How Low (psi) Can You Go

[Brewone0to]

For how long can you store air in a cylinder for it to be usable?

It should be ok for at least a few months,but if there is anything in the tank it could contaminate the air.
Also rust and corrosion Will consume the oxigen in your stowed air
and not sure (maybe someone else knows for sure)but I think I read somewhere
that rust in steel tank actually increases Co2 levels.
Both these conditions combined with breathing compressed air at depths, could put you into the hospital or worst yet the morgue.

 

[Brewone0to]

(getting SO close to 3000 posts....)

You Made It !!!

 

[Dive-aholic]

It should be ok for at least a few months,but if there is anything in the tank it could contaminate the air.
Also rust and corrosion Will consume the oxigen in your stowed air
and not sure (maybe someone else knows for sure)but I think I read somewhere
that rust in steel tank actually increases Co2 levels.
Both these conditions combined with breathing compressed air at depths, could put you into the hospital or worst yet the morgue.

If you had a good VIP and don't empty your tanks, then this won't be a problem. The air doesn't go bad, even if it's nitrox. I have some tanks that only get used once every few months. I just don't have a need for them here in Arizona, but when I head to Florida, they definitely get used.

 

[ClayJar]

not sure (maybe someone else knows for sure)but I think I read somewhere that rust in steel tank actually increases CO2 levels.

Steel tanks have at least some carbon in the alloy, but the fraction is so very low that I wouldn't think it'd be relevant. I've read that high oxygen concentrations can react with some types of O-rings to create carbon monoxide, but it does not seem at all common for people to die from CO2 or CO from oxidation reactions between their tank and "recreational" breathing gases.

As far as how low you can go with the pressure in scuba cylinders, if you've breathed the cylinder down to the point that the cylinder pressure is below the nominal intermediate pressure (eg. 150 psig at 1 ata ambient), it'd probably be a good idea to be ending your dive before you get to feel what it's like when you go to zero (guage), since you're probably soloing in the pool.

(I seem to store mine around 2700-2800 psig, but that's just because Vortex gives hot, fast, short fills [and wet, too!]. If the fills were from my LDS, I'm right near 3000 psig.)

 

[piikki]

As far as how low you can go with the pressure in scuba cylinders, if you've breathed the cylinder down to the point that the cylinder pressure is below the nominal intermediate pressure (eg. 150 psig at 1 ata ambient), it'd probably be a good idea to be ending your dive before you get to feel what it's like when you go to zero (guage)

This is what I was told too... and especially when I was diving buddy's upstream regulator... not good to let tank too close to the intermediate pressure or reg will spit the last 145 PSI. Never tested.
With steel tanks I do not drain tanks below 500PSI. One reason being that there are (some) local shop(s) that require a VIP if a steel tank is brought for a fill with <500PSI in it (!!!) Can someone explain why 450PSI would require this?

For long term storage I leave 500-700PSI in the tank.

 

[teknitroxdiver]

This is what I was told too... and especially when I was diving buddy's upstream regulator... not good to let tank too close to the intermediate pressure or reg will spit the last 145 PSI. Never tested.
With steel tanks I do not drain tanks below 500PSI. One reason being that there are (some) local shop(s) that require a VIP if a steel tank is brought for a fill with <500PSI in it (!!!) Can someone explain why 450PSI would require this?

For long term storage I leave 500-700PSI in the tank.

More dollars in their pocket. Thats it.

 

[piikki]

More dollars in their pocket. Thats it.

That's what I suspected and decided not to return to argue the case further since it really was not a burning issue for me...

 

[JeffG]

One reason being that there are (some) local shop(s) that require a VIP if a steel tank is brought for a fill with <500PSI in it (!!!) Can someone explain why 450PSI would require this?

Dive shop monkeys are idiots.

 

[teknitroxdiver]

That's what I suspected and decided not to return to argue the case further since it really was not a burning issue for me...

Did you ask them their reasoning?

 

[piikki]

Did you ask them their reasoning?

You mean from the guy whose mouth hangs to his navel? It's for my safety of course! Don't be silly