| 摘要 |
When an abrasive mixture is supplied through conduits (191) containing valves (309), considerable wear is experienced by the valve when it is operated with abrasive material within it. The present invention aims to reduce wear on such valves by providing means (193, 308) to flush the valve before operation so that the abrasive material content is reduced preferably to zero. This avoids abrasive particles becoming caught between working parts of the valve and causing undue wear. When the conduit leads to a nozzle (222) from which the abrasive mixture is jetted for cutting purposes, the flushing of the valve will cause a reduction in the concentration of abrasive mixture at the nozzle in the normal circumstances. In order to avoid this reduction of concentration, the outlet of the valve can be fed to the nozzle through an abrasive mixture reservoir (310) which will smooth out variations in the abrasive mixture concentration and so maintain the efficiency of the jet from the cutting nozzle. |
