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A screening apparatus for grading particulate material includes a grading screen having apertures for water and/or undersize particles to pass through. The grading screen is supported on a frame mounted on a chassis via resilient linkages, and the grading screen being vibrated by a vibrating device

A screening apparatus for grading particulate material includes a grading screen having apertures for water and/or undersize particles to pass through. The grading screen is supported on a frame mounted on a chassis via resilient linkages, and the grading screen being vibrated by a vibrating device that imparts circular or reciprocating motion to the grading screen. The grading screen is set at a predetermined slope whereby material to be graded can be delivered onto an upper end while the grading screen is vibrated to convey the material over the grading screen and to cause undersize material to pass through the apertures. Oversize material is discharged from a lower end of the screen onto a conveyor or into a collection bay or hopper. A sump beneath the grading screen receives under-sized material passing through the grading screen, and a jet pump conveys material from the sump to a dewatering screen.

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1. A screening apparatus for grading particulate material, comprising: a grading screen having apertures formed therein for water and/or undersize particles to pass through, the grading screen being supported on a frame mounted on a chassis via resilient linkages;a vibrating device operable to vibra

1. A screening apparatus for grading particulate material, comprising: a grading screen having apertures formed therein for water and/or undersize particles to pass through, the grading screen being supported on a frame mounted on a chassis via resilient linkages;a vibrating device operable to vibrate the frame and the grading screen;wherein the grading screen is arranged at a predetermined slope whereby material to be graded can be delivered onto an upper end of the grading screen while the grading screen is vibrated by the vibrating device to convey the material over the grading screen and to thereby cause undersize material to pass through the apertures of the grading screen, wherein the grading screen is operable to discharge oversize material from a lower end thereof onto a conveyor or into a collection bay or hopper;a sump mounted beneath the grading screen for receiving under-sized material passing through the openings of the grading screen; anda jet pump in fluid communication with the sump for conveying the under-sized material from the sump to a dewatering screen;wherein the grading screen comprises a split screen divided into an upstream section having a relatively small aperture size and a downstream section having a relatively larger aperture size, wherein the grading screen is configured so that undersized material passing through the apertures of the downstream section is collected in a separate region of the sump, and wherein the jet pump is configured to pass the undersized material from the separate sump region to the dewatering screen; andwherein under-sized material passing through the apertures of the upstream section of the grading screen are received in a main sump region, and wherein the apparatus comprises a further pump for pumping material from the main sump region to a hydrocyclone. 2. The apparatus of claim 1, wherein the jet pump is operable to entrain material from the sump into a high pressure stream of water. 3. The apparatus of claim 1, wherein the jet pump is mounted on an outer wall of the sump. 4. The apparatus of claim 3, wherein the jet pump comprises a suction chamber in communication with the sump via a feed passage, material being entrained into the jet pump via an opening in the outer wall of the sump. 5. The apparatus of claim 4, wherein the feed passage narrows from the outer wall of the sump towards the suction chamber of the jet pump. 6. The apparatus of claim 4, wherein a water inlet is provided at an upstream end of the jet pump, wherein the water inlet is connectable to a high pressure water supply of the apparatus, the water inlet communicating with a converging venturi section terminating in an outlet nozzle for supplying high pressure water into the suction chamber of the jet pump. 7. The apparatus of claim 6, wherein the outlet nozzle comprises a replaceable and interchangeable nozzle insert mounted within the venturi section of the jet pump, whereby a plurality of the nozzle inserts having different internal bores can be inserted within the venturi section of the jet pump to provide a desired water velocity within the suction chamber of the jet pump. 8. The apparatus of claim 4, further comprising a replaceable wear liner provided within the suction chamber. 9. The apparatus of claim 8, wherein the replaceable wear liner is formed from cast iron. 10. The apparatus of claim 9, wherein the replaceable wear liner is formed from high chromium cast iron. 11. The apparatus of claim 4, wherein the jet pump includes a mixing section downstream of the suction chamber, the mixing section having substantially parallel side walls. 12. The apparatus of claim 11, wherein an upstream end of the mixing section is provided with a radiused or rounded edge. 13. The apparatus of claim 11, wherein the jet pump includes a diverging diffuser section downstream of the mixing section. 14. The apparatus of claim 13, wherein the mixing section and/or diffuser section are replaceable. 15. The apparatus of claim 13, wherein the mixing section and/or diffuser section are formed from a high chromium cast iron. 16. The apparatus of claim 1, wherein the jet pump is mounted on a wall of the separate region of the sump outside of the sump. 17. The apparatus of claim 16, wherein the separate region of the sump comprises an auxiliary sump mounted within the sump of the grading screen. 18. The apparatus of claim 1, wherein the further pump comprises a centrifugal pump. 19. The apparatus of claim 1, wherein an underflow from the hydrocyclone is delivered to the dewatering screen. 20. The apparatus of claim 1, wherein the dewatering screen is split in a first section which receives material from the separate sump region via the jet pump and a second section which receives an underflow of the hydrocyclone. 21. The apparatus of claim 1, wherein the apparatus comprises a multi-deck screening apparatus and the grading screen comprises a lower deck of the multideck screening apparatus. 22. A screening apparatus for grading particulate material, comprising: a grading screen having apertures formed therein for water and/or undersize particles to pass through, the grading screen being supported on a frame mounted on a chassis via resilient linkages;a vibrating device operable to vibrate the frame and the grading screen;wherein the grading screen is arranged at a predetermined slope whereby material to be graded can be delivered onto an upper end of the grading screen while the grading screen is vibrated by the vibrating device to convey the material over the grading screen and to thereby cause undersize material to pass through the apertures of the grading screen, wherein the grading screen is operable to discharge oversize material from a lower end thereof onto a conveyor or into a collection bay or hopper;a hydrocyclone operable to dispense an underflow to the grading screen;a sump mounted beneath the grading screen for receiving under-sized material passing through the openings of the grading screen; anda jet pump in fluid communication with the sump for conveying the under-sized material from the sump to a dewatering screen;wherein the grading screen is configured so that undersized material passing through the apertures of a downstream section is collected in a separate region of the sump, and wherein the jet pump is configured to pass the undersized material from the separate sump region to the dewatering screen; andwherein the dewatering screen is split in a first section which receives material from the separate sump region via the jet pump and a second section which receives the underflow of the hydrocyclone.