Service Contract No 2007 / 147-446 - Swaziland

4.3.1 M a i n l i n e s i z eThe South African Irrigation Institute (SABI) norm suggests that for raising main lines with adiameter of 200mm or smaller a maximum of 1.5% is allowed (ARC, 2003). Mainlines withpipe sizes greater than 200mm are evaluated by determining the most economical pipediameter; capital and annual cost for different pipe diameters are compared and the followingequation is used;dkQ0.37i …..……………………….……… (8)Where: di = inside diameter of pipe, mmK= constantQ= flow rate (m3/h)No information was available on mainline pipe sizes, lengths and class and because thereare no pressure measuring points on hydrants, friction loss through the mainline could not becalculated. An undisputed conclusion, therefore, on whether the supply system was correctlydesigned or not cannot be drawn until details on pipe size, pipe classes, and distancesoccupied by the different sizes are obtained.4.3.2 M a i n l i n e c l a s sJust like above, this evaluation could not identify as to whether the mainline classes wereover-specified or not. Pipe bursts are one major indicator of under-specification in pipeclasses and recurrent pipe breakages were experienced only in phase one mainlines, submainsand laterals.4 . 4 S y s t e m C a p a c i t y E v a l u a t i o nPhase One:‣ Phase one of 56 hectares is supplied by one pump and requires at least 222m3/hr.‣ Pressure requirements are estimated at approximately 80m‣ This pump duty point is within the operating range of the installed ETA 125-50/2 pump. Infact, a smaller and cheaper ETA 100-250 single stage pump could have been used.‣ Pressure measurements results reflected that this pump is operating below their designduty point.Maphobeni Farmers Association Report - 2009 Page - 31 -