Working principle of solenoid valve
The solenoid valves at home and abroad are currently divided into three categories in principle (ie: direct-acting type, distributed direct-acting type, pilot type), and the difference in valve flap structure and material and the difference in principle are divided into six Sub-category (direct-moving diaphragm structure, step-by-step heavy diaphragm structure, pilot membrane structure, direct-moving piston structure, step-by-step direct-moving piston structure, pilot piston structure)
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 turned off, the electromagnetic force disappears, the spring presses the closing member against the valve seat, and the valve closes.
Features: It can work normally under vacuum, negative pressure and zero pressure, but the diameter is generally not more than 25mm.
Distributed direct acting solenoid valve
Principle: It is a combination of direct acting and pilot type. When there is no pressure difference between the inlet and the outlet, after energization, the electromagnetic force directly lifts the pilot small valve and the main valve closing part in sequence and the valve opens. When the inlet and outlet reaches the starting pressure difference, after energization, the electromagnetic force pilot small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber decreases, thereby using the pressure difference to push the main valve upwards; Force or medium pressure pushes the closing piece and moves downward to close the valve.
Features: It can operate reliably at zero pressure difference or vacuum and high pressure, but the power is large, and it must be installed horizontally.
Pilot solenoid valve
Principle: When the power is turned on, the pilot hole is opened by electromagnetic force, the pressure in the upper chamber drops rapidly, and a high and low pressure difference is formed around the closing member. The fluid pressure pushes the closing member upward and the valve opens; when the power is turned off, the spring force controls the pilot The orifice is closed, and the inlet pressure quickly forms a low, high, and high pressure differential around the valve closing member through the bypass hole. The fluid pressure pushes the closing member downward to close the valve.
Features: The upper limit of the fluid pressure range is higher, and can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions.
Working principle of solenoid valve:
The drawing is a sectional view of the solenoid valve, so-called solenoid valve. If there is no current in the electromagnetic coil, no magnetic field exists, and the armature is not pushed by the magnetic force but by the pressure spring. The center rod of the piston is connected with the armature, so the center rod is pushed down and the piston cone is sleeved into the cone seat. In this way, the passage from the inlet to the outlet is blocked. If a current flows through the coil, a magnetic field is generated, and the magnetic force pushes the armature upward. The armature must overcome the force of the spring to push the center rod and the piston cone away from the cone seat, and the passage from the inlet to the outlet can be unblocked. Electromagnetics are two-position devices, that is, either fully open or fully closed. So it is the device used in the open and close control system. 
Parabolic graph
The current to the solenoid valve can be either AC or DC, depending on the design, but it is still more common for AC drivers.
AC solenoid valves have a serious disadvantage that DC solenoid valves do not. If the AC solenoid valve is stuck in the closed or semi-closed position, it is likely to burn out after the current is applied. This is because the armature cannot enter the center of the coil, and the inductance of the coil is always low. (The inductance of the coil is very different depending on the magnetic permeability of the central material. The iron material differs from air by more than a thousand times.) Because of the low inductance and low inductance, a large current will flow Coil. Finally the coil was burned due to overheating.
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