Some junctions have Special Conditions which alter the normal state of the junction. For example, a valve can be closed, a compressor turned off, or a relief valve opened.

The special conditions are set in one of three ways:

• By selecting the junction(s) on the Workspace and choosing Special Conditions from the Edit Menu

• By selecting the junction(s) on the Workspace and clicking the Special Condition icon on the Toolbar

• By opening the junction’s Properties window and clicking the appropriate condition on the Optional tab

The junctions which have special conditions set are shown using a special symbol before the ID number (an X by default). This symbol can be customized in the Tools/User Options window.

When the special condition results in a section of the model being closed or "turned off", the pipes which will have zero flow are display as dotted lines. This indicates visually that they are cut off from flow; the junctions are outlined with a dotted line. The default dotted line can be changed in the Tools/User Options window.

The user can specify Special Conditions for Control Valves to be either closed or fully open. Similarly, compressors/fans can be turned off and either allow flow through or stop the flow.

Special Condition: Ignore

The Relief Valve junction has a unique kind of Special Condition called Ignore. This makes the steady-state and transient solvers ignore the presence of the junction. Thus not only is the data ignored, the junction itself is ignored. This is convenient when locating a relief valve by trial and error. Rather than having to delete the junction, it can be ignored.

As an example, assume that one is trying to find the best location for a relief valve. If one does this with a single relief valve junction, it will be required to run a case, view the results, then relocate the junction by changing the pipe lengths and rerunning. If one uses the Special Condition Ignore, one can place multiple relief valve junctions in the model and then set all of them except one to Ignore so that only one of the junctions is used at a time.