US 3738254 A
A backdraft damper comprises a frame defining an air control opening and a plurality of vanes mounted on the frame for closing the opening. The frame is assembled from frame sections of lightweight material all having identical cross sections. The frame sections are joined by a corner bracket which is complementally received and engages a large surface area of the sections. The respective sections are pulled together and locked in place as the assembled frame is placed in a jig to stake the corner bracket to the frame sections. The vanes are biased against opening by a spring which is disposed to provide a constant tension on the vanes regardless of the extent to which the blades are already open. The spring is disposed on a shaft and exerts a force tangentially of the shaft. The constant tention assures that any given change in air pressure will result in the same quantity of compensating air flow through the damper regardless of whether the pressure change occurs at near the fully closed or near the fully open position of the vanes. The spring may be wound more or less tightly on its mounting shaft to vary the tension against the vanes as required for different static pressures in different installations.
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Description (OCR text may contain errors)
United States Patent Root [ June 12, 1973 BACKDRAFT DAMPER  Inventor:
 Assignee: Ruskin Manufacturing Company, Grandview, Mo.
 Filed: May 15, 1972  Appl. No.: 253,324
Related US. Application Data  Continuation-impart of Ser. No. 86,698, Nov. 4, 1970,
James R. Root, Independence, Mo.
Primary Examiner-William F. ODea Assistant Examiner-Peter D. Ferguson Attorney-J. David Wharton  ABSTRACT A backdraft damper comprises a frame defining an air control opening and a plurality of vanes mounted on the frame for closing the opening. The frame is assembled from frame sections of lightweight material all having identical cross sections. The frame sections are joined by a corner bracket which is complementally received and engages a large surface area of the sections. The respective sections are pulled together and locked in place as the assembled frame is placed in a jig to stake the corner bracket to the frame sections. The vanes are biased against opening by a spring which is disposed to provide a constant tension on the vanes regardless of the extent to which the blades are already open. The spring is disposed on a shaft and exerts a force tangentially of the shaft. The constant tention assures that any given change in air pressure will result in the same quantity of compensating air flow through the damper regardless of whether the pressure change occurs at near the fully closed or near the fully open position of the vanes. The spring may be wound more or less tightly on its mounting shaft to vary the tension against the vanes as required for different static pressures in different installations.
8 Claims, 9 Drawing Figures BACKDRAFT DAMPER This application is a continuation in part of my earlier application entitled Backdraft Damper, Ser. No. 86,698, filed Nov. 4, 1970 and now abandoned.
This invention relates to fluid control apparatus, and more particularly to a damper for controlling the flow of air through an opening.
Control dampers have long been utilized for fire control and air pressure control in the building industry. A major factor in the cost of constructing such dampers is the need to provide dampers of numerous sizes. In fact, the absence of any standard size damper has required suppliers to construct dampers largely on a custom basis to meet the requirements of a particular building. In those instances where a backdraft damper is utilized to maintain a constant static pressure by allowing compensating air to flow through the damper when the negative pressure on one side decreases, a biasing means must be utilized to urge the damper vanes toward their closed positions.
It has heretofore been the practice to use helical compression springs or the like to bias the damper vanes and such springs are not capable of maintaining a constant tension on the vanes over their complete range of extendability. This results in a non-uniform compensating air flow depending upon whether a given pressure change occurs when the vanes are largely closed or largely open. The previously used springs also tend to cause fluttering of the damper vanes because of the non-linear tensile forces acting on the vanes and the absence of any compensating damping effect.
It has also been found that it is often difficult to specify in advance the tension requirements of the spring. Thus, it frequently happens that a spring of a particular strength will be specified for maintaining the desired static pressure in a particular building installation, but when the damper is actually installed a different spring of a different strength will have to be utilized because of a different static pressure than was originally contemplated.
It is therefore an object of the present invention to provide a backdraft damper wherein biasing means is provided for maintaining a constant biasing force on the damper vanes in all positions of the vane to assure that any given change in the static pressure will result in the same compensating air flow through the damper.
As a corollary to the above object, one of the aims of this invention is to provide a control damper wherein the biasing force exerted against the damper vanes may be varied after installation of the damper by a simple control knob disposed on the damper frame.
It is also an object of this invention to provide a backdraft damper having the advantages specified in the foregoing objects and wherein the damper frame is comprised of a plurality of interconnected frame sections all having a uniform cross section, and with the damper vanes likewise having a uniform cross section, to allow the damper to be easily constructed to any specified size.
A further aim of this invention is to provide a damper frame comprised of a plurality of sections of identical cross section which are interconnected by a clamp fastener having a wide surface area for engagement with an adjacent pair of frame sections thereby permitting a relatively lightweight material to be utilized in the frame construction.
Still another object of this invention is to provide a damper having the advantages specified in the foregoing objects and wherein the damper vanes are of a generally S-shaped configuration to thereby provide a selflocking and self-sealing construction.
Other objects of the invention will be made clear or become apparent from the following description and claims.
In the drawings:
FIG. 1 is a perspective view of an air control damper constructed according to the teachings of the present invention;
FIG. 2 is a horizontal cross-sectional view taken along line 22 of FIG. 1;
FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;
FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2;
FIG. 5 is a cross-sectional view on an enlarged scale, taken along line 55 of FIG. 1;
FIG. 6 is a vertical cross-sectional view, on an enlarged scale, taken through one of the damper vanes and illustrating portions of adjacent vanes;
FIG. 7 is a fragmentary detailed view of the mounting component which is disposed at either end of each vane to mount the same on the frame;
FIG. 8 is a fragmentary view of an alternate type of spring means which may be utilized to urge the damper vanes toward their closed positions; and
FIG. 9 is an elevational view, with portions broken away, of the alternate spring construction shown in FIG. 8.
Referring initially to FIGS. 1, 5, and 8, it is seen that the control damper of the present invention designated generally by the numeral 10, comprises a generally rectangular frame 12 defining an air control opening and a plurality of vanes designated generally by the numeral 14 for closing the opening. Frame 12 is comprised of a plurality of longitudinally extending frame sections 16 of identical cross-sectional configuration. Each section 16 has a pair of opposed, spaced-apart peripheral ribs 18 that are separated by a proximal planar surface area 20 which, together with an integral U- shaped offset 22, spans the distance between ribs 18. The two opposed ribs cooperate to present a channel for receiving a corner bracket designated generally by the numeral 24. Corner bracket 24 comprises a pair of integral planar intersecting sections 26 which when received in the channel present a wide planar contact surface for engagement with area 20. When the frame is assembled a bracket 24 is inserted into the tracks of two adjacentframe sections and the latter placed in a jig where they are pulled tightly together and locked in place. Finally, the frame sections are staked to the bracket 24 as indicated at 25.
Referring additionally to FIG. 6, each of the vanes 14 is identical and comprises an upper blade section 28 whichisparallel to and spaced from a lower blade section 30, the two sections 28 and 30 being interconnected by an angularly disposed intermediate section 32 which extends from the leading edge of section 28 to the leading edge of section 30. Integral with the lowermost edge of section 30 is a flange section 34 which extends in the direction of section 28 of the next adjacent vane. Flange section 34 terminates in a channeldefining are 36 which receives a yieldable sealing element 38. Vanes 14 are constructed from initially flat stock and the points of interconnection of sections 28-34 are defined by lines of bend 40-44 from top to bottom of the vane. This results in a vaneof increased strength as well as an inherently self-locking and selfsealing construction. 7
As best illustrated in FIG. 7, each vane 14 has a notch at each end of intermediate section 32 for receiving a rotatable coupling component designated generally by the numeral 46. Component 46 comprises a pair of spaced-apart arcuate arms 48 which engage opposite sides of section 32 and an integral axle member 50 which is received in an appropriate opening in offset 22. With each vane 14 so disposed for pivotal movement, section 28 will abut one side of offset 22 and section 30 the opposite side when the damper vane is in its fully closed position. Each vane 14 is also provided with a bifurcated bracket which is riveted or otherwise rigidly secured to blade section 28. Brackets 52 pivotally mount a vertical connecting link 54 which lies in a plane traversing the opening presented by frame 12.
Referring additionally now to FIGS. 2-4, disposed on the lowermost frame section 16 is an L-shaped bracket 56 which serves to mount a frame box 58. Box 58 mounts a shaft 60 having a knurled end 62 projecting therefrom to receive a control knob 64. Knob 64 is provided with a plurality of radially extending spokes 66 which project from a centrally disposed annular wall 58 that defines a cavity into which knurled end 62 extends.
The end of shaft 60 opposite knob 64 is journaled through a collar 70 which mounts an actuating link 72. Actuating link 72 is provided with a longitudinally extending slot 74 that receives a connecting pin 76 extending from link 54 to connect the latter with link 72. Constant tension biasing means in the form of a coil spring 78 has a plurality of convolusions wound around shaft 60 with one end of the spring being secured by a pin 80 on the shaft and the other end being coupled with actuating link 72 so as to urge the latter in a counter-clockwise direction, when viewing FIG. 3, to close the vanes 14. A spring biased locking pin 80 extends through box spring 58 and into engagement with control knob 64. Pin 80 may be moved against the action of its spring to permit rotation of knob64 and when the pin is released, one of the spokes 66 will engage the pin. to hold the knob in the selected position.
In normal operation, damper is disposed to maintain a constant static pressure within a building by allowing a compensating air flow to pass through the damper whenever the negative pressure on one side thereof increases above the desired limit. The positive air pressure on the opposite side of the damper will force vanes 14 open against the action of spring 78 to allow for a compensating air flow. This opening will result in link 72 being moved to the broken line position in FIG. 3. For any given pressure change, vanes 14 will open more or less depending upon the requirements for maintaining the desired static pressure. It has been found that with a spring such as 78 wound around shaft 60 to exert a biasing force tangentially of the shaft, the torque is distributed over the length of the shaft and the biasing force remains substantially constant in all positions of the spring. Thus, when vanes 14 are only open a small distance, a given pressure change will result in the vanes opening (or closing) a definite distance and this distance will be the same as will result when the pressure change occurs after the vanes are in their nearly fully open positions. The result is much more accurate and even control of the static pressure within a building that has heretofore been impossible with conventional biasing means, and the problem of vane fluttering is eliminated because of the linear nature of the biasing force. Manifestly the slot and pin coupling between links 54 and 72 accomodates a certain degree of lost motion which further contributes to biasing force linear over the complete range of movement of the vane.
When it is desired to decrease the extent of move-. ment of the vanes for any given pressure change, locking pin may be held against the action of its spring to permit rotation of control knob 64 to wind spring 78 tighter on its shaft 60. Pin 80 is then released to hold the knob in its new positionand the biasing force acting against vanes 14 will have been correspondingly increased. This obviates the necessity for ordering a different spring after the damper is installed should the static pressure requirements dictate a different spring setting than what was originally contemplated.
An alternative type of spring which may be utilized in the present invention is illustrated in FIGS. 8 and 9. A mounting bracket 82 which is secured to uppermost frame section 16 mounts a nut and bolt assembly 84 that presents a shaft for a spindle assembly 86. Wound around the shaft on spindle 86 in stacked relationship are a plurality of convolutions of an elongated tension spring 88. An end of spring 88 is secured by a fastener such as screw 90 to link 54. Manifestly, the structure for adjusting the biasing force has been omitted from spring 88. This alternative form of biasing means has also been found highly effective for exerting a constant force against vanes 14 over the complete range of movement of the latter.
Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:
1. In a backdraft damper of the type having a frame defining an air control opening, and a vane coupled with the frame and movable over a range of positions from fully open to fully closed for controlling the flow of air through the opening, wherein a constant negative pressure .is maintained on one side of said damper by selectively opening and closing said vane to permit a compensating air flow in the direction of said negative.
pressure, the combination with said vane and said frame of: r
a shaft coupled with said frame; constant tension biasing means comprising a plurality of convolutions wound around said shaft for exerting a force tangentially of said shaft, said biasing means having an end coupled with said vane to resist movement of the latter to an open position, said vane being movable against the action of the biasing means while the latter maintains a constant 'tension on the vane over the complete range of movement of the vane whereby the extent of opening and closing of the vane in response to the air pressure acting thereon is constant in all positions of the vane.
2. The invention of claim 1, wherein said convolutions are disposed in stacked relationship one around the other.
3. The invention of claim 1, wherein said convolutions are disposed in spiral relationship along the length of said shaft.
4. The invention of claim 1, said biasing means having another end secured to said shaft, said shaft being rotatable about its axis for winding the biasing means tighter to thereby vary the force exerted by the biasing means on the vane.
5. The invention of claim 4, wherein is included means for locking said shaft in any one of a plurality of rotatable positions.
6. The invention of claim 4, wherein is included a knob disposed on one end of said shaft to facilitate rotation of the shaft.
7. The invention of claim 1, said vane being disposed for pivotal movement about an axis and wherein is included link means coupling said biasing means with said vane, said link means comprising:
a first link keyed to said shaft and projecting from the latter in perpendicular relationship to the longitudinal axis of the shaft;
a second link coupled with said vane and said first link and disposed in a vertical plane traversing the plane of said axis of pivotal movement,
said one end being received by said first link to bias the latter in a direction to urge said vane toward said fully closed position.
8. An air control damper comprising:
a plurality of frame sections disposed to define an opening;
each of said sections having an identical uniform cross section and being provided with opposed spaced apart'ribs at opposite sides of the section which ribs present opposed channels,
each section further including a generally planar surface area at least partially spanning the distance between said ribs in proximal relationship to said channels,
a comer bracket for rigidly interconnecting a pair of sections at an angle of said bracket comprising a pair of intersecting planar components adapted to be received in the channels of a pairof adjacent sections and to engage said surface area of each adjacent section;
a vane coupled with said frame and movable over a range of positions from fully open to fully closed for controlling the flow of air through the opening;
a spring-mounting shaft coupled with said frame; and
coiled spring means comprising a plurality of convolutions wound around said shaft for exerting a force tangentially of said shaft,
one end of said spring means being coupled with said vane to resist movement of the latter to an open position,
said vane being movable against the action of the spring means while the latter maintains a constant tension on the vane over the complete range of movement of the vane.