7.1: 3/2 Direct Control Valve Function

Fluids 1: Fluid Power and Pneumatics (NWTC) · LibreTexts

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    The 3/2 DCV

    A 3/2 directional control valve (DCV) is a key component used to control the operation of single-acting cylinders. This valve has three ports:

    A pneumatic schematic showing the three valves in a 3/2 DCV
    Figure \(\PageIndex{1}\): A pneumatic schematic showing the three ports of a 3/2 directional control valve (ISO 1219).
    • Port P (Supply): Provides the air supply.
    • Port A (Actuator): Connects to the cylinder.
    • Port E (Exhaust): Vents air when the cylinder retracts.

    In its de-energized (normal) position, the 3/2 DCV blocks the air supply at port P and connects port A to the exhaust port E. This allows the spring in the cylinder to retract the rod without any need for pressurized air.

    Types of 3/2 DCVs

    A pneumatic schematic of a Normally Closed 3/2 DCV
    Figure \(\PageIndex{2}\): A pneumatic schematic of a Normally Closed 3/2 DCV (ISO 1219).

    Normally Closed (N.C.): In this configuration, the valve blocks the air supply in its default position. This type is typically used in clamping applications where the release of pressure (such as unclamping) is achieved without the need for additional air pressure, relying instead on the spring force.

    A pneumatic schematic of a Normally Open 3/2 DCV 
    Figure \(\PageIndex{3}\): A pneumatic schematic of a Normally Open 3/2 DCV (ISO 1219).

    Normally Open (N.O.): Here, the air flows by default, keeping the actuator powered. This configuration is often used in safety circuits where pneumatic power is required to hold or lock a machine in place. In the event of a power loss, the valve automatically vents, stopping or releasing the actuator.

    Application of a 3/2 Pneumatic DCV

    In a typical application, the 3/2 DCV powers the cylinder to extend and then vents the air to allow the spring to retract the rod. For example, in a cylinder clamping circuit, the N.C. configuration of the 3/2 DCV would keep the clamp in place using air pressure. When the cylinder needs to release the clamping force, the valve is de-energized, allowing the spring to retract the cylinder rod and unclamp the part without additional air.

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