Here is my submission for the vent design competition. I liked the durable water proof features of the example vent and focused on designing a closing mechanism that would be simple, fast to operate, and resistant to seizing.
Two guide pins screwed into the white plastic cylinder inside the vent are used to guide the long aluminum center post. The guide pins fit into the tree design of the aluminum center post and the center post is used to raise and lower the stainless steel airflow control disk. The tree design on the center post allows the vent to be closed, partially opened, or fully opened very quickly.
When the vent is closed, four magnets set in the top of the white plastic center cylinder also apply additional downward force on the stainless steel airflow control disk. The additional downward force improves the seal of the vent and prevents it from moving around and accidentally opening. Magnets were chosen rather than springs to reduce the number of moving parts and help extend the life of the vent.