PC Backflow Prevention & Cross-Connection Control 1 — Questions and Answers
Question 1: What is a cross-connection in a plumbing system?
- A pipe fitting used to join four separate pipes
- Any physical link between a potable water supply and a potentially contaminated source (Correct answer)
- A valve used to redirect water between two supply lines
- A joint connecting two different pipe materials together
Correct answer: Any physical link between a potable water supply and a potentially contaminated source
A cross-connection is any physical connection between a potable water system and a non-potable source that could allow contamination to enter the drinking water supply.
Question 2: What type of backflow occurs when negative pressure develops in a supply line and draws contaminants backward?
- Backpressure
- Backsiphonage (Correct answer)
- Hydraulic surge
- Reverse osmosis
Correct answer: Backsiphonage
Backsiphonage occurs when a drop in supply pressure below atmospheric creates a siphon effect that pulls contaminants back into the potable water system.
Question 3: Which backflow prevention method provides protection solely through physical separation with no mechanical parts?
- Double check valve assembly
- Pressure vacuum breaker
- Air gap (Correct answer)
- Reduced pressure zone assembly
Correct answer: Air gap
An air gap is the only non-mechanical backflow prevention method, relying on physical separation between the water outlet and flood level rim to prevent contamination.
Question 4: What is the minimum air gap required between a water supply outlet and the flood level rim of a receiving fixture under most plumbing codes?
- One-half inch regardless of pipe size
- Twice the effective opening of the supply outlet, but not less than 1 inch (Correct answer)
- Three times the pipe diameter
- 1 inch for all pipe sizes up to 2 inches
Correct answer: Twice the effective opening of the supply outlet, but not less than 1 inch
The required air gap is at least twice the effective opening (diameter) of the water supply outlet, with an absolute minimum of 1 inch to prevent backsiphonage.
Question 5: Which backflow prevention assembly is specifically required for high-hazard cross-connections to a public water supply?
- Double check valve assembly (DCVA)
- Atmospheric vacuum breaker (AVB)
- Reduced pressure zone (RPZ) assembly (Correct answer)
- Hose bib vacuum breaker
Correct answer: Reduced pressure zone (RPZ) assembly
The reduced pressure zone assembly provides the highest level of mechanical protection and is required by code for high-hazard cross-connections due to its relief valve between two independent check valves.
Question 6: What is backpressure as it relates to plumbing cross-connections?
- Water pressure that exceeds the maximum allowable system pressure of 80 psi
- A condition where downstream pressure exceeds the potable supply pressure, pushing contaminants backward (Correct answer)
- Pressure buildup caused by a clogged drain or stoppage in the drainage system
- The residual pressure reading taken at the water meter during peak demand
Correct answer: A condition where downstream pressure exceeds the potable supply pressure, pushing contaminants backward
Backpressure occurs when a downstream system (such as a booster pump or pressurized vessel) develops pressure higher than the supply, potentially forcing contaminants into the potable water supply.
Question 7: A pressure vacuum breaker (PVB) is most appropriate for which of the following applications?
- Chemical feed systems connected to public water supply
- Fire suppression systems with foam additives
- Irrigation systems where the device is installed above the highest outlet (Correct answer)
- Hospital dialysis equipment connections
Correct answer: Irrigation systems where the device is installed above the highest outlet
PVBs are widely used for irrigation systems and must be installed at least 12 inches above the highest downstream outlet, making elevated irrigation applications ideal.
PC Backflow Prevention & Cross-Connection Control 1
What is a cross-connection in a plumbing system?