Description

The IGI BDD operates purely on differential air pressure. When the fan starts and forward airflow pressure exceeds the weight of the blades (or, on the High Pressure model, the counterbalance spring tension), the blades pivot open on their out-of-airstream linkage, allowing air to pass freely. When the fan stops or airflow reverses, the blades fall closed under their own weight, and the overlapping blade-to-jamb profile forms a tight seal that blocks reverse airflow, backdraft, and cross-contamination between connected ducts or fans.