The Flow Characteristic of a Control Valve is the Relationship between the Control Valve Capacity and valve stem travel.
Inherent Characteristics represents this relationship with constant pressure drop across the valve.
Installed Characteristics represents the same relationship but with varying pressure drop due to losses in the pipeline and any equipment installed in series.
Equal Percentage is considered to be the most common characteristic used in process control. The inherent characteristic of a equal percentage plug allows for flow capacity to increase exponentially with valve stroke. i.e. equal increments in valve stroke result in equal percentage change in the existing Cv. When Installed, an equal percentage plug will tend to behave similarly to a Linear Characteristic valve in Inherent conditions.
The Linear characteristic creates equal changes in Cv per unit of valve stroke, when the pressure drop is constant. Linear plugs are frequently used in systems where the differential pressure through the valve corresponds to the major part of the total differential pressure of the system. When installed, and due to the changes in pressure drop across the valve, a Linear trim will tend to behave similarly to Quick-Open trim.
Quick-open plugs are used in on-off services and are designed to create large increments of flow rate, even from small opening percentages.