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Normally Closed Solenoid Valve
Normally closed solenoid valve is a type of solenoid valve that remains closed when not energized, preventing the medium from passing through the valve. The working principle of a normally closed solenoid valve is that when the coil is energized, it generates an electromagnetic field that pushes the valve core or plunger upward, overcoming the force of the spring. This action separates the sealing element from the valve seat and opens the orifice, allowing the medium to flow through the valve. When the power is cut off, the spring forces the valve to automatically return to its original position and restore its closed state.
Types of Solenoid Valve
Solenoid valves are essential fluid control devices widely used across various industrial sectors. Based on their operating principles, solenoid valves can be classified into three main types:
• Direct acting
A direct-acting solenoid valve uses the solenoid to open or close, without the need for differential pressure. These valves are often used for controlling the flow of gas or liquid in a system. Direct-acting solenoid valves have the fastest operation, are reliable, and have a compact design.
• Semi-direct acting
The semi-direct-acting solenoid valve combines the advantages of both direct-acting and pilot-operated solenoid valves, enabling it to function without a pressure differential and without requiring a minimum operating pressure. Its structure resembles that of a pilot valve, featuring a diaphragm, small pressure relief holes, and upper and lower pressure chambers. However, its plunger is directly connected to the diaphragm, allowing it to actively lift the diaphragm and release pressure from the upper chamber, resulting in rapid opening. This design permits operation under zero pressure differential while accommodating larger flow rates, thereby broadening its range of applications.
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• Pilot-operated
The pilot-operated solenoid valve operates based on fluid pressure differentials, typically requiring a minimum pressure differential of approximately 0.3 bar. It incorporates a piston mechanism; when the solenoid coil is energized, the pilot port opens, releasing pressure from the upper chamber of the main valve. This action creates a pressure differential that drives the piston upward, thereby opening the main valve port. This design leverages the pressure differential amplification effect, enabling a small solenoid coil to control a larger flow rate.
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