Abstract: An apparatus which tests the internal integrity of, or isolates, a segment of pipe having an internal diameter. The apparatus comprises an annular body with opposite annular faces and defining on its outer perimeter, an annular recess, a pair of bosses, a pair of resilient annular members adapted to be respectively juxtaposed between an adjacent boss and annular face; means for urging the bosses respectively against the adjacent resilient annular member so as to urge the same in frictionally engage and to seal against the internal diameter of the selected pipe segment and, means communicating through the apparatus to that plenum now defined by said recess, the resilient annular members and the internal diameter of the pipe whereby the integrity of that pipe segment may be determined. The apparatus further includes a vent or passage through which the contents of the pipe upstream of the apparatus are allowed to pass.