Backflow Prevention Flashcards
6 cards from real Journeyman Plumbers Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Backflow Prevention flashcards as text
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?
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.
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?
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.
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?
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.
An Atmospheric Vacuum Breaker (AVB) is a common backflow prevention device. What is a key installation requirement and operational limitation of an AVB?
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.
Which of the following scenarios describes an unprotected cross-connection that could lead to a dangerous backflow event?
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.
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?
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.