There is a closed cavity in the solenoid valve, and there are through holes in 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. On the other hand, different oil discharge holes are opened or closed by controlling the movement of the valve body, while the oil inlet hole is normally open, the hydraulic oil will enter different oil discharge pipes, and then the piston of the cylinder is pushed by the pressure of the oil, and the piston again Drive the piston rod, and the piston rod drives the mechanical device. In this way, the mechanical movement is controlled by controlling the electric current on and off of the electromagnet.
1. Solenoid valves are divided into three categories in principle:
Principle: When energized, 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 on the valve seat, and the valve closes.
Features: It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.
Principle: It is a combination of direct-acting and pilot-operated principles. When there is no pressure difference between the inlet and outlet, after power is applied, the electromagnetic force directly lifts up the pilot small valve and the closing member of the main valve in sequence, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower cavity of the main valve rises, and the pressure in the upper cavity drops, so that the main valve is pushed upward by the pressure difference; when the power is off, the pilot valve uses a spring Force or medium pressure pushes the closing member, which moves down and closes the valve.
Features: It can also operate safely under zero pressure difference or vacuum or high pressure, but the power is relatively large, and it must be installed horizontally.
Principle: When energized, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly, forming a pressure difference around the closing member, and the fluid pressure pushes the closing member to move upward, and the valve opens; when the power is turned off, the spring force opens the pilot hole. The hole is closed, and the inlet pressure quickly passes through the bypass hole to form a pressure difference around the valve closing member, and the fluid pressure pushes the closing member to move down and close the valve.
Features: The upper limit of the fluid pressure range is relatively high, and it can be installed arbitrarily (customization is required) but must meet the fluid pressure differential condition.
2. Solenoid valves are divided into six sub-categories from the difference in valve structure and material and principle: direct-acting diaphragm structure, step-by-step direct-acting diaphragm structure, pilot diaphragm structure, direct-acting piston structure, Step-by-step direct-acting piston structure, pilot piston structure.
3. Solenoid valves are classified according to their functions: water solenoid valves, steam solenoid valves, refrigeration solenoid valves, low temperature solenoid valves, gas solenoid valves, fire solenoid valves, ammonia solenoid valves, gas solenoid valves, liquid solenoid valves, micro solenoid valves, Pulse solenoid valve, hydraulic solenoid valve normally open solenoid valve, oil solenoid valve, DC solenoid valve, high pressure solenoid valve, explosion-proof solenoid valve, etc.
Selection principle
Safety:
1. Corrosive medium: plastic king solenoid valve and all stainless steel should be selected; for strong corrosive medium, isolation diaphragm type must be selected. For neutral medium, it is also advisable to choose a solenoid valve with copper alloy as the valve housing material, otherwise, rust will often fall off in the valve housing, especially in occasions where the action is not frequent. Ammonia valves cannot use copper.
2. Explosive environment: products with corresponding explosion-proof grade must be selected, and waterproof and dust-proof varieties should be selected for outdoor installation or dusty places.
3. The nominal pressure of the solenoid valve should exceed the maximum working pressure in the pipe.
applicability:
1. Medium characteristics
1) Different types of solenoid valves are selected for gas, liquid or mixed state;
2) Products with different medium temperature, otherwise the coil will burn out and the seal will age, which will seriously affect the service life;
3) Medium viscosity, 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 selected;
5) If the medium is directional and does not allow backflow, two-way circulation 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 requirements of the medium flow direction and the pipeline connection method;
2) Select the nominal diameter according to the flow rate and the Kv value of the valve, or the inner diameter of the pipe;
3) Working pressure difference: If the minimum working pressure difference is above 0.04Mpa, the indirect pilot type can be selected; if the minimum working pressure difference is close to or less than zero, the direct-acting or step-by-step direct type must be selected.
3. Environmental conditions
1) The maximum and minimum temperature of the environment should be selected within the allowable range;
2) In the environment where the relative humidity is high and there are water droplets and rain, a waterproof solenoid valve should be selected;
3) Special varieties should be selected for occasions where there are often vibrations, bumps and shocks in the environment, such as marine solenoid valves;
4) For use in corrosive or explosive environments, the corrosion-resistant type should be selected according to safety requirements;
5) If the environmental space is limited, a multi-function solenoid valve should be selected, because it eliminates the bypass and three manual valves and is convenient for online maintenance.
4. Power conditions
1) According to the type of power supply, select AC and DC solenoid valves respectively. Generally speaking, the AC power supply is easy to access;
2) The voltage specification is preferably AC220V.DC24V;
3) The power supply voltage fluctuation is usually +%10%.-15% for AC, and ±%10 for DC is allowed. If it is out of 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 relatively high during AC starting, and the indirect pilot solenoid valve should be preferred when the capacity is insufficient.
5. Control precision
1) Ordinary solenoid valves only have two positions of on and off, and multi-position solenoid valves should be selected when the control accuracy requirements are high and the parameters are stable;
2) Action time: refers to the time from when the electrical signal is turned on or off to when the main valve action is completed;
3) Leakage: The leakage value given on the sample is a commonly used economic grade.
reliability:
1. Working life, this item is not included in the factory test item, but belongs to the type test item. In order to ensure the quality, famous brand products from regular manufacturers should be selected.
2. Working system: long-term working system, repeated short-time working system and short-time working system. For the situation that the valve is opened for a long time and only closed for a short time, it is advisable to choose a normally open solenoid valve.
3. Working frequency: When the operating frequency is required to be high, the structure should be a direct-acting solenoid valve, and the power supply should be AC.
4. Action reliability
Strictly speaking, this test has not been officially included in the professional standards of China's solenoid valves. In order to ensure the quality, brand-name products from regular manufacturers should be selected. In some occasions, the number of actions is not many, but the reliability requirements are very high, such as fire protection, emergency protection, etc., and must not be taken lightly. Especially important, should also take two consecutive double insurance.
Economy:
It is one of the selected scales, 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 and maintenance and other accessories.
More importantly, the cost of a solenoid valve in the entire automatic control system is very small in the entire automatic control system and even in the production line.
Working principle
