Cross-Connection Control and Backflow Prevention
Cross-Connection Control and Backflow Prevention tests whether you can identify a cross-connection and choose the correct protection. Expect questions on backsiphonage, backpressure, air gaps, RPZs, DCVAs, PVBs, and annual testing.
Core rules and concepts
- A cross-connection is any actual or potential link between potable water and a contamination source.
- Backsiphonage is caused by negative pressure; backpressure is caused by a downstream pressure higher than supply pressure.
- An air gap is the best protection because it provides a physical separation.
- A reduced-pressure zone backflow preventer (RPZ) protects against both backpressure and backsiphonage and is used for health hazards.
- A double check valve assembly (DCVA) is for lower hazards, not health hazards. A pressure vacuum breaker (PVB) protects against backsiphonage, not backpressure.
- Containment protection is at the service connection; isolation protection is at the fixture or process.
- Devices must be tested by a certified tester at installation and at required intervals.
Worked example
A greenhouse injects fertilizer into irrigation water. The irrigation line is connected to the potable supply. This is a health hazard and requires an RPZ at the service connection or an air gap. If the connection were only a hose bibb with no injection, an atmospheric vacuum breaker or hose-connection vacuum breaker might be acceptable, but it would not protect against backpressure from a pump.
Traps
Using a DCVA for a health hazard; using a PVB where backpressure is possible; assuming a hose bibb vacuum breaker is containment protection; skipping annual testing; failing to check thermal expansion after installing a backflow device.