Cv is in US customary units (GPM of 60°F water at 1 psi pressure drop), while Kv is in metric units (m³/h of 15°C water at 1 bar pressure drop). The exact conversion factor is Cv = 1.156 × Kv, or Kv = 0.865 × Cv.

The Liquid Pressure Recovery Factor (FL) represents the ratio of the actual pressure drop across the valve to the internal pressure drop from inlet down to the vena contracta. Rotary valves (such as ball and butterfly valves) have high recovery (low FL ~ 0.55 to 0.70), meaning vena contracta pressure dips much lower than globe valves (FL ~ 0.85 to 0.92), making rotary valves choke and cavitate at significantly lower applied pressure drops.

Incipient cavitation begins when local vena contracta pressure briefly touches vapor pressure, producing tiny micro-bubbles that collapse downstream with audible hiss. Choked flow occurs when vapor cavities blanket the vena contracta, preventing any increase in flow rate despite lowering downstream pressure. Flashing occurs when downstream pressure remains below liquid vapor pressure, so vapor bubbles never collapse and two-phase vapor-liquid exits the valve.

Valve authority (Na = ΔP_valve / (ΔP_valve + ΔP_system)) measures the fraction of total system friction loss controlled by the valve. If authority drops below 0.30 (30%), the valve's installed characteristic distorts severely (e.g. an equal-percentage valve behaves like quick-opening), leading to hunting, oscillation, and poor control stability near closed positions.

Line-sized control valves are almost always oversized, forcing the valve to operate at 5% to 15% travel where flow control is erratic, seat wire-drawing is severe, and clearance flow causes hunting. Proper sizing per IEC 60534 typically selects a valve one to two sizes smaller than line size operating between 20% and 80% stroke.