This item is a 12" x 12" Barometric Damper manufactured by Arzel Zoning.
For simple bypass applications with PSC blowers. Economical solution to eliminate objectionable air noise. Automatically bypasses excess air when static pressure in duct increases due to dampers being closed. Weighted arm opens as static pressure increases. Recommended for systems with 2 or 3 zones where zones are nearly equal in size. Not compatible with variable speed blowers.