Page 325 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch08_265-296.qxd 8/2/10 9:53 PM Page 285

8.6 Types of Distributing Reservoirs 285

Solution 1 (U.S. Customary System):
Average daily consumption 2 MGD 1,388 gpm
Maximum daily consumption 3.4 MGD 2,360 gpm
Peak hourly demand 4.8 MGD 3,331 gpm
With sufficient water storage capacity available in the future, two pumps of equal capacity
should be operating in parallel to supply the maximum daily consumption of 2,360 gpm. Each
pump is to supply 1,215 gpm, and both pumps 2,430 gpm.
2
Head loss at 2,360 gpm, H 40 (2,360>1,600) 87 ft
The effective head of each pump should be 87 ft less the difference in water surface
elevations.
Difference in water surface elevation 500 ft 490 ft 10 ft
Effective head of each pump, H 87 ft 10 ft 77 ft.

Water horsepower (WHP) (Q H)>3,957
(1,215)(77)>3,957 23.6 hp

Brake horsepower (BHP) horsepower input to each pump WHP>E pump
23.6>0.8 29.5 hp

Motor horsepower (MHP) horsepower input to motor BHP>E motor
29.5 hp>0.9 32.8 hp

Solution 2 (SI System):
3
Average daily consumption 7.57 MLD 0.088 m /s 88 L/s
3
Maximum daily consumption 12.87 MLD 0.150 m /s 150 L/s
3
Peak hourly demand 18.17 MLD 0.210 m /s
With sufficient water storage capacity available in the future, two pumps of equal capacity
3
should be operating in parallel to supply the maximum daily consumption of 12.87 MLD 0.150 m /s
150 L/s.
3
3
Each pump is to supply 0.077 m /s, and both pumps 0.153 m /s.
3
3
2
3
Head loss, at 12.87 MLD or 0.150 m /s, H (12.19 m)(0.150 m /s>0.101 m /s) 26.5 m
The effective head of each pump should be 26.5 m (87 ft) less the difference in water surface
elevations.
Difference in water surface elevation 152.4 m 149.3 m 3.1 m
Effective head of each pump, H 26.5 m 3.1 m 23.4 m
Water power (WMP) 9.8066 (Q H)
9.8066 (0.077)(23.5) 17.7 kW
Brake power (BMP) power input to each pump WMP>E pump
(17.7)>0.8 22.2 kW

Motor power (MMP) power input to motor BMP>E motor
22.2>0.9 24.6 kW
The sketch of the selected centrifugal pump will have the pump characteristic curves shown in
Fig. 8.12.