WTO Equipment Maintenance & Troubleshooting 3 — Questions and Answers
Question 1: An operator notices that a backwash flow rate has decreased significantly over several weeks despite no changes to settings. What is the most probable cause?
- Filter media has expanded due to temperature
- Backwash pump impeller or strainers are partially clogged (Correct answer)
- Backwash duration has increased
- Filter effluent turbidity has improved
Correct answer: Backwash pump impeller or strainers are partially clogged
Gradual reduction in backwash flow usually indicates fouling or wear in the backwash pump, its strainers, or the supply piping.
Question 2: What is the primary purpose of a check valve installed on the discharge side of a pump?
- To regulate flow rate
- To prevent backflow when the pump stops (Correct answer)
- To relieve excess pressure
- To measure flow velocity
Correct answer: To prevent backflow when the pump stops
Check valves allow flow in one direction only, preventing water from flowing backward through the pump when it is shut down.
Question 3: During a routine check, an operator finds that a chemical feed pump is running but delivering no chemical. Which cause should be investigated first?
- The motor is overloaded
- The chemical supply tank is empty or the suction line is air-locked (Correct answer)
- The discharge pressure is too low
- The pump speed is set too high
Correct answer: The chemical supply tank is empty or the suction line is air-locked
An empty chemical tank or air in the suction line are the most common reasons a metering pump runs but delivers nothing.
Question 4: A mechanical seal on a centrifugal pump is leaking more than a slow drip. What should the operator do?
- Tighten the gland bolts to stop the leak
- Schedule immediate seal replacement (Correct answer)
- Increase pump speed to build back pressure
- Wrap the seal area with PTFE tape
Correct answer: Schedule immediate seal replacement
Excessive leakage from a mechanical seal indicates seal face wear or failure; the seal must be replaced to prevent further damage and chemical contamination.
Question 5: Which condition would cause a pressure relief valve to open repeatedly during pump operation?
- Suction head is too high
- Discharge pressure exceeds the relief valve set point (Correct answer)
- Pump is operating below design speed
- Suction strainer is partially blocked
Correct answer: Discharge pressure exceeds the relief valve set point
A relief valve opens when discharge pressure exceeds its set point, which may indicate a closed valve, excessive system resistance, or an oversized impeller.
Question 6: What is the correct procedure when taking a pump offline for maintenance in a water treatment plant?
- Stop the pump, then close the discharge valve, then close the suction valve
- Close the suction valve, then stop the pump, then close the discharge valve
- Stop the pump, isolate both valves, lock out/tag out, then de-energize (Correct answer)
- De-energize the motor, then open discharge valve to relieve pressure
Correct answer: Stop the pump, isolate both valves, lock out/tag out, then de-energize
Proper lockout/tagout (LOTO) requires stopping the pump, isolating all energy sources with valves, applying lockout devices, and verifying zero energy before work begins.
Question 7: An operator observes that a polymer feed system is forming large clumps in the solution tank. What adjustment should be made?
- Increase polymer concentration to improve mixing
- Reduce make-down water temperature and check dilution ratio (Correct answer)
- Switch to a cationic polymer type
- Increase the mixer speed to break up clumps
Correct answer: Reduce make-down water temperature and check dilution ratio
Polymer clumping (fish-eyes) is typically caused by improper dilution water temperature or incorrect concentration; adjusting these parameters prevents agglomeration.
WTO Equipment Maintenance & Troubleshooting 3
An operator notices that a backwash flow rate has decreased significantly over several weeks despite no changes to settings.
What is the most probable cause?