Journeyman Plumbers Exam Venting and Backflow Prevention 5 — Questions and Answers
Question 1: Which plumbing code section governs the maximum number of fixture units allowed on a wet-vented horizontal branch?
- Trap sizing table
- Wet vent fixture unit table (Correct answer)
- Drain pipe sizing table
- Vent stack sizing table
Correct answer: Wet vent fixture unit table
The wet vent fixture unit table in the IPC sets the maximum drainage fixture units permitted on a wet-vented horizontal branch based on pipe diameter.
Question 2: A combination drain and vent system (CD&V) is most commonly used for:
- Multi-story commercial buildings
- Floor drains and sinks in slab-on-grade construction (Correct answer)
- Rooftop mechanical equipment
- Fixture groups above the third floor
Correct answer: Floor drains and sinks in slab-on-grade construction
CD&V systems are designed for floor drains and similar fixtures in slab-on-grade construction where conventional venting is difficult to install.
Question 3: What is the purpose of the air gap in a dishwasher drain connection?
- To increase drain velocity
- To prevent backflow of contaminated water into the dishwasher (Correct answer)
- To reduce noise in the drain line
- To allow air into the drain for venting
Correct answer: To prevent backflow of contaminated water into the dishwasher
The dishwasher air gap provides a physical break in the drain line to prevent contaminated sink water from siphoning back into the dishwasher.
Question 4: Under the IPC, what is the maximum vertical distance a trap arm may run before connecting to the vent?
- Twice the trap diameter
- Four times the trap diameter
- The developed length limit from the sizing table (Correct answer)
- 8 feet regardless of pipe size
Correct answer: The developed length limit from the sizing table
The maximum trap-to-vent distance (trap arm length) is determined by the developed length limits in the IPC trap arm sizing table, which varies by pipe diameter.
Question 5: A reduced pressure zone (RPZ) assembly must be installed in which orientation?
- Vertical only, with flow upward
- Horizontal only
- Horizontal or vertical per manufacturer approval (Correct answer)
- Vertical only, with flow downward
Correct answer: Horizontal or vertical per manufacturer approval
RPZ assemblies may be installed horizontally or vertically depending on the manufacturer's listing and local code requirements.
Question 6: Which vent type serves multiple fixtures and allows a single vent pipe to serve as both the vent and the drain for upstream fixtures?
- Individual vent
- Relief vent
- Wet vent (Correct answer)
- Stack vent
Correct answer: Wet vent
A wet vent carries both drainage flow from upstream fixtures and serves as the vent for those fixtures, combining two functions in one pipe.
Question 7: What is the minimum height above finished grade for the installation of an air admittance valve (AAV) in a crawl space?
- 2 inches
- 4 inches (Correct answer)
- 6 inches
- 12 inches
Correct answer: 4 inches
AAVs installed in crawl spaces must be located at least 4 inches above the insulation or other materials in the crawl space to ensure proper air access.
