Abstract: An apparatus for cutting openings at arbitrarily selectable intervals into a pipe which has a smooth inside or outside surface or a transversely corrugated inside or outside surface comprising a knife disposed inside or outside said pipe, and a movable element whose movement is responsive to a signal to move the knife and pipe wall into mutual contact so that the knife cuts into the pipe wall. Disclosed herein is an apparatus which cuts an opening through the surface of a smooth inner pipe disposed within an outer pipe having transverse corrugations. Also disclosed is an apparatus whose knife is disposed exteriorly and is employed to cut openings into the exteriorly disposed transversely corrugated pipe. The application further discloses an apparatus comprising a pipe forming machine, an apparatus which cuts a hole in a pipe from within the pipe and an apparatus which cuts a hole in a pipe from outside the pipe.

Abstract: In the manufacture of double-wall plastic tubing in which the outer wall has transverse corrugations and the inner wall is smooth, in the case of annular transverse corrugations the air pressure between the two walls cannot be balanced with the external air pressure, resulting in deformations of the inner tube. To permit an equilibrium of pressure before the inner wall hardens, openings are pierced in the outer wall or openings are produced between the two walls for communication between the inner chambers of the transverse corrugations. After the hardening of the inner tube, these openings are reclosed by fusion.