If metal fines are filling the vacuum hose connected to the Valve-Less Vacuum Blocks or reaching farther into the vacuum system, you may need to install a filter closer to the block. This will require regular cleaning of the filter so as to maintain a free outflow of air from the cavity. Alternatively, you can disconnect the hose section and blow it out as needed. Either solution is satisfactory and depends upon the specific casting process.
Systemically metal dust may be caused by velocity of metal entering the chill vent as it “freezes” off. It is possible to reduce this in some cases by reviewing exit runners to ensure proper reduction in velocity.