A device for accumulating articles within a system may include a frame, a mass-flow infeed conveyor supported by the frame for receiving articles from the system, and a mass-flow outfeed conveyor supported by the frame for receiving articles from the infeed conveyor and returning the articles to the system. A single-filing device is supported by the frame and includes a plurality of parallel endless loop conveyors. The endless loop conveyors each have an upstream end located laterally from and between upstream and downstream ends of the infeed conveyor.