HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Blogs
Sherlock Ohms

The Mystery of the Water Hammering

NO RATINGS
View Comments: Newest First|Oldest First|Threaded View
Page 1/2  >  >>
loadster
User Rank
Gold
Re: Water Hammer stopped but not cured.
loadster   1/7/2013 12:31:04 PM
NO RATINGS
Thanks for that enlightenment. I wondered about the vertical dampener and if it was really effective or if the air woud dissolve in time. The key is a correct and overbuilt original install and then an independent inspection by someone who knows and must be obeyed. I grew up in an older middle class residence built in late 1940s that had some bathrooms added on and remodeled. The results were percussive when more loads and larger capacity clothes- and dishwashers showed up. The copper pipes had been carefully threaded through some of the beams and joists and the inaccessible long runs were resonant. The runs we could see were silent and carefully fastened with clamps. Every appliance had a tell-tale announcement of where it was in the wash cycles. Dad never minded cuz he was gainfully employed and rarely witnessed. The rest of us could have experienced a meteor shower and never paid attention. I guess its great testimony to the quality of the pipesweating in earlier times. When father did hear it on the weekends, he threatened to call a plumber with the know-how to install a proper hammer arrestor. That house went to sale and the next remodeling with its signature drum beat.

bobjengr
User Rank
Platinum
WATER HAMMER
bobjengr   12/21/2012 5:02:27 PM
NO RATINGS
I worked as an engineer in the water heater industry for about eleven years and water hammer is a significant problem with some homes.  The "hammer" can actually cause real issues and make repairs necessary.  Ruptured piping and leakage are not uncommon.  One "fix" was to install a pump tank; i.e. hydropneumatic vessel with a diaphragm that will "flex" and allow absorption of the pressures inside the piping system.  It was always amazing to me how rapid closing of solenoid valves driving dishwashers and clothes washers could produce the water hammer.  Equally amazing as to the pressures that could be developed. 

Tool_maker
User Rank
Platinum
Lakehouse Hammer
Tool_maker   12/20/2012 1:18:15 PM
NO RATINGS
  We own a lake house in which we had a hammmer following every toilet flush. It sounded like something was busting through the wall. None of the plumbing is easily accesible so we tolerated it for the first month we owned the house and I figured sooner or later I would have to open a wall and put an arrestor in. One Sunday as we prepred to go home, the weather was getting cold enough that I closed the water main. The next time we came down and I turned the water back on, the hammer had disappeared and in the ensuing 4 years it has not returned.

  I do not know what I did, but the silence is a pleasure

Critic
User Rank
Platinum
Re: Water Hammer stopped but not cured.
Critic   12/19/2012 9:30:01 AM
NO RATINGS
A water hammer arrestor, field-fabricated from a short section of capped vertical pipe, is essentially useless.  In some cases, these are installed by plumbers to meet code requirements.  In other cases, they are installed by plumbing-ignorant people who think they are useful.

Why do I say they are useless?  Because the air head diffuses into the water after a while, and the pipe becomes filled with water.  This can happen in just a few weeks or less.  It is possible to drain the water out of the arrestor (so it will work for up to a few weeks before again being drained), but homeowners generally never do this.

I once owned an older home that had a well and pressure tank equipped with a non-functional air volume control.  The purpose of the air volume control is to maintain a head of air above the water in the pressure tank, so that the system pressure does not vary as much with water volume.  This allows the pump to run longer and less frequently than it would with no air head in the tank.  Most air volume controls were notoriously unreliable, so now most pressure tanks contain bladders that separate the water from the air.  Every few weeks, I would have to turn off the power to the pump and drain a few buckets of water from the tank to create an air head.

Manufactured water hammer arrestors are available, which remain functional even if the homeowner does not drain them every few weeks.  These are more costly than a short, capped section of pipe, so they are not used very often.  In most household cases, water hammer is just a minor annoyance, not a serious problem.

warren@fourward.com
User Rank
Platinum
Re: Toilet valve water hammer
warren@fourward.com   12/18/2012 3:22:18 PM
NO RATINGS
This valve is a good example of a closed loop servo system. The damping was set all wrong in the feedback loop. Unfortunately you probably can't adjust the loop. Fortunately it is a cheap replacement, but a pain in the neck...

Cadman-LT
User Rank
Platinum
Nice Solution
Cadman-LT   12/10/2012 4:27:41 AM
NO RATINGS
What a nice solution to what was thought to be a complicated problem. I had never even heard of "Water Hammering" before.

William K.
User Rank
Platinum
Water hammer and means to reduce it.
William K.   12/7/2012 9:16:14 PM
NO RATINGS
The repeated hammering is caused by the pressure wave reflecting back and forth in the line. The returning wave may cause the valve to open momentarily, and then it will close again and generate another wave. A method of reducing this is to usen a valve with a slow closure, and a method to damp the wave is to use an elasomeric connection hose. That provides the needed cusioning without adding anything extra to the system. The slower closing valve is equivalent to slew-rate limiting, used in electrical circuits to reduce interference.

Damage from water hammer is why piping should be well anchored, since there is often enough energy available to break the piping if it is unrestrained.

Charles Murray
User Rank
Blogger
Re: Water Hammer stopped but not cured.
Charles Murray   12/7/2012 6:59:05 PM
NO RATINGS
I agree, Bob from Maine. It took some good sleuthing to make the connection between the toilet valve and the water hammer noise.

btlbcc
User Rank
Gold
Toilet valve water hammer
btlbcc   12/7/2012 3:21:30 PM
NO RATINGS
I had a similar problem recently.  The fill valve (a Watermaster brand) was intermittently leaking, and for some reason (I didn't bother to autopsy the old valve, which I installed back in 1996, and which performed faithfully for nearly 15 years - no complaints) this would trigger the fill action; the float (or something internal) would stop the flow and then it would start again.  Since this particular model of the valve shut off with a snap, there was a definite water hammer, at a frequency of about 2 cycles per second. This osillation could be started by a sudden pressure drop in the system (such as the washing machine fill valve opening) or it could self-start (usually about 3AM).

Needless to say, this was not likely to improve the plumbing system.  I could generally stop it for a while (days) by jiggering the float valve arm, but a replacement valve solved the problem completely. 

If there is a lesson from all this, it is that, in most houses, the toilet fill valve is the only automatic system in the plumbing.  Everything else - washing machines, dishwashers, various faucets, etc. tends to operate only upon command.  The toilet fill valve will operate whenever the water level in the tank drops or (in my case) from an internal malfunction.  Way back when, I worked as a plumber for a few years, and the most common problem was toilet repair, so I learned to hate fixing toilets!

bob from maine
User Rank
Platinum
Re: Water Hammer stopped but not cured.
bob from maine   12/7/2012 10:15:31 AM
NO RATINGS
In all the houses and remodels I have done, I've always required my plumber to install water hammer arrestors like the ones described by Sliderulefarmer in the hot/cold lines adjacent to every electrically operated valve; washing machine, dish washer. Water hammer probably destroys more water mains and causes more damage inside houses than most other single events. I've seen 30 ton fire trucks actually moved sideways when a valve was incorrectly slammed shut on a 5" line. Good observation, connecting the toilet valve and knocking noise.

Page 1/2  >  >>
Partner Zone
More Blogs from Sherlock Ohms
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Design News Webinar Series
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
6/25/2014 11:00 a.m. California / 2:00 p.m. New York
5/13/2014 10:00 a.m. California / 1:00 p.m. New York / 6:00 p.m. London
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Jul 21 - 25, Design Products With Bluetooth Low Energy
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: August 12 - 14
Sponsored by igus
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service