Back-pack cutting torch outfit

"B"Acet tanks work well for being portable and for both cutting and brazing. Good guess would be about 1-1/2hrs total use time at 4psi/Acet, 20psi/Oxy.

At the above pressures there is no concern about over drawing the Acetylene cyl for either cutting or brazing. I've went thru 1000's of cylinders over the past 35yrs for both applications.

Never exceed 15psi Acetylene for any reason.

Cost effective? Nope! But it's beats dragging larger cylinders up on the roof!

For normal shop use get 100cft Acetylene and 200cft Oxygen size cylinders.

T_Bone

I would be more concerned about withdrawal rates for flame cutting with small tanks. For safety sake, withdrawal rates from acetylene cylinders should not be more than 1/7 the cylinders capacity per hour. This is called the rule of seven. Withdrawal rates greater than that can cause the acetone that the acetylene is absorbed into, to be withdrawn from the cylinder. This can and will cause flashback. It also leaves less acetone in the cylinder where it belongs, helping to keep the acetylene separated and its pressure down below 30 psi throughout the fiber. At pressures greater than 30 psi, acetylene can ignite in the cylinder, without the presence of oxygen. I know acetylene cylinders generally show 250 psig or more on a full cylinder, but again the acetone and the filler material actually keep the pressure in the filler low.

To determine safe withdrawal rates for acetylene using the rule of seven, simply divide the cylinders capacity by seven. Withdrawal rates should not exceed that number per hour. B size cylinders (40cf), should not have withdrawal rates greater than 5.7 cfh. Most welding tips, never mind flame cutting tips have withdrawal rates greater than that. The manufacturer of your torch & tips can tell you withdrawal rates for each tip size. Your cylinder size should be matched to your withdrawal rates.

Thickness of material cut is determined by cutting tip size. Guess what, thicker material needs larger tips = more cfh withdrawal.

Any particular reason you want a backpack? It costs nearly as much to fill those mini-bottles, and you won't get a tenth the work out of them that you will a full size unit.