Pressure vs volume

[HazeGray]

Okay so this may not be the best place to post this but I'm betting the members in here will absolutely have the answer.
My question is gas theory based and some may find it basic but... is gas volume directly proportional to pressure. So is the first 1000 psi in a tank the same amount of air as the last 1000? I tried googling and likely due to poor phrasing couldn't come up with much.

 

[NAM001]

yes

lets assume that you tank is a 75 cuft tank and is 3k psi every 1000 psi is 25 cuft

an al80 is 77.x cuft so every 1k psi is rounded to 26 cuft.

what is nice about this is you can keep track of your usage based on psi.
in this case every 100 psi is 2.6 cuft. every 10 psi is 1/4 cuft. so is yo have a sac of .5 you are using about 20 psi a min at one atmosphere. at 4 atm (100 ft) you would use 4 times that or 80psi a min. 5 atm 100 psi a min.

hope this helps.

 

[Storker]

In theory, yes. For an ideal gas, P*V is constant.

For a real gas, not quite. But below ~250 bar, the effect of compressibility is negligible. Above ~250 bar, the effect can be noticed. A 300 bar tank carries about 10% less gas than would be expected for an ideal gas.

So unless you pump your tanks up beyond 232 bar / 3400 psi, the answer is yes.

 

[HazeGray]

Thank you for the quick response. Greatly appreciated.

 

[Kevrumbo]

Yes for an ideal gas as above.

In metric, a dive cylinder like an AL80 tank is rated at 11 liters per bar of pressure, which is its internal water volume at the reference surface pressure of 1.01 bar (1 atm). Unlike water though, the regular Air we breath can be compressed to the normal working pressure of 200 bar for the AL80, so the cylinder now carries an equivalent fill volume of free gas greater than its water capacity: In this case for the AL80 tank, 200 bar x 11 liters/bar equals 2200 liters.

Okay so this may not be the best place to post this but I'm betting the members in here will absolutely have the answer.
My question is gas theory based and some may find it basic but... is gas volume directly proportional to pressure. So is the first 1000 psi in a tank the same amount of air as the last 1000? I tried googling and likely due to poor phrasing couldn't come up with much.

So yes (with a cylinder fill cooling bath compensation for adiabatic heating), in metric terms -the first 100 bar in an AL80 tank is the same amount of Air (100 bar x 11 liters/bar equals 1100 liters) as the the last 100 bar. . .

 

[rossh]

The Information to answer this is the gas compressibility z factor. These are usually contained in tables in the back of a chemistry reference handbook.

For our purposes, its the O2 and N2 that have changing values, and make blending difficult. The Helium is very consistent across the pressure range.

The wikipedia shows air graphs. Compressibility factor - Wikipedia