Determine the flow velocity in ft/s for water flowing at 315 gpm through an 8.0 in pipe.

• A. 1.50 ft/s
• B. 2.50 ft/s
• C. 3.00 ft/s
• D. 2.01 ft/s

Answer: (D)

Flow velocity in a pipe comes from Q = V A, so V = Q / A. Convert the pipe diameter to feet to get the cross-sectional area: diameter is 8 inches, which is 0.6667 ft, radius is 0.3333 ft. Area A = π r^2 ≈ π × (0.3333 ft)^2 ≈ 0.3491 ft^2.

Convert the flow rate to cubic feet per second: 315 gal/min × (1 ft^3 / 7.48052 gal) ≈ 42.11 ft^3/min, which is 42.11 / 60 ≈ 0.7018 ft^3/s.

Now V = Q / A ≈ 0.7018 ft^3/s ÷ 0.3491 ft^2 ≈ 2.01 ft/s.

So the flow velocity is about 2.01 ft/s.