Service Contract No 2007 / 147-446 - Swaziland

The analysis showed by table 4 reflects that there are high pressure losses on the longdraglines. Some dragline pressure losses are as high as 360kPa and this is not acceptable.Phase two laterals are 108m and 50m dragline are used. These are more accommodatingthan the above but could be more efficient if shortened to at least 20m.Hydraulic Valves:Hydraulic valves maintain the design lateral/block pressure ensuring uniform pressurethroughout the system. S.I.I. dragline irrigation system was installed in such a way that alllaterals have individual hydraulic valves. These hydrants are equipped with Gulf hydraulicvalves but without pilots for pressure regulation. A mechanical choke was installed on thevalve head instead. Pressure regulating pilots must be installed and preset to give at least350kPa sprinkler operating pressure on all blocks. Most of the hydraulic valves in this phaseare vandalised, incomplete and not properly looked after (figure 19).Figure 19. Lateral hydraulic valvePhase one does not have any hydraulic valves and lateral and dragline pressure on someblocks increases to beyond pipe class rating. For example, the pressure of the first lateralwas measured to be approximately 65m which is higher that the installed class six pipe.Draglines have a pressure rating of about 40m and with such pressure breakages arerecurrent thus increasing system operational/maintenance costs. All laterals must beequipped with hydraulic valves equipped with a pressure-regulating pilot.Maphobeni Farmers Association Report - 2009 Page - 40 -