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The World of Backflow Preventers: Backflow’s Gotta Go!

Nick B

There are over 10,000 reported cases of backflow contamination each year, but with the proper backflow preventer you can protect your potable water systems from potential hazards.  Backflow devices are required by law and must be installed in accordance with plumbing or building codes.  Be sure to select the correct types of backflow preventers for the application it will be used for.



Reduced Pressure Zone (RPZ) Assemblies
A Reduced Pressure Zone Assembly (RPZ) contains two independently acting spring loaded check valves separated by a spring loaded differential pressure relief valve, two shutoff valves, and four test cocks.  During normal operation the pressure between the two check valves, referred to as the zone of reduced pressure, is maintained at a lower pressure than the supply pressure.  If either check valve should leak the relief valve is designed to open and discharge water.  An RPZ will periodically discharge small amounts of water due to fluctuation in line pressure.  For this reason the RPZ should be installed in areas that are not subject to water damage and allow for adequate drainage.


Vacuum Breakers 
A vacuum breaker is an accessory placed on a faucet valve, toilet, or flush valve that prevents the reverse flow of polluted water from entering into the potable water supply due to back-siphonage.  Atmospheric Vacuum Breakers (AVB’s) are among the simplest and least expensive mechanical types of backflow prevention assemblies available. 


Dual Checks 
A check valve ensures that water only flows in a single direction of a plumbing system.  This prevents contaminated water from flowing back into the system once it has been used.  A dual check valve contains two independently acting, spring-loaded check valves.  Dual check valves are most often used in connection with city water supplies, sewer systems, and water service connections to single-family homes.


Double Check Valve Assemblies 
The Double Check Valve Assembly (DCVA) is essentially two single check valves assembled within one body and furnished with four test cocks and two shut-off valves.  A DCVA is commonly used to protect against low to medium hazard installations such as food processing equipment or lawn sprinkler systems.


Double Check Detector Assemblies 
A Double Check Detector Assembly (DCDA) is primarily utilized in fire line installations.  It protects the potable water supply line from possible contamination or pollution from a fire system, back-pressure from fire line booster pumps, stagnant “black water” that sits in fire lines over extended periods of time, and the addition of non-potable water through outside fire district connections (FDCs).  They also detect if there is any water being used in the fire line due to leaks or deliberate water theft.  It consists of two spring loaded check valves, a by-pass assembly with water meter and double check valve, and two tightly closing OS & Y gate valves.


Reduced Pressure Detector Assemblies
The Reduced Pressure Detector Assembly (RPDA) is typically only used on fire line applications.  However, this assembly is intended to protect the potable water supply from fire sprinkler systems that contain chemical additives or can be connected to auxiliary non-potable water sources.  An RPDA contains a mainline reduced pressure backflow assembly equipped with OS&Y gate valves, a bypass configuration containing a smaller reduced pressure backflow assembly, and a water meter.  This meter detects ground leaks and illegal taps which can greatly reduce annual water expenses.


Test Cocks 
Test cocks are used to facilitate backflow assembly testing.  They may also be utilized as isolation valves for gauges or small equipment lines.  A typical backflow assembly has test cocks, shut-off valves, and must be tested each year.


Want to learn more?  Check out the video below:


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2 Responses to The World of Backflow Preventers: Backflow’s Gotta Go!

  1. Sarah Smith says:

    I didn’t know there were so many different types of backflow preventers. It was also news to me that these backflow devices are required by law and have to be installed in accordance with specific plumbing codes. Preventing hazards in my drinkable water is a must and if I ever have a problem I will call a plumber.

    • Nick B says:

      Hey Sarah,
      I’m glad you found this useful! Backflow preventers are certainly important and precise, so leaving them to the pros is a good call.

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