2 impeller selection and design

Impeller Selection & Design

The Municipal Task

Pumping municipal sewage means to pump

Water + X

And sewage pumps, large and small must be designed to cope with these „X“ up to a reasonable limit.

Design Criteria for Sewage Pumps

•X stands for everything, which can enter the sewer

•X can be things, which can pass a toilet or a gully and which we expect in sewage:

•Faecal, toilet paper•Grease from Restaurants•Sand from roads

•X can also be things which can pass a toilet or gully, but which we should not expect in a municipal sewer:

•Textiles•Paper•Plastic articles•…

Limits of Sewage Pumps

There may also be things in sewage, which we cannot expect, also if all the water has to pass a toilet or a gully:

•Big amounts of sand from construction areas•Trash from farms, markets, small industry, etc

In these cases the responsibles have to investigate and probably to educate!

If the sewer is broken or e.g. gully grills are removed, we have to face probably:

•Briggs and stones•Lockwood•Dogs, cats, …•Cars, bicycles, furniture, tyres, …

Here the system has to be improved and pumping stations and equipment have to be protected, e.g. by screens

The large pumps Motors with high kilowatt rating Long running hours Large hydraulics

Importance of Design Criteria:1. Motors with good efficiency (costs of motor)

2. Hydraulics with good efficiency (classical optimization)

3. Resistance against blockage (easy to achieve, as large flow means large passage, multi-vane, high power)

Design of Pumps for Municipal Sewage

The small pumps Motors with low kilowatt rating (90% of all

sewage pumps in Europe have 1.5 to 7.5kW)

A few running hours (typically in Europe 1000 hours per year)

Small hydraulics (80 to 150 mm)

Importance of Design Criteria:

1. Resistance against blockage (not easy to

achieve, as pumps are small and power is low) 2. Hydraulics with reasonable efficiency

(not easy, as blockage resistance needs low number of impeller vanes and special design)

3. Motors efficiency (not so important, as low running hours and low kilowatts)

Design of Pumps for Municipal Sewage

Q [l/s]

Impellers For Sewage Pumping

For small and medium sized pumps Vortex Impellers

Very good resistance against blockageLow wear by abrasivesVery low efficiencySmall to reasonable solids passage

Impellers For Sewage Pumping

Closed channel impellersInsufficient resistance against blockageHigh wear by abrasivesGood efficiencySmall solids passage

Open channel impellersContraBlock® Very good resistance against blockageMedium wear by abrasivesReasonably good efficiencyLarge solids passageThe compromise

The old way of design and optimization First trial

DesignPattern makingCastingMachiningHydraulic testBlockage test

First optimizationPattern modificationCastingMachiningHydraulic testBlockage test

….

Impellers For Sewage Pumping

Pump head vs. impeller position

CFD Simulation of Sewage pumps

Hybride Meshing

Impeller prototyped directly from 3D-CAD Systems

Impeller prototyped directly from 3D-CAD Systems

Contrablock Patent

United States Patent No. 3,447,475Titel: Centrifugal PumpRegistration: Jan 9, 1967Patent filed: June 3, 1969Inventor: Albert Blum

The oldest Leaflet including Contrablock: 1966

R&D tests– according to ABS Works Standard– documentation by Video

Field tests– in selected places around the world

• municipalities• hotels• jails, ...

ContraBlock®

Tested - tested - tested - ...

ContraBlock® Clogging Test

ContraBlock® Clogging Test

ContraBlock® Clogging Test