A device for sealing a pipeline passageway, said device comprising: a rigid tube having a longitudinal centerline which is inclined with respect to the condition of perpendicularity with an axis of a stationary disc by an angle between 3° and 6°; said stationary disc located toward a lower end of the rigid tube and having a truncated cone-shaped face opposite to the one facing the tube; a movable disc located opposite the stationary disc and having a truncated cone profile symmetrical to that of the truncated cone-shaped face of the stationary disc, the moveable disc including a shank, said shank adapted to run slidably within an axial through hole of the stationary disc; an elastomeric sealing ring located between the stationary and moveable discs and having a side profile complementary to the truncated cone profile, respectively, of the stationary and movable discs; a control rod is introduced slidably into the rigid tube; at least one slider projecting transversely from a lower portion of the control rod, the at least one slider including two faces (71, 72) parallel to each other but sloping with respect to the logitudinal axis of the rod, the faces configured to engage a complementary portion of the shank; wherein said slider being intended to engage in a complementary groove formed in said shank, so that an axial thrust exerted on said control rod, in the one or the other direction, generates a component of a force directed parallel to the axis of said discs (3, 4) by means of the contact surfaces between said slider and said groove, and causes axial movement of the movable disc away or closer with respect to the stationary disc, in the direction of the groove. a rigid tube having a longitudinal centerline which is inclined with respect to the condition of perpendicularity with an axis of a stationary disc by an angle between 3° and 6°; said stationary disc located toward a lower end of the rigid tube and having a truncated cone-shaped face opposite to the one facing the tube; a movable disc located opposite the stationary disc and having a truncated cone profile symmetrical to that of the truncated cone-shaped face of the stationary disc, the moveable disc including a shank, said shank adapted to run slidably within an axial through hole of the stationary disc; an elastomeric sealing ring located between the stationary and moveable discs and having a side profile complementary to the truncated cone profile, respectively, of the stationary and movable discs; a control rod is introduced slidably into the rigid tube; at least one slider projecting transversely from a lower portion of the control rod, the at least one slider including two faces (71, 72) parallel to each other but sloping with respect to the logitudinal axis of the rod, the faces configured to engage a complementary portion of the shank; wherein said slider being intended to engage in a complementary groove formed in said shank, so that an axial thrust exerted on said control rod, in the one or the other direction, generates a component of a force directed parallel to the axis of said discs (3, 4) by means of the contact surfaces between said slider and said groove, and causes axial movement of the movable disc away or closer with respect to the stationary disc, in the direction of the groove.