The anti-siphon valve is the primary type of valve used for residential irrigation systems. If you don't plan to use an anti-siphon valve you can skip the rest of this page.
Anti-Siphon Valve Installation Detail A
Note: Be very careful not to over-tighten the metal pipe where it connects to the valve and pvc ell when using this detail. It is easy to crack the plastic if the metal pipe is over-tightened. Hand tighten it only, if you must use a wrench (not all of us are that strong) be extremely cautious! Use 3 wraps of Teflon tape on the male threads as a sealant. You can buy Teflon tape at any plumbing store.
The most important thing to remember when installing an anti-siphon valve is that it MUST be installed higher than the sprinkler heads or emitters it turns on and off. If it isn't higher, the built-in backflow preventer will not work. In many areas you are required by code to use metal pipe on the inlet side of the anti siphon valve. This is because the Uniform Plumbing Code only allows PVC plastic pipe to be used on pressure lines if it is at least 18" deep. Anything less than 18" deep must be metal. (A pressurized line is defined as any pipe which is under constant pressure, such as a mainline. Isolation valves don't count unless they are automatic and closed after each irrigation cycle.) Keep in mind that PVC pipe should not be left exposed to sunlight for long period of time (more than a few months). The PVC breaks down when exposed to light and will break. If you have PVC pipe above ground paint it with several coats of silver paint (silver paint contains metal flakes which block the light), or wrap it with aluminum foil held in place by a layer of black polyethylene tape. Another solution is to build a wood or metal box to go over the pipe to keep it in the dark. This is also a good way to hide the valves and protect them from vandalism. The Battery Operated Controller Detail (2batcntr.gif) shows a method of enclosing an above ground valve using a plastic valve box that works well with anti-siphon valves.
One important note on installing the anti-siphon valve on the house supply pipe as shown in the detail above. Only install valves where the water supply ENTERS the house. Some house builders provide a sprinkler connection on the opposite side of the house as well. I strongly recommend that you NOT use this connection. Run a new supply pipe around the house for the valves on the opposite side. There are two reasons why. The first is that there may very well be, and often is, a restriction in the pipe running through the house that severely reduces the water flow. The other reason is that when your sprinklers are running at night, all that water will be screaming through the pipes in your house! If you're lucky you won't hear it. If you're not... sweet dreams will be a thing of the past! Each time a valve closes your house will shake like a bulldozer just ran into it. For more information on things that go bump in the night, check out my comments on water hammer.
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