Water Supply and Distribution Systems
Water Supply and Distribution Systems
This domain tests pressure, sizing, materials, and control devices. Expect questions on fixture-unit sizing, pressure-reducing valves, thermal expansion, water hammer, and protection of the potable supply.
Core rules
- Size supply piping by fixture units and developed length, not by pipe diameter alone; account for elevation and friction loss.
- Maintain adequate residual pressure at the farthest fixture; excessive pressure wastes water and damages fixtures, so a pressure-reducing valve is commonly required above 80 psi.
- A closed system with a backflow preventer or check valve needs a thermal expansion tank to absorb heated water expansion.
- Provide shutoff valves, drain valves, and access; slope horizontal piping for drainage and support it at code intervals.
- Protect potable water with backflow prevention; do not connect a potable line directly to a boiler, irrigation system, or chemical feeder.
Worked example
A building has 70 psi static pressure and a new check valve at the service. The water heater is now a closed system. The correct response is to install a thermal expansion tank on the cold supply to the heater, not to rely on the T&P valve. The reasoning: the T&P valve is a safety device, not normal expansion control.
Traps that cost marks
Sizing by velocity alone, omitting a PRV where pressure exceeds the local limit, installing an expansion tank on the hot outlet instead of the cold inlet, and using a valve as a test device without a drain.