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