If my understanding of a break pressure tank is correct, I believe you could approximate this with a PRV. Or, you could end the system at a reservoir at the elevation equal to the upstream HGL, then start the downstream system at another reservoir, set at the elevation equal to the tank's water surface elevation.
We have some training classes available, which cover Darwin Designer. See below for more information, or contact your Bentley account manager:
If you have technical questions or problems, you can contact technical support.
Manager, Technical Support
Hydraulics and Hydrology product line
Bentley Communities Site Administrator
Bentley Systems, Inc.