TABLE OF CONTENTS One of the most noticeable and uncomfortable problems associated with valves is noise. To the human, not only can noise be annoying, but it can also cause permanent hearing loss and unsafe working conditions. Extensive studies have shown that human hearing is damaged by long exposures to high noise levels. Hearing damage is cumulative and irreversible and begins with the loss of high frequencies. As hearing loss continues, lower frequencies are eventually lost, which affects the ability to understand normal speech patterns. When subjected to noise at lower frequencies, the performance of human organs, such as the heart or the liver, can also be affected. In addition, noise and the accompanying vibration can affect the valve s performance and cause fatigue in the valve, piping, and nearby process equipment.
In essence, noise is generated when vibration produces wide variations in atmospheric pressure, which are then transferred to the eardrums as noise. Noise spreads at the speed of sound [which is 1100 ft/s (335 m/s) or 750 mi/h (1200 km/h)]. Noise in valves can be created in a number of different ways; however, the most common cause is turbulence generated by the geometry of the valve, which is radiated by the downstream piping (Fig. 9.25). In many cases, noise does not radiate from the valve itself, because the body itself is stiff and unyielding.
Process turbulence...
