Hmm, you know, I never gave the sacrificial anode even a passing
thought before your post. I do drain the bottom of the tank
periodically, whenever I think of it, which might range from
weekly to once a season, depending.

I was just looking at mine; oil fired type: I can't see any
evidence of a sacrificial anode that could be changed - guess
I'll move on to zero's link and see what I can see.

Good post,

Pop


"Paul Franklin" wrote in message
...
: On Fri, 18 Nov 2005 07:48:42 -0500, "Robert11"

: wrote:
:
: Hello:
:
: Never had the opportunity to look inside one, but as we just
had a new wter
: heater installed, I became curious. It's the typical upright
cylindrical
: kind, gas fired.
:
: Was wondering:
:
: Is the unit designed to keep a certain water level always in
the tank, or is
: it designed to trap an air bubble at the top ? There isn't
any float
: regulator inside, to the best of my knowledge.
: How does this work ?
:
: If it truly fills totally with water, isn't the internal water
pressure,
: with no elastiucity, a problem ?
:
: How do they maintain such a good (hopefully) seal at the top
of the tank ?
: I imagine that the tank is fabricated from rolled steel, with
a top and
: bottom fastened on somehow. How is this done and sealed ?
:
: Any pix on the web showing internal construction ?
: Couldn't find any.
:
: Thanks,
: Bob
:
: Having recently "deconstructed" one (never mind why) I can tell
you
: how they were constructed 10 years ago or so...I doubt they are
much
: different now, except for the flame arrest combustion chamber.
:
: The tank sides are formed from steel about 1/8 inch thick.
There is a
: welded side seam, and the domed top and bottom pieces, also
steel, are
: welded to the sides. Both with dome up, by the way. Threaded
openings
: for the drain, inlet, outlet, sacrificial anode, and
temperature and
: pressure relief valve are provided by steel blocks about 1/2
inch
: thick welded to the appropriate locations, with threaded holes.
The
: entire inside of the tank is coated with "glass". This isn't a
thick
: coating, but more of a very thin layer that I suspect is done
the way
: porcelain is done: a fine power is applied and then baked in a
large
: oven to melt and adhere the powder into a continuous film. This
is
: done for corrosion protection, and it is the failure of this
coating
: that usually leads to water heater failure.
:
: For gas fired heaters, in the center of the tank is another,
smaller
: diameter tube (about 3-4 inches in diameter. This runs all the
way
: through the tank, from top to bottom, and provides the path for
the
: flue gases to flow from the burner to the flue. This tube is
also
: steel and is welded top and bottom as well. Inside this tube,
which
: is outside of the tank, but inside the tank too (if you can
follow
: that!) is a spiral steel baffle that is designed to slow down
the flow
: of flue gasses and transfer as much heat from them to the tank
as
: possible.
:
: In operation, the tank is completely full of water, at full
water
: pressure. The thick steel walls are more than capable of
withstanding
: normal water pressure and more. The T&P relief valve is
designed to
: prevent the pressure from rising high enough to cause tank
failure, as
: might happen if the burner control failed and the heat source
did not
: turn off. Another poster mentioned the use of external
expansion
: tank. This is not intended to prevent the tank from failing,
rather
: it is intended to prevent the internal pressure from rising
high
: enough (during normal operation) to either cause the T&P relief
valve
: to open, or to cause premature failure of washers and seals in
: plumbing fixtures. An external expansion tank is really only
needed
: if there is a check valve or equivalent in the path of the cold
water
: inlet such that water cannot flow back into the water mains or
the
: well pressure tank. As the water is heated, it expands, and if
it
: some can't flow back out the inlet to the water source, then
internal
: pressure will increase, sometimes significantly. This is the
situation
: that calls for an external expansion tank, which uses an air
bladder
: to provide expansion space.
:
: The outside of the tank is covered with spray applied foam
insulation,
: more or less depending on the efficiency and cost of the
heater. The
: foam insulation is wrapped with the thin sheet steel outer
jacket that
: you see when you look at the heater.
:
: The sacrificial anode is a metal rod, usually zinc I think,
sometimes
: aluminum, that screws into one of the openings on the top of
tank and
: extends into the tank. It's whole purpose in life is to extend
the
: life of the tank. The glass coating on the tank inevitably has
: pinholes, if not at first, eventually. These pinholes provide
a place
: for corrosion to start, and once started, it proceeds rapidly
until
: you have a leak. The metal of the sacrificial anode is chosen
so that
: it corrodes first, before the steel, thus preventing the tank
from
: corroding. Checking the sacrificial anode every few years and
: replacing it when it is nearly used up is the best way to
extend water
: heater life, especially if you have soft water that is
aggressive to
: the steel. The other way to prolong life is to periodically
drain out
: the sediment that builds up on the bottom
:
:
:
: