COUPLING TRUNKING OR THE LIKE

Abstract: A removable section of trunking is sealingly coupled to a relatively fixed length of trunking or duct by means of a flexible, preferably elastic, sleeve which is attached to one of the lengths of trunking towards one end thereof and at its other end to a relatively stiff collar which is shaped to fit closely over the adjacent end of the other duct or length of trunking. The elasticity of the sleeve tends to retain the collar in position and to maintain a tight seal whilst permitting a degree of relative movement including longitudinal thermal growth.

Description: The invention relates to coupling trunking or the like and has for one of its objects to provide means for releasably but sealingly coupling in end to end relationship adjacent lengths of air trunking in an aircraft installation where are of the lengths is needed to be removable. According to the invention means for coupling trunking in end-to-end relationship comprises a length of flexible sleeve (20) having one end thereof attached to a first length of trunking (6) at one end thereof, the sleeve further having a second end opposite said first end terminated by a circumferential collar (28) the length of sleeve being such that the collar can be moved in one direction so that the sleeve is rolled back on itself to overlie the first length of trunking (6) thereby putting the coupling in its inoperative condition, and such that the collar can be moved in the opposite direction so that the sleeve is extended to overlap a further length of trunking (14) placed end-to-end with the first length of trunking thereby putting the coupling in its operative condition, characterised in that the collar is provided with a lip (30) extending radially outwards from the sleeve. Preferably the flexible sleeve is formed of resilient or elastic material and the collar fits closely on the sleeve and trunking. In a known form of coupling for trunking as described in AT-B-329938 a pair of trunking members are coupled in end-to-end relationship by means of a coupling member which comprises an annular body portion of generally rectangular cross-section from the outer surface of which extend annular sleeves in opposite directions. From the inner surface of the body portion extends a single relatively short annular sleeve in parallel with the outer sleeve such that the outer sleeve and the short inner sleeve together engage the end of one piece of trunking. The other of the two annular sleeves may be rolled back over the sleeve which engages the trunking so as to enable a second piece of trunking to be located in end-to-end relationship with the first piece of trunking, whereupon the rolled back sleeve portion may be unrolled upon the second piece of trunking to establish the coupling. This arrangement however suffers from the disadvantage that it is very difficult to grip the end of the sleeve so as to roll it out of contact with the removable trunking and accordingly an object of the present invention is to provide means for enabling the sleeve to be gripped for the purpose of uncoupling trunking lengths from one another. The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Fig 1 shows a removable length of air trunking running alongside a gas turbine engine and coupled at either end by coupling means of the invention, Figs 2 and 3 show cross-sections through the joints at opposite ends of the trunking of Fig 1, and Fig 4 shows a partially sectioned view of one of joints. Referring firstly to Fig 1, there is shown in outline only, generally indicated at 2, a helicopter gas turbine engine which is provided with an integral inlet particle separator 4 which protects the engine from erosion and foreign object damage by scavenging solid particles, and water droplets, from incoming air before its ingress to the engine. The scavenged debris is ducted via trunking 6 to an ejector 8 where it is dumped into the engine exhaust. The trunking 6 runs alongside the engine and is squeezed in between the outer casing of the engine 2 and the existing aircraft envelope (not shown). It has to carry a fairly large volume of air at low excess pressure over ambient so in order to comply with the constraints on available space, a large area non-circular duct the section of which changes along its length, see figs 2 and 3, has been adopted. In this particular embodiment environmental conditions are not extreme and for reasons of low cost and weight the trunking 6 is constructed of laminated glass fibre reinforced materials. In normal running conditions the pressure drop between outside and inside the trunking is of the order of 1 psi (0.00015 N M2). However the couplings at opposite end joints have to be tolerant of some longitudinal movement due to differential thermal expansion rates between the engine outer casing and the trunking. Also, the trunking 6 has to be removed periodically for routine maintenance of engine ancillary equipment over which it passes. At either end of the lengths of trunking 6 there are provided coupling means 10 and 12 by which the trunking is joined respectively to the outlet 14 of inlet particle separator 4 and the inlet 16 of ejector 8. The coupling means 10, 12 straddle the joints effectively forming a sealing band between adjacent ducts whilst providing the flexibility required. Fig 4 shows in greater detail the components of the coupling means 10, although the second coupling 12 at the opposite end of the duct it will be understood is essentially identical. The illustrated coupling means 10 comprises a length of flexible sleeve 20 composed of silicon rubber material which is attached at its rearward end 22, by a suitably glued joint or by bonding, to the length of trunking 6 towards its forward end 24. The length of the sleeve 20 is sufficiently long that it extends well beyond the end 24 of the duct 6. The free or distal end 26 of the sleeve 20 is rolled back on itself and is attached to the forward end of a relatively stiff collar 28. The collar 28 preferably made of glass fibre reinforced plastics material which may be formed integrally with the free end 26 of the sleeve, alternatively the collar may be made of a light metal such as aluminium and bonded to the sleeve. As shown by the solid lines in Fig 4, to couple together the two lengths of trunking 6 and 14, the first length 6 is positioned end to end, and preferably abutting the particle separator outlet duct 14. The collar 28 is then moved forwards to overlap the end of the duct 14 and to extend the sleeve 20. The sleeve is sufficiently long that it overlaps the ducts 6 and 14 by similar amounts. As will be apparent from Fig 2 the shape of the collar 28 conforms closely with the shape of the ducts 6 and 14 in the region of the coupling. The internal dimensions of the collar closely match those of the duct 14 plus the sleeve thickness thus there is a degree of frictional engagement between the collar and the sleeve. In addition, the elastic properties of the material of sleeve 20 ensure that the portion of the sleeve which is rolled back over and attached to the outside of collar 28 exerts an axial pull on sleeve 20 tending to unroll, and therefore to further extend, the sleeve. The elasticity of the sleeve also assists in gripping the outer surface of the duct 14 producing a seal sufficient to withstand at least the modest differential pressure to which it is subjected in use. The unattached margin 30 of collar 28 is upturned to provide a lip by which it may be more easily manipulated. The inherent resilience provided by the coupling means enables the coupling to accomodate lateral movements of the duct without damage to either the coupling or the duct, and also without detachment. If required positive engagement means may be provided to retain the collar and sleeve 20, 28 in the extended, sealing position. For example, as shown at 32 the exterior of duct 14 and a corresponding mating portion formed in the collar 28 which mutually engage when the sleeve is extended. Said interengaging formations comprising a raised feature on the outer periphery of the second length of ducting towards the coupled end thereof and a complementary depression on the inner surface of the sleeving collar. The opposite end of the removable duct 6 may be provided with a similar extending sleeve arrangement at 12. Alternatively, the ejector inlet 16 and the duct end may be adapted to fit one within the other with suitable sealing means to provide the desired airtightness. With such an arrangement the effects of differential thermal expansion are compensated by the flexible sleeve joint at the other end of the duct. As previously mentioned the cross-section of the ducts or lengths of trunking, including the inlet and outlet ducts are non-circular as will be appreciated from even the briefest study of Figs 2 and 3. This presents no problem with the invention, quite simply the collar is formed with a shape conforming to the shape of the trunking over which it is to fit. Obviously the collar must also be capable of passing over the other section of trunking also but otherwise the sections of trunking need not possess the same or a constant cross-section.

Claims: Means for coupling trunking in end-to-end relationship comprises a length of flexible sleeve (20) having one end thereof attached to a first length of trunking (6) at one end (24) thereof, the sleeve (20) further having a second end (26) spaced from said first end (24) by a length of sleeve such that it may be extended to overlap and grip a further length of trunking (14) placed end-to-end with the first length of trunking (6) and the sleeve (20) may be rolled back on itself to overlie the first length of trunking (6) thereby releasing the second length of trunking (14) characterised in that the second end (26) of the flexible sleeve (20) is secured to a rigid collar (28) provided for grip with a radially outwards extending lip (30). Coupling means as claimed in claim 1 wherein the flexible sleeve (20) is formed of elastic material. Coupling means as claimed in claims 1 or 2 wherein the collar (28) is provided with a radially inward surface conforming with the cross section of the trunking. Coupling means as claimed in any preceding claim wherein the collar (28) is formed of glass fibre reinforced plastics material. Coupling means as claimed in claims 1 to 3 wherein the collar (28) is formed of metal bonded to the sleeve (20). Coupling means as claimed in claim 1 further comprising means for positively retaining the collar (28) in engagement with the further length of trunking (14) in the operative condition comprising interengaging features on the collar (28) and said further length of trunking (14). A helicopter gas turbine engine installation including an inlet particle separator having a length of outlet trunking (14) for scavenged debris which is coupled to a first length of trunking (6) in end-to-end relationship by coupling means comprising means for coupling trunking in end-to-end relationship comprises a length of flexible sleeve (20) having one end thereof attached to the first length of trunking (6) at one end (24) thereof, the sleeve (20) further having a second end (26) spaced from said first end (24) by a length of sleeve such that it may be extended to overlap and grip the length of outlet trunking (14) placed end-to-end with the first length of trunking (6) and the sleeve (20) may be rolled back on itself to overlie the first length of trunking (6) thereby releasing the length of outlet trunking (14) characterised in that the second end (26) of the flexible sleeve (20) is secured to a rigid collar (28) provided for grip with a radially outwards extending lip (30).

Inventors: SPERINCK, JOHN
Applicants: ROLLS-ROYCE PLC
Application year: 1990
Main classification: F16L21
IPC codes: F02K3, F16L21, F02C7