For more than 100 years, people have used various sealing materials such as packing to continuously reduce the leakage of liquid from the pump housing along the main shaft. Although liquid pumps are used in modern processes, the oldest sealing design, the stuffing box, is still widely used because it has a low initial cost and is familiar to factory workers. However, due to environmental issues, the use of packing seals has gradually become unacceptable, especially for highly corrosive liquids that are common in modern processes. Therefore, in practical applications, mechanical seals are increasingly used instead of packing seals. The seal between the rotating surface and the stationary surface is the most critical factor that determines the sealing performance of the mechanical seal. There are 4 leakage paths that need to be sealed: 1) The passage between sealing surfaces; 2) The passage between the rotating surface and the spindle; 3) The passage between the fixed surface and the gland; 4) The passage between the gland and the stuffing box. The latter two leakage paths are generally statically sealed because there is no relative movement between the two parts. This part of the seal is usually called the third seal, and the sealing material is a gasket or an O-ring that is compatible with the process liquid. In newer seal designs, the secondary seal is stationary, thus avoiding wear and corrosion problems on the spindle. In normal operation of the liquid pump, the pressure between the rotating surface and the stationary surface is maintained in a sealed state by the pressure generated by the liquid in the stuffing box. During startup and shutdown, the pressure in the stuffing box is maintained by the pressure generated by the spring. Most mechanical seal designs use softer materials to make the rotating surface so that it rotates and rubs against the harder stationary surface. For many years, the most common combination utilized a carbon material as a rotating surface, running on a ceramic stationary surface. From this point of view, it is very important that these sealing contact surfaces must be handled carefully and installation instructions strictly followed to ensure that the sealing surfaces are properly protected and correctly seated. Flexibility of sealing: The axial and radial movement of the spindle needs to maintain a certain degree of flexibility with the spring to ensure sealing between the contact surfaces. However, only a certain degree of flexibility is provided. The mechanical condition of the liquid pump and its length-to-diameter ratio (a measure of the ratio of the diameter of the spindle to its extended length, the lower the ratio, the better) play an important role in the reliability of the seal. Sealing flexibility is generally provided by a large main spring and a series of small springs or bellows sealing devices. The traditional seal design used in the chemical industry applies sealing pressure to a rotating surface. This type of seal is called a rotary seal because the spring or bellows seal device rotates with the main shaft. A relatively new design in which a spring or corrugated sealing device is mounted on a stationary surface. In today’s mechanical seals, the above two sealing methods are very commonly used, which allows a certain degree of flexibility in installation. Many mechanical seals designed in the early days used a single large spring arranged around the main shaft, which can provide a strong sealing force for the sealing surface during the starting process of the liquid pump. The sealing function relies on the rotation of the main shaft to tighten the spring roll. The seal designed later uses a series of smaller springs arranged around the main shaft, which can produce a relatively uniform load pressure on the sealing surface. Since smaller springs can be installed in advance, most of these seals are completely isolated from the liquid being pumped.  

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