The Valve junction type requires two connecting pipes, unless you specify it as an exit valve, in which case only one connecting pipe is allowed. This junction type allows you to model the irrecoverable loss that occurs through a flow control component. You also have the ability to specify loss factors as a function of a flow parameter.
The Valve Properties window follows the first of the two basic Properties window formats, displaying the connecting pipes in a fixed format. A flow direction through the junction is adopted from the defined directions of the connecting pipes.
Valve Data Source and Loss Model
In order to completely define a valve junction, you must specify the valve data source by clicking on the appropriate radio button under Valve Data Source. For this data source, you can use handbook data from the Arrow library by clicking the radio button next to Handbook Data and then specifying what type of valve you are modeling to use a loss factor from handbook data, or you can choose User Specified and separately input the valve loss information.
Standard valve loss models are used from
The valve loss model can be defined using one of four different valve parameters. These four parameters include specifying the valve: Cv, Kv, K factor, or resistance curve.
The Cv is defined according to the ANSI/ISA-75.01.01-2012ANSI/ISA Standard 75.01.01-2012, Industrial-Process Control Valves - Part 2-1: Flow Capacity - Sizing equations for fluid flow under installed conditions, 2012, published by International Society of Automation, Research Triangle Park, North Carolina, USA standard. The valve Xt data is also required when using Cv. When Cv 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.
A special reduced port configuration can be specified by selecting User Specified under Valve Data Source, and then checking the box next to Reduced Port Losses in the center of the window under the Loss Model tab. Once this section has been enabled, you will need to specify the valve type and complete any required input for the specified valve.
If select to model the valve loss with a Resistance Curve, the Valve Properties window makes additional features available. Use these features to input the pressure drop versus flow data by specifying polynomial constants, fitting a curve to available data, or using interpolated x-y data.
CdA for Sonic Choking
An optional input in the Valve Properties window is the CdA for Sonic Choking. 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 test data.
Valves that are used as exit flow control mechanisms are specified as exit valves. These valves require an associated back pressure definition. Exit valves can only be connected to a single upstream pipe. To specify an exit valve, check the Exit Valve check box, located at the bottom of the Loss Model tab. After this box is checked, you will be required to input the exit pressure and temperature.
Open Percentage Data
You can optionally input Cv and Xt vs. open percentage on the Optional tab. If you complete this table, AFT Arrow will calculate the valve Cv. A graph of the open percentage, Cv, and flow area data can be displayed by clicking on the Show Graph... button to the right of the Open Percentage Data table.
The Special Condition for a valve always closes it.