What is the working principle of a piston solenoid valve?

According to the principle, it is divided into three categories: direct-acting, step-by-step direct-acting, and pilot-driven.
Direct-acting solenoid valve: When energized, the solenoid coil generates electromagnetic force, which directly attracts the spool, and the spool is displaced. When the power is off, the electromagnetic force disappears, and the valve core is reset by the spring.

Step-by-step direct-acting solenoid valve: It is a combination of direct-acting and pilot-acting principles. Normally closed type-when there is no pressure difference between the inlet and the outlet, the electromagnetic force directly opens the pilot hole connected to the main valve after energization, and the piston is lifted upward in turn, and the valve opens; when the inlet and outlet reach the starting pressure difference, the electromagnetic force opens first after energization Pilot hole, the pressure in the upper cavity of the main valve piston drops, so that the main piston is pulled by the pressure difference and electromagnetic force, and the valve port is opened; when the power is off, the pilot hole is closed by the spring reset, the upper cavity of the main piston is pressurized, and the main piston is pushed down. , The valve is closed. Normally open is the opposite of normally closed.

Pilot solenoid valve: Normally closed type-when energized, the electromagnetic force attracts the pilot valve core, the pilot hole opens, the pressure in the upper cavity of the main valve piston drops, and the upper cavity and the lower cavity of the main piston form high pressures. The cavity pressure pushes the main piston to open the valve; when the power is off, the spring force is reset to close the pilot hole, the upper cavity of the main piston is pressurized, and the upper and lower chambers of the main piston form high and low pressures, and the medium pressure and spring force push the main piston , The valve is closed. Normally open is the opposite of normally closed.