Working principle and selection principle of solenoid valve

Solenoid valve is an industrial equipment controlled by electromagnetics . It is an automatic basic component used to control fluids. It belongs to an actuator and is not limited to hydraulic and pneumatic. It is used in industrial control systems to adjust the direction, flow , speed and other parameters of the medium. Solenoid valves can be used with different circuits to achieve the desired control, and the accuracy and flexibility of the control can be guaranteed. There are many kinds of solenoid valves, and different solenoid valves play a role in different positions of the control system. The most commonly used ones are one-way valves, safety valves, directional control valves, speed control valves, etc.
There is a closed cavity in the solenoid valve, with through holes opened at different positions. Each hole is connected to a different oil pipe. There is a piston in the middle of the cavity and two electromagnets on both sides. The valve body will be attracted to which side the magnet coil is energized. By controlling the movement of the valve body to open or close different oil drain holes, and the oil inlet hole is normally open, the hydraulic oil will enter different oil drain pipes, and then the piston of the oil cylinder is pushed by the oil pressure , and the piston drives the piston rod, and the piston rod drives the mechanical device. In this way, the mechanical movement is controlled by controlling the current on and off of the electromagnet . 1. Four major selection principles for solenoid valves1. Safety:　　1. Corrosive media: Plastic King solenoid valves and all-stainless steel should be selected; for highly corrosive media, isolation diaphragm type must be selected. For neutral media, it is also advisable to use solenoid valves with copper alloy as the valve body material, otherwise, rust chips will often fall off the valve body, especially in occasions where the valve is not frequently operated. Copper cannot be used for ammonia valves. 　　2. Explosive environment: Products with corresponding explosion-proof grades must be selected. Waterproof and dustproof varieties should be selected for outdoor installations or dusty occasions. 　　3. The nominal pressure of the solenoid valve should exceed the maximum working pressure in the pipe. 2. Applicability:　　1. Medium characteristics
1) Different types of solenoid valves should be used for gas, liquid or mixed state;
2) Different specifications of products should be used for medium temperature , otherwise the coil will burn out and the seal will age, seriously affecting the service life;
3) The viscosity of the medium is usually below 50cSt. If it exceeds this value, when the diameter is greater than 15mm, use a multi-function solenoid valve; when the diameter is less than 15mm, use a high-viscosity solenoid valve.
4) When the cleanliness of the medium is not high, a recoil filter valve should be installed in front of the solenoid valve. When the pressure is low, a direct-acting diaphragm solenoid valve can be used;
5) If the medium is directional and backflow is not allowed, two-way flow is required;
6) The medium temperature should be selected within the allowable range of the solenoid valve.
2. Pipeline parameters
1) Select the valve port and model according to the medium flow requirements and pipeline connection method;
2) Select the nominal diameter according to the flow rate and valve Kv value, and the same pipe inner diameter can also be
selected; 3) Working pressure difference: If the minimum working pressure difference is above 0.04Mpa, an indirect pilot type can be selected; if the minimum working pressure difference is close to or less than zero, a direct-acting type or a step-by-step direct type must be selected.
3. Environmental conditions
1) The maximum and minimum temperatures of the environment should be within the allowable range;
2) In environments with high relative humidity and water droplets and rain, a waterproof solenoid valve should be selected;
3) In environments with frequent vibrations, bumps and impacts, special varieties should be selected, such as marine solenoid valves;
4) When used in corrosive or explosive environments, corrosion-resistant types should be selected according to safety requirements;
5) If the environmental space is limited, a multi-functional solenoid valve must be selected because it eliminates the bypass and three manual valves and is easy to maintain online.
4. Power supply conditions
1) According to the type of power supply, select AC and DC solenoid valves respectively. Generally speaking, AC power supply is easy to use;
2) For voltage specifications, AC220V.DC24V is preferred as much as possible;
3) For power supply voltage fluctuation, AC usually uses %10%.-15%, and DC allows about ±%10. If it exceeds the tolerance, voltage stabilization measures must be taken;
4) The rated current and power consumption should be selected according to the power supply capacity . It should be noted that the VA value is higher when AC starts, and indirect pilot solenoid valves should be preferred when the capacity is insufficient.
5. Control accuracy
1) Ordinary solenoid valves have only two positions, open and closed. When the control accuracy requirements are high and the parameters require stability, multi-position solenoid valves must be selected;
2) Action time: refers to the time from the electrical signal being connected or cut off to the completion of the main valve action;
3) Leakage: The leakage value given on the sample is the commonly used economic level. 3. Reliability: 　　1. Working life, this item is not included in the factory test items, but belongs to the type test items. To ensure quality, brand-name products from regular manufacturers should be selected. 　　2. Working mode: divided into three types: long-term working system, repeated short-time working system and short-time working system. For the situation where the valve is open for a long time and only closed for a short time, it is advisable to use a normally open solenoid valve. 　　3. Working frequency: When the action frequency requirement is high, the structure should preferably be a direct-acting solenoid valve, and the power supply should preferably be AC. 　　4. Action reliability 　　Strictly speaking, this test has not yet been officially included in the professional standards of Chinese solenoid valves. To ensure quality, famous brand products from regular manufacturers should be selected. In some occasions, the number of actions is not large, but the reliability requirements are very high, such as fire protection, emergency protection , etc., which must not be taken lightly. It is particularly important to use two double insurances in succession.
4. Economy:
It is one of the criteria for selection, but it must be economical on the basis of safety, applicability and reliability.
Economy is not only the price of the product, but also its function and quality as well as the cost of installation, maintenance and other accessories.
More importantly, the cost of a solenoid valve in the entire automatic control system and even in the production line is negligible. If you choose it wrongly for the sake of cheapness, the damage caused by the group is huge. 2. Six selection criteria 　　1. Select the solenoid valve according to the pipeline parameters: diameter specification (ie DN), interface mode 　　1. Determine the diameter (DN) size according to the inner diameter size or flow requirement of the on-site pipeline. 　　2. Interface mode, generally > DN50 should choose flange interface, ≤ DN50 can be freely selected according to user needs. 2. 　　Select the solenoid valve according to the fluid parameters: material, temperature group 　　1. Corrosive fluid: It is advisable to use corrosion-resistant solenoid valves and all stainless steel; edible ultra-clean fluid: It is advisable to use food-grade stainless steel solenoid valves. 　　2. High-temperature fluid: It is necessary to choose a solenoid valve made of high-temperature resistant electrical materials and sealing materials, and a piston-type structure type should be selected. 　　3. Fluid state: mostly gaseous, liquid or mixed state, especially when the diameter is larger than DN25. 　　4. Fluid viscosity: usually any value below 50cSt can be selected. If it exceeds this value, a high viscosity solenoid valve should be selected. 3. 　　Select solenoid valve according to pressure parameters: principle and structure variety 　　1. Nominal pressure: This parameter has the same meaning as other general valves and is determined according to the nominal pressure of the pipeline. 　　2. Working pressure: If the working pressure is low, the direct-acting or step-by-step direct-acting principle must be selected; when the minimum working pressure difference is above 0.04Mpa, direct-acting, step-by-step direct-acting and pilot-operated types can be selected. 　　4. Electrical
Selection: AC220V and DC24 should be preferred as far as possible for voltage specifications, which are more convenient.
5. Choose according to the length of continuous working time: normally closed, normally open, or continuously energized
1. When the solenoid valve needs to be opened for a long time and the duration is longer than the closing time, the normally open type should be selected.
2. If the opening time is short or the opening and closing time is not much, the normally closed type should be selected.
3. 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 energized for a long time should be selected.
6. Select auxiliary functions according to environmental requirements: explosion-proof, check, manual, waterproof fog, water spray, diving
1. Explosive environment: solenoid valves with corresponding explosion-proof levels must be selected.
2. When there is a backflow phenomenon in the fluid in the pipe, a solenoid valve with a check function can be selected.
3. When the solenoid valve needs to be manually operated on site, a solenoid valve with a manual function can be selected.
4. Waterproof and dustproof varieties (protection level above IP54) should be selected for outdoor installation or dusty occasions.
5. Submersible solenoid valves (protection level above IP54) must be used for fountains.
The above is the selection method of solenoid valves. We can refer to these methods to buy suitable solenoid valves in future purchases! 3. Installation points 　　1. During installation, it should be noted that the arrow on the valve body should be consistent with the flow direction of the medium. It cannot be installed in places with direct dripping or splashing water. The solenoid valve should be installed vertically upward; 　　2. The solenoid valve should ensure normal operation within the power supply voltage fluctuation range of 15%-10% of the rated voltage; 　　3. After the solenoid valve is installed, there must be no reverse pressure difference in the pipeline. It needs to be powered on several times to make it suitable for temperature before it can be officially put into use; 　　4. The pipeline should be thoroughly cleaned before the solenoid valve is installed. The medium introduced should be free of impurities. Install a filter before the valve; 　　5. When the solenoid valve fails or is cleaned, a bypass device should be installed to ensure the continued operation of the system.