1. Working Principle of Check Valve
The valve that opens or closes itself by relying on the flow and power of the medium to prevent backflow of the medium is called a check valve. Check valves belong to the category of automatic valves. They are mainly used in pipelines where the medium flows in one direction, and only allow the medium to flow in one direction to prevent accidents. Check valves are also called check valves, check valves or check valves. Check valve is a valve that can automatically prevent the backflow of fluid. The valve flap of the check valve opens under the action of fluid pressure, and the fluid flows from the inlet side to the outlet side. When the pressure on the inlet side is lower than the outlet side, the valve flap automatically closes under the effect of the fluid pressure difference, its own gravity and other factors to prevent the fluid from flowing backward. When the check valve is closed, water hammer pressure will be generated in the pipeline. In severe cases, it will cause damage to the valve, pipeline or equipment, especially for large-mouth pipelines or high-pressure pipelines. . Do not allow the check valve to bear weight in the pipeline. The large check valve should be independently supported so that it is not affected by the pressure generated by the piping system. When installing, pay attention to the direction of the medium flow should be consistent with the arrow direction of the valve body.
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Second, the classification of check valves
Check valves can be divided into three types: lift check valves, swing check valves and butterfly check valves. Lift check valve can be divided into vertical and horizontal. The swing check valve is divided into three types: single-petal type, double-petal type and multi-petal type. The butterfly check valve is a straight-through type, the following check valve legend:
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Figure 1. Lifting check valve
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Figure 2. Swing check valve
Figure three, butterfly check valve
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The above types of check valves can be divided into three types: threaded connection, flange connection and welding. Since most of the check valves installed in the water supply and heating pipelines of our company are mostly rotary check valves, the following mainly introduces the maintenance methods of rotary check valves.
Third, the standardized operation process for the repair of the swing check valve
1. Unscrew the bonnet bolt and remove the bonnet. A
2. Loosen the nut at the end of the shaft first, open the pin shaft, and then take out the valve core and connecting rod together, and dig out the packing at the pin shaft.
3. Clean all parts.
4. Check the valve body and bonnet for cracks, shrinkage holes, slag inclusions, corrosion and other defects. Whether the flange is intact and smooth, with no groove marks and corrosion, and the packing room has no groove marks.
5. Check whether the sealing surface of the valve seat and valve core is smooth, whether there are groove marks and cracks, and apply red powder to check the contact.
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6. Check whether the sealing surface is tight.
7. Check whether the surface of the pin is smooth, whether there is wear and bending, and check the gap between the pin and the connecting rod.
8. Check whether the connection between the valve core and the connecting rod is flexible and wear-free.
9. After all parts are cleaned and checked, they are assembled in the reverse order of disassembly.
10. During assembly, the contact surfaces of the parts and the threads should be coated with black lead powder for lubrication.
11. Replace the pressure pad of the bonnet. If there is packing at the pin, replace the packing.
12. Before installing the valve cover, move the connecting rod to open and close the valve to check whether the switch is flexible.
13. Install the bonnet and tighten the bonnet fixing bolt.
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