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Equal percentage Valve

Equal percentage Valve

Equal percentage Valve

Hi Everyone,

Can someone please share with me any document that has detailed step-wise procedure to calculate Flow rate through Control Valve having Equal Percentage Trim Characteristic? I have a gas pipeline (with some liquids as well, though minor quantity) in which I need to know flow rate, but, the line is not having any flow meter. But, there's a control valve in it, and I have datasheet of the Control Valve. Also, dP across the valve is known. So, I want to know the flow through the valve with percent of valve opening. Can someone please help me out? In case if you are giving some info, please do mention the standard as per which the data is presented, for authenticity. Thanks in advance.

RE: Equal percentage Valve

You can also find generic % Cv vs % open for equal % control valves in the GPSA in the chapter on control valves.

RE: Equal percentage Valve

Hi ,
Consider to get a copy of Chemical Engineering fluid mechanics , 3rd edition by Ron Darby and Raj.P Chhabra
Chapter 11 "Matching valve trim to the system .
Article was published in Chemical engineering magazine (June 1997) Ron Darby

Good luck

RE: Equal percentage Valve

LittleInch's Spirax Sarco link has a sample calculation under Control Valve Characteristics

RE: Equal percentage Valve

The easiest way to find third value from Cv-dP-Q is to use a calculator from a reputable vendor. Input data from datasheet to calculation:
Note modelling of actual fluid properties is a common source of inaccuracy. It is not so easy to find a suitable model for a particular fluid.
Note that dP is reffered to straight run pipe (see figure 1 ISA 75.01.01) and therefore is not totally relevant to your particular control valve piping.

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