Robert Gammon wrote:
A tank with a bladder has what it sys inside, a rubbery bladder that
separates air and water.

The bladder maintains a back pressure on the water, helping it to flo
out and up when the water drain is opened.

A bladder less tank is a simple reservoir, giving the system expansion
room as the temperature of the water changes. Yes, if the tank begins
to get full, the air above will dissolve in the water.


So, what does the application need, expansion room for fluctuating water
levels, or a pressure maintainer to give positive flow?

You have a misconception of how the tanks work. They both work the
same way. A bubble of air is compressed by water pumped. The
compressed air bubble is what forces the water through the system when
the pump is off. The only difference between the two types is:

Bladder - has a membrade (actually more of a balloon) separating the
air and water.
Bladderless - only has an air bubble. Over time, the air is absorbed
into the water and disappears resulting in what is known as a
waterlogged tank. Thus the need for a "snifter valve" or float type
vavle to let more air into the tank.

Harry K