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Thread: A Big Thud after flushing toilet

  1. #1
    DIY Junior Member Bucky Badger's Avatar
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    Default A Big Thud after flushing toilet

    We have two bathrooms, first floor and second floor bathroom. After the first floor bathroom tank fills up after every flush, I hear one big thud. I don't hear this thud when the second floor bathroom tank fills up after every flush, I only hear this happening in the first floor bathroom. I noticed this happening after doing a renovation in the second floor bathroom.

    How can I fix this problem?
    Do you think this happened after shutting the main water valve a few times where the water pressure changed in the first floor bathroom and causing the pipes to make a thud sound?

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    Forum Admin, Expert Plumber Terry's Avatar
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    More likely you fixed a leak somewhere, making the system tighter. You now have water hammer that occures at the end of the fill.
    You can pick up a fill valve that shuts off a little smoother. I like the Korky MP for that.

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    DIY Senior Member wjcandee's Avatar
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    Quote Originally Posted by Terry View Post
    More likely you fixed a leak somewhere, making the system tighter. You now have water hammer that occures at the end of the fill.
    You can pick up a fill valve that shuts off a little smoother. I like the Korky MP for that.
    This is the valve Terry is talking about. Should take you less than 15 minutes to install, probably without any tools. It is available at many hardware stores as well. You need the silver-cap MP version, not the white cap, blue cap or red cap versions. http://www.lowes.com/pd_336988-868-5...rky&facetInfo=

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    DIY Junior Member Bucky Badger's Avatar
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    So you guys think it's not air in the line causing this.

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    DIY Senior Member wjcandee's Avatar
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    Quote Originally Posted by Bucky Badger View Post
    So you guys think it's not air in the line causing this.
    Absolutely.

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Bucky Badger View Post
    So you guys think it's not air in the line causing this.

    Air will normally work itself out. But your pressure could be to high.

    Terry is right on, I think.

    Good luck.
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    Forum Admin, Expert Plumber Terry's Avatar
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    "Air in the line" is code for somebody asked a handyman what the problem was, and having never worked on plumbing said the first thing that came to mind.

    Air in the line has got to be the biggest urban legend in plumbing ever.
    As soon as you use a faucet, any air from having been drained down quckly comes out. You would have to shut off and drain the home down for thirty minutes got get air in the pipes. Once the water is turned back on, and you use the plumbing; all the air escapes. Even air chambers get waterlogged. And air chambers are meant to cure water hammer, not make it worse.

    When all the leaks are fixed on a home, the water has no place to go when something shuts off quickly. In a new home with a check valve at the water meter, we would be installing hammer arrestors at the washer, dishwasher, and the icemaker. All of these have quick closing solonoid valves.

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Terry View Post
    "Air in the line" is code for somebody asked a handyman what the problem was, and having never worked on plumbing said the first thing that came to mind.

    Air in the line has got to be the biggest urban legend in plumbing ever.
    As soon as you use a faucet, any air from having been drained down quckly comes out. You would have to shut off and drain the home down for thirty minutes got get air in the pipes. Once the water is turned back on, and you use the plumbing; all the air escapes. Even air chambers get waterlogged. And air chambers are meant to cure water hammer, not make it worse.

    When all the leaks are fixed on a home, the water has no place to go when something shuts off quickly. In a new home with a check valve at the water meter, we would be installing hammer arrestors at the washer, dishwasher, and the icemaker. All of these have quick closing solonoid valves.

    Nice Terry.

    That reminds me when people have a problem in electrical or electronics it must have a "Short"


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    DIY Junior Member Bucky Badger's Avatar
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    Update:
    I just want to thank the forum for helping me out, specifically Terry and wjcandee for suggesting the Korky silver cap MP fill valve. I ignored the problem for a few months and lets just say it wasn't the smart thing to do. A plummer came over to work on another maintenance issue then asked him how to solve the problem with the toilet making the thud sound after flushing. He suggested to install a hammer arrester (hot and cold) on the washer and should fix the issue but that didn't work.

    I bought the Korky silver cap MP fill valve and asked if it would work in relieving the thud. He said no because the water pressure was too high.

    Well, finally I ignored the plumber and followed Terry and wjcandee's advice and guest what, the toilet has a "smooth landing" so to speak when it approaches a full tank after flushing. No more thud sound.


    Thanks guys!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If your water pressure is >80psi, you should (code requires it!) install an PRV and an expansion tank...the Korky valves do turn off slower, and the hammer arresters on the WM are still a good idea.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member kcodyjr's Avatar
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    Just to put a bit more science behind what Jim and Terry are saying.

    Water, like any other matter, possesses momentum when it's moving. Turn off a valve, and that column of still-moving water in the pipe has nowhere to go except to slam into the closed valve. The quicker the valve closes, the faster the water is still moving at the moment of zero flow. This creates a high pressure spike, which travels backward through the pipe at the speed of sound, and can blow out joints and fittings, or soft spots in pipe walls, if it's already getting weak. This can happen anywhere in the system, not just right next to the source of the hammering. If there is a small leak already, much of the pressure escapes there. If not, the pipe itself must absorb the energy, by recoiling and slamming against a nearby wall. That's your thud.

    Having the pipes perfectly secured to the wall can eliminate the thud, and I've heard a few licensed plumbers working shifts at HD advocate this as the solution to hammering, but it does nothing to suppress the pressure wave itself, so the eventual blowout risk is still there.

    A hammer arrester is just an air chamber with a piston inside, so the air and water never touch. Place one right next to the quick-closing valve that causes the hammering, the air cushion absorbs the momentum, and the pressure spike is prevented altogether. Place one anywhere else, and it protects whatever is nearby from the effects of a pressure spike that starts elsewhere.

    +1 to arresters on the WM (and DW) being a good idea. I'd put one on the toilet, too, even if the new valve has helped.

    +1 to checking your incoming pressure as well. If it's high, that means the hammering is that much more powerful and more likely to cause damage at some point down the road. You'll just need a lazy hand pressure gauge. Set it somewhere and leave it overnight.

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    DIY Junior Member Bucky Badger's Avatar
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    One of the copper water line did leak and unfortunately was an expensive fix because it was imbedded underneath the concrete floor in the family room and had to be rerouted temporarily but that's another story. Right now I concerned about the water pressure that was mentioned and if I should install a pressure relief valve. The house built around the early 60's and never had a pressure relief valve. It's an expensive fix so right now I'm wondering if I turning down the water flow in the home will alleviate the pressure.


    Yes, the water pressure is greater than 80 psi. It's at about 100 according to the plumber. I turn down the flow of water on the shut off valve after the main water valve to about half of what it was. I don't know how much the pressure reading is at now.

    My question is, did I actually turn down the water pressure to about half to maybe 50-60 psi now that the incoming water is about half of what it was. I'm I making sense? I'm thinking the water pressure is less than 100 psi now that the shut off valve after the main water valve has been turn to half of what it was.


    Here is the main water valve in the first photo.

    [IMG][/IMG]


    This is the shut off valve after the main water valve in this second photo. This shut off valve is on the cement wall, just above the main water valve coming from the ground. It's no longer fully open, I turned it half way down. I notice the water pressure in the house has decreased but still acceptable for showering. Did I actually turn down the water pressure to maybe 50-60 psi or maybe 70-80 psi now that the flow of incoming water is less? [IMG][/IMG]

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by jadnashua View Post
    If your water pressure is >80psi, you should (code requires it!) install an PRV and an expansion tank...the Korky valves do turn off slower, and the hammer arresters on the WM are still a good idea.

    Code does not require it here because 80 psi will never happen.

    But your advice is good, even if it is not required by code.


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    DIY Senior Member kcodyjr's Avatar
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    You haven't altered the pressure squat by partly closing a ball valve. You've limited its maximum flow rate somewhat, though. I'd imagine shower pressure sucks if you try to take one while the DW or WM is running?

    You need a pressure reducing valve (also called a regulator or PRV) to bring those numbers down to sane levels. This is a different animal than the pressure relief (TPR) valve that's supposed to be on the side of your water heater. If you really lack one of those, you have a serious safety issue that needs addressing NOW. Unlikely, though, they've been standard practice for a very long time.

    IMO, and remembering I'm a lowly DIY, I think regulators are always a good idea, unless there isn't enough pressure to begin with. Street pressure tends to vary through the 24-hr period, making it hard to set your expansion tank properly.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    When it comes to pressure, think soda straw verses fire hose...same pressure, much less capacity on the soda straw. Same idea with wires and current...small wire may end up burning up with a high current, but a huge one may not (a fuse isn't a bad example of a smaller wire)...same voltage (pressure), just throttling the flow some.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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