No BCD?

[NeilB]

Correct me if I am wrong but if you fill a cylinder to it's working pressure of 300bar and then pump sea water in to start your dive you change the volume. Half the volume, double the pressure. I hope the cylinders are good for 600bar!

[Neilwood]

Correct me if I am wrong but if you fill a cylinder to it's working pressure of 300bar and then pump sea water in to start your dive you change the volume. Half the volume, double the pressure. I hope the cylinders are good for 600bar!

Of course, you then have to take into account that gas pressure over a certain level does not behave in accordance with ideal gas laws and you will also have a certain proportion of the gas that will be absorbed within the liquid under pressure.

[TheMacallan]

....... and you will also have a certain proportion of the gas that will be absorbed within the liquid under pressure.

In a hydraulic accumulator (which this is) the gas and liquid do to come into contact.
The gas is in the bladder and the liquid is in the shell.
In its industrial application an inert gas (N2) is used rather than air as as the liquid will be a hydrocarbon (e.g. pump seal oil).
The concept is very well proven.