Service Contract No 2007 / 147-446 - Swaziland

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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 -
Figure 20. Measuring apparatus for sprinkler nozzle sizeLeaksTimely maintenance and repair of minor leaks are often neglected in this system. The leaks inthe pipes of the supply network of this irrigation system caused a drop in operating pressureand an increase in pump flow. This increase in pump duty reduces the efficiency at which thepump operates, causing further pressure and delivery reductions. A drop in the operatingpressure causes a change in the performance of sprinkler, as shown in table 4 above. Theeffective application rate of the system decreased. Mainly, these leaks are observed insprinklers, sprinkler stand-dragline connections, broken dragline, pipelets, hydromatics,mainline, etc. it is important that all leaks are located quickly and repaired. A leak preventionprogram should include regular replacement of damaged draglines.Figure 21. Phase one dragline leakagesMaphobeni Farmers Association Report - 2009 Page - 42 -
Page 1 and 2: Restructuring and DiversificationMa
Page 3 and 4: DISCLAIMERThe contents of this repo
Page 5 and 6: 5.2 Delivery tests ................
Page 8 and 9: LIST OF APPENDICESAppendix 1: SEB u
Page 10 and 11: 1 I N T R O D U C T I O NAssociatio
Page 12 and 13: pumps. 2 x Howden 100-400 in the ri
Page 14 and 15: 3.1.2 R e v i e w o f C o n t a c t
Page 16 and 17: 9 SCHEDULE OF BLOCKS THAT IRRIGATE
Page 18 and 19: Maphobeni Farmers Association Repor
Page 24 and 25: Based on equation 1 above the flow
Page 26 and 27: ReducersThe inlet on the pump sucti
Page 28 and 29: d1.5d0.5dd3d 3d 1.5dFigure 9. Spaci
Page 30 and 31: hf6375kQ4d2……………………
Page 32 and 33: Table 1. Pump and motor specificati
Page 34 and 35: Table 2. Irrigation pumps evaluatio
Page 36 and 37: Phase two river pump station‣ Pum
Page 38 and 39: Filters: 3%Capital Recovery Rate (C
Page 40 and 41: 4.3.1 M a i n l i n e s i z eThe So
Page 42 and 43: 5 F I E L D E V A L U A T I O N O F
Page 44 and 45: 5.1.2 S p r i n k l e r p r e s s u
Page 46 and 47: 0 L/4 L/2 3L/4 LL3L/4LL/2Test block
Page 48 and 49: Phase two booster Pumps running und
Page 52 and 53: Old AgePhase one of the irrigation
Page 54 and 55: The effects of different nozzles/em
Page 56 and 57: Interest RatesIt can be argued that
Page 58 and 59: 6 . 2 M a n a g e m e n t P r a c t
Page 60 and 61: 6 . 3 M a i n t e n a n c e S u r v
Page 62 and 63: 7 C O N S T R A I N T S T O E F F I
Page 64 and 65: phase one and two was found to be 1
Page 66 and 67: 8 R E C O M M E N D A T I O N STo e
Page 68 and 69: OVERALL MANAGEMENT AND MAINTENANCEM
Page 70 and 71: 10 L I T E R A T U R E R E F E R E
Page 72 and 73: 11 P R O D U C T I N F O R M A T I
Page 86 and 87: SEB usage for River pump station Ph
Page 88: Appendix 2: capital recovery factor

Service Contract No 2007 / 147-446 - Swaziland

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