How To Look At A House

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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 gurgling 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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