Master Plumber Backflow Prevention and Safety Questions and Answers — Questions and Answers
Question 1: A commercial irrigation system that utilizes chemical injectors for fertilization is being installed. This system operates under continuous pressure. Which backflow prevention assembly is required to protect the potable water supply from this high-hazard cross-connection?
- Double Check Valve Assembly (DCVA)
- Atmospheric Vacuum Breaker (AVB)
- Reduced Pressure Zone (RPZ) Assembly (Correct answer)
- Hose Bibb Vacuum Breaker (HBVB)
Correct answer: Reduced Pressure Zone (RPZ) Assembly
A Reduced Pressure Zone (RPZ) Assembly is required for high-hazard applications, such as chemical injection, where the system is under continuous pressure. [4, 12, 21] An RPZ provides the highest level of protection among mechanical devices by creating a zone of reduced pressure and discharging water via a relief valve if backflow conditions occur. [16, 25]
Question 2: Which of the following statements is a mandatory and correct installation requirement for an Atmospheric Vacuum Breaker (AVB)?
- It must be installed at least 6 inches above all downstream piping and outlets. (Correct answer)
- It is suitable for installation in a location subject to continuous pressure.
- It is designed to protect against both backsiphonage and backpressure.
- It must have a shutoff valve installed immediately downstream for service.
Correct answer: It must be installed at least 6 inches above all downstream piping and outlets.
An Atmospheric Vacuum Breaker (AVB) must be installed at least six inches above the highest point of use (e.g., sprinkler head, faucet outlet). [4, 11, 14] This allows air to enter and break any siphon if supply pressure is lost. AVBs are not designed for continuous pressure, do not protect against backpressure, and must not have any valves installed downstream. [3, 11, 14]
Question 3: A backflow event caused by a significant pressure drop in the municipal water main, such as from a main break or firefighting activities, is defined as what condition?
- Backpressure
- Backsiphonage (Correct answer)
- Water hammer
- Hydrostatic shock
Correct answer: Backsiphonage
Backsiphonage is the reversal of flow caused by a negative or sub-atmospheric pressure in the supply piping, which can pull contaminants into the potable water system. [1, 5, 7] This is distinct from backpressure, where the downstream system pressure is higher than the supply pressure. [1, 6]
Question 4: When installing a Reduced Pressure Zone (RPZ) backflow preventer inside a building, what is a critical requirement specific to this type of assembly to ensure its proper function and prevent property damage?
- It must be installed with the relief valve pointing up.
- It can be installed vertically or horizontally without restriction.
- It must be installed at least 36 inches above the finished floor.
- It must have a provision for adequate drainage from its relief valve. (Correct answer)
Correct answer: It must have a provision for adequate drainage from its relief valve.
An RPZ is designed to discharge water through its relief valve during a backflow event or due to pressure fluctuations. [2, 16] Therefore, a provision for adequate drainage, typically to a floor drain via an air gap, is a mandatory installation requirement to prevent flooding and water damage. [2, 13, 15] While there are height requirements (typically 12-18 inches minimum from the floor), the drainage provision is a unique and critical aspect of an RPZ installation. [2, 13, 18]
Question 5: A potable water line supplies the make-up water for a large fire sprinkler system that does not contain antifreeze or other chemical additives. Which backflow prevention assembly is most commonly used for this non-health hazard, continuous pressure application?
- Pressure Vacuum Breaker (PVB)
- Double Check Valve Assembly (DCVA) (Correct answer)
- Atmospheric Vacuum Breaker (AVB)
- Air Gap
Correct answer: Double Check Valve Assembly (DCVA)
A fire sprinkler system without chemical additives is considered a low-hazard (non-health hazard) but is under continuous pressure. The Double Check Valve Assembly (DCVA) is specifically designed for these conditions, preventing stagnant water from the sprinkler system from re-entering the potable supply. [10, 24, 27] PVBs and AVBs are for backsiphonage only, and an air gap, while effective, is generally impractical for a direct fire system connection. [23]
Question 6: In the hierarchy of backflow prevention methods, which of the following is considered the most positive and absolute form of protection?
- An Air Gap (Correct answer)
- A Reduced Pressure Zone (RPZ) Assembly
- A Double Check Valve Assembly (DCVA)
- A Pressure Vacuum Breaker (PVB)
Correct answer: An Air Gap
An air gap is the physical, unobstructed vertical separation between the outlet of a potable water supply and the flood-level rim of a receiving vessel. [8, 23] It is the only non-mechanical method and provides the highest possible level of protection because there is no physical path for contaminants to enter the potable water system.
Master Plumber Backflow Prevention and Safety Questions and Answers
A commercial irrigation system that utilizes chemical injectors for fertilization is being installed.
This system operates under continuous pressure.
Which backflow prevention assembly is required to protect the potable water supply from this high-hazard cross-connection?