There is disclosed a drip-forming device and system for drip irrigation. The device includes a tube and a rod having one end inserted into the tube by an adjustable amount, the rod being formed with at least one longitudinal groove which extends along at least part of the length of the rod and which is in communication with the part of the interior of the tube not occupied by the rod and whose depth decreases progressively away from the said one end over at least part of the length of the groove. With such devices, the output of each device can be simply adjusted to suit the local requirements, irrespective of the size, alignment and supply pressure of the complete irrigation apparatus, by adjustment of the depth of insertion of the rod in the tube. For a constant pressure the water output decreased with increasing depth of rod insertion - i.e., as the minimum cross-section of the groove at the point of insertion of the rod in the tube decreases. At different pressures depending, for example, on gradient, the water output from different devices can be made equal by varying the depth of insertion of the rods in the tubes appropriately, such depth being increased as the pressure increases - i.e., the minimum cross-section has to be decreased.
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