Support for this study was provided by The Southeastern Peanut Research Initiative of the National Peanut Board and the Georgia Peanut Commission.

Rationale:The most common low-pressure sprinkler package on Georgia pivots are sprays directly on the boom. Normally designed to discharge water with inlet pressures of 10 to 20 psi, the nozzles must be carefully sized and spaced and the pivot operated under the package design. Because pressures vary along the pivot during operation, some packages are designed with some or all nozzles fitted on pressure regulators. When operators change sprinkler nozzles, remove regulators, remove end-gun booster pumps or otherwise change operating pressures, the sprinklers may be operating at 10 to 50 psi over design. More water may be pushed out of the nozzle at higher pressure, but finer droplets and altered spray patterns result. This study examined water delivery and water losses from over-pressurization.

Study Objectives: No Data

Methods and Equipment: For the Over-Pressurization Study, a standard package of Senninger Low Drift Nozzles (LDNŽ) for top of boom operation was designed by Senninger.In this study, three commercially-available center pivot (CP) irrigation systems were fitted with 27 spray nozzles on top of the mainline. The spray nozzles were installed on 9 ft spacing along the mainline. The spray nozzles were sized for an irrigation system operating at 10 psi at the pivot point. Two higher pressures (25 and 40) were selected that would represent approximately a 2.5X and a 4X pressure increase and would be typical of irrigation systems being retrofitted. The three pressure regulator sizes (10, 25, 40) were installed on the 3 center pivot systems in a 3 x 3 Latin Square pattern for statistical analysis purposes. Nine regulators of each size were installed in a group along the mainline of each system to create three approximately 80 ft zone lengths. Table 1 describes the arrangement of the regulators on the three systems. Water was supplied from two deep wells that supply water into a pressurized piping system. Pressure sustaining valves (CycleStop, Lubbock, TX) at each well allow the supply lines to remain pressurized at a nominal 60 psi.



A cluster of 10 catch-buckets was randomly placed around the points centered at 80, 150, and 220 ft. The 3 CP systems were operated to apply 0.5 inch of irrigation water. After the CP systems completely passed beyond the cluster of catch-buckets, the collected volume was measured in a 500 ml graduated cylinder. A total of 15 replications, including a mixture of forward and reverse travel direction, were performed. Through multiple replications, it was determined that there was no difference in forward/reverse travel directions.


Results to Date: The results from the 15 replications are shown in Figure 1. The mean application depth for each of the 10 psi zones showed no significant difference (p= 0.05) among center pivot systems.

In the 40 psi zones, application depth also exceeded design for all 3 systems, and there was a significant difference in mean application depth among the 3 center pivots. Although they were different brands, the primary difference was location along the flow path (pivot point to end) where the over-pressurized sprinklers was placed. When they were closer to the end, the was more water delivered than when they were closer to the pivot.

For the 25 psi zones, application depth also exceeded design for all 3 CP systems. Additionally, there was a significant difference in application between the pivots 1 and 2 but not between pivots 2 and 3 or between 1 and three.

Results show that failure to install pressure regulators that match sprinkler package requirements can result in unpredictable and variable water delivery. If regulators are sized incorrectly, water application will likely exceed desired application depths. However, the effect of over pressurization problems is likely greater as one moves further out the mainline.

If system pressure is variable over time because of end gun use, end gun pumps, main pump variation, or multiple deliveries, pressure regulators should be used to maintain design pressures for each sprinkler.



Reports Prepublished Document