Maintenance of mechanical seals for pumps
There are many types of mechanical seals for maintenance pumps with mechanical seals, with different models, but there are mainly five leakage points: (l) the seal between the shaft sleeve and the shaft; (2) the seal between the moving ring and the shaft sleeve; (3) the dynamic , The seal between the static ring; (4) The seal between the static ring and the static ring seat; (5) The seal between the sealing end cover and the pump body. Generally speaking, it is easier to find and solve the leakage between the shaft sleeve, the sealing end cover and the pump body, but it needs careful observation, especially when the working medium is liquefied gas or high pressure, toxic and harmful gas, it is relatively difficult some. The rest of the leakage is difficult to distinguish and judge intuitively. It is necessary to observe, analyze, and study the leakage symptoms on the basis of long-term management and maintenance practices in order to draw a correct conclusion.
1. Analysis and Judgment of the Causes of Leakage
1. Leakage during installation static test. After the mechanical seal is installed and debugged, a static test is generally performed to observe the leakage. If the amount of leakage is small, it is mostly a problem with the moving or static ring seals; when the amount of leakage is large, it indicates that there is a problem between the moving and static ring friction pairs. On the basis of preliminary observation of the leakage and judgment of the leakage location, the manual cranking observation is performed. If there is no obvious change in the leakage, the static and moving ring seals are defective; if the leakage changes significantly during cranking, it can be concluded that the leakage is moving or moving. The static ring friction pair has problems; if the leaking medium is sprayed along the axial direction, there are mostly problems with the moving ring seal. If the leaking medium is sprayed around or leaks from the water cooling hole, the static ring seal is mostly ineffective. In addition, leakage channels can also exist at the same time, but generally there is a primary and secondary difference. As long as you observe carefully and are familiar with the structure, you will be able to make a correct judgment.
2. Leakage during trial operation. After the mechanical seal for the pump has undergone static testing, the centrifugal force generated by the high-speed rotation during operation will inhibit the leakage of the medium. Therefore, the mechanical seal leakage during trial operation is basically caused by the damage of the dynamic and static ring friction pairs after the failure of the shaft and the end cover seal is eliminated. The main factors that cause the failure of the friction pair seal are: (l) During operation, due to abnormal phenomena such as evacuation, cavitation, pressure holding, etc., a large axial force is caused to separate the contact surfaces of the dynamic and static rings; (for the installation of mechanical seals) When the compression is too large, the end face of the friction pair will be severely worn and scratched; (3) The moving ring sealing 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, when the moving ring When axially floating, the static ring separates from the static ring seat; (5) There are granular materials in the working medium, and the friction pair is entered during operation, and the sealing end faces of the moving and static ring are detected; (6) The design selection is wrong, and the sealing end face ratio Low pressure or large shrinkage of the sealing material, etc. The above phenomenon often occurs during trial operation, and sometimes it can be eliminated by appropriate adjustment of the static ring seat, but most of them need to be disassembled and replaced, and the seal is replaced.
3. Suddenly during normal operation Leakage. A few of the sudden leaks of centrifugal pumps during operation are due to normal wear or have reached the service life, and most of them are caused by large changes in working conditions or improper operation or maintenance. (1) Evacuation, cavitation or long-term hold-up (2) The actual output of the pump is too small, a large amount of medium circulates in the pump, and heat accumulates, causing the medium to vaporize, resulting in seal failure; (3) The return flow is too large, causing the suction pipe side container ( Towers, kettles, tanks, pools) bottom sediments appear, damage the seal; (4) For a long time out of service, there is no manual cranking when restarting, the friction pair will tear the sealing surface due to adhesion; (5) Corrosion in the medium (6) Sudden changes in ambient temperature; (7) Frequent changes or adjustments in working conditions; (8) Sudden power failure or shutdown, etc. The centrifugal pump leaks suddenly during normal operation. If it is discovered in time, it will often lead to larger accidents or losses, which must be paid attention to and effective measures must be taken.
Second, several misunderstandings in the maintenance of pump mechanical seals
1. The greater the spring compression, the better the sealing effect. In fact, it is not the case, the spring compression Excessive amount can cause the friction pair to wear out rapidly and burn instantly; excessive compression makes the spring lose its ability to adjust the end face of the moving ring, resulting in seal failure.
2. The tighter the moving ring seal, the better. In fact, if the moving ring seal is too tight, it is harmful and useless. One is to aggravate the wear between the sealing ring and the shaft sleeve, and to leak prematurely; the second is to increase the resistance of the axial adjustment and movement of the moving ring, which cannot be adjusted in time when the working conditions change frequently; the third is that the spring is easily damaged due to excessive fatigue; It deforms the moving ring sealing ring and affects the sealing effect.
3. The tighter the static ring seal, the better. The static ring seal is basically in a static state, and the sealing effect will be better if it is relatively tight, but too tight is also harmful. The first is that the static ring seal is excessively deformed, which affects the sealing effect; the second is that the static ring is mostly made of graphite, which is generally brittle, and excessive stress can easily cause fragmentation; the third is that it is difficult to install and disassemble, and it is easy to damage the static ring.
4. The tighter the impeller lock nut, the better. In the mechanical seal leakage, the leakage between the sleeve and the shaft (inter-shaft leakage) is relatively common. It is generally believed that the leakage between the shafts means that the impeller lock nut is not locked. In fact, there are many factors that cause the leakage between the shafts, such as the failure of the shaft pads, offsets, impurities in the shafts, and large shapes in the matching parts of the shafts and sleeves. Position errors, damage to the contact surface, gaps between parts on the shaft, and excessively long shaft head threads will cause leakage between the shafts. Over-locking the lock nut will only cause premature failure of the inter-axis pad. On the contrary, properly lock the lock nut so that the inter-axis pad always maintains a certain compression elasticity. During operation, the lock nut will be automatically locked in time to keep the shafts in good condition. The sealed state.
5. The new one is better than the old one. Relatively speaking, the effect of using the new mechanical seal is better than the old one, but the quality or material of the new mechanical seal is not properly selected, and the large size error of the fit will affect the sealing effect; in polymerizing and permeable media, the static ring is not excessive. Worn, it is better not to replace. Because the static ring stays in a static state for a long time in the static ring seat, the polymer and impurities are deposited as a whole, which has a better sealing effect.
6. It is better to dismantle and repair than not to dismantle. Once the mechanical seal leaks, it is eager to dismantle and repair. In fact, sometimes the seal is not damaged, and the leakage can be eliminated by adjusting the working conditions or properly adjusting the seal. This can not only avoid waste but also verify one’s own fault judgment ability, accumulate maintenance experience and improve the quality of maintenance.
Nanjing Yaqin Technology & Trade Co., Ltd. always believes and strives to make the products it sells the best, but the development of everything follows the laws of nature, even if we take good care of it. Therefore, we treat the imported water pumps we sell The products are all stocked with spare parts, so that users can be prepared and use high-quality imported water pumps with real peace of mind. Our spare parts are all vulnerable parts of the water pump and are imported with original packaging, such as mechanical seals, impellers, capacitors, pump casings, etc. The brands involved in spare parts include: calpeda, lowara, DAB, SIXteam, EBARA, NOCCHI, SAER, etc., especially the mechanical seals are imported from Europe and the United States, and are commonly used in foreign pumps, which have great versatility. Therefore, we Although only a few brands are listed, imported pump brands that are not listed can also be used. As long as you report the brand and model of the pump, the fluid mechanics engineers of our technical center can find out the model and size of the mechanical seal for you. Professional sales staff will quote you the best price based on this, and solve your urgent needs in the shortest time.
The company’s modern management of the following brand products:
American ITT-LOWARA commercial pump
Italy NOCCHI stainless steel pump
Italy SAER water pump
Italy CALPEDA clean water pump, hot oil pump
Italy DAB clean water pump, automatic pump
American ITT-GOULDS deep well pump
American ITT-ROBOT submersible sewage pump
Japan YAMADA Yamada pneumatic diaphragm pump
Italy ZILMET expansion tank, pressure tank
Italy CALEFFI thermal system valve
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