Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 36

■ Example 2.79
Problem : An 8-in.-diameter pipeline has water flowing at a velocity of 3.5 ft/sec.
What is the flow rate in gpm?
Solution :
8 in. ÷ 12 in./ft = 0.667 ft
Q = 0.785 × (0.667 ft) 2 × 3.5 ft/sec = 1.222 ft 3 /sec
Use the flow chart in Figure 2.1 to convert:
Q = 548.4 gpm
■ Example 2.80
Problem : A channel is 3 ft wide with water flowing to a depth of 3 ft. If the velocity
in the channel is found to be 1.9 fps, what is the flow rate in the channel in cubic feet
per second?
Solution :
Q = 3 ft × 3 ft × 1.9 ft/sec = 17.1 ft 3 /sec
■ Example 2.81
Problem: A 12-in.-diameter pipe is flowing full. What is the ft 3 /min flow rate in the
pipe if the velocity is 120 ft/min?
Solution :
12 in. = 1 ft
Q = 0.785 × (1 ft) 2 × 120 ft/min = 94.2 ft 3 /min
■ Example 2.82
Problem: A water main with a diameter of 18 in. is determined to have a velocity of
184 ft/min. What is the flow rate in gallons per minute?
Solution :
18 in. ÷ 12 in./ft = 1.5 ft
Q = 0.785 × (1.5 ft) 2 × 184 ft/min = 324.99 ft 3 /min
324.99 ft 3 /min × 7.48 ga l /f t 3 = 2430.93 gal/min
■ Example 2.83
Problem : A 24-in. main has a velocity of 210 ft/min. What is the gpd flow rate for
the pipe?