CPO Exam Operation and Maintenance 1 — Questions and Answers
Question 1: When backwashing a sand filter, the operator should stop the backwash cycle when:
- The pump motor begins to run cooler
- The sight glass or waste discharge line runs clear (Correct answer)
- The filter pressure gauge returns to its original clean starting pressure
- 30 minutes have elapsed regardless of water clarity
Correct answer: The sight glass or waste discharge line runs clear
Backwashing should continue until the water visible in the sight glass (or the waste discharge line) runs clear, indicating that trapped debris and dirty water have been fully flushed from the filter bed. Time alone is not a reliable stopping point.
Question 2: After backwashing a diatomaceous earth (DE) filter, what is the required next step before returning the system to normal filtration?
- Add fresh DE powder through the skimmer at the manufacturer's recommended dose (Correct answer)
- Run the pump on 'waste' mode for an additional five minutes to purge residual DE
- Adjust the pH to 7.2 before restarting to protect newly exposed filter grids
- Increase pump speed temporarily to compress the remaining DE on the grids
Correct answer: Add fresh DE powder through the skimmer at the manufacturer's recommended dose
Backwashing removes the spent DE coating from the filter grids. Fresh DE must be added through the skimmer so it coats the grids and restores filtration efficiency. Without recoating, the filter cannot remove fine particles.
Question 3: A pool pump is running but return flow is noticeably weak, and the filter pressure gauge reads lower than normal. What is the most likely cause?
- The filter media is severely clogged with debris
- An air leak or obstruction on the suction side of the pump (Correct answer)
- A partially closed return valve downstream of the filter
- Excessive chemical buildup on the inside of the return lines
Correct answer: An air leak or obstruction on the suction side of the pump
Low flow combined with lower-than-normal pressure points to the suction side: an air leak, blocked skimmer, or cavitation prevents the pump from priming and moving water properly. A clogged filter would show high pressure, not low pressure.
Question 4: What is the correct procedure when changing the position of a multiport (spider) valve on a pool filter system?
- Slowly rotate the handle while the pump runs at low speed to avoid water hammer
- Turn the valve quickly in one motion to minimize seal wear
- Always shut the pump off completely before moving the valve handle (Correct answer)
- Switch to recirculate mode first, then reposition the valve without stopping the pump
Correct answer: Always shut the pump off completely before moving the valve handle
The pump must be turned off before rotating a multiport valve handle. Turning the valve under pressure damages the internal spider gasket, which can cause internal bypassing, leaks, and costly repairs.
Question 5: What is the primary function of the floating weir flap located inside a pool skimmer throat?
- To regulate chemical feeder flow entering the pool through the skimmer
- To maintain a constant pool water level by blocking overflow
- To draw surface debris inward on a thin sheet of flow and prevent it from floating back out when the pump stops (Correct answer)
- To act as a secondary strainer, capturing large debris before it reaches the pump basket
Correct answer: To draw surface debris inward on a thin sheet of flow and prevent it from floating back out when the pump stops
The skimmer weir creates a continuous thin sheet of surface water flowing into the skimmer, which efficiently collects floating debris. When the pump shuts off, the weir falls closed, trapping debris inside the skimmer rather than letting it return to the pool.
Question 6: A pool operator must achieve a 6-hour turnover rate for a 90,000-gallon commercial pool. What minimum flow rate (in GPM) is required?
- 150 GPM
- 200 GPM
- 250 GPM (Correct answer)
- 300 GPM
Correct answer: 250 GPM
Flow rate = Pool volume ÷ Turnover time in minutes. 90,000 gallons ÷ (6 hours × 60 min/hr) = 90,000 ÷ 360 = 250 GPM. This is the minimum rate the circulation system must deliver to meet the 6-hour code requirement.
CPO Exam Operation and Maintenance 1
When backwashing a sand filter, the operator should stop the backwash cycle when: