Solubility of gas in a hydraulic fluid

Fluids have the characteristic of dissolving certain amounts of gases. In mineral oil this ability increases linearly with pressure up to approx. 300 bar.

Dalton's law states:

V G = dissolved gas volume at the reference pressure

V öl = volume of fluid

α = Bunsen coefficient for common mineral oils, for air 0.09 and for nitrogen 0.08

p = related absolute pressure

p o = reference pressure (atmospheric pressure).

The saturation state characterised with this law does not of course always have to be reached.

At atmospheric pressure 1 l of oil contains approx. 90 cm3 of air, at 100 bar however as much as 9 l. Attention: As long as gas is dissolved, it does not cause malfunctions in the circuit! (see Air in oil).