Continuously Spitting Watts 909 RP Backflow Preventer

Greetings All, I'm looking for advice on how best to proceed with a continuously spitting 3" Watts 909 RP Backflow Preventer. I'm on the board of a 47 unit condo in northern NJ and about 3 weeks ago the relief valve on the 909 began spitting large amounts of water regularly throughout the day and hasn't stopped this behaviour since first noticed. A floor drain captures the water. Our property manager dispatched a plumber who informed us that "the vacuum breaker assembly of your backflow preventer is defective". He reached this conclusion in about 3 minutes and without having touched any part of the assembly. He told us "the vacuum breaker relief can't be purchased independently of the backflow preventer so you'll need to replace everything" and quoted us $8,200 for the job. I have an engineering background and it took me about an hour to determine that virtually everything this plumber said is inconsistent with information on Watts website as well as other sites, most importantly you can't diagnose anything on the 909 without proper testing and diagnostics, which wasn't done. I'm not posting here to get info to prove this plumber wrong, he has his motivations, and our condo board has ours. I'm simply looking for professionals opinions on possible causes, and best course of action to properly diagnose and fix the problem. If it has to be replaced, we're fine with doing so, it's 10 years old, was submerged for a week during hurricane Sandy, maybe it's due. But I want to be satisfied that replacing it is the best option before spending the money to do so. Thanks in advance for any guidance.

Start with working the valves on both sides. Close the supply side and then the private side, open the supply side and repeat a few times. Most of the time it is a piece of sand or debris stuck in the relief valve and fluctuating the pressure will clean it up. If that doesn't work call a backflow certification company and ask them to come look at it. They can repair it or rebuild it, no need to replace. Should cost you a few hundred for that. For a replacement I would charge anywhere from 2k - 4K depending on cost of the 909 in the first place.

They are very sensitive to debris and any work done on the main line in the streets stirs stuff up. Should last you another 20-30 years if you service it and take care of it. Like I said before rebuildable which takes a lot of cost out of it.

Chris, I really appreciate your input and recommendations. My (uneducated) guesses from reading through Watts technical documents was either an o-ring failure in either the first check valve or relief valve or something preventing proper seating like debris. After reading your second comment, I checked our street facing CCTV camera around the time our problem was noticed and found that some kind of work was being done on our street by our water company the day before. I don't know what they were doing, but the timing is conspicuous.

I'm going to take your advice on opening and closing the valves, in the order you specified and keep my fingers crossed. If no resolution, I'll get a licensed tester to properly check it out. It occurred to me that with Watts selling so many repair kits - rubber/total, etc - for the 909, that this problem must be common enough to justify doing so.

Again, my thanks for your help. I'll post a follow up after I try the valves.

Cheers.

most likely trash from being submerged. those things can be dismantled and repaired.
but, HERE it must be done by a certified tech, who will also vet the equipment test it and sign off.
you need to find out the law in your municipality,

do not use pipe dope on them, teflon tape only, the dope will cause it to leak

my guy charges me $125.00 to test/certify and $125.00 to repair if leaking simple oring

So I have a new piece of information that might be helpful diagnistically, maybe it will mean something to professionals. Earlier tonight I was in our plumbing/sprinkler room and noticed a Neptune meter upstream from the RP 909. It had a little spinning dial that I assume indicates rate of flow and after simultaneously watching the dial and the relief valve for about 15 minutes I noticed that when water flow increased beyond a certain point the relief valve stopped producing water and about 15 seconds after flow decreased to a certain point and remained there, the relief valve started spitting again. Hopefully this observation means something to someone more knowledgeable than me.

Probably debris. when the flow increases the pressure reduces which stops the leak until it builds back up.

Please shut off the water using the shut off 2 in your backflow (#1 shut off is the one on the inlet and the #2 the one on the outlet) and report what happen.

This should help. I'll try to login later to check your test after shut off 2nd valve (I'm in Florida and a bit busy with hurricane). Try the last one to flush any debris, if still dripping then a backflow certified shall be clean/fix it.

Thanks Gargalaxy, I plan on trying your suggestion but I'm going to wait until after midnight tonight to minimize disruption of water to the tenants. What's not clear is whether the nibco gate valves that flank the 909 will turn or not, there's a fair amount of rust buildup left over from hurricane sandy. I'll report back with the results.

Thanks again and stay safe. Hopefully youre not in the direct path of Matthew, I've lived that experience twice now and it's not fun.

Work in NYC for a plumbing company , a few years ago I took the course to become certified in backflow inspections and certifications.
I would hire someone who is certified to test your backflow but someone who is also a licensed plumber or works for one so if something is wrong they will be able to fix it . They will be able to tell you exactly what is wrong and where it is failing by isolating the two check valves and the relief valve .
Most of the time when I run across an issue like you are having all I have to do is Clean it out and this works 99% of the time to correct the issue.
A 3" watts RPZ should cost between $1,200-$1,500 to buy new , add in another few hundred for material but nowhere near $8k unless they say they need to repipe everything but unless you have an an engineer say that you need to relocate your drain line that picks up the RPZ discharge your cost shouldn't be that high .
If you have to replace your device I would recommend talking with your engineer, I know on new Installations where there was no decide before the entire set up must be approved by the engineer and he will tell you / the plumber what device is needed in your application but not sure on replacing an existing device with the same model # .
Last thing - don't know it works in NJ, but in NY the backflow is required to be tested at time of install and once a year after that .
Hope this helps

Wanted to report back on this situation, my deepest thanks to those that have offered guidance. So I was able to close (I think) the downstream shutoff and it had no noticeable effect on the spitting from the relief valve. I wasn't able to close the upstream shutoff valve - got it about 80% of the way, but the force required to continue seemed unreasonable and decided the safe route is to have a professional do it who would know what to do if something went seriously wrong, it's unfortunate because I've gone through Watts service videos and think I could've resolved this problem (assuming, of course, the cause was something simple, like debris or an o-ring needed replacing.) As it stands now, both shutoff valves have a very slight leak from the stem - unintended consequences. So, as suggested, I'm going to start looking around for a certified backflow tester and go from there. Thanks again for everyone's help.

Those guys are everywhere. You can look them up or call you local water district and they should have a list of their approved ones.

Thanks again folks, unfortunately things have gone from bad to worse. (Maybe I should open a new thread?)
Our property manager sent someone to test our 909 backflow preventer and after 30 minutes he informed us that it couldnt be serviced or even tested because the two 3" OS&Y gate valves flanking the RPZ are bad. Apparently he was able to get them to the fully closed position such that there was less than 3/4" of stem remaining above the wheel and it had no impact on water flow. Additionally, there is a third gate valve upstream, right where the main line emerges from the foundation, which was just as useless as the other two. I dont even see how this is possible unless the gate itself has simply broken off or eroded to nothing - its only 14 years old. So now we have to replace all 3 gate valves (I assume we have to replace all three?) and what I dont understand is why we cant just replace them with 3" ball valves for less than $150 each versus $800 each for these massive gate valves. Arent ball valves considered universally better?

Quick clarification and an update - it appears that the Watts 909 usually comes with its own OS&Y shutoff valves. For some reason ours has two NibCo OS&Y valves instead, and those are the gate valves I referenced in my last post that no longer function. I didnt realize they're usually considered part of the backflow assembly.

I've now spoken to three local plumbing companies who would be happy to replace the 909, but they dont service them. Am I missing something?

Plumbers don't service the 909, the backflow guys do. A plumber is who would replace the valve or and underground utility company like what I do. Are your gate valves flanged or threaded? and yes theyare usually part of the 909 unit.If it is flanged it is really a 30 minute job to replace the entire 909 as it is 4 bolts each side and drop the new unit in.

You must have some bad water to kill one in 14 years that and I bet it never got excersized? Every 6 months to a year you need to open and close the valve a few times.

On an OS&Y the stem will barely be showing once the valve finally shuts down which leads me to believe you have a flanged unit. Those valves cost less than 400 bucks each.

On the old valves try closing them and opening them several times to help clean them up and get them to shut. He probably had them within 1/4 inch of closing.

Finally some good news. Finally found someone with the requisite skills, he took a look at the entire system and said everything BUT the backflow preventer needs to go, but the RPZ is easily repairable. And he's going to do all of it for a third of the cost we were first quoted to replace the RPZ. Thanks again for all the help. Cheers.