Analysis And Judgment of The Leakage Cause of Mechanical Seal for Pump

1. Leakage during installation static test. After the mechanical seal is installed and debugged, it is generally necessary to conduct a static test to observe the leakage. If the leakage is small, it is mostly due to problems with the dynamic ring or static ring seal; if the leakage is large, it indicates that there is a problem between the dynamic and static ring friction pairs. After initially observing the leakage and determining the leakage location, manually turn the machine to observe. If the leakage does not change significantly, there is a problem with the static and dynamic ring seals; if the leakage changes significantly during turning, it can be determined that there is a problem with the dynamic and static ring friction pairs; if the leakage medium sprays along the axial direction, the dynamic ring seal is mostly a problem; if the leakage medium sprays around or leaks from the water cooling hole, it is mostly due to the failure of the static ring seal. In addition, leakage channels can also exist at the same time, but generally there is a primary and secondary difference. As long as you observe carefully and are familiar with the structure, you can make a correct judgment [2].

2. Leakage during test operation. After the pump mechanical seal has been static tested, the centrifugal force generated by the high-speed rotation during operation will inhibit the leakage of the medium. Therefore, after eliminating the failure of the shaft and end cover seals, mechanical seal leakage during trial operation is basically caused by the damage of the dynamic and static ring friction pairs. The main factors causing the failure of the friction pair seal are:

(1) During operation, due to abnormal phenomena such as vacuuming, cavitation, and pressure holding, a large axial force is caused, causing the dynamic and static ring contact surfaces to separate;

(2) The mechanical seal is compressed too much during installation, resulting in serious wear and scratches on the friction pair end faces;

(3) The dynamic ring seal is too tight, and the spring cannot adjust the axial floating amount of the dynamic ring;

(4) The static ring seal is too loose, and when the dynamic ring floats axially, the static ring separates from the static ring seat;

(5) There are granular substances in the working medium, which enter the friction pair during operation, and the dynamic and static ring seal end faces are inspected;

(6) The design selection is incorrect, 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 properly adjusting the static ring seat, etc., but most of them need to be disassembled and replaced.

3. Sudden leakage during normal operation. Sudden leakage of centrifugal pumps during operation is rarely caused by normal wear or reaching the end of service life, but most of them are caused by large changes in working conditions or improper operation and maintenance.

(1) Vacuuming, cavitation or long-term pressure holding, resulting in seal damage;

(2) The actual output of the pump is too small, a large amount of medium circulates in the pump, heat accumulates, causing the medium to vaporize, resulting in seal failure;

(3) The reflux volume is too large, causing the sediment at the bottom of the container (tower, kettle, tank, pool) on the suction side to rise and damage the seal;

(4) When the pump is stopped for a long time, there is no manual cranking when restarting, and the friction pair is torn due to adhesion and the sealing surface is damaged;

(5) The amount of corrosive, polymerizing and gelling substances in the medium increases;

(6) The ambient temperature changes sharply;

(7) Frequent changes or adjustments in working conditions;

(8) Sudden power outage or fault shutdown, etc. If a centrifugal pump suddenly leaks during normal operation, if it is not discovered in time, it will often lead to major accidents or losses. It must be taken seriously and effective measures must be taken.