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                    292  Chapter 8  Pumping, Storage, and Dual Water Systems
                    8.7  Changing the speed of a centrifugal pump will change its                      B   C
                    operating characteristics, including the head. Determine the
                    new head, if                                                    R 1 Elevated  R 2  A       D
                                                                       WTP   P
                           H 1   rated head   120 ft   36.58 m                         reservoir
                           N 2   pump speed now   1,320 rpm              Pipe  d, in  L, ft  d, mm  L, m  F  E
                           N 1   rated pump speed   1,650 rpm.                 24  35,000  600  10,668
                                                                          PR 1
                                                                          R A  24  15,000  600  4,572
                                                                           2
                    8.8  Changing the speed of a centrifugal pump will change its  AB  14  8,000  350  2,438
                    operating characteristics, including the power requirement.  BC  12  10,000  300  3,048
                    Determine the new power requirement, if               CD    8   5,000  200  1,524
                                                                          DE    8   5,000  200  1,524
                           P 1   rated head   16 hp   12 kW               EF   12  10,000  300  3,048
                           N 2   pump speed now   1,320 rpm               AF   14   8,000  350  2,438
                           N 1   rated pump speed   1,650 rpm.        Figure 8.14 Water System for Problem 8.10
                    8.9  A water pumping station is designed to raise water from a
                    lake at an elevation of 50 ft (15.24 m) to a reservoir located at  The water consumption during the maximum day demand
                    an elevation of 140 ft (42.67 m). Water is pumped through a  in the city is as follows:
                    16-in. (40.64-cm) cast-iron pipe that develops a head loss of
                    19 ft (5.79 m) of water at a discharge of 1,000 gpm (63 L/s).  Period     Flow rate (gpm)
                    The pumping station has two pumps, each of which possesses  Midnight to 4 a.m.  2,000
                    the following characteristics:
                                                                            4 a.m. to 8 a.m.      4,000
                                                                            8 a.m. to noon        6,000
                           Flow (gpm)               Head (ft)
                                                                            Noon to 4 p.m.        5,000
                                                                            4 p.m. to 8 p.m.      4,000
                               500                    195
                             1,000                    180                   8 p.m. to midnight    3,000
                             1,500                    150
                             2,000                    110
                             2,500                     50                   Period             Flow rate (L/s)
                                                                            Midnight to 4 a.m.     126
                                                                            4 a.m. to 8 a.m.       252
                            Flow (L/s)             Head (m)
                                                                            8 a.m. to noon         379
                                32                  59.44                   Noon to 4 p.m.         315
                                63                  54.86                   4 p.m. to 8 p.m.       252
                                95                  45.72                   8 p.m. to midnight     189
                               127                  33.53
                               158                  15.24           Assume that the water withdrawal from the network is equally
                           Shutoff head   200 ft (60.96 m).         distributed among the points A, B, C, D, E, and F, which are at
                                                                    the same elevation of 2,300 ft (701.04 m) and that all pipes are
                                                                    ductile iron with C   100. Also consider that the pump pos-
                                                                    sesses the following characteristics:
                        What will be the discharge of the two pumps when operat-
                    ing in parallel?
                                                                    Flow (gpm)   0  2,000  4,000  6,000  8,000 12,000
                    8.10  The water supply system shown in Fig. 8.14 is designed
                    to serve city ABCDEFA. Water is treated and collected in a  Head (ft)  400  390  370  345  310  225
                    water tank in the treatment plant (WTP). A pump delivers the
                    water through the main PR 1 to an elevated reservoir (water  Flow (L/s)  0  126  252  379  505  757
                    level 2,700 ft, or 822.96 m) at the top of a hill. Pumping is done
                    at a constant rate and only for a period of 16 hours per day  Head (m)  121.92 118.87 112.78 105.16  94.49 68.58
                    from 4 a.m. to 8 p.m. Water flows from the elevated reservoir
                    into the distribution main network ABCDEF through a 24-in.  (a) Calculate the volume of the elevated reservoir
                    main R 2 A.                                             needed to balance supply and demand.
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