Abstract:
A mechanical dual temperature damper closing mechanism having a primary link that separates when the ambient temperature reaches approximately 74° F., closing the damper. The new mechanism provides a reliable means for reopening the damper to allow airflow for the control of smoke spread. A secondary link is engaged within the new mechanism to reopen the damper. When the ambient temperature reaches 180° F. the secondary link separates, closes the damper such that it cannot be reopened.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to fire dampers and more particularly to a fire damper closing mechanism that closes a fire damper at two different temperatures. 
     2. Description of the Related Art 
     A major consideration in the design of commercial and residential buildings is the spread of fire and smoke in the event that a fire breaks out within the building. The walls and ceilings within the buildings serve as the primary barrier to the spread and are most effective if they have no breaks or holes. Most buildings have heating, ventilation, and air conditioning (HVAC) systems that distribute conditioned/heated air throughout the building by air ducts. The ducts are directed to the various rooms and the air enters the rooms through a vent. However, the vents and ducts penetrate the walls/ceilings, providing a hole that reduces the ability to prevent the spread of fire and smoke. To address this problem, dampers are often provided in the ducts that allow air to pass when open, but block airflow, flames, and hot gasses when closed. At elevated temperatures (such as in the case of fire) the dampers automatically close, effectively closing the duct and vent holes and restoring the full integrity of the fire and/or smoke barrier. 
     In many fires, death and injury are caused by smoke, not fire. It was originally thought that closing the dampers would most effectively prevent the spread of both smoke and fire. However, the majority of smoke is spread by changes in pressure, with the smoke spreading from the area with increased pressure to an area with lower pressure. Fire increases air pressure and smoke commonly spreads to adjacent rooms and/or floors having a lower air pressure. Closing the dampers around a fire does not prevent the spread of smoke from fire pressure, and in some instances can cause an increase in fire pressure. 
     It was then discovered that the smoke spread could be retarded by providing air pressure opposing and surrounding the fire pressure. If the fire can be kept in a positive “pressure sandwich”, smoke will spread much more slowly. One way to create this pressure sandwich is through the HVAC system, which can provide positive airflow to the fire zone. In the ducts surrounding the fire zone, the dampers in the supply air ducts are opened and the dampers in the return air ducts are closed. 
     However, most building code standards require dampers to automatically close at predetermined temperature, such as 74° Celsius (C) (165° Fahrenheit), to prevent the spread of fire. This prevents the dampers from being used to create a pressure sandwich at temperatures above the closing temperature. More recently, many building code standards allow dampers to be selectively reopened after they are initially closed so they can be used to control the spread of smoke. However, at a second higher temperature, such as 180° C. (350° Fahrenheit) the fire is considered out of control. The damper must again close and not be allowed to reopen. 
     Accordingly, there is a need for a damper that closes automatically at a predetermined lower temperature and can then be selectively reopened for smoke control. The damper must then close permanently at a predetermined higher temperature. 
     U.S. Pat. No. 4,463,896 to Schaus discloses a fire damper equipped with two thermally responsive electric switches. The first switch closes the damper at a predetermined temperature (74° C.). Control circuitry permits an override of the first switch, allowing the damper to be reopened. The second thermally responsive switch closes the damper again at a second higher predetermined temperature (180° C.). One disadvantage of this damper is that it is overly complex, relying on electrical circuitry and switches. This damper also relies on an electrical motor and circuitry that consume electricity. In larger buildings having many dampers, this energy consumption can add significant operating costs. Finally, this damper is a “power to open” product that requires electrical power to open. In some applications, it is desirable to have a power to close product where the damper stays closed with power and opens when power is lost. 
     Imperial Damper and Louver Company provides a dual link damper closure mechanism (Model Nos. 770 and 771), that closes a conventional damper at ambient temperatures greater than 74° C. The damper can be reopened by engaging a secondary link that enables the damper to function normally until the ambient temperature exceeds 180° C. At this temperature, the mechanism again closes the damper and it cannot be reopened. A primary disadvantage of this device is that it does not reliably engage the secondary heat responsive device and as a result, it will not reliably reopen the damper at temperatures exceeding 74° C. 
     SUMMARY OF THE INVENTION 
     The present invention provides a simple and reliable mechanical dual temperature damper closing mechanism. It automatically closes a damper at ambient temperatures exceeding a predetermined lower level, allows the damper to be reopened, and then automatically closes at ambient temperatures exceeding a second higher temperature. When it closes the second time, the damper cannot be reopened. 
     The new mechanism comprises a shaft that is mounted on a damper and connected to a motor that rotates the shaft around its longitudinal axis. The motor controls the opening and closing of the damper during normal operation. A driver arm and spring arm are perpendicularly mounted on the shaft adjacent to one another. The driver arm is fixed to the shaft such that rotation of the shaft will cause the driver arm to turn in an arc. The spring arm is not fixed to the shaft but can freely rotate about it. The spring arm is also attached to the damper blades such that rotation of the spring arm controls the opening and closing of the damper blades. 
     The two arms are connected by a primary link that separates at a predetermined temperature, such as 74° C. A spring arm pin passes through a hole in the spring arm and into a hole in the primary link. A driver arm pin passes through a hole in the driver arm and into a hole at the opposite side of the fuse link. As a result of the connection between the arms, turning of the driver arm causes the spring arm to turn, which in turn causes the damper blades to open or close. 
     The new mechanism also has a guide to increase the reliability in reconnecting the driver arm to the pin arm after the primary ling separates. The preferred guide is an elongated tongue having a U-shaped cross-section that forms a channel and it is mounted between the spring arm and driver arm. The tongue has a closed end and the spring arm pin passes through a hole at the closed end, connecting the spring arm to the tongue. The driver arm pin rides in a longitudinal tongue slot, connecting the driver arm to the tongue. A secondary link that separates at a higher temperature (180° C.) is also mounted on the driver arm pin and its end opposite the driver arm pin rests on the outside of the tongue&#39;s closed end. 
     A shaft spring is also mounted on the shaft and coupled to the spring arm, providing a bias to close the damper blades. When the temperature exceeds the primary link&#39;s separation temperature (74° C.), it separates and disconnects the driver arm from the spring arm. The bias from the closing spring causes the spring arm to close the damper blades. This also causes the driver arm pin to slide down the tongue slot to the end of the tongue opposite its closed end, dragging the secondary link with it. 
     By cycling the motor to the closed position, the secondary link will be pushed back down the tongue channel by the driver arm pin, towards the tongues closed end. When it reaches the end of the tongue it engages the spring arm pin, reattaching the driver arm to the spring arm. Rotation from the driver arm again causes rotation of the spring arm such that the blades can be opened or closed through rotation of the shaft by the motor. When the ambient temperature exceeds the secondary link&#39;s separation temperature (180° C.), it separates and the bias of the closing spring will again cause the spring arm to permanently close the damper blades. 
     The new mechanism is robust, reliable and less complex than the prior art. The tongue provides a channel that guides the secondary link to engage the primary pin, reliably reattaching the driver and spring arm after the primary link separates. This allows selected dampers to be reliably reopened after the primary link separates and used for the control of smoke spread until the second link separates. 
     These and other further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the new damper mechanism attached to a damper blade; 
     FIG. 2 is a perspective view of the new mechanism from its left side; 
     FIG. 3 is a perspective view of the new mechanism from its right side; 
     FIG. 4 is the front elevation view of the new mechanism; 
     FIG. 5 is a side elevation view of the new mechanism; 
     FIG. 6 is a top and side elevation view of the spring arm pin; 
     FIG. 7 is a top and side elevation view of the driver arm pin; 
     FIG. 8 is a perspective view of the tongue; 
     FIG. 9 is a perspective view of the new mechanism attached to a damper blade after the primary link has separated; and 
     FIGS. 10 a - 10   e  are sectional views of the tongue, driver arm pin, secondary link and spring arm pin in the normal operating position, after the primary link separates, and thereafter engages the secondary link. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1-5 in conjunction, they show a dual temperature fire damper releasing mechanism constructed in accordance with the invention in its operating below the primary link&#39;s separation temperature. The mechanism  10  is mounted adjacent to a damper blade  11  within a damper, to open and close the blade. Each damper has numerous blades  11  that are interlinked and mounted in a damper frame  11   a . By opening or closing a single blade  11 , all of the blades in the damper are opened or closed in unison. Thus, a single mechanism  10  can be used control a damper. 
     The size and shape of the components that comprise the mechanism  10  can vary. The mechanism  10  shown in FIGS. 1-5 comprises a metal shaft  12  that is ½ inch in diameter and has different lengths depending on the size of the damper. It is connected to the damper frame by a shaft bracket  11   b  and is connected to and rotated about its longitudinal axis by a motor or pneumatic actuator  10   a . A metal driver arm  13  and spring arm  14  are mounted the shaft  12 , perpendicular to the shaft&#39;s longitudinal axis. Both arms have a similar shape and are about 4 inches long and have a width of about 1 at their base. Both are folded over at their base to provide a hook shaped longitudinal cross-section. Both have a hole  13   a  and  14   a  passing through their respective hook end, each hole being the appropriate size to mate with the shaft  12  for mounting the arms on the shaft  12 . 
     The driver arm  13  is fixed on the shaft  12  by nut and bolt assembly  15  that compresses the shaft  12  between two flanges  13   b  and  13   c  at the base of the driver arm  13 . When the shaft  12  rotates, the driver arm  13  turns in an arc with the rotation of the shaft. 
     The spring arm  14  is not fixed to the shaft  12  but can turn freely about it. The spring arm  14  is also attached to a damper blade  11  by a knee coupling  16 . To open the blade  11  the spring arm  14  is rotated counter clockwise and to close the blade, the spring arm  14  is rotated clockwise. A shaft spring  27  is mounted on shaft  12  adjacent to and connected to the spring arm  14 , biasing the spring arm  14  to close the blade  11 . 
     At ambient temperatures below a first predetermined temperature (74° C.), the driver arm  13  is connected to the spring arm  14  by a primary link  17 . A driver arm pin  18  passes through a hole on the driver arm  13  and through an aligned hole in the primary link  17 . A spring arm pin  19  passes through a hole on the spring arm  14  and through an aligned hole in the primary link  17  that is opposite the driver arm pin  19 . Accordingly, when the motor rotates the shaft  12 , the fixed driver arm  13  turns and the spring arm  14  turns with it. This causes the damper blade  11  to open or close under control of the motor depending on the direction of rotation. The arms  13  and  14  are not aligned on the shaft but have a rotational offset from the primary link  17 . 
     The primary link  17  separates when the ambient temperature reaches the predetermined first level. Many commercially available fusible links can be used, but the preferred link is provided by Star Sprinkler Corporation, part number 1882-02. The Star Fusible Link consists of a two piece stainless steel strut, locked together by a fusible alloy sealed in the center of a bronze tube by a stainless steel ball. When the alloy melts, the fusible assembly compresses, allowing it to eject from between the two piece strut. The strut assembly separates by the tension the shaft spring  27  on the spring arm  14 . The separation of the primary link  17  disconnects the driver arm  13  from the spring arm  14  and the blade  11  will be closed by the bias of the shaft spring  27  on the spring arm  14 . 
     The new mechanism also has a guide that allows the driver arm  13  to reliably reconnect to the spring arm  14 , a described below. One embodiment of the guide is an elongated tongue  20  mounted between and connected to the driver arm  13  and spring arm  14 . FIG.8 shows a perspective view of the tongue  20  that has a U-shaped cross-section forming a longitudinal channel  25 . The tongue  20  is made of conventional sheet metal, is wide enough to allow the secondary link  26  to rest within its channel  25 , and is long enough to allow for the full range of motion as the driver arm  14  is cycled after separation of the primary link  17 . In the embodiment shown, the tongue  20  is approximately 3.5 inches long, 0.6 inches wide and has a closed hollow end  21 . Its U-shaped cross-section is formed by folding its longitudinal sides  20   a  and  20   b  at right angles, such that the sides of are approximately 0.25 inches high. Its closed end  21  is formed by folding a flap of sheet metal  20   c  back over the tongue approximately 0.3 inches, with the tongue&#39;s U-shape cross-section and the flap  20   c  defining the tongue&#39;s closed end  21 . 
     The tongue has a slight bottleneck  24  such that its closed end  21  narrows slightly to guide the secondary link  26  to engage the spring arm pin  19 , as described below. In the embodiment shown, the closed end is about 0.55 inches wide. The closed end  21  has a hole  22  on the surface opposite the flap  20   c . The tongue  20  also has a slot  23  starting near its open end and running down its longitudinal centerline for approximately ¾ of its length. In the embodiment shown, the slot starts approximately 0.2 inches from the tongue&#39;s open end and running approximately 2.2 inches toward its closed end. 
     Referring again to FIGS. 1-5, after the spring arm pin  19  passes through the spring arm  13  and the hole in the primary linkage  17 , it passes through the tongue hole  22 , attaching the spring arm  14  to the tongue  20 . After the driver arm pin  18  passes through the driver arm, it passes through the longitudinal tongue slot  23  and then into the primary link  17 . The driver arm pin  18  in not fixed in one location in the slot  23 , but slides within it. 
     A secondary link  26  is also mounted on the driver arm pin  18 , between the tongue  20  and the driver arm  13 . At a second predetermined temperature (180° C.) that is higher than the first predetermined temperature, the secondary link separates. Many commercially available links can be used, with the preferred link being a Model A or B fusible link provided by Elsie Manufacturing Company. The end of the secondary link  26  opposite the driver pin  18  rests against the outside surface of the tongue&#39;s closed end  21 . The same end of the secondary link  26  has a hole  26   a  that mates with the spring arm pin  19  to reopen the blade  11  after the primary link  17  has separated. 
     The spring arm pin  19  is shown in FIG.  6 . When installed, the head  60  rests against the surface of the spring arm  14 . The pin  19  has two axial slots  61  and  62  for holding retaining washers, such that the tongue  20  is held between the washers. A bias spring  63  is mounted on the pin  19  between the tongue  20  and primary link  17 , spreading the two and biasing the primary link  17  against the inside surface of the spring arm  14 . The end of the spring arm pin  19  passes into the tongues closed end  21  and it has an angled end  64  to engage the secondary link  26 . It also has a notch  65  that holds the secondary link on the spring arm pin once the two are engaged. 
     FIG.7 shows the driver arm pin  18 . When installed its head  70  rests against the driver arm  13 . The pin  18  has two slots  71  and  72  for retaining washers, and also has a bias spring  73 . The primary link  17  is held on the pin  18  by a retaining washer mounted in slot  72 . The tongue  20  is held between the retaining washer in slot  71  and the spring  73  with the secondary link between the spring  73  and the tongue  20 . The bias of spring  73  holds the end of the secondary link against the tongues closed end. The spring  73  also separates the driver arm  14  from the secondary link  26  and the tongue  20 , and biases the tongue against the retaining washer in slot  71 . 
     If the mechanism  10  is in the damper blade open state when the primary link  17  separates, the driver arm  13  and spring arm  14  will be rotationally separated as the spring arm is turned to the damper blade closed position by the shaft spring  27 . As this occurs, the tongue  20  is pulled along with the spring arm  14  and the tongue slot  23  slides on the driver arm pin  18 . The end of the secondary link  26  is also pulled down the tongue&#39;s channel  25  with the pin  18 . This allows the end of the secondary link  26  resting on the tongue&#39;s closed end  21  to fall within the channel  25 . When the blade is closed, the driver arm pin  18  will be at the end of the slot  23  opposite the tongue&#39;s closed end  21 , with the link  26  fully within the tongue channel. FIG.9 shows the state of the mechanism  10  after the primary link  17  separation, when the mechanism  10  was blade open position prior to separation. 
     If the mechanism  10  was in blade closed position when the primary link  17  separated, the spring arm  13  would already be in the closed location on the shaft  12 . The driver arm  13  and spring arm  14  would be disconnected, but the shaft spring  27  would not rotate spring arm  13  away from the driver arm  13 . As a result, there would be no separation between the driver arm and spring arm, and the tongue slot  23  would not slide down the driver arm pin  18 . The end of the secondary link  26  would remain on the tongue&#39;s closed end  21 . 
     To reopen the blade  11 , the mechanism  10  must be brought to the state shown in FIG.  9 . The motor rotates the shaft to the blade open position, turning the driver arm  13 . Because the two arms are now disconnected, the turning of the driver arm  13  will not turn the spring arm  14 . The driver arm pin  18  will slide within the tongue slot  23  until it reaches the end of the slot opposite the tongue&#39;s closed end  21 . As this occurs, the secondary link  26  will fall from the outside of the tongue&#39;s closed end and will be pulled within the tongue&#39;s channel  25  by the driver arm pin  18 . 
     From the disconnected and separated state of the mechanism  10  shown in FIG. 9, the driver arm  13  and spring arm  14  must be reconnected by the secondary link  26 . The arms must be repositioned such that the link&#39;s open hole  26   a  engages the angled end  64  of the spring arm pin  19  in the tongues closed end  21 . 
     FIGS. 10 a  through  10   e  show sectional views of the tongue  20 , secondary linkage  26 , driver pin  18  and spring arm pin  19  in different operational states. In FIG. 10 a , the driver arm pin  18  and spring arm pin  19  have not been separated and end of the secondary link  26  having the hole  26   a , is resting on the tongues closed end  21  as described above. In FIG. 10 b , the primary link has separated and the pins  18  and  19  have separated as shown in FIG.  9 . The secondary link is pulled within the tongue&#39;s channel  25  as the pins separate. To reattach the driver arm  13  to the spring arm  14 , the motor is cycled to the closed position and the secondary link  26  is pushed by the driver arm pin  18  toward the spring arm pin  19 . Referring to FIGs. 10 c  and  10   d , when the secondary link  26  reaches the end of the spring arm pin  19 , it rides up the end&#39;s angled surface  64 . Referring to FIG. 10 e , when the driver arm reaches the closed position the link hole  26   a  mates with the pin  19 , and the link falls back against the bottom surface of the tongue&#39;s channel  25  with the pin  19  in the hole  26   a . The notch  65  in the pin  19  holds the secondary linkage on the pin  19 . 
     The driver arm  13  is now reattached to the spring arm  14  by the secondary link  26 . To reopen the damper blade  11 , the motor rotates the shaft  12  and moves the driver arm  13  to the open position. This movement will be translated to the spring arm  14  through the secondary link  12 , opening the blade  11 . The damper can again be opened and closed under control of the motor. 
     At the second predetermined temperature (180° C.) the secondary link separates and the driver arm  13  is again separated from the spring arm  14 . The bias from the shaft spring  27  turns the spring arm  14  to the closed position, closing the damper blade  11 . Once the secondary link is separated, the mechanism  10  cannot reopen blade  11 . 
     Although the present invention has been described in considerable detail with reference to certain preferred configurations, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the preferred variations described above.