Journeyman Plumber ExamPlumbing Code and RegulationsMedium
A journeyman plumber is installing a backflow prevention assembly on a potable water supply line to a commercial irrigation system. According to the Uniform Plumbing Code (UPC), what is the minimum air gap required for an atmospheric vacuum breaker (AVB) in this application?
- A1 inch or twice the effective diameter of the supply pipe, whichever is greater.
- B6 inches or twice the effective diameter of the supply pipe, whichever is greater.
- C1 inch or the effective diameter of the supply pipe, whichever is greater.
- D6 inches or the effective diameter of the supply pipe, whichever is greater.
Show answer & explanationAnswer & explanation
Correct answer: A. 1 inch or twice the effective diameter of the supply pipe, whichever is greater.
The UPC specifies the minimum air gap for an atmospheric vacuum breaker to prevent back-siphonage. This ensures that contaminated water cannot be drawn back into the potable water supply.
Why the other options are wrong
- B. 6 inches is incorrect for an AVB; this is often associated with other backflow prevention methods or larger air gaps.
- C. This option incorrectly states 'the effective diameter' instead of 'twice the effective diameter' and uses an incorrect minimum.
- D. This option incorrectly combines an incorrect minimum with an incorrect diameter multiplier.
Atmospheric Vacuum Breaker (AVB) Air Gap
The minimum vertical distance between the lowest opening of a potable water supply pipe and the flood level rim of the fixture or receptor.
- Prevents back-siphonage only.
- Not for continuous pressure applications.
- Specific air gap requirements by code.
Memory trick: Air Gap: Keep water clear, for safety's sake, a gap twice wide, or one inch to make.