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So what's the deal with getting air fills? Should I be upset if I don't get 3000psi on the mark? The reason I ask is, in my limited experience, 2750 or 2800 psi seems to be the norm. However, I was out at a local scuba park on Sunday and after lugging my tank from the fill station back to the water, i hook my reg up and see that I'm only at 2200psi. I felt like going back and demanding that they finish the fill, but laziness got the better of me and I went ahead and dove with the under filled tank since we'd planned a short dive anyways.
What is the actual protocol here. If a full tank is 3000psi, then why does it seem that you never get that, or have I just been unlucky so far (again, I am a pretty new diver)? Would anyone have gone back and asked that they top off the tank, or stopped by the fill station on the way out, explained the situation and asked for a free fill to compensate? Heck, I even tipped the guy for the poor service... what a sucker I am.
For quick fills, if they fill to 3000 psi, you will never get that. This is due to the cooling of the air in the tank. The slower the fill, the more pressure you will have after it cools. If you end up with a short fill, all you can do is bring it back and have them top it up. It may be a good idea to hook up a regulator before you lug the tank to the dive site. If you were getting nitrox, you would have to do this anyway as you are required to sign off on the pressure and percent oxygen.
At 2200 psi, I definitely would have had the tank topped up.
When I dive AL80s, getting a 2,700 or 2,800 psig fill does not bother me, because I get tired of looking at rock after 30 minutes, and that fill would have lasted me a good 60 minutes. But if I got 2,200 psig fill, I would have felt like I got screwed, and they owe me a full fill.
When I am allowed to fill my own tanks, I bump the regulator up to 3,200 psig, so I can get a good fill.
A hot fill will cool, and the pressure will drop. But it is always a good idea to gauge your tanks at the shop, before you take them away. That's the easiest time to correct an inadequate fill. It's way more annoying to discover the 2200 psi at the dive site!
More on temperature. We top off tanks to 2800 or more for open water students, because when they hit the 60 degree water, the air in the tanks will cool and psi drops a bit more. If I am paying for a tank fill I expect 3000 in a 3000 tank. Slow down the fill, I'll wait.
Last edited by DivemasterDennis; June 4th, 2012 at 06:52 PM.
I love my shop. When I take my tanks there, they can have them filled AND topped up in a few hours on the same day, with around 3300-3400psi (on a 3500psi tank), meaning that they had the initial fill, waited for it to cool, and then filled it to the max again. If I leave it for over a day, it's nearly max, max, or slightly over max.
I've never gotten an Al80 filled there, but I'd be happy with around 2800-2900psi. Any decent shop shouldn't deny you a top up, though, if you ask and they aren't excessively busy at that time. I start to get disappointed with anything lower than 2700psi.
You likely never get the full 3000psi because sometimes shops don't like going even a bit over the limit, so even with a top up, it still might not be maxed out. The tank will inevitably still cool a bit.