The flow characteristics of a control valve show the rate of flow of fluid for the range of valve travel or operation. There are two basic types of flow characteristics for control valves:(a) Inherent flow characteristics (b) Installed flow characteristics
Inherent Flow Characteristics:
Inherent flow characteristics is determined under laboratory conditions by testing the valve flow versus valve lift or travel using a constant differential pressure drop across the valve throughout the test. The inherent flow characteristics for each control valve are published by manufacturers and they are standardized for a fixed pressure drop as defined by the use of the valve flow coefficient value, Cv.
Installed Flow Characteristics:
This could be regarded as the actual flow characteristics of the control valve because it is determined for each installation by the actual differential pressure drop across the valve when in service. In operation, the differential pressure across the control valve varies throughout the valve position due to the system characteristics.