Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is installing a pressure vacuum breaker (PVB) on a supply line to a commercial kitchen fixture that requires backflow protection. What is the minimum required height that the critical level (CL) of the PVB must be installed above the flood level rim (FLR) of the fixture it serves?
- A12 inches
- B2 inches
- C4 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 12 inches
Pressure Vacuum Breakers (PVBs) are designed to provide backflow protection by introducing air into the system when pressure drops. To function correctly and prevent back-siphonage, the critical level (CL) of the PVB must be installed at least 12 inches (one foot) above the highest flood level rim (FLR) of the fixture or equipment it serves. This ensures that even under vacuum conditions, contaminated water cannot siphon back into the potable water supply.
Why the other options are wrong
- B. 2 inches is the minimum air gap for indirect waste, not for PVB installation height.
- C. 4 inches is a common trap seal depth, not a PVB installation height.
- D. 6 inches is insufficient for a PVB; it does not provide the necessary air gap for reliable backflow prevention.
PVB Critical Level Height
The minimum vertical distance required between the critical level (CL) marking on a Pressure Vacuum Breaker and the flood level rim (FLR) of the fixture or equipment it protects.
- Ensures proper functioning of the PVB's air inlet valve.
- Prevents back-siphonage contamination of potable water.
- Standard minimum is 12 inches (1 foot).
- CL must be above the highest FLR served.
Memory trick: PVB: Twelve Inches Up, Water Safe to Sup.