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1. Affinity laws for dredge pumps

The usual details

Usually, the characteristics of dredge pumps can be described as second order polynoms, derived from the so called affinity laws. These are well discussed in the textbooks. Also, my professor Vlasblom had a special lecture about them.
Warning to dredging students end other theoretical orientated visitors who stumbled on this site and read this article: Do read the theory!. Once you understand the processes, you will be using them everywhere in your dailing dredging job.

The unusual details

Most text books on dredge pumps start with the laws of Bernouilli and work out the affinity laws from there and than they end up with a second order polynom. This means that you can describe the characteristics of a dredge pump like a parabola. However, if you have ever seen a dredge pump characteristic, you will know that in practice, this is usually not looking like a parabola. At zero flow, you have an extra drop in head because of the no flow condition. At very high flows, the curve wanders of, because irragularities in the impeller come forward much more than at the design condition, so you also have another additional drop. My opinion is that you can describe the characteristic much better by a fourth order polynom. This means you need five parameters to fix the form of the curve.

I would like to add more details to this story, to make it a little more accesible. If you've ever wrapped your mind around the things I am talking about, than you can follow my reasoning. Later I will clean up this article, so please come back again.



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Updated: 17-04-2009