6" Duct Tee Valve with self centering

thingiverse

I wanted to both naturally vent my attic and also allow a blower to power vent without installing a motorized damper, so I built a one-way valve that 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 it was a piece of scrap iron about 6" long. It has to be attached rigidly to the screw so it hangs vertically when the flap is vertical and moves diagonally with the screw when the flap is blown against the seat. Trimming is needed to adjust the weight and length of the weight depending on your blower airflow; it's a delicate balance to achieve.