Non Return Dampers (Pressure Relief Dampers) are used in ventilation systems and rooms of buildings in case of overload-risk. If a defined opening pressure difference is exceeded, the blades open automatically a cross section to discharge the pressure. Pressure peaks, e. g. resulting from fast-closing fire dampers or shut-off dampers, will thus be relieved reliable. The locking of the blades in the closed position is realised via factory-set permanent magnets. For further information please consult the product information PI/3/2/EN/1.