In pneumatic and hydraulic schematics, what does a 4/2 valve indicate?

• A. A four-port, two-position valve with two ports for supply/exhaust and two for the actuator.
• B. An adjustable flow valve with four ports and two positions.
• C. A three-port valve used in small actuators.
• D. A two-port valve that can operate in two positions.

Answer: (A)

In pneumatic and hydraulic schematics, how many ports a valve has and how many stable positions it has determine its function as a directional control valve. A four-port, two-position valve has four ports: a supply (pressure) port, a return/exhaust port, and two ports that connect to the actuator. In one position, the supply port feeds one actuator port while the other actuator port is vented; in the other position, the roles swap so the opposite actuator port is pressurized and the first is exhausted. This setup lets the actuator extend in one state and retract in the other. It’s not an adjustable flow valve, and it isn’t a three-port or a two-port valve—the four ports and two positions are what define it in this context.