A 3/2 valve (pronounced "three-two valve") is a pneumatic directional control valve with three ports and two states (positions) used to control single-acting actuators like cylinders, allowing fluid (air or liquid) to flow from an inlet (P) to an outlet (A) in one state, and from the outlet (A) to an exhaust (R) in the other state, effectively switching flow on/off and venting pressure.