Journeyman Plumbers Exam Venting and Backflow Prevention 4 — Questions and Answers
Question 1: When a common vent connects two fixture drains at the same level, each drain must enter the vertical stack at:
- The same fitting with a double-wye (Correct answer)
- Different heights at least 8 inches apart
- Opposite sides of the same tee fitting
- Any point on the horizontal branch
Correct answer: The same fitting with a double-wye
A common vent requires a double-wye or similar approved fitting that allows both fixture drains to enter at the same elevation.
Question 2: What is the minimum slope for a horizontal wet vent pipe?
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
- No slope is required
Correct answer: 1/4 inch per foot
Horizontal wet vent pipes must slope at least 1/4 inch per foot toward the drain to maintain proper flow and self-scouring velocity.
Question 3: An atmospheric vacuum breaker installed on an irrigation system must be located at least how far above the highest downstream outlet?
- 3 inches
- 6 inches (Correct answer)
- 12 inches
- 18 inches
Correct answer: 6 inches
Atmospheric vacuum breakers must be installed at least 6 inches above the highest downstream outlet to prevent submersion and backflow.
Question 4: Which situation requires a backflow preventer on a potable water supply to a boiler?
- When the boiler operates below 212°F
- When chemical treatment is added to the boiler water (Correct answer)
- When the boiler is gas-fired
- When the boiler is on the same floor as the meter
Correct answer: When chemical treatment is added to the boiler water
Chemical additives in boiler water create a high-hazard cross-connection, requiring at minimum an RPZ assembly to protect the potable supply.
Question 5: A relief vent is used to:
- Provide ventilation at the base of a stack
- Restore air circulation in a system where excessive positive pressure occurs (Correct answer)
- Replace a broken trap seal
- Connect a fixture directly to the main vent stack
Correct answer: Restore air circulation in a system where excessive positive pressure occurs
A relief vent is installed to restore air circulation and relieve positive or negative pressure at a critical point in the drainage system.
Question 6: What is the minimum size vent stack required for a building drain carrying 100 drainage fixture units (DFU)?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
Per IPC venting tables, a vent stack serving a building drain with 100 DFUs requires a minimum 4-inch vent stack.
Question 7: Where must a relief vent connect to the vent stack when installed at a branch interval?
- Below the branch drain connection
- Between the branch drain and the next higher branch (Correct answer)
- At the crown of the trap
- Above the roof terminal
Correct answer: Between the branch drain and the next higher branch
A relief vent at a branch interval must connect to the vent stack at a point between the branch drain it serves and the next higher branch drain connection.
