8 - Analysis of valve and piping noise

Abstract

This chapter focuses on the analysis of valve and piping noise. It also explains cavitation in liquid systems. Piping system noise can be produced in many ways, some of which are cavitation, water hammer, mechanical vibration of valve trim, and the noise of the fluid itself. Valve cavitation occurs when the pressure of a liquid is momentarily reduced below the vapor pressure. While crossing the valve orifice, the liquid passes through a low-pressure region. If the Vena Contracta pressure is lower than the vapor pressure of the liquid, small vapor bubbles are formed. The most common source of noise in valves and piping systems is the sound produced by the fluid itself. All operating piping systems produce some noise. When the noise level created in the piping system exceeds the background noise level in any audible frequency band it may become objectionable. A useful and accurate control valve noise prediction method is now available. It is based on theoretical considerations and actual tests. Acoustic insulation does not reduce the sound energy produced within the valve or pipe. The noise created by a valve or other restrictions in the pipeline can be transmitted for relatively long distances through the pipe wall and fluid stream. An installation of a properly sized valve planned to keep approach and exit velocities low, utilizing tapered expansions and specified straight lengths of pipe, is a better way of assuring a quieter reducing station.