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 Fathom assumes that the check valve is initially open. If the flow solution indicates that the specified Forward Velocity to Close is not met, AFT Fathom closes the valve and solves the flow distribution again. By default, the Check Valve will close at a velocity of 0. If a negative velocity value is specified, some amount of reverse flow will be allowed to occur before the valve closes. A positive velocity value means that the check valve will close while there is still forward flow through the valve.

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. When you select Resistance Curve, the Check Valve Properties window makes additional features available. Using these features, you can input Check Valve pressure drops that vary with flow. To enter these factors, you can specify polynomial constants, fit a curve to available data, or use interpolated x-y data. When a variable loss is specified, AFT Fathom dynamically modifies the loss factor in the Solver to agree with your input. You can choose any of the optional flow and pressure parameters provided; you can also specify the most convenient units.

An optional input in the Check Valve Properties Window is the Restricted Flow Area. This parameter describes the effective area restriction in the valve. This is done for the purpose of assessing cavitation. In most cases, information on the size of the restricted area must be obtained from the manufacturer or from test data.