Abstract: The invention provides an abrasive jet system having a high-pressure fluid supply (10) means supplying fluid to a vessel (11) which includes a layer of abrasive slurry and a top layer that contains substantially of fluid over the layer of abrasive slurry. The system also includes a first conduit (14) which leads from the fluid supply means to the top layer of fluid in the vessel and as high-pressure fluid is fed into the vessel, causes displacement of abrasive slurry from a discharge conduit (16). The system further includes a second conduit (21) which connects at different points to the first conduit and the discharge conduit, and including a fluid valve (13) between the operative connection to the first conduit and the discharge conduit, that controls the fluid flow within the second conduit.