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How to Install a Backflow Preventer

Protecting the quality of your drinking water should be a top priority. When you have an irrigation line attached to your incoming water line, contaminants can enter the lines that provide your family with tap water. To prevent this, you need a backflow preventer. The backflow preventer is installed to prevent polluted and contaminated water from affecting potable water supplies. Contamination can occur when the main water line has been shut down for repair, or when there is a sudden drop in water pressure. Knowing how to install a backflow preventer will safeguard your family from potential illness.


These instructions apply to meters located in warm climates that are buried directly into the ground. If you live in a colder climate, your meter may be located in the basement. If so, you will not have to dig to reach the installment area. Before you go any further, check local zoning and coding laws for the proper height, depth, and installation rules. To avoid zoning issues and other obstacles that may arise, hiring a contractor is recommended.

Step one - The water line from the meter outlet to the house will have to be dug up. You may have to dig a trench several feet long. Dig at least five inches under the pipe to avoid installing the preventer in a watery mess and to have moving room. Once you know where you want the backflow preventer is to be placed, make sure there is enough room for the preventer and the preventer case.

Step two - You will have to shut the water off at the meter on the street side using and an angle valve. Disconnect the main water line going to your house. The outlet side of the meter will be the easiest place to disconnect. A meter nipple is attached to the line with a nut. The nut, after being unscrewed, will allow you to pull the pipe apart. All other joints can now be unscrewed.

Step three -  Time to install the new tee. You may have to dig some more to allow the shut-off valve room to move. Placing the tee on the downhill side of the shut-off valve is recommended. Using Teflon tape, wrap both ends of the nipple, and any other threaded pipe ends that have been removed. Screw the nipple into the shut-off valve, then screw the new tee into the nipple. The other end of the tee screws into the pipe.

Step four - After installing the new tee, your water line will likely be too long to reconnect to the meter. You will have to remove a section of the line. Measure how much line will be removed and add 1/8 inch from the large plastic pipe coming from the house. Make sure the new tee is at an angle that the backflow preventer will hook up correctly and that all threaded pipe has been taped. You will need to place a coupling onto the large PVC pipe. Smooth off the rough edge of the pipe and add the coupling. Before the glue on the coupling has dried, tighten the bolt of the meter nipple. This ensures the repaired line will fit correctly.

Step five - Wrap the threaded end of a male adapter with Teflon tape and screw it into the new tee. If you want to change the direction of the pipes, you can use plumbing ells. This allows you to run lines from any direction to the meter and the backflow preventer.

Step six - Before you install the backflow preventer, make sure you have the correct height. If the unit is going to be above ground, you need to know if you measure above grade or measure to the highest sprinkler. If you are placing the backflow preventer underground, there may be restrictions. Check with your local water utility or building permit office for information. Once you have the correct height regulations, the backflow preventer can be installed. A contractor usually performs this portion.

Why is a backflow preventer necessary?

If you have a landscaping irrigation system, there is nothing preventing contaminants from entering your potable water source. Irrigation lines are known to pull water backward into the water lines known as backflow or a siphon. Over time, your irrigation lines are exposed to pesticides, weed killer, and other poisons. To prevent such poison from reaching your inside tap, you need a backflow preventer.

There are two types of backflow: back siphon and back pressure.

Back siphon can occur during a water break or when a fire hydrant is opened, causing a vacuum and water is pulled backward in the water line.

Backpressure occurs when water pressure downhill from the irrigation line is greater than water pressure uphill. A knocking noise in the lines known as water hammer is an example of back pressure.

Choosing the right backflow preventer

Both forms of backflow can occur at any time. Thus it is important to know the different types of preventers. If you have an anti-siphon valve in place, you will not need to install a backflow preventer. If you installed a Globe or Angle Valve, you can install one of the following.

Atmospheric Vacuum Breaker (AVB) - This backflow preventer has a reputation of being very unreliable. Not only is the AVB one of the cheapest preventers on the market, but most cities also will not allow them due to their poor performance.

Pressure Vacuum Breaker (PVB) - This breaker is comparable to the AVB, but only requires one breaker instead of two or more. The PVB must be installed on the main irrigation line that leads to all control valves and must be 6” above the tallest sprinkler head.

Reduced Pressure Backflow Preventer (RPBP) - Considered the most reliable and economic preventer on the market. While this preventer is used mainly in commercial sprinkler systems, it works well for your home irrigation needs. The reduced pressure backflow preventer allows you to apply chemicals and fertilizer in the irrigation lines. No other preventer has this option. This preventer should be placed 12” above ground.

Double Check Backflow Preventer - This preventer is usually placed in your basement or a storage space underground below the freeze line. Water can flow effortlessly without being exposed to air contaminants and pollution.

Preventing problems

The best way to avoid issues with your backflow preventer is to have it installed by a contractor. If the slightest mistake is made, you can be faced with multiple health, financial, and legal issues. Once your backflow preventer has been installed, regular testing should be performed by your contractor.

A backflow preventer installation in your home can be a very complicated process, and as such it should be completed by a licensed contractor. There are many things you can do to prepare for the contractor, and a few important factors you should keep in mind before beginning the process. If you still have questions, you can speak to a qualified Expert on JustAnswer for the solutions to your backflow preventer questions.

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