Journeyman Plumbers Backflow Prevention Questions and Answers — Questions and Answers
Question 1: A commercial kitchen is installing a new chemical dispensing unit that connects directly to the potable water supply to mix cleaning solutions. This is considered a high-hazard application. Which of the following backflow prevention devices is required for this installation?
- Double Check Valve Assembly (DCVA)
- Atmospheric Vacuum Breaker (AVB)
- Reduced Pressure Zone Assembly (RPZ) (Correct answer)
- Pressure Vacuum Breaker (PVB)
Correct answer: Reduced Pressure Zone Assembly (RPZ)
A Reduced Pressure Zone (RPZ) assembly provides the highest level of protection and is required for high-hazard applications where contaminants like cleaning chemicals could cause illness or death if they enter the potable water system. A DCVA is for low-hazard situations, while AVBs and PVBs only protect against back-siphonage, not back-pressure.
Question 2: What type of backflow is caused by a negative or sub-atmospheric pressure in the water supply piping, often resulting from a water main break or firefighting activities nearby?
- Back-pressure
- Back-siphonage (Correct answer)
- Hydraulic shock
- Cross-contamination
Correct answer: Back-siphonage
Back-siphonage is the reversal of flow caused by a reduction in system pressure, which creates a partial vacuum that can pull contaminants into the potable water supply. This is different from back-pressure, which occurs when downstream pressure is higher than the supply pressure.
Question 3: Which of the following backflow prevention devices is considered the most effective and simplest form, providing a physical separation between the potable water outlet and a potential contaminant?
- Double Check Valve Assembly (DCVA)
- Air Gap (Correct answer)
- Reduced Pressure Zone Assembly (RPZ)
- Pressure Vacuum Breaker (PVB)
Correct answer: Air Gap
An air gap is a physical separation between the free-flowing discharge end of a potable water supply pipe and the flood-level rim of a receptacle. It is the most reliable and simplest method of backflow prevention because there is no physical connection for contaminants to cross.
Question 4: An Atmospheric Vacuum Breaker (AVB) is a common backflow prevention device. What is a key installation requirement and operational limitation of an AVB?
- It can be installed below the flood level rim of the fixture it serves.
- It is suitable for applications with continuous line pressure.
- It is designed to protect against both back-siphonage and back-pressure.
- It must be installed at least 6 inches above all downstream piping and outlets. (Correct answer)
Correct answer: It must be installed at least 6 inches above all downstream piping and outlets.
An AVB must be installed vertically and at least 6 inches (or as specified by code) above the highest point of use to allow air to enter and break a vacuum. It cannot have any shut-offs downstream and is not designed for continuous pressure or to protect against back-pressure.
Question 5: Which of the following scenarios describes an unprotected cross-connection that could lead to a dangerous backflow event?
- A faucet spout terminating 2 inches above the flood level rim of a lavatory.
- A garden hose with its end submerged in a bucket of pesticide solution. (Correct answer)
- A commercial boiler connected to the potable water supply via an RPZ assembly.
- A toilet fill valve with an integral anti-siphon device installed above the critical level.
Correct answer: A garden hose with its end submerged in a bucket of pesticide solution.
A cross-connection is any actual or potential link between a potable water system and a source of contamination. Submerging a hose connected to the potable supply into a non-potable solution like pesticides creates a direct cross-connection. If a back-siphonage event occurs, the pesticide will be drawn into the water supply. The other options describe properly protected connections.
Question 6: A plumber notices that the relief valve on a newly installed Reduced Pressure Zone (RPZ) assembly is constantly discharging a small amount of water. What is the most likely cause?
- The device is functioning perfectly as designed.
- The number 2 check valve is fouled or leaking. (Correct answer)
- The inlet water pressure is too low.
- The outlet shutoff valve is partially closed.
Correct answer: The number 2 check valve is fouled or leaking.
The relief valve on an RPZ opens if the pressure in the zone between the two check valves approaches the supply pressure. This is typically caused by a leaking No. 2 check valve, which allows downstream pressure to build in the zone, or a fouled No. 1 check valve. A fouled No. 2 check is a common reason for intermittent or light discharge.
