What is a check valve?

Check valves are also known as non return valve or one way valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, and are an automatic valve. Check valves are used in piping systems to prevent backflow of media, prevent pump and drive motor reversal, and bleed of container media. The check valve can also be used to supply a line in which the pressure may rise to an auxiliary system that exceeds the system pressure. It can be divided into a swing type (by gravity center) and a lift type (moving along the axis).

Check valve selection criteria

1.   In order to prevent backflow of the medium, a check valve should be installed on the equipment, equipment and pipelines;

2.   check valve is generally suitable for clean media, not suitable for media containing solid particles and viscosity;

3.   Generally, horizontal lift check valves should be used on horizontal pipes with a nominal diameter of 50 mm;

4.   Straight-flow lifting check valves can only be installed in horizontal pipes;

5. For the inlet pipe of the pump, the bottom valve should be selected. The bottom valve is generally installed only on the vertical pipe of the pump inlet, and the medium flows from bottom to top;

6. The lift type has better sealing performance than the swing type, and the fluid resistance is large. The horizontal type should be installed on the horizontal pipe and installed vertically on the vertical pipe;

7. The installation position of the swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines. If it is installed on vertical pipelines, the flow direction of the medium should be from bottom to top;

8. The swing-type check valve should not be made into a small-diameter valve, which can be made into a high working pressure. The nominal pressure can reach 42 MPa, and the nominal diameter can also be made very large, and the maximum can reach 2000 mm or more. Any working medium and any operating temperature range can be applied depending on the material of the housing and the seal. The medium is water, steam, gas, corrosive medium, oil, medicine, and the like. The working temperature range of the medium is between -196 and 800 °C;

9. The rotary check valve is suitable for low pressure and large diameter, and the installation is limited;

10. The installation position of the butterfly check valve is not limited. 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. The diaphragm can well eliminate the water hammer generated when the medium is reversed. It is generally used on low pressure normal temperature pipelines, especially for tap water pipelines. The temperature is between -12--120 °C, the working pressure is <1.6 MPa, but the diaphragm type check valve can achieve a larger diameter, and the DN can reach 2000 mm or more;

12, spherical check valve is suitable for medium and low pressure pipelines, can be made into large diameter;

13. The shell material of the spherical check valve can be made of stainless steel. The hollow sphere of the seal can be wrapped with PTFE engineering plastic, so it can also be applied on the pipeline of general corrosive medium. The working temperature is -101--150. Between °C, its nominal pressure is ≤4.0MPa, and the nominal passage range is between DN200-DN1200;

14. For the selection of incompressible fluid check valves, the required closing speed must first be evaluated. The second step is to select the type of check valve that may meet the required closing speed;

15. For the selection of the check valve for the compressible fluid, it can be selected according to a similar method of the non-compressible fluid check valve. If the medium flow range is large, the check valve for the compressible fluid can be used. a speed reducing device, if the medium flow is quickly stopped and started continuously, such as the outlet of the compressor, a lift check valve is used;

16, the check valve should determine the corresponding size, the valve supplier must provide the data of the selected size, so that you can find the valve size when the valve is fully open at a given flow rate;

17. For high and medium pressure check valves below DN50mm, vertical lift check valves and straight 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, a swing check valve should be used;

20. For medium and low pressure check valves with DN greater than 200mm and less than 1200mm, wear-free ball check valves should be used;

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 less water hammer impact or waterless blow when shutting down, a slow-closed swing-start check valve and a slow-closed butterfly check valve should be used.

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