as an inner sealing element 7 disposed between the inner limiting ring 4 and the central limiting ring 5 and an outer sealing element 8 disposed between the central limiting ring 5 and the outer limiting ring 6 the inner sealing element 7 and the outer sealing element 8 are each embodied as flat circular ring disc whose inner diameter is less than the outer diameter of the shaft 3 so that the inner edge of the circular ring disc is turned up and thus forms a sealing lip 9 abutting the shaft 3 the limiting rings 4 5 and 6 comprise at suitable points grooves into which o rings 10 are laid which serve for sealing the limiting rings 4 5 and 6 against one another or against the sealing elements 7 and 8 as well as against the bearing seat 1 the central limiting ring 5 comprises two holes which on one side empty between the inner sealing element 7 and the outer sealing element 8 and on the other side are connected to channels which are provided in the bearing seat 1 these are a gas intake duct 11 and a gas suction duct 12 the suction duct 12 serves to generate a fore.