Core tips: there are various types of mechanical seals for pumps, but the leakage points mainly have five: (l) the seal between the shaft sleeve and the shaft; (2) the seal between the moving ring and the shaft sleeve; (3) the seal between the moving and static rings; (4) the seal between the static ring and the static ring; (5) the seal between the sealing end cover and the pump body.

　　Generally speaking, the leakage between the shaft and the sealing end cover and the pump body is easier to find and solve, but it needs careful observation, especially when the working medium is liquefied gas or high pressure, toxic and harmful gas, it is relatively difficult. The rest of the leakage is intuitively difficult to distinguish and judge, but only on the basis of long-term management and maintenance practice, the leakage symptoms of observation, analysis, analysis, in order to draw a correct conclusion.

　　1.Leak during installation and static test. After the mechanical seal is installed and adjusted, the static test should be carried out to observe the leakage.If the leakage is small, most of the moving ring or static ring sealing ring problems;When the leakage amount is large, it indicates that there is a problem between the dynamic and static ring friction pairs.On the basis of observing the leakage amount and judging the leakage site, if the leakage amount does not significantly change, the static and moving ring sealing ring has problems; if the leakage volume has changed significantly during the rolling, it can be concluded that the dynamic and static ring friction secondary problems; if the leakage medium along the axial injection, the moving ring sealing ring problems, the leakage medium to all around or leakage from the water cooling hole, then the static ring sealing ring failure. In addition, the leakage channel can also exist at the same time, but generally there are the primary and secondary differences, as long as the observation is careful, familiar with the structure, must be able to correctly judge.

　　2.Leak occurring during mechanical pump commissioning. After the mechanical seal of the pump passes through static test, the centrifugal force generated by high-speed rotation during operation will inhibit the leakage of medium.Therefore, the mechanical seal leakage during the test run is caused by the seal failure between the shaft and the end cover, which is basically caused by the dynamic and static ring friction auxiliary damage.(l) In the operation, due to abnormal phenomena such as evacuation, cavitation and pressure, a large axial force is caused, separating the contact surface of dynamic and static ring;(2) the compression amount is too large when installing the mechanical seal, resulting in serious wear and abrasion of the friction auxiliary end surface;(3) the moving ring sealing ring is too tight, the spring cannot adjust the axial floating amount of the moving ring; (4) the static ring sealing ring is too loose, when the moving ring axial floating, the static ring from the static ring seat;(5) there are granular substances in the working medium, the friction side enters the operation, the damage and static ring sealing end surface; (6) the design selection is wrong, the sealing end surface is lower than the pressure or the sealing material is large.The above phenomenon often appears in the test operation, and sometimes it can be eliminated by proper adjustment of the static ring seat, but most of them need to rebuild the disassembly and replace the mechanical seal.

　　3.The mechanical pump leaks suddenly during normal operation. The sudden leakage of centrifugal pump in operation is due to normal wear or has reached the service life, while most of them are caused by large changes in working conditions or improper operation and maintenance.(1) evacuation, cavitation or long time pressure, resulting in mechanical seal damage;(2) The actual output of the pump is small, a large number of medium circulation in the pump, heat accumulation, causing medium gasification, resulting to the failure of mechanical seal;(3) The return flow is large, resulting in the subsidence of the bottom of the suction tube side container (tower, kettle, tank and pool), and damaging the mechanical seal;(4) for long time shutdown, re-starting (5) more corrosive, polymerizing and gelating substances in the medium; (6) rapid change of environmental temperature; (7) frequent change or adjustment of working conditions; (8) sudden power failure or fault shutdown, etc.Centrifugal pump leakage in the normal operation of the sudden, if not found in time, often lead to greater accidents or losses, must be paid attention to and take effective measures.