Check Valve
The Check Valve junction type requires two connecting pipes. This junction type allows you to model the effect of a check valve which closes to prevent back 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 for calculating loss. The user can define the base area for the loss model, though the default is set to use the upstream flow area.
A check valve is a device that allows flow in only one direction. AFT xStream assumes that the Check Valve is initially open (unless modeled as Closed on the Optional tab). If the flow solution indicates that the velocity at the check valve is insufficient to keep the check valve open based upon the check valve input, AFT xStream closes the valve. The valve can close during the steady-state or transient portion of the simulation.
AFT xStream allows you to model the check valve by entering a User Specified closing velocity.
The Loss Model for the open valve can be specified as a Cv, Kv or K factor by choosing an option on the Valve Model tab and entering the Full Open value.
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.
User Specified
The User Specified option opens and closes based on user-defined values for velocity to close and a delta pressure to reopen. For steady-state analysis the valve is either fully open, or fully closed. In a transient analysis, the valve opens and closes instantaneously.
The inputs are as follow:
- Forward Velocity to Close Valve - By default this value is zero. Some valves are designed to start closing at some reverse velocity - you can specify that here as a negative value. Entering a positive value in this field would imply that the check valve closes while the flow is still continuing forward.
- Delta Pressure to Reopen - Frequently after a check valve closes, there is pressure across the valve at which it will open again. You can specify that delta pressure here.
Special Conditions
A check valve can have a Special Condition of None, Closed (stays closed or allowed to reopen in transient), or Open (stays open).
