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

[azstinger11]

Not really. The pressure is irrelevant. The AL80 has an internal volume in liters that does not depend on pressure.

The problem is the assumption that a tank will be filled to 200 bars. That does not quite fill an AL80 to its rated working pressure and comes nowhere close to filling an AL100.

Wait what does my hiking pole comment have to do with the gas capacity of an AL80 lol?

 

[Subcooled]

We have a lot of European customers, and the AL80 tanks are refered to as 12L tanks.

The 200 ATM AL80 cylinders are not 12 litre cylinders by internal volume, but 11 litre.
Besides, their buoyancy is hugely different from the standard 12L 232 bar steels we use here.

I've been trying to get my head around this 80 cubic feet conversion, and read up on the following threads:

Untangling cubic feet, litres, PSI, bar for scuba tanks and RMV / SAC calculations

Cuft to liter conversion

I do understand that liters refer to liquid internal volume of a cylinder whereas
U.S. measurements refer to the total CF of gas at a maximum rated pressure, but
also found the following OMS conversion chart for steel tanks listing:

Air capacity (cuft) - Liquid capacity (L)
130cuft - 17L
100cuft - 13L
80cuft - 10L
65cuft - 8L
45cuft - 7L

and US manufacturer websites listing the following conversions:

steel 66/72 cuft = 10 L
steel 98 cuft = 15 L

A little confusing, but seems to point to AL80 = 10L rather than 12L.

You forget one thing: Amount is Pressure times Volume.
Aluminum cylinders tend to hold 200 ATM pressure. Steels can hold 200, 232 or 300.
You are comparing amount (cuft in normal 1ATM pressure) to volume alone.
You omit an 1x (200 ATM), 1.15x (232 ATM) or 1.5x (300 ATM) factor.
The latter would actually be 1.35x (270 ATM) due to the limited compressibility of air.

I am sure one table is for 200 ATM aluminum cylinders while the other is for 232 ATM steel cylinders.
The rest is rounding errors.

 

[darksider]

Not really. The pressure is irrelevant. The AL80 has an internal volume in liters that does not depend on pressure.

The problem is the assumption that a tank will be filled to 200 bars. That does not quite fill an AL80 to its rated working pressure and comes nowhere close to filling an AL100.

Yes, it's obvious that the internal volume of a tank doesn't change. The pressure is relevant if you want to know how much gas you get .

The point was that you get much less gas than you think you are getting. They call it 15L, but it's 13.2L and if they don't fill it up to 228 bar you don't get 13.2L either. At 200 bar you get the equivalent of an 11.57L tank, so it's quite close to the AL80 tank.

Btw. I have never seen an AL100 tank filled to 230 bars. Usually, it is 200 bars, if you are lucky it's 210 bars. I'm not sure what's the problem to fully fill tanks. Probably too weak compressor?

So when you call for a 15L aluminum tank in a diving center and you get it filled @ 200 bars it's like choosing between 300ml Coke and 500ml Coke, but once you order the bigger one you get 350ml of Coke in 500ml glass .

 

[tursiops]

Yes, it's obvious that the internal volume of a tank doesn't change. The pressure is relevant if you want to know how much gas you get .

The point was that you get much less gas than you think you are getting. They call it 15L, but it's 13.2L and if they don't fill it up to 228 bar you don't get 13.2L either. At 200 bar you get the equivalent of an 11.57L tank, so it's quite close to the AL80 tank.

Btw. I have never seen an AL100 tank filled to 230 bars. Usually, it is 200 bars, if you are lucky it's 210 bars. I'm not sure what's the problem to fully fill tanks. Probably too weak compressor?

So when you call for a 15L aluminum tank in a diving center and you get it filled @ 200 bars it's like choosing between 300ml Coke and 500ml Coke, but once you order the bigger one you get 350ml of Coke in 500ml glass .

You are still confusing tank size and contained gas volume .The former is fixed; the latter depends on fill pressure.
"They call it 15L, but it's 13.2L and if they don't fill it up to 228 bar you don't get 13.2L either."
You mean if not filled to 228bar, you don't get the full amount of gas that tank will hold, It is still a 13.2 liter tank.
Apparently you think all tanks should be filled to 200 bar. Nonsense.

 

[tursiops]

Wait what does my hiking pole comment have to do with the gas capacity of an AL80 lol?

Nothing. I did not mean to respond to you. I've removed your quote from my post.

 

[L13]

Yes, it's obvious that the internal volume of a tank doesn't change. The pressure is relevant if you want to know how much gas you get .

The point was that you get much less gas than you think you are getting. They call it 15L, but it's 13.2L and if they don't fill it up to 228 bar you don't get 13.2L either. At 200 bar you get the equivalent of an 11.57L tank, so it's quite close to the AL80 tank.

Btw. I have never seen an AL100 tank filled to 230 bars. Usually, it is 200 bars, if you are lucky it's 210 bars. I'm not sure what's the problem to fully fill tanks. Probably too weak compressor?

So when you call for a 15L aluminum tank in a diving center and you get it filled @ 200 bars it's like choosing between 300ml Coke and 500ml Coke, but once you order the bigger one you get 350ml of Coke in 500ml glass .

You always get 13.2L with a 13.2L cylinder. even if it is empty!

At 200 bar, a 13.2L holds ~2640L of air, but it is still a 13.2L cylinder. At 1 bar it holds 13.2l of air, at 100 bar it holds ~1320L of air, and at 300 bar it holds ~2960L of air, but it is still a 13.2L tank! (and even those numbers are off because of the Z factor, air is not perfectly compressible).

 

[BlueTrin]

Do you guys use the z-factor when planning gas (out of curiosity)?

 

[inquis]

Do you guys use the z-factor when planning gas?

Depends on the goals of the dive. When I want a specific gas quantity, yes. If a plan is infeasible, I'd like to know before getting wet and scale down to something that is.

OTOH, for a reef dive where the plan is to just swim around looking at stuff until reaching Minimum Gas, then no. (Conveniently, gas behaves pretty ideally at such pressures.)

 

[darksider]

You are still confusing tank size and contained gas volume .The former is fixed; the latter depends on fill pressure.
"They call it 15L, but it's 13.2L and if they don't fill it up to 228 bar you don't get 13.2L either."
You mean if not filled to 228bar, you don't get the full amount of gas that tank will hold, It is still a 13.2 liter tank.
Apparently you think all tanks should be filled to 200 bar. Nonsense.

Of course, it is still a 13.2 liter tank. I meant that you don't get the amount of gas that a full 13.2 liter tank offers. Instead, you get an equivalent of a full 11.57L hypothetical tank if your 13.2 is filled only to 200 bar.

Apparently you think all tanks should be filled to 200 bar. Nonsense.

Of course not, my whole post was about the problem that in Egypt they fill AL100 to 200 bars when they should be filled to 228 bars .

The point is that you go to diving center and they tell you that you can get 12L or 15L, so you think that by choosing 15L you get 25% more gas (hell yeah 25% longer diving). But in reality, it turns out that those tanks are actually 11.1 and 13.2, so now you get ~19% more gas, still not bad. But then it turns out that you can get 11.1L fully loaded @ 200 bar or 13.2L @ 200 bar where this type of tank is fully loaded at 228 bar. So now you get only ~5% more gas if you compare full 11.1L vs 13.2 @ 200 bar.

But most people don't know the technical details about tanks, so they think that they get 25% gas by choosing "15L"

 

[L13]

Of course, it is still a 13.2 liter tank. I meant that you don't get the amount of gas that a full 13.2 liter tank offers. Instead, you get an equivalent of a full 11.57L hypothetical tank if your 13.2 is filled only to 200 bar.


Of course not, my whole post was about the problem that in Egypt they fill AL100 to 200 bars when they should be filled to 228 bars .

The point is that you go to diving center and they tell you that you can get 12L or 15L, so you think that by choosing 15L you get 25% more gas (hell yeah 25% longer diving). But in reality, it turns out that those tanks are actually 11.1 and 13.2, so now you get ~19% more gas, still not bad. But then it turns out that you can get 11.1L fully loaded @ 200 bar or 13.2L @ 200 bar where this type of tank is fully loaded at 228 bar. So now you get only ~5% more gas if you compare full 11.1L vs 13.2 @ 200 bar.

But most people don't know the technical details about tanks, so they think that they get 25% gas by choosing "15L"

Who doesn't think pressure effects how much gas you have?

if both are at the same pressure, a 13.2L vs an 11.1L has exactly 13.2/11.1=1.19 times more gas, or 19% more gas, regardless of the pressure (not the ~5% you stated). Every diver has (or should have) a pressure gauge.