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

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 ?

The tank is completely filled with water at service pressure and there
is no air cushion.

If it truly fills totally with water, isn't the internal water pressure,
with no elastiucity, a problem ?


Yes, that is why an expansion means is specified and usually required
for most homes.


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

Hi George:

Thanks for reply.

I have an expansion tank on my hot water heating system, =but to the best of
my knowledge i don't see any for the hot water system (the cylindrical hot
water heating system).

House is 30 yrs old.
Just replaced the hot water heater, but nobody ever said anything about an
expansion tank for it . Should there be ?

What types are used for this purpose ?
I don't think I've ever seen one for the hot water system ?

Not to sharp with this stuff; the feed water is of course common to both
systems; does the one expansion tank on what I take to be (only) for the
heating system help the hot water system in this regard ?

Bob

-----------
"George" wrote in message
...
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 ?

The tank is completely filled with water at service pressure and there is
no air cushion.

If it truly fills totally with water, isn't the internal water pressure,
with no elastiucity, a problem ?


Yes, that is why an expansion means is specified and usually required for
most homes.


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

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

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


Here ya go: http://home.howstuffworks.com/water-heater.htm


-zero

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
:
:
:
: