There is a closed cavity in the solenoid valve, with through holes in different positions, each hole is connected to a different oil pipe, the middle of the cavity is a piston, and the two sides are two electromagnets. At the same time, by controlling the movement of the valve body to open or close different oil discharge holes, and the oil inlet hole is normally open, the hydraulic oil will enter different oil discharge pipes, and then the piston of the oil cylinder is pushed by the pressure of the oil, and the piston is again Drive the piston rod, and the piston rod drives the mechanical device. In this way, the mechanical movement is controlled by controlling the current on and off of the electromagnet.

Solenoid valves can be divided into three categories in terms of working principle:

1. Direct acting solenoid valve

Principle: When the normally closed type is energized, the electromagnetic coil generates electromagnetic force to lift the opening piece from the valve seat, and the valve opens; when the power is off, the electromagnetic force disappears, the spring presses the opening piece on the valve seat, and the valve opens. (Normally open is the opposite of this)

Features: It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.

2. Step-by-step 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 upper and lower parts is formed around the opening, and the fluid pressure pushes the opening to move upward, and the valve opens; The hole is opened, and the inlet pressure quickly forms a pressure difference around the valve closing member through the bypass hole, and the fluid pressure pushes the opening member to move downward to open the valve.

Features: Small size, low power, high upper limit of fluid pressure range, can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions