Low viscosity impact to CV of control valve
Low viscosity impact to CV of control valve
(OP)
I am using the CV curve from control valve vendor to calculate the liquid flowrate, I found the actual flowrate is higher than predicted.
I know the CV value of control valve was generated with water, for viscosity fluid, a factor should be used for correction, and actual CV will less than calculated CV.
The service I have calculated is lower viscosity (0.2cP), does it means I will gain a higher CV than calculated. How to correct the CV value of control valve for a very low viscosity fluid?
I know the CV value of control valve was generated with water, for viscosity fluid, a factor should be used for correction, and actual CV will less than calculated CV.
The service I have calculated is lower viscosity (0.2cP), does it means I will gain a higher CV than calculated. How to correct the CV value of control valve for a very low viscosity fluid?





RE: Low viscosity impact to CV of control valve
Good luck,
Latexman
RE: Low viscosity impact to CV of control valve
There's a nomograph in the Emerson literature.
Emerson
Siemens
Womack
Good on ya,
Goober Dave
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RE: Low viscosity impact to CV of control valve
Liquid viscosities < 1 cP seem to be a "non-issue". The flow is becoming a little more turbulant. No change in flow regime. Whereas liquid viscosities > 1 cP, and definately >> 1 cP, are heading into a different flow regime, laminar flow. So, large changes are to be expected.
Good luck,
Latexman
RE: Low viscosity impact to CV of control valve
Good on ya,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Low viscosity impact to CV of control valve
I have calculate the friction loss of the fluid (viscosity=0.2cst) for pipeline, it was 6% lower than fluid with 1cst. I suspect a similar thing may happen to a control valve, which mean lower pressure drop for low viscosity (higher CV).
What do you think?
RE: Low viscosity impact to CV of control valve
For small pressure drops, you can use the Cv value to reasonably estimate the performance of the valve with a gas, much less with a slightly less viscous liquid.
By the way, if you end up with a reduced port globe valve or worse still a needle-type control valve with a viscous liquid, don't put too much stock in the viscosity correction. Even the ones who publish values for the geometry factors (Cd etc.) necessary to calculate the ISA control valve viscosity correction Fr, often haven't based those numbers on actual testing using viscous liquids. In our experience, the results of the viscosity correction are frequently wrong, and sometimes by many trim sizes.
RE: Low viscosity impact to CV of control valve
Good luck,
Latexman
RE: Low viscosity impact to CV of control valve
Standard Disclaimer, I don't work for Samson, I have just bought some of their valves.
Regards
StoneCold
RE: Low viscosity impact to CV of control valve
RE: Low viscosity impact to CV of control valve
Good luck,
Latexman