Newsletter February 2016

Low Pressure – How important is it really?

In our advertising we always state that we aim to achieve ‘low pressure’ operation, why is this?

From a purely mathematical point of view and by using the standard formula-

kW = Head(mtrs) x Volume(m3/hr)  / 360 x pump efficiency as a decimal

We can see that if we can lower the pressure at our water pump (Head) we are also proportionally lowering the hp(kW) required to drive the pump and therefore also lower our running costs.

  • In simple terms, if we can half the pressure, we can half our running costs.

Long term running costs is one of the most important factors in achieving an efficient irrigation system. Over the life of a centre pivot system, let’s use 20 years in this example, there are 2 main steps we can take to help reduce operation pressure. The first is to minimise friction loss in both the delivery pipeline and also in the pivot itself. This is done by utilising large bore PVC pipes for the mainline and the use of some larger diameter span pipes for the first few spans of the pivot.  The second method is to use a sprinkler and regulator package with a lower design pressure. The difference between a ‘cheap’ poorly designed pivot system compared to one of a more efficient design can typically mean a reduction of around 15-20 psi at the pump.

  • On a diesel driven pump set this can equate to a saving of around $2000 per year on an average centre pivot system. This becomes $40,000 over the 20 life of the pivot. Just by saving 15 psi.

A typical ‘mistake’ we encounter is people attempting to save money by using an older existing pipeline. In years gone by pipelines may have been installed with less consideration to overall operating costs. There are quite a few cases of irrigation systems requiring 40-50 psi more operating pressure than they truly need to, this can mean spending an extra $120,000 over 20 years in pumping costs alone. How much is that ‘cheap’ irrigation system really costing you?

Is there such a thing as going too low? Yes. Different sprinkler heads require different operating pressures and are specifically designed for particular applications. A rotator head below a 20 psi regulator will provide a large coverage area and superior crop penetration but is not required in most crop conditions where a spinner head or wobbler with a 10 psi regulator will do. This change alone can mean a 10 psi saving before looking at pipeline losses. Going too low with a 6 psi regulator and basic spray body may work ok in a LEPA (low energy precision application) system where there are very close sprinkler outlets but in general it will not provide enough water spread to effectively cover the distance between sprays or penetrate a tall crop. Your irrigation dealer or agronomist would be best to advise you on the most suitable sprinkler head for your application.

Thanks for reading,

Paul Upton

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