical signal is induced within apparatus  202 . Apparatus  202  may be used with large machines including, but not limited to steam turbines, and may therefore be exposed to an environment that includes steam exiting a turbine bearing housing. The steam will normally increase the relative humidity and temperature levels within the vicinity of the bearing, and therefore, apparatus  202 . 
     Apparatus  202  has a housing  204  that is normally cast from a material that can withstand environments that include extended high temperatures, vibration, humidity, and exposure to steam. In the exemplary embodiment, housing  204  is cast from stainless steel. Alternatively, other materials including, but not limited to, titanium alloys may be used. Housing  204  has a plurality of cavities formed during the casting process. Alternatively, at least some of these cavities may be formed using standard machining techniques subsequent to the casting process. Apparatus  202  also has an instrumentation/electronics cavity  206  that is formed by a plurality of interior walls (not shown in  FIG. 1 ) of housing  204  to a set of predetermined dimensions to house the electronics and instrumentation (not shown in  FIG. 1 ) used to measure the relative movement within the associated component, for example, a journal bearing, and subsequently transform an induced electronic signal into a signal that is transmitted to computer  102 . Cavity  206  typically houses electrical power and electronic interconnections (not shown in  FIG. 1 ). Therefore, cavity  206  is normally the largest cavity within housing  204  and houses the components that may be sensitive to vapor ingression. 
     Housing  204  also has a cable cavity  208  that is positioned and dimensioned within housing  204  to facilitate pulling a cable  210  into housing  204 . Cable  210  has an outer jacket  212  that surrounds at least one electrical conductor (not shown in  FIG. 1 ). Cavity  206  and cavity  208  may be formed integrally or as separate cavities. Substantially annular cavity  208  is formed by a substantially annular cable cavity interior wall  214  and a cable cavity housing neck  216 . Neck  216  extends radially inward from the aforementioned housing inner wall and forms a substantially circular cable cavity open passage  218  and a cable cavity open passage sealing surface  220 . Neck  216  and passage  218  are discussed further below. 
     Housing  204  further has a substantially annular open passage  222  that is formed by a substantially annular housing open passage interior wall  224  and neck  216 . Furthermore, housing  204  has an annular housing opening  228  that is a widened portion of open passage  222  that is defined by an annular housing open passage vertical sealing surface  230  and an annular housing open passage horizontal sealing surface  232 . Sealing surface  230  protrudes axially inward from a housing outermost surface  234  and sealing surface  232  extends substantially radially perpendicular to surface  230 . Cavity  208 , open passage  218 , open passage  222  and housing opening  228  define a cable penetration. 
     Seal  200  includes a plurality of elastic media. In the exemplary embodiment the elastic media is a plurality of O-rings  236  and  238 . Alternatively, elastic media such as tapes, foams, putties, or other materials that meet or exceed the predetermined characteristics of O-rings  236  and  238  may be used. Seal  200  also has a heat-shrinkable tubing  240  and a housing cap  226 . Housing cap  226  is inserted over cable  210  and inserted into an annular housing opening  228 . Alternative, other media and materials that meet or exceed the predetermined characteristics of cap  226  may be used, for example, tapes, foams and putties. O-rings  236 ,  238  and tubing  240  are discussed further below. 
       FIG. 2  is an enlarged view of exemplary cable seal  200 .  FIG. 2  illustrates many of seal  200  components illustrated in  FIG. 1  and discussed above. 
     In the exemplary embodiment, heat-shrinkable tubing  240  has two layers, tubing outer layer  242  and tubing inner layer  244 . Outer layer  242  is formed with polytetrafluoroethylene (PTFE). As a stand-alone material, PTFE heat-shrinkable tubing generally has a shrink ratio in the 2:1 to 4:1 range, i.e., the inner diameter of a section of PTFE tubing will be reduced by approximately 50% to 75% subsequent to heat application at a temperature range of approximately 325° C. to 340° C. (617° F. to 644° F.). PTFE typically has a continuous temperature rating of approximately 250° C. (482° F.) that is usually sufficient to protect an underlying cable from a nearby steam source that may have a temperature of approximately 100° C. (212° F.) at substantially atmospheric pressures. PTFE also is substantially non-porous and normally exhibits chemical resistance properties that are sufficient for many industrial applications. Furthermore, PTFE typically exhibits a smooth outer surface that facilitates a resistance to strain as discussed further below. 
     Inner layer  244  is formed with fluorinated ethylene-propylene (FEP). As a stand-alone material, FEP heat-shrinkable tubing generally has a shrink ratio in the 1.3:1 to 1.6:1 range, i.e., the inner diameter of a section of PTFE tubing will be reduced by approximately 23% to 37.5% subsequent to heat application at a temperature range of approximately 190° C. to 210° C. (374° F. to 410° F.). FEP typically has a continuous temperature rating of approximately 204° C. (400° F.) that is usually sufficient to protect an underlying cable from a nearby steam source that may have a temperature of approximately 100° C. (212° F.) at substantially atmospheric pressures. FEP, similar to PTFE, also is substantially non-porous and normally exhibits chemical resistance properties that are sufficient for many industrial applications. However, FEP typically does not exhibit as smooth an outer surface as PTFE. 
     In the exemplary embodiment, a section of tubing  240  is cut to a predetermined length. The length may be determined from the dimensions of the length of housing open passage  222  and the predetermined lengths of heat-shrinkable tubing that extend beyond passage  222  in either of the two axial directions along cable  210 . The section of tubing  240  is inserted over cable  210 . Normally, it may be more convenient to slide tubing segment  240  over the end of cable  210 . 
     Heat is applied to dual-layer tubing  240  to form a tubing-enclosed cable portion  246  (illustrated as the section of cable  210  enclosed by tubing  240  in  FIG. 2 ). Inner FEP layer  244  melts and flows to encapsulate cable outer jacket  212 . Since outer jacket  212  is also formed from FEP, jacket  212  also melts slightly and a chemical bond between tubing inner layer  244  and jacket  212  is formed. Inner FEP layer  244  does not shrink as much as outer PTFE layer  242  does, therefore, layer  242  shrinks tightly over inner FEP layer  244  to form a tight, smooth seal in conjunction with inner layer  244  on cable outer jacket  212 . In the exemplary embodiment, tubing  240  has a continuous service temperature rating of approximately 200° C. (392° F.). 
     Alternatively, tubing  240  may have more than two layers, for example a neutral middle layer. Tubing  240  may also have one layer of a composite material that obtains substantially similar results as the exemplary embodiment. 
     Upon cooling of tubing-enclosed cable portion  246 , housing cap  226  is inserted over cable portion  246  in a manner substantially similar to that used to insert tubing  240  over cable  210  as described above. Cap  226  has an open passage (not shown in  FIG. 2 ) of sufficient diameter to facilitate insertion over cable portion  246  while having a clearance between an outermost surface  248  of cable portion  246  that is small enough to facilitate a mitigation of vapor ingression between cap  226  and cable portion  246  as well as provide additional structural support to cable portion  246  to mitigate strain of cable portion  246 . Cap  226  is positioned over cable portion  246  at approximately the midpoint of cable portion  246  so that sufficient length of cable portion  246  extends beyond passage  222  in either of the two axial directions along cable portion outermost surface  248  to facilitate sufficient strength in the layers of cable portion  246 , to mitigate strain in cable portion  246 , and to establish a small clearance between the outermost surface  248  of cable portion  246  and the cable cavity open passage sealing surface  220  as discussed below. 
     In the exemplary embodiment, two O-rings  236  and  238  are inserted over cable portion  246  to assemble a tubing/O-ring-enclosed cable portion  250 . O-rings  236  and  238  are substantially circular and annular. O-rings  236  and  238  are inserted over cable portion  246  in a manner substantially similar to that used to insert tubing  240  over cable  210  as described above. O-ring  236  and O-ring  238  expand to mitigate a clearance between a surface  252  of O-ring  236  and a surface  254  of O-ring  238  and the radially outermost surface  248  of cable portion  246  to mitigate strain of cable portion  246  and facilitate a seal that tends to mitigate vapor ingression into cavity  208  along the outermost surface  248  of cable portion  246 . The smooth outermost surface  248  of tubing-enclosed cable portion  246  formed by tubing outer layer  242  facilitates the sealing action between O-rings  236  and  238  and surface  248 . O-ring  238  is a redundant backup for O-ring  236 . 
     Tubing/O-ring-enclosed cable portion  250  is inserted into housing  204  through housing open passage  222  pulled into cavity  206  (shown in  FIG. 1 ) for subsequent electrical connection to the appropriate terminals (not shown in  FIGS. 1 and 2 ). Cable  210  is pulled through housing  204  until O-ring  236  contacts a housing open passage vertical O-ring sealing surface  256 . The aforementioned expansion of O-ring  236  also tends to mitigate clearances between surface  252  of O-ring  236  and sealing surface  256  and a housing open passage horizontal O-ring sealing surface  258 . O-ring  238  expands in a similar manner, however, instead of expanding against housing open passage vertical O-ring sealing surface  256 , surface  254  of O-ring  238  expands against surface  252  of O-ring  236 . The expansion of O-ring  236  against surfaces  256  and  258  and the expansion of O-ring  238  against surface  258  facilitate a seal that tends to mitigate vapor ingression into cavity  208 . Housing open passage void  260  permits additional expansion of O-rings  236  and  238  in the axial direction. 
     Inserting Tubing/O-ring-enclosed cable portion  250  in housing  204  also tends to decrease a clearance between the outermost surface  248  of cable portion  246  and the cable cavity open passage sealing surface  220  to facilitate a mitigation of vapor ingression into cavity  208  and to mitigate strain of cable portion  246 . 
     Assembly of seal  200  is completed by inserting cap  226  into housing opening  228  such that a substantial portion of cap  226  sealing surface is in contact with a substantial portion of surfaces  230  and  232  to facilitate a mitigation of vapor ingression into cavity  208  and to mitigate strain of cable portion  246 . In the exemplary embodiment, cap  226  forms a friction seal with surface  232 . Alternatively, an adhesive suitable for the associated environment may be used to affix cap  226  to surfaces  230  and  232 . Also alternatively, at least one set screw may be inserted into a channel formed radially through housing  204  and cap  226 . 
     The methods and apparatus for a cable seal described herein facilitate operation of a cable penetration sealing system. More specifically, designing and installing a cable seal as described above facilitates operation of a cable penetration sealing system by mitigating an cold flow of a cable jacket. As a result, degradation of cable jacket integrity, effectiveness and reliability, extended maintenance costs and associated system outages may be reduced or eliminated. 
     Although the methods and apparatus described and/or illustrated herein are described and/or illustrated with respect to methods and apparatus for a cable penetration sealing system, and more specifically, an apparatus cable seal, practice of the methods described and/or illustrated herein is not limited to apparatus cable seals nor to cable penetration sealing systems generally. Rather, the methods described and/or illustrated herein are applicable to designing, installing and operating any system. 
     Exemplary embodiments of cable seals as associated with cable penetration sealing systems are described above in detail. The methods, apparatus and systems are not limited to the specific embodiments described herein nor to the specific cable seals designed, installed and operated, but rather, the methods of designing, installing and operating cable seals may be utilized independently and separately from other methods, apparatus and systems described herein or to designing, installing and operating components not described herein. For example, other components can also be designed, installed and operated using the methods described herein. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.