Analysis and Judgment of Leakage Cause of Mechanical Seal

1. Leakage during static test. After the mechanical seal is installed and debugged, the static test should be carried out to observe the leakage. If the leakage is small, it is mostly the problem of the dynamic ring or the static ring seal ring; if the leakage is large, it indicates that there is a problem between the friction pairs of the dynamic ring and the static ring. On the basis of preliminary observation of the leakage and judgment of the leakage position, the manual turning observation is carried out. If there is no obvious change in the leakage amount, there is a problem with the static and dynamic ring sealing rings; if there is a significant change in the leakage amount during turning, it can be concluded that there is a problem with the friction pairs of the dynamic and static rings; if the leakage medium is sprayed along the axis, there are many problems with the dynamic ring sealing ring, and the leakage medium is sprayed around or cooled by water. In addition, the leakage channel can also exist at the same time, but generally there are primary and secondary differences. As long as the observation is careful and familiar with the structure, it can be correctly judged.

2. Leakage during commissioning. After static test, centrifugal force produced by high-speed rotation of pump mechanical seal will restrain the leakage of medium. Therefore, the leakage of mechanical seal during test run is basically caused by the damage of friction pairs of dynamic and static rings after eliminating the failure of seal between shafts and end covers. The main factors that cause the failure of the friction pair seal are:

(1) During the operation, the large axial force caused by the abnormal phenomena such as suction, cavitation and pressure holding cause the separation of the contact surfaces of the dynamic and static rings;

(2) The excessive compression of the mechanical seal during the installation causes the severe wear and abrasion of the end surface of the friction pair;

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

(4) The static ring seal ring is too loose, when the dynamic ring is floating axially, the static ring is separated from the static ring seat;

(5) There is granular substance in the working medium, it enters the friction pair and detect the sealing end faces of the dynamic and static rings during operation;

(6) The design and selection are wrong, the specific pressure of the seal face is low or the seal material has a large shrinkage. The above phenomenon often occurs in the test run, sometimes it can be eliminated by properly adjusting the static ring seat and so on, but most of them need to be disassembled and replaced.

3. Sudden leakage during normal operation. The sudden leakage of centrifugal pump in operation is caused by normal wear or reached service life in a few cases, most of them are caused by large change of working conditions or improper operation and maintenance.

(1) Vacuuming, cavitation or holding pressure for a long time, resulting in seal damage;

(2) The actual output of the pump is too small, a large number of media pump internal circulation, heat accumulation, resulting in medium gasification, leading to seal failure;

(3) The return flow is too large, resulting in sediment at the bottom of suction side container (tower, kettle, tank, pool) overflowing, which causes seal damage

(4) For long-term shutdown, there is no manual barring during restart, and the friction pair damages the sealing surface due to adhesion;  

(5) The corrosive, polymerizable and gelling substances in the medium increase;

(6) The environment temperature changes rapidly;

(7) The working condition changes or adjusts frequently;

(8) Sudden power failure or fault shutdown and so on. Sudden leakage of centrifugal pump in normal operation, if it can not be found in time, it will often lead to major accidents or losses, we must pay attention to it and take effective measures.