Control Valve Cv/Kv

Definition

The flow coefficient characterizes a valve at a given opening. Manufacturers publish Cv (or Kv) against valve travel, defining the valve’s inherent characteristic — linear, equal percentage, or quick opening. The installed characteristic, what the loop actually sees, depends on how much of the system’s total pressure drop the valve takes: its valve authority.

Engineering context

A control valve cannot be sized in isolation. The pressure drop available to the valve depends on the pump, the pipe friction, and every other resistance in the path — all of which shift as flow changes. FluidFlow sizes valves from the solved network, so the Cv/Kv requirement reflects real upstream and downstream conditions across the operating range rather than a single assumed pressure drop, and checks for choked flow, flashing, and cavitation risk at the same time. The sizing method follows the international control-valve sizing standard (ISA 75.01.01 / IEC 60534-2-1), and the valve-cavitation check is anchored on the pressure recovery factor F_L used within those equations. The choked-flow mechanism itself differs by fluid: in liquids it is driven by flashing and cavitation, while in gases it is sonic (critical) flow. See the control valve sizing solution page for the full method.

Related definitions

Cavitation · System curve · Darcy-Weisbach equation · Backpressure · Auto sizing

See it in FluidFlow

Size control valves against the real network, not an assumed pressure drop. FluidFlow computes the required Cv/Kv from solved system conditions and checks for cavitation and choked flow.