What pressure do you store tanks at for long(ish) term?

[Jonny Wishbone]

The change in pressure from high to low as in exiting the valve is what causes the valve to get frost on it. The dry air inside the tank is not subjected to a pressure change that will create humidity out of an environment that has no humidity in it. What did we learn in OW class about tanks? To always keep a few hundred psi in them to keep moisture out right? Of course unless you get a fill monkey that doesn't blow out your Din valve and blows the few drops of water in the threads into your tank.

 

[TMHeimer]

I leave them either full or with whatever's in them--usually 500+ PSI. I have heard that either 4 months or 6 months is a "maximum" to use the stored gas. Then again, others have disagreed with that. I figure no one really knows for sure.

 

[TrimixToo]

The gas should be good for at least three weeks, or three days past forever. Nobody really knows, but I routinely put aside fills for planned dives that I use a year or two later. If they analysis matches what they were put away with, I don't worry. Never have I had one *not* match, but there's always a first time, I suppose.

From a safety standpoint, aluminum cylinders should be stored either full or with a few hundred PSI in them but no more. Otherwise, in a fire the walls can lose strength before the burst disc blows and the tank can go "boom." Or something (I have never heard one go in a fire, but I'd imagine that one with air would just make a big "whoooosh!" noise.) Lest you think this is mere theory, I saw this tank in a Florida dive shop a few years ago...you will note that if the burst disc had blown, the tank would be intact (though still destroyed):

Steel tanks should be find either way. It's hard to imagine the tank getting hot enough to blow before the disc goes from heat or pressure unless the heating is very localized (think "Oxyacetylene torch").

 

[Doc]

From a safety standpoint, aluminum cylinders should be stored either full or with a few hundred PSI in them but no more. Otherwise, in a fire the walls can lose strength before the burst disc blows and the tank can go "boom."

Same result 30 years ago on a liveaboard tied up at CoCoView Roatan. Full tanks? Just a burst disc, but...empty tanks, kaboom. The splayed open tank is still hanging on a wall down there on island.

 

[KentB]

The gas should be good for at least three weeks, or three days past forever. Nobody really knows, but I routinely put aside fills for planned dives that I use a year or two later. If they analysis matches what they were put away with, I don't worry. Never have I had one *not* match, but there's always a first time, I suppose.

From a safety standpoint, aluminum cylinders should be stored either full or with a few hundred PSI in them but no more. Otherwise, in a fire the walls can lose strength before the burst disc blows and the tank can go "boom." Or something (I have never heard one go in a fire, but I'd imagine that one with air would just make a big "whoooosh!" noise.) Lest you think this is mere theory, I saw this tank in a Florida dive shop a few years ago...you will note that if the burst disc had blown, the tank would be intact (though still destroyed):

View attachment 460645

Steel tanks should be find either way. It's hard to imagine the tank getting hot enough to blow before the disc goes from heat or pressure unless the heating is very localized (think "Oxyacetylene torch").

That tank-WOW

 

[BRT]

That tank-WOW

And yet it looks like it just released the air and did not bang around or fragment. Even a burst disc failing can tip a tank.

 

[Brilig]

I would think the wear and tear on a tank comes from the changing pressure from emptying and filling. That flexes the walls of the tank. If it's empty or full and just sitting there I would think no further stress is occurring.

 

[Mustard Dave]

I have tanks that are left filled semi-permanently. My bailout cylinders for my CCR have expensive mixes in them, so I would rather not drain for no good reason. I've just had to get one filled, having donated most of its contents when my buddy had a regulator failure. It was two years out of test, so it has been full for at least that amount of time.

Repeatedly filling and draining will cause greater fatigue than leaving it full.

 

[Tug]

As I'm a rebreather diver, I leave my tanks filled semi-permanently like the previous poster. My non bailout tanks get left in the previous state after the last dive but most of the time they are left filled.