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

[stepfen]

As to why dive stores/LoBs don't fill tanks to their working pressure but only to ~200bar, in all the places I have been diving (Greece, Indonesia, Egypt, Jordan, Malaysia) 200 bars is the standard/default fill pressure (usually with a shutoff valve or regulators set at the said pressure). Dive stores and LoBs just don't bother with anything else/more.

Imagine the hassle of having different valves and fill whips for different kind of tanks, or manually fill each tank to its working pressure etc in a group of 10 divers or so. Not to mention that compressor wear increases (a lot) as pressure increases.

It might look like a waste of resources (to dive with pressure lower than the tank's max capacity), but it is the way it is. So many divers live/dive with this.

From what I read here in SB, all these don't apply to the left side of the Atlantic, where tanks are (supposed to be) filled to working pressure (and occasionally do get overfilled, + ratings, cave fills, whatever), but that's another story.

As for @darksider 's case, there are real 15lt tanks (steel - not aluminiums) and they are quite common in some countries. If you paid/asked for 15lt and they gave you 13.2lt you can ask (nicely) the operator for real 15lt tanks and if they are not available, ask/negotiate for discount for the extra money you paid or ask your (extra) money back and use the standard 11.1lt. Whatever makes more sense to you. In any way, usually these are group dives, so more gas for some diver(s) doesn't necessarily mean extra time for the group.

All the best and welcome to SB @darksider

 

[Angelo Farina]

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

Because this is what you get in most places.
But the point is another.
In US and associated countries, you rent a tank asking for a nominal capacity in Cuft.
The SPG is graduated in PSI, and there is no easy way to evaluate how much air you really have while diving (perhaps being partially narched).
In other countries the tank is rated in liters of "liquid capacity" (the real internal volume) and this value is MARKED ON THE TANK with precision, with 0.1 liter rounding.
The tanks are not identical: in a batch of 50 "10-liters" Faber steel tanks I found the smallest was 9.3 liters and the larger was 10.8.
So we are used, very simply, to read the value in liters directly from the marking on the tank.
While diving, we watch the SPG, which is graduated in bars. At any instant we know the real amount of gas still available, multiplying the real capacity in liters by the current pressure in bars.
So the filing pressure is not really the problem, as the diver evaluates the real amount of gas at the beginning and during the dive doing that simple multiplication.

Of course the fact that a tank is marked improperly can be a problem, resulting in divers finding themself short of gas.
So I suggest that in a serious diving center where the tanks (for reasons I do not know) are not already properly marked by the manufacturer, each tank is weighted twice (full of water and empty) and the exact value of the weight difference is permanently impressed on the tank.
This is what an European diver expects in a professionally-managed diving center, even if at Maldives or in Malaysia.
Getting a 13.2 liters tank marketed as ""15 liters" will upset many customers.
Remember, the filling pressure is irrelevant: we need to know the real value in liters, the pressure is always measured by the SPG.
Giving a 11 liters tank overfilled so it contains 2400 liters does not make it a 12 liters tank.

 

[Joneill]

deleted

 

[Edward3c]

Hello all,

I work in Asia, and we mostly use AL80 tanks, along with "15L" aluminium tanks.

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

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.

If this is correct, I'm trying to understand why the AL80 tanks are not simply metrified to 10L (or 11L?) and refered to as 12L tanks.

Is calling AL80 tanks 12L just a habit to align them on common European steel tank sizes?

Thanks a bunch!
b

Nothing to do with conversions.

Easier to boast about warm water air consumption figures when back home.

 

[jborg]

Easier to boast about warm water air consumption figures when back home.

Pretending an 11.1L tank is 12L makes your measured SAC look higher than it actually is. If they wanted to wow customers with their low gas usage they should lie in the other direction, saying the tank is smaller than it really is.

 

[L13]

Giving a 11 liters tank overfilled so it contains 2400 liters does not make it a 12 liters tank.

Exactly!

 

[darksider]

Pretending an 11.1L tank is 12L makes your measured SAC look higher than it actually is. If they wanted to wow customers with their low gas usage they should lie in the other direction, saying the tank is smaller than it really is.

Exactly, I saw many people using 15L in calculations while they were diving using aluminum 100 which is 13.2L. That's because diving centers call them incorrectly 12s and 15s and people think that they really get 15L. Recently, on my trip I had this discussion with other guys that are experienced divers and instructors and even they weren't aware of that.

Thank you @stepfen, finally an answer related to my point .

 

[Edward3c]

Nothing to do with conversions.

Easier to boast about warm water air consumption figures when back home.

Got that the wrong way round.

 

[BlueTrin]

Exactly, I saw many people using 15L in calculations while they were diving using aluminum 100 which is 13.2L. That's because diving centers call them incorrectly 12s and 15s and people think that they really get 15L. Recently, on my trip I had this discussion with other guys that are experienced divers and instructors and even they weren't aware of that.

Thank you @stepfen, finally an answer related to my point .

I went to Egypt recently, the dive centre couldn’t even tell me what cylinders they were advertising as 15L.

I don’t think the clientele is so bothered by these details for most of these shops.