: so, the question is: how long will the air in such volume would last ?
: I mean when I inhale from it & exhale into it - closed system.

: Any help appreciated,

: Erez

I do not know the answer to your question... I suspect it is roughly 1/2 an hour, but that is pure speculation.

However it reminds me, when I took my course on learning to roll, the instructure was going on about the one guy who put a tube down under the skirt to practice rolling. She was pretty disguisted, called it a Fart Tube.

Me and one other engineer in the class thought it was pretty brilliant. Rob brought one in the next class (I forgot). He would make several attempts under water before giving up and doing a wet exit/ or assisted rescue.

I found that after three evenings I could not quite get the roll (not once), what really helped me was borrowing some Eye goggles, soon as I did that I got my next two rolls. I went from 0% to about 85% with the goggles and about 60% when I gave them back. Another thing that surprised me, when finally got tired on my good side... I tried the 'other side', on the first try, I rolled so hard that I went right back over the other side.

Long live the Fart Tube!

Myrl