I. Understanding Root Causes: Cavitation vs. Flash Vaporization

First, it is essential to distinguish between cavitation and flash vaporization, as their causes and solutions differ.

1. Flash Vaporization

Mechanism: When the downstream pressure (P2) falls below the saturated vapor pressure (Pv) of the liquid, the liquid continuously vaporizes, forming a two-phase gas-liquid flow downstream of the valve.

Phenomenon: The downstream fluid is a stable gas-liquid mixture. Damage to the valve plug and seat typically manifests as smooth, scouring erosion.

Key Solution: Prevent P2 < Pv.

Cavitation

Noise: Popping sounds from bubble collapse, combined with high-frequency vibrations, produce a piercing noise.

Damage: Causes “pitting” or “honeycombing” mechanical damage to the valve plug, seat, and downstream piping.

Vibration: Induces severe vibration in pipes and fittings.

Mechanism: At the valve's flow constriction point, pressure first drops below the saturated vapor pressure (Pv), causing liquid vaporization and bubble formation. Subsequently, in the recovery zone where flow velocity decreases, pressure rises again above the saturated vapor pressure, causing bubbles to collapse instantaneously. This collapse generates extremely high localized impact forces (reaching thousands of atmospheres).

Phenomenon:

Key Solution: Control pressure recovery to prevent bubble formation and collapse.