The first main flexible but rotationally secured bellows (14) are mounted between the wall (2) and shaft (1). The second backup bellows (15) connects the outer edge (17) to the inner edge (20) of the first bellows (14). In order to avoid inflation of the hollow cavity and thus to increase the service life at least a cavity (23) between the two bellows (14, 15) contains a viscous fluid with low heat expansion. This fluid only boils above a maximum operating temperature and only solidifies below a lowest operating temp. USE/ADVANTAGE - Sealing system for shaft with backup bellows. The second bellows remains completely sealed for a certain time.