Solenoid valve is an automatic basic element used to control the direction of fluid, which belongs to the actuator; it is usually used in mechanical control and industrial valves to control the direction of the medium, so as to achieve the control of the valve switch.
working principle
There is a closed cavity in the solenoid valve, and there are through holes in different positions, each hole leads to a different oil pipe, the middle of the cavity is a valve, and two electromagnets on both sides, which side of the magnet coil is energized, the valve body will be attracted Where, by controlling the movement of the valve body to block or leak different oil discharge holes, and the oil inlet hole is normally open, the hydraulic oil will enter the different oil discharge pipes, and then use the pressure of the oil to push the cylinder The piston drives the piston rod, and the piston rod drives the mechanical device. In this way, by controlling the current of the electromagnet, the mechanical movement is controlled.
classification
1. Solenoid valves are divided into three categories in principle:
1) Direct-acting solenoid valve:
Principle: When the power is turned on, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; when the power is turned off, the electromagnetic force disappears, the spring presses the closing member against the valve seat, and the valve closes.
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 acting and pilot type. When there is no pressure difference between the inlet and the outlet, after energization, 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 reaches the starting pressure difference, after energization, the electromagnetic force pilot small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber decreases, thereby using the pressure difference to push the main valve upward; when the power is turned off, the pilot valve uses a spring Force or medium pressure pushes the closing piece and moves downward to close the valve.
Features: It can operate 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 the power is turned on, the pilot hole is opened by electromagnetic force, the pressure in the upper chamber drops rapidly, and a high and low pressure difference is formed around the closing member. The fluid pressure pushes the closing member to move upward and the valve opens; when the power is turned off, the spring force controls the pilot The orifice is closed, and the inlet pressure quickly forms a low, high, and high pressure difference around the valve closing member through the bypass hole, and the fluid pressure pushes the closing member to move downward to close the valve.
Features: The upper limit of the fluid pressure range is high, and can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions.
2. Solenoid valves are divided into six subcategories from the differences in valve structure and materials and the differences in principle:
Direct-moving diaphragm structure, stepped heavy diaphragm structure, pilot membrane structure, direct-moving piston structure, stepped direct-moving piston structure, pilot piston structure.
Cautions for solenoid valve selection
1. Applicability
The fluid in the pipeline must be consistent with the medium calibrated in the selected solenoid valve series model.
The temperature of the fluid must be lower than the calibration temperature of the solenoid valve.
The solenoid valve allows the liquid viscosity to be generally below 20CST, and should be noted if it is greater than 20CST.
Working pressure difference, when the maximum pressure difference of the pipeline is less than 0.04MPa, such as ZS, 2W, ZQDF, ZCM series and other direct-acting and step-by-step direct-acting types should be used; when the minimum working pressure is greater than 0.04MPa, the pilot type (pressure Differential) solenoid valve; the maximum working pressure difference should be less than the maximum calibration pressure of the solenoid valve; generally the solenoid valve is a one-way work, so pay attention to whether there is a back pressure difference, 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, the solenoid valve requires good cleanliness for the medium.
Pay attention to the flow aperture and the diameter of the connection; the solenoid valve is generally only controlled by two switches; if conditions permit, please install a bypass tube for easy maintenance; when there is a water hammer phenomenon, the opening and closing time of the solenoid valve should be customized.
Note the effect of ambient temperature on the solenoid valve.
The power supply current and power consumption should be selected according to the output capacity. The power supply voltage is generally allowed to be around ±10%. It must be noted that the VA value is higher when the AC starts.
2. Reliability
Solenoid valve is divided into two types: normally closed and normally open; normally choose the normally closed type, turn on when the power is turned on, and turn off when the power is turned off; but when the opening time is very long, the normally open type is selected when it is very short.
Life test, the factory is generally a type test project, to be precise, my country does not yet have professional standards for solenoid valves, so be careful when choosing solenoid valve manufacturers.
When the action time is short and the frequency is high, the direct-acting type is generally selected, and the large-diameter rapid series is used.
3. Security
Generally, the solenoid valve is not waterproof. Please choose the waterproof type when the conditions do not allow. The factory can customize it.
The maximum nominal pressure of the solenoid valve must exceed the maximum pressure in the pipeline, otherwise the service life will be shortened or other unexpected situations will occur.
Corrosive liquids should use all stainless steel type, strong corrosive fluids should use plastic king (SLF) solenoid valve.
Explosive environments must use corresponding explosion-proof products.
4. Economic
There are many solenoid valves that can be used universally, but the most economical product should be selected on the basis of meeting the above three points.
