I never understood the working principle of solenoid valves; after reading this, I get it instantly!

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There are many types of solenoid valves, and different ones serve various functions within control systems. The most commonly used ones include check valves, safety valves, direction control valves, and speed control valves. * J& x5 C& _% ]3 t$ W3 s0 T. U, F First, let’s explain the working principle of the solenoid valve: Inside the solenoid valve there is a sealed chamber, with holes opened at different positions; each hole is connected to a different oil pipe. At the center of the chamber is a piston, with two electromagnets on either side. When the coil of the magnet on one side is energized, the valve body is drawn toward that side. By controlling the movement of the valve body, it is possible to open or close various oil outlet holes. The oil inlet hole remains open at all times, allowing hydraulic oil to flow into the different oil outlet pipes. The pressure of the oil then pushes the piston in the cylinder, which in turn drives the piston rod, and the piston rod operates the mechanical device. In this way, mechanical motion is controlled by regulating the on and off of current to the electromagnet. http://5b0988e595225.cdn.sohucs.com/images/20190607/db6870e4c960499093971a0f1d443aee.gif▲ Just like this. 6 W- H5 G8 ]& s& ^ z Solenoid valves can be divided into three main categories based on their working principle; q! R V! O( H( U 1. Direct-acting solenoid valve principle: In the normally closed type, when electricity is applied, the electromagnetic coil generates an electromagnetic force that lifts the moving part away from the valve seat, thereby opening the valve ； When the power is cut off, the electromagnetic force disappears, and the spring presses the open part against the valve seat, causing the valve to stay open. (Contrary to normally open types) Feature: It can operate properly in vacuum, negative pressure, and zero pressure conditions, but the diameter generally does not exceed 25 mm. http://5b0988e595225.cdn.sohucs.com/images/20190607/969a9c347b26420584fad7027efa591f.jpeg http://5b0988e595225.cdn.sohucs.com/images/20190607/c6d5a7c94cb1431f9e9d3cb05e071622.jpeg Animation demonstration —— http://5b0988e595225.cdn.sohucs.com/images/20190607/295cda07f55c49929b09655bf0c9d716.gif 2. Step-type direct-acting solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/abf71d86bf8149ef8648e9b3569fce9a.jpeg ▲ Overall structure http://5b0988e595225.cdn.sohucs.com/images/20190607/38766cfbd2984f51b96e585e134f02dd.jpeg Principle: It operates based on a combination of direct-acting and pilot-operated mechanisms; when there is no pressure difference between the inlet and outlet, energization causes the electromagnetic force to lift the pilot valve and the main valve’s closing element upward sequentially, 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, but it requires a large power supply and must be installed horizontally. http://5b0988e595225.cdn.sohucs.com/images/20190607/86d8076f197a472cbb30658af258fe67.jpeg0 W1 Q. v+ k! I 3、Pilot-operated solenoid valvehttp://5b0988e595225.cdn.sohucs.com/images/20190607/a0a1b415eafe4444b5bcbc21b1864844.gifhttp://5b0988e595225.cdn.sohucs.com/images/20190607/707e5deaf1504d89ab4c77f6f288e2ff.jpegPrinciple: When power is applied, the 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 moving part, and the fluid pressure pushes this part upward, thereby opening the valve ； When power is lost, the spring force keeps the pilot hole open; the inlet pressure passes through the bypass hole, creating 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 opening element downward, thereby opening the valve. Features: Small size, low power consumption, high upper limit for fluid pressure range; can be installed in any position (customization required), but must meet the fluid pressure difference requirements. http://5b0988e595225.cdn.sohucs.com/images/20190607/99a1e325791d43bf982672bc2ee895ef.jpeg Two-way solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/53b46a658b114d2b8af81666d3ffddb2.gif Three-way solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/e4dbd91273394dd3bd6df477dc5b9399.gif Four-way solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/2c99cb6115f6444995bbefd0b03b3074.gif Three-way pilot-operated solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/336c1b6545b7415987ceeb447bc62007.gif Four-way pilot-operated solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/23fb45f2d2654873b78b32cd29e5cedd.gif Inline solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/b29c1690e3754911ba4663170b19b023.gif Direct-actuation solenoid valve http://5b0988e595225.cdn.sohucs.com/images/20190607/12a1db5275d949948878fef3ae3f7f41.gif