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 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 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 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 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. <EOS>