Level 3 · Advanced sample questions
5 free sample questions on pumps and hydraulics for the Level 3 · Advanced wastewater treatment operator exam. Try each one, then open the answer to check your work.
Solids in a gravity-thickener overflow are increasing. What should the operator review?
Answer: B. Review loading, blanket, and withdrawal
Thickener loading, blanket condition, and underflow withdrawal directly affect solids capture and overflow quality.
A centrifugal pump loses flow and begins to rattle. Wet-well level is normal. Suction vacuum is higher than usual, while discharge pressure and motor current are lower. A parallel pump on the same wet well runs normally. Which condition best fits the readings?
Answer: C. A restriction in this pump's suction
Higher suction vacuum shows that this pump is pulling against increased resistance. The reduced flow, discharge pressure, and motor current—while the parallel pump operates normally—fit a restriction in this pump's suction path.
A positive-displacement sludge pump starts opening its relief valve. The valve opens at its correct pressure setting. Pump speed, sludge thickness, and sludge temperature are unchanged. Common-header pressure is normal, but pressure at the pump discharge rises sharply. What is the most likely cause?
Answer: B. A restriction between the pump and header
The relief valve is responding at its correct setting, while pressure is high at the pump but normal in the common header. That pressure difference locates the likely restriction between the pump discharge and the header.
Two identical pumps each meet their pump curve when tested alone at the same speed. Both discharge check valves open fully. With both pumps running, discharge head rises sharply, but total flow increases only slightly. Suction conditions remain adequate. What best explains the limited flow gain?
Answer: D. System resistance limits the gain from parallel pumping
Each pump performs normally alone, both check valves open, and suction remains adequate. When both run, higher combined flow produces much more system head, so the operating point shifts along the system curve and limits the added flow.
An equalization basin delivers steady flow, but discharge TSS varies sharply. Samples show much more solids near the bottom than at the surface. Incoming load is steady, and basin DO meets its target. Mixing and aeration have separate controls. Which change best stabilizes the discharged solids load?
Answer: C. Improve mixing throughout the basin
Flow and incoming load are steady, but the strong top-to-bottom solids difference shows solids are not uniformly suspended. Because DO already meets target and mixing is controlled separately, improving basin mixing should stabilize the discharged solids concentration.
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