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I just learned water heaters have an "anode" and its important davidlaska 06-08-2007
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Posted by Grandpa on June 9, 2007, 5:21 pm
Ook wrote:
>>>> Labor can't replace material. Its called a "sacrificial" anode for a
>>>> good
>>>> reason. See here:
>>>>
<http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-anodes.html>
>>>>
>>>> --
>>>> Grandpa
>>> Why do they call it an anode?
>> http://en.wikipedia.org/wiki/Anodes
>>
>
> I know what an anode is. I also know what a cathode is. But that doesn't
> answer my question....I stick this rod in the middle of my water heater -
> what makes it an anode, and not a cathode?
>
>
Did you read down to the part where it says "sacrificial anode" or
just skip it? It says:
"Sacrificial anode

In cathodic protection, a metal anode that is more reactive to the
corrosive environment of the system to be protected is electrically
linked to the protected system, and partially corrodes or dissolves,
which protects the metal of the system it is connected to. As an
example, an iron or steel ship's hull may be protected by a zinc
sacrificial anode, which will dissolve into the seawater and prevent
the hull from being corroded. Sacrificial anodes are particularly
needed for systems where a static charge is generated by the action
of flowing liquids, such as pipelines and watercraft."

--
Grandpa

Posted by Ook on June 9, 2007, 6:31 pm

> Ook wrote:
>>>>> Labor can't replace material. Its called a "sacrificial" anode for a
>>>>> good
>>>>> reason. See here:
>>>>>
<http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-anodes.html>
>>>>>
>>>>> --
>>>>> Grandpa
>>>> Why do they call it an anode?
>>> http://en.wikipedia.org/wiki/Anodes
>>>
>>
>> I know what an anode is. I also know what a cathode is. But that doesn't
>> answer my question....I stick this rod in the middle of my water heater -
>> what makes it an anode, and not a cathode?
> Did you read down to the part where it says "sacrificial anode" or just
> skip it? It says:
> "Sacrificial anode
>
> In cathodic protection, a metal anode that is more reactive to the
> corrosive environment of the system to be protected is electrically linked
> to the protected system, and partially corrodes or dissolves, which
> protects the metal of the system it is connected to. As an example, an
> iron or steel ship's hull may be protected by a zinc sacrificial anode,
> which will dissolve into the seawater and prevent the hull from being
> corroded. Sacrificial anodes are particularly needed for systems where a
> static charge is generated by the action of flowing liquids, such as
> pipelines and watercraft."
>
> --
> Grandpa

I read it. It still doesn't explain why it's not a "sacrificial cathode".



Posted by Ook on June 9, 2007, 6:39 pm

> Grandpa
>
> I read it. It still doesn't explain why it's not a "sacrificial cathode".
>
I found the answer:

"Galvanic anodes are designed and selected to have a more "active" voltage
(technically a more negative electrochemical potential) than the metal of
the structure (typically steel). For effective CP, the potential of the
steel surface is polarized (pushed) more negative until the surface has a
uniform potential. At that stage, the driving force for the corrosion
reaction is halted. The galvanic anode continues to corrode, consuming the
anode material until eventually it must be replaced. The polarization is
caused by the current flow from the anode to the cathode. The driving force
for the CP current flow is the difference in electrochemical potential
between the anode and the cathode."
(http://en.wikipedia.org/wiki/Cathodic_protection)



Posted by davidlaska on June 23, 2007, 12:27 pm
> Ook wrote:
> >>>> Labor can't replace material. Its called a "sacrificial" anode for a
> >>>> good
> >>>> reason. See here:
> >>>> <http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/wat...>
>
> >>>> --
> >>>> Grandpa
> >>> Why do they call it an anode?
> >>http://en.wikipedia.org/wiki/Anodes
>
> > I know what an anode is. I also know what a cathode is. But that doesn't
> > answer my question....I stick this rod in the middle of mywater heater-
> > what makes it an anode, and not a cathode?
>
> Did you read down to the part where it says "sacrificial anode" or
> just skip it? It says:
> "Sacrificial anode
>
> In cathodic protection, a metal anode that is more reactive to the
> corrosive environment of the system to be protected is electrically
> linked to the protected system, and partially corrodes or dissolves,
> which protects the metal of the system it is connected to. As an
> example, an iron or steel ship's hull may be protected by a zinc
> sacrificial anode, which will dissolve into the seawater and prevent
> the hull from being corroded. Sacrificial anodes are particularly
> needed for systems where a static charge is generated by the action
> of flowing liquids, such as pipelines and watercraft."
>
> --
> Grandpa
First: Thanks for the helpful information and links.

The water that was going into the tank had enough rust to make it a
light tea colored. The tank cleaned out very well, I dropped a light
inside at night and saw that the inside was very shinny. The only
corrosion was at the base lip of the steel container. I put
everything back together and added an additional anode. Not of this
is worth it for your average homeowner, but I am retired so my time is
free.


Posted by dpb on June 9, 2007, 5:37 pm
Ook wrote:
>>>> Labor can't replace material. Its called a "sacrificial" anode for a
>>>> good
>>>> reason. See here:
>>>>
<http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-anodes.html>
>>>>
>>>> --
>>>> Grandpa
>>> Why do they call it an anode?
>> http://en.wikipedia.org/wiki/Anodes
>>
>
> I know what an anode is. I also know what a cathode is. But that doesn't
> answer my question....I stick this rod in the middle of my water heater -
> what makes it an anode, and not a cathode?

Then you don't really "know" what an anode (or cathode) is... :)

It's an anode if it attracts anions, and a cathode of it attracts
cations...I'm pretty sure that's the definition you know. (DOH! :) )

Which, of course is sort of a circular definition. What actually makes
it one or the other is the relative position on the scale of electrical
potential of the material from which it is made with respect to the
other material.

--

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