loud banging at water service entry to house

[Aaron Carl]

I'm hoping someone may have a guess on what might be causing this sound? Please see the link and listed to the audio. I help my phone up against the pipe a few times to get louder audio.
https://drive.google.com/open?id=11uo692xU5yF5HaYxNqcKt7MIhvIfFpVN

This is right at my house water entry point, the noise fades dramatically as I walk away from this location. There is a meter and stop valve in a pit at the street, utility company says it all seems okay and say it's from my plumbing somehow. I had the main house valve and PRV replaced and it's still doing it. Typically it does it when there is no water flowing in the house, and is not associated with any on/off operation of plumbing fixtures (water hammer). When I shut off my main valve the noise stops, and continues when I turn it back on. The closest plumbing fixture is an exterior hose bibb about maybe 6-8' away. Water pressure comes in at about 80psi, and is regulated down to about 65psi. We have no noticeable issues with water service or pressure. The noise is very intermittent and unpredictable... but is driving us absolutely nuts and has been going on for a long time to different degrees. Any help would be very appreciated, I do not want to keep throwing money at plumbers and not fixing the problem.

Thank you!

 

[Diehard]

That's a tough one.
First off I don't hear a loud banging sound. I hear something like a loud pulsating flowing sound. Tough to say through a recording. What if anything did you feel when you touched the pipe and PRV?

My first thought was possibly the water meter but if the utility company says it all seems okay and it's happening without flow(that you know of), that wouldn't appear to be the problem.

Do you happen to know if the noise was heard at the location of the meter? Or if you could feel anything at the meter when feeling it with your hand? Is it possible for you to access the meter to check it while the noise is present in the house? Not just for the noise and feel but also for flow since there is supposedly no flow in the house.

Since sounds resonate and travel through a water pipe it's not unusual for a meter to cause noise and travel to the house. That's why it's critical that we confirm that there is no flow going through that meter while the noise is present.

The fact that the noise stops when you shut your main valve is the best clue we have. Did you try opening and shutting that main valve slowly while the noise was present? If it affected the sound, that would be an indication that there is, in fact, flow.

Are you absolutely sure nothing is using water without your knowledge. Like an automatic ice maker or makeup water to a heating system or anything else you could think of? Or something like a toilet that may be leaking slowly into the bowl and causing the fill valve to open slightly? That could cause a vibrating noise similar to what I could hear.

 

[Aaron Carl]

Thank you for the reply. The noise does not usually last very long, I was pretty lucky to get to the basement before it stopped so I could record it. if it doesn't seem loud in the recording, let me tell you..it's loud, and can be heard all through our house. I could open the meter pit, but trying to get out there in time to check while it's banging would be nearly impossible. The pipe is definitely vibrating when the noise happens, but not violently or anything. The feel of the pipe and PRV was the same, and the sound did not seem louder at any single point... just loud along that whole vertical section and then fading in towards the house.

The utility company guy said they replaced the meter last year for routine maintenance reasons, and I know the noise dates back prior to that. Seems unlikley 2 meters would both cause such a phenomenon. Can a bad valve at the street cause something like that? I need to ask my neighbor who shares the same pit (separate meter) if he ever hears anything like that.

I have not tried operating the valve slowly to see the result, I will try that as soon as I can and report back.

I am not absolutely positive there is no flow whatsoever, but I quite confident it is the case. I can usually hear if a toilet (or anything else) is running, is there another way to check if a toilet fill valve is open slightly?

Appreciate your efforts to assist!

 

[Diehard]

Thank you for the reply. The noise does not usually last very long, I was pretty lucky to get to the basement before it stopped so I could record it. if it doesn't seem loud in the recording, let me tell you..it's loud, and can be heard all through our house. I could open the meter pit, but trying to get out there in time to check while it's banging would be nearly impossible. The pipe is definitely vibrating when the noise happens, but not violently or anything. The feel of the pipe and PRV was the same, and the sound did not seem louder at any single point... just loud along that whole vertical section and then fading in towards the house.

The utility company guy said they replaced the meter last year for routine maintenance reasons, and I know the noise dates back prior to that. Seems unlikley 2 meters would both cause such a phenomenon. Can a bad valve at the street cause something like that? I need to ask my neighbor who shares the same pit (separate meter) if he ever hears anything like that.

I have not tried operating the valve slowly to see the result, I will try that as soon as I can and report back.

I am not absolutely positive there is no flow whatsoever, but I quite confident it is the case. I can usually hear if a toilet (or anything else) is running, is there another way to check if a toilet fill valve is open slightly?

Appreciate your efforts to assist!

Yes I understand, if the noise doesn't last very long, it makes it even tougher to track down.
The fact that it doesn't happen when the main valve is shut, kind of indicates that it's related to flow. Don't you think?

 

[Diehard]

It would be nice to figure out the source of the problem.
As you likely know, banging noise in water piping is typically caused by the sudden change in velocity, and resulting shock waves. Like fast closing valves, loss washer in valves, check valve functions, even PRV,s(I know yours was just replaced).
The best location for a water hammer arrestor(air chamber) is typically close to the source of the culprit causing the problem.

 

[Aaron Carl]

Just curious... could having a 22 year old water heater without an expansion tank somehow be causing this? Seems like a long shot, but thought I'd ask your opinion. The water line goes right toward the water heater roughly 20ft. from the entry point, before distributing to the rest of the house.

 

[Diehard]

You have a PRV and a water heater without an expansion tank! It's a wonder you're not seeing some water release from you water heaters P&T relief valve.
Well it's certainly possible. But either way I think the next thing for you to do is get that expansion tank. You can look up the recommended size expansion tank for your heater. Typically based on size of heater tank, your maximum water service pressure and maximum water temperature setting. Don't hesitate going to the next larger size tank if it's at all close or questionable.
Even if you have a plumber do it, you should know what tank size is recommended, as a double check, if nothing else.

As a side note, some PRV now come standard with a bypass feature that permits the flow of water back through the valve into the main when pressures, due to thermal expansion on the outlet side of the valve, exceed the pressure in the main supply. However, Watts also says,"The bypass feature will not prevent the pressure relief valve from opening on the hot water supply system with pressure above 150psi. After looking closely at yours, it looks like it could be a Zurn.
Either way an expansion tank is a must on a tank type water heater with a PRV or backflow preventer on the cold water supply.

 

[Aaron Carl]

Yes I guess they weren't always enforced by code around here that long ago (90's), anything newer has to have one. I am getting close to having a new heater installed and planned on putting a expansion tank in as well, maybe I'll move that project ahead of schedule a little and see if anything improves.

 

[Diehard]