In some mechanical equipment (such as casting machines, calenders, sheet machines, steel converters, hydraulic equipment, etc.) that require rotation or reciprocating motion while also requiring fluid media, the fluid sealing components with the most severe working conditions belong to dynamic machinery. sealed. For example, the thrust bearing of the equipment rotates to bear the axial force; another example is the heat exchanger to dissipate the generated heat for heat dissipation. It is already difficult to achieve static sealing in high temperature, high pressure, corrosion-prone parts, and it is even more difficult to achieve dynamic sealing on the sealing end face with a width of several millimeters during the rotating movement of the equipment. In order to solve this practical problem, two ways have been found after long-term practice: one is to start from the design of the sealing structure and the sealing material. In order to achieve a good dynamic sealing effect, the cost of this method is relatively high, and The fundamental dynamic seal problem cannot be fundamentally solved; once the seal fails, it will cause greater economic losses and production safety accidents. Another method is to improve the working environment of the dynamic seal through auxiliary facilities. Nowadays, dynamic seals that do not use any auxiliary facilities from actual work are rare. Through auxiliary facilities, some harsh working environments are changed to those acceptable to the seal, so that the effect of the mechanical seal is greatly improved and the scope of use is wider. The frictional heat generated in the work of the mechanical seal increases the temperature of the seal end face. If the corresponding facilities are not adopted, many adverse consequences will occur. Therefore, the rotary joint has become the first choice for dynamic sealing, and it is irreplaceable.

Hazards of an impermissible temperature rise:
       1. The increase in temperature causes the liquid film between the seal end faces to vaporize, and the wear is aggravated, making the seal invalid;
       2. The rise in temperature causes thermal deformation of the dynamic and static rings, increasing leakage and aggravating wear;
       3. The increase in temperature also aggravates the corrosion of the medium to the mechanical seal;
       4. The temperature rise makes the auxiliary sealing ring age and deteriorate and fail;
       5. When the temperature rises, the graphite impregnated with synthetic resin will decrease in performance due to carbonization of the resin, and the graphite ring impregnated with metal will leak due to the melting of the metal.

From the five major hazards of abnormal temperature rise, it is not difficult to see that the unacceptable temperature rise is the enemy of mechanical seals, and even fatal hazards. The purpose of the rotary joint as a dynamic seal auxiliary facility is to reduce this undesired temperature rise, maintain a good lubrication state between the seal end faces, and make the mechanical seal parts run well and work normally; in the easily vaporized medium, to ensure the seal The pressure in the cavity can prevent it from vaporizing; it can play the role of heat preservation and heat supply in low temperature sealing; for the sealing of crystallization and strong corrosive media with solid particles, it can also keep the sealing from being damaged. It has different auxiliary facilities according to different conditions, which completely solves the problem of dynamic mechanical seal. Practice has proved that often the structure is reasonable, the material is good and the auxiliary facilities are neglected, resulting in difficult working conditions, resulting in early failure of the seal. On the contrary, in some occasions, the structure and materials are not enough to meet the requirements of working conditions, and effective rotary joint auxiliary facilities are used, as a result, the seal meets the requirements of working conditions and runs smoothly. Some mechanical seals do not have high working temperature, pressure and speed, and can work without rotary joint auxiliary facilities. However, from the standpoint of seal stability and service life, it is advantageous to employ a rotary joint auxiliary facility. Therefore, the auxiliary facilities of the rotary joint should be regarded as an integral part of the mechanical seal, and different auxiliary facilities should be used according to different working conditions. The international standard of the American Petroleum Institute (API610) has made specific provisions on this. The correct and reasonable selection of sealing auxiliary facilities is of great significance not only to the stability of the seal but also to prolonging the service life; it has a certain effect on safe production, reducing leakage, reducing maintenance workload and reducing production costs, and must be given sufficient of attention.