Can I run my acetylene tank until it's completely empty?

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Hopefully this doesn't sound too dumb, but I was welding quite a bit today and by the end my acetylene tank was very close to empty...the regulator doesn't provide much precision, but the tank was sitting somewhere less than 20psi I think. My question is, is there some point where you're supposed to stop using the tank before it's actually empty, or can you just run it until it's completely empty? I feel like I've heard that if one of the gases loses pressure then it's possible for a flashback or something to occur...is that the case? If I can run it until it's completely empty, will I just lose my flame all of a sudden or is there some other phenomenon I should expect? Also, is the situation any different once I run out of oxygen instead of the acetylene?Thanks in advance, - Ian
Reply:It's best to not run any tank completely empty.Leo
Reply:When either of the gases gets to the point where you're having to readjust your mixture knobs regularly to keep the flame lit, that's when it's time to put another tank on.  If your high pressure gauge is inaccurate, you can be giving a lot of usable gas back to your supplier by turning the tank in based on gauge reading alone.Having a set of flashback arrestors on your torch is good practice regardless of what you believe about tank emptying.
Reply:You can, If it's warm and you have a 2 stage regulator but you risk getting acetone in your regulator. As delivery pressure drops, Tank pressure can go up making you think you have more gas than you do. Make sure you have check valves so you dont send the wrong gas into the wrong tank..
Reply:I do have check valves on the regulator ends of the hose, but I don't have flashback arrestors. They didn't come with my smith setup. Are there any recommendations for reasonably priced ones?So, from the sounds of it I shouldn't run until it's empty but I can still run it until the flame starts fluctuating?
Reply:Originally Posted by NVWIt's best to not run any tank completely empty.
Reply:Originally Posted by weldbeadwhy?i can see not wanting acetone to come out..but why not empty oxygen, argon, ?
Reply:Acetylene is a bit different than other gases in that a point comes when the low pressure won't provide enough fuel gas to keep the flame big enough to do much, (assuming you're not using a jewelers torch). With acetylene, you're not likely to just leave the tank open to bleed off into the atmosphere, which is easy to do with argon, nitrogen and most others.I also think that, when the pressure has dropped to a fairly low value, it's much harder to draw the acetylene off at a rate high enough to bring acetone up with it, although that might be somewhat temperature dependent; at very high temperature, it's probably easier. I believe the processor is supposed to carefully check (weigh?) the cylinder to be sure it has the required amount of acetone present every time it's refilled, and occasionally (periodically?) the cylinder needs to be checked to be sure voids haven't developed in or above the filler material. The best procedure IMHO, is as stated above by tbone550, and that is to stop using a cylinder when the pressure drops enough that the flame keeps getting oxidizing and the regulator needs to be constantly adjusted. Remember that starting with a full tank, as the contents of the tank are reduced, the rate it will supply gas does go down so the tip size that can be used will also decrease. Ultimately, the pressure will reach a point that even a small tip can't be properly supplied.
Reply:Originally Posted by burnit2You can, If it's warm and you have a 2 stage regulator but you risk getting acetone in your regulator. As delivery pressure drops, Tank pressure can go up making you think you have more gas than you do. Make sure you have check valves so you dont send the wrong gas into the wrong tank..
Reply:I have heard that if the pressure gets low somewhere under 10-20psi you will get the packing or something coming out, black stuff. It will clog your regulators and torch and they will need taken apart and cleaned. I haven't seen this first hand but I have taken my tank down to around 15psi without seeing this.
Reply:Originally Posted by jereI have heard that if the pressure gets low somewhere under 10-20psi you will get the packing or something coming out, black stuff. It will clog your regulators and torch and they will need taken apart and cleaned. I haven't seen this first hand but I have taken my tank down to around 15psi without seeing this.
Reply:Originally Posted by Stick-manAcetylene is unstable at pressures higher than 15 psi. Your torch never sees acetylene pressures higher than 15 psi because your regulator, regulates it down to the psi  you need, usually between 5-10psi. So whoever told you that story, either does not know what he is talking about or you had misunderstood. I have never heard of a regulator clogging from acetlyene.