Solenoid valves are widely used in our production processes, and during maintenance, we've encountered numerous issues related to these valves. Over time, we've resolved various failures and accumulated a wealth of experience in troubleshooting. Compared to other instrument control problems, dealing with solenoid valve faults is relatively simpler. Today, I'd like to share my insights on this topic and eagerly look forward to learning from your experiences as well, so we can all improve together.
To begin with, let's have a basic understanding of what a solenoid valve is. A solenoid valve consists of a solenoid coil and a core, along with one or more holes in the valve body. When the coil is energized or de-energized, the magnetic core moves, allowing or blocking the flow of fluid through the valve body, thus changing the direction of the fluid flow. The electromagnetic components include a fixed iron core, a moving iron core, and a coil. The valve body includes a spool, a sliding sleeve, and a spring base. The solenoid coil is directly mounted on the valve body, which is enclosed in a sealed housing, making it a compact and efficient unit.
In our production, we commonly use two-way, four-way, and five-way solenoid valves. Let me explain the meaning of the first two: a two-way solenoid valve controls the opening and closing of the valve when power is applied or removed. In our oxygen meter control system, the most frequently used type is the two-way three-port solenoid valve. It is used to connect or cut off the gas source, thereby switching the pneumatic control membrane head’s air path. This device consists of a valve body, cover, electromagnetic component, spring, and sealing structure. The sealing block at the bottom of the moving iron core closes the air inlet via spring pressure. When powered, the electromagnet pulls the moving core, lifting the sealing block and allowing airflow into the membrane head. When power is lost, the spring pushes the moving core back, opening the exhaust port and releasing the air from the membrane head, returning it to its original position.
In our oxygen plant, such valves are also used for emergency shut-off of the turbo-expander inlet regulating valve. The four-way solenoid valve has many applications in our production. Its working principle is as follows: when current flows through the coil, an electromagnetic field is generated, pulling the fixed core and moving core, which then drives the spool and compresses the spring, changing the fluid flow direction. When the coil is de-energized, the spring returns the spool to its original position, restoring the initial flow direction. In our oxygen production, the molecular sieve switching system uses a two-position four-way solenoid valve to control the valve switch by supplying air to both ends of the piston, enabling precise control over the opening and closing of the valve.
Solenoid valve failures can directly affect the operation of switching and regulating valves. Common issues include failure to act, which should be checked from the following aspects:
1. Loose connections or missing threads: Ensure the valve is properly tightened.
2. Burned-out coil: Use a multimeter to check for open circuits. If the coil is burned, it may be due to moisture causing poor insulation or excessive current. Prevent water ingress and check coil design, including the number of turns and spring strength.
3. Stuck valve: Due to small gaps between the sleeve and spool (less than 0.008mm), impurities or lack of lubrication can cause sticking. Try using a steel wire to dislodge it, but the best solution is to disassemble, clean, and reassemble carefully.
4. Leaks: Caused by damaged seals or worn spools. Check for blockages in the oil mist hole and ensure proper lubrication.
When dealing with solenoid valve failures in the switching system, choose the right timing. If it occurs outside of the switching cycle, the system can be paused for safe handling. Always remain calm and methodical when addressing such issues.
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