Abstract: An apparatus for sealing a junction where a branch line joins a header having a packer. The packer has an inflatable packer sleeve for the header and an inflatable side sleeve for the branch line that protrudes from said header in the inflated state. A tunnel passes from an end of the packer through an interior space to a collar, in which a feed line for introducing sealing material runs to the junction at the collar. In a deflated state, the side sleeve is inverted in the interior space of the packer sleeve. When the packer is placed, the packer sleeve to which compressed air is admitted comes to rest against the inside wall of the header and, subsequently, the side sleeve moves into the branch line by inversion.