Reason：
1. Sealing surface grinding uneven, can not form a close line.
2. The stem and the closure of the connection between the top of the heart is left hanging, not right or wear.
3. Stem bending or assembly is not, so that the closure of a skew or not.
4. Sealing surface material quality selection is improper or not according to the working conditions of the selection valve.
Maintenance method:
1. According to the conditions of the correct choice of materials and types of British gasket.
2. Carefully adjusted, smooth operation.
3. Should be uniform and symmetrical twist bolt, if necessary, should use a torque wrench, preload should meet the requirements, can not be too large or small. Flange and threaded joints should be a certain degree of pre - tight clearance.
4. Gasket assembly should be on the right, the force is uniform, the gasket is not allowed to lap and use a double gasket.
5. Static sealing surface corrosion, damage to the processing, processing quality is not high, should be repaired, grinding, coloring inspection, so that the sealing surface to meet the relevant requirements.
6. The installation should pay attention to clean the gasket, the sealing surface of the application of kerosene, the gasket should not be born.
