Flow direction

Flow direction is determined by the definition of a run. Flow is always away from a From Item and towards a To Item. Ports may have flow direction assigned to them, such that flow is limited to being into or out of a port. If a port is defined to have flow going in, that port cannot be defined as the From Port of a From Item. Conversely, if a port is defined to have flow going out, that port cannot be defined as the To Port of a To Item.

Flow Direction is determined by the system when a run is defined, by assigning flow to the segments of the run where possible. If flow direction cannot be determined automatically, flow direction may be assigned manually. If a From or To Item of a Run is defined as a Virtual Item, flow is not determined.

If a flow-sensitive component is placed onto a segment with flow assigned, the only placement solutions are those that do not contradict flow direction. If flow-sensitive components exist in the run that contradict the flow direction assigned to the segments, a Design Rule Violation is created. A component is considered flow sensitive if one or more of its ports have Flow Direction (In or Out) assigned.

Flow Direction is shown by temporary Flow Indicators along segments to which flow direction is assigned. Additionally, permanent Flow Arrows may be placed onto segments, usually done in Logical diagrams.

Flow direction algorithm

The algorithm that automatically determines flow direction is based on the definition of a run. If a section of a routing system is not part of a run, no flow direction exists in that section. When a run is defined or edited, the Flow Direction Algorithm assigns flow direction to each segment of the run, where possible.

A run, by definition, has at least one From Item and one To Item. The flow direction in a stock connected directly to a From Item is always away from the Item. The flow direction in a stock connected directly to a To Item is always towards the Item.

Flow direction does not change at a point in which there are only two directions possible. Therefore, where two segments meet and one has flow assigned, the flow direction of the other segment must be the same direction as the first. If more than two segments meet at a point and two or more of them do not have Flow Direction assigned, flow direction cannot be further determined.

Flow indicators

The direction of flow is displayed as temporary markers for quick reference.

Flow Indicators are presented as cone markers at the midpoint of all linear segments for which flow direction is assigned. By using a cone head rather than a flat arrow, the direction of flow is indicated regardless of the view orientation (Top, Front, Left, Isometric, and so forth).

Flow Indicators are displayed by choosing the Show Flow option of the right-click menu in the Run Navigator when a run is selected. Indicators appear on the segments of all selected runs.

The position and orientation of the cone is determined by the segment: the tip of the cone is positioned at the segment center point and the base of the cone is centered along the segment.

Segments that do not have flow direction assigned display double opposing cone heads.

Related topics

• How do I: Assign flow direction to a run
• Learn more: Assign flow direction
• Look up more details: Flow setting, Place Flow Arrow dialog box, Flow design rules, Assign Flow Direction dialog box