Flow Characteristics
Linear Characteristic
The linear inherent characteristic gives flow directly proportional to travel: at 50 % open the valve passes 50 % of its rated capacity, at 80 % it passes 80 %. Loop gain (dQ/dh) is constant across the whole stroke — one property that defines the characteristic.
Where it fits: installations where the valve holds most of the system pressure drop, so the installed curve stays close to the inherent one — pressure-dropping stations, recirculation and bypass lines, and level control of vessels with nearly constant gain. In these services the controller sees a constant process-valve gain product and tunes simply.
Where it misleads: in low-authority installations (valve ΔP a small, falling share of the total), the installed linear curve becomes quick-opening-like — very high gain at small travel, dead above mid-travel. That combination produces loops that oscillate at low load and are sluggish at high load. In those systems specify equal percentage instead. See the full comparison in flow characteristics compared.