Abstract: A separating hopper for separating grit and dust feeds downwardly through a valve into a grit transfer hopper which feeds downwardly through a valve into a grit supply hopper. The grit supply hopper is connected to a blasting nozzle, and a return conduit extends from the nozzle to the separating hopper. A dust collector housing is connected to the separating hopper, and bleed conduits connect the dust collector housing to the interior of the grit supply hopper and grit transfer hopper. Controlled valves in the bleed conduits simultaneously open and close the connection between the dust collector housing and the grit supply hopper and grit transfer hopper. A compressed air source is connected by a control unit to the grit supply hopper and grit transfer hopper, and also to the blasting nozzle. The control unit as well as the controlled valves are controlled by a switch at the blasting nozzle.