+ rating on tank question

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enchantmentdivi
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+ rating on tank question

Post by enchantmentdivi »

I need some info to settle a debate….

If a diver has a 85cf tank that is stamped 2400psi but has a + rating, is it full with 85cf of gas at 2400psi or 2640psi?

TIA!
Jenn
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Dominick Gheesling
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Re: + rating on tank question

Post by Dominick Gheesling »

2640psi is the full working pressure of that tank.
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eh.haole
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Re: + rating on tank question

Post by eh.haole »

The direct way to know this is to fill it with clean water to measure its internal volume (e.g. weigh empty vs. full, 1kg = 1 liter volume), then multiply that volume by the number of atmospheres of pressure when filled with compressed gas.

DGX claims a steel LP85 has an internal volume of 13 liters
https://www.divegearexpress.com/library ... capacities

At 165 bar (~2400psi) that would contain
13 L * 165 bar = ~2150 L*bar = ~76 cf*atm

At 183 bar (~2650psi)
13 L * 183 bar = ~2375 L*bar = ~84 cf*atm

This really underscores another area where finally switching to metric would be so helpful! The cylinders are even fabricated in a metric country.

In Florida, it is reportedly commonplace for cave divers to fill their modern steel Faber 'LP' cylinders to ~200+ bar (even 250 bar), which is in the 3000 to 3500 psi range. That would be up to ~110 cf for an '85?'. As far as they are concerned, the US D.O.T. LP 2400(+)psi rating was just a government stamp to get the cylinders imported. No public dive shop here would be crazy enough to risk this so you would need to 'know a guy'
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60south
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Re: + rating on tank question

Post by 60south »

eh.haole wrote: Wed Apr 26, 2023 7:43 am At 183 bar (~2650psi)
13 L * 183 bar = ~2375 L*bar = ~84 cf*atm
Hm.

In other words, you need to fill it to the full+ rating, 2650 psi, to achieve the 85 cu ft.
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enchantmentdivi
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Re: + rating on tank question

Post by enchantmentdivi »

Thanks everyone!! Y’all helped me win the debate! :)
Jenn
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