Tracing the history of the development of electromagnetic valve, so far, the solenoid valve at home and abroad from the principle is divided into three categories (ie: direct acting, step-by-step pilot), and from the valve structure and material differences The difference between the principle is divided into six sub-categories (direct acting diaphragm structure, step-grate structure, leading diaphragm structure, direct acting piston structure, step-by-step piston structure, pilot piston structure). Direct-acting solenoid valve: Principle: When the power is on, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, the valve opens; when the power is off, the electromagnetic force disappears, the spring presses the closing member against the valve seat, and the valve is closed. Features: In vacuum, negative pressure, zero pressure can work normally, but the path generally does not exceed 25mm. Distribution of direct-acting solenoid valve: Principle: It is a direct acting and pilot-based combination of principles, when the inlet and outlet without pressure, the power, the electromagnetic force directly to the pilot valve and the main valve closing member up The valve opens. When the inlet and outlet to achieve the start of the pressure difference, the electricity, the solenoid pilot small valve, the main valve lower chamber pressure rises, the pressure on the chamber down, so that the use of pressure to push the main valve open; power, the pilot valve spring Force or media pressure to push the closure, move down, the valve closed. Features: At zero pressure or vacuum, high pressure can also be * action, but the power is larger, the requirement must be horizontal installation. Pilot solenoid valve: Principle: When the power is on, the pilot force opens the pilot hole and the pressure in the upper chamber quickly drops. The low and high pressure difference is formed around the closing member. The fluid pressure pushes the closing member to move upward and the valve opens. , The spring force to close the pilot hole, the inlet pressure quickly through the bypass hole in the chamber around the valve to form a low pressure on the high, the fluid pressure to promote closure of the move down to close the valve. Features: high fluid pressure range high, can be installed (to be customized), but must meet the fluid pressure conditions