Noise is a byproduct of a control valve doing its job. However, sometimes the sound you hear may be a warning of cavitation damage. The noise, if loud enough, may also pose a health hazard to nearby employees. To protect workers from hearing damage, OSHA has set a noise-exposure limit of a weighted 90-dBA maximum over 8 hours [1]. So, it is important to know just how loud the noise from a control valve will be.

Unfortunately, there is no standard prediction method based on fundamental physical concepts. This article is the first to offer one. It presents a simplified explanation of the factors involved in liquid-flow system noise prediction. It presents both a numerical method and a graphical method, for turbulent liquid flow and cavitation. Based on extensive test data, the method uses factors published by valve manufacturers.

Turbulent noise
Valves cause a fluid to lose pressure. Potential energy (pressure) converts to kinetic energy by velocity increase through the valve orifice, and to thermal energy (turbulence).

Some of the turbulence vibrates the pipe wall. We detect that as noise in the form of pressure waves of the air surrounding the pipe. Sound power is the total acoustic energy created by the noise source. Sound pressure is the level of sound that the ear perceives. The measuring unit is the decibel.¹

Preliminary research on aerodynamic jet noise was done by Lighthill [2]. Baumann [3] used this research to develop an equation for the internal sound-pressure level produced by gases in turbulent flow. This equation is the basis for the current ISA [4] and IEC [5] control valve aerodynamic-noiseprediction methods. He wrote a summary in the December 1996 issue of Chem. Eng., pp.78-81.

Noise is a byproduct of a control valve doing its job. However, sometimes the sound you hear may be a warning of cavitation damage. The noise, if loud enough, may also pose a health hazard to nearby employees. To protect workers from hearing damage, OSHA has set a noise-exposure limit of a weighted 90-dBA maximum over 8 hours [1]. So, it is important to know just how loud the noise from a control valve will be.

Unfortunately, there is no standard prediction method based on fundamental physical concepts. This article is the first to offer one. It presents a simplified explanation of the factors involved in liquid-flow system noise prediction. It presents both a numerical method and a graphical method, for turbulent liquid flow and cavitation. Based on extensive test data, the method uses factors published by valve manufacturers.