How much air does an LP85 hold at 2400 PSI?

[-JD-]

Thanks for being decent to me @tursiops

So, no info on a 26.5 length tank or I am measuring the length incorrectly. Anyway, that is close so I will use it for my calculations.

If you are measuring with a tank boot on, that will give you a longer measured length - 1/2" is reasonable additional length added for a boot, but depends of course on the exact style.

The specification tables are generally for the raw cylinder - no boot, no valve. The tables are also nominal values and can vary some from cylinder.

 

[runsongas]

Are you defending imperial as "easier" or less confusing?? Liters x bar is about as clear as you get.

I mean a lp85 at 3800 holds more gas than a hp119 at 3300 too.

easier from the view of purchasing a tank. a 100cf tank will hold more than a 80cf tank. whereas a 12.9 liter tank might hold less than a 10 liter tank if the service pressures are very different.

 

[Degenerate]

easier from the view of purchasing a tank. a 100cf tank will hold more than a 80cf tank. whereas a 12.9 liter tank might hold less than a 10 liter tank if the service pressures are very different.

It's not like it's hard to multiply volume with the service pressure and figure out the amount of gas you'll have in a full tank though.
In fact, it's so easy you could train a monkey to do it with a calculator (which we all have in our phones) in a few minutes.
It also makes for really simple calculations during the dive.
Of course you can learn to do the same calculations with imperial units, but it's not as dead simple as metric.
Different tank pressures also tell us a lot about how much extra weight we'll need to bring on a dive.
A 10L 300 bar tank will need less lead than a 12L 232 bar tank because it's heavier in the water, although because of how gas compresses at higher pressures they will hold roughly the same amount of gas when filled to their service pressure.

 

[JohnnyC]

easier from the view of purchasing a tank. a 100cf tank will hold more than a 80cf tank. whereas a 12.9 liter tank might hold less than a 10 liter tank if the service pressures are very different.

Really? How much gas does an AL80 hold? The idea that calculating tank volume in metric is problematic is silly considering calculating in imperial is just as problematic. An HP100 is only 100 if you can get it filled to its service pressure. A 10L tank's capacity is whatever it is based on elementary math. Same same, only one isn't deceptive and obviously confusing to people, hence this thread exists.

A 10L tank has how many liters of gas at 184 bar?

An HP100 has how many cuft of gas at 2400 psi?

 

[CaveSloth]

If you are measuring with a tank boot on, that will give you a longer measured length - 1/2" is reasonable additional length added for a boot, but depends of course on the exact style.

The specification tables are generally for the raw cylinder - no boot, no valve. The tables are also nominal values and can vary some from cylinder.

Just want to state for the record that my tanks do not have boots.

 

[rjack321]

I just went and looked at my LP steels out of curiosity. They're stamped both with air volume "LP108" and water

If you do it in PSI up front then you don't have to do math at any point during the dive. Unless you have a gauge rated in tank factors or something like that. Just memorize or write down your turn pressure and viola. At least, that's how we did it in my cave class.

And how did you account for dissimilar tank sizes?
If I have 95s and you have 108s both filled to 3600, what is your turn pressure?

 

[Storker]

A 10L tank has how many liters of gas at 184 bar?

*Raises hand*

10 liters, of course. Or about 1840 surface liters. Or 920 liters at 2 barA/10m. Or 460 liters at 4 barA/30m.

EDIT: Damn, I forgot that you didn't specify the tank's service pressure nor its tank factor. Oh well.

 

[Lorenzoid]

you have the problem that a 12.2 liter tank with a 184 bar service pressure will have lower capacity than a 11 liter tank with a 232 bar service pressure.

I thought the context of the discussion was the concept of tank factors--are they useful or superfluous? I didn't think we were talking about selecting a tank. All I want to know is how many (surface-adjusted) liters or cubic feet of gas I have in my tank when I read my SPG before I begin the dive.

edit: You know, you're right. My first reply was to the OP's expression of confusion over the "+" rating for tank capacity. It was I who got the context wrong.

 

[runsongas]

An HP100 is only 100 if you can get it filled to its service pressure.

How is that relevant? Are tanks only filled to the service pressure correctly if they are stamped in metric units now? Do you get a better fill if you use the real SI unit for pressure of megapascals?

If euro tanks were sold as 2500 liters, 3000 liters, etc then it would be a direct comparison to CF ratings. the liter ratings are just as unreliable as CF because you fail to account for compressibility still.

 

[Ghetto Diver]

@CaveSloth I am curious to what size tanks you have given your measurements. Your tanks are similar in dimension to the older Faber LP76 (which I have).
26.5" tall x 7"