A self-closing valve for flushing drip-irrigation lines at the beginning of every irrigation cycle. The valve comprises a housing defining an enclosed space, having an inlet portion mountable to the line end, allowing free communication with the water of the line. The housing comprises an elastic membrane dividing the enclosed space into upstream and downstream compartments with respect to said flow, with a passage communicating between the said compartments. A discharge opening is formed in the upstream compartment. Flow impeding means are associated with said passage for restricting the flow of water from the upstream compartment into the downstream compartment, said flow being effective to flex the membrane in the upstream direction until it closes against the discharge opening.