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1. Working principle of mechanical seal: A mechanical seal, also known as an end-face seal, is a dynamic seal for rotating shafts. Mechanical seals offer reliable performance, low leakage, a long service life, low power consumption, and require little maintenance. They are also capable of meeting the sealing requirements in harsh operating conditions such as automation in production processes, as well as high/low temperatures, high pressure, vacuum, high speeds, and environments with highly corrosive media or media containing solid particles. A mechanical seal is a shaft sealing device that prevents leakage by relying on a pair or several pairs of end faces that slide relative to each other perpendicular to the axis; these end faces remain in contact under the action of fluid pressure and the elastic force (or magnetic force) of a compensation mechanism, along with the help of additional sealing elements. A comparison between mechanical seals and soft packing seals is as follows: Advantages: (1) Reliable sealing – the sealing condition remains stable during long-term operation, with very low leakage levels; the leakage is approximately 1% of that in soft packing seals ； (2) It has a long service life; in oil and water media, it can generally last 1–2 years or even longer, while in chemical media it can function for more than half a year ； (3) It has low friction power consumption; its friction power is only 10% to 50% of that of soft packing seals ； (4) The shaft or bushing is essentially free from wear ； (5) It has a long maintenance cycle; automatic compensation is available after end-face wear, and regular maintenance is generally not required ； (6) It has good vibration resistance and is insensitive to vibrations of the rotating shaft as well as any deviation of the shaft relative to the sealing chamber ； (7) It has a wide range of applications; mechanical seals can be used for sealing in high-temperature, low-temperature, high-pressure, vacuum conditions, as well as at various rotation frequencies, and in the presence of various corrosive media and media containing abrasive particles. Disadvantages: (1) It is relatively complex and requires high processing standards ； (2) Installation and replacement are rather troublesome, requiring workers to have a certain level of skill ； (3) In the event of accidental incidents, handling them is more difficult ； (4) High price. Preparatory work before installing the mechanical seal: (1) Check whether the model and specifications of the mechanical seal meet the requirements of the design drawings, and inspect all components (especially the sealing surfaces and auxiliary sealing rings) for any damage, deformation, cracks, etc. If any defects are found, they must be replaced or repaired. (2) Check whether the fit dimensions, roughness, and parallelism of all components of the mechanical seal meet the design requirements. (3) When using a small spring mechanical seal, it is necessary to check whether the lengths and rigidity of the small springs are the same. (4) Check whether the shaft’s displacement, oscillation, and deflection meet the technical requirements, whether the sealing chamber conforms to the installation dimensions, and whether the sealing end cover is perpendicular to the shaft. The general requirement is that the shaft’s displacement should not exceed ±0.5 mm ； The shaft swing amount (at the rotating ring seal) shall not exceed 0.06 mm ； The maximum deflection of the shaft shall not exceed 0.05 mm ； The allowable deviation of the non-perpendicularity of the contact plane between the sealed end cover and the gasket relative to the center line is 0.03–0.05 mm. (5) It should be kept clean; in particular, the sealing surfaces of the rotating ring and the stationary ring, as well as the surfaces of the auxiliary seals, must be free from impurities and dust. It is not allowed to wipe the sealing surface with unclean cloths. (6) It is allowed to use tools to tap on the sealing element in order to prevent the seal from being damaged. 2. Mechanical seal materials – Friction pair materials. According to statistics, approximately 80% to 95% of leaks in mechanical seals are caused by the seal surfaces and the friction pairs. Apart from maintaining the parallelism of the sealing surfaces, the main issue is the material of the friction pair. Friction materials should meet the following requirements: (1) High mechanical strength, capable of withstanding pressure and pressure-induced deformation ； (2) It has resistance to dry friction, high load capacity, and good self-lubricating properties ； (3) The mating materials have good run-in properties, with no excessive wear or galling corrosion ； (4) Good wear resistance and long service life ； (5) Good thermal conductivity and heat dissipation performance ； (6) Good high-temperature resistance ； (7) Good resistance to thermal cracking ； (8) Strong corrosion resistance ； (9) Low linear expansion coefficient, capable of withstanding thermal deformation and exhibiting good dimensional stability ； (10) Good machinability and good formability ； (11) Good airtightness ； (12) Low density.