I get 4-6 or so but can't say I ever really counted it, plus I share the balloon with my wife
(differs per balloon and lung size as well, basically fill half your lungs when you suck).
I'm in the process of making the move from joints to volcano (meaning I haven't bought it yet). I have an allergy that in combination with smoking joints (certain strains it seems even) makes my lungs build up slime, even have an inhaler for really bad days. About two months ago I tried a volcano for the first time and I was sold after the first hit, and I was in love with the thing after two balloons. Felt like my lungs got 10 years younger putting a smile on my face that makes the joker look like a sad guy.
Used it several times know and I really think I'll end up using it daily instead of it disappearing in a closet.
It's besides healthier supposedly more sufficient but I can see myself smoking, err.. vaping, only more (not saying that's a downside).
Another major benefit imo is that fluffy/popcorn buds and (frosty) sugar leaves don't have to be turned in to hash anymore.