# Pipe Knocking



## broke

Hi everyone,

I have a pipe clunking periodically in the wall.  It seems to be related to the toilet downstairs.  It knocked and then I heard the toilet making a running kind of a noise.  

What is this and is it harmful?  What can I do to stop it?  

Thanks.


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## PaPaDan

The knock is the pipe moving when pressure changes in it.(someone flushes)  You need to get access to the pipe and secure it to a stud to keep it from moving. It normally would not cause a problem other then the noise, but could cause the pipe to crack at the nearest joint and leak.


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## broke

I've lived here for 25 years.  Why now?  Could it be because I have open plumbing in the house (removed old sink and a toilet which are not hooked up yet). 

I don't know when it started but it's been a while.  Think maybe it's during cold weather but I'm sure it's coming from my unit.  

thanks.


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## PaPaDan

Most likely a strap that was holding it has broken or just stretched enough to allow movememnt


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## glennjanie

Knocking pipes are caused by rushing water being stopped suddenly; for instance a solenoid on your automatic washer suddenly closes, bang! Anything that shuts off quickly will cause "water hammer". To cure the problem there needs to be a tee near the sudden cut-off site with a pipe standing vertical for at least a foot and capped off. When this is installed properly there will be air trapped in the vertical pipe which will compress upon cut-off, thus easing the hammering effect. There are also water hammer arrestors manufactured specifically for this problem but the vertical pipe is the less expensive way to go.


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## CraigFL

I agree with glennjanie but you may already have a water hammer absorber pipe and it just got "waterlogged". Over time, the air cushion in the pipe can become filled with water and then there is no cushioning effect. If this happens, all you need to do is drain the water from a low point in the system and then turn on the water again which will trap new air in the pipe.


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## broke

CraigFL said:
			
		

> I agree with glennjanie but you may already have a water hammer absorber pipe and it just got "waterlogged". Over time, the air cushion in the pipe can become filled with water and then there is no cushioning effect. If this happens, all you need to do is drain the water from a low point in the system and then turn on the water again which will trap new air in the pipe.



So, I'm going to try this.  I hear the knock and then I hear the a running noise with the toilet.  

Do you mean shut off the water main and then let the water run till it's done -- from a low point would be downstairs where no sink is hooked up right now.  Maybe I could use the washer instead.  Is this what you mean to do???

Thanks much.


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## PaPaDan

Usually one of the easiest places to drain a system down would be the clean out drain on the bottom of the water heater. Turn off the main and drain the system down there with a faucet open upstairs. Then close drain and open a  and turn main back on. My responses were based on my own experience. I replumbed my house completely about 14 years ago. Last year a knock developed and I found a broken strap behind the shower.


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## milehigh_woodcrafter

propper strapping will stop that. after 25 years a strap may have come undone.  rip the wall out, then when you find the smalll leak it caused and massive mold problem, rip out walls and rebuild until it's all fresh.


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## pqglen

It seems you have two problems or possibilly three.  # 1 check your water pressure. Your water regulator should be adjusted to 60lb. # 2 check for leaking. shut off the water read the meter in the street if it is moving slightly you have something leaking. I would shut off the angle stop to the toilet that makes a funny noise then check it again. From what you said I suspect the funny noise is a faulty fill valve and or flapper. If so repair toilet to stop 
      " funny noise " . I would also strap the pipes on the open plumbing as they may be knocking if they are not already straped. I would try expanding foam in the wall near the angle stop of the toilet. This will often solve the problem of a loose strap in the wall. I would not try the foam until I was ceartain there was not  a leak. The foam is a quick problem solver without being to destuctive

pqglen


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## milehigh_woodcrafter

the last post is highly educational and correct. but on the side, it might seem like an annoyance and it might be just that.  However Let me see if I can find pics of what happened to me.

Same thing old house, noise, opened wall for a peak, mold everywhere.  mold seems to like damp, cool, dark places, like inside a shower wall.  It went everywhere.  I ended up tearing all of the walls from the room and others and rebuilding.  nip it in the scrotum if you have to.


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## milehigh_woodcrafter

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this was just the beginning, i'll throw together some resized pics for all to see the importance soon.  cheers!  wtf, comments apply to following pic.


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## milehigh_woodcrafter




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## bjd6

glennjanie said:


> Knocking pipes are caused by rushing water being stopped suddenly; for instance a solenoid on your automatic washer suddenly closes, bang! Anything that shuts off quickly will cause "water hammer". To cure the problem there needs to be a tee near the sudden cut-off site with a pipe standing vertical for at least a foot and capped off. When this is installed properly there will be air trapped in the vertical pipe which will compress upon cut-off, thus easing the hammering effect. There are also water hammer arrestors manufactured specifically for this problem but the vertical pipe is the less expensive way to go.




I just drained my system and refilled the pipes.  Problem solved!!


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## Redwood

The pipe with just an air chamber is a short lived fix.
The air in the chamber is rapidly absorbed into the water.

Hammer arrestors are the best way to go they have a piston that travels back and forth in the tube preventing the air from mixing with the water.


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