Flow Phenomena

Valve Noise

Control valve noise comes in three distinct mechanisms, and the treatment depends on which one you have:

• Aerodynamic (gases, steam): turbulence and shock structures generated by the large pressure ratio and jet velocities in the trim — by far the most common, predicted by IEC 60534-8-3/8-4 methods from valve geometry and gas properties.
• Hydrodynamic (liquids): flow turbulence plus the implosion of cavitation bubbles — cavitation noise has a characteristic "gravel" sound and rises steeply toward the choked condition.
• Mechanical: resonance of trim parts or loose components vibrating in the flow — often narrow-band and tonal, sometimes destructive, and usually cured by stiffness/flow-direction changes rather than noise trims.

Control ladder: reduce the velocity and split the pressure drop (multi-stage, multi-path drilled cages), diffuse the jets downstream (perforated diffuser plates), add mass/insulation as a last resort, and use low-noise trim sized per the standard's predicted SPL. Always predict noise at both the normal and the maximum flow case — quiet at design flow can be loud at turndown.

Related glossary terms

• Cavitation
• Cavitation Index (σ, Kc, xFz)
• Choked Flow