1. What is a Solenoid Valve?

A solenoid valve is a device that controls fluid flow using electromagnetic force. It consists of an electromagnetic coil, iron core, iron core winding, valve core, valve seat, and valve stem. By controlling the current in the electromagnetic coil, the valve's on-off state is regulated, thereby adjusting the flow of fluid. Solenoid valves can be used to control the flow of fluids such as gas, liquid, and steam.

2. Principles of Solenoid Valves

Solenoid valves are divided into three main categories: step-by-step direct-acting solenoid valves, direct-acting solenoid valves, and pilot solenoid valves. Their working principles correspond to these three categories respectively.

2.1 Working Principle of Step-by-Step Direct-Acting Solenoid Valves

The step-by-step direct-acting solenoid valve adopts a combined principle of direct-acting and pilot-type. When there is no pressure difference between the inlet and outlet, the electromagnetic force directly lifts the pilot small valve and the main valve closing part upward in sequence after energization, opening the valve. When the inlet and outlet reach the starting pressure difference, the electromagnetic force acts on the pilot small valve after energization: the pressure in the lower chamber of the main valve rises while the pressure in the upper chamber drops. The main valve is then pushed upward by the pressure difference. When de-energized, the pilot valve uses spring force or medium pressure to push the closing part downward, closing the valve.

2.2 Working Principle of Direct-Acting Solenoid Valves

For the normally closed type direct-acting solenoid valve: when energized, the electromagnetic coil generates electromagnetic force to lift the opening part from the valve seat, opening the valve. When de-energized, the electromagnetic force disappears, and the spring presses the opening part against the valve seat, closing the valve. (The normally open type works in the opposite way.)

2.3 Working Principle of Pilot Solenoid Valves

The indirect pilot solenoid valve operates as follows: when energized, the electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. A pressure difference (lower pressure above, higher pressure below) is formed around the opening part, and fluid pressure pushes the opening part upward to open the valve. When de-energized, the spring force opens the pilot hole, and the inlet pressure quickly fills the chamber through the bypass hole. A pressure difference (lower pressure below, higher pressure above) is formed around the valve closing part, and fluid pressure pushes the opening part downward to close the valve.

3. Functions of Solenoid Valves

What is the function of a solenoid valve? As an electromagnetic-controlled industrial device, it is a basic automated component for fluid control. Classified as an actuator, it is not limited to hydraulics and pneumatics. In industrial control systems, it is used to adjust the medium's direction, flow rate, speed, and other parameters.

Solenoid valves can be matched with different circuits to achieve the intended control, and both control accuracy and flexibility are guaranteed. There are many types of solenoid valves, and different ones play roles in different positions of the control system. The most commonly used include one-way valves, safety valves, directional control valves, and speed control valves.