Is 'old' air not advisable with a dive tank?

[dtdukok]

I am just getting back into airguns again. I still have an old 15lr 232bar cylinder. I realise it is out of test but it is still full of air. Is it advisable to just get it retested and refilled or will the 'old' air still be safe to use.

Apologies if it is a silly question but I was thinking condensation might possibly be an issue?

The cylinder is about 25 years old and so is the air in it!

Any helpful advice is appreciated.

Cheers,

Darren

[Josie & John]

Hi Darren,

I would suggest leaving the old air and tank alone until it has been tested. Just not worth the risk to gun or person to do otherwise.

John

[R10_Mark]

Best to be safe and get it tested. You don't know if the seals are still intake.

[zanes]

Hi Darren,

I would suggest leaving the old air and tank alone until it has been tested. Just not worth the risk to gun or person to do otherwise.

John

+1.

The air will be fine (assuming it was good to begin with), but if it was me I'd be draining it down to low pressure (not empty) pronto and getting it down the test centre ASAP. I'd also be emptying it somewhere well away from people/property.

This is not something to mess around with.

http://www.scubaengineer.com/picture..._blo_small.jpg

[Turnup]

The air will be fine - it is dry when put into the bottle so there will be no condensation. HOWEVER, you have no assurance that the bottle and/or valve is safe. The air is only worth a few quid anyway. That bottle could be right on the edge of failing. What to do? Well I would not like to transport it while still under pressure, but equally I would be rather nervous about fiddling around with valves to de-pressurise it. Suggest you speak to your chosen test facility for advice, sooner rather than later.

[RobF]

Test first, ask questions later.

[dtdukok]

Thank you gents for all the sound advice (and the crap-your-pants picture!)

I will take it over the field out the back and gently let it empty then get it down to Dive-Line for a test and fill, all being well.

Is it cost effective to bother with an old cylinder though if it needs work to get it back in test?

Thanks again,

Darren

[zanes]

Failure of the test will result in compulsory destruction of the cylinder (assuming it doesn't catastrophically fail during test). My test centre charges a nominal £10 if a cylinder fails and has to be destroyed.

Go-dive charges about £200 for a complete 12ltr 300 bar fill kit IIRC.

Only work possible on them is replace valve and/or valve seals. Pretty sure the centre I use changes the valve seals as part of the test.

Prepare to be amazed at just how much air they hold and how long it takes to empty....

[zanes]

A lot of 'safety first' replies here but what can actually go wrong with using up the existing fill? With regards to subsequent fills then clearly it must be tested otherwise no reputable dive shop will fill it up again. I personally would use it for anything other than breathing.

Is it worth the risk of an unknown cylinder for the sake of a few quid's worth of air?

Yes, the cylinder could be OK- but the consequences of it not being (if the fill back in the 80s was a little bit damp?) are absolutely catastrophic.

[dtdukok]

"Hi Darren,

You can bring it into us in your car as long as you don’t allow it to roll around and knock the pillar valve.
Do not depressurise the bottle as it would have been filled with dry air and if you depressurise the cylinder you will allow normal ( moist air in and you run the risk of internal rusting.

We can’t guarantee that it will pass, but it should do !"

So I will wrap it up in cotton wool and get it down there.

Cheers,

Darren

[slinger69]

+1.

The air will be fine (assuming it was good to begin with), but if it was me I'd be draining it down to low pressure (not empty) pronto and getting it down the test centre ASAP. I'd also be emptying it somewhere well away from people/property.

This is not something to mess around with.

http://www.scubaengineer.com/picture..._blo_small.jpg

A pic that really tells a story. A salutary reminder Zanes.

Sometimes I wonder whether I'm developing a penetrating insight into the bloody obvious.

[Turnup]

"Hi Darren,

You can bring it into us in your car as long as you don’t allow it to roll around and knock the pillar valve.
Do not depressurise the bottle as it would have been filled with dry air and if you depressurise the cylinder you will allow normal ( moist air in and you run the risk of internal rusting.

We can’t guarantee that it will pass, but it should do !"

So I will wrap it up in cotton wool and get it down there.

Cheers,

Darren

Bit worried about that advice.

1) They will have to depressurise it to test it

2) How on earth will moist air get in?

[Nicks10]

Bit worried about that advice.

1) They will have to depressurise it to test it

2) How on earth will moist air get in?

Nope, that's spot on, when you depressurise a cylinder the gas undergoes a cooling process. This causes condensation and ice to form on the outside of the cylinder. When the cylinder returns to room temperature this can cause the cylinder to expand drawing in moist atmospheric air through the open valve. Moisture is a big problem in steel cylinders mainly for obvious reasons, but I do fill mixtures contains water into aluminium cylinders (at work)��

Only ever use divers air, it doesn't really have a shelf life. You would need a test before any one would refill it anyway, so just leave as is and transport it as you would if you were going shooting, down to the dive shop.
Cheers

[zanes]

Nope, that's spot on, when you depressurise a cylinder the gas undergoes a cooling process. This causes condensation and ice to form on the outside of the cylinder. When the cylinder returns to room temperature this can cause the cylinder to expand drawing in moist atmospheric air through the open valve. Moisture is a big problem in steel cylinders mainly for obvious reasons, but I do fill mixtures contains water into aluminium cylinders (at work)��

Only ever use divers air, it doesn't really have a shelf life. You would need a test before any one would refill it anyway, so just leave as is and transport it as you would if you were going shooting, down to the dive shop.
Cheers

This would be why I said " I'd be draining it down to low pressure (not empty) ".

However, the test centre are the experts here so I'd follow their advice over my own.

[Turnup]

Nope, that's spot on, when you depressurise a cylinder the gas undergoes a cooling process. This causes condensation and ice to form on the outside of the cylinder. When the cylinder returns to room temperature this can cause the cylinder to expand drawing in moist atmospheric air through the open valve. Moisture is a big problem in steel cylinders mainly for obvious reasons, but I do fill mixtures contains water into aluminium cylinders (at work)��

Only ever use divers air, it doesn't really have a shelf life. You would need a test before any one would refill it anyway, so just leave as is and transport it as you would if you were going shooting, down to the dive shop.
Cheers

I get it that venting will cause cooling, so, de-pressurise to low pressure, allow temperature to stabilise, vent last little bit, CLOSE VALVE. (I would have thought it obvious that the valve should be closed - apart from anything else this runs the risk of letting dirt in). I really don't like the idea of transporting a pressurised cylinder that is many years outside of it's test.

Also, were you aware that testing a cylinder involves FILLING it with WATER?