BACKGROUND OF THE INVENTION In heating, ventilation and air-conditioning ducts it is necessary to have fire dampers between separate rooms or floors of a building where these ducts pass through a wall, ceiling or floor to prevent fire transfer between floors or rooms.

This is particularly necessary where ducting is made from heat softenable materials such as plastics materials.

Mechanical dampers have been provided. These are generally placed within the ducts of the ventilating system and can be activated by many ways including fusible links and fire and smoke alarms.

Intumescent dampers in the form of grilles may be placed within the ventilating system and are activated by heat.

These prior art devices, however, must be inspected regularly but it is difficult to inspect a device which is within an air-conditioning duct.

International Standards require dampers associated with air ducts to close rapidly when fire occurs. In addition air leakage tests are carried out after closure to ensure the effectiveness of a closure system and hence it is desirable that a ring damper close off an aperture as soon as possible and provide an effectively permanent seal. Australian Patent No. 575098 dated 6th December 1984 in the name of Fire Research Pty Ltd describes a device for shutting off a plastics pipe passing through a partition in the event of a fire. The device has a flexible refractory fabric and a spring to apply a radially compressive force to close off the pipe after a fire has softened the plastics pipe. This device was intended to be placed over an existing pipe.

PCT publication WO 87/00761 dated 28th July 1986 in the name of Fire Research Pty Ltd describes a device which has a plastics sleeve which fits over a plastic pipe.

A combination of intumescent material and a flexible refractory fabric and a spring is used to close of the pipe in the event of a fire. Again this device was intended to be placed over an existing pipe.

It is the object of this invention to provide a ring damper system for an air- conditioning or ventilation duct which may be easier to inspect and install and is maintenance free.

The invention will generally be discussed in relation to its use with heating, ventilation and air-conditioning ducts but it is to be realised that it is also suitable for ventilation and similar ducting systems such as ducting for fume cupboards.

BRIEF DESCRIPTION OF THE INVENTION In one form therefore, although this may not necessarily be the only or broadest form, the invention is said to reside in a ring damper for a heating, ventilation and air-conditioning system where ducting is to pass through an aperture in a wall or soffit; the ring damper including an annular housing adapted to be fastened to or into the wall or soffit, a concentric heat softenable annular member within the annular housing and extending from each end thereof, a heat resistant fabric around a resilient device restrained by the annular member and between the housing and the annular member wherein a damping effect is obtained in the event of a fire when the annular member collapses upon application of heat and the heat resistant fabric is drawn across the aperture by the resilient device to close off the aperture.

It will be seen by this invention that can be installed into a wall or soffit with the annular housing extending each side so that an air conditioning duct can be connected on each side. As a fire softens the heat softenable annular member the resilient device draws the heat resistant fabric across the aperture to close off the aperture to prevent smoke and fire passing along the ducting and through the aperture. As the ducting is for relatively low pressure air the heat softenable annular member can be of relatively small wall thickness and therefor be easily softened by heat to closed off by heat resistant fabric drawn across the aperture by the resilient device.

In one embodiment the annular housing may include a radially outward extending flange so that the device is able to be mounted onto or set into a wall, floor or ceiling.

There may be two sets of the heat resistant fabric around a resilient device restrained by the annular member and between the housing and the annular member, a set being positioned towards each end of the annular member so that if there is a fire on either side of the wall, floor or ceiling the resilient device on that side will compress the annular member and draw the fabric across the aperture.

In a further form the invention is said to reside in ring damper for plastics material heating, ventilation and air-conditioning ducting passing through an aperture in a wall or soffit; the ring damper including an annular housing adapted to be fastened to or into the wall or soffit, a concentric heat softenable annular member within the annular housing and extending from each end thereof, an annular portion of intumescent material between the housing and annular member and a heat resistant fabric around a resilient device restrained by the annular member and between the housing and the annular member wherein a three stage damping effect is obtained in the event of a fire, a first stage being when the annular member collapses upon application of heat, a second stage being when the heat resistant fabric is drawn across the aperture by the resilient device and the third stage being when intumescent material expands and chars to close off the aperture.

It will be seen that by this invention there is provided a device which can be fitted to a wall around an aperture through air conditioning or ventilation is to pass and the ducting connected on each side of it and then in the event of fire the plastics material of the air-conditioning duct collapses and the heat softenable annular member collapses which allows the resilient device to pull the fabric across the aperture and heat to get to the intumescent material to cause that to expand and char to close off the aperture through the wall, ceiling or floor.

Preferably the housing includes a flange to allow the damper to be fastened to a wall of soffit around the aperture. Alternatively the device may be fitted completely or partially into a wall aperture.

In a preferred embodiment of the invention the intumescent material is placed adjacent the flange end of the housing. The resilient device and fabric is at the other end of the housing.

In an alternative arrangement there may be two sets of the heat resistant fabric around a resilient device restrained by the annular member one to each side of the intumescent material.

The heat resistant fabric is preferably a material which is resistant to flame and heat. This may be a fibre glass cloth impregnated with a heat resistant material.

Preferably at least one end of the heat resistant fabric is fastened to the housing.

The fastening may be by clipping, crimping or adhesive.

Preferably the resilient device is a coil spring which is held under tension by being stretched around the heat softenable annular member and with the fabric wrapped or rolled or folded around it when the spring contracts when the heat softenable annular member is softened it draws the fabric across the aperture.

The housing may be made for metal or plastics material or any other convenient material.

The heat softenable annular member may be formed from a plastics material such as PVC or a wax or the like.

In one embodiment of the invention the housing may extend out from a wall or soffit and in an alternative embodiment the housing may be fitted within the wall or soffit and may in fact be cast in place during construction of the wall or soffit.

The housing and heat softenable annular member may be circular, square or rectangular or any other cross sectional shape.

There may be an annular cap between the housing and the annular member at each end of the housing.

The heat softenable annular member may include an circumferential groove approximately midway between the ends of the tube to assist with location of the resilient device such as the coil spring. The circumferential groove may also assist with concentration of the load of the coil spring to speed up closure in the event of a fire.

In a further form the invention is said to reside in a ring damper for heating, ventilation and air-conditioning duct work passing through an aperture in a wall or soffit; the ring damper having an annular housing adapted to be fastened to or into the wall or soffit, a heat softenable tube within the annular housing and extending from each end of the housing, a circumferential inwardly extending groove in the tube, an annular portion of intumescent material between the housing and the tube, a heat resistant fabric joined to the housing at one end thereof and extending into the housing between the housing and tube, a coil spring received in the circumferential groove and stretched around and restrained by the annular member and the heat resistant fabric passing between the coil spring and the tube.

Preferably the heat resistant fabric is loosely folded and packed into the either side of the coil spring and the fabric is joined to the housing by crimping.

There may be included an annular cap between the housing and the tube at each end of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS This event generally describes the invention but to assist with understanding reference will now be made to the accompanying drawings which show a preferred embodiment of the invention.

In the drawings: Figure 1 shows a cut-away perspective view of a ring damper according to one embodiment of the invention; Figure 2 shows a cross-sectional of the view shown in Figure 1; Figure 3 shows an end on view of the embodiment shown in Figure 1; Figure 4 shows a cross-sectional of an alternative embodiment of a ring damper according to the present invention; Figure 5 shows a cross-sectional of a still further embodiment of a ring damper according to the present invention; Figure 6 shows a perspective view of a ring damper according to an alternative embodiment of the invention; and Figure 7 shows a longitudinal cross sectional view of the ring damper shown in Figure 6.

DESCRIPTION OF PREFERRED EMBODIMENTS Now looking more closely at the drawings and in particular the embodiment shown in Figures 1 to 3 it will be seen that the ring damper according to this embodiment of the invention comprises an annular housing 1 with a flange 3 at one end of the housing. The flange 3 has apertures 5 so that the flange can be mounted to a wall using screw fastenings or the like.

Within the housing 1 and concentric with it is an annular heat softenable material tube 7 which extends beyond each end of the housing.

In the cross sectional view shown in Figure 2 with the ring damper shown mounted onto a wall 13 with fastening passing through the flange 3 it can be seen that the annular heat softenable material tube 7 which extends through the housing 1 also extends through the wall 13 so that air-conditioning ducting 9 can be fastened to it either side of the wall using tape 10 or any other suitable fastening method.

Between the housing 1 and the tube 7 and near the flange 3 end of the housing 1 is an annular portion of intumescent material 15. The intumescent material is a material which when heated expands and chars to close off an aperture such as the aperture 11 in the wall 13 in Figure 2.

An intumescent material reacts relatively slowly to heat and while providing a robust barrier when activated it takes some time to close off an aperture. It is desirable for heating, ventilation and air-conditioning ducting that the duct be closed off as soon as possible to stop smoke and fire entering adjacent rooms and hence there is also provided a fast close off arrangement which has a spring 17 with a fabric 19 passed between the tube 7 and the spring and one end of the fabric being joined to the end of the housing at 21. Either side of the spring 17 the fabric 19 is loosely folded and packed into the annular space between the housing 1 and the tube 7. It has been found to be not necessary to fasten the fasten the end of the fabric 19 near the intumescent material 15.

When, in the case of a fire, the heat softenable tube 7 is heated the spring 17, which is held under tension by being stretched around the heat softenable tube 7, crushes the plastics material and draws the fabric 19 across the aperture to assist with closing off the aperture as soon as possible.

The heat resistant fabric 19 may in time burn, however, by that time the intumescent material 15 will have sufficiently expanded to close off the aperture.

In the embodiment shown in Figure 4 the ring damper of this embodiment of the invention has a housing 20 which may be circular, square or rectangular or any other required cross sectional shape. One end of the housing has a flange 24 so that the housing can be fastened to a wall or soffit. Within the housing 20 is a length of ventilation ducting 22 made from a heat softenable material such as a thermoplastics material. The ducting 22 extends out either end of the housing so that further lengths of ducting can be fastened to them during installation of a ventilation system. Between the housing 20 and the ducting 22 is a coil spring 26 under tension with a heat resistant fabric 28 passed between it and the ducting 22.

The fabric 28 is joined to the housing at 30 by a crimped over end 31 of the housing 30 and loosely folded and packed as at 29 into the space either side of the spring 26.

In the event of a fire the ducting 22 will soften and the spring 26 will crush the softened plastics material ducting 22 and draw the heat resistant fabric across the aperture to close off the duct. The loose fabric can be drawn across the aperture by the spring from where it is retained at the end of the housing 30.

In Figure 5 the ring damper of this embodiment of the invention has a housing 40 which may be circular, square or rectangular or any other required cross sectional shape. The housing is adapted to be mounted into a wall or soffit during construction of the wall. Within the housing 40 is a substantially concentric length of ventilation ducting 42 made from a heat softenable material such as a thermoplastics material. The ducting 42 extends out either end of the housing so that further lengths of ducting can be fastened to them during installation of a ventilation system. Between the housing 40 and the ducting 42 is an annular portion of intumescent material 44. The intumescent material is a material which when heated expands and chars to close off an aperture such as in the event of a fire.

At each end of the housing and between the housing 40 and the ducting 42 is a coil spring 46 under tension with a heat resistant fabric 48 wrapped around it. The fabric 48 is joined to the housing at 50. In the event of a fire, initially the ducting 42 will soften and the spring 46 will crush the softened plastics material ducting 42 and draw the heat resistant fabric across the aperture to close off the duct.

Subsequently the intumescent material 44 will be heated and expand and char to fully close of the aperture into which the ring damper is mounted.

Figures 6 and 7 show a further embodiment of the present invention.

In this embodiment, the ring damper 50 has a cylindrical housing 52 with a radially outwardly extending flange 54 substantially midway along the housing. The flange 54 has apertures 56 to enable it to be mounted to a wall or socket and right angle brackets 58 on one edge so that the flange can easily be mounted in a wall adjacent a ceiling.

Passing through the housing 52 is a length of heat softenable tube 60 and this tube extends beyond each end of the housing. Closing off the gap at each end between the housing 52 and the tube 60 are annular end caps 62. These end caps 62 may be made from metal or from plastics or rubber or other suitable material.

The tube 60 includes a circumferential groove 64 approximately midway between the ends of the tube as can particularly be seen in Figure 7. This circumferential groove 64 assists in location of a coil spring 66 which is received in the annular space 53 between the housing 52 and the tube 60. The groove 64 also assists in focussing the compressive force of the coil spring 66 when the tube 60 is softened in the event of a fire.

A length of heat resistant fabric 68 is joined to the housing by crimping to the housing at one end 70 and is packed or folded loosely in the annular space 53 between the housing 52 and the tube 60 and passes between the coil spring 66 and the circumferential groove 64 and is packed loosely again on the other side of the coil spring. The end 69 of the heat resistant fabric 68 is loose with in the housing 52.

An intumescent material 72 is also received in the annular space between the housing and the tube 60.

Ventilation ducting can be joined by the use of adhesive tape or similar methods to the tube 60 where it extends beyond each end of the ring damper 50.

In the event of a fire, the tube 60 which is formed from a heat softenable material can soften quite quickly and the coil spring 66 can then draw the heat resistant fabric 68 across the aperture within the tube 60 and then with continued application of heat the intumescent material 16 can char and expand to fully close off the aperture.

It has been found that the initial closing off can occur in as quickly as 26 seconds from the application of heat.

The housing and flange may be made from any suitable material such as metal or plastics material.

It will be seen therefore by this invention is provided an arrangement by which speedy closing of a plastics material air-conditioning duct can be achieved by use of a single or multiple stage closing process.

Throughout this specification various indications have been given as to the scope of this invention but the invention is not limited to any one of these but may reside in two or more of these combined together. The examples are given for illustration only and not for limitation.