Back draft damper
A back draft damper includes a rectangular shell having a central opening which air can pass through. A plurality of vanes rotatably mounted in the shell are rotatable between open positions where air can pass through the shell and closed positions where air cannot pass through the shell. The axes the vanes rotate about are slightly offset from vertical.
Large air handling systems often require back draft dampers to be placed at critical locations to prevent air from flowing in the direction opposite normal air flow when the fan that is creating the airflow is not operating. This is particularly true with multi-fan systems such as shown in Hopkins, U.S. Pat. Nos. 7,137,775 and 7,727,468. With multi-fan systems it is common to shut off one or more of the fans to allow the remaining fans to run at peak efficiency. When this occurs some air from the operating fans will flow back through the non-operating fans if the non-operating fans do not have back draft dampers.
There basically are three types of back draft dampers: manual systems where a blank off plate or damper is deployed to prevent reverse airflow; remotely actuated dampers where actuators are used to close a damper; and gravity actuated dampers where the damper is opened by the pressure of air passing through it and is closed by the force of gravity acting on its vanes. The prior art gravity actuated dampers typically comprise several stacked side-by-side vanes which are mounted in a shell and rotate about horizontal axes. The rotational axes are typically near the leading edge of the vanes to maximize the effect of gravity on the vanes so that gravity causes the vanes to be fully closed when there is no positive airflow past them. However, the down side of this is that it takes a considerable amount of airflow to fully open the vanes and if the airflow is to low to fully open the vanes they will create excess drag and overall efficiency of the system is reduced. While the gravity effect on damper vanes that rotate about horizontal axes can be reduced by counter weighting the vanes in some manner, this adds to the cost and in many situations the counter weighting has to be customized.SUMMARY OF THE INVENTION
The subject invention typically mounts the vanes of a back draft damper generally vertically in the shell but with their rotational axes being slightly offset from vertical so that a small amount of gravitational force acts on the vanes to make them rotate to their closed positions. As a result, a small amount of force is required to overcome this gravitational force and rotate the vanes to their fully opened positions. This means that the vanes will open more quickly and with less force than vanes that rotate about horizontal axes and be more fully open at lower airflow levels.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.
A plurality of vanes 22 extend between the top and bottom surfaces, 18, 20 of the shell 10. The vanes move between open positions,
If desired the axes 36 of the vanes 22 can also be offset at an angle B from side-to-side with the tops of the vanes being closer to the vertical center line L of the shell than the bottoms of the vanes,
In the embodiment illustrated in
Referring now to
Preferable the vanes rotate independently of one another so that each vane is aligned with the localized direction of the air flowing over it. In most cases this means that most of the blades will be oriented at an oblique angle with their trailing edges being closer to the center of the shell than their leading edges. This, along with the axes 36 of the vanes being offset from vertical causes the vanes on one side of the shell to rotate clockwise as they rotate to toward their closed positions and the vanes on the other side of the shell to rotate counterclockwise as they rotate toward their closed positions. Preferable there are an even number of vanes 22, one half of which are located on each side of the vertical center line of the shell. In the embodiment illustrated there are six vanes and they slightly overlap when they are in their closed position to provide a seal between them.
Referring now to
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.
1. A damper comprising:
- a. a shell having a central opening through which air passes;
- b. a plurality of vanes mounted rotatably in said shell;
- c. said vanes are rotatable, about axes which are slightly off set from vertical at a predetermined angle, between open positions where air can flow through said central opening and closed positions where air substantially cannot flow through said central opening.
2. The damper of claim one wherein at least some of said vanes rotates independently of at least some of the other vanes so that when in its open position each said blade is aligned with the localized direction of the air flowing over it.
3. The damper of claim 1 wherein said shell is rectilinear in cross section.
4. The damper of claim 1 wherein said shell is elliptical in cross section.
5. The damper of claim 1 wherein said shell is circular in cross section.
6. The damper of claim 1 wherein said vanes have leading edges and trailing edges, and said axes are proximate said leading edges.
7. The damper of claim 1 wherein said vanes have top ends and bottom ends and said axes are closer to said inlet at said top ends than at said bottom ends.
8. The damper of claim 1 wherein said shell has a vertical center line and said axes are closer to said vertical center line at said top ends than at said bottom ends.
9. The damper of claim 6 wherein said shell has a depth and said vanes have a width which is not greater than said depth.
10. The damper of claim 9 wherein said vanes are substantially located within said shell.
11. The damper of claim 1 wherein said shell has a vertical center line and a portion of said vanes located on one side of said vertical center line rotate clockwise when rotating toward their closed positions and a portion of said vanes located on the other side of said vertical center line rotate counterclockwise when rotating toward their closed positions.
12. The damper of claim 11 wherein there are an even number of vanes with one half of said vanes on one side of said vertical center line and the other half of said vanes on the other side of said vertical center line.
13. The damper of claim 1 wherein said vanes are symmetrical in cross section and have a shape which minimizes drag.
14. The damper of claim 1 wherein said predetermined angle is between 0.5 degrees and 45 degrees.
15. The damper of claim 1 wherein said predetermined angle is 1.6 degrees.
16. The damper of claim 1 wherein said predetermined angle is such that said vanes are free to start rotating towards said open positions when there is any airflow through said shell from said inlet to said outlet.
17. The damper of claim 1 where said predetermined angle is such that said vanes move to their closed positions when there is no airflow through said shell from said inlet toward said outlet.
18. The damper of claim 1 wherein said vanes have tops and bottoms and there is a bearing between the top of each vane and said shell and the bottom of each vane and said shell.
19. The damper of claim 18 wherein said bearing is a ball bearing.
20. The damper of claim 1 wherein said vanes have a thickness of between 0.250 inches and 0.400 inches at a leading edge thereof and of between 0.050 inches and 0.100 inches at a trailing edge of said vane.
21. The damper of claim 20 wherein said vanes have a thickness of 0.32 at said leading edge and a thickness of 0.086 at said trailing edge.
22. The damper of claim 1 wherein said vanes weight approximately 2 pounds.
23. The damper of claim 1 wherein said shell has a horizontal center line and a vertical center line and said axes are offset from vertical by positioning said shell such that said vertical center line is offset from vertical.
24. The damper of claim 1 wherein said shell has a horizontal center line and a vertical center line and said axes are offset from vertical by positioning said shell such that said horizontal center line is offset from horizontal.
Filed: Jul 29, 2009
Publication Date: Feb 3, 2011
Inventors: Lawrence Hopkins (Happy Valley, OR), Emily Jones (Tualatin, OR), Albert Passadore (Beaverton, OR), David Benson (West Linn, OR)
Application Number: 12/462,172
International Classification: F24F 13/14 (20060101);