CSLB C-27 Landscaping ContractorIrrigation SystemsHard
A C-27 contractor is preparing to connect a new irrigation system to a potable water supply. To ensure compliance with health and safety regulations, what is the minimum required air gap distance for an atmospheric vacuum breaker (AVB) in relation to the highest point of water discharge downstream?
- A6 inches or twice the diameter of the supply pipe, whichever is greater.
- BNo specific air gap is required for an AVB.
- C12 inches or the diameter of the supply pipe, whichever is greater.
- D1 inch or twice the diameter of the supply pipe, whichever is greater.
Show answer & explanationAnswer & explanation
Correct answer: A. 6 inches or twice the diameter of the supply pipe, whichever is greater.
For an Atmospheric Vacuum Breaker (AVB), the critical air gap must be at least 6 inches, or twice the diameter of the supply pipe, whichever is greater, above the highest point of water discharge (e.g., sprinkler head) downstream. This ensures that a vacuum cannot siphon contaminated water back into the potable supply.
Why the other options are wrong
- B. An air gap is absolutely critical for AVBs to function as backflow prevention devices.
- C. While 12 inches is a safe practice, 6 inches or twice the pipe diameter is the mandated minimum, making this an overly conservative and potentially incorrect minimum.
- D. This measurement is too small and would not provide adequate air gap protection for an AVB.
AVB Air Gap Requirement
An Atmospheric Vacuum Breaker (AVB) requires a minimum air gap of 6 inches or twice the supply pipe diameter (whichever is greater) above the highest downstream discharge point to prevent back-siphonage.
- Air gap prevents back-siphonage by creating a physical break.
- AVBs are non-pressure compensating devices.
- Specific height requirement is mandated by plumbing codes.
Memory trick: AVB's gap: six inches high, or double pipe, to keep water shy.