Just a question??

[chickdiver]

I beg to differ on the "nasty egressions and dropoffs" requiring redundant wings. I've done plenty of 200' + cave dives, and I have NEVER needed a redundant wing for any egress Or dropoff- heloo? bouyancy control??). In fact, my 55# does just fine for my 5'3" self, up to 7 stage bottles (I think thats the most I have carried at once), doble 104's and 2 long body Gavins.

 

[Divesherpa]

chickdiver once bubbled...
I beg to differ on the "nasty egressions and dropoffs" requiring redundant wings. I've done plenty of 200' + cave dives, and I have NEVER needed a redundant wing for any egress Or dropoff- heloo? bouyancy control??). In fact, my 55# does just fine for my 5'3" self, up to 7 stage bottles (I think thats the most I have carried at once), doble 104's and 2 long body Gavins.

I haven't had to use a long hose -EVER-, but I still use one when diving back mount. Have you ever used it in a true emergency?



You are very accomplished in your tasks and that is fantastic. The only point is that an extra wing takes up very little room and add to safety (in my opinion). You obviously disagree. Good thing that we have the right to disagree, eh?

 

[nradov]

padiscubapro once bubbled...


lets do some simple math.. from luxfers site they claim their s80 is 4.4 lbs pos empty thats out starting point..

we need to figure out our weight of the gass lets choose a 21-40 trimix

we need to convert the volume into liters so 77.4cu ft is approx 2192 liters of gas.. why is this important because 1 mole of gas is 22.414 liters, and we can then use the atomic weight to figure out the weight for 1 liter in grams..

using the atomic weights of he, n and o it works out to about 1.5 grams per liter of gas.. this works out to 3289 grams of gas or 7.25 lbs, add this to the buoyancy of 4.4 lbs, means a 21-40 trimix is 2.85 lbs negative at the start of the dive.. luxfer doesn't specify if valve is included in their buoyancy specs.. this is about 1lb ,pre negative than they state.. so I don't know what they used as a gas. or if their empty buoyancy is wrong.

I'm not sure where you're coming up with those numbers. From the Air Liquide web site (http://www.airliquide.com/) densities in lb/ft^3 for the various gasses at STP are as follows:
O2: 0.084
N2: 0.073
He: 0.01
So when filled with 21/40 to the rated pressure a standard Luxfer S080 will contain right about 3.9lbs of gas, not anywhere near 7.25lbs. The actual buoyancy of the entire package depends on the valve, regulator, hardware, etc. so you'll have to tie it to a fish scale and dunk it in the swimming pool to get an accurate number (not that it really matters much).

-Nick

 

[nradov]

faye once bubbled...
Well this is the most assinine thing I have ever heard.
I dive air. I can't afford HE on a regular basis.

Once again we see that if you do one thing wrong, you end up also having to do a bunch of other things wrong in an attempt to work around the problem you've created for yourself. Good luck with that air diving, and try not to hurt yourself.

-Nick

 

[padiscubapro]

nradov once bubbled...


I'm not sure where you're coming up with those numbers. From the Air Liquide web site (http://www.airliquide.com/) densities in lb/ft^3 for the various gasses at STP are as follows:
O2: 0.084
N2: 0.073
He: 0.01
So when filled with 21/40 to the rated pressure a standard Luxfer S080 will contain right about 3.9lbs of gas, not anywhere near 7.25lbs. The actual buoyancy of the entire package depends on the valve, regulator, hardware, etc. so you'll have to tie it to a fish scale and dunk it in the swimming pool to get an accurate number (not that it really matters much).

-Nick

I'm not sure where they came up with the numbers but their rounding is wrong..

basic chemistry 1 mole of any gas occupies 22.414l
so oxygen is 32 g/mol, nitrogen is 28g/mole and he is 4 g/mole at stp

thats using this with the appropriate fractions 21/40 would be 26.92 g/mole, dived by 22.414 to turn into liters thats 1.5 grams per liter of gas
an al80 (77.4 cu ft) has 2192 liters of gas, so 2192*1.5 g/l = 3288 grams, converting this to imperial, 7.25 lbs which is definately in the ballpark..

 

[nradov]

padiscubapro once bubbled...


I'm not sure where they came up with the numbers but their rounding is wrong..

basic chemistry 1 mole of any gas occupies 22.414l
so oxygen is 32 g/mol, nitrogen is 28g/mole and he is 4 g/mole at stp

thats using this with the appropriate fractions 21/40 would be 26.92 g/mole, dived by 22.414 to turn into liters thats 1.5 grams per liter of gas
an al80 (77.4 cu ft) has 2192 liters of gas, so 2192*1.5 g/l = 3288 grams, converting this to imperial, 7.25 lbs which is definately in the ballpark..

You've got to be kidding. Are you saying Air Liquide doesn't know the properties of gasses? Too funny. By the way, the numbers on the Air Products web site (http://www.airproducts.com/) are the same and I suspect they know a little more about this stuff than you do.

Instead of running your mouth about things you do not understand I recommend you go weigh an empty 77.4ft^3 tank, then fill it with 21/40 to 3000psi and weight it again. You'll find the change is rather less than 7lbs. Be sure to come back and let us know the results, OK?

-Nick

 

[padiscubapro]

nradov once bubbled...


You've got to be kidding. Are you saying Air Liquide doesn't know the properties of gasses? Too funny. By the way, the numbers on the Air Products web site (http://www.airproducts.com/) are the same and I suspect they know a little more about this stuff than you do.

Instead of running your mouth about things you do not understand I recommend you go weigh an empty 77.4ft^3 tank, then fill it with 21/40 to 3000psi and weight it again. You'll find the change is rather less than 7lbs. Be sure to come back and let us know the results, OK?

-Nick

I have a strong understanding of gas properties..
for example oxygen using exact numbers is 31.997 g/mol/22.414 mol/l x 28.32 l/cuft comes out to 40.428082 grams convert this to lbs = .0891287 @stp
find me a different chemistry book that gives different molar weights .. these are basic chemical definitions..
science isn't done with imperial numbers depending where its rounded it will make a difference (not a great difference though)..

I found a missing decimal point(actually 1 of my cells (in excel)were supposed to be divided by 100 which was missing) in my spreadsheet for 21/40 tmx, my weights were right but the he portion of the molar weight was wrong

the total should have been .8584 g/liter, or 1881 gm or 4.14 lbs, for air the weight was in the ball park which is 1.29 gm/l or 2827 gm or 6.23 lbs. I knew it looked a bit high (like I said in the earlier numbers comparing it to luxfer) but the spreadsheet looked fine and at work its hard doublechecking work i'm not supposed to be doing..

That what I get for doing it in excel instead of by hand.

 

[omar]

Joe,

*[The 26.92 g/mol is wrong, eg (32 * .21) + (28 * .39) + (4 * .4) = 19.24 g/mol]
**[ Dividing 26.92 by 22.414 is also wrong. The result is 1.2]
You need to go back and check your math and how you got the answer you did.

77.4 cuft ~ 2191.7 L

2191.7 L ~ 97.78 mol

(97.78 * .21) = 20.53 mol O2 ~ 657.1g
(97.78 * .4) = 39.11 mol He ~ 156.4g
(97.78 * .39) = 38.13 mol N2 ~ 1,067.8 g
For a total of 1881.4 g ~ 4.14 Lb

omar

by the way your new numbers are screwed up as well

 

[padiscubapro]

oops I copied the wrong numbers tmx numbers air was ok
I edited it.. thanks..
I have to stop doing this while working

the spreadsheet had errors.. it had the weight as 33.64 in one place and 26.92 in another..

 

[Doppler]

omar once bubbled...
Joe,

*[The 26.92 g/mol is wrong, eg (32 * .21) + (28 * .39) + (4 * .4) = 19.24 g/mol]
**[ Dividing 26.92 by 22.414 is also wrong. The result is 1.2]
You need to go back and check your math and how you got the answer you did.

77.4 cuft ~ 2191.7 L

2191.7 L ~ 97.78 mol

(97.78 * .21) = 20.53 mol O2 ~ 657.1g
(97.78 * .4) = 39.11 mol He ~ 156.4g
(97.78 * .39) = 38.13 mol N2 ~ 1,067.8 g
For a total of 1881.4 g ~ 4.14 Lb

omar

by the way your new numbers are screwed up as well

Closer... did you factor gas compressibility?

I find unless I'm mixing gas by atomic weight, my relationships are off anyway, so it's not science any more but art...

So the selected gas will weight= "somewhere in the region of..."

And don't pick on me... I'm a physics major -- properties of light -- Chemistry came a distant second.

Anyhow, interesting postings guys... you gotta take that one into your local scuba shop !