6" Duct Tee Valve with self centering

I wanted to both naturally vent my attic and also allow a blower to power vent and didn't want to install a motorized damper. So I built a one way valve which will self center the flap vertically to naturally exhaust through one of the Tee openings but when the blower airflow comes into the other side of the Tee, the airflow will blow the flap against the seat and direct that airflow out the Tee exit port and out the roof.

I used a 30mm long M3 screw and attached to that was a piece of scrap