Common sense of solenoid valve selection

Common Sense for Selecting a Solenoid Valve When selecting a solenoid valve, it's essential to ensure that the fluid in the piping matches the medium for which the valve is calibrated. The temperature of the fluid, such as helium, must be below the rated operating temperature of the selected valve. Generally, solenoid valves are designed for liquids with viscosity up to 20 CST; if the viscosity exceeds this, special considerations should be made. The working pressure difference is another critical factor. If the pressure difference in the pipeline is less than 0.04 MPa, direct-acting or distributed direct-acting models like ZS, 2W, ZQDF, and ZCM series are recommended. For low-pressure differences above 0.04 MPa, pilot-operated valves are more suitable. It’s important to ensure that the maximum working pressure difference does not exceed the rated pressure of the valve. Most solenoid valves are unidirectional, so check for backpressure and consider installing a check valve if necessary. If the fluid has poor cleanliness, install a filter before the valve. Solenoid valves typically require clean media to function properly. Pay attention to the flow passage and nozzle diameter, as these valves are generally controlled by two-position switching. A bypass pipe can be installed for easier maintenance. In cases of water hammer, custom adjustments to the opening and closing time may be required. Environmental temperature can also affect the performance of the valve. Ensure that the power supply current and power consumption match the output capacity, and note that AC startup may have a higher VA value. The voltage is usually allowed to vary by ±10%. Reliability is key when choosing a solenoid valve. There are two types: normally closed and normally open. Normally closed valves are more commonly used, as they remain closed when power is off. However, if the opening time is long and closing time is short, a normally open model might be better. Life testing is often part of factory testing, but there is no official Chinese standard for solenoid valves, so it’s wise to choose reputable manufacturers. High-frequency applications typically use direct-acting types, especially for larger diameters. Safety is another concern. Most solenoid valves are not waterproof, so use a waterproof model if conditions demand it. The rated pressure of the valve must exceed the maximum pressure in the pipeline to avoid premature failure. For corrosive liquids, stainless steel valves are recommended, while plastic (SLF) valves are suitable for highly corrosive fluids. In explosive environments, explosion-proof models must be used. Economical considerations should come after ensuring proper functionality, reliability, and safety. Choose cost-effective models only when all requirements are met. Structure and Working Principle of Solenoid Valves Direct-acting solenoid valves come in normally closed and normally open types. In the normally closed version, the valve remains closed when power is off. When energized, the electromagnetic force overcomes the spring force, allowing the moving core to open the valve and enable fluid flow. When de-energized, the core returns to its original position, closing the valve. These valves operate reliably at zero pressure difference and are suitable for small flow paths, such as DN6. Step-by-step direct-acting valves work by sequentially opening the main valve through the pilot valve. When the coil is energized, the pilot valve opens, allowing pressure to release from the upper chamber, which moves the main spool upward to allow fluid flow. When de-energized, the pilot valve closes, and pressure builds up in the upper chamber, forcing the main valve to close. This type is reliable and works well under low-pressure conditions. Examples include ZQDF, ZS, and 2W. Indirect-pilot solenoid valves consist of a pilot valve and a main spool. In the normally closed version, the valve remains closed when not powered. When energized, the pilot valve opens, reducing pressure in the upper chamber of the main spool, allowing it to lift and open the valve. When de-energized, the main spool closes due to spring force. This type is ideal for higher pressure applications. Common examples include ZCZ.