Water hammer on main line when no water running?

[Mr. Newb]

Hello, the main supply line vibrates like a water hammer randomly when no water is running or has been running. The main line comes in through a hole in the concrete slab in the basement; you can feel a water hammer in the pipe and it makes a noise even though the pipe is secure and can't really move and no water is running (the pipe is cpvc with a small length of PEX that I used when I replaced the main shut off and PRV so the pipe has some flex). No appliances (including ice maker) or turning the water on and off at any facet/toilet can recreate the issue. It seems to happen more at night and mornings. The water hammer will last anywhere from a few seconds to 30 seconds or longer.

The water pressure sits around 42 PSI. However, it will spike to almost 80 PSI and sometimes way over 80 PSI. I see the spikes on the red needle and have never seen the black needle over 50 PSI. I've never looked at my water pressure before this issue started so I don't know if the pressure spikes are normal or maybe the cause of the water hammer. I have county water and my house is 21 years old.

I have tried the following but the problem persists.

1 - added clamps and foam to secure main line
2- installed new PRV and have it set for around 42 PSI
3 - installed new 4 gallon water heater expansion tank
4 - installed water hammer arrestor right above the main shutoff
5 - purged any air trapped in the system by turning on all facets at once

I would appreciate any thoughts and suggestions, thanks!

 

[wwhitney]

Where are you measuring the pressure, relative to the main shutoff / water hammer arrestor location?

If you are able to detect the water hammer aurally, does it still happen with the main valve shut off? If the pressure pulse is coming from the water service, I would think it would still happen then. If it doesn't, I would think that means you have missed some internal water use that generates a water hammer.

Cheers,
Wayne

 

[Sponsor]

 

[Mr. Newb]

Where are you measuring the pressure, relative to the main shutoff / water hammer arrestor location?

If you are able to detect the water hammer aurally, does it still happen with the main valve shut off? If the pressure pulse is coming from the water service, I would think it would still happen then. If it doesn't, I would think that means you have missed some internal water uses that generates a water hammer.

Cheers,
Wayne

Thanks for the reply Wayne. I'm measuring the pressure on an outside hose bib. It's probably 30 feet from the main shutoff.

I haven't left the water supply off long enough to test your second point but that's a good idea; I'll give it a try overnight.

 

[wwhitney]

So the gauge on the hose bibb still shows the same pressure spike after the installation of the water hammer arrestor? That means either (1) the pressure spike originates outside the house but the water hammer arrestor isn't able to arrest the spike or (2) the pressure spike originates on the house side of the main shutoff.

Cheers, Wayne

 

[Reach4]

The water pressure sits around 42 PSI. However, it will spike to almost 80 PSI and sometimes way over 80 PSI. I see the spikes on the red needle and have never seen the black needle over 50 PSI. I've never looked at my water pressure before this issue started so I don't know if the pressure spikes are normal or maybe the cause of the water hammer. I have county water and my house is 21 years old.

Are you near a pumping station? Maybe ask the water supplier about these symptoms.

 

[Bannerman]

It sounds as though the PRV is either malfunctioning, or is not adjusted correctly.

You said the PRV is set for 42 psi. Why so low?

A PRV is not normally utilized unless the incoming pressure exceeds 80 psi. As many municipal water systems deliver 60 psi, those will typically function very satisfactorily without a PRV. Assuming the municipal supply is 80 psi+, 60 psi would be an appropriate setting for your PRV. Perhaps 42psi is below the minimum pressure your PRV can reliably regulate.

When adjusting the PRV setting, do so while there is a small trickle of water flowing from a downstream faucet.

The expansion tank is to be connected to the home's cold water plumbing, and there should be no closed isolation valves or back flow prevention devices between the Exp tank and WH, and preferably not between the Exp tank and the PRV.

The air pre-charge within the expansion tank should be equal to or slightly below the system pressure downstream of the PRV. If the pre-charge pressure is too high, then the system pressure or shock wave will need to exceed the pre-charge pressure before any water can flow into the expansion tank, thereby reducing or negating the effectiveness of the Exp tank.

Test and adjust the Exp tank pre-charge pressure while the main valve to the home plumbing system is shut-off and the system is drained to 0 psi.

 

[Mr tee]

Check your toilets to make sure the tank isn't leaking into the bowl. With some fill valves in some circumstances if they open then close quickly it causes a wave to slosh back and forth so they they open and close quickly again and so on. This can cause hammer. An easy fix if that happens to be the case.

 

[Jadnashua]

Is your PRV one that has an internal bypass valve? IF so, if you did not also install an expansion tank, after using hot water while heating the cold up, that water in the tank will expand. This expanded water will instantly create increased pressure. That increased volume must go somewhere, and it could be forcing its way back through the PRV, or some internal valve is chattering, releasing some of that increased volume (a toilet valve is a common place). If that increased volume and therefore pressure isn't released in a tight home system, it will easily get up to 150psi by the T&P valve on the water heater. If it doesn't get that high, something is relieving that pressure, either a leaking valve somewhere, or the PRV has a bypass, or it's defective.

So, first thing, if you don't have an expansion tank, add one sized and precharged appropriately for your system. Then, see whether the symptoms change.

 

[Mr. Newb]

So the gauge on the hose bibb still shows the same pressure spike after the installation of the water hammer arrestor? That means either (1) the pressure spike originates outside the house but the water hammer arrestor isn't able to arrest the spike or (2) the pressure spike originates on the house side of the main shutoff.

Cheers, Wayne

Yes. Prior to the changes listed in the original post the water hammer was violent and my water pressure was sitting 85-90 with spikes around 120. After all the changes the water hammer is much less but still there. I was thinking of adding a second water hammer arrestor just after the first.

 

[Mr. Newb]

It sounds as though the PRV is either malfunctioning, or is not adjusted correctly.

You said the PRV is set for 42 psi. Why so low?

A PRV is not normally utilized unless the incoming pressure exceeds 80 psi. As many municipal water systems deliver 60 psi, those will typically function very satisfactorily without a PRV. Assuming the municipal supply is 80 psi+, 60 psi would be an appropriate setting for your PRV. Perhaps 42psi is below the minimum pressure your PRV can reliably regulate.

When adjusting the PRV setting, do so while there is a small trickle of water flowing from a downstream faucet.

The expansion tank is to be connected to the home's cold water plumbing, and there should be no closed isolation valves or back flow prevention devices between the Exp tank and WH, and preferably not between the Exp tank and the PRV.

The air pre-charge within the expansion tank should be equal to or slightly below the system pressure downstream of the PRV. If the pre-charge pressure is too high, then the system pressure or shock wave will need to exceed the pre-charge pressure before any water can flow into the expansion tank, thereby reducing or negating the effectiveness of the Exp tank.

Test and adjust the Exp tank pre-charge pressure while the main valve to the home plumbing system is shut-off and the system is drained to 0 psi.

At first I had the PSI set closer to 50 but tried lowering it to see if it would make any difference in the water hammer which it didn't.

Yes, my street pressure is 85-90. My old PRV and expansion tank had failed which I only noticed because the water hammer started which prompted me to check them. I double checked and my PRV was factory set at 45 psi and adjustable between 10 - 70 psi.

When I lowered the pressure I did not have a trickle of water flowing. What issue could that have caused? I run an indoor facet after adjusting the pressure and before I go outside to check the gauge.

Yep, the expansion tank is on the cold water intake to the water heater with no closed valves in between. I had my expansion tank set equal to the system pressure. I also tested turning off my water heater for the night and still had the water hammer so I think that means that the water hammer is not water heater or expansion tank related.

Thank you for your reply.

 

[Mr. Newb]

Check your toilets to make sure the tank isn't leaking into the bowl. With some fill valves in some circumstances if they open then close quickly it causes a wave to slosh back and forth so they they open and close quickly again and so on. This can cause hammer. An easy fix if that happens to be the case.

I wish that were the case. I think they are all good. If a toilet was the issue, would the water hammer be strongest at the toilet supply line or would it go all the way back to where the water line enters the house which is where mine seems to be?

Thanks for your reply.

 

[Mr. Newb]

Is your PRV one that has an internal bypass valve? IF so, if you did not also install an expansion tank, after using hot water while heating the cold up, that water in the tank will expand. This expanded water will instantly create increased pressure. That increased volume must go somewhere, and it could be forcing its way back through the PRV, or some internal valve is chattering, releasing some of that increased volume (a toilet valve is a common place). If that increased volume and therefore pressure isn't released in a tight home system, it will easily get up to 150psi by the T&P valve on the water heater. If it doesn't get that high, something is relieving that pressure, either a leaking valve somewhere, or the PRV has a bypass, or it's defective.

So, first thing, if you don't have an expansion tank, add one sized and precharged appropriately for your system. Then, see whether the symptoms change.

That's a good point. When this first started I did find that my old expansion tank had failed and was also undersized. I installed a new appropriately sized tank. However, I still have the problem even with my water heater turned off so I don't think it's water heater / expansion tank related.

I don't know if my PRV has an internal bypass valve. I don't think it does. I don't think it was mentioned on the packaging. Is that bad?

Thanks for your reply.

 

[Mr. Newb]

Are you near a pumping station? Maybe ask the water supplier about these symptoms.

I don't know if I'm near a pumping station. That's a good point. It doesn't hurt to ask them about my symptoms. I do know that before my issue started my neighbor had a pipe blow out in her kitchen and just this week she got a leak in her main line before it enters the house so maybe the supplier changed something. They are also building apartments a few miles down the road from me, maybe hooking them to the system is causing some pressure issues?

Thanks for your reply.

 

[Reach4]

You could try turning off the first valve in your house for a while, and see if the sound continues.

 

[Bannerman]

I did not have a trickle of water flowing. What issue could that have caused?

Allowing a small trickle downstream of the PRV, will relieve the downstream pressure when the PRV adjustment is being performed to lower the pressure setting. When a pressure gauge is also located directly at the PRV, then adjustment results will be observed immediately as adjustments are being performed.

A bypass will allow excess pressure downstream of the PRV, to flow in reverse through the PRV to the upstream side. This could only occur when the downstream pressure is higher than the upstream pressure.

A PRV is an automatically controlled valve. When there is no water being drawn downstream, the PRV should be completely closed once the set pressure downstream has been established. Excessive pressure or water hammer upstream of the PRV, should not be passing through the PRV to the downstream side.

Because you are experiencing much higher pressure downstream compared to the PRV set point, that would indicate either:
1) the excess pressure is being created downstream of the PRV such as from thermal expansion within the WH. With an expansion tank in place to absorb the additional water volume, the resulting pressure increase will typically result in only a few additional psi, not 35+.

2) the PRV is not fully shutting off flow once the set pressure has been achieved. If the water hammer is occurring before the PRV and is resulting in shockwaves passing through the PRV when there is no water flowing into the home, that suggests there is a defect with the PRV which is not fully closing and is allowing leakage through.

 

[Jadnashua]

WHen a new complex is being added to a water distribution system, sometimes, the utility will need to add additional pumps, or play with the pressure to satisfy the additional load.

With many of the utilities adding a check valve on their supplies, a bypass on a PRV is just a waste of money, as there's no place for that water to go.

I'd shut the main off, open a faucet to relieve pressure, and double-check that the ET is still holding pressure properly.

An interesting/frustrating problem you have there! One reason why I participate on these forums...keeps my mind active trying to work out possibilities.

FWIW, when you shut the WH off, depending on what water may have been used in the meantime (say all of the expansion had happened, you use some with the WH off which will empty the ET), as the water cools off, it will shrink, and if the main shutoff is shut, the pressure in your system will be dropping, that could cause some issues as it would cause a vacuum in the system. WH are designed for pressure, but not vacuum.

 

[Jeff H Young]

Its worse when you have a customer paying you or youve done work and then this happens and look kinda silly trying to figure out a simple problem. like a puzzle with 4 pieces why cant i figure it out ha ha . youll get it! cant give up. PRV are expensive I had to rebuild mine only 2 or 3 years old almost the same price as new . Somehow I expect something w prv might ask neighbor if they got hammer? or water company

 

[Mr. Newb]

Allowing a small trickle downstream of the PRV, will relieve the downstream pressure when the PRV adjustment is being performed to lower the pressure setting. When a pressure gauge is also located directly at the PRV, then adjustment results will be observed immediately as adjustments are being performed.

A bypass will allow excess pressure downstream of the PRV, to flow in reverse through the PRV to the upstream side. This could only occur when the downstream pressure is higher than the upstream pressure.

A PRV is an automatically controlled valve. When there is no water being drawn downstream, the PRV should be completely closed once the set pressure downstream has been established. Excessive pressure or water hammer upstream of the PRV, should not be passing through the PRV to the downstream side.

Because you are experiencing much higher pressure downstream compared to the PRV set point, that would indicate either:
1) the excess pressure is being created downstream of the PRV such as from thermal expansion within the WH. With an expansion tank in place to absorb the additional water volume, the resulting pressure increase will typically result in only a few additional psi, not 35+.

2) the PRV is not fully shutting off flow once the set pressure has been achieved. If the water hammer is occurring before the PRV and is resulting in shockwaves passing through the PRV when there is no water flowing into the home, that suggests there is a defect with the PRV which is not fully closing and is allowing leakage through.

Thanks for the info! I still get the water hammer with the water heater off so I don't think it's thermal expansion related.

That's a good point on the PRV. It's brand new and is reducing pressure but sounds like maybe it's not fully working right by allowing spikes. OK, Saturday I'm going to turn off the water for an extended period so if I still have a water hammer that proves the pulse if coming from outside of the house in which case I need to return/exchange my PRV.

 

[Reach4]

OK, Saturday I'm going to turn off the water for an extended period so if I still have a water hammer that proves the pulse if coming from outside of the house

Sounds good

in which case I need to return/exchange my PRV.

How would you reach that deduction? OK, I am inferring that your PRV is outside of your house. But still, I don't know if the PRV would be proved guilty at that point. Is there a shutoff for your use before the PRV?

 

[Mr. Newb]

WHen a new complex is being added to a water distribution system, sometimes, the utility will need to add additional pumps, or play with the pressure to satisfy the additional load.

With many of the utilities adding a check valve on their supplies, a bypass on a PRV is just a waste of money, as there's no place for that water to go.

I'd shut the main off, open a faucet to relieve pressure, and double-check that the ET is still holding pressure properly.

An interesting/frustrating problem you have there! One reason why I participate on these forums...keeps my mind active trying to work out possibilities.

FWIW, when you shut the WH off, depending on what water may have been used in the meantime (say all of the expansion had happened, you use some with the WH off which will empty the ET), as the water cools off, it will shrink, and if the main shutoff is shut, the pressure in your system will be dropping, that could cause some issues as it would cause a vacuum in the system. WH are designed for pressure, but not vacuum.

I've checked my ET a couple of times but I didn't shut off the main and relieve the pressure first. Thanks, I'll do that and when I shut the water off to check if the water hammer still happens I'll make sure no one uses any water so we don't get a vacuum.