OA20712A - Semi-rigid duct system. - Google Patents

Abstract

A duct system is formed from a plurality of tubular sections each formed from a flexible panel with tapering sides. Inner and outer joiner plates are attached to one side edge and the second side edge is inserted in the recess between the plates and fastened such that each section has a first open end and a second slightly larger open end. Anchors are spaced around each end of each tubular section. The first end of each tubular section is inserted into the larger second end of an adjacent tubular section and an end pulling element is connected between the anchors on adjacent sections an operated to draw the connected first and second anchors together to make a substantially air tight seal between the tubular sections.

Description

O.A.P.I. - B.P. 887, YAOUNDE (Cameroun) - Tel. (237) 222 20 57 00-Site web: http:/www.oapi.int - Email: oapi@oapi.int

SEMI-RIGID DUCT SYSTEM

This disclosure relates to the field of duct Systems for carry îng air streams in mines, tunnels, and the like and in particular a semi-rîgid duct system that can be transported readily and assembled on site.

BACKGROÜND

Air ducts are required to carry air to underground locations such as mines and tunnels. Such ducts are commonly made from flexible fabrîc which is light and can be collapsed for transport down into underground installation sites where space is limited. Such fabnc ducts however hâve limitations when air pressures are quite high or when dealing with négative air pressures.

United States Patent Number 8,336,925 to Paquet et al. discloses a duct system where flexible panels, which can be readily moved into a confined area such as a mine, are formed into tubular sections with edges connected and sealed on site. The sections are then connected end to end with collars sealed over ends of abutting adjacent tubular sections.

United States Patent Number 5,472,768 to Anson discloses a tubular duct system where tapered flexible panels are formed into tapered tubular sections with edges that overlap and are fastened together. The panels hâve tapering edges such that when the edges are connected the diameter of one end îs smaller than the diameter ofthe other end and the sections are joined by inserting the smaller end of one section into the larger end of the adjacent section in a telescoping manner. Sealing is not required in the illustrated application of a débris chute.

SUMMARY OF THE INVENTION

The présent disclosure provides a semi-rigid duct System that overcomes problems in the prior art.

In a first embodiment the présent disclosure provides a plurality of tubular sections connected together, each tubular section comprising a flexible panel having a length between first and second end edges thereof, a first wîdth between first and second side edges at the first end edge, and second wîdth between first and second side edges at the second end edge, wherein the first width is less than the second wîdth. Inner and outer joiner plates are attached to inner and outer faces of the flexible panel along the first side edge and extend outward from the first side edge such that a recess is formed between the inner and outer joiner plates, and the second side edge is inserted into the recess and fastened in the recess to form the flexible panel into the tubular section with the inner joiner plate on an interior of the tubular section and the outer joiner plate on an exterîor of the tubular section. Each tubular section has an open substantially circular first end with a first diameter at the first end edge of the panel and an open substantially circular second end with a second diameter at the second end edge of the panel, and wherein the first diameter is less than the second diameter. A plurality of first end anchors are spaced around each tubular section at a first anchor distance from the first end of the tubular section and a corresponding plurality of second end anchors are spaced around each tubular section at a second anchor distance from the second end of the tubular section. The first end of each tubular section is inserted into the second end of an adjacent tubular section such that a portion of the outer face of each tubular section proximate to the first end thereof bears against a portion of the inner face of the adjacent tubular section proximate to the second end thereof. Each of a plurality of end pullîng éléments is connected between one of the first anchors on one tubular section and one of the second anchors on the adjacent tubular section, and each end pulling element is operative to exert a force drawing the connected first and second anchors together.

In a second embodiment the présent disclosure provides a method of providing a duct System. The method comprises formîng a plurality of tubular sections, each tubular section formed by: providing a flexible panel having a length between first and second 5 end edges thereof, a first width between first and second side edges at the first end edge, and second width between first and second side edges at the second end edge, wherein the first width is less than the second width; attaching inner and outer joiner plates to inner and outer faces of each pane! along the first side edge such that the joiner plates extend outward from the first side edge such that a recess is formed between the inner 10 and outer joiner plates; inserting the second side into the recess and fastening the second sîde edge in the recess to form the panel into the tubular section with the inner joiner plate on an interior of the tubular section and the outer joiner plate on an exterior of the tubular section; wherein each tubular section has an open substantially cîrcular first end with a first diameter at the first end edge of the panel and an open substantially cîrcular 15 second end with a second diameter at the second end edge of the panel, and wherein the first diameter is less than the second diameter; attaching a plurality of first end anchors spaced around each tubular section at a first anchor distance from the first end of the tubular section; attaching a corresponding plurality of second end anchors spaced around each tubular section at a second anchor distance from the second end of the tubular 20 section; inserting the first end of each tubular section into the second end of an adjacent tubular section; and connecting an end pulling element between each of the first and second anchors and operating each end pulling element to exert a force drawing the connected first and second anchors together such that the first end of each tubular section is forced into the second end of the adjacent tubular section and such that a portion of the 25 outer face of each tubular section proximate to the first end thereof bears against a portion of the inner face of the adjacent tubular section proximate to the second end thereof.

The duct System of the présent disclosure can be transported to a confined work site such as a mine or like tunnel, where the tubular sections can be quickly formed and installed by roiling the flexible panels such that the side edges can fastened together to form the tapered tubular sections. Then the smaller first end of one tubular section is simply 5 inserted into the larger second end of the next tubular section and secured and tightened with the end pulling éléments to form the duct System.

DESCRIPTION OF THE DRAWINGS lÛ While the invention is claimed in the conckiding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagram s are labeled with like n uni bers, and where:

Fig. I is a schematic eut away side view of an embodiment of the duct System of the présent disclosure;

Fig. 2 is a schematic top view of a flexible panel of the embodiment of Fig. I ;

Fig. 3 is a schematic sectional end view of the embodiment of Fig. 1 ;

Fig. 4 is a schematic end view of the first and second open ends of a tubular section of the embodiment of Fig. 1;

Fig. 5 is a schematic sectional view along line 4 - 4 in Fig. 4 of the connection of one tubular section with another tubular section of the embodiment of Fig. 1 ;

Fig. 6 îs a schematic side view of the embodiment of Fig. I showing the joiner plates and first and second anchors aligned;

Fig. 7 is a schematïc sectïonal side vïew of the connection of one tubular section with another tubular section of the embodiment of Fig. I showïng the arrangement of the joïner plates and first and second ends of the tubular sections;

Fig. 8 is a schematïc perspective view of a tubular section of the embodiment of Fig. I ;

Fig. 9 is a schematïc top view showïng the lock tab in position to be inserted into the lock notch;

Fig. 10 is a schematïc side view of the half rings that form the reinforcing rings;

Fig. Il is a schematïc side view of a band wrapped around the second end of the tubular section 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Fig. I schematically illustrâtes an embodiment of a duct system l of the present disclosure comprising a plurality of tubular sections 3 connected together.

As shown in Fig. 2, each tubular section 3 comprises a flexible panel 5 having a length L between first and second end edges 7A, 7B thereof, a first width Wl between first and second tapering side edges 9A, 9B at the first end edge 7A, and a second width W2 between first and second side edges 9A, 9B at the second end edge 7B. The first width Wl is less than the second width W2 such that when the panel 5 is rolled up so the first and second side edges 9A, 9B are abutted, the tubular section 3 is formed with a slightly tapering shape so that the first end l IA of the tubular section 3 can be inserted into the second end l IB of an adjacent tubular section as iliustrated in Fig. 1. Typîcally the différence between Wl and W2 will be less than one centimeter, and the différence in the widths Wl, W2 shown in Fig. I exaggerated to illustratethe concept.

Inner and outer joiner plates 13, 15 are attached to inner and outer faces 5A, 5B of each panel 5 along the first side edge 9 A thereof, typically by rivets, adhesives, or the like, such that the joiner plates 13, !5 extend outward from the first side edge 9A. The flexible panel 5 is then rolled by raising the side edges 9A, 9B shown in Fig. 2 and brînging them together as shown in Fig. 3 and inserting the second side edge 9B into the recess 17 formed between the inner and outer joiner plates 13 and 15 and fastening the second side edge 9B in the recess 17 to form the panel 5 into the tubular section 3. As seen in Fig. 4 the inner joiner plate 13 is on an interior of the tubular section 3 and the outer joiner plate 15 is on an exterior of the tubular section 3.

Because of the taperîng side edges 9A, 9B of the panel 5, each tubular section 3 has, as shown in Fig. 4, an open substantially circulai first end l IA with a first diameter Dl at the first end edge 7A of the panel 5 and an open substantially circulai second end l IB with a second diameter D2 at the second end edge 7B of the panel 5. The first diameter Dl îs less than the second diameter Dl allowing the first end I IA ofeach tubular section 3 to be inserted into the second end l IB of the adjacent tubular section 3 to form the duct system L

As shown in Fig. 5, a pluralîty of first end anchors 19A are spaced around each tubular section 3 at a first anchor distance ADI from the first end HA of the tubular section 3, and a corresponding pluralîty of second end anchors 19B are spaced around each tubular section 3 at a second anchor distance AD2 from the second end l IB of the tubular section 3. The first end 11A of each tubular section 3 is inserted into the second end 11B of an adjacent tubular section 3 such that a portion of the outer face 5B of each tubular section proximate to the first end l IA thereof bears against a portion of the inner face 5A of the adjacent tubular section 3 proximate to the second end l IB thereof.

The first end HA of each tubular section 3 is înserted into the second end HB of the adjacent tubular section 3 an insertion distance ID, and the first anchor distance ADI is at least equal to or greater the insertion distance ID so the anchors do not interfère with the insertion. Typically the second anchor distance AD2 îs greater the insertion distance ID so that the second anchors can be attached with fasteners 27 that extend past the inner face 5A of the tubular section 3 so that the fasteners 27 do not interfère with insertion.

An end pullîng element, such as the illustrated cinch strap 25 is connected between the first end anchor 19A on one tubular section 3 and the second end anchor 19B on the adjacent tubular section 9. Pulling on the tait end 25A of the cinch strap 25 exerts a force F drawing the connected first and second end anchors 19A, 19B together, and when the tail end 25A is released. tension is maintained on the cinch strap 25. Tightening the cinch straps 25 around the periphery of the tubular section 3 causes the first end 11A of the tubular section 3 to move into the second end 11B of the adjacent tubular section 3 such that the outer face 5B of each tabular section bears quîte tightly against the inner face 5 A of the adjacent tubular section 3 to form a substantially air tight seal. The duct Systems of the présent disclosure are sometîmes subjected to significant blast forces during mining operations and it is contemplated that the end pulling éléments could be provided by a résilient elastic strap which would give rather than break in response to such blast forces.

As shown in Fig. 6, the first end l IA of each tubular section îs înserted into the second end l IB of the adjacent tubular section 3 such that the joiner plates 13, 15 and first end anchors 19A on each tubular section 3 are substantially aligned with the joiner plates 13, 15 and second end anchors 19B on the adjacent tubular section 3. Such configuring of the tubular sections 3 allows the user to align the visible outer joiner plates 15 and then the corresponding first and second end anchors 19A, 19B will be aligned as well.

Each tubular section 3 is formed such that each tubular section 3 is substantîally aîrtight from the first end 11A thereof to the second end thereof 11A since the fit of the second side edge 9B in the recess 17 between the joiner plates 13, 15 is quite tight, and the connection of each tubular section 3 to the adjacent tubular section 3 is substantîally aîrtight since the cinch straps 25 exert sufficient force to push the outer face 5B of each tubular section against the inner face 5A of the adjacent tubular section 3 such that little air escapes. While not completely air tight the connections are sufficiently air tight for the relatively low pressure, high flow rate ducting purposes contemplated for use with the disclosed System 1.

As schematicaily illustrated in Fig. 7, the first end HA of each tubular section 3 is înserted into the second end of the adjacent tubular section the insertion distance ID. The outer joiner plate 15 is configured to extend from a first end 15A thereof located the insertion distance ID from the first end 11A of the tubular section 3 to a second end 15B thereof located at the second end 1 IB of the tubular section 3. Thus, when assembled as in Fig. 6, the outer joiner plates 15 do not interfère with insertion and form a continuous plate along the outside of the duct.

The inner joiner plates 13 are configured to extend from a first end 13A thereof located format or near the first end 1 IA of the tubular section 3 to a second end 13B thereof located the insertion distance ID from the second end I IB of the tubular section 3. With this configuration the inner joiner plate 13 does not interfère with insertion, and the recess 17 enclosing the second side edge 9B extends substantîally the fu11 exposed length of each tubular section 3 to prevent air from escaping.

As seen in Fig. 8 in each tubular section 3 the second side edge 9B is fastened in the corresponding recess 17 by a plurality of side pulling éléments 29, each extending over the outer joiner plate 15 and connected to side anchors 31 attached to the tubular section 3 on each side of the outer joiner plate 15. The side pulling éléments 29 can conveniently be provided by cinch straps 25, similar to the end pulling éléments, that are operative to exert a force drawing the second side edge 9B into the recess 17.

To facilitate guiding the second side edge 9B into the recess 17, outer joîner plate 15 5 extends from the first side edge 9A of the flexible pane 5 a greater distance than the inner joiner plate 13, as best seen in Fig. 3. When folding the edges 9A, 9B together the outer joîner plate 15 will keep the second side edge 9B from sprînging up before it is actually in the recess. The inner and outer joiner plates 13, 15 adjacent to the recess 17 are also chamfered with bevels 33 helping to guide the second side edge 9B into the recess 17.

To further facilitate forming the flexible sheet 5 into the tubular section 3 the illustrated System l also comprises a lock tab 35 extending from the second side edge 9B of each flexible panel 5 and a corresponding lock notch 37 defined in the first side edge 9A of each flexible panel 5. The lock tab 35 and lock notch 37 are configured such that when 15 the second side edge 9B is inserted into the recess 17, the lock tab 35 flexes as it enters the lock notch 37 and locks into the lock notch 37.

As seen in Fig. 9, as the lock tab 35 moves in the direction of the arrow into the lock notch 37 the lock arms 39 will be flexed outward until the protrusions 41 on the tab 35 20 coïncide with the indents 43 of the notch 37, where the lock arms 39 will flex back with the protrusions 41 locked in the corresponding indents 43.

To facilitate inserting the first end 1 IA of a tubular section 3 into the second end 1 IB of an adjacent tubular section 3, the first end edge 7A of each flexible panel 5 comprises a 25 shoehorn element 45 extending from a middle portion of the first end edge 7A as seen in

Figs. 2 and 8. The shoehorn element 45 on one tubular section can be rested inside the second end 11B of the adjacent tubular section to help align the ends 1 ΙΑ, I IB for insertion.

To maintain the desired circular shape of the open ends 11 of the tubular sections 3, first and second reînforcing rings 47A, 47B are spaced along and extend around each tubular section 3.. The illustrated reînforcing rings 47 each comprise two half rings 49A, 49B fastened to each other wîth bolts 51 or the like after the second side edge 9B is inserted into the recess 17 to form the tubular section 3.

The reînforcing rings 47 are configured to correspond to an outside diameter of the tubular section 3 to substantially prevent deformation of the open ends 11 and maintaîn the circular shape to facilitate insertion. Since the tubular sections 3 are tapered slightly, the outside diameter will vary slightly along the length of the tubular section 3, and the bolts 51 can be tightened or loosened somewhat to accommodate these variations. .

Where négative air pressures are contemplated further reinforcing rings may be added spaced along the length of the tubular sections 3 between the first and second reînforcing rings 47A, 47B.

Fig. 11 schematically illustrâtes a sealing band 53 wrapped around the second end l IB of each tubular section 3, and a band tightener 55, such as a ratchet or buckle, operative to exert a tightening force on the sealing band 53 to force the inner face 5A of the second end portion of each tubular section 3 against the outer face 5B ot the first end portion of the adjacent inserted tubular section. Typically the sealing band 53 will be wrapped around the second end of the tubular section before the cinch straps 25 are connected between the adjacent tubular sections so the band 53 will lie fiat against the outer surface of the tubular section 3. The sealing band 53 can be tightened after the insertion îs complété and will act to further seal the connection of the tubular sections.

The présent disclosure also provides a method of providing a duct system l. The method comprises forming a plurality of tubular sections 3 where each tubular section 3 is formed by providing a flexible panel 5 having a length between first and second end edges 7A,

7B thereof, a first width Wl between first and second side edges 9A, 9B at the first end edge 7A, and second width w2 between first and second side edges 9A, 9B at the second end edge 7B_f wherein the first width Wl is less than the second width W2, attaching inner and outer joîner plates 13, 15 to inner and outer faces 5A, 5B of each panel 5 along the first side edge 9A such that the joiner plates 13, 15 extend outward from the first side edge 9A such that a recess 17 is formed between the inner and outer joiner plates 13, 15 and inserting the second side edge into the recess 17 and fastening the second side edge 9B in the recess 17 to form the panel 5 into the tubular section 3 with the inner joiner plate 13 on an interiorof the tubular section and the outer joiner plate 15 on an exterior of the tubular section 3, wherein each tubular section 3 has an open substantially circutar first end 11A with a first diameter Dl at the first end edge 7A of the panel 5 and an open substantially cîrcular second end l IB with a second diameter D2 at the second end edge 7B of the panel 5, and wherein the first diameter Dl is less than the second diameter D2; attaching a plurality of first end anchors 19A spaced around each tubular section 3 at a first anchor distance ADI from the first end of the tubular section HA; attaching a corresponding plurality of second end anchors I9B spaced around each tubular section at a second anchor distance AD2 from the second end I IB ofthe tubular section 3; inserting the first end l IA of each tubular section into the second end l IB of an adjacent tubular section 3; and connecting an end pulling element 25 between each of the first and second end anchors 19A, 19B and operating each pulling element 25 to exert a force F drawing the connected first and second anchors 19A, I9B together such that the first end l IA of each tubular section is forced into the second end l IB of the adjacent tubular section 3 and such that a portion of an outer face 5B of each tubular section proximate to the first end HA thereof bears against a portion of an inner face 5A oi the adjacent tubular section 3 proximate to the second end 11B thereof.

The duct system 1 of the present disclosure can be transported to a confined work site such as a mine or like tunnel, where the tubular sections 3 can be formed and installed. The flexible panels 5 are rolled such that the side edges 9 can fastened together to form il the tapered tubular sections 3 and then the smaller first end of one tubular section 3 is inserted into the larger second end of the next tubular section 3 and secured with the pulling éléments 25 to form the duct System. The resulting duct System l is substantially airtight without the need for extra sealant.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those ski lied in the art, it is not desîred to Iimit the invention to the exact construction and operation shown and described, and accordingly, ail such suitable changes or modifications in 10 structure or operation which may be resorted to are intended to fa!I within the scope of the claimed invention.

Claims (18)

1. CLA1MS

   What is claimed is:

   l. A duct System comprising:

   a plurality of tubular sections connected together, each tubular section comprising:

   a flexible panel having a length between first and second end edges thereof, a first wîdth between first and second side edges at the first end edge, and second wîdth between fîrst and second side edges at the second end edge, wherein the first widih îs less than the second wîdth;

   inner and outer joiner plates attached to inner and outer faces of the flexible panel along the first side edge and extending outward from the first side edge such that a recess îs formed between the inner and outer joiner plates, and wherein the second side edge is inserted into the recess and fastened în the recess to form the flexible panel into the tubular section with the inner joiner plate on an interior of the tubular section and the outer joiner plate on an exterior of the tubular section;

   wherein each tubular section has an open substantially cîrcular first end with a first diameter at the first end edge of the panel and an open substantially cîrcular second end with a second diameter at the second end edge of the panel, and wherein the first diameter is less than the second diameter;

   a plurality of first end anchors spaced around each tubular section at a first anchor distance from the first end of the tubular section;

   a corresponding plurality of second end anchors spaced around each tubular section at a second anchor distance from the second end of the tubular section;

   wherein the first end of each tubular section is inserted into the second end of an adjacent tubular section such that a portion of the outer face of each tubular section proximate to the first end thereof bears against a portion of the inner face of the adjacent tubular section proximate to the second end thereof; and a plurality of end pulling éléments, each end pulling element connected between one of the first anchors on one tubular section and one of the second anchors on the adjacent tubular section, and each end pulling element operatîve to exert a force drawing the connected first and second anchors together.
2. 2. The System of claim l wherein each second side edge is fastened in the corresponding recess by a plurality of side pulling éléments, each side pulling element extending over the outer joiner plate and connected to side anchors attached to the tubular section on each side of the outer joiner plate; each side pulling element operatîve to exert a force drawing the second side edge into the recess.
3. 3. The System of claim i comprising a lock tab extending from the second side edge of each flexible panel, and a corresponding lock notch defined in the first side edge of each flexible panel, the lock tab and lock notch configured such that when the second side edge is inserted into the recess, the lock tab flexes as the lock tab enters the lock notch and locks into the lock notch.
4. 4. The System of daim 3 wherein the lock tab slopes inward from the outer face of the flexible panel toward the inner face of the flexible panel.
5. 5. The System of claim 1 wherein outer joiner plate extends from the first side edge of the flexible panel a greater distance than the inner joiner plate.
6. 6. The System of claim 1 wherein outer edges of the inner and outer joiner plates adjacent to the recess are chamfered.
7. 7. The System of claim 1 comprising a reinforcing ring extending around each tubular section.
8. 8. The System of claim 7 comprising a first reinforcing ring extending around each tubular section adjacent to the first end anchors such that the first end anchors are between the first end of the tubular section and the first reînforcing ring, and a second reinforcing ring extending around each tubular section adjacent to the second end anchors such that the second end anchors are between the second end of the tubular section and the second reinforcing ring, wherein an inner diameter of each reinforcing ring substantially corresponds to an outer diameter of the tubular section.
9. 9. The System of claim 8 wherein the first reinforcing ring comprises two half rings fastened to each other after the second side edge is inserted into the recess to form the tubular section.
10. 10. The System of claim 1 wherein the first end edge of each flexible panel comprises a shoehorn element extending from amiddle portion ofthe first end edge.

    1 L The System of claim 1 wherein the first end of each tubular section is inserted into the second end of the adjacent tubular section such that first anchors on each tubular section are substantially aligned with second anchors on the adjacent tubular section.
11. 12. The System of claim l wherein the first end of each tubular section is inserted into the second end of the adjacent tubular section such that the joiner plates on each tubular section are substantially aligned with the joiner plates on the adjacent tubular section.
12. 13. The System of claim l wherein the first end of each tubular section is inserted into the second end of the adjacent tubular section an insertion distance substantially equal to the first anchor distance, and wherein on each tubular section, the outer joiner plate extends from a first outer plate end thereof located the insertion distance from the first end of the tubular section to a second outer plate end thereof located at the second end of the tubular section.
13. 14. The System of claim 13 wherein on each tubular section, the inner joiner plate extends from a first inner plate end thereof located at or in proximity to the first end ofthe tubular section to a second inner plate end thereof located the insertion distance from the second end of the tubular section.
14. 15. The System of claim I comprising a sealing band around the second end of each tubular section, and a band tightener operative to exert a tightening force on the sealing band to force the inner face of the second end of each tubular section agaînst the outer face of the first end of the adjacent inserted tubular section.
15. 16. The System of claim l wherein at least one end pulling element is provided by a résilient strap.
16. 17. A method of providing a duct System, the method comprising:

    forming a plurality of tubular sections, each tubular section formed by:

    \Ê providing a flexible panel having a length between first and second end edges thereof, a first wïdth between first and second side edges at the first end edge, and second width between first and second side edges at the second end edge, wherein the first width is less than the second wîdth;

    attachîng inner and outer joiner plates to inner and outer faces of each panel along the first side edge such that the joiner plates extend outward from the first side edge such that a recess îs formed between the inner and outer joiner plates;

    inserting the second side edge into the recess and fastening the second side edge in the recess to form the panel into the tubular section with the inner joiner plate on an interior of the tubular section and the outer joiner plate on an exterior of the tubular section;

    wherein each tubular section has an open substantîally circular first end with a first diameter at the first end edge of the panel and an open substantîally circular second end with a second diameter at the second end edge of the panel, and wherein the first diameter is less than the second diameter;

    attaching a plurality of first end anchors spaced around each tubular section at a first anchor distance from the first end of the tubular section;

    attaching a corresponding plurality of second end anchors spaced around each tubular section at a second anchor distance from the second end of the tubular section;

    inserting the first end of each tubular section into the second end of an adjacent tubular section; and

    Vf connecting an end pu!Iing element between each of the first and second anchors and operating each end pulling element to exert a force drawing the connected first and second anchors together such that the first end of each tubular section is forced into the second end of the adjacent tubular section and such that a portion of the outer face of each tubular section proxi mate to the first end thereof bears against a portion of the inner face of the adjacent tubular section proximate to the second end thereof.
17. 18. The method of claim 17 comprising forming each tubular section such that each tubular section is substantially aîrtight from the first end thereof to the second end thereof, and Înserting each tubular section into the adjacent tubular section such that the connection between the tubular sections is substantially aîrtight.
18. 19. The method of claim 17 comprising maintaînîng the circular shape of the first and second open ends by pfacing a first reînforcing ring tightly around each tubular section adjacent to the first anchors such that the first anchors are between the first end of the tubular section and the first reînforcing ring, and a second reinforcing ring tightly around each tubular section adjacent to the second anchors such that the second anchors are between the second end of the tubular section and the second reînforcing ring.