Editing Air gun (section)

==== High-pressure air ====
[[High-pressure air]] (HPA) system, or ''N<sub>2</sub>'', was originally developed for [[paintball markers]] as a replacement for CO<sub>2</sub> cartridges, and uses Powerlet interface-compatible [[diving cylinder]]s filled with either pure [[nitrogen]] or [[compressed air]] (which is 78% nitrogen). Because nitrogen is more [[chemically inert|inert]] than CO<sub>2</sub>, it remains in the [[gas]]eous state longer when compressed; when it expands, it cools due to the [[Joule-Thomson effect]] but at a far lower rate than [[liquid carbon dioxide|liquid CO<sub>2</sub>]] because there is no change in [[state of matter|state]] [[boiling|from liquid to gas]]. This [[thermostability]] reduces the variation in output pressure associated with rapid successions of firing cycles, improving accuracy and reliability in extreme climates. However, because compressed air is stored at higher pressures (up to {{cvt|34|MPa|disp=or|lk=on}}) than liquid CO<sub>2</sub> (stored at around {{cvt|8|MPa|disp=or}}), HPA cylinders are more expensive. Cylinders smaller than {{cvt|1.1|L|cuin|lk=on}} may not even last as long as a standard CO<sub>2</sub> cartridge when subjected to frequent uses.

It is also possible to power an HPA-compatible gun directly from a plug-in [[air compressor]] without using a gas cylinder, though this type of setup is rare.