Could not find something that fitted my needs.
so here is Yet Another self closing vent cover for a ~150 mm pipe.
Top, bottom and centre flaps are are slightly different.
print 3x center flap
I tapped the wholes in the flaps with an M3 and used
10x hex head screws (10-20 mm) for the flaps
Fusion360 included
cheers
The author marked this model as their own original creation.