What is the difference between inherent and installed valve characteristics?

Inherent characteristics describe valve behavior at constant pressure drop (test bench condition). Installed characteristics describe actual behavior in the piping system where pressure drop varies with flow. In real systems, increasing flow reduces available pressure drop across valve (more drop in piping). This distorts inherent characteristic - equal percentage becomes more linear, linear becomes quick opening. Installed characteristic depends on valve pressure drop as percentage of total system drop. Design for valve to have 25-50% of system delta P at normal flow to maintain reasonable installed characteristic.