Always follow manufacturer’s repair instructions

This is an expanded guide that is following the manufacturer’s exact repair instructions. Test Gauge Inc. has provided tips to make repair safer and easier based on industry experts.

Repairing a backflow preventer so it meets the original specifications is a critical step in protecting our potable water resources.

To begin, make sure both the inlet and outlet control valves are closed tight. Slowly open test cocks 2, 3, & 4 to verify the control valves have closed before removing the cover assembly

Remove the six relief valve cover bolts while holding the cover down.

Next, remove the stainless steel flathead screw that holds the brass sensing line in place.

Lift the cover straight off.

The stem and diaphragm assembly will normally remain with the cover as it is removed.

The relief valve spring will be free inside the body at this point.

Inside view of the assembly after cover has been removed.

The relief valve seat is located at the bottom of the body bore, and can be removed, if necessary, for cleaning.

View from the bottom side. The stainless steel relief valve seat is sealed into the body with an o-ring. Simply push from the bottom and the seat will come free.

Note: If the seat cannot be removed by hand, gently tap on the outside ring of the seat. Be careful to not bend or break the center guide.

The disc can be cleaned without disassembly of the relief valve module.

If it is determined that the relief valve diaphragm and/or disc should be replaced, the relief valve module can be readily disassembled without the use of special tools.

Note: pay special attention when disassembling the relief valve module so that re-assembly goes smooth.

Remove the nut on the top of the relief valve stem to access the diaphragm rubber and o-ring.

Remove all individual parts for cleaning/replacement.

Pictured are all of the individual components that will be accessible after removing the top nut of the relief valve module.

Note: When each component is removed, set them face down in the order that they were taken off.

Start by holding the relief valve with threaded stud to the top. Slide the smaller metal washer (flat side up) over the stud.

Next, slide the larger rubber diaphragm (smooth, solid black side up) over the threaded stud.

After the large diaphragm is installed, slide the large metal washer (“cup” side up) onto the assembly

Set the smaller rubber gasket into the “cup” of the large metal washer

Next, thread nut onto the assembly making sure that the small black o-ring is in place. Lubricate o-ring with FDA approved silicone grease. When tightening, make sure all components are centered properly.

Do not over tighten nut. Replace orange o-ring on nut and use an FDA approved silicone grease to lubricate

If the relief valve disc needs to be replaced, unthread the stem guide. The disc rubber is molded into the disc holder and is supplied as a disc holder assembly. The rubber disc cannot be flipped, so the complete disc holder assembly will need to be replaced.

To reassemble the relief valve, press the seat firmly into place in the body, center the spring on the seat, and insert the cover and relief valve module as a unit straight into the bore. Press down on the cover to assure proper alignment. Insert and tighten bolts.

If cover will not press flat against body, stem assembly is crooked and damage can result. Realign stem and cover before bolts are inserted.

Note: look up from the bottom and make sure relief valve stem guide is properly aligned thru center hole of the relief valve seat.

Remove the retainer from the body bore.

The check valve modules can now be removed from the valve by hand or with a screwdriver.

NOTE: The seats and springs of the first and second check modules are not interchangeable. The heavier spring and smaller diameter seat belong with the first check module. The first and second check o-rings are also specific, make sure to use the correct size o-ring with the corresponding check assembly.

The check seats are attached to the cage with a bayonet type locking arrangement. Holding the cage in one hand, push the seat inward and rotate counterclockwise.

The seat, spring cage, spring and disc assembly are now individual components.

The disc assembly may now be cleaned. Depending on its condition, the check disc may need to be replaced. To replace the check disc on this size model, remove the nut and washer holding the disc in place.

O-rings should be cleaned or replaced as necessary and lightly greased with an FDA approved silicon grease. DO NOT grease the red silicone check rubbers.

Reassemble the check valve modules. Check modules are installed in the valve body with the seat facing the valve inlet. The modules must be securely in place before the retainer can be replaced.

Replace relief valve assembly and cover.