Journeyman Plumber ExamWater Supply SystemsEasy
A plumber is installing a new atmospheric vacuum breaker (AVB) on a sillcock for an outdoor hose connection. What is the minimum vertical distance the AVB's critical level (CL) must be installed above the highest point of usage or flood level rim of the fixture it serves?
- A4 inches
- B6 inches
- C2 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 6 inches
According to most plumbing codes (e.g., UPC, IPC), an atmospheric vacuum breaker (AVB) must be installed with its critical level (CL) at least 6 inches (152 mm) above the flood level rim of the fixture or the highest point of usage it serves. This ensures proper air gap for back-siphonage prevention.
Why the other options are wrong
- A. 4 inches is also insufficient; 6 inches is the minimum code requirement.
- C. 2 inches is insufficient for proper back-siphonage protection with an AVB.
- D. 12 inches provides adequate protection but is not the minimum required distance; 6 inches is sufficient.
AVB Critical Level
The critical level (CL) of an atmospheric vacuum breaker (AVB) is the point on the device that must be positioned at a specific minimum height above the flood level rim to prevent back-siphonage.
- AVBs protect against back-siphonage, not backpressure.
- The CL is typically marked on the device.
- Minimum 6 inches (152 mm) above flood level rim.
Memory trick: AVB always Aims At least Six Above.