Using "fuller" tanks.

[Frosty]

A bit of a spin off from the multiple threads asking what tank size to use.
Given the improvements in material quality over the past 40 or so years why are we still sticking with our tanks pressure restricted to 200 bar 3000psi or thereabouts?
Are there compressor limitations in play as well as first stage/burst disk etc?


sorry folks-yep 200bar /3000psi -not 200psi as I typed

 

[tbone1004]

200psi? 200bar?

Aluminum tanks can't take it, in Europe they actually have 300bar/4400psi steel tanks. It's a lot of extra wear on the regulators when the pressures are that high as well, so 300bar is about as high as you really want to go. The other issue is compressors. Three stage compressors are expensive enough, in order to compress much above 300 bar you need at least 4 stages, if not more because the more stages you have the better the cooling, but then it has to run slower, so lots of factors.

 

[victorzamora]

There are some 10,000PSI tanks that have been designed for diving. They are one "big" tank filled with a cluster of smaller tanks, each at 10k PSI, with a linear regulator internally down to ~3000PSI. You then put your normal first stage on it and dive it that way. One problem there is that with a "normal" sized scuba tank, it's FAR too easy to get in trouble....and it's hard to rig a smaller total-sized tank that's about 80ft3.

The biggest problem with those is the infrastructure. 10k PSI compressors aren't anything to scoff at. You also start getting away from the linear, "Ideal Gas" peformance at "lower" pressures. Up to 3000PSI, gas volume is linear(ish). Even at just 300bar/4500psi, compressibility effects means that it's not 50% more total gas than at 200bar/3000psi. At 690bar/10000psi, you are even further from linear. Losing linearity means a) harder math and b) less benefit.

 

[Carl_F]

Also, there has not been that much improvement in basic materials. Certainly more exotic alloys have been developed with different properties but "exotic" equates to $$$$. Basic Al and steel alloys are pretty much the same as they have been. Improvements have been made in durability such that a tank will last for more fills before developing flaws requiring destruction of the tank. But that doesn't equate to higher strength for increased pressure capacity.

 

[Redshift]

It doesn't make much sense to try to achieve greater pressures as gases can no longer be treated as ideal gases and the pressure will increase much faster than new gas molecules are being pushed in. That's already noticeable at 300 bar. A 15 l cylinder at 200 bar has more gas than a 10 l at 300 bar.

 

[Frosty]

It doesn't make much sense to try to achieve greater pressures as gases can no longer be treated as ideal gases and the pressure will increase much faster than new gas molecules are being pushed in. That's already noticeable at 300 bar. A 15 l cylinder at 200 bar has more gas than a 10 l at 300 bar.

Im hering ya-but then a 10l is a shed load easier to carry than a 15.
I was thinking a 12 with 300bar would be more uiseable gas than a 15 with 200

 

[rivers]

Im hering ya-but then a 10l is a shed load easier to carry than a 15.
I was thinking a 12 with 300bar would be more uiseable gas than a 15 with 200

A 300bar 12 is a beast of a tank. Also, most of the tanks are 232 bar, so a 300 bar 12 has a marginal amount more gas than a 232 bar 15 (about 120 litres). Plus, you need to find somewhere that will fill to 300 bar...

 

[Storker]

A 15 l cylinder at 200 bar has more gas than a 10 l at 300 bar.

About 10% or so, if the compressibility numbers I've been able to dig up are reasonably correct.

Im hering ya-but then a 10l is a shed load easier to carry than a 15.

It's also noticably more negative, which is a good thing if you dive in cold water. My rig is some 3-4kg heavier when I use a 15x200 than when I use a 10x300.

I was thinking a 12 with 300bar would be more uiseable gas than a 15 with 200

What about a 15x232? Compressibility really isn't an issue until you pass ~250 bar.

Around here, 232 bar is a quite popular pressure rating. AFAIK most new doubles in the shops here come in 232 bar flavor (typically D8.5x232 for a small set and D12x232 for a large), and I know quite a few who use 12s or 15s in 232 bar. The 12x232 holds roughly the same amount of gas as a 10x300 or a 15x200.



--
Sent from my Android phone
Typos are a feature, not a bug

 

[victorzamora]

A 300bar 12 is a beast of a tank. Also, most of the tanks are 232 bar, so a 300 bar 12 has a marginal amount more gas than a 232 bar 15 (about 120 litres). Plus, you need to find somewhere that will fill to 300 bar...

So, this isn't actually correct. My understanding is that the 12Lx300bar tank might actually contain less air than the 15Lx232bar team due to the van der Waals effects.

I'm convinced US tanks stop at 3500psi due to our inability to pronounce "van der Waals."

 

[rivers]

So, this isn't actually correct. My understanding is that the 10Lx300bar tank might actually contain less air than the 12Lx232bar team due to the van der Waals effects.

I'm convinced US tanks stop at 3500psi due to our inability to pronounce "van der Waals."

i didn't mention a 300bar 10 in my post. i mentioned a 300 bar 12