The present invention relates to a sealing device for closing an introduction aperture (1), the sealing device comprising a fixed support (2) and a shutter (3) mounted movably in translation relative to the support between an extended position and a final retracted position, wherein the sealing device is in a final retracted configuration and wherein the shutter closes introduction aperture. The device includes locking means for preventing any movement of the shutter when it is in the final retracted position. The sealing device further comprises an intermediate retracted configuration, wherein the shutter is at least partly retracted. The sealing device also comprises motion guiding means (5,7) for guiding the movement of the shutter and designated so that the extension of the shutter is required to move the shutter from the intermediate retracted position to the final retracted position.