A rundown screen is a no-moving part separator with a very simple principle of cascading slurry down a wedge wire screen to remove the solid fraction.
Wedge wire is a very simple and effective technology that is incorporated into many products that require a screen/grating that is difficult to clog – triangular shaped steel wire profiles equally spaced apart creating voids that enlarge away from the surface. Rundown screens consist of many Stainless Steel wedge wire profiles running across the width of the screen, the profile size of wire and spacing distance (void) is determined by the solid removal requirement.
Slurry is pumped into the unit’s top chamber, flows over its full width weir and cascades down the curved screen. The liquid fraction passes through the void areas into a collection chamber to be pumped away to larger storage or flushing tank/s. Entrained solids larger than the void size, start to collect on the screen surface towards the top, and as the solids build-up due to the continuous process, are driven down the screens surface being gently compacted and further dewatered as the mass moves down. When the solid fraction eventually reaches the end, simply drops onto the dung pile.
Throughput speed is determined by several factors:
- Slurry DM (whether raw or recycled from flushing)
- Desired particle size removal (wedge wire and void size)
- Unit width (spec’d for desired throughput)
- Speed of the slurry flow (set inlet valve position)