Judge the good and bad check valve can be considered from the following aspects:

First, the sealing performance: check valve should have good sealing performance to prevent the medium back-flow. You can judge the sealing performance by observing whether there is water leakage after the valve is closed.

Second, the circulation capacity: a good check valve should have a large circulation capacity, can minimize flow resistance, reduce pressure loss. Can be measured by measuring the pressure drop when flowing through the valve to determine the flow capacity.

Third, corrosion resistance: a good check valve should have good corrosion resistance, can be in a variety of media under long-term stable operation. You can refer to the corrosion resistance of the valve material to judge.

Fourth, service life: a good check valve should have a long service life, to maintain good performance. You can refer to the durability of the valve material, the reliability of the structural design to judge the service life.

Fifth, ease of operation: a good check valve should be easy to operate, can easily close or open the valve. You can judge the ease of operation by operating the valve.

In summary, to judge the good or bad check valve need to consider the above aspects and assess them according to the specific circumstances. At the same time, you can refer to the relevant industry standards and product quality certification to choose the right check valve.