Hi Tsaone - if your underflow pumps are blocking there are many reasons for this and is usually caused by poor operating technique, assuming good design and the pumps are in good condition. Cheers

Hi Tsoane

If you are dewatering grits, the underflow material may be too coarse to transport through the suction line to the pumps. In other words the average settling velocity may be greater than the velocity required to suspend the solids in the pipeline. This would certainly result in blockages in the underflow line.

A thickener is not the best way to dewater grits. A spiral classifier or cyclone may be more appropriate for this.The classifier overflow would be dewatered in the thickener in the usual way. 

Hope this helps.

The UltraSep is normally used in the diamond industry as a rakeless thickener. Several mines have these thickeners and they all give similar results and challenges.

Ultraseps are difficult to control because there are not many instruments to get readings from and establish what is happening in the thickener.

My first guess without any more information is that the flocculant dosing is not controlled well and therefore the yield stress in the underflow varies to such an extent that the underflow pump is difficult to operate.  The flow to the pump also varies because of the lack of racking and the bridging of the bed in the cone of the thickener.  This bridging is often the cause of failure within the thickener and the internals to shear off from the bridge and fall to the bottom.

Should I be correct in all or most of the assumptions made regarding your application, I can assist with how to mitigate many of these challenges.