306A Water Supply Systems 4 — Questions and Answers
Question 1: When using the fixture unit method to size water supply piping, what does the conversion to litres per second account for?
- Only the maximum flow of the largest fixture
- The probability that not all fixtures will be used simultaneously (Correct answer)
- The elevation of the building only
- The temperature of the water
Correct answer: The probability that not all fixtures will be used simultaneously
The fixture unit method uses probability theory to account for the fact that in most buildings, not all fixtures operate at the same time. This diversity factor allows smaller pipe sizes than if every fixture were assumed to run simultaneously.
Question 2: What is the standard test pressure for a water supply system in a residential building?
- 100 psi for 15 minutes
- Working pressure plus 50% for 2 hours
- 150 psi (1034 kPa) for a minimum of 2 hours (Correct answer)
- 200 psi for 30 minutes
Correct answer: 150 psi (1034 kPa) for a minimum of 2 hours
The water supply system is typically tested at 100 psi (690 kPa) or 1.5 times the working pressure, whichever is greater, and held for a minimum of 2 hours with no visible leaks or pressure drop.
Question 3: What is the purpose of an expansion tank on a closed-loop domestic hot water system?
- To store extra hot water for peak demand
- To absorb the volume increase when water is heated and the system has a backflow preventer (Correct answer)
- To mix hot and cold water
- To filter sediment
Correct answer: To absorb the volume increase when water is heated and the system has a backflow preventer
When a backflow preventer creates a closed system, heated water expands with nowhere to go, causing dangerous pressure increases. An expansion tank absorbs this thermal expansion safely.
Question 4: What is the minimum size of an individual fixture supply pipe for a lavatory?
- ¼ inch
- ⅜ inch (Correct answer)
- ½ inch
- ¾ inch
Correct answer: ⅜ inch
A ⅜-inch supply pipe is the minimum size for a lavatory faucet, providing adequate flow for handwashing while conserving water.
Question 5: What is the effect of installing a water softener on the hot water supply only?
- No effect on the system
- Reduced scale buildup in the water heater and hot water pipes (Correct answer)
- Increased corrosion in all pipes
- Lower water pressure throughout the system
Correct answer: Reduced scale buildup in the water heater and hot water pipes
Installing a softener on the hot water supply reduces scale buildup (calcium and magnesium deposits) in the water heater and hot water piping, improving efficiency and extending equipment life.
Question 6: What valve type is NOT acceptable as an isolation valve on a water supply branch because it restricts flow?
- Ball valve
- Gate valve
- Globe valve (Correct answer)
- Butterfly valve
Correct answer: Globe valve
A globe valve creates significant flow restriction due to its internal design, which forces water to change direction through the valve body. Ball and gate valves provide full-port (unrestricted) flow and are preferred for isolation.
306A Water Supply Systems 4
When using the fixture unit method to size water supply piping, what does the conversion to litres per second account for?