At one time I had a table that listed flow coeficients versus percent open for Cameron ball valves but I can no longer find it.It seems to be a somewhat vague enquiry. Why not contact the manufacturer that on the basis of a specific model would give the most appropriate answer?
By the way I've always thought that a ball valve (I mean a quarter-turn ball valve) had to be operated fully open or closed. This item is not conceived for throttled (flow control) operations.
 They should be operated O/C when in steady state, however when conducting transient analysis involving the opening and closing of these valves, especially around pumps, flow coefficients with percent open can become an important topic.
I have a similar table and there should be little difference, if any, between ball valve manufacturers, if you're talking full ports.

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