Relation between flowrate and butterfly valve opening

[balotpinoy]

is it right to say that valve opening for both ball & butterfly valve is directly proportional to flowrate passing through it?

say 100 m^3/hr at 100% opening
50 m^3/hr at 50% opening??

thanks in advance..

 

[russ_watters]

Definitely not. Flow starts fast, then levels-out. Think a sideways parabola, with valve position horizontal and flow vertical.

 

[balotpinoy]

so i need to compute the flowrate using bernoulli taking into account % opening of the valve in the friction loss term?

if so, where can i find values of Kf for both ball and butterfly valves..

tnx a lot..