Journeyman Plumbers Exam Drainage, Waste, and Vent Systems 3 — Questions and Answers
Question 1: Which of the following fixtures is assigned the highest drainage fixture unit (DFU) value under the IPC?
- Lavatory
- Bathtub
- Water closet (flush tank) (Correct answer)
- Kitchen sink
Correct answer: Water closet (flush tank)
A flush-tank water closet is rated at 3 DFUs, which is higher than a lavatory (1), bathtub (2), or kitchen sink (2).
Question 2: What type of vent is installed downstream of a fixture trap and connects to the vent stack above the fixture's flood level rim?
- Circuit vent
- Individual vent (back vent) (Correct answer)
- Common vent
- Island fixture vent
Correct answer: Individual vent (back vent)
An individual vent (also called a back vent or revent) connects the fixture's trap arm to the vent stack and runs upward past the fixture's flood level rim.
Question 3: An island fixture vent loop is required when:
- A fixture is located more than 6 feet from the main stack
- A sink or similar fixture is installed in an island where a standard vent cannot go up through a wall (Correct answer)
- Any fixture is on the second floor
- The drain slope exceeds 1/2 inch per foot
Correct answer: A sink or similar fixture is installed in an island where a standard vent cannot go up through a wall
Island fixture vent loops route the vent piping under the floor and back up alongside the drain when there is no adjacent wall to run a conventional vent.
Question 4: What is the minimum size of a vent stack serving a soil stack that receives discharge from water closets?
- 1-1/2 inches
- 2 inches
- 3 inches (Correct answer)
- 4 inches
Correct answer: 3 inches
When water closets connect to the soil stack, the vent stack must be at least 3 inches in diameter per IPC sizing requirements.
Question 5: A crown vent is prohibited because:
- It increases sewer gas pressure in the trap
- It is too expensive to install
- Solids can accumulate and block the vent opening at the top of the trap (Correct answer)
- It does not meet the 1/4-inch-per-foot slope requirement
Correct answer: Solids can accumulate and block the vent opening at the top of the trap
A crown vent connects at the crown (top) of the trap, where waste material can collect and plug the vent, rendering it ineffective.
Question 6: Under the IPC, a vent pipe that terminates through an exterior wall must terminate at least how far above the top of the opening it is near?
- 6 inches (Correct answer)
- 12 inches
- 24 inches
- 36 inches
Correct answer: 6 inches
A vent terminating through an exterior wall must end at least 6 inches above the top of any nearby opening such as a window or door.
Question 7: Which of these conditions would cause a trap to lose its water seal due to self-siphonage?
- The vent pipe is too large
- A fixture drain discharges a full slug of water through a long, unvented trap arm (Correct answer)
- The water supply pressure is too high
- The building drain slope is too shallow
Correct answer: A fixture drain discharges a full slug of water through a long, unvented trap arm
Self-siphonage occurs when a full flow of water down an unvented or inadequately vented trap arm creates enough suction to pull the water seal out of the trap.
Journeyman Plumbers Exam Drainage, Waste, and Vent Systems 3
Which of the following fixtures is assigned the highest drainage fixture unit (DFU) value under the IPC?