Solenoid valves are electromechanical devices that control the flow of liquids or gases by using an electric coil (solenoid) to move a valve mechanism. Depending on their design, function, and operation, solenoid valves come in several types, each suited for different industrial and automation applications.
The main types of solenoid valves are:
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Direct-acting solenoid valve – In this type, the magnetic field from the solenoid directly lifts or closes the valve seat. It operates without external pressure and is ideal for low-flow or small-diameter systems, such as fuel and air control.
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Pilot-operated (indirect) solenoid valve – Here, the solenoid controls a pilot passage that uses system pressure to open or close the main valve. It’s suitable for high-flow or large systems, such as water pipelines or process control systems.
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Normally closed (NC) and normally open (NO) valves – A normally closed valve stays shut when power is off and opens when energized. A normally open valve does the opposite — it allows flow until the coil is energized. The choice depends on whether you want flow in the default (power-off) condition.
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2-way, 3-way, and 4-way solenoid valves – These refer to the number of ports and flow paths. A 2-way valve controls flow in one direction (ON/OFF). A 3-way valve switches between two outlets, while a 4-way valve is commonly used for pneumatic cylinders to alternate between extend and retract motions.
In simple terms, solenoid valves are classified by how they operate (direct or pilot), their default state (NC or NO), and their number of ports (2-way, 3-way, or 4-way). Selecting the right type depends on your system pressure, fluid type, and control requirement. Each type serves a unique purpose — from precise automation to heavy-duty industrial control.