I have searched this site and others to find information on whether Dielectric Unions are really necessary when joining copper and galvanized pipes. The problem; I have found conflicting advice.
In my own case I decided to use them after replacing galvanized for copper at the lav. But both leaked at the threads... exchanged those for two others they leaked, searched the web and found posts by people with the same trouble, also found posts claiming brass fittings between the confliting metals will do nearly the same thing.

Anybody have advice or experience with or without these unions before I go down the road with toilet and shower supply lines?

O

"I have searched this site and others to find information on whether or not Dielectric Unions are really neccessary when joining copper and galvanized pipes. The problem; I have found conflicting advice."

If you recall from high school chemistry, two dissimilar (different) metals, when placed in an acidic solution, will create a battery. And one metal will usually erode away as the chemical reaction progresses. The other metal may have a buildup of new material, which may be a chemical combination of the eroded metal and the acid. Since virtually all domestic water is slightly acidic or slightly basic, this electro-galvanic action can occur in any metal plumbing system.

When copper and steel pipes are connected together directly, the "battery" has a path for electrical current to flow. (This current is tiny, and the voltage is not a safety hazard.)

If the current cannot flow, because there is no electrical connection (interrupted by the plastic insulators) then the "battery" never discharges. In theory there will always be a small voltage between the different metals. The metals do not erode.

This electro-galvanic action is called electrolysis and in time it will eat pin holes in copper pipe. Dielectric Unions are insurance and well worth the money. If you had leaks at the threads did you tape them with Teflon Tape before installing? Hope this helps, Tom

Thanks for the response Tom,
The threads were taped up well; the leak I am having on the Dielectric union appears to be coming from the female threaded end of the union at a galvanized step down bushing used to fit the 3/4" union on the existing 1/2" line... the hardware store only carried 3/4" dielectric unions.....I called the nearby low-depot big box and they have three varieties of dielectric unions, including the 1/2" in stock. So I'll try another.

"The noise is emanating at each dielectric coupling like a loudspeaker."
Please describe the nature of the noise. Is it a loud thump, a high or low vibration? A shrill squeel? Describe it as best you can. Thanks, tom

The noise is not a thump nor vibration, more like a shrill. It seems to increase in volume depending on how open my neighbors faucet/shower is.

The other pipe is for a common faucet outside and behaves the same way, based on how open the valve is.

The noise does travel down the pipes, but insulating and trying different straps has no effect on the noise coming from the coupling/union.

Any thoughts?
Thanks.

Antonio

Noise is caused by vibration. Vibration is caused by the water rushing past a object that's loose enough to vibrate. In your case the larger volume of water the more vibration,(noise).
In a dielectric union there's only one componate that's not a part of either part of the union and that's the black washer,( see images).
The only other thing it could be is a loose pebble that got sucked up and is caught in the union, but since it's happening in both unions we can discount that.
Has any body put a wrench on the nut and tried to tighten it while its making the sound? Perhaps it's just tight enough so it holds water pressure but a tiny part of the washer catches the flow and vibrates. Tip: While tighting the nut put a pipe wrench on the copper side to back the other wrench up and stop the fitting from giving or turning. If all else fails why not simply replace the unions? Regards, Tom

Hydraulic "water hammer" occurs when there is no shock absorber in the line. Union has nothing to do with your squeal.

Find a line at a convenient joint and place a Tee, open pointed up. To the open install a vertical pipe, with a reducer opening in one size larger. To this larger opening place a 6"-8" nipple, with a cap on the open end.

When all joints are sealed, turn on the water. The "air spring" you have made will trap and hold air, compressed by the water pressure in the Tee. When a vibration is caused by a small pressure flow or other sudden pressure change, the air spring will react to cancel the noise.

Or, the device can be bought ready to install at the lowedepo.

Bobby99

Bobby has just giver you iinstnstructions on how to build and install a "air chamber".

Doesn't sound like hammering. Could be that unions are not tight enough. Also, did plumber ream copper pipe after cutting. Ridges in pipe cause turbulence and noise.

The origenal post is more than 4 years old, Thanks.

John

Nice & helpful answer. Thank you.

Hi,
The main function of the dielectric union is just to separate the two dissimilar pipes to avoid galvanic reaction as what Tom explained.Galvanic reaction will not only damage your pipes but definitely will shorten also the life span of your water heater or what ever equipment attached on it.

Proper plumbing installation method certainly will avoid leaking and abnormal noise in the system. The best thing will you do, call an experienced plumber to install the dielectric union and learn directly from him.

Moncatar M.