Aluminum Doubles??

[FW]

I guess it depends how you define "volume".

Faber LP 95s could be:

1. 15 liter tanks (volume at 1 bar/ATM);
2. 86 cu ft tanks (filled to the 2400 psi service pressure);
3. 95 cu ft tanks (filled to the 2640 psi "+" rated pressure); or
4. 129 cu ft tanks (at a cave filled 3600 psi).

Around cave country, if I call them "Faber 95s" everyone I now knows exactly how much gas I'm talking about.

He is talking about internal volume, like item #1.

[Nitrogenius]

He is talking about internal volume, like item #1.

Correct..
there is no guesswork or speculation whatsoever..
this volume times pressure = gas volume carried..


With the Gas volume nomenclature you need two additional values to make your gasplanning..
With volume of tank that's all you need. you choose the pressure and number of tanks according to what your gas needs are..
It's quick and simple..

[DA Aquamaster]

I get what he's driving at Forrest, and it was a loaded question, as use of tank volume is not limited to liters.

Now, for full disclosure I like working in liters for rebreathers, since I started with no other frame of reference. A 2L O2 tank at 250 bar = 500 liters of 02, 500L / .8 lpm = 625 minutes. Pretty straight forward stuff.


However for a Faber LP 95 you have a 15L tank, so it's 15 x 250 bar = 3,750 liters for available gas.

But wait - that final volume of available gas is still dependent on tank pressure. Depending on the fill pressure it could also be 180 bar and 2,700 L, or 165 bar and 2,482 L.

On the other hand if working in PSI I can use a tank factor of 3.6 for an LP 95, which is in essence tank volume at 1 atm / 14.5 PSI / 1 bar. (95 cu ft / 2640 psi = .036 cu/psi x 100 = 3.6 cu ft per 100 psi.) Consequently;

2400 psi is 24 x 3.6 = 86 cu ft,
2640 psi is 26 x 3.6 = 94 cu ft,
3600 psi is 36 x 3.6 = 130 cu ft.

So it's a not a "95", it's "3.6" and if know my gas requirements in cu ft per minute the planning is just as straight forward - and I'm working in imperial units that I am more familiar with.

It's exactly the same concept, just in different units the diver may be more familiar with.

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You see a similar issue with competing units and systems in long range precision shooting.

All the cool kids train in Mils, which for mil-dot reticle range estimation purposes are designed to be used with metric units for estimate of target size in cm, and in turn estimate of range to target in meters, based on the number of mils the target subtends in the reticle.

Where the system falls apart is that many of those shooters who feel the need to work in mils like a military trained operator are unfortunately not native to the metric system and are much more familiar with inches and yards. Consequently, they start using a mil dot reticle while estimating target size in inches and tying to produce range estimates in yards, which significantly complicates the math.

If you work the problem with a mil reticle, cm and meters, a reasonably intelligent shooter can do the math in his or her head.

However, that same shooter can't do the math when mixing mils, inches and yards with any accuracy in their head, so they end up either using a table, slide rule style calculator, or a phone app to figure it out, and thus become dependent on equipment to over come a skills (or in this case a "unit") deficit. In many cases, they just skip learning to do range estimation using the reticle entirely (although many still want a first focal plane reticle and the downsides that come with it, even though they now have no practical use for it).

Unfortunately, when you explain to them that a reticle with hash marks in MOA in stead of mils is ideally suited to inches and yards, and allows you to once again do the calculations in their heads, they get all upset as it's not cool to use mils. They'll indicate they can compensate for it with a Mil-dot Master, and they'll point to a number of other shooters they know who also muddle through mixing units - and totally fail to miss the point that what they are doing is far less than optimum and far harder than it has to be.

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The moral here is that a cave diver should also be using what ever system he or she is most familiar with and has the greatest facility with when it comes to the math, and that diver should not be trying to mix and match two different systems.

If you use liters for tank volume, stick with bar for tank pressure, and if you use psi, stay with cu ft for tank volume expressed via tank factors.

What matters is that pre-dive, at the start of the dive and during the dive, the diver is able to do what ever math is required without fancy electronics that might fail, or be sitting in the back of the truck.

[Nitrogenius]

If you use liters for tank volume, stick with bar for tank pressure, and if you use psi, stay with cu ft for tank volume expressed via tank factors.

Yes tank factor would be the same concept in imperial ..
Just you have to learn/calculate the tank factors for the tanks you are using first..
In metric that is not necessary as already the nomenclature of the tank size specifies your tank factor..
Nevertheless using a litre volume does not get you very far using imperial units otherwise..

[OutOfTest]

I have some steel 7L 232bar cylinders that were recently filled to 390bar for a project.

I was very careful carrying them through the cave!

(57cuft at 3364psi normally, 96cuft at 5656psi when I filled em)

I was very careful carrying them through the cave to the sump...

And that's not mentioning the 450bar 3Ls that were also on that trip...


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[johnny boy]

His 3's ended up looking like LP104s

[OutOfTest]

I was more scared filling them...


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[webmasterj]

Have seen a couple guys in Bonaire diving AL 80 doubles (in open water) but am sure that is due to limited availability of other tanks like some others have mentioned in Mexico etc.

[Al]

Have seen a couple guys in Bonaire diving AL 80 doubles (in open water) but am sure that is due to limited availability of other tanks like some others have mentioned in Mexico etc.

Bonaire has warm water (no/thin wetsuit) and the drop-off isn't super deep.

[JohnnyC]

You see a similar issue with competing units and systems in long range precision shooting.

All the cool kids train in Mils, which for mil-dot reticle range estimation purposes are designed to be used with metric units for estimate of target size in cm, and in turn estimate of range to target in meters, based on the number of mils the target subtends in the reticle.

Where the system falls apart is that many of those shooters who feel the need to work in mils like a military trained operator are unfortunately not native to the metric system and are much more familiar with inches and yards. Consequently, they start using a mil dot reticle while estimating target size in inches and tying to produce range estimates in yards, which significantly complicates the math.

If you work the problem with a mil reticle, cm and meters, a reasonably intelligent shooter can do the math in his or her head.

However, that same shooter can't do the math when mixing mils, inches and yards with any accuracy in their head, so they end up either using a table, slide rule style calculator, or a phone app to figure it out, and thus become dependent on equipment to over come a skills (or in this case a "unit") deficit. In many cases, they just skip learning to do range estimation using the reticle entirely (although many still want a first focal plane reticle and the downsides that come with it, even though they now have no practical use for it).

Unfortunately, when you explain to them that a reticle with hash marks in MOA in stead of mils is ideally suited to inches and yards, and allows you to once again do the calculations in their heads, they get all upset as it's not cool to use mils. They'll indicate they can compensate for it with a Mil-dot Master, and they'll point to a number of other shooters they know who also muddle through mixing units - and totally fail to miss the point that what they are doing is far less than optimum and far harder than it has to be.

That is, quite literally, not true. Completely untrue comparison.

A milradian is completely independent of any system of unit. In the case of shooting, a mil is 1/1000th of whatever unit of measure you are using. It is much much faster, and much much easier, to do mental math if you work in metric because you are using a base 10 system. You can absolutely use mils with feet and yards but the math is stupid. Here's the distance formula in imperial: Distance in yards = 1000 / 36 x (Object size in inches) / Object size in Mils. And much easier in metric: Distance = Object size in meters / Object size in mils is much easier to do in your head. Either requires you to know the size of the target, the primary failure point of ranging regardless of the unit of measure, but actually correcting and holding is an order of magnitude easier in mils. It has nothing to do with "being cool," it has everything to do with using a much better system.

The really stupid stuff comes in when you're dealing with MOA since people use true MOA (1.047 inches), "shooters MOA" (1" per 100 yards), optics manufacturers may use any stupid combination of either, including mismatching reticles and turrets within the MOA system, and since the difference compounds at distance, when you're telling someone to crank 40 MOA and hold another 10 it gets stupid. Why do you think the top 100 shooters in the 2015 Precision Rifle Series ALL used mil-based reticles? Because it's smarter. And there's absolutely zero need to mix mils, inches, and yards. There's no need to compensate with a phone or a slide rule, it's still smarter, and faster, than using anything MOA. That's the top 100 precision rifle shooter in the world, in the most demanding precision rifle competitions, and quite literally, NONE of those top 100 shooters used any minute of arc-based reticle system. Going back every year until 2012 (where the data ends) it's something like, only 7% of all shooters in the series use MOA-based reticles, and none of them are in the top 20.

Maybe you're unable to work in mils, but that's not a failing of the system. That fact that so many people use it with zero issue whatsoever is proof of that.

So no, it's not like scuba tanks at all. I'm still trying to figure out how "10 liters x 200 bar = 2200 available liters" is more difficult than dealing with pressure plus tank factors based on different rated pressures coupled with a whole host of other silly imperial measurements. Easy math is better than hard math.

Related to the OP's question, yes, primarily in Mexico, but I've got a set at home just for piddling around with. They're fun to get in the pool with to suss out gear changes and such.