The standard irrigation system evaluation protocol for Centre Pivot irrigators has been amended. The main change is the removal of the Circular Uniformity test.
The updated protocol can be downloaded from: http://www.pagebloomer.co.nz/wp-content/uploads/2010/04/COP%204-7%20Centre%20Pivot.pdf
The Circular Uniformity test was adopted on recommendation from the Irrigation Association publication, “Center Pivot Design” 2000, pp179 – 181.
Our experience found the test to be problematic; much variability noted during such tests has been due to the radial variation (differences as you move along the length of the machine) rather than elevation difference or hysteresis effects.
The Evaluation Code Centre Pivot Evaluation protocol retains the Radial Uniformity test, and recommends multiple radial tests with and without any end gun, corner arm or other major variable operating. Repeating radial tests in up-slope and down-slope positions would also appear more useful than a circular uniformity test.
The most common failings we have identified to date are associated with incorrect nozzle selection and or insufficient system pressure.
Nozzle package selection should provide a machine with high performance. Unfortunately, too often this is not the case. The ‘blame’ is usually identifiable and there is no one answer.
In some cases, system purchasers (farmers) provide water / well flow rate information that is optimistic. Perhaps the information originates with well drillers, perhaps it is simple misunderstanding or forgetfulness. Regardless, once built and the true flow measured, it becomes obvious that the possible flow will never match the demand of the nozzle package supplied.
In other cases the specifications for the machine length have changed but the nozzle selection not redone. And in a couple, the package was just wrong!
Low (unsatisfactory) end pressure is also relatively common. Often there is insufficient flow available to fill the system, as noted above. Other times we find incorrect settings in variable speed drive controllers. It is good to set systems to minimise energy consumption, but excessively low pressure is false economy. Make sure the pumps are working to design specs so the system does the job for which you bought it.
We like to see a pressure test point or pressure gauge mounted above the regulator on the last dropper on the main machine. If the pressure there is less than 40kPa higher than the regulator setting, we expect to find low performance.