I can comment on the material property involved, i.e., permeability. The finer powder has a much lower permeability. If it settles in any place, it will consolidate to a cohesive solid.

The potential solutions include:

  • be sure that the hopper and line charger are feeding a uniform rate and density*
  • be sure that the line charger is not leaking air back into the feed hopper
  • carefully eliminate any locations in the system where the velocity drops below the settlement velocity
  • minimize the length and eliminate any lines that taper down in elevation

*The finer material may not be suitable for the feed hopper. If the material is forming a rat hole due to an improper hopper shape, periodic flushing can cause a swing in bulk density of up to 30%, which will unbalance the line.