So Ted, are you saying that there is no mechanical check valve, rather a case of the membrane providing a check valve action? This is what I suspected, and in fact that old diffuser I destroyed was very clean on the inside....proof that it works in my book.

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.