Flow Characteristics
Inherent Characteristic
The inherent flow characteristic is the flow-versus-travel curve of a valve measured at a constant pressure drop. It is purely a trim property — set by the plug contour or cage window shape — and it is what valve datasheets publish.
Do not confuse it with the installed characteristic, which is what the loop actually experiences once the valve sits in a system whose pressure drop varies with flow. The installed curve is the inherent curve reshaped by the falling valve ΔP (quantified by the pressure-drop ratio; see valve authority). A linear valve in a low-authority installation behaves quick-opening; an equal-percentage valve behaves closer to linear.
Standard names: linear, equal percentage, quick-opening (see linear, equal percentage, quick-opening), plus modified parabolic and hyperbolic forms offered by some vendors. Interchangeable cages are the usual way to re-characterize a globe valve in the field. Full comparison: flow characteristics compared.