i use a 4500psi firefighter's scba with a regulator from a co2 bar setup. it works excellent with breathing air. i can fill it up anytime i am at work. co2 has a higher expansion rate so actual volume becomes an issue. I carry 3 tanks for spares if i have to fill 35's. For me, it was a hell of a lot cheaper tha buying a powertank. Free tanks + $10 regulator(ebay)= cheap
