Control Valve Sizing
Emerson can help you size and select the Fisher control valve most appropriate for existing service conditions.
Emerson can help you size and select the Fisher control valve most appropriate for existing service conditions.
Standardization activities for control valve sizing can be traced back to the early 1960s when a trade association, the Fluids Control Institute, published sizing equations for use with both compressible and incompressible fluids. The range of service conditions that could be accommodated accurately by these equations was quite narrow, and the standard did not achieve a high degree of acceptance. In 1967, the ISA established a committee to develop and publish standard equations. The efforts of this committee culminated in a valve sizing procedure that has achieved the status of American National Standard. Later, a committee of the International Electrotechnical Commission (IEC) used the ISA works as a basis to formulate international standards for sizing control valves. The ANSI/ISA-75.01.01 and IEC 60534-2-1 valve sizing standards have been harmonized, so either standard may be used.
It is important to provide the following information in order to size a control valve properly:
•Physical details (pipe size, pressure class, trim type)
•Process conditions (upstream pressure, downstream pressure, temperature, noise limit)
•Fluid properties (flow rate, density)
Step 1: Specify the variables required to size the valve
•Desired design,
•Process fluid (water, oil, etc.), and
•Appropriate service conditions
•q or w, P1, P2 or ΔP, T1, ρ1/ρo, Pv, Pc, and n
The ability to recognize which terms are appropriate for a specific sizing procedure can only be acquired through experience with different valve sizing problems.
Step 2. Determine the equation constraints, N1 and N2
N1 and N2 are numerical constants contained in the flow equations to provide a means for using different systems of units.
Step 3. Determine the piping geometry factor (FP) and the liquid pressure recovery factor (FLP)
For these calculations, an estimated CV value and the corresponding FL is used. FP is a correction factor that accounts for pressure losses due to piping fittings such as reducers, elbows, or tees that might be attached directly to the inlet and outlet connections of the control valve to be sized. If such fittings are attached to the valve, these must be accounted for. The standard sizing procedure provides a method to calculate the FP factor for concentric reducers and expanders. If, however, no fittings are attached to the valve, FP has a value of 1.0 and simply drops out of the sizing equation. Also, FLP = FL.
Step 4. Determine the pressure drop to use for sizing (ΔPsizing)
When the difference between the upstream and downstream pressure is high enough, the liquid may start to vaporize, causing choked flow. If the actual pressure drop across the valve, ΔP, is higher than the pressure drop that causes choked flow, the choked flow pressure drop, ΔPchoked, must be used in place of the actual pressure drop.
Step 5. Calculate the required flow coefficient (Cv)
Learn the step-by-step process for sizing control valves for compressible fluid using the ISA and IEC’s recommended procedure.
This webinar focuses on control valve sizing and selection. We discuss equipment parameters, flow media states, applications, preliminary sizing calculations, control valve selection, and re-performing the sizing calculation to confirm the selection.
Emerson Control Valve Solution Architect Mark Nord dicsusses control valve flow characteristic. How do I figure out what kind of trim characteristic I should use in my control valve and why do I want it. The webinar dicusse:s linear vs non-linerar processes; right sizing; inherent and installed gain; and general guidelines for characteristic selection.
What is Pressure Drop?
How to Size a Control Valve for Liquid Flow
Learn the step-by-step process for sizing control valves for compressible fluid using the ISA and IEC’s recommended procedure.
This webinar focuses on control valve sizing and selection. We discuss equipment parameters, flow media states, applications, preliminary sizing calculations, control valve selection, and re-performing the sizing calculation to confirm the selection.
Emerson Control Valve Solution Architect Mark Nord dicsusses control valve flow characteristic. How do I figure out what kind of trim characteristic I should use in my control valve and why do I want it. The webinar dicusse:s linear vs non-linerar processes; right sizing; inherent and installed gain; and general guidelines for characteristic selection.
What is Pressure Drop?
How to Size a Control Valve for Liquid Flow
