GB2468292A

GB2468292A - Damper with spring clutch to permit or prevent movement of the damper blade by relative position of spring legs on the spring clutch.

Info

Publication number: GB2468292A
Application number: GB0903565A
Authority: GB
Inventors: Richard Perrin
Original assignee: Tri Air Innovations Ltd
Current assignee: Tri Air Innovations Ltd
Priority date: 2009-03-02
Filing date: 2009-03-02
Publication date: 2010-09-08
Also published as: GB0903565D0; WO2010100403A1

Abstract

A damper 1 comprises a blade 3 pivotably mounted by an axle 7 in ducting 5 to regulate (air) flow through ducting 5, whereby a portion 33 of axle 7 extends through the wall of ducting 5 and a spring clutch 39 is mounted on portion 33 for controlling the position of blade 3. A handle 31 may be provided for adjusting the position of axle 7 and clutch 39 fixes blade 3 in position or allows it's rotation in one direction while inhibiting rotation in the other by including a spring 41 of inner diameter similar to that of portion 33 and first (fixed) and second (free to move) legs 43, 47 at opposing ends of spring 41 that alter the inner diameter of spring 41 by relative movement. A bracket 37 may be mounted outside ducting 5 with openings where legs 43, 47 of possibly two clutches 39 are held or pass through (e.g. Z or S shaped slots). Damper 1 may be used as an air balancing damper, volume control damper or a fire damper where blade 3 is biased to rotate to close ducting 5.

Description

A damper This invention relates to a damper. In particular, this invention relates to an air balancing damper, a volume control damper or a fire damper used within ventilating and air conditioning systems.

Air balancing dampers are used in air conditioning systems to regulate the volume of air passing through ducts of the air conditioning system by partially closing off a channel of the duct. By regulating the volume of air flowing in each duct the air conditioning system is balanced so that the conditioned air reaches all parts of the system at desired flow rates. Such dampers are also known as regulating dampers.

The air balancing damper comprises one or more blades to partially close off the channel. Typically the or each blade is mounted on an axle to pivot in the channel between a closed position, where the blade is perpendicular to the axis of the ducting and the channel is substantially blocked, and a fully open position, where the plane of the blade is parallel to the axis of the ducting.

To adjust the balancing damper the blade is rotated to the required inclination and fixed in place. The fixing in place of the damper is typically performed using a screw tightening arrangement. For example, the "Circulair" air balancing dampers sold by Actionair (RTM) employ a toothed locking nut to grip a toothed quadrant to set an inclination of the blade. Volume control dampers sold by CCL Veloduct Limited use a lockable control knob. Air balancing dampers are also supplied with motors to electrically control the degree of opening but these dampers are consequently more expensive and prone to electrical failure.

US-A-4372342 describes a balancing damper comprising a plurality of connected blades and a semi-circular plate mounted on the outer side of a frame and attached to one of the blades of the damper. The plate has an arcuate slot through which a locking screw fits to grip the plate and fix the angle of inclination of the blades.

Volume control dampers are also used in air conditioning systems to regulate the volume of air passing through the ducts but primarily volume control dampers are used to close off a duct. For example, a volume control damper is used during maintenance of the ducting downstream of the volume control damper to seal a channel of the ducting or if a section of the ventilating system is to be temporarily decommissioned.

Hence, the main difference between air balancing dampers and volume control dampers is the degree to which the channel is sealed when the damper is closed. In this application an air balancing damper is described and the skilled person will understand that the teaching of the invention can equally be applied to a volume control damper.

A fire damper comprises a damper having a structure similar to a volume control dampers as described above and additionally biasing means, such as a spring, for biasing the blade to rotate to a closed position. The biasing means typically takes the form of a spring coiled around the axle. The fire damper is further provided with a means of holding the blade open against the biasing means, for example a fusible cartridge as described in GB-A-2392092. In the event of heat or fire the blade is released so that the biasing means drives the blade to close the channel of the ducting, to prevent fire from passing through the ducting. Thus, fire dampers are used to isolate areas of a building in the event of a fire and to prevent fire spreading through a building via the air conditioning system.

It is an object of the invention to provide an improved damper.

According to a first aspect of invention there is provided a damper comprising: ducting; a blade pivotably mounted in the ducting to regulate flow of fluid through the ducting, the blade being fixed to an axle or shaft which pivots in the ducting, a portion of the axle extending through a wall of the ducting; and a first spring clutch mounted on the portion of the axle extending through the wall of the ducting for controlling a position of the blade.

Using a spring clutch to control the position of the blade provides a simple, economic and mechanically reliable method of setting the inclination of a damper blade and provides single handed operation of the damper.

The spring clutch may be arranged on the axle to fix the position of the blade or to allow rotation of the blade in one direction and to inhibit rotation of the blade in the other direction.

The damper may further comprise a handle for adjusting the position of the axle and the blade.

The first spring clutch may comprise: a coiled portion having an inner diameter similar to the diameter of the portion of the axle on which the spring clutch is mounted; a first leg at one axial end of the coiled portion; and a second leg at the other axial end of the coiled portion, wherein relative movement of the first and second legs alters the inner diameter of the coiled portion. The relative diameters of the coiled portion and the axle are such that the coiled portion grips the axle when at rest and the degree to which the coiled portion grips the axle further depending on the resilience of the coiled portion.

The first leg may be fixed in place and the second leg may be free to move relative to the first leg. This means that only one leg of the spring clutch need be moved to alter the grip of the spring clutch on the axle.

The damper may further comprise a bracket mounted on an outside of the ducting, the axle passing through a first opening in the bracket, the second leg of the spring clutch passing through a second opening in the bracket and the first leg being held in a third opening in the bracket.

The damper may further comprise a second spring clutch similar to the first spring clutch. In a preferred embodiment both spring clutches are identical. The second spring clutch provides greater control over the position of the damper.

The first leg of the second spring clutch may be fixed or anchored in place and the second leg of the second spring clutch may be free to move relative to the first leg of the second spring clutch, thereby providing convenient means for altering the grip of the spring clutch on the shaft.

The second leg of the second spring clutch may pass through the second opening in the bracket and the first leg of the second spring clutch may be fixed in the third or a fourth opening in the bracket.

In an alternative embodiment the first and second legs may be free to move relative to the rest of the damper. In this case the damper may further comprise a bracket mounted on an outside of the ducting, the axle passing through a first opening in the bracket and the legs of the spring clutch passing through a second opening in the bracket.

When the or each spring clutch is untensioned the coiled portion may grip the portion of the axle on which the spring clutch is mounted.

When the or each spring clutch is untensioned the inner diameter of the coiled portion may be greater than the diameter of the portion of the axle on which the spring clutch is mounted or the inner diameter may identical to or less than the diameter of the axle.

Movement of the second leg towards the first leg may increase the inner diameter of the coiled portion and movement of the second leg away from the first leg may decrease the inner diameter of the coiled portion. Alternatively, movement of the second leg towards the first leg may decrease the inner diameter of the coiled portion and movement of the second leg away from the first leg may increase the inner diameter of the coiled portion.

The damper may further comprise a catch or catch means for restraining the free to move leg or legs. The second opening may comprise the catch means. The second opening may comprise a slot having corners constituting the catch means.

The second opening may be a Z-shaped slot or an S-shaped slot.

According to a second aspect of the invention there is provided an air balancing damper comprising the damper as described above.

According to a third aspect of the invention there is provided a volume control damper comprising the damper as described above, wherein the blade seals the ducting when the blade is in the closed position.

According to a further aspect of the invention there is provided a fire damper comprising the damper as described above and further comprising: biasing means for biasing the blade to rotate to a closed position, wherein the spring clutch is arranged on the axle to allow the blade to rotate to close the ducting and to inhibit the blade from rotating in the other direction.

The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a balancing damper forming a first embodiment of the invention; Figure 2 is an end view of the damper of Figure 1 in direction II; Figure 3 is an exploded perspective view of the damper of Figure 1; Figure 4A is a perspective view of a spring clutch of the damper of Figure 1; Figure 4B is a side view of the spring clutch of Figure 4A; Figure 5 is a perspective view of a clutch housing of the damper of Figure 1; Figure 6 is a perspective view of a fire damper according to a second embodiment of the invention; Figure 7 is a sectional view of the fire damper of Figure 6 along line Vu-Vu; Figure 8 is a perspective view of a balancing damper forming a third embodiment of the invention; Figure 9 is a partial cut-away end view of the damper of Figure 8 in direction IX; Figure 10 is an exploded perspective view of the damper of Figure 8; Figure 1 1A is a perspective view of the spring clutches of the damper of Figure 8; Figure 1 lB is a side view of one of the spring clutches of Figure hA; and Figure 12 is a perspective view of a clutch housing of the damper of Figure 8.

With reference to Figures 1, 2 and 3, a damper 1 forming an embodiment of the invention comprises a length of ducting 5 within which a tubular rim 17 is fitted. A blade 3 is pivotably mounted in the rim 17 by means of an axle 7 to which the blade 3 is fixed. The axle 7 passes through an opening 9 in a wall 11 of the ducting 5 and through openings 13 in opposed walls portions 15 of the rim 17. Both the rim 17 and the ducting 5 are circular in cross section and the blade 3 is round. The blade 3 is a similar size and shape to an opening 19 in an end of the rim 17. The diameter of the opening 19 of the rim is less than the inner diameter of the ducting 5 to allow the blade 3 to rotate inside the ducting 5 without being fouled by the wall 11 of the ducting 5. The rim 17 acts to strengthen the ducting 5 and to providing bearing points for the axle in the form of the openings 13.

The blade 3 is fixed to the axle 7 by means of a suitable fixing means (e.g., a screw, bolt or rivet, not shown) which passes through a hole 21 in the blade 3, a washer 23 arid a bore 25 passing through the axle 7. Two spacer tubes 27 are placed over the axle 7 on either side of the hole 25 in the axle 7 to centralise the blade. The damper 1 shown in Figures 1 to 3 shows the plane of the blade 3 perpendicular to the axis of the ducting 5 so that the ducting 5 is closed, but not necessarily sealed.

The axle 7 forms part of an L-shaped bar 29. The portion 31 of the bar 29 perpendicular to the axle portion 7 serves as a handle to allow a user to alter the orientation of the axle 7 and consequently the inclination of the blade 3 within the ducting 5.

A clutch housing 37 is provided in the form of a bracket mounted on the outside of the ducting 5. As can be seen from Figures 2 and 5, the clutch housing or bracket 37 is a plate bent in the shape of a top hat, having a top wall, two side walls and flanges extending from the ends of the side walls distal to the top wall. A circular first opening is provided in the top' of the clutch housing 37 in line with the opening 9 in the wall 11 of the ducting and the openings 13 in the rim 17. A portion 33 of the axle 7 extends through the hole 9 in the wall 11 of the ducting 5 and the first opening 35 of the clutch housing 37. A second opening 53 is provided in a side wall of the clutch housing 37 in the form of an S-shaped slot. The S-shaped slot 53 comprises a body slot portion 55, which runs parallel to the axis of the ducting 5; and a foot slot portion 57 and a head slot portion 59 which each form an acute angle with the body slot portion 55 to provide corners 61, 63 in the wall 65 of the S-shaped slot 53 between the body portion 55 of the slot 53 and the respective foot 57 and head slot portions 59 of the slot 53.

A spring clutch 39 is mounted on the portion 33 of the axle 7 inside the clutch housing 37 to control the position of the blade 3. The spring clutch 39 is shown in greater detail in Figures 4A and 4B and comprises a coiled portion 41, a first leg 43 at a first axial end 45 of the coiled portion 41 and a second leg 47 at a second axial end 49 of the coiled portion 41. Each of the first and second legs 43, 47 extends tangentially from their respective ends 45, 49 of the coiled portion 41. When the spring clutch 39 is located on the portion 33 of the axle 7 inside the clutch housing 37, the first and second legs 43, 47 pass through the S-shaped slot 53 of the clutch housing. The end portions 51 of the legs 43, 47 are bent into a curve to provide the legs 43, 47 with a gripping position where the legs 43, 47 can conveniently be gripped between an operator's fingers.

Referring to Figures 4A and 4B, the inner diameter D of the coiled portion 41 is uniform through the axial length of the coiled portion 41 and is of the order of the diameter d of the portion 33 of the axle 7 on which the spring clutch 39 is mounted (see Figure 2) in the relaxed, untensioned position of the spring clutch 39.

When the end portions 51 of the legs 43, 47 of the spring clutch 39 are moved towards each other the coiled portion 41 is partially unwound and the inner diameter D of the coiled portion 41 increases. Conversely, when the end portions 51 of the legs 43, 47 of the spring clutch 39 are moved away from each other then the coiled portion 41 is wound tighter such that the inner diameter D of the coiled portion 41 decreases.

Jn use, when the legs 43, 47 of the spring clutch 39 are in the body slot portion of the S-shaped slot 53 the spring clutch 39 is in an untensioned state and the coiled portion 41 of the spring clutch 39 grips the portion 33 of the axle 7 sufficiently loosely to allow rotation of the axle 7 relative to the spring clutch 39.

To open the damper 1 the axle 7 is rotated clockwise (as seen in Figure 1) by means of the handle 31 to alter the inclination of the blade 3 in the ducting 5. Once the desired position of the blade 3 is reached, the blade 3 is fixed in place by moving the first and second legs 43, 47 of the spring clutch 39 away from each other along the body slot portion 55 of the slot 53 to the foot and head slot portions 57, 59 respectively of the S-shaped slot 53, thereby decreasing the inner diameter D of the coiled portion 41 of the spring clutch 39, to grip the portion 33 of the axle 7 on which the spring clutch 39 is mounted. By fixing the legs 43, 47 in the foot and head portions 57, 59 of the slot 53 and by gripping the portion 33 of the axle 7, the spring clutch 39 sets the position of the blade 3.

In this manner, the foot 57 and head 59 portions of the S-shaped slot 53 act as engagement slots and the corners 61, 63 of the inner wall 65 of the S-shaped slot 53 act as catch means for restraining the respective first and second legs 43, 47 of the spring clutch 39.

Alternatively, the spring clutch 39 can be used to control the position of the blade to allow rotation of the blade 3 in one direction and to inhibit rotation of the blade 3 in the other direction. In this arrangement the spring clutch 39 behaves like a ratchet.

For example, if the blade 3 is set at a position and it is desired to allow the blade 3 to open further (clockwise in Figure 1) from the position at which it is set but not to close from this position then the first leg 43 is disposed in the foot engagement slot portion 57 and the second leg 47 is disposed in the body slot portion 55. Thus, if the handle 31 is turned clockwise as shown in Figure 1 then due to friction between the coiled portion 41 and the portion 33 of the axle 7 on which the coiled portion 41 is mounted, the portion 33 of the axle 7 on which the coiled portion 41 is mounted will rotate against the coiled portion 41 to partially unwind the coiled portion 41 arid increase its inner diameter D, thereby allowing rotation of the axle 7 relative to the spring clutch 39. Conversely, if the handle 31 is turned in an anti-clockwise direction as shown in Figure 1 then the portion 33 of the axle 7 will attempt to rotate within the coiled portion 41 in a direction to tighten the coiled portion 41 due to the frictional force therebet'ween and hence this tightening of the coiled portion 41 will prevent the blade 3 rotating in an anti-clockwise direction.

Similarly, if the blade 3 is set at a position and it is desired to allow the blade 3 to close (anti-clockwise in Figure 1) from the position at which it is set but not to open further from this position then the second leg 47 is disposed in the head engagement slot portion 59 and the first leg 43 is disposed in the body slot portion 55. Thus, if the handle 31 is turned anti-clockwise as shown in Figure 1 then the portion 33 of the axle 7 on which the coiled portion 41 of the spring clutch 39 is mounted will rotate against the coiled portion 41 to partially unwind the coiled portion 41 and increase its inner diameter D, thereby allowing rotation of the axle 7 relative to the spring clutch 39.

Conversely, if the handle 31 is turned in a clockwise direction as shown in Figure 1 then the portion 33 of the axle 7 will attempt to rotate within the coiled portion 41 in a direction to tighten the coiled portion 41 and hence this tightening of the coiled portion 41 will prevent the blade 3 moving in a clockwise direction.

The ratchet behaviour of the spring clutch 39 described above can be used in a fire damper, for example, in the Tn-Pro damper sold by Tn-Air Innovations Limited and as described in GB-A-2369571 and GB-A-2392092, the contents of which are incorporated herein by reference.

When a fire damper is triggered it is important that the blade remains closed.

During a fire an increased pressure may be generated in the ducting of an air conditioning system, for example as a result of rising temperature or an explosion, and this increased pressure may push against a closed blade of a fire damper to attempt to open the fire damper. Therefore it is important that once the blade of a fire damper is closed by means of the biasing means it is subsequently kept shut. In order to achieve this the spring clutch and clutch housing described above can be incorporated into the fire damper and arranged in such a manner that the spring clutch allows the blade to rotate to close the fire damper and to inhibit rotation of the blade in the opposite direction. In this arrangement the blade closes when the means for holding the blade open against the biasing means is disapplied and once the blade has been released to close the ducting the spring clutch prevents the blade from being opened.

With reference to Figures 6 and 7, a fire damper 1 a comprises a cylindrical rim 17 mounted in a length of ducting 5 and a pivoting damper element or blade 3 on a transverse axle 7 passing through the rim 17 similar to the fire damper of GB-A- 236957 1 and GB-A-23 92092, the contents of which are incorporated herein by reference. In the closed position shown in Figures 6 and 7, the periphery of the blade 3 bears against the rim 17, to seal the duct. Two helical springs 71 bias the blade 3 into its closed position. The blade 3 is opened by rotating the axle 7 clockwise as shown in Figure 6.

A generally sector-shaped retention member or quadrant 73 is held in a slot in the blade 3 and secured by the axle 7 which passes through a hole in the quadrant 73 so that the quadrant 73 is fixed relative to the blade 3. The quadrant 73 has a series of cut-outs or notches adjacent its periphery.

A U-shaped support member 77 is mounted in position in the following manner.

The U-shaped support member 77 has at right angles thereto a profiled limb extension which has a bore by which the extension 75 is secured to the inner circumference of the ducting 5 by securing means in the form of a rivet 76. The other limb 79 of the support member 77 is internally of the quadrant 73.

Externally of the quadrant 73, a sprung L-bracket 81 is riveted to the base 83 of the support member 77. The bracket 81 has pressed in it a dimple 85 which is roughly the same size as the cut-outs in the quadrant 73 and which, in the set position of the damper, engages in a cut-out in the quadrant 73.

A cartridge assembly 87 is passed through a hole 89 in the ducting 5 and screwed into a tapped opening and is held in place by a lock-nut 91. The cartridge assembly 87 is formed of a body member or cartridge holder 93 and a cylindrical casing 95. On the end of the casing 95 there is a short end cap 97 carrying two elongate detents or claws 99. The claws 99 have inturned ends which engage in an annular groove in the casing 95. The claws 99 have circular openings 101 near their roots, to make them less rigid, and adjacent each opening 101 a heat-soflenable or meltable (fusible) material in the form of solder is applied so that it adheres both to the claws 99 and to the outside of the casing 95. As the force on the ends of the claws 99 is always in a radial direction before the solder melts, the solder is under tension.

The fire damper la is provided with a clutch housing 37 and spring clutch 39 as shown in Figures 4 and 5, in a similar manner to the embodiment of Figures 1 to 3.

In order to set the fire damper la, the legs 43, 47 of the spring clutch 39 are disposed in the body slot portion 55 of the S-shaped slot 53 of the clutch housing 37 to allow unencumbered rotation of the axle 7. The blade 3 is opened (by turning the blade clockwise as shown in Figure 6) to a suitable inclination. The cartridge assembly 87 is then screwed in and the blade 3 positioned so that the dimple 85 engages in a cut-out.

The end cap 97 should abut firmly against the spring bracket 81, which acts as an engaging member, pressing the quadrant 73 against the limb 79, which then acts as a backing piece, thereby securing the quadrant 73 and holding the blade 3 in an open position. The lock nut 91 is applied. The second leg 47 of the spring clutch 39 is moved to the head engagement slot portion 59 and the first leg 43 remains in the body slot portion 55.

If the temperature rises excessively, the solder melts. The springs 71 are sufficiently strong to cam the dimple 85 out of the cut-out, pushing the end cap 97 to the right as shown in Figure 7 and camming the ends of the claws 99 out of the groove (in a radial direction). The biasing means 71 urges the blade 3 to the closed position (anti-clockwise as shown in Figure 6) arid the portion 33 of the axle 7 on which the coiled portion 41 of the spring clutch 39 is mounted rotates within the coiled portion 41 in a direction to partially unwind the coiled portion 41 and increase its inner diameter D, thereby allowing rotation of the axle 7 relative to the spring clutch 39. Once the blade 3 is in its closed position as shown in Figure 6, if a build up of pressure in the ducting 5 applies a force to the blade 3 to urge the blade 3 in a clockwise direction then the portion 33 of the axle 7 will attempt to rotate within the coiled portion 41 in a direction to tighten the coiled portion 41. This tightening of the coiled portion 41 increases the frictional force between the coiled portion 41 and the axle 7 which prevents the blade 3 opening from its closed position. Hence incorporating the spring clutch 39 and clutch housing 37 in the fire damper la enhances the ability of the fire damper la to seal the ducting 5 in the event of a fire or explosion.

Figures 8 to 12 show a balancing damper 1 a forming a further embodiment of the invention and parts thereof. The same reference numerals are used in Figures 8 to 12 to indicate like parts to those shown in the embodiment of Figures ito 5 and reference should be made to the description of the first embodiment in relation to the like parts.

With reference to Figures 8, 9 and 10, a damper la comprises a length of ducting 5, a blade 3 and an axle 7 similar to the first embodiment, with the axle 7 passing through an opening 9 in a wall 11 of the ducting 5. Unlike the damper of the first embodiment, the damper 1 a does not comprise spacer tubes over the axle 7 or a rim inside the ducting 5. Instead of spacer tubes the damper Ia comprises an inwardly extruded flange around the opening 9 in the wall 11 of the ducting 5 which centralises the blade 3 as well as provides a bearing surface and seal on the axle 7.

With reference in particular to Figure 12, a clutch housing 37a is provided in the form of a bracket mounted on the outside of the ducting 5. The clutch housing 3 7a has a similar shape to the clutch housing 37 of the first embodiment but differs from that housing 37 in that an opening 53a in a side wall of the housing 37a is a Z-shaped slot 53a; and concave portions 101 are provided in the side walls in the vicinity of the flanges 103 which extend from the ends of the side walls.

The Z-shaped slot 53a comprises a body slot portion 55a, which runs generally parallel to the axis of the ducting 5; and a foot slot portion 57a and a head slot portion 59a which provide corners 61a, 63a in the wall 65a of the Z-shaped slot 53a between the body portion 55a of the slot 53a and the respective foot 57a and head slot portions 59a of the slot 53a.

Returning to Figures 8, 9 and 10, two spring clutches 39a, 39b are mounted on the portion 33 of the axle 7 inside the clutch housing 37a to control the position of the blade 3. The spring clutches 39a,b are identical and are shown in greater detail in Figures hA and 11B. Each spring clutch 39a,b comprises a coiled portion 41, a first leg 43a at a first axial end 45 of the coiled portion 41 and a second leg 47a at a second axial end 49 of the coiled portion 41. First portions 44a, 48a of the respective first and second legs 43a, 47a closest to the coiled portion 41 extend tangentially in opposite directions from the respective ends 45, 49 of the coiled portion 41 when the spring clutch is at rest in an untensioned state.

A second portion 44b of the first leg 43a distal to the coiled portion 41 is bent at right angles to the first portion 44a in a direction perpendicular to the axis of the coiled portion 41, such that both portions 44a, 44b of the first leg 43a lie in a plane perpendicular to the axis of the coiled portion 41. A second portion 48b of the second leg 47a distal to the coiled portion 41 is bent at an angle of around 25 degrees to the first portion 48a, such that both portions 48a, 48b of the second leg 47a lie in a plane perpendicular to the axis of the coiled portion 41 and parallel to the plane in which the first portion 44a and second portion 44b of the first leg 43a lie. A third, end portion 48c of the second leg 47a distal to the first portion 48a of the second leg 47a is bent into a curve to provide the second leg 47a with a gripping position where the leg 47a can conveniently be gripped between an operator's fingers.

The two spring clutches 39a,b are located on the portion 33 of the axle 7 inside the clutch housing 37a, with the axial end 49 (from which the second leg 47a extends) of one spring clutch 39a adjacent the axial end 49 of the other spring clutch 39b. The second leg 47a of each spring clutch 39a,b passes through the Z-shaped slot 53a of the clutch housing 37a. In this manner there is an angle of around 50 degrees between the second portions 48b of the second legs 47a of the two spring clutches 39a,b. The second portion 44b of the first leg 43a of each spring clutch 39a,b is fitted through an opening 40 (visible only for spring clutch 39b) in the side wall of the clutch housing 37a opposite the side wall in which the Z-shaped slot 53a is formed. A clutch cover 105 is placed inside each open end of the clutch housing 37a; one of the clutch covers 105 is not shown in Figure 9, to provide a view of the spring clutches 39a,b inside the clutch housing 37a.

The inner diameter D of the coiled portion 41 is slightly less (between 0.1mm to 0.4mm less) than the diameter d of the portion 33 of the axle 7 on which the spring clutches 39a,b are mounted (see Figure 9) in the relaxed, untensioned status of the spring clutches 39a,b, such that the coiled portion 41 grips the portion 33 of the shaft 7.

Since the first legs 43a are fixed relative to the clutch housing 37a, when the end portions 48c of the second legs 47a of the spring clutches 39a,b are moved towards each other the coiled portions 41 of the spring clutches 39a,b are partially unwound and the inner diameter D of the coiled portion 41 increases. Conversely, when the end portions 48c of the second legs 47a of the spring clutches 39a,b are moved away from each other then the coiled portions 41 are wound tighter such that the inner diameter D of each coiled portion 41 decreases.

In use, when the second legs 47a of the spring clutches 39a,b are in the body slot portion 55a of the Z-shaped slot 53a, the spring clutches 39a,b are in an untensioned state and the coiled portion 41 of each spring clutch 39a,b grips the portion 33 of the axle 7 sufficiently tightly to impede rotation of the axle 7 relative to the coiled portion 41 of the spring clutches 39a,b. Since the first legs 43a of the spring clutches 39a,b are anchored in the clutch housing 37a the coiled portions 41 are held in place and the axle 7 and blade 3 are also held in place.

To adjust the inclination of the blade 3, the end portions 48c of the free-to-move second legs 47a of the spring clutches 39a,b are moved towards each other along the body slot portion 55a of the Z-shaped slot 53a by squeezing the end portions 48c between an operator's fingers, to release the grip of the coiled portion 41 on the axle 7.

To open the damper lathe axle 7 is rotated clockwise (as seen in Figure 8) by means of the handle 31 to alter the inclination of the blade 3 in the ducting 5. Once the desired position of the blade 3 is reached, the blade 3 is fixed in place by releasing the end portions 48c of the free second legs 47a of the spring clutches 39a,b so that the coiled portions 41 once again grips the axle 7. The axle 7 can be locked in place by moving the end portions 48c of the second legs 47a of the spring clutches 39a,b further away from each other along the body slot portion 55a of the slot 53a to the head and foot slot portions 59a, 57a respectively of the Z-shaped slot 53a, thereby decreasing the inner diameter D of the coiled portion 41 of each spring clutch 39a,b, to increase the grip on the portion 33 of the axle 7 on which the spring clutches 39a,b are mounted. By fixing both second legs 47a in the foot and head portions 57a, 59a of the slot 53a and by gripping the portion 33 of the axle 7, the spring clutches 39a,b lock the position of the blade 3.

In this manner, the head 59a and foot 57a portions of the Z-shaped slot 53a act as engagement slots and the corners 61a, 63a of the inner wall 65a of the Z-shaped slot 53a act as catch means for restraining the respective second legs 47a of the spring clutches 39a,b.

The mechanism of the damper of Figures 8 to 12 may be used in a fire damper similar to the fire damper shown in Figures 6 and 7.

Various modifications will be apparent to those in the art and it is desired to include all such modifications as fall within the scope of the accompanying claims.

The air balancing damper described above may be adapted to operate as a volume control damper by adapting the blade and rim so that when the damper is closed the blade seals against the rim. A sealing blade and rim arrangement is described in GB-A-23 69571, the contents of which are incorporated herein by reference.

The damper and blade may have a cross-section other than circular, for example a square, rectangular or oval cross-section, to match the shape of the ducting of the rest of the ventilation system of which the damper forms a constituent part. The damper may comprise a plurality of blades which operate together.

The slot 53 in the clutch housing 37 of the first two embodiments may have a shape other than S-shaped. For example the slot may be C-shaped, i.e., the foot and head slot portions may be on the same longitudinal side of the body slot portion, or the slot may be substantially straight and have protrusions towards its end to act as engagement points for the legs 43, 47 of the spring clutch 39. The purpose of the S-shaped slot is to provide engagement points for the legs of the spring clutch and the skilled person will understand that there are other arrangements for providing engagement points for the legs. Similarly, the slot 53a in the clutch housing 37a of the third embodiment may have a shape other than Z-shaped.

In the embodiments described above the spring clutches 39, 39a, 39b are arranged such that when the legs 43, 47, 47a are moved away from each other the inner diameter of the coiled portion 41 decreases. In other embodiments the spring clutches may be arranged so that when the legs 43, 47, 47a are moved away from each other the inner diameter of the coiled portion 41 increases.

The spring clutches 39, 39a, 39b described above are made of a bent wire having a round cross-section. Wire of other cross sections, such as square cross-section, may be used to form the spring clutch. If a wire have a square cross section is used then this increases the surface contact area between the spring and the shaft to provide an increases clamping force.

The axle 7 may be comprised of two stub axles rather than a single axle which passes through the channel of the ducting 5. In this arrangement applied to the first embodiment each stub axle would rotate in the openings 13 in the opposed wall portions l5oftherim 17.

In the third embodiment of Figures 8 to 12, two spring clutches 39a,b are used, each spring clutch 39a,b having an anchored leg and a free leg. In other embodiments only a single spring clutch having an anchored leg and a free leg may be used. As described above, moving the free leg alters the diameter of the coiled portion 41 to increase or decrease the grip of the spring clutch on the axle. When only a single spring clutch is used and if the free leg is fixed in place to lock the axle or if two spring clutches are used but only one free leg is fixed in place to lock the axle then it is possible that if a sufficient force is applied to rotate the axle then this force will unwind part of the coiled portion, loosening the grip of the coiled portion and possibly damaging the spring clutch. Therefore, in a preferred embodiment two spring clutches 39a,b are used as shown in the third embodiment described above but a single spring clutch can also be used.

Claims

CLAIMS: 1. A damper comprising: ducting; a blade pivotably mounted in the ducting to regulate flow of fluid through the ducting, the blade being fixed to an axle which pivots in the ducting, a portion of the axle extending through a wall of the ducting; and a first spring clutch mounted on the portion of the axle extending through the wall of the ducting for controlling a position of the blade.
2. A damper as claimed in claim 1, wherein the spring clutch is arranged on the axle to fix the position of the blade.
3. A damper as claimed in claim 1, wherein the spring clutch is arranged on the axle to allow rotation of the blade in one direction and to inhibit rotation of the blade in the other direction.
4. A damper as claimed in claim 1, 2 or 3, further comprising a handle for adjusting the position of the axle and the blade.
5. A damper as claimed in any one of the preceding claims, the first spring clutch comprising: a coiled portion having an inner diameter similar to the diameter of the portion of the axle on which the spring clutch is mounted; a first leg at one axial end of the coiled portion; and a second leg at the other axial end of the coiled portion, wherein relative movement of the first and second legs alters the inner diameter of the coiled portion.
6. A damper as claimed in claim 5, wherein the first leg is fixed in place and the second leg is free to move relative to the first leg.
7. A damper as claimed in claim 6, further comprising a bracket mounted on an outside of the ducting, the axle passing through a first opening in the bracket, the second leg of the spring clutch passing through a second opening in the bracket and the first leg being held in a third opening in the bracket.
8. A damper as claimed in claims 5, 6 or 7, further comprising a second spring clutch similar to the first spring clutch.
9. A damper as claimed in claim 8, wherein the first leg of the second spring clutch is fixed in place and the second leg of the second spring clutch is free to move relative to the first leg of the second spring clutch.
10. A damper as claimed in claim 9 when dependent on claim 7, wherein the second leg of the second spring clutch passes through the second opening in the bracket and the first leg of the second spring clutch is fixed in the third or a fourth opening in the bracket.
11. A damper as claimed in claim 5, wherein the first and second legs are free to move relative to the rest of the damper.
12. A damper as claimed in claim 11, further comprising a bracket mounted on an outside of the ducting, the axle passing through a first opening in the bracket and the legs of the spring clutch passing through a second opening in the bracket.
13. A damper as claimed in any one of claims 5 to 12, wherein when the or each spring clutch is untensioned the coiled portion grips the portion of the axle on which the spring clutch is mounted.
14. A damper as claimed in any one of claims 5 to 12, wherein when the or each spring clutch is untensioned the inner diameter of the coiled portion is greater than the diameter of the portion of the axle on which the spring clutch is mounted.
15. A damper as claimed in any one of claims 5 to 14, wherein movement of the second leg towards the first leg increases the inner diameter of the coiled portion and movement of the second leg away from the first leg decreases the inner diameter of the coiled portion.
16. A damper as claimed in any one of claims 5 to 14, wherein movement of the second leg towards the first leg decreases the inner diameter of the coiled portion and movement of the second leg away from the first leg increases the inner diameter of the coiled portion.
17. A damper as claimed in any one of claims 5 to 16, further comprising catch means for restraining the free to move leg or legs.
18. A damper as claimed in claim 17 when directly or indirectly dependent on any one of claims 7, 10 and 12, wherein the second opening comprises the catch means.
19. A damper as claimed in claim 18, wherein the second opening comprises a slot having corners constituting the catch means.
20. A damper as claimed in claim 19, wherein the second opening is a Z-shaped slot.
21. A damper as claimed in claim 19, wherein the second opening is an S-shaped slot.
22. An air balancing damper comprising the damper as claimed in any one of the preceding claims.
23. A volume control damper comprising the damper as claimed in any one of the preceding claims, wherein the blade seals the ducting when the blade is in the closed p*sition.
24. A fire damper comprising the damper as claimed in claim and further comprising: biasing means for biasing the blade to rotate to a closed position, wherein the spring clutch is arranged on the axle to allow the blade to rotate to close the ducting and to inhibit the blade from rotating in the other direction.
25. A balancing damper substantially as hereinbefore described with reference to the Figures ito 5 or Figures 8 to 12.
26. A fire damper substantially as hereinbefore described with reference to Figures 4 to 7.