This invention relates to fluid flow ductτ:.rk. ' e invention relates particularl to duct ^w ork of t e kind in which adjacent duct ends carry annular grooves which in use locate the terminal radially inwardly directed flanges of a split clamp ring v.'hich in turn retains a flexible annular seal whose radially inwardly directed terminal lips make sealing engagement against the correε- ponding ducts between the annular grooves and the duct ends. This kind of coupling will he referred tc hereinafter as "of the type specified", as will also ducts designed for use with, such couplings. In the design of couplings of the ^' type specified, which have been in use for many decades, the annular seal is so formed that positive fluid pressure within the seal acts to force the sealing lips into contact with the duct walls, thereby enhancing the sealing effect.

In normal practice the engagement of the clamp ring in the grooves leaves a certain amount of play, and thus runs of ductwork joined in this manner have a degree of free movement which in particular can accommodate longitudinal expansion and contraction. This does not affect the seals, since the flexibility of the latter tolerates this free movement. However, in recent years the development of high- rise buildings has in the provision of adequate flexibility in long runs of duct-work vhich experience wide variation in temperature, and alternative

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and contraction has been sought. Concurrently with the long history of use of ductwork with couplings of tk* specified, there has also been a long history of the a range of expansion joints, one widely used type being the so-called bellows joint. As the name implies, these expan¬ sion joints have ^" oeen regarded as extraneous components provided "cj their respective manufacturers in a full range each having its appropriate means for securing in a run of ductwork. For example, some expansion joints are provided with flanged ends, some with threaded ends, and some with plain weidable end sections; but in each case when such a joint is used to join ducts of the type specified, this has re uired modification of the ends of the adjacent ducts which it joins, as well as the provision of extraneous f st- ening components or the use of welding e uipment.

This invention serves to provide enhanced lexibility in ductwork of the type specified while eliminating all need for the introduction of extraneous joint components, and accordingly comprises a fluid low duct of which at least one end is formed with an annular clamp-locating groove in its outer surface and which is formed intermediate its ends with a flexible portion. The flexible portion may provide longitudinal, lateral or angular movement, or any relevant combination of these. In tractice the construction of the duct will normally incorporate movement co trol means to restr c ϊ on or tne αuct to t e αe.-ireu. t -^ oi movement, m ;ment control means may be secured to one end only of

the c ct, or to cotn e s, to ac. eve tne ce ireo

^' when intended for installa ion in a:; intermediate position in a run of duc /-or.: of the type specified. both er.ds of the duct will be formed with respective annular 5 clamp—locating grooves.

The invention also comprises a run of fluid flow duct¬ work including at least one duct as defined in either of the three preceding paragraphs joined in the r y coupling means of the type specified. 10 The invention will now be described in greater detail with reference to the accompanying Drawings, in which: Figure 1 shows a partly-sectioned side elevation of a fluid-flow duct embodying the invention, coupled to a second duct by means of a coupling 15 of the type specified, and Figures 2A to 2D are respective side elevations, also partly sectioned, of four ducts embodying the invention and provided with respective movement control means. 20 _ e duct embodying the invention, represented at 1, is coupled to a second duct 2 by a split clamping ring 3- The ends of the ducts 1 and 2 are grooved at i ¹ and 2 ¹ -respect- i-- l , ana the clamping ring has terminal radially inwardly ^" langes 3 ¹ which engage the grooves and secure the ther. The two halves of the clamping ring 2 are ^■ video with mating flanges 3_a, which are secured together b lts 4- and co-operating nuts (not shown). The clamping in securing the two

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ducts together, also serves to accommodate an annular seal 5- The seal has inwardly directed lips 5' which engage the ends of the duct 1 and the duct 2 , and the re-entrant radial cross-section of the seal, which can be seen in the Figure, ensures that positive pressure in the fluid within the ductwork forces the lips 5' into sealing engagement with the duct walls, thus enhancing the sealing action. Referring now to the duct 1, it will be seen that it com¬ prises two end portions la, which carry the grocves 1'. and a central bellows portion lb, whose ends are' secured under sealing rings lc, which together with the bellows are welded to the end portions at Id, thus providing an integral and expansible duct which may be connected as a standard duct of the type specified. In this way, the run of ductwork can be provided with enhanced expansibility, without the need for extraneous flexible joints and alternative coupling means.

I e arrangement illustrated in Figure 1 of the Drawings is primarily intended to illustrate the principle of the invention, although it can be used in the illustrated form. In practice this ^: type of flexible duct is generally provided integrally with means s c- t-1 tc at least one end portion to restrict the freedom of r.oveient of the flexible portion so that it will deform: in a required manner, but will not "snake" uncontrollably. Figures 2A to 21 £ ^" according to the invention with a range of movement control means. In each of these Figures, the duct i ∑ ^* τlf is similar to that illustrated in Figure 1 and so

will not be described in detail . The s implest movement control means is shown in Figure 2A, which illustrates a longitudinal expansion joint. Here the desired stability against lateral movement is provided by a rigid internal sleeve 1C extending generally parallel to the duct wi ^' tnin the latter. The sleeve 10 is flared slightly outwardly at its left-hand end, contacting the inner surface of the duct en . la. to which it is secured by a weld. ^" n ^' e sleeve 1C thus acts as a guide for the bellows, and also serves to reduce turbulence which woul otherwise be induced in fluid lowing through the tube by the corrugations of the bellows. As indicated at 11a, lljb, a telescopically sliding protec¬ tive cover ^' may be s ^' ecured outside the bellows to protect it from da age or obstruction. Figure 2B illustrates an angular joint constructed in accordance with the invention. Here, pairs of lugs 20a, 20b_ welded to the duct ends carry links 21a, 21b_ which in turn are pivotally connected by pins 22. The pins 22 are retained in position by circiips (unreferenced). It will be readily understood that the linkage 20, 21, 22 permits only angular movement of the joint.

Figure 2C illustrates a lateral joint constructed in accordance with the invention. In- this case each of the duct ends la carries a pair of welded-on brackets 3 , each of which has a flange 31 extending generally in a plane perpendicular to the longitudinal axis of the duct end. Ξach flange 31 is bored at 32, parallel to the longitudinal axis cf the duct end, and that end of each bore 2 adjacent

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the open end of the αuct end la is lor eα v; th a sp er-

_ ically concave flare 32'. The flarrεd portions 32' serve to seat ball-ended nuts 33 which are threaded on to the ends of a pair of tie-rods 34 each of -which passes through 5 the Lores 32 in two corresponding flanges 31 ε-t opposite ends of the unit. The nuts 33 s.re screwed tight en the tie- rods, and the spherical mating surfaces of the flared portions 32' and the nuts 33 then permit relative lateral movement of the end portions la without permitting expan-

10 sion of the bellows, which here takes the form of two separate bellows sections linked by a central section of rigid tube.

Figure 2D illustrates another form of joint providing lateral movement. Eere the control of movement is i ple-

15 merited- by means of a braided metal sleeve 40 welded to collars 41 which are themselves welded to the duct ends la. The woven structure of the sleeve 40 renders it substantia¬ lly inextensible parallel to its longitudinal axis, with the result that the duct is substantially inextensible

20 parallel to its length, and has little ability to undergo angular-deflection about a central point. However, the braided sleeve can be deformed into a shallow "S" shape and thus the joint can accommodate relative lateral displace¬ ment of the duct ends.

25 Obviously, other movement-control means could be employed, for example a gimbal mount to give pivotal artic¬ ulation in three dimension-, about the centre of the joint, but in each case the result will be a self-contained

expansion joint, i:..:ecist _y vaij.ac_e :cr installation m ductwork employing coupling means of the type specified.

This in itself will permit much greater efficiency in the installation and maintenance of this type of ductwork, ~cy the elimination of the extraneous coupling mechanisms -which have always been used hitherto, and reduction of the amount

» of on-site labour involved. Furthermore, the inherent reliability of the connections in ductwork of the type specified can by virtue of the invention now be applied throughout any given installation, without the possibility of failure introduced by on-site measures such as welding and flange jointing. '