The compensation mechanism is the bellows, where one sealing ring (moving ring or static ring) and bellows are made into a whole, with no auxiliary sealing ring (see Figure 8), thus reducing a leakage point; reducing the friction resistance of the compensation mechanism and improving the following; the temperature of the welding metal bellows seal (Figure 8b) is not limited by the auxiliary sealing ring; for the tetrafluoro bellows seal (Figure 8a) can be used in corrosive medium. The disadvantage is that some bellows are less elastic, need to add auxiliary spring, as shown in (Figure 8a).