Dielectric action question

For years I used dialetric unions to trans. from Galv. pipe to copper. About 3 years ago I started using brass nips. and a Fem. adp. to do it on 1/2" lines in peoples homes who didn't want to change out all the water pipe. For some reason I thought this was O.K. I have done some checking and it seems it is not.

My question is if 2 dissimilar metals coming in contact with each other in the presence of an electrolyte, in our case water, and where a conductive path exists creates the problem, then why do Water Heater Mfgrs. use brass T&P valves and some brass drain valves?

dielectric

Your original premise is correct, and it is not just water heaters. Brass valves have been used on steel pipes since the two were invented. How many connections between them have you ever had to change because the pipe deteriorated? The companies that use plastic drain valves are using them because they are cheap, not because of any dielectric problem. And what would they make a T&P valve out of?

hj said:

Your original premise is correct, and it is not just water heaters. Brass valves have been used on steel pipes since the two were invented. How many connections between them have you ever had to change because the pipe deteriorated? The companies that use plastic drain valves are using them because they are cheap, not because of any dielectric problem. And what would they make a T&P valve out of?

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O.K. Thanks !!!!

One reason the WH has an anode rod is to prevent corrosion at places where the steel of the tank is exposed, such as at the threaded bosses.

tanks

There is not supposed to be any exposed steel. The anode rod is to protect against cracks, chips, and imperfect glass lining. However the steel in a water heater element base can cause rusting if you do not use one with its own cathode protection.