Hydraulic systems and pneumatic systems are both examples of what are called “fluid power systems,” according to Hydraulics and Pneumatics.com, the online resource for fluid power engineers. Hydraulic systems use oil, water or some other fluid to produce mechanical work. Pneumatic systems used compressed air, nitrogen or some other gas. Pneumatic systems are considered fluid power systems because these compressed gases work very much like fluids.
Uses of Hydraulics
Most hydraulic systems feature a reservoir that holds the oil or other hydraulic fluid and one or more pumps to transmit this fluid from one chamber to another. This hydraulic fluid is nearly incompressible and transmits forces very efficiently. Hydraulic systems operate at higher pressure and tend to produce greater force than pneumatic systems. For this reason, hydraulics are often used to lift things and crush things. They are used in jacks and automobile lifts. They are also used in baling machines, which compress loose material like cardboard, hay or garbage into compact, easy to store bales.
Uses of Pneumatics
Any pneumatic system gets its power, ultimately, from an air compressor, which puts the gas in the system under high pressure, giving it the power to perform mechanical work. These compressed gases are easy to transport and can be taken anywhere. Pneumatic systems are used to run equipment, such as drills, in wet or dirty environments where electrical equipment would be difficult or dangerous to use. As such, they are used extensively in mining and construction operations where electrical power isn't always available or might create risk of explosion. They are used in factories to transmit signals to equipment, and often feature in factory safety systems.
Pneumatic systems tend to be simpler than hydraulic systems, and therefore less expensive to purchase and install. However, their operating costs tend to be higher than those of hydraulic systems, making hydraulics more cost-effective in the long run.
Pneumatic systems, unlike hydraulic systems, cannot hold a load in place rigidly, as the air in pneumatic systems is compressible and hydraulic fluid isn't. Hydraulic systems take up less room than pneumatic systems. Leaks can be a bigger problem with hydraulic systems, and maintenance on hydraulic systems requires more highly trained personnel than pneumatic systems.