Abstract: A device for obturating leaky tubes in heat exchangers, characterized in that it comprises a sleeve adapted to be sealingly mounted in an orifice, or port, of the upper wall of said heat-exchanger, a vertical stem provided, at the lower end thereof, with an arm of variable length at right angles to said stem, the free end of said arm being integral with an assembly carrying a deformable capsule with a vertical axis adapted to penetrate into one of said tubes and to obturate said tube after having been deformed, means integral with said assembly adapted to deform said capsule, means for dissociating said capsule from said assembly, means for carrying said arm to rotate about the vertical axis of said stem, means for vertically moving said arm and means for varying the length of said arm.