PNEUMATICS

PLC Solenoid Valve Output

PLC-controlled pneumatic machines use digital outputs to energize the coils on directional control valves. This diagram shows one protected 24 VDC output path: the PLC output drives an interface relay, the relay supplies a 5/2 valve coil, and a diode suppresses the inductive voltage spike when that coil turns off. The isolation relay is useful when the PLC output current or wiring practice calls for an interface. In a complete machine schematic, add the matching retract coil, cylinder sensors, terminal numbers, and the PLC input circuit. Confirm whether the output is sinking or sourcing before wiring the installed hardware. Verify the valve coil polarity before adding suppression.

UPDATED 2026-09-24

TYPECircuit

EXAMPLEPLC Solenoid Valve Output

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CASE ANALYSIS

Scenario

PLC-driven pneumatic valve

Key decisions

Output: Use a PLC output or interface relay to switch the coil.
Suppression: Put a flyback diode across a DC valve coil.
Protection: Fuse the valve supply separately.

When to reuse this

Use for one DC solenoid valve controlled from a PLC output.

FAQ

Frequently asked questions

Why use a flyback diode on a valve coil?01

It limits the voltage spike created when current through the DC coil is interrupted.

Can a PLC output drive a valve directly?02

Yes if its voltage, current, and output type match the coil; otherwise use an interface relay.

What is a 5/2 valve coil?03

It is the electrical actuator on a five-port, two-position directional valve commonly used with double-acting cylinders.

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