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?