The invention relates to a sealing device of a system for sealing a fluid passage from a first component (1) to a second component (2), comprising at least one first sealing element (3) which is of an annular design to allow fluid to pass through it, includes at least one expansion slot (4) and has a first sealing surface (5) sealingly associated with the first component (1) and has a second sealing surface (8) sealingly associated with the second component (2), said at least one first sealing element (3) being flexible and said expansion slot (4) being designed in such a way that radial and resultant axial pressure of the fluid passing through there will cause the first sealing element (3) to expand in the radial direction and thus press radially in the direction against the first component (1), with said first sealing surface (5) with the expansion slot (4) being sealed against the first component (1) by abutment in the direction of the latter, and in such a way that the first sealing element (3) will press axially in the direction against the second component (2), with the second sealing surface (8) with the expansion slot (4) being sealed against the second component (2) by abutment in the direction of the latter.