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Problems/Questions 191
5.4 The elevation of a city distribution reservoir is 400 ft velocity of 5 ft/s (1.5 m/s). To increase the flow, a pipe 1.5 ft
(122 m) and that of the city is 250 ft (76 m). When city water (450 mm) in diameter is laid parallel alongside the first pipe
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consumption is at the rate of 16 ft /s (453 L/s), the pressure in for the last mile.
the city is 60 psi (416 kPa). Find the increase in flow between the reservoirs assuming the
Assuming that during a fire the minimum required pres- same value of f for the two pipes. Also assume that the water levels
sure is 20 psi (139 kPa), determine the fire flow available if the in the reservoirs remain the same. (1 mi 5,280 ft or 1,610 m.)
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coincidental city demand is 14 ft /s (396 L/s). (Neglect velocity 5.7 In the water supply system shown in Fig. 5.18, the pump-
heads and the variation of f with Reynolds number.) ing station is operating at a flow capacity of 125 L/s against a
5.5 Given the system shown in Fig. 5.17 and neglecting minor total dynamic head of 50 m. Determine the maximum depth of
losses, velocity heads, and the variation of f with Reynolds number: water that can be stored in the elevated reservoir.
(a) What will be the flow rate from A to D if the pressure Elevation of water level in underground tank 500 m
at D is to be maintained at 20 psi (139 kPa)? Elevation of bottom of elevated reservoir 520 m
(b) What will the rate of flow be if the water level in reser- C for all pipes 100.
voir A drops 10 ft (3 m), that is, to El. 170 ft (51.8 m). 5.8 In the water supply system shown in Fig. 5.19, water
(c) What size of ductile iron pipe (f 0.020) is required flows by gravity from reservoir A to points C and D as well as
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to carry an additional 22 ft /s (623 L/s) from A to D to reservoir E. The elevations of known points are as follows:
with the reservoir at 180 ft (55 m) and residual pres- Water level A 650.00 m
sure at D to be maintained at 20 psi (139 kPa)? Elevation B 590.00 m
5.6 A pipe 2 ft (600 mm) in diameter and 3 mi (4.83 km) Elevation C 550.00 m
long connects two reservoirs. Water flows through it at a Elevation D 570.00 m
Figure 5.17 Water System for El. 180 ft.
Problem 5.5. Conversion
factors: 1
1 ft 0.3048 m;
1 1 in. 25.4 mm. A

18"d − 1,500' − f0.030 El. 100 ft.
18" d − 2,000' − f 0.025
18"d − 1,000' − f0.025
B C
16"d − 1,500' − f0.020 D
Figure 5.18 Water System for Q = 50 L/s Q = 40 L/s
Problem 5.7.

Pumps Branch Branch Elevated reservoir
pipe pipe
Ground
water P
reservoir d = 400 mm d = 300 mm d = 250 mm
L = 2,000 m L = 1,500 m L = 1,000 m
Figure 5.19 Water System for Problem 5.8. C
d = 300 mm
L = 3,640 m
Water A B D
reservoir d AB d = 300 mm
L = 10,000 m L = 2,500 m
E Water
d = 400 mm reservoir
L = 11,760