In the mechanical seal design, the secondary seal under the torsion surface has a certain mechanical seal

In older mechanical seal designs, the secondary seal located under the rotating face has some clearance to move back and forth on the main shaft, so it is prone to wear and premature failure. However, in newer seal designs, the secondary seal is at rest, so fretting corrosion problems on the main shaft are avoided.

In the normal operation of the liquid pump, the pressure between the torsion surface and the static surface is connected in a sealed state by the pressure generated by the liquid in the stuffing box. When starting and stopping, the pressure of the stuffing box is connected by the pressure generated by the spring ( can even be replaced by the pressure of the spring). Most mechanical seal designs use a softer material to make the torsion surface, making it torsionally rub against a harder, static surface. For many years, a very common combination has been to use a carbonaceous material as the torsion surface running on a ceramic stationary surface. This material is still widely used today, but the static surface is made of stainless steel or a harder material such as tungsten carbide or silicon carbide.