Service Contract No 2007 / 147-446 - Swaziland

7 C O N S T R A I N T S T O E F F I C I E N T S Y S T E MP E R F O R M A N C EThe following constraints were identified to have an effect on productivity once the system isoperated.River pump station:‣ A proper intake structure was not constructed on phase one pump station. The suctioninlets (foot valves) are suspended at the end of the Usuthu River. The foot valves are notprotected in any way and are intermittently in direct contact with the bottom of the channeland debris carried with the river water.‣ Phase two river pump station, on the other hand, has an improperly constructed sump.During operations, the pumps suck debris like mud and sand which affect pumpperformance and the lifetime of the pumps.‣ Suction pipe flow velocity for these pumps through the 200mm suction pipe in PS 1exceeded the 1,5m/sec maximum allowed in norms - causing pump cavitations hencefrequent wearing of impellers and high maintenance cost.‣ Incorrectly sized fittings in suction and delivery manifolds of all pump stations affectsystem performance. The effects of these are severe on the eccentric reducer because itis directly attached to the pump and the sudden restriction in size increases turbulenceoccurrences and cause irregular feeding of the pump hence cavitation. With such aninstallation wearing and maintenance cost of the pump will increase.‣ The evaluation of pumps could not identify whether the pumps are optimally operating ornot because of the absence of flow and on some pressure measuring devices.‣ The water depth above the suction inlet was measure to be less than the acceptedminimum water depth according to suction pipe flow velocities. This reduces pumpefficiency and performance.‣ Based on the duty point of the installed ETA 125-50/2 phase one pump, a smaller andcheaper ETA 100-250 single stage pump could have been used. Pressure measurementsresults reflected that this pump is operating below the design duty point.‣ Pressure requirements from the balancing dam to the critical sprinkler in phase two areestimated at 90m. The impellor diameter of these pumps is 246mm and in order for thesepumps to generate the required pressure a 255mm impellor diameter must be installed inthese pumps.‣ High speed pumps are used in phase two booster pump stationMaphobeni Farmers Association Report - 2009 Page - 53 -