How to Install an Anti Siphon Valve

An anti siphon valve is used in your water sprinkler system to help prevent water that has been potentially contaminated from flowing back in to the pipe leading from your home's main water supply.

When an in-ground water sprinkler system is used to water a lawn, there is always the possibility that fertilizer or other toxic chemicals could find their way back into the pipes, and the anti siphon valve is a cheap way to make sure that does not happen. They are easy to install and this simple how-to guide will show you what you need to do.

Step 1 - Knowing Where to Start

Before you begin, you must know that the anti siphon valve must be installed so that it is at least 6 inches higher than any of the sprinkler head valves in your lawn's watering system. If the anti siphon valve is not installed in this manner, the back-flow prevention mechanism in the valve will not work.

Also, the Universal Plumbers Code (UPS) in almost all municipalities requires that the pipe on the inlet side of the anti siphon valve be made of metal unless the pipe is buried more than 18 inches deep. You can use any type of pressure-rated metal pipe for the project.

Step 2 - Place Siphon Valve After Isolation Valve

When installing a siphon valve it is best to place it directly after the isolation valve in the pipe system. The isolation valve is the main shut-off valve for your sprinkler system. It is usually placed directly after the coupling made with the main water line in your plumbing system. Ideally the isolation valve should be about 6 to 18 inches above ground so that your anti siphon valve will remain higher than the sprinkler heads.

Step 3 - Install Inlet Pipe

First, you will need to insert a piece of metal pipe with dual threaded ends into the isolation valve. Then insert the other threaded end into the metal elbow the same diameter as the pipe. Be sure to wrap the ends with plumber's Teflon tape before tightening.

Step 4 - Install Siphon Valve

Wrap Teflon tape on the male threaded end of the anti siphon valve and insert into the metal elbow connector. If the valve has no threaded end, install a short piece of pipe with two male threaded ends, and then install the anti siphon valve.

Step 5 - Install First Sprinkler Head

Many anti siphon valves come with a sprinkler head attached; however, if yours does not, you will need to install one. To do this, use a three-inch piece of PVC pipe. Use the PVC primer on the female connectors and both ends of the pipe. Then, secure the pipe to the valve and the sprinkler head with PVC glue.

Step 6 - Continue Running Sprinkler Inlet Pipe

After you have attached the first sprinkler head to the anti siphon valve, you can begin running your pipe to the rest of the sprinkler heads. So, install a vertical piece of PVC pipe to the bottom of the sprinkler head, and make sure the first PVC elbow is buried at least 18 inches deep before installing more sprinkler heads.