referring to the drawings in general and to fig1 and 2 in particular a smoke damper is designated generally 10 and has a base 16 , a top 18 and upstanding first and second side frame members 20 , 22 . mounted within smoke damper 10 are a plurality of smoke damper blades designated generally 12 . smoke damper blades 12 are pivotally mounted via suitable bearings or other fittings , which are designated generally 24 and shown only schematically in the drawings , for pivotal rotation of blades 12 respecting first and second side frame members 20 , 22 . blades 12 are rotatable about pivotal mounts 24 from a position at which the blades are essentially parallel one with another , illustrated in fig1 defining an &# 34 ; open &# 34 ; position of smoke damper 10 , to a position at which blades 12 are substantially co - planar one with another , defining a &# 34 ; closed &# 34 ; position of smoke damper 10 , illustrated in fig2 . conventionally , some means is provided to rotate smoke damper blades 12 to open and to close smoke damper 10 as required ; the means for moving smoke damper blades 12 has been illustrated schematically in fig1 and is designated generally 26 . as illustrated schematically in fig1 means 26 for moving smoke damper blades 12 includes a plurality of shafts 28 connected to blades 12 via pivotal mounts 24 . shafts 28 are rotated by a suitable chain , designated generally 30 and shown only schematically in fig1 . chain 30 is driven along a track of suitable shape and size by a motor designated schematically 32 in fig1 . motor 32 may be actuated by a smoke sensor or detector illustrated schematically and designated 34 in fig1 . all of the above - described structure , as illustrated in fig1 and 2 , is conventional and well - known in the art . typically , smoke dampers as designated generally 10 are constructed of galvanized steel , to be rugged and to withstand high temperature environments as may be experienced when fires break out . smoke dampers of the type designated generally 10 are installed within heating , ventilating and air - conditioning ducts in buildings to prevent the spread of smoke throughout a building when a fire breaks out . typically , smoke detector 34 detects presence of smoke , actuates motor 32 and causes smoke damper 10 to close , with blades 12 moving from the position illustrated in fig1 to the position illustrated in fig2 . fig3 illustrates a smoke damper blade 12 , in section . in this regard , in fig1 directional arrow l indicates the longitudinal direction respecting a smoke damper blade 12 . the transverse section illustrated in fig3 is , of course , taken perpendicularly to the longitudinal direction illustrated in fig1 and indicated by arrow l . sectioning lines have been omitted from fig3 to aid drawing clarity . still referring to fig3 a smoke damper blade designated generally 12 has , at its right - hand edge illustrated in fig3 a receptacle formed therein where the receptacle is designated generally 37 and is formed in a shape so that the open mouth portion 36 of receptacle 37 faces generally along the plane within which the major portion of smoke damper blade 12 substantially lies . when mouth 36 and receptacle 37 are fabricated by bending one of the ends of blade 12 , one of the longitudinal extremities of blade 12 into the shape shown generally in fig3 the mouth is positioned so that it opens at an angle of about 12 degrees to the plane within which blade 12 generally lies . this angle is designated generally b in fig3 . the end of blade 12 at which mouth 36 is formed includes a longitudinally extending blade transverse tip 38 , a shortened straight portion indicated generally by bracket 40 , a curved portion defining a closed bottom of mouth 36 where this closed bottom is denoted generally 42 , a second generally straight , shortened portion indicated generally by bracket 44 and two straight portions 46 , 48 positioned substantially at right angles to each other and connected via bend 50 . the concave surface portion of blade 12 defined by inwardly facing surfaces 52 and 54 of straight portions 46 , 48 respectively defines a recess designated generally 56 in fig3 which is proximate to but slightly inwardly removed from the longitudinally extending transverse extremity of blade 12 which is closest to the right - hand side of the paper in fig3 ; this transverse extremity is numbered 58 in fig3 . recess 56 , particularly straight portion 48 forming a bottom portion thereof , joins the central portion of blade 12 , which central portion is designated generally 60 in fig3 . at a second , opposite longitudinally extending transverse extremity designated generally 62 in fig3 blade 12 is bent to have two sections 64 , 66 preferably disposed generally at right angles respecting one another . inwardly facing surfaces of bent portions 64 , 66 are numbered 68 , 70 in fig3 while the longitudinally extending , transversely extreme left - hand facing end surface of blade 12 is numbered 72 in fig3 . surface 72 is preferably substantially perpendicular to surface 68 and , therefore , substantially parallel with surface 70 . surfaces 68 , 70 are formed by bending blade 12 and are formed from a surface portion of blade 12 which faces generally in the direction indicated by arrow i in fig3 while surfaces 52 , 54 and the surfaces defining the inner portion of receptacle 37 are formed generally of a larger surface portion of blade 12 which faces generally in the direction of arrow ii in fig3 . bent portions , 64 , 66 are preferably of substantially the same length so that longitudinally extending transverse tip 72 of blade 12 lies generally in the plane in which the major portion of blade 12 lies . this plane is indicated generally by dotted line p in fig3 ; the geometry is also clearly illustrated in fig6 . portions 46 , 48 are bent in a manner that portion 48 is preferably slightly longer than is portion 46 . this geometry and fabrication is desirable so that the center line of receptacle 37 is essentially within plane p when a bayonet - shaped gasket is inserted into receptacle 37 and shortened portion 40 is bent in a manner to reduce angle b from approximately 12 degrees to 0 degrees , thereby clamping the bayonet - shaped gasket within receptacle 37 . the shortened length of portion 46 relative to portion 48 results in receptacle 37 , when closed about the bayonet - shaped gasket , aligning the gasket essentially in plane p . this is illustrated in fig5 . referring to fig4 the bayonet - shaped gasket is designated generally 14 . gasket 14 includes a hilt 74 , a handle 76 and a saber portion 78 . gasket 14 is preferably silicon rubber , to withstand high temperature environments in fire conditions . saber portion 78 is sufficiently thin in dimension , as designated by double - ended arrow t in fig4 to flex in response to relatively light air pressures and resulting forces . in the preferred embodiment of the invention , saber portion 78 has thickness indicated generally by dimension t of 0 . 062 inches , as illustrated in fig8 . in the preferred embodiment of the invention , gasket 14 further includes a cord member 80 , preferably manufactured of kevlar , a high strength polyamide material manufactured by dupont , of about 0 . 025 inches diameter ; gasket 14 is extruded with cord 80 in place . in the preferred embodiment of the invention , gasket 14 is preferably about 3 / 4 of an inch in length ; this is indicated by dimension d in fig4 . saber portion 78 is preferably about 0 . 42 inches in length and has a rounded , slightly tapered tip as indicated by 82 in fig4 . still referring principally to fig4 gasket 14 when extruded has the shape substantially as illustrated in solid lines in fig4 . however , because the rubber is warm when it emerges from the extruder and the gasket is on its side when conveyed away from the extruder head to cool , resting on planar surface of the conveyor designated generally by the line g in fig4 as gasket 14 cools , it assumes a shape or a set as indicated by dotted line s in fig4 whereby the tip portion 82 of gasket 14 is no longer aligned with the gasket center line but is displaced therefrom , as illustrated in dotted lines in fig4 . this is advantageous to the seal of the invention , as described below . the surface of the conveyor carrying gasket 14 after gasket 14 exits the die , and on which gasket 14 lies as it cools is designated schematically by line g in fig4 . fig5 illustrates three separate gaskets 14 installed in receptacles 37 of blades 12 in a smoke damper according to the invention . smoke damper blades 12 have been broken for purposes of clarity in the drawing . fig5 illustrates a portion of the smoke damper of the invention in the closed position , as represented generally by the smoke damper illustrated in fig2 . to open the smoke damper , blades 12 are rotated in the directions indicated by arrows m in fig5 . as illustrated in fig5 bayonet - shaped gaskets 14 are secured within receptacles 37 of blades 12 by having shortened portions 38 bent against handle portions 76 of gaskets 14 , to reduce angle b in fig3 from the approximate 12 degrees at which blade 12 is fabricated to 0 degrees . with this construction and the geometry of receptacle 37 and the end of blade 12 illustrated in detail in fig3 and 7 , bayonet - shaped gasket 14 assumes the position at which its center line ( without deformation or any &# 34 ; set &# 34 ;) is essentially within the plane p of the major portion of blade 12 . this is illustrated in fig5 . as depicted generally at the center of fig5 bayonet - shaped gasket 14 &# 39 ; is positioned so that its saber 78 &# 39 ; is essentially coplanar with the major portion of blade 12 . blade 14 is configured such that the length of saber portion 78 , indicated generally by dimensional arrows f in fig4 is slightly shorter than the distance , illustrated by dimensional arrows h in fig3 from the beginning of recess 56 ( which is defined by juncture of central portion 60 of blade 12 and straight portion 48 ) to blade tip 38 . because distance f , namely the length of saber portion 78 of gasket 14 , is slightly less than distance h , namely the transversely extending length of longitudinally extending recess 84 in fig3 a slight gap or mouth , indicated generally 86 at the central portion of fig5 results between tip 82 of gasket 14 and juncture of straight portion 48 and central portion 60 where such juncture has been designated generally as vertex 88 in fig3 . this is also apparent from fig6 and 8 . presence of mouth 86 permits air , moving in the direction indicated by the arrow labeled &# 34 ; air &# 34 ; in fig5 to enter mouth 86 as generally illustrated by the curly arrow &# 34 ; a &# 34 ; in fig5 . as the air encounters surfaces 52 and 54 defining recess 56 , force from the air results against saber 78 of gasket 14 , as indicated by curly arrow &# 34 ; a &# 34 ; in fig5 . this causes saber portion 78 of gasket 14 to deflect or to balloon slightly , moving into contact with tip 72 , or more tightly contacting tip 72 if saber portion 78 and tip 72 are already in the preferred tangential contact one with another . the movement of saber portion 78 of gasket 14 may manifest itself as some rotational movement of tip 82 of saber portion 78 relative to hilt 74 of gasket 14 , about an apparent center located in the vicinity of juncture of saber portion 78 and hilt 74 of gasket 14 . such rotational movement is indicated schematically by arrow n in fig5 . in any event , action of air filling recess 56 causes this bowing , ballooning , rotation or deflection of saber portion 78 with saber portion 78 moving against tip 72 , creating a tight seal at the point of contact between saber 78 and tip 72 when two adjacent blades 12 of smoke damper 10 are positioned as illustrated in fig5 with their most adjacent longitudinally extending transverse extremities or edges substantially contiguous one with another . the property of the bayonet - shaped gasket whereby it may be provided with a slight set or bend as illustrated generally in dotted lines in fig4 may be advantageously used to enhance performance of the seal of the invention . when the bayonet is provided in the bowed or set disposition , it is installed in a position , relative to the smoke damper blades 12 , as illustrated generally by bayonet - shaped gasket portion 14a in fig5 . this is so that the concave surface 90 of saber portion 78 of gasket 14a may contact a respective tip portion 72 ; such contact between a concave gasket surface and a damper blade tip provides an even better seal than contact between a straight or planar surface of the bayonet - shaped gasket 14 and a blade tip 72 . in the preferred embodiment of the invention , blade 12 may be fabricated of 16 gauge galvanized steel . in fabricating the invention , when the bayonet - shaped gasket is inserted into receptacle 37 and shortened portion 40 is bent to secure gasket 14 , shortened portion 40 need only be bent sufficiently to clamp around the handle portion of bayonet - shaped gasket 14 to retain it in place . because the seal of the invention is fabricated without use of adhesives , no maintenance or replacement of the seal or the gasket is required . smoke dampers according to the invention , when tested , have exhibited substantially improved performance characteristics over smoke dampers known heretofore . one important criteria for evaluating a smoke damper is the amca ( air movement and control association ) specification for damper air leakage . a smoke damper is considered to be a class 1 smoke damper if it provides leakage of 8 or less cubic feet of air per minute , per square foot of smoke damper , at a pressure differential of 4 inches of water across the smoke damper . similarly , a smoke damper is considered to be a class 2 smoke damper if it provides leakage of 20 or less cubic feet of air per minute per square foot of smoke damper , at a pressure differential of 4 inches of water across the smoke damper . prior art smoke dampers , utilizing the various seals described above in the discussion of the prior art , meet the class 2 specification criteria . however , smoke dampers manifesting the invention meet the class 1 specification criteria . during tests , smoke dampers according to the invention have been exposed to high temperature environments of 350 degrees fahrenheit for 30 minutes . when tested after being exposed to such high temperatures , smoke dampers according to the invention have performed without degradation of their seals . in other words , the smoke dampers performed as well , with respect to minimizing air flow through the damper when in the closed position , after being exposed to the high temperature as before being exposed to the high temperature . in life testing , smoke dampers according to the invention have been tested for over one million cycles of opening and closing without any degradation in performance of the damper ; smoke dampers according to the invention have still met the amca class 1 specification after one million cycles of testing . silicon rubber is the preferred material for gasket 14 . silicon rubber is a necessity for use in fire environments because of silicon rubber &# 39 ; s resistance to high temperatures . note that prior to the invention , it has not been generally possible to use silicon rubber as a gasket material for a smoke or fire damper because silicon rubber could not be glued or secured by other adhesives to galvanized steel smoke damper blades . however when utilizing mechanical fixation resulting from the geometry according to the invention , silicon rubber performs admirably . smoke dampers according to the invention have been exposed to falling water and have , surprisingly , been found to provide water - tight seals when the water has been applied to the smoke damper of the invention in the direction indicated by the arrow &# 34 ; air &# 34 ; in fig5 . in one test of a smoke damper according to the invention having blades 8 inches wide in the transverse direction , the smoke damper according to the invention permitted only two and one - half cubic feet per minute of air leakage per square foot of smoke damper at a differential pressure of four inches of water across the smoke damper . the smoke damper seal of the invention is designed so that point or line contact results between the saber portion of gasket 14 and tip 72 of blade 12 when the blades are closed and no air pressure differential exists across the damper . the ballooning effect when air pressure deflects or deforms saber portion 78 of gasket 14 against tip 72 is the principal factor producing the seal . due to dimensional variations , which are unavoidable in the manufacturing process , the desired point or line contact between saber portion 78 of gasket 14 and tip 72 of blade 12 sometimes does not result . even in such circumstances , the seal of the invention functions adequately . hence , there is a certain amount of built - in tolerance for error in the seal design according to the invention . when air flow is in the direction opposite to that indicated by the arrow &# 34 ; air &# 34 ; in fig5 while this is not the direction of airflow for which the invention seal is primarily designed , the invention seal nevertheless results in an amca class 2 smoke damper . another advantage provided by the invention is that in the configuration illustrated in fig5 the invention provides a fire damper as well as a smoke damper . ( a fire damper is one in which there is no &# 34 ; see through &# 34 ; when the gasket or other material at the juncture of contiguous damper blades burns away in a fire .) due to the good performance of smoke dampers embodying the invention when air flows in either direction , smoke dampers according to the invention have increased flexibility over those known heretofore . because gasket 14a is preferably provided in the curved , deformed condition when installed in receptacle 37 , when the smoke damper is closed contact of tip 72 against saber portion 78 deforms the rubber material of saber portion 78 back to an essentially straight condition as manifested by the assembly shown in fig5 . cord 80 is provided as a portion of gasket 14 to prevent gasket 14 from stretching during installation in blade 12 . fig5 at its right - hand side illustrates a seal according to the invention where the gasket contacts a stationary angular member 92 affixed to a portion of the frame of the smoke damper . in the preferred embodiment of the invention , blade portions 46 and 48 are at substantially right angles one to another and are each at 45 degree angles to the plane of the major portion of the blade , indicated as p in fig3 . additionally , blade portions 64 , 66 are preferably at right angles one to another and also at 45 degree angles to plane p . in the preferred embodiment of the invention , blade portion 66 has been about 0 . 68 inches in length while blade portion 64 has been about 0 . 616 inches in length . this results in the unnumbered right angle corner defining juncture of the surface of tip 72 with surface 68 being aligned with the surface of central portion 60 of blade 12 which faces in the direction of ii in fig3 . these details are also shown in fig6 . further respecting the preferred embodiment of the invention , short portions 40 , 44 have preferably been parallel one to another and have each been about 0 . 3 inches in length . receptacle 37 has had transverse width of about 0 . 14 inches while handle portion 76 of gasket 14 has had width of about 0 . 10 inches at its position of maximum width remote from the hilt portion of gasket 14 ; handle portion 76 has tapered at an angle of about 14 1 / 2 degrees from its position of maximum width to contact with hilt 74 . complete dimensional details of the blade and gasket portions of the preferred embodiment of the invention are set forth in fig6 and 8 which illustrate the geometry of the preferred embodiment of the invention . the following table correlates the letter codes given in fig6 and 8 to the dimensional details of the preferred embodiment of the invention : ______________________________________fig6 letter measurement______________________________________6a 45 . 000 ° 6b . 618 inches6d . 660 inches6e . 217 inches6f 2 . 033 inches6g 3 . 040 inches6h 6 . 235 inches6j . 302 inches6k . 456 inches6l . 268 inches6m 2 . 034 inches6n . 680 inches6p 6 . 000 ° 6q 3 . 195 inches______________________________________ ______________________________________fig7 letter measurement______________________________________7a 45 . 000 ° 7b 6 . 000 ° 7c 12 . 000 ° 7d 90 . 000 ° 7e . 035r typ plcs7f tangent typ 2 plcs7g . 3027h . 010r7j . 268 inches7k . 140 (+. 010 ) (-. 000 ) ______________________________________ ______________________________________fig8 letter measurement______________________________________8a 14 . 588 ° 8b . 102 inches8c . 010r8d . 250 inches8e . 125 inches8g . 750 inches8h . 389 inches8j . 049 inches8k 35 . 321 ° 8l . 016r______________________________________
a smoke damper which includes a rectangular frame and blades mounted in the frame such moveable between a position in which all of the blades are essentially coplanar with adjacent edges of adjacent blades being contiguous one with another , and a position in which the blades are rotated 90 degrees from the previous position with individual blades in planes parallel one with another . at least one of the blades has a recess formed along the length of the blade surface proximate to an edge of the blade and an elastomeric gasket mechanically secured to the edge of the blade having the recess which extends part - way across the recess from the edge of the blade towards the blade central portion . a second blade adjacent to the first blade has an edge along its length extending angularly towards the first blade when the blades are coplanar and the smoke damper is closed , the edge of the second blade being tangent to the elastomeric gasket such that upon the smoke damper being closed and the blades being coplanar , the gasket deforms against the edge of the second blade responsively to air flow directed against the blades towards the recess and entering the recess .