For flushing after installation, what are the minimum and preferred velocities?

• A. 2.5 ft/s, 3.5 ft/s
• B. 1.0 ft/s, 2.0 ft/s
• C. 3.0 ft/s, 4.0 ft/s
• D. 4.0 ft/s, 5.0 ft/s

Answer: (A)

When flushing after installation, the goal is to move debris and fines out of the new line by creating enough flow to scour the interior surface. The minimum velocity of 2.5 ft/s provides the baseline shear needed to start mobilizing particles and flush them out. The preferred velocity of 3.5 ft/s increases flushing effectiveness, helping to remove finer sediments more reliably while keeping water use reasonable. Velocities lower than 2.5 ft/s won’t scour effectively, leading to poor flushed cleanliness, while much higher velocities (around 4–5 ft/s) are unnecessary and can waste water and create excessive turbulence.