Loud Hum from Water Pipe - High-Rise Condo

[michellelukezic]

I live on the 11th floor of a multi-unit building. Over the past year a humming from the main water pipe that runs straight up through the building has gotten much louder. We recently re modeled out kitchen 2 years ago. The noise wasn't there before, and it didn't show up directly after the remodel. The building maintenance people turned off the motor that pumps the water up through the pipe to all the units. The noise went completely away. The noise can be heard from other "06" units above and below us, but not nearly as loud. We have a 2x2' hole behind the slide-in stove where we can see / touch the water pipe. It definately is the vibration. The ceiling and floor are concrete, and the humming travels through out the entire condo. It's very loud, and driving us nuts. We tried seeing if anything was touching / vibrating on the pipe, and nothing is (from the hole behind the oven).

What would be our next step? Does anyone have any ideas? Any advice would be fantastic.

[kingsotall]

You can let the building management know about the problem. Whether they do anything is the question. As far as stopping the sound at your end is futile. I mean the pipe in question can be fitted with an isolator (foam, rubber matting, etc) where it penetrates the wall but that will most likely result in very little in eliminating the hum.

[FloridaOrange]

How old is the building? Where the pipe penetrates the floor there should be vibration isolators; springs or neoprene. The incorrect size or lack of one could be an issue. The same applies to the pump(s). Those are the 2 starting points for an issue as described.

[michellelukezic]

Thanks for the replies. The building was built in the late 70's.

So far it sounds like it could be one of these problems (from this board and others):
- loose support / something lodged against (from our remodel)
- vibration isolators; springs or neoprene at the floor needed
- vibration isolators at the pump connections
- partially throttled valve

Again, appreciate the help!
Michelle

[FloridaOrange]

I would, if possible, ask your management company to hire a forensic engineer if the problem persists. There are mechanical engineers who specialize in tracking down problems, you would benifit by having an overseer on the project who may be necessary if legal problems arise.

[michellelukezic]

Just had a thought... we are in the exact middle of the building. Would it be possible that the pipe is moves most in the middle, like a guitar string? Just a shot in the dark... Went to other 06 units today, and the units two above and below us have the noise... but not nearly as loud as ours.

The forensic person sounds like a good idea...

[FloridaOrange]

Not if it is supported at every floor penetration.

[geniescience]

Yes. Standing waves inside the pipe will come out much more strongly at specific regular intervals. Halfway inside the building is where all the even-number-divisible waves combine.

The vibration (wave) consists of a number of waves of different frequencies. The math term for adding things together in one spot is superposition. Here, in this case, multiple small noises combine. Each noise is independent, and simply by summing them up, simple arithmetic, you get an aggregate result, extremely small or big in one area or another.

In your case, they combine to make a more audible hum where you are. This is where they penetrate the pipe wall and come out as audible noise.

If you press your ear (or finger) against the pipe anywhere else in the building it will be heard (or felt) but it remains mostly inside the pipe. I'll bet you'll hear something similar when you put an ear underwater when you take a bath in the tub. The noise is in the water. It does not matter that the pipe is securely fastened at each floor as it goes through the concrete slab.

Fine adjustments can remove most of the noise. Neoprene pads (as thin as 1/16th inch) can be placed like washers under the bolts holding your pump in the basement. It can be even better insulated by using a slightly more complex hanging bolt system. On the web, look at images showing how air handling systems hang securely from ceilings so as to eliminate transfer of noise to the building structure, and you'll see how to copy this for a pump.

I also live halfway up in a high rise condo building. As each new batch condo administrators get elected every few years, I have been sharing what I've observed and learned. Eliminating vibrations improves quality of life everywhere in the building. When the water has a "noise" in it to start with, this noise can be audible when someone turns on a tap partially and a hissing / whistling noise is generated. The tension from water movement across a partial obstruction amplify the background vibration which was not audible beforehand. I call it noisy supply line plumbing.

[michellelukezic]

Thanks for the reply. My husband happens to be a sound engineer, and we determined that the hum is 177hz. It's constant, and never stops. The motor/pump on the 21st floor emits the same pitch and you can feel the same vibration running through it.

Now I guess the questions is figuring out exactly what next steps are with our building manager, as they pretty much said that the problem is in our unit only and that we are responsible for what's behind the wall. I'd hate to tear up our kitchen and "fix" it only to find out nothing changes. What expert sounds like the next best step? A forensic mechanic/engineer? Not sure.

Thanks again!

[geniescience]

... they pretty much said that the problem is in our unit only....

This part you already knew.

... we are responsible for what's behind the wall. ....

Here is the huge mistake. Either you mis-heard, or they mis-spoke, or someone's hoping to send you away once and for all by saying something dumb (once only) on the hope that you won't be able to quote them later, or they truly don't know the truth about their responsibility. It is possible that they are a bit of both, playing cutesy with the truth and also not interested in knowing the truth.

Getting a Condo board to accept responsibility for a building problem is sometimes a challenge. In the long term they'll understand this subject better. Gently make them all aware that you would vote in favor of fixing things that affect others too. Talk to the other condo owners, about this and other problems. Whatever human inertia seems insurmountable will all evaporate like dew under sunlight one day soon. Don't make enemies or adversaries and it will happen faster.

[strick33]

Michelle-
I see you posted on several blogs about this problem . This is exact same thing is happening to me. I live in a condo with concrete floors. I am desperately trying to figure it out in conjunction with the building management - did you ever get a a resolution?

Steve Strickland

[Thatguy]

177hz.

x 60 is 10,620 RPM. That's kind of fast for a motor. Maybe the pump impeller blades are hitting something.

If you can get your hands on a spectrum analyzer you can get the "signature". It's like doing an EKG on the thing.
Caterpillar, among others, can diagnose mechanical problems using these signatures long before humans notice them and without lifting a wrench.