Working principle of solenoid valve
It is an automation basic component used to control fluids and belongs to actuators; Not limited to hydraulic and pneumatic. Used to control the direction of hydraulic flow, the mechanical devices in factories are generally controlled by hydraulic cylinders, so their working principle is used. There are sealed chambers with through holes at different positions, each hole leading to a different oil pipe. The middle of the chamber is a valve, and there are two electromagnets on both sides. The magnetic coil on which side is energized will attract the valve body to which side. By controlling the movement of the valve body, different oil discharge holes will be blocked or leaked out. The oil inlet hole is normally open, and hydraulic oil will enter different oil discharge pipes. Then, the oil pressure will push the piston of the oil rod, and the piston rod will drive the mechanical device to move. In this way, the mechanical motion is controlled by controlling the current of the electromagnet.
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Tracing back to the development history, up to now, domestic and foreign systems can be divided into three major categories based on their principles (i.e., direct acting, step-by-step child pilot), and six sub categories based on differences in valve disc structure and materials and principles (direct acting diaphragm structure, step-by-step heavy plate structure, pilot diaphragm structure, direct acting piston structure, step-by-step direct acting piston structure, pilot piston structure).
Direct acting:
Principle: When powered on, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; When the power is cut off, the electromagnetic force disappears, and the spring presses the closing member against the valve seat, closing it.
Characteristics: It can work normally under vacuum, negative pressure, and zero pressure, but the diameter generally does not exceed 25mm.
Distributed direct acting:
Principle: It is a combination of direct action and pilot operated principle. When there is no pressure difference between the inlet and outlet, after being energized, the electromagnetic force directly lifts the pilot small valve and the main valve closing member upward in sequence, and the valve opens. When the inlet and outlet reach the starting pressure difference, after being energized, the electromagnetic force pilot small valve, the lower chamber pressure of the main valve rises, and the upper chamber pressure drops, thereby using the pressure difference to push the main valve upwards; When the power is cut off, the pilot valve uses spring force or medium pressure to push the closing component downwards, causing it to close.
Features: It can also operate under zero pressure difference, vacuum, and high pressure, but with high power, it must be installed horizontally.
Pilot type:
Principle: When powered on, the electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to rapidly decrease, creating a high and low pressure difference around the closure. The fluid pressure pushes the closure to move upward and open; When the power is cut off, the spring force closes the pilot hole, and the inlet pressure quickly forms a lower and higher pressure difference around the closing valve through the bypass hole. The fluid pressure pushes the closing valve to move downward and close.
Features: The upper limit of the fluid pressure range is relatively high, and it can be installed freely (customized), but it must meet the fluid pressure difference conditions.
