Working principle of solenoid valves, common faults and solutions

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How to deal with solenoid valve failures? The rated voltages for solenoid valve coils include DC12V, DC24V, AC24V (50/60Hz), AC110V (50/60Hz), AC220V (50/60Hz), and AC380V (50/60Hz). In electrical design, either AC220V is generally used (no need for an switching power supply, low cost, simple wiring and easy maintenance), or DC24V is used (a commonly used safe voltage; switching power supplies and solenoid coils are easy to repair and replace). Method to check the condition of a solenoid valve: First, supply the solenoid valve with the medium to be controlled (a pressurized liquid or gas, with the pressure at an intermediate value within the range suitable for use with that solenoid valve). Then, power the coil of the solenoid valve. If there is a change in the state of the medium from on to off or from off to on, then the solenoid valve is in good condition; otherwise, it has a problem. What are the common faults of solenoid valves? 1. Coil short circuit or open circuit: Testing method: First, use a multimeter to check for continuity; if the resistance is close to zero or infinite, it indicates that the coil is either short circuited or open circuited. If the measured resistance is normal (around a few dozen ohms), it does not necessarily mean that the coil is good (once I measured the resistance of an solenoid coil at around 50 ohms, but the solenoid did not function; after replacing the coil, everything worked normally). Perform the following final test: place a small screwdriver near the metal rod inserted into the solenoid coil, then power on the solenoid. If you feel a magnetic force, then the solenoid coil is good; otherwise, it is faulty. Solution: Replace the solenoid coil. 2. Problem with the plug/socket: Symptoms of the fault: If the solenoid valve has a plug/socket, issues such as problems with the metal reeds in the socket (which I have encountered myself) or problems with the wiring on the plug (for example, connecting the power cable to the ground wire) can prevent power from reaching the coil. It is best to develop a habit: after inserting the plug into the socket, tighten the fixing screw, and on the coil, tighten the fixing nut behind the valve stem. If the plug of the solenoid coil is equipped with a LED power indicator, it must be connected correctly when using a DC power supply to drive the solenoid; otherwise, the indicator light will not turn on. Additionally, do not interchange power plugs with LED power indicator lights of different voltage levels; this can cause the LEDs to burn out, result in a short circuit in the power supply (when a plug with a lower voltage level is used), or lead to very weak lighting from the LEDs (when a plug with a higher voltage level is used). If it lacks a power indicator light, the polarity of the solenoid coil does not need to be distinguished (unlike transistor time relays with DC coil voltage and intermediate relays with DC coil voltage that have diodes/resistors in parallel to form a leakage circuit, where polarity needs to be considered). Solution: Correct wiring errors, repair or replace plugs and sockets. 3. Valve spool issue: Fault symptom 1: When the pressure of the medium flowing through the solenoid valve is normal, pressing the red manual button on the solenoid valve results in no reaction from the valve (no change in the flow of the pressurized medium), which indicates that the valve spool must be damaged. Solution: Check whether there are any issues with the medium – for example, whether there is a lot of water in the compressed air (sometimes the oil-water separator does not function very well, especially when the pipeline design is poor, resulting in a large amount of water in the compressed air that reaches the solenoid valve) – and whether the liquid medium contains many impurities. Then remove any water or debris from the solenoid valve and the pipelines. If that doesn’t work, please repair it (if you have the time, patience, and it’s necessary @_@), or replace the valve core, or simply replace the entire solenoid valve. Fault symptom 2: Upon inspection, the coil is the original one and its magnetism is normal when powered, but the solenoid valve still does not operate (at this point, the manual button of the solenoid valve may function normally), indicating that the valve core is damaged. Solution: Please repair or replace the valve core, or simply replace the entire solenoid valve. As for the repair of solenoid valve bodies, there are so many different types that I can’t go into detail about all the various repair methods; therefore, I won’t discuss them further here. Faults and Troubleshooting of Solenoid Valves

I. The solenoid valve does not function after being powered on
- Check whether the power connections are faulty → Reconnect the wires and check the connections of the plugs.
- Verify that the power voltage is within the ± operating range → Adjust it to the proper range.
- Check if the coil has come unseated → Resolder the coil.
- If there is a coil short circuit, replace the coil.
- Check whether the operating pressure difference is inappropriate → Adjust the pressure difference or replace it with a suitable solenoid valve.
- If the fluid temperature is too high, replace it with a suitable solenoid valve.
- If impurities cause the main spool and moving core of the solenoid valve to get stuck, clean it; if the seals are damaged, replace them and install a filter.
- If the fluid viscosity is too high, the operating frequency is too high, or the valve’s lifespan has expired, replace it.

II. The solenoid valve cannot close
- The seals of the main spool or moving core are damaged → Replace the seals.
- Is the fluid temperature or viscosity too high? → Replace it with a suitable solenoid valve.
- If impurities enter the solenoid valve and cause problems with the spool or moving core, clean it.
- If the spring’s lifespan has expired or it is deformed, replace it.
- If the throttle holes or balance holes are blocked, clean them promptly.
- If the operating frequency is too high or the valve’s lifespan has expired, choose a different product or upgrade it.

III. Other situations
- Internal leakage: Check whether the seals are damaged or if the springs are improperly installed.
- External leakage: Loose connections or damaged seals → Tighten the screws or replace the seals.
- Noise when powered on: The fasteners on the valve body may be loose; tighten them. The voltage fluctuation is outside the acceptable range; adjust the voltage accordingly. If there are impurities or irregularities on the core mating surface, clean it promptly or replace it. Methods for quickly determining the condition of solenoid valves on-site: First, check whether there is a fault with the solenoid coil. Send an open or close signal to the two-position valve via the DCS, and then see if the solenoid valve receives power or not; generally, it’s possible to hear a sound to determine this on-site. If no sound is heard, there is definitely a problem with the coil. As for whether there is a problem with the solenoid valve itself? (Explanated below.) If there is an issue with the solenoid coil, first check the wiring to see if there are any loose connections or short circuits. If there are no problems with the wiring, then the solenoid coil is damaged. The wiring of the solenoid valve can be removed and measured using a multimeter; if there is an open circuit, it means the solenoid coil is damaged. The reason is that moisture gets into the coil, leading to poor insulation and magnetic leakage, which in turn causes an excessive current in the coil and results in its burnout; therefore, it is necessary to prevent rainwater from entering the solenoid valve. Furthermore, an overly stiff spring, excessive reaction force, too few turns of wire, and insufficient suction can also cause the coil to burn out. II. If the coil is fine, then it’s a problem with the solenoid valve itself. Generally, it is possible to use a flathead screwdriver at the manual adjustment mechanism to move it from position 1 to position 0, thereby opening the valve. If the valve opens, it confirms that the issue lies with the coil; in that case, replacing the coil will resolve the problem. If the valve does not open, then the solenoid valve needs to be disassembled to check whether the valve core is stuck or blocked by debris. CCL4 should be used for cleaning, but if such conditions are not available on site, gasoline can be used as a substitute; water can also be used in emergencies. After cleaning, the parts can be dried using the gas available on site. It is essential to remember the order of the various components when disassembling them; otherwise, mistakes may occur during reassembly. Even if the solenoid valve has been cleaned properly and is functioning correctly, it still may not open if the order of assembly is incorrect!