When there are multiple inlet streams to the flash drum at different pressures, specifying the outlet pressure calculation helps to calculate the pressure for the outlet stream. Suppose if Outlet Pressure Calculation is specified as inlet minimum, then the outlet pressure is the minimum pressure of the inlet streams. Similarly inlet average results in outlet streams with pressure equivalent to average of all inlet streams.

In case the flash is to be operated at temperature/pressure other than what is there at inlet streams, it can be overridden by specifying override separation temperature ans override separation pressure accordingly.