Irrigation purge valve

Claim 1

An irrigation purge valve for connection to the end of a lateral irrigation water line to which a predetermined operating water pressure is applied, said valve comprising: a. an internally threaded, cylindrical cap having a closed end except for a single small opening of diameter d1 between 0.05 and 0.50 the inside diameter D of said cap; b. means defining an annular shoulder of outside diameter corresponding to the inside diameter of said cap and of inside diameter D' between 0.5 and 0.9 said outside diameter, said shoulder having a thickness T1 between 0.0125 and 0.125, the inside diameter of said cap being disposed at the internal closed end of said cap; c. a resilient disc of outside diameter corresponding to the inside diameter of said cap and having a single small opening of diameter d2 between 0.05 and 0.5 the inside diameter of said cap and a thickness T2 lying between 0.0125 and 0.2 the inside diameter of said cap, said disc being seated on said annular shoulder, the single opening in said closed end of the cap and the single opening in said disc being radially off-set from each other by a distance greater than the sum of their diameters d1 plus d2, the disc having an outside diameter and thickness value T2 and being of sufficient resiliency that it can flex so that its central area engages the closed end of said cap to completely close off said single small opening in said disc; and d. a coupling tube having stem means at one end for connection to said lateral and externally threaded at its other end in threaded engagement with the internal threads of said cap, whereby when the water pressure in said lateral is below a given value, water can pass through the small opening in said disc to the area inside of the shoulder and thence out the small opening in the closed end of said cap and, whereby when said water pressure exceeds said given value, the central area of said disc is moved into at least a portion of the area inside the shoulder to seat against the closed end of the cap and block water flow through the small opening in said disc and thereby block water flow through said cap.