I'm not convinced that 300 bar is a high enough pressure for this rule to start breaking down.
I did not say it breaks down, merely that it gets interesting. 300bar is not going to give a significant difference,but it is not a linear comparison to 200bar. In reality the difference would be more marked in smaller cylinders 3li or less although the ten bar for the valve would be a bigger loss when working out thirds.
cylinders filled to two or three hundred bar are starting to approach the regime where the simplified Ideal Gas Laws no longer predict reality particularly well. The behaviour of pressure, volume and temperature are no longer linear and things get a bit harder to work out.
The best bet is to use Van der Waal's Equation
An ``ideal gas'' consists of molecules that occupy negligible space and have negligible forces between tham. All collisions made between the molecules, and between the molecules and the walls of the container, would be perfectly elastic since the molecules have no means of storing kinetic energy except as translational kinetic energy (i.e. movement).
The simplest of the equations to try and deal with Real Gases was developed empirically by Johannes van der Waals. He recognised that by adding correction terms to the Ideal Gas Law it could be made to more closely approximate reality. Van der Waals equation is
( P + an2 / V2 )( V - nb ) = nRT
where a is a correction term for intermolecular forces, and b is a correction term for the real volume of the gas molecules. Values of a and b will be different for each gas. Typically all intermolcular forces are refered to as Van der Waals forces.
Andrew.
Cheers AMW its good to have an informed opinion on this website instead of the usual b****cks that has become all too regular from certain contributors;