Reporting the velocity of air through an air valve in HAMMER

  Applies To 
  Product(s): HAMMER
  Version(s): CONNECT Edition, V8i
  Area:  Modeling
  Original Author: Jesse Dringoli, Bentley Technical Support Group

Problem

Can HAMMER report the velocity of air through an air valve?

Solution

Because of the ability to use custom air valve curves where the opening area is not defined, the user can use one of the following methods to report the air valve air velocity:

1) Compute the transient simulation with a number entered in the air valve's "Report Period" field, open the "Extended Node Data" tab of the Transient Results Viewer, select the air valve, then select "free air outflow" as the "graph type"'. Click "Plot", click the Data tab, click the square in the upper-left corner (to select the table), click the Copy button, then paste into an external application such as Excel and calculate the velocity based on the flow and the known area of the air valve opening. 

Note:

  • The ability to calculate free air flow rate was added in version 10.03.04.05 so you will need this version or higher. Check under File > Help > About.
  • Positive values indicate air outflow (egress) and negative values indicate air inflow (ingress)
  • "Free air outflow" refers to the flow rate of air at the opening to the atmosphere, as opposed to the air flow rate inside the pipe at pipeline pressure (which can be different due to air density). See more about this in the article in the "See Also" section below.



2) Another option would be to place the air valve node at a "tee" from the main pipeline. You will likely need a smaller timestep to avoid excessive length adjustment in the short lateral pipe, but then you'll be able to graph velocity in the time history tab of the Transient Results Viewer, for the pipe adjacent to that valve. It is important to note that this is the velocity of the water column as it moves away from the air valve opening (for air inflow) or toward it (for air outflow). When dealing with an air valve, there are two flow rates (and two velocities) one for the "free air flow" at the air valve opening and the other for the air flow at pipeline pressure. The difference is due to the difference in air density as the air pocket can be compressed. The air flow rate reported in the aforementioned detailed report is also the flow at pipeline pressure (inside the air valve).

See Also

Modeling Reference - Air Valves

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