The retaining wall in Harlingen is the last stretch of dike that has been raised to delta height. The retaining wall has a roller door that will normally be open, but will close during storms and / or extremely high water. Molenmaker Techniek B.V. provides the roller door with a hydraulic system, which consists of a hollow rod cylinder of Ø140 / Ø90 with a stroke of 5400 [mm] and a hydraulic power unit consisting of, among other things, an accumulator and a motor / pump combination with adjustable output.