What is the minimum flow velocity that must be maintained in pressurized sewers?

• A. 1 foot per second
• B. 3 feet per second
• C. 2 feet per second
• D. 4 feet per second

Answer: (C)

Maintaining a self-cleansing flow is essential in sewer design to keep solids in suspension and prevent buildup. In pressurized sewers, if the velocity drops too low, solids can settle and form blockages, reducing capacity and risking odors. The minimum velocity used to avoid deposition is two feet per second. This speed provides enough shear to move typical wastewater solids without incurring unnecessary energy costs. Velocities lower than this increase the chance of sedimentation, while higher speeds require more energy and can cause more wear.