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Views: 6890 Author: Site Editor Publish Time: 2020-01-29 Origin: Site
Control valves are very important in the automatic control of modern factories. By receiving the control signal output by the control unit, it changes the medium flow, pressure, temperature, liquid level and other process parameters. It can be said that the control valve is the last gate in the process loop. Therefore, how to choose the correct control valve in order to achieve the best control effect? It becomes a critical problem.
General Selection Principle
1. The valve difference is small, the set value is small, and the main process of the process is small. To absorb the control object with S> 0.75, the linear flow characteristic should be selected.
2. For slow production process, when S> 0.4, linear flow characteristics should be selected.
3. In some occasions, a large adjustable range is required, the pressure loss of the piping system is large, the opening degree change and the pressure difference on the valve are relatively large, and equal percentage flow characteristics should be selected.
5. Quick opening feature is suitable for occasions with two-position action or when it is necessary to quickly obtain the maximum flow capacity of the regulating valve. When the regulator must be set to a wide proportional band, its regulating valve can also be selected with a quick-open feature.
1. Comprehensively select the type of control valve based on process variables, fluid characteristics, requirements of the control system, and connection form of control valve piping.
2. In general, it is preferred to use straight-through single and double-seat control valves and ordinary sleeve valves with large volume and advanced technology. You can also choose a low S value energy-saving valve and a compact valve.
3. According to different occasions, the following types of regulating valves can be selected.
It is generally suitable for the occasions where the process requires small leakage, small flow, and small pressure difference before and after the valve. However, valves with a diameter of less than 20mm are also widely used in applications with large differential pressure; they are not suitable for applications with high viscosity or fluids containing suspended particles.
It is generally suitable for occasions with less strict requirements on leakage, large flow rate and large pressure difference before and after the valve. But it is not suitable for occasions with high viscosity or fluid containing suspended particles.
It is generally suitable for occasions where the fluid is clean and contains no solid particles. Where the pressure difference between the front and back of the valve is large and the liquid may flash or cavitation.
Suitable for high viscosity, fiber containing, granular and dirty fluids. The adjustment system requires a wide adjustable range. When the seat gasket is made of soft material, it is suitable for occasions requiring strict sealing.
"O" ball valve is generally suitable for two-position shut-off. "V" ball valve is generally suitable for continuous adjustment systems, and its flow characteristics are approximately equal percentages.
It is generally applicable to the following occasions where there is high viscosity or suspended solids fluids, gas-liquid miscible fluids or fluids that are easy to flash or the pipes that require right angle piping.
In addition to occasions mentioned above, it is also suitable for high static pressure and large pressure difference. However, the material and structure of the valve trim must be reasonably selected to extend the service life.
It is generally suitable for high viscosity, particles, crystals and fibrous fluids pressure pad or corresponding corrosion-resistant material. Its flow characteristics are better than diaphragm valves.
It is suitable for occasions with large flow capacity, wide adjustable ratio, large pressure difference, and tight sealing.
It is suitable for the occasions with large caliber, large flow and low-pressure difference. It is generally suitable for dense turbid liquid and fluid containing suspended particles. When it is required to be tightly sealed, a rubber or polytetrafluoroethylene soft seal structure should be used. In the case of corrosive fluids, a corresponding corrosion-resistant lining is required.
It is suitable for splitting and merging occasions where the fluid temperature is below 300 ° C, for simple ratio adjustment. The temperature difference between the two fluids should not be greater than 150 ° C.
It is suitable for occasions with strong corrosion, high viscosity or fluids containing suspended particles and fibers, and at the same time, the flow characteristics are not strict. Due to the limitation of the diaphragm lining, it can only be used in situations where the pressure is less than or equal to 1 MPa and the operating temperature is less than 150 ° C.
This kind is suitable for vacuum systems and occasions where the fluid is highly toxic, volatile, and rare precious fluids.
It is suitable for low-temperature conditions and deep freezing. When the medium temperature is between 100 ° C and 40 ° C, a valve with heat sink and flexible graphite packing can be selected. When the medium temperature is -200 ~ -100 ° C, a long neck cryogenic valve should be used.
It is suitable for the occasion where the process load changes greatly or when the S value is less than 0.3.
It is suitable for the occasions where the liquid produces flashing, cavitation, and the velocity of the gas at the valve contraction surface is greater than the speed of sound and the estimated noise exceeds 95dB (A).
It is suitable for the occasion that the valve needs to be opened or closed urgently when the two-position regulating system and the process fail.
It is suitable for occasions with small changes in flow, low adjustment accuracy requirements, or difficult supply of instrument air supply. In the special process production process, a special regulating valve should be selected according to the experience of use.
Having introduced about so many kinds of valves, I believe you can choose the suitable one. If you are interested, please click https://www.jz-pipe.com/VALVES-pl8639115.html to learn about more details.
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