During troubleshooting of a pneumatic dryer system, several solenoid valves were investigated because the expected valve operation was not occurring.
The first electrical check was coil resistance.
Most coils showed approximately 300 ohms, which initially indicated that the coils were electrically intact.
However, resistance measurement alone could not confirm that the complete solenoid valve was functioning correctly.
The valve inputs and outputs were then checked by applying the control voltage and observing the actual valve state.
This revealed that some valves were not changing state correctly even though their coils had measurable resistance.
The solenoid valves were subsequently dismantled for further inspection. Mechanical condition, seals, piston movement, and valve matching were considered.
A replacement valve was later found to be mismatched with the original configuration and did not provide a satisfactory replacement.
Key Lesson
A normal coil resistance does not prove that a solenoid valve is functionally healthy.
A solenoid valve has at least two separate aspects to verify:
Electrical condition
and
Mechanical/pneumatic operation
A coil may have normal resistance while the valve spool, piston, seal, spring, or internal mechanism is defective.
Similarly, applying voltage and hearing a click does not necessarily prove that the valve is providing the required pneumatic flow.
Practical Troubleshooting Sequence
- Check supply voltage.
- Measure coil resistance.
- Check coil current where practical.
- Apply the correct control voltage.
- Confirm actual valve-state change.
- Check pneumatic inlet and outlet pressure.
- Verify exhaust/vent operation.
- Inspect mechanical movement.
- Check seals, piston and spool condition.
- Confirm replacement valve specifications before installation.
- Test the valve under actual operating conditions.
Troubleshooting Principle
For control components, always distinguish:
Electrical test → Mechanical test → Process/function test
Passing the first test does not automatically mean the component will pass the third.