Regulator

Sitting between the tank and the gun, either on the tank itself or inline in the hose, the regulator holds output steady regardless of how full the tank is — a nearly empty tank still delivers the same output pressure as a full one, right up until it can't sustain that pressure at all.

Adjustable regulators let a player tune output pressure to hit a target FPS without opening the gun, which is one of HPA's biggest advantages over spring or gas systems where power changes mean swapping physical parts. A failing regulator is a common cause of inconsistent HPA shots, since it's the component actually setting shot-to-shot pressure.

A second, smaller in-line regulator is sometimes added purely as a safety backstop, so a primary regulator failing wide open still can't send full tank pressure straight to the solenoid — cheap insurance against a rare but serious failure.