An extrusion blow molding method includes detecting an exit velocity of a tube exiting a head during a blow molding cycle for forming the tube. A melt accumulator receives part of the melt conveyed by an extruder or discharges melt in addition to the melt conveyed by the extruder in dependence on the detected exit velocity. The melt accumulator discharges melt if the detected exit velocity is less than a target value for the exit velocity and receives melt if the detected exit velocity is greater than the target value for the exit velocity.

A piece insertion method for a pipe, for example an irrigation pipe, including: ejecting at least one piece, for example a dripper, from an ejection unit, advancing the at least one dripper inside the irrigation pipe by a dripper advancing unit, lifting the dripper towards the inner surface of the irrigation pipe by using a lifting device such that the dripper is parallel or substantially parallel to this inner surface of the irrigation pipe on impact with this inner surface. The method according to the invention allows also coordination between the lifting device, the ejection unit and the dripper advancing unit such that the dripper spacing can be maintained in tight tolerances.

Pipe corrugators having opposed series of pushed mold blocks forming a moving mold tunnel are subject to significant thermal expansion and are designed with a thermal expansion gap. The present invention provides a method and apparatus for measuring changes in this expansion gap and preferably recognizing potential thermal issues before serious problems occur. A sensor is provided adjacent a mold block drive that preferably detects a time duration between sensing a trailing portion of a lead mold block and a leading edge of a following mold block separated from the lead mold block by the thermal expansion gap. This time duration in combination with a speed of the pushed mold blocks is used to calculate the size of the thermal expansion gap.