Check valve selection criteria

Check Valve selection criteria are as follows:

1. In order to prevent reverse flow of medium, check valves should be installed on equipment, devices and pipelines;

2. Check valve is generally suitable for clean media, not for media with solid particles and high viscosity;

3. Generally, the horizontal lifting check valve should be used in the horizontal pipeline with nominal diameter of 50 mm;

4. Straight through lifting check valve can only be installed in horizontal pipeline;

5. For the pump inlet pipeline, the bottom valve should be selected. Generally, the bottom valve is only installed on the vertical pipeline at the pump inlet, and the medium flows from bottom to top;

6. Lifting type is better than swing type in sealing and fluid resistance. Horizontal type should be installed on horizontal pipeline and vertical type on vertical pipeline;

7. The installation position of 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 medium should be from bottom to top;

8. Swing check valve should not be made into small diameter valve, but can be made into 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. According to the different materials of shell and seal, 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 of the medium is between - 196 ℃ and 800 ℃;

9. Swing check valve is suitable for low pressure and large diameter, and its installation is limited;

10. The installation position of butterfly check valve is not limited. It can be installed on horizontal pipeline, vertical or inclined pipeline;

11. The diaphragm check valve is suitable for the pipeline prone to water hammer. The diaphragm can well eliminate the water hammer caused by medium countercurrent. It is generally used in low-pressure and normal temperature pipeline, especially suitable for tap water pipeline. Generally, the working temperature of medium is between - 12 ℃ and 120 ℃, and the working pressure is less than 1.6Mpa. However, the diaphragm check valve can achieve a larger diameter, and the maximum DN can reach more than 2000mm ;

12. Ball Check Valve is suitable for medium and low pressure pipeline, 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 the pipeline of general corrosive media. The working temperature is between - 101 ℃ and 150 ℃, the nominal pressure is less than or equal to 4.0Mpa, and the nominal diameter range is between DN200 and DN 1200;

14. When selecting the check valve for incompressible fluid, the first step is to evaluate the required closing speed. The second step is to select the type of check valve that may meet the required closing speed;

15. Check valve for compressible fluid can be selected according to the similar method of check valve for incompressible fluid. If the range of medium flow is large, check valve for compressible fluid can use a deceleration device. If medium flow stops and starts continuously and quickly, such as the outlet of compressor, lift check valve is used;

16. The corresponding size of the check valve shall be determined, and the valve supplier must provide the data of the selected size, so as to find the valve size when the valve is fully open at a given flow rate;

17. For the high and medium pressure check valve under dn50mm, the vertical lifting check valve and straight through lifting check valve should be selected;

18. Butterfly check valve, vertical lift check valve and diaphragm check valve should be selected for low pressure check valve under dn50mm;

19. For high and medium pressure check valves with DN greater than 50 mm and less than 600 mm, swing check valve should be selected;

20. For the medium and low pressure check valves with DN greater than 200 mm and less than 1200 mm, the ball check valve without wear should be selected;

21. Butterfly check valve and diaphragm check valve should be selected for low pressure check valve with DN greater than 50 mm and less than 2000 mm;

22. Slow closing swing check valve and slow closing butterfly check valve should be selected for the pipeline with small water hammer impact or no water hammer when it is required to be closed.

Troubleshooting

Disc broken

What is the cause of disc breakage

The medium pressure in front of and behind the check valve is in a state of close balance and "sawing" each other. The valve disc often beats with the valve seat, and the valve disc made of some brittle materials (such as cast iron, brass, etc.) is broken.

The preventive method is to use the check valve whose disc is made of ductile material.

Medium backflow

There are several reasons for medium backflow

① The sealing surface was damaged; 2.

Repairing the sealing surface and cleaning impurities can prevent back flow.