Valve Authority

Definition

Valve authority (N) = ΔP_{valve, open} / (ΔP_{valve, open} + ΔP_variable), where ΔP_{valve, open} is the pressure drop across the control valve at its design (fully open) condition and ΔP_variable is the pressure drop across the rest of the variable circuit at the same flow. Authority is a number between 0 and 1. The higher the authority, the closer the valve’s installed characteristic stays to its inherent characteristic, giving more stable and predictable control.

Engineering context

When a control valve takes only a small fraction of the circuit pressure drop (low authority), its installed characteristic becomes distorted and control near the closed position turns coarse and unstable. Designers therefore size the valve so it keeps meaningful authority at the design flow — a value of roughly 0.25–0.5 or higher is commonly recommended, depending on the application. Because FluidFlow solves the pressure drop across every component in the network, the drop taken by a control valve relative to the rest of the circuit — and therefore its authority — can be read directly from the solved results at the design condition.

Related definitions

Control valve Cv/Kv · System curve · Pump curve

See it in FluidFlow

Check valve authority straight from a solved model. FluidFlow reports the pressure drop across a control valve and across the rest of the circuit at the design flow, so the authority follows from the network results rather than a separate hand calculation.