There are many differences between hydraulic control systems and pneumatic control systems (in addition to the fact that one uses oil while the other uses compressed air), and these differences can be summarized as follows:
The air used in pneumatic systems is compressible, while the oil used in hydraulic systems is incompressible.
Pneumatic systems are considered open systems, meaning that the compressed air is discharged into the outside atmosphere after use, while hydraulic systems are considered closed, as the used oil is reclaimed back into the tank and reused again.
Pressure levels. The pressure used in pneumatic systems usually ranges between 6 and 10 bars, while the pressure used in hydraulic systems usually reaches 200 bars and may rise in some applications to about 500 bars.
Power. Pneumatic systems, due to their relatively small pressure, are used with small or medium loads, while hydraulic systems are used with large loads that require high forces or torques to move them.
Actuator speed, the speed of pneumatic actuators is high compared to the speed of hydraulic actuators.
Controlling the speed of actuators, in pneumatic systems it is difficult to control the speed of actuators because air is compressible, while in hydraulic systems it is easy to control the speed of actuators with high accuracy.
Source of fluid power. In hydraulic systems pumps are used while in pneumatic systems compressors are used.
