Common sense of solenoid valve selection

Common Sense for Solenoid Valve Selection When selecting a solenoid valve, it is crucial to ensure that the fluid in the piping matches the medium for which the valve was calibrated. The temperature of the helium fluid must be below the rated temperature of the selected solenoid valve. Solenoid valves typically handle liquids with viscosity up to 20 CST. If the viscosity exceeds this, special attention should be given to the valve's compatibility. Regarding pressure differences, if the pressure difference in the pipeline is less than 0.04 MPa, direct-acting or semi-direct-acting models like ZS, 2W, ZQDF, and ZCM series are recommended. For low-pressure differential applications where the pressure difference is above 0.04 MPa, pilot-operated valves are more suitable. The maximum working pressure difference should always be lower than the rated pressure of the valve. Most solenoid valves operate in one direction, so it's important to check for backpressure and consider installing a check valve if necessary. If the fluid is not clean, a filter should be installed before the solenoid valve, as these valves generally require high fluid cleanliness. Pay attention to the flow orifice and nozzle diameter. Solenoid valves are typically two-position on/off controls, so a bypass line is often recommended for maintenance. In cases of water hammer, custom adjustments to the opening and closing times may be required. Environmental temperature can also affect the performance of the solenoid valve. Additionally, power supply current and power consumption should match the output capacity. The voltage is usually allowed to vary by ±10%, but note that AC startup requires higher VA values. Reliability is another key factor. Solenoid valves come in normally closed and normally open types. Normally closed valves are most commonly used, as they close when power is off. However, if the opening time is long and closing time is short, a normally open type may be more appropriate. Life testing is usually part of factory testing, though there is no official standard for solenoid valves in China. It’s wise to choose reputable manufacturers. High-frequency operation usually favors direct-acting types, especially for larger diameters. Safety considerations include using waterproof valves in wet environments, ensuring the rated pressure of the valve exceeds the maximum pressure in the system, and using stainless steel or specialized plastic valves for corrosive media. In explosive environments, explosion-proof models must be used. Economically, while many solenoid valves are universal, cost-effective options should be chosen only after meeting the requirements of applicability, reliability, and safety. The structural principle of a solenoid valve varies depending on its type. Direct-acting solenoid valves have two configurations: normally closed and normally open. In a normally closed valve, the valve remains closed when de-energized. When energized, an electromagnetic force pulls the movable core against the spring, opening the valve. When power is cut, the spring returns the core to the closed position. These valves work well under zero pressure difference and are commonly used for small flow paths (e.g., DN6). Step-by-step direct-acting valves use a combination of a main valve and a pilot valve. When the coil is energized, the pilot valve opens, allowing pressure to release from the upper chamber of the main valve. This pressure difference, combined with electromagnetic force, lifts the main spool to open the flow path. When the coil is de-energized, the pilot valve closes, and the upper chamber refills, causing the main valve to shut. These valves are reliable and suitable for low-pressure applications, such as ZQDF, ZS, and 2W series. Indirect pilot solenoid valves consist of a pilot valve and a main spool. In a normally closed configuration, the valve is closed when de-energized. Upon energization, the magnetic force pulls the core, opening the pilot valve and allowing fluid to flow out. This reduces the pressure in the upper chamber of the main spool, creating a pressure differential that lifts the spool and opens the main valve. When de-energized, the spring pushes the core back, closing the valve. These valves are commonly used in high-pressure applications, such as ZCZ series.