On Sun, 22 Nov 2015 08:48:08 -0700, Don Y
wrote:

On 11/22/2015 7:06 AM, Doug Miller wrote:
Don Y wrote in :

On 11/21/2015 5:20 PM, Doug Miller wrote:
Don Y wrote in :

On 11/21/2015 10:55 AM, Doug Miller wrote:
Micky wrote in
news:n3605btdvs9avi246kpt1j8vvfrfptkeas@
4ax.com:

How did we get along without these tanks for so many years?

Because for many years, municipalities allowed the sort of behavior described by
Don
Y -- if
the pressure in the residential system rises above the supply pressure, water will be
forced
out of the residence and into the supply.

This is now prohibited in many locations, and homes are required to have backflow
preventers to insure that this cannot happen.

Heated water has to expand somewhere, and if it can't expand into the municipal
supply,
you'd better have an expansion tank.

You can find lots of videos "exploding water heaters". There's a lot
of pent-up pressure in those systems and the heater is often the weakest
link.

And that has absolutely nothing to do with expansion tanks. Water heaters explode due
to a
combination of runaway heating *and* a failed temperature-pressure relief valve. If *that*
happens, no expansion tank is going to contain the enormous increase in pressure that
precedes a catastrophic steam explosion.

Water heaters explode due to the fact that water EXPANDS when heated.

False. Water heaters explode due to the fact that water expands by several orders of
magnitude when it is BOILED. Simple thermal expansion of water due to heating in normal
operation does not cause water heaters to explode.

Do you know how to boil water *without* HEATING it? (bring the tank into
the vacuum of space??)
If the thermostat on a water heater is functioning properly and the
water heater is not on the top of a high mountain (or in an airplane)
it is almost impossible for water to boil in the water heater, with
maximum high limit temperatures for domestic water heaters in north
america well below 190F or 90-ish C.

Years ago, many "boilers" had no thermostat or only rudimentary
thermostats and a good friend of min's family home "blew up" one
sunday morning when the rivetted copper water heater tank let go. Toot
the floorboors off the joints on the main floor and upstairs except
where the beds were located, took out all windows and doors, and
unseated the roof. It was aver a month untill the farmhouse was
habitable again and neighbors iver a mile away heard and felt the
bang. Fortunately no-one was injured although their ears rang for a
while. (and nobody fell through the floor getting out of bed!!