The difference between direct-acting solenoid valve and pilot solenoid valve.

Principle of direct-acting solenoid valve: when electrified, the electromagnetic coil generates electromagnetic force to lift the closing piece from the valve seat and open the valve; When the power is cut off, the electromagnetic force disappears, the spring presses the closing piece on the valve seat, and the valve closes. Features: It can work normally under vacuum, negative pressure and zero pressure, but its diameter is generally less than 25mm.

Principle of pilot solenoid valve: When power is on, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly, forming a pressure difference between the upper and lower parts around the closed part, and the fluid pressure pushes the closed part to move upward, thus opening the valve; When power is cut off, the pilot hole is closed under the action of spring force, the inlet pressure quickly forms a low-high pressure difference around the closing valve through the bypass hole, and the fluid pressure pushes the closing piece to move downwards to close the valve.

Direct-acting solenoid valve has fast speed and short action time. When the frequency is high, the direct-acting solenoid valve is generally selected. The pilot solenoid valve uses a small valve to open a large valve, with a large flow rate, and the pilot type uses a large caliber.