Solenoid valve selection and working principle
Solenoid valves are divided into three categories in principle:
1) Direct acting solenoid valve:
Principle: When energized, the electromagnetic force generated by the electromagnetic coil lifts the closing part from the seat, and the valve opens; When the power is off, the electromagnetic force disappears, the spring presses the closing part on the 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.
2) Distributed direct acting solenoid valve:
Principle: It is a combination of direct action and pilot principle, 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 small valve and the main valve closing part in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after power, the electromagnetic force pilot small valve, the main valve lower chamber pressure rises, the upper chamber pressure drops, so as to use the pressure difference to push the main valve upward; When the power is off, the pilot valve uses spring force or medium pressure to push the closing part and moves downward to close the valve.
Features: It can also be operated at zero pressure difference or vacuum and high pressure, but the power is large, and it must be installed horizontally.
3) Pilot operated solenoid valve:
Principle: When energized, the electromagnetic force opens the pilot hole, the upper chamber pressure drops rapidly, forming a low and high pressure difference around the closing part, the fluid pressure pushes the closing part to move upward, and the valve opens; When the power is off, the spring force closes the pilot hole, and the inlet pressure forms a low and high pressure difference around the valve closing part through the bypass hole rapidly, and the fluid pressure pushes the closing part to move down and close the valve.
Features: The upper limit of the fluid pressure range is high, can be installed arbitrarily (need to be customized), but must meet the fluid pressure difference conditions.
The solenoid valve is divided into six branch subclasses from the difference in valve structure and material and the difference in principle: direct acting diaphragm structure, step multiple plate structure, pilot film structure, direct acting piston structure, step direct acting piston structure, pilot piston structure.
Solenoid valve in the selection of precautions
1. Applicability
The fluid in the line must be consistent with the designated medium in the selected solenoid valve series model. The temperature of the fluid must be less than the calibrated temperature of the solenoid valve. The liquid viscosity allowed by the solenoid valve is generally below 20CST, and greater than 20CST should be indicated.
Working pressure difference, pipeline high pressure difference is less than 0.04MPa should be used such as ZS,2W,ZQDF,ZCM series and other direct acting and step by step direct acting type; When the low working pressure difference is greater than 0.04MPa, the 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; General solenoid valves are one-way work, so pay attention to whether there is a reverse pressure difference, such as installing a check valve.
When the fluid cleanliness is not high, the filter should be installed before the solenoid valve, and the general solenoid valve requires a better cleanliness of the medium. Pay attention to the flow aperture and nozzle diameter; Solenoid valve generally only switch two control; If conditions permit, please install bypass pipe for easy maintenance; When there is water hammer phenomenon, the opening and closing time of the solenoid valve should be customized. Pay attention to the impact of ambient temperature on the solenoid valve. The power supply current and power consumption should be selected according to the output capacity, and the power supply voltage is generally allowed to be about ±10%, and it is necessary to pay attention to the high VA value when AC starting.
2. Reliability
Solenoid valve is divided into normally closed and normally open two kinds; Generally choose normally closed type, power on, power off; But when the opening time is very long and the closing time is very short, the normally open type should be selected. Life test, the factory generally belongs to the type test project, to be exact, there is no professional standard of solenoid valve in our country, so the selection of solenoid valve manufacturers should be careful. When the action time is very short and the frequency is high, the direct action type is generally selected, and the fast series is selected for large caliber.
3. Security
General solenoid valve is not waterproof, when the conditions do not allow, please choose waterproof type, the factory can be customized. The high nominal pressure of the solenoid valve must exceed the high pressure in the pipeline, otherwise the service life will be shortened or other accidents will occur. Corrosive liquids should be selected all stainless steel type, strong corrosive fluids should be selected plastic king solenoid valve. Explosion-proof products must be selected for explosive environments.
4. Economy
First, the four principles of safety, reliability, applicability and economy should be followed, followed by the selection of six field conditions (namely pipeline parameters, fluid parameters, pressure parameters, electrical parameters, action modes and special requirements).
Solenoid valve selection basis:
According to the pipeline parameters, select the solenoid valve: diameter specification (that is, DN) and interface mode
1. Corrosive fluids: corrosion-resistant solenoid valves and stainless steel should be selected; Food ultra-clean fluid: food grade stainless steel solenoid valve should be selected.
2, high temperature fluid: to choose the use of high temperature electrical materials and sealing materials made of solenoid valves, and to choose the type of piston structure.
3, fluid state: as large as a gaseous, liquid or mixed state, especially when ordering larger than DN25, it must be distinguished.
4, fluid viscosity: usually below 50cSt can be arbitrarily selected, if more than this value, you should choose a high-viscosity solenoid valve.
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