Definition and principle of solenoid valves

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Solenoids are basic automated components used to control flow, and they belong to the category of actuators; they are not limited to hydraulic or pneumatic systems. Solenoids are used to control the direction of hydraulic flow. The mechanical devices in power plants are generally controlled by hydraulic cylinders, which is why solenoids are employed. Working principle: The solenoid valve has a sealed chamber with openings at different positions. Each hole leads to a different oil pipe. There is a valve in the middle of the cavity. There are two electromagnets on each side. By controlling the movement of the valve body, different oil discharge ports can be blocked or allowed to leak, while the oil inlet port remains open. Hydraulic oil enters the various oil discharge pipes, and then the pressure of the oil pushes it towards the piston; the piston in turn moves the piston rod, which drives the mechanism. Therefore, the mechanical motion is the current that controls the electromagnet. 1. Principle of direct-acting solenoid valve: When the power supply is turned on, the electromagnetic force generated by the solenoid coil lifts the closing element from the valve seat, allowing the valve to open; when the power supply is turned off, the electromagnetic force disappears, and the spring pushes the closing element back against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, or zero pressure, but the diameter must not exceed 25 millimeters. 2. Principle of the distributed direct-acting solenoid valve: It combines the direct-acting and pilot-operated principles; when there is no pressure difference between the inlet and outlet, upon power application, the electromagnetic force acts directly to lift the pilot valve and then the closing parts of the main valve in sequence, thereby opening the valve. When the inlet and outlet pressures reach the operating differential pressure, 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. This pressure difference pushes the main valve upward. The pilot valve, driven by spring force or medium pressure, moves its closing part downward, thereby closing the valve. Features: It can also operate at high pressure under zero pressure difference or in a vacuum condition, but it requires a higher power level and must be installed horizontally. 3. Principle of the pilot solenoid valve: When current and electromagnetic force open the pilot hole, the pressure in the upper chamber drops rapidly, creating a pressure difference between the high and low pressure areas surrounding the valve. The fluid pressure then pushes upward, causing the valve to open. The spring force closes the pilot hole, and the inlet pressure passes through the bypass hole, thereby creating another pressure difference around the valve that causes the fluid pressure to push downward and close the valve. Features: High upper limit for fluid pressure range; can be installed in any position (customization required), but the fluid pressure difference conditions must be met. When using it, certain characteristics such as dielectric properties, ambient temperature, operating frequency, and power should be taken into account.