Cylinder Volume ( Technical Detail )

[bany39]

Hi all dear advanced divers
There is very simple question about cylinder volume and it is : what is the volume of 10 liter cylinder in 200 bar ?
Air volume = cylinder volume + pressure = 200 * 10 = 2000 liter
But in next they say what is the air volume of 10 liter cylinder in 300 bar and 400 bar ....and when I want to ask the questions , they say wait and ask question wisely because the answer is more complicated that you thought .and at the end why in scuba diving use cylinder with low pressure more than cylinder with high pressure ( because of valve pressure resistance ??!!! ) ????
could anyone say what is the complication of above question ???

 

[KevinNM]

Once you get somewhere above 200 bar gasses start being noticeably different than ideal gasses and don't compress like the equation shows. So tanks with 300 bar of gas don't contain 300 times the water volume of gas.

 

[bany39]

Once you get somewhere above 200 bar gasses start being noticeably different than ideal gasses and don't compress like the equation shows. So tanks with 300 bar of gas don't contain 300 times the water volume of gas.

Thank kevin and can we estimate the exact volume with formula or no ??? in 300 bar

 

[rjack321]

Thank kevin and can we estimate the exact volume with formula or no ??? in 300 bar

Yes but it depends on the gas. Air and nitrox are basically the same, but trimix won't be.

 

[bany39]

Yes but it depends on the gas. Air and nitrox are basically the same, but trimix won't be.

ok , so what is that formula to calculate the exact amount of volume for 10 liter cylinder in 300 and 400 bar ...

 

[rjack321]

ok , so what is that formula to calculate the exact amount of volume for 10 liter cylinder in 300 and 400 bar ...

Its temperature dependent and not linear. The wiki page explains it well.
Compressibility factor - Wikipedia, the free encyclopedia

 

[Diver0001]

Hi all dear advanced divers
There is very simple question about cylinder volume and it is : what is the volume of 10 liter cylinder in 200 bar ?
Air volume = cylinder volume + pressure = 200 * 10 = 2000 liter
But in next they say what is the air volume of 10 liter cylinder in 300 bar and 400 bar ....and when I want to ask the questions , they say wait and ask question wisely because the answer is more complicated that you thought .and at the end why in scuba diving use cylinder with low pressure more than cylinder with high pressure ( because of valve pressure resistance ??!!! ) ????
could anyone say what is the complication of above question ???

Just to clarify; you're saying "air volume" and "cylinder volume". The cylinder volume does not change. A 10 liter tank at zero bar has the same volume as a 10 liter tank at 200 bar, namely 10 liters.

The volume of air it holds is simply 10*bar (for every 1 bar, 10 liters)...... to a point. if you google "real gas versus ideal gas" then you'll see a number of experiments and explanations that the pressure/volume/temperature relationships will deviate from the math at higher pressures.

So the long story is that Charles Law and Boyles law in the *real* world don't seem to act exactly like you think they would in mathematical models. There are many web sites you can cite if you need a source.

In terms of diving, the short story is that a HP tank @300 bar still holds more air than a LP tank of the same volume @150 or 200 bar. The real problem for divers is that HP tanks have to be very robust so they are very heavy/negative. The real issue for divers, therefore, isn't that there is something wrong with how much air they hold, the issue is how heavy they are.

R..

 

[dberry]

Just to clarify; you're saying "air volume" and "cylinder volume". The cylinder volume does not change. A 10 liter tank at zero bar has the same volume as a 10 liter tank at 200 bar, namely 10 liters.

This is true ("the cylinder volume does not change".) But in the off-chance the OP is diving in the U.S. or other countries that use the archaic "imperial" system of units, he should be aware that the "volume" used to designate a cylinder is the air volume (at a specific pressure and temperature), not the cylinder volume.

I.e. a European 15L cylinder has an internal volume of 15L, but an American "HP120" holds 120 cubic feet of air, IF pressurized to 3442 psi of pressure (ca. 234 bar). The HP120 cylinder volume is about 15.3L, but no one will tell you that!

Sorry if this is confusing. It is also confusing to many of us who have to use cylinders labeled this way.

 

[bany39]

rner, post: 7682706, member: 7781"]Just to clarify; you're saying "air volume" and "cylinder volume". The cylinder volume does not change. A 10 liter tank at zero bar has the same volume as a 10 liter tank at 200 bar, namely 10 liters.

The volume of air it holds is simply 10*bar (for every 1 bar, 10 liters)...... to a point. if you google "real gas versus ideal gas" then you'll see a number of experiments and explanations that the pressure/volume/temperature relationships will deviate from the math at higher pressures.

So the long story is that Charles Law and Boyles law in the *real* world don't seem to act exactly like you think they would in mathematical models. There are many web sites you can cite if you need a source.

In terms of diving, the short story is that a HP tank @300 bar still holds more air than a LP tank of the same volume @150 or 200 bar. The real problem for divers is that HP tanks have to be very robust so they are very heavy/negative. The real issue for divers, therefore, isn't that there is something wrong with how much air they hold, the issue is how heavy they are.

R..[/QUOTE]
This is besy

Just to clarify; you're saying "air volume" and "cylinder volume". The cylinder volume does not change. A 10 liter tank at zero bar has the same volume as a 10 liter tank at 200 bar, namely 10 liters.

The volume of air it holds is simply 10*bar (for every 1 bar, 10 liters)...... to a point. if you google "real gas versus ideal gas" then you'll see a number of experiments and explanations that the pressure/volume/temperature relationships will deviate from the math at higher pressures.

So the long story is that Charles Law and Boyles law in the *real* world don't seem to act exactly like you think they would in mathematical models. There are many web sites you can cite if you need a source.

In terms of diving, the short story is that a HP tank @300 bar still holds more air than a LP tank of the same volume @150 or 200 bar. The real problem for divers is that HP tanks have to be very robust so they are very heavy/negative. The real issue for divers, therefore, isn't that there is something wrong with how much air they hold, the issue is how heavy they are.

R..

thank you so much , as i read the problem of HP tank are :
1- High pressure tanks are hard to fill with compressor and make more heat
2-this is essential to use DIN valve with HP cylinder because of pressure
3-they need more frequent hydro static test and the fail rate of them is more than LP tank also the gear change like valve and o rings are more than the LP

 

[JohnN]

rner, post: 7682706, member: 7781"]Just to clarify; you're saying "air volume" and "cylinder volume". The cylinder volume does not change. A 10 liter tank at zero bar has the same volume as a 10 liter tank at 200 bar, namely 10 liters.

The volume of air it holds is simply 10*bar (for every 1 bar, 10 liters)...... to a point. if you google "real gas versus ideal gas" then you'll see a number of experiments and explanations that the pressure/volume/temperature relationships will deviate from the math at higher pressures.

So the long story is that Charles Law and Boyles law in the *real* world don't seem to act exactly like you think they would in mathematical models. There are many web sites you can cite if you need a source.

In terms of diving, the short story is that a HP tank @300 bar still holds more air than a LP tank of the same volume @150 or 200 bar. The real problem for divers is that HP tanks have to be very robust so they are very heavy/negative. The real issue for divers, therefore, isn't that there is something wrong with how much air they hold, the issue is how heavy they are.

R.
This is besy

thank you so much , as i read the problem of HP tank are :
1- High pressure tanks are hard to fill with compressor and make more heat
2-this is essential to use DIN valve with HP cylinder because of pressure
3-they need more frequent hydro static test and the fail rate of them is more than LP tank also the gear change like valve and o rings are more than the LP

1. I've never had a problem getting my HP tanks filled
2. Nope, HP (3442 PSI) tanks are sold with yoke valves
3. Hydro intervals are set by DOT (in USA), TC (in Canada). 5 years irregardless of HP or LP designation

So why LP cylinders? If you live in a place where you can get them over-filled them, they would be wonderful (good luck getting a 'cave' fill in the PNW), otherwise they are bigger and heavier for the same volume of gas.