water hammer arrestor location and orientaion - unusual pipe setup


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Old 11-30-23, 09:26 PM
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water hammer arrestor location and orientaion - unusual pipe setup

Recently had my dish washer professionally replaced and started having water hammer issue when using the dish washer. The old dish washer had a really thin supply line (my guess is 1/4") and even though I have only used the old machine a few times (I think the old washer is as old as the house which was built in 1980) and I never heard any hammering sound. The new dish washer's manual recommended the 3/8" supply line and that was what's used.

I am planning to add an arrestor. Water line under the kitchen is a little oddball. I have drew out 2 possible locations and orientations of the arrestor. Picture attached at the bottom. Option red is obviously straight forward, just shut the valve off at the angle stop, unhook the 3.8" supply line and add a 3/8" arrestor from there, resulting in a diagonal orientation for the arrestor. Option green requires shutting off the main water line, adding an elbow, then a T, to fit a screw-in 1/2" arrestor, then an short extension of pipe, then relocate the whole angle stop + supply line from there, all because I hear that the arrestor must be vertical and face up.

Which set up is most appropriate?

Bonus question: since the manual just "recommends" 3/8" line, what if the installation used 1/4" line like the old machine did, could it have possibly avoided the water hammer problem altogether?


 
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Old 11-30-23, 10:12 PM
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The hammer is caused by the larger line and the abrupt solenoid shutoff.
Some appliances have a different solenoid available.

The arrestor mounted on the end of the valve is fine.
Turning the valve is ok too. Not a major problem as it's a compression valve.

The 3/8" line would allow for faster fill up. Not really a problem but dishwashers fill with water based on a timed setting. If you restrict the flow the tub may not fill properly.
 
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Old 12-01-23, 11:08 AM
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Most (all?) newer water hammer arrestors can be installed in any direction. So you don't have to reorient the shutoff unless it's more convenient. It also connects to the existing 3/8" shutoff, making installation simple.

https://www.supplyhouse.com/Oatey-34...ammer-Arrestor


 
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Old 12-01-23, 03:17 PM
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I appreciate the answers and the product link.I have already purchased a 3/8" arrestor from the local hardware store, that's the same style as in the one found on supplyhouse.com and will go ahead and install it and report back.
 
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Old 12-06-23, 07:17 AM
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arrestor installed

Here is the installed arrestor. Hammer did not go away but the sound of it has lessened greatly. I used to be able to feel it through the floor also and now no more. I don't think the problem is solved and only through this I realized that the hot water plumbing in the house may have bigger issues as intermittent knocking sound in the pipes can be heard when the hot water is running in both the upstairs and downstairs bathroom, sound goes away when faucet is shut. Will do some research and perhaps post questions in another thread. Any additional advice is appreciated.


 
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Old 12-06-23, 08:38 PM
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It would be a good idea to get a baseline pressure measurement.
Your water pressure may be too high.
You may have a PRV (pressure reducer) on your service and could benefit from a pressure tank in the system.

3/4" pressure gauge
 
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Old 12-12-23, 11:12 AM
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...intermittent knocking sound in the pipes can be heard when the hot water is running
This is likely the pipes expanding as they get warm. If the holes through the joists are too tight, the pipes expand, and get 'stuck', and then release as they expand more, rubbing/knocking against the joists.

It's conceptually easy to fix, you just need bigger holes... but in reality, it's a hard problem to actually solve since there's no easy answer without removing pipes (and wallcoverings too). I've been in a house that all the heating pipes have this problem and it's annoying to say the least.
 
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Old 12-28-23, 11:14 AM
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Are there better brands than others? I tried EFIELD on a washing machine and they worked well for 3 weeks and then the hammering returned. I returned those and am trying Sioux Chief. It's not quite as good as when the EFIELDs were first installed but they are working. It's been about 3 weeks. EFIELDs on the toilets didn't work at all. No change. Can there still be residual hammering or should it be completely eliminated?

As mentioned in another thread where it was said hammering doesn't happen turning water on, I also have a single hammer knock when I turn the kitchen hot water on. I can't explain it but I wanted to add that I see it also.
 
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Old 12-28-23, 12:37 PM
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The best arrestors are like mini pressure tanks with a rubber bladder inside. Those type often can be installed in any orientation. Old school was to simply T into the water line and have a foot or so of pipe vertical and capped off so it trapped air. This type of arrestor usually says it must be installed vertically. The old pipe ones work great at first but depending on your water can become water logged (loose the air by dissolving into the water) and stop working.
 
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Old 12-28-23, 12:50 PM
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Does a whole house arrestor exist? And work? Like an expansion tank or are arrestors only useful at the valve? I was hoping someone might say Sioux Chief or Oatey are the best and avoid knock offs. I notice all of the cheap ones on Amazon appear to have the same silver mechanism, where Sioux Chief seems to be a different design.

I read a time ago if you install a one or 2 foot vertical pipe air arrestor to put a T with a spigot below it to let the water out of the vertical pipe. I suppose if you have a lower drain than the vertical pipe this isn't needed.
 
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Old 01-01-24, 02:49 PM
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I've never used the knockoff arrestors. I'd imagine they are similar design, but who knows?

Have you checked the water pressure? I'm wondering if there's a bigger issue with too-high pressure in the house that would be better solved with a PRV or expansion tank.
 
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Old 01-05-24, 10:03 AM
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Thank you. I got a toilet stuck to run intermittently so I could test this more. This toilet has a new arrestor on it (I tried EFIELD and currently installed a Sioux Chief). So I found the problem! I have recirculating hot water and the input to the pump has a swing check valve. A spring loaded one was too strong for the pump to open. It's got a decent Grundfos pump. If I turn off the cutoff after the check valve, no hammer. Before I waste time, do you think a hammer arrestor after the check valve will solve this? Interesting: I've had this pump in for over 4 years and only a few months ago has this gotten really noticeable. Oh, my street water PSI was 60 PSI last time I checked.
 
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Old 01-08-24, 10:53 AM
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my street water PSI was 60 PSI last time I checked.
Great, so that's likely not a contributing issue.

​​​​​​​do you think a hammer arrestor after the check valve will solve this?
That's a good question and to be honest, I'm not sure. A swing check valve shouldn't be causing the hammer. I would imagine the pump isn't causing enough velocity in the piping to cause it either. But it's not something I've had much experience with, so I'll defer to others who may have a better suggestion.

​​​​​​​At least you've narrowed it down to the recirc system.
 
 

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