Why do mechanical seals use auxiliary facilities? （I）

Auxiliary facilities of mechanical seals are also called cycle protection systems of seals, or simply sealing systems or protection systems of seals.
In fluid machinery (such as pumps, compressors, stirring tanks and centrifuges, etc.), the parts with the harshest working conditions are mechanical seals: they bear axial force like thrust bearings; they export the generated heat like heat exchangers .

The frictional heat generated during the operation of the mechanical seal increases the temperature of the sealing end face. If no corresponding measures are taken, many adverse consequences will occur:
1)As the temperature rises, the liquid film between the sealing end faces of the mechanical seal will vaporize, and the wear will intensify, making the seal fail;
2)The increase in temperature causes thermal deformation of the rotary face & stationary seat of the mechanical seal, increasing both leakage and wear of the seal;
3) The increase in temperature also intensifies the corrosion of the medium on the mechanical seal;
4) The temperature rise causes the auxiliary sealing ring to age, deteriorate and fail;
5) When the temperature rises, the performance of the graphite impregnated with synthetic resin will decrease due to the carbonization of the resin, and the graphite ring impregnated with metal will leak due to the melting of the metal.

It can be seen that the unacceptable temperature rise is the enemy of mechanical seals. It is already difficult to achieve static sealing in high temperature, high pressure, corrosion-prone parts, etc. It is even more difficult to achieve dynamic sealing on the sealing end face of mechanical seals with a width of several millimeters in high-speed rotation.

 In order to solve this thorny problem, after a long-term practice, we have found two ways: one is to start with the structures and materials of the mechanical seals to make it suitable for harsh working conditions.The cost of this approach is relatively high, but even so, it still cannot fundamentally solve the problem. Once the mechanical seal fails, the consequences can be serious. Another approach is to improve the working environments through auxiliary facilities. At present, mechanical seals without any auxiliary facilities in actual work are rare. For example,the series mechanical seal used for high pressure and the mechanical seal of high temperature pump must adopt corresponding auxiliary facilities. Through auxiliary facilities, some harsh working environments can be changed to acceptable sealing, so that the performances of mechanical seals are greatly improved, and the application ranges of them also become wider.Next article we will discuss it in detail.