• Backflow prevention valves prevent potentially contaminated water from entering a clean water supply. There is a variety of backflow prevention valve types that are used for different applications. It is important to check with your local water company and local administrative codes before any installation to ensure the proper backflow prevention valve is used.
  
  

Antisiphon Valve

• The antisiphon valve can be either an automatic or manual control valve that has an atmospheric vacuum breaker that is built in. It must be installed 6 inches higher than the sprinkler head that is at the highest level. When using a backflow prevention valve for residential irrigation systems, the antisiphon valve is the most commonly used valve. You cannot install any other types of valves on the pipes that are downstream of the antisiphon valve; this will prevent the antisiphon valve from working properly.
  
  

Atmospheric Vacuum Breaker

• The atmospheric vacuum breaker, otherwise known as the AVB, is a backflow prevention valve. The atmospheric vacuum breaker is installed on the pipe, after the control valve. If you use this type of valve for backflow prevention, you must install an atmospheric vacuum breaker after every control valve. It must be installed 6 inches higher than the highest sprinkler head, drip emitter outlet or bubbler that is switched on and off by that control valve.
  
  

Double-Check Backflow Prevention Valve

• A double-check backflow prevention valve has two manual valves. One valve is at the inlet and the other is at the outlet. These valves can be used to turn off the water flow in an emergency. The valves are also necessary to test the backflow prevention valve for proper operation. Test gauges can connect to the test cocks that are located on the side of the backflow prevention valve. This type of backflow prevention valve can be installed underground, making it ideal for cold climates. Some municipalities do not allow the use of double-check backflow prevention valves. It is a good idea to check with your local water company before purchasing and installing this type of backflow prevention valve.
  
  

Pressure Vacuum Breaker

• This is similar to an atmospheric vacuum breaker, with the exception that you install just one of them and it is installed on the mainline which leads to the control valves. This must be installed above the ground and it must be 6 inches above the highest sprinkler head or drip emitter that is controlled by the valves. Some authorities require the pressure vacuum breaker to be installed within 18 inches of the connection to the water source; this means you can't use the pressure vacuum breaker unless your water source is at the high end of your irrigated area. You will need to check with authorities, as some cities do not allow the use of pressure vacuum breakers.
  
  

Reduced Pressure Backflow Preventer

• The reduced pressure backflow prevention valve is also known as the RP unit. This type of valve is normally used for commercial irrigation systems. Reduced pressure backflow prevention valves are made for high hazard use. They offer maximum backflow protection from contaminated water or pollutants. The RP unit has to be installed 12 inches above the ground; however, it does not need to be higher than any of the sprinklers.