Water hammer arrestor for dishwasher

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Chris Tjoumas

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Hi,

I am installing a new dishwasher and was curious if I should install a water hammer arrestor. I have cpvc running through the house and had seen that this may not require a water hammer, but the builder installed one on the supply line to the dishwasher in the kitchen, so I thought I should.

Assuming I should install one, I wanted to know if there is a specific way of doing it. Right now, there is a shutoff valve with one outlet where the hot supply for the faucet is connected to. The pipe from the wall is about halfway up the cabinet. In my kitchen, the supply lines come from the bottom of the cabinet, so the arrester comes out horizontally and then a pipe is coupled out of the top of that T so it goes straight up and then a shutoff is installed. So for this cabinet, I was thinking of having a T on the pipe from the wall so that one end faces the front of the cabinet where I’ll instal the shutoff for the faucet and then the other end would face to the right towards the dishwasher. From there, I was thinking of using a coupling to extend out a few inches and putting a T there with one end facing to the right towards the dishwasher where I’d install the hammer and the other end facing up where I’d put an inch or so coupling going straight up to the sink and install a shutoff there for the dishwasher.

Hopefully that all makes sense. A couple of questions: 1) when making the first coupling to go towards the dishwasher for the arrestor and shutoff, does it need to be any specific distance apart from the faucet shutoff 2) on the last T where I add a vertical coupling to go up, does it matter if it goes up (arrestor then shutoff above) or down (arrestor then shutoff below)?

Thank you!
 

WorthFlorida

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It wouldn't hurt to add one. I'm assuming you're adding a second dishwasher in another part of the home, or did you meant to say the builder added for the the washing machine?

There are various ways a add one, just google "water hammer arrestor for dishwasher". BTW, if you get a higher end DW that is rated less the 50db for noise, the water valve closes much slower to eliminate noise. We had a Bosch unit rated around 48 db and you could not hear the water shut on and off. Recently, I replaced it with a SAMSUNG rated at 38db. It's dead quite. My home is all CPVC and the only place with a hammer arrestor is at the washing machine.
 

Chris Tjoumas

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Yep, 2nd dishwasher in another part of the home. I had been searching quite a bit and it seems that there isn't really a wrong way to install it - I was messing around with some dry fitting and think the best way is to add a T to the stub from the wall so the openings point up and towards the opening of the cabinet, then on the up part, install the shutoff for the faucet and for the other opening towards the front of the cabinet, extend out a few inches with a coupler and add a T there so it points up and down and on the up, I'd add the arrestor and on the down, i'd extend it a little and add a shutoff for the dishwasher. All of this probably makes zero sense without a picture ;)

That's exactly what I was wondering - I have a bosch 800 series that is 40db. I didn't see anything in the manual or anything I googled on that model that stated whether an arrestor was required or not. I wasn't so much worried about any hammer noise, but any possible impact to the pipes or the dishwasher itself if any pressure did occur.

I may end up just installing an arrestor with the configuration I tried to explain, unless you or anyone else thinks it's not needed. However, I would also love to use compression shutoff valves, but I cannot find any at home depot which are for CPVC; only copper, unless I'm not searching properly online or just not seeing it in the store.

Thanks!
 

WorthFlorida

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There are no compression fittings for CPVC. I glue, use shark bite or push and connect fittings. Most of my home is Push and Connect or Sharkbite. New dishwasher water valves does not slam shut as they did many years ago, therefore, a hammer affect is minimal. If you have a separate water heater, adding an expansion tank is more effective keeping pressure down.

1/2-in Push-to-connect x 3/8-in Od Compression Brass Quarter Turn Stop Angle Valve https://www.lowes.com/pd/SharkBite-...mpression-Quarter-Turn-Angle-Valve/1000413639
 

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Chris Tjoumas

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I wonder then what the plumber used for the shutoff! I took it off but the ring is stuck on so I got a sleeve puller to remove it - until then I can't tell what it is, but it didn't look like a copper ring. I do have an expansion tank on my water heater as well, so maybe it's not worth adding an arrestor, but I do think it would be good to have one shutoff for for the faucet and one for the dishwasher, so I'll still re-plumb and add the arrestor. I did pick up some shark bite valves as well as valves I can cement to cpvc so I'll choose betwen them; just adding a compression coupling to the stub out of the wall so I don't ever have to cut that.

Thanks again!
 
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