Service Contract No 2007 / 147-446 NYANYALI ... - Swaziland

5 F I E L D E V A L U A T I O N O F S P R I N K L E R I R R I G A T I O NS Y S T E MTable 2. Sprinkler valuated block summaryBlock Area (ha) 43Type of sprinkler systemDraglineName of DesignerMENDIPName of contractorMENDIPDesignMeasuredSprinkler spacing (m x m) 18 17-19Lateral spacing (m) 108 107-110Stand pipe height (m) 3 3Pressure regulator - NoDragline diameter (mm) 20 20Dragline length (m) - 50 – 100A complete system evaluation could not be conducted because the irrigation system was shutdown. The assessment was carried out after a period of heavy rains which not only raised theriver level but also conceded a lot of iron oxide. According to Nyanyali management irrigatingduring this time causes this material to accumulate inside the pipelines and in the long runreduces pipeline capacity. Pump performance is, also, seriously affected when operatedduring the time, more so, because the iron oxide changes the specific gravity of the water. Itis strongly recommended to conduct the distribution and delivery tests to determine defects, ifany, in the design and installation of the infields.Hydraulic ValvesLaterals of this dragline irrigation system are connected to the mainline through mechanicalvalves (figure 14). For better performance of the system hydraulic valves must be installedinstead and equipped with pressure-regulating pilots.The installation of hydraulic valves equipped with pressure regulating pilots reduces a higherinlet pressure to a lower constant outlet pressure, regardless of fluctuating flow rates and orvarying inlet pressure. The pilot would sense down-stream pressure and modulates open orclose, causing the main valve to throttle, thus maintaining constant delivery pressure.Nyanyali Farmers Cooperative Report - 2009 Page - 25 -