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Hi everyone. This is my first time on this forum.

I am actually calculating the flow coefficient of a ball valve using air as a compressible fluid.
I am using the standard IEC 60534-2-3 equations for the calculation of the valve style modifier Fd under these conditions.

For non turbulent flow and reduced trim valves where C/d^2<0.016N18, they suggest the following formula..page 33 (15)

Fd=N31*v*Fr^2*Fl^2*sqrt(C*FL)/(Q(1+N32(C/d^2)^(2/3))

The truth is that in my case im getting really small values for Fd completely non sense.
Does anyone know the accuracy of this equation??

Is there any other way to determine the valve style modifier Fd using the model geometry?

Thanks
Jorge