A 10 in main line needs to be flushed. if the desired length of the pipeline to be flushed is 1,625 ft, how many minutes will it take to flush the line at 50 gpm?

• A. 120 min
• B. 110 min
• C. 125 min
• D. 132 min

Answer: (D)

Calculating how long a line must be flushed requires turning the pipe into a water volume in gallons and dividing by the flushing flow rate. Start with a 10-inch diameter. The radius is 5 inches, which is 0.4167 feet. The cross-sectional area is πr^2 ≈ 3.1416 × (0.4167)^2 ≈ 0.545 square feet. The volume of 1,625 feet of pipe is area × length ≈ 0.545 × 1,625 ≈ 885 cubic feet. Convert to gallons: 1 cubic foot equals about 7.4805 gallons, so the total volume is ≈ 885 × 7.4805 ≈ 6,620 gallons. At 50 gallons per minute, the time needed is 6,620 ÷ 50 ≈ 132 minutes. So roughly 132 minutes are required to flush the line, assuming the pipe is completely filled and the flow remains constant.