> if you squeeze one of these check-valve kinds properly, the airflow is just as good as with a free-flow one That hasn't been my experience, and if you look a

> if you squeeze one of these check-valve kinds properly, the airflow is just as good as with a free-flow one That hasn't been my experience, and if you look at one closely you can see that it can't be the case. The size of the opening is substantially smaller even at maximum expansion, and the path for the air is less direct.