Recently, in oil hydraulic systems, depressing of vibration and noises, which is caused by bubbles in the working liquid,
has been becoming an important subject of study while quick and refining controlling is becoming an urgent demand.
Diffusion from gas to oil is the primary physical phenomenon to form these bubbles. It is necessary, therefore, to study
the diffusion behavior between gas and the mineral oil which was used in hydraulic systems. In this study, first, equations
were derived to calculate the diffusion volume of the gas into mineral oil individually or into an oil-rubber double layer.
On the other hand, a method was proposed to measure the minute change of the gas volume, which was caused by
diffusion, using an installation consists of laser heterodyne interferometer and a U-tube. Then the gas diffusion volumes
to oil or to the oil-rubber double layer were measured respectively and compared to the values calculated from the
equations mentioned above. As a result, the experimental values were good agreed with the ones calculated from the
theoretical equation. Furthermore, the diffusion volume was affected because the rubber layer was added.