Knocking noise in pipes

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Old 12-31-10, 07:30 AM
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Knocking noise in pipes

HAPPY NEW YEAR

our master bedroom is adjacent to garage and water heaters/heater are right behind the wall.

around septemebr this year (we lived in the house since june 05) i started noticing knocking noise coming from the water pipes, behind the garage wall, after water was used.

it's a descending knock, 4-5 knocks. every time someone flushes toilet, or takes shower, or opens faucet, and then water is shut down - TUMMM!!! TUMM tumm tum

just cascading down like this. it's the loudest after shower was used.

i was told that it's due to water pressure drop down, but we never had this before. also, it sorta starts getting louder.

any ideas? what gets me is that it was not there, then started not so long ago. this is never good news.
 
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Old 12-31-10, 07:44 AM
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Sounds like a pipe came loose in the wall. Sometimes pipe starps break in the wall and the sound is the pipe hitting something. Hard at first then softer. Look around at all exposed pipes and maybe you may see it and restrap it.

Now why pipe banging? What is the pressure of your house? Do you have a pressure reducing valve where your water line comes into the house? Is there a expansion tank by the HWH?

Let us know.

Mike NJ
 
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Old 12-31-10, 08:23 AM
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thank you

no, no exposed loose pipes.

have no idea what pressure is. i know it was checked out by irrigation folk 3 yrs ago and was found to be on the high end for their needs.

this is what is behind the wall, in the garage. noise is coming from somewhere behind my head, when i am in bed, so it's mid-level of the wall.

the only pressure valve i am aware of is in the irrigation system. i think, it's backflow preventer though. otherwise, simply don't know. main water valve/meter are over 200 feet away, outside property.





 
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Old 12-31-10, 08:26 AM
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oh, and speaking of loose pipe. we have had hot water noise ever since we bought the house. when hot water starts running through the system, esp for showering, it starts making fast tuk-tuk-tuk noise, for about 15 seconds. but that's somewhere under the floor. i assume pipe is expending and rubbing on something. no worried.
this noise though is almost like drum beat. toommm-toomm...
 
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Old 12-31-10, 08:45 AM
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I would check the expansion tank at the HWH. There is and air valve there and needs to be check with the water off and pressure drained off. Close that valve to the HWH and open a HW faucet to drain pressure off. Then thest the valve on the expansion tank with a tire gauge. It should be set to what your house pressure is. Ex: If house pressure is 70psi then tank should have 70psi of air in it.

Get one of these for a outside house bib so you can check your house pressure.



Let us know.

Also for the life of me I dont know why they piped the HWH in series. You are running the first on the line more then the second. They should be pipe in parallel. At least if one HWH takes a dump you will still have HW. In your current set up if the second heater goes the first heater will be dumping HW in a cold heater. Get it????

Plus I am going to have to look this up but I think I am positive that both relief valves cannot be piped together like that. That may be dangerous.

Mike NJ
 

Last edited by lawrosa; 12-31-10 at 10:17 AM.
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Old 12-31-10, 09:28 AM
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yes, i get it. we, also, run out of hot water very easy, surprisingly for 2 heaters.

let me get this first:
HWH=hot water heater?
expansion tank is that large canister sitting on top of corrugated line leading to the right hand heater? yes, it does have nipple, like for tire, on the very top.



my son's good friend is a plumber. i'll call him in to look at all this. he's a good kid, he won't rip me off.

now, just to make sure - water is coming into the right heater via that corrugated pipe with tank on the top, then goes into the left heater and then goes into the house via the corrugated pipe coming up into the wall from the left heater?

look at this before we go to any conclusions:




does it look like in series to you?

also, please, explain:

Plus I am going to have to look this up but I think I am positive that both relief valves can be piped together like that. That may be dangerous.
 
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Old 12-31-10, 09:41 AM
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How to increase hot water quantity using multiple water heaters in series for lower hot water cost

Some buildings use water heaters installed in series to handle variations in hot water demand more economically. Unlike the illustration of parallel water heaters shown above, water heaters connected in series means that incoming cold water flows first into heater #1, then out of heater #1 into heater #2, then out of heater #2 into the building hot water supply piping (or into additional water heaters if more than two are used.)

A synonym for water heaters connected in series is a cascaded water heater design. Cascaded or in-series water heaters is an economical way to handle large variations in hot water demand in a building.

* When the anticipated hot water demand is low, only water heater #2 may be running.

* When the anticipated hot water demand is high, water heater #1 is turned on as well, doubling the volume of hot water available (if the heaters are of the same capacity in gallons or liters).

* Water heater controls can be adjusted so that the "upstream" water heater, (water heater #1 in our example), is left turned off or perhaps set to a very low temperature. In either of these cases, the upstream water heater or tank functions as a "booster water warmer" reducing the energy use by water heater #2 by pre-warming water entering the active heater#2.


How to connect multiple water heaters in parallel to increase total hot water quantity

hot water heaters installed in parallelWhere hot water volume requirements are high, in addition to installing a single larger-capacity water heater, one can install a several water heaters connected in parallel. You can see this design in our sketch at left, provided courtesy of Carson Dunlop.

Parallel water heaters means that all of them are "on" and heating water at the same time, providing a very large quantity of hot water to the building.

We see this installation most often when building occupants find that they do not have enough hot water but their present water heater is in good condition.

Rather than scrapping a perfectly good water heater to install a single larger unit, a second water heater is simply added, installed in parallel to the first one.

well, i am not sure we really need LARGE hot water quantities. but yes, i do see what can happen if upstream heater goes boink.
 
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Old 12-31-10, 09:49 AM
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yes, it's cascaded installation. left corrugated pipe is hot, right is cold. one U-shaped connecting both heaters is hot either. one in the center (goes into the wall? comes out of the wall?) that is T-d to both heaters is cold. have no idea why there's 2 cold water pipes in this setup.
green handle on the wall, above that T-d pipe, is main shut off valve. will turn off water for the house appliances/heaters/outside faucets.
 
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Old 12-31-10, 10:26 AM
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This is parrallel. It draws evenly from both heaters. Notice the tee for outgoing hot water is a tee with evenly spaced pipes to heaters. This is critical for even draw. Also notice two expansion tanks.



In series like you have the first heater works harder because cold water is dumping in it when you use HW. The second would rarley come on until you deplete the first.

i am still looking up info on relief valves.

Mike NJ
 
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Old 12-31-10, 10:56 AM
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basically, expansion tank is prolly making the noise? it just plain does not sound like pipe hitting, sounds more like air bubbles going through pipes.

and how exactly do i set pressure in the expansion tank? with compressor, just like tire?
 
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Old 12-31-10, 11:38 AM
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ok, i know how to check and adjust tank pressure. will do it later, wife sleeps after night shift.
 
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Old 01-13-11, 03:09 PM
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ok, got it fixed. checked pressure in thermal expansion canister, if was only 15 psi. adjusted to 55 psi. that was it.
 
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