CPO Filtration and Circulation Systems 3 — Questions and Answers
Question 1: What is the recommended flow rate range for sand filters used in commercial pools?
- 1–3 gallons per minute per square foot
- 3–5 gallons per minute per square foot (Correct answer)
- 5–10 gallons per minute per square foot
- 10–15 gallons per minute per square foot
Correct answer: 3–5 gallons per minute per square foot
Sand filters for commercial pools operate at a flow rate of 3–5 gallons per minute per square foot of filter surface area.
Question 2: After backwashing a sand filter, what position should the multiport valve be set to before returning to filter mode?
- Waste
- Recirculate
- Rinse (Correct answer)
- Closed
Correct answer: Rinse
After backwashing, the valve should be set to the Rinse position for about 30–60 seconds to reseat the sand and clear any debris from the laterals before returning to Filter.
Question 3: The turnover rate for a wading pool or kiddie pool is typically:
- Every 6 hours
- Every 4 hours
- Every 2 hours or less (Correct answer)
- Every 1 hour
Correct answer: Every 2 hours or less
Wading or kiddie pools require a faster turnover — typically every 1–2 hours — due to higher bather load relative to volume and greater contamination risk.
Question 4: Which of the following best describes the function of the skimmer weir?
- It filters large debris before water enters the pump
- It maintains a consistent water level in the skimmer basket
- It regulates the flow of surface water into the skimmer (Correct answer)
- It prevents air from entering the circulation system
Correct answer: It regulates the flow of surface water into the skimmer
The skimmer weir is a floating flap that regulates the flow of surface water into the skimmer, maximizing removal of oils and debris from the water surface.
Question 5: What is cavitation in a pool pump?
- The buildup of calcium deposits on impeller blades
- Formation and collapse of vapor bubbles due to low suction pressure (Correct answer)
- The normal churning of water through the volute
- Excessive air entering through loose fittings
Correct answer: Formation and collapse of vapor bubbles due to low suction pressure
Cavitation occurs when low suction pressure causes water to vaporize, forming bubbles that collapse violently and damage the pump impeller.
Question 6: What does 'filter aid' refer to in the context of DE filtration?
- A chemical added to help coagulate particles
- Fresh DE powder added after backwashing to recoat the grids (Correct answer)
- A fine sand used alongside DE to improve filtration
- A maintenance log used to track filter performance
Correct answer: Fresh DE powder added after backwashing to recoat the grids
Filter aid is fresh diatomaceous earth added through the skimmer after backwashing to recoat the filter grids and restore filtration efficiency.
Question 7: The pressure gauge on a filter system reads 28 psi and the normal operating pressure is 15 psi. What is the most likely cause?
- The pump impeller is worn
- The filter media is clogged and needs cleaning or backwashing (Correct answer)
- The return lines have a major leak
- The chemical feeder is overdosing chlorine
Correct answer: The filter media is clogged and needs cleaning or backwashing
A pressure reading significantly higher than the baseline (28 vs. 15 psi) indicates the filter media is clogged, restricting flow and building pressure.
CPO Filtration and Circulation Systems 3
What is the recommended flow rate range for sand filters used in commercial pools?