Solenoid Valve is an automation basic component that uses electromagnetically controlled automation equipment to control fluid media. It is equivalent to the actuator of four links in the negative feedback loop of industrial automation control.
In industrial automation control, the solenoid valve can adjust the flow direction of the fluid medium, the flow rate of the fluid medium and other fluid medium parameters. It can realize the desired control according to different control circuits and can better ensure control accuracy and control flexibility. What the title says is that the category of solenoid valves is a bit broad because there are many types of solenoid valves. Different types of solenoid valves play different roles in the automation control of the industry. The role of different control positions in industrial automation control is different. The common work in chemical plants is gas and hydraulic. Solenoid valves, direct-acting solenoid valves, pilot solenoid valves, distributed solenoid valves, etc.
The working principle of pneumatic solenoid valve: solenoid valve is equipped with wire fixing and armature. When the coil is powered and the iron is sucked, the piston inside the valve body will shift and change the air path to open or close the actuator. For example, a two-position two-way solenoid has two air holes. One is the air source inlet and the other two are the air source outlet. When the solenoid valve is not powered from the air source inlet to the other two outlets. It doesn't work. In fact, it is similar to a relay, except that the contacts are switched on and off to make the air circuit on and off. The main object of this type of solenoid valve is the actuator.
Direct-acting solenoid valves, pilot solenoid valves, and step-by-step direct-acting solenoid valves, these three types of solenoid valves directly act on the liquid medium and change the flow area of the solenoid valve seat by closing or opening the solenoid valve core.
The working principle of the direct-acting solenoid valve is that when it is energized, the coil generates magnetic force to lift the closing part (spool), open the valve  to make the medium flow, the coil is de-energized, and the spring of the solenoid valve is reset, and the closing part is pressed tightly on the solenoid The valve seat makes the valve close.
The working principle of the pilot solenoid valve. The coil is energized and the solenoid force opens the pilot hole first so that the pressure in the solenoid valve chamber drops. At this time, the closing part will push the closing part (spool) due to the high-pressure difference formed around it. Move upward to open the valve. When the power is off, the solenoid valve's spring is reset to close the pilot hole, then the pressure F] passes through the bypass hole. The chamber pressure rises to form a high and low-pressure difference around the closing member. At this time, the fluid pressure will push to close. The piece (spool) moves down to close the valve.
The working principle of the stepped direct-acting solenoid valve is a combination of direct-acting and pilot-acting principles. If the pressure difference between the inlet and outlet of the solenoid valve is zero, the solenoid valve coil is energized, and the solenoid force directly moves the pilot small valve and the closing part of its main valve upwards in turn to open the valve. When the inlet and outlet pressure difference reaches the solenoid valve activation pressure, the pressure in the lower chamber of the solenoid pilot valve and the main valve rises, and the pressure in the upper chamber drops so that the solenoid main valve closing part is lifted up by the pressure difference and the valve is opened. After a power failure, the pilot valve of the solenoid valve uses the force of the spring reset or the pressure of the medium to push the closing member to move to a small distance to close the solenoid valve.
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