Any Plumbers Here?

[Souschef]

I think it was mentioned earlier, you could have a water hammer problem near that DW.

A nearby faucet or other solenoid valve shutting off/on can cause a high pressure shock wave down the pipe. It would weaken as it goes down the line, so other units would not be affected.

I didn't realize they make them with screw on fittings too, you might not even need a plumber, or need to do any soldering. They come in a variety of configurations, two examples:

https://www.homedepot.com/p/Homewer...rrestor-with-No-Lead-526-4-38-38B-Z/304826664

https://www.homedepot.com/p/Homewer...ater-Hammer-Arrestor-526-1-34-34B-Z/304826698

These have a bladder in them, which is better than the old "solder a vertical stub" approach. The trapped air eventually is absorbed by the water, the bladder prevents that.

I will sometimes get some water hammering at a couple fixtures, and draining the water from the pipes to get air back in those stubs helps, but it's a pain. I might get a couple of these myself.

-ERD50

+100
I had a problem with water hammer when the drip irrigation solenoids opened. I put one with a 3/4 inch thread next to the valves. Problem solved.

 

[target2019]

Out of all the dishwasher intake valves I've been through, the last one was a non-Miele valve. The Miele valves lasted a couple of years before they stopped working, whereas the non-Miele valve (Frigidaire) lasted only less than four months.

My valve is on the hot water line (even though I think the dishwasher has the ability to heat the water if it was on the cold water line). I'm wondering if anyone knows if it could be possible that my intake valves failed because of the high water temperature. I couldn't find anything about acceptable maximum water temperature in the specs of the Frigidaire valve. It would seem kind of odd to me if that were the case.

Dishwasher manual should have the specs for temperature and pressure. Those would apply if the replacement valve is to manufacturer's specs.

 

[NgineER]

Out of all the dishwasher intake valves I've been through, the last one was a non-Miele valve. The Miele valves lasted a couple of years before they stopped working, whereas the non-Miele valve (Frigidaire) lasted only less than four months.


My valve is on the hot water line (even though I think the dishwasher has the ability to heat the water if it was on the cold water line). I'm wondering if anyone knows if it could be possible that my intake valves failed because of the high water temperature. I couldn't find anything about acceptable maximum water temperature in the specs of the Frigidaire valve. It would seem kind of odd to me if that were the case.

All dishwashers I have experience with are on a hot water line, so I don’t think that would be an issue.

 

[Vincenzo Corleone]

I think I just realized what might be causing, at least part of, my problem. I have a tendency to slam the dishwasher door shut every time I open it. I wonder if that is causing a shot of air to travel back into the hose and valve.


Am I completely off my rocker with this thought?

 

[ERD50]

I think I just realized what might be causing, at least part of, my problem. I have a tendency to slam the dishwasher door shut every time I open it. I wonder if that is causing a shot of air to travel back into the hose and valve.


Am I completely off my rocker with this thought?

Yes.

The thing about water hammers - liquids are (essentially) non-compressible. So when a valve closes and pushes on the water behind it, that "push" has to go somewhere. It doesn't compress, it is just like hitting the end of the pipe with a hammer (hence the name). For all intents and purposes, that contained liquid acts just like a strong steel bar.

This is how our car brakes work (since about 1930). Hydraulic oil in "pipes" (brake lines) is compressed by your brake pedal (and assisted with power brakes), and travels all the curves and corners to the brake cylinder, and pushes just as hard on the end as your (assisted) push at the pedal.*

Air is compressible. It just goes "ooomh" a little. No harm done. Not like a hammer at all.


* This is why it is important to not ride the brakes on a long downhill slope, and to keep your brake fluid clean. If the brake fluid has absorbed any moisture, that water will turn to steam if the brakes get really hot. Steam is a gas, and is compressible;e. Yikes - no pushing at the brake cylinder! It just compresses rather than pushing like a solid.

-ERD50

 

[Vincenzo Corleone]

I read about water hammer in the context of solenoid valves and came to better understand the issue. I'll look into installing a water hammer arrestor.

Thanks for your help, everybody.

 

[Winemaker]

I don't know if this was mentioned earlier. Does your water heater have a pressure/expansion tank installed on the output? If you don't, I believe that is the culprit of your problem. As ERD50 states liquids are non compressible, and as the hot water expands in these newer plumbing systems because of lower pressure settings(150#), the cheaper plastic faucet cartridges leak. I have Moen faucets installed in my apartments and in one apartment the faucet always develops a leak after a few months on the hot side. After installing the expansion tank, problem solved. Since your dishwasher is/should be tapped to your hot hot line, the dishwasher valve is the weak link that fails. Install a expansion tank, or check the age/pressure on the existing one, they do fail also.

 

[Vincenzo Corleone]

I don't know if this was mentioned earlier. Does your water heater have a pressure/expansion tank installed on the output? If you don't, I believe that is the culprit of your problem. As ERD50 states liquids are non compressible, and as the hot water expands in these newer plumbing systems because of lower pressure settings(150#), the cheaper plastic faucet cartridges leak. I have Moen faucets installed in my apartments and in one apartment the faucet always develops a leak after a few months on the hot side. After installing the expansion tank, problem solved. Since your dishwasher is/should be tapped to your hot hot line, the dishwasher valve is the weak link that fails. Install a expansion tank, or check the age/pressure on the existing one, they do fail also.

Thanks for the input, but I don't live in a house. I live on the 25th floor of a 31-story high-rise building, so no access to water heaters, tanks, boilers, etc.

 

[Ronstar]

Thanks for the input, but I don't live in a house. I live on the 25th floor of a 31-story high-rise building, so no access to water heaters, tanks, boilers, etc.

I’ve heard that high rise buildings deal with water on a floor by floor basis. Easier to maintain standard water pressure. Unchecked, there would be huge pressure differences between upper and lower floors.

 

[Vincenzo Corleone]

I’ve heard that high rise buildings deal with water on a floor by floor basis. Easier to maintain standard water pressure. Unchecked, there would be huge pressure differences between upper and lower floors.

This animation might explain what I think is happening and how the water hammer arrestor would help. Imagine the valve in the video is my dishwasher intake solenoid valve.

When the solenoid shuts the valve closed, the surge of water pressure - without the arrestor - hits the plastic, closed valve.

 

[Vincenzo Corleone]

It's now past the point in time where the previous intake valve failed. So far, so good with the new valve. It looks like my problem was indeed water hammer.

Thanks all.

 

[Vincenzo Corleone]

It's now been over two years since I replaced the valve and installed the water hammer arrestor and all is still well. Thanks to Winemaker, ERD50 and others who pointed me in the right direction.

I wonder - is the only way to find out when a water hammer arrestor fails is when a leak develops? Anyone know how often those things need to be replaced?

 

[freedomatlast]

Did you use teflon tape and/or pipe thread sealant on those threads when you installed the elbow? If not, disassemble, apply the sealant, and reassemble.

Please don't EVER EVER EVER use teflon tape or sealant on the threads of a compression fitting.

Teflon tape is only used on tapered threads such as pipe thread.

Nothing screams amateur louder than seeing teflon tape or sealant on non-tapered threads.

Another misuse of teflon tape I've seen is on flared brake line fittings on cars. Unbelievable!

Again, if it's not tapered thread, you don't need or want tape or sealant on the threads.

Come to think of it, maybe this belongs in the pet peeve thread.

 

[ERD50]

It's now been over two years since I replaced the valve and installed the water hammer arrestor and all is still well. Thanks to Winemaker, ERD50 and others who pointed me in the right direction.

I wonder - is the only way to find out when a water hammer arrestor fails is when a leak develops? Anyone know how often those things need to be replaced?

Thanks for the update.

I'm normally made aware of water hammering by the.... "hammering" sound of the pipes when the valve closes. Since this isn't exactly predictable on a dishwasher, you'll have to make a point of listening for it. I don't know of any other way.


-ERD50

 

[Vincenzo Corleone]

Thanks for the update.

I'm normally made aware of water hammering by the.... "hammering" sound of the pipes when the valve closes. Since this isn't exactly predictable on a dishwasher, you'll have to make a point of listening for it. I don't know of any other way.


-ERD50

In my case, any hammering sound was never really noticeable before I installed the arrestor - maybe just one quick "thunk" when the valve closed. I'll have to pay attention.

 

[JoeWras]

Please don't EVER EVER EVER use teflon tape or sealant on the threads of a compression fitting.

Teflon tape is only used on tapered threads such as pipe thread.

Nothing screams amateur louder than seeing teflon tape or sealant on non-tapered threads.

Another misuse of teflon tape I've seen is on flared brake line fittings on cars. Unbelievable!

Again, if it's not tapered thread, you don't need or want tape or sealant on the threads.

Come to think of it, maybe this belongs in the pet peeve thread.

Yesterday, as I was wrenching down a new compression shut off valve for my dishwasher, I actually pondered the genius of soft brass digging into copper and backing against a hard cone shaped nut.

It's a very old sealing method and is simple and clever.

 

[ERD50]

Please don't EVER EVER EVER use teflon tape or sealant on the threads of a compression fitting.

Teflon tape is only used on tapered threads such as pipe thread.

Nothing screams amateur louder than seeing teflon tape or sealant on non-tapered threads.

Another misuse of teflon tape I've seen is on flared brake line fittings on cars. Unbelievable!

Again, if it's not a tapered thread, you don't need or want tape or sealant on the threads.

Come to think of it, maybe this belongs in the pet peeve thread.

I agree that it should never go on the threads of anything other than a tapered pipe thread fitting. Never on the threads of a compression or gasket-ed fitting.

But...

I was able to find this video I watched years ago, where the creator "SeeJaneDrill" shows a trick (at the end of the video) of applying some Teflon tape to the ferrule of a compression fitting. It shouldn't normally be needed, but in a tough case (slightly malformed ferrule that would be difficult to remove) it could save the day. Tip is near the end of the video, but the rest is right on as well.

Yesterday, as I was wrenching down a new compression shut off valve for my dishwasher, I actually pondered the genius of soft brass digging into copper and backing against a hard cone shaped nut.

It's a very old sealing method and is simple and clever.

I haven't taken it apart, but the valve for my CO2 tank (for home-brew beer dispensing) is at ~ 860 PSI, and it sure feels like a steel needle valve setting into brass when you close it. As you say, that would just force the brass to conform - no leaks!

-ERD50

 

[freedomatlast]

I was able to find this video I watched years ago, where the creator "SeeJaneDrill" shows a trick (at the end of the video) of applying some Teflon tape to the ferrule of a compression fitting. It shouldn't normally be needed, but in a tough case (slightly malformed ferrule that would be difficult to remove) it could save the day. Tip is near the end of the video, but the rest is right on as well.

-ERD50

I sure hope people don't consider that a permanent fix. I'd only ever do that as a temporary fix till I went to the store to get the materials to come back and fix it correctly. Why people would take a chance on that starting to seep over time, causing major damage is beyond me.

That little "tip" certainly qualifies for the Shoddy Workmanship Thread.

Over the years, I've helped many different people out with problems that almost always originated because someone at some time tried to take a shortcut, and didn't use the right materials or didn't apply or work with them, the correct way. And it's usually at the most inconvenient times, that they have to go back and redo the job correctly after they repair all the damage that was caused as a result.

And if I witnessed a plumber doing that, it would be the last job he would do for anyone I know.

 

[JoeWras]

I sure hope people don't consider that a permanent fix. I'd only ever do that as a temporary fix till I went to the store to get the materials to come back and fix it correctly. Why people would take a chance on that starting to seep over time, causing major damage is beyond me.
...
And if I witnessed a plumber doing that, it would be the last job he would do for anyone I know.

My dad was a master journeyman plumber from 1948 to 1990. Long career, and he had the joint (human) replacements to prove it.

He's rolling over in his grave (RIP, Dad, all in fun) over some wise-person suggesting using Teflon tape anywhere near a compression fitting.

Look, he embraced the tape when it appeared sometimes in the 70s. He was more than happy to put the pipe dope can down.

But man, no way on compression. It is all about the beautiful metal which just conforms to the perfect seal.

 

[ERD50]

I sure hope people don't consider that a permanent fix. I'd only ever do that as a temporary fix till I went to the store to get the materials to come back and fix it correctly. Why people would take a chance on that starting to seep over time, causing major damage is beyond me.

That little "tip" certainly qualifies for the Shoddy Workmanship Thread.

... .

...
He's rolling over in his grave (RIP, Dad, all in fun) over some wise-person suggesting using Teflon tape anywhere near a compression fitting.

Look, he embraced the tape when it appeared sometimes in the 70s. He was more than happy to put the pipe dope can down.

But man, no way on compression. It is all about the beautiful metal which just conforms to the perfect seal.

No question that it isn't the 'proper' way to do it. But IMO, you *might* just be being a bit too much of a purist.

Just like tape fills a gap in the tapered threads, some small malformation of that compression ring could be filled by the tape. I don't see any reason it should be any more likely to leak down the road.

Tape on the threads of anything but a tapered thread is a no-no because it can restrict the parts from threading all the way on, which is needed to compress the gasket or ferrule. A *little* tape on the ferrule is unlikely to interfere with that.

Not trying to change your mind, just giving a different perspective.

-ERD50

 

[JoeWras]

No question that it isn't the 'proper' way to do it. But IMO, you *might* just be being a bit too much of a purist.

Just like tape fills a gap in the tapered threads, some small malformation of that compression ring could be filled by the tape. I don't see any reason it should be any more likely to leak down the road.

Tape on the threads of anything but a tapered thread is a no-no because it can restrict the parts from threading all the way on, which is needed to compress the gasket or ferrule. A *little* tape on the ferrule is unlikely to interfere with that.

Not trying to change your mind, just giving a different perspective.

-ERD50

Yeah, I concede your point.

I think Dad was just trying to teach me right and not let me get lazy and use crutches.

He was the same way about cutting threads on galvanized pipe. "If you have to use that much dope, you cut the thread wrong! Start over."

 

[freedomatlast]

No question that it isn't the 'proper' way to do it. But IMO, you *might* just be being a bit too much of a purist.

Just like tape fills a gap in the tapered threads, some small malformation of that compression ring could be filled by the tape. I don't see any reason it should be any more likely to leak down the road.

Tape on the threads of anything but a tapered thread is a no-no because it can restrict the parts from threading all the way on, which is needed to compress the gasket or ferrule. A *little* tape on the ferrule is unlikely to interfere with that.

Not trying to change your mind, just giving a different perspective.

-ERD50

Correct. I agree the tape is made so that as you turn the tapered pipe fitting, it packs into the threads creating a seal.

I don't see this working the same way on a ferrule of a compression fitting because it seems tape would be more likely to just tear as the fittings are rotated. I would think the teflon paste would have a better chance of working in that application, however I certainly would not recommend it either. This is just my opinion and I have no data to back this up, just a hands on feel from working with the stuff for five decades.

 

[skyking1]

Yes best of luck thinking that tape will stay where you intend when you rotate a part against it as it tightens down.
I've used both tape and dope on some tricky tapered pipe threads. That is my common practice on PVC threaded adapters I don't want to worry about. They are soft and sloppy threads.
Single properly applied lick of tape, followed by the teflon dope.
If at all possible i use the banded female adapters, but sometimes you arrive at female threads.