Pneumatics is a fluid power technology that transmits force through a pressurized medium to create useful work. In the simplest explanation, air will compress to half its volume when subjected to double the pressure.
Compressibility is an asset for pneumatic systems, allowing for extremely high acceleration and inherent shock absorption. As compressed air moves from high pressure to one of lower pressure, the expansion accelerates the air. The acceleration occurs at the loads of the actuators to provide the snappy movement pneumatic systems are known for. But, of course, the compressibility of air prevents it from being the first choice for load-holding applications. Still, air-over-oil systems provide a versatile solution when hydraulic power units are unavailable.