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I. Advantages 1. The structure is reliable, and the leakage can be kept to a very low level. As long as the surface roughness and flatness of the main sealing surface meet the required standards, and provided that the material has good wear resistance, the mechanical seal can achieve minimal leakage, to the point where no leakage is visible to the naked eye. 2. Long lifespan. In mechanical seals, the main part that experiences wear is the end face of the sealing friction pair; since the wear on these sealing end faces is minimal under normal operating conditions, they can generally be used for 1 to 2 years, and in special cases, even for 5 to 10 years. 3. No adjustment is required during operation. Since a mechanical seal keeps the friction pair in contact by means of spring force and fluid pressure, it maintains this contact automatically during operation; therefore, after installation, there is no need to adjust the compression as is required for ordinary soft packing. 4. It has vibration resistance. At a rotational speed of 3000 r/min, the maximum amplitude should not exceed 0.05 mm; the PV value is increased continuously to achieve this. 5. Low power loss. A packing seal functions by compressing the packing against the shaft or shaft sleeve. The packing seal comes into direct friction with the shaft; the tighter the packing is pressed, the greater the friction force, and thus the higher the power consumption. The friction in mechanical seals operates in a semi-liquid friction state, resulting in a very low friction coefficient; the power loss associated with mechanical seals is 10–50% of that in packing seals. Additionally, the shaft or bushing of a bellows seal does not experience wear, and it is not sensitive to the vibration of the rotating shaft or to any deviation of the shaft relative to the housing. 7. Wide range of applications. When the medium is flammable, explosive, toxic, or harmful, a mechanical seal can ensure proper sealing. It is also suitable for sealing equipment in high-temperature, low-temperature, high-pressure, vacuum environments, as well as at various rotational speeds, in the presence of corrosive media. II. Disadvantages: 1. Its structure is more complex than that of a packing seal, it requires high precision in manufacturing, as well as certain installation skills; the installation requirements are even higher for dry gas seals. Moreover, sealing technology is developing rapidly, with new technologies emerging that present new challenges for our maintenance work. 2. Complex structure, difficult to disassemble and assemble. Compared to other seals, mechanical face seals require a larger number of components, demand high precision, and have a more complex structure. Especially, assembly is difficult; when removing or installing it, the seal ring must be pulled out from the shaft end, requiring the disassembly of part of the machine (the coupling) or the entire machine. Some improvements have been made to this issue, such as the use of split and modular mechanical seals that are easy to disassemble and assemble while ensuring assembly quality.