Page 332 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal
P. 332
JWCL344_ch08_265-296.qxd 8/2/10 9:53 PM Page 292
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.