In a residential irrigation setting, backflow prevention devices are installed where the
irrigation supply line connects to the main water line for the home, referred to as the
point of connection.
Their purpose is to prevent contaminants such as fertilizer or pesticides from potentially
being drawn back through the irrigation lines and into the drinking water supply.
Backflow can be caused by a variety of reasons but a couple of examples would include the
opening of a nearby fire hydrant or a break in a city mainline.
One of the more common backflow prevention devices used in residential application is
the pressure vacuum breaker or PVB.
As a result of age, debris, or improper winterization, the internal components of a PVB can become
worn or damaged.
The sign that you have a problem is usually obvious.
You will see water flushing out from under the canopy that covers the air vent.
The most common PVB models sold in the U.S. include the Zurn-Wilkins model 720A and the
Febco 765.
While both devices are similar in design, in this video, we'll focus on how to repair
the Febco 765.
To do the job, you'll need a crescent wrench, a flathead screwdriver, and a pair of needle-nose
pliers will also come in handy.
Due to the possible health risks involved, it is important to note that some water districts
may require this work to be completed and tested by a certified technician.
Check your local codes before you begin installing or repairing any type of backflow preventer.
To get started, close the valve on the outlet side of the device, then close the inlet valve.
The valve handles will be parallel to the pipe when in the open position and then perpendicular
when closed.
Using your screwdriver, open test cock number two to relieve any residual pressure.
This can be done with a counterclockwise turn of the valve control on the side of the test
cock.
Close the valve when done.
You can now remove the canopy from the top of the housing to reveal the bonnet assembly.
Made of plastic, you may find the bonnet assembly in pieces.
The parts are designed to break if freezing occurs while the pressure vacuum breaker is
filled with water.
This design helps protect the brass housing from freeze damage.
Remove the bonnet assembly by unscrewing it from the body.
You can use a screwdriver for leverage if needed.
Underneath the bonnet assembly is the poppet.
This should just lift right out.
The bonnet and poppet are usually the parts that fail so you can likely replace them and
be done.
However, while you had the device taken apart, you may want to replace the check valve assembly
as well.
To get to the check valve and the spring, you will need to remove the retaining bracket.
The spring is directly underneath the retainer so press down evenly and rotate it counterclockwise
to free it from the slots that hold it in place.
Now remove the spring and the check assembly.
Inspect the interior of the body and clean out any debris before installing the replacement
parts in reverse order.
Also inspect the new parts as well as those you plan to reuse.
Check for damage to seals and seating surfaces as well as cracks in the plastic.
Rinse the parts in clean water before you begin reassembly.
When you install the retaining bracket, make sure that the spring is oriented with the
narrow end up and that it's centered in the recessed top of the check valve assembly and
the base of the bracket.
Before you install the new bonnet assembly, apply the food grade silicone grease that
comes in the kit to the O-ring that sits just above the threads.
This will help preserve the O-ring and provide a better seal.
Only use the provided grease.
Other products may be chemically incompatible with the rubber.
Install the bonnet by sliding the guide pin into the hole at the top of the poppet, then
screw the bonnet assembly into the housing until it seats.
It only needs to be hand-tightened.
Now use the new nut that came in the kit to reattach the canopy to the top of the bonnet.
Be careful not to over-tighten it.
Just make it snug enough so that the canopy cannot spin freely.
Finally, rapidly open the inlet ball valve to minimize the spillage through the air vent.
Then slowly open the outlet valve to restore the water supply tot he irrigation system.
Remember that backflow prevention devices are a legal requirement in many areas.
Your location may also require regular testing by a certified technician including after
a repair has been made.
Backflow devices and repair parts can be found at your local Ewing branch.
To find the location nearest you, or to shop online, visit us at ewingirrigation.com.