This warning occurs when the user selects Prevent Backflow on a pipeline and the network analysis would result in the calculated flow rate being in the opposite direction that that assumed by the direction in which the pipe is drawn. Many customers use this feature if the pipeline has a check valve installed in it.
If PIPE-FLO calculates the flow going in the opposite direction, it will close the pipe to prevent flow in that direction.
CAUTION: Having too many pipelines specified as Prevent Backflow may prevent the network analysis from converging to a solution.
The alternative is to not designate the pipe with Prevent Backflow and to manually close the pipe when the Reverse Flow message is generated.