Solenoid valves are divided into three categories in principle:
1, direct acting solenoid valve
Principle: When energized, the electromagnetic force generated by the electromagnetic coil lifts the closing part from the seat, and the valve opens; When the power is off, the electromagnetic force disappears, the spring presses the closing part on the seat, and the valve is closed.
Features: It can work normally under vacuum, negative pressure and zero pressure, but the diameter is generally not more than 25mm.
2, pilot solenoid valve
Principle: When the power is on, the electromagnetic force pulls the pilot hole spool, opens the pilot hole, the pressure of the upper chamber of the main valve piston decreases, and the upper chamber and lower chamber of the main piston form a low and high pressure, so that the lower chamber pressure pushes the main piston to move up and open the valve; When the power is off, the spring force closes the pilot hole, the upper chamber is pressurized, the upper chamber and the lower chamber are formed, the lower pressure is high, the medium pressure and the spring force push the closing part to move down and close the valve.
Features: The upper limit of the fluid pressure range is high, and it can be installed arbitrarily, but the fluid pressure difference conditions must be met.
3, step direct acting solenoid valve
Principle: It is a combination of direct action and pilot principle, when there is no pressure difference between the inlet and the outlet, after the power is turned on, the electromagnetic force directly lifts the pilot small valve and the main valve closing part in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after power, the electromagnetic force pilot small valve, the main valve lower chamber pressure rises, the upper chamber pressure drops, so as to use the pressure difference to push the main valve upward; When the power is off, the pilot valve uses spring force or medium pressure to push the closing part and moves downward to close the valve.
Features: Zero pressure difference or vacuum, high pressure can also be operated, but the power is large, it must be installed horizontally.
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