How does a solenoid valve work?

Tracing the development history of solenoid valves, to date, solenoid valves worldwide can be divided into three main categories based on their principle (namely: direct-acting type and pilot-operated type). Furthermore, due to differences in valve disc structure, materials, as well as principles, they are further classified into six subcategories (direct-acting diaphragm structure, step-type diaphragm structure, pilot diaphragm structure, direct-acting piston structure, step-direct-acting piston structure, and pilot piston structure). Direct-acting solenoid valve: Principle: When electric current is applied, the electromagnetic coil generates an electromagnetic force that lifts the closing element away from the valve seat, thereby opening the valve ； When power is cut off, the electromagnetic force disappears, and the spring presses the closing element against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, and zero pressure, but the diameter generally does not exceed 25 mm. Direct-acting solenoid valve: Principle: It operates on a combination of direct-acting and pilot-operated mechanisms; when there is no pressure difference between the inlet and outlet, upon power application, the electromagnetic force lifts the pilot valve and the main valve’s closing element upward one after another, thereby opening the valve. When the pressure difference between the inlet and outlet reaches the starting value, 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, and this pressure difference is used to push the main valve upward ； During a power outage, the pilot valve uses spring force or medium pressure to push the closing element downward, thereby closing the valve. Features: It can operate at zero pressure difference or in vacuum as well as under high pressure; however, it requires a higher power level and must be installed horizontally. Pilot-operated solenoid valve: Principle: When powered, electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure difference with higher pressure below and lower pressure above the closing element; the fluid pressure then pushes the closing element upward, thereby opening the valve ； When power is lost, the spring force closes the pilot hole; the inlet pressure rapidly creates a pressure difference around the valve closing element, with lower pressure at the bottom and higher pressure at the top. The fluid pressure then pushes the closing element downward, thereby closing the valve. Features: High upper limit for fluid pressure range; can be installed in any position (customization required), but must meet the fluid pressure difference requirements

Solenoids are basic automated components used to control fluids, and they belong to the category of actuators； It is not limited to hydraulic or pneumatic systems. Solenoids are used to control the direction of hydraulic flow. The mechanical devices in factories are generally controlled by hydraulic systems, which is why solenoids are employed. The working principle of a solenoid valve involves a sealed chamber within it, with holes positioned at various locations; each hole leads to a different oil duct. At the center of the chamber is a valve, and on either side of it are two electromagnets. When the coil of one of these magnets is energized, the valve body is attracted to that side. By controlling the movement of the valve body, it is possible to block or allow fluid to pass through different oil discharge holes. The oil inlet hole remains open at all times, allowing hydraulic oil to flow into the various oil discharge ducts. The pressure of the oil then drives the piston inside the cylinder, which in turn moves the piston rod, and the piston rod drives the mechanical mechanism. In this way, controlling the current to the electromagnet controls the mechanical motion. What was mentioned above is the basic principle of solenoid valves. In reality, it depends on factors such as the temperature and pressure of the fluid flowing through them; for example, there is pressure in the pipes while there is no pressure in the case of natural flow. The working principle of solenoid valves is different. For example, in cases where zero-pressure starting is required in the gravity-fed mode, the coil pulls up the gate entirely once power is applied. In the pressurized state, the solenoid valve draws in a pin inserted into the valve body once the coil is energized, and the pressure of the fluid itself is used to lift the valve body. The difference between these two methods is that for solenoid valves in the self-priming mode, the coil needs to lift the entire valve body, which results in a larger size; whereas for solenoid valves in the pressurized mode, only the pin needs to be lifted, allowing for a smaller size. Direct-acting solenoid valve: Principle: When electric current is applied, the electromagnetic coil generates an electromagnetic force that lifts the closing element away from the valve seat, thereby opening the valve ； When power is cut off, the electromagnetic force disappears, and the spring presses the closing element against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, and zero pressure, but the diameter generally does not exceed 25 mm. Direct-acting solenoid valve: Principle: It operates on a combination of direct-acting and pilot-operated mechanisms; when there is no pressure difference between the inlet and outlet, upon power application, the electromagnetic force lifts the pilot valve and the main valve’s closing element upward one after another, thereby opening the valve. When the pressure difference between the inlet and outlet reaches the starting value, 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, and this pressure difference is used to push the main valve upward ； During a power outage, the pilot valve uses spring force or medium pressure to push the closing element downward, thereby closing the valve. Features: It can operate at zero pressure difference or in vacuum as well as under high pressure; however, it requires a higher power level and must be installed horizontally. Pilot-operated solenoid valve: Principle: When powered, electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure difference with higher pressure below and lower pressure above the closing element; the fluid pressure then pushes the closing element upward, thereby opening the valve ； When power is lost, the spring force closes the pilot hole; the inlet pressure rapidly creates a pressure difference around the valve closing element, with lower pressure at the bottom and higher pressure at the top. The fluid pressure then pushes the closing element downward, thereby closing the valve. Features: High upper limit for fluid pressure range; can be installed in any position (customization required), but must meet the fluid pressure difference requirements. Reference: http://baike.baidu.com/view/89856.html?wtp=tt

Hehe, in my understanding, a solenoid valve is simply an electromagnet; the magnetic force generated by the electromagnet drives the plunger valve element. To ensure that the valve element returns to its original position when there is no electricity, a spring is used. So essentially, a solenoid valve is like a competition between a spring and an electromagnet – the one that wins will drive the valve element to move. If a two-coil solenoid involves two coils competing with each other, in order to ensure consistency regardless of whether both coils are powered or not, it is specified that the solenoid should not be used when both coils are powered.