The check valve’s common malfunction:①The disc-break；②The medium-backflow 

1.The reason of the disc-break: The medium pressure before and after the check valve approaches to equilibrium phase ,also "see-saw" to each other. The disc flaps frequently with the seat and it will be broken if the disc is of some brittle material such as cast iron,brass and so on. The precaution is to adopt  the  check valve whose disc is of the ductile material.

2.The reason of the medium-backflow:① the sealing surface’s damage;②adulterated with the impurities.

Repairing the sealing surface and getting rid of the impurities can prevent the back-flow.

The principle of the check valve:It relies on the flowing of the medium itself to automatically open and close the disc. It is used to prevent the  medium-backflow, also called cut-off valve、one-way valve and back pressure valve.

Its function is to allow the medium to flow in one direction and to prevent it from flowing in the opposite direction. Usually this valve works automatically. The disc opens under the fluid pressure in one direction; when the fluid flows in the opposite direction, the disc functions on the seat and cut the flow.