The chief difference between a pneumatic system and a hydraulic system is the media used to transfer power. Pneumatic systems use compressed gases, such as air or nitrogen, to transfer power. Hydraulic systems use fluids, such as oil or water, to transfer power from one point to another.
A pneumatic system is typically less expensive to design, install and implement than a similar hydraulic system. The reason for the lower cost is that pneumatic systems operate at much lower pressures. The lower pressures used in pneumatic systems allow the components used in these systems to be made of much less-costly materials than are required for a hydraulic system. Although pneumatic systems may be less expensive to design and install due to their relative simplicity and lower pressures, they are often more expensive to operate due to the high energy consumption of air compressors.
Other differences between pneumatic and hydraulic systems include the cleanliness of the system, the complexity of maintenance and the operating pressure. Pneumatic systems are typically cleaner than hydraulic systems. If a pneumatic system leaks, nothing is vented but compressed gases. If a hydraulic system leaks, the fluid used in that system creates a housekeeping problem. Hydraulic systems do have an advantage of pneumatic systems because of the high pressures that can be utilized. The higher pressure of a hydraulic circuit allows a smaller actuator to produce more work than a similar-sized actuator in a pneumatic system.