Abstract: The invention relates to a seal for the shaft of a flue gas flap or the blast pipe of a soot blower for boilers or industrial furnaces subjected to excess pressure, having a shaft or pipe which is enclosed by at least two corotating coaxial sealing rings bounding between themselves an annular chamber for the supply of barrier air and each bearing on the inside metal bristles which bear against the shaft or blowing pipe and are arranged in at least two groups of brushes disposed in a circle one beside the other, an annular coaxial gap being left between the two annular groups of brushes of each sealing ring, such gap opening in the direction of the shaft or blowing pipe and being acted upon with barrier air.