IKEA UTDRAG recirculation extractor hood installation problem

Hello everyone,

first of all, hello to everyone, I hope someone here can help me.

We bought a kitchen at Ikea and assembled it ourselves, everything worked out so far. Only with our Utdrag extractor hood for recirculation operation, I don’t understand something.

What is this part for? And do you need it? We only had one in our package and the next Ikea is 80 km away.

Without knowing the part, it looks to me very much like a filter for the recirculation control (activated carbon?)?

This is a passive flap that prevents air from coming out of the extraction hood (wind from outside). Air can only flow in one direction. There should be two semicircles, otherwise the system does not work.

I don't know if the part makes sense in [Umluftbetrieb].