Currently I have an 80 cuft nitrogen tank for supplying nitrogen to Betsy. The pressure is regulated down to 125 psig by a regulator.
I also bought a small 20 cuft nitrogen tank with the idea of attaching it directly to Betsy to speed up the setup and take down time.
I use nitrogen as the propelant because it is non flamable.
I believe that one could use air if the the design was made of sch 80 pipe instead of sch 40 like I have now. The possible problem would be an explosion inside the gas resvior. My rule of thumb until told otherwise is that a mixture of air and fuel can reach a pressure 3X the starting pressure. For 125 psig air this would be 375 psig which is over the rated pressure of sch 40 fittings.
Sch 80 fitting usually can take 3000 pisg.