I've been given some test data on a butterfly valve that I'm trying to validate. My validation information is in gallons per minute. The acceptance criteria was given as being from 22 to 26 turns, and I was told that +/- 2 handwheel turns from the nominal 24 turns equated out to +353 gpm to -426 gpm. Can I calculate a flowrate assuming a linear increase (i.e., 11*353=3883 gpm) or do I get a larger increase when the valve first opens? What information would I need in order to figure out the flowrate? The valve supposedly is an Enertech butterfly 15".Butterfly valve? The butterfly valves I know close in 90 degrees.Aren't you looking at the data of a globe valve. These valves have a correlation opening x flow rate. Large butterfly valves could have gears and such in the spindel but normally a butterfly valve will close in 90 deg - so unless the gear is really funny the closure of the valve will also be linear.This does however not mean that the "resistance" introduced by closing the valve will increase linear. As i recall it the flow will only decrease slowly when close and then drop abruptly when the valve is almost fully closed (the last 20-30 % introduceses almost all of the pressuredrop)

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