Troubleshooting Backflow Assembly Relief Valves

If you encounter a situation in which a newly repaired relief valve continuously discharges, here are some tips to keep in mind

Troubleshooting Backflow Assembly Relief Valves

Anthony Pacilla

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You have an easy day scheduled testing backflow assemblies for your commercial clients.

An RP you tested last week had a failing relief valve (did not open). You are expected to make the repair first thing in the morning before finishing out your day with the remainder of your tests. You rebuild the RP, turn the water on, and now the valve continuously discharges. No matter what you seem to do, the valve continues to discharge. You take it apart again, reassemble, and it is still discharging. You can already hear the customer: “It didn’t do that until you got here today!”

Now what?

The first thing you should do, since you already have the water off, is triple-check that no foreign matter has entered the system preventing the No. 2 check valve from seating. Remove the check valve and inspect the rubber disc for any debris. Next, you should take the rebuilt relief valve apart and inspect it for debris. Also, check the seats for any nicks or gouges that can allow water to pass through and cause the relief valve to dump.

Assuming there are no signs of debris, nicks, gouges, or wear and tear, you should now reassemble the RP. Once reassembled, take one of the hoses off of your test gauge and connect it to the No. 3 test cock. Close the No. 2 shutoff valve and make sure the No. 1 shutoff valve is on. Once you have your hose connected to the No. 3 test cock, open the No. 3 test cock and bleed water into a drain or bucket for a few minutes. Many times, after a repair, air will get trapped in the body of the valve not allowing it to fully seat. You can get erratic assembly behavior. Most times, this problem will present itself when you notice the device stops discharging when someone in the building runs water. When someone stops running water, the relief valve will begin to discharge once more. After you run water for a few minutes, restore the assembly to its full operational capacity and see what happens. Usually this will have fixed the problem. 

If you bleed the system as mentioned above and the relief valve is still discharging, it’s time to talk to the customer. Explain that you ran into a troubleshooting situation, and you may be there for a while. You need uninterrupted time to concentrate and brainstorm about a possible teardown session on the RP device. 

There could be a handful of reasons why this assembly is discharging. The easiest check to start with is making sure that the line running water to the relief valve isn’t clogged. That is as simple as removing the hose in most cases and running water through to clean it out. If it has an internal throughway, you should disassemble the relief valve package and do a comprehensive inspection on the new parts you’ve just installed. Did you replace the rubber kit? Maybe the spring was also bad. Does the spring appear to have been manipulated by a former technician? Sometimes old, veteran plumbers would “field modify” the spring by cutting it down. Is the spring broken?

Another easy check is to verify that the air vent is open and unclogged. It is true that the relief valve opens and dumps into a drain or onto the floor when it’s malfunctioning, but did you know that if anything near the relief hole is fouled, it could lead to erratic assembly behavior?

When you have the relief portion of the assembly in hand, pay close attention to the rubber diaphragm. The rubber may look great to you, but over time these rubbers will either swell, stretch, or become rock hard, preventing it from doing its job. If you think the rubber diaphragm has stretched too far in one direction, try flipping it over (as a temporary troubleshooting tactic) and reinstalling.

As for the O-rings, even though they may appear to be in good shape, they could be worn due to a past repair. Many older plumbers put grease on everything that moves. It is still a great idea to grease any and all working parts (unless otherwise stated by manufacturer specs), however using the wrong kind of grease can cause issues. For example, using certain types of grease like petroleum-based ones will cause some O-rings to fail prematurely. Make sure that when you grease the backflow parts, you are using food-grade grease, such as NSF 61 grease, that is approved for rubber material as well as potable water applications.

As you can see, these RP assemblies have a lot of moving parts, with rubbers, springs, seats, check valves, etc. There are so many moving parts within an enclosed space that it can be frustrating to diagnose an issue. Stick to the basics and don’t overthink things.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 23 years' experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College.



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