Arizona Plumbing Practice Exam

What is the maximum drainage fixture unit capacity for a 4-inch trap arm?

1. 4 units

2. 6 units

3. 8 units

4. 10 units

The correct answer is: 6 units

The maximum drainage fixture unit capacity for a 4-inch trap arm is indeed 6 units. This capacity is derived from the guidelines set forth by plumbing codes, which provide specific values for different pipe sizes. A 4-inch trap arm is capable of handling a certain volume of drainage effectively, and this limit helps ensure proper flow and venting, thus preventing issues like sewer gas backflow and maintaining adequate drainage efficiency. The flow capacity is determined based on factors such as the diameter of the pipe, the length of the arm, and the expected volume of wastewater from typical fixtures. By adhering to these guidelines, plumbers can design systems that meet code requirements and provide reliable service. The correct answer reflects the standard practice in plumbing design, ensuring the system functions optimally under typical usage conditions.