Thread: tapping pipes in wall

hey all
wonder if anyone has come across this.

condo inspection,second floor,and all condos are self sufficient,own water heater and furnace.
when i went up to second floor bath {only bath in unit} ,i turned on the sink and tub to check for flow and leaks. when i went back down stairs client and agent said there was a tapping behind wall. so back up i went and ran water again and listend to every wall NOTHING.

client closed and called me last week and said the noise is back and persistant. so over i went.

turned on bath sink and sure enough there it was,slight tapping. but now the mystery starts. it only makes this noise on the first turn on . i turned that water on and off 20 times after that and nothing. client says let it rest for an hour or two and it will do it again.

expanding pipes or what.
thought i would ask the board before i called a plumber

thanks
charlie

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Sounds like maybe the pipes in the wall were not strapped. I've actually drilled a small hole on the backside of the wall where the fixtures are doing this and injected a bit of the expansive foam into the wall void and "magically" it stopped.

Only other option is opening up the drywall and securing the pipes.

rick

rick
wouldn't they tap everytime--its an older unit
charlie

Charlie,

I actually had this same problem at a previous home I owned. Our master shower would do this same thing "tapping" your mentioning.

It would not do it all the time either. One day I just did the foam injection thing as I mentioned and it put an end to it. Later when we did our remodel of that bathroom, when I removed the shower tiles from the wall I did find just as I suspected that the plumber had left out the strap to secure the plumbing lines. Great thing was that the foam was hold the line tightly not allowing it to move. I used to have some pictures of this but I'd have to do some serious searching for them.

rick

Water hammer. This happens sometimes when water starts to move, either on opening a valve or closing a valve. Usually happens on a fixture that is higher than another one. There are hammer arrestors that can be installed to prevent this.

Does the noise happen with the hot or cold pipes?

Originally Posted by Wayne Carlisle

Water hammer. This happens sometimes when water starts to move, either on opening a valve or closing a valve. Usually happens on a fixture that is higher than another one. There are hammer arrestors that can be installed to prevent this.

Wayne is correct on the term water hammer. The hammer arrestors are probably going to solve the problem, but that is where the plumber come$ into the picture.

isn't a water hammer when you turn the water off and pow---the air hits it, and again wouldn't happen everytime??? thanks for all the help

Not necessarily. It all depends on the operating pressure. Water pressure fluctuates all of the time and the “hammer” is when the water starts to move suddenly or stop suddenly. Normally it is when you shut the flow off suddenly but I have seen both. The pressure of the water is what activates the hammer. The higher the pressure the more likely you are to get hammer.

this sound does not start happening until maybe a minute after water is turned on--hot or cold--but i started with the hot---then it goes away as i stated--i can turn that water on twenty times and i won't hear it again,but leave water off for an hour and there it is again

Water hammer is where, when a valve closes suddenly (usually associated with automatic closing valves such as on dishwashers, clothes washers and the like) the lack of high pressure under the open valve suddenly goes to full pressure upon closing the valve (the pressure actually spikes up higher than full pressure).

With a properly designed and installed system, you should not have water hammer. However, leave a section of pipe unsecured and you will hear that section slamming around when a valve is closed quickly.

Try this: Open the valve s-l-o-w-l-y and see if it makes the noise, then close the valve s-l-o-w-l-y and see if it makes the noise.

*It could be expansion*, yes.

If it does it 'the first time every time', you can isolate DWV from supply by using a hose to run water down that drain. Then use a hose with an adapter to run water from that sink down another drain. You should be able to isolate the pipe which is causing the noise that way.

thats exactly what it sounds like and it happens with sink and shower--i thought it may be drain pipes, but i am now going to give it to plumber

thanks all

OK, teach me something. How can the flow of water through waste pipes create a knocking/tapping noise.

I didn't know ABS was that sensitive.
I haven't seen ABS since the 70's if it's what I am thinking about.
Is that the old black stuff?
Is it still used in your area? Still allowed???
Just wondering.

That means 30mm = 1.181 inches. I don't see that happening. You sure on your math? I used a conversion chart...is my calculation right?

Ohhhhh. That still seems like a lot. You would think that it would pull joints lose and other stuff with that kind of movement.

Keep in mind that the fittings are the same material, and should expand at roughly the same incremental rate. Unless you installed the entire system at ridiculously high temps with ridiculously long runs, (i.e., with everything at max expansion) I can't see that it would pull away from the joints significantly as it contracted with very low temps. However, to be safe, I wouldn't want any fittings restrained too tightly at the ends of long runs.

Wayne,

Go here: http://www.kmisystemsinc.com/files/T...es/ExpofPP.pdf

Let's say the pipe inside the wall is 75 degrees F and you run 120 degree water down it, the change in temperature is 50 degrees F.

Looking in the right column of that link, it shows, at Table 2, that PVC expands 0.456 inches per 10 degree F per 100 feet length.

That means that PVC will expand 0.456 x 5 (50 degrees instead of 10 degrees) per 100 feet, or 2.28 inches per 100 feet.

That means that each foot expands 2.28 / 100, or 0.0228 inches, and let's presume the vertical height from below a slab to the sanitary tee is 12 feet (8 foot ceiling + 2 feet floor system + 2 feet high sanitary tee), which means 12 x 0.0228 = 0.2736 or just over 1/4 inch expansion.

That means that PVC is standing there, minding its own business, when someone decides to pour really hot water down its back, so it screams ssscceeerrrccchh ... 1/4 inch worth, then it says "don't do that again", but, of course, the next batch of really hot water feels good, as it is now already hot ... like getting into a nice hot shower ... Yikes! That's HOT! ... But it sure feels good now.

Let it cool again and ...

Sometimes just changing the washer or the cartridge might help.

expericenced th same problem myself on 2nd floor tub. changed washer on hot water tap & presto,,, problem solved

now if i can only get my kitchen sink delta faucet to stop whistling when running th hot water..........

Just a 'by the way', the expansion of the waste pipe only needs to be enough to come in contact with the framing, usually at the point it passes through the plate. There is almost always an junction, elbow, 45 or some other fitting at the plate and a little expansion starts the sound.