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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.