Control Valve Flow Coefficient Cv Basic Concept

"What is Cv in Control Valve? Cv is Flow Co-efficient or Capacity Index for the control valves. Cv is the important component in Control Valve sizing and every technician should understand its meaning. The Cv can be roughly assumed as the Valve seat orifice area and the valve plug opening although this assumption is inaccurate but it helps us to understand the abstract term easily.
The higher Cv will give higher volumetric flowrate compared to low Cv value. Note that Cv value will vary depending on the opening percentage of control valve. The higher the valve opening, the higher the Cv value."
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[@InstrumentationTechnician]

"What is Cv in Control Valve? Cv is Flow Co-efficient or Capacity Index for the control valves. Cv is the important component in Control Valve sizing and every technician should understand its meaning. The Cv can be roughly assumed as the Valve seat orifice area and the valve plug opening although this assumption is inaccurate but it helps us to understand the abstract term easily.
The higher Cv will give higher volumetric flowrate compared to low Cv value. Note that Cv value will vary depending on the opening percentage of control valve. The higher the valve opening, the higher the Cv value."

[@nguyenvandieu318]

Hi, when studying valve, i always wondered that if i remain valve stem position or valve opening percentage, does the Cv remain the same value?. I think it right but still not sure about.

[@InstrumentationTechnician]

Hi @nguyenvandieu318, to my understanding as an ordinary technician, the Cv will change when the valve opening percentage is changed. Theoretically speaking, If the valve opening stays at the same opening, then its Cv should stays the same value at this mentioned valve opening percentage too.

[@adam-gi8re]

Hi, can you advise what is the term of required Cv, Selected Cv, Valve Cv and Rated Cv.

[@InstrumentationTechnician]

Hi , I tried my best to explain this terminology based on my limited knowledge as an ordinary technician.
The Cv (Flow Coefficient or Flow Capacity) of the control valve is the value that shows how much liquid or gas flows through the control valve when it is fully open at a specific pressure difference drops across the valve.
The terms of different Cv are explained as follows ;
Required Cv : Calculated Flow Coefficient based on process requirements.
Selected Cv : The Flow Coefficient selected to meet the Required Cv.
Valve Cv : The actual Flow Coefficient value of the installed valve in the field.
Rated Cv : The Flow Coefficient specified by the manufacturer in their data sheet.