Plumbing Question---Pipe Knock/Rattle

[Shelby Griggs]

I live in a house that is pretty new, completed in late 2005. Recently I have noticed the cold water pipes knocking or rattling when the toilet shuts off. This is something new or at least much more pronounced. It sounds like the pipes in the wall behind the shower are loose and make this noise when the toilet tank fills and then abruptly shuts off. I believe I have heard this too with other devices in the house, dishwasher, washing machine, etc.



What causes this? Why would this start or at least be louder after 2-3 years? Has a pipe in the wall come loose? Does this cause harm or is it something I should get fixed?



Lots of questions, but I am pretty ignorant about plumbing, LOL.



SHG

 

[seafish]

When any valve is turned off suddenly, there exists an effect called "water hammer".
Water hammer occurs because the momentum of the moving water in the pipe has no where to go when the valb=ve is turned off. Thus, the momentum of the water moves inertially towrds the end of the pipe, or valve, and then slams against it, recoils and then does it again and again until the energy dissipates . The higher the pressure or volume of water, as well as the more suddenly the valve is closed, causes a more violent water hammer. Some homes are plumbed with T's and a vertical extension of the pipe right before the pipe exits the wall to the fixture that it supplies. Thus when the valve, or fixture is turned off, the water coming through the pipe has a place to go (up the extension in the wall) rather then slamming against the valve. This also dissipates the energy without rattling the pipes.
Toilet flush valves, by their nature, tend to turn off the water very suddenly as the float valve reaches its level and shuts off almost instantly (as opposed to a slowly handle turning on a sink or shower). IT IS possible that the noise and rattle has gotten worse because someome has either turned the valve supplying the toilet all the way up, or higher then it was before. Its also possible that the water hammer has finally "shaken" loose the holdown clamps or pipe straps that hold the pipe to the studs inside the wall, and that they are now so loose that there is more motion of the pipe, and thus more momentum of the pipe as it rattles in the wall.
Water hammer can be a VERY powerful force. A freind of mine was upgrading a small townships water lines and pumps to a new storage tank up the mountain a ways. When he turned on the new valves he spotted a small leak (small, that is for a 6" main) and turned off the new valve. Well, the force of all the inrushing water stopped when it hit the closed valve, and literally blew the pump right before it 30' into the air, cause it wasn't strapped down yet! Needless to say, the pump was destroyed when it hit the ground again. It was an expensive and potentially dangerous mistake on his part. The water hammer that you are experiencing is, of course, a much less intense force.

If you don't mind a slow filling toilet, try turning down the valve which supplies the toilet WAY down, so the toilet fills more slowly. That SHOULD make the water hammer effect less powerful, and thus the pipe rattle less intense. Good Luck.

 

[strick]

I wonder if your pressure switch is defective. Causing your line pressure to be higher than the recommended pressures. Typically 40 psi on and 60 psi off. My sister had a toilet valve and kitchen sink faucet blow apart, because her pressure switch failed and caused the line pressure to sky rocket. It pegged the gauge! It's a wonder more didn't bust. I'm assuming that you're on a well. I've experienced water hammer on a 6" irrigation line before and it wasn't pretty! An emergency shutoff valve failed while I was charging up the line, and when it slammed shut it blew a rather large aluminum check valve on the pump unit apart and almost knocked me into the pond. I just thank god that the line wasn't charged up to full pressure. A guy that I used to work for had a 6" water hammer almost blow an irrigation motor into a pond that was chained down with 1/2" log chain! Yessir, water hammer is a more powerfull force than most know. See ya, Jason.

 

[Shelby Griggs]

Thanks for the input guys. I am on City water. Unless the City has increased pressure, I don't think I have anything to adjust there???



I did change the toilet "guts" a couple of months ago, other than that no recent changes.



I tried shutting the toilet wall valve most of the way off, no change.



I have tried letting the adjacent sink run during the toilet fill, no change, still get a loud knock when the toilet fill valve closes.



I suspect a pipe has come loose or broke a retaining strap in the wall, likely not going to be an easy fix for that.



I have heard this type of noise before in older homes, BUT I didn't expect this in a new home!



SHG

 

[DLausche]

How about making sure the finish collar/ring around the pipe where it exits the wall is tight to the wall? Pull on the pipe gently while pushing in on the ring so it is tight against the wall? Does this help lessen the clunk or hammer? If so, then maybe a bunch o electrical tape around the pipe holding the finish ring tight against the wallboard would do the trick. Might not be the prettiest solution but is easier than tearing down and redoing wallboard. Another solution might be to pull the finish ring back and then fill the small gap in the hole by the pipe with expanding foam or similar. This will only work of course if the hammer is at the end or really close to where the pipe exits the wall.



-Deon

 

[DennyDay]

Shelby - - There is a chance that water got up into the riser that prevents hammers thru use. Try shutting off the water at the house inlet, then drain the water from the toilet area by flushing the toilet to empty the tank and taking the lid off the tank and holding the valve open so the feed line will drain completely. This should allow the hammer preventer to drain. Had this problem with a house in Texas, and called a plumber the first time (for $75. 00) second time about three years later I did the same thing myself. Lasted another three years. If this doesn't work, let me know - - I've got another suggestion to try.



Denny

 

[ACoyle]

Shelby, While I agree with everything said here, I would like to add a couple thoughts.

First, it is not impossible that the city has increased, or at least changed water pressure.

Second, Testing the pressure of your city water would be an excellent idea regardless of it's effect on this particular problem. I have heard of damage to home plumbing from over pressure and pressure spikes form the city.

Third, I had not heard of that technique of preventing hammer, but it is a great idea. I have done a lot of plumbing and looked at a lot of others, even though, I am not a plumber.

Fourth, The idea about draining the pipe to recreate an air cussion is a good one. I had to do that to my well tank (I know you don't have one) every so often, because the trapped air gets dissolved in the water. Draining and refilling restores the cushion. This presumes that your pipes were done this way.

Fifth and final point. The laws of hydraulics state that pressure is everywhere equal. In other words, the pressure that is causing the hammer is felt throughout your pipes. So, then my suggestion would be that you could put an expansion tank anywhere in the cold water system and it should help. Expansion tanks are used in wells. they are small maybe 8" by a foot.

Hope this helps

AC

 

[daveshoe]

''Ask this old house'' had this problem recently

Rich did a segment on water pipe noise recently. The homeowner turned the valve under his sink nearly closed to reduce flow and prevent splashing and the restriction in combination with the rubber in the shutoff valve made quite a noise. Rich then turned the valve fully open and the noise disappeared.

Rich [Tretheway] the plumber also mentioned that the rubber bonnet in the toilet valve sometimes wears out or gets dirt in it that causes the same problem. These bonnet valves can be taken apart and cleaned out,but have a new replacement handy in case something breaks. If you have a cheap OEM toilet valve,you may want to upgrade to a Fluidmaster--about 6 bucks at a Lowes or Depot store. These valves also do away with the ballcock type float. Hope this helps

 

[Elite1]

Re: city water pressure... where I live, we have about 120 psi city water pressure coming in from the street. All the homes have pressure regulators, which reduces the incoming pressure to your home. The regulator is usually mounted outdoors, were the mainline comes into the house & it is adjustable. Most keep it at about 50 to 60 lbs. A water hammer is, of course much worse at high pressures. These regulators go out periodically and many times take toilet and sink parts out with them...



This is a picture of a typical regulator, the further you tighten the bolt, the more water pressure you get:

#ad

 

[ekroman]

I had the same problem about 10 years ago. Borrowed a home made pressure gauge from work, and set it up, and tested. Turns out the pressure regulator at the inlet to the house was bad.



Replaced the regulator and it works fine. I've had occasion to drain the plumbing in the house since - more than once!



Eddie

 

[Shelby Griggs]

Thanks again for all the helpful comments.



I recently replaced the toilet fill valve with the Fluidmaster mentioned here, the other two toilets in the house have also had this same valve installed. The problem primarily seems to be from one of the two upstairs toilets.



I opened the faucets and let the system drain out and it might of helped every so slightly. Is there supposed to be a section of pipe installed that acts as an air cushion in a typically home installation? I assume this house was built to current code in Oregon, house completed in late 2005.



If there is a pressure regulator, it must integral to the meter box at the curb, I will take a peek in there.



SHG

 

[BoeingDiesel]

Shelby, I'm not a plumber, however I was raised by a plumbing contractor and spent many days with him in the field. Your problem is the diaphragm in the top of the ballcock. Fluidmaster sells the repair kits which include this part. They don't last long if you have poor water quality and/or high pressure. As the diaphragm ages it hardens and slams shut rather than closing slowly. With your home being relatively new I seriously doubt there are air chambers in the wall. That is old school technology and there is a major difference between an air chamber and a water hammer arrestor. If re-kitting the ballcocks doesn't work (check out these links) you have other options. Good luck

gregg



http://www.siouxchief.com/B_WaterHammer_Fall.cfm



http://www.siouxchief.com/B_Product_Detail.cfm?GroupID=350250



http://www.siouxchief.com/B_Product_Detail.cfm?GroupID=350200

 

[Shelby Griggs]

BD, thanks, I had no idea the arrestors were available so inexpensively ! I wouldn't think it would be the Fluidmaster valve, it is only a couple of months old, but I suppose that would be the cheap place to start, I think the whole darn thing was under $10, not hardly worth trying to repair.



There is a Mini-Rester specifically made for teeing onto a ballcock at the toilet. A quick online search has those at about $25 and I believe Ace Hardware is a retailer, so that will probably be my next stop.



EDIT



Well I installed the Mini-Rester at the ballcock on the bottom of the toilet tank and I still have the issue. I was able to turn the water supply valve way down, open about 3/4 of a turn and get it subdued quite a bit, just a bit disappointed that the Mini-Rester didn't fix the problem.



SHG

 

[Motorhead]

Shelby, Like Elite1 said... Check your water pressure. Too high is also hard on the pipes, even copper. The regulator is usually mounted where the water pipe comes up to the house. Water pressure should be set 50-60 psi MAX.

 

[rbattelle]

I found my city water pressure was about 75 psi! Installed my own industrial regulator and turned it down to just over 60 psi.

I hate plumbing... everything I do leaks.

Ryan