Linear – For equal stem movements the change of flow resulting from the movement is constant throughout the stroke.
Equal Percentage – For equal stem movements the change of flow resulting from the movement is directly proportional to the flow rate immediately before the change took place.
Besides the loop gain and installed characteristic considerations, equal percentage valve trim will generally give better rangeability and better control at low flow rates. Linear trim will give better control at flow rates over 50% of the valve capacity.