Understanding Flow Direction and Inspection Direction

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This page aims to clarify and explain how the concepts of flow direction and inspection direction are tied together inside WinCan VX.

Background

Before getting into the details of the relationships between flow direction and inspection direction, there are some ground rules that must be observed when dealing with WinCan VX data, which may be considered differently in other software applications:

• WinCan VX works on the Upstream-Downstream concept at all times.

  • What this means is that in our data we always specify the manholes at the ends of a pipe as the upstream end and the downstream end, and we therefore assume that the flow direction is always from the upstream end to the downstream end.

• The inspection direction is relative to the flow direction, so a downstream inspection is ‘with the flow’ and upstream inspection is ‘against the flow’.

  • From this, it is clear that the inspection direction cannot be defined if the flow direction is unknown, except in the case where we define the inspection direction as going ‘from manhole A to manhole B’ - this method of description is independent of the flow direction.

• In most standard, both the flow direction and the inspection direction can have 1 of 4 values in the data:

  • Downstream

  • Upstream

  • Unknown

  • Not Defined

For the first part of this page, we will consider only the cases where the flow directions are either of the first 2 options in the list above (upstream or downstream) and towards the end we will consider what happens if either or both of these values is unknown or not defined.

Flow Direction Logic

So by default, the flow direction is considered to be always downstream. What this means is that the flow direction actually defines which manhole is the upstream manhole and which is the downstream manhole, so the manhole positions in the data are defined by the flow direction, not the other way around.

Let’s assume we have:

• Upstream manhole = A

• Downstream Manhole = B

• Flow Direction = Downstream.

What does this mean? It means the water flows from A → B, it’s very simple.

So, what happens if we flip the flow direction over to the other way around? In this case, the flow direction actually stays the same and does not change, and what happens in reality is the manholes swap positions, because the flow direction defines which is the upstream manhole and which is the downstream manhole, so after switching the flow direction, we now have B → A, not A ← B.

See that the arrow still goes the same way, and it is the manholes that are swapped over.

The overriding concept here that we cannot get away from in terms of how WinCan VX works is described at the top of the page in the Background section where the water flows from the upstream node towards the downstream node at all times in our data and in all standards - this is the direction of flow.

Inspection Direction Logic

Let’s go back to the first pipe with flow direction A → B and now consider the inspection direction and remember that the inspection direction is a child of the flow direction:

• For a downstream inspection:

  • Flow direction is from A → B

  • Start and end manholes are A → B (i.e. starts at A and ends at B)

  • Inspection direction is A → B (i.e. starts at A, ends at B and is with the flow)

• For an upstream inspection:

  • Flow direction is from A → B

  • Start and end manholes are B → A (i.e. starts at B and ends at A)

  • Inspection direction is B ← A (i.e. starts at B, ends at A and is against the flow)

What happens now if we decide to flip the flow direction to the opposite way around?

• For a downstream inspection:

  • Flow direction is now from B → A

  • Start and end manholes are B → A (i.e. starts at B and ends at A)

  • Inspection direction is B → A (i.e. starts at B, ends at A and is with the flow)

• For an upstream inspection:

  • Flow direction is now from B → A

  • Start and end manholes are A → B (i.e. starts at A and ends at B)

  • Inspection direction is A ← B (i.e. starts at A, ends at B and is against the flow)

It should be noted that when we display text such as A (D/S) B in the inspection direction field or B ← A on the OSD, we are actually providing 3 pieces of information to the viewer. These are:

• The start manhole is on the left and the end manhole is on the right.

• The flow direction is defined by the arrow on the OSD (this can also be changed to show the inspection direction in the OSD controls if needed, so can show start → end).

• The inspection direction and flow direction are defined by the text in the brackets in the header field because they are linked - downstream is ‘with the flow' and upstream is ‘against the flow’.

Furthermore, when we use the option to display just the direction text in the inspection direction field (i.e. Upstream or Downstream), then what we are actually saying is ‘with the flow’ or ‘against the flow’, so again, this can only be defined if the flow direction is defined.

Conclusion Part 1

What all this means is that if we attempt to switch the flow direction of the pipe in the data, then what actually must happen on this action is the flow direction stays the same, but the upstream and downstream manholes swap places, the direction of all the inspections connected to the pipe are reversed, and there are no changes to observation positions.

Unknown and NULL Values

Of course, most standards include an ‘unknown’ value option for both the flow direction and the inspection direction, and in the data, there could be situations where the definition simply does not exist. Both of these situations will give the same results if they exist in the data.

If the flow direction is unknown or NULL, then:

• For a downstream inspection:

  • Flow direction is A – B (notice that there is no arrow and we simply show the manhole that is defined in the upstream field on the left and the manhole that is defined in the downstream field on the right)

  • Start and end manholes are A → B (i.e. starts at A and ends at B)

  • Inspection direction is A – B (there is no arrow because the inspection direction cannot be defined without the flow direction being defined or vica versa)

• For an upstream inspection:

  • Flow direction is A – B (as above)

  • Start and end manholes are B → A (as above)

  • Inspection direction is B – A (as above)

Conclusion Part 2

If the either the flow direction or the inspection direction are unknown or not defined, then it is not possible to show an arrow in the pipe graph or the printing reports because the inspection direction and flow direction are mutually exclusive.

The only thing we can define clearly with any confidence in these cases is the ‘start’ manhole and the ‘end’ manhole.