What Is The Reason Why The Fluorine-lined Check Valve Cannot Stop Water?

I saw a case on a website. It said that there were three pipelines in a system, but some fluorine-lined check valves could not stop water sometimes, and sometimes even all check valves could not stop water. When the pipeline was disassembled, no foreign matter was found in the check valve. However, when the valve was installed on the pipeline, the equipment would have backflow, and the fluorine-lined check valve could not stop water. The fluorine-lined check valves were all newly purchased, and the water outlet pressure was sufficient, all above 0.4MP. The check valve is located at the outlet of the water pump. When the water pump stops, the pressure of the pipeline will flow back into the tank behind the water pump. The water inlet pressure of the tank was originally about 0.3MPa.

So, what is the reason why Lined Check Valve cannot stop water?
In fact, it can be said that there is no check valve that does not leak. As long as the leakage is within the specified value, it is qualified. The above-mentioned check valve cannot stop water and leaks. The editor summarizes that it may be caused by the following reasons:
1. The pressure difference before and after the check valve is not enough, which may cause leakage.
2. The valve seat may not return to its position, and the valve seat is sometimes stuck. The spring does not work and the leakage is not large. Or the seal is not good.
3. The direction is installed wrong. This vertical installation method can be installed upside down if you are not careful. The valve disc can be opened by its own gravity.
4. It may be caused by the mismatch between the sealing surface and the rubber.
5. In the pipeline, if there is a fine amount of sand and gravel in the water, it will affect the reset of the fluorine-lined check valve, and the contact position between the valve core and the valve body is also poorly sealed. In the case of pressure difference, the seal will not be tight.