Take a look at this link to see how a constant pressure system and a old style pressure tank will work side by side. http://www.cyclestopvalves.com/simple/home.php
Constant pressure can be done using a regular pump and a constant pressure valve, or a constant pressure pump that uses a computer to vary the RPM of the pump. The regular pump and constant pressure valve is inexpensive and will last a long time. The variable speed pump is more expensive and is not known for lasting very long.