Understand Flow Network check valves and flow direction

By default, a segment will allow the product to flow in either direction within it. This can be limited by adding a check valve to a segment. If a check valve exists on a segment, the product will only be allowed to flow in a single direction within it. This control can be extremely useful when dealing with multiple sources of flow or sources of flow that provide indeterminate flow direction.

The following is an example of a tank connected to a model that has three segments in a row. The tank tells the Flow Network that it has an indeterminate flow direction and could be filling or emptying. The result of this communication is that all of the segments will have an indeterminate flow direction.

To resolve this situation, add a check valve to the center segment. The direction of flow in the first segment remains unaffected by the check valve because flow has not yet reached it. Once the indeterminate flow reaches a segment with a check valve defined, the segment filters out the flow that does not align to the direction of the check valve. The final segment also has flow limited to the right direction because there is no flow device that could provide a direction of flow to the left.

Similarly, if the tank were only providing flow in a single direction that opposed the check valve, then the second and third segments would be in a directionless no-flow state.

The example below is more complicated as an indeterminate flow direction can occur in the middle of a line. Notice that the third segment along the main line has been calculated as having an indeterminate direction. This is due to the injection tank along the bottom acting as an injection device. Once this side-stream injection reaches the main line, it could travel either left or right, resulting in an indeterminate flow direction along the main line. This example illustrates the importance of check valve placement when configuring a Flow Network.

Below is an example of small uncontrolled loops that can also result in indeterminate flow direction. The path the product will follow cannot be reliably determined based on connectivity.