Severe leakage in the mechanical seal

There are a wide variety of mechanical seals used in pumps, with different models available, but there are mainly five potential leakage points: (l) the seal between the shaft sleeve and the shaft； 　　(2) Sealing between the rotating ring and the shaft sleeve ； 　　(3) Sealing between the rotating and stationary rings ； 　　(4) Sealing between the stationary ring and the stationary ring seat ； 　　(5) Sealing between the seal end cover and the pump body. 　　Generally, leaks between the shafts where the shaft sleeves protrude, as well as between the sealing end caps and the pump body, are relatively easy to detect and resolve; however, careful observation is required, especially when the working medium is a liquefied gas or a high-pressure, toxic, or harmful gas, in which case it becomes more difficult. The remaining leaks are difficult to identify and assess intuitively; it is necessary to observe, analyze, and evaluate the symptoms of these leaks based on long-term management and maintenance practices in order to arrive at correct conclusions. 　　I. Analysis and determination of the cause of leakage 　　1. Leakage during static installation testing. After the mechanical seal is installed and adjusted, a static test is generally carried out to observe the leakage rate. If the leakage amount is small, it is usually due to a problem with the seal ring of the rotating ring or the stationary ring ； A large leakage amount indicates a problem in the friction pair between the rotating and stationary rings. Based on the initial assessment of the leakage amount and identification of the leakage location, manual rotation of the shaft is carried out for further inspection; if there is no significant change in the leakage amount, then there is a problem with the static or dynamic ring seals ； If there is a significant change in the leakage amount during cranking, it can be concluded that there is a problem with the friction pair between the rotating and stationary rings ； If the leaking medium sprays axially, there are usually problems with the rotating ring seal; if the leaking medium sprays in all directions or leaks out through the water cooling holes, it is often due to a failure of the stationary ring seal. Furthermore, leakage channels can also exist simultaneously, but there is usually a primary and secondary distinction; with careful observation and familiarity with the structure, it is definitely possible to make the correct judgment. 　　2. Leaks that occur during trial operation. After a static test, the mechanical seal used in pumps prevents leakage of the medium due to the centrifugal force generated by high-speed rotation during operation. Therefore, during commissioning, mechanical seal leakage, after ruling out failures in the shaft-to-shaft and end-cover seals, is basically caused by damage to the friction pair of the rotating and stationary rings. The main factors that cause seal failure in friction pairs are: (l) During operation, abnormal conditions such as evacuation, cavitation, and pressure buildup generate significant axial forces, leading to the separation of the contact surfaces between the moving and stationary rings ； 　　(2) Excessive compression during the installation of the mechanical seal leads to severe wear and scarring of the end faces of the friction pairs ； 　　(3) The rotating ring seal is too tight, preventing the spring from adjusting the axial movement of the rotating ring ； 　　(4) The seal ring of the stationary ring is too loose; when the moving ring moves axially, the stationary ring comes loose from its seat ； 　　(5) There are particulate substances in the working medium, which enter the friction pair during operation, affecting the sealing surfaces of the moving and stationary rings used for flaw detection ； 　　(6) Incorrect design selection, too low specific pressure at the sealing surface, or high cold shrinkage of the sealing material, etc. The above phenomenon occurs frequently during trial operation; sometimes it can be eliminated by making appropriate adjustments to the stationary ring seat, but in most cases it is necessary to disassemble and reassemble the components and replace the seals. 　　3. Sudden leakage during normal operation. Sudden leakage from a centrifugal pump during operation is caused in a few cases by normal wear or reaching the end of its service life, while in most cases it is due to significant changes in operating conditions or improper operation and maintenance. 　　(1) Vacuum, cavitation, or prolonged pressure retention leading to seal failure ； 　　(2) The actual output volume of the pump is too low; a large amount of fluid circulates within the pump, heat accumulates, causing the fluid to vaporize and leading to seal failure ； 　　(3) Excessive backflow causes the sediment at the bottom of the container on the suction pipe side (tower, reactor, tank, pool) to be disturbed, damaging the seal ；

Thank you to the expert upstairs for their answer! ! ! The mechanical seal of the acetal centrifugal pump that I repaired does not leak during testing, but it leaks heavily when the pump is operating normally. It worked fine for several months prior; could it be a quality issue with these mechanical seals?

It is a British AES mechanical seal manufacturer – the fourth largest seal producer in the world, and highly reliable! ! ! 151861804

OP, what brand of mechanical seal are you using? That’s very important.

Contact the machine seal manufacturer to resolve the issue on-site