An equal percentage valve is a characterized control valve where equal increments of valve opening produce equal percentage changes in flow through the valve. The flow increases exponentially as the valve opens, providing superior control authority across the full stroke. This design compensates for system pressure variations, making it ideal for variable load applications.
Technical Details
Equal percentage valves follow a logarithmic flow curve with a rangeability of 20:1 or greater, meaning maximum to minimum controllable flow ratios exceed 20 times. They maintain relatively constant valve authority from 10% to 100% open position, typically between 0.4 and 0.8. The shaped plug design creates increasing orifice areas as the stem rises.
Applications in HVAC
These valves are preferred for chiller loops, condenser water circuits, and heating applications where system resistance varies with pump speed. They prevent control hunting and provide stable operation across partial load conditions.
Practical Significance
Equal percentage valves cost 15-25% more than linear types but provide superior control stability. They are the industry standard choice for modern variable flow HVAC systems and should be specified for most comfort control applications.