Model SD-A-U is a UL555S classified multi blade Smoke Damper with 3V style Blades. It is designed for closure of the HVAC duct opening in Smoke situations. It is ClassIII Leakage Rated under UL555S at Elevated Temp of 350° F and is designed for velocities up to 2000 fpm at 4”w.g. pressure
Model SD-A-U can be installed vertically, with blades running horizontally with air flow in either direction.