Air receiver

Hi There,
I have a need for an air supply of about 300 psi and quite a lot of cubic feet too. It's for starting an old engine and using a descaler and I have been using 2 old refridgerant cylinders which work OK but are 20 years old. I have a Bedford lorry compressor.
I do have an old acetylene cylinder that appears much heavier construction and I have emptied all the charcoal out and inspected it and it looks OK. How much should this safely cope with and how could I verify it up to a certain pressure without too much danger of loosing it? I have an oxygen cylinder which is obviously very able to stand any pressure I could muster, but it's the wrong shape!
Any comments welcome. Thanks, George.

  Quoted Text Here  
I don't know what pressure such a cylinder would take but 300psi would be way above its normal rated use. Acetylene can explode violently if pressurised above about 15psi and I believe it is illegal to pressurise it in the UK. In cylinders the gas is dissolved in (typically) acetone absorbed on a porous solid, so the pressure is very low.
Don't try to test it with gas pressure. At 300psi there is a lot of stored energy ( the volume of gas in there at atmospheric preesure is 20x the volume of the cylinder) and if it were to fail you would get a nasty bang. The only safe way to test would be hydraulically - fill it with water then pressurise that.
Personally I would regard anything that size at that pressure as a potential bomb and I'd want professional assurance that it was well inside safety limits. BOC or air products could probably tell you the safe limits for an acetylene cylinder - they also have hydraulic test facilities.

Norman Billingham wrote:
  Quoted Text Here  
Thanks for that Norman,
I have an acetylene regulator with two pressure gauges in my workshop, so I will look tomorrow and see what the HP one reads, that will give me an idea. Stamped on the neck of the cylinder is TP 50 - which I took to mean 50 atmospheres. 50 psi seems extremely low for such a heavy duty tank. I have had it up to about 150 psi already, which compared to the refridgerant cylinders is about a third of their working pressure.
I do take your point about acetylene though. I have a carbide generator and its safety valve release is about 30 psi. I shall also try and ring BOC. The generator was rescued and rebuilt in the middle east and is described on my website. It's at the end of the old engine section:
http://www.maribelecosystems.com/OldEngines.html
Regards George.

most tp on cylinders is in bars i.e. a normal argon cylinder has 300 bars of gas in it
I would avoid using the acetylene cylinder just to be safe as it will explode between 2.5% and 81 % to air mix i.e. you don't need much
  Quoted Text Here  
most tp on cylinders is in bars i.e. a normal argon cylinder has 300 bars of gas in it
I would avoid using the acetylene cylinder just to be safe as it will explode between 2.5% and 81 % to air mix i.e. you don't need much

  Quoted Text Here  
generator
ring
is
section:
George,
Interesting site. I hope I'm not teaching granny the egg trick here, but are you aware that the oxy-acetylene torches used with acetylene generators are different from the (now) standard ones, and are designed for lower pressures?
AWEM

  Quoted Text Here  
of
descaler
but
it
could I
  Quoted Text Here  
loosing
stand
would be
  Quoted Text Here  
pressurise it
  Quoted Text Here  
stored
the
bang.
water then
  Quoted Text Here  
potential
safety
for an
  Quoted Text Here  
IIRC most UK cylinders have the safe working pressure, test pressure and test date impressed into the neck
AWEM

  Quoted Text Here  
Why not consider a surplus propane cylinder instead? The vapour pressure of propane at 50C is 252 PSI and I think the test pressure is about 400 PSI. I would however be very careful about pressurising a fuel gas cylinder of any sort with air until I had purged every last vestige of gas from it. Filling it to overflowing with water is one way of achieving that. Propane bottles come in various sizes up to 49Kg which can hold about 110 litres, and have a handy 3/4" BSP taper thread in the neck.
If it were me, I'd want to carry out a hydrostatic test on anything of any volume that I was proposing to pressurise to 300 PSI - as others have pointed out, that will make a hell of a bang if it comes unglued.
I was looking for a photo I once saw of the roof of a garage where an employee had been inflating a truck tyre when it exploded. The unfortunate chap was killed, and the roof had a perfect outline of his body marked on it, where the explosion had blown him. I couldn't find it, so these will have to do:
http://www.alberthaviation.com/TireCageVideos.htm
Regards
Pete

George wrote:
  Quoted Text Here  
Is that for your Diesels for compressed air starting? I have read your site. Very nice engines!
Nick

Nick Mueller wrote:
  Quoted Text Here  
Thanks for all the useful comments. I looked at two old acetylene regulators I have and they both read up to 40 Atms. So I think the cylinder TP IS 50 Atms which is 700 psi. - seems safe enough for 300. I may fill it up with water and blow it up to 500 to verify this. In view of the fact that I took about two days vacuuming all the charcoal bits out of it, I doubt if there is any gas left.
Or, in view of BOC's negative comments about it being a welded construction (I should have asked how oxygen ones are made!) I may make a safe stand for the spare oxygen cylinder I have - the reason I wanted to use the acetylene one is that it is a lot less liable to fall over. I could pump that up to 500 psi with no problem at all and this one cylinder could replace the two refrigerant ones I currently use for the Blackstone.
I have not actually used the carbide generator in anger, so the torch issue has not come up. I have a variety of torches ranging from truly ancient to pretty modern and currently use propane for cutting and bronze welding. Surely the pressure in a carbide generator being about the middle of that selectable from an acetylene regulator anyway, it should not need a special torch.
Anyway, thanks again. If it does pop you will probably hear the bang.
Regards George.

George wrote:
  Quoted Text Here  
My acetylene tank says 60 bar. But then I don't know wether this is the maximum allowed pressure or the test pressure (I guess the later). They are filled with a pressure of 15 bar, red bar on the regulator is at 18 bar. Certainly, the 60 bar are not with acetylene inside!
My oxygen tank says 300 (without unit), my Corgon and my argon tank says 300bar, allowed pressure is 200bar. So they might have a 50% safety margin for allowed pressure and test pressure.
Maybe you can find a manufacturer of such tanks and verify the numbers before the big bang happens.
Nick