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                                          Chapter 8
                                                Pumping characteristics of system in Example 8.4
                                       Table 8.1
                                                                   1
                                       Pumps in service, no.
                                                                                                               1 and 3
                                                                                                                            2 and 3
                                                                                                 1 and 2
                                                                             2
                                                                                        3
                                                          3
                                                                                                 27 (1.18)
                                                                                                              36 (1.58)
                                                                10 (0.44)
                                                                          21 (0.92)
                                                                                                                           42 (1.84)
                                       Rate of pumping MGD (m /s)
                                       Head ft (m)
                                                                          83 (25.3)
                                                                                                 85 (25.9)
                                                                                     88 (26.8)
                                                                                                                           93 (28.3)
                                                                                                              90 (27.4)
                                                                81 (24.7)
                                                                           88 (88)
                                                                                      88 (88)
                                       Efficiency (%)
                                                                80 (80)
                                                          3
                                                                15 (0.66)
                                                                          25 (1.10)
                                                                                                 34 (1.49)
                                                                                                                           49.5 (2.17)
                                                                                                             43.5 (1.91)
                                                                                     37 (1.62)
                                       Rate of pumping MGD (m /s)
                                                                                                                           89 (27.1)
                                                                                                              85 (25.9)
                                                                                     84 (25.6)
                                                                          78 (23.8)
                                                                66 (20.1)
                                                                                                 80 (24.4)
                                       Head ft (m)
                                                                                                            71, 89 (71, 89)
                                       Efficiency (%)
                                                                89 (89)
                                                                                                                         79, 87 (79, 87)
                                                                                      89 (89)
                                                                                               82, 88 (82, 88)
                                                                           89 (89)
                                                          3
                                                                                    40.5 (1.77)
                                                                                                 40 (1.75)
                                                                          28.5 (1.25)
                                                                                                                           56.5 (2.47)
                                       Rate of pumping MGD (m /s)
                                                               16.5 (0.72)
                                                                                                             49.5 (2.17)
                                                                                                                           84 (25.6)
                                                                                     73 (22.3)
                                                                          66 (20.1)
                                                                                                              79 (24.1)
                                                                62 (18.9)
                                       Head ft (m)
                                                                                                 73 (22.3)
                                                                           84 (84)
                                       Efficiency (%)  Pumping, Storage, and Dual Water Systems  33.5 (1.47)  71, 86 (71, 86)  35, 87 (35, 87)  68, 64 (68, 64)
                                                                                                                         79, 89 (79, 89)
                                                                                                            83, 88 (83, 88)
                                                                                      86 (86)
                                                                                               88, 88 (88, 88)
                                                                88 (88)
                                                                3
                                       Conversion factors: 1 MGD = 0.0438 m ∕s = 43.8L∕s;1 ft = 0.3048 m.
                                    8.3 SERVICE STORAGE                                   2. Calculate the amounts of water drawn up to certain
                                                                                             times, that is, the cumulative draft.
                                    The three major components of service storage are as follows:
                                                                                          3. Plot the cumulative draft against time.
                                        1. Equalizing, or operating, storage              4. For steady supply during 24 h, draw a straight line
                                        2. Fire reserve                                      diagonally across the diagram, as in Fig. 8.6a. Read
                                                                                             the storage required as the sum of the two max-
                                        3. Emergency reserve
                                                                                             imum ordinates between the draft and the supply
                                                                                             line.
                                    8.3.1 Equalizing, or Operating, Storage               5. For steady supply during 12 h (e.g., by pumping )
                                    Required equalizing,or operating, storage can be read from  draw a straight line diagonally from the beginning
                                    a demand rate curve or, more satisfactorily, from a mass  of the pumping period to its end—for example, from
                                    diagram. As shown in Fig. 8.6 for the simple conditions of  6 a.m. to 6 p.m., as in Fig. 8.6b. Again read the
                                    steady inflow, during 12 and 24 h, respectively, the amount of  storage required as the sum of the two maximum
                                    equalizing, or operating, storage is the sum of the maximum  ordinates.
                                    ordinates between the demand and supply lines. To construct
                                    such a mass diagram, proceed as follows:              Achieving a steady supply at the rate of maximum daily
                                                                                       use will ordinarily require an equalizing storage between
                                        1. From past measurements of flow, determine the draft  15% and 20% of the day’s consumption. Limitation of supply
                                          during each hour of the day and night for typical days  to 12 h may raise the operating storage to an amount between
                                          (maximum, average, and minimum).             30% and 50% of the day’s consumption.
                                       5.0                                 5.0
                                                                                Storage = 0.86 MG  Draft or
                                                    Storage
                                      Supply and demand (MG)  3.0  Uniform inflow  Supply and demand (MG)  3.0  Uniform inflow or  Figure 8.6 Determination of
                                                                           4.0
                                       4.0
                                                    0.42 MG
                                                                                                  demand
                                                           or supply
                                                            for 24 h
                                                                           2.0
                                       2.0
                                                                                                            equalizing, or operating, storage by
                                                       Draft or demand
                                                                                            supply for 12 h
                                                                                                            Uniform inflow, or supply, (a)
                                       1.0
                                                    Storage                1.0           Storage 5 0.84 MG  mass diagram; see Example 8.5.
                                                    0.40 MG                                                 extending over 24 h; (b) confined to
                                                                                                            12 h. Total storage = 0.40 + 0.42 =
                                        0                                   0
                                         12  4    8   12   4   8   12       12   4    8   12   4   8   12   0.82 MG; (b) total storage = 0.84 +
                                        Mid-  a.m.  a.m. Noon  p.m.  p.m.  Mid-  Mid-  a.m.  a.m. Noon  p.m.  p.m.  Mid-  0.86 = 1.70 MG. Conversion factor:
                                        night                     night     night                     night  1MG = 1 million gallons =
                                                                                                                           3
                                                      (a)                                 (b)               3.785 ML = 3,785 m .
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