The working characteristics of water pumps require mechanical seals to have high precision and reliability, and their sealing performance plays a crucial role in the operation and lifespan of the unit. This article analyzes the phenomenon and causes of leakage in mechanical seals based on their composition and principles, and proposes effective countermeasures to prevent leakage based on practical experience. The aim is to reduce human design defects or usage issues, ensuring the long-term and reliable performance of mechanical seals and guaranteeing the safety of water pump operation.

　　1. Analysis of the phenomenon and causes of water leakage in mechanical seals of water pumps

　　1.1 Composition and working principle of mechanical seals in water pumps

　　When transporting high-temperature and high-pressure water, mechanical seals are often chosen to prevent leakage. Mechanical accidents caused by leakage account for about 50% of the total maintenance of water pumps, indicating that the reliability of mechanical seals is crucial for the operation and lifespan of water pumps. Mechanical seals generally consist of rotating rings, stationary rings, sealing rings or gaskets, and elastic compensation elements. The working principle involves a pair of end faces perpendicular to the rotating axis being in close contact and rotating relative to each other, maintaining a very thin liquid film between the end faces. With the assistance of sealing, the end faces are subjected to the pressure of the medium fluid and the elastic force of the compensation mechanism, maintaining a tight fit to achieve sealing.

　　1.2 Analysis of leakage phenomena and their causes

　　1.2.1 Leakage phenomena caused by design issues

　　Reasonable design is the foundation for mechanical seals to achieve their function. However, in actual engineering, the overall design optimization of the water pump, the selection of equipment parts, and the choice of materials for various components directly affect the sealing performance of the water pump. Taking the magnetic separator in the water pump as an example, this component not only has disadvantages such as being unable to separate and filter non-metallic particles, being large in size, and difficult to maintain, but it may also cause friction between metallic substances in the water and the non-metallic rotating or stationary rings due to magnetic attraction, leading to wear of the components. The non-metallic substances produced from wear cannot be filtered out, exacerbating wear, and long-term operation will inevitably lead to a decline in sealing performance.

　　1.2.2 Leakage phenomena caused by installation issues

　　Improper construction during the installation phase may also cause sealing damage.

　　For example, if the hexagon screw that plays an axial positioning role in the mechanical seal is not tightened, it will cause axial movement of the seal. When the movement is excessive, and the compression spring cannot keep the stationary ring tightly against the rotating ring, leakage will occur; if the axial end face of the ring sealing ring and the sealing pressure cover end face of the stationary ring are not smooth enough, it may damage the rotating and stationary rings during installation; the compression amount of the mechanical seal's spring is also a key point in installation. If the error exceeds ±2 mm, excessive compression may lead to increased end face pressure and friction heat, exacerbating wear and thermal deformation of the end face, or insufficient pressure on the end face of the stationary ring due to insufficient compression, affecting the sealing effect.

　　1. Installation too tight

　　Observing the plane of the dynamic and static rings of the mechanical seal, if there are severe burn marks, deep black marks on the plane, and the sealing rubber has hardened or lost elasticity, these are all caused by excessive tightness during installation.

　　Solution: Adjust the installation height. After installing the impeller, use a screwdriver to pull the spring; if the spring has strong tension, it will reset after being released, with a movement distance of 2-4 mm.

　　2. Installation too loose

　　Observing the dynamic and static ring planes of the mechanical seal, if there is a very thin layer of scale (which can be wiped off) and the surface shows little wear, this is caused by the loss of elasticity of the spring and poor assembly, or by axial movement of the motor.

　　1.2.3 Leakage phenomena in the production phase

　　For example, caused by the static ring chamber of the pump cover. If the processing size error of the inner hole of the static ring chamber is large and the surface is rough, it may result in axial water spraying, with gaps between the static ring and the inner hole, or rough inner holes causing the static ring to rotate and rubber wear.

　　1.2.4 Leakage phenomena in the usage phase

　　(1) Pressure causing leakage. When the pressure in the sealing chamber exceeds 3 MPa during use, it may lead to excessive end face pressure, making it difficult to form a liquid film, resulting in severe wear of the sealing end face and increased heat generation, causing thermal deformation of the sealing face. During the startup and shutdown of the pump, due to blockage at the pump inlet or the presence of gas in the medium being pumped, negative pressure may occur in the sealing chamber, leading to dry friction of the sealing end face, causing leakage in internal mechanical seals.

　　(2) Medium issues. First, since sealing rings and other auxiliary components often use organic materials that are not resistant to acids, bases, and high temperatures, long-term use in mediums containing weak acids or weak bases will cause them to lose elasticity or even rot; when solid particles appear in the medium, they can also scratch the end face, causing wear. Additionally, scale, oil stains, etc., may accumulate on the shaft surface. Furthermore, excessive water temperature is also a major reason for the decline in mechanical seal performance, so when the cooling capacity of the heat exchanger is insufficient, the service life of the seal is often greatly shortened. (Welcome to follow: Pump Manager)

　　(3) Fatigue damage of the rotating and stationary rings. Misalignment of the water pump shaft or improper adjustment of bearing clearance can cause vibration in the water pump, leading to friction between the dynamic and static parts of the mechanical seal assembly, which can damage the water film on the contact surface.

　　(4) Lack of production management. Failure to follow operating procedures during unit operation, improper startup and shutdown, or human operational errors leading to power fluctuations causing the water pump to reverse can also cause sealing leakage.

　　(5) Dry wear damage caused by lack of water. This phenomenon is often seen at the inlet of bottom valve installations where negative pressure occurs, with air in the water intake pipe and air in the pump chamber. After the pump starts, the friction of the mechanical seal generates high temperatures during high-speed operation, unable to cool down. Upon checking the mechanical seal, the spring tension is normal, but the friction surface is burned and blackened, and the rubber has hardened and cracked. Solution: Bleed air from the pipeline and pump chamber or replace the mechanical seal.

　　(6) Presence of gas, mainly occurring in hot water pumps. Since the medium is hot water, excessive water temperature generates steam, and the gas enters the high part of the pump chamber, which cannot be expelled, leading to dry operation and failure of the mechanical seal.

　　(7) Mechanical seal adhesive failure. The reasons for mechanical seal adhesive failure include aging and deformation of rubber components, mainly in hot water pumps. The manifestation of mechanical seal adhesive failure is high water temperature and the medium dissolving the rubber. Visually, the surface of the rubber components appears loose and rough, losing elasticity, which leads to rubber failure.

　　II. Preventive measures for mechanical seal water leakage

　　2.1 Issues to pay attention to during the design process

　　Different types of mechanical seals should be selected based on the working characteristics of different pumps. Each sealing component should be optimally selected based on a careful analysis of material, service life, and other characteristics, with a focus on performance aspects such as high temperature resistance, corrosion resistance, fatigue resistance, and vibration resistance. Although there are significant design differences among different models of mechanical seals, the focus of the design should always be on the sealing between the rotating ring and the stationary ring, between the shaft sleeve and the rotating ring, between the stationary ring and the ring seat, between the shaft sleeve and the shaft, and between the sealing end cover and the pump body. In particular, the design quality of the first three areas is key to preventing leakage.

　　2.2 Issues to pay attention to during use

　　2.2.1 Countermeasures to prevent leakage during installation

　　It is essential to improve the quality awareness of installation projects and strictly implement the institutionalization and standardization of installation and maintenance. Taking the tightness of the sealing ring as an example, if the rotating ring sealing ring is too loose, it will affect the sealing effect, but if it is too tight, it may exacerbate wear between it and the shaft sleeve, and easily cause fatigue and deformation of the rotating ring; while the stationary ring is correspondingly tighter, excessive tightness can also lead to deformation or brittleness. Therefore, it is necessary to measure and adjust according to the installation manual to ensure that the compression amount meets the requirements.

　　2.2.2 Prevention and handling of leakage during mechanical seal use

　　Regular inspection and use of the pipeline system of mechanical seals are essential for their normal operation. Therefore, the responsibility for equipment management should be assigned to individuals, and strict maintenance and repair systems should be established and implemented. Check all valves related to the operation of the mechanical seal to ensure that safety monitoring instruments are intact; check the self-circulating water of the mechanical seal, the pump body, the mechanical seal water pipeline, the heat exchanger, and the cooling water of the mechanical seal to ensure smooth flow and no abnormal temperature changes. If problems are found, investigate the causes promptly and address them accordingly.

　　Due to the significant harm caused by the blockage of magnetic filters to the normal operation of mechanical seals, regular inspection and cleaning are necessary, and damaged components should be replaced promptly. The mechanical seal water system should maintain one magnetic filter in operation and have another as a backup, switching regularly to ensure normal operating conditions. After regular cleaning, the magnetic filter should be put into standby mode after filling with water and venting air. The exhaust pipe of the mechanical seal water system must be installed above the outlet pipeline of the heat exchanger's mechanical seal water. Before normal operation, all air in the mechanical seal water chamber and pipeline must be thoroughly vented. Air can also be vented during low-speed operation, but care should be taken not to fully open the exhaust valve. Incomplete venting may result in a lack of lubricating liquid between the sealing friction pairs, causing dry grinding and thermal cracking of the rotating ring, severely affecting the safe and normal operation of the mechanical seal. Additionally, regarding pressure issues during use, in addition to strictly adhering to the specified spring compression amount during installation, special treatment measures should be taken under high-pressure conditions. To ensure reasonable force on the end face and reduce deformation, materials with high pressure resistance, such as hard alloys and ceramics, can be used, and lubrication measures for cooling should be strengthened. For leakage caused by operation in a vacuum state, double-end mechanical seals should be used to improve lubrication conditions and enhance sealing performance.

　　III. Conclusion

　　In summary, the working characteristics of pumps require mechanical seals to have high precision and reliability, with strict process requirements in design, processing, installation, and use. In the use of mechanical seals, in addition to strictly following process standards, efforts should be made to improve the operating environment, reasonably select various components, and establish and implement relevant maintenance and care systems to reduce human-induced design defects or usage issues, ensuring the long-term and reliable performance of mechanical seals and guaranteeing the safety of pump unit operation.