Solenoid valves are an essential component in the control of fluid and gas flow in various industrial applications. They are used to control the flow of liquids and gases in a wide range of industries, from oil and gas to food and beverage production.
However, like any other mechanical device, solenoid valves can develop faults and require maintenance or replacement. In this article, we will explore the common faults of solenoid valves and the solutions to fix them. We will also provide a guide on how to test the quality of a solenoid valve and troubleshoot it on-site.
Whether you are an engineer, technician or simply curious about the inner workings of solenoid valves, this article will provide you with valuable insights into the workings of these essential devices.
So, sit back, relax and let’s dive into the world of solenoid valves!
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
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
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
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.
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. Quick judgment method of solenoid valve on site
4.1 First, check whether the solenoid coil of the solenoid valve is faulty.
On the DCS, the two-position valve receives an “on” or “off” signal.
To determine if the solenoid valve is powered on or off, listen for any sounds on the site. If no sound is detected, there may be an issue with the coil.
If there is a problem with the solenoid valve itself, the following steps should be taken. First, inspect the wiring for any issues, including virtual connections or short circuits.
If the wiring appears to be in good condition, the solenoid valve coil may have burned out. To check for an open circuit, disconnect the wiring and use a multimeter to measure it. If an open circuit is found, the solenoid valve coil has likely burned out.
This can occur when the coil is damp, leading to poor insulation and magnetic leakage, which causes excessive current and burning. To prevent this from happening, it’s important to keep rainwater from entering the solenoid valve.
In addition, if the spring is too stiff, resulting in a large reaction force and too few coil turns, or if the suction force is insufficient, the coil may also burn out.
4.2 If the hot wire coil is good, the solenoid valve itself has problems.
Generally, the valve can be opened by adjusting the manual adjustment position from 1 to 0. If the valve can be opened, it indicates a problem with the coil and replacing the coil will solve the issue.
However, if the valve cannot be opened, remove the solenoid valve to check if the valve core is stuck or if there is debris blocking it.
To clean the solenoid valve, CCL4 is the preferred cleaning agent. If CCL4 is not available, gasoline or water can be used as an alternative. After cleaning, the field instrument should be blown dry with gas.
When disassembling the solenoid valve, it’s important to remember the sequence of each part to avoid mistakes during reassembly. If the sequence is incorrect, the valve may not be able to be opened after cleaning or turning on the solenoid valve.