Greenheck Model HBT-221 is a commercial grade rectangular bubble-tight damper with square blades. The rectangular blade design allows for lower pressure drop than bubble-tight dampers with circular or oval blade designs. Model HBT-221 features a blade seal mechanically fastened to the blade that is field replaceable and a flanged damper frame for mounting ease, and is available with a full range of electric, pneumatic or manual actuator options. Each damper unit is factory-tested to ensure bubble-tight leakage performance per AMCA 500-D up to 10 in. wg (2.5 kPa) prior to shipping. Designed for isolation or decontamination applications, the HBT-221 damper is ideal for medical facilities, universities, test laboratories and food processing.