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There are many types of mechanical seals for pumps with different models. But there are five main leak points: (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 stationary rings, (4) The seal between the stationary ring and the stationary ring seat, (5) The seal between the sealing end cover and the pump body. Generally speaking, between the shaft where the shaft sleeve extends, the sealing end cover and Leakage between pump bodies is relatively easy to find and solve. However, careful observation is required. Especially when the working medium is liquefied gas or high-pressure, toxic and harmful gases, it is relatively difficult. The remaining leaks are difficult to identify and judge intuitively. Only by observing, analyzing, and judging the leakage symptoms based on long-term management and maintenance practices can we draw the correct conclusion. kmIP {? i+ 1. Analysis and judgment of leakage causes?pz 1. Leakage during installation and static test. After the mechanical seal is installed and debugged, it is generally necessary to conduct a static test and observe the leakage amount. If the leakage amount is small, there is usually a problem with the moving or static ring seal. If the leakage amount is large, it indicates that there is a problem between the dynamic and stationary ring friction pairs. Based on the preliminary observation of the leakage amount and the judgment of the leakage location, manually turn the machine to observe. If the leakage amount does not change significantly, there is a problem with the static and moving ring seals. , if the leakage 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 leaking medium is sprayed along the axial direction, the problem is mostly with the dynamic ring sealing ring. The leaking medium is sprayed around or leaks from the water cooling hole. This is mostly due to the failure of the static ring sealing ring. In addition, leakage channels can also exist at the same time. But there is generally a primary and secondary distinction. As long as you observe carefully and are familiar with the structure, you will be able to make a correct judgment. #yp$q gM_ 2． Leakage that occurs during trial operation. After the mechanical seal of the pump has been statically tested, the centrifugal force generated by high-speed rotation during operation will inhibit the leakage of the medium. Therefore, the mechanical seal leakage during trial operation is basically due to the dynamic and static ring friction pairs after excluding the failure of the shaft and end cover seals. Caused by damage. The main factors causing the failure of the friction pair seal are: (l) During operation, due to abnormal phenomena such as evacuation, cavitation, and pressure suppression, a large axial force is caused, which separates the contact surfaces of the dynamic and stationary rings. (The amount of compression is too large when installing the mechanical seal, causing the end face of the friction pair to be severely damaged. Heavy wear and scratches, (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 floats axially, the static ring separates from the static ring seat, (5) there are granular substances in the working medium. The friction pair is inserted during operation. Flaw detection Dynamic and static ring sealing end faces, (6) wrong design and selection. The specific pressure of the sealing end face is low or the sealing material has large cold shrinkage, etc. The above phenomenon often occurs during trial operation. Sometimes it can be eliminated by appropriately adjusting the static ring seat, etc. But most of them need to be disassembled and replaced. ~_ * `_\ 3． Sudden leakage during normal operation. A small number of centrifugal pumps suddenly leak during operation due to normal wear or reaching the end of their service life. Most of them are caused by large changes in working conditions or improper operation and maintenance. (1) Evacuation, cavitation or long-term hold-up pressure. Leading to seal damage, (2) the actual output of the pump is too small. A large amount of medium circulates in the pump, causing heat accumulation, causing the medium to vaporize, leading to seal failure, (3) the return flow is too large, causing the bottom of the container (tower, kettle, tank, pool) on the side of the suction pipe. The sediment appears and the seal is damaged. (4) For a long period of shutdown, there is no manual cranking when restarting. The friction pair tears the sealing surface due to adhesion. (5) There is an increase in corrosive, polymeric and gelling substances in the medium. (6) The ambient temperature rises sharply. Changes, (7) frequent changes or adjustments in working conditions, (8) sudden power outages or shutdowns, etc. The centrifugal pump suddenly leaks during normal operation. If it cannot be discovered in time, it will often lead to major accidents or losses. Attention must be paid to it and effective measures must be taken. l9 ?U fH 3 2. Several misunderstandings in the maintenance of pump mechanical seals L y{nL2O 1. The greater the spring compression, the better the sealing effect. In fact, this is not the case. Excessive spring compression can lead to rapid wear and tear of the friction pair. Instantaneous burning, excessive compression makes the spring lose the ability to adjust the end face of the moving ring, leading to sealing failure. pRJ"; E 2. The tighter the dynamic ring sealing ring, the better. In fact, too tight the dynamic ring sealing ring is harmful and useless. First, it increases the wear between the sealing ring and the sleeve and causes premature leakage. Secondly, it increases the resistance of the axial adjustment and movement of the moving ring. It cannot be adjusted in time when the working conditions change frequently. Thirdly, the spring is easily damaged due to excessive fatigue. Fourthly, it deforms the dynamic ring sealing ring and affects the sealing effect. s_FqA6 1 3. The tighter the static ring seal, the better. The static ring seal is basically in a static state. A relatively tight sealing effect will be better. But too tight is also harmful. First, it will cause excessive deformation of the static ring seal, which affects the sealing effect. Second, the static ring material is mostly graphite. It is generally brittle. Excessive force can easily cause fragmentation. Third, it is difficult to install and disassemble. It is easy to damage the static ring.|K3] &i; 4． The tighter the impeller lock nut, the better. Leakage between the shaft sleeve and the shaft (inter-shaft leakage) is relatively common in mechanical seal leakage. It is generally believed that inter-shaft leakage means that the impeller lock nut is not locked. In fact, there are many factors leading to inter-shaft leakage, such as failure of the inter-shaft pad, offset, impurities in the shaft, and large shape and position errors at the fit between the shaft and the shaft sleeve. Damage to the contact surface, gaps between components on the shaft, excessive thread length of the shaft head, etc. will lead to leakage between shafts. Excessive locking of the lock nut will only lead to premature failure of the inter-shaft pad. On the contrary, lock the lock nut appropriately so that the inter-shaft pad always maintains a certain compression elasticity. During operation, the lock nut will automatically lock in time to ensure that the shaft is always in a good sealing state. e: gu5 ?0 5． The new one is better than the old one. Relatively speaking, the effect of using a new mechanical seal is better than the old one. However, when the quality or material selection of the new mechanical seal is not appropriate, a large error in the matching size will affect the sealing effect. In polymeric and permeable media, if the static ring is not excessively worn, it is better not to replace it. Because the static ring is in a static state for a long time in the static ring seat, the polymer and impurities are deposited as one, which plays a better sealing role. 6. It is better to dismantle and repair than not dismantle. Once a mechanical seal leaks, you will be eager to dismantle and repair it. In fact, sometimes the seal is not damaged. Just adjust the working conditions or adjust the seal appropriately to eliminate the leakage. This can avoid waste and verify your fault judgment ability. Accumulate maintenance experience to improve the quality of maintenance.