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How to prevent air lock in the eye of your froth pump 

One of the key challenges in pumping slurry with air entrained is that the air will naturally centrifuge into the centre of the pump, the eye of the impeller, where it forms an ‘air lock’ which physically blocks the slurry from progressing through the pump. 

Eventually, this will block enough slurry to create a surge, where the amount of slurry in the sump builds up so much that the pressure it exerts eventually forces the air through the pump, which can cause significant strain on the pump’s bearings via a cyclic axial load, and a radial load on the pump’s impeller and shaft, decreasing their wear life.  

Firstly, it’s important to ensure the pump’s discharge pipe is either at the top or positioned at a 45° angle to allow air which has been trapped in the pump’s casing to escape outwards. Pumps using the horizontal discharge at the bottom will quickly build up air inside the casing, rendering them ineffective.  

When this isn’t enough, the most effective way of alleviating this problem is using a pump with an integrated Continual Air Removal System (CARS), which is available with the Warman® AHF, MF and LF pumps for applications which require it. With CARS, the pump uses vent holes in the impeller to move gas into a dedicated collection chamber in the back end of the pump. From here a flow inducer facilitates the movement of the air through vent pipe and out of the pump. 

This continuous removal prevents air build-up in the impeller’s eye and promotes efficient slurry transport. 

How to manage tenacious froths  

Mineral froths are generally classified as either brittle or tenacious. Brittle froths feature large bubbles that break easily, while tenacious froths often feature very fine bubbles which can be much harder to separate from the surrounding slurry liquid.  

As ore grades drop around the world, two trends in mineral liberation are producing increasingly tenacious froths, which contribute to the pumping difficulties site operators are encountering. 

Firstly, the increasing percentage of fines and ultra-fines being ground are leading to smaller bubble formations and more tenacious froths. Secondly, increasing amounts of flocculants are being added into the slurry which lock up the air into even smaller bubbles.  

Together, these can result in a highly tenacious froth which forces operators to design a more accommodating froth pumping circuit by adhering to best-practice design as outlined above or reduce the flocculant of fines being deployed into the slurry.  

Weir Minerals has a long history with froth pumping and its specialist engineers can help you resolve issues in your flotation circuit. To find out more, download the whitepaper below.