Mechanical seal has the advantages of reliable sealing performance, small leakage, long service life, less power loss and wide range of application, etc., which is widely used in various technical fields, especially for high speed, high pressure difference working conditions and expensive or toxic and strong corrosive process medium. However, mechanical sealing is one of the weakest links of the unit. In order to extend its service life, in addition to choosing the right friction side material and the right end surface specific pressure, the proper installation and repair can also play an important role. Through practice, people have found out the main cause of mechanical seal failure and leakage, and summed up a set of practical maintenance experience, and achieved good benefits.

　　1.Cause analysis of mechanical seal failure and leakage

　　(1)No matter what type of mechanical seal, the most prominent feature is that the sealing surface is perpendicular to the end surface of the rotating axis, that is, the axial seal that is easy to leak to the end surface seal that is not easy to leak. Therefore, the main form of mechanical seal failure is the wear failure between the static and moving ring. Dynamic and static ring end surface friction pair is usually pressed by spring thrust to prevent leakage. The tighter the dynamic and static ring is, the more difficult it is to leak, but the friction in the meantime also increases, and the contact end surface of the dynamic and static ring will soon wear out under the action of greater friction, and finally fail and leak.

　　(2)The process condition is unstable and poor installation of vibration, centrifugal pump time gasification, instantaneous disconnection can lead to mechanical seal dual ring between liquid film damage, make mechanical seal under the condition of no lubrication "dry" operation, sealing ring temperature rise rapidly, some directly burned, others because the pump back to normal working state is sharp cooling, the formation of heat shock and fragmentation. Poor flushing fluid and flushing conditions can also form heat shock, leading to radial cracks in the sealing ring and aggravating the wear and failure of the dual ring. For example, when the graphite ring exceeds the use temperature, the crystal will precipitate on the surface, and carbonization occurs near the friction surface with high temperature. When the particles enter the friction interface, the components wear sharply and fail.

　　(3)The failure of the mechanical seal sealing ring is also the main cause of the seal leakage. Assembly of the moving ring sealing ring or assembly of the static ring; the surface of the shaft or shaft sleeve compatible with the sealing ring is not clean enough, or the grinding size is small; the physical or chemical reaction of the sealing ring and the sealing medium, corrosion deformation and aging can lead to leakage.

　　(4)Inthorough cleaning before assembling mechanical seal, touch and scratch components; assembly is not in place; spring loading deviation, fastening screws are not fixed; damage during disassembly, etc., are the reasons of early failure of mechanical seal.

　　(5)When the mechanical sealing is used for different sealing media, each element should choose the best material collocation to extend its service life.

　　2.Solution to mechanical seal failure and leakage

　　According to the above analysis, the following measures and maintenance methods shall be applied to extend the service life of mechanical sealing.

　　(1)Adjust the spring compression amount correctly to extend the service life of the mechanical seal during the assembly.

　　(2)Strict process operation and process index control, in the flow adjustment and parking, avoid vibration, pump evacuation and flushing fluid flow off phenomenon. Impurities in the filter sealing medium, reasonable use of balance or external forced circulation washing way, improve the flushing cooling conditions, or enlarge the aperture of the flushing system, increase the amount of flushing fluid, ensure the supply balance and sufficient, improve the lubrication and heat dissipation of mechanical sealing, prevent the mechanical sealing due to overheating, burn and crystallization, extend the service life of mechanical sealing.

　　(3)When assembling the mechanical sealing moving ring "0", apply a small amount of lubricant on the shaft or sleeve to make the sealing ring easy to assemble and prevent the "0" ring from winding. The static ring assembly should be perpendicular to the axis of rotation. The roughness of the shaft or shaft sleeve should be below the surface roughness of 6.3, and the outer diameter matching size is less than the minimum limit size should be replaced.

　　(4)The careful assembly process is also very important. Before mechanical seal assembly, carefully clean each element, wipe the sealing element with clean and soft cotton yarn or cloth, and wipe the moving, static ring end surface, especially not scratches. Check whether all components are damaged; strictly check the friction end surface of moving and static rings, without any subtle bumps or scratches. When assembling, the dynamic and static ring end surface should be coated with a layer of clean engine oil. Each element is installed in place in order to determine the correct installation location and optimal parameters. Fighten the screws, tighten the screws evenly to avoid deflection and seal failure. After the repair, open all valves, do not directly start the motor, first use the hand drive, check the tightness of the mechanical seal, whether the rotation is flexible, listen to the same sound, observe no leakage, and then start the start.