Why are AL80 tanks often refered to as 12L tanks (rather than 10L?)

[afieldofblue]

A metric, steel 10L tank will have 2320 L of gas at rated pressure (232 BAR)
An imperial, 11L AL80 will have 2277 L at rated pressure (207 BAR)

In terms of gas carried, an AL80 is therefore equivalent to a 10L steel, I believe that is where the verbal shortcut has come up. The tank is in fact 11L but breathes like a 10L steel.

Ah ha! I was wondering if it was something like that, this 10L conversion that kept popping up at times... thanks for adding another layer of complexity

Ok - so when I'm describing our aluminium tanks to European (or Japanese) customers used to diving metric steel tanks, should I really describe them as 10L (and freak them out even more, less gas!), 11L or, as most around me do... 12L (which feels more and more like false advertising)?


Thanks!

 

[Centrals]

The filled pressure is the deciding factor.
11L aluminium tank at 200 bar = 2200 free liter.
10L steel tank at 200 bar = 2000 free liter.

 

[afieldofblue]

The filled pressure is the deciding factor.
11L aluminium tank at 200 bar = 2200 free liter.
10L steel tank at 200 bar = 2000 free liter.

Thanks - I'm assuming a standard (erhm) 200 bar fill for an AL80 (ie 11.1L), which is what people are aiming for when filling in these parts (rather than max fill pressure)

Logically, should an AL80 @ 200 Bar be described as a 10L or 11L tank, the important factor being to allow divers used to metric steel tank capacities (also filled to a standard 200 bar) to estimate their actual gas reserve for a dive?

One thing seems clear, calling AL80s 12L is misleading, right?

 

[almostDIR]

AL80's are always called AL80's here or someone may call them "11L aluminium" like I sometimes do.
I have never heard anyone calling them "12L tanks" because they are nowhere near 12L and we normally use steel tanks here for anything other than stage/deco gas use... so a "12L tank" really means 12L capacity and almost always it's a steel 12L/235bar or 230bar tank nowadays. some might use a 300bar steel but that is not very common because persons like to switch to doubles instead at that point

 

[NAM001]

what would the c-80 be could it be a 10L

just did the math 80 cu ft 220 bar (3300 psi) 10.1 liter

 

[afieldofblue]

AL80's are always called AL80's here or someone may call them "11L aluminium" like I sometimes do.
I have never heard anyone calling them "12L tanks" because they are nowhere near 12L and we normally use steel tanks here for anything other than stage/deco gas use... so a "12L tank" really means 12L capacity and almost always it's a steel 12L/235bar or 230bar tank nowadays. some might use a 300bar steel but that is not very common because persons like to switch to doubles instead at that point

Yes - this is why I really want to make sure that they're correctly described in liters, so that divers used to steel tanks know what to expect - so no more 12L for AL80s, and probably no more 15L for AL100 for instance.

What about Rain Pilot's post above explaining that an AL80 is actually equivalent to a 10L steel?

I guess describing them (to divers used to metric steel tanks) as aluminium 11L, roughly equivalent to a 10L steel tank in terms of capacity - could work.

Thanks!

 

[stepfen]

All the European aluminium tanks of that size that I've seen are clearly marked as 11.1Lt. Everybody still calls them 12Lt though. No idea why

 

[almostDIR]

personally I think that cubic feets are pretty useless as tank volume measurement, they just complicate things especially if you need to calculate something quickly underwater. The filling pressure can also be anything after the tank is cooled so with litres and bars you can just re calculate everything on the fly which is much more useful than using the cubic feet "nominal capacity at 'normal fill pressure' which can be anything" weirdness

 

[almostDIR]

What about Rain Pilot's post above explaining that an AL80 is actually equivalent to a 10L steel?

if you fill them by yourself and are therefore allowed to fine tune the filling regulator 7 bar up then it would make sense, otherwise not
The 207 vs 232bar difference is significant.
Though it is pretty common here to have fills of either exactly 200 bar or exactly 300bar and then the tank cools down and the end pressure can be anything. You can ask for different fill of course.
Tech guys like to fill to the tank rated max pressure or more (at least to the 230bar if tank rated to that when rec divers normally are perfectly happy with just 200 bar of air)

anyway, alu tanks are normally chosen here only for their buoyancy characteristics and sometimes cheaper price which has led to them being normally only for deco gas /stage use by tech divers. Steel is more practical for main tanks here

 

[afieldofblue]

All the European aluminium tanks of that size that I've seen are clearly marked as 11.1Lt. Everybody still calls them 12Lt though. No idea why

So I'm not the only one hearing 11.1L tanks called 12L - I wonder where this comes from... I guess it's because 10 / 12 /15L steel tanks are common, so aluminium 11.1L tanks somehow got upgraded to 12L?