Chemical Technology August 2016

PUMPS AND VALVES

centre of the impeller is where the velocity is greatest. If there is material at the centre of the impeller, there is insuf- ficient speed to eject the material which means that a swirl has to be created to remove the material. The swirl comes from the radius and shape inside the impeller vanes and this swirl is three-dimensional and it is this which moves the materials through the system. The F-Max achieves a highly effective swirl motion through a slight convex profile at the hub of the impel- ler, achieving efficiencies that have previously only been

Fibrous materials, such as hygienic wipes, have become a major problem in waste water transport as their use has markedly increased in the last few years. As a result of the trend towards conserving drinking water and separat- ing stormwater and waste water, the waste water to be handled has become ‘thicker’. This is why operators now demand non-clogging impellers that offer reliable operation without sacrificing high efficiencies, even for small waste water pumps. Based on decades of experience in free-flow impeller design, KSB’s hydraulic experts employed Computational Fluid Dynamics (CFD) to gain detailed knowledge about the complex flow processes inside the pump via computer-aided simulations. The F-Max Impeller combines outstanding hydraulics efficiency in a vortex impeller with the free pas- sage of rigid and non-rigid solids through the pump. The six vanes on the surface of the vortex impeller are spaced at irregular intervals (Figure 2) that creates gaps which allow rigid solids to pass through the impeller, even when the impellers is close to the suction cover. Machining grooves into the surface of the reverse side of the impeller spread out from the centre balances the axial thrust. Making a groove rather than a vane means that the impeller can be moved closer to the suction cover, thereby minimising the gap. Having resolved the issue with rigid solids, KSB’s designers turned their attention to that of soft tissues and similar fibrous materials. Blockages involving soft ma- terials start at the hub or ‘eye’ of the impeller and there is a physical reason for this. The revolving motion of the impeller introduces velocity and the greater the distance from the

Figure 2: The six vanes on the surface of the vortex impeller are spaced at irregular intervals.

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Chemical Technology • August 2016