What is working principle of a solenoid valve? How many types of solenoid valves are there?

Solenoid valve is a type of electromagnetic field controlled industrial equipment. It is an automatic basic component used to control fluid, adjust direction, flow, speed and other environmental parameters in an industrial control system, and control various circuits. .

The principle of operation of solenoid valve

The inside of solenoid valve is a closed cavity with through holes in different positions. Each hole is connected to a separate tube with a piston in middle of cavity and two electromagnets on sides. Whichever side of solenoid coil is energized, valve body will be attracted to that side. By controlling movement of valve body, various oil outlets will open or close, while oil inlet is normally open and hydraulic oil flows into different oil outlet lines.

The piston of oil cylinder is then pushed by oil pressure, which in turn drives piston rod, which drives mechanical device. Thus, mechanical movement is controlled by controlling electrical current supplied to electromagnet.

Types of solenoid valves

According to principle, we divide solenoid valve into 3 categories: direct-acting solenoid valve, step direct-acting solenoid valve, pilot solenoid valve. Let's present them separately.

1. Direct movement

When power is applied, solenoid coil generates an electromagnetic force to lift obturator from valve seat and valve opens; when power is turned off, electromagnetic force disappears and spring presses shut-off element against valve seat. and valve closes. It can work normally under vacuum, negative pressure and zero pressure.

2. Pilot

When power is applied, electromagnetic force opens pilot hole, pressure in upper chamber drops rapidly, and a pressure differential forms around closing part. Fluid pressure pushes closing element upward and valve opens; when power is removed, spring force closes pilot port, inlet pressure quickly passes through bypass port, and a pressure differential is created in chamber from low to high around check valve element. Fluid pressure moves obturator down, closing valve.

The characteristic of this type is that upper limit of liquid pressure range is high, and it can be set arbitrarily after setting, but liquid pressure differential condition must be met.

3. Step-by-step direct movement

This is a combination of direct and pilot action. When there is no pressure difference between inlet and outlet, electromagnetic force will directly lift pilot small valve and closing part of main valve in sequence after power is turned on, and valve will open. When initial pressure difference is reached between inlet and outlet, after power is turned on, electromagnetic force will drive small valve, pressure in lower chamber of main valve will increase, pressure in upper chamber will fall, and main valve will rise up due to pressure difference. When power is turned off, control valve pushes closing element under action of spring force or medium pressure and moves down, closing valve.

It can also operate at zero differential pressure, vacuum or high pressure, but it has more power and must be installed horizontally.

Besides principle, it can also be classified according to function, which can be divided into water solenoid valve, refrigeration solenoid valve, gas solenoid valve, etc. There are many types, so I will not introduce them. in detail here. I hope above content is helpful for you~