It's an "old school mechanical damper", also known as a "balancing damper". If you've been doing this kind of stuff since 2003, is this seriously the first time you've ever heard of a balancing damper?

I'm guessing it looked something like this?

 

Just the old rusty rod. No handle. It has a square bracket holding the rod steady and a set screw no different than one for a blower motor hub. I am curious how moving the rod in or out regulates the air.

 

Balancing damper

 

it's called a --spitter damper-- push in and out and see if you feel any resisstance. used to send more or restrict air flow to one section of duct instead ot the other. see if you can determine what portion of the house each branch of duct supplies air to and adjust acordingly. Or just call your local contractor.

 

Thank you! It’s for a dental office. I noticed when pulling it choked airflow to the area where we wanted more. I was using my TSI airflow hood checking the airflow and we made a great improvement and made the clients happy. I haven’t seen a one in almost 25 years. Thanks again Micdundee!

 

Yes, that is a splitter damper....and it is used to control or divert airflow (sometimes at a T fitting...etc..) to help achieve design airflow in the ductwork...

That splitter is adjusted to achieve design airflows...then locked down never to be touched again.....

It should be marked in some manner at the point where it was set and then locked down tight....