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
Semi-direct acting solenoid valves combine characteristics of both direct and indirect valves, allowing them to operate at zero pressure while handling high flow rates. They resemble indirect valves with a movable diaphragm, small orifice, and pressure chambers on each side, but the solenoid plunger is directly attached to the diaphragm. When the plunger lifts, it opens both the main valve and an additional orifice, causing a pressure drop that raises the diaphragm. This design enables the valve to function from zero pressure and control large flows. These semi-direct acting valves, also called assisted-lift solenoid valves, typically use stronger coils than those in indirect-operated valves.
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• Pilot-operated
Pilot-operated solenoid valves, rely on pressure differentials for operation, typically needing a minimum of 0.5 bar. These valves feature a diaphragm with a small opening that permits flow from the inlet to the outlet when the solenoid is energized, causing a pressure drop. This mechanism amplifies the pressure, enabling a small solenoid to manage a high flow rate. Indirect solenoid valves are ideal for applications with adequate pressure differential and high flow requirements, and they allow media to flow in only one direction.
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