Check Valve
The Check Valve junction type requires two connecting pipes. This junction type allows you to model valves that prevent reverse flow.
The Check Valve Properties window follows the first of the two basic Properties window formats, displaying the connecting pipes in a fixed format. The Check Valve junction does not have an explicit flow direction, but adopts a flow direction from the connecting pipes.
AFT Arrow assumes that the check valve is initially open. If the flow solution indicates that forward flow will not occur, AFT Arrow closes the valve and solves the flow distribution again.
Note: If the check valve closes during the simulation, it will not re-open. If there is an unsteady situation in which the check valve would continuously open and close, there may be unexpected results. It is good practice to close check valves with a Special Condition if it is known that they will be closed. This event can be seen in the Solution Progress window as Re-running Solver because one or more special junction states changed...
A check valve Special Condition can be either open or closed.
Specifying Losses
You specify the losses for the Check Valve on the Loss Model tab in the Properties window. The Check Valve junction allows the Cv or Kv to be specified for pressure loss calculation. The Cv/Kv is defined according to the ANSI/ISA standard as described in the Kv and Cv Loss Model topic. The valve Xt data is also required when using Cv/Kv. When Cv/Kv is selected, data for FL and FD can optionally be entered for valves with low Reynolds numbers to calculated correction factors. If the valve diameter is entered, AFT Arrow will automatically calculate correction factors for cases where pipe diameter differs from the valve.
When you select Resistance Curve, the Check Valve Properties window makes additional features available. Using these new features you can input Check Valve loss factors or pressure drops that vary with flow. To enter these factors, you can fit a curve to available data, or use interpolated x-y data. You can choose any of the optional flow and pressure parameters provided; you can also specify the most convenient units.
CdA for Sonic Choking
An optional input in the Check Valve Properties window is the CdA. This parameter describes the effective area restriction in the valve for the purpose of calculating sonic choking. In most cases, information on the CdA must be obtained from the manufacturer or from test data. Note that the CdA input field is disabled if Cv or Kv loss is used, as the Xt value is used for sonic choking calculations in that case.
