Ci

[actio]

[Andyman]

its the amount in side the tank. if its a 68ci, it will hold 68 ci of air

[Z-man]

Yes it refers to the volume inside of the tank. It does not refer to the pressurized capactiy (as you have probably seen 3Kpsi 68ci tanks and 4500psi 68ci tanks)

[Thermus]

CI means cubic inches, so a 68 ci tank will hold 68 cubic inches of air.

[actio]

so CI is how much it holds and PSI is the force it comes out with

[deadeye9]

A 68 ci tank will hold 68 cubic inches of water (or other non-compressable liquid). It will hold 68 ci of air at 14.7 psi (sea level). It will hold more air at a higher psi.