The big difference between hydraulic cylinder and pneumatic cylinder is actually the way the cylinder works. Pneumatic cylinders use gas, usually air or pure gas, to transmit power through compressed gas. On the other hand, the hydraulic system of the hydraulic cylinder uses fluids, usually oil, ethylene glycol and other flame retardant liquid options.
Generally speaking, pneumatic cylinders are compressed air or gas, which will produce linear force. They are pressurized systems that compress air or gas to produce forces that allow movement. The disadvantage of pneumatic systems of pneumatic cylinders is that they really can't produce more than 100 pounds per square inch. Because pneumatic cylinders work with compressed air, the movement is delayed, and a constant "compressor" source is needed to keep things going.
On the other hand, the hydraulic cylinder consists of a pressurizing system rather than pressurizing gas or liquid. The pressurized hydraulic cylinder uses the flowing liquid to move the pressure to different areas, thereby generating the force for moving these areas as needed. Hydraulic cylinders can produce more force, usually ranging from 1500 to 10000 psi, which is obviously much more than pneumatic cylinders can do.
