Solenoid Valve Troubleshooting: Expert Tips

The solenoid valve coil is rated for a voltage of DC12V, DC24V, AC24V (50/60Hz), AC110V (50/60Hz), AC220V (50/60Hz), or AC380V (50/60Hz).

In electrical design, AC220V is often used because it does not require a switching power supply and is low cost, with a simple circuit and easy maintenance. Alternatively, DC24V is commonly used due to its widely used safety voltage and ease of repair and replacement of the switching power supply and solenoid valve coil.

1. The method of testing the quality of the solenoid valve

To test the solenoid valve, first connect it to the controlled medium (such as a pressurized liquid or gas like air) with a pressure value in the middle range of the solenoid valve’s pressure range. Then, activate the solenoid coil.

If the controlled medium can change from on to off or off to on, the solenoid valve is functioning properly. If this is not the case, there may be an issue with the valve.

2. Common faults of the solenoid valve

2.1 Short circuit or circuit break of coil

Detection method:

To diagnose the condition of a solenoid valve, use a multimeter to measure its on-off state. If the resistance tends towards zero or infinity, it indicates that the coil is either short-circuited or has an open circuit.

Even if the measured resistance is normal (around tens of Ω), it does not guarantee that the coil is functioning properly. I have encountered a case where the resistance of a solenoid valve coil was measured to be about 50 Ω, but the solenoid valve still did not work, and it was only after replacing the coil that everything returned to normal. To perform a final test, follow these steps:

• Obtain a small screwdriver.
• Place the screwdriver near the metal rod inside the solenoid valve coil.
• Turn on the power to the solenoid valve.
• If you feel a magnetic pull, the solenoid valve coil is functional. If not, it is likely to be damaged.

Solution: replace the solenoid valve coil.

2.2 Problems of the plug/socket

Fault phenomenon:

If the solenoid valve has a plug and socket connection, problems may arise with the metal spring of the socket or the wiring of the plug (such as connecting the power line to the ground wire), preventing power from reaching the coil.

It is recommended to develop a habit of securing the plug into the socket with a fixing screw, and securing the valve core rod with a fixing nut on the coil.

If the solenoid valve coil plug is equipped with an LED power indicator, it should be driven by a DC power supply, otherwise the indicator will not light up.

Note that different voltage level power plugs with LED power indicators should not be interchanged, as this may cause the LED to burn out, the power supply to short circuit, or the LED light to be very weak.

If there is no power indicator, the solenoid valve coil does not need to distinguish the polarity, unlike some transistor time relays with DC coil voltage or intermediate relays with a DC coil voltage and diode/resistor leakage circuit in parallel on the coil (mainly from Japan) that require polarity differentiation.

If there is a problem, the solution is to correct the wiring error, repair or replace the plug and socket.

2.3 Problems of the valve core

Problem 1:

If the medium pressure in the solenoid valve is normal, but the red manual button of the solenoid valve fails to produce a response (i.e., no change in the on-off state of the pressure medium), it is likely that the valve core is broken.

Solution: First, check for problems in the medium, such as an excessive amount of water in compressed air (poor pipeline design can result in water in the compressed air reaching the solenoid valve, even if an oil-water separator is present) or impurities in the liquid medium.

Then, remove the water or impurities from the solenoid valve and pipeline. If this does not solve the problem, repair or replace the valve core, or the entire solenoid valve if necessary.

Problem 2:

If inspection shows that the coil is original and producing normal magnetism when powered on, but the solenoid valve still fails to act (at this time, the manual button of the solenoid valve may still function normally), it indicates that the valve core is broken.

Solution: Repair or replace the valve core, or the entire solenoid valve if necessary.

Note: There are many methods for maintaining solenoid valve bodies, but they will not be discussed here.

3. Troubleshooting of solenoid valve

3.1 The solenoid valve does not work when it is energized

• Check the power wiring for faults and rewire and connect the connector if necessary.
• Ensure that the power supply voltage is within the ± working range and adjust it to the normal position range if necessary.
• Check if the coil has been desoldered and reweld it if necessary.
• If the coil is short-circuited, replace it.
• If the working pressure difference is not appropriate, adjust it or replace the corresponding solenoid valve.
• If the fluid temperature is too high, replace the appropriate solenoid valve.
• If impurities cause the main valve core and moving iron core of the solenoid valve to become stuck, clean it and replace the seal and install a filter if the seal is damaged.
• If the liquid viscosity is too high, the frequency is too high, and the service life has come to an end, replace the product.

3.2 The solenoid valve cannot be closed

• If the seal of the main valve core or moving iron core is damaged, replace it.
• If the fluid temperature and viscosity are too high, replace the corresponding solenoid valve.
• If impurities have entered the valve core or moving iron core of the solenoid valve, clean it.
• If the spring has reached the end of its life or has become deformed, replace it.
• If the throttle balance hole is blocked, clean it promptly.
• If the working frequency is too high or the service life has been exceeded, consider changing the product or upgrading to a newer model.

3.3 Other circumstances

• If there is internal leakage, check if the seal is damaged and if the spring is poorly assembled.
• If there is external leakage, it may be due to a loose joint or damaged seal. Tighten the screw or replace the seal to resolve the issue.
• If there is noise when the power is on, it may be due to loose fasteners on the head. Tighten them to resolve the issue.
• If the voltage fluctuation is outside of the allowable range, adjust the voltage to bring it within the range.
• If the iron core suction surface has impurities or is uneven, clean it or replace it in a timely manner.

4. On-site Quick Diagnosis Method for Solenoid Valves

4.1 Assessing Solenoid Coil Functionality

When a two-position valve receives an “on” or “off” signal from the Distributed Control System (DCS), the first step is to verify the solenoid coil’s operational status.

At the installation site, listen for any audible clicking or humming sounds associated with the valve’s actuation. The absence of such sounds may indicate a coil malfunction.

If a coil issue is suspected, follow these diagnostic steps:

1. Inspect the electrical connections: Check for loose terminals, damaged insulation, or signs of short circuits.
2. Coil continuity test: If wiring appears intact, disconnect the coil and use a multimeter to measure its resistance. An open circuit (infinite resistance) suggests a burned-out coil.

Common causes of coil failure include:

• Moisture ingress: Can lead to insulation breakdown and magnetic flux leakage, resulting in excessive current draw and thermal damage. Ensure proper environmental protection to prevent water infiltration.
• Mechanical issues: Overly stiff return springs or insufficient magnetic pull can cause coil overheating. Verify proper matching of coil specifications to valve requirements.
• Insufficient coil turns: May result in inadequate magnetic field strength, leading to increased current draw and potential burnout.

4.2 Troubleshooting Valve Mechanism Issues

If the coil tests satisfactorily, focus on the valve mechanism:

1. Manual override test: Attempt to actuate the valve using its manual override feature (typically adjusting from position 1 to 0). Successful manual actuation indicates a coil-related issue, which can be resolved by replacement.

2. Valve inspection: If manual actuation fails, remove the valve for internal examination. Look for:

• Stuck valve stem or poppet
• Debris or contamination in the valve body
• Damaged seals or seats

3. Cleaning procedure:

• Preferred cleaning agent: Carbon tetrachloride (CCl₄)
• Alternatives: Isopropyl alcohol or specialized valve cleaning solvents
• Last resort: Clean water (ensure thorough drying)
• Post-cleaning: Use compressed air or nitrogen to dry all components thoroughly

Important: When disassembling the valve, document or photograph the component arrangement to ensure correct reassembly. Improper reassembly can result in valve malfunction or failure to open/close when energized.

Note: Always follow manufacturer guidelines and safety protocols when performing maintenance on solenoid valves. Ensure proper personal protective equipment (PPE) is used, especially when handling cleaning solvents.