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Old 01-13-2011, 09:39 PM   #1
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Damper Theory


What exactly does a damper accomplish? Is it similar to putting your finger on a garden hose? Decrease flow but increase velocity?

So in an HVAC situation, would a damper decrease air CFM while increasing air FPM?

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Old 01-13-2011, 09:44 PM   #2
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Damper Theory


Acts as the same purpose as closing a door, or closing a window. Allows for airflow to either travel down the duct, or not. That means the air will go somewhere else, just not out that register.

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Old 01-13-2011, 09:57 PM   #3
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Damper Theory


Ok, I understand the door analogy.

So that means the damper would restrict the CFM of air into the duct but the air that does make into the duct has the same FPM velicity based upon the duct's size (restriction)? Or would the FPM decrease also?
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Old 01-14-2011, 04:33 AM   #4
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Damper Theory


If a 6 inch round pipe has 100 CFM moving in it with the damper open, the air velocity in the 6" pipe is 509 FPM. If you turn the damper to restrict air flow to 60 CFM, then the air velocity in that 6" pipe drops to 305 FPM.

So no, the velocity does not remain the same if you restrict air flow.
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Old 01-14-2011, 06:47 AM   #5
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Damper Theory


Gee, why was that so hard for me to figure out? Makes complete sense now.

Thanks Greg and BT.
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