AIR DUCTS, WITH FOLDABLE WALLS, WITH INTERNAL EXPANSION STRUCTURES

Abstract

Air ducts with folding walls and internal expansion structures are described. An exemplary air duct system includes a shaft within the duct that extends longitudinally and is under longitudinal compression. The duct system also includes a plurality of ribs that engage with the shaft and an internal surface of the duct, and a spring within the duct that engages with the shaft. The spring under tension contributes to the longitudinal compression of the shaft and the longitudinal tension of the duct. A method for retrofitting an existing air duct system with an internal expansion structure is also described.

Description

AIR DUCTS, WITH FOLDABLE WALLS, WITH INTERNAL EXPANSION STRUCTURES FIELD OF DESCRIPTION This patent generally refers to air ducts and more specifically to air ducts with a folding wall, with internal expansion structures. BACKGROUND Ducts are often used to transport conditioned air (e.g., heated, cooled, filtered, etc.) discharged from a fan and distribute the air to a room or other areas within a building. Ducts are typically made of rigid metal such as steel, aluminum, or stainless steel. In many installations, ducts are concealed above ceilings or suspended ceilings for convenience and aesthetic reasons. But in warehouses, production plants, and many other buildings, ducts are suspended from the building's ceiling and are thus exposed. In such storage or manufacturing environments, where it is critical to prevent airborne contamination of inventory, metal ducts can create problems. For example, temperature variations within the building or temperature differences between the ductwork and the air being transported can create condensation both inside and outside the ductwork. The presence of condensed moisture inside the ductwork can lead to the growth of mold or bacteria, which the ductwork then carries into the room or other areas supplied by the air conditioning system. In the case of exposed ductwork, condensation on the outside of the ductwork can drip onto inventory or personnel. IVIA / a / ZUZZ / U 14 I 0 / which is below. The consequences of dripping can range from minor irritation to a dangerously slippery floor or complete destruction of products below the pipe (particularly in food processing facilities). Furthermore, metal ducts with localized discharge registers have been known to create uncomfortable drafts and unbalanced localized heating or cooling within the building. In many food processing facilities where the target temperature is 5.6 degrees C (42 degrees F), a cold draft can be especially uncomfortable and likely unhealthy. Many of the problems previously associated with metal ductwork are overcome by the use of flexible fabric ductwork, such as DUCTSOX from DuctSox Corporation of Dubuque, Iowa. These ducts typically have a foldable (often porous) fabric wall that inflates into a generally cylindrical shape due to the pressure of the air being carried through the duct. Fabric ductwork appears to inhibit condensation formation on its outer wall, possibly because fabric has lower thermal conductivity than metal ductwork. Furthermore, the fabric's porosity and / or additional holes distributed along the length of the fabric ductwork disperse air widely and evenly throughout the room being conditioned or ventilated. This uniform airflow distribution also effectively ventilates the duct walls themselves, further inhibiting the growth of mold and bacteria. In many cases, however, once the room's air conditioning demand has been met, the supply air fan is turned off or until it is required again. When the fan is turned off, the IVIA / a / ZUZZ / U 14 I 0 / The resulting loss of air pressure in the duct deflates the fabric tube, causing it to sag. Depending on the application and the fabric material, in some cases, the sagging creates a less than optimal appearance or can interfere with anything directly below the duct. Furthermore, when the duct is reinflated, it may produce a popping sound as the duct fabric is once again taut with air pressure. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of an air duct system IVIA / a / ZUZZ / U 14 I 0 / de-energized specimen with an exemplary internal frame to maintain the system's collapsible duct in a generally expanded form. Figure 2 is a side view similar to Figure 1, but showing the system's blower energized. Figure 3 is a side view similar to Figure 1, but showing another exemplary air duct system. Figure 4 is a side view similar to Figure 3, but which The system blower is energized. Figure 5 is a cross-sectional side view showing a portion of the frame from Figure 2. Figure 6 is a perspective view of an exemplary radial support member. Figure 7 is a perspective view of another exemplary radial support member. Figure 8 is a perspective view of another exemplary radial support member. Figure 9 is a perspective view of yet another exemplary radial support member. Figure 10 is a cross-sectional side view showing one end of a frame in Figures 1-4 with the end cap disconnected. Figure 11 is a side cross-section view similar to Figure 10, but showing the elongated frame and the installed end cap. Figure 12 is a cross-sectional side view of an exemplary end cap. Figure 13 is a rear view of the end cap shown in Figure 12 with the folding end cap blade being relatively loose. Figure 14 is a rear view similar to Figure 13 but showing the folded end cap sheet under tension. Figure 15 is a side cross-sectional view similar to Figure 12 but showing the end cap ready to be installed. Figure 16 is a side cross-sectional view similar to Figure 15 but showing the end cap connected to a folding wall air duct. Figure 17 is a top view of an exemplary air duct system in an L-shaped configuration. Figure 18 is a cross-sectional perspective view of an exemplary flow reducer connected to an exemplary radial support member within a collapsible air duct. Figure 19 is a perspective view showing the assembly of an embedded or nested stack of exemplary radial support members. IVIA / a / ZUZZ / U 14 I 0 / Figure 20 is a side view of an existing folding wall air duct about to be retrofitted with an exemplary frame. Figure 21 is a side view similar to Figure 20 but showing a selection of two exemplary racks about to be inserted into the air duct of Figure 20. Figure 22 is a side view similar to Figure 20 but showing an exemplary frame installed inside the duct. Figure 23 is a side view similar to Figure 22 but showing the frame that is lengthened in an adjustable way. Figure 24 is a side view similar to Figure 20 but showing an exemplary frame installed and axially compressed inside the duct. Figure 25 is a side cross-sectional view similar to Figure 11 but showing another exemplary air duct system. Figure 26 is a side cross-sectional view showing the manually adjusted duct system of Figure 25. Figure 27 is a side cross-sectional view similar to Figure 26 but showing another exemplary duct system that is manually adjusted. Figure 28 is a side cross-sectional view similar to Figure 26 but showing another exemplary duct system. Figure 29 is a side cross-sectional view showing the duct system of Figure 28 after it has been adjusted. Figure 30 is a side view of an exemplary air duct system with an exemplary shaft in a withdrawn configuration. Figure 31 is a cross-sectional side view of the doctor system in Figure 30, but showing the shaft in an installed configuration. Figure 32 is a side view of an exemplary shaft for an air duct system. Figure 33 is a cross-sectional side view of the shaft in Figure 32, but showing the shaft in an installed configuration. Figure 34 is a side view within the exemplary shaft for an air duct system. Figure 35 is a cross-sectional side view of the shaft in Figure 34, but showing the shaft in an installed configuration. Figure 36 is a side cross-sectional view similar to Figure 35 but showing an exemplary duct system with an alternating tubular sidewall. Figure 37 is a cross-sectional side view showing an exemplary air duct system with an exemplary linear clutch. Figure 38 is a side cross-sectional view similar to Figure 37 but showing the linear clutch used to lengthen an exemplary shaft assembly. Figure 39 is a cross-sectional side view similar to Figure 38 but showing the linear clutch with an elongated shaft assembly. Figure 40 is a side cross-sectional view similar to Figure 39 but showing the linear clutch configured in a more airflow shape. Figure 41 is a cross-sectional view similar to Figure 38 but showing the linear clutch that releases compression in the shaft assembly. Figure 42 is a graph that shows various aspects of IVIA / a / ZUZZ / U 14 I 0 / air doct system illustrated in Figures 37 - 41. Figure 43 is a cross-sectional side view of the linear clutch shown in Figure 37 with the clutch reciprocator in its relaxed position and the clutch release lever in its normal position. Figure 44 is a side cross-sectional view similar to Figure 43 but showing the linear clutch reciprocator in its taut or under tension position. Figure 45 is a side cross-section view similar to Figure 43 but showing the linear clutch release lever in its release position. Figure 46 is a side cross-sectional view similar to Figure 39 but showing another exemplary linear clutch. Figure 47 is a side cross-sectional view similar to Figures 39 and 46 but showing yet another exemplary linear clutch. Figure 48 is a cross-sectional side view showing another exemplary air duct system with another exemplary linear clutch. Figure 49 is a side cross-sectional view similar to Figure 48 but showing the inflated air duct and illustrating an exemplary extended shaft assembly due to duct inflation. Figure 50 is a side cross-sectional view similar to Figure 49 but showing the duct deflated while the shaft assembly remains extended. Figure 51 is a side cross-sectional view similar to Figure 43 but showing the linear clutch of Figures 48-50. Figure 52 is a side cross-sectional view similar to the Figures 43 and 51 show another example of a linear clutch. Figure 53 is a side cross-sectional view showing another exemplary duct system. Figure 54 is a side cross-sectional view similar to Figure 53 but showing the system in a different configuration. Figure 55 is a side cross-sectional view similar to Figures 53 and 54 but showing the system in yet another configuration. Figure 56 is a side cross-sectional view similar to Figure 47 but showing another example of an air duct system. Figure 57 is a side cross-sectional view similar to Figure 56 but illustrating the air duct under greater tension. DETAILED DESCRIPTION Certain examples are illustrated in the figures identified above and are described in detail below. In describing these examples, similar or identical reference numbers are used to identify identical or similar elements. The figures are not necessarily to scale, and certain features and views of the figures may be illustrated in exaggerated scale or schematically for clarity and / or conciseness. In addition, several examples have been described throughout this specification. Any feature of any example may be included with, replaced by, or otherwise combined with features of other examples. Exemplary air ducts comprising foldable tubular sidewalls are provided with exemplary internal frames that support the duct in a generally expanded shape even when the duct is depressurized. The frame tensions the foldable sidewall material over the IVIA / a / ZUZZ / U 14 I 0 / Duct length to maintain tension in the material. In some examples, the frame is constrained within the duct such that the tensioned side wall of the duct supports the frame in longitudinal compression. In this way, in the longitudinal direction, the duct is in tension and the frame is in compression. To prevent the frame from bending under the compressive force, some exemplary frames comprise a central longitudinal shaft with a plurality of radial spokes and rings that help to keep the shaft straight. In some examples, the rings also help to support the radially expanded duct. In some examples, the frame is spring-loaded. Figures 1-4 show exemplary air duct systems 10 and 12 for conveying air 14 discharged from a blower 16 and for dispersing or otherwise supplying air 14 to a room or other areas of a building. The duct system 10 in Figures 1 and 2 will be explained first, and the differences between duct systems 10 and 12 will be explained later. To convey air 14, the duct system 10 includes an air duct 18 comprising a tubular sidewall 20 made of a foldable material. As used herein, the term “sidewall” refers to the full circumferential extent of the fabric tube, even if the sidewall portion runs over the top or bottom of the tube or any intermediate portion. Examples of foldable sidewall materials include, but are not limited to, a polymer-impregnated or coated fabric, an uncoated fabric, a polyester sheet, other polymer or non-metallic sheets, and various combinations thereof. To release air 14 from the interior of the duct 18 into the room or area it serves, the sidewall 20 and / or an end cap 22 of the duct 18 includes one or more discharge openings, such as, for example, IVIA / a / ZUZZ / U 14 I 0 / cutting openings, plastic or metal discharge registers and / or porosity in the sidewall material itself. In some examples, the duct system 10 is mounted below a ceiling 24 with a plurality of hangers 26 suspending the duct system 10 from an upper support structure 28 (e.g., a cable, rail, channel, beam, ceiling, etc.). An exemplary frame 30 comprising the shaft 32 and a plurality of ribs 34 installed within the duct 18, and which is made of a relatively rigid material (e.g., rigid plastic, fiberglass, steel, aluminum, etc.) that is more rigid and less flexible than the sidewall 20, supports the duct 18 in a generally expanded shape, regardless of whether the blower 16 is energized or idle.In this way, frame 30 helps to prevent or minimize pneumatic shock and the resulting explosive noise from a collapsible air duct that suddenly inflates as blower 16 is turned on. This can abruptly increase the air pressure within duct 18 from idle ambient air pressure to active positive air pressure. Frame 30 also eliminates or minimizes the extent to which duct 18 sags, sags, or otherwise suffers cosmetic degradation when blower 16 is de-energized. In some installations of the frames and / or shaft mounts described herein, these structures also help to keep duct 18 open when it is used as a return air duct carrying sub-atmospheric air to the suction inlet of a blower. The frame 30 is contained within the duct 18 in such a way that the frame 30 exerts a tensile force 36 that tensions the duct 18 in a generally longitudinal direction 38 such that at least the sidewall 20 is maintained at a minimum tension level whether or not the IVIA / a / ZUZZ / U 14 I 0 / blower 16. In some examples, the frame 30 tensions all and / or substantially all of the circumference of the duct 18. Tensioning the duct 18 along its length subjects the shaft 32 of the frame 30 to a longitudinal reactive compressive force 40. To prevent the compressive force 40 from buckling the shaft 32 and to help maintain the duct 18 in a radially expanded shape, ribs 34 are sized to keep the duct 18 open and are spaced apart over the length of the duct 18 to limit radial deflection of the shaft 32. Although the specific design details of the frame 30 and means for mounting it within a collapsible air duct may vary, some examples are illustrated in the reference figures. In Figure 5, for example, the frame 30 includes a radial support member 44 comprising a plurality of spokes 42 connecting the rib 34 to a hub 46. In this example, the rib 34 is a complete 360-degree ring, but in other examples, the rib 34 is a curved rod extending less than 360 degrees around the inside diameter of the duct 18. Also in this example, the rib 34, spokes 42, and hub 46, which constitute the radial support member 44 in this instance, comprise a single fabricated construction or member, such as a welded part. The radial support member 44 can be installed at various locations along the length of the shaft 32, as illustrated in Figure 1. When the radial support member 44 is installed at one end 48 of the duct 18, as illustrated in Figure 5, a retainer 50 holds the rib 34 substantially fixed to the adjacent side wall 20 of the duct 18, such that this particular radial support member 44 can resist compressive force 40 and transmit the corresponding reactive force as a tensile force 36, which tensions the side wall 20. The retainer 50 can be any means for supporting a rib or member IVIA / a / ZUZZ / U 14 I 0 / of radial support generally fixed with respect to an adjacent side wall of a duct. Examples of this retainer include but are not limited to a fastener (spring-loaded or rigid), a strap (elastic or rigid), an axial clamp between rib 34 and the blower housing, a narrow-band type hose clamp (e.g., retainer 52 of Figures 3, 4, 17 and 22 24), a screw, rivet, fastener, etc. In examples where the retainer 50 is in the form of an elastic strap or a spring-loaded fastener, the elasticity of the retainer 50 can help compensate for permanent longitudinal stretching of the duct 18, which may occur slowly over time, depending on the sidewall material 20. Alternatively or additionally, elastic compensation for permanent longitudinal duct stretch may be incorporated within the frame 30 itself at almost any other location along the length of the frame 30. When the radial support member 44 is installed at various intermediate locations within the length of the duct 18, the retainer 50 at these locations may be omitted. Without the retainer 50, the rib 34, or indeed an imaginary plane 54 defined by the rib 34, may still be substantially maintained perpendicular to a longitudinal centerline 56 of the duct 18 by rays 42 connecting the rib 34 to the hub 46 in combination with a telescoping connection 58 (or comparable rigid connection) between the hub 46 and the attached shaft segment 32a. The shaft segment 32a is one of a plurality of segments that, when connected to a plurality of hubs 46, provide an assembled shaft (shaft 32) that lies generally on the centerline 56. The perpendicular orientation of the ribs 34 within the duct 18 is further ensured by virtue of rays 42 that are inclined (e.g., the rays 42 lie at a IVIA / a / ZUZZ / U 14 I 0 / angle 60 that is not perpendicular to axis 32) as shown in Figure 5. This arrangement creates an axial displacement assembly in which the spokes 42 connect to the hub 46 (e.g., the spokes 42 connect to the hub 46 at a plurality of points 62 and 64 that are distributed and spaced longitudinally over the hub 46), thereby making the spokes 42 effective angle clamping. In the example shown in Figure 5, the hub 46 is a solid rod and the shaft segment 32a is a tube with the rod telescopically fitting inside the tube. In other examples, the hub 46 is a tube and the shaft segment 32a is a solid rod, wherein the solid rod of the shaft segment telescopically fits inside the tubular hub. In some examples, both the hub and the shaft segment are tubes of different diameters, with the smaller diameter tube telescopically fitting inside the larger one. In some examples, the hubs 46 provide a coupling that interconnects a plurality of shaft segments 32a, and in other examples, the hub and shaft segments are a single piece or a single weld. In still other examples, the hub and shaft segments are joined by some other means for connection.In still other examples, as shown in Figure 21, a frame 30' comprises ribs 34 that are interconnected by one or more shafts 32' at the periphery of the ribs, thereby eliminating the need for spokes 42 and the hub 46. Figure 6 shows an example where one end 66 of the hub 46 fits within a shaft segment 32b with a fastener 68 (e.g., a screw, pin, spring-loaded button, etc.) holding the two together. Alternatively or additionally, the hub 46 includes a spring-loaded button 70 that selectively projects into a multi-hole node 72 on a shaft segment 32c to provide discrete axial fit between the hub 46 and the segment. IVIA / a / ZUZZ / U 14 I 0 / axis 32c. This axial adjustment can be extended to adjust the total length of the frame 30. Figure 7 shows an example where solid shaft segments 32d and 32e fit within a tubular hub 46a. A self-tapping or shear-tapping screw 74 secures shaft segment 32d to one end of the hub 46a. To provide the frame with an adjustable length, a pin 76 is selectively inserted into one of a series of holes 78. Once inserted, the pin 76 maintains the selected fixed axial relationship between the hub 46a and shaft segment 32e. Figure 8 shows an example where a radial support member 30a has a tubular hub 46b that can telescope about a continuous shaft 32f, instead of a segmented one. When inserted into the duct 18, in some examples, the rib 34 connects to the side wall 20 and the hub 46b has limited freedom to slide about the shaft 32f, but in other examples, the hub 46b is clamped to the shaft 32f to hold it axially in place about the shaft 32f. Figure 9 shows an example where a radial support member 30c includes a ring 34' that can be formed from a flat bar, which can make the radial support member 30c more suitable for clamping with a band-type hose clamp such as retainer 52 of Figures 3, 4, 17 and 22-24. In the illustrated example shown in Figures 10 and 11, the end cap 22 comprises a folding end sheet 78 with a fastener 80 for connecting the end cap 22 to the duct end 18. The radial support member 44a comprises a plurality of spokes 42 connecting the rib 34 to a hub 46c. Some examples of the fastener 80 include, but are not shown in, the following: IVIA / a / ZUZZ / U 14 I 0 / limited to a rack, a touch-and-retain fastener, snap fasteners, clamps, etc. To ensure that the frame 30 is long enough to tension the duct 18 when the end cap 22 is installed, a telescoping connection 82 between the hub 46c and a shaft segment 32g enables the overall length of the frame 30 to be suitably increased by sliding the radial support member 44a out of the dashed line 84, as shown in Figure 10. When the frame 30 is adjusted to the proper length, that length is held fixed by fastening the hub 46c to the shaft segment 32g by means of the screw 74, for example. Alternatively or additionally, a pin 86 selectively inserted into one of a series of holes 88 can be used to adjust a minimum length of the frame 30, which can be an auxiliary feature during installation of the duct system 10. After the frame 30 is adjusted to the proper length, the duct 18 and its end cap 22 are forcibly pulled together over the rib 34 and the fastener 80 is closed, as shown in Figure 11. In some examples, the appropriate length of the frame 30 is determined based on the anticipated air pressure 14 that the blower 16 discharges into the duct 18. In some examples, the length of the frame 30 is dimensioned so that the mechanical force exerted by the frame 30 in the longitudinal direction 38 is greater than the pneumatic force applied to the duct end cap 22, so that the application of the pneumatic force does not expand or cause the duct 18 to burst or pop beyond the end of the frame 30.In other words, air duct 18 is at a first magnitude of stress in the longitudinal direction 38 when the air inside air duct 18 is at idle ambient air pressure, air duct 18 is at a second magnitude of stress in the longitudinal direction 38, when the. IVIA / a / ZUZZ / U 14 I 0 / The air inside duct 18 is at active positive air pressure, and the first stress magnitude is greater than the difference between the first and second stress magnitudes. Also, the first stress magnitude is less than the second stress magnitude. Furthermore, frame 30 is at a first compression magnitude in the longitudinal direction 38 when the air inside duct 18 is at inactive ambient air pressure. Frame 30 is at a second compression magnitude in the longitudinal direction 38 when the air inside duct 18 is at active positive air pressure, and the first compression magnitude is greater than the difference between the first and second compression magnitudes. Also, the first compression magnitude is greater than the second compression magnitude. Once contained within duct 18, the frame 30 requires no additional support because duct 18, which can be suspended independently of the upper support structure 28, carries most, if not all, of the frame's total weight. In some examples, however, as shown in Figures 3 and 4, backup hangers 88 extending through the side wall 20 attach the frame 30 directly to a certain upper support (e.g., a support structure 28) so that the frame 30 has a redundant source of support if the frame support provided by duct 18 fails. Figures 12-16 show an exemplary end cap 90 that can be used in place of end cap 22 and can be employed on a wide variety of collapsible or inflatable air ducts, regardless of whether or not the air duct has any other internal frame. The end cap 90, in this example, comprises an end piece 91 over which a collapsible sheet is stretched or held tightly. In the illustrated example, end piece 91 is provided by rib 34 with an optional hub 92 and optional spoke assembly 94. The hub 92 and spokes 94 can be employed when the end cap 90 is used in conjunction with a frame, such as the frames shown in Figures 1-11. Furthermore, while the example shown here uses rib 34, any member with a shape complementary to end cap 22 can be employed. In the case of a round duct, this complementary shape will be circular.Accordingly, in addition to a ring, a circular plate or similar structure can also be used. It may not even be necessary for the structure to be circumferentially continuous. In some examples, the end cap 90 also includes a hem 98, fastener 80, an extension 102, and a constricting member 104. The sheet 96 with the hem 98 has a peripheral portion 106 and overlaps an outer periphery 107 of the rib 34. In some examples, the hem 98 is sewn to the outer peripheral portion of the sheet 96. In other examples, the hem 98 is an integral extension of the sheet 96. The fastener 80 is illustrated to represent any means for connecting the hem 98 to the end of a tubular collapsible air duct, such as the duct 18. In other examples, the extension 102 projects from a virtual circular line 100 (Figure 13) in the general vicinity where both the hem 98 meets the sheet 96 and where the sheet 96 overlaps the rib 34. In this example, the restraining member 104 is connected to the extension 102 and is used to tension the sheet 96 in an outward radial direction, thereby preventing a loose-fitting appearance of the sheet 96. In some examples, the restraining member 104 is an adjustable cord and IVIA / a / ZUZZ / U 14 I 0 / Extension 102 is a circular frame having an inner sleeve 108 through which the adjustable cord (member 104) is threaded. In other words, Extension 102 comprises a plurality of circumferentially spaced tabs distributed along the circular line 100. In any case, manually pulling the ends 104a and 104b of the adjustable cord pulls Extension 102 radially inward toward a central point 110 of rib 34, thereby tensioning blade 96 in a radially outward direction. The adjustable cord is then tied, fastened, or otherwise secured to maintain blade 96 in a tensioned state. More generally, the constriction member 104 has a tensioned state (Figures 14, 15, and 16) and a loose state (Figures 12 and 13), wherein the folding sheet 96 is tighter when the constriction member 104 is in the tensioned state than when it is in the loose state, and the extension 102 is closer to the center point 110 when the constriction member 104 is in the tensioned state than when it is in the loose state. After the sheet 96 is tensioned, the fastener 80 connects the end cap 90 to the collapsible air duct 18, as shown in Figure 16. Regardless of the shape and other design features of the end piece 91, the constricting member 104, which pulls the extension 102 radially inward to the center point 110, pulls the folding blade 96 over the outer periphery 107 of the end piece 91 and pulls the folding blade 96 radially outward. The resulting radial tension in the folding blade 96 gives the end cap 90 a clean appearance with minimal creasing, if any. IVIA / a / ZUZZ / U 14 I 0 / Various additional features and benefits of the aforementioned examples are illustrated in Figures 17-19. Figure 17 is a top view of an exemplary L-shaped air duct system 112 comprising a collapsible elbow duct 114 connecting two collapsible air ducts 18a and 18b. To substantially maintain the entire L-shaped duct in an inflated position, a first frame 30a is positioned within duct 18a to create longitudinal tension and / or tensile force 36 in that duct, wherein radial support members 44 and 44a are circumferentially attached to or otherwise retain duct 18a by any convenient means, including but not limited to strap fasteners 25.In addition to, or as an alternative to, strap fasteners 25 in some examples, a short, collapsible air duct segment with one or more retainers 50 holds the radial support members 44 and / or 44a in place, while circumferential zippers at either end of the duct segment connect the duct segment to the remainder of the air duct 18a. Similarly, a second frame 30b is placed inside the duct 18b to create longitudinal tension or tensile force 36 in that duct, wherein one or more radial support members 44 are circumferentially attached to the duct 18b by any convenient means, including but not limited to strap fasteners 205. One or more radial support members 44 are placed inside the elbow 114 to maintain the elbow 114 in its generally inflated state.In some examples, a curved arrow interconnecting the radial support members 44 within the elbow 114 helps to hold the radial support members 44 in place. The curved arrow is not shown because not all examples of an elbow with radial support members include this arrow. Figure 18 shows an exemplary flow reducer 116 connected to the IVIA / a / ZUZZ / U 14 I 0 / radial support member 44. The flow reducer 116, in some examples, is a fabric cone with a reduced airflow outlet 118. In some examples, the outlet 118 is a fixed opening, and in other examples the opening downstream of the outlet 118 is regulated by an adjustable constriction cord 120. Figure 19 shows how a plurality of radial support members 44 can be stacked into a compact, transportable assembly. This nested arrangement is possible due to the offset between the radial connection points 62 and 64, where points 62 and 64 are longitudinally offset (dimension 122) and lie on opposite sides of the cube 46. More specifically, the illustrated assembly / apparatus 124 comprises a plurality of ribs 34, where each rib 34 lies on an imaginary plane 126 to define a plurality of imaginary planes 126. The apparatus / assembly 124 also includes a cube 46 connected to each rib 34, creating a plurality of cubes 46. The rings 34 are in a transportable, stacked assembly with rings 34 arranged adjacent to each other, such that the plurality of imaginary planes 126 are substantially parallel to each other.The plurality of cubes 46 are radially offset from each other (dimension 128), and the plurality of ribs 34 are radially offset from each other. In the illustrated example, at least one cube 46 extends across more than one imaginary plane 126. Figures 20–24 illustrate an exemplary method for taking an existing, previously functional air duct system 130, which includes an inflatable air duct 18, and retroactively modifying the system 130 with frame 30 or a similar one. In some instances, the method involves gaining access to the interior volume of duct 18 by opening the duct at a certain point, for example, at the duct end cap 22, as shown in Figure 20. Figure 21 shows IVIA / a / ZUZZ / U 14 I 0 / Install the 30 rack inside duct 18. In some examples, alternate styles of racks are installed instead, such as the 30' rack. In some examples, frame 30 is progressively assembled as it is inserted into duct 18. Figure 22 shows frame 30 inside duct 18 with the exemplary retainer 52 holding a radial support member 44 in place. Figures 22 and 23 show how a longitudinal section 132 of frame 30 is adjustable, where frame 30 is longer in Figure 23 than in Figure 22. Arrow 134 in Figure 23 represents closing the end cap 22, thereby enclosing frame 30 within the internal volume of duct 18. Forcibly enclosing frame 30 within duct 18, as shown in Figure 24, results in compressing frame 30 and tensioning the air duct 18 in the longitudinal direction 38. With previous air ducts that have collapsible tubular sidewalls and an internal frame, the sidewall material still tends to sag with the loss of internal air pressure and / or as the sidewall material stretches over time. An example of an air duct that is able to maintain continuous tension in the sidewall material, and thus maintain tension in the duct, utilizes compression stored in a spring, which supplies continuous force to the end cap in the longitudinal direction of the duct. With this example, the compression stored in the spring can be released when the duct is deflated, resulting in duct elongation. The stored compression is used because the internal frame has a variable overall length, and the spring provides the current force to change the length.Figures 25 and 26 illustrate an exemplary air duct system 136 with features that facilitate installation and ensure air duct tension. IVIA / a / ZUZZ / U 14 I 0 / system 18 even when the duct 18 is deflated. In this example, the air duct 18 includes a tubular folding sidewall 20 (FIGURE 26) and a connected end cap 22. The tubular sidewall 20 is suitable for conveying air 14 in a longitudinal direction 138 through the duct 18 and eventually releasing the air 14 in a radial and / or axial direction through pores or other outlets in the duct 18. To keep the side wall 20 taut so that the duct 18 appears inflated when the duct 18 is in fact deflated (without pressure), an exemplary spring-loaded frame 140 is installed inside the duct 18, as shown in Figure 25. The frame 140, in this example, comprises a shaft 142 supporting a plurality of ribs 34. The ribs 34 engage an inner surface 144 of the side wall 20 to maintain the duct 18 in a radially expanded shape.To keep the side wall 138 taut in the longitudinal direction, the shaft 142 comprises a first shaft segment 32h, a second shaft segment 46d, a bypass or spring element 146, and a telescopic connection 148 between shaft segments 32h and 46d (e.g., first and second shaft segments include, but are not limited to, previously mentioned hubs 46, 46a, 46b, 46c, and 92); wherein the various shaft components and other elements of system 136 are designed to hold the duct 18 in longitudinal tension in reaction to the shaft 142 being in longitudinal compression. Longitudinal adjustment of the internal structure is provided by a pin that engages a helical spring, making the length continuously (as opposed to in discrete increments) adjustable. For example, in some instances, spring 146 is a helical compression spring with one end 150 connected to a fixed point 152 on a second shaft segment 46d. An intermediate section 154 of spring 146 threads onto a pin 156 or comparable feature at a fixed point 158 ​​on a first shaft segment 32h. The distance between points 152 and 158, in addition to other physical dimensions of the system 136, determines the overall length of the shaft 142 and / or the compression of spring 146. To adjust the shaft length and / or spring compression, a first rotational joint 160 in the telescopic connection 148 enables the second shaft segment 46d to be rotated relative to the first shaft segment 32h. Depending on the direction of rotation, manual rotation of the second shaft segment 46d relative to the first shaft segment 32h, as shown in Figure 26, effectively threads the two shaft segments 32h and 46d together or apart because the two shaft segments 32h and 46d are threaded together by the spring section 154, which engages the pin 156. In this way, the spring 146 acts as an adjusting screw for the overall length of the shaft 142 when the shaft 142 is not longitudinally constrained by the duct 18 (unconstrained, for example, when the end cap 22 is removed or when the shaft 142 is appreciably shorter than the duct 18).When the length of shaft 142 is restricted by the finite length of duct 18 with end cap 22 installed, spring 146 serves as an adjusting screw for spring compression 146 and thus serves as a means of adjusting the longitudinal compression of shaft 142. Adjusting the longitudinal compression of shaft 142, in turn, adjusts the longitudinal tension in duct 18 accordingly. In some examples, the adjustment of shaft 142 is carried out as follows: First, the length of frame 140 is adjusted as shown in Figure 26, where the relatively short uncompressed length of the frame allows that IVIA / a / ZUZZ / U 14 I 0 / A portion 162 of the end cap 22 is easily rack-fastened or otherwise connected to the side wall 20. With another portion 164 of the end cap periphery released from the rack or otherwise not connected to the side wall 20, as shown in Figure 26, a person can extend their arm 166 through the unrack-fastened opening 168 into the duct to manually rotate the second shaft segment 46d relative to the first shaft segment 32h such that the relaxed, uncompressed length of the shaft becomes greater than the length of the duct 18 and side wall 20. However, with the end cap 22 restricting the shaft's ability to fully extend to its relaxed, uncompressed length, the spring 146 and shaft 142 are compressed within the confines of the duct 18. The person then removed its arm 166 and closes the opening 168.The end cap 22, now fully connected to the side wall 20, keeps the spring 146 and shaft 142 in compression. The shaft 142, when compressed, subjects the side wall 20 to longitudinal tension 170, as shown in Figure 25. To make it easier to manually rotate the second shaft segment 46d about the first shaft segment 32h without the rib 34 tending to rotate the end cap 22 in the process, some exemplary shafts, such as shaft 172 in Figure 27, include a second swivel joint 174 between a second shaft segment 46e and a hub 46f that causes the second shaft segment 46e to rotate further about the end cap 22. In some examples, as shown in Figures 28 and 29, a shaft 176 includes a release lock 178 in the telescopic connection 180. The function of the release lock is to temporarily store some of the length / adjustable spring compression and release it only when the end cap is in place. IVIA / a / ZUZZ / U 14 I 0 / react to force. The release lock 178 can make it easier to close the connection between the side wall 20 and the end cap 22 while the spring 146 and shaft 176 are under compression. For example, the lock 178 in the retaining position of Figure 28 holds the shaft 176 to a retracted length that easily fits inside the duct 18. Just before fully closing the fastener between the end cap 22 and side wall 20, a person can reach into the duct 18 to move the lock 178 to its release position of Figure 29. This allows the spring 146 to extend the shaft 176 to the length shown in Figure 29, whereby the spring 146, still under some compression, provides the axial force to place the side wall 20 in longitudinal tension. After releasing the lock 178, the person can complete the closure between the end cap 22 and side wall 20. Although the actual structure of the lock 178 may vary in some examples, the lock 178 is a hand screw that threads a second shaft segment 46g to an axial end 182 that selectively butts the first shaft segment 32h. In the retained position, the axial end 182 presses firmly against the first shaft segment 32h to hold the 32h segment fixed relative to the second shaft segment 46g. In the released position, the axial end 182 is separated from the first shaft segment 32h to allow relative movement between the 32h and 46g shaft segments. In some examples, as shown in Figures 30 and 31, an air duct system 184 includes a new elbow particularly suited to redirect an airflow 146 through a tubular folding sidewall 188 of an air duct 190. In Figure 31, the air duct 190 defines a nonlinear airflow path 192 from an inlet 194 to an outlet 195 of the duct 190. IVIA / a / ZUZZ / U 14 I 0 / To support the air duct 190 in a radially expanded form, the illustrated example includes a plurality of ribs 34 supported by a shaft 196 that selectively adjusts to a withdrawn configuration and an installed configuration. In the withdrawn configuration, shaft 196 is withdrawn from the interior of duct 190 and follows a first shape that in some examples is relatively or somewhat straight (e.g., straighter than a 90-degree elbow), as shown in Figure 30. In the installed configuration, shaft 196 is installed inside duct 190 with ribs 134 that engage an inner surface 198 of sidewall 188, as shown in Figure 31. In the installed configuration shown in Figure 31, shaft 196 has a second shape that is distinguishable from its first shape illustrated in Figure 30. In the illustrated example, shaft 196 has a longitudinal centerline 200 that is straighter in Figure 30 than in Figure 31. In Figure 31, the centerline 200 lies on a nonlinear line. Figure 30 shows centerline 200 arranged on a substantially linear line or at least on a line that deviates from the nonlinear line shown in Figure 31.The variable shape of the 196 shaft can be beneficial during installation, shipping, and / or manufacturing of the 196 shaft. The variable shape of the 196 shaft can also be useful for adjusting the 196 shaft to fit duct elbows of various shapes. In some examples, the variable shape of shaft 196 is achieved by having the shaft 196 comprise a plurality of shaft segments 202 interconnected by at least one joint 204, wherein the joint 204 makes the plurality of shaft segments 202 angularly movable relative to each other when the shaft 196 is in the retracted configuration. In some examples, the joint 204 is a helical spring that is more flexible than the plurality of shaft segments 202. In other examples, as shown in Figures 32 and 33, an exemplary joint 206 is a tube made of a polymer that can be elastically bent (e.g., rubber, polyurethane, etc.). Still in other examples, as shown in Figures 34 and 35, an exemplary joint 208 is a pivot joint such as for example two interconnected eyelets (for example, two interconnected ring bolts or a disconnectable fastener). In the examples shown in Figures 30-35, the air duct 190 is selectively inflated and deflated. The air duct 190 has an internal deflated volume 210. When the air duct 190 is deflated, the internal deflated volume is greater when the shaft 196, 196a, or 196b is in the installed configuration (Figures 31, 33, and 35, respectively) than when the shaft is in the withdrawn configuration. In some examples, as shown in Figure 36, an elbow-shaped air duct 212 has a tubular foldable sidewall 214 with at least some elastic material 216 that helps control the gathering of the sidewall 214 to evenly distribute a plurality of creases or gathers 220. In some examples, the material 216 is an elastic strip sewn intermittently or otherwise connected to an inside radius 218 of the tubular sidewall 214. In other examples, most, if not all, of the sidewall 214 comprises elastic material. With previous air ducts that had foldable tubular sidewalls and an internal frame that could be adjusted longitudinally, adjustment could only be made in discrete increments. Also, adjusting the length of the internal frame of the previous duct to achieve adequate sidewall tension was difficult due to the relatively high tensile forces required. An example of an air duct having an internal frame of IVIA / a / ZUZZ / U 14 I 0 / Adjustable length, a clutch device not only provides continuous (not discrete) length adjustment, but also uses mechanical advantage to achieve the required tension in the sidewall. In this example, the sidewall material can be sufficiently pre-tensioned so that it does not sag even when deflated. In some examples, as shown in Figures 37–45, an air duct system 222 includes an exemplary shaft assembly 224 with an exemplary linear clutch 226 to hold the air duct 18 in longitudinal tension 228 (Figure 39) in response to a shaft assembly 224 that is in longitudinal compression 230. The term "linear clutch" means any mechanism having at least one configuration in which the mechanism facilitates longitudinal extension of an elongated assembly (e.g., shaft assembly 224) while resisting longitudinal retraction of the elongated assembly.Examples of Linear Clutch 226 and other linear clutches include, but are not limited to, Lever Action Cargo Bar, P / N-08907, supplied by Erickson Manufacturing LTD. of Marine City, MI; Pro Grip Cargo Control Cargo Bar, P / N 900912, supplied by USA Products Group, Inc. of Lodi, CA; Ratcheting Cargo Bar, P / N 05059 (U.S. Patent No. 5,443,342), supplied by Keeper Corp. (Hampton Products International) of North Windham, CT; Haul-Master 2-in-1 Support Cargo Bar, P / N 66172, supplied by various distributors (e.g., Harbor Freight of Camarillo, CA; Amazon.com, Inc. of Seattle, WA; and Sears Holdings Corp. of Hoffman Estates, IL). In the illustrated example, to extend the shaft assembly 224 from its length in Figure 37 to that in Figure 38, a person extends their arm 166 through the opening 168 to repeatedly move or cycle a reciprocating shaft 232 that extends from the linear clutch 226. The term, reciprocating shaft IVIA / a / ZUZZ / U 14 I 0 / means any member that is operated by repeated back-and-forth motion. The repeated motion reciprocator 232 between its relaxed position (Figure 43) and its tense position (Figure 44) and doing so for a plurality of cycles 234 (Figure 42) during a given period 236 extending from a start 238 to an end 240, lengthens the shaft assembly 224. In this way, an adjustable length 242 of the shaft assembly 224 is longer at the end of period 240 than at the beginning of period 238, and the length 242 increases with each cycle, as shown in the example in Figure 42. Once the linear clutch 226 extends the shaft assembly 224 to a desired length, placing the air duct 18 under tension and the shaft assembly under compression, the rack 162 is closed, as illustrated in Figure 39, and the air duct system 222 is ready for use. To minimize airflow resistance in the duct 18, in some examples, the reciprocator 232 and a handle 244 are moved to a stowed position, as illustrated in Figure 40. If, for any reason, it is desired to relieve the tension in the air duct and the compression of the shaft assembly by shortening the shaft assembly 224, a person can extend the arm 166 into the duct 18, as shown in Figure 41, and actuate a release lever 246, which allows the linear clutch 226 to retract the shaft assembly 224. Although the actual design and operation of the linear clutch 226 may vary, Figures 43–45 illustrate an example, where the linear clutch 226 is selectively movable to a holding configuration (Figure 43) and a releasing configuration (Figure 45). Figure 44 shows the linear clutch 226 in another holding configuration, but with the linear clutch 226 having an incrementally lengthened shaft assembly 234.In this illustrated example, the linear clutch 226 comprises a housing 252, a handle 244 connected to the housing 252, a reciprocator 232 attached to the housing 252, a shaft segment 254 slidably positioned within the housing 252, a first ring-jointing member 256 surrounding the shaft segment 254, a second ring-jointing member 258 surrounding the shaft segment 254, releasing the lever 248 extending integrally from the second ring-jointing member 258, a first compression spring 260 displacing the first ring-jointing member 256 to its free position (illustrated in Figures 43 and 45), and a compression spring segment 262 displacing the second ring-jointing member 258 to its clamping position (shown in Figure 43). In this example, the pivotal motion reciprocator 232 from its relaxed position (Figure 43) to its tensioned position (Figure 44) tilts the first annular joint member 256 from its free position (Figure 43) to its clamping position (Figure 44) such that the first annular joint member 256 clamps the shaft segment 254. While the first annular joint member 256 clamps the shaft segment 254, moving the reciprocator 232 from its relaxed position (Figure 43) to its tensioned position (Figure 44) pushes the first annular joint member 256 and the shaft segment 254 to the left 264, an increment 266 (Figures 42 and 44), thereby extending the shaft assembly 224.The second annular connecting member 258 allows this movement because, as the shaft segment 254 moves to the left, the axial friction between shaft segment 254 and the second annular connecting member 258 is in a direction that decreases the frictional holding force between shaft segment 254 and the second annular connecting member 258. Subsequently releasing the reciprocator 232 from its tensioned position (Figure 44) to its relaxed position (Figure 43) allows the... IVIA / a / ZUZZ / U 14 I 0 / The first spring 260 pushes the first annular joining member 256 back to its free position in Figure 43, while the second spring 262 displaces the annular joining member 258 to its clamping position (Figure 43), preventing the shaft segment 254 from retracting to the right back to where it was previously in Figure 43. This cycle is repeated to incrementally extend the shaft assembly 224. To subsequently retract the shaft assembly 224, in this example, the release lever 248 tilts from its normal linkage position in Figure 43 to a release position in Figure 45. In the release position, the second ring-joint member 258 releases its linkage clamp from the shaft segment 254. With both ring-joint members 256 and 258 in their release positions, as shown in Figure 45, the linear clutch 226 allows the shaft assembly 224 to retract. In the example shown in Figure 46, an air duct system 266 includes a shaft assembly 268 with another exemplary linear clutch 270. The linear clutch 270 includes a ratchet mechanism 272 comprising a retainer 274 that engages a support 276 having a plurality of discontinuities 278. The term ratchet means any movable element that selectively engages one or more discontinuities in a support. Examples of a ratchet include, but are not limited to, a pivoting bar or lever that engages one or more teeth or other discontinuities in a support, and a partial or complete pinion gear (e.g., retainer 274) with teeth that engage with one or more teeth or other discontinuities in a support. The term support generally means a linear elongated member with a plurality of discontinuities (e.g., teeth, projections, holes, retainers, etc.) distributed along its length. IVIA / a / ZUZZ / U 14 I 0 / Examples of a support include, but are not limited to, a tube with a plurality of holes distributed along its length, a tube with a plurality of retainers distributed along its length, and an elongated bar with a plurality of gear teeth distributed along its length. A specific example of a linear clutch 270 is a Ratcheting Cargo Bar, P / N 05059 (U.S. Patent No. 5,443,342), supplied by Keeper Corp. (Hampton Products International) of North Windham, CT. In the example illustrated in Figure 46, repeated motion (in a cyclic manner 280) of a reciprocator 282 of the linear clutch 270 lengthens the shaft assembly 268. The shaft assembly 268 can be shortened by manually actuating a release lever 284 to disengage the lever 284 from the ratchet 272, wherein the arrow 288 represents the actuation of the release lever 284. Figure 46 is similar to Figure 39 in that the linear clutch 270 is illustrated having the extended shaft assembly 268 to place the duct 10 in tension 228 and the shaft assembly 268 in compression 230. An example of an air duct capable of automatic tension adjustment of the foldable sidewall material in the longitudinal direction of the duct is illustrated in Figures 48-51. In another example, shown in Figure 47, an air duct system 286 includes an exemplary threaded-style linear clutch 288 for placing the duct 18 in tension 228 in reaction to a shaft assembly 290 that is in compression 230. To adjust the length of the shaft assembly 290 and / or to adjust the tension in the duct 18, a head 292 of the linear clutch 288 is rotated by a tool 294 in a cyclic manner (e.g., by rotating the tool 294 a plurality of continuous revolutions 296, or by rotating the tool 294 a plurality of partial revolutions 298). This action varies the extent to which a screw IVIA / a / ZUZZ / U 14 I 0 / for turning 300 (helically threaded member) extends into a shaft tube 302 of shaft assembly 290. In some examples, the linear clutch 288 comprises the screw 300 threaded into an internally threaded member 304 fixed to the shaft tube 302 (for example, a nut welded to the end of the tube 302, or the tube 302 is internally threaded), a stem 306 fixed to the screw 300 such that the stem 306 and the screw 300 rotate as a unit, a tubular hub 46h radially supporting the stem 306, and the head 292 of the stem 306. In some examples, the tool 294 is a crank that generally extends permanently from the head 292. In some examples, the tool 294 is a dedicated crank that is detachably connected to the head 292. In some examples, the tool 294 is a general-purpose wrench, such as a ratchet wrench with a socket that engages the head 292.The direction and amount that tool 294 and screw 300 are rotated with respect to the internally threaded member 304 determine the extent to which screw 300 extends within the shaft tube 302 and thus determines the adjusted length of shaft assembly 290. The adjusted length of shaft assembly 290, in turn, determines the tension and compression of duct 18 and shaft assembly 290, respectively. In some examples, as shown in Figures 48–51, a linear clutch 308 allows the extension of a shaft assembly 310 (e.g., frame) by inflating the air duct 18 from a deflated state in Figure 48 to an inflated state in Figure 49, while a retainer 312 (e.g., strap, fastener, clamp, cavity, loop, etc.) couples a distant end 314 of the shaft assembly 310 to the air duct end cap (e.g., end cap 22). In addition to the retainer 312 and / or alternatively, in some examples, IVIA / a / ZUZZ / U 14 I 0 / the distant end 314 connects to the duct end cap in the manner illustrated in Figures 12-16. Since inflation naturally extends the length of duct 18, the resulting elongation of the air duct lengthens shaft assembly 310 because the far end of shaft assembly 314 engages with the duct end cap. Once shaft assembly 310 extends from its shortest length in Figure 48 to its longest length in Figure 49, the one-way clamping action of linear clutch 308 holds shaft assembly 310 at its extended length even after duct 18 is subsequently deflated, as illustrated in Figure 50. In some examples, the linear clutch 226 used in shaft assembly 224 is identical to the linear clutch 308; however, many parts of the linear clutch 226 can be made redundant. Removing the unused parts leaves the exemplary linear clutch 308, as illustrated in Figures 48-51. Figure 51 shows the removal of the handle 244, reciprocator 232, first annular connecting member 256, and first compression spring 260. In this way, the linear clutch 308 is left to comprise the housing 252, shaft segment 254, the annular connecting member 258 surrounding the shaft segment 254, the releasing lever 248 extending integrally from the annular connecting member 258, and the compression spring 262. The function of the parts included in the linear clutch 308 operates in the same way as that of the same parts described with reference to the linear clutch 226. Figure 52 illustrates an exemplary linear clutch 316 that is functionally similar or identical to the linear clutch 308 and in some examples is used as a substitute for the linear clutch 308 in the air duct system illustrated in Figures 48–50. Structurally, the linear clutch 316 includes a housing 318 in place of the housing 252 and a tension spring 320 in place of the compression spring 262. The tension spring 320 displaces the annular connecting member 258 to its clamping position shown in Figure 52. As with several methods belonging to the examples illustrated in Figures 1 through 52, Figure 21 provides at least one example illustrating the insertion of a shaft assembly into an air duct. An arrow 322 in Figures 37 and 38 provides at least one example illustrating the manipulation of the actuator in a cyclic manner involving a plurality of cycles. An arrow 324 in Figure 42 provides at least one example illustrating the elongation of the shaft assembly in a plurality of increments corresponding to the plurality of cycles. Figure 39 provides at least one example illustrating, as a consequence of the elongation of the shaft assembly, subjecting the air duct to tension (arrow 228) in the longitudinal direction and subjecting the shaft assembly to compression (arrow 230) in the longitudinal direction. Arrow 322 in Figures 37 and 38 provides at least one example illustrating manipulating the actuator in a reciprocating motion.Arrow 296 in Figure 47 provides at least one example illustrating the rotation of a helically threaded member a plurality of revolutions. Arrow 280 in Figure 46 and arrow 298 in Figure 47 provide at least one example illustrating the manipulation of a ratchet mechanism in a reciprocating motion. The airflow 14 in Figure 49 and comparing the relatively clean air duct in Figure 48 (deflated with no appreciable airflow 14) to the taut, inflated air duct in Figure 49 provides at least one example of inflating the air duct. Compare dimension 326 in Figure 48 with a longer dimension 328 in. Figure 49 provides at least one example illustrating that, as a consequence of inflating the air duct, the longitudinal elongation of the frame to an extended length (e.g., L2 in Figure 42). Figure 50 without arrow 14 provides at least one example illustrating reducing the air duct to a deflated state. Arrow 228 in Figure 50 provides at least one example illustrating subjecting the air duct to at least some longitudinal tension while the air duct is in the deflated state. Arrow 230 in Figure 50 provides at least one example illustrating subjecting the air duct to at least some longitudinal compression while the air duct is in the deflated state.Arrows 228 and 230 and axle assembly 310 (example of a frame) in Figure 50 provide at least one example illustrating the frame supporting the air duct in longitudinal tension while the air duct is in the deflated state and supporting the frame in longitudinal compression while the air duct is in the deflated state. In some examples, as shown in Figures 53-55, the air duct 18 of an air duct system 330 is held in longitudinal tension by a compression spring 332 that is adjustablely compressed between a collar 334 and a tubular hub 46i. In the illustrated example, spokes 42 and rib 34 couple the end cap 22 to the hub 46i, and the collar 334 surrounds a tubular shaft 32i such that the axial position of the collar on the shaft 32i can be changed to adjust and determine the tension of the air duct 18. Figure 53, for example, shows collar 334 in a position with less tension on shaft 32i to place spring 332 in a less compressed state. Spring 332 is compressed between collar 334 and a shoulder 336 on hub 46i, which holds air duct 18 in tension 228 and shaft 32i in compression 230. IVIA / a / ZUZZ / U 14 I 0 / Figure 54 shows collar 334 in a position with greater tension which places spring 332 in a more compressed state, which subjects air duct 18 to greater tension 228 and shaft 32i to greater compression 230. To adjust the position of collar 334 on shaft 32i, collar 334 and / or shaft 32i include a collar retention mechanism for selectively holding and releasing collar 334 relative to shaft 32i. Releasing collar 334 allows it to be manually slid axially to another position on shaft 32i. In the illustrated example, the retention mechanism is a hand screw 338 that threads into a threaded hole in collar 334 to selectively engage or release shaft 32i. Figures 53 and 54 show the hand screw 338 engaging shaft 32i to place collar 334 in a locked condition such that collar 334 remains axially fixed with respect to shaft 32i. Figure 55 shows the hand screw 338 partially unscrewed from inside the threaded hole of the collar to release collar 334 from shaft 32i, thereby placing collar 334 in a released condition. In the released condition, collar 334 is free to slide axially on shaft 32i to adjust spring compression 332, which determines the tension in duct 18. In the released condition, collar 334 can also be moved to completely release spring compression 332, as shown in Figure 55. In some examples, a pin 340 fixed to the shaft 32i projects through one or more slots 342 that extend longitudinally over the hub 46i. This limits the range of axial adjustment or relative movement between the hub 46i and the shaft 32i. In some cases, if the end cap 22 is removed, the limited range of movement of the pin 340 over the slot 342 prevents a compressed spring from IVIA / a / ZUZZ / U 14 I 0 / 332 push the hub 461 completely off the axis 32!. In some examples, as shown in Figures 56 and 57, an air duct system 344 comprises a shaft assembly 346 from which spokes 42 extend radially outward to support a plurality of ribs 34, which in turn support the air duct 18. The length of the shaft assembly 346 is adjustable to hold the duct 18 in longitudinal tension 228, which places the shaft assembly 346 in longitudinal compression 230. In this example, the adjustment of the shaft assembly 346 is by virtue of a telescoping connection 348 between a first shaft segment 350 and a second shaft segment 352, in combination with an adjustable threaded connection 354 between a screw 356 (e.g., threaded rod, bolt, etc.) and an internally threaded member 358 (e.g., a conventional nut, block with a branch hole, plate with a branch hole, etc.).The 346 shaft assembly is shown more extended in Figure 57 than in Figure 56, such that the air duct tension is greater in Figure 57 than in Figure 56. To increase the length of the shaft assembly and thereby increase the tension in the duct 18, the head 292 on the screw 356 is rotated in a direction relative to the threaded member 358 such that the threaded member 358 travels axially along the length of the screw 356, away from the head 292, to push the first shaft segment 350 partially out from the inside of the second shaft segment 352. As the shaft assembly 346 is lengthened, a shaft retainer 360 that butts a plate 362 into the end cap 22 prevents the front end 364 of the screw 356 from being forced axially out of the inside of the duct 18. Examples of retainers 360 include, but are not limited to, a nut, washer, or pin welded to the screw 356; a shoulder on the screw 356; IVIA / a / ZUZZ / U 14 I 0 / a fastener or clamp E or fastener C on the screw 356, etc. Examples of the plate 362 include but are not limited to a washer, a disc, a cable gland, etc. The rotating head 292 in the opposite direction moves the threaded member 358 toward the head 292, which allows the first shaft segment 350 to retract into the second shaft segment 352 and thereby cut the shaft assembly 346 to reduce duct stress. Relative rotation of the screw 356 and the threaded member 358 is achieved, in some examples, by an anti-rotation feature between the threaded member 358 and a longitudinal groove 366 in the second shaft segment 352. In some examples, the anti-rotation feature is a disk 368 connected to the threaded member 358 and surrounding the screw 356, wherein the disk 368 has a radial projection 370 extending into the groove 366. The projection 370 extending into the groove 366 inhibits relative rotation between the disk 368 and the second shaft segment 352. Since the disk 368 connects to the threaded member 358, the projection 370 extending into the groove 366 also inhibits relative rotation between the threaded member 358 and the second shaft segment 352.In other words, the projection 370 extending into the groove 366 provides limited relative rotation between the internally threaded member 358 and the second shaft segment 352, where the expression "limited relative rotation" means that, with reference to a second shaft segment 352, the threaded member 358 is rotatable less than 360 degrees, and in some instances, the relative rotation of the threaded member is limited to zero degrees. The disc 368 also provides a bearing surface for pressing against an axial end of the first shaft segment 350. It should be noted that as head 292 is rotated to extend or retract shaft assembly 346, screw 356 is in a longitudinal position IVIA / a / ZUZZ / U 14 I 0 / substantially fixed with respect to the second shaft segment 352, and the internally threaded member 358 has a substantially fixed axial position with respect to the first shaft segment 350. Although certain methods, apparatus, and articles of manufacture have been described herein, the scope of this patent is not limited to them. On the contrary, this patent covers all methods, apparatus, and articles of manufacture that fall precisely within the scope of the appended claims, either literally or under the doctrine of equivalents.

Claims

1. An air duct system including a tubular folding sidewall and an end cap that, when connected, defines an interior volume of the air duct system, the end cap being characterized in that it comprises: an end piece defining a center point and an outer periphery substantially fixed relative to the center point; a folding blade extending through the end piece and having an outer peripheral portion overlapping the outer periphery of the end piece; a fastener coupled to the folding blade and connectable to the tubular folding sidewall; and an extension extending from the outer peripheral portion of the folding blade.and a constriction member connected to the extension, the constriction member having a tensioned state and a loose state, the folding sheet is more tensioned when the constriction member is in the tensioned state than when the constriction member is in the loose state, and the extension is closer to the center point of the end piece when the constriction member is in the tensioned state than when the constriction member is in the loose state.

2. The air duct system according to claim 1, characterized in that it further comprises a frame, the tubular folding side wall comprises an air duct, the frame is arranged within and coupled to the air duct, the frame comprises a material of less flexibility than that of the air duct, the frame is in compression along a length of the air duct, and the air duct is in tension along the length of the air duct.

3. The air duct system according to claim 2, characterized in that the frame comprises a shaft extending along the length of the air duct, the shaft being compressed to keep the air duct under tension.

4. The air duct system according to claim 2, characterized in that the air duct includes an elbow.

5. The air duct system according to claim 1, characterized in that it further comprises a frame disposed within and coupled to the tubular folding side wall, the tubular folding side wall defining a longitudinal direction, and the tubular folding side wall being held in tension in the longitudinal direction by virtue of the frame being held in compression in the longitudinal direction.

6. The air duct system according to claim 5, characterized in that the foldable side wall is more flexible than the frame.

7. The air duct system according to claim 5, characterized in that the tubular folding side wall is at a first stress magnitude in the longitudinal direction when the air inside the tubular folding side wall is at an inactive ambient air pressure, the tubular folding side wall is at a second stress magnitude in the longitudinal direction when the air inside the tubular folding side wall is at an active positive air pressure, and the first stress magnitude is less than the second stress magnitude.

8. The air duct system according to claim 5, characterized in that the frame is at a first compression magnitude in the longitudinal direction when the air inside the tubular folding side wall is at an inactive ambient air pressure, the frame is at a second compression magnitude in the longitudinal direction when the air inside the tubular folding side wall is at an active positive air pressure, and the first compression magnitude is greater than the second compression magnitude.

9. The air duct system according to claim 5, characterized in that the frame is supported by the tubular folding side wall.

10. The air duct system according to claim 5, characterized in that it further comprises an upper support structure from which the tubular folding side wall is suspended independently of the frame.

11. The air duct system according to claim 5, characterized in that it further comprises an upper support structure to which both the tubular folding side wall and the frame are independently connected.

12. The air duct system according to claim 5, characterized in that the frame has a longitudinally adjustable length.

13. The air duct system according to claim 1, characterized in that the end piece includes a ring that defines the center point and provides the outer periphery of the end piece.

14. The air duct system according to claim 1, characterized in that it further comprises a hem arranged along the outer peripheral portion of the folding leaf, the fastener being attached to the folding leaf by means of the hem. IVIA / a / ZUZZ / U 14 I 0 / 15. The air duct system according to claim 1, characterized in that the constricting member is an adjustable cord.

16. The air duct system according to claim 1, characterized in that the extension and the constriction member are arranged within the inner volume of the air duct system when the end cap is coupled to the tubular folding side wall.

17. The air duct system according to claim 1, characterized in that the fastener is a zipper.

18. The air duct system according to claim 1, characterized in that the end piece is captured between the folding blade and the extension.

19. The air duct system according to claim 1, characterized in that it further comprises: a ring disposed within the tubular foldable sidewall and arranged substantially perpendicular to a flow direction, the tubular foldable sidewall defining the flow direction along which the air duct system carries an air stream; a hub disposed substantially at a central point of the ring, the hub extending longitudinally in the flow direction; and a plurality of spokes extending between the ring and the hub, the plurality of spokes attaching to the hub at a plurality of points distributed longitudinally along the hub.

20. The air duct system according to claim 19, characterized in that it further comprises: a second ring disposed within the tubular folding side wall and separated from the ring; a second hub disposed substantially at a central point of the second ring; and a shaft extending between the hub and the second hub, the shaft for keeping the tubular folding side wall under tension.

21. The air duct system according to claim 19, characterized in that the tubular folding side wall forms an elbow duct.

22. A method of installing the air duct system according to claim 1, the method being characterized in that it comprises: having access to an interior volume of the tubular folding side wall; installing a frame within the interior volume of the tubular folding side wall; attaching the frame to the tubular folding side wall; and compressing the frame and tensioning the tubular folding side wall in a longitudinal direction by virtue of the frame being installed within the interior volume of the tubular folding side wall.

23. The method according to claim 22, characterized in that the frame has a total weight that is supported by the tubular folding side wall.

24. The method according to claim 22, characterized in that it further comprises suspending the tubular folding side wall without load-carrying assistance from the frame.

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