wall forms a so called inner ring or casing ring in the region of each rotating blade ring 46 at the rotor side not shown in fig1 and encloses the respective rotating blade ring 46 radially on the outside besides the casing rings 17 of the radially inward lying housing wall the housing 11 further comprises a radially outward lying housing wall 18 as already mentioned the radially inward lying housing wall forms a so called casing ring 17 in the region of each rotating blade ring at the rotor side not shown which encloses the rotating blade ring radially on the outside thus between the radially outward lying ends of the rotating blades 44 of each rotating blade ring 46 and the respective casing ring 17 is formed a radial gap 48 fig4 which is subject to considerable changes during the operation of the compressor since on the one hand the rotating blades and the respective casing rings have different thermal behavior and on the other hand the rotating blades undergo a change in length 50 due to the centrifugal forces at work during operation it is quite difficult to maintain definite dimensions of the respective gap between the radially outward lying ends of the rotating blades of a rotating blade ring and the respective casing ring 17 during operation yet it is of critical importance for optimized efficiency the present invention concerns only those details which can be used to exactly maintain radial gaps between radially outward lying ends of rotating blade rings and the respective casing ring 17 per fig1 the casing rings 17 which extend between the guide blade rings 13 and 14 as well as 15 and 16 are connected by curved and elastically flexible walls.