High Pressure Air (paintball)
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High Pressure Air (HPA) systems are used in paintball for powering the propulsion of paintballs. Tanks are either steel, or lighter weight aluminum wrapped in fiberglass. Steel tanks can hold up to 3000 lbf/in² (20 MPa or 200 bar), while wrapped tanks can range up to 5000 lbf/in² (34 MPa or 340 bar). Average pressure for HPA tanks used in paintballing is 31 MPa (4,500 lbf/in² or 310 bar).
Tank capacity ranges from 48 to 114 in³ (0.8 to 2 L). The 68 in³ (1.1 L) size is considered average.
High pressure systems are advantageous over systems that utilize carbon dioxide in that they contain propellant in a gas state only. Carbon dioxide tanks contain liquid, which must boil into gas for use by the gun. The delay time in boiling of liquid to gas can cause a problem during rapid fire known as shootdown. Another side effect is the variable pressure of the gas, giving a variable muzzle velocity to the projectile.