Page 231 - Water Engineering Hydraulics, Distribution and Treatment

209
Problems/Questions
fire flow is 12,200 L/min. The residual pressure in mains ABCDA
are located downhill at an elevation of 600 m (Fig. 6.34). All pipes
is 4 bars. Domestic demand can be neglected during firefighting.
in the network have a Hazen–Williams C of 100. The fire hose lines
3
1
2
available are 150 m long. If the residual pressure in the mains is 4
B
A
bars, how much water (Q in L/s) can be withdrawn for firefighting
F
at point x located at the top of the hill (elevation 619 m) without
225 m
lowering the residual pressure at the hydrants below 150 kPa?
4
A
B
150 mm
200 mm
225 m
X
250 m
5
225 m 6.18 The main pipes of a city water distribution loop (ABCDA)
150 mm
250 m
6
750 m X
225 m
200 mm
D C
225 m 225 m 225 m 225 m
Figure 6.32 Water network for Problem 6.16. D C
(a) Determine the residual pressure at the hydrants (elevation = 750 m
645 m) if there is a fire at the center of the loop. Figure 6.34 Water network for Problem 6.18.
(b) What sizes should lines 2 and 5 be replaced with if the minimum
required pressure at the hydrants is 150 kPa? 6.19 In the water network shown in Fig. 6.35, the Hazen–
6.17 The layout of a loop in a water distribution system is shown Williams coefficient C for all pipes is 100.
in Fig. 6.33. All pipes of the gridiron network have the same ele- (a) Using the Hardy Cross method, determine the flow in each pipe
vation and a Hazen–Williams C of 100. The grid ABCDA serves to the nearest 20 gpm.
an area that requires a design fire flow of 9,000 gpm. The pressure
(b) Find the residual pressures at points B and C, given that the
in the primary feeders ABCDA is 30 psi, and the fire hose lines
pressure at point A is 50 psi.
available are 410 ft long.
(c) If the flow input at A is doubled, what would be the residual
Supposing there is a fire at the middle of the grid (point X),
pressure at C?
(a) Find the residual pressure at the hydrants.
(b) How many lines (minimum) should be changed from 8 in. to
10 in. in order to maintain a residual pressure of at least 20 psi 1600 gpm A Elevation
at the hydrants? A 100 ft
B 150 ft
1500 ft C 140 ft
8 in
2400 ft 500 ft
10 in
A B
C
B
8 in 8 in
1000 ft 10 in
1000 gpm
8 in 600 gpm
Figure 6.35 Water network for Problem 6.19.
X 2400 ft
6.20 The water supply system shown in Fig. 6.36 is designed to
800 ft 8 in
serve a summer resort. The flow from the reservoir is delivered to
network ABC by gravity through a 14 in. main. The elevations of
800 ft points A, B, and C are as follows:
A = 100 ft;
D C
B = 150 ft;
Figure 6.33 Water network for Problem 6.17. C = 140 ft.