Page 276 - Water Engineering Hydraulics, Distribution and Treatment

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Chapter 8
EXAMPLE 8.8 PUMPING AND STORAGE SYSTEM
Draw a sketch, showing a system (including the raw water reservoir, pump station, water transmission lines, elevated water storage
tank, hydraulic grade line, and elevation in ft or m) based on the following information: the raw water reservoir of a city is at an
elevation of 500 ft (152.4 m). An automatic booster pumping station is proposed, having for its control point a 550,000 gal (2,082 m )
water storage tank. The design tank water level is at an elevation of 490 ft (149.4 m).
Measurement of the water storage tank level is to be transmitted to the pumping station and is to be the only variable used for
the control of the pumps in the pumping station. The head losses of the water transmission line between the raw water reservoir and
the elevated water storage tank (including the miscellaneous head losses in the proposed pumping station) computed for the rate of
flow of 1,600 gpm (101 L/s) are 40 ft (12.2 m), which is to be overcome by the pumps. A chlorination system is used for treating the
water entering the elevated water storage tank. The chlorinated water from the tank is transmitted to the city’s water filtration plant
for further treatment prior to domestic consumption.
Solution: Pumping, Storage, and Dual Water Systems 3
Figure 8.11 shows a sketch of the required water supply system.
El. 500 ft
El. 490'
Hydraulic
grade line
40 ft
at 1600 gpm
Figure 8.11 Sketch of water supply system for Example 8.8.
3
′
Conversion factors: 1 = ft = 0.3048 m; 1 gpm = 3.785 L∕min = 0.0000631 m ∕s = 0.0631 L∕s.
EXAMPLE 8.9 PUMPS AND WATER STORAGE TANKS
The water supply system shown in Example 8.8 provides water to a city at the rates of 2.0 MGD (88 L/s) for average daily water
demand, 3.4 MGD (150 L/s) for maximum daily water demand, and 4.8 MGD (210 L/s) for peak hourly water demand. The total
head losses are 40 ft (12.2 m) at a flow of 1,600 gpm (101 L/s).
What are the head losses of the transmission line between the raw water reservoir and the elevated water storage tank (including
all miscellaneous head losses), which must be overcome by the pumps at 2, 3.4, and 4.8 MGD (88, 150, and 210 L/s; or 7.6, 12.9, and
18.2 MLD)? Explain which water demand is used for the design of a pumping station between the raw water reservoir and the water
storage tank, and why. Is the size of the existing water storage tank sufficient for the city in accordance with the current Ten-States
Standards for Water Works?
The following equation shows the relationship between the head loss and the water flow:
H = H (Q ∕Q ) 2
1
2
1
2
where
3
Q = the first water flow, gpm (m /s)
1
3
Q = the second water flow, gpm (m /s)
2
H = head loss at flow of Q ,ft(m)
1
1
H = head loss at flow of Q ,ft(m)
2
2
Solution 1 (US Customary System):
Head loss at average daily water demand of 2 MGD (or 1388 gpm):
2
H = (40)(1,388∕1,600) = 30 ft.
2
Head loss at maximum daily water demand of 3.4 MGD (or 2,360 gpm):
2
H = (40)(2,360∕1,600) = 87 ft.
2