1. Solenoid valves are divided into three categories in principle:
1) Direct acting
solenoid valve:
Principle: When energized, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; when the power is off, the electromagnetic force disappears, the spring presses the closing member on the valve seat, and the valve closes.
Features: It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.
2) Distributed direct acting solenoid valve:
Principle: It is a combination of direct action and pilot type. 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 valve and the main valve closing member upwards in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber drops, so that the main valve is pushed up by the pressure difference; when the power is off, the pilot valve uses a spring The force or medium pressure pushes the closing member, moving downward, causing the valve to close.
Features: It can also operate under zero pressure difference or vacuum and high pressure, but the power is large, and it must be installed horizontally.
3) Pilot solenoid valve:
Principle: When the power is turned on, the electromagnetic force opens the pilot hole, the pressure in the upper chamber drops rapidly, and a pressure difference between the upper and lower sides is formed around the closing member, and the fluid pressure pushes the closing member to move upward, and the valve opens; When the hole is closed, the inlet pressure passes through the bypass hole to quickly form a pressure difference between the lower and upper parts around the valve closing member, and the fluid pressure pushes the closing member to move down to close the valve.
Features: The upper limit of the fluid pressure range is high, which can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions.
