Service Contract No 2007 / 147-446 - Swaziland

The installation of this unit (on the valve head) reduces a higher inlet pressure to a lowerconstant outlet pressure, regardless of fluctuating flow rates and or varying inlet pressure.The pilot would sense down-stream pressure and modulates open or close, causing the mainvalve to throttle, thus maintaining constant delivery pressure.When down –stream pressure falls below the pilot setting, the pilot and main valve wouldmodulate open to increase pressure and maintain pilot setting. When downstream pressurerises above the pilot setting, the pilot and main valve would throttle close to decreasepressure and maintains pilot setting. The pilot has an adjusting screw to preset the desiredpressureSprinkler pressure regulators:The project was implemented on an uneven topography with approximately 20m elevationdifferent between the project and this directly affect sprinkler operating pressure. When flowis downhill pressure is gained and the reverse is true. Sprinkler pressure regulators were notinstalled hence the increased pressure variation. Pressure regulators are a necessity in thisproject and will have to be incorporated into the system. Some blocks are fairly flat and othersteep. When considering the quantity of the pressure regulators this fact must be kept inmind.Nozzle wearing:Measurements of the amount of sprinkler nozzle wear (mm) taken from phase 1 and twoblocks averaged 3.2% and 5.5% respectively. Nozzle wearing was on maximum 12% in bothphases. An increase of 5% in nozzle area means a 10% increase in flow and power demand,which means additional operating costs and over-irrigation. The ARC therefore recommendssprinkler replacement if wear is greater than 5% and in this project this exercise is longoverdue. Nozzle wearing is hastened, amongst others, by the age of the irrigation system (12years), no intake sump, improper operation and maintenance schedules, etc.Sprinkler nozzles were measured after the system was switched off with a specially machinedapparatus (Figure 20).Maphobeni Farmers Association Report - 2009 Page - 41 -