CPD Water Supply & Distribution Systems 3 — Questions and Answers
Question 1: When sizing a cold water branch serving a bathroom group (lavatory, water closet, bathtub), what WSFU value is commonly assigned per the IPC?
- 3.5 WSFU
- 5 WSFU (Correct answer)
- 6 WSFU
- 7.5 WSFU
Correct answer: 5 WSFU
The IPC assigns 5 WSFU to a full bathroom group (lavatory, water closet, and bathtub/shower) for sizing purposes.
Question 2: Which formula relates head loss to flow velocity, pipe diameter, and friction factor in water distribution design?
- Hazen-Williams equation
- Darcy-Weisbach equation (Correct answer)
- Manning equation
- Colebrook-White equation
Correct answer: Darcy-Weisbach equation
The Darcy-Weisbach equation calculates head loss due to friction as a function of the Darcy friction factor, pipe length, diameter, and flow velocity.
Question 3: What is the primary purpose of a pressure-reducing valve (PRV) in a water supply system?
- To boost low incoming pressure
- To reduce high street pressure to a safe working range (Correct answer)
- To measure flow rate
- To prevent water hammer
Correct answer: To reduce high street pressure to a safe working range
A PRV reduces high incoming street pressure (often 80–150 psi) to a safe, code-compliant working pressure typically set at 60–80 psi.
Question 4: Galvanic corrosion in a water supply system is most likely to occur when:
- Water velocity exceeds 8 fps in copper pipe
- Dissimilar metals are connected without dielectric isolation (Correct answer)
- Water pH drops below 9.0
- Pipe insulation is omitted in a chase
Correct answer: Dissimilar metals are connected without dielectric isolation
Galvanic corrosion occurs at the junction of dissimilar metals in the presence of an electrolyte (water), driving electrochemical current that degrades the anodic metal.
Question 5: For a booster pump system in a high-rise, the pump is typically selected to provide adequate pressure at the:
- Lowest fixture in the building
- Most remote and highest fixture in the zone (Correct answer)
- Water meter connection point
- Mechanical room header
Correct answer: Most remote and highest fixture in the zone
Booster pumps must overcome both elevation head and pipe friction to deliver adequate pressure at the most hydraulically remote and elevated fixture.
Question 6: What does a 'demand factor' account for in water supply system design?
- The pipe material's flow resistance
- The probability that not all fixtures will operate simultaneously (Correct answer)
- The daily peak-hour water usage
- The seasonal variation in water temperature
Correct answer: The probability that not all fixtures will operate simultaneously
A demand factor (or diversity factor) acknowledges that in any system, all fixtures are statistically unlikely to operate at full flow simultaneously.
Question 7: Which type of water hammer arrestor installation location is most effective per PDI standards?
- At the water meter
- Within 6 pipe diameters of the quick-closing valve it protects (Correct answer)
- At the main shutoff valve
- At the pressure-reducing valve outlet
Correct answer: Within 6 pipe diameters of the quick-closing valve it protects
PDI standards recommend installing water hammer arrestors as close as possible to the quick-closing valve (within 6 pipe diameters) to most effectively absorb the pressure surge.
CPD Water Supply & Distribution Systems 3
When sizing a cold water branch serving a bathroom group (lavatory, water closet, bathtub), what WSFU value is commonly assigned per the IPC?