Reference Positive Flow Direction

Next to each pipe's ID number is an arrow that indicates the reference positive flow direction for the pipe. AFT Fathom assigns a flow direction corresponding to the direction in which the pipe is drawn. You can reverse the reference positive flow direction by choosing Reverse Direction from the Arrange menu or selecting the reverse direction button on the Toolbar.

The reference positive flow direction is used for reference purposes only and need not be the actual flow direction. If the reference positive direction is the opposite of that obtained by the Solver (the part of AFT Fathom that applies the governing incompressible flow equations to obtain a solution to the pipe system), the output will show the flow rate as a negative number.