Control Valve Selection Using Fisher Valve Specification Manager
step-1- Enter Process and Piping Data
Take the previous example and once again input the process data, piping data, and default values into the valve sizing software and click calculate.
step-3- verify sizing result
Based on the sizing calculation, confirm that there is no chocking, cavitation, flashing, or excessive noise in the system. This can be identified by the below output parameters. If there any cavitation and chocked flow message will appear on the window and necessary trim shall be selected to reduce the cocked flow or cavitation.
cavitation pressure drop
The cavitation pressure drop is greater than that of the differential pressure.Hence no chance of cavitation.
Chocked pressure drop
The chocked pressure drop is greater than that of differential pressure drop hence no chocking issue.
Noise
sound level is less than 85 DB .Hence no noise issue.
Based on the above result and process conditions select
Valve type: Globe valve – As per the application. The control valve is used for modulation application. Globe valve is best suited for this application.
Trim type: Standard trim- Based on the sizing calculation results there is no chocked flow, cavitation and flashing.
Flow characteristic: Equal percentage
After confirming these parameters, click Next to proceed to the Fisher valve model selection step.
step-4- select valve model
Choose a general-purpose control valve model, such as the Fisher ET Control Valve, with equal percentage flow characteristics, based on the sizing output.Once the valve model is selected, the Cv table will appear at the bottom of the screen.
This table shows the Cv values corresponding to different valve sizes and travel percentages. Review the Cv Table and conform the selected Cv is as per client control valve specification.
step-5-select appropriate vave size
Select the valve body size based on the calculated Cv from the sizing results.
In this example:
Maximum required Cv = 99
Therefore, choose a valve with a rated Cv higher than the required maximum Cv. While selecting the valve size, also verify the operating conditions at minimum, normal, and maximum flow, according to typical control valve engineering practice:
Minimum flow: Valve travel should be greater than 20%
Normal flow: Valve travel should be approximately 50–70%
Maximum flow: Valve travel should typically be below 90%
In this application, a 3-inch valve was selected because:
Minimum flow occurs at approximately 50–60% valve travel
Normal flow occurs at approximately 60–70% valve travel
Maximum flow occurs at approximately 80–90% valve travel
This operating range provides good controllability and stable valve performance.
After selecting the valve size, click Next.
step-6- software default value update( auto update after selecting the valve)
A message will appear indicating that the default parameters will be updated according to the selected valve model. At this stage, there may be a small change in the calculated Cv values because the software updates the internal parameters based on the selected valve characteristics. However, this change is usually very small and does not significantly affect the valve selection.
step-7 – verify updated sizing result
Finally, go back to the Valve Sizing tab and review the updated results.
You will notice that:
The default parameters are updated automatically. The Default values like recovery factor(Fl), valve style modifer(Fd),cavitation coefficient(Kc) has been updated based on the selected valve. The Cv values are slightly adjusted. The sizing results now correspond to the selected valve model. This confirms that the valve selection process has been completed correctly.
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