1958 house, slab foundation, HVAC supply ducts are hard pipe in slab done at time of pour (NOT typical in Texas).
Supply vents are therefore in floor throughout home.
Each vent has a mechanical damper control (spring loaded) with a felt-type product to seal supply pipe when there is no air flow.
Can anyone help with some history of such a control? I’m just curious to learn more. It worked great … will work better once vents are cleaned real good and “guck” is removed from hinge points, etc., etc.