text: Improvements to this early design included a focus on the weight and wear of the downcomer. The downcomer was originally built with polyurethane-lined steel, and then changed to a high-density polyethylene ("HDPE") construction with seven elements.
  The orifice plate used to generate the slurry jet was a high-wear item and its materials of construction were also a focus of the development effort. After testing high-chromium hardened steel and various ceramics, high-density alumina was found to have excellent wear properties, and it became the standard.