Knocking noise pipes

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JB_12

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Charlotte, NC
Hi all,

I need some expert advice in diagnosing the problem I have been having for a while.

Whenever I open a tap (hot mostly, cold sometimes) or close a tap , or when the toilet stops flushing, or when the washer starts fill or stops fill I hear a knocking noise from behind the wall (upstairs room).

I also hear the same noise at the PRV. I did some pressure tests and the high pressure was 78-80 psi, static pressure around 70 psi. I did call a plumber and all he kept saying was maybe the pipe is loose and cut open a piece of drywall but didn't see much, and he wanted to cut more drywall but I told him to let it be.

Any idea if it's perhaps the pressure too high causing this or is it infact a bad PRV that needs to replaced or is it really a loose pipe somewhere? I am not sure how old the PRV is because the house predates me.

Any help would appreciated.

Thank you,
JB.
 
Water hammer is when a valve shuts off quickly and all the pipes move. When the house was built they put in dead end pipes that were full of air and that stopped it from happening. Over time those pipes fill up with water and stop working. So now you can add new ones to the toilet and washer lines,

 
They stopped using the expansion pipes about 40yrs. ago.
 
I would install arrestors before I open the wall, it is expansion and hammering that loosens the pipe.
 
Thank you all. Am getting the PRV checked for now and will set the pressure to 60 psi for now, will look into arrestors too if the PRV is not the issue.
 
Do they commonly put PRVs in homes, other than like on a water heater? I've never seen that.
 
Do they commonly put PRVs in homes, other than like on a water heater? I've never seen that.

When I plumbed the house I put one at every fixture. Just a home made "T" with a short vertical pipe & cap. All it takes is a little trapped air in the vertical pipe to create a dampening effect when the water is shut off abruptly. Watched plumbers do that when I worked construction back in the day. Cheap insurance against noisy pipes.
 
Up here the laundry rooms have them in all new houses
upload_2019-2-15_7-32-33.jpeg

I have to put one on the toilet because the line going to the fridge bounces all over the place.
 
One thing that i would try first. it is possible that you have air chambers installed on your pipes that are now water logged.
os this is what i would do . shut of all you water and drain all the water lines. be sure to open everything so the the water drains out . the shut everything and turn the water back on. this is how to recharge air chambers. if this does not work then go ahead and water hammer arrestors wherever you have access. for example. at the toilet shut off, at the sink shut off, at the water tank , I would do this first before opening walls ect.
 
maxdad118 said:
PRV can be 2 things: pressure relief valve(water heaters) and the one you are referring to is pressure reducing/regulating valve
Click to expand...
Only boilers and tankless water heaters have a pressure release valve. Tank water heaters have a t&p valve (temperature and pressure.
 
68bucks said:
Do they commonly put PRVs in homes, other than like on a water heater? I've never seen that.
Click to expand...
What you see on a water heater is a TPR valve which stands for Temperature Pressure Relief valve. It dumps water or steam to the floor if the pressure in the water heater starts to exceed ~180 degrees or 3/5ths the pressure rating of the Water Heater. A PRV, on the other hand, is a Pressure Regulating Valve. It limits the water pressure at the water meter to a level that most plumbing and water using appliances can handle without excessive stress. PRVs do this by partially closing or opening a valve to the point were the water passing through it is at the set pressure. The adjusted cross section of the valve causes enough pressure loss to reduce the supply pressure to the selected value.

--
Tom Horne
 
JB_12 said:
Thank you all. Am getting the PRV checked for now and will set the pressure to 60 psi for now, will look into arrestors too if the PRV is not the issue.
Click to expand...
You had mentioned earlier that you "did some pressure tests and the high pressure was 78-80 psi, static pressure around 70 psi".
So I take it that you have a pressure gauge either associated with your PRV(Pressure Reducing Valve) or installed somewhere nearby. Or other.
PRV's are typically adjustable, which would allow you to reduce the pressure on the house side, yourself.
Counterclockwise to reduce the pressure downstream from the valve.
However, to allow the downstream pressure to adjust for the change, just crack open and close a nearby valve or faucet to let out a bit of water, allowing the pressure to be reduced. (Depending on the PRV's design this is not always necessary.)
One thing I couldn't understand is how a high pressure was 78-80 psi when you say the static was 70 psi. Were your pressure gauges at different elevations or was the higher pressure when someone opened or closed a valve or faucet?

I think it's important for you to understand that although a higher pressure may contribute to water hammer it's not the actual cause. As i believed already touched upon, it's the rapid change in the velocity of the water flowing through the pipe. So with higher pressure you would typically get higher flows(velocities) and higher chance and sounds of water hammer. And of course what contributes to the noise is the ability of the pipe to be able to move and knock against something.
So as someone mentioned, you could still have water hammering at 60 psi or even less.
You may have a combination of the conditions that cause and or contribute to water hammer. Even a loose washer in a valve can cause different types of water hammering sounds. Like vibrating, for example.

Why are you getting your PRV checked? To verify the actuaries of the pressure readings you got???
 
I had the same issue with knocking noise in the upstairs bathroom behind the shower cabin.
Plumber came, opened the wall, installed additional arrestor... still the same...
Then he installed a big arrester in the basement on water intake pipe .... still the same knocking noise...
At the end, he called to the manufacturer of shower faucet (it was under the warranty), they sent a tech guy who changed some washers in the faucet and finally the knocking noise is gone.
 
It was probably the cartridge that was replaced. When Balancing spools go bad sometimes they have a tendency to make the problem seem like its in the toilet or sink valve. Shock stops rarely fix a knocking pipe issue years after installation. They are a feel good first step. Kind of like turning the radio up in your car to stop the brakes from squealing. It sounds better but doesn't fix the problem.
 
Diehard said:
You had mentioned earlier that you "did some pressure tests and the high pressure was 78-80 psi, static pressure around 70 psi".
So I take it that you have a pressure gauge either associated with your PRV(Pressure Reducing Valve) or installed somewhere nearby. Or other.
PRV's are typically adjustable, which would allow you to reduce the pressure on the house side, yourself.
Counterclockwise to reduce the pressure downstream from the valve.
However, to allow the downstream pressure to adjust for the change, just crack open and close a nearby valve or faucet to let out a bit of water, allowing the pressure to be reduced. (Depending on the PRV's design this is not always necessary.)
One thing I couldn't understand is how a high pressure was 78-80 psi when you say the static was 70 psi. Were your pressure gauges at different elevations or was the higher pressure when someone opened or closed a valve or faucet?

I think it's important for you to understand that although a higher pressure may contribute to water hammer it's not the actual cause. As i believed already touched upon, it's the rapid change in the velocity of the water flowing through the pipe. So with higher pressure you would typically get higher flows(velocities) and higher chance and sounds of water hammer. And of course what contributes to the noise is the ability of the pipe to be able to move and knock against something.
So as someone mentioned, you could still have water hammering at 60 psi or even less.
You may have a combination of the conditions that cause and or contribute to water hammer. Even a loose washer in a valve can cause different types of water hammering sounds. Like vibrating, for example.

Why are you getting your PRV checked? To verify the actuaries of the pressure readings you got???
Click to expand...


- Got the PRV changed (Pressure regulating valve not relief) because the pressure was dipping too much when two taps were open. Now the pressure is properly regulated.

- Sorry wasn't clear on the different pressures ...
The transient pressure was 78-80 psi (if you think of a PID loop , it's when the proportional gain acts on an error you get an immediate overshoot, once the Integral acts upon the accumulated error (even though overshoot can become worse, the steady state error settles) . So, the steady state(static) pressure after settling was around 70 psi. Similarly, opening taps together made the pressure delta difference too much. I wish we had electronic PRVs rather than mechanical but oh well.

- The knocking noise went away but after opening the shower a new chattering noise has emerged when faucets shut off. I will have to drain the system and see if it was an air bubble that got induced during the PRV replacement as the water main was shut off. The current steady state/static pressure is 60 psi.

- I am also thinking of dropping the pressure to 50 psi since now it's properly regulated to see it helps with the noise.

- I will look into water hammer arrestors also as per other people who have suggested it.
 
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