An 8.0-in.-diameter pipeline needs to be flushed. If the desired length of pipeline to be flushed is 145 ft, how many minutes will it take to flush the line 3 times at 45 gpm?

• A. 15 min
• B. 40 min
• C. 25 min
• D. 30 min

Answer: (C)

Flushing time is found by calculating how much water the pipe segment contains and then dividing that volume by the flushing flow rate, accounting for how many times you run the water through the line.

First, determine the pipe’s volume for the 145 ft length. The diameter is 8 inches, so the radius is 4 inches, which is 0.333 feet. The cross-sectional area is πr^2 ≈ π(0.333)^2 ≈ 0.349 ft^2. Multiply by the length: 0.349 ft^2 × 145 ft ≈ 50.6 ft^3. Convert to gallons: 50.6 ft^3 × 7.4805 ≈ 379 gallons.

Since the line is flushed 3 times, total volume to move is about 379 × 3 ≈ 1,137 gallons. With a flushing rate of 45 gpm, the time required is 1,137 ÷ 45 ≈ 25 minutes.

So the flush will take about 25 minutes.