SKEDSOFT

Comparison between pneumatic systems and hydraulic systems:

The fluid generally found in pneumatic systems is air; in hydraulic systems it is oil. And it is primarily the different properties of the fluids involved that characterize the differences between the two systems. These differences can be listed as follows:

• Air and gases are compressible, whereas oil is incompressible.

• Air lacks lubricating property and always contains water vapor. Oil functions as a hydraulic fluid as well as a lubricator.

• The normal operating pressure of pneumatic systems is very much lower than that of hydraulic systems.

• Output powers of pneumatic systems are considerably less than those of hydraulic systems.

• Accuracy of pneumatic actuators is poor at low velocities, whereas accuracy of hydraulic actuators may be made satisfactory at all velocities.

• In pneumatic systems, external leakage is permissible to a certain extent, but internal leakage must be avoided because the effective pressure difference is rather small. In hydraulic systems internal leakage is permissible to a certain extent, but external leakage must be avoided.

• No return pipes are required in pneumatic systems when air is used, whereas they are always needed in hydraulic systems.

• Normal operating temperature for pneumatic systems is 5° to 60°C (41° to 140°F). The pneumatic system, however, can be operated in the 0° to 200°C (32° to 392°F) range. Pneumatic systems are insensitive to temperature changes, in contrast to hydraulic systems, in which fluid friction due to viscosity depends greatly on temperature. Normal operating temperature for hydraulic systems is 20° to 70°C(68° to 158°F).

• Pneumatic systems are fire- and explosion-proof, whereas hydraulic systems are not.