larry moe 'n curly wrote:
Jeff Wisnia wrote:
larry moe 'n curly wrote:
I recently bought a State brand heater containing two
anode rods. One rod screws in the normal way, but
the other hangs from the hot water outlet by a 1" piece
of plastic, and it's definitely insulated from the tank.
So does this mean that the anode doesn't have to directly
contact the tank?
Is there any possibility that that "second piece" is somehow
in the wrong place and it's really the "drop tube" for the
cold water inlet? You did call it a "rod" and not a tube,
so excuse me if I'm making a WAG in the wrong direction.
But I too would like to know its function if it's really
insulated from the tank shell.
Maybe the plastic hanger is conductive?
The second anode rod looks a lot like this:
www.waterheaterrescue.com/images/ComboRodTop.jpg
Only with mine the plastic between the nipple and anode is blue instead
of white. The big horizontal hole through the plastic is for letting
water flow out of the heater. I measured infinity ohms between the
nipple and anode (digital meter), so I don't think that the plastic is
conductive.
Roger that, I guess we're hopefully going to learn something new about
galvanic protection, but HEY, maybe it ISN't actually an "anode" to
retard galvanic corrosion?
I practically flunked chemistry, but I'm thinking maybe there's ways of
inhibiting NON-galvanic corrossion of the tank by the nasty chemicals in
some water supplies, by putting a "more easily corroded" material inside
the tank.
Like, maybe if you've got a dish of acid it'll eat up a piece of steel
you drop in it, but if you dump in some strong base the acid will get
neutralized and not bother the steel as much?
I hope this thread continues until someone "in the know" educates us
about that second rod.
BTW, your excellent photo shows the plastic extending through the inside
the nipple right to top. That may just be to give it a "good grip" but
I'm betting it's also to prevent water from touching the inside of the
nipple. If the top end of an unlined steel nipple is attached to copper
piping, the galvanic corrosion will be at its absolute worst inside the
nipple.
The anode in the tank won't do ****e to protect the nipple because the
sacrificial current flow won't go very far up inside the nipple. (The
same reason it's hard to get electroplating to "throw" inside the holes
on a workpiece without having to stick additional anodes into the holes.)
I may have posted this here before, but at the risk of repeating myself,
here's a photo of the inside of one of the galvanized steel nipple I
used the last time I replaced my electric water heater. I'd dutifully
bought a pair of dielectric (insulated steel/brass) unions and steel
nipples and replaced the copper parts which were there before.
"Everybody" said to use dielectric unions to prolong the life of the new
tank.
In less than six months both of the steel nipples were nearly clogged
with clumps of rust and one had started a pinhole corroded through the
"thin spot" at the root of an exposed thread.
http://home.comcast.net/~jwisnia18/jeff/nipple.html
That's when I started thinking about what I'd done and realized that
because the heater tank and the house piping were both connected to
ground per code, the galvanic unions were "shorted out" and (worse than)
useless.
I put the all copper parts back in.
Later, I stumbled onto this document from Rheem, a major water heater
manufacturer, which confirmed what I'd figured out on my own.
http://www.rheem.com/includes/resour...ryPDF/1221.pdf
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"As long as there are final exams, there will be prayer in public
schools"