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.Apparatus to produce widenings at tube ends with precise dimension of the inner surfaces of the widened zone which includes a holding device for the tube to be worked, a variable form core arranged axially in front of the center of the holding device, a device for axially displacement of the core, a cylinder axially movable over the tube for exterior calibration and adaptation of the tube end to the core, and a device to bring the core to a shape in which it can be drawn from the formed tube end. .Iaddend.

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.