Multi-louvre dampers are designed to provide a guaranteed sealing efficiency of 99.9%, or better, on the cross-sectional area. They incorporate various flexible metallic sealing systems made of austenitic stainless steel or high nickel alloys. Louvre Dampers can also be provided with a double row of seals ensuring 100% leak tightness with purge air. Units can be supplied for both circular and rectangular ducts with various options for blade profiles and bearing arrangements.