Air under greater than atmospheric pressure, especially when used to power a mechanical device or to provide a portable supply of oxygen. Air reduced in volume and held under pressure. Force from compressed air is used to operate numerous tools and instruments, including rock drills, train brake systems, riveters, forging presses, paint sprayers, and atomizers. Bellows have been used since the Early Bronze age to provide air for smelting and forging. The 20th century witnessed a large increase in the use of compressed-air devices. The introduction of jet engines for military and passenger aircraft stimulated the use and improvement of centrifugal and axial-flow compressors. Digital-logic pneumatic-control components (developed in the 1960s) can be used in power and control systems (see pneumatic device)
or Nitrogen - the same as the air we breath A gas used to power the paintball out of a marker This may not be used in the same cylinders as the CO2 is stored