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Specifying Control Valve Data

by Engineered Software, Inc.

If you want to manually set control valves to a particular position, or calculate the position from an automatic flow or pressure setting, then you must supply valve performance data for your control valves. There are a couple of ways to specify control valve data. If you have the full range of performance data available from the manufacturer, you can manually enter the data on the Control Valve Data tab. If you do not have the data available, you can estimate the valve's performance data by selecting from a list of design and flow characteristics and supplying a single flow coefficient value for the valve.

 

Manually Specifying Control Valve Data

When you select a control valve and right click on the mouse, you will have the option to "Enter Valve Data". PIPE-FLO® Professional Version 12+ will then display the Control Valve Data dialog box shown in Figure 1.

Figure 1. Control Valve Data

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.

Nominal Size:  The size of the valve body.

Valve style modifier (Fd):  A valve capacity factor.  The default value is 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 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 Estimate Valve Data button .  When you click on this button you will see the Control Valve Data Estimator dialog box like the one shown in Figure 2.  Data must be entered from top to bottom in order.


Figure 2. Control Valve Data Estimator

Enter Valve Design Characteristics:

The valve design characteristics are used to determine the valve capacity factors.

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".

These design characteristics are used to find typical values from the standard as shown in Table 1 above.

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.

Select Valve

If you have a legacy control valve catalog created in C-Library, then you can use  to access these catalogs. Without the older C-Library catalogs, this feature is non-functional.

For reference to older versions of PIPE-FLO® see attachments below. .

Attachments

Specifying Control Valve Data old.pdf