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

[afieldofblue]

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

Ok - we just get fills between 190 to (oops) 220+ bar, aiming for 200 bar on the boat ambient temp - trying to clamp down on overfills due to valve stress issues...

 

[afieldofblue]

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

Couldn't agree more - but alas, metric our aluminium tanks are not. At least our gauges are in bar

 

[Vicko]

In Europe it just makes things easier considering we have 10L 12L and 15L steel. Easier then calling them 9.6 11.1 and 13.6...
Plus we overfill them to 230 so they are closer to 12L 210 Bars...

 

[afieldofblue]

In Europe it just makes things easier considering we have 10L 12L and 15L steel. Easier then calling them 9.6 11.1 and 13.6...
Plus we overfill them to 230 so they are closer to 12L 210 Bars...

Hmm, so what of AL80s, 80 cubic feet, one of the most common aluminium tanks worldwide for warm water use?

Tomorrow when my French CMAS diver used to diving steel asks me about our tanks as most do, should I say they're aluminium 80, roughly 11L at 200 bar and tell people around me to stop calling them 12L?

 

[almostDIR]

I would not be surprised if all aluminium and steel tanks would vary a little in size. they are made by extruding a single metal plate to a "capped tube" and then forming the neck and valve seat by pressing the open end smaller so they SHOULD be some variations from the process

 

[almostDIR]

In Europe it just makes things easier considering we have 10L 12L and 15L steel. Easier then calling them 9.6 11.1 and 13.6...
Plus we overfill them to 230 so they are closer to 12L 210 Bars...

It would not be an overfill if the tank is rated for 230bar or more, it is just using fully the tank rated capacity

 

[almostDIR]

Hmm, so what of AL80s, 80 cubic feet, one of the most common aluminium tanks worldwide for warm water use?

Tomorrow when my French CMAS diver used to diving steel asks me about our tanks as most do, should I say they're aluminium 80, roughly 11L at 200 bar and tell people around me to stop calling them 12L?

You should call them just "aluminium 80"s and if someone asks how much they would be in litres you can say that "they come from a weird country which is not using the metric system and where one can not simply calculate anything by the decimal system and all measurements taken are fractional and difficult to interpret without tables and calculator and extensive knowledge.... but if you really want to know how much the tank volume would be in the real world it is something close to 11.1 litres though NOT EXACTLY that because that would be considered high treason in that weird country which manufactures them"

 

[Storker]

A metric, steel 10L tank will have 2320 L of gas at rated pressure (232 BAR)

My metric, steel 10L tanks will nominally have 3000 L of gas at rated pressure (300 bar).
(In reality, they will hold about 10% less due to compressibility showing itself at above 230 bar).


Light sarcasm aside, this is an example of the fact that when dealing with metric tanks, the water volume only tells half the story about the tank's capacity. You have to know the pressure rating as well, and that's normally either 200, 232 or 300 bar. Some years ago, I had two 15L tanks. One was rated for 200 bar, the other for 300 bar. That's a 50% (OK, 40% if we take compressibility into account) difference in capacity. I've sold both and have only 10L 300 bar tanks now, BTW.

If you PP blend, 300 bar tanks suck, also because of compressibility. If you don't take that into account, you'll get a richer mix than expected. For continuous blending it makes little to no difference, and you can shave some weight off your belt since the smaller volume makes them more negative.

 

[JackOfDiamonds]

Around here we also refer to them as 12L even though the internal volume is 11.1L, im not sure why it is so prevalent but im assuming its because people got used to it in those areas.
Also im not sure how accurate that conversion is considering the 2 different systems.

 

[almostDIR]

If it would be 11L internal volume then people would probably call them that. but the decimal probably bothers them and thus they round if upwards to 12.
As long as they don't calculate that .9 made up litre in their gas volumes they should be fine


anyway, I have always wondered why the alu tanks are so common in other parts of the world than Europe and some other places. Maybe it is because they are just cheaper there than steel? or the aluminium industry sponsoring them?
sometimes I thought it might be due to the more salty ocean water rusting steel more aggressively but that doesn't seem to be the reason at all. Though it would be frustrating to re paint dozens of mishandled steel tanks all the time in ocean setup especially if the extra negative weight is not needed in water.
Aluminium is heavier and alu tanks have lower pressure rating so the maintenance and price might be the factors I think