The first thing I had in mind for this design was reliability. I would not want my vent stuck opened in the middle of a storm. So my focus went 100% on the mecanism. I think that I ended up with a very long lasting and reliable design.
It works with a simple spiral groove.
When you move the lever, the Grooved Sleeve goes up and down. The rubber Sleeve is there to add friction to the mecanism so that intermediate positions are possible.
The mecanism could be made of stainless steel OR plastic.
I think the best option would be a combinaison of PTFE plastic and ABS plastic for the mecanism.
In the case of plastic mecanism, the grooved cylindre and the Sealing Scoop would be one piece and the Guiding Cylinder and the Holding Ring too. If it is Stainless, it could be welded.
The upper and lower covers are made of ABS.
Symbols should be added to show if the vent is opened or closed.

Note that the colors on the rendered images do not represent reality,