Used AL80s

[halocline]

My LDS doesn't do VE tests and probably doesn't really understand what they are. If your LDS is adding $10 for the VE test, they are surely marking it up quite a bit.

I would suggest just keep calling fire extinguisher places in your area and eventually you'll find one that will do scuba tanks. You can also ask other SB members from your area where they take theirs.

 

[tbone1004]

@JamesBon92007 no aluminum 80's actually hold 80 cubic feet at their working pressure.

we usually fill our 72's to 3200-3300 ish psi. This is still fairly similar to the cave fills to 3600psi on the 2400psi low pressure bottles in terms of % over rated pressure, and since they are built to the same engineering standards, it seems fair and mine have been getting filled like that long before I purchased them and most are on at least their 8th hydro.

@guruboy 's high failure rate is on a small sample size and the tanks could have been abused during their life. I don't know of any unlined 72's to have failed hydro within the group of guys that I know and dive with that haven't been full of water at one point and failed the VIP before we even got around to hydro.

in terms of finding the hydro shops, just call the shops up directly. None of them are likely to advertise that they do it, but if you call them, they likely have the ability to do it.

 

[redacted]

@JamesBon92007 no aluminum 80's actually hold 80 cubic feet at their working pressure.
.

All the specs I find have them coming in 2+/- cu ft short.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

 

[tbone1004]

@awap
L6X® aluminium SCUBA cylinders

Luxfer S080 and S80N both show 77.4cf at working pressure. Yeah, it's only 2.5cf short, but it's almost 5%

 

[guruboy]

we usually fill our 72's to 3200-3300 ish psi. This is still fairly similar to the cave fills to 3600psi on the 2400psi low pressure bottles in terms of % over rated pressure, and since they are built to the same engineering standards, it seems fair and mine have been getting filled like that long before I purchased them and most are on at least their 8th hydro.

I'm not an expert at steel tank dynamics, but you are filling 72s to about 90% test pressure. It seems to me that that would basically keep stretching the tank and give you a lower PE during the actual hydro test.

For example, if I take the tank whose last hydro was in '75 and failed with 11% PE and re-tested it, I bet it would pass with 4% or less.

 

[JamesBon92007]

@JamesBon92007 no aluminum 80's actually hold 80 cubic feet at their working pressure.

we usually fill our 72's to 3200-3300 ish psi. This is still fairly similar to the cave fills to 3600psi on the 2400psi low pressure bottles in terms of % over rated pressure, and since they are built to the same engineering standards, it seems fair and mine have been getting filled like that long before I purchased them and most are on at least their 8th hydro.

@guruboy 's high failure rate is on a small sample size and the tanks could have been abused during their life. I don't know of any unlined 72's to have failed hydro within the group of guys that I know and dive with that haven't been full of water at one point and failed the VIP before we even got around to hydro.

in terms of finding the hydro shops, just call the shops up directly. None of them are likely to advertise that they do it, but if you call them, they likely have the ability to do it.

According to a chart that I read some AL 80s hold more than others, but no, none appear to hold 80 cu/ft at 3000 which was the practical part of my statement. As most of us here (in this thread) are probably aware of you need about 3300 psi to attain 80 cu/ft. The problem seems to be getting it filled to 3300 which I have only seen once or twice while on dive boats. Usually it's right around 3000 and occasionally a little less.

If you fill a 72 to 3300 psi, how many cu/ft is that? I'm happy to hear that the tanks survive being repeatedly over-filled but, based upon my experience with the 72s, I'm not really surprised. This, of course, wouldn't help the OP much unless he can find someone who will fill "over" fill them. I have my compressor set to stop filling at 2475. Maybe it's time to make an adjustment.

 

[tbone1004]

According to a chart that I read some AL 80s hold more than others, but no, none appear to hold 80 cu/ft at 3000 which was the practical part of my statement. As most of us here (in this thread) are probably aware of you need about 3300 psi to attain 80 cu/ft. The problem seems to be getting it filled to 3300 which I have only seen once or twice while on dive boats. Usually it's right around 3000 and occasionally a little less.

If you fill a 72 to 3300 psi, how many cu/ft is that? I'm happy to hear that the tanks survive being repeatedly over-filled but, based upon my experience with the 72s, I'm not really surprised. This, of course, wouldn't help the OP much unless he can find someone who will fill "over" fill them. I have my compressor set to stop filling at 2475. Maybe it's time to make an adjustment.

the math isn't quite linear, but it's 71.9*3300/2475=~95cf. There is some non linear compression that starts to occur at those pressures, but they have the same water volume as HP100's.

I would at least adjust the compressor to 3000psi because by the time it cools off and what not you'll at least have a full fill there. Just make sure you have the right burst discs in

 

[JamesBon92007]

I would at least adjust the compressor to 3000psi because by the time it cools off and what not you'll at least have a full fill there. Just make sure you have the right burst discs in

Thanks for the reminder on the burst discs! I'm so used to not thinking about them I could have forgotten.

I fill my tanks in water plus my compressor is rather slow so with the way I have it set now it works out to very close to 2475 when they are cooled off.

Thanks for the formula too. That's a lot of air in a 72!

 

[halocline]

Most people would not fill LP72s to 3300 PSI, myself included. If t-bone wants to do it, that's his business. You only need to get them to 2700 to get 77 cft (same as an AL80) and that's not a huge overfill. At 3000 they're around 86 cft. It quickly gets to the point where you have to ask yourself, if you need that much gas on a dive, why not use a bigger tank instead?

 

[dumpsterDiver]

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