1. Improper assembly of mechanical seal

When replacing the mechanical seal at the non power end, it was found that the O-ring on the moving ring was not installed properly. The O-ring should have been installed in the seal groove on the moving ring seat. However, the disassembly inspection found that the O-ring was not installed in this way, but was wrongly installed in the spring positioning piece, resulting in the deformation of the spring, completely unable to play the role of axial static sealing, resulting in leakage.

2. Excessive pressure of cooling water for mechanical seal

The adhesion force of the sealing surface of the dynamic and static ring of the mechanical seal is exerted by the spring on the moving ring. When the cooling water pressure is too high, the water pressure will act on the dynamic and static rings. Since the static rings are fixed, the water pressure will push the moving rings and compress the springs in the opposite direction of the static rings, thus weakening or counteracting the adhesion force between the static and dynamic ring surfaces, resulting in the leakage of the sealing surfaces. After maintenance, feed cooling water into the mechanical seal at the power end for leakage test. If the inlet valve is opened below 2 / 3, the mechanical seal is in good condition without leakage. When the water valve is opened more than 2 / 3, the mechanical seal leaks. According to the preliminary judgment, it is caused by excessive water pressure. It is suggested that the motor should be started up for operation after the maintenance of the motor, and the real cause of the leakage should be further tracked and found out.

3. The sealing surface of the moving and stationary ring is broken

This is the main reason for the leakage of mechanical seal in the previous replacement of the pump. The mechanical seals of power end and non power end are assembled on the same shaft, the impeller is installed in the middle of the shaft, and the two ends of the shaft are installed with bearings to support and fix. When the mechanical seal of power end or non power end is replaced separately, the bearing (bearing pedestal) of corresponding end must be disassembled before taking out the old mechanical seal and installing the new mechanical seal. At this time, due to the gravity of shaft and impeller, the impeller and shaft losing bearing support at one end must collapse down and the shaft inclines to the bearingless end. Since the stationary ring at the end of the pump is fixed on the pump end cover with bolts, while the moving ring is fixed on the shaft and rotates with the shaft. In addition, due to the small fit clearance between the inner ring of the static ring and the shaft, when the shaft collapses and inclines, the following results will be caused:

a. The relative displacement of the moving and stationary rings at the UN removed end makes the sealing surfaces of the dynamic and static rings squeeze each other illegally, causing fragmentation;

b. The shaft is directly pressed on the inner ring of the stationary ring at the UN disassembled end, resulting in fracture or breakage of the sealing surface of the stationary ring.