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.
: >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
: >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
: >regulator inside, to the best of my knowledge.
: >How does this work ?
: >If it truly fills totally with water, isn't the internal water
: >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.
: Having recently "deconstructed" one (never mind why) I can tell
: how they were constructed 10 years ago or so...I doubt they are
: 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
: welded to the sides. Both with dome up, by the way. Threaded
: for the drain, inlet, outlet, sacrificial anode, and
: pressure relief valve are provided by steel blocks about 1/2
: thick welded to the appropriate locations, with threaded holes.
: entire inside of the tank is coated with "glass". This isn't a
: coating, but more of a very thin layer that I suspect is done
: porcelain is done: a fine power is applied and then baked in a
: oven to melt and adhere the powder into a continuous film. This
: done for corrosion protection, and it is the failure of this
: that usually leads to water heater failure.
: For gas fired heaters, in the center of the tank is another,
: diameter tube (about 3-4 inches in diameter. This runs all the
: through the tank, from top to bottom, and provides the path for
: flue gases to flow from the burner to the flue. This tube is
: steel and is welded top and bottom as well. Inside this tube,
: is outside of the tank, but inside the tank too (if you can
: that!) is a spiral steel baffle that is designed to slow down
: of flue gasses and transfer as much heat from them to the tank
: In operation, the tank is completely full of water, at full
: pressure. The thick steel walls are more than capable of
: normal water pressure and more. The T&P relief valve is
: prevent the pressure from rising high enough to cause tank
: might happen if the burner control failed and the heat source
: turn off. Another poster mentioned the use of external
: tank. This is not intended to prevent the tank from failing,
: it is intended to prevent the internal pressure from rising
: enough (during normal operation) to either cause the T&P relief
: to open, or to cause premature failure of washers and seals in
: plumbing fixtures. An external expansion tank is really only
: if there is a check valve or equivalent in the path of the cold
: inlet such that water cannot flow back into the water mains or
: well pressure tank. As the water is heated, it expands, and if
: some can't flow back out the inlet to the water source, then
: pressure will increase, sometimes significantly. This is the
: that calls for an external expansion tank, which uses an air
: to provide expansion space.
: The outside of the tank is covered with spray applied foam
: more or less depending on the efficiency and cost of the
: foam insulation is wrapped with the thin sheet steel outer
: you see when you look at the heater.
: The sacrificial anode is a metal rod, usually zinc I think,
: aluminum, that screws into one of the openings on the top of
: extends into the tank. It's whole purpose in life is to extend
: life of the tank. The glass coating on the tank inevitably has
: pinholes, if not at first, eventually. These pinholes provide
: for corrosion to start, and once started, it proceeds rapidly
: you have a leak. The metal of the sacrificial anode is chosen
: it corrodes first, before the steel, thus preventing the tank
: corroding. Checking the sacrificial anode every few years and
: replacing it when it is nearly used up is the best way to
: heater life, especially if you have soft water that is
: the steel. The other way to prolong life is to periodically
: the sediment that builds up on the bottom