Classification of solenoid valves

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A solenoid valve is an industrial device controlled by electromagnetism; it is an essential automated component used to control fluids, and it belongs to the category of actuators. It is not limited to hydraulic or pneumatic systems. It is used in industrial control systems to adjust parameters such as the direction, flow rate, speed, and other aspects of the medium. Solenoid valves can be used in conjunction with various circuits to achieve the desired control, ensuring both precision and flexibility in control. There are many types of solenoid valves, and different ones serve various functions within control systems. The most commonly used ones include check valves, safety valves, direction control valves, and speed control valves. Solenoid valves can be classified into three main categories based on their principle of operation: 1. Direct-acting solenoid valves – Principle: When electricity is applied, the electromagnetic coil generates an electromagnetic force that lifts the closing element away from the valve seat, thereby opening the valve ； When the power is cut off, the electromagnetic force disappears, and the spring presses the closing element against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, or zero pressure, but the diameter generally does not exceed 25 mm. Principle: It operates on a combination of direct-acting and pilot-operated mechanisms. When there is no pressure difference between the inlet and outlet, when power is applied, the electromagnetic force lifts the pilot valve and the closing element of the main valve upward one after another, thereby opening the valve. When the pressure difference between the inlet and outlet reaches the starting value, upon power application, the electromagnetic force acts on the pilot valve; as a result, the pressure in the lower chamber of the main valve rises while the pressure in the upper chamber drops, and this pressure difference is used to push the main valve upward ； During a power outage, the pilot valve uses spring force or medium pressure to push the closing element downward, thereby closing the valve. Features: It can operate at zero pressure difference or in vacuum as well as under high pressure; however, it requires a higher power level and must be installed horizontally. III. Pilot-operated solenoid valve: Principle: When electric current is applied, electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure difference with higher pressure below and lower pressure above the closing element; the fluid pressure then pushes the closing element upward, thereby opening the valve ； When power is lost, the spring force closes the pilot hole; the inlet pressure rapidly creates a pressure difference around the valve closing element, with lower pressure at the bottom and higher pressure at the top. The fluid pressure then pushes the closing element downward, thereby closing the valve. Features: High upper limit for fluid pressure range; can be installed in any position (customization required), but must meet the fluid pressure difference requirements. IV. Based on differences in valve structure, materials, and operating principles, solenoid valves can be divided into six subcategories: direct-acting diaphragm structure, step-type direct-acting diaphragm structure, pilot diaphragm structure, direct-acting piston structure, step-type direct-acting piston structure, and pilot piston structure. V. Classification of solenoid valves by function: water solenoid valves, steam solenoid valves, refrigeration solenoid valves, low-temperature solenoid valves, gas solenoid valves, fire protection solenoid valves, ammonia solenoid valves, gas solenoid valves, liquid solenoid valves, miniature solenoid valves, pulse solenoid valves, hydraulic solenoid valves, normally open solenoid valves, oil solenoid valves, DC solenoid valves, high-pressure solenoid valves, explosion-proof solenoid valves, etc.