Bleed old air from tank?

[Airfree]

I have a fairly new (2-3yrs) steel tank that was filled and inspected at that time about a year ago.I will not be using it until next Spring,how can I safely bled the compressed air out? I live in a remote/mountain area and would like to avoid a long trip to the nearest scuba shop if possible.

 

[cmburch]

I do not think it is a good idea to bleed the air out.

If there is no pressure in the tank it will have to be inspected.

I guess it will have to be inspected anyway since it is over a year old.

I have used tanks that have sit for over a year without any problem.

To bleed air just crack the valve a little and wait a while. That is what I have seen them do when they do an inspection on my tank before. I would just leave the air until next time I get it inspected or filled and let the shop do it.

I found this link
Scuba Tanks : A Guide on how to maintain your scuba tanks.

 

[tfsails]

If you really want to bleed the air out, leave about 200 psi in it so that moisture won't get into it and cause the inside to rust. However, if it were my tank I'd leave all the air in it until you either need to VIP the tank or decide to dive with it. It probably won't go bad, but since it's a steel tank there is a chance that there is enough moisture in the air in it to cause rust, which will deplete some of the oxygen in it. Of course, this isn't a good thing, so I'd drain it, VIP it, and refill it.

If it were an aluminium tank, I'd just leave the air in it and use it next time I went diving.

 

[diver 85]

I'd leave it as is & think about about using it next spring-----air in a good tank will last a (good)while....

 

[Doc Harry]

You don't need to bleed the air.

However, if you let gas sit in a steel cylinder for longer than 2-3 months, you should analyze the gas for oxygen content before you dive with it, even if the tank is filled with plain air.

There are documented cases of rust in steel cylinders consuming oxygen, sometimes to the point that the gas is no longer compatible with life. There is even one documented case when a diver died because the oxygen in his steel cylinder dropped to 2% to 3% because of rust. The cylinder in this fatal case had not been used in 3 months.

There have even been some documented cases where rust has increased carbon monoxide levels in the gas.

Most people would say that there isn't rust inside of their cylinder. But how can you know unless you drain the gas, remove the valve and look inside? So it's a lot easier to just analyze the gas before you use it.

The data suggests that this sort of problem does not exist in aluminum cylinders.

 

[GrumpyOldGuy]

^^ Do you have links to documentation on these cases?

 

[Doc Harry]

There are documented cases of rust in steel cylinders consuming oxygen...

There have even been some documented cases where rust has increased carbon monoxide levels in the gas.

Corrosion of steel and aluminum scuba tanks

There is even one documented case when a diver died because the oxygen in his steel cylinder dropped to 2% to 3% because of rust. The cylinder in this fatal case had not been used in 3 months.

A FATALITY FROM BREATHING A CORROSION-INDUCED HYPOXIC MIXTURE

Schench, Hilbert V., and McAniff, John J. United States Underwater Fatality Statistics-1974. NOAA Report URI-SSR-75-10

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My detailed review of the data:

http://www.scubaboard.com/forums/tanks-valves-bands/260189-scuba-cylinder-long-term-storage-fact-fiction.html

 

[GrumpyOldGuy]

Thanks for the link. My first read of the articles only revealed compressor / intake / bad fill issues, not C02 from a corroding tank with a clean fill. I will reread in the morning, maybe I missed something.

 

[LouieLouie]

Thanks for the link. My first read of the articles only revealed compressor / intake / bad fill issues, not C02 from a corroding tank with a clean fill. I will reread in the morning, maybe I missed something.

The problem with a corroding tank isn't CO2, but FeO2. The O2 is drawn from the gas, hence leaving a hypoxic mixture. The corrosion process itself is definitely a result of a bad fill, as there isn't enough moisture in up to specs gas to make corrosion an issue.

 

[Airfree]

thanks Doc for your reply.It was by far the most alarming,which is usually the direction of advice that I go.Alsoit spurred additional posts which I appreciate.I do not have a regular buddy to bounce problems/ideas around with.The store where I bought the tank 3 years ago is good for this kind of advice but always heavy on selling me stuff .I have come to not trusting them because of their over zealous sales pitch and when I ask tech /questions he tends to put me down-"like I should know answer to the question".So,thank you!