Pneumatics · beginner
Pneumatic Solenoid Valve
An electrically shifted air valve. A PLC output energises a coil, the internal spool moves, and compressed air is routed to one side of an actuator.
Why it exists
Translate an electrical PLC command into controlled airflow for cylinders, grippers, gates, and process valves.
Quick answer
What is a pneumatic solenoid valve?
A pneumatic solenoid valve converts an electrical command into an airflow path. Energising its coil creates a magnetic force that shifts a plunger or spool, connecting the pressure port to one actuator port while opening another path to exhaust. A spring or second solenoid determines the state when the command is removed.
Inside the control system
How the PLC relates to it
The PLC output commands the valve coil, but the PLC should use cylinder end switches or process feedback to prove that the commanded movement actually happened. A healthy output LED only proves the electrical command reached the module. It does not prove air pressure is present, the spool moved or the actuator completed its stroke. Use a timeout and a clear fault such as EXTEND_COMMAND_WITHOUT_EXTENDED_LIMIT. Fit the correct coil suppression and account for polarity when a diode is built into the connector.
Cause and effect
How it works, step by step
- 01
The PLC output energises the solenoid coil.
- 02
The magnetic plunger pushes the valve spool.
- 03
Supply port P connects to work port A while the other side exhausts.
- 04
A spring or second solenoid returns the spool when the command changes.
01 / Open the case
Watch the mechanism do the work
Follow one highlighted causal link at a time, then operate the component and deliberately create the fault.
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Know the terminals
- A1 / A2 — 24 VDC coil
- P — pressure supply
- A / B — actuator ports
- R / S — exhaust
Recognise the faults
- No air supply despite healthy coil
- Stuck spool from contamination
- Suppressor polarity reversed
- Silencer blocked
Read the field guide
Go deeper on sizing, wiring conventions, test procedure, and the mistakes that damage equipment.
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Selection checks
- Valve function such as 2/2, 3/2 or 5/2 and its normal state.
- Flow capacity, pressure range, medium and seal compatibility.
- Single-solenoid spring return versus double-solenoid memory behaviour.
- Coil voltage, power, connector and suppression.
- Manual override, exhaust treatment and required response time.
Commissioning sequence
- 1Confirm valve function and port numbering from the symbol: pressure, work ports and exhausts.
- 2Verify coil voltage, connector polarity and suppression match the PLC output.
- 3Apply clean regulated air and use the manual override before automatic control.
- 4Energise each coil and observe both actuator movement and end-position feedback.
- 5Create loss-of-air, blocked-exhaust and stuck-spool symptoms and confirm the PLC times out safely.
Troubleshooting answers
Frequently asked questions
What do P, A, B, R and S mean on a pneumatic valve?
P is normally pressure supply, A and B are actuator work ports, and R and S are exhaust ports. Always confirm the markings and symbol for the actual valve.
Why can the coil be on while the cylinder does not move?
Possible causes include no air supply, a jammed spool, blocked exhaust, a mechanical cylinder jam, low pressure or a wiring problem after the output module.
What is the difference between single and double solenoid valves?
A single-solenoid valve normally returns by spring when power is removed. A double-solenoid valve can remain in its last shifted state, so the PLC sequence must manage that memory deliberately.
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