Solenoid Valve Troubleshooting and Repair Guide: Fix Common Issues
Solenoid Valves: Fundamentals, Fault Diagnosis, and Maintenance
The solenoid valve, an essential automation component playing a critical role in fluid control, is indispensable. It is widely used not only in hydraulic and pneumatic control systems but also performs crucial functions in numerous scenarios. Key members of the solenoid valve family include check valves, safety valves, directional control valves, and flow control valves. Each serves its specific purpose, collectively ensuring the stable operation of fluid control systems. Now, let's delve into the principles of solenoid valve operation.
Should the video content not fully address your queries, the following provides a more professional explanation to deepen your understanding of solenoid valve working principles.
Fault Handling and Routine Maintenance
Solenoid valve coils are available in various rated voltages, such as DC 12V, DC 24V, AC 24V (50/60Hz), AC 110V (50/60Hz), AC 220V (50/60Hz), and AC 380V (50/60Hz). In electrical design, AC 220V is often chosen as it eliminates the need for an additional switching power supply, reducing cost and simplifying wiring for easier maintenance. Alternatively, DC 24V, a common safe voltage, is frequently selected because both its switching power supply and solenoid valve coil are easy to repair and replace.
Testing Solenoid Valve Functionality:
To check if a solenoid valve is functioning correctly, apply the controlled medium (e.g., pressurized liquid or gas) and simultaneously supply the rated voltage. Observe whether the controlled medium changes state (from open to closed or vice versa). If such a change occurs, the solenoid valve is operational. If not, a fault is likely present.
Other common faults include coil burnout and spool sticking. Specific corrective actions depend on the nature of the fault.
1. Coil Short Circuit or Open Circuit:
Detection Method: First, use a multimeter to measure coil continuity. A reading approaching zero indicates a short circuit; infinity indicates an open circuit. Note: A normal resistance reading (e.g., tens of ohms) does not guarantee the coil is good. For example, a coil once measured approximately 50 ohms yet the valve failed. Replacing the coil resolved the issue. For a more reliable test: Place a small screwdriver near the metal rod passing through the solenoid coil. Apply power to the valve. If magnetism is felt, the coil is likely functional. If not, the coil is probably damaged.
Action: Replace the coil immediately upon confirmation of failure.
2. Plug/Socket Issues:
Faults: If the solenoid valve uses a plug/socket connection, potential problems include faulty socket contacts, incorrect plug wiring (e.g., connecting the live wire to ground), preventing power from reaching the coil.
Prevention: Tighten the fixing screw after inserting the plug into the socket. Ensure the fixing nut is securely tightened after mounting the coil onto the valve stem.
LED Indicator Note: If the solenoid coil plug has an LED power indicator, ensure correct polarity when using a DC supply; otherwise, the LED won't light. Avoid mixing plugs with LED indicators designed for different voltage levels to prevent LED burnout or power short circuits.
Polarity Note: Solenoid valves without power indicators have coils that are non-polarized (unlike DC coil voltage transistor timers and relays, which require correct polarity).
Action: Correct wiring errors. Repair or replace faulty plugs/sockets.
3. Spool Issues:
Fault Symptom 1: With confirmed normal medium pressure applied, press the red manual button. If the valve shows no response (no change in medium flow state - open/close), the spool is likely damaged.
Action: First, check for medium issues. Examples: Excessive water in compressed air (oil-water separators may be ineffective, especially with poor piping design, leading to wet air reaching the valve), or impurities in the liquid medium. Subsequently, clear water or debris from the solenoid valve and its piping.
Fault Symptom 2: If the coil is confirmed original and exhibits normal magnetism when powered, but the valve still fails to actuate (manual button may function normally), the spool is damaged.
Action: Repair or replace the spool assembly, or replace the entire solenoid valve.
(Note: Specific repair methods for solenoid valve bodies vary greatly by type and are not detailed here.)
4. Valve Fails to Operate When Energized:
Check and secure power wiring connections/re-plug connectors.
Verify power voltage is within the specified operating range; adjust if necessary.
Re-solder any loose coil connections.
Replace the coil if short-circuited.
Check if the working pressure differential is suitable; adjust or replace the valve if needed.
Replace the valve if fluid temperature is too high.
Clean the spool and armature if jammed by debris; replace damaged seals; install a filter.
Replace the valve if fluid viscosity is too high, operating frequency is excessive, or the product has reached its end of life.
5. Valve Fails to Close (De-energized):
Replace damaged seals on the main spool or armature.
Replace the valve if fluid temperature or viscosity is too high.
Clean the valve thoroughly if debris is jamming the spool or armature; replace damaged seals.
Replace the spring if its life is expired or it is deformed.
Clean blocked orifice or balance holes.
Consider replacement or upgrading the product if operating frequency is too high or its service life has ended.
6. Other Situations & Actions:
Internal Leakage: Check seal integrity and proper spring assembly.
External Leakage: Tighten connections or replace seals if loose or failed.
Noise When Energized: Tighten loose fasteners on the solenoid head. Ensure voltage is stable within the allowable range; adjust if needed. Clean or replace components if the armature mating surfaces are dirty or uneven.
Field Method for Quick Solenoid Valve Diagnosis:
Check the Solenoid Coil:
Issue an open/close command to the 2-position valve via the DCS. Observe if the valve energizes/de-energizes as expected. Audibly checking for a "click" at the valve is common practice. If no sound is heard, the coil is likely faulty. Note: A silent coil doesn't rule out other valve issues.
If a coil fault is suspected, inspect wiring for poor connections or shorts. If wiring is sound, the coil is probably burnt out. Disconnect the coil leads and measure with a multimeter. An open circuit confirms coil burnout. Causes include: Moisture ingress degrading insulation; leakage flux causing overcurrent; excessive spring force/reaction force; insufficient magnetic pull due to too few coil turns. Implement measures to prevent water ingress (e.g., rain protection).
If the Coil is Functional, Check the Valve Itself:
Use a flathead screwdriver to manually operate the valve from position 1 (e.g., normally closed) to 0 (open). If the valve opens manually, the problem is confirmed as the coil; replace it. If it doesn't open, disassemble the valve.
Inspect the spool for sticking or blockage by debris. Clean thoroughly. Recommended cleaning agents include CCl4 (carbon tetrachloride). If unavailable, gasoline or water can be used as alternatives. Dry thoroughly using instrument air after cleaning.
Critical: Carefully note the sequence and orientation of all components during disassembly to ensure correct reassembly. Incorrect reassembly will prevent the valve from functioning.
