The Assigned Pressure junction allows for the specification of a fixed boundary pressure and temperature.
This junction is very similar to the Tank in that it fixes a pressure at a boundary. However, the Assigned Pressure allows the definition of either a static or stagnation pressure boundary, whereas Tanks are always stagnation pressure. Typically, any pressure gauge on a pipe will be reporting static pressure - it is important to select static pressure if this is the actual boundary in the real system. A Tank would be inappropriate to represent such a piping connection with non-zero flow.
If stagnation is selected, the Assigned Pressure accepts the connection of up to twenty-five pipes. Static selection limits the connection to one pipe.
There is also the option to Balance Energy in the junction - this adjusts the temperature in order to make incoming and outgoing energy balance. This option is only appropriate for closed loop systems, read more here: Open vs Closed Systems - Balancing Energy.
CdA for Sonic Choking
An optional input in the Assigned Pressure window is the CdA. This parameter describes the effective area restriction for the purpose of calculating sonic choking. This is useful if you are using the assigned pressure junction as a vent to atmosphere and a restriction exists at the pipe exit. If sonic choking occurs at the vent exit, the CdA will be the limiting area for flow. The CdA will only apply when there is one connecting pipe.
On the Loss Coefficients tab, loss factors can be entered to account for losses due to fittings or components at the entry/exit to each of the connected pipes.