Abstract:
A push plug designed to interact with and seal an open end of a length of conduit containing a cable. The plug is comprised of a cap, a neck, and a body. The body contains a number of saw-toothed annular ridges. The plug is manufactured from an elastomeric material which allows the plug to be inserted into a conduit opening of a diameter smaller than the diameter of the saw toothed ridges which creates a frictional seal which resists removal of the plug. The plug body further contains passages running longitudinally through the center of the plug. These passages allow cable run through the conduit to be drawn through the plug and inserted through a thin, flexible membrane covering the plug cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority in U.S. Provisional Patent Application No. 61/145,300, filed Jan. 16, 2009, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to conduit end seals, and in particular a weather-tight plug for sealing cables exiting circular conduits and related applications. 
     2. Description of the Related Art 
     Plastic conduits are used to provide protection and ease of installation of telecommunication and electrical cables traveling between service boxes. Conduits used to house such cables are typically circular and manufactured from polyvinyl chloride (PVC) or high density polyethylene (HDPE). The conduits can run great lengths underground and into structures before terminating at a service box. 
     Cables are typically installed within the conduits after the conduit is buried underground. Cables exist in a variety of sizes and shapes, and are often accompanied by a conducting wire permitting the conduit to be located accurately. Cables are connected to telecommunications equipment by an installer, and the opening at the end of the conduit where the cables exit the conduit is sealed to prevent intrusion by contaminants such as air, water, and animals. Sealing is typically accomplished by encasing the exiting cables within a pliable compound that is capable of adhering to both the cables and the conduit thereby preventing infiltration of contaminants, and maintaining the integrity of the conduit and the cables contained therein. 
     Existing methods and materials used to seal cables exiting conduits are expensive, time consuming, messy and create difficulty when cables are added to an existing conduit. Conduit openings sealed with expanding spray foam, or clays and potting compounds are messy to apply, and the material is difficult to remove when making adjustments to installed cables, or when adding cables to the conduit. Mechanical plugs having a split gasket, a threaded housing and a threaded nut are difficult to install due to the several parts, and the tendency of the gasket to bunch during installation. A method and materials for sealing conduit is needed that is inexpensive, fast and easy to install, and permits adaptation and installation with new and existing conduits that have added or pre-existing cables. 
     Heretofore there has not been available a conduit sealing method and materials with the advantages and features of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     An improved conduit sealing system and method is provided for sealing cables exiting circular conduits. The system includes a monolithic plug manufactured from an elastomeric material having a body at the distal end containing circular sawtooth-shaped ridges, and a circular cap at an opposite, distal end. The plug has one or more passages disposed therein that taper from an opening at the proximal end, and terminate at an enclosure at the distal end comprising a membrane. The membrane consists of the outer layer of the cap and the interior surface of the passage at the distal end. A plurality of passages of varying dimensions may be formed within the plug for receiving cables of corresponding dimension exiting a conduit. 
     Prior to installation of cables through the conduit, the plug is installed by sliding it into the end of the conduit. Frictional sealing engagement is formed between the sawtooth ridges and the interior of the conduit. The membrane across the distal end allows the plug to create a seal equal to that of a solid plug. After cables are installed the plug is removed, mated with the cable, and reinstalled by sliding the plug back into the end of the conduit. Mating the plug and cable consists of either cutting the membrane above a passage and threading a cable into the plug from the proximal end through the membrane, or cutting through the plug from end to end at a depth sufficient to penetrate a passage and its corresponding membrane, and pushing a cable laterally through the side of the plug into the passage thereby creating a sealing engagement between the cables and plug. After either approach to mating the plug and cable, the plug is slid down the cable into the end of the conduit to make a frictional sealing engagement between the sawtooth ridges and the interior of the conduit, and a sealing engagement between the cap and end of the conduit. 
     Several modified embodiments of the plug include exemplar quantity, arrangement and sizes of passages for receipt of a multitude of complementary cables having respective openings at a proximal end and a membrane at the distal end. 
     Manufacture of the single unit plugs is accomplished using a steel forming tool having a first and second half capable of mating in an enclosed sealing arrangement and separating for forming and discharging the plug. The first half of the tool consists of an ejector pin perpendicularly disposed with an ejector plate. The ejector pin is slidably received within a tool base and head insert thereby providing an interior forming surface for molding the cap of the plug. Opposite slide halves are slidably disposed parallel to the tool base for forming the sawtooth-shaped ridges of the plug. The second half consists of one or more core pins for forming the passages within the plug, orientated toward the first half and disposed within a core insert, both of which are disposed within a tool base. Each elongated core pin is substantially hollow and vented to the atmosphere, and has a plug of permeable metal at its tip with a porosity sufficient to permit passage of air but prohibit passages of heated elastomeric material. 
     Heated elastomeric material is injected under pressure into the closed tool from the core insert and substantially fills the cavity within the tool surrounding the core pin. The air displaced by the injected material is discharged through the core pin through the permeable plug and to the atmosphere thereby permitting complete forming of the plug within the tool and around the core pin creating a circular plug with a cap, sawtooth-shaped ridges, and an open-ended passage with a membrane at one end. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments of the present invention illustrating various objects and features thereof. The aspects and features of the drawings are not necessarily to scale relative to each other. 
         FIG. 1  is an isometric view of a push plug embodying the principles of the present invention. 
         FIG. 2  is an enlarged isometric view of the push plug taken generally within circle  2  in  FIG. 1 . 
         FIG. 3A  is a side elevational view of the push plug. 
         FIG. 3B  is a top view of the push plug. 
         FIG. 3C  is a bottom view of the push plug. 
         FIG. 4  is an enlarged side elevational view of the push plug. 
         FIG. 5A  is a side elevational view of a first alternative embodiment push plug. 
         FIG. 5B  is a top view of a first alternative embodiment push plug. 
         FIG. 5C  is a bottom view of a first alternative embodiment push plug. 
         FIG. 6A  is a side elevational view of a second alternative embodiment push plug. 
         FIG. 6B  is a top view of a second alternative embodiment push plug. 
         FIG. 6C  is a bottom view of a second alternative embodiment push plug. 
         FIG. 7  is an isometric view of a third alternative embodiment push plug. 
         FIG. 8  is an enlarged isometric view of a third alternative embodiment push plug taken generally within circle  8  in  FIG. 7 . 
         FIG. 9A  is a side elevational view of a third alternative embodiment push plug. 
         FIG. 9B  is a top view of a third alternative embodiment push plug. 
         FIG. 9C  is a bottom view of a third alternative embodiment push plug. 
         FIG. 10  is an enlarged side elevational view of a third alternative embodiment push plug. 
         FIG. 11A  is a side elevational view of a fourth alternative embodiment push plug. 
         FIG. 11B  is a top view of a fourth alternative embodiment push plug. 
         FIG. 11C  is a bottom view of a fourth alternative embodiment push plug. 
         FIG. 12A  is a cross-sectional view of the manufacturing method of an embodiment of the push plug of the present invention with the tooling in a closed and forming position. 
         FIG. 12B  is a cross-sectional view of the manufacturing method with the tooling in an open position. 
         FIG. 12C  is a cross-section view of the manufacturing method with the tooling in a position releasing the plug. 
         FIG. 13A  is a top view of an alternative embodiment of the invention showing a cable being inserted into a plug through a cut slit. 
         FIG. 13B  is a top view of the same, showing the cable fully inserted into the plug through the cut line. 
         FIG. 14A  is a split side elevational and cross sectional view of a fifth embodiment push plug, the cross sectional view along cut-line  14 A shown in  FIG. 14B . 
         FIG. 14B  is a top view of a fifth alternative embodiment push plug. 
         FIG. 14C  is a bottom view of a fifth alternative embodiment push plug. 
         FIG. 15A  is a split side elevational and cross sectional view of a sixth embodiment push plug, the cross sectional view along cut-line  15 A shown in  FIG. 15B . 
         FIG. 15B  is a top view of a sixth alternative embodiment push plug. 
         FIG. 15C  is a bottom view of a sixth alternative embodiment push plug. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     I. Introduction and Environment 
     As required, detailed aspects of the present invention are disclosed herein; however, it is to be understood that the disclosed aspects are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art how to variously employ the present invention in virtually any appropriately detailed structure. 
     Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, up, down, front, back, right and left refer to the invention as orientated in the view being referred to. The words, “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the aspect being described and designated parts thereof. Forwardly and rearwardly are generally in reference to the direction of travel, if appropriate. Said terminology will include the words specifically mentioned, derivatives thereof and words of similar meaning. 
     Referring to the drawings in more detail, the reference numeral  2  generally designates a push plug for sealing a cable  4  exiting a conduit  6 . Without limitation on the generality of useful applications of the plug  2 , it is particularly well suited for use with circular conduits such as fiber optic conduit manufactured with PVC or HDPE. However, the plug  2  can be used with conduits manufactured with different materials and of varying diameters. 
     II. Preferred Embodiment Push Plug  2   
     The plug  2  is a single component device generally comprising a neck  12  disposed between a distal end  9  having a cap  10 , and a proximal end  11  having a body  13 . Without limitation on the generality of useful materials, the plug  2  may be composed of an elastomeric material which includes, but is not limited to rubber, silicone, plastics and urethane, preferably flexible PVC having a hardness of approximately 60 A durometer. 
     The body  13  includes a plurality of annular, sawtooth-shaped ridges  22  projecting outwardly away from the longitudinal axis  24 . Each ridge  22  includes an upper and lower edge  26 ,  27 . The upper edge  26  is formed by the intersection of a distal face  28  lying generally in a plane perpendicular to the longitudinal axis  24 , and a proximal face  30  which slopes distally and outwardly to the upper edge  26  from the lower edge  27 . The diameter of the ridges  22  is less than the diameter of the cap  10  but greater than the diameter of the inner surface  7  of the conduit  6 . The result is a sealing engagement between the plug  2  and conduit  6  due to the frictional and compressive forces exerted by the ridges  22  upon the inner surface  7  of the conduit  6  thereby providing a tight seal against water, air, and animals. 
     One or more passages  32  extend between an opening  34  at the proximal end  11  and the inner surface  21  of the membrane  20  at the distal end  9  having a proximal inside diameter ID. 1  and a lesser, distal inside diameter ID. 2 . In the exemplary embodiment, the plug  2  has two passages  32  with a distal inside diameter ID. 2  dimensioned to securely receive a cable  4  of the ribbon-type for optical fiber. The type, shape, or diameter of the cable  4  that may be used with the plug  2  includes, but is not limited to coaxial cable, multi-core cable, optical fiber cable, ribbon cable for optical fiber, mineral insulated copper-clad cables, and electrical power cables. The quantity, arrangement, and size of the distal inside diameter ID. 2  of the passages  32  can vary according to the type and shape of cables used with the plug  2 . The distal inside diameter ID. 2  of the passage  32  is slightly less than the particular cable  4  that is received therein thereby securely engaging the exterior of the cable  4  as a result of the elastomeric properties of the plug  2 . 
     The cap  10  is generally circular in shape and includes an upper and lower surface  14 ,  16 , bound by an edge  18 . The diameter of the cap  10  is substantially equivalent to the diameter of the exterior  15  of the particular conduit  6  used. The upper surface  14  and inner surface  21  define a membrane  20  at the distal end  9  of the plug  2  that is punctured and through which the cable  4  protrudes. 
     III. Use 
       FIGS. 1-2  show the plug  2  mounting a cable  4  exiting a circular conduit  6 . The plug  2  is installed at the open end  8  of a conduit  6  by either threading the cable  4  into the passage  32  and through the membrane  20 , or by wrapping the plug  2  around an in-place cable  4 . In situations where the end of a cable  4  is free, the cable  4  can be threaded through the plug  2 . Threading the cable  4  into the plug  2  is accomplished by first positioning a knife at the distal end  9  of the plug  2  over the top of a passage  32  and cutting one or more slits in the upper surface  14  and through the membrane  20 , no greater than the distal inside diameter ID. 2 , to allow the cable  4  to pass through. Next, the end of a cable  4  is inserted into the passage  32  at the proximal end  11  and pushed into the inner surface  21  and through the membrane  20  emerging at the distal end  9  of the plug  2 . The plug  2  is then slid down the cable  4  and inserted into the open end of a conduit  4  until the lower surface  16  rests flush with the end  8  of the conduit  10  thereby creating a sealing engagement between the plug  2  and conduit  6 , and the plug  2  and cable  4 . 
     In situations where a length of cable  4  has been drawn through the opening of the conduit  6  and an end of the cable  4  is not free, the plug  2  can be wrapped around the cable  4  by first creating a cut-line  36 . A plug is first prepared by making a cut-line  36  through the plug  2  longitudinally beginning at either the proximal end  11  or the distal end  9  through to the opposite end at a depth sufficient to penetrate the passage  32  from the lateral edge of the plug  2 . A cut is then made in the membrane  20  above the passage  32  as described above. Alternatively, the membrane  20  can be cut first, followed by the cut-line  36 . This process can be repeated for additional passages as necessary depending on the number and arrangement of passages  32  of the particular plug  2  in use, and the specific passages  32  desired to be used in a particular application. The plug  2  may then be installed by first orientating the plug  2  so that the proximal end  11  is orientated toward the open end  8  of the conduit  6 . Next, the cable  4  is passed laterally into the plug  2  through the cut-line  36  from the side ensuring the cable  4  is orientated properly relative to the passage  32  in the plug  2 , and the particular cable  4  used. Once the desired number of cables  4  have been installed, the plug  2  is then slid down the cables  4  into the open end  8  of the conduit  6  as described above. 
       FIGS. 13A and 13B  more clearly demonstrate the effect of the cut-line  36  on the plug  2 .  FIG. 13A  demonstrates a cable  4  being forced into the passage  34  through the opening accommodated by the cut-line  36 .  FIG. 13B  demonstrates the plug  2  returning to its original cylindrical shape once the cable  4  has been fully inserted into the passage  34 . This method provides an alternative way for a cable  4  to be inserted into a plug  2 , after which the plug  2  is placed into the open end of a conduit carrying the cable  4 . 
     IV. Alternative Embodiments 
     Alternative embodiment push plugs in accordance with the present invention are shown in  FIGS. 5A-11C  and  14 A- 15 C, having alternative quantity, arrangement and size of passages for particular applications of the aforementioned invention. The alternative embodiment plugs are used in the same manner as described for the plug  2  above. Many of the characteristics and uses of the alternative embodiment push plugs are substantially similar to those described for the push plug  2  described above and are not reiterated below in detail. However, distinguishing features are described below. 
     A first alternative embodiment push plug  52  in accordance with aspects of the present invention is shown in  FIGS. 5A-5C , and includes five evenly-spaced passages  54  arranged in a circular array centered on the longitudinal axis  55  and are of a type and shape dimensioned to receive a cable of the ribbon-type for optical fiber. The passages  54  have an opening  57  at the proximal end  56  and taper to a lesser diameter at a membrane  60  sealing the distal end  58 . 
     A second alternative embodiment push plug  62  in accordance with aspects of the present invention is shown in  FIGS. 6A-6C , and includes two passages  64  of a type and shape dimensioned to receive a cable of the ribbon-type for optical fiber, and one passage  65  of a type and shape dimensioned to receive a circular cable such as, but not limited to, coaxial cable, multiline cable, optical fiber cable, or copper cables. As above, the passages have an opening  66  at the proximal end  67  and taper to a lesser diameter at a membrane  68  sealing the distal end  69 . 
     A third alternative embodiment push plug  72  in accordance with aspects of the present invention is shown in  FIGS. 7-10 .  FIG. 7  shows the plug  72  mounting a circular cable  74  within a circular passage  80 , and exiting a circular conduit  76 . The plug  72  includes one passage  78  of a type and shape dimensioned to receive a cable of the ribbon-type for optical fiber, and one passage  80  of a type and shape dimensioned to receive a circular cable  74  as described above. The passages  78 ,  80  have an opening  82  at the proximal end  84  and taper to a lesser diameter at a membrane  86  sealing the distal end  88 . As described above, the plug  72  can be installed at the end of a conduit  76  by making a cut-line  90  along the length of the plug  72  and through the membrane  86  to pass a cable  74  laterally into the passage  80 . Alternatively, a cut can be made in the membrane  86  above a passage  80 , and the end of the cable  74  can be inserted into the opening  82  of the circular passage  80  and drawn through membrane  86 . 
     A fourth alternative embodiment push plug  92  in accordance with the present invention is shown in  FIGS. 11A-11C , and includes three evenly-spaced passages  94  arranged in a circular array, centered on the longitudinal axis  96 , of a type and shape dimensioned to receive a circular cable as described in  FIGS. 7-10  above. The passages  94  have an opening  98  at the proximal end  100  and taper to a lesser diameter at a membrane  102  sealing the distal end  104 . 
     A fifth alternative embodiment push plug  212  in accordance with the present invention is shown in  FIGS. 14A-14C , and includes at least one passage  214 , here shown centered on the longitudinal axis  216  and of a type and shape dimensioned to receive a circular cable. However, this alternative embodiment can accommodate any size passage and any sized cable proportionate to that passage. The passage  214  has an opening  218  at the proximal end  202  and ends at a membrane  206  sealing the distal end  200 . At least one interior rib  204  of diameter less than the diameter of the passage  214  is centrally located within the passage. As a cable  4  is pulled through the opening  218  and into the passage  214  it will come into contact with the internal rib  204 . The rib provides a tight seal against the cable  4 . 
     A sixth alternative embodiment push plug  232  in accordance with the present invention is shown in  FIGS. 15A-15C . A central passage  234  is located along the longitudinal axis  236  and is a circular shape. A series of concentric, coaxial, cylindrical sections  230  allow the passage  234  to be selectively enlarged to accommodate larger cable types. The passage  234  has an opening  238  at the proximal end  222  and ends at a membrane  226  sealing the distal end  220 . The user can selectively remove one or more of the cylindrical sections  230 , each expanding the diameter of the opening  238  and the passage  234 , accommodating larger cable types. 
     It will be appreciated that the embodiments of the aforementioned plugs can be used for various other applications. Moreover, the plugs can be fabricated in various sizes, having different arrangements and sizes of passages, and from a wide range of suitable materials, using various manufacturing and fabrication techniques. 
     V. Manufacture 
     The push plug  2 , and all alternative embodiments above are manufactured using the method described below.  FIGS. 12A-12C  show the manufacturing method for an exemplary embodiment circular plug  112 . As previously described, the plug  112  consists of a neck  114  disposed between a distal end  116  having a cap  118 , and a proximal end  120  having a body  122  containing a plurality of annular, sawtooth-shaped ridges  124  as described above. The plug  112  has a passage  126  with an opening  128  at the proximal end  120  tapering to an inner surface  130  of the membrane  132  at the distal end  116 . 
     Referring to the drawings in more detail,  FIG. 12A  shows the plug  112  formed within a forming tool  136 . The components of the forming tool  136  are manufactured from steel and consist of first and second halves  152 ,  154 . The first half  152  consists of an ejector pin  156  perpendicularly disposed within an ejector plate  158 . The ejector pin  156  is slidably received within a tool base  160  and head insert  162 . Opposing slide halves  164  are slidably disposed parallel to the tool base  160 . The second half  154  consists of a core pin  168  orientated toward the first half  152 , having a tip  172  tapering to a wider diameter at a base  174  disposed within a core insert  170 , both of which are disposed within the tool base  166 . The core pin  168  is an elongated, substantially hollow structure having a plug  176  disposed at the tip  172  with a passage  178  extending between the end of the plug  174  and the base  174 . The plug  176  consists of a permeable metal having a porosity sufficient to permit passage of air but prohibit passage of heated elastomeric material. The passage  178  exits the tool  136  along the base of the core pin  168  and vents to the atmosphere. 
     With the tool  136  in a closed position ( FIG. 12A ), the periphery of a an enclosed cavity is defined by the inner surfaces of the core insert  170 , sawtooth-shaped inner relief of the slides  164 , head insert  162 , and an ejector pin  156 . A volume of the cavity is displaced by the presence of one or more core pins  168  residing therein. The quantity, arrangement, and dimensions of the core pins  168  are determined by the particular characteristics of the cable that is to reside in the passage  126  formed in the plug  112 . The distance between the tip  172  of the core pin  168  above the core insert  170  is less than the distance between the surface of the core insert  170  and the surface defined by the interface of the ejector pin  156  and head insert  162 . 
     The plug  112  is formed by injecting, under pressure, heated elastomeric material, preferably PVC, into the plug-shaped cavity through ports (not shown) at the edge of the core insert  170 . During operation, the metallic components of the first and second halves  152 ,  154  of the tool  136  are cooled to permit curing of the heated elastomeric material. As the material is injected into the cavity, it substantially fills the cavity within the tool  136  surrounding the core pin  168 . Material accumulates within the entire volume of the cavity including the space created by the separation between the tip  172  of the core pin  168 , and the interface created by the ejector pin  156  and head insert  162 . Pressure created by injection of material into the closed cavity displaces air within the cavity that is vented from the tool  136  through the plug  172  and out the passage  178 . Providing a plug  176  and passage  178  for discharge of trapped air allows the elastomeric material to substantially fill the cavity including the space between the tip  172  of the core pin  168 , and the inner surface of the ejector pin  156  and head insert  162 . The material that fills the aforementioned space forms the membrane  132  of the plug  112 . 
     After curing of the injected material, the plug  112  is disengaged from the tool  136  by first separating the first half  152  from the second half  154  ( FIG. 12B ). The opposing slides  164  are drawn laterally away from the plug  112  either concurrently with the separation of the halves  152 ,  154 , or shortly after the core pin  168  is drawn out of the passage  126 . After separation of the halves, the plug  112  is separated from contact with the head insert  162  by sliding the ejector pin  156  and ejector plate  158  toward the second half  154  while the remaining components of the first and second halves  152 ,  154  remain static. Once the plug  112  is free of the components of both the first and second halves  152 ,  154 , the tool  136  is returned to the starting position in  FIG. 12A  and formation of another plug  112  may begin. 
     It is to be understood that while certain aspects of the invention have been shown and described, the invention is not limited thereto and encompasses various other embodiments and aspects.