JP7749844B2 - Blowable flexible inner duct - Google Patents

Description

[0001] The present invention relates to blowable fabric internal duct structures, particularly for use in conduit systems.

[0002] Flexible internal duct structures have chambers and are used within conduits to help separate individual cables into compartments or channels within the internal duct, to maximize the number of cables that can be placed within the conduit, and to prevent cable-to-cable friction and facilitate cable insertion into the conduit by providing tape or rope within each compartment of the internal duct.

[0003] To form two or more chambers within an internal duct structure, a seam is typically used to attach layers together (which can be multiple pieces of fabric, fabric folded over itself, or a combination of both). In some applications, the cable is pulled through the internal duct chamber, while in other applications, the cable is preferably blown into the chamber. To allow for blowing into the internal duct, the chamber needs to be airtight (or essentially airtight) and strong enough not to rupture under the blowing pressure.

[0004] In addition to being able to be pulled or pushed into a conduit/inner duct, it is desirable to have a blowable flexible inner duct that allows the inner duct and/or the cable within the inner duct to be blown into the conduit using air or another compressed gas.

[0005] In one embodiment, the present invention relates to a blowable flexible internal duct including an outer internal duct structure and an inner internal duct structure. The outer internal duct structure includes at least one outer longitudinal chamber formed from at least one fabric. The inner internal duct structure includes at least one inner longitudinal chamber, each inner longitudinal chamber disposed within an outer internal duct fabric chamber, and the at least one inner longitudinal chamber includes an inflatable tube. The inflatable tube has a wall thickness of less than about 0.5 mm. Only the inner longitudinal chamber has an air permeability of less than about 1 cfm, only the outer longitudinal fabric chamber has an air permeability greater than about 100 cfm, and both the outer and inner longitudinal fabric chambers have an air permeability of less than about 1 cfm.

[0006] In another embodiment, the present invention relates to a conduit system that includes a conduit and a blowable flexible inner duct disposed within the conduit.
The blowable flexible inner duct includes an outer inner duct structure and an inner inner duct structure.
The outer internal duct structure includes at least one outer longitudinal chamber formed from at least one fabric. The inner internal duct structure includes at least one inner longitudinal chamber, each inner longitudinal chamber disposed within an outer internal duct fabric chamber, and the at least one inner longitudinal chamber includes an inflatable tube. The inflatable tube has a wall thickness of less than about 0.5 mm. Only the inner longitudinal chamber has an air permeability of less than about 1 cfm, only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and both the outer and inner longitudinal fabric chambers have an air permeability of less than about 1 cfm.

[0007] In another embodiment, the present invention relates to a process for forming a blowable flexible internal duct, comprising forming an internal internal duct structure comprising at least one internal longitudinal chamber, the at least one internal longitudinal chamber comprising an inflatable tube.
The process also includes forming an outer internal duct structure including at least one outer longitudinal chamber formed from at least one fabric, and simultaneously forming the outer internal duct structure, inserting at least one inner longitudinal chamber into at least one of the outer longitudinal chambers. The inflatable tube has a wall thickness of less than about 0.5 mm. Only the inner longitudinal chamber has an air permeability of less than about 1 cfm, only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and the outer longitudinal fabric chamber, together with the inner longitudinal chamber located inside the outer longitudinal fabric chamber, has an air permeability of less than about 1 cfm.

[0008] Figure 1 illustrates one embodiment of a conduit system in which the outer internal ductwork is a seamless tube. [0009] Figure 2A shows the relationship between the outer and inner internal ductwork during installation and use. FIG. 2B shows the relationship between the outer and inner internal ductwork during installation and use. FIG. 2C shows the relationship between the outer and inner internal ductwork during installation and use. [0010] Figure 3 illustrates one embodiment of a conduit system in which the outer internal duct structure is a plurality of seamless tubes attached to one another. [0011] Figure 4 illustrates an embodiment of a conduit system in which the outer internal ductwork is a pipe with a seam. [0012] Figure 5 shows one embodiment of a conduit system where the outer internal duct structure is a tube with a seam such that two chambers are formed. [0013] Figure 6 shows an embodiment of a conduit system in which the outer internal ductwork is a plurality of tubes attached together at seams. [0014] Figure 7 illustrates one embodiment of a conduit system in which the outer internal duct structure has a teardrop configuration with one chamber. [0015] Figure 8 illustrates one embodiment of a conduit system in which the outer internal duct structure has a teardrop configuration with multiple chambers. [0016] Figure 9 illustrates one embodiment of a conduit system having multiple chambers with the outer internal duct structure formed from a single strip of fabric. [0017] Figure 10 is a photograph of one embodiment of a blowable flexible inner duct.

[0018] Figure 1 shows a conduit system 10. The conduit 200 (as shown in Figure 1) into which the internal ductwork is inserted may be of any suitable size (inner or outer diameter), material, and length. The conduit may also be referred to as a duct, pipe, elongated cylindrical element, etc. Typically, the conduit 200 is made of a polymer, although other materials, such as metal, may also be used.

[0019] In one embodiment, conduit 200 is a very small conduit having an inner diameter of less than about 75 mm, more preferably less than about 60 mm, more preferably less than about 50 mm, more preferably less than about 40 mm, more preferably less than about 35 mm, more preferably less than 33 mm, and more preferably less than 30 mm. In another embodiment, conduit 200 is a medium to large conduit having an inner diameter of greater than about 100 mm, more preferably between about 1 and 3 inches, and more preferably between about 3 and 10 inches.

[0020] The blowable internal duct structure 310 includes an outer internal duct structure 100 and an inner internal duct structure 115. The outer internal duct structure 100 includes at least one outer longitudinal fabric chamber. The inner internal duct structure 115 includes at least one inner longitudinal chamber 110 (FIG. 1) in which pull tapes, cables, etc. are to be placed, with each inner longitudinal chamber 115 disposed within the outer internal duct fabric chamber 100.

[0021] The blowable flexible inner duct 310 has a longitudinal length and a cross-sectional area.
In one embodiment useful for smaller conduits, the blowable flexible internal duct 310 has a width of less than about 100 mm, more preferably less than about 75 mm, and more preferably less than about 50 mm. The width of a fabric internal duct is measured by flattening the fabric internal duct structure (as the natural cross-sectional state of the internal duct is circular, or the lobes may be slightly rounded, and therefore the width may appear smaller), and then the maximum measurement across the cross-sectional area is defined to be the width. In one embodiment, the width of the fabric internal duct structure is less than about 35 mm, and more preferably less than about 30 mm.

[0022] The outer internal duct structure 100 includes at least one fabric arranged such that the outer internal duct structure 100 includes at least one outer longitudinal chamber. The shape and structure of the outer internal duct structure 100 may be any suitable shape, so long as it is formed by fabric and includes at least one outer longitudinal chamber.

[0023] Referring to FIG. 1, one embodiment of the outer internal duct structure 100 is shown as a seamless fabric tube (shown in conduit 200 of conduit system 10). The seamless fabric tube may be formed, for example, using a circular weave or knit. The seamless tube may be formed in any suitable width. In one embodiment for smaller conduits, the width of the seamless tube is less than about 60 mm, more preferably less than about 50 mm, and more preferably less than about 40 mm. A seamless tube may be preferred in some embodiments because further processing of the fabric may not be required after the tube is formed into the outer internal duct structure 100, and the tube can be formed in small widths. In another embodiment, the fabric may be a shuttle-woven fabric.

[0024] Small seamless tubes may be used singly, as shown in FIG. 1, or in multiples. Multiple separate seamless tubes may be placed in the conduit simultaneously or sequentially, with the tubes not attached to each other (in one embodiment, the tubes may be temporarily attached to each other during installation to facilitate insertion into the conduit). In another embodiment, shown in FIG. 3, multiple (at least two) seamless tubes may be joined together before being inserted into the conduit. FIG. 3 shows an outer internal duct structure 100 including three seamless tubes connected along one of the tube sides using attachment 300.

[0025] The attachment 300 may be formed using any suitable method. In one preferred embodiment, the attachment 300 is a sewn seam created by sewing layers of fabric together. Other methods of forming the attachment include stapling, riveting, ultrasonically welding the fabric at intervals along its length, or securing the fabric with a hot melt or solvent-based adhesive. The fabric may also be provided with relatively low-temperature melt fibers that can melt and cool, thereby fusing the structure together at the attachment.

[0026] The attachment 300 may be on one of the sides of the internal duct, as shown in FIG. 3, or may be toward the center of the tube, where it functions to divide each tube into two chambers. This attachment may be in a different location on each tube. The three outer internal duct structures in FIG. 3 form three outer longitudinal chambers. Within each of these outer longitudinal chambers is an inner duct longitudinal structure 115 that forms inner longitudinal chambers 110, 120, and 130. If the attachment 300 were in the center of the internal duct structure 100 in FIG. 3, six chambers would be formed (although each chamber would be smaller). The outer and inner internal duct structures may be different sizes, and the attachment may be at different points within the blowable flexible internal duct.

[0027] In another embodiment, as shown in FIG. 4, another embodiment of a blowable flexible internal duct as part of a conduit system 10 is shown, where the outer internal duct structure 100 is a seamed tube made from fabric with a single seam along its longitudinal length to form the tube. The seamed tube includes a single inner internal duct structure 115 forming the inner longitudinal chamber 110 and is formed from a strip of fabric material, which is then made into a tube with a seam 350 along the longitudinal length of the tube. This seam 350 can be stitched, ultrasonically welded, melted, or any other suitable attachment means.

[0028] Creating a tube from a strip of textile material instead of a seamless tube (e.g., using a circular weave or knit) has many advantages. The first advantage is around splicing. It is much easier to splice a flat strip of textile material to create a longer length and then form the strip into a tube than to splice a seamless tube. Second, different sizes of tube can be more easily produced with less machine downtime. Tubes with different diameters can be created by simply slitting the strip of textile material into different widths before forming it into a tube. In many seamless tube manufacturing processes, changing the diameter of the tube being produced requires redoing the warp and/or weft setup.

[0029] The spliced tubing may be used as is, as shown in FIG. 4, or may have attachments 300 that divide the tubing into multiple chambers, as shown in FIG. 5. The outer internal duct structure 100 of FIG. 5 includes attachments 300 that form two outer longitudinal chambers. Each of these outer longitudinal chambers includes an inner internal duct structure 115 that forms an inner longitudinal chamber 110, 120. In one embodiment, the attachments 300 are within a central blowable, flexible internal duct defined approximately equidistant from the two edges of the structure. This is preferable for forming chambers of approximately equal size. In another embodiment, the attachments 300 are off-center, meaning that the attachment is not in the center of the structure. This creates a larger chamber than the chamber on the other side. This may be preferable for accommodating various sizes of wires, cables 800, pull tapes 900, etc.

[0030] In another embodiment shown in FIG. 6, the exterior internal ductwork 100 includes a plurality of seamed fabric tubes attached to one another by attachments 300. The seams 350 may be located at any suitable location around the circumference of the tubes, and even in the area of the attachments 300 themselves. The seams of each tube within the interior ductwork 100 may be in different locations.

[0031] In one embodiment, attachment 300 is at the center of a defined middle region that is approximately equidistant from the two edges of the structure. This is preferable for creating chambers of approximately equal size. In another embodiment, attachment 501 is off-center, meaning that the attachment is not at the center of the structure. This results in a larger chamber on one side of the margin region than on the other side. This may be preferable for accommodating various sizes of wires, cables, pull tapes, etc.

[0032] In FIG. 7, the outer internal duct structure 100 is in the form of a single teardrop configuration within the conduit 200. In the single teardrop configuration, a strip of fabric is folded around its longitudinal axis and the edges are attached to one another with attachment 300, thereby forming an outer longitudinal chamber that includes the inner longitudinal chamber 110. Pull tapes, cables, mini-cables, etc. can be placed inside the chamber 110. In one embodiment, the edges of the strip of fabric of the outer internal duct structure 100 are folded over to improve seam strength and reduce friction.

8, the outer internal duct structure 100 is a multi-chamber teardrop configuration. While the inner duct structure of FIG. 8 includes two outer longitudinal chambers, the inner duct structure can include any suitable number of outer longitudinal chambers, such as two or more, three or more, four or more, five or more, or six or more. In one embodiment, the multi-chamber teardrop configuration is formed from multiple strip-shaped lengths of fabric folded to form individual compartments, which can then be attached to one another. The outer internal duct structure 100 is configured with a common seam that secures the folds and cut edges along the length of the folded-under fabric to improve seam strength and reduce friction. In another embodiment, the teardrop shape and chambers may be formed from a single piece of fabric folded multiple times. This embodiment is shown in FIG. 8, in which a single strip-shaped fabric is folded and attached to form two outer longitudinal chambers. Within each of these chambers is an inner internal duct structure 115.

[0034] Referring to FIG. 9, another embodiment of a blowable flexible internal duct within a conduit 200 is shown. The external internal duct structure 100 includes three regions: a first region, a middle region, and a second region. In the external internal duct structure 100 of FIG. 9, the structure 100 includes a stripe-shaped fabric that forms four flexible outer longitudinal chambers. Each of the outer chambers includes an inner longitudinal chamber.

[0035] For the embodiment shown in FIG. 9, each strip of fabric has a first edge and a second edge. The first and second edges are located in an intermediate region of the flexible internal duct structure. Each fabric strip extends outward from the central region to either the first region or the second region, and then returns to the central region to form an outer longitudinal chamber. The internal duct structure may include two or more strips of fabric, at least one of which extends from the first region to the second region. The internal duct structure includes at least one strip of fabric including a fold in the first region and a fold in the second region.

[0036] In one preferred embodiment, the desired number of chambers can be created with a minimum number of strip-shaped fabric edges in the central region of the structure 100, so that all chambers are formed from a single strip-shaped fabric, as shown in FIG. 9.

[0037] In some embodiments, the edges of the strip-shaped fabric are folded over. This may be preferable to prevent the edges of the fabric from catching on other materials during manufacture, installation, and/or use of the internal duct structure, and also helps prevent the edges of the strip-shaped fabric from coming off the attachment 300. For example, the attachment 300 may be a line of stitching, and if there is some fraying of the edges of the strip-shaped fabric, some of the fabric may become loose and one or more of the chambers may not be fully closed.

[0038] Preferably, the fabrics of the outer longitudinal structure are only attached to each other and to themselves with attachments 300, and not to the first region, second region, first edge, or second edge. This allows the chamber to expand and better fill the conduit. In the configuration shown in FIG. 9, when placed in a conduit, the chamber of the blowable flexible inner duct expands to fill the conduit and has the appearance of a dragonfly or butterfly in cross section.

[0039] In one embodiment, the attachment means 300 is in the center of a defined middle region that is approximately equidistant from the two edges of the structure. This is preferable for creating chambers of approximately equal size. In another embodiment, the attachment means 300 is off-center, meaning that the attachment means is not in the center of the structure. This allows the chamber in one region to be larger than the chamber in the other region. This is preferable for accommodating wires, cables, pull tapes, etc. of various sizes.

[0040] In one preferred embodiment, the outer internal duct structure 100 is preferably made using a woven fabric. The fabric has a plurality of warp threads that extend in the warp direction of the fabric. The woven fabric also includes a plurality of weft threads that run generally perpendicular to the warp direction of the fabric. The weft threads are interwoven with the warp threads, and the warp threads extend above and below the weft threads in a predetermined cross pattern. In one preferred embodiment, the fabric is a plain weave fabric. The fabric may be any other suitable weave pattern, including twill and satin weaves. In other embodiments, nonwoven fabrics or knits may be used as the fabric for the outer internal duct structure.

[0041] The yarns in a woven fabric may be any suitable yarn. The selection of the type, size, and relative proportions of each yarn in a woven fabric contributes to the final product of the woven fabric. In this application, "yarn" as used herein includes monofilament elongated bodies, multifilament elongated bodies, ribbons, strips, threads, tapes, fibers, etc. A woven fabric may contain one type of yarn, or multiple yarns of any one or combination of the above. The yarns may be in any suitable form, such as spun staple yarn, monofilament, or multifilament, monocomponent, bicomponent, or multicomponent, and may have any suitable cross-sectional shape, such as round, multilobal, square or rectangular (tape), and oval.

[0042] The fabric can be formed from a single plurality of yarns or a single type of yarn (e.g., the fabric can be formed only from yarns including a blend of cellulose fibers and synthetic fibers such as polyamide fibers), or the fabric can be formed from several plurality of yarns or different types of yarns (e.g., the fabric can be formed from a first plurality of yarns including cellulose fibers and polyamide fibers and a second plurality of yarns including inherent flame resistant fibers). The yarns may be formed from (but are not limited to) cellulosic fibers (such as cotton, rayon, linen, jute, hemp, cellulose acetate, and combinations, mixtures, or blends thereof), polyester fibers (e.g., poly(ethylene terephthalate) fibers, poly(propylene terephthalate) (PET) fibers, poly(trimethylene terephthalate) fibers), poly(butylene terephthalate) fibers, and blends thereof), polyamide fibers (e.g., nylon 6 fibers, nylon 6,6 fibers, nylon 4,6 fibers, and nylon 12 fibers), polyvinyl alcohol fibers, elastomeric polyester-polyurethane copolymers (SPANDEX®), flame-retardant meta-aramid (NOMEX®), and combinations, mixtures, or blends thereof. Some embodiments of the fabrics of the present invention contain yarns comprising inherently flame-resistant fibers. As used herein, the term "intrinsically flame-resistant fibers" refers to synthetic fibers that exhibit flame resistance without the need for further flame-retardant treatment due to the chemical composition of the material from which they are made. In such embodiments, the inherently flame-resistant fibers may be any suitable inherently flame-resistant fibers, such as polyoxadiazole fibers, polysulfonamide fibers, poly(benzimidazole) fibers, poly(phenylene sulfide) fibers, meta-aramid fibers, para-aramid fibers, polypyridobisimidazole fibers, polybenzylthiazole fibers, polybenzyloxazole fibers, melamine-formaldehyde polymer fibers, phenol-formaldehyde polymer fibers, oxidized polyacrylonitrile fibers, polyamide-imide fibers, and combinations, mixtures, or blends thereof. In some embodiments, the inherently flame-resistant fibers are preferably selected from the group consisting of polyoxadiazole fibers, polysulfonamide fibers, poly(benzimidazole) fibers, poly(phenylene sulfide) fibers, meta-aramid fibers, para-aramid fibers, and combinations, mixtures, or blends thereof.

In a preferred embodiment, the warp yarns are monofilament yarns. Monofilament yarns may be preferred due to a lower amount of crimp in the woven fabric (compared to multifilament yarns), and therefore have less elongation when the internal duct is pulled through the conduit. By way of example, the warp yarns may be selected from polyolefins such as polyester, polypropylene, polyethylene, and ethylene-propylene copolymers, as well as polyamides such as nylon and aramids, e.g., Kevlar®. Yarns having a peak elongation at peak tensile load of 45% or less, preferably 30% or less, are preferred. Monofilament yarns, including bicomponent and multicomponent yarns, have been found to be particularly useful in internal duct applications. These materials have been found to impart desirable properties to the woven fabric. In one embodiment, all of the warp yarns are PET monofilament yarns, as PET monofilament yarns have a good balance of properties versus cost.

[0044] By selecting warp yarns with a relatively low elongation at peak tensile load, it is possible to minimize longitudinal elongation of the internal duct structure during installation of the internal duct within the conduit, thereby avoiding "bunching" of the internal duct. Furthermore, the potential for warp elongation of the fabric incorporated into the internal duct can be minimized by reducing warp crimp during the weaving process. For example, warp crimp can be reduced by increasing the tension on the warp yarns during weaving to achieve a warp crimp of less than 5%, as measured by ASTM D3883—Standard Test Method for Yarn Crimp and Yarn Take-Up in Woven Fabrics. Reducing the warp crimp of fabrics, particularly plain-weave fabrics, results in increased weft crimp, which has the added benefit of increasing seam strength along the longitudinal edges of the section of fabric used to construct the internal duct.

[0045] In one embodiment, warp yarns having a denier of 350 to 1,200, preferably 400 to 750, can be used. The end count (threads per inch in the warp) typically ranges from 25 to 75 ends per inch, preferably 35 to 65 ends per inch. In one embodiment of the present invention, a plain weave fabric is provided having monofilament polyester warp yarns of 400 to 750 denier at 35 to 65 ends per inch.

[0046] The weft yarn may be any suitable yarn, including polyolefins such as polyester, polypropylene, polyethylene, and ethylene-propylene copolymers, as well as polyamides such as nylon and aramid, e.g., Kevlar®, and mixtures thereof. Yarns having a peak elongation at peak tensile load of 45% or less, preferably 30% or less, are preferred.

[0047] The terms "pick," "picks," "picks per inch," and "ppi" are intended to refer to (a) one weft yarn that is carried through a shed formed during the weaving process and interwoven with warp yarns, and (b) two or more weft yarns that are carried separately or together through a shed and interwoven with warp yarns during the weaving process. Thus, for purposes of determining the picks per inch of a fabric, a multiply inserted weft yarn counts as a single pick.

[0048] The terms "multiple insertion" and "double insertion" are intended to include (a) multiple wefts that are inserted together into the loom shed, (b) multiple wefts that are inserted separately while the loom shed remains the same, and (c) multiple wefts that are inserted separately while the loom shed remains substantially the same, i.e., the positions of 25% or less of the warp yarns change between yarn insertions. In one preferred embodiment, at least some of the weft picks are multiple insertions.

[0049] Other suitable weave patterns may be used as the weave pattern in the first weaving zone. The terms "woven" and "interwoven" are meant to include any structure incorporating interlocking forming strips. By way of example only and not limitation, it is contemplated that a weft yarn may pass over two or more adjacent warp yarns 100 before moving into position beneath one or more adjacent warp yarns, thereby forming a so-called twill weave. Suitable twill weaves include both warp and weft twills, such as 2/1, 3/1, 3/2, 4/1, 1/2, 1/3, or 1/4 twills. The fabric may also be, for example, a satin, basket weave, poplin, jacquard, and crepe weave fabric. In one embodiment, a woven fabric may be included.

[0050] The fabric may include one weave pattern along the length of the fabric, or may have different zones of varying weave patterns along the machine direction of the fabric. In embodiments in which the fabric includes multiple zones, the first weave zone may have any suitable weave pattern. FIG. 10 shows one possible weave pattern in which the warp and weft yarns in the first weave zone are plain woven, with each weft yarn passing over a warp yarn and then repeatedly passing under adjacent warp yarns across the entire width of the fabric. Suitable plain weaves include, but are not limited to, ripstop weaves, which are produced by incorporating additional or reinforcing yarns at regular intervals into the warp, weft, or both warp and weft yarns of a fabric material during formation. Plain weaves are preferred because they provide stability and structure to the fabric. If the first weave zone is too small or eliminated entirely, the fabric may be too loose (the warp and weft yarns move too easily relative to each other) and not suitable for internal duct construction. In one embodiment, the woven fabric may be a partial float woven fabric as described in Patent Nos. 10,254,498, 10,829,874, and 11,008,680, which are incorporated herein by reference.

[0051] In the weft direction, it is preferable to use a variety of different yarns to tailor the physical properties of the final fabric and structure. Monofilament yarns are stiffer than multifilament yarns (keeping denier and material the same). Multifilament yarns are more flexible. Using both monofilament and multifilament weft yarns provides a balance between flexibility and stiffness. Also, incorporating several multifilament yarns (due to their lower stiffness) reduces the internal duct opening force, i.e., the amount of force required to push a cable through an individual cell. Multiple or doubly inserted multifilament yarns are preferred because they have a larger denier, and therefore the cable "rides" along these ridges in the fabric. Because there is less surface area of fabric in contact with the cable, friction is reduced and the pulling tension required to retract the cable is typically lower.

[0052] In one embodiment, the fabric comprises a UV stabilizer. The stabilizer may be incorporated into the yarn or otherwise formed, may be a coating on the yarn, or may be a coating on the entire fabric. While placing a UV stabilizer on a product that enters underground in a pipe is somewhat counterintuitive, it is recognized that prior to installation, a roll of interior ducting may be located outside in the elements and sun for up to a year. The UV stabilizer helps protect the physical properties of the fabric and interior ducting until it is installed and protected from UV sources. UV stabilizers include materials that inhibit photoinitiation (e.g., UV absorbers (UVA) and excited-state quenchers) and materials that inhibit subsequent oxidation processes (e.g., radical scavengers and alkyl hydroperoxide decomposers). Any suitable UV stabilizer can be used, such as carbon black, titanium dioxide, and hydrobenzophenone.

[0053] Referring back to FIG. 1, the blowable flexible internal duct 310 includes an internal internal duct structure 115 that forms at least one internal longitudinal chamber 110. Each internal longitudinal chamber 110 is disposed within an outer longitudinal chamber formed by the outer internal duct structure. In the embodiment shown in FIG. 1, there is one internal longitudinal chamber within the outer longitudinal chamber, but there are embodiments in which two or more internal longitudinal chambers may be located within a single outer longitudinal chamber. In other embodiments in which there are multiple outer longitudinal chambers (such as FIG. 3), not all of the outer longitudinal chambers need include an internal longitudinal chamber, and it may be desirable for at least one outer longitudinal chamber each to not include an internal longitudinal chamber.

[0054] The inner longitudinal chamber comprises an inflatable tube. This tube can be any suitable inflatable tube, but is preferably air-, vapor-, and water-impermeable, lightweight, and flexible. In one embodiment, the inflatable tube is seamlessly formed from a process such as blow extrusion. In another embodiment, the tube is formed from a thin plastic sheet folded over itself, and its edges are attached and sealed to one another. The edges may be sealed to align to form a teardrop-like shape for the tube, or the edges may be on top of one another to form a more circular cross-sectional shape. This bond can be formed from a pressure-sensitive adhesive, a thermal adhesive, ultrasonic welding, or any other known manufacturing process.

The inflatable tube may be made from any suitable material, including any thermoplastic and thermosetting resin. Preferably, the inflatable tube comprises a thermoplastic polymer. In one embodiment, the polymer is selected from the group consisting of low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), low-density polyethylene (LLDPE), polypropylene (PP), polyester (PET), and polyamide (PA). In one embodiment, the thermoplastic is polyethylene, preferably medium-density polyethylene. The material forming the inflatable tube is preferably airtight (air-impermeable), has good strength at low weight, low friction, and low cost. The inflatable tube may contain a single polymer or a blend of polymers, may have additional fillers added to the polymer, and/or may have a single layer or be co-extruded to have multiple layers.

[0056] Polyethylene has been found to have a low coefficient of friction (making it easier for cables or other elongated members to slide within the tube compared to materials with higher coefficients of friction, such as some urethane elastomeric-type materials). The inflatable tube, in one embodiment, has a wall thickness of about 0.1 to 1 mm, more preferably less than about 0.5 mm, more preferably less than 0.25 mm. This thickness has been found to produce an inflatable tube with good physical properties and be cost-effective. Inflatable tubes of this thickness have also been shown to be sufficient (in combination with an external chamber) to withstand typical pressures used in cable and internal duct blowing systems (which are typically much lower than water-based systems).

[0057] The goal of a blowable flexible inner duct is to have the strength and properties of a flexible inner duct while being nearly impermeable to air, vapor, and water, thereby allowing the blowable flexible inner duct and/or cables placed within the inner duct structure to be blown. Some previous attempts to create blowable flexible inner duct structures have involved using fabrics with coatings thereon. Prototypes using coated fabrics tended to fail due to air leakage at the stitching (attachment areas), or the seams/stitches tended to fail during blow testing. The combination of an inner inner duct structure that is an inflatable tube, which provides air impermeability, and an outer inner duct structure that is a fabric structure, which provides strength, creates a blowable flexible inner duct. Air permeability is typically measured using ASSM D737. When combined into a blowable flexible inner duct, the inner and outer chambers exhibit a desirable low air permeability.

[0058] The inner longitudinal chamber (which is the inflatable tube) alone has an air permeability of less than about 2 ^cm3 / ^cm2 /s (at 10 inches of water) or 1 cfm, more preferably less than about 1 ^cm3 / ^cm2 /s, more preferably less than about 0.5 ^cm3 / ^cm2 /s (at 10 inches of water). In another embodiment, the inner longitudinal chamber (which is the inflatable tube) alone has an air permeability of about 0 to 0.5 ^cm3 / ^cm2 /s (at 10 inches of water), more preferably about 0.001 to 0.5 ^cm3 / ^cm2 /s, or more preferably less than about 0.2 cfm.

The outer longitudinal chamber (which is the fabric) preferably has a very open structure, meaning that a significant portion of the surface of the fabric is open or thread-free. This creates a very porous fabric that allows air, water, and light to pass through easily. The fabric alone has an air permeability of greater than about 5 ^cm / ^cm /s (at 10 inches of water), more preferably greater than about 10 ^cm / ^cm /s, more preferably greater than about 25 ^cm / ^cm /s, preferably greater than 100 cfm, more preferably greater than 200 cfm. In another embodiment, the outer longitudinal chamber (which is the fabric) alone has an air permeability of about 5 to 200 ^cm / ^cm /s (at 10 inches of water), more preferably about 10 to 100 ^cm / ^cm /s.

[0060] When the inner and outer internal duct chambers combine to form a blowable flexible internal duct (the inner chamber located within the outer chamber), the blowable flexible internal duct has an air permeability of less than about 2 ^cm3 /cm2/ ^s (at 10 inches of water), more preferably less than about 1 ^cm3 / ^cm2 /s, and more preferably less than about 0.5 ^cm3 / ^cm2 /s (at 10 inches of water). In another embodiment, the inner and outer internal duct chambers (wherein the inner chamber is located within the outer chamber) that combine to form the blowable flexible internal duct have an air permeability of about 0 to 0.5 ^cm3 / ^cm2 /s (at 10 inches of water), more preferably about 0.001 to 0.5 ^cm3 / ^cm2 /s. In another embodiment, the inner and outer inner duct chambers that combine to form a blowable flexible inner duct (the inner chamber disposed within the outer chamber) have an air permeability of less than 0.05 cfm, more preferably less than about 0.2 cfm.

[0061] A custom test setup was used to conduct the burst test. The sequence consisted of an air regulator, a valve, a first pipe, the inner duct structure to be tested, and a second pipe, with the end of the pipe opposite the inner duct capped. The inner duct structure was clamped onto the pipe, and pressurized air was applied, slowly increasing in steps over time until the inner duct failed, leaked, or burst. The maximum psi before the inner duct structure failed (fractured, leaked, or burst) was considered the burst strength. When combined with the blowable, flexible inner duct, the inner and outer chambers possess a desirable high burst strength.

[0062] In one embodiment, the inner longitudinal chamber (which is the inflatable tube) alone has a burst strength of less than about 50 psi, more preferably less than about 35 psi. In another embodiment, the inner longitudinal chamber (which is the inflatable tube) alone has a burst strength of about 5 to 40 psi, more preferably about 10 to 25 psi. In another embodiment, the inner longitudinal chamber (which is the inflatable tube) alone has a burst strength of less than about 75 psi, more preferably less than about 70 psi. In another embodiment, the inner longitudinal chamber (which is the inflatable tube) alone has a burst strength of between about 25 psi and 80 psi, more preferably between about 40 psi and 70 psi.

[0063] The outer longitudinal chamber (which is fabric) is much stronger. When the inner and outer inner duct chambers are combined to form a blowable flexible inner duct (with the inner chamber disposed within the outer chamber), the blowable flexible inner duct has a burst strength of greater than about 50 psi, more preferably greater than about 60 psi, and in another embodiment, about 55 to 100 psi.

[0064] In one embodiment, the polymer forming the expandable tube preferably has an elongation to break of less than about 50%, more preferably less than about 30%. This is in contrast to other tubes that are more elastic and have elongations to break of 200 to 300% or more. In other embodiments, the polymer forming the expandable tube preferably has an elongation to break of greater than about 50%, greater than about 100%, and more preferably greater than about 200%.

[0065] Preferably, the inner internal duct chamber is movable within the outer internal duct chamber. This means that the inner internal duct chamber can move relative to the outer internal duct chamber and is not permanently attached to the outer internal duct structure, or attached at all.

[0066] Figure 2A shows one embodiment of a blowable flexible internal duct 310 in which an inner internal duct structure 115, which is an inflatable tube, is positioned within an outer internal duct structure 100, which is a seamless fabric. The inner internal duct structure may be folded, crimped, or otherwise manipulated to make it easier to insert the inner internal duct structure into the outer internal duct structure. Figure 2B shows what the blowable flexible internal duct 310 looks like when air is introduced into the inner internal duct structure 115. The inner internal duct structure 115 expands or opens to fill the outer internal duct structure 100, which restrains the inner internal duct structure 115, providing burst strength to the inner internal duct structure 115 and preventing the inner internal duct structure 110 from bursting. FIG. 2C shows the blowable flexible inner duct 310 after air pressure has been released from the blowable flexible inner duct 310. In this case, the inner inner duct structure 115 can remain against the inner surface of the outer inner duct structure 100, or can collapse/contract/fold back away from the outer inner duct structure 100.

[0067] The relative sizes of the two chambers are important because the outer internal duct structure 100 restrains the inner internal duct structure 115 and provides burst strength to the inner internal duct structure 110. If the inner longitudinal chamber is too small (has too small a diameter), it will burst or leak when it expands from air pressure before reaching the inner surface of the outer longitudinal chamber. The diameter of the longitudinal chamber is measured as the diameter when the chamber is completely flat. In one embodiment, the diameter of the inner longitudinal chamber is about 50 to 200%, more preferably about 60 to 100%, more preferably about 70 to 95%, and more preferably about 75 to 90% of the diameter of the outer longitudinal chamber. The more elastic (stretchable) the inner longitudinal chamber is made, the smaller its diameter can be relative to the outer longitudinal chamber because it can stretch to the size of the outer longitudinal chamber without breaking. In another embodiment, the inner longitudinal chamber occupies at least about 60% of the cross-sectional area of the outer longitudinal chamber. In a preferred embodiment, the inner longitudinal chamber occupies at least about 75% of the cross-sectional area of the outer longitudinal chamber, or about 70 to 95% of the cross-sectional area of the outer longitudinal chamber.

[0068] The blowable flexible internal duct can be constructed in any suitable manner. In one embodiment, an outer internal duct structure is formed, and then the inner longitudinal chamber from the inner internal duct structure is placed inside the outer longitudinal chamber. This is preferred for making an existing internal duct structure blowable. The inflatable tube may be retracted or blown into an existing internal duct structure (blowable or non-blowable), or may be piggybacked on a first cable that is blown or retracted into the internal duct structure.

[0069] In another embodiment, the inner longitudinal chamber is inserted while the material (preferably fabric) of the outer internal duct structure is being formed into at least one outer longitudinal chamber. In the case of a seamless tube as the outer longitudinal chamber, as shown in Figures 1 and 3, the inflatable tube is introduced while the tube is being fabricated (knitted, woven, circular woven, shuttle woven, etc.). At least one inner longitudinal chamber is inserted into at least one of the outer longitudinal chambers simultaneously with forming the outer internal duct structure.

[0070] When the fabric is folded into the outer internal duct structure as shown in Figures 4 to 9, the inflatable tube is preferably introduced while the fabric is folded and secured within the chamber. At the same time as forming the outer internal duct structure, at least one inner longitudinal chamber is inserted into at least one of the outer longitudinal chambers.

[0071] A blowable internal duct structure may be drawn, blown into, or incorporated into the conduit while the conduit is being manufactured. Cables or other elongated members disposed within the internal duct structure can be blown or drawn into the chamber.

[0072] The figures also show that in some embodiments, the interior chambers have cables 800 and/or pull tapes or ropes 900 therein. To pull optical fiber, coaxial cable, or other cables through the interior duct structure, it is desirable in one embodiment to provide a pull line for such purpose. The pull line is preferably placed within a section of the interior duct prior to installing the interior duct within the conduit. By way of example, the pull line may be a tightly woven, relatively flat strip of material, or may be a stranded rope or multi-layered cord having a substantially circular cross-section. A pull line that is a pull rope is shown as element 900 in Figures 3, 5, 6, 8, and 9. In one embodiment, at least one of the interior chambers contains a cable.

[0073] Preferably, the internal duct and the pull line have respective values of elongation that are substantially equal for a given tensile load. If the elongation of the internal duct is substantially different from the elongation of the pull line, one of these structures may lag relative to the other when pulled together through the conduit during installation, resulting in bunching of the internal duct. The pull line may be formed from a tightly woven polyester material exhibiting a tensile strength of about 400 to about 3,000 pounds. In one embodiment, the pull line is a pull tape having a flat cross-sectional shape. In another preferred embodiment, the pull line is a pull rope having a circular or oval cross-sectional shape. Pull ropes are preferred because the internal duct structures (and their associated chambers) are very small, allowing the pull rope to occupy less space within the conduit. Preferably, the internal duct structures (all of the internal duct structures disclosed within this application) include at least one pull rope within at least one chamber. In another embodiment, each chamber of the internal duct structure includes a pull rope.

[0074] In one embodiment, the internal duct structure contains a cable 800 after being placed in the conduit (or in other embodiments, before being placed in the conduit). Preferably, at least one of the chambers of the internal duct structure contains a cable. Cable 800 may be any suitable cable, small or large diameter. In one embodiment, the cable is a mini-cable having a smaller diameter than conventional cables. Preferably, mini-cables have a diameter of less than about 15 mm, more preferably less than about 11 mm. The term "cable" is intended to include fiber optic cables, electrical wires, coaxial and triaxial cables, and any other line for transmitting electrical and/or electromagnetic signals.

[0075] The conduit 10 shown in the figures may be any suitable conduit; for example, the conduit may be made of metal, a synthetic polymer such as a thermoplastic polymer, clay, or concrete. The passages through the conduit may have circular, oval, rectangular, polygonal, or other cross-sectional shapes. The present invention finds utility in conjunction with virtually any conduit system. Depending on the relative size of the passages within the inner ducts, typically calculated as the internal diameter, one skilled in the art can select from the width of the inner ducts, the number of compartments within each inner duct, and the number of individual inner ducts to maximize the capacity of the conduit.

example
[0076] A blowable flexible inner duct was fabricated according to one embodiment of the present invention. Air permeability was tested using ASTM D737. A custom test setup was used to conduct a burst test. The sequence consisted of an air regulator, a valve, a first pipe, the inner duct structure to be tested, and a second pipe, with the end of the pipe opposite the inner duct capped. The inner duct structure was clamped onto the pipe, and pressurized air was applied, slowly increasing in steps over time until the inner duct failed, leaked, or burst. The maximum psi before the inner duct structure failed (broke, leaked, or burst) was considered the burst strength.

[0077] Outer Internal Duct Structure: A woven fabric was constructed having warp and weft yarns. The warp yarns were 520 denier monofilament polyester yarns in a 48 epi construction. The weft yarns were 350 denier nylon monofilament yarns alternating with 600 denier multifilament textured polyester yarns in a 24 weft threads per inch construction. The fabric was folded and sewn together as shown in the diagram in Figure 9 and the photograph in Figure 10 to create an outer internal duct structure having a width of approximately 2.5 inches and including four outer longitudinal chambers. Each of the outer longitudinal chambers had a diameter of approximately 1.2 inches. The air permeability of the woven fabric was approximately 10 to 100 ^cm3 / ^cm2 /s at 10 inches of water.

[0078] Internal inner duct construction: A plastic tube made from medium density polyethylene (MDPE) having a nominal wall thickness of about 7 mils (0.18 mm) and a folded diameter (defined as diameter in this application) of about inches. The air permeability of the plastic tube was about 0 ^cm3 / ^cm2 /s at 10 inches of water. The burst strength of the plastic tube was about 18 psi.

Four inner internal duct structures were added to the outer internal duct structure so that each outer longitudinal chamber contained one plastic tube. The inner tubes were approximately 87% of the diameter of the outer chamber. The air permeability of one outer longitudinal chamber with one inner tube inside was approximately 0 ^cm3 / ^cm2 /s at 10 inches of water. The combined burst strength of the outer longitudinal chambers and plastic tubes was 90 psi.

[0080] As can be seen from the above data, the combination of an inner longitudinal chamber inside an outer longitudinal chamber produces a blowable flexible inner duct having the desired low air permeability and high burst strength desired for a blowable flexible inner duct.

[0081] All references cited herein, including publications, patent applications, and patents, are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0082] Use of the terms "a," "an," and "the" and similar referents in the context of describing the subject matter of this application (particularly in the context of the claims below) should be construed to encompass both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" should be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended merely to better clarify the subject matter of the present application and does not impose any limitations on the scope of the subject matter unless otherwise asserted. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the subject matter described herein.

[0083] Preferred embodiments of the subject matter of this application are described herein, including the best mode known to the inventors for carrying out the claimed subject matter. Variations of these preferred embodiments will become apparent to those of skill in the art upon reading the foregoing description. The inventors anticipate that skilled artisans will employ such variations as appropriate, and the inventors intend for the subject matter described herein to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or clearly contradicted by context.
The inventions described in the claims of the present application as originally filed are set forth below.
[1] A blowable flexible internal duct,
an outer internal duct structure comprising at least one outer longitudinal chamber formed from at least one fabric;
an inner internal duct structure comprising at least one inner longitudinal chamber, each inner longitudinal chamber located within an outer internal duct fabric chamber, the at least one inner longitudinal chamber comprising an inflatable tube, the inflatable tube having a wall thickness of less than about 0.5 mm;
A blowable flexible inner duct, wherein only the inner longitudinal chamber has an air permeability of less than about 1 cfm, and only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has an air permeability of less than about 1 cfm.
[2] The blowable flexible inner duct of [1], wherein the outer longitudinal fabric chamber, together with the inner longitudinal chamber disposed inside the outer longitudinal fabric chamber, has a burst strength of greater than about 60 psi.
[3] The blowable flexible inner duct of [1], wherein the inner longitudinal chamber occupies at least about 75% of the cross-sectional area of the outer longitudinal chamber.
[4] The blowable flexible inner duct of [1], wherein the expandable tube has an elongation at break of greater than about 50%.
[5] The blowable flexible inner duct of [1], wherein the at least one fabric comprises a woven fabric.
[6] The blowable flexible inner duct of [1], wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber.
[7] A conduit system,
a conduit; and a blowable flexible inner duct disposed within the conduit, the blowable flexible inner duct comprising:
an outer internal duct structure comprising at least one outer longitudinal chamber formed from at least one fabric;
an inner internal duct structure comprising at least one inner longitudinal chamber, each inner longitudinal chamber located within an outer internal duct fabric chamber, the at least one inner longitudinal chamber comprising an inflatable tube, the inflatable tube having a wall thickness of less than about 0.5 mm;
A conduit system wherein only the inner longitudinal chamber has an air permeability of less than about 1 cfm, only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has an air permeability of less than about 1 cfm.
[8] The conduit system of [7], wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber disposed inside the outer longitudinal fabric chamber, has a burst strength of greater than about 60 psi.
[9] The conduit system of [7], wherein the inner longitudinal chamber occupies at least about 75% of the cross-sectional area of the outer longitudinal chamber.
[10] The conduit system of [7], wherein only the inner longitudinal chamber has a burst strength of less than about 35 psi.
[11] The conduit system of [7], wherein the outer internal duct structure comprises a strip of fabric folded about a centrally located longitudinal axis and having two longitudinal edges abutted along the longitudinal edges to define at least one outer longitudinal chamber, the fabric being folded about a centrally located longitudinal axis and abutted with stitches.
[12] The conduit system of [7], wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber.
[13] A process for forming a blowable flexible internal duct, comprising:
forming an interior internal duct structure comprising at least one interior longitudinal chamber, said at least one interior longitudinal chamber comprising an inflatable tube;
forming a fabric;
forming an outer internal duct structure from the fabric having at least one outer longitudinal chamber while simultaneously inserting at least one inner longitudinal chamber into at least one of the outer longitudinal chambers, wherein the inflatable tube has a wall thickness of less than about 0.5 mm;
wherein only the inner longitudinal chamber has an air permeability of less than about 1 cfm, and only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has an air permeability of less than about 1 cfm.
[14] The process of [13], wherein forming the outer internal duct structure comprises folding at least one strip-shaped fabric having two longitudinal edges of the fabric about a centrally located longitudinal axis and abutting the longitudinal edges to define at least an outer longitudinal chamber.
[15] The process of [13], wherein forming the outer internal duct structure comprises folding at least two strip-shaped fabrics, each having two longitudinal edges of the fabric about a centrally located longitudinal axis, and abutting the longitudinal edges to define at least two outer longitudinal chambers.
[16] The process of [13], wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has a burst strength of greater than about 60 psi.
[17] The process of [13], wherein only the inner longitudinal chamber has a burst strength of less than about 35 psi.
[18] The process of [13], wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber.
[19] A process for forming a blowable flexible internal duct, comprising:
forming an interior internal duct structure comprising at least one interior longitudinal chamber, said at least one interior longitudinal chamber comprising an inflatable tube;
forming an outer internal duct structure having at least one outer longitudinal chamber and simultaneously inserting at least one inner longitudinal chamber into at least one of the outer longitudinal chambers, wherein the inflatable tube has a wall thickness of less than about 0.5 mm;
A process wherein only the inner longitudinal chamber has an air permeability of less than about 1 cfm, only the outer longitudinal fabric chamber has an air permeability of greater than about 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has an air permeability of less than about 1 cfm.
[20] The process of [19], wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber, has a burst strength of greater than about 60 psi.
[21] The process of [19], wherein only the inner longitudinal chamber has a burst strength of less than about 35 psi.
22. The process of claim 19, wherein the inner longitudinal chamber fills at least about 60% of the cross-sectional area of the outer longitudinal chamber.
23. The process of claim 19, wherein the inner longitudinal chamber is configured to surround and carry at least one cable.
[24] The process of [19], wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber.

Claims (24)

A blowable flexible inner duct,
an outer internal duct structure comprising at least one outer longitudinal chamber formed from at least one fabric;
an inner internal duct structure comprising at least one inner longitudinal chamber, each inner longitudinal chamber being located within an outer internal duct fabric chamber, the at least one inner longitudinal chamber comprising an inflatable tube, the inflatable tube having a wall thickness of less than 0.5 mm;
A blowable flexible inner duct, wherein only the inner longitudinal chamber has an air permeability of less than 1 cfm, and only the outer longitudinal fabric chamber has an air permeability of greater than 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has an air permeability of less than 1 cfm. 10. The blowable flexible inner duct of claim 1, wherein said outer longitudinal fabric chamber, together with an inner longitudinal chamber disposed inwardly of said outer longitudinal fabric chamber , has a burst strength of greater than 60 psi. 2. The blowable flexible inner duct of claim 1, wherein said inner longitudinal chamber occupies at least 75 % of the cross-sectional area of said outer longitudinal chamber. 10. The blowable flexible inner duct of claim 1 , wherein the expandable tube has an elongation at break of greater than 50 %. The blowable flexible internal duct of claim 1, wherein the at least one fabric comprises a woven fabric. The blowable flexible inner duct of claim 1, wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber. 1. A conduit system comprising:
a conduit; and a blowable flexible inner duct disposed within the conduit, the blowable flexible inner duct comprising:
an outer internal duct structure comprising at least one outer longitudinal chamber formed from at least one fabric;
an inner internal duct structure comprising at least one inner longitudinal chamber, each inner longitudinal chamber located within an outer internal duct fabric chamber, the at least one inner longitudinal chamber comprising an inflatable tube, the inflatable tube having a wall thickness of less than 0.5 mm;
A conduit system wherein only the inner longitudinal chamber has an air permeability of less than 1 cfm, only the outer longitudinal fabric chamber has an air permeability of greater than 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has an air permeability of less than 1 cfm. 8. The conduit system of claim 7, wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber disposed inwardly of the outer longitudinal fabric chamber , has a burst strength of greater than 60 psi. 8. The conduit system of claim 7, wherein the inner longitudinal chamber occupies at least 75 % of the cross-sectional area of the outer longitudinal chamber. 8. The conduit system of claim 7, wherein only the inner longitudinal chamber has a burst strength of less than 3.5 psi. The conduit system of claim 7, wherein the outer internal duct structure comprises a strip of fabric folded about a centrally located longitudinal axis and having two longitudinal edges adjoined along the longitudinal edges to define at least one outer longitudinal chamber, the fabric being folded about the centrally located longitudinal axis and adjoined with stitches. The conduit system of claim 7, wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber. 1. A process for forming a blowable flexible internal duct, comprising:
forming an interior internal duct structure comprising at least one interior longitudinal chamber, said at least one interior longitudinal chamber comprising an inflatable tube;
forming a fabric;
forming an outer internal duct structure from the fabric having at least one outer longitudinal chamber and simultaneously inserting at least one inner longitudinal chamber into at least one of the outer longitudinal chambers, wherein the inflatable tube has a wall thickness of less than 0.5 mm;
wherein only the inner longitudinal chamber has an air permeability of less than 1 cfm, and only the outer longitudinal fabric chamber has an air permeability of greater than 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has an air permeability of less than 1 cfm. The process of claim 13, wherein forming the outer internal duct structure comprises folding at least one strip-shaped fabric having two longitudinal edges of the fabric about a centrally located longitudinal axis and abutting the longitudinal edges to define at least an outer longitudinal chamber. The process of claim 13, wherein forming the outer internal duct structure comprises folding at least two strips of fabric, each having two longitudinal edges of the fabric about a centrally located longitudinal axis, and abutting the longitudinal edges to define at least two outer longitudinal chambers. 14. The process of claim 13, wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has a burst strength of greater than 60 psi. 14. The process of claim 13, wherein only the inner longitudinal chamber has a burst strength of less than 35 psi. The process of claim 13, wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber. 1. A process for forming a blowable flexible internal duct, comprising:
forming an interior internal duct structure comprising at least one interior longitudinal chamber, said at least one interior longitudinal chamber comprising an inflatable tube;
forming an outer internal duct structure having at least one outer longitudinal chamber and simultaneously inserting at least one inner longitudinal chamber into at least one of the outer longitudinal chambers, wherein the inflatable tube has a wall thickness of less than 0.5 mm;
wherein only the inner longitudinal chamber has an air permeability of less than 1 cfm, and only the outer longitudinal fabric chamber has an air permeability of greater than 100 cfm, and the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has an air permeability of less than 1 cfm. 20. The process of claim 19, wherein the outer longitudinal fabric chamber, together with an inner longitudinal chamber located inside the outer longitudinal fabric chamber , has a burst strength of greater than 60 psi. 20. The process of claim 19, wherein only the inner longitudinal chamber has a burst strength of less than 3.5 psi. 20. The process of claim 19, wherein the inner longitudinal chamber fills at least 60 % of the cross-sectional area of the outer longitudinal chamber. The process of claim 19, wherein the inner longitudinal chamber is configured to surround and carry at least one cable. 20. The process of claim 19, wherein the inner longitudinal chamber is movable within the outer longitudinal fabric chamber.