This video will help you understand the importance of installing a backflow preventer in your sprinkler system, how they work and which backflow preventing device you should choose for your system. An anti-siphon valve is generally less expensive and less work to install. An anti-siphon valve can be purchased both as a manual or automatic control valve with a built-in atmospheric vacuum breaker. It must be installed 12 inches or higher than the highest sprinkler head or drip emitter outlet. If you install any valves of any type on the pipes downstream of the anti-siphon valve the anti-siphon valve will not work. The downstream valve creates back pressure on the anti-siphon valve which causes the vent in it to jam in the closed position. If this vent can open the anti-siphon valve will not prevent backflow. Anti-siphon valves may not be installed in any location where it might ever be submerged underwater. A pressure vacuum breaker or PVB is similar to an atmospheric vacuum breaker except that you only need to install one. It is attached to the main line leading to the control valves. Like the atmospheric vacuum breaker it must also be installed above ground and it must be at least six inches higher than the highest sprinkler head or drip emitter controlled by any of the valves. In a slope yard it would typically need to be installed at the highest point in the yard with a mainline pipe running up to it from the water source and then another mainline running back to the control valves. Some local municipalities require that pressure vacuum breakers must be installed within 18 inches of the connection to the water source and or prohibit their use with drip irrigation systems. And others don't allow the use of pressure vacuum breakers at all. Make sure to check the codes regulation and laws in your area before installing one. Pressure vacuum breakers are known to spew spit or spill water from under the cap when a backflow occurs. Because of this it should only be installed in a location where water spillage will not cause problems. The standard for commercial irrigation installations and a bit more expensive option is to use a reduced pressure backflow preventor or RP assembly. Like a PVB it should be installed in a location where it will never be submerged. It has to be installed at least 12 inches above the ground but it does not have to be higher than the sprinkler heads in the system. All backflow preventors must be installed correctly. Backflow preventors should be checked at least yearly for proper operation and the backflow preventor should be protected from freezing. And remember sprinkler warehouse has everything for your irrigation needs so that your trees, lawns, flower beds and gardens are lush and beautiful. And if you have any questions about our products give us a call or chat with one of our customer service agents on sprinklerwarehouse.com. They really know their stuff and they'll get you squared away. And don't forget to subscribe to our YouTube channel for more how-to videos and irrigation tips. For sprinkler warehouse I'm Alfred Castillo your sprinkler warehouse pro.