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Solenoids are widely used in our production processes. During maintenance activities, we have certainly encountered many issues related to solenoids and have dealt with various types of faults. Everyone must have accumulated considerable experience in dealing with solenoid-related problems. As for me, I handle solenoid faults less frequently compared to other instrument control-related issues. Now I would like to discuss this topic with everyone, hoping to learn more from you all in order to improve together. Today’s focus: Let’s first get a basic understanding of solenoid valves. A solenoid valve consists of an electromagnetic coil and a magnetic core, along with a valve body that contains one or several holes. When the coil is energized or de-energized, the movement of the magnetic core causes the fluid to pass through or be blocked by the valve body, thereby changing the direction of the fluid. The electromagnetic components of a solenoid valve consist of a fixed core, a moving core, a coil, and other components ； The valve body part consists of a spool, a spool sleeve, a spring base, etc. The electromagnetic coil is directly mounted on the valve body, which is enclosed in a sealed tube, forming a simple and compact assembly. The solenoid valves commonly used in our production include 2/3-way, 2/4-way, 2/5-way, etc. Let’s first explain what these two terms mean: for solenoid valves, they refer to being powered and unpowered; for the valves they control, they refer to being open and closed. In our oxygen generator control system, two-position three-way solenoid valves are used the most; they can be employed in production to connect or disconnect the gas supply, thereby switching the air paths for pneumatic control diaphragms. It consists of components such as a valve body, a valve cover, an electromagnetic assembly, springs, and sealing structures; the sealing block at the bottom of the moving iron core closes the air inlet of the valve body under the pressure of the springs. When powered on, the electromagnet attracts, and the spring-loaded sealing block at the upper part of the moving core closes the exhaust port; air flows in through the intake port to the diaphragm head, thereby serving a control function. When there is a power loss, the electromagnetic force disappears; the moving core moves away from the fixed core under the action of the spring force, moving downward to open the exhaust port and block the intake port. The air flow from the diaphragm passes through the exhaust port, and the diaphragm returns to its original position. In our oxygen production equipment, it is used in places such as the emergency shut-off valve at the inlet diaphragm control valve of the turbine expander. Four-way solenoid valves are also widely used in our production. Their working principle is as follows: When an electric current flows through the coil, an excitation effect is generated, causing the fixed core to attract the moving core. The moving core then drives the slide valve core and compresses the spring, thereby changing the position of the slide valve core and thus altering the direction of the fluid flow. When the coil loses power, the elastic force of the spring pushes the spool core, pushing back the moving core and allowing the fluid to flow in its original direction. In our oxygen production process, the operation of the on/off valve in the molecular sieve switching system is controlled by a two-position four-way solenoid valve, with air flow being supplied to both ends of the piston of the forced valve. Thereby controlling the opening and closing of the relief valve. Failures of the solenoid valve will directly affect the operation of the switch valve and control valve. Common faults include the solenoid valve not functioning; such issues should be investigated from the following aspects: (1) The wiring connections of the solenoid valve may be loose or the wires may have come loose, resulting in the valve not receiving power; in this case, the connections can be tightened. (2) If the solenoid coil is damaged, the wiring of the solenoid can be removed and measured with a multimeter; if there is an open circuit, then the solenoid coil is damaged. The reason is that moisture gets into the coil, leading to poor insulation and magnetic leakage, which results in excessive current flowing through the coil and causing it to burn out; 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. In emergency situations, the manual button on the coil can be switched from the “0” position used during normal operation to the “1” position, thereby opening the valve. (3) The solenoid valve is stuck. The clearance between the spool sleeve of the solenoid valve and the valve core is very small (less than 0.008 mm); it is usually assembled as a single unit. When mechanical impurities get in or there isn’t enough lubricating oil, jamming can easily occur. The solution is to insert a steel wire through the small hole at the head to make it bounce back. The fundamental solution is to remove the solenoid valve, take out the spool and its sleeve, and clean them with CCI4 so that the spool can move freely within the sleeve. When disassembling, pay attention to the assembly sequence of the various components as well as the locations of the external wiring, so as to ensure proper reassembly and wiring. Also, check whether the oil mister nozzles are clogged and whether there is sufficient lubricating oil. (4) Air leakage. Air leakage can lead to insufficient air pressure, making it difficult for the check valve to open and close; this is caused by damaged gaskets or worn spools, which result in air leaking between various chambers. When dealing with valve failures in the switching system, it is necessary to choose the right moment to carry out repairs – waiting until the valve is de-energized. If the repairs cannot be completed within one switching interval, the switching system can be paused to allow for proper handling of the issue.