Chemical Technology August 2016

Chemical Technology • August 2016

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

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

Figure 2: The six vanes on the surface of the vortex impeller

are spaced at irregular intervals.

PUMPS AND VALVES