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What devices are code approved for backflow prevention at a sprinkler (lawn irrigation) system?

Tuesday, June 11, 2019

Whenever a sprinkler system is connected to the same water supply as the house there is the potential for “cross contamination,” which can happen after a loss of water pressure. This presssure drop causes a vacuum in the pipes that literally sucks the water backwards, and may bring dirt and contaminants into the water supply of a home.

    Also called a “cross connection,” this was once a route for spreading bacterial and viral diseases before modern plumbing codes were instituted throughout the U.S. less than 100 years ago. See our blog post What is a "cross connection" in a home's plumbing system? to learn more, including about the 1933 Chicago World’s Fair, where 98 visitors died and over 1,400 became sick due to cross contamination at a hotel near the fair. 

     Here’s what the 2017 Florida Plumbing Code says about backflow prevention in a sprinkler systems:

    The International Plumbing Code and Uniform Plumbing Code have a corresponding citation. The are three types of backflow prevention devices approved by the code:

Pressure vacuum breaker - This is the most common type we see in Florida. A pressure vacuum breaker (PVB) must be installed a minimum of 12-inches above the highest piping downstream of it and, in the case of sprinklers, that would be the tallest sprinkler head. Also, a PVB is rated for use under continuous water pressure, and will have two shut-off valves, as shown below.

Atmospheric vacuum breaker - This is a simpler version of a pressure vacuum breaker that looks similar to a PVB, but has a several limitations. It cannot be used in a system with continuous water pressure, and no valves are allowed downstreamfrom an AVB. 

Reduced pressure principle backflow prevention assembly - A more complicated device we have not seen used for residential sprinkler systems, primarily for systems that introduce chemicals into the water flow. 

    A check valve, like the one shown below, is an example of a device that is not approved for backflow prevention for a sprinkler system.

    Also, see our blog post Will a sprinkler system work without a vacuum breaker (backflow preventer)?

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Here’s links to a collection of our other blog posts about PLUMBING PIPES:

How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

Can galvanized steel pipe still be used for new water lines in a house? 

How can I tell if I have cast iron pipes in my house? 

Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection? 

What is the difference between green and white sewer drain pipes?

Is a washing machine drain hose required to be secured at the standpipe?

What are the abandoned pipes sticking out of the wall in my house?  

What are the code requirements for plumbing vent terminations?

What are the code requirements for layout of drain piping under sinks?

What causes a grgling sound when a bathtub or sink drains? 

What is a "combination waste and vent" in a plumbing system? 

What is a building trap?  

What is a galvanized nipple?

What are the pipes sticking out near my water valves?

How do you accurately find a broken water pipe leak under the floor slab?

What is the difference between water pipe and sewage (waste) pipe? 

Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water? 

Is a hot water faucet handle required to be on the left? 

What is a dielectric union? 

What's that powdery crust on the pipe connections at the water heater? 

If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?  

How can I tell what type of plumbing pipe I have?

Why is there a flexible accordion pipe under the sink? 

What is the difference between PVC and ABS plumbing pipe?

What is the difference between water service pipe and water supply pipe? 

What are the pipes on my roof? 

What is a P-trap?

Why is old galvanized steel water pipe a problem for homebuyers?

What does polybutylene pipe look like? Why is it a problem? 

• Which water pipes are an insurance problem and possibly uninsurable?

• Can you connect CPVC pipe directly to a gas water heater?  

     Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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