Both are similar in that they both use a fluid pressure to do work.
However where oils (or water) are nearly incompressible and will transmit forces very similar to what is applied, the compressibility of air means it cannot be used to control fine emovements, e.g. moving a ram a controlled distance and stopping it, while maintaining the position it has stopped in regardless of the variations in load on the ram at the time. Using air, the ram would continue to move independently of the controls.
Air as a medium where full strokes and fast action (e.g. of a ram) are used is OK, but if fine movement control and high pressures are required, an oil (water) medium is far superior.
However where oils (or water) are nearly incompressible and will transmit forces very similar to what is applied, the compressibility of air means it cannot be used to control fine emovements, e.g. moving a ram a controlled distance and stopping it, while maintaining the position it has stopped in regardless of the variations in load on the ram at the time. Using air, the ram would continue to move independently of the controls.
Air as a medium where full strokes and fast action (e.g. of a ram) are used is OK, but if fine movement control and high pressures are required, an oil (water) medium is far superior.