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                                                                                              Problems/Questions  293
                         (b) Compute the maximum flow in each pipe of the  constant rate and only for a period of 12 hours from 6 a.m. to
                            network.                                6 p.m. Each pump possesses the following characteristics:
                         (c) Determine the elevation of the water tank at the treat-
                            ment plant                              Flow (gpm)   0    951  1,427  1,902  2,378 2,853
                         (d) At what rate of flow can you pump the water to the  Head (ft)  54.86  50.29  46.63  41.15  32.00 19.20
                            elevated reservoir if another identical pump is in-
                            stalled in parallel with the existing pump?
                                                                    Flow (L/s)   0     60    90    120   150   180
                    8.11 The water supply system shown in Fig. 8.15 is planned to
                    serve a small village. Treated water from the treatment plant  Head (m)  180  165  153  135  105  63
                    (WTP) flowing at a uniform rate throughout the day is collected in
                    a ground tank. Water is then pumped to an elevated reservoir at the  The Hazen-Williams coefficient C for all mains is 100. The
                    top of a hill through the main AB. Water flows from the elevated  total equivalent length of main AB is 8,202 ft (2,500 m) and
                    reservoir into the distribution network through the main CD.  main CD is 29,527 ft (9,000 m).
                                                                         (a) Determine the volumes needed for the ground tank
                                                                            and elevated reservoir (each separately) to balance
                                                                            supply and demand. (Storage for firefighting and
                                                         Elevated
                     From     Ground tank                                   emergencies is not required.)
                     WTP                  P              reservoir
                                       A               B
                                                          Level          (b) Determine the minimum standard size needed for
                            Level 445.00 m
                                                        565.00 m            the water main AB so that the two operating pumps
                                                           C                can deliver the required flow from the ground tank to
                            Pumping station
                                                                            the elevated reservoir.
                                                                    8.12  A water pumping station is designed to raise water from
                                                                    a treatment plant ground reservoir at an elevation of 1,968 ft
                                                                    (600 m) to an elevated reservoir located on the opposite side of
                                                                    town at an elevation of 2,165 ft (660 m). The trunk line and the
                                                                    water distribution network connecting the two reservoirs is
                                                                    equivalent to a pipe line (C   100) 16 in. (400 mm) in diameter
                                       Elevation 493.00 m
                                                         D          and 82,020 ft (25,000 m) long.
                                                                        The pumping station has three pumps, two of which oper-
                                                       To distribution
                                                         network    ate in series and the third pump is a standby. Each pump pos-
                                                                    sesses the following characteristics:
                    Figure 8.15 Water System for Problem 8.11
                                                                    Flow (gpm)  0  634 1,268 1,902 2,536 3,170 3,804

                       Water consumption during the maximum day in the village  Head (ft)  328  321  308  285  259  230  197
                    is as follows:

                            Period             Flow rate (L/s)      Flow (L/s)  0   40    80   120  160   200  240
                                                                    Head (m)  100   98    94    87   79   70    60
                            Midnight to 6 a.m.      60
                            6 a.m. to noon         240
                            Noon to 6 p.m.         120              During night hours, when consumption is low, the pumped
                            6 p.m. to midnight      90              water is greater than demand and excess water is stored in the
                                                                    elevated reservoir. Considering this mode of operation, deter-
                                                                    mine the flow rate that can be delivered through the system
                            Period            Flow rate (gpm)       under the following pumping conditions:

                            Midnight to 6 a.m.     951                   (a) Two pumps are operational.
                            6 a.m. to noon        3,804                  (b) One pump is operational, that is, one pump failed
                            Noon to 6 p.m.        1,902                     and the standby is under maintenance.
                            6 p.m. to midnight    1,427
                                                                    8.13  A water pumping station is designed to raise water from
                                                                    a treatment plant ground reservoir at an elevation of 190 ft
                    The pumping station has three pumps, two of which operate in  (57.91 m) to a downtown elevated reservoir located at an eleva-
                    parallel and the third pump is a standby. Pumping is done at a  tion of 415 ft (126.49 m). Water is pumped through a 20-in.
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