Automatic shutter to be inserted into the pipe. Prevents warm air from escaping and unwanted cold air from entering when the fan is switched off. Automatic function in both negative and positive pressure operation (installation position can be rotated) thanks to spring locking. For horizontal flow, position the rotation axis vertically. For vertical flow, only functions in ascending air flow. Housing made of galvanized sheet steel, flaps made of aluminum, return spring made of stainless steel.