Page 268 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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228 Chapter 6 Water Distribution Systems: Components, Design, and Operation
pipes in the network have a Hazen-Williams C of 100. The fire 6.21 The water supply system shown in Fig. 6.37 is designed
hose lines available are 150 m long. If the residual pressure in to serve a small town ABDCA. The flow from the reservoir is
the mains is 4 bars, how much water (Q F in L/s) can be with- delivered to the town by gravity through a 400-mm main. All
drawn for firefighting at point x located at the top of the hill pipes have a Hazen-Williams C of 100. Determine the flow rate
(elevation 619 m) without lowering the residual pressure at the in each pipe.
hydrants below 150 kPa?
6.19 In the water network shown in Fig. 6.35, the Hazen-
Williams coefficient C for all pipes is 100 Water
reservoir
(a) Using the Hardy Cross method, determine the flow in
each pipe to the nearest 20 gpm 400 mm
(b) Find the residual pressures at points B and C, given 20 L/s 60 L/s
that the pressure at point A is 50 psi. Point Elevation, m 400 m
(c) If the flow input at A is doubled, what would be the A 100 300 mm 1600 m B
residual pressure at C? B 110 A
C 80 400 m 400 m
D 100
1,600 gpm Elevation
A A 100 ft
B 150 ft 200 mm 200 mm
1,500 ft C 140 ft C 150 mm 1600 m D
8 in
500 ft
10 in 25 L/s 55 L/s

Figure 6.37 Water Network for Problem 6.21
C
B
1,000 ft 10 in
1,000 gpm
600 gpm 6.22 The water supply system shown in Fig. 6.38 was designed
10 years ago to serve a small town. A water pump P delivers the
Figure 6.35 Water Network for Problem 6.19
required flow through a 12-in. water main from the water reser-
voir to the water distribution loop ABDCA.
At present the water demand has increased to 2,000 gpm,
6.20 The water supply system shown in Fig. 6.36 is designed
to serve a summer resort. The flow from the reservoir is deliv- which is assumed to be withdrawn at points A, B, C, and D as
ered to network ABC by gravity through a 14-in. main. The el- shown in the figure. At these drafts the pump can deliver a head
evations of points A, B, and C are as follows: of 200 ft. All pipes are made of PVC with a Hazen-Williams co-
efficient C of 140. Find the flow in each pipe.
A 100 ft
B 150 ft
C 140 ft Elevation, ft
(a) Find the flow in each pipe. 250 gpm
(b) If the pressure at any point in loop ABC is not al- Reservoir 1,200 B
Loop ABDCA 1,250
lowed to drop below 60 psi, determine the required
elevation of the water reservoir.
Water A
reservoir P D 600 gpm
750 gpm
400 gpm C
Water 10,000 ft 14 in A
reservoir 1,500 ft 400 gpm
8 in
500 ft Figure 6.38 Water Network for Problem 6.22
10 in 1,000 gpm
B
1,000 ft 10 in C 6.23 The regional water supply system shown in Fig. 6.39 is
600 gpm
designed to serve four small towns W, X, Y, and Z. Water is de-
Figure 6.36 Water Network for Problem 6.20 livered from the reservoir to the four towns by pump P. The