A characterized control valve is a modulating valve with an internal contour that produces a specific flow-to-lift relationship, enabling precise system control across varying conditions. Unlike linear valves with proportional flow changes, characterized valves compensate for system resistance variations to maintain consistent control authority. These valves contain shaped plugs or cams that alter the orifice area in a predetermined manner.
Technical Details
Characterized control valves typically use equal percentage trim, where flow changes logarithmically with valve position. This design maintains relatively constant authority throughout the valve’s stroke, typically between 0.3 and 1.0 on the authority scale. They are available in two-way and three-way configurations with sizes ranging from DN10 to DN100.
Applications in HVAC
These valves excel in chiller loops, heating water circuits, and fan coil unit control where system resistance varies significantly. They prevent hunting and oscillation that occurs with linear valves in variable load conditions. Common applications include condenser water isolation and supply temperature control.
Practical Significance
Characterized valves cost 20-30% more than linear valves but provide superior control stability and reduce commissioning time through better authority performance across full load range.