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I am trying to decide on the best Allys to use as stages. I have just been using 10.7 litres in the red sea, and some 12's at one point and they all worked well. Have decided to use the same strategy in the uk.

I can't decide between the luxfer 207 bar or 232 bar. Has anyone got a view on the comparative buoyancy of the 207 vs the 232.

I figured I would get 230 fills in the 207 most of the time as the fill stations tend to miss this..

Anyone got a view or helpful experience??
 

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aka Chimp 1 or Mavis...
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Do a search on here, there are loads of threads about this subject and it does get heated, especially when Chasey gets involved :D
 

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A short fat well off crap cave diver. Likes wrecks
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I am trying to decide on the best Allys to use as stages. I have just been using 10.7 litres in the red sea, and some 12's at one point and they all worked well. Have decided to use the same strategy in the uk.

I can't decide between the luxfer 207 bar or 232 bar. Has anyone got a view on the comparative buoyancy of the 207 vs the 232.

I figured I would get 230 fills in the 207 most of the time as the fill stations tend to miss this..

Anyone got a view or helpful experience??


I can tell you the 207 bar ali with a full load of 50% gas is 3lb negative in fresh water, without a reg

I beleive the 235 bar version is much more negative. Thicker tank walls and more gas.

The 207 bar Ali 80 seems to be the one most used. I use one for my 50%

I use a steel 10 for my deep trimix bailout of 18/45 because that is only 1lb negative in fresh water with a 250 bar fill of mix. This only works with mix with nitrox it will be a lot heavier. Which is why I dont use two steel tanks.


ATB

Mark Chase
 

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Driving my truck with my high-heels on...
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Calculation ?

I know there is this :- UK Scuba - Cylinder Buoyancy Calculation for cylinder buoyancy but is there one anywhere for working out the buoyancy with various mixed gas in ? nitrox & trimix .
 

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aka Chimp 1 or Mavis...
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Joe Hesketh across on DIRx created a .pdf which loads of information regarding buoyancy characteristics of different mixes which can be downloaded from here
 

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A short fat well off crap cave diver. Likes wrecks
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I know there is this :- UK Scuba - Cylinder Buoyancy Calculation for cylinder buoyancy but is there one anywhere for working out the buoyancy with various mixed gas in ? nitrox & trimix .

But it dosent work in real life.

Using Archimedes principle, buoyancy is equal to the weight of the displaced water minus the weight of the cylinder.

The cylinder is made of 14.2 kg of aluminium, (which has a density of 2.7 kg/litre).
The aluminium therefore has a volume of 14.2 / 2.7 = 5.26 litres, so the total volume is 11 + 5.26 = 16.26 litres.
The density of fresh water is 1 kg/litre, giving 16.26 x 1 = 16.3 kg

Air has a density of 0.0012 kg/litre.
The air in a full cylinder weighs 0.0012 x 207 bar x 11 litres = 2.7 kg.

The cylinder when empty has a buoyancy of 16.3 kg - 14.2 kg = 2.1 kg
The cylinder when full has a buoyancy of 16.3 kg - 14.2 kg - 2.7 kg = -0.5 kg



So why is the cylinder 3lb or 1.4Kg negative?




First time Janos handed me a full Ali 80 in Vobster I expected it to weigh nothing. We were at 20m but dispite this he went up, i went down . I was shocked. So i decided to carry out some real world tests. The Ali 80 full of 50% was 3lb neg without a regulator 5 1/2 lb neg with a Ocianic First stage reg and suit hose on it. Tank is rigged DIR with two bolt snaps and a single J clip but it does have an additional D ring on it.


Note how the Ali 80 (left of the pic) floats up under my arm and the steel 10right of the pic dosent ??

Oh hang on thats bollocks they both hang down the same :D



ATB

Mark Chase
 

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i have been told thats a great way to get it to fail the neck crack test, or damage the neck theads, after a couple of years (or test cycles)
Yep - you really need to make the gas monkey/technician aware that it is a 207 bar cylinder - either verbally or via a pre-fill sticker..

its really quite annoying - in the States these cylinders are so cheap ($130-$140) that after a couple years - you just bin the old ones and get new ones.. :(
 

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more weaselly than a weaselly thing
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I figured I would get 230 fills in the 207 most of the time as the fill stations tend to miss this..

Anyone got a view or helpful experience??

Yep. Al's physical properties don't cope well with over-pressuring, dont do it.

If you're lucky it will end its life when it fails its test early, if you're unlucky it will be during your unscheduled testing (ie when you overblow it).

Get a big black marker pen and fil in the 207 bar marks on the tank top.... or write them in big letters yourself.
 

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Utrinque Paratus
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I pump my Ali 80's to 230 and 250 bar regular and they pass the service every year no problems, the only failure i have had picked up was the valve on the ALi 80 i brought from digger !!

my Ali 80's i have had from day 1

Graham
 

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I provide much-needed sarcasm.
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The cylinder when empty has a buoyancy of 16.3 kg - 14.2 kg = 2.1 kg
The cylinder when full has a buoyancy of 16.3 kg - 14.2 kg - 2.7 kg = -0.5 kg[/I]


So why is the cylinder 3lb or 1.4Kg negative?
Is it 1.4kg empty or full? The valve must weigh about a kilo.

Jason
 

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A short fat well off crap cave diver. Likes wrecks
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Is it 1.4kg empty or full? The valve must weigh about a kilo.

Jason


Full valve but no 1st stage and according to the math above it should be 0.5kg positive but its definatly not.


Note Ali 80 (210bar) doing a good impersonation of a house brick and the steel 10 (250bar) floating arse in the air.



ATB

Mark Chase
 

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I provide much-needed sarcasm.
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Full valve but no 1st stage and according to the math above it should be 0.5kg positive but its definatly not.
No the maths doesn't include the valve as it says on Greg's website. They must weigh about a kilo and I would imagine their buoyancy is neglible.

Jason
 

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GUE Instructor
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Full valve but no 1st stage and according to the math above it should be 0.5kg positive but its definatly not.


Note Ali 80 (210bar) doing a good impersonation of a house brick and the steel 10 (250bar) floating arse in the air.
Mark Chase
IMHO: Ali80 when full= Heavy bag of shit. Ali80 when empty= Nightmare floaty Bag of shit. Ali80 between about 50 bar and 150 bar. luvvverly.
 

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A short fat well off crap cave diver. Likes wrecks
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IMHO: Ali80 when full= Heavy bag of shit. Ali80 when empty= Nightmare floaty Bag of shit. Ali80 between about 50 bar and 150 bar. luvvverly.

Yes this prety acuratly sums up months of personal reserch :D


It can be extended to steel 10s. Steel 10 with 250bar of 50% in weighs a tone. Steel 10 with 250bar of 18/45 in weighs bugger all and is lovley to dive with.

An ali80 with 210 in is a brick but no where near as brick like as the 10 with 250bar in.


So in conclusion I dive one of each in the interests of trim and screw style :D

ATB

Mark Chase
 

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An ali80 with 210 in is a brick but no where near as brick like as the 10 with 250bar in.


So in conclusion I dive one of each in the interests of trim and screw style :D
So, we now know that the gas weighs something. Excellent.

The other option is to pump the things to their correct pressures, or heaven forbid, maybe a little lower.

Rich
 

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So, we now know that the gas weighs something. Excellent.

The other option is to pump the things to their correct pressures, or heaven forbid, maybe a little lower.

Rich
I tend to get my ALI80's pumped to 200 bar, which then cools to 190, then use it to fill the argon bottle. I usually jump in with about 160-170 bar in them, which works out quite nicely.
 

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aka Chimp 1 or Mavis...
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The other option is to pump the things to their correct pressures, or heaven forbid, maybe a little lower.

Rich
Heretic!
 

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A short fat well off crap cave diver. Likes wrecks
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So, we now know that the gas weighs something. Excellent.

The other option is to pump the things to their correct pressures, or heaven forbid, maybe a little lower.

Rich

Not an option, not enough gas for the dive @ 160bar.

I dont think 210 is a big deal in a tank with a 207bar rating?? It just happens to be 210 in that pic.


Hers my last dive:




Here is my no 02 rebreather no drop tank OMG profile for bailout:




I wouldent make even 10/120 GF on a 160bar fill.





ATB

Mark Chase
 
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