Installing Water Hammer Arrestor at the End of a Long Pipe Run

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WorldPeace

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Location of a Water Hammer Arrestor.

I'm trying to minimize the water hammer emanating from my fixtures. I know they are typically placed as close as possible to the fixture's valve. But, instead of placing one at every single fixture, I was thinking about creating a whole-house arrestor by placing it at the end of a long run of pipe right before it goes into the home-run manifold. Is this a good place, considering the physics of the water hammer?

I'm speculating the water hammer is created because of the long run which allows the water to pick up momentum. By placing a water hammer arrestor directly at the end of the run, it'll take the full force of the impact. I'm also considering using water hammer arrestors built into elbows rather than a coupling. I'm speculating they are more effective than ones located above a coupling. If it's located at an elbow, I'm speculating it would soften the direct run more effectively. At the top of the coupling, most of the water momentum would simply travel forward, bypassing the arrestor. Does anyone know if this is true?

Where can I buy the chamber-style arrestors with a diaphragm?

I've read the ones with pistons eventually fail while the ones with a diaphragm are much more reliable. And, some are even rechargeable. Does anyone know where I can buy them for a fair price?
 

LLigetfa

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It is less about the direction of travel and more about the mass but I do factor in an abrupt change of direction as a consideration. If there is enough mass after the hammer arrestor, there will still be water hammer and the arrestor depending on style can in theory reflect energy into the flow.

There are arrestors made to go inline on the supply hoses which are at the end of the run. Watts make a diaphragm version with garden hose thread.
https://www.watts.com/products/plum...ing-specialties/water-hammer-arrestors/lf150a
 

Reach4

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'm trying to minimize the water hammer emanating from my fixtures.
Fixtures that trigger water hammer are dishwasher, clothes washer, ice maker, maybe toilet, right? Anything else? Showers, tubs, lavatories should not cause water hammer.

What is your water pressure?
 

Terry

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From the Sioux Chief web site.

What Is Water Hammer The term “water hammer” is used to describe the pressure surges, audible noise and destructive forces associated with the transfer of kinetic energy into the piping system due to an abrupt change in velocity of a non-compressible fluid. For the purpose of this discussion, the non-compressible fluid is usually water, and the change in velocity usually occurs when the flowing water comes to a sudden and complete stop due to valve or faucet closure. Thus, in the equations below, the initial flowing velocity is always equal to the change in velocity. (Example: Initial flowing velocity is 8 feet per second and, when the flow is completely stopped, zero feet per second. The change in velocity is 8 - 0 or 8 fps, which is equal to the initial flowing velocity of 8 fps.) The two main factors necessary to create water hammer in a piping system are the initial speed (velocity) of the flowing water and an abrupt change to this flowing water velocity. When a water column is stopped abruptly, the momentum force in the flowing water (kinetic energy) quickly transforms into a pressure rise within the pipe. The amount of force (KE ft/lbs) within the flowing water can be calculated by the formula for kinetic energy:

KE = ½ mv²

When considering KE within a piping system, the mass (m) can be substituted with the physics characteristics of water within a cylindrical pipe (i.e., specific weight, cross-sectional area, length, plus gravitational constant). Velocity (v) is calculated in feet per second (fps), which can easily be converted from the known gpm and pipe size. For a plumbing or piping system, the kinetic energy formula can be expressed as this: This section covers the physics of uncontrolled water hammer and its damaging effects as they pertain to any piping system. We also review the history of water hammer in plumbing systems, previous attempts to control water hammer, and why these methods failed. KE = .97 x A x L x v²

A = Cross sectional area of pipe I.D. in square feet

L = Length of effective pipe in feet

v = Velocity of flowing water in feet per second

Since we can calculate the kinetic energy, we can also calculate the actual “pressure rise” within a piping system by using Joukowsky’s Formula:

pr = wav / 144g pr = Pressure rise above flow pressure (psig)

w = Specific weight of liquid (water = 62.4 lbs/ft ³)

a = Velocity of pressure wave in feet per second (fps) (4000 – 4500 fps in metal pipe)

v = Change in flow velocity in feet per second (fps)

g = Gravitational constant (32.2 fps²)

water-hammer-arresters---engineer-report.pdf (siouxchief.com)

icemaker-box-install-3.jpg


Icemaker box with hammer arrestor.
 
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WorldPeace

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Hey, Reach,

Actually, my shower and tub also cause water hammer in addition to the toilet, dishwasher, etc. I don't know what my water pressure is. I just ordered a pressure gauge to check to see if it's below 85 PSI. I'll let you know what it is once I measure it. If it's too high, I guess I have to install a pressure-reducing valve.

Fixtures that trigger water hammer are dishwasher, clothes washer, ice maker, maybe toilet, right? Anything else? Showers, tubs, lavatories should not cause water hammer.

What is your water pressure?
 

jadnashua

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It all depends on the design of the valve whether using it is subject to water hammer. There are some tub/shower valves that call for a hammer arrester to be installed. MOst won't need one. Some toilet valves could use one. IT gets worse when your water pressure is higher, as that causes the water to flow faster, thus having more kinetic energy (K=1/2 mv^2, so the velocity factor goes up non-linearly).
 

WorldPeace

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I'm wondering what people's opinions are with respect to a home water pressure of 60. I finally received my water gauge, and I determined that the water pressure is 60 at the exterior hose bib.

Is this high enough to warrant installing a pressure-reducing valve to 50 PSI?

Or, should I install water hammer arrestors at each of the fixtures (e.g. Bathtub, kitchen sink, dishwasher, clothes washer, and toilets)?
 

Terry

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Most PRV's come factory set for 60 PSI.
Plumbing code allows up to 80 PSI.
Normally we only install hammer arrestors at the dishwasher, washer and icemaker.
 
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Reach4

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Actually, my shower and tub also cause water hammer in addition to the toilet, dishwasher, etc.
Water hammer is a single bang that happens as you suddenly turn off a valve that stops a flow. Does that describe what you hear?
Is this high enough to warrant installing a pressure-reducing valve to 50 PSI?
No.

To try your idea of a whole house hammer arrestor, you could connect a small well pressure tank. I don't expect much result, unless your house is being supplied by a really long run of fairly small diameter pipe. is an example of a quality small tank. You would set the air precharge to maybe 55 psi.
 
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WorldPeace

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Water hammer is a single bang that happens as you suddenly turn off a valve that stops a flow. Does that describe what you hear?

No.

To try your idea of a whole house hammer arrestor, you could connect a small well pressure tank. I don't expect much result, unless your house is being supplied by a really long run of fairly small diameter pipe. is an example of a quality small tank. You would set the air precharge to maybe 55 psi.

Thanks for the recommendation! It sounds like a small well pressure tank is just a larger form of a water arrestor like the Watts LF150A. I'll try it out and let you know if it works.

*Btw, the water hammer does come with a single bang that I can hear/feel in the rest of the house. For example, when someone turns off the tub quickly upstairs, you can hear it downstairs with a thud. Same thing with our dishwasher, clothes washer, toilet, etc. It's not a big deal but just slightly annoying.
 

WorldPeace

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Most PRV's come factory set for 60 PSI.
Plumbing code allows up to 80 PSI.
Normally we only install hammer arrestors at the dishwasher, washer and icemaker.

Thanks for the helpful info. I had thought of forgetting the hammer arrestors and just installing a PRV but scratch that idea. I'm actually going to try Reach's idea.
 

Jeff H Young

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real world Water hammers occur on any fixture and their is no substitute for piping a house correctly and strapping correctly . You can put an arrestor in the proper place and get the best results . I've put them other places and gotten improvement. usually ripping all the walls open isn't an option . and all that mathematical stuff is very handy at understanding why but seldom helps on an existing build because it is what is.
undersized piping poorly strapped are the 2 biggest causes in my opinion , yea we should have one at the A/W , D/W and IM but if they don't hammer and I'm not building it or repiping I don't bring it to owners attention . like if I'm called out to install a garbage disposal or water heater I don't go looking around for a missing water hammer or ask them if they want me to check
 
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