The damper has a tubular element (1) mounted in an air supply duct and including a transversal section defining a maximal opening of the damper. A valve (2) is mounted in the element so as to pivot between a position corresponding to the maximal opening of the damper and a position corresponding to closing of the damper. A blocking surface is lower than the transversal section of the valve so that the minimal air flow through the damper is permanently possible when the valve is in the position corresponding to closing of the damper. An independent claim is also included for a ventilation system comprising a probe.
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