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Backflow Preventer Installation Instructions


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Hooking up to your water supply
Hooking up the backflow preventer to your water supply is the task that causes the most concern for most people. That's simply because most people don't know how to do it, or don't know how to choose between the different options they've seen. The easiest way to eliminate this worry is to become educated, and that's what this page is all about. After reading this page you should know several ways to hook up your backflow preventer and what the advantages and disadvantages of each option are.

Purpose of the backflow preventer
The purpose of the backflow preventer is to stop presumably contaminated water in your sprinkler system from flowing back into the public water supply in the event the supply pressure is dropped to make periodic repairs. It's common for the supply pressure to drop to a partial vacuum, literally trying to suck water from your home and sprinkler system into the public supply. This is unavoidable when repairs take place downhill from your home, as all the water in the main tries to run out the hole at the repair site. Not all homes can be isolated from the repair by valves.

Obtain a list of code requirements
The first thing you should do is obtain a list of related code requirements from your local building code permit office or water utility supplier. They should be able to give you the requirements for depth of the pipe, dimensions of the backflow preventer box, installation heights, etc. These instructions will refer to typical dimensions, but you should verify these are adequate in your area. Factors such as average winter temperatures can have a major effect on the minimum depth requirement for the pipe, for instance.

A typical home water supply example
A typical home water supply connection in southern climates consists of a 1 inch copper pipe connected to the water main under the curb. In cold climates the location or depth of the meter may be different, but the method of hookup can be similar. The 1 inch pipe may split into two 3/4 inch pipes at the meter box in the case where two homes have their meters in a shared meter box. The 3/4 inch pipe will pass through an angle valve owned by the water utility, and then a meter (often 5/8 inch or 3/4 inch) usually owned by the water utility as well. Everything past the meter is usually owned by the homeowner. After the meter is found a gate valve used to shut off water to enable repairs in the house. If the supply pressure is high enough to require it, a pressure reducing valve (PRV, or pressure regulator) will be found near the shut-off valve. A length of 3/4" copper pipe about 6 feet long is usually connected to the shut-off valve (or PRV), then a large piece of PVC pipe may be used for most of the distance to the house. Other types of pipe may be recommended in very cold climates. A sprinkler system may be installed anywhere after the meter, but the best place is after the shut-off valve, either before or after the PRV (trade-offs to be discussed later). The connection can be made in the portion with the copper pipe, or in the PVC section.

This photo below shows two meters exposed during maintenance of a public water main. You won't have to dig up this much to install your backflow preventer (thank goodness!) but we thought this was a nice clear example of how the water utility company installs meters. In this example, the shut-off valve is installed after the PRV (which is uncommon) and just out of the field of the photo. You can, however, just barely make out the 1 inch pipe supplying the two meters, the two angle shut-off valves, both meters (with dial covers closed) and the line to the PRVs. The meter nip ples are also easy to distinguish in this shot, and they are very important to know about if you plan to install a threaded and glued connection.


photo of two water meters

Two methods to connect
There are two basic methods to connect your system to the water supply- with a threaded and glued connection, or through a compression fitting. We prefer threaded/glued joints due to their higher reliability. If you use the tricks we describe here, it usually isn't much harder to use a threaded/glued connection than a compression connection, and it is usually less expensive to boot!

Method 1: Threaded and glued connections
Making a threaded or glued connection usually means inserting a threaded tee into the existing pipe somewhere and connecting to the tee through a PVC male adapter. Since the inserted tee will add additional length to the line, a small section of line must be removed and a joint added to repair the shortened section.

Method 2: Compression fittings
Compression fittings depend on a rubber washer to obtain a seal around the outside of the supply pipe. They are installed by cutting out a very small section of line and installing the compression fitting over the cut. They work best when the pipe over which they are installed is not damaged and is smooth on the outside. Try to find a metal compression fitting with rubber washers (as opposed to plastic and rubber) and be sure to measure the supply pipe carefully to make sure you get the correct size. For more details on installing a compression connection, see the description below.

How to make a threaded/glued connection
How to make a compression fit connection
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