Journeyman Plumbers Drainage, Waste, and Venting Questions and Answers — Questions and Answers
Question 1: What is the primary purpose of a plumbing vent system in a drainage, waste, and vent (DWV) installation?
- To provide a direct path for sewer gas to escape the building.
- To equalize atmospheric pressure within the drainage system, protecting trap seals. (Correct answer)
- To increase the velocity of wastewater flowing through the pipes.
- To serve as an overflow for the drainage system in case of a blockage.
Correct answer: To equalize atmospheric pressure within the drainage system, protecting trap seals.
The primary function of a vent system is to allow air to enter the drainage pipes. This prevents the formation of negative pressure (a vacuum) that could siphon water out of fixture traps. By protecting the trap seals, the vent system prevents dangerous sewer gases from entering the living space.
Question 2: A plumber is installing a horizontal 3-inch drainage pipe. According to most model plumbing codes, what is the minimum required slope or grade for this pipe?
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
- 1 inch per foot
Correct answer: 1/4 inch per foot
For horizontal drainage pipes 3 inches in diameter or smaller, the standard minimum slope required by most plumbing codes is 1/4 inch per foot. This ensures that solid waste is carried along with the liquids and prevents blockages. While a 1/8 inch per foot slope may be permissible for pipes 4 inches or larger in some jurisdictions, 1/4 inch per foot is the standard for 3-inch pipes.
Question 3: Based on the Uniform Plumbing Code (UPC), what is the maximum allowable developed length of the trap arm for a 1 1/2-inch P-trap?
- 3 feet, 6 inches
- 5 feet (Correct answer)
- 6 feet
- 8 feet
Correct answer: 5 feet
Plumbing codes limit the distance between a trap and its vent to prevent self-siphonage. For a 1 1/2-inch trap, the maximum developed length of the trap arm (the pipe between the trap weir and the vent fitting) is typically 5 feet.
Question 4: A residential bathroom group consists of a standard toilet (3 DFU), a lavatory (1 DFU), and a bathtub with a shower (2 DFU). What is the total Drainage Fixture Unit (DFU) load that must be used to size the horizontal branch drain serving these fixtures?
- 4 DFU
- 5 DFU
- 6 DFU
- The sum of the individual fixture DFU values (Correct answer)
Correct answer: The sum of the individual fixture DFU values
To size a horizontal branch drain, you must sum the Drainage Fixture Unit (DFU) values of all fixtures connecting to it. In this scenario, the total load is the sum of the toilet (3), lavatory (1), and bathtub/shower (2), which equals 6 DFU. This total value is then used with code tables to determine the minimum required pipe size.
Question 5: Which of the following is a code requirement for the installation of cleanouts in a horizontal drainage system?
- A cleanout is required every 50 feet on straight runs.
- Cleanouts must be installed at each 45-degree change in direction.
- Cleanouts are required for each run of piping more than 100 feet in total developed length. (Correct answer)
- The minimum size for any cleanout is 2 inches.
Correct answer: Cleanouts are required for each run of piping more than 100 feet in total developed length.
Model plumbing codes, such as the IPC and UPC, require that horizontal drainage pipes be provided with a cleanout for each 100 feet of developed length, or fraction thereof. They are also required at the upper end of each horizontal drain and for aggregate changes in direction exceeding 135 degrees.
Question 6: A plumber needs to install a cleanout for a 4-inch horizontal drain pipe located in an accessible space. According to the International Plumbing Code (IPC), what is the minimum required clearance in front of the cleanout for rodding?
- 12 inches
- 18 inches (Correct answer)
- 24 inches
- 36 inches
Correct answer: 18 inches
The IPC specifies minimum clearances in front of cleanouts to allow for the use of drain cleaning equipment. For pipes 6 inches and smaller, a clearance of not less than 18 inches must be provided. For pipes larger than 6 inches, the clearance requirement increases.
Journeyman Plumbers Drainage, Waste, and Venting Questions and Answers
What is the primary purpose of a plumbing vent system in a drainage, waste, and vent (DWV) installation?