Waterhammer Problem, please help!

texasranger · Aug 31, 2011

(Sorry for the length of this message, but I wanted to try and provide a thorough recap of my problem and the steps I've already taken to try and correct.)

I live in a 2-story house that is 10 years old and we never experienced waterhammer noise until 3 weeks ago after we purchased and installed a new high-efficiency washing machine. The waterhammer noise initially was a loud, constant thumping (almost like a jackhammer) that was primarily eminating in the wall on the opposite side of the house from my washing machine and the noise occurred while my washing machine was in the wash cycle.

I did some research on the internet and installed two arrestors on the hot and cold lines on the back of my washing machine, but the problem persisted. The waterhammer noise next occurred when the shower was in use and I decided to phone the city water department. They came out and checked the water pressure from the city line to my house and said everything was normal for my neighborhood. They then checked my water pressure at one of my house's external faucet bibs and said the pressure reading was as high as 100 psi, but then came down to around 80-85 psi. They suggested that my Pressure Reducer Valve (PRV) on my main water supply line was faulty and needed to be replaced. I purchased and installed a new PRV valve and adjusted it to where my water pressure is now a consistent 60-65 psi. I thought this new PRV corrected my problem as I did not experience any more waterhammer noise until about 10 days later when we heard it reoccur (but not quite as loud) after an upstairs toilet was flushed and the bathroom faucet was turned on next to the toilet. I was able to duplicate this waterhammer sound several times by flushing this same toilet and turning on the faucet. (The waterhammer noise always occurs within the walls on the same side of my house.)

I again phoned the city water department and they suggested the problem could be a faulty valve in this upstairs toilet. I bought and installed a new flushing valve today for this toilet, but unfortunately I was able to again produce the water hammer noise by flushing this toilet and turning on the faucet. I decided to try flushing another upstairs toilet and turning on this same faucet and the waterhammer occurred again! The washing machine was not running at this same time, but we did do a load about one hour before. The automatic dishwasher downstairs was running at the same time this waterhammer sound occurred.

I am at my wits end and am hoping someone can help me to correct this problem. I have little doubt that the problem started as a result of the new HE washing machine, but now the waterhammer occurs seemingly at random.

Thanks in advance for your help and unlike others, I promise to report back if someone's suggestion corrects my problem!

LiQuId · Aug 31, 2011

I assume you install mechanical arrestors and not Captive air chambers?

I ask because it was common for a plumber years back to Field manufacture arrestors that were nothing more than a bigger pipe installed ( usually on the tops of risers ) to trap air... these were eventually eliminated by mechanical arrestors ( spring with a diaphragm to separate the air, spring and water ) because the water would, over time saturate the chamber and the system wound need to be drained and then re-filled to again trap and air pocket.

so to repeat the question, did you install mechanical arrestors or Captive air ?

location could be better.... usually they are better installed ( from my experience ) somewhere in the line... like the top of a riser.

If they ARE mechanical arrestors, perhaps they are undersized, OR there is a leaking Diaphragm, pictures of the installation would help also.

And...... The science.

Water hammer occurs because water is NON compressiblle. A common misconception is that you need lots of psi in a system... this Is WRONG, the pressure only needs to be there to get the water to its point of use, which in the case of some Fixtures and valves there IS a minimum pressure, For the sake of this example lets think of a old house with only a bathroom and a kitchen sink. Now, the pressure must be great enough to overcome
1. Gravity 2. Friction losses ( type of pipe, bends REAMING of joints <- tossed reaming in for good measure ) and must 3. Be at a useablle pressure at its Point of use.

Ask yourself simply " do I want a shower with 1 gmp of water at 100 psi or the opposite? "

..now you understand pressure a little better. When the pipe is sitting full of water and not being used it is at a static pressure, And as you open a valve that pressure is converted into momentum as the pressure outside the pipe ( atmosphere ) is less that that of the pressure inside the pipe the liquid must go from posative to negative pressure. When a valve is closed quickly ( sometimes even slowly ) the momentum of the liquid is suddenly stopped and becomes Force ( pressure over area ) which resonates through the pipe causing the water hammer you experience. This is why the Air chambers worked for a while as the air inside is compressablle and can do so under a dynamic load.

think of a linebacker. If he leans aginst you you may be able to hold his weight ( water static and not running )
but if he's running and you try to slam a door infront of him, he might not get through, but there WILL be a loud noise, and eventually he WILL get through. ( door representing the valve )

gah, I need to eat.... hope this helps you.

to simplify this I will ask you to

Mr_David · Aug 31, 2011

LiQuId said:
think of a linebacker. If he leans aginst you you may be able to hold his weight ( water static and not running )
but if he's running and you try to slam a door infront of him, he might not get through, but there WILL be a loud noise, and eventually he WILL get through.

Liquid, What you said does make since, but it doesn't explain why he's getting a constant thumping noise.

Check you main water service valve. What type is it . Ball valve, Globe valve or a gate valve?
Globe valve has a disc that seals on a seat.
If the disc is worn or loose it will vibrate.
Do you have any check valves? maybe on the water heater.
Do you have any automatic irrigation sprinkler valves.
Isolate Them from the house if you can.
Try isolating the Water heater and flushing the toilet.

Very common noise IF it was related to a single fixture and the angle stop valve was not open all the way.

texasranger · Sep 1, 2011

Thank you for your responses and I only have a minute this morning to quickly respond to the question on the type of arrestors I installed. I installed two Sioux Chief Mini-Rester shown at this link:

Sioux Chief 44556 Mini Rester Water Hammer Arrester 3/4"

I will try and respond back to your other points later today...thanks again it is very much appreciated!

speedbump · Sep 1, 2011

I'm not a Plumber, but do run into water hammer in my line of work. Your link had this statement: "Engineered especially for single fixture residential or light commercial use." Maybe you need more of these or maybe something larger for the whole system.

LiQuId · Sep 1, 2011

Ahhh yes Mr david is absolutelly right, the water "hammer" only really happnens at the opening and closing of the valve.... A flapping Washer, or a swing check would produce more of a continuos sound like the one you describe.

Is this the sound that gets more random, rapid and chunky ( sometmes Humm's also )when a valve is Almost but not quite closed mr David? ( a venturi is formed withing the piping i gather )

where i live most houses have Pex installed so water hammer is not something a come across often.

texasranger · Sep 5, 2011

Thanks again for the responses to my plea for help! Update---I had the city water department come back to my house to double-check their pressure readings against my own. We decided to try increasing the water pressure to 75-76 psi via the new PRV (pressure reducer valve) to see if that would alleviate the problem and I am pleased to report that so far that simple adjustment has eliminated the waterhammering noise. I was able to easily reproduce the waterhammer noise upstairs when my psi was around 65 and was only able to register a slight vibration once only after really stressing the system to the extreme by flushing my two toilets upstairs several times and turning on multiple faucets (and unlikely scenario with our normal usage). It has been several days and so far so good. Again, I want to thank you all for your input and I will try your suggestions if for some reason the noise returns. Happy Labor Day!