Patent ID: 7232360

Claim:
A method of maintaining a substantially uninterrupted flow of a pressurised abrasive slurry, the method including the steps of: (a) discharging abrasive slurry from one vessel of a plurality of vessels while charging another of the plurality of vessels with an abrasive material, (b) successively repeating step (a) to recharge each vessel in turn with abrasive material while alternately discharging abrasive slurry from each vessel in turn, and (c) passing the abrasive slurry discharged from the vessels through respective flow-controlling outlet valves to a common outlet at which the substantially uninterrupted flow is maintained, wherein a position of each of the outlet valves is not changed from i) an opened to a closed position or ii) from a closed to an open position unless there is substantially no pressure differential across the valve and substantially no flow through the valve.