Master Plumber Exam Plumbing System Design & Sizing 5 — Questions and Answers
Question 1: Under IPC, what is the maximum number of fixture units permitted on a 3-inch horizontal branch drain at 1/4-inch per foot slope?
- 12 DFU
- 20 DFU (Correct answer)
- 35 DFU
- 48 DFU
Correct answer: 20 DFU
Per IPC Table 710.1(1), a 3-inch horizontal branch at 1/4-inch per foot slope has a maximum capacity of 20 drainage fixture units.
Question 2: What is the minimum trap-to-vent distance for a 1.5-inch fixture drain per IPC?
- 2 feet
- 3.5 feet (Correct answer)
- 5 feet
- 8 feet
Correct answer: 3.5 feet
IPC Table 909.1 specifies a maximum 3.5-foot distance from the trap weir to the vent connection for a 1.5-inch pipe.
Question 3: In a high-rise building, which system is used to prevent positive pressure surges in the drainage stack from blowing trap seals?
- Wet venting
- Air admittance valves on each floor
- Sovent or aerator/deaerator fittings (Correct answer)
- Increased stack diameter only
Correct answer: Sovent or aerator/deaerator fittings
Sovent single-stack systems use aerator and deaerator fittings to manage air entrainment and pressure differentials, preventing both siphonage and positive pressure blow-out.
Question 4: When sizing a thermal expansion tank for a closed water heating system, which factor is most critical?
- The length of hot water supply piping
- The system volume, temperature rise, and incoming cold water pressure (Correct answer)
- The BTU rating of the water heater only
- The number of hot water fixtures served
Correct answer: The system volume, temperature rise, and incoming cold water pressure
Expansion tank sizing requires knowing the system water volume, the temperature differential, and the cold water supply pressure to calculate the volume of expansion.
Question 5: A sewage ejector pump system is required when fixtures are located how relative to the building drain?
- More than 50 feet from the main stack
- Below the level of the public sewer or building drain (Correct answer)
- On any floor above the second story
- More than 100 feet from the street connection
Correct answer: Below the level of the public sewer or building drain
Fixtures located below the elevation of the building sewer or public sewer cannot drain by gravity and require a sewage ejector or lift station.
Question 6: What is the design intent of a loop vent (circuit vent) in a plumbing system?
- To provide individual venting for each fixture in a battery
- To vent a battery of fixtures with a single vent connected upstream and looped back to the stack (Correct answer)
- To replace the stack vent in small buildings
- To vent fixtures on different floors of the building simultaneously
Correct answer: To vent a battery of fixtures with a single vent connected upstream and looped back to the stack
A circuit vent (loop vent) connects near the upstream end of a branch serving multiple fixtures and ties back into the vent stack, serving the entire battery with one vent pipe.
Question 7: Which of the following conditions requires a backwater valve (backflow preventer) on a building drain per IPC?
- When the public sewer is more than 200 feet away
- When fixtures are installed at an elevation that may be subject to flooding from sewer backflow (Correct answer)
- When more than 10 water closets connect to the same stack
- When the building has more than 3 stories
Correct answer: When fixtures are installed at an elevation that may be subject to flooding from sewer backflow
IPC Section 715 requires a backwater valve where fixtures could be flooded by sewage backup due to their elevation relative to the upstream manhole or sewer.
Master Plumber Exam Plumbing System Design & Sizing 5
Under IPC, what is the maximum number of fixture units permitted on a 3-inch horizontal branch drain at 1/4-inch per foot slope?