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1. In order to prevent the reverse flow of the medium, check valves should be installed on the equipment, devices and pipelines;
2. Check valves are generally suitable for clean media, and should not be used for media containing solid particles and large viscosity;
3. Generally, horizontal lifting check valves should be selected on horizontal pipelines with a nominal diameter of 50mm;
4. The straight-through lift check valve can only be installed in the horizontal pipeline;
5. For the inlet pipeline of the pump, it is advisable to choose the bottom valve, which is generally only installed on the vertical pipeline of the pump inlet, and the medium flows from bottom to top;
6. The lifting type has better sealing performance and greater fluid resistance than the rotary opening type, and the horizontal type should be installed on the horizontal pipeline, and the vertical type should be installed on the vertical pipeline;
7. The installation position of the swing check valve is not limited, it can be installed on horizontal, vertical or inclined pipelines, such as installed on vertical pipelines, and the medium flow direction should be from bottom to top;
8. The swing check valve should not be made into a small-caliber valve, and can be made into a very high working pressure, the nominal pressure can reach 42MPa, and the nominal diameter can also be very large, the maximum can reach more than 2000mm. Depending on the material of the housing and seals, it can be used with any working medium and any operating temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The operating temperature range of the medium is between -196 and -800°C;
9. The swing check valve is suitable for low-pressure and large-diameter, and the installation occasion is limited;
10. The installation position of the butterfly check valve is not limited, and it can be installed on the horizontal pipeline or on the vertical or inclined pipeline;
11. Diaphragm check valve is suitable for pipelines that are prone to water hammer, diaphragm can well eliminate water hammer generated when the medium is reversed, it is generally used in low-pressure and normal temperature pipelines, especially suitable for tap water pipelines, the general medium working temperature is between -12-120 °C, working pressure< 1.6MPa, but the diaphragm check valve can achieve a larger diameter, and the maximum DN can reach more than 2000mm;
12. The spherical check valve is suitable for medium and low pressure pipelines, and can be made into large diameters;
13. The shell material of the spherical check valve can be made of stainless steel, and the hollow sphere of the seal can be wrapped with PTFE engineering plastics, so it can also be applied in the pipeline of general corrosive media, the working temperature is between -101 and -150 °C, the nominal pressure is ≤ 4.0MPa, and the nominal passage range is between DN200 and DN1200;
14. When selecting the check valve for incompressible fluid, the required closing speed should first be evaluated, and the second step is to select the type of check valve that may meet the required closing speed;
15. When selecting the check valve for compressible fluid, it can be selected according to the similar method of check valve for incompressible fluid, if the medium flow range is large, the check valve for compressible fluid can use a deceleration device, and if the medium flow is continuously and quickly stopped and started, as is the case at the outlet of the compressor, then the lifting check valve is used;
16. The check valve should determine the corresponding size, and the valve supplier must provide the data of the selected size, so that the valve size can be found when the valve is fully open at a given flow rate;
17. For high and medium pressure check valves below DN50mm, vertical lifting check valves and straight-through lift check valves should be selected;
18. For low-pressure check valves below DN50mm, butterfly check valves, vertical lifting check valves and diaphragm check valves should be selected;
19. For high and medium pressure check valves with DN greater than 50mm and less than 600mm, it is advisable to choose rotary check valves;
20. For medium and low pressure check valves with DN greater than 200mm and less than 1200mm, it is advisable to choose wear-free spherical check valves;
21. For low-pressure check valves with DN greater than 50mm and less than 2000mm, butterfly check valves and diaphragm check valves should be selected;
22. For pipelines that require that the water hammer impact is relatively small or there is no water hammer when closing, it is advisable to choose the slow-closing swing-start check valve and the slow-closing butterfly check valve.
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