Abstract: In a plastic filler neck cap including therein a receptacle for a pressure control valve and a receptacle for an anti-leakage assembly, a positive-negative pressure valve is compactly constructed in such a manner that the valve body retainer plate is formed into a hat-like configuration including an upper portion with a passing hole at its center, an outer peripheral wall and a spring reception tongue; the valve body is in engagement with the valve body retainer plate whose passing hole sustains a portion of the valve body; the valve body presents a double-disk shape with a smaller upper disk and a larger lower disk having on the upside a peripheral upper ridge and on the downside a lower ridge inside the upper ridge, and further a center communication opening extending through both the disks; the diameter of the negative pressure valve body is predetermined larger than the extension of the lower ridge on the bottom of the valve body, forming a pan-like shape setting the opening side down with a skirt portion