Hydraulics vs Pneumatics

There are almost no significant differences between hydraulics and and for non-engineers but if you examine further, there are lots of technical uniqueness in each system.

By definition alone, hydraulics is very different from pneumatics because it is used in controlling, transmitting and harnessing power using pressured fluids. The latter is dealing more on studying the impact of pressurized gases and how it influences mechanical movement. Hydraulics is frequently used in the concepts of dams, rivers, turbines and even erosion whereas pneumatics is applied in various fields of dentistry, mining and general construction among others.

Another difference between the two when applied is the strength of the pressures used in their applications. Hydraulic systems use a greater amount of pressure compared to pneumatic applications. In pneumatics, only 80-100 psi (pounds per square inch) of pressure is used for its industrial applications. Hydraulic-based applications frequently use pressures that range from 1,000-5,000 psi. Nevertheless, other more advanced hydraulic systems even use pressures of up to 10,000 psi. Because of this high power demand, hydraulic systems chiefly use bigger components while pneumatic systems use smaller ones in most applications.

Gases used in pneumatic systems

Pneumatic systems in fixed installations, such as factories, use compressed air because a sustainable supply can be made by compressing atmospheric air. The air usually has moisture removed, and a small quantity of oil is added at the compressor to prevent corrosion and lubricate mechanical components.
Factory-plumbed pneumatic-power users need not worry about poisonous leakage, as the gas is usually just air. Smaller or stand-alone systems can use other compressed gases that present an asphyxiation hazard, such as nitrogen—often referred to as OFN (oxygen-free nitrogen) when supplied in cylinders.

Comparison to hydraulics

Both pneumatics and hydraulics are applications of fluid power. Pneumatics uses an easily compressible gas such as air or a suitable pure gas—while hydraulics uses relatively incompressible liquid media such as oil. Most industrial pneumatic applications use pressures of about 80 to 100 pounds per square inch (550 to 690 kPa). Hydraulics applications commonly use from 1,000 to 5,000 psi (6.9 to 34 MPa), but specialized applications may exceed 10,000 psi (69 MPa).

Advantages of pneumatics

• Simplicity of design and control—Machines are easily designed using standard cylinders and other components, and operate via simple on-off control.
• Reliability—Pneumatic systems generally have long operating lives and require little maintenance. Because gas is compressible, Equipment is less subject to shock damage. Gas absorbs excessive force, whereas fluid in hydraulics directly transfers force. Compressed gas can be stored, so machines still run for a while if electrical power is lost.
• Safety—There is a very low chance of fire compared to hydraulic oil. Machines are usually overload safe.

Advantages of hydraulics

• Liquid (as a gas is also a 'fluid') does not absorb any of the supplied energy.
• Capable of moving much higher loads and providing much higher forces due to the incompressibility.
• The hydraulic working fluid is basically incompressible, leading to a minimum of spring action. When hydraulic fluid flow is stopped, the slightest motion of the load releases the pressure on the load; there is no need to "bleed off" pressurized air to release the pressure on the load.