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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