What are the main sources and mechanisms of control valve noise in gas and liquid applications?

1 Noise sources

The main sources of control valve noise are turbulence, cavitation, flashing, and aerodynamic effects. Turbulence is the chaotic flow of fluid that creates pressure fluctuations and vibrations. Cavitation is the formation and collapse of vapor bubbles in a liquid when the pressure drops below the vapor pressure. Flashing is the transition of a liquid to a vapor when the pressure drops below the vapor pressure and stays there. Aerodynamic effects are the noise generated by the flow of gas or steam through the valve, especially when it reaches sonic or supersonic speeds.

2 Noise mechanisms

The noise mechanisms are the ways that the noise sources produce sound waves. There are four main noise mechanisms: mechanical, hydrodynamic, aerodynamic, and acoustic. Mechanical noise is the sound caused by the vibration of the valve components, such as the stem, plug, seat, and body. Hydrodynamic noise is the sound caused by the pressure fluctuations and vibrations of the fluid due to turbulence, cavitation, and flashing. Aerodynamic noise is the sound caused by the shock waves and expansion waves of the gas or steam flow due to aerodynamic effects. Acoustic noise is the sound caused by the interaction of the fluid flow and the valve geometry, such as the orifice, outlet, and pipe.

3 Noise characteristics

The noise characteristics are the features that describe the quality and intensity of the noise. They include the frequency, spectrum, level, and directivity. The frequency is the number of cycles per second of the sound wave, measured in hertz (Hz). The spectrum is the distribution of the sound energy over different frequencies, measured in decibels (dB). The level is the magnitude of the sound pressure, measured in decibels (dB) or sound pressure level (SPL). The directivity is the directionality of the sound radiation, measured in degrees.

4 Noise measurement

The noise measurement is the process of quantifying and evaluating the noise characteristics. There are different methods and standards for measuring control valve noise, depending on the type of fluid, the application, and the purpose. Some of the common methods are the sound intensity method, the sound pressure method, and the sound power method. Some of the common standards are the International Electrotechnical Commission (IEC) 60534-8-3, the American National Standards Institute (ANSI)/Instrumentation, Systems, and Automation Society (ISA) S75.17, and the American Petroleum Institute (API) RP 521.

5 Noise prediction

The noise prediction is the process of estimating the noise characteristics before installing or operating the control valve. There are different models and formulas for predicting control valve noise, depending on the type of fluid, the noise mechanism, and the valve geometry. Some of the common models are the IEC 60534-8-3 model, the ISA S75.17 model, and the API RP 521 model. These models use empirical or theoretical data to calculate the noise level and spectrum based on the flow conditions, valve dimensions, and pipe properties.

6 Noise reduction

The noise reduction is the process of minimizing or eliminating the noise sources and mechanisms. There are different strategies and techniques for reducing control valve noise, depending on the type of fluid, the application, and the noise characteristic. Some of the common strategies are selecting the appropriate valve type, size, and trim, optimizing the valve operation and control, installing noise attenuation devices, such as silencers, diffusers, and baffles, and isolating or insulating the valve and pipe from the surroundings.