Causes of leakage in mechanical seals of pump machinery

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The mechanical seal of pump machinery is an essential component in power and fluid machinery devices, and it plays a crucial role in ensuring the safety of such machinery. There are various reasons for leaks in the mechanical seals of pumps, such as issues with the seal flushing water, defects in the device itself, the corrosive effect of the filling medium on the device, and insufficient sealing performance. To address these problems, it is necessary to tackle them at their root cause by addressing issues related to processes, equipment, maintenance, and operation. Only by eliminating faults in all aspects can the mechanical sealing problems be completely resolved, ensuring the proper operation of the pump. In actual production, different operating and production conditions can have a significant impact on the mechanical seals of pumps; they may even cause these seals to lose their basic functional capabilities. Therefore, analyzing the reasons for leakage in pump mechanical seals is of great importance both from a practical production perspective and from a safety standpoint. A thorough analysis of the causes can enhance safety, improve the operational efficiency of the machinery, and extend its lifespan. As such, the selection of appropriate mechanical seals has always been a top priority for many companies. I. Causes of failure in mechanical seals of pumps and motors Corrosion is a factor that leads to the failure of mechanical seals; such corrosion affects the metal rings, non-metallic rings, as well as the auxiliary sealing rings and the contact areas. 　 1. Corrosion of metal rings: Metal rings do not possess corrosion resistance; when in direct contact with corrosive substances, they will corrode. In the initial stages, issues such as unusual noises, leaks, and wear may occur. Corrosion will spread inward at a certain rate. Under the action of external forces, the metal ring undergoes stress-induced deformation; the exposed areas as a result are prone to corrosion, and this corrosion gradually affects other areas through the weak points, leading to leakage in the mechanical seal. 2. Corrosion of non-metallic rings: The corrosion of graphite rings is also one of the major reasons for problems in mechanical seals. Excessively high temperatures at the interface, improper selection of impregnating resin, and insufficient depth of resin impregnation are all factors that lead to the corrosion of graphite rings. When the graphite ring is in an oxidizing medium, and cooling is inadequate or friction occurs, temperatures of three to four hundred degrees in such an environment cause an oxidation reaction between the graphite and the oxidizing medium, resulting in the loss of performance of the end face. 3. Corrosion of the auxiliary sealing ring and contact areas: Different materials have varying degrees of corrosion resistance. The material for auxiliary sealing rings is usually elastic rubber; however, when rubber is corroded, its surface becomes extremely rough and it loses its original elasticity. Moreover, rubber has poor high-temperature resistance, generally not exceeding 200 degrees Celsius. 　　 The area in contact with the auxiliary seal ring remains relatively stationary; gaps and friction between them can both lead to corrosion. Moreover, the corroded areas are generally wide and deep. II. Fault manifestations of mechanical seals in pumps During the production process, the leakage of mechanical seals in pumps can be attributed to both internal and external factors. The choice of materials, as well as the methods of installation and operation, can all lead to the failure of these seals. The symptoms of failure vary from case to case; learning to identify these different symptoms and make accurate and timely judgments can provide significant support for actual production processes. 1. Leakage during hydrostatic tests: During installation, carelessness on the part of the staff can often result in damage to the sealing surfaces, leading to deformation and damage. Inadequate cleaning can cause particulate impurities to get trapped between the sealing surfaces. Additionally, loose setting screws, insufficient compression of the gland, or low precision of the machinery can all prevent the sealing surfaces from fitting together properly, thereby causing the mechanical seal to fail and resulting in fluid leakage. If the shaft sleeve is leaking, the reason may be that insufficient compression was applied to the sealing ring during installation, or it may not have been compressed properly; it’s also possible that the device is damaged. 2. Periodic leakage: The periodic rotation of the rotor components within the mechanical seal assembly, as well as excessive axial movement, can lead to leakage in the mechanical seal. The sealing surfaces of the mechanical seal must be subjected to certain stress in order to provide an effective seal. To meet the above requirements, the spring mechanism of the mechanical seal must have a certain degree of compression in order to apply stress to the end faces, thereby enabling the mechanical seal to achieve the desired sealing effect. At the same time, to keep the stress within an appropriate range, the pump shaft must not move much. However, in practical design, various unreasonable factors often arise that result in the pump shaft moving more than expected, which has a significant negative impact on the performance of the mechanical seal. 3. Frequent leakage of mechanical seals: (1) Frequent leakage caused by damage to the sealing surface is manifested by uniform ring-shaped grooves on the graphite surface of the mechanical seal, deep ring-shaped grooves formed at the graphite interface, wear on the inner edges of the graphite, wear of the steps in the graphite ring, notches on the outer edge of the graphite ring, fracture of the graphite ring, corrosion pits on the graphite ring, cracks in the cemented carbide surface, as well as burns. (2) Common leakage problems caused by the auxiliary sealing ring include end face wear and loosening of the insert ring. (3) Leaks caused by springs include rotor vibration, loose components, medium-related issues, and damage to the auxiliary mechanisms of mechanical seals. 4. Other types of mechanical seal leakage: In addition to the common leakage patterns mentioned above, there are also cases of excessive vibration of the mechanical seal, leakage caused by pump cavitation, leakage resulting from cavitation within the seal chamber, leakage due to vaporization at the seal surface, leakage caused by excessive pump vibration, and leakage issues arising from the lack of flushing. III. Measures to address mechanical seal leakage: 1. Install fault-prevention devices. The occurrence of faults is related to actual operating conditions as well as the internal structure of the machinery; certain factors can lead to faults under specific conditions. By identifying these factors, it is possible to eliminate them using appropriate fault-prevention devices. For example, an electric contact pressure gauge can be installed at the pump outlet to create a linkage between the pressure in the pump and that at the outlet; if the pressure drops, the power supply will be automatically cut off. To prevent backflow when the automatic pump stops, a check valve can be installed at the outlet of the automatic pump. 2. Improve the equipment structure: The mechanical seal has certain structural flaws in its design, and these flaws increase the risk of leakage for the mechanical seal. Where conditions permit, the structure of the mechanical seal can be redesigned to minimize the risk of leakage. For example, the end faces of mechanical seals are mostly designed with a double-end face configuration; this doubles the contact area between the device and the medium, thereby increasing the risk of corrosion. From a safety perspective, the double-end design can be modified to a single-end sealed bellows mechanical design. 3. Select appropriate constituent materials. Different materials have different corrosion resistances. Given the corrosive nature of the medium, the materials used in mechanical seals must possess good corrosion resistance. Selecting inappropriate materials can shorten the service life of the equipment. Ceramics are composed of chemically inert materials that do not readily undergo oxidation reactions with media; therefore, ceramic sealing rings can be considered as a good option when purchasing mechanical seals. 4. Improve the professional skills of operators. The failure of mechanical seals is caused not only by mechanical factors but also by human factors; for example, insufficient professional knowledge on the part of operators and improper operation can lead to adverse consequences. To prevent the occurrence of such avoidable errors, it is necessary to provide operators with specialized training, develop operation manuals and safety guidelines, promote standard procedures, implement foolproof measures, and conduct regular equipment maintenance in order to minimize the impact of human factors. 5. Improve the effectiveness of maintenance work. Regular maintenance is an important means of identifying and preventing problems, yet many employees treat it as a mere routine task, considering it to be a formality with no real substance – they just go through the motions during maintenance. The employees’ work attitude prevented some issues from being detected early, and by the time they erupted fully, it was already too late. During maintenance, employees should pay attention to every detail and not overlook anything. The company can implement certain incentive measures to encourage employees’ enthusiasm for maintenance, thereby improving the overall effectiveness of the process. Mechanical seals in pump systems frequently experience leakage problems during operation; it is necessary to address these issues specifically. By analyzing the causes of such failures and making improvements to the equipment, as well as by installing devices that prevent failures and carrying out regular maintenance, it is possible to minimize the likelihood of such problems occurring.