Master Plumber Practice Exam

A vent in a combination waste and vent system should be approximately equal in area to one-half of which dimension?

1. Area of the house sewer

2. Cross-sectional of the drain pipe served

3. Area of the public sewer

4. Diameter of the drain pipe served

The correct answer is: Cross-sectional of the drain pipe served

In a combination waste and vent system, the design principle is that the vent's cross-sectional area needs to be sufficient to allow for the proper venting of gases and the maintenance of a neutral pressure within the drainage system. The correct answer states that the vent should be approximately equal in area to one-half of the cross-sectional area of the drain pipe it serves. This is based on established plumbing codes and practices, which dictate that the vent must provide enough capacity to allow air to enter or exit the system without creating vacuum conditions that could draw water out of traps. By designing the vent to be half the size of the drain's cross-sectional area, you ensure effective air flow and prevent potential backpressure issues that can compromise the drainage system, thus protecting the integrity of the plumbing throughout the structure. In contrast, the other dimensions listed do not relate directly to the necessary size of the vent in a combination waste and vent system. The area of the house sewer, the area of the public sewer, and the diameter of the drain pipe served do not provide the appropriate guideline for vent sizing, as they involve different aspects of the plumbing system that do not directly govern the vent’s ability to function effectively in concert with the drain pipe.