Further test machines were then built in larger diameters and fitted with variable speed drives. This led to the discovery that the device would also work very effectively at very low speeds and with a very large range of products. It was also found that surprisingly large clearances could be used between the inside of the rotating tube and the screw, thus avoiding damage to fragile products.
From these findings it was realized that the device worked in two distinct modes and that, at very slow speeds, centrifugal force and the boundary layer theory did not count.