Introduction

The solenoid valve is the most "power-hungry" component on a pneumatic valve — it is responsible for switching the direction of the air circuit and giving the actuator the open or close command. Many "valve won't move" faults in the field ultimately trace back to the solenoid valve wiring. Starting from identifying the model, this article explains the wiring methods and common mistakes of single-control and double-control, AC and DC, and normally open and normally closed, all at once.

1. Before Wiring, First Identify Which Solenoid Valve You Are Using

Pneumatic valves commonly use two kinds of solenoid valves: the two-position five-way (for double-acting actuators) and the two-position three-way (for single-acting actuators), mostly mounted directly on the side of the actuator with the standard NAMUR interface. By control method they are divided into two categories:

  • Single-control (single solenoid): one coil, energize to switch, and on power loss it returns automatically by spring. When paired with a single-acting actuator, it returns to the safe position on power loss.

  • Double-control (double solenoid): two coils control opening and closing respectively; energizing one switches to open, energizing the other switches to close, and on power loss it holds its position (with memory function).

By de-energized state they are further divided into normally closed (NC) and normally open (NO): normally closed means the air circuit is cut and the actuator receives no air when power is off; normally open is the opposite. Which one to choose depends on the "fail-safe position" required by the process.

2. Three Things You Must Do Before Wiring

  1. Read the nameplate to set the voltage: AC220V, AC110V and DC24V are all different, and wrong voltage is the most common cause of a burned coil — an AC coil connected to a DC supply is basically ruined on the spot.

  2. Count the coils: single-control has only one set of lead wires (usually 2, or 3 with grounding), double-control has two sets (4 or 6 wires); a wrong count means the wrong model was picked.

  3. Confirm the control method: is it a PLC output (mostly DC24V) or relay/contactor control? DC must distinguish positive from negative; AC does not distinguish positive from negative, but the live and neutral wires must be told apart, with reliable grounding.

3. Single-Control Solenoid Valve: 2 Wires + Telling Normally Open from Normally Closed

Single-control wiring is the simplest; the key is that "normally open/normally closed" must be chosen correctly:

  1. Connect the power supply positive pole (or live wire) to the coil terminal "+" (or marked "1")

  2. Connect the negative pole (or neutral wire) to "-" (or marked "2")

  3. If there is a grounding terminal, ground it reliably with a yellow-green wire

  4. Power on and test the action: one that switches direction on energizing and returns automatically on power loss is the normally closed type; one that returns on energizing and switches on power loss is the normally open type

In one sentence: single-control is "act on power, return on power loss" — the return relies on the spring, and the spring's specification must match the operating conditions.

4. Double-Control Solenoid Valve: Pulse Signal + Never Energize Both Coils at Once

  1. Wire the two coils separately: one set controls open, one set controls close; they must match the manufacturer's markings, and you must not guess by wire color

  2. At the control end, use a jog (pulse) signal — a short pulse switches it fully into place, while long-term energizing makes the coil heat continuously

  3. Never energize the two coils at the same time: it causes the spool to be pushed from both sides and jam, and in serious cases burns out the coils

  4. After wiring, jog-test the two directions separately to confirm both open and close travel to position

5. Differences Between AC220V and DC24V

Item AC220V DC24V
Polarity Does not distinguish positive from negative Must distinguish positive from negative
Wire requirements Pay attention to insulation and wire gauge Pay attention to line voltage drop, and the wire should not be too long
Terminal correspondence Live wire into the coil, neutral wire back "+"/"-" correspond one to one
Common faults Poor contact, insulation damage Reverse connection burns out the coil

A field shortcut that saves trouble: connect a freewheeling diode in parallel across a DC solenoid valve to suppress the reverse electromotive force at the moment of power loss and protect the PLC output point.

6. Comparison of 5 Common Pitfalls

Stage ❌ Wrong approach ✅ Correct approach
Voltage Apply DC24V to everything by rule of thumb Check AC/DC and the voltage value against the nameplate
Polarity Connect DC positive and negative at will "+" to positive, "-" to negative; reversing it will definitely burn the coil
Normally open/normally closed Ignore the NO/NC difference Select according to the fail-safe position and verify
Grounding Leave the grounding terminal floating Ground reliably with a yellow-green wire
Double-control Energize both coils at once Send only pulses, with the two coils interlocked

Two more that are often overlooked: an exposed conductor will cause a short circuit; and not rechecking after wiring before powering up directly.

7. Three Commissioning Steps After Wiring

  1. Recheck with power off: all terminals tightened, nothing exposed, nothing misaligned

  2. Manual test: first press the manual emergency button on the solenoid valve to confirm the air circuit switches normally and the actuator travels to position

  3. Power-on test: switch on the supply and observe whether the open and close actions and the status feedback match the command; cut the power and troubleshoot immediately if anything is abnormal

8. Common Fault Quick Reference

Symptom Possible cause Handling direction
No action when powered Voltage mismatch, burned coil Measure the coil terminal voltage and continuity with a multimeter
Cannot return after acting Single-control spring failure, insufficient air supply pressure Check the air pressure and the return spring
Frequent coil burnout Long-term energizing, reversed polarity, no freewheeling protection Switch to pulse control and connect a diode in parallel
Powered but the air circuit does not switch Stuck spool, impurities and moisture in the air supply Disassemble and clean, and improve the air supply quality

Conclusion

For wiring a pneumatic valve solenoid valve, remember three things: voltage by the nameplate, polarity never reversed, and normally open/normally closed chosen correctly. Cutting the power before wiring and verifying manually before powering up after wiring can avoid the vast majority of field faults. For technical support on solenoid valve selection and wiring, please contact our service team.

Zhejiang Huaershi Auto-control Instrument Valve Co., Ltd.

Since 1989 · 30+ years focused on pneumatic actuators and pneumatic valves

Website: www.hesvalve.com