Using "fuller" tanks.

[victorzamora]

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

Thanks, it's been corrected now. I meant to put 12L. Theoretically, 12Lx300bar has 3600L and a 15Lx232bar tank has 3480L. This would give the 12x300 tank a 120L advantage (about 3.5%). However, the van der Waals effect makes the amount of air (mols) LESS in the 12x300 than in the 15x232. My understanding is you'd get a bit of extra gas out of the 15x232 due to non linear compressibility effects (van der Waals).

 

[Storker]

My understanding is that the 12Lx300bar tank might actually contain less air than the 12Lx232bar team due to the van der Waals effects.

No, that's physically impossible. Go from 232bar to 300 bar, and you'll have more gas. You just won't have as much more as you expect from ideal gas calculations.

Here are some numbers, calculated using Wikipedia's compressibility factor numbers and a temperature of 20 degrees C:
12x232: ~2700L (95cuf, nominally 2800L
10x300: ~2700L (95cuf), nominally 3000L
15x200: ~2900L(100cuf), nominally 3000L
12x300: ~3300L (115cuf), nominally 3600L
15x232: ~3300L (115cuf), nominally 3500L
D8.5x232: ~3800L (130cuf), nominally 3900L
D7x300: ~3800L (130cuf), nominally 4200L
15x300: ~4100L (145cuf), nominally 4500L
D10x232: ~4400L (155cuf), nominally 4600L
D12x232: ~5300L (185cuf), nominally 5600L

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

Besides, y'all would have to change your beloved yoke regs to DIN

---------- Post added June 5th, 2015 at 11:08 AM ----------

i mentioned a 300 bar 12

The 300 bar 12 is nicknamed "long twelve" around here and is a very common choice for those who think their standard 10x300 or 15x200 doesn't pack enough gas for them. It's usually either that or a small double set like a D8.5x232.

Me, I'm quite happy with 3000L nominal capacity. With my SAC, I run into the NDLs about at the same time as I approach minimum reserve gas unless I'm on nitrox. Besides, with a sound profile, I can get almost an hour run time on that reserve, and that's usually about the same time I have to haul ass ashore to take a leak...

 

[Itsacon]

Also: An empty 300 Bar tank is a lot heavier than an empty 200 Bar tank with the same volume (thicker walls, sturdier construction), so you don't lose as much weight going from a 200 Bar 12L to a 300 Bar 10L as you'd expect (you do lose bulk, obviously)

 

[RJP]

Ultimately there are many other cheaper, easier ways for the relative handful of divers (in the grand scheme of things) who want to carry more gas to do so than to upgrade the industry to costly new compressors/materials/tanks/etc.

In an industry where a fair bit of the customer-base will go 100mi and two weeks out of their way to save $5 on a $100 mask... think anyone is gonna pay $20 for a fill to help a shop cover the cost of their new super-duper compressor?

 

[Storker]

Also: An empty 300 Bar tank is a lot heavier than an empty 200 Bar tank with the same volume (thicker walls, sturdier construction), so you don't lose as much weight going from a 200 Bar 12L to a 300 Bar 10L as you'd expect (you do lose bulk, obviously)

If you compare total rig weight for different tanks, the volume of the tank is the only really significant factor IME.

In my family, we used to have three different types of tanks: 10L 300 bar, 15L 200 bar and 15L 300 bar since we bought used gear when we were newly certified. The total weight of my rig, including weights, was the same for both 15L tanks. The lower weight of the 15x200 compared to the 15x300 had to be compensated with more lead on my belt and in my pouches so my rig weighted almost the same, since the difference in outer volume was very small. With a 10x300 tank, I could shave off some 3-4kg, which makes a difference to me when donning/doffing, on shore dives and on climbing the stairs into the boat.

I've sold my 15x300 now, since it was a b!tch to haul and stow due to the weight (it weighed almost 25kg empty, while the smaller tanks weighed in at 15-16kg...), and as I've said, I almost never really needed the extra capacity. I doubt I'll get much for my 15x200, otherwise I'd be selling that, too, and standardized on 10x300s.

You can, in fact, calculate both total rig weight differences and weighting requirements and get quite decent estimates which usually aren't more than about one kilo off.

Tank weight when empty is stamped on the tank.
Tank weight when full is weight empty plus weight of gas (capacity times gas density)
Tank outer volume is capacity plus weight divided by wall density (steel is about 7.8 kg/dm3)
Tank buoyancy is tank outer volume (in liters) minus tank weight (in kg).

Do the math, and you'll get pretty good estimates for changes in weighting requirements, and differences in total rig weight (including weighting). The buoyancy of the rest of the rig (valves, regs, exposure suit etc.) is constant, so it doesn't influence the difference between tanks.

 

[Bob DBF]

Besides, y'all would have to change your beloved yoke regs to DIN

Since I still have an old Sherwood yoke Reg from the early '70's that was made for 4000# service, I don't think it would be a big problem to make a yoke connection for higher service pressure since the regs themselves are now made for the same pressure regardless of their connection type. Not saying it would be better or worse, just saying...


Bob
--------------------------
I may be old, but I'm not dead yet.

 

[victorzamora]

No, that's physically impossible. Go from 232bar to 300 bar, and you'll have more gas. You just won't have as much more as you expect from ideal gas calculations.

Dad-gummit. I've fixed it now. Look, it was early. I was tired. What I meant was what you said: 12x300 is NOT more gas than 15x232. Van der Waals forces included, you get diminishing returns and harder math (things like cave diving thirds, this matters). The higher-er pressure you go (like 10,000PSI) the even lesser the benefit of the added pressure. It's not the happy linear relationship we see below 232bar here in the US.

Besides, y'all would have to change your beloved yoke regs to DIN

I'm glad you liked my joke, but I wasn't completely kidding. As far as Yoke vs DIN.....yoke can burn in hell. Divers that prefer yoke? THEY CAN JOIN THEM! I'm a Cave Diver and an Engineer. I'll never comprehend Yoke valves for the life of me. They should have died out the instant ther germans were like, "Ja, dis ees ein guten idea....ja?" with the DIN valves

 

[Storker]

Look, it was early. I was tired.

Sure. That's what they all say.

What I meant was what you said: 12x300 is NOT more gas than 15x232.

Totally agree. In practice, they hold the same amount (a 12x300 holds a smidgen less than a 15x232, but it's probably not a significant difference).

I'm glad you liked my joke, but I wasn't completely kidding. As far as Yoke vs DIN.....yoke can burn in hell. Divers that prefer yoke? THEY CAN JOIN THEM! I'm a Cave Diver and an Engineer. I'll never comprehend Yoke valves for the life of me. They should have died out the instant ther germans were like, "Ja, dis ees ein guten idea....ja?" with the DIN valves

Good thing I didn't say that, 'cause that'd probably started another metric-vs-imperial/'murrica-vs-euro flamefest...

 

[Dnaber]

I'm glad you liked my joke, but I wasn't completely kidding. As far as Yoke vs DIN.....yoke can burn in hell. Divers that prefer yoke? THEY CAN JOIN THEM! I'm a Cave Diver and an Engineer. I'll never comprehend Yoke valves for the life of me. They should have died out the instant ther germans were like, "Ja, dis ees ein guten idea....ja?" with the DIN valves

Please don't hold back..... tell us how you really feel about yoke divers.......

 

[kelemvor]

I thought LP tanks were always supposed to be filled to 3800? Sheesh, you guys and the light fills.