Schauberger
The speed of the ore, which moved silently along the pipe-axis, was so great that the passage of lumps of ore larger than fist-size could not even be observed in the crystal-clear water through the observation windows. Even at the point of discharge, the speed was too great to be able to discern the stones, etc. [The Energy Evolution - Harnessing Free Energy from Nature, The Transport of Ore in Double-Spiral-Flow Pipes]