CA1080022A - Shut-off damper - Google Patents

Abstract

TO ALL WHOM IT MAY CONCERN:
BE IT KNOWN THAT WE, ROBERT JOHN MAGILL, a British Subject, of Blarney House, Kingsdown Park, Tankerton, Whitestable, Kent, England, and SYDNEY JAMES FIELD, a British Subject, of 5 the Street, Hothfield, Ashford, Kent, England, have invented a certain new and useful "SHUT-OFF DAMPER"
of which the following is a specification:-ABSTRACT OF THE DISCLOSURE
A shut-off damper having blades of a generally stream-lined shape with the trailing edges of the blades comprising fluid sealing means extending along those edges so that a seal is formed between adjacent blades when the blades are in their closed positions.

Description

~r -` - ~0~30~22 ~ his invention relates to shut-o~f damper~, that is to say, dampers which are used to allow the flow of air through a duct or, in their closed position, to shut off o~ stop that flow completely. More specifically, the in~ention relates to shut-o~f dampers of the kind comprieing a li~e o~ blade~ which can be swung about parallel æes to open or close an opening in a frame supporting the blades, the frame being adapted to be mounted in an air duct. ~he~low of air through the frame can thus be varied by varying the angle through which the blades æ e rotated. -In some shut-off damper~ of this general con~truction, the blades are linked together in such a way that they all move in uni~on with eaoh other and alway~ in the same direction or ~en~e as ea¢h other. In other shut-of~ dampers, the linkage between the blades is such that pairs of blades ~o~e towards and ;l awa~ from each other as the blades are rotated about their respec-tive a~e30 In other word~, adjacent blades move in opposite senses or direction~ to each other. ~he effect however in both forms of damper i9 the same, namely, that swinging movement of the blades about their axes moves them either towards their closed position or towards their open po~ition.
~ he presen~ invention i9 primarily concerned with a shut-o~ damper of the second type mentioned above, iOe., it has pair~ of blades which mo~e towards and away from each other. It is to be understood, howe~er, that the i~ention can also be applied to the fir t ~orm of construction in which the blades move always in the same direction .~nd sense as each other.
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From one aspect, the present invention is directed to a shut-off damper comprising a hollow metal frame defining an opening for the passage of fluid therethrough9 a line of hollow, sheet-steel, aerofoil-section, open-ended blades arranged in said opening of said frame with each blade having a leading edge and a trailing edge, a plurality of blade bearing components, one at each end of each blade, to support the blades on said frame for rotation about parallel axes extending longitudinally of the blades, said blades being swingable about said axes to open and close the said opening in the frame, a shaft on each blade bearing component and a respective aperture in said frame to rotatably receive said shaft, an intermediate flange on each blade bearing comp~nent, a surface on said ~lange opposing the adjacent open end of the respective blade, a spigot projecting from said flange ~urface and shaped in cross-3ection to enter the ~aid adjacent open end of the blade and to support that end of the blade for rotation about the longi-tudinal axes of the blade, a pair of spaced~art flange-like ridges projecting from said flange surface of said blade bearing component to snugly receive the extreme end-portion of the blade between them9 the ridges being in sealing contact with said extreme end portion to give additional support to the blade end and to provide a seal at the blade end, a plurality of ro-tary elements, one for each blade, keyed onto the blade bearing components at one side of said frame ~or the purpose of ef~ecting swinging movement of the blades about their parallel axe~, the said rotary elementæ being rotatable in unison to cause corresponding swinging movement of the blades between their fully-open and fully-closed positions, and fludid sealing means extending along the tralling edge of each blade whereby a seal is formed between adjacent blades when - .- . , ............. . . , , . . . . :
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, ~ ~0E~0(~2 the blades are in their closed positions, said trailing edge sealing means comprising a compressible sealing member faætened . to the trailing edge of the respective blade, there also being additional fluid sealing means interposed between the flange on ` each blade bearing component and the said frame.
From another aspect9 the invention is also directed to a shut-off damper comprising a hollow metal frame defining an opening for the passage of fluid therethrough, a line of hollow, sheet-steel, aerofoil-section, open-ended blades arranged in said opening of said frame with each blade having a leading edge and a trailing edge, a plurality of` blade bear-ing components, one at each end of each blade, to support the blades on said frames for rotation about parallel axes extend-; i.ng longitudinally to the blades, said blades being swingable about ~aid axes to open and close the said openlng in the frame, a sha~t on each blade bearlng component and a respective aperture in said frame to rotatably receive said shaft, an : intermediate flange on each blade bearing component, a surface on said flange opposing the adjacent open end of the respective blade, a pair of spaced-apart flange-like ridges projecting .
from said flange surface of said blade bearing component to snugly receive the extreme end-portion of the blade between :.
them, the ridges being in sealing contact with said extreme end-portion to provide a seal at -the blade end, a plurality of rotary elements, one for each blade, keyed onto the blade bear-ing components at one side of said frame for the purpose of effecting swinging movement of the blades about their parallel axe~, the said rotary elements being rotatable in unison to cause corresponding swinging movement of the blades between their fully-open and fully-closed positions, and fluid sealing means ,: . . ~ , . , - ,, ., :
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extending along the trailing edge of each blade whereby a seal is formed between adjacent blades when the blades are in their closed positions, said trailing edge sealing means comprising a compressible sealing member fastened to the trailing edge of the respective blade, there also being additional fluid sealing - means interposed between the flange on each blade bearing component and the said frame.
Some examples of shut~off dampers in accordance w~th the invention are shown in the accompanying drawings, in which :-Figure 1 is a perspective view of one form of shut-off damper with a small portion shown in section;
Figure 2 is an exploded view in perspective of paxt of the shut-o~f damper ~hown in Figure l;
Figure 3 i9 an enlarged si.de view o~ a bearing com-ponent for supporting an end o~` a blade;
Figure 4 i~ a ~ection taken on the lineIV-IV in ~igure 3;
Figure 5 is an end view of the bearing component as seen from the line V-V in Figure 3;
Figure 6 is a section taken on the line VI-VI in ~igure 5;
Figures 7 and 8 are enlarged diagrammatic sectional views showing the blades in their open and closed position~
respectively;
Figure 9 is a greatly-enlarged section through the : trailing edge portion of one of-the blades of the damper;
~: Figure 10 is a sectional view, on a reduced scale, showing the damper of Figure 1 mounted in an air duct;
,r Figureg 11~ 12 and 13 are views corresponding to Figures 1, 2 and 10 of a second form of shut-off damper; :
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Fig~re 14 is a perspective view illu~trating a modi~ica- -~
tion to the damper of ~igure~ 11 and 12; ænd ~ igures 15-19 illustrate ~ive ~urther alterna~ive ~orms of sealing mean3 provided on the traili~.g edge~ c~ de~
~ he ~hut-off damper shown in ~igures 1 and 2 comprises a roll-formed galvani~ed sheet steel outer ~rame 10 o~ girder ~.
section and a sheet steel inner frame 12. ~he outer frame 10 - has continuously-welded corners and has elongated holes 14 punehed in it to permit the damper to be bolted to the flanges of a~ air duct and to be adju~ted for height on tho~e ~langes. ~e attach-ment by welding, bolting, rivetting or other means o~ the ~nner and outer ~rames together prod~ces a double-skin air-tight oasing o~ high rigidity and substantial strength.
As will be see~ from ~igure 2, the in~er frame 12 has a series o~ holes 16 punohed in its two vertioal ~ides, the punching operation being ~uoh that the holes 16 have a length greater than the actual thiokness of the metal. ~he holes 16 serve to support the shafts 18 o~ blade bearing oomponent3 19 which fit into and onto the ope~ ends of blades 20 wh~oh are thus mounted for rot2-tion in the frame about parallel aæes. ~he blade3 20 are low- :.
profile aspeot ratio aerofoil stainless steel blades to provide low re~istance to air or other gaseous fluid flowing through the d~mper, especially when the blades are in their ~ully open posit-ions (i.e~, the posltions o~ the blade~ shown in ~igure 1 of the ~.
dra~hng~ he aerofoil ~ecti~n of the blades also reduces tur~
bulence and ~oise a~d provides excellent protection again t corro~ion re~ulting from the presence o~ corroQi~e paxticles in ~ the air stream. Another ad~antage is that the narrow blade w1dth ,: ' e . .:

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readil~ pe~mits the withdrawal o~ the complete damper ~rom a duct, regardless of the positions o~ the blades within the damper casing, without materially disturbing the ~low o~ alr through the duct ~rame as a whole~
Rotation of the blades 20 about their respective axes can ~-be e~fected either masuall~ or through power-operated mean~. In Figure 2, a masually-rotated control knob 22 mounted on the out-~ide of the outer ~rame 1Q has a ~ha~t 24 ~ixed to it, and this sha~t is provided with a ~mall gear wheel 26 meshing ~ith a larger gear wheel 28 on a sha~t 30 to provide a low-torque 4:1 rotation gear. ~hs sha~t 30 passes through a hole 32 in a ba~e-plate 34 attached to the outer ~rame 10. ~he hole 32 is i~ alignment with a hole 35 ~n the outer ~rame 10 so as to permit the keyed end 36 o~ the sha~t 30 to enter a rectangular-section hole 38 in the shaft 18 o~ one of the blade be æing components 19. In 90 doing, the sha~t 30 passes through a gear wheel 40 which is keyed on to the same sha~t 18. Each blade has a re~pective gear wheel 42 o~ the same diameter and co~struction as the said gear l~heel 40, the ge æ
wheels 42 and the gear wheel 40 being arranged in meshing engage-ment a~d disposed in a line vertically of the damper.
By making the sha~t 30 longer, a~ shown at 30a, an hydraulic, pneumatic, electric or electro-magnetic motor (not shown) ma~ be connected to the shaft so as to turn it. Remote control o~ the blade~ then becomes possible.
It will there~ore be seen that, by rotating -the knob 22 to rotate the gear wheel 26 and thus the gear wheel 28, or, alte~nat-ively, by actuating a motor coupled to the shaft 30, the sha~t 30 - :lQ8~ 2 will be made to rota~e the particular blade 20 to which it is connected as well as the gear wheel 40. Rotation of the gear wheel 40 will cause rotation of all the gear wheels 42 so that all the blades 20 will move together about their respective a~es.
However, alternate gear wheels 40, 42 will rotate in opposite senses so that adjacent pa~rs o~ blades will likewi~e rotate in opposite senses or directions to open or close the central pa~sage through the damper according to which way the shaft 30 is rotated.
In order to lock the blades in a selected setting ~rhere rotation o~ the shaft 30 is ef~ected ma~ually, a c~li~drical locking nut 44 is provided on the sha~t 24 which carries a screw-thre~d 46 fox this purpose. A window 48 is also provided ad~acent the knob 22 on the co~er plate 50 80 that the setting o~ the blades betwee~ their ~ully-open and their ~ully-closed positions can be obsexved. ~here rotation of the 3ha~t 30 i9 e~ected by a motor, the latter ca~ be provided with suitable locking means to lock the sha~t. ~lso, visual indicat~ng means can be associated with a moving part o~ the motor to indicate the positions of the blades.
In order that the v æ ious gears a~d bearings may be quiet in operation and ha~e high strength, low weight and long li~e wlth sel~-lubricating properties~ the gear wheels and bearings are pre~erabl~ all made o~ a sel~-lubricating synthetic plastics material such as mol~bdenum disulphide-impregnated nylon or poly-e~ter. Such gear wheels and bearings can be precision-moulded and are then totally enclosed and completely shut o~f from the ai~
stream thro~gh the damper by the outer and inner ~rames 10 and 12.
~hi~ e~sures that the gear wheels and bearing~ do not become dirty ~A or contaminated~with impurities in the alr stream.

~0~ 22 Figures 3-6 illustrate the detailed construction of the blade be æing components 19 ~hich support the ends of the blades 20. As already described abo~e9 the sha~t 18 of each component 19 has a rectangular-section hole 38 90 that any selected one of the components 19 ca~ be used to receive the keyed end 36 of the sha~t 30. ~he keying of the gear wheels 40 a~d 42 on their respective shaIts 18 is effected by providing each sha~t 18 with two longitud-inally-extending external slots 52 as shown in ~igures 3 and 49 the said gear wheels being pro~ided with internal keys which enter those slot.~ to lock the ge æ wheels against rotation on their shafts.
~ he shaft 18 of each component 19 leads up to an intermediate flange 54 on the component which forms a sur~ace 56 opposing the ad~ac0~t end o~ its respective blade 20. Projecting from that surface 56 of the flange 5~ is a spigot 58 which is specially shaped in cross--section (see ~igure 5) to enter the adjacent open end o the blade 20 and to support that end of the blade for rotation about an axis parallel to the leading and trailing edges o~ the blade~ A pair of ridges 60 and 62 are also formed on the flange 54 of the blade bearing component to receive the egtreme end-portion of the blade between them. ~hese ridges give additional support to the blade Qnd and also give the latter a neat appearance while ha~ing a beneficial sealing e~fect.
As already indicated in the introductory p æ t of the Speci~ication, the shut-off damper of the present invention has been devised to provide low resistance to air flow by the blades, especially when they are i~ their fully-open positions, and, at the same time, to ensure that there is a minimum or negligible "
le~kage of air past the blades when they are in their fully-closed ......... ~.............. . . . ~, ., " .~, .

positions. In this connection, it needs to be borne in mind that shut-off dampers as used in air ducts do not generall~ ha~e to cope with high pressure air but, in the great majority of cases, only with air at comparatively low pressure.
~ o prevent leakage at the longitudinal edges o~ the blades, each blade 20 has fluid sealing means exte~ding along it~ trailing edge so that a good seal is foxmed betwee~ adjacent blades when they are in their closed positions. ~he sealing means and the precise shape o~ the blade trailing edge c~n take various ~orms -as will be seen ~rom the description c~ alternati~e constructions described below - but the pre~erred blade shape ~d seal~ng means is illustrated in ~igures 7 to 9. From these figures it will be ~een that, after the blade has been bent into blade-shape ~rom a ~lat rectangular sheet of stainless steel, it is sealed by being welded, bra~ed, rivetted or otherwise connected alo~g a zone 64 ~see Figure 9) adjacent its ~railing edge~ At the same time, its trailing edge portions 66 and 68 are "opened-out" to ~orm a V-section fish tail portion which is thus adapted to embrace the respective rounded leading edge portions o~ ad~acent blades when the latter are in their closed positions. ~his is illustrated i~
~igure 8. It will be noted that, whereas the "turned-out" trail-ing edge portion 68 i~ entirely straight, the trailing edge portion 66 is straight ~or part o~ its total area and is then curved æ cuately over the remaining part ~or an angul æ distance o~ 60.
~hi~ permitæ the tralling edge portion 68 to conform clo~ely to the rounded leading edge of an a~jacent blade whe~ the blades æ
in their closed position~.
Bonded or otherwise fastened along the trailing edge o~
each blade is a tubular sealing member 70 as ~hown in ~igure 9 : ~ ~ 10 , - . . .
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~ ~ ~0 ~ Z 2 and the fo~r uppexmosl blades in Figures 7 and 8. Alternatively, a solia strip 72 of sealing material as exemplified by the lower-most blade in Figures 7 and 8 c2n be used instead of the tubular sealing member 70. The sealing tube 70 or the sealing strip 72 can be made of neoprene, polyvinyl chloride, foamed synthetic plastics material, or some other rubbe~y or resilient sealing material. ~ecause the sealing tube 70 or the sealing strip 72 is located partially within the V of the fish-tail portion, the tube 70 or the strip 72 will be highly compressed by the leading edge of an adjacent blade when the blades are in the poæitions shown in Figure 80 By this means 7 leakage o~ air at the leading and trailing edges of the blades can be reduced~ in practioe, to a negligible amount.
~ o æeal the leading edge of the uppermost blade 20, a sealing ~trip or tube 7~ of the ~ame mater~al as the tube 70 or the strip 72 is bonded along the upper inner surface of the inner frame 12 as shown in Figure 8. Alternatively, springy metal sealing strips 72a and 73a can be used in place of the sealing strips 72 and 73.
~ he damper illu~trated in ~igure~ 9 is designed to be in-serted in a duct by ha~ing the flanges 74 of the outer casing 10 bolted to corresponding flanges 76 of the duct by bolts 77 as shown in ~igure 10, In other words, the damper is inserted in a "break"
in the duct so that the inner frc~me 12 is substanbially flush with the internal surfaces 78 of the duct. Howe~er, in certain coun-tries - particularly the United States of America - it is customary to position dampers entirely within a duct. Figures 11 and 12 illustrate a damper having a frame 80 ~hich permits this to be done. ~he frame 80 iæ, in effect, the 3ame as the inner ~rame 12 in ~ig~lre 2 except that the frame 80 has .
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~L0800Z2 flanges 82 which lie against the inner surface 84 of a duct as shown in ~igure 13a The duct itself therefore form~ an outer frame for the damper so that the outer frame 10 of ~igure 1 is no longer needed. Apart from thi~s e~d the omi~sion of the base-plate 34 shown in ~igure 2 7 the damper shown in Figures 11 and 12 is essentially the same as that shown in Figures 1-97 and the same reference numerals have been applied to like parts.
Figure 14 illustrates a small modification to the damper shown in Figures 11 and 12 in that the cover plate 50 is designed to be screwed or bolted to the inside or outsiae of a duct 86, the cover plate having a pair of flanges 88 with bolt or screw holes 90 in it to permit this to be done. A small window 92 is cut in the wall of the duct 86 to allow the shafts 24 and/or 30a to pro-ject through that wall and thus enter.the cover plate 50. Screw or bolt holes 9~ are also provided in the duct wall to match the holes 90 in the ~langes 88.
In order to strengthen the inner frame 12 of Figure 2 and the frame 80 of ~igures 12 and 13, I-shaped metal corner pieees 96 are welded 7 rivetted or otherwise fixed to the corners of those ~rames .
Figures 15 to 19 illustrate alternati~e forms of blade 20 and alternative trailing edge sealing means in accordance wlth the invention, and these will now be described.
In Figure 15, the trailing edge o~ the blade 20 is formed by the two edge portions 98 and iO0, the edge portion 100 being ~ormed by doubling over the extreme edge o~ the blade O ~he two edge portions 98 and 100 nip between them a root portion 102 of a sealing strip 104 fo~med of neoprene or other rubbery sealing ' , . 1 ~
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materialO The said sealing strip has a well-rounded external surface 106 which faces away ~rom the metal trailing edge o~
the bl~de, and from this 3urface 106 there e~tend~ two webs i08 and 110, one on each side of the blade, so as to provide a smooth stream-lined surface with the metal portion of the blade 20~ .
~ he sealing strip shown at 112 in ~igure 16 has a stem 102 like that shown in Figure 15 ~ut is here formed with a circular-section portion 114. ~his construction is not there~ore ~o stream-lined as the ~ealing ~trip shown in ~igure 15 with itq lateral webs 108 and 110.
~ igure 17 illustrates another alternative in which the metal portion of the blade 20 is formed with a flat trailing edge ~ace 116 which has, bonded to it, the flat face of a DL
section hollow 3ealing strip 118.
~ igure 18 shows a blade 20 ha~ing an edge portion 120 which is be~t over so as to lie ~lat against the outer ~urface o~ the edge portion 122, the two overlapping portions being spot welded at regular points along the length of the blade. ~he sealing means at the trailing edge of the blade compri~e a ~trip 12~ of ~lexible neoprene or other rubbery sealing material whlch has been folded over in a C~shape and removably held on the trailing edge portlon o~ the metal blade 20 by a C-section springy metal clip 126. ~he longitudinal edge~ of this clip 126 are bent back at 128 and 130 80 as to nip the longitudinal edge portions 132 ~nd 134 of the se~1ing strip.
It has been found that the existence o~ the small shoulder 136 formed by the tur.ned-over edge portion 120 of the metal blade J~
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is suf~icient to prevent the clip 126 from coming off the bladeO
~aturally, the spring clip 126 will ha~e su~ficient resilience to grip the blade quite strongl~.
Yet another alternative construction is shown in ~igure 19.
In this case, the sealing strip 124 has its longitudinal edge portions 138 and 140 ~olded under.neath the longitudin~l edge portions 142 and 144 of the spring cli.p 126. A further di~fer- ..
ence is that the said edge portions of the spring clip 126 æ e located inwaxdly of the strip 124 and not externally o~ it as i~ ~igure 18.
In order tha~ air may not leak round the ends of the blades when they æe in their ~ully-closed posi-tions, sealing strip~ or pad~ 146 made o~ felt or other ~eallng material are provided on the blade bearing component~ as ~hown in ~igure~ 3 5 and 6.
~ he extent to which the blades cc~n be rotated about their respective axes can be va~ied to suit the requirements of di~fe =
ent customers. ~ormally they will be rotatable through ~0 to provide for maxlmum ~lexibility in use.

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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows :-

1. A shut-off damper for shutting-off the flow of gaseous fluid through a duct, said damper comprising: a hollow metal frame defining an opening for the passage of fluid therethrough, a line of hollow, sheet-steel, aerofoil-section, open-ended blades arranged in said opening of said frame with each blade having a leading edge and a trailing edge, a plurality of blade bearing components, one at each end of each blade, to support the blades on said frame for rotation about parallel axes ex-tending longitudinally of the blades, said blades being swing-able about said axes to open and close the said opening in the frame, a shaft on each blade bearing component and a respective aperture in said frame to rotatably receive said shaft, an intermediate flange on each blade bearing component, a surface on said flange opposing the adjacent open end of the respective blade, a spigot projecting from said flange surface and shaped in cross-section to enter the said adjacent open end of the blade and to support that end of the blade for rotation about the longitudinal axis of the blade, a pair of spaced-apart flange-like ridges projecting from said flange surface of said blade bearing component to snugly receive the extreme end-portion of the blade between them, the ridges being in sealing contact with said extreme end portion to give additional support to the blade end and to provide a seal at the blade end, a plurality of rotary elements, one for each blade, keyed onto the blade bearing components at one side of said frame for the purpose of effecting swinging movement of the blades about their parallel axes, the said rotary elements being rotatable in unison to cause corresponding swinging movement of the blades between their fully-open and fully-closed positions, and fluid sealing means extending along the trailing edge of each blade whereby a seal is formed between adjacent blades when the blades are in their closed positions, said trailing edge seal-ing means comprising a compressible sealing member fastened to the trailing edge of the respective blade, there also being additional fluid sealing means interposed between the flange on each blade bearing component and the said frame.

2. A shut-off damper according to claim 1, wherein the blade bearing components are made of a self-lubricating synthetic plastics material.

3. A shut-off damper according to claim 1, wherein said additional sealing means are carried on the blade bearing components.

4. A shut-off damper according to claim 1, wherein locking means are provided on the damper to lock the blades in a selected setting.

5. A shut-off damper according to claim 1, wherein the frame has flanges adapted to lie against the inner surface of a duct after the damper has been positioned entirely within the duct.

6. A shut-off damper according to claim 1, wherein said additional sealing means are in the form of sealing strips.

7. A shut-off damper for shutting-off the flow of gaseous fluid through a duct, said damper comprising: a hollow metal frame defining an opening for the passage of fluid therethrough, a line of hollow, sheet-steel, aerofoil-section, open-ended blades arranged in said opening of said frame with each blade having a leading edge and a trailing edge, a plurality of blade bearing components, one at each end of each blade, to support the blades on said frames for rotation about parallel axes extending longitudinally to the blades, said blades being swingable about said axes to open and close the said opening in the frame, a shaft on each blade bearing component and a res-pective aperture in said frame to rotatably receive said shaft, an intermediate flange on each blade bearing component, a surface on said flange opposing the adjacent open end of the respective blade, a pair of spaced-apart flange-like ridges projecting from said flange surface of said blade bearing com-ponent to snugly receive the extreme end-portion of the blade between them, the ridges being in sealing contact with said extreme end-portion to provide a seal at the blade end, a plurality of rotary elements, one for each blade, keyed onto the blade bearing components at one side of said frame for the purpose of effecting swinging movement of the blades about their parallel axes, the said rotary elements being rotatable in unison to cause corresponding swinging movement of the blades between their fully-open and fully-closed positions, and fluid sealing means extending along the trailing edge of each blade whereby a seal is formed between adjacent blades when the blades are in their closed positions, said trailing edge sealing means comprising a compressible sealing member fastened to the trailing edge of the respective blade, there also being additional fluid sealing means interposed between the flange on each blade bearing component and the said frame.

8. A shut-off damper according to claim 7, wherein the blade bearing components are made of a self-lubricating syn-thetic plastics material.

9. A shut-off damper according to claim 7, wherein said additional sealing means are carried on the blade bearing components.

10. A shut-off damper according to claim 7, wherein locking means are provided on the damper to lock the blades in a selected setting.

11. A shut-off damper according to claim 7, wherein the frame has flanges adapted to lie against the inner surface of a duct after the damper has been positioned entirely within the duct.

12. A shut-off damper according to claim 7, wherein said additional sealing means are in the form of sealing strips.