Patent Publication Number: US-6991536-B2

Title: Air flow controller and fire damper in an air flow duct

Description:
The present invention relates to a fire damper for use in an air flow duct, and to a damper which can be used to regulate the flow of air in the duct. 
   Fire dampers in air flow ducts are well known. A commonly used form of damper consists of a flap inside the duct, which is held in an open position, extending along the duct axis. A heavy spring biases the flap to a closed position where it is transverse to the duct axis to block off the duct. A temperature sensitive trigger holds the flap in the open position and releases the flap in the event of a temperature rise caused by fire, such as a flame front moving through the duct. 
   The prior art system suffers from a number of drawbacks. 
   The seal between the duct wall and the flap relies only on the flap edge abutting the duct wall, and so smoke can move past the flap, although soot and other debris eventually help to form a seal. Distortion of the duct wall is a common occurrence and this impairs the seal. 
   Building regulations typically require installation of a fire damper in the wall of the room or compartment through which the duct passes. This makes access to the flap, to reset it, difficult. However, regulations also require that the flap be triggered many times on installation to ensure that it is functioning properly. Typically, the flap is mounted on an axle extending across the duct, and a handle on the axle extends outside the duct to enable an operator to return the flap to the open duct position. 
   Another draw back with the prior art system is that the flap is either fully opened or fully closed. It is often desirable to balance or control the flow through a duct, but the prior art design cannot use the flap for this additional purpose. 
   A first aspect of the present invention provides a fire damper in a ventilation duct, the damper comprising a flap which is pivotably mounted in the duct for movement from an open position, allowing air flow along the duct, to a closed position under the action of a biasing force to inhibit air flow or the passage of flame along the duct, wherein a rim is provided on the duct wall and the flap overlaps and bears on the rim when in the closed position. 
   Preferably the flap is pivoted about a centre axis. The rim may be stepped to accommodate opposite sides of the flap, but preferably the rim is in a single plane and the flap is stepped to mate with the flange. 
   As well as providing a better seal, the construction of the flap closing down onto a rim is more robust and better able to withstand continuous testing without distortion of the flap or surrounding duct. The rim, when mounted on the wall of the duct, serves to reinforce the duct shape. The rim may have a flange which extends laterally across the duct, the flap bearing on the flange when the flap is closed. Preferably the rim forms a corner and a co-operating corner is provided on the flap to form a seal at the corner. 
   Another aspect of the invention provides a damper in a ventilation duct, the damper comprising a flap which extends within the duct, wherein the flap is biased towards a first position, tending to open or close the duct, and a cable extends from the flap to the exterior of the duct, and means is provided for gripping the cable to hold the flap against the biasing force, whereby the orientation of the flap in the duct can be adjusted via the cable. 
   Preferably the flap is biased to a position closing the duct and a temperature actuated release is provided to trigger the release of the cable by the gripping means. 
   Very preferably the cable is gripped by a ball clutch. The cable may be pulled through the ball clutch, in the direction of flap opening, manually or by other means such as an electric motor or pneumatic device. It will be appreciated that the cable could also be turned around a pulley wheel which is rotated by a stepper motor or the like and released automatically to release the flap under control of a temperature sensor, override switch, etc. 
   Other aspects and preferred features of the invention will be apparent from the following description and the accompanying claims. 

   
     The invention will now be described by way of example with reference to the accompanying drawings, in which: 
       FIG. 1  shows schematically in cross-section a first embodiment of the invention, which is particularly suitable for small size ducts, typically up to 25 cm or 35 cm across but can also be used with larger size ducts; 
       FIG. 2  is a view on arrow A of  FIG. 1 ; 
       FIG. 3  shows a modification of the embodiment of  FIG. 1 ; 
       FIG. 4  shows in cross-section a second embodiment of a flap of the invention, which is particularly suitable for larger size ducts; 
       FIG. 5  is a plan view of the flap of  FIG. 4 ; 
       FIG. 6  is a cross-section view illustrating a control mechanism of the invention; 
       FIG. 7  is a detail of the control mechanism of  FIG. 6  with some parts omitted; 
       FIG. 8  is a side view of the control mechanism of  FIG. 6 , when it is being set; 
       FIG. 9  is a side view of the control mechanism of  FIG. 6 , when it is set; 
       FIG. 10  is a view on Arrow C of  FIG. 9 ; 
       FIGS. 11   a  and  11   b  show the operation of a manual override lever in the mechanism of  FIG. 6 , and  FIG. 11   b  also shows a visual indicator of the flap position; 
       FIG. 12  is a cross-sectional view of a temperature actuated release of the mechanism of  FIG. 6 ; 
       FIG. 13  is a cross-sectional view of a modification of the temperature actuated release mechanism of  FIG. 12 ,  FIG. 13   a  showing a detail, and 
       FIG. 14  is a side view of the mechanism of  FIG. 13 . 
   

     FIGS. 1 and 2  show duct wall  2  which is circular in cross-section. A continuous circular rim  4  having an inwardly extending flange  6  is riveted to the duct wall  2  at several positions around the rim by sealed rivets (not shown). The rim  4  has a step  8 , to form a wall portion  10  which is spaced from the duct wall  2 . The rim serves to provide a mounting and a stable mating surface for a flap or blade  12 , and also strengthens the duct to maintain the duct shape in the region of the flap  12  to provide improved operation. 
   The flap or blade  12  is pivotably mounted on the rim  4  and is shown in full outline in its closed position, and in dotted outline in the open position. 
   As seen in  FIG. 1 , the blade is stepped or joggled at a diameter region  12   a  so that the halves of the flap  12   b ,  12   c  occupy planes to either side of and parallel to the plane of the flange  6 , when the flap is in the closed position. 
   Referring to  FIG. 2  the flap  12  is mounted on two stub axles  14  which rotate in sockets  16  formed on the rim  4 . The stub axles  14  are a good fit in the sockets  16  to reduce any tendency of the flap to wobble, and also to provide a degree of sealing against the passage of smoke when the flap is closed. A single axle extending across the diameter of the flap may be used. The ends of the axle(s) may be sealed. 
   Heavy duty, i.e. strong, coil springs  18  surround the axles  14 , and have one leg  20  bearing on the flange  6 , and the other leg  22  bearing on the flap  12  to bias the flap into the closed position, against the flange  6 . 
   The flap  12  is cut away at the edge  12   e  of the diameter region  12   a , near the stub axles  14 , to just clear the flange  6 . 
   A cable  24  is attached at one end  26  to the flap region  12   b  and extends diagonally of the duct to exit through the duct wall  2 , as will be described more fully hereinafter with reference to  FIG. 6  et seq. 
   The flap  12  is overturned at its outer perimeter to form an axially extending flange  12   d  and a corner  12   f  to embrace the rim at the corner  11  formed at the radially outer edge of the flange  6  in portion  12   c , and sit snugly at the corner  11  formed between the flange  6  and wall  10  at flap portion  12   b . The flange  12   d  serves to strengthen the flap  12  to retain the shape of the flap during repeated operation and also provides an improved seal, as will be described hereinafter. 
   In operation, the cable  24  is pulled to rotate the flap  12  into the open position, shown in dotted outline, against the force of the springs  18 . In the event of a fire, the cable  24  is released, allowing the flap to rotate to the closed position under the force of the springs  18 . The overlap of the perimeters of the flap portions  12   b ,  12   c  adjacent flange  12   d  with the flange  6 , and particularly the overlap at the corners  11 ,  12   f  ensures a good seal. The regions  12   e , where the flap  12  is cut away may allow a small mount of air or smoke to pass but this will be rapidly blocked by soot etc., in the event of a fire. 
   By means of the cable  24 , the flap  12  can be held in an intermediate position, thus serving to control the flow of air through the duct during normal operation. Typically, the degree of opening of the flap  12  would be set on installation of the system to balance air flow through the system, and then left. 
   In  FIG. 3 , the cross-section of the rim  4 ′ is modified to replace the step  8  by an angled wall  10 ′. 
   In the duct  2  the normal air flow is in the flow direction of arrow A. Thus the fixings, such as the rivets holding rim  4  in place and the exit for cable  24 , are closed or sealed. This reduces the risk of smoke escaping through the fixings once the flap  12  is closed. It will be appreciated the arrangement could be reversed, with air flowing in the direction of arrow B. 
     FIGS. 4 and 5  shows a flap  26  which is a modified form of the flap  12 . The centre portion  26   a  of the flap is flat. The outer perimeter of the flap is stepped to mate with the flange  6  of  FIG. 1  At portion  26   c  the edge of the flap is dished, ending in a circumferential rim  26   d  forming a corner  26   e  and the flap  26  is stepped at portion  26   b , with circumferential rim  26   d  forming a corner  26   e.    
   The control of the flap  12 ,  26  by means of the cable  24  will now be described in more detail with reference to  FIGS. 6 to 12 . 
     FIG. 6  shows a flap  26  closing a duct  2  by bearing on a rim  4 ′. The stub axle mounting and spring biasing of the flap  26  are not shown but are as described with reference to  FIGS. 1 to 5 . The cable  24  exits the duct  2  at an angled tube  28  which extends through an aperture  30 . A grommet (not shown) is provided on an end of the tube  28  to form a seal with the cable  24 . Tube  28  is mounted on a control mechanism  32  which is riveted to the duct  2 . Also shown in  FIG. 6  is a fusible cartridge  34  which provides the temperature sensor of the temperature actuated control for releasing the cable  24  to allow the flap  26  to close. 
   Referring to  FIG. 7 , this shows a cross-section through the control mechanism  32 . Mechanism  32  is contained in a housing  40  which is riveted to the duct  2  by sealed rivets (not shown). Cable  24  passes through tube  28  which is fixed to the housing  40  by nuts  42 ,  43 . The cable  24  passes through the housing  40  and a ball clutch  45  mounted at the end of the housing  40  opposite inlet tube  28 . 
   Ball clutches are well known and described for example in Ingenious Mechanisms by Franklin D. Jones, Vol. 2, Industrial Press Inc., Page 428. In brief, the cable  24  passes through a piston  46  and is gripped by two or more balls  44  which are held in the piston  46 . Piston  46  is contained in a block  52  and is urged towards a conical surface  48  by a spring  50 . Conical surface  48  forces the balls  44  inwards, to grip the cable  24 . If the cable  24  is pulled to the left as seen in the drawing, which will open the flap  12 ,  26 , this causes the piston  46  to move leftwards against the force of the spring, releasing the balls  44 , so that the cable can then be pulled freely through the clutch. 
   Piston  46  extends outwards of block  52 . Thus, the clutch can be released by urging piston  46  leftwards from outside the block  52 . This forms the basis of a release mechanism for releasing cable  24 , triggered by cartridge  34 , to allow the flap  12 ,  26  to close. 
     FIGS. 8 and 9  are side view shows showing a release mechanism  53 .  FIG. 8  shows the mechanism  53  being set, and  FIG. 9  shows the mechanism  53  after it has been set. 
   Referring to  FIG. 8 , a first lever  54  is pivotally mounted at a pivot point P 1  at one end  54   a  in the housing  40 . A second lever  56  is pivotably attached to the other end  54   b  of the first lever  54  at a pivot point P 2 , and attached to a coil spring  61 . Coil spring  61  passes around the block  52  of ball clutch  45  and is attached at each end to the lever end  56   a.    
   A release member  58  is pivotally attached at one end  58   a  to a central region  54   c  of lever  54  at a pivot point P 3 . Release member  58  is U-shaped and a web  58   b  has an aperture  58   c  which passed over a stub axle  60  formed on the end of the piston  46  where it projects from the block  52 . 
   It can be seen that as the free end  56   b  of lever  56  is urged downwards, it will urge lever end  54   b  downwards, in turn moving lever portion  54   c  down and to the left as it pivots about pivot P 1 , thus urging the release member  58  leftwards. Release member  58  pivots at pivot P 3 . 
   A U-shaped break member  62  is also pivotably mounted on lever  54  at pivot point P 3 . Member  62  has a web  62   a  which, when the mechanism is “loaded”, bears on the head  34   a  of cartridge  34 . Break member  62  limits the downward movement of lever  54  ( FIG. 9 ), and so limits the leftward travel of the release member web  58   b.    
   Referring to  FIG. 9 , the lever  56  has been pushed fully downwards, and is clipped under a finger  62   b  formed at the end of arm  62   c  of brake member  62 . 
   It can be seen that lever end  54   a  is fixed by pivot point P 1 , and lever  54  is held against further downward movement by brake member  62  bearing on head  34   a  of cartridge  34 . The mechanism is tensioned by spring  61  which pulls lever end  56   a  downwards. In this “set” position, web  58   b  of the release member  58  rests just short of an adjustable nut  64  on stub axle  60 . 
   As will be described with reference to  FIG. 12 , when release cartridge  34  is heated, as by flames in duct  2 , head  34   a  drops, allowing brake member  62  and lever  54  to pivot further downwards, urging release member web  58   b  leftwards to bear on nut  64 , and hence urge the piston  46  leftwards to release the ball clutch  45 . Cable  24  is thus released, and flap  12 ,  26  is forced closed by the springs  18 . Head  34   a  of cartridge  34  will seal the aperture  59  formed in housing  40  and the duct wall  2 . 
   Referring to  FIG. 10 , a lug  62   d  on the other arm  62   k  of break member  62  prevents the member pivoting past the head  34   a  when the mechanism is being set. 
   To test that the flap  12 ,  26  closes, a manual release mechanism is provided, as shown in  FIGS. 11   a  and  11   b . A manually operated lever  70  pivots at one end  70   a  in a notch  72  and has a slot. (not shown) which embraces the stub axle  60 . As the lever is pivoted to the left about notch  72 , as shown in  FIG. 11   b , the piston member  46  is urged leftwards to release the ball clutch  45 . Lever  70  slides in a slot  40   b  in the housing cover  40   c.    
   Also shown in  FIG. 11   b  is an indicator for allowing visual inspection of the flap portion. The indicator is an elongate pin  80  which is screwed at one end  80   a  into a nipple  82  fixed in position on the cable  24 , and extending through slot  40   b . As shown in  FIG. 11   b , the cable has been released and the flap  12 ,  26  is in the closed position. As the cable is pulled leftwards, opening the flap, the pin  80  is slid along the slot  40   b.    
   To allow for release of the flap  12 ,  26  by other devices, e.g. smoke alarms or fire alarms external of the duct, an electromechanical actuator may be mounted on lever  70  at the outer end  70   b.    
   The release cartridge  34  is carried by the base of the housing  40  and projects into the duct  2 .  FIG. 12  shows a cut-away detail view of release cartridge  34 . A pin casing  34   b  is of brass and swaged over at its outer end  34   c  and a push fit in the extruded aperture  59  in the housing  40 . Steel pin  34   d  has a brass cup  34   e  mounted on its lower end by a rivet  34   f . Cup  34   e  is attached to casing  34   b  by solder  34   g , holding the pin  34   d  raised in the casing  34   b . When heated, as by flames, solder  34   g  melts, so that the break member  62 , which urged against the pin head  34   a  by spring  61 , will force the pin  34   d  downwards through the casing  34   b , at the same time triggering the release of the cable via release member  58 . Cup  34   e  remains on the end of the pin  34   d , and so there is no risk of it fouling the flap  12 ,  26 . 
   The release cartridge is intended to trigger or fuse close to a pre-determined temperature governed by the melting point of the solder  34   g , say at about 70° C. However, the solder may soften appreciably below this temperature. 
   From  FIG. 12  it can be seen that the solder  34   g  is in shear between the casing  34   b  and the wall of cup  34   e . Hence it is possible for the cartridge to trigger below the designated temperature because the sustained pressure on pin  34   d  from the release mechanism, via break member  62 , will slowly cause the solder to shear, allowing pin  34   d  to drop into the cylinder  34   b.    
   To overcome this, the embodiment of  FIGS. 13 and 14  uses a mechanical or form-locking connection between the cup  34   e  and the casing  34   b  which resists the shearing force between cup  34   e  and casing  34   b.    
   A circumferential slot  34   h  is provided in the outer surface of the casing  34   b . Cup  34   e  has two diametrically opposed legs  34   j  which extend upwards and end in inturned nibs or lips  34   k  which engage in slot  34   h . Solder  34   g  holds the legs  34   j  against the outer surface of casing  34   b . Slot  34   h  has a sloping lower wall  34   m  on which the lip  34   k  bears. 
   The pressure on pin head  34   a , from break member  62 , will tend to force the lips  34   k  out of engagement with slot  34   h . This requires outward flexing of the legs  34   j  which is resisted by the solder  34   e  bonding the legs  34   j  to the cylinder  34   b . Solder  34   e  is not under substantial shear, and the force tending to separate the legs  34   j  is lower than the shearing force of the  FIG. 12  embodiment because the force is acting in a different direction. Thus solder  34   g  will not creep or give significantly until it is at or near its designed melting point, of about 70° C. in this example. 
   When the solder  34   g  reaches its melting point, the legs  34   j  are released, and the force on head  34   a  of pin  34   d  is sufficient to drive the cup  34   e  down, disengaging the lips  34   k  from sloping wall  34   m  of slot  34   h . In turn, the trigger mechanism releases the flap  26 , as described above. 
   The flap  26 , rim  4  and release mechanism  32  may be provided as an assembly or kit to be fitted in a length of duct. Preferably a length of duct is pre-fitted with the assembly, ready for installation in a building etc. To further strengthen the duct against deformation, a rim or band  90  may be fixed upstream of the flap  26 . 
   Although the invention has been particularly described with reference to a circular cross-section duct it may also be used with a square or rectangular cross-section duct. 
   Various modifications will be apparent to those in the art. Although the invention has been described with particular reference to circular cross-section ducts, it can be used with rectangular or other cross-section ducts.