Analysis And Judgment Of Leakage Causes Of Water Pump Mechanical Seal
1. Leakage during installation and static test. After the mechanical seal is installed and debugged, a static test is generally carried out to observe the leakage amount. If the leakage amount is small, there are mostly problems with the moving ring or static ring sealing ring; When the leakage is large, it indicates that there is a problem between the friction pairs of the moving and static rings. On the basis of preliminary observation of the leakage amount and judgment of the leakage part, and then manually rotated to observe, if the leakage amount does not change significantly, there is a problem with the static and moving ring sealing ring; If the leakage amount changes significantly during turning, it can be concluded that there is a problem with the friction pair of the dynamic and static rings; If the leakage medium is sprayed along the axial direction, there are many problems with the moving ring sealing ring, the leakage medium is sprayed around or leaked out of the water cooling hole, then most of the static ring sealing ring failure, in addition, the leakage channel can also exist at the same time, but generally there is a primary and secondary difference, as long as the observation is meticulous, familiar with the structure, must be able to judge correctly.
2. Leakage during test operation. After the static test of the mechanical seal for the pump, the centrifugal force generated by high-speed rotation during operation will suppress the leakage of the medium. Therefore, the leakage of the mechanical seal during the test operation is basically caused by the failure of the friction pair of the dynamic and static rings after the failure of the seal between the shafts and the end cover. The main factors that cause the failure of the friction pair seal are:
(l) During operation, due to abnormal phenomena such as evacuation, cavitation, and pressure holding, large axial forces are caused, and the contact surfaces of the dynamic and static rings are separated;
(2) The compression of the mechanical seal during installation is too large, resulting in serious wear and abrasion of 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 static ring sealing ring is too loose, and when the moving ring floats axially, the static ring is separated from the static ring seat;
(5) There is granular matter in the working medium, and the friction pair is entered during operation, and the end face of the flaw detection and static ring is sealed;
(6) The design selection is wrong, the specific pressure of the sealing end face is low or the cold shrinkage of the sealing material is large. The above phenomenon often occurs in trial operation, and can sometimes be eliminated by properly adjusting the static ring seat, etc., but most of them need to be reassembled and replaced with seals.
3. Sudden leakage during normal operation. A small number of sudden leakage of centrifugal pumps during operation is due to normal wear or service life, while most of them are caused by large changes in working conditions or improper operation and maintenance.
(1) Evacuation, cavitation or long-term pressure holding, resulting in seal damage;
(2) The actual output of the pump is too small, a large number of media pump internal circulation, heat accumulation, causing medium vaporization, resulting in seal failure;
(3) The return flow is large, resulting in the sediment at the bottom of the container (tower, kettle, tank, pool) on the side of the suction pipe, and the seal is damaged;
(4) For a long time of downtime, there is no manual turning when restarting the car, and the friction pair tears the sealing surface due to adhesion;
(5) The corrosive, polymeric and gumming substances in the medium increase;
(6) Rapid changes in ambient temperature;
(7) Frequent changes or adjustments in working conditions;
(8) Sudden power failure or fault shutdown, etc. Sudden leakage of centrifugal pump in normal operation, if not detected in time, will often cause large accidents or losses, must be paid attention to and take effective measures.
