Mechanical seal
Thread Content
Our unit has a horizontal, single-stage, single-suction, cantilever-type centrifugal pump that is used for transporting diesel. When I turned on the power supply to the pump’s motor, oil suddenly burst out from the pump’s mechanical seal and sprayed upward; it sprayed for a moment before stopping. The pump is operating normally. What could be the cause of this?
In my opinion, the compression amount of the mechanical seal is too small, and the pump lacks thrust bearings or has excessive bearing clearance.
During startup, the pump generates an axial force, which causes a change in the compression amount of the mechanical seal and leads to leakage; once operation is normal, the axial force reaches equilibrium and the compression amount returns to its normal level.
It is caused by the too small compression amount of the pump’s mechanical seal and excessive axial movement； The tension of the spring can be adjusted, as well as the movement of the pump, in order to make adjustments
When the pump starts up, a large axial force is generated suddenly, which causes changes in the compression volume; this is mainly due to the misalignment of the rotating ring. Once the pump is running steadily, there is no problem anymore
High axial force at startup, biasing of the moving ring, temporary leakage
At startup, the axial force generated exceeds the design value, resulting in compressive injection. During use, it remains within the design parameters
At startup, the axial force generated exceeds the design value, resulting in compressive injection. As long as it ensures proper use, it is within the design parameters!
Reason: The compression amount of the mechanical seal is too small, and the axial positioning clearance of the bearing is too large. A centrifugal pump with a single stage, single suction, and cantilever design experiences an axial force directed toward the inlet during operation. At startup, the pressure is low and the compression amount is insufficient, so fuel is injected. After stable operation, the rotor moves axially, and the compression amount meets the requirements. So the pump is operating normally
There is another scenario: after the pump is repaired, the maintenance workers use too much cleaning agent when installing the mechanical seal, and this residue accumulates at the mechanical seal; as a result, spraying or smoking occurs right when the pump is started up. The axial play of the bearings in a centrifugal pump should not be too large; firstly, it affects the lifespan of the bearings, and secondly, it also impacts the lifespan of the mechanical seal, causing fatigue in the moving ring! It should be kept under twenty deniers.