Well for giggles I put it on my reactor anyhow tonight, because my cheap check valve was .. well .. cheap and jammed up anyhow.
Don't ask me to explain it but it works for CO2 ... I can't for the life of me push any air through it, but CO2 seems to pass through.
I guess it IS some kind of "magical" method for "CO2 only".
Thanks to Wendell for the kick in the rear end to TRY it before completely giving up on it.
PS. I still wonder how it knows CO2 isn't air??
