Abstract: In order to draw water free of sand from a well bored into a water-bearing strata a cylindrical permeable body is located concentrically within the perforated wall of the well. The cylindrical body may in turn comprise concentric outer and inner slotted tubes with a permeable cylinder or a granulate therebetween. The lower end of the cylindrical body is closed and the upper end is connected to a pump.

Abstract: .Iadd.An improved extrusion method is provided to produce plastic tubes having at least one end thereof an increased wall thickness. The method includes the steps of continuously advancing plastic material through an extruder to form a cylinder, cooling the extruded cylinder as it passes from the extruder, periodically increasing the speed at which the plastic material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder to produce a section having an increased wall thickness and dividing the cylinder thus formed. .Iaddend.