Massachusetts Plumbers Journeyman Practice Exam

How should the minimum required air gap be measured according to the text?

1. Horizontally

2. By volume

3. Vertically

4. By pressure

The correct answer is: Vertically

The correct method for measuring the minimum required air gap is vertically. This is important because the air gap is designed to prevent backflow and ensure that contaminants do not enter the potable water supply. By measuring the air gap vertically, it accurately reflects the distance between the lower outlet of a plumbing fixture and the maximum flood level of the receiving vessel, which is crucial for maintaining proper health and safety standards. In this context, other methods such as measuring horizontally, by volume, or by pressure do not appropriately account for the critical vertical distance needed to effectively prevent backflow. Each of these methods lacks the specific focus on the necessary vertical separation that ensures the air gap is sufficient to protect the water supply from potential contamination.