Valve
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. 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.
Loss Source
In order to completely define a valve junction, you must specify the valve loss source by clicking on the appropriate radio button under Loss Source:
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User Specified - This is the best option if manufacturer data is known. Manually input the loss information using one of the Loss Models listed in the next section.
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From Characteristic - This option is useful if no information about the valve is known aside from the type, and an estimate needs to be made. Automatically calculate Cv based on the selection of a common valve geometry type and a Full Open Cv value. With the exception of the User Defined characteristic from the dropdown, the window will automatically populate an Open Percent vs Cv data table by scaling the shape of the characteristic curve to fit the provided Full Open Cv. Then, choose an Open Percentage under the Loss Parameters area to automatically calculate a Cv. The data for the characteristic shapes comes from Val-Matic 2009Val-Matic Valve and Manufacturing Corp., Surge Control in Pumping Systems, Val-Matic Valve and Manufacturing Corp., Elmhurst, IL, 2009..
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Handbook - Uses standard valve loss models from
Loss Model
Depending on the selection of the Loss Source, various loss models will be displayed:
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Flow Coefficient - Cv for English units or Kv for Metric units
A special Reduced Port configuration is available when using the Handbook loss source, and requires the selection of a valve type and several geometric inputs. Once specified, a K Factor from the Handbook source will be calculated.
Valves that are used as exit flow control mechanisms are specified as Exit Valves. These valves require an associated ambient pressure definition (also called a back pressure). Exit Valves can only be connected to a single upstream pipe. To specify an Exit Valve, select the Exit Valve checkbox, and input the required Exit Pressure. If a heat transfer fluid model is used, the Exit Temperature must also be specified to define the thermal boundary condition.
Restricted Area & Optional Losses
The Restricted Area is optional input available for the User Specified and Handbook loss sources which describes the effective area restriction in the valve for the purpose of assessing cavitation. By default, Fathom will check for cavitation in pipes since an area is specified as part of the required pipe properties. Cavitation in a junction can only be checked if a Restricted Area is provided. In most cases, information on the size of the restricted area must be obtained from the manufacturer or test data.
Note: Fathom does not model cavitation but can provide a warning if the static pressure is below the vapor pressure. If a User Defined fluid is used, the optional input parameter for Vapor Pressure must be defined in the Fluid Properties. Fathom only models single phase flow, and assumes all pipes are fluid-full as stated in the Engineering Assumptions.
The Basis Area is available for the K Factor, Resistance Curve, Equivalent Length, 3-K (Darby), and Reduced Port loss models and describes the area from which loss factors are referenced from.
Optional data may be entered for special valve characteristics. Specifically, the Open Percentage vs Cv and Flow Area can be specified. This data does not affect the Solver’s flow solution; however, engineers frequently desire to know the valve’s open percentage during operation to ensure it meets design requirements. The Valve Summary in the Output window always displays the valve Cv, and if data is specified for open percentage and flow area it will also display open percentage and flow area at the operating point. A graph of the open percentage, Cv, and flow area data can be displayed by selecting the Characteristic Graph tab below the table.
The Characteristic Source parameters can be used to create an Open Percent vs Cv curve that follows the shape of several common valve types including Ball, Butterfly, Equal Percentage, Globe, Linear, Plug, and Quick Opening.
Transient (XTS Module Only)
The Transient tab is only visible if the XTS Module is active, and a transient Cv or K Factor vs time table can be entered to simulate the opening or closing of the valve. If the optional open percentage table is entered, it can also be used to specify an open percent vs time transient. For a closed valve, the K Factor is infinite. To account for this, a K Factor of -1 (negative one) can be used in the transient data table. For more information on transient data, including event transients, see the Junction Transient Data topic.
Special Conditions
The Special Condition on the Optional tab allows the valve to be specified as Closed, which is useful to turn off a valve while retaining the input data for future use.
