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Manually Specifying Control Valve Data:
When you click on the Data tab for a control valve, you will see the data dialog box for the valve like the one shown in Figure 1.
Figure 1. Control Valve Data
Enter Dimension Data:
Valve size: The diameter of the valve body.
Seat size: The diameter of the seat area.
Stroke: The amount of linear valve travel available for the valve stem from fully closed to fully open.
Enter Data Values:
Actuator: Select Linear or Rotary.
Flow coefficient: Cv or Kv.
Cv = volume of 60°F water (US gpm)which will flow through the valve at 1 psi d.
Kv = volume of 5°C-40°C water (m3/hr) which will flow through the valve at 1 bar-d.
Valve style modifier (Fd): A valve capacity factor. The default value is 1.
Laminar flow factor (Fs): A valve capacity factor. The default value is 1.1.
Cv (or Kv) Column: The valve flow coefficients at each of the given valve positions.
Fl Column: The liquid pressure recovery factor. This a measure of the valve's ability to convert the kinetic energy of the fluid at the vena contracta back into pressure. Must be specified for use with liquid applications.
Xt Column: The rated pressure drop ratio factor. Must be specified for use with gas applications.
Valve Capacity Factors
If you have the flow coefficient data, but do not have the data for the valve capacity factors then you can use representative values taken from the ISA Standard S75.01 – 1985 for the valve capacity factors XT, FL, Fs and Fd. Table 1 lists these representative values.
Table 1. Valve Capacity Factors
* Flow direction tends to open or close the valve, i.e., push the closure member away from or towards the seat.
** In general, an Fd value of 1.0 can be used for valves with a single flow passage. An Fd value of 0.7 can be used for valves with two flow passages, such as double-ported globe valves and butterfly valves.
Estimating Control Valve Data:
If you don't have all of the Cv data or valve capacity data for a valve, you can estimate the valve data by clicking on the Control Valve Calculator button
. When you click on this button you will see the Control Valve Calculator dialog box like the one shown in Figure 2. Data must be entered from top to bottom in order.
Figure 2. Control Valve Calculator
Enter Valve Design Characteristics:
The valve design characteristics are used to determine the valve capacity factors.
Actuator motion: Select Linear or Rotary as on the control valve Data tab.
Valve body style: Select Globe, Angle, Ball or Butterfly valve depending on the actuator.
Trim type: The characterization of the opening and closing member of the valve. Selections depend upon actuator and valve body.
Flow direction: Select "flow to open" or "flow to close".
Enter Valve Flow Characteristics:
The valve flow characteristics are used to determine the full range of flow coefficients and valve positions.
Characteristic curve: This determines the flow characterization of the valve. Options include Equal Percentage, Linear, Modified Equal Percentage, Modified Linear, and Quick Opening. Refer to Figure 3 below for a graphic representation of valve opening vs. fraction of full flow for each of these curves.
Valve position: Specify the valve position (in percent or degrees) at which your single flow coefficient is determined. Most manufacturers will at least give one Cv or Kv value at the fully open position (100% or 90 degrees).
Flow Coefficient Cv (or Kv): the Cv or Kv value at the given valve position.
Figure 3. Control Valve Flow Characteristics
NOTE: These flow characteristic curves were developed after extensive research and comparisons of the performance curves of many different valve manufacturers. These characteristic curves are smoothed, best fit representations of an average of those manufacturers' curves.
After you've entered the design and flow characteristics for your valve, click the OK button. This will generate all of the valve data necessary for use within the program.
