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knocking water pipes

09/16/2008 11:12 PM

What is making my water pipes knock? When I turn on the cold water in my kitchen the pipe rattles very loud. What is making this happen and how do I fix it?

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#1

Re: knocking water pipes

09/16/2008 11:22 PM

Hello migo-1

Shock waves up/down the water pipe are causing the "knocking".

If the "knocking" is almost continuous when the tap is turned on, it is probable that the tap interior spindle, which is the tap-washer carrier spindle, has worn inside the spindle carrier tube.

If so, the only remedy is to lower the water pressure, or best solution is to replace that faulty tap.

There are improved "washer" designs, see picture at left.

You could replace the tap with one which uses ceramic seals, then no further bother in your lifetime.

Also please refer here: http://www.cairnscorp.com/Water%20Hammer%20Notes.htm

Kind Regards....

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#9
In reply to #1

Re: knocking water pipes

09/18/2008 1:40 AM

Hello Sparkstation:

come on mate, give us a chance to give an answer!

Good answer by the way............

stay safe

babybear

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#10
In reply to #1

Re: knocking water pipes

09/18/2008 1:43 AM

very good information

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#22
In reply to #1

Re: knocking water pipes

04/19/2010 3:01 PM

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#25
In reply to #1

Re: knocking water pipes

05/25/2015 6:05 PM

I'm a 71 year old female and have a question re: Sparkstation's answer. Does this mean that the problem (continuous knocking when I turn on the kitchen faucet; that is the only faucet that has this noise) is in the faucet itself and all I really need to do is replace the Kitchen water faucet? Thanks for your help. Trevena

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#2

Re: knocking water pipes

09/17/2008 8:04 AM

Is there air in the cold water system?

Is the pipe upstream of the tap adequately supported?

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#3
In reply to #2

Re: knocking water pipes

09/17/2008 11:20 PM

The knocking noise could be comming for just a LOOSE washer on the cold steam.Remove the cold water steam and check if the screw that is holding down the washer is loose.If it is the newer type ,change small rubber seat and spring,If not that change cold steam.

Good luck.

If none of this works.Turn house water off,and go over neighbors house and use their water.

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#4

Re: knocking water pipes

09/17/2008 11:38 PM

The knock is apressure wave running down the pipe. When you turn the tap off the water flow stops suddenly,but the flow stopping is not instantaneous along the length of pipe. The water backs up against the tap causing a high pressure area which runs backward down the pipe. The knock can be the expansion of the pipe wall but more often than not it is the (loosely mounted) pipe hitting its support when the flow goes around a corner.

There are three steps to take:

1. make sure the pipes are securely mounted; you can add a rubber insulator between pipe and bracket.

2. Lower the water pressure, though this seldom works as the problem is the waters momentum/velocity not it's pressure.

3. Install Water hammer valves in the line. These are one way valves designed to stop the pressure wave. A cheaper alternative is to connect the taps with a length of rubber hose, though these only last for around ten years before they can break so put a second tap in on the pipe side so you can shut off the water when that happens! YOu can also get special watter hammer resisting tap washers which can work SOMETIMES. only old style taps use these, the new style half turn taps often cause the problem.

My first choice would be 1. then the (steel braided) rubber pipes followed by either fancy washers or hammer arresters.

P.S. bad hammer will cause rubber pipes to wear more quickly

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#6
In reply to #4

Re: knocking water pipes

09/17/2008 11:52 PM

All well and good info for eliminating knock when water is turned OFF, but OP stated his water system knocks when the water is turned ON. Often, a simple fix for the ON-KNOCK problem is to just turn the main water valve a bit more open or closed.

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#5

Re: knocking water pipes

09/17/2008 11:48 PM

To answer your question. you should clarify a few things,

1. is the system new or it started recently to knock?

2. did you replaced the pipe work or tap?

usually the main reason for piping system to start rattling is the velocity of the water inside the pipe passes the maximum speed which is around 10 ft/s (3 m/s). so to avoid this matter they usually use a next bigger size pipe to overcome the velocity effect, by reducing it.

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#7

Re: knocking water pipes

09/18/2008 12:21 AM

Hi Migo-1

We solve the problem by leaving the taps to the washing machine on, as the connection is plastic hose, acts as a damper, probably try this first.

Tony

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#8

Re: knocking water pipes

09/18/2008 1:33 AM

Short bends in pipes can also cause "knocking" ... If you use large bends, the sudden pressure changes will be absorbed by these large curves.

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#11

Re: knocking water pipes

09/18/2008 2:33 AM

little dudes with hammers that live in the pipes and dont like when you turn on the water and flush away their furniture.

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#12

Re: knocking water pipes

09/18/2008 6:01 AM

Greetings.

We use an expansion tank on boiler systems to eliminate water hammer.

On new plumbing they require water expansion capped tubes teed off of the valves to eliminate water hammer.

Hope this helps. It is relatively easy to install.

Have a great day.

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#13

Re: knocking water pipes

09/18/2008 7:46 AM

The picture below is a "water hammer arrestor". It doesn't have to be this fancy, a simple capped 6" tube teed off the offending faucet (presuming there's space to install it) will usually do the trick. Make sure the cap is threaded, though, because sometimes the air space fills with water over time and becomes ineffective. You have to uncap it and allow the air space (which acts as a shock absorber) to regenerate.

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#14
In reply to #13

Re: knocking water pipes

09/18/2008 9:17 AM

Many older homes have the capped "T" type of "water hammer arrester." They do fill with water over time. Sometimes they can be recharged with air by shutting off the water to the house and draining the entire system (excluding the hot water heater), leaving it sit for about half an hour, then refilling it. That gives all the arresters time to drain out.

-Dennis

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#23
In reply to #14

Re: knocking water pipes

07/13/2010 8:23 AM

This worked for me, perfect solution Non Invasive . Thanks a lot. Keep up the good work.

Cheers

Sean

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#15

Re: knocking water pipes

09/18/2008 11:11 AM

Eviroman has the best answer and the only answer. Sparky needs to spend more time working then answering these forums, stick with what you know Sparky it's obvious it's not hydronis.

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#16
In reply to #15

Re: knocking water pipes

09/18/2008 11:54 AM

'Tain't necessarily so, SparkY's answer also could be correct - but I think perhaps a little less likely. FWIW, I rated Zoomer a GA vote also.

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#17

Re: knocking water pipes

09/18/2008 3:00 PM

You may have what I call "water hammer" and probably from having air in the line or not having an expansion tank in your water system. Your lines may also not be supported very well and you could have a line jumping around somewhere behind a wall beating on the wall. The momentum of the water rushing down the pipe when you turn it on makes it jump at a 90/45 ell or tee and if it is against or near something will make a loud clang or bumping sound.

pipewelder

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#18

Re: knocking water pipes

09/18/2008 9:07 PM

if tap washers okay add damper a peace of pipe 8 to 12 inch long to the cold water pipe above the level of the tap

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#19

Re: knocking water pipes

09/18/2008 10:50 PM

Hello migo-1

Perhaps there is an updated variety of Tommyknockers at your home.

Kind Regards....

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#20

Re: knocking water pipes

09/19/2008 8:42 AM

It is called "water hammering".

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#21

Re: knocking water pipes

09/21/2008 10:58 PM

Knocking in water pipes is caused by a flow rate through a constriction somewhere in the supply stream narrow enough that the pressure drop through the constriction is great enough to intermittently boil the water.

The collapse of the boiled bubble creates the shock wave you hear as a knock.

Find and fix the constriction is the perfect cure. Not easy to do. You can use a long rod held to your ear to find the loudest knock and then cut out and replace the pipe section. Or you can simply run the tap slower.

If this section of piping has a secondary shut off valve downstream of the faucet then that valve not being fully open or having a wobbly sealing washer is a pretty good candidate as the culprit. Check that possibility before committing surgery on your plumbing.

Sincerely,

Mr. Gee

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#24

Re: knocking water pipes

05/18/2013 9:17 PM

Answers 1 and 13 are good answers. However, you should identify why your pipes developed water hammer. Are you on a well with a pump and pressure tank? You could have a faulty foot valve, check valve, or back flow preventer. If your pressure tank is water logged the pump will start and stop frequently to keep up with water flow. That starting and stopping will rattle pipes.

Another aspect of water hammer on wells could be developed with gases within the water coming out of solution. These gases could be air, O2, CO2, methane, H2, or even H2S. The water itself will not compress but the gases will and can hammer and rattle pipes. If you are on municipal water, check for back flow prevention on hoses and the respective anti-syphon that should be installed. If you have had a break in a water line (it can be off your property) air can become entrained in the plumbing. Drain (bleed) lines to remove the air or gas trapped.

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Users who posted comments:

44mEurope (1); Anonymous Poster (6); babybear (1); djacob (1); EnviroMan (2); gadgetman (1); Hamid K Saberi (1); kevinm (1); Mr Gee (1); OlympiaWA (1); pipewelder (1); PWSlack (1); R.Radhakrishnan (1); Skeeter (1); Sparkstation (2); Tonymech (1); trevena (1); Zoomer (1)

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