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Solenoid valves are one of the essential accessories for pneumatic control valves, and they are widely used in various industries such as chemicals, power, metallurgy, pharmaceuticals, and food processing. There are many types of solenoid valves. Broadly speaking, there are low-flow two-way solenoid valves used in the medical and healthcare fields, as well as 4-way to 10-way sampling valves used in environmental analysis instruments. Pressure transducer valves that control the amount of fuel supplied to automobiles can also be classified as solenoid valves (some of them operate on the principle of the piezoelectric effect, such as those in Japan) ； Some are based on electromagnetic principles, such as proportional valves used in the United States and other countries. In recent years, due to increasing demands for safety and automation, safety barriers are often required after DCS systems, which necessitates that the power of the solenoid coils be low. The advantage of this is that the coil can remain charged for an extended period, meeting ESD requirements. Moreover, the coil generates little heat. If most requirements are less than 4W, individual operating conditions require less than 2W. For solenoids used with pneumatic valves, there are pilot-operated types and direct-acting types. The power can be kept below 4W; it’s even easier for pilot-operated solenoid valves, with 1W or less being no problem at all. Since the pilot mechanism does not directly drive the valve spool based on whether the coil is charged or not, it draws in air through a pilot block structure to first move the piston, which in turn pushes the valve spool. It is for this reason that an electromagnetic valve with a pilot mechanism requires an air supply to operate; it cannot function without a pressure difference. This is the biggest difference between pilot-operated solenoid valves and direct-acting solenoid valves. In a direct-acting solenoid valve, the coil being energized directly pulls the valve core, allowing it to start without any pressure difference and without the need for an external air source. Currently, solenoids used to control valve opening and closing tend to have a pilot structure due to their lower cost. The pilot structure solenoid valves experience blockages in some cases, as the air holes in the pilot section are very small (with a diameter of 1 mm). Therefore, in applications with harsh gas source conditions, it is best to choose a direct-acting type. Materials such as silicone and PVC generate a lot of dust, making gas treatment difficult. Overall, the lifespan and reliability of the direct-acting structure are superior to those of the pilot-operated structure solenoid valve. Since the direct-acting structure has no pilot section and does not require pilot exhaust, etc., the coil directly pulls the valve core, reducing potential failure points. Because solenoid valves all operate based on Maxwell’s equations, their principles are well understood. A relatively important aspect is the selection and calculation of magnetic permeability. Magnetic permeability is an important parameter in the valve core of solenoid valves. The coil must generate a sufficient magnetic field to attract the valve core. At the same time, the material of the valve core must not reach magnetic saturation; otherwise, no matter how strong the magnetic field or how large the coil current, it will be ineffective. The coil is a relatively important component in solenoid valves. All power consumption is on the coil. The selection and calculation of coil power must take into account the actual requirements of the solenoid valve. Low-power solenoid coils have relatively thin wire diameters, often 0.0236 or less (according to IEC standards), with a large number of turns to ensure sufficient inductance. It can be calculated specifically using the formula. The coil insulation class, H grade, F grade, is also very important. Qualified copper wire manufacturers are required, providing oxygen-free electrolytic copper with uniform wire diameter, to ensure consistent resistance and power consumption per batch of coils. The calculation of the air gap in the coil is directly related to the effective stroke of the solenoid valve (especially in direct-acting designs). Valve manufacturers are seeking ways to achieve the optimal combination, taking into account the magnetic saturation coefficient of the valve core material, while ensuring a proper air gap.