The selection criteria for check valves are as follows:
1. In order to prevent the backflow of the medium, check valves should be installed on equipment, devices and pipelines;
2. Check valves are generally suitable for clean media and are not suitable for media containing solid particles and high viscosity;
3. Generally, horizontal lift check valves should be used on horizontal pipelines with a nominal diameter of 50mm;
4. The straight-through lift check valve can only be installed on horizontal pipelines;
5. For the water pump inlet pipeline, a bottom valve should be used. The bottom valve is generally only installed on the vertical pipe at the pump inlet, and the medium flows from bottom to top;
6. The lifting type has better sealing and greater fluid resistance than the swing type. The horizontal type should be installed on horizontal pipes, and the vertical type should be installed on vertical pipes;
7. The installation position of the swing check valve is not restricted. It can be installed on horizontal, vertical or inclined pipelines. If installed on a vertical pipeline, the medium flow direction must be from bottom to top;
8. The swing check valve should not be made into a small-diameter valve. It can be made into a very high working pressure. The nominal pressure can reach 42MPa, and the nominal diameter can also be very large, up to 2000mm or more. Depending on the materials of the shell and seals, it can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196--800℃;
9. The swing check valve is suitable for low pressure and large diameter, and the installation location is limited;
10. The installation position of butterfly check valve is not restricted and can be installed on horizontal pipelines, vertical or inclined pipelines;
11. The diaphragm check valve is suitable for pipelines prone to water hammer. The diaphragm can well eliminate the water hammer produced when the medium flows back. It is generally used on low-pressure and normal temperature pipelines, especially suitable for tap water pipelines and general medium work. The temperature is between -12--120℃, and the working pressure is <1.6MPa, but the diaphragm check valve can have a larger diameter, and the maximum DN can reach more than 2000mm;
12. Ball check valve is suitable for medium and low pressure pipelines and can be made into large diameter;
13. The shell material of the ball check valve can be made of stainless steel, and the hollow sphere of the seal can be wrapped with polytetrafluoroethylene engineering plastic, so it can also be used in pipelines with general corrosive media. The working temperature is -101--150 ℃, the nominal pressure is ≤4.0MPa, and the nominal throughput range is between DN200-DN1200;
14. When selecting a check valve for incompressible fluids, you must first evaluate the required closing speed. The second step is to select the type of check valve that may meet the required closing speed;
15. When selecting check valves for compressible fluids, you can select them in a similar way to check valves for incompressible fluids. If the medium flow range is large, check valves for compressible fluids can be used. A reduction device. If the medium flow stops and starts quickly in succession, such as at the outlet of a compressor, a lift check valve is used;
16. The check valve should be sized accordingly, and the valve supplier must provide data on the selected size so that the valve size when the valve is fully open at a given flow rate can be found;
17. For high and medium pressure check valves below DN50mm, vertical lift check valves and straight-through lift check valves should be used;
18. For low-pressure check valves below DN50mm, butterfly check valves, vertical lift check valves and diaphragm check valves should be used;
19. For high and medium pressure check valves with DN greater than 50mm and less than 600mm, swing check valves should be used;
20. For medium and low pressure check valves with a DN greater than 200mm and less than 1200mm, it is advisable to choose a wear-free spherical check valve;
21. For low-pressure check valves with DN greater than 50mm and less than 2000mm, butterfly check valves and diaphragm check valves should be used;
22. For pipelines that require relatively small or no water hammer when closing, slow-closing swing check valves and slow-closing butterfly check valves should be used.