Cause analysis and judgement of leakage of mechanical seal for pumps

　　Cause analysis and judgement of leakage of mechanical seal for pumps

1. Leak during installation of static test. After the installation and commissioning of mechanical seals, it is necessary to carry out static tests and observe the leakage. If the leakage is small, it is mostly the problem of the moving ring or the static ring seal; if the leakage is large, it indicates that there are problems between the dynamic and static ring friction pairs. On the basis of preliminary observation of leakage volume and judgment of leakage position, manual observation by turning on the car shows that if there is no obvious change in leakage volume, the static and dynamic ring sealing rings are problematic; if the leakage volume has obvious change during turning on the car, it can be concluded that there are problems in the friction pairs of the dynamic and static rings; if the leakage medium is injected along the axial direction, the dynamic ring sealing rings are problematic. Most of the leakage media leak to the surrounding area or leakage from the water cooling hole, mostly static ring seal failure. In addition, the leakage channel can also exist at the same time, but generally there are primary and secondary differences, as long as careful observation, familiar with the structure, will be able to correctly judge.

　　2. Leakage during commissioning. The centrifugal force produced by the high speed rotation of the mechanical seal used in the pump after static test will restrain the leakage of the medium. Therefore, the mechanical seal leakage in the trial run is basically caused by the damage of the dynamic and static ring friction pairs after eliminating the failure of shaft and end cover seals.  The main factors that cause the failure of friction pairs are:

　　(L) In operation, abnormal phenomena such as evacuation, cavitation and compression lead to large axial force, which separates the dynamic and static contact surfaces.

　　(2) when the mechanical seal is installed, the amount of compression is too large, resulting in serious wear and abrasion of the friction pairs.

　　(3) the dynamic ring seal ring is too tight, and the spring can not adjust the axial floating volume of the moving ring.

　　(4) the static ring seal is too loose. When the moving ring is floating in an axial direction, the static ring is separated from the static ring seat.

　　(5) There are granular substances in the working medium, which are fed into the friction pairs during operation, and the sealing faces of the dynamic and static rings are detected.

　　(6) incorrect design and selection, low sealing surface pressure or large cold shrinkage of sealing material. These phenomena often occur in the trial run, and can be eliminated by adjusting the static ring seat, 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 due to normal wear and tear or has reached the service life, and most of them are due to large changes in operating conditions or improper operation and maintenance.

　　(1) evacuation, cavitation or prolonged holding up, resulting in sealing failure.

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

　　(3) The excessive return flow causes the bottom of the suction pipe side container (tower, kettle, tank, pool) to be flooded with sediment and damages the seal;

　　(4) For long-term outage, there is no manual disc when restarting, and the friction pair will tear the sealing surface because of adhesion.

　　(5) corrosive, polymerizable and colloidal substances increased in the medium.

　　(6) the abrupt change of ambient temperature.

　　(7) frequent changes or adjustments in working conditions;

　　(8) sudden power failure or downtime. Centrifugal pump in the normal operation of sudden leakage, if not found in time, often lead to greater accidents or losses, we must pay attention to and take effective measures.