A check valve (36, 136) for a screw (24) is provided. The check valve (36, 136) includes a retainer tip (54, 154), operable to be attached to a distal end of a screw shaft (52, 152), the retainer tip (54, 154) defining at least one melt channel (30). A first ring (60) is coaxially mounted to and rotationally-coupled with the retainer tip (54, 154). A second ring (66) is coaxially and slidably mounted to the retainer tip (54, 154), and is operable to rotate relative to the retainer tip (54, 154). The second ring (66) is operable to reversibly move between an open position which permits melt to flow through the check valve (36, 136) and a closed position which prevents backflow of the melt.