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A Real Water Hammer Mystery!

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Old 09-08-2010, 07:52 PM   #1
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A Real Water Hammer Mystery!

Hi folks, I could really use some new ideas on this one!
I recently replaced a 50 gal, 36k btu tank and got a call back for water hammer. Customer now has water hammer on opening and closing of all fixtures and valves. While troubleshooting I found that by closing the full bore ball valve on the inlet the hammer disappears and reappears as soon as the valve is opened. The most puzzling thing for me is how closing the inlet valve would have any effect on water hammer on the cold pipes...there should be no flow through the tank at that time! There is also a small hammer on the hot pipes that also goes away when valve is closed. I have only tried one thing so far which was a hammer arrestor before the valve...no luck! I certainly would appreciate any feedback I think my customer is losing confidence in me already!!
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Old 09-08-2010, 08:07 PM   #2
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Re: A Real Water Hammer Mystery!

are you certain it wasnt like that before and now there tryin to blame you so you fix there existing problem???

man long time lurker eh?

is there a circ line on the system?


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Old 09-08-2010, 08:08 PM   #3
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Re: A Real Water Hammer Mystery!

Well if all you did was install a water heater on an existing water systems, water hammer is mainly caused by worn out fixtures like shower valves, faucets, toilet fill valves, sprinkler anti syphon valves. usually anything that has seats, stems, cartriges, or diaphrams, so is it possible, that he already had the problem and just tried to pin it on you=). just find out what fixture or fixtures are triggering the water hammer by process of elimination. make sure none of the fixtures are dripping, and or leaking at the time your testing it . good luck, if this is not it, then man im stummped.
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Old 09-08-2010, 08:27 PM   #4
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Re: A Real Water Hammer Mystery!

Did you check that the main valve was fully open before turning it off? Reason being is it may have been closed down slighty to stop water hammer in the past. I have seen this quite a few times and normally done by the homer owner or plumber who last worked on the house for a quick fix. If your not sure shut the line down a little and see if the water hammer stops. If it does then this was more than likely your problem.
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Old 09-08-2010, 09:11 PM   #5
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Re: A Real Water Hammer Mystery!

No I don't think the problem was there before, she was quite horrified at the intense boom that echos through her house every time any fixture is both opened or closed!! You can actually hear the pressure waves cycle back and forth throughout the system multiple times after each boom...I can't stress enough how loud and violent this is never heard it so bad before.
There is no circ line on the system, I put a gauge on it reads 70 PSI from the town supply.
I had tried monkeying with the main shut off as well and I found that the more it was open the more hammer on closing of fixtures, the less it was open the more hammering on opening of fixtures and it occurs on every valve....this is even more odd, I checked the outdoor garden hose and it does it as well! I would have thought that the hose would have enough flex in it's wall to soften it a bit but not.
The only thing that stops the hammering completely is shutting off the supply valve to the water tank.
I did not replace any pipe with a smaller size or restrict it in any way which could increase velocity at the transition and cause hammer.

Thanks for the help guys!
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Old 05-17-2016, 11:39 AM   #6
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Re: A Real Water Hammer Mystery!

Is this a closed system? (rpz after the water meter) When a water system has no place for expansion, opening and closing supply valves can cause unfastened pipes to rattle. Installing an expansion tank on the water heater can reduce this.
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Old 05-17-2016, 11:56 AM   #7
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Re: A Real Water Hammer Mystery!

Hope this was fixed long ago.
Adapt, Improvise, Overcome.
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Old 05-17-2016, 08:04 PM   #8
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Re: A Real Water Hammer Mystery!

we will never know i think they all passed on
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Old 05-18-2016, 12:26 PM   #9
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Re: A Real Water Hammer Mystery!

googled the problem for you, the very first result gives 3 possible (and most popular) reasons why water hummer might appear:

"The first variable is the length of the pipe the water is traveling through. We can't do much about the length of your pipes, assuming that you can't move your house closer to the water source. But it is an important factor in creating water hammer, so it is useful to take a look at it, especially as it relates to the pipe size. For example, in some situations you can force a high rate of flow through a small pipe without problems, provided the length of the pipe is short, say, a few feet. The shorter the pipe, the smaller it can be. Knowing this will help you when you try to identify the source of the water hammer. So keep in mind that a small pipe may not be a problem if it is a very short length.

The second variable is time, or specifically how fast the water is being stopped. When a closing valve is causing water hammer, time is how long it takes for the valve to close. Most irrigation valves take several seconds to close. Theoretically this would not cause a problem, as several seconds is very slow when dealing with water hammer. The valve may take a few seconds to go from full open to full closed, but it has a tendency to snap closed. Realistically the actual closing time of a typical irrigation solenoid valve is around 1/2 to 1 second. But it varies greatly, even when testing the same valve. For example, an irrigation valve closes much faster if there is higher water pressure present. It also closes faster as you increase the flow through the valve (increasing the flow creates a greater pressure differential across the valve, which causes it to close faster.) So a valve that would not cause a water hammer problem at a low flow and low pressure, will cause all kinds of problems if you increase the flow through the valve and/or the water pressure.

The third factor that influences water hammer is the velocity of the water. The faster the water is traveling in the pipe, the greater the water hammer. It is this last factor which is easiest for us to correct in a sprinkler system, so most of the suggested solutions for water hammer will be aimed at reducing the water velocity."

Hope it helps


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