Analysis on the Leakage Point of the Mechanical Seal of the Submerged Slurry Pump

2022-01-07

Analysis and judgment of the cause of leakage

1. Leakage during installation static test. After the mechanical seal is installed and debugged, a static test is generally performed to observe the leakage. If the amount of leakage is small, there is usually a problem with the moving or static ring seals; when the amount of leakage is large, it indicates that there is a problem between the moving and static ring friction pairs. On the basis of preliminary observation of the leakage and judgment of the leakage location, the manual cranking observation is performed. If there is no obvious change in the leakage, the static and moving ring seals are faulty; if the leakage changes significantly during cranking, it can be concluded that it is a moving, There are problems with the static ring friction pair; if the leakage medium is sprayed along the axial direction, there are mostly problems with the moving ring sealing ring. If the leakage medium is sprayed around or leaks from the water cooling hole, the static ring sealing ring is mostly ineffective. In addition, leakage channels can also exist at the same time, but there are generally primary and secondary differences. As long as you observe carefully and are familiar with the structure, you will be able to make a correct judgment.

2. Leakage during trial operation. After the mechanical seal for the pump undergoes a static test, the centrifugal force generated by the high-speed rotation during operation will inhibit the leakage of the medium. Therefore, the leakage of the mechanical seal during the trial operation is basically due to the damage of the dynamic and static ring friction pairs after the failure of the shaft and the end cover seal is eliminated. The main factors that cause the failure of the friction pair seal are:
(L) During operation, due to abnormal phenomena such as evacuation, cavitation, pressure holding, etc., a large axial force is caused to separate the contact surfaces of the moving and static rings;
(2) The compression is too large when installing the mechanical seal, causing serious wear and scratches on the end face of the friction pair;
(3) The sealing ring of the moving ring is too tight, and the spring cannot adjust the axial floating amount of the moving ring;
(4) The sealing ring of the static ring is too loose. When the moving ring is floating in the axial direction, the static ring is separated from the static ring seat;
(5) There are granular materials in the working medium, and the friction pair is entered during operation to detect the dynamic and static ring sealing end faces;
(6) The design and selection are wrong, the seal end face pressure is low or the seal material has a large cold shrinkage, etc. The above phenomenon often occurs during trial operation, and sometimes it can be eliminated by appropriately adjusting the static ring seat, etc., but most of them need to be disassembled and replaced, and the seal is replaced.

3. Sudden leakage during normal operation. A few of the sudden leakages of centrifugal pumps during operation are due to normal wear or have reached the service life, and most of them are caused by large changes in working conditions or improper operation or maintenance.
(1) Evacuation, cavitation or holding pressure for a long time, resulting in damage to the seal;
(2) The actual output of the pump is too small, a large amount of media circulates in the pump, and heat accumulates, which causes the media to vaporize and cause the seal to fail;
(3) The recirculation flow is too large, causing the sediment on the bottom of the suction pipe side container (tower, kettle, tank, pool) to appear and damage the seal;
(4) For a long period of shutdown, there is no manual cranking when restarting, and the friction pair will tear the sealing surface due to adhesion;
(5) The corrosive, polymerizable, and gelling substances in the medium increase;
(6) The ambient temperature changes sharply;
(7) Frequent changes or adjustments in working conditions;
(8) Sudden power failure or shutdown due to failure, etc. If the centrifugal pump leaks suddenly during normal operation, if it cannot be found in time, it will often lead to larger accidents or losses, which must be paid attention to and effective measures must be taken.