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The types of backflow preventers available and their uses

by itworldofi

Last Updated on November 2, 2021 by itworldofi

Multiple kinds of backflow preventers are available, and each kind is designed to provide water systems with a different level of protection, for various kinds of residential and commercial applications.

It would be a wise choice for people to learn about the various kinds of backflow devices in existence, and familiarize themselves with them. Why should they do that? Because that will help them select the one that meets their needs in the best manner possible.


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The pressure vacuum breaker (PVB)

The pressure vacuum breaker (PVB) is one of the most common and low-priced options available in the category of complete high flow backflow preventer systems. It comprises of the following:

  • An inlet shutoff valve is located at the lower end.
  • A single valve body comprising a pressure vacuum breaker.
  • A check valve.
  • Two test cocks.
  • An outlet shutoff valve.

Along with being an inexpensive option, a PVB is relatively simple in design, is easy to install, maintain and fix. In fact, some PVBs also offer in-built freeze protection but this only protects its assembly. Inlet and outlet pipes can still freeze if the system is not properly protected during the winters.

One of the cons of using a PVB is that they will at times eject some water on an occasional basis. Hence, selecting a spill-resistant model of PVB for installing it indoors is a better option. Else, water spillages can cause a lot of inconveniences.

Assembly features

  • It is installed almost 12 inches above the highest downstream point present in the system.
  • It can be installed vertically with the inlet located at the bottom.
  • It can only prevent reverse siphonage instead of back-pressure.
  • No danger of chemical contamination.
  • It cannot be installed at places having back-pressure as a potential threat.

Double-check valves (DCV)

Double-check valves (DCV) are also known as Double check assemblies (DCA). They are a sensible choice when it comes to installations that are either indoor or underground. DCVs comprise of the following:

  • An inlet shutoff valve.
  • Two spring-loaded check valves that work independently (and are located in a single valve body).
  • Four test cocks
  • An outlet shutoff valve.

They can be installed vertically but only if the local building codes and rules allow them to be.

Double-check valves are the most common kind of approved backflow prevention device for use in either underground or in-line installations. In-line indicates that the device is parallel with the sprinkler system’s piping but unlike the PVB, these valves do not need to be installed almost a foot above the highest point in the system.

Some areas of DCVs do require above-ground installation. Hence, residents and plumbers should always get it checked with the local authorities before installing this below the ground. It is possible to create a double check valve assembly from entirely new components. However, this isn’t the best option due to an increased risk of built assemblies not meeting local building codes.

For the sake of convenience, cost-savings and restrictions due to building code, a better option would be to purchase a pre-assembled double check valve assembly.

Assembly features

  • Can be installed either underground (inline) or above the ground.
  • Cannot be used with chemical spraying systems.
  • Can be installed horizontally and vertically (the former is preferable).
  • It can be installed at places having the potential for a back-siphonage.

Reduced Pressure Zone (RPZ)

Reduced pressure zone (RPZ) assemblies are also referred to as reduced pressure principle (RPP) assemblies. They are the most complicated and expensive backflow preventers available. But if they are installed properly and work properly, then they are the most secure and reliable of all backflow preventers.

It consists of the following:

  • An inlet shutoff valve.
  • Two independently operating spring-loaded check valves, separated by a pressure differential relief valve.
  • Four test cocks.
  • An outlet shutoff valve.

Local building codes are variable and can be strict regarding reduced pressure zone assemblies. It is wise for both residents and plumbers alike to have a thorough understanding of local requirements before proceeding.

Assembly features

  • They are compatible with both underground and above ground installation (the latter is preferable).
  • Can be used for fumigation with chemicals.
  • Horizontal installation is only needed when it is configured for factories or for alternate installation.
  • It protects against back-pressure and reverse-siphonage.

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Atmospheric Vacuum Breaker (Anti-Siphonage system)

Atmospheric vacuum breakers (AVB) are the simplest and most affordable of all backflow preventers. They are ideal for one or two-zone irrigation systems. AVBs need to be installed directly on the pipings after each control valve. But for systems with more than almost six control valves, they are not an affordable option.

However, Atmospheric Vacuum Breakers are among the least reliable systems and are often not recommended. They are not allowed for use in large cities and suburbs in lawn sprinklers and are also not recommended for use in areas of constant pressure.

Other areas where AVBs are not recommended for use are shutoff valves in downstream areas having potential for backpressure, as well as other systems incorporating techniques of chemical fumigation.

Assembly features

  • It can be installed at least six inches above the highest outlet in the zone.
  • Vertical installation is possible with the bonnet on top, as it only stops reverse-siphonage.
  • Requires one unit pet zone installed downstream from zone control valves.
  • It isn’t usable where it is subject to continuous pressure beyond 12 hours at a time.
  • Cannot be used for chemical fumigation.
  • The AVB cannot be installed for areas prone to backpressure.




















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