How to select a solenoid valve? What is the working principle?

Electromagnetic valves are divided into three categories in principle:

1) Direct acting solenoid valve:

Principle: When energized, the electromagnetic coil generates electromagnetic force to lift the closing part from the valve seat, and the valve opens; When the power is cut off, the electromagnetic force disappears, and the spring presses the closing part against the valve seat, causing the valve to close.

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

2) Distributed direct acting solenoid valve:

Principle: It is a combination of direct action and pilot type principle. When there is no pressure difference between the inlet and outlet, the electromagnetic force directly lifts the pilot small valve and the main valve closure part upwards after being energized, and the valve opens. When the starting pressure difference between the inlet and outlet is reached, after being energized, the electromagnetic force leads the small valve, causing the pressure in the lower chamber of the main valve to increase and the pressure in the upper chamber to decrease, thereby using the pressure difference to push the main valve upwards; When the power is cut off, the pilot valve uses spring force or medium pressure to push the closing element downwards, causing the valve to close.

Features: It can also operate at zero pressure difference, vacuum, and high pressure, but with high power, it is required to be installed horizontally.

3) Pilot operated solenoid valve:

Principle: When energized, electromagnetic force opens the pilot hole, causing a rapid decrease in pressure in the upper chamber, creating a high and low pressure difference around the closing element. Fluid pressure pushes the closing element upwards, causing the valve to open; When the power is cut off, the spring force closes the pilot hole, and the inlet pressure quickly forms a pressure difference of low to high around the closing valve through the bypass hole. The fluid pressure pushes the closing valve downward to close the valve.

Features: The upper limit of the fluid pressure range is high, and can be installed arbitrarily (customized), but the fluid pressure difference condition must be met.

2. Electromagnetic valves are divided into six sub categories based on differences in valve structure, materials, and principles:

Direct acting diaphragm structure, step heavy plate structure, pilot diaphragm structure, direct acting piston structure, step direct acting piston structure, and pilot piston structure.

Precautions for selection of solenoid valves

1： Applicability

The fluid in the pipeline must be consistent with the medium calibrated in the selected electromagnetic valve series model.

The temperature of the fluid must be lower than the calibrated temperature of the selected solenoid valve.

The allowable liquid viscosity of solenoid valves is generally below 20CST, and should be noted if it is greater than 20CST.

When the working pressure difference and pipeline pressure difference are less than 0.04MPa, direct acting and step-by-step direct acting types such as ZS, 2W, ZQDF, ZCM series should be selected; When the low working pressure difference is greater than 0.04MPa, a pilot type (pressure difference type) solenoid valve can be selected; The high working pressure difference should be less than the large calibration pressure of the solenoid valve; Generally, solenoid valves work in one direction, so it is important to pay attention to whether there is a back pressure difference, and if a check valve is installed.

When the cleanliness of the fluid is not high, a filter should be installed in front of the solenoid valve. Generally, solenoid valves require better cleanliness of the medium.

Pay attention to the flow aperture and nozzle diameter; Electromagnetic valves are generally only controlled by a switch with two positions; If conditions permit, please install a bypass pipe for easy maintenance; When there is a water hammer phenomenon, it is necessary to customize the opening and closing time adjustment of the solenoid valve.

Pay attention to the impact of environmental temperature on the solenoid valve

The power supply current and consumption power should be selected based on the output capacity, and the power supply voltage is generally allowed to be around ± 10%. It is necessary to pay attention to the high VA value during AC starting.

2、 Reliability

Electromagnetic valves are divided into two types: normally closed and normally open; Generally, the normally closed type is selected, which opens when powered on and closes when powered off; But when the opening time is long and the closing time is short, the normally open type should be selected.

Life test is generally a type test project for factories, and to be precise, there is no professional standard for solenoid valves in China. Therefore, when selecting solenoid valve manufacturers, caution should be exercised.

When the action time is short and the frequency is high, the direct action type is generally selected, and the fast series is selected for large caliber.

3、 Security

Generally, solenoid valves are not waterproof. When conditions do not allow, please choose a waterproof type, which can be customized by the factory.

The high rated nominal pressure of the solenoid valve must exceed the high pressure inside the pipeline, otherwise its service life will be shortened or other unexpected situations will occur.

All stainless steel type should be used for corrosive liquids, while plastic king solenoid valves should be used for highly corrosive liquids.

Corresponding explosion-proof products must be selected for explosive environments.

4、 Economy

Firstly, the four principles of safety, reliability, applicability, and economy should be followed in sequence. Secondly, the selection should be based on six aspects of on-site operating conditions (i.e. pipeline parameters, fluid parameters, pressure parameters, electrical parameters, action methods, and special requirements).

Selection basis for solenoid valves:

1、 Select the solenoid valve according to the pipeline parameters: diameter specification (i.e. DN) and interface method

1. Determine the diameter (DN) size based on the internal diameter or flow requirements of the on-site pipeline.

2. The interface method is generally to choose a flange interface when it is greater than DN50, and can be freely selected according to user needs when it is less than or equal to DN50.

2、 Select the material and temperature group of the solenoid valve based on the fluid parameters

1. Corrosive fluid: It is recommended to use corrosion-resistant solenoid valves and all stainless steel; Edible ultra clean fluid: It is recommended to use food grade stainless steel electromagnetic valves.

2. High temperature fluid: Choose solenoid valves made of high-temperature resistant electrical and sealing materials, and choose piston type structures.

3. Fluid state: It can be as large as gaseous, liquid or mixed, especially when ordering with a diameter greater than DN25. It is important to distinguish between them.

4. Fluid viscosity: Usually, it can be selected arbitrarily below 50cSt. If it exceeds this value, a high viscosity solenoid valve should be selected.

3、 Principle and structural variety of selecting solenoid valves based on pressure parameters

1. Nominal pressure: This parameter has the same meaning as other general-purpose valves and is determined based on the nominal pressure of the pipeline.

2. Working pressure: If the working pressure is low, the principle of direct action or step-by-step direct action must be selected; When the low working pressure difference is above 0.04Mpa, direct action, step-by-step direct action, and pilot type can be selected.

4、 Electrical selection: The voltage specifications should prioritize AC220V and DC24, which are more convenient.

5、 Choose based on the duration of continuous operation: normally closed, normally open, or continuously energized

If the opening time is short or the opening and closing time is not long, select the normally closed type.

However, for some working conditions used for safety protection, such as furnace and kiln flame monitoring, the normally open type cannot be selected, and the type that can be powered on for a long time should be selected.

6、 Select auxiliary functions according to environmental requirements: explosion-proof, check, manual, waterproof fog, water immersion, diving

1. Explosive environment: solenoid valves with corresponding explosion-proof levels must be selected

2. When there is backflow of fluid in the pipe, a solenoid valve with a check function can be selected.

3. When on-site manual operation of the solenoid valve is required, the solenoid valve with manual function can be selected.

4. Waterproof and dustproof varieties (with a protection level of IP54 or above) should be selected for outdoor installation or in dusty environments.

5. Submersible electromagnetic valves (with a protection level of IP68 or above) must be used for fountains.

6. When the solenoid valve needs to be opened for a long time and the duration exceeds the closing time, the normally open type is selected.