How to solve the problem of excessive noise from a control valve

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When control valves are in use, they can sometimes generate some noise, and many methods for reducing this noise have been developed. 1) Resonance noise elimination method: Intense noise of over 100 decibels is generated only when the control valve resonates, due to energy buildup. Some exhibit strong vibration with low noise, while others have weak vibration but very high noise levels ； Some have significant vibration and noise. This noise produces a single-toned sound, with a frequency generally ranging from 3000 to 7000 hertz. Obviously, by eliminating resonance, the noise disappears as well. 2) Method of eliminating cavitation noise: Cavitation is the main source of hydrodynamic noise. During cavitation, the bursting of bubbles generates high-speed shock waves, causing intense local turbulence and resulting in cavitation noise. This noise has a wide frequency range and produces a rattling sound, similar to the noise generated by sand and stones present in the fluid. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise. 3) Use of thick-walled pipeline method: Employing thick-walled pipes is one of the methods for acoustic path treatment. Using thin walls can increase noise by 5 decibels, while using thick-walled tubes can reduce noise by 0 to 20 decibels. The thicker the wall for a given diameter, and the larger the diameter for a given wall thickness, the better the noise reduction effect. For a DN200 pipe, when the wall thicknesses are 6.25, 6.75, 8, 10, 12.5, 15, 18, 20, and 21.5 mm respectively, the noise reduction is -3.5, -2 (i.e., an increase), 0, 3, 6, 8, 11, 13, and 14.5 decibels respectively. Of course, the thicker the wall, the higher the cost. 4) The use of sound-absorbing materials is also a common and highly effective method for handling sound paths. The noise source and the pipelines behind the valve can be covered with sound-absorbing materials. It must be noted that since noise can travel over long distances through fluid flow, the effectiveness of noise reduction ends wherever sound-absorbing materials are installed and thick-walled pipes are used. This method is suitable for situations where the noise level is not high and the pipeline length is not long, as it is a relatively expensive approach. 5) Series silencer method: This method is suitable for reducing aerodynamic noise; it can effectively eliminate noise within the fluid and suppress the noise level transmitted to the solid boundary layer. For applications with high mass flow rates or a high pressure drop across the valve, this method is the most effective and economical. Using absorptive series silencers can significantly reduce noise. However, from an economic perspective, it is generally limited to attenuating to about 25 decibels. 6) Soundproof box method: Soundproof boxes, houses, and buildings are used to enclose the noise source, thereby reducing the noise from the external environment to an acceptable level. 7) Series throttling method: In cases where the pressure ratio of the control valve is high (△P/P1≥0.8), the series throttling method is employed, which involves distributing the total pressure drop across both the control valve and a fixed throttling element located after the valve. Using diffusers or porous flow restrictors is the most effective method among those for reducing noise. To achieve optimal diffuser efficiency, it is necessary to design the diffuser (its shape and size) based on the installation conditions of each unit, so that the noise level generated by the valve is equal to that generated by the diffuser. 8) Use low-noise valves. These valves work by allowing the fluid to slow down gradually as it passes through the complex flow paths within the valve core and seat (multiple channels or grooves), thereby preventing supersonic speeds from occurring at any point in those flow paths. There are various forms and structures of low-noise valves (some designed for specific systems) available for use. When the noise level is not very high, using a low-noise sleeve valve can reduce noise by 10–20 decibels; it is the most cost-effective low-noise valve available.