30 replies to this topic

[Scubatooth]

hate to break your bubble simon but those tanks where designed for rebreathers like the mark 15 & 16 as those tanks are spheres and not shaped like normal tanks. the info i remember seein those tanks hold like 60 ft3 of gas/



The tanks are the spheres just above the scrubber.

[peterbj7]

Who has a compressor that can fill tanks to 6000psi? And who has a first stage that can handle it?

[shadragon]

hate to break your bubble simon but those tanks where designed for rebreathers like the mark 15 & 16 as those tanks are spheres and not shaped like normal tanks. the info i remember seein those tanks hold like 60 ft3 of gas

I see. So I would need two to replace my S120. No way to place them on my BC. I would have to let them dangle off the front of my weightbelt. There's a mental image for you...

Who has a compressor that can fill tanks to 6000psi? And who has a first stage that can handle it?

If you build them, compressors will come.

I suspect if I had a T140 @ 6000 psi my buddy would have a half full AL50 and call the dive after 20 minutes anyway. hahaha Well, if I wanted 3 hour submersion time I would get a rebreather. Less explosion danger at depth too.

[Scubatooth]

thats not a mental image i want to have, thank goodness the meds from my procedure are still working so i wont need a bunch of mind bleach to get rid off that thought.

[JimG]

Who has a compressor that can fill tanks to 6000psi?

Probably nobody, as it doesn't make a whole lot of sense to do that. Once you get a tank up around 3500-4000 PSI, you start to get into the non-linear portion of the gas compression curve, due to Van der Waals effects. The result of this is that you do not get as much gas into the cylinder for the same amount of pressure increase. We operate a 4500 PSI cascade system in our dive program at the university, but hardly ever fill the banks above 4000 PSI because there's no real point to it - takes too long to fill the bottles, and then you don't get that much extra gas out of it anyway. It's actually quicker and more cost-effective to just run the compressor more often.

-JimG

[BeachJunkie]

Who has a compressor that can fill tanks to 6000psi?

Chuck Norris... and he fills them with his lungs like a balloon.

[Victoria]

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[Fordan]

I wonder whether people here, mostly American, know how tank sizes are measured? This is one example where I think the American way of doing things is simply crazy, and I can't begin to imagine how it arose. Note that I don't feel that way about all, or even most, American ways of doing things where they differ from the rest of the world.

As a user, not a filler, the American method tells me how much air I'm going to get from the tank. I don't really care that much about whether it's a big low-pressure tank vs smaller high-pressure tank, I know when I go underwater that I have 80 (or 100, or 120) cubic feet of air I can consume, and generally have an idea of how long the dive will last.

I was horribly confused when my first dives after certification were down on the GBR in Australia. "11 liters, that doesn't seem like much air..." (plus adapting to bar, and going deeper than I planned since meters seem shallower than feet)

[shadragon]

I was horribly confused when my first dives after certification were down on the GBR in Australia. "11 liters, that doesn't seem like much air..." (plus adapting to bar, and going deeper than I planned since meters seem shallower than feet)

Fret not. I suspect in under 20 years rebreathers will be the norm and tank size will become moot.

Well, unless this technology takes off.

[peterbj7]

As a user, not a filler, the American method tells me how much air I'm going to get from the tank. I don't really care that much about whether it's a big low-pressure tank vs smaller high-pressure tank, I know when I go underwater that I have 80 (or 100, or 120) cubic feet of air I can consume, and generally have an idea of how long the dive will last

But you don't know (exactly) how much air you have. An 80 (say) only contains 80 cu.ft. if it's filled to the pressure that the 80 was measured at, and that isn't standard across tanks.

[Landlocked Dive Nut]

We're all used to the systems & equipment we use regularly, and I'm pretty sure what I can get out of an AL80 filled to a particular psi.

All that really matters in the end is, do you have enough air to get to the surface safely? Guess this is why we're all taught to watch our gauges often.

[JimG]

I'm with Peter on this one, The imperial method of measuring tank capacity is just insane. The math is 10 times harder, and makes "on the fly" calculations really tough (although you do get better at it with practice). Metric is so much easier - an 11L cylinder only holds 11 liters when it is unpressurized. To find the pressurized volume, you simply mulitply by the pressure in bar. So a cylinder pressure of 100 bar is 1100 liters, 200 bar is 2200 liters, 230 bar is 2530 liters, and so on.

Even air consumption calculations (based on depth) are a breeze in the metric system, since you have 1 additional atm for every 10 meters of depth. So you take your depth in meters, divide by 10 and add 1, and multiply your SAC rate in lpm by that number. That's your depth compensated SAC rate. Divide that into the starting volume of gas in the cylinder, and that tells you how much time you have at that depth. That's much easier than dividing everything by 33 and using tank factors.

I really wish the US would switch to the metric system, but alas it will never happen.

-JimG

Edited by JimG, 10 February 2009 - 07:58 PM.

[Quero]

Well, back to the OP....

Some dive centers have bigger tanks and some don't. Here where I work we can easily get bigger tanks for bigger guys, but I have only one partner operation on Bali that can get big tanks for my divers when I send them there, and I think they're the only ones on the whole island who do have them.

So two bits of advice:
1--ask ahead of time; even when we do have these tanks, they are often in limited supply and reserved for other divers, or not filled and ready to go when you jump on the boat.
2--work on your air consumption; I recently had a DMT who is a body-builder--lots of muscle that needed lots of oxygen to fuel. He managed to wean himself from the big tanks and get his consumption down enough to do a whole hour-long dive to 80 feet on a standard tank. And he did this by becoming a more efficient diver.

Q.

[dive_sail_etc]

*ka-snip!* I recently had a DMT who is a body-builder--lots of muscle that needed lots of oxygen to fuel. He managed to wean himself from the big tanks and get his consumption down enough to do a whole hour-long dive to 80 feet on a standard tank. And he did this by becoming a more efficient diver.
Q.

Though I sport a slightly larger than average mass (5'11" @ 200lbs.) I have been Blessed from the beginning with below average air consumption. I usually return to the boat with the most air remaining, yet am right in there with the rest of the group depth-wise. I do this by remaining a more lazy diver.

P.S. Kudos on your traniee's achievement! I'm sure you had a hand in coaching him to his vastly improved psi/min rate.

[Quero]

*ka-snip!* I recently had a DMT who is a body-builder--lots of muscle that needed lots of oxygen to fuel. He managed to wean himself from the big tanks and get his consumption down enough to do a whole hour-long dive to 80 feet on a standard tank. And he did this by becoming a more efficient diver.
Q.

Though I sport a slightly larger than average mass (5'11" @ 200lbs.) I have been Blessed from the beginning with below average air consumption. I usually return to the boat with the most air remaining, yet am right in there with the rest of the group depth-wise. I do this by remaining a more lazy diver.

P.S. Kudos on your traniee's achievement! I'm sure you had a hand in coaching him to his vastly improved psi/min rate.

LOL, I'm sure that in your case there's more to it... some people are just naturals but well, there's a grain of truth in the "laziness" idea, too.

I sometimes tell my students who are blowing through their air by waving their arms around and kick-kick-kicking nonstop that they're "working too hard." It seems like a nicer way to say it than telling them their technique sucks, and after all, they can't help being awkward beginners, can they? Certainly relaxing and just letting it happen is a great air saver. As far as my DMT went, we worked hard on things like efficient finning, yoga breathing, trim, and other things to get him dialled in. But the achievement is all his.... I just facilitated.