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. 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

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 Fathom 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 in the Handbook Data are used from IdelchikIdelchik, I. E., Handbook of Hydraulic Resistance, 4th edition, Begell House, Redding, CT, 2007., MillerMiller, D. S., Internal Flow Systems, 2nd edition, Gulf Publishing Company, Houston, TX, 1990., and CraneCrane Co., Flow of Fluids Through Valves, Fittings, and Pipe, Technical Paper No. 410, Crane Co., Joliet, IL, 1988..

Loss Model

The valve loss model can be defined using one of four different valve parameters. These four parameters include specifying the valve: C_v, K_v, K factor, or resistance curve.

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.

Restricted Flow Area

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

Exit Valves

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, if a heat transfer fluid model is used, the exit temperature.

Open Percentage Data

The Optional tab allows data to be entered for special control valve characteristics. Specifically, the valve C_v and Flow Area can be specified vs. the Open Percentage of the valve. This data does not affect AFT Fathom’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 C_v, 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, C_v, and flow area data can be displayed by selecting Show Graph to the right of the Open Percentage Data table.

A C_v vs Open Percentage table can be generated quickly for common C_v vs Open Percent profile types by choosing the Create C_v/Open %... button next to the table. This then opens a window in which a curve can be defined using one of the following options:

Transferred - If a table has already been defined on the Optional tab of the Properties window, it can be copied over
User Defined - Data can be entered directly into the table, or imported from existing data
Linear - A linear curve is generated based on the user defined full open C_v and percent increment
Equal Percentage - Generated as an equal percentage curve
Pre-Defined - Pre-defined curves for several common valve C_v vs. Open profiles can be chosen and adjusted for a defined full open C_v value based on data from Val-Matic 2009Val-Matic Valve and Manufacturing Corp., "Surge Control in Pumping Systems," Val-Matic Valve and Manufacturing Corp., Elmhurst, IL, 2009..

Transient (XTS Module Only)

On the Transient tab, a transient C_v or K table, or open percent table can be entered to simulate the opening or closing of the valve. For a closed valve, the K-factor is infinite. To account for this, enter a K-factor of -1 (negative one) in the transient data table. For more information on transient data, including event transients, see Junction Transient Data.

Special Conditions

The Special Condition for a valve always closes it.