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

[tursiops]

So calling AL80 12L would come from a 30 bar overfill? 30 bar = one extra liter?
interesting
we aim for 200 on the boat, though the station overfills so that it's roughly back 200/210 bar a few hours later at ambient temp.

Anything higher is frowned upon as the valves start wearing down fast, leaking etc.

Oppo, in your attempts to make this simpler for you, you are actually making it more difficult, I think.
The only two numbers than matter are volume and pressure. In Europe you use the unfilled tank volume (liters) and bars. In the US we use the volume of gas in a pressured tank (cubic feet), and pounds per square inch (psi). Here is how those relate, for an AL80:
First the volume gas in a filled AL80 (to 3000 psi working pressure) is not 80 cubic feet, it is only 77.4 cuft...it is rounded up for convenience,

• 77.4 cuft is 2192 liters. That is just a volume conversion....no scuba in it.
• 3000 psi is 206.9 bar. That is just a pressure conversion....no scuba in it.
• That means the "volume in European speak" of the AL80 is 2192/206.9 = 10.6 liters. (If you had based that calculation on 80 cu ft you'd get 11 liters.)
• But if you fill overfill the cylinder to 230 bar (3333 psi), then it has 11% more gas in it, or 2435 liters. That is like having a 12 liter tank at 200 bar.

Good luck.

 

[Centrals]

I should have visited more places in SE Asia because I have yet to come across any operators over last 22yrs filled the tank other than 200 Bar. Tec dive excluded.
Aluminium tank is more or less the de facto standard in this part of the world, only a handful few operators that I had came across would have steel tank available.
Personally I do not like to dive steel tank because it leaves me with no ditch-able weight.

80 cu ft is 11L(just ignore the decimal place).
The filled pressure will determine the actual amount of gas that the tank has.

 

[clownfishsydney]

In Australia an 11.2 litre aluminium tank is a 90 cf tank as they are all 235 bar max pressure (all the new ones at least). The older ones we called 88 cf as they were nominally a little bigger inside but only filled to 207 bar.

 

[Storker]

It’s only because in Europe you only see 10l, 12l and 15l for the common sizes.

I have never seen yet an AL80 because I have dived only in Europe (I am a newbie too so not seen too many people doing complicated dives)

AFAIU 11L Al tanks (Al80s) are the most popular stage tanks among the tech crowd, and deco tanks are Al40s. It's apparently easier to sling a near-neutral tank than to sling a distinctly negatively buoyant tank. Not that I'd know from personal experience, since IANAtechdiver.

For backmounting, it's steel all the way.

 

[Schwob]

probably AL100. Which is also probably what is sold as 15L tanks in these parts.... I'll check on the boat tomorrow, we've got a diver on a "15"...

You'd help me also if you could check on (and communicate) the actual markings on so called 15l ALU tanks "in your parts".... Thanks.

 

[BlueTrin]

AFAIU 11L Al tanks (Al80s) are the most popular stage tanks among the tech crowd, and deco tanks are Al40s. It's apparently easier to sling a near-neutral tank than to sling a distinctly negatively buoyant tank. Not that I'd know from personal experience, since IANAtechdiver.

For backmounting, it's steel all the way.

Yea this is why I added a caveat that I am a newbie

I read that AL80 is the best stage tank as it is neutrally buoyant.

However I suspect that many new divers or vacation divers never used or even saw a stage tank.

This is possibly why OP had so many customers who call them 12L tanks: if these customers are mostly casual or new divers from Europe they may think this is a 12L.

May be wrong though, so as always feel free to correct me

 

[Diving Dubai]

Also if you give me an AL80 and don’t tell me how many litres equivalent, I’ll have no clue what a cubic feet mean or represent as I have never used this unit in my life, I’ll have to convert in litres to make sense of it.

Same if you gave me psis instead of bars.

Edit: is the AL80 the same size than a steel12l ? That would make sense if the customers didn’t realise that there is no 12l and would intuitively think it must be a 12 because it is too big to be a 10l.

Generally speaking the following applies for the most common tanks you will see with the volume's rounded to the nearest whole

AL80 also known as S80 = 11l
AL50 also known as S50 = 7l
AL40 also known as S40 = 6l
AL30 also known as S30 = 4L

If you want to be really really exact. take CF size and * by 0.035317 (1 L = 0.035317cf) which gives you the total volume in L

So S80 should hold 2265l But it's never exactly that because of variances between manufacturers. If you want to be super precise on yoru own cylinder, either look up the manufactures specific volume, or fill your cylinders with water and measure the actual volume

But for gas planning rounding to the nearest whole number is good enough close enough

Why Al over steel?

Al is cheaper to purchase and requires less maintenance (for hard used rental cylinders)

Steel cylinder are generally favoured by those in colder climes as they're negative in salt, or (like here in the UAE) people prefer steels because they hold more gas for a given size (greater rated pressure)

A 10l Steel pumped to 232bar holds 2320l (81cf) Where as a Al80 only holds 2200l @200 Bar (or 2277l at the rated 207 bar)

To further confuse you...

An Al 80 weighs less (in air) than a 12L steel. However when you move up beyond this, an AL cylinder will weigh more than it's steel equivalent - because a greater mass of material is required in the cylinder construction (even though Ali is less dense it's substantially weaker.

Short 12l steels (dumpies or shorties) are more popular than you'd imagine. Lots of people dive them here, for 2 reasons

The main being that because they're shorter it's easier to don the kit whilst sitting on a boat, and can be more comfortable in the water having a shorter tank

Because they're shorter the mass is concentrated more over the lungs giving slightly better trim

 

[afieldofblue]

Oppo, in your attempts to make this simpler for you, you are actually making it more difficult, I think.
The only two numbers than matter are volume and pressure. In Europe you use the unfilled tank volume (liters) and bars. In the US we use the volume of gas in a pressured tank (cubic feet), and pounds per square inch (psi). Here is how those relate, for an AL80:
First the volume gas in a filled AL80 (to 3000 psi working pressure) is not 80 cubic feet, it is only 77.4 cuft...it is rounded up for convenience,

• 77.4 cuft is 2192 liters. That is just a volume conversion....no scuba in it.
• 3000 psi is 206.9 bar. That is just a pressure conversion....no scuba in it.
• That means the "volume in European speak" of the AL80 is 2192/206.9 = 10.6 liters. (If you had based that calculation on 80 cu ft you'd get 11 liters.)
• But if you fill overfill the cylinder to 230 bar (3333 psi), then it has 11% more gas in it, or 2435 liters. That is like having a 12 liter tank at 200 bar.

Good luck.

understood, thanks. We're filling to 200 bar as explained. I'm just trying to give a figure that makes sense to European customers used to their steel tanks.

I get asked this all the time "they're 12L, right?"
However saying it's a the same as a steel 12L because of a 230 bar overfill doesn't make much sense. Especially since we're not overfilling.

It's more of a 11 liter - ie less gas than what they're used to if they usually dive 12L steel.

And we're doing longuer dives than most cold water divers are used - up to 60 minutes including a 3 minute safety stop if air consumption allows (60 minutes or 50 bar, whichever comes first).

Let's make one thing clear. I'm also European trained. Dived 12L steel tanks. The only reason I bother with imperial measurements is because AL80s are the most common warm water tanks in the world, and they're 80 cubic feet under a full moon on a clear night. They're what you will dive most in Asia, South and Central America etc etc.

And I get asked are they 12L - People around me say yes, but they're actually 11L (at 200 bar ambient temp...).

I was trying to understand why - the answer seems to be to make it more like what people are used to at home, or because some people overfill them to 230 (which we don't).

I've checked our "15L tanks", they are aluminium 100 cubic feet tanks....

cheers

 

[afieldofblue]

I should have visited more places in SE Asia because I have yet to come across any operators over last 22yrs filled the tank other than 200 Bar. Tec dive excluded.
Aluminium tank is more or less the de facto standard in this part of the world, only a handful few operators that I had came across would have steel tank available.
Personally I do not like to dive steel tank because it leaves me with no ditch-able weight.

80 cu ft is 11L(just ignore the decimal place).
The filled pressure will determine the actual amount of gas that the tank has.

Yep.
You will find steel tanks in places with lots of German customers - some resorts in Bunaken in Indonesia, some German operators in the Maldives or in Khao Lak in Thailand - I've also seen some steel tanks in La Paz in Mexico, mostly for French customers, I think the Aggressor fleet worldwide has them on request and Egypt is a mixed bag of steel and aluminium tanks for instance.

11L it is

 

[afieldofblue]

You'd help me also if you could check on (and communicate) the actual markings on so called 15l ALU tanks "in your parts".... Thanks.

Ok - I didn't write them down today but they're 100. We don't have a "15L" on tomorrow but I'll take a snap at the filling station if I have time.
I think they're all from dive supply so probably the ones listed on page 93 here -
The 13L has a higher service pressure, but we also fill to 200 bar.

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