Small Drip Backflow Preventer

KC1

Hi All-
Over the last 4 weeks I have had my backflow preventer on the supply side of my oil boiler replaced 3 times due to a slight drip (like a handful a drips a day; the water doesn't collect, just evaporates). The drip appears to occur only when the washer or tub is turned on full crank cold water (or is shut off). My heating tech told me the dripping is not due to the BFP (Watts), since it has been replaced 3 times, but rather something upstream, possibly a slight clog from my Town water supply or a pressure issue. He told me that as long as the dripping is ony a few drops a day, not to worry about it unless the drip becomes "dripping". The only change that has been made to the boiler system was a swapped a Beckett AquaSmart control for a Honeywell Control, which is a whole other story. I caught the slight dripping right after the control change, but it could of been dripping before then.

Thoughts? Is this a common occurance? I am not a professional heat tech, but from my reading, the drip may be the result of a "water hammer", and that the BFP is functioning correctly. Should I be worried about coming home to a flood some day or is that highly unlikely due to the design of the BFP? What should I do?

Thank you for your time!

bob young

install a swing check or spring loaded check downstream of the rpz as per nys boiler code & your troubles are over.the problem will never hit the watts 9D. bob young nyc lic. plbr.

KC1

So install the new valve between the BFP and where the water enters the system? I am guessing that will prevent the jerk of water reaching the watts?

KC1

I guess my other question is a confirmation that the change in control (beckett to honeywell) has a low probability of being related to the drip. I can't see how the two issues would be related.

kcopp

No probability it is related to the control swap out...
What model backflow? Watts 9D?
These are prone to doing this. I installed mine a good long time ago and put a very small bucket under the vent. It drips from time to time.
Unless you have a total loss of pressure in the house no substantial amount of water will come out.
What is the water pressure in the home?

KC1

The Backflow is a Watts 9D.

I don't know what the water pressure is in the house, but I guess I can buy a pressure gauge and attach it to one of my outdoor spigots. I am guessing the spigot closest to the water entry point to the house would be ideal.

What should be the water pressure in the house be when I have no water use, and when I have a tub or washer running? I am guessing that you asked the question to see if the domestic water pressure is falling below the boiler's pressure (about 21PSI when hot), which I think would result in the BFP drip (I think).

In the end, should I bother looking into the water pressure situation, other than to give me piece of mind, since it is only a few drops? I called the town to see if there had been any reported issues with pressure in my neighborhood.

hot_rod

water hammer or "elastic shock" will cause them to spit from time to time. Often this is caused by a fast acting valve closing, like a washer machine fill valve, flushometers, even dishwashers and ice makers. It is more common if the home or building has high water pressure.

The best fix is a water hammer arrester. ideally it would be located at the source of hammer. Sioux Chief builds water hammer arrestors for wash machine connections, dishwashers and ice makers. Also large whole house sized versions.

I have heard that adding an additional swing check will eliminate the problem, but I have not tried it.

If the valve drips from day one, it could have dirt, teflon, rust, etc stuck under the spool seat. Most can be disassembled and cleaned out.

Ideally a vent pipe is used on the relief port and piped to the floor, or drain so any discharge does not spray on the equipment in the room.

They only spit or leak if the valve releases from the seat, or dirt particles hold them open. Most need 25 psi incoming to shut and seat properly. Caleffi seats tightly at 20 psi

I carry a cut away to all my trainings to explain the operation and troubleshooting procedure. Notice the seal that is made when the pressure is applied. the only way for fluid to leak out the relief port is that seal is compromised, or defective.

KC1

Thank you for the information. Given I am on my third BFP, does that pretty much eliminate the possibility of having something stuck under the spool seat? And if so, does that make the only explanation for the slight dripping (once again only a few drops daily primarily when the tub or washing machine is using cold water) to be either a water hammer or low water pressure on the supply side of the boiler?

I was going to run over to Lowe's to grab a water pressure gauge. My theory is that when the tub/washer is on, or the toilet is flushed, my water pressure drops below ~25 PSI point, hence the leaking. Does my theory make sense?

bob young

you are over engineering a simple issue. don't have time to teach you the history of plumbing. slap in a check valve & the back pressure wil never hit the rpz......yep, ever.problem solved & F.O.C.

KC1

I went home at lunch to check the water pressure, which is 50 PSI with nothing on, 40 PSI with the tub on, so the water pressure is good.

Funny thing happened however. When I got home the boiler was cold (114F) and I put on the tub faucet. There was no dripping from the BFP. However, after I cranked the heat up to get the boiler to the high limit, I turned on the tub and a few drops of cold water came out. The drip immediately stopped after I turned off the tub.

Why would the drip be dependent on the temperature of the boiler? Also (now for a slightly dumb question but I am running out of ideas) is it normal for the top a an expansion tank, the piping between the expansion tank through the Feed Water Pressure Regulator and the Feed Water Pressure Regulator to be hot when the boiler is at the high limit? I am trying to connect the reason why the drip only occurs when the boiler is hot.

Bob-
I am far from a handy man, so the next time I have my oil tech give the system a tune up, I will have him put in a check valve.

Thank you all again!

hot_rod

Look at the cutaway to see there are 3 seals that need to be "made". First the incoming water pressure slides a spool, which seats against an o-ring. This basically forms a "tube" for the flow. Next the pressure opens the two checks.

The only way for water to drip from the vent port is the spool seal must be compromised. If not dirt or debris, then an intermittent drop of pressure below the 25 psi required to close and seal the spool.

If it drips constantly the spool seal is the reason.

Have you dis-assembled any of the leakers? It should be clear, what and where the drip is getting out. It just takes a spec of debris to cause a small o-ring seal to fail.

By far the most often returned valve in the industry, and rarely are they faulty valves

Caleffi brand now includes a fine mesh strainer in the inlet port to try and prevent potential spool leaks.

A gauge that could record pressure hi and lows would be helpful to see if it is a drop in pressure causing the seal to leak. Easy confined lazy hand high pressure gauges, not sure about a gauge to record low pressure conditions, maybe a digital version or pressure data logger.

If you have tried 3 different valves, it's probably not the valve.

KC1

Interesting. So since the valve is not dripping constantly (and the valve has been replaced 3 times!), it isn't the spool seal. According to the tech, the last BFP was squeaky clean as well.

So that leaves the only culprit to be a pressure on the supply side dipping below 25 PSI then correct? I wonder why it happens when the boiler is hot and not cold however. Perhaps the hot boiler raises the PSI of the boiler at the BFP to a point that exceeds the inflow water PSI when the domestic cold water is on. I did however test the PSI where the water enters the house and I did have about between 40 to 50 PSI. Maybe there is something going on between where I tested the pressure and the backflow...

Unless there is another explanation...

If there is no risk of flooding in my basement, I will probably leave it until my next tune up and get a check valve put in as Bob suggests. I hate to have any water coming out of the boiler, but it seems like this is a common issue.

hot_rod

I would suspect a low pressure condition on the inlet, not boiler temperature. But you would need to babysit it to see it happen, or a quick acting pressure data logger.

In the meantime a piece of pex, PVC, copper, dishwasher hose, whatever to pipe the port down to the floor or drain.

Don't be tempted to plug the relief port, it renders the valve useless, and will cause water to leak from the table rivet holes.

Report back if you go with an additional check. I've heard plumbers tell me they add an additional check upstream of the BFD to catch pressure spikes??

bob young

YOU HAVE WAY TOO MUCH TIME ON YOUR HANDS, BRO EITHER TAKE A COURSE IN PLUMBING ENGINEERING OR......YEP, CHECK VALVE. CASE CLOSED. NO CHARGE !! LOL

bob young

THATS FOR KCI, NOT YOU HOT ROD !!!! LOL

KC1

Thanks hot rod! The slight drip appears to primarily happen when the boiler is hot and when their is a significant call for cold water. Since watching water drip is as fun as watching paint dry, I will just catch the water with a pan for now. I have the BFP preventer vent connected to a copper pipe which goes down to my basement floor. I'll slide the pan under that.

My tech is actually going to call Watts to see what they suggest. I will update this post when he tells me what the recommendation is.

hot_rod

A call for cold water? Not sure what you mean? The boiler should not be taking on water, unless you have a leak somewhere. Or the back flow is allowing water out of the system?d

KC1

Sorry hot rod. I think I used the wrong terminology.

What I meant was when the tub or washer are being used and is using a lot of cold domestic water, there is a slight drip out of the backflow when the boiler temp is near the high limit. The boiler is not leaking, just the BFP located on the supply side.

Sorry for the miscommunication.

Hilly

AWWA suggests a 'soft seating check valve' upstream of BFP w/ atmospheric ports to alleviate 'dripping relief port' problems.... when caused by fluctuations of the system supply pressure. This has already been mentioned a couple of times above... but forget waiting on watts and their suggestions. Just put the check on there.

bob young

if his " tech " is calling watts instead of slapping in a 1/2 " check......yeah, he has the wrong " tech " just saying