Abstract:
A drogue for drawing an elongated item through a conduit is disclosed. The drogue includes a flexible bag having a closed end and an oppositely disposed end opening. Shroud lines attached to the bag at the end opening allow attachment of the drogue to the item. A biasing member, preferably in the form of a continuous loop of flexible, resilient interconnected wire legs, is attached to the bag and positioned proximate to the end opening. The loop engages the bag over a portion of its length and biases the end opening into an open configuration to prevent its collapse and loss of pneumatic pressure as it is propelled through the conduit.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to pneumatically inflated drogues for drawing lines and other elongated items through conduits.  
       BACKGROUND OF THE INVENTION  
       [0002]     Communication networks for voice communication, data links for computer systems, as well as remote sensing and control systems, often require that communication lines linking various nodes of the system be drawn through extensive lengths of conduit between the nodes. The conduit defines a path for the communication network and may be buried underground or may be positioned throughout a building or other structure. Access to the conduit is typically afforded only at isolated points where connections are made to system nodes. The conduit often has one or more bends as sharp as 90° which the communication lines must negotiate, as well as horizontal, vertical and angled segments of various lengths. Obstructions, in the form of other communication lines, are also often present within the conduit.  
         [0003]     The communication lines to be drawn through the conduit may include, for example, simple wires, wiring harnesses, coaxial cable or optical fiber bundles. Other elongated items such as flexible sleeves for protecting the communication lines are also drawn through the conduit. Such protective sleeves often have pull cords pre-positioned within them for later drawing communication lines though the sleeve. As these lines and sleeves cannot be pushed through the conduit, it is found advantageous to draw them through the conduit by first drawing a high-strength pull cord in the form of a tape through the conduit, attaching the tape to the item to be drawn through the conduit, and drawing the item by pulling the tape.  
         [0004]     The tape may be pneumatically drawn through the conduit by attaching it to a small parachute-like drogue, positioning the drogue within the conduit and forcing compressed air into the conduit behind the drogue. The drogue is inflated by the compressed air, preferably so that it fills the conduit. The differential pressure within the conduit which results from the inflated drogue will drive it through the conduit, the drogue drawing the pull tape along with it.  
         [0005]     Unfortunately, parachute-like drogues, being fabric membranes, often collapse when negotiating bends such as elbow joints or obstacles within the conduit. Once collapsed, the differential pressure is lost and forward progress of the drogue, and its tape are halted. It can be very difficult to re-inflate a drogue which deflates deep within the conduit. The drogue must be drawn back to its starting point, re-inflated and another attempt made to negotiate the conduit. This process may be repeated many times before success is achieved, if at all. There is clearly a need for a device which can reliably negotiate conduit having bends and obstacles for positioning communication lines, as well as other elongated items such as protective sleeves.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention concerns a drogue for drawing an elongated item through a conduit. The drogue comprises a flexible bag having an end opening. The end opening allows the drogue to be inflated and pneumatically propelled along a conduit. The elongated item is attachable to the bag at the end opening, preferably by a plurality of shroud lines attached to the bag.  
         [0007]     A biasing member, preferably in the form of a flexible resilient wire loop, is attached to the bag and positioned proximate to the end opening. The biasing member engages the bag over a portion of its length and applies a biasing force outwardly, thereby biasing the end opening into an open configuration which allows the drogue to fill the conduit and be readily inflated.  
         [0008]     The biasing member is, however, resiliently yieldable towards a collapsed configuration wherein the bag&#39;s end opening is substantially closed in response to restricting forces experienced within the conduit. The biasing member acts to restore the end opening to an open configuration in the absence of restricting forces. This capability allows the drogue to negotiate bends and obstructions within the conduit. As the drogue encounters a bend or obstruction, the biasing member resiliently collapses to change the shape of the end opening sufficiently to allow it to pass by the obstruction or through the bend. Once beyond the bend or obstruction, the biasing forces of the biasing member expand the end opening to its full open configuration so that the differential pressure within the conduit is maintained and the drogue may continue on through the conduit.  
         [0009]     Preferably, the bag takes the form of an elongated, tapered tubular member. The biasing loop preferably comprises a plurality of flexible, resilient legs interconnected to one another end to end. The legs are angularly oriented with respect to one another in a zig-zag pattern. A vertex is formed at each end of each leg joining the legs one to another. The legs are attached to the tubular member at a plurality of discrete attachment points positioned in spaced relation along the legs and around the end opening of the bag. Preferably, the attachment points coincide with the vertices. Individual loops are formed in the legs at each vertex to provide flexibility to the biasing loop and to facilitate its attachment to the bag. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a drogue according to the invention;  
         [0011]      FIG. 2  is a longitudinal sectional view taken at line  2 - 2  of  FIG. 1 ;  
         [0012]      FIG. 3  is a detailed view of a biasing element before being formed into a biasing loop used with the drogue according to the invention;  
         [0013]      FIG. 4  is a detailed partial view on an enlarged scale taken at line  4 - 4  in  FIG. 3 ; and  
         [0014]      FIGS. 5 and 6  are side views showing the drogue in use within a conduit. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0015]      FIG. 1  shows a drogue  10  according to the invention. Drogue  10  comprises a bag  12 , preferably in the form of a flexible elongate tubular member, having a substantially circular cross section, a closed end  14  and an end opening  16 . Preferably, the bag  12  is formed of a woven fabric such as nylon to provide flexibility, strength, toughness and abrasion resistance. Other materials are also feasible, including polyester and polyimides, as well as natural fibers such as cotton.  
         [0016]     The bag  12  may be woven as a tube or constructed from triangular pieces  18  sewn together along seam lines  20 . The fabric forming bag  12  has a weave density which is substantially fluid tight, allowing it to be pneumatically inflated as described below. Alternatively, the bag  12  may be formed from a continuous sheet material, such as expanded polytetrafluoroethylene, vinyl as well as other polymers capable of forming thin flexible sheets.  
         [0017]     When bag  12  is in an open configuration, its end opening  16  preferably has a substantially circular cross-section and is sized to sealingly fit within a conduit (see  FIG. 6 ). Bag  12  is preferably tapered or partially tapered lengthwise with the closed end  14  being smaller than the end opening  16 .  
         [0018]     A plurality of shroud lines  22  are attached to bag  12  at the end opening  16 . The shroud lines  22  preferably extend from the end opening to form closed loops  24  to which a pull tape  26 , a communication line (not shown), a protective sleeve (also not shown) or other elongated item may be attached. The shroud lines  22  preferably have a high tensile strength and may be attached to the bag  12  by sewing or using fasteners such as rivets. Multiple shroud lines  22  are preferred to more evenly distribute the tensile force to the end opening  16  occasioned when the drogue is inflated and drawing a line through a conduit as illustrated in  FIG. 5 .  
         [0019]     As further shown in  FIG. 1 , a biasing member  27  is attached to the bag  12  and positioned proximate to the end opening  16 . Biasing member  27  provides a means for biasing the end opening  16  outwardly into an open configuration. Biasing member  27  is, however, resiliently yieldable towards a collapsed configuration wherein the end opening of the bag  12  is substantially closed in response to restricting forces, as may be encountered within a conduit. The biasing member acts to restore the end opening  16  to an open configuration in the absence of restricting forces within the conduit as described in further detail below.  
         [0020]     The engagement length between the biasing member  27  and the bag  12  may be between about ¼ to about ½ of the length of the bag, or the biasing member  27  may have a length approximately equal to the diameter of the end opening  16  over which it engages the bag  12 . By limiting the engagement length between the bag  12  and the biasing member  27 , a large portion of the bag remains flexible and readily bendable so as to facilitate negotiation of bends in the conduit as described below.  
         [0021]     Biasing member  27  preferably takes the form of a flexible, resilient biasing loop  28 . The biasing loop  28  extends substantially continuously around the end opening  16  and engages bag  12  over a portion of its length proximate to the end opening. Biasing loop  28  is preferably concentric with end opening  16  and positioned on the inside of the bag  12  to prevent the loop from snagging on obstructions as the drogue passes through a conduit.  
         [0022]     The biasing loop  28  applies an outward biasing force around the bag  12  which acts to restore the end opening  16  into the open configuration as described above so that the bag will always be inflatable within the conduit. Biasing loop  28  is resilient and flexible and will resiliently yield, as described above, when negotiating obstructions or a bend. The biasing loop  28  also preferably biases the end opening  16  into sealing contact with the conduit to help maintain the differential pressure propelling the drogue  10 .  
         [0023]     As shown in  FIG. 2 , the biasing loop  28  is preferably formed of a plurality of wire segments  30  connected end to end in a zig-zag pattern. Being angularly oriented relative to one another, each segment  30  meets its neighboring segment at a vertex  32 . Preferably, the wire segments are substantially continuous and a wire loop  34  is formed at each vertex  32 . Wire loops  34  increase the flexibility of the biasing loop  28 , allowing it to collapse to a substantially flat configuration. The wire loops  34  provide stress relief by lowering the stresses in the wire segments when they bend as the biasing loop  28  deforms. The wire loops  34  also provide a plurality of discrete points at which the biasing loop  28  may be conveniently attached to the bag  12 . The wire loops  34  may be sewn to the bag  12  as shown at  36 , attached using fasteners such as rivet  38 , or using a self locking strap  40  such as a “tie wrap” which passes through both the wire loop  34  and the fabric of the bag  12 .  
         [0024]      FIG. 3  illustrates a method of forming biasing loop  28 . An elongated wire  42  is bent into a zig-zag shape defining wire segments  30  separated from one another by wire loops  34 . One end  44  of the wire  42  is formed into a socket  46  by forming multiple turns of the wire  42 , the elongated wire  42  is curved back upon itself and the other end  48  is inserted into the socket  46 .  
         [0025]     Elongated wire  42  is preferably music wire although other resilient metals having a high yield strength and modulus of elasticity, such as stainless steel, are also feasible. As shown in  FIG. 4 , each wire segment  30  is preferably curved and has a radius of curvature  50  sized to support the bag  12  in a substantially circular shape over a region proximate to the end opening  16 . The curvature of wire segments  30  is designed to match the natural curvature of the bag  12  and facilitate sealing between the drogue  10  and round conduits. The convex side  52  of the curved wire segment  30  faces outwardly from the biasing loop  28 .  
         [0026]     The length of each wire segment  30  may be approximately equal to the diameter of the end opening  16  of the bag  12 , and the biasing loop  28  is sized so that its diameter, in an unstressed state, is about 50% greater than the diameter of the end opening. This relation between the diameter of the biasing loop  28  and the bag  12  ensures that the drogue  10  will always be biased toward the open configuration.  
         [0027]     The preferred diameter of the wire may be chosen in proportion to the diameter of the end opening so that the stiffness of the biasing loop  28  increases in proportion to the cube root of the diameter of the bag  12 . This relation provides a similar “feel” to the stiffness of drogues of various sizes so that the biasing force provided by the biasing loop  28  is strong enough to maintain the end opening  16  substantially open, yet flexible enough to allow the end opening to deform and accommodate obstructions or bends in the conduit in which the drogue  10  is deployed. For music wire, a preferred diameter is approximately equal to the cube root of the quotient of the diameter of the end opening divided by 34,000. The constant will be different for other types of wire and the formula will yield a different diameter wire.  
         [0028]      FIG. 5  shows a drogue  10  pulling a line  54  through a conduit  56  in a direction indicated by arrow  58 . Compressed air is forced into conduit  56  behind drogue  10 , inflating it to substantially seal the conduit. Differential pressure on either side of the drogue  10  forces it to move through the conduit and draw the line  54  with it.  
         [0029]     When, as shown in dotted line, drogue  10  encounters an obstruction, such as may occur when previously installed optical fiber cables  60  become twisted over one another and align abreast with each other, thereby reducing the space within conduit  56 , contact between the obstruction and the drogue applies restricting forces to the drogue which tend to collapse the end opening  16 . The biasing loop  28  within the drogue allows the end opening  16  to resiliently yield toward the collapsed configuration to accommodate the is obstruction, but the biasing forces generated by the biasing loop tend to restore the end opening  16  to the open configuration. This action keeps the bag  12  partially inflated and maintains a degree of differential pressure which continues to propel the drogue  10 . The drogue is thus able to traverse the obstruction within the conduit  56 .  
         [0030]     The advantage obtained by tapering the bag  12  is clear as this feature allows the closed end  14  to find a narrowed path past the obstruction. Once past the obstruction, the biasing force of the biasing loop  28  again expands the end opening  16  of the bag  12  to its full diameter, as shown in solid line in  FIG. 5 .  
         [0031]      FIG. 6  shows a drogue  10  traversing a bend  64  in a conduit  66 . When the closed end  14  encounters the bend  64 , restricting forces are applied to the bag  12 , which, being unsupported by any biasing means at the closed end, bends and kinks in an effort to follow the air flow around the bend. Closed end  14  thus acts as a lead enabling the bag  12  to change direction in response to the bend in the conduit.  
         [0032]     As the bag  12  further traverses the bend  64 , the end opening  16  will also experience restricting forces which may tend to cause its collapse, but being biased by biasing loop  28 , the end opening remains partially open, keeping the bag inflated and maintaining at least a partial differential pressure that continues to propel the drogue  10  around the bend  64 . Once the drogue  10  is past the bend  64 , the restricting forces engendered by contact with it are removed and the biasing loop  28  restores end opening  16  to its full diameter and the drogue  10  continues along the conduit in the direction of arrow  68 .  
         [0033]     The advantage of positioning the biasing means at the end opening  16  of the bag  12 , as opposed to biasing the bag substantially along its entire length, is apparent when the drogue negotiates a bend. The bag  12 , being stiffened over a substantial portion of its length only by the differential pressure within the conduit, is free to kink and bend as needed to guide the drogue  10  around the bend. Once the turn is initiated by the closed end  14 , the biasing loop  28 , positioned proximate to the end opening  16 , deforms resiliently as needed to negotiate the bend and then restores the bag  12  to the open configuration once free of the bend.  
         [0034]     Drogues according to the invention provide a device for pneumatically drawing lines through conduit without the need to repeat the effort due to failure of the device when traversing bends or obstructions common to conduit systems. This will save time and cost in the installation of communication systems.