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Discussion Starter · #1 ·
Back in mid-2009 dunbar plumbing (known as roast duck at that time) posted some pics of a water heater with out of plumb heater connections at the top. I believe the cause of the failure was water hammer.

Read here: http://www.hotwater.com/bulletin/bulletin11.pdf
 

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Discussion Starter · #2 ·
"Water hammer is the destructive forces, pounding noises and vibration in a piping
system when water flowing through a pipeline is stopped abruptly. When water
hammer occurs, a high intensity pressure wave travels back through the piping
system until it reaches a point of some relief. The shock wave will then surge back
and forth between the point of relief and the point of stoppage until the destructive
energy is dissipated in the piping system. The violent action accounts for “banging”,
“thumping”, and/or intense vibration in the pipe line. Although noise is generally
associated with the occurrence of water hammer, it can occur without audible sound
or noise. Quick closure always causes some degree of shock with or without noise.
The common cause of water hammer is single lever faucets (sinks/lavatories) or
automatic solenoid valves (dishwashers, washing machines, etc.). The speed of the​
valve closure time is directly related to the intensity of the surge pressure."

"The damage from water hammer can manifest itself in a number of ways. The most
common are:​
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Expanded Tank Shell - This can be demonstrated by measuring the circumference at
various locations along the shell. Pressures in excess of the maximum design working
pressure can cause permanent deformation of the shell
.

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Collapsed Flue Tube - This will choke off the ability to vent the products of combustion
causing the flame and/or combustion to spill out from the combustion chamber. Often
this will occur where thinning of the flue tube walls has occurred due to contamination
of the combustion air or because of excessive condensation
.

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Inverted or Deformed Tank Heads - Often this accompanies collapsed flues, but one

or both heads can be deformed."
 

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The Old (antique) Master
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"Water hammer is the destructive forces, pounding noises and vibration in a piping
system when water flowing through a pipeline is stopped abruptly. <snip>

All new homes we have done for the past 13-14 years have had thermal expansion tanks installed as all new houses have backflow valves. Not RPZ or testable double checks. The muncipal authorities install Watts # 7's Now the placement of the tanks was where the water came in on the house side of the meter. This did two things, took care of the thermal expansion, but also gave each house a shock absorber. Now older homes are getting a meter changeover with backflow. We have an inspector here [yep there charging a $54.00 permit fee to install a tank] that won't allow a tank to be installed if there is a valve between the tank and the water heater.
So the placement at the meter in that township is null and void. Couple that with the one authority increasing static pressure to 100+ PSI means that all tank jobs will also need a PRV. People [HO] don't understand the cost or why as a plumber I was constantly being asked questions. I put a page on the web site now they can read it
take a look ....​

 

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Discussion Starter · #5 ·
I don't see the cpvc handling the kind of static pressure it would take to deform a tank. Now if it was a galvanized system it would be a different story.

Thermal expansion can cause the same.
 

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I don't know whose technical bulletin that is, so I will take it a face value. I would not have expected water hammer....normally a brief occurrence...to cause deforming of the shell. So be it.

One thing I have seen for sure....at HD when water heaters come off the truck, they are 4 to a pallet and I have peeked back into receiving and seen them stacked 5 pallets high. Those heaters on the bottom of the stack are tweaked! I have seen wh out in the store with the nipples bent, and I assumed it was from the stacking.
 

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www.DunbarPlumbing.com
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I've encountered this problem more than once...and I actually have a few pictures of the ones I replaced, somewhere on my hard drive.

I'm not sure what caused it....but I'm thinking heat and a serious negative force. I've even seen the tops and bottoms bubbled out like a soda can in a freezer. :eek:

All I can say that most times, high pressure was part of that equation almost always, and there was no check valve at the meter or otherwise.

I was thinking possibly a hard pressure loss from hydrant cleaning or nearby fire where the fire department was called upon to save lives, and hence the hard drop in pressure without protection to the plumbing systems.
 

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Discussion Starter · #11 ·
Again, I can't see how the cpvc would hold while the tank deformed. Are you really going to tell me that the tank would go before the cpvc would due to over pressure/temp?
 

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Again, I can't see how the cpvc would hold while the tank deformed. Are you really going to tell me that the tank would go before the cpvc would?
I never saw anything said about cpvc on this thread until after I posted my 1st post.

Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?
 

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Discussion Starter · #13 ·
Simple, it has a better modulus of elasticity.

It would also withstand deep vacuum where the tank will not.


I never saw anything said about cpvc on this thread until after I posted my 1st post.

Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?[/quote]
 

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Simple, it has a better modulus of elasticity.

It would also withstand deep vacuum where the tank will not.


I never saw anything said about cpvc on this thread until after I posted my 1st post.

Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?[/quote]
The correct answer is it can be caused from thermal expansion and water hammer. Simple....as per your original reference to A.O. Smith technical bulletins both can cause the problem.
 

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Discussion Starter · #15 ·
You asked "Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?"

I answered: "Simple, it has a better modulus of elasticity."

THAT is the correct answer.

The cpvc (when new anyway) will withstand pressure cycling (water hammer) better than the steel tank will. The steel tank fails before the cpvc does.

I was also stating that the damage could have been from vacuum as well. The MIP’s would have been point out though (instead of in) if vacuum was the case I suspect.

Simple, it has a better modulus of elasticity.

It would also withstand deep vacuum where the tank will not.




The correct answer is it can be caused from thermal expansion and water hammer. Simple....as per your original reference to A.O. Smith technical bulletins both can cause the problem.
 

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You asked "Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?"

I answered: "Simple, it has a better modulus of elasticity."

THAT is the correct answer.

The cpvc (when new anyway) will withstand pressure cycling (water hammer) better than the steel tank will. The steel tank fails before the cpvc does.

I was also stating that the damage could have been from vacuum as well. The MIP’s would have been point out though (instead of in) if vacuum was the case I suspect.

You'll never convince me that cpvc will hold up to serious water hammer and the water heater will fail everytime first.
 

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Discussion Starter · #17 ·
Perhaps you should read up on material properties then. The cpvc is more elastic than the tank is. Each pressure wave will cause both the pipe and the heater swell as the wave spikes the pressure. The difference is that the cpvc will absorb the wave and bounce back where the tank will permanently deform slightly on each cycle.

Material will give to a certain degree and bounce back to it's original shape. It that deformation point is surpassed, the material will not return to it's original shape.

Think of a balloon. You can pump air into it and let it back out. It will return to it's original shape. If you pump too much into it, it will be slightly larger when it deflates. If you go even further, it will pop. The same is true for aluminum foil. If you made a sphere out of aluminum foil and piped it to the balloon they would both be pressurized to the same degree. If you were to repeatedly pressurize both of them, the foil would eventually fail because it will permanently deform on each cycle and the balloon won't.

Make's sense?

You asked "Answer me how the cpvc will survive water hammer that will deform the tank from a sudden violent pressure surge vs a static pressure surge?"

I answered: "Simple, it has a better modulus of elasticity."

THAT is the correct answer.

The cpvc (when new anyway) will withstand pressure cycling (water hammer) better than the steel tank will. The steel tank fails before the cpvc does.

I was also stating that the damage could have been from vacuum as well. The MIP’s would have been point out though (instead of in) if vacuum was the case I suspect.

You'll never convince me that cpvc will hold up to serious water hammer and the water heater will fail everytime first.
 

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Perhaps you should read up on material properties then. The cpvc is more elastic than the tank is. Each pressure wave will cause both the pipe and the heater swell as the wave spikes the pressure. The difference is that the cpvc will absorb the wave and bounce back where the tank will permanently deform slightly on each cycle.

Material will give to a certain degree and bounce back to it's original shape. It that deformation point is surpassed, the material will not return to it's original shape.

Think of a balloon. You can pump air into it and let it back out. It will return to it's original shape. If you pump too much into it, it will be slightly larger when it deflates. If you go even further, it will pop. The same is true for aluminum foil. If you made a sphere out of aluminum foil and piped it to the balloon they would both be pressurized to the same degree. If you were to repeatedly pressurize both of them, the foil would eventually fail because it will permanently deform on each cycle and the balloon won't.

Make's sense?


Sure it would make sense in a Lab but not in a residental house. The pipe is gonna move and those stainless water supply lines you use will help relieve the surge. Thats why that cpvc broke behind the ice maker you posted pics of.....the crap gets brittle and then the water hammer will break it. I bet the water heater in that house was fine but that cpvc failed.

I was simply stating that deformed tanks can be caused by water hammer AND thermal expansion....then cpvc suddenly became the topic out of thin air:whistling2:
 

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Here is a very informative link about plastic vs metal and water hammer. It seems that pvc/cpvc is so elastic that it only creates about 1/3 of the pressure surge as a metal system would. It appears to be so elastic that it deminishes the surge....When you get time read this entire page in the link.

http://www.docstoc.com/docs/22034422/Characteristics-of-PVC-Pipe
 
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