A propeller type flow meter is NOT recommended for WWTP because of _______.

• A. Gas Bubbles
• B. The Debris in the Liquid
• C. Oil Slicks
• D. High Viscosity

Answer: (B)

Propeller flow meters rely on a freely rotating impeller to relate rotor speed to flow rate, so they need the liquid to be relatively clean and free of obstructions. In wastewater treatment plants, the liquid carries debris such as grit, rags, and other solids that can strike and jam the blades, wear bearings, or foul the rotor. This can cause stuck or misreadings and require frequent maintenance, making the meter unreliable in this environment. Gas bubbles could cause some measurement jitter but don’t cause the physical blockage and damage that debris does, oil slicks are less typical in WWTPs and high viscosity changes the response but is not the primary issue here. Debris in the liquid is the main reason a propeller type flow meter is not recommended.