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acetylene... not getting enough pressure, need advice

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I have my oxygen and acetylene cylinders (both 40 CF), and I'm only getting about 6 psi on the output gauge of the acet regulator.  I got my tanks from praxxair and used them for the first 3 or 4 days with no problems at all.  About a month later I was home from school for a long weekend and was met with this problem. 

Would you guys suspect that the problem is in the regulator or the tank itself?  My acet regulator does have a tank pressure gauge, but it doesn't work (got most of this stuff extremely cheap from a school equipment liquidation sale), so i can't determine by using that.  I tried cracking the tank to see if I get the sharp woosh, and it was definately weaker than before.  I've tried using it twice now since finding this problem, and for the first minute it can give almost 10 psi, then it quickly drops to 4.  My uncle has been using oxy/acet torches for years and he seemed pretty confident that it was the regulator, and said I should send it to the manufacturer and they should be able to clean it, but I'd like some other opinions before doing so. 

The main reason I think it could be the tank is because it's the type that requires a tank wrench, and it's just way to difficult to turn.  I really can't beleive that it's supposed to be this hard.  I have to hold my tank wrench in a vice grip to get enough leverage to close it.  Could it have a slow leak? 

Everything I read online when I was considering a torch states that the tank wrench style is the norm, but my uncle said that's crap, cause his has a knob and almost all of the tanks either of us have seen in person do too.  What gives? 

If it's the regulator, is there a good way I can try to clean it myself?  If it's a leaky tank, could/would Praxxair test it and credit me toward a replacement if it proves faulty?

thanks for any help,


If you had a leak you would smell the actelyne and if it was in an enclosed area could have had an explosion. So if you don't smell the gas then I'd say either a faulty tank valve not allowing you to open the valve all the way on the tank or the regulator is not working properly. Best to get a new set of regulators, much cheaper than blowing up your place of work, home, yourself and others.


DO NOT mess with the regulator, If you have no clue as to what you are doing you can can your family a lot pain and suffering. You don't list where you live the colder the temp outside or the bottle temp the lower the pressure of the gas in the bottle.

If you have bought used tanks, from a private party you may have gotten burned on the tank valve being damaged.  Could the acetylene tank that has a tank wrench be a B tank instead of a 40 cuft one.
Does it look like the larger tank Which is called a bus tank from the old days of being the size they used on the lighting systems for buses. Now used as an tank for air/acetylene torches.

The valve can be leaking, because it is bent, or the seals are damaged from the repeated cranking down to seal it when closing.  @ 70'F the pressure on an acetylene tank is 225psi When full. Because of the low pressure compared to oxygen 2,250psi @70psi.

You open the tank valve no more than one turn, but I was taught in the 60's that turn works and if there is a problem is faster to turn off.

Because the acetylene tanks valve has only one seat and @ relatively low pressure leak by isn't considered a problem. Oxygen tank valves have two seals and should be opened all the way to seat the back seal to stop any leak by.

And the newer tanks all have valve handles, older tanks (acetylene) had wrenches. As the B and MC sized tanks in the above picture.

If the ambient temp and all other things are ok. best safest and cheapest is find out what the LWS will charge for valve replacement. And check what they will charge for a rebuild of the gauges. And remember always take the pressure off the regulator when you turn off the set up. This prevents problems with the springs, diaphragms and seals on both the regulators.
It also can prevent blow out of the regulator when opening a full fresh tank.

good luck and be safe.

I bought new tanks on ebay and then took them to praxxair and traded them for full tanks.  From what I understand, gas supply places have to make sure that all the tanks they sell people are within their pressure test date, correct? 

and it's the B tank, not the MC.

Should I take it back to the place where I got it and have them take a look?  The thing about the tank valve not allowing proper flow seems pretty likely.


If you had the tank exchanged at the local Welding supply then by all means take it back and have it checked. The B tank is no way near 40cu ft. I have had a bad valve tight like you describe. And have taken it back, it is now a Praxair. But then I have been dealing with the guy behind the counter for 25 plus years.

And while you are there, check into what the regulator will cost to get repaired. Again DO NOT ATTEMPT repairs on the gauges or regulator itself.



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