On Sun, 22 Nov 2015 00:24:09 -0000 (UTC), Doug Miller
wrote:

Micky wrote in
:

On Sat, 21 Nov 2015 17:55:45 -0000 (UTC), Doug Miller
wrote:

Micky wrote in
news:n3605btdvs9avi246kpt1j8vvfrfptkeas@
4ax.com:

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

For the record, I'm not talking about the pressure valve. I can see
that that's a good thing, and the house was built with one, which
hasn't required a bit of maintenance in 36 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.

But what's wrong with my water going into the city supply. It's the
same water they gave me in the first place. If it was good enough
for me, why isn't it good enough for them again? Do they think I
squeezed into the pipes and poisoned it?

The water utility can guarantee its purity only until they put it into your house.

And even if it does back up, is it going to back up all the way
through my basement, under the front yard to the water main? Seems
to me it will back up no more than 20 feet,

Nope, more like 20 yards.

So if I had a yard 100 yards deep, I wouldn't need the tank?

and when I use the water
again, the backed up water will come back into my own house.

Or your next-door neighbor's.

Okay, I promise not to take the tank out, and to replace it if the
bladder fails.