Patent ID: 7448151

Claim:
A tool for excavating an object, the tool comprising: a jetting system having a nozzle means arranged to receive a fluid and abrasive particles via an abrasive particle inlet, and arranged to impinge the object to be excavated with a jetted stream of the fluid mixed with the abrasive particles; a recirculation system arranged to recirculate at least some of the abrasive particles from a return stream, downstream of impingement of the jetted stream on the object to be excavated, back to the jetting system via the abrasive particle inlet, and a filtering means disposed in a path fluidly connecting said return stream with the abrasive particle inlet, wherein the filtering means includes an opening that is sized to keep the abrasive particle inlet free from objects of the same size or larger than the abrasive particle inlet, which filtering means allows passage of the abrasive particles; wherein the recirculation system comprises a transport device for transporting the abrasive particles in a selected direction towards the abrasive particle inlet, the abrasive particle containing a magnetic material, and the transport device comprising: a support member having a support surface for supporting the abrasive particles, the support surface extending the selected direction; a separator magnet arranged to generate a magnetic field for retaining the particles on the support surface whereby the magnetic field on the support surface is arranged to have a high-field band, a low-field band, and a magnetic field gradient in a gradient zone between said high- and low-field bands whereby the magnetic field strength in the high-field band is higher than that in the low-field band; and means for advancing the high- and low-field bands relative to the support surface in a direction having a component in the direction of the magnetic field gradient on the support surface, whereby the high-field band is followed by the low-field band.