GB2375045A

GB2375045A - Fire damper assembly, such as may be located in a duct, with breakable fusible link for emergency closure in response to elevated temperature

Info

Publication number: GB2375045A
Application number: GB0110848A
Authority: GB
Inventors: Keith William Morgan
Original assignee: Advanced Air Technologies Inc
Current assignee: Advanced Air Technologies Inc
Priority date: 2001-05-03
Filing date: 2001-05-03
Publication date: 2002-11-06
Also published as: GB0110848D0

Abstract

A fire damper comprises a casing 10 and a damper blade 12, normally held open by a fusible link mechanism 32, comprising two relatively moveable components, 48, 50, such as flat plates, secured together by a fusible compound, and held within a guide member 44. The guide member 44 permits a controlled smooth sliding separation of the components 48, 50 in the event that a predetermined raised temperature, such as that caused by a fire, melts the fusible compound, allowing springs 16, such as tension coil springs, to close the damper. The fusible compound may be a solder compound. The damper may further include a system including a control box (fig.9) for non destructively disengaging the fusible link mechanism to test the integrity of the closure springs 16. The damper casing 12 may be circular (figs. 4 and 5). The damper may be used in ducting, such as that in a building, or directly in a building wall.

Description

Fire Damper This invention relates to a fire damper and to a mechanism for ensuring that the damper closes in the event of a fire.

Fire dampers are placed in a duct or passage in order to close the duct or passage if a fire breaks out, to thereby prevent air movement and to limit the spread of the fire.

According to the present invention, there is provided a fire damper comprising a casing and a damper blade movable within the casing between a first position where it provides a minimum restriction to air flow through the casing, and a second position where it substantially prevents air flow through the casing, wherein a spring means is provided to move the blade from the first position to the second position, and the blade is normally held in the first position, against the force of the spring means, by a fusible link mechanism, the fusible link mechanism including two relatively movable components normally secured together by a fusible compound, the components being housed within a guide member which guides the components for movement over one another when the fusible compound melts.

The guide member protects the relatively movable components when they are being handled, and ensures that when separation occurs, in the event of a fire, the components move correctly over one another to give the designed release function.

The two components are preferably flat plates which are mounted in overlapping relationship with one another. Preferably they are metal plates and the fusible compound

is a solder compound.

The plates are preferably elongate strips both of which have a securing means at one end. The securing means may be a hole for receiving a bolt or the like. The plates are arranged so that they separate in the direction of

their length.

The fusible link mechanism preferably comprises two arms pivoted to one another. A first of the arms can be mounted on a shaft which is normally held against rotation. The second arm includes the two relatively movable components and their guide member. The second arm is connected between the baffle plate and the first arm.

If the fusible link releases in the event of a fire, the baffle plate is released and is closed by the spring means.

The operation of the springs and baffle plate can however be tested without the fusible link releasing, by allowing the shaft on which the first arm is mounted to rotate. To this end, the shaft can extend to a location externally of the damper, where a peg mounted eccentrically on the shaft impinges on a detent which prevents the shaft from rotating. To test the operation of the damper, the detent is moved to remove the restraint on the shaft which then rotates under the influence of the spring means.

The spring means preferably comprises at least one constant tension spring band, mounted between an edge of the damper blade and a position on the housing beyond the rest position of the blade in the closed position. If the damper has a circular cross section, there may be one such spring band mounted on the point of maximum diameter of the circular damper blade. If the damper has a

rectangular cross section, there may be two spring bands, mounted symmetrically on either side of the damper blade centre line. In any case, the spring band or spring bands are to be mounted so that they do not produce any twisting force on the blade.

The invention will now be further, described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a damper in accordance with the invention, in the open position; Figure 2 is a side view of the damper, with the damper blade open; Figure 3 is a view from in front of the damper; Figures 4 and 5 are views similar to Figures 2 and 3 but showing a damper of circular cross-section; Figure 6 is a cross-section through the damper of Figures 2 and 3 showing the damper blade held in the open position; Figure 7 is a view similar to that of Figure 6, but showing the blade in its closed position, after triggering of the fusible link; Figure 8 is a view similar to Figures 6 and 7, but showing the blade and fusible link mechanism after the blade has been

manually moved to its closed position; Figure 9 is an exploded view of a control box forming part of the damper shown in the preceding Figures; Figure 10 is a perspective view of the fusible link in its normal, assembled condition; and Figure 11 shows the link of Figure 10 after the link has separated as a result of exposure to an elevated temperature.

Figure 1 shows a fire damper for installation in an air ducting system. The damper has a casing 10 and a damper blade 12 which is pivoted at 14. In Figure 1 the damper blade 12 is shown in the open position where it allows air flow through the duct. In the event of a fire however the damper is to move from the fully open position shown in Figure 1 to a fully closed position where it entirely blocks the flow cross section through the casing 10, to hinder the spread of fire.

The blade 12 is a single or multi-layer construction, with at least one of the layers being of insulating material, such as calcium silicate. Intumescent strips may be fitted around the periphery of the blade, to form a seal with the casing if/when the damper closes.

The blade 12 is held in the open position by a linkage connected to a control box 34 (Figure 2), against the force of springs 16 which will close the damper blade when the blade is released by the linkage.

The casing 10 has flanges 18,20 at its opposite faces. These flanges allow the casing to be connected into a ducting system, with the flanges being bolted or otherwise fastened to corresponding flanges in the ducting system.

The casing 10 is to be built into a building wall such that, when the damper blade is closed, there is no communication through the casing from one side of the wall to the other. Figure 2 shows clearly an intermediate flange 22 of the casing which will be built into a wall.

This flange is closed by through bolts 24, each of which is provided with protruding tangs 26 to assist in tying the casing into the structure of a masonry wall. A layer of insulating material such as calcium silicate can be sandwiched in the flange 22, to form a thermal break between the two sides of the casing.

The closure springs 16 are shown more clearly in Figures 2 and 3. There are two springs, each positioned near one end of the blade 12. These springs are constant tension band springs. In their relaxed state, these spring bands coil up around a spindle mounted in a bracket 28. The brackets 28 are securely fixed to the inside of the casing 10, as can be seen in Figure 3 at positions beyond the closed position of the damper blade, and the free end of each band is secured at 30 to a lower edge of the blade 12. When the end of the band is pulled down to the position 30, energy is stored in the spring which is constantly trying to return the blade 12 to its closed position.

The blade is however normally held in an open position by means of a linkage 32 mounted within the casing and acting between the casing 10 and the blade 12. The linkage 32 is under the control of the control box 34. The structure

and operation of this linkage will be shown in more detail in Figures 6,7 and 8.

Figures 4 and 5 show an alternative form of damper which has a circular casing lOa, in place of the rectangular casing 10 shown in Figures 1 to 3. Within the casing lOa is a circular blade 12a, a linkage 32a and a single constant tension spring band 16a. The linkage 32a is under the control of the control box 34. It will be seen that the casing lOa is without flanged ends, reflecting the different way in which such circular casings will be assembled into corresponding circular ducting.

Operation of the rectangular section damper of Figures 1 to 3 and of the circular section damper shown in Figures 4 and 5 is basically similar, and the following description will apply to both.

Figures 6,7 and 8 show a cross section through the damper of Figures 1 to 3, on the line VI-VI from Figure 3.

The linkage 32 which holds the blade 12 in the open position, against the force of the spring 16, has two arms 36 and 38. The arm 36 is rigid and is non-rotatably mounted at one end on a shaft 40 which extends through the side of the casing 10. At the other end, the arm 36 is connected by a pivot 42 to the arm 38.

The arm 38 includes a fusible link at 44.

Under normal operating conditions with the damper open, the shaft 40 is prevented from rotating and thus prevents the arm 36 from rotating. The geometry of the arms 36 and 38 then holds the damper blade in the open position.

The fusible link 44 is shown in more detail in Figures 10 and 11. The arm 38 has a channel section 46 at one end for receiving and guiding two connected plates 48,50.

The plates 48 and 50 overlap with one another and are soldered or brazed together with a material which will melt and release the connection between the two plates at a specified temperature. When the link is assembled the plate 48 will be fixed to the arm 38 by means of a bolt 52 passing through holes in the plate 48 and the arm 38. The end of the plate 50 will be attached directly to a bracket 58 mounted on the damper blade 12, by a bolt 56.

The arm 38 has an aperture in the form of a window 58 to ensure that the area of overlap between the plates 48 and 50 is always exposed to ambient temperature. The bolt 56 is normally received within a cut out region 60 in the arm 38.

When the ambient temperature rises sufficiently high for closure of the damper to be indicated, the solder between the plates 48 and 50 melts thus releasing the blade 12 from the linkage 32. The springs 16 then retract (Figure 7) and the blade moves to its closed position. In its closed position, the blade seats against landing strips 62,64 which are fixed on the internal faces of the casing 10.

Dampers of this type have to be tested periodically, and it is necessary to ensure that the damper blade will reliably move to its closed position once the holding effect of the linkage 32 is removed, but without needing to activate (and thus destroy) the fusible link 44.

To do this, rotary restraint is removed from the shaft 40 which can then rotate freely, and the damper blade and the

linkage will move to take up the positions shown in Figure 8. Once this testing has been carried out satisfactorily, the damper can be reset.

The shaft 40 is under the control of the control box 34 which is shown in more detail in Figure 9. The control box has a base plate 62 and a cover 64. The base plate 62 is fixed to an external surface of the casing 10, at the position where the shaft 40 passes through that casing.

The shaft 40 passes through the base plate 62 and is fitted with a radially extending peg 66, and a hexagonal head recess 68.

A release plate 70 is mounted on two columns 72 and is held at the top of these columns by coil springs 74 surrounding the columns. In its normal position, the release plate 70 is held parallel to the base plate 62, in a position where an edge 76 of the plate registers with the peg 66, to prevent the shaft 40 from rotating in a clockwise direction. A lever 78 is fitted and welded into a recess 80 in the plate 70.

To carry out a testing operation, the top end of the lever 78 is pushed away from the shaft 40. This causes the release plate 70 to capsize so that the peg 66 can rotate past the edge 76. The damper blade will then move into the closed position (see Figure 8) to complete a testing operation. When the force on the lever 78 is released, the plate 70 will return to its normal position, and the damper can be moved back to its normal position by engaging a suitable tool with the hexagonal recess 68 and manually rotating the shaft 40 back to its original position when it will snap into place behind the edge 76.

The cover 64 fits over the base plate 62 and normally

conceals the internal components. The hexagonal recess 68 is accessible through an opening 82, and the lever 78 is accessible through an elongate opening 84 which allows the lever to be tipped away from the shaft 40.

The base plate 62 also carries an indicator post 86 linked to an indicator pointer 88 on the outside of the casing 64. The post 86 is fixed to a linkage (not shown) which is connected to the blade and which moves as the blade moves. The post 86 is rotated by the linkage when the blade moves, so that the indicator pointer 88 provides an external indication of the position of the blade, ie whether it is in the open or the closed position.

The release plate 70 is symmetrical and has an edge corresponding to the edge 76 on the opposite side, so that the shaft 40 with its peg 66 can be held either against clockwise rotation or against counter-clockwise rotation.

This means that the control box is non-handed and can be mounted on either side of the damper.

The use of a fusible link which separates in a longitudinal direction, and the use of a channel in which the two halves of the link are guided offers significant advantages.

Because the fusible link is separate from the control box, it is easy to replace if this becomes necessary, either because the damper has closed after being subjected to a high temperature, or because the link needs to be replaced, for example with a link rated at a different temperature.

The tension band springs are positioned symmetrically on the damper blade so that the blade is uniformly loaded by

the spring force and is not subjected to any twisting forces.

Although the invention has been described with reference to a single blade damper, the principles of the invention can also be applied to a damper with multiple damper

blades, and a man skilled in the art will understand how i this could be done.

Claims

Claims 1. A fire damper comprising a casing and a damper blade movable within the casing between a first position where it provides a minimum restriction to air flow through the casing, and a second position where it substantially prevents air flow through the casing, wherein a spring means is provided to move the blade from the first position to the second position, and the blade is normally held in the first position, against the force of the spring means, by a fusible link mechanism, the fusible link mechanism including two relatively movable components normally secured together by a fusible compound, the components being housed within a guide member which guides the components for movement over one another when the fusible compound melts.
2. A fire damper as claimed in Claim 1, wherein the two components are flat plates which are mounted in overlapping relationship with one another.
3. A fire damper as claimed in Claim 2, wherein the plates are metal plates and the fusible compound is a solder compound.
4. A fire damper as claimed in Claim 2 or Claim 3, wherein the plates are elongate strips both of which have a securing means at one end.
5. A fire damper as claimed in Claim 4, wherein the securing means is a hole for receiving a bolt or the like.
6. A fire damper as claimed in Claim 4 or Claim 5, wherein the plates are arranged so that when they separate on being subjected to a high temperature, they do so in

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the direction of their length.
7. A fire damper as claimed in any preceding claim, wherein the fusible link mechanism comprises two arms pivoted to one another with a first of the arms being mounted on a shaft which is normally held against rotation and the second arm being connected between the blade and the first arm and including the two relatively movable components and their guide member.
8. A fire damper as claimed in Claim 7, wherein the shaft extends to a location externally of the damper, and a peg mounted eccentrically on the shaft impinges on a detent which prevents the shaft from rotating.
9. A fire damper as claimed in any preceding claim, wherein the spring means comprises at least one constant tension spring band, mounted between an edge of the damper blade and a position on the housing beyond the rest position of the blade in the closed position.
10. A fire damper as claimed in Claim 9, wherein the damper has a circular cross section, and one such spring band is mounted on the point of maximum diameter of the circular damper blade.
11. A fire damper as claimed in Claim 9, wherein the damper has a rectangular cross section, there two spring bands are mounted symmetrically on either side of the damper blade centre line.
12. A fire damper as claimed in any preceding claim, wherein the spring means is mounted so that it does not produce any twisting force on the blade.

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13. A fire damper substantially as herein described with reference to any one embodiment shown in the accompanying drawings.