CSLB C-36 Plumbing ContractorPlanning and EstimatingMedium
A plumbing contractor is reviewing plans for a new medical office building that specifies the installation of specialized plumbing fixtures requiring an air gap. What is the primary function of an air gap in a plumbing system?
- ATo regulate water pressure to specific fixtures.
- BTo prevent cross-connection and backflow contamination.
- CTo provide a cleanout for drain line maintenance.
- DTo allow for thermal expansion of hot water lines.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent cross-connection and backflow contamination.
An air gap is a critical backflow prevention device. It provides a physical separation between the lowest point of a potable water outlet and the flood level rim of the receiving fixture, ensuring that contaminated water cannot siphon back into the potable water supply.
Why the other options are wrong
- A. Pressure regulation is handled by pressure-reducing valves, not air gaps.
- C. Cleanouts are separate access points for drain cleaning, not related to air gaps.
- D. Thermal expansion is managed by expansion tanks, not air gaps.
Air Gap (Plumbing)
A physical, vertical separation between the free flowing discharge end of a potable water supply pipe and the flood level rim of a receiving fixture or container.
- Considered the most reliable method of backflow prevention.
- Prevents direct connection between potable and non-potable water.
- Commonly used on dishwashers, washing machines, and indirect waste receptors.
Memory trick: Air gap: water can't jump the gap.