Drip irrigation system

A drip irrigation system comprising a thermoplastic conduit for conducting irrigation liquid, outlet apertures formed in said conduit in an axially spaced relationship, a plurality of discrete, substantially flat emitter units, respectively heat welded to axially spaced apart locations of an inner surface of said conduit which locations respectively include said apertures, each emitter unit comprising a body member of a substantially rigid thermoplastic material which is heat sealable with respect to the conduit, said body member having a first portion thereof heat welded to one of said spaced apart inner surface locations in a juxtaposed relationship with one of said outlet apertures and having a second and opposite portion thereof with an elongated groove formed therein, a cover member juxtaposed with respect to said second portion and defining with said groove a flow restricting flowpath spaced and thermally shielded from said first portion, said flowpath being directed towards the interior of said conduit and being located substantially in the flow direction of said conduit, emitter unit inlets serving respectively to effect communication between the conduit interior and the inlet portions of the flowpaths, and emitter unit outlets serving respectively to effect communication between adjacently formed outlet apertures of said conduit and outlet portions of said flowpaths, said outlet portion of said flowpath including a recessed cavity formed in said second portion of said unit and being of extended dimensions as compared with the width of said groove and wherein said unit outlet comprises an outlet bore formed in a base portion of said recessed cavity, said outlet bore having a rim area substantially less than that of said cavity, said cavity constituting an outlet control chamber, and wherein said cover member is constituted by a resiliently flexible membrane formed of an elastomeric material and displaceable toward and away from said flow restricting flowpath in accordance with flow pressure variations in said conduit so as to stabilize the output rate of said emitter unit with respect to said variations, said emitter unit body member comprising a transverse wall portion, a peripheral rim formed integrally with and extending from a first face of said wall portion and defining a well of extended dimensions as compared with said outlet aperture, said groove and cavity being formed in a second and opposite face of said wall portion, a peripheral skirt extending from said second face and around said groove and cavity and formed integrally with a plurality of retaining flanges, and said membrane being retained by said flanges so as to define with said groove and cavity said flowpath, said outlet bore extending through said wall portion.