Excavator solenoid valve working principle and troubleshooting

The solenoid valve uses an electromagnet to push the spool to control the direction of the compressed air, thereby controlling the direction of the pneumatic actuator switch.
Electromagnets for manipulating solenoid valves are divided into AC and DC:
1. The voltage of the AC electromagnet is generally 220 volts. It is characterized by large starting force, short commutation time and low price. However, when the valve core is stuck or the suction force is insufficient to make the iron core unable to be sucked, the electromagnet is easily burnt due to excessive current, so the work reliability is poor, the impact is caused during operation, and the life is low.
2. The DC electromagnet voltage is generally 24 volts. The utility model has the advantages that the work is reliable, the burnt is not caused by the valve core being stuck, the service life is long, the volume is small, but the starting force is smaller than that of the AC electromagnet, and the rectifier device is needed when there is no DC power supply.
In order to improve the operational reliability and life of electromagnetic reversing valves, in recent years, wet electromagnets have been increasingly used at home and abroad. There is no need to seal between the electromagnets and the slide valve push rods, eliminating the friction at the O-ring seals. The outer part of the electromagnetic coil is directly sealed with engineering plastics, and no metal outer casing is used. This ensures insulation and heat dissipation, so the work is reliable, the impact is small, and the service life is long.
So far, the solenoid valves at home and abroad have been divided into three major categories (ie, direct-acting, step-by-step pilot), and the differences in principle and principle between the valve flap structure and materials are further divided into six. Branch subclasses (direct-acting diaphragm structure, step-and-repeat structure, pilot-membrane structure, direct-acting piston structure, step-by-step linear motion 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 is opened; when the power is off, the electromagnetic force disappears, the spring presses the closing member against the valve 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.
Distributed direct-acting solenoid valve:
Principle: It is a combination of direct motion 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 member upward, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the energization, the electromagnetic force leads the small valve, the pressure of the lower chamber of the main valve rises, and the pressure of the upper chamber drops, so that the main valve is pushed upward by the pressure difference; when the power is off, the pilot valve uses the spring The force or medium pressure pushes the closure and moves down to close the valve.
Features: It can also be operated at zero pressure difference or vacuum or high pressure, but the power is large, and it must be installed horizontally.
Pilot solenoid valve:
Principle: When energized, the electromagnetic force opens the pilot hole, the pressure in the upper chamber drops rapidly, and a pressure difference between the upper and lower parts is formed around the closing member. The fluid pressure pushes the closing member upward to move the valve open; when the power is off, the spring force leads the pilot. The hole is closed, and the inlet pressure passes through the bypass hole. The rapid chamber forms a lower low and high pressure difference around the valve member, and the fluid pressure pushes the closing member downward to close the valve.
Features: The upper limit of the fluid pressure range is high, it can be installed arbitrarily (customized), but the fluid pressure difference condition must be met.