Journeyman Plumbers Drainage, Waste, and Venting Questions and Answers

Question 1

What is the primary purpose of a plumbing vent system in a drainage, waste, and vent (DWV) installation?

Accepted Answer

To equalize atmospheric pressure within the drainage system, protecting trap seals.

Answer

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?

Accepted Answer

1/4 inch per foot

Answer

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?

Accepted Answer

5 feet

Answer

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?

Accepted Answer

The sum of the individual fixture DFU values

Answer

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?

Accepted Answer

Cleanouts are required for each run of piping more than 100 feet in total developed length.

Answer

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.

Journeyman Plumbers Exam Practice Test

Journeyman Plumbers Exam Practice Test

Journeyman Plumbers Drainage, Waste, and Venting Questions and Answers