What cylinder characteristics are preferred

silent running

Hi Joe, isn't the gas's compressibility related to it's density in some way, and temp as well?

dive2dive2000

Joe,

Could you elaborate a little more on this quote, The little amount of blending that I have done, we would -18% of HE and -9% of O2 off of our psi results when PPB Trimix. Also keep in mind the HE bottle was about 10' from the Haskell, where the O2 bank was 30' away. We came up with this formula so we could dump the gases in the hose into the mix and not waste it by clearing out every time. This also added in an ideal mix factor, or should I say took out?

__________________
Safe Diving,
Martin

jradomski

Cant comment on the hose lengths I had to try and work out the numbers and see how everything is actually plumbed.... usually you subtract a little bit of o2 and add a bit of he to get it right..

Oxygen is a funny gas, at low pressures (it behaves almost ideal..) as pressure increases it becomes more compressible(up to about 2400psi about 6.3% more compressible, then it starts getting less compressible as pressure increases).. by 3000psi its about 5.5% more compressible than ideal gas laws predict.. if a tank held 100cuft of an ideal gas it would hold 105.5 cuft of oxygen..

Helium on the otherhand becomes less compressible as pressure increases by 3000 psi Helium is about 9.5% less compressible than an ideal gas predicts so a 100 cuft tank of ideal gas would only have 90.57 cuft of Helium.. so if you filled a tank with 50% oxygen (by pressure) and 50% Helium by pressure for a 100 cuft tank you would have about 2.75 cuft more oxygen than you expect and ~ 4.7 cuft less helium In this case the tanks actual capacity is quite near its ideal ( about 2% less) but it wount be a 50/50 mix.. (about 46% helium, 54% oxygen)

bump the pressure to 3500 psi and there is now about 11% less helium (for a tank with helium only)

I estimated some of the numbers above so please don't get anal if I'm a % or two off..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

silent running

Hi Joe, can you help me out here? I'm wondering what the relationship is btw different gases relative molecular density and their compressibility. Surely they are dependant/related someway, no ? Also, I'm assuming that when gas is cooled, it contracts and when it's heated, it expands. How do compressibility and temp. relate, especially in addition to the differing types of gas? Sorry to squeeze you and I know you're not a Physics Prof, but maybe it's not so obvious to me. Is there an easy way to explain these relationships? Thanks -Andy

jradomski

There really is no simple explanation.. The compressibility of gas can be figured out using Vad Der Waal's equation (among other methods)..

see

http://www.ac.wwu.edu/~vawter/Physic...atOfState.html


I also just remembered this link..
http://www.atomox.com/mixing.html

It gives some good explanations of gas compressibility..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

silent running

Thanks for the info Joe. Time for some homework... -Andy

leadking

This is all true and the Van der Waals table works that out. Internal volume at ideal gas laws are what 99.9% of divers in the U.S. use. We can really educate/confuse the **** out of them. So 3 liters is 183 C.I. use your own mix/pressure and the Van der Waals table and knock yourself out. The total gas voulume shift is not worth the trouble.

leadking

If we build them the will be hot dip galvanized

jradomski

yes but the higher pressure you go the more you lose in general.. and when you are talking about cylinders with a small capacity to start with every cuft makes a difference..

using air at 2400 psi your only about 1% short, but using air at ~3130 psi your about 4% short..
so for a tank thats "rated" as a 19 for 3130 its really only a ~18, while a tank thats rated as a 19 @ 2640 (canada) or DOT with+ its still basically a 19 (17 @ 2400)..
alot of people will only fill oxygen to around 2400.. so the lp cylinder has around 18 cuft of oxygen, while the 3130 cylinder only has around 15 cuft of oxygen and is carrying a heavier tank..

for the average CCR diver thats at least 1.5 hours difference of duration..

If you guys are applying for exemptions to start with why not just go with a steel with a higher tensile strength like used in the UK.. The cylinders are lighter and are rated for higher pressures..

as for making the cylinders 4in diameter rather than 3.9 you'll lose some of the inspiration/evolution users since that little bit of differense willmake the case harder to close.. There isn't much room to spare as these cases were designed around the faber cylinders..
You should keep up to your "30" at 3.9 inches (its easier to use a smaller cylinder than a larger cyinder),you have the length to spare.. or at least make the 30 the same diameter as your 13 and 19s..

about the only thing a dumpy 30 is good for is an ass mounted bailout cylinder..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

leadking

If you guys are applying for exemptions to start with why not just go with a steel with a higher tensile strength like used in the UK.. The cylinders are lighter and are rated for higher pressures..


This is exactly what I'm planning. An exempt cylinder at 3442 psi, the metallurgy is similar to high strength European models. 3 liter cylinders will hold 25 cf of gas-hot dip galvanized finish.