Backflow Basics: Testing and Installation

One plumber’s tutorial on backflow prevention devices continues in part three of this four-part series

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In this series, we have covered why you need backflow prevention devices and what types there are. It’s time to go over the test equipment you will be using, valve location, orientation and clearances.

Test Equipment

Since a backflow prevention device legally needs to be inspected once a year by a licensed professional, it is important to cover how you test the different types of valves. First, I should mention that there are four test ports on the two most-common devices — reduced pressure zone (RPZ) and double check (DC) — called test cocks. You need to get a backflow test gauge in order to test these devices.

There are two kinds of test gauges: a three-valve and a five-valve. The three-valve set includes a high valve, a low valve and a bypass valve. The five-valve set includes a high valve, a low valve, and a bypass valve, with the addition of a high-side bleed and a low-side bleed. In my experience, the three-valve devices are becoming extinct and everyone is going with the five-valve manifolds.

Testing each and every device is different depending on which test gauge you have. You can obtain the test procedures online or when you register for the backflow certification class through ASSE International or whatever your local certification class is.

A last note about the test equipment is that it needs to be calibrated every single year. When you attend a certification class, you will be provided with a local list of places that are certified calibration businesses that can calibrate your gauge. Make sure you call a few weeks or months in advance to get on their schedule.

Gauge Care and Maintenance

Every time you finish testing, open up all five valves and shake all the water out of the gauge. Get in a habit of doing this or when the temperature drops, it will freeze. The internal ports inside the gauge are so small that once it freezes, the gauge will be destroyed.

You will notice that the hoses are glorified refrigeration hoses with a black bulge a quarter of the way up the hose. That black bulge is a rock filter. Make sure you only use this type of hose since the chances of debris coming in through the water supply are high. When you set the gauge in your box, leave all five ports open so that remaining water has a chance to escape.

Valve Location, Orientation and Clearance

The backflow device should be installed after the water meter, near the entry point of the water service and before the first takeoff. Backflow devices come in a range of sizes and locations. If you are working on a large commercial building, more than likely the valves are in a vault in the ground outside, come up out of the ground outside (in warmer climates), or are located where the water supply first enters the building. They must be installed 12 to 36 inches above grade and must be easily accessible. If you are in a situation where a plumber piped in a bypass around the backflow preventer, the bypass line must have the same level of protection as the mainline. So if your 6-inch main has a 6-inch RPZ, then your 2-inch bypass line needs a 2-inch RPZ.

There are also clearances to pay attention to for the test cocks. You need 12 inches of clearance above any and all test cocks and 24 inches of clearance if the test cocks are located on the side of the valve against a wall or obstruction.

Since RPZs have a discharge relief valve, they need to have an approved air gap installed that needs to be piped to or near a drain. Every RPZ valve has a matching air gap that is ordered separately. It screws onto the bottom of the discharge on one side. In the middle there is the air gap, and a female thread connection helps you pipe it to a drain. Do not reduce the size of the drain from its original size, and don’t try to be cheap and go without the air gap. It is important — especially when the device fails and threatens to flood your customer’s business.

DCs can be installed vertically or horizontally, but RPZs can only be installed horizontally.

In the final article of this series, I will cover check detectors, cause of failure, fire systems, and basic repairs.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years' experience in the plumbing and HVAC trades and has a bachelor’s in business and economics from Thiel College. 


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