Filling scuba tanks
I have a compressor and fill my own tanks . Last week I bought two more tanks and was told not to even over fill them by as little as 100 – 200 psi or I would be shortening the life span of my tanks greatly and they would not pass a hydro test . I called another scuba store and they say that is what they do all the time so when it cools down you have a filled tank at the max fill rate . I stopped and thought about this and realized that they are also takeing a tank with only 200 – 300 psi and filling it in a matter of 3 -5 minutes were I am filling mine from 2000 psi to 3250 in 10 minutes . Which I think is much less stressful on the tank . I did some web serfing and here are a couple articles I wanted to share . As well as what a hydro test really is . Marvin
http://www.fillexpress.com/library/dryfills.pdf
http://www.deep-six.com/page37.htm
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Most good shops will have a fill bath. It is a bathtub with chilled water in it. You immerse your tank in it so that while you fill it cools the tank and air so when it stabilizes in temp you have a genuine 3000psi fill. With a chilled tank, you have to watch your tank. I’ve been on dives before where the tank was left out in the sun on the boatrack or shore, and the safety disc blew before we hit the water. I’m in hawaii, it gets hot here.
For pcp runs, fill slowly and let the heat bleed. I fill my own tanks using my own compressor and deliberately slow the compressor down to take longer to fill. While I’m rotating tanks for filling, the others get a chance to cool down so I can top them off in 20 minutes or so.
As far as life of the tank, hell, I’ve owned and used ball ended tanks from the dinosaur age, old military 92’s (alum). They will outlive you and me. The service life is not limited by expansion and contraction. It is limited only by onset of corrosion.
walt
One thing that can be done is to bring the tanks out into the sunlight. This gives you about a 100 Psi bump.
Marvin your right on the reduction of stress. We fill ours from 2000-2500 to 3K. So, most times we are only adding 500 Psi. which doesn’t generate much heat. We usually drop them off, they fill to 3K, then give them one final check before we leave to see that they are at a full 3K. I wish I could get them to overfill a little bit. But they won’t.
test
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I live in Hawaii. It gets hot here. TA LOCO! It gets over 100 here. I bet its never got to 100 there. Just messin with you walt.