Abstract: A drip irrigation system which includes a flow control valve having an inlet opening which constricts in response to pressure increases to provide a uniform flow despite pressure variations. The inlet opening of the valve has a rectangularly cross-sectioned central section and end sections which are non-rectangular, such as triangular or semi-circular, in cross section. During normal flow conditions the rectangular central section of the inlet opening is pressed closed and irrigation liquid flows at a constant rate through the two end sections.

Abstract: An emitter for use in drip irrigation systems which is both self-purging and pressure responsive to provide substantially constant flow rates with varying inlet pressures. The emitter includes a flow path which consists of a series of interconnected openings in each of which is positioned a valve including a valve lip which extends across the opening in which it is located and is directed in an upstream direction so that as the pressure drop across any one valve increases, the effective area of the flow path at that valve will decrease to maintain a substantially constant flow rate. When the pressure drop at a particular valve increases above a predetermined amount, as when a particle of dirt or other foreign substance clogs the valve, the valve lip travels over center and allows the clogging particle to pass, thereby purging that particular valve and permitting it to return to its normal operating position.