Page - 53 - in Clean Water Using Solar and Wind - Outside the Power Grid

Water supply 53 of 1 bar (=105 Pa) corresponds to a water column (ρ = 1000 kg/m3) of  10.2 m. If the rotational speed (n) of the pump is changed, then the QH curve is changed according to Figure 4.2. A lower speed means that the pump produces a lower head at a given flow rate, or produces a lower flow rate, given the head. If the pump is aimed to work at only one given head and flow rate, then the slope of the QH curve has no  importance. The operating point (or duty point) of a pump is determined by the intersection of the pump (QH curve) and system characteristics, as shown in Figure 4.3. The QH curve defines what the pump can produce, while the system curve (the load) defines which pressure is  needed. Figure 4.3 The duty point A of a pump is determined by the intersection of the QH curve and the system curve. The efficiency for a typical centrifugal pump is also shown. This indicates that the pump should be designed so that the maximum efficiency appears at the duty point. Expressed differently, the efficiency should be close to its maximum at the most common flow rates. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user