The fluid employed in hydraulics is incompressible; force is transferred instead of absorbed in hydraulic systems, according to Science Ray. The air in pneumatics is compressible; force is absorbed instead of transferred in pneumatic systems.
Hydraulic systems are typically operated at between 1,000 and 5,000 pound per square inch (PSI) pressures, according to Science Ray. Pneumatic systems on the other hand, are typically operated at pressures under 100 PSI.
Hydraulic systems are linked with higher operating costs than pneumatic systems. However, the initial purchase costs associated with hydraulics is traditionally lower than the initial purchase costs associated with pneumatics.