What is Cavitation in Valves? How Should We Address It?

What is Cavitation and its Effects on Valves and Equipment？

        Cavitation is a phenomenon that occurs when pressure drops below the vapor pressure of a fluid, leading to the formation of vapor bubbles. These bubbles collapse violently when they travel to regions of higher pressure, generating intense shock waves, noise, and vibration. Cavitation can significantly damage industrial equipment, particularly valves and downstream piping systems. The primary impacts of cavitation are:

Noise and Vibration: The collapse of vapor bubbles generates high noise levels and large amplitude vibrations. These vibrations can cause severe damage to valve components, including springs, thin membranes, and cantilever structures. They can also affect instruments like pressure gauges, transmitters, thermocouples, flow meters, and sampling systems.

Accelerated Wear and Corrosion: The intense vibrations from cavitation can lead to accelerated wear and corrosion. Metal surfaces can become eroded, leading to micro-wear and the formation of abrasive oxides. This process speeds up damage to valves, pumps, check valves, and any rotating or sliding mechanisms. Cavitation can also crack valve parts and pipe walls, compromising the integrity of the system.

Contamination: The materials that get eroded by cavitation, such as metal particles and corrosive chemical compounds, can contaminate the fluid inside the pipe. This is particularly problematic in sanitary or high-purity systems where even minor contamination can have significant consequences.

How to Prevent and Mitigate Cavitation？

Several design and operational approaches can help prevent or mitigate cavitation damage:

Valve Design Modifications:

• Flow Splitting: By dividing a large flow into smaller flows through multiple parallel openings, the size of the cavitation bubbles can be reduced. Smaller bubbles create less noise and cause less damage.

• Staged Pressure Drop: Instead of a single large pressure drop, valves can be designed with multiple stages of pressure reduction. Each stage reduces the pressure incrementally, preventing the fluid from reaching its vapor pressure and thus avoiding cavitation.

Valve Location and Fluid Conditions:

• Higher Pressure at Valve Inlet: Positioning the control valve where the pressure is higher (e.g., further upstream or at a lower elevation) can prevent cavitation by maintaining the fluid’s pressure above its vapor pressure.

•     Lower Temperature: In certain cases, controlling the temperature of the fluid (e.g., in a heat exchanger) can reduce the vapor pressure, thus lowering the risk of cavitation.

Predictive Measures: Valve manufacturers may estimate the risk of cavitation by calculating the pressure drop and the expected noise levels. A noise level below certain thresholds (e.g., 80 dB for valves up to 3 inches, 95 dB for valves 16 inches and above) is considered safe to prevent cavitation-induced damage.

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