form of pulses from the feeder pipes 20 to the water chambers 22 since the pulsator devices pass the water into the water chambers 22 intermittently in the form of pulses rather than continuously and since the volume of the annular water chambers 22 is relatively small being the difference between the volume defined by the inner surface of the outer pipe 21 and the outer surface of the inner feeder pipe 20 the illustrated construction permits very low discharge rates to be produced from the dripper devices 23 even though such driper devices have relatively large passageways and thereby a low sensitivity to clogging the dripper devices 23 may be any of the known constructions with or without pressure compensation e g as described in u s pat nos 3 981 452 4 281 798 4 307 841 4 687 143 or 5 236 130 however if pressure compensated pulsators are used each section of the line defined by a pipe assembly 2 becomes pressure compensated thereby obviating the need for pressure compensation in the dripper devices fig3 illustrates a system as described above with respect to fig1 and 2 in which the dripper devices carried by the outer tubes 21 are off line dripper devices as shown at 23 39 attachable in discharge openings formed in the outer tubes 21 of the pipe assemblies 2 except for this difference the structure and operation of the apparatus illustrated in fig3 is the same as described above with respect to fig1 and 2 and therefore corresponding reference numerals have been used to identify corresponding parts while the.