Repair of mechanical seals for pumps

There are many types of mechanical seals for pumps, each with different models, but there are five major leaks: (l) Sealing between shaft sleeves and shafts; (2) Sealing between moving rings and sleeves; (3) Sealing between moving and stationary rings (4) The seal between the stationary ring and the stationary ring seat; (5) The sealing between the sealed end cover and the pump body. Generally speaking, the leakage between the shaft sleeves and the sealed end caps and the pump body is easy to find and solve, but it requires careful observation, especially when the working medium is liquefied gas or high-pressure, toxic and harmful gases, it is relatively difficult some. The remaining leaks are intuitively difficult to distinguish and judge, and on the basis of long-term management and maintenance practices, leakage symptoms must be observed, analyzed, and judged in order to draw correct conclusions. First, the leakage analysis and judgment 1. Leak during installation test. After installation and debugging of mechanical seals, it is generally necessary to conduct a static test to observe the leakage. If the leakage is small, there are problems with the moving ring or the static ring seal ring; when the leakage amount is large, it indicates that there is a problem between the friction pair of the dynamic and static rings. After initially observing the leakage amount and judging the leakage location, observe the manual operation. If there is no significant change in the leakage amount, there will be problems with the static and dynamic ring seal rings; if the leakage amount of the disc brakes changes significantly, it can be concluded that There are problems with the static ring friction pair; if the leakage medium is ejected in the axial direction, there are many problems with the dynamic ring seal ring. If the leaking medium is injected around or leaks from the water cooling hole, the static seal ring is mostly ineffective. In addition, leakage channels can also exist at the same time, but there are generally differences between the primary and secondary, as long as the observation of detailed, familiar with the structure, we can certainly determine correctly. 2. Leakage during commissioning. After the mechanical seal of the pump is subjected to a static test, the centrifugal force generated by the high-speed rotation during operation will suppress the leakage of the medium. Therefore, the leakage of the mechanical seal during the trial operation after eliminating the shaft and the seal failure of the end cap is basically caused by the destruction of the friction and static pair of the dynamic and static rings. The main factors that cause the failure of the friction pair seal are: (1) During operation, due to vacancy, cavitation, and pressure anomalies, large axial forces are induced and the moving and stationary ring contact surfaces are separated; (2) Installation Excessive compression in mechanical seals causes severe wear and scratches on the frictional face; (3) The ring seal is too tight and the spring cannot adjust the axial float of the ring; (4) The ring seal is too loose. When the moving ring is axially floating, the stationary ring is detached from the stationary ring seat. (5) There is a granular substance in the working medium, and the friction pair in operation is in operation, and the flaw detection and static sealing end surface are sealed; (6) The design is incorrectly selected and sealed. The pressure of the end face is lower or the sealing material is more cold-shrinkable. The above phenomenon often occurs during the test operation, and sometimes it can be eliminated by appropriately adjusting the stationary ring seat, but most of them need to be disassembled and replaced. 3. Sudden leakage during normal operation. A sudden loss of a few centrifugal pumps during operation is due to normal wear or has reached the service life, and most of them are caused by large changes in operating conditions or due to improper operation or maintenance. (1) The evacuation, cavitation, or long-time rolling pressure leads to the destruction of the seal; (2) The actual output of the pump is too small, a large number of medium pumps circulate, heat builds up, and the medium gasifies, causing the seal to fail; (3) Return flow is too large, causing the bottom of the suction pipe side container (tower, kettle, tank, tank) to lift up and damage the seal; (4) For a long time outage, there is no manual turning when re-starting, friction due to adhesion And tear the sealing surface; (5) Corrosion of the medium, polymerization, gelling substances increased; (6) Rapid changes in ambient temperature; (7) Frequent changes or adjustments in operating conditions; (8) Sudden power failure or downtime . Centrifugal pump suddenly leaks during normal operation. If it cannot be discovered in time, it often leads to a larger accident or loss. Attention must be given and effective measures must be taken. Second, the pump mechanical seal overhaul several errors 1. The greater the amount of spring compression, the better the sealing effect. Actually, excessive spring compression can lead to rapid wear of the friction pair and instant burnout. Excessive compression causes the spring to lose its ability to adjust the end face of the moving ring, resulting in failure of the seal. 2. The tighter the dynamic ring seal, the better. In fact, the dynamic ring seal is too harmful and harmful. One is to intensify the wear between the seal ring and the sleeve and cause premature leakage; the other is to increase the axial adjustment of the moving ring and the resistance of the movement. When the operating conditions change frequently, it cannot be timely adjusted; third, the spring is fatigued and easily damaged; The deformation of the dynamic ring seal affects the sealing effect. 3. The tighter the ring seal, the better. The static ring seal is basically in a stationary state, and the relatively tight seal effect is better, but too tight is also harmful. The first is caused by excessive deformation of the static ring seal, affecting the sealing effect; Second, the static ring material is mostly graphite, generally more brittle, excessive stress can easily cause fragmentation; Third, installation, removal difficult, very easy to damage the static ring. 4. The tighter the impeller locks, the better. Leakage between shaft sleeves and shaft (leakage between shafts) is common in mechanical seal leakage. It is generally believed that the leakage between shafts means that the impeller lock is not locked. In fact, there are many factors that lead to leakage between shafts. For example, the inter-axis mat fails, the shaft is misaligned, and the shaft has impurities in the shaft. Bit error, failure of the contact surface, gaps between the parts on the shaft, and excessive shaft thread length can cause shaft to leak. Locking the female lock excessively will only lead to premature failure of the inter-shaft pad. On the contrary, it will lock the lock mother properly so that the inter-axial pad always maintains a certain compression elasticity. In operation, the female lock locks automatically and timely so that the shaft is always in good condition. The sealed state. 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, but the quality or material selection of the new mechanical seal is not appropriate, and the larger dimensional error will affect the sealing effect; in polymeric and permeable media, the static ring is not excessive. Worn, or not replaced as well. Because the stationary ring is in a stationary state for a long time in the stationary ring seat, the polymer and the impurities are deposited as a whole, which plays a good sealing role. 6. Renovation is better than not dismantling. Once the mechanical seal leaks, it will be eager to repair, in fact, sometimes the seal is not damaged, just adjust the working conditions or adjust the seal properly to eliminate the leak. This not only avoids waste but also verifies its own fault diagnosis capabilities, accumulates maintenance experience and improves the quality of inspections.