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

Design of Pumps for Municipal Sewage The large pumps  Motors with high kilowatt rating  Long running hours  Large hydraulics

Importance of Design Criteria:  Motors with good efficiency (costs of motor)  Hydraulics with good efficiency (classical optimization)

 Resistance against blockage

(easy to achieve, as large flow means large passage, multivane, 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 hours per year)

 Small hydraulics

(typically in Europe 1000

(80 to 150 mm)

Importance of Design Criteria:  Resistance against blockage

(not easy to achieve, as pumps are small and power is low)

 Hydraulics with reasonable efficiency

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

 Motors efficiency

(not so important, as low running hours and low kilowatts)

Impellers For Sewage Pumping

Q

[l/s]

Impellers For Sewage Pumping

For small and medium sized pumps Vortex Impellers

Very good resistance against blockage Low wear by abrasives Very low efficiency Small to reasonable solids passage

Open channel impellers ContraBlock® Very good resistance against blockage Medium wear by abrasives Reasonably good efficiency Large solids passage The compromise

Closed channel impellers Insufficient resistance against blockage High wear by abrasives Good efficiency Small solids passage

Impellers For Sewage Pumping

The old way of design and optimization First trial Design Pattern making Casting Machining Hydraulic test Blockage test

First optimization Pattern modification Casting Machining Hydraulic test Blockage test

….

CFD Simulation of Sewage pumps STRATEGY The strategy adopted is the combination of the Design of Experiments method (DOE) with Numerical Simulation (CFD). • Design of Experiments is a numerical regression method. It allows efficient analysis of multiple design parameters. In this case, factors critical to blockage performance were selected. • Full transient numerical simulations are carried out in CFX-5. Unsteadiness in the flow is exaggerated by the single blade impeller, thus inducing inaccuracy in the less computationally expensive steady state analysis.

CFD Simulation of Sewage pumps Pump head vs. impeller position

Hybride Meshing

Impeller prototyped directly from 3D-CAD Systems

Impeller prototyped directly from 3D-CAD Systems

Contrablock Patent

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

The oldest Leaflet including Contrablock:

1966

ContraBlock® Tested - tested - tested - ...  R&D tests – according to ABS Works Standard – documentation by Video

 Field tests – in selected places around the world

• municipalities • hotels • jails, ...

ContraBlock® Clogging Test

ContraBlock® Clogging Test

ContraBlock® Clogging Test

ContraBlock® Clogging Test

ContraBlock® Clogging Test