Check valve for an injection molding machine

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