Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is installing a fixture trap for a dishwasher that discharges into a standpipe. What is the maximum developed length from the trap weir to the vent fitting?
- A4 feet
- B2 feet
- C5 feet
- D3 feet
Show answer & explanationAnswer & explanation
Correct answer: D. 3 feet
For a standard 1 1/2-inch fixture trap, the maximum developed length from the trap weir to the vent fitting is 3 feet 6 inches (42 inches). Therefore, 3 feet is the closest and most appropriate answer among the options.
Why the other options are wrong
- A. This exceeds the maximum developed length for a 1 1/2-inch fixture trap arm.
- B. This is too short for a typical 1 1/2-inch fixture trap arm developed length.
- C. This significantly exceeds the maximum developed length for a 1 1/2-inch fixture trap arm.
Fixture Trap Arm Developed Length
The developed length of a fixture trap arm is the total length of the drainage pipe from the trap weir to the vent pipe fitting, measured along the centerline of the pipe.
- Prevents trap siphonage.
- Length varies by trap/pipe size.
- Typically 3'6" for 1 1/2" pipe.
- Prevents excessive pressure fluctuations.
Memory trick: Trap Arms Must Be Short Enough to Vent, Long Enough to Connect.