The function of the compensation mechanism is to make the sealing end face close fit, in order to achieve this purpose, there are two methods used, one is elastic force, the other is magnetic force. Magnetic mechanical sealing is used only when the pressure in the system is low (Figure 7), most with the former. In addition to the spring to form elastic force there are bellows, called bellows type mechanical seal. The materials of the bellows can be rubber, polytetrafluoroethylene (Figure 8a) and welded metal sheets (Figure 8b).