Explain different control valve characteristics and their applications.

Linear: flow proportional to opening - used when valve takes most system dP and dP is constant. Equal percentage: equal increment of opening gives equal percentage change in flow - most common, provides linear installed characteristic when valve dP varies with flow. Quick-opening: large flow change at small opening - used for on-off or relief service. Selection based on: system pressure drop distribution, process gain requirements, and rangeability needs. Equal percentage preferred for most process control applications.