How long can air sit in a tank?

[faster7581]

I bought 2 nice clean al80's, one had 700psi, the other was 3k.. I'm not sure when it was filled, but the last vis was August 2011, so at the most, it's been in there for 4 months.. Will the air go stale, or bad after awhile?
thanks
mike b

 

[JBRES1]

Hi,
Most likely the air is good.
Open the valve a little, cup your hand over the opening and smell the air as it comes out.
If you smell anything, dump out the air and have it re checked.

Jim Breslin

 

[smellzlikefish]

The only scenario I can think of where otherwise good air will go bad is if there is moisture in the tank that is causing corrosion of the metal, decreasing the O2 in the tank over time.

 

[j yaeger]

ditto the above
ive personally used a fine vintage 3 year old mix and am no worse off for it
...as far as i can tell

have fun
yaeg

 

[Brendon]

The only scenario I can think of where otherwise good air will go bad is if there is moisture in the tank that is causing corrosion of the metal, decreasing the O2 in the tank over time.

Which is more likely in a steel stank...

 

[halocline]

It's probably okay. Unless you're sure of the source, I would drain it and inspect the inside of the tank while it's empty. If you're confident that the source of the fill was good, dive with it. The idea of smelling a bit of the air is a good one, although it's not going to tell you for sure that it's good, but it will alert you to bad-smelling air. 4 months is nothing for air to sit in a clean tank, so it's not the time, so IMO the only issues are your knowledge of the source of the air, and do you want to look in the tank yourself before using it.

 

[mathauck0814]

Probably fine, but for a $4-5 fill (assuming that it's actually air since your question stated "air") isn't it better to drain it and have it dealt with?

 

[300bar]

A whole 4 months old :shocked2:

I recently used a steel tank that was filled last in ...... 1987,yep still at 200bar.
It was a shallow dive but no smell or taste at all.Not even a steel taste.
I'm still here, so you'll be fine

Bottomline, nothing comes in when under pressure and when dry no O2 will be lost.

4 months 50% of my tanks will sit atleast that long. (I've 20 full tanks waiting for me all the time)

 

[tbone1004]

where are you getting $4 air fills? luckily I have compressor access, but the shops here charge $8 for an al80 and $12 for anything bigger for air...

he said nothing can ENTER the tank, which is true. If it is pressurized, nothing can enter the tank. Physics right there. What can happen is what was in the tank can become more hazardous than it was. i.e. any moisture problems. You can leave a tank in the ocean for years and the only moisture in it will be what was pumped into it or left in it during it's vip. Condensation only really occurs with rapid cooling of the tank, and again, that is only what moisture was left in the tank coming out of solution, not anything that has entered the tank. I'm not saying I'd dive a tank that was last filled in the 80's, nor one with unknown history, but you won't see any moisture enter the tank except from a fill whip or when the valve is removed.

@the OP, if you know it was vipped in august, and you know it hasn't been empty, and only been filled by a shop or someone with a good clean compressor, I'd dive it. Our school tanks sit from early May until late September, and we'll dive them. They get their vip as a christmas present, and our compressor is clean and dry so it's not a problem. If you're any bit hesitant about it, then drain it and vip it

 

[ktomlinson]

8-12$ for air? That's crazy man. We pay $4-5 down here for air..it doesn't really matter what size tank. Nitrox is $12. At $12 I think I'd buy a nice used compressor.