Rebuild Guide

Backflow rebuild Guide

This tip sheet provides some helpful pointers for rebuilding assemblies 1" and under (contact us if your assembly is over 1").

NOTE: Anybody performing a repair is responsible for following all applicable plumbing and safety rules. Due to the serious dangers of low oxygen in large underground work spaces (such as utility vaults), DO NOT attempt a DIY repair in a vault. Please consult a repair company with the equipment and knowledge necessary to safety enter a vault following OSHA's confined space rules.

Step one: information gathering

Review the repair section of our FAQ for a general overview on when, and by whom, repairs should be done. Always use the manufacturer's repair instructions, and make sure you're following local rules.
Have your test report ready. This will have important information on what's failing, and the assembly information provided by your tester (make, model, and size) will be needed to locate manuals and parts.
Get a repair manual for your assembly. This will contain model-specific diagrams, step-by-step service instructions, and additional helpful information. Some manufacturers also offer repair videos. We have collected most common manuals and videos in the Manuals and Videos section of our repair library.

Step two: order parts

A rubber parts kit, while not strictly necessary for all repairs, is an excellent insurance policy. They're often cheaper than an extra test if the assembly fails again due to worn/damaged seals (and you can't always tell if they're damaged just by looking at them).
For a DCVA, DCDA, PVBA, or SVBA (consult the check boxes below the assembly address on your report), you'll usually order a complete rubber parts kit.
For an RPBA or RPDA (consult the check boxes below the assembly address on your report), you can be more selective. If the only reason for failure is that the relief valve is opening below 2.0 PSID, a relief valve rubber parts kit will usually suffice. Otherwise, we recommend the complete rubber parts kit.
Mesher Supply is a local supplier of kits - give them the make, model, and size from your report, and ask for the kit indicated above. They can ship, or you can pick up at their warehouse near the SE Portland waterfront. If Mesher doesn't carry the parts you need, there are online suppliers that offer wider selections. Some of these companies only sell to industry professionals, so please contact us if you need assistance.

Step three: gather your tools
At minimum, we recommend having on hand:

A stubby, medium-sized slot screwdriver
A medium-sized (at least 8") adjustable wrench
A socket wrench (only needed for assemblies with cover bolts - 1/2" and 7/16" are the most common bolt sizes)
A pair of needle-nose pliers (only needed for assemblies with cartridge-style check valves)
A Scotch-brite or other abrasive pad to gently clean the seats
Time: most repair take 30 minutes or less, but give yourself up to an hour, just in case. In rare cases (for assemblies or boxes that are in poor repair, or installed in a way that interferes with visibility and access), repairs may take longer or not even be possible.

Also very helpful:

A knee pad, if you're working in a box below grade
Robust clothing you don't mind getting wet and dirty
Ample light, whether natural or artificial (we often use our phone lights as a compact, portable light that can get in most spaces)
If your check valves open at an angle that prevents you from seeing down into the body of the assembly, having a telescoping inspection mirror like this one can be a big help. There are also larger, fancier versions with built-in lights.
A small bucket or container with fresh, clean water for cleaning off the assembly parts
Clean towels for cleaning off assembly parts (and your work area)
A small trowel, if your box needs to be dug out to provide access to the check valves
Tough, waterproof gloves to protect your hands
A Phillips screwdriver (used to remove the bonnet of some PVB assemblies, or the retaining washer that secures the seals in some models)

Less often needed:

If you're working inside, you'll probably want some way to collect water. Depending on how an assembly is installed, a generously-sized bucket or tub, or a small gathered tarp, will often catch most drips.
Food-grade o-ring lubricant (this is usually included with your parts kit).
Vise grips or a 6" adjustable wrench, if your assembly handles are in very poor condition or are stiff with reduced clearances.

Step four: rebuild your assembly
Using the repair manual you obtained in step one, carefully follow manufacturer instructions for repairs. These may be listed in the manual as instructions for maintenance, repair, servicing, and/or troubleshooting - if you're not sure which instructions to follow, you can contact us for clarification. Some helpful tips:

Keeping your work area clean is VERY important. If any debris is introduced to the check valves or interior parts during repair, this can result in a failing assembly. Before undertaking any repair, it's always a good idea to carefully but thoroughly dig out the area around the assembly, with particular care given to cleaning off the areas around the check valve covers. You can wipe down the exterior parts with a wet towel or hose them off if the work area is particularly messy. Be sure to have a clean surface ready for any parts you may need to set down during the repair.
Be sure to turn water OFF at the up- and down-stream assembly handles before you begin any repair. The shutoff valve can be stiff, and we often use an adjustable wrench to provide extra leverage if needed. After water is off, you can relieve water pressure inside the assembly by slowly opening any test ports between the closed backflow shutoff handles (usually requires your stubby slot screwdriver) and waiting for water to stop flowing.
Always use care when opening up an assembly and interacting with the internal components - these are spring-loaded, so parts can unexpectedly pop out of place.
If you're working inside, you may find it helpful to use a bucket, tub, or small gathered tarp to catch excess water during the work.
Check to make sure that test ports are closed and that any parts removed have been fully resecured before restoring water service. When you do restore service, do so very slowly, checking for drips and leaks as you go.

Step five: order a retest

Contact us to schedule a retest. Assuming you're rebuilding your assembly due to a failed test, your water district will require a new test to show that the assembly is now passing. Not all repairs are successful the first time, and your water district wants to make sure everything's fully operational. For DIY repairs, we recommend waiting at least a week between repairs and retesting - an extra few days can give the seals time to conform to the seat and provide a better seal. We offer a $5.00 discount for retesting after repair or replacement, provided the second test is done within the same calendar year as the failure.