Control Valve Characteristics

 Simply put it is:-

"The relationship between the control valve's flow capacity and travel measured with a constant differential pressure across the valve". 

Quick Opening Flow Characteristic

A valve with quick opening flow characteristic provides a maximum change in flow rate at low travels and small changes when the valve plug is near maximum. Control valves with quick opening flow characteristics are often used for on/off applications where significant flow rate must be established quickly as the valve begins to open. Consequently they are often used in relief valve applications.

Quick opening valves can also be selected for many of the same applications for which linear flow characteristics are recommended.

Linear Flow Characteristic

A valve with linear characteristic provides a flow rate directly proportional to travel. Linear characteristics are commonly specified for liquid-level and flow-control applications.

Equal Percentage Flow Characteristic (EQP)

In equal percentage flow characteristic, equal increments of valve travel produce equal percentage changes in the existing flow. A valve with an inherent equal percentage flow characteristic provides precise throttling control through the lower portion of the travel range and rapidly increasing capacity as the valve plug nears the wide open position. Valves with equal percentage flow characteristics are used on pressure control applications, on applications where a large percentage of the pressure drop is normally absorbed by the system itself with only a relatively small percentage available at the control valve, and on applications where highly varying pressure drop conditions can be expected.