How long is a tank of air good?

[OWSI176288]

I would have to pull out some old textbooks to figure out the details but your point is how I remember things. The condensate on the outside was pulled from the air outside. The air inside should contain very little moisture so it would be hard for it to saturate the inside of the vessel. If the air inside the vessel has a high moisture content then your fill station is a problem.

Exactly!

Both Grade D and E breathing air should have a dew point of -50 oF. So, you don’t have to worry about moisture while emptying a tank if you have good air (breathing air quality). Because I don’t believe you can get a tank that cold while emptying it - so no moisture formation.

A quick and “rough” calculation, without even taking into account that pressure inversely effects dewpoint, suggest dropping from 75 oF to hit a dew point of 40 oF (a reasonable tank temperature with valve wide open) would require a relative humidity slightly higher then 40%. If you have air with a relative humidity of 40% in your tank, you got bigger problems to be worrying about - like hygroscopic corrosion, first stage freeze up, etc.

 

[miketsp]

Older relevant thread:
http://www.scubaboard.com/showthread.php?t=57838

Here is a thread where I did a calculation of steel & O2 used to form rust
http://www.scubaboard.com/showthread.php?t=58076

 

[farrakhan]

C'mon if you have any doubt just empty them and pay the $5 for a new fill. You've probably spent more time and effort worrying about it then you would have to drain the tank and have it re-filled.

 

[waynne fowler]

First smell the air.. if all good then analyze the gas to make sure oxidation hasn't reduced the O2 content below acceptable limits.
Too easy.

 

[DandyDon]

First smell the air.. if all good then analyze the gas to make sure oxidation hasn't reduced the O2 content below acceptable limits.
Too easy.

:doh:
Thanks - the simple answers take me a while...??​

 

[Migu31]

Oooooo, would you like to breath old air from that tank? Again, we hope for dry fills, but how would we know...?
Test breathing it is one thing, diving it with depth and pressue would scare me. Get a viz, hydro, and new fill. Need to service the Reg, too.

I agree, but I think I would get a kick out of breathing 'vintage air' from back when Elvis was still alive and flairs were in fashion ... oh wait, aren't they back in fashion? ... er and the Elvis sightings too ... ahhh forget I said anything

 

[markfm]

Personally, I'd like to think of air as having a 7 day expiration -- keep diving, every week!

 

[NSDiver]

Oooooo, would you like to breath old air from that tank? Again, we hope for dry fills, but how would we know...?

Test breathing it is one thing, diving it with depth and pressue would scare me. Get a viz, hydro, and new fill. Need to service the Reg, too.

Funny thing about that. He took the stuff to the LDS and got the tank a hydro (it's fine). The shop said the regulator and the BC could be checked out for $90 - but they don't have parts to fix this stuff. SO, if anything was wrong with them, they couldn't fix it. Needless to say, he didn't pay for the service.

-Nick

 

[terrasmak]

When in doubt , change it. It may be perfectly fine , but piece of mind is always better.

 

[BarryNL]

The only real risk is with steel tanks rusting inside, which uses up O2 and means you could conceivably be diving with a tank with a dangerously low oxygen level. It certainly wouldn't hurt to put an O2 analyser on a tank that's been stored a long time just to check.