One way air valve

[TheRealPapaK]

Does anyone have any decent ideas or a place to find a one way air valve so it will be closed when my dry room vent van isn't on but when it starts blowing it will push it open? I am envisioning a trap door time thing. It's basically a 6" vent right now with a large case fan.

 

[RVflyfish]

How bout an HVAC damper?

 

[Sheep Shagger]

Personally I’d steer clear of anything designed for RV or house, as they simply don’t stand up. I’ve had really good luck with marine grade equipment. So something like a marine scupper valve would probably be the place I’d start looking depending on where you’d want to place it.
something like this.

Telescoping Scuppers | West Marine

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