Reference Manual

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Table 1-3. Control Valve Characteristic Recommendations
Liquid Level Systems
Control Valve Pressure Drop
Best Inherent
Characteristic
Constant ΔP Linear
Decreasing ΔP with increasing load, ΔP at maximum load > 20% of minimum load ΔP Linear
Decreasing ΔP with increasing load, ΔP at maximum load < 20% of minimum load ΔP Equal-percentage
Increasing ΔP with increasing load, ΔP at maximum load < 200% of minimum load ΔP Linear
Increasing ΔP with increasing load, ΔP at maximum load > 200% of minimum load ΔP Quick Opening
Pressure Control Systems
Application
Best Inherent
Characteristic
Liquid Process Equal-Percentage
Gas Process, Large Volume (Process has a receiver, Distribution System or Transmission Line Exceeding 100 ft. of
Nominal Pipe Volume), Decreasing ΔP with Increasing Load, ΔP at Maximum Load > 20% of Minimum Load ΔP Linear
Gas Process, Large Volume, Decreasing ΔP with Increasing Load, ΔP at Maximum Load < 20% of Minimum Load ΔP Equal-Percentage
Gas Process, Small Volume, Less than 10 ft. of Pipe between Control Valve and Load Valve Equal-Percentage
Flow Control Processes
Application Best Inherent Characteristic
Flow Measurement Signal to
Controller
Location of Control Valve in Relation
to Measuring Element
Wide Range of Flow Set Point
Small Range of Flow but
Large ΔP Change at Valve
with Increasing Load
Proportional to Flow In Series Linear Equal-Percentage
In Bypass* Linear Equal-Percentage
Proportional to Flow Squared In Series Linear Equal-Percentage
In Bypass* Equal-Percentage Equal-Percentage
*When control valve closes, flow rate increases in measuring element.