Piston ring type seal for the compressor of a gas turbine

The engine has a sealing unit including an annular segment (50) whose inner radial part (51) is housed in a radially sliding manner and seals a groove. The groove is provided at a periphery of an upstream port of an outer case of a diffuser grid (10). Periphery of the segment is supported by an inner surface of a sleeve which is integrated with an annular structure and surrounds the segment.