Solenoid valves can be classified into double-controlled and single-controlled types. Double-controlled valves have two electromagnetic coils, and double-coil valves are usually considered electromagnetic directional control valves. Single-coil is always energized and the air intake is open, while double-coil is energized instantaneously. The slide valve of a single-coil solenoid valve is spring-return. When the solenoid valve loses power, it automatically resets. For a double-coil solenoid valve, the other coil needs to be energized to change positions.
The operating principle diagram of a single electrically controlled direct-acting solenoid valve
The operating principle diagram of the double electrically controlled direct-acting solenoid valve
The double-coil solenoid valve has two coils, A and B. The operation is as follows: A is not electrified, B is not electrified, and the solenoid valve is in the initial position. If A is electrified at this time and B is not electrified, the solenoid valve will act to reverse the direction. Next, when A is powered on and then loses power, B is not energized. The solenoid valve will no longer act, maintaining the state when A is energized and B is not energized. Next, if A is not electrified and B is electrified, the solenoid valve returns to its initial position. Next, A is not energized, B is de-energized, the solenoid valve does not act, and it remains in the initial position. In general, if coils A and B are not energized at the same time, the solenoid valve remains in the state when A is energized (while B is de-energized) or B is energized (while A is de-energized).
In simple terms, when a single coil is powered on, the mechanical part of the valve core operates. When it is powered off, it returns to its original position by mechanical force. The double-coil operates mechanically when coil 1 is energized and its position becomes inconvenient when it is de-energized. When coil 2 is energized, the mechanical part changes from position 1 to position 2, and remains so after the power is lost.
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