in a modification not shown of the embodiment described with reference to fig1 to 4 the flaps or diaghragms are attached to the tubes by press studs whereas in the embodiments described with reference to fig1 to 4 the tubes are made as closed sections and place high requirements on production manufacture of the irrigation system can be considerably simplified if in accordance with the modifications to be described hereinafter the tube is open in the as made condition fig5 a 6a 7a and 8a show the respective open section as made and fig5 b 6b 7b and 8b show the respective subsequently closed section in the condition of installation and use the tube of fig5 a 5b and 5c is extruded in strip or band form from plastics material and is provided at one longitudinal edge with a flange in the form of a pressure or slide fastener section 16 a cooperating flange is provided at 17 intermediate the longitudinal edges the flap 18 is extruded in one piece with the band the outlet apertures 19 are stamped out subsequently when the closed section has been made by interlocking the pressure or slide fastener sections 16 17 the flap 18 underlies the outlet aperture 19 the pressure or slide fastener sections should be such that the connection 20 fig5 c is watertight and cannot become automatically undone the modification of fig6 a 6b differs from that of fig5 a to 5c merely in that the flanges 21 22 are interconnected.