Solutions to high noise in control valves

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(1) Method of eliminating cavitation noise: Cavitation is the main source of hydrodynamic noise. During cavitation, the bursting of bubbles creates high-speed shock waves, which induce intense local turbulence and generate cavitation noise. This noise has a wide frequency range and produces a rattling sound, similar to the noise generated by sand and gravel in the fluid. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise. (2) The method of eliminating resonance noise is effective only when energy builds up due to the resonance of the control valve, resulting in intense noise of over 100 decibels. Some exhibit strong vibration with low noise, while others have weak vibration but very high noise levels ； Some have relatively high vibration and noise levels. 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. (3) The thick-walled pipeline method involves the use of thick-walled pipes, which is one of the acoustic path treatment approaches. Using thin walls can increase noise by 5 decibels, while using thick-walled pipes 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 can be -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) Use of sound-absorbing materials. This is also a relatively common and effective method for treating sound paths. The noise source and the pipelines behind the valve can be wrapped 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 applied and thick-walled pipes are used. This method is suitable for situations where the noise level isn’t very high and the pipelines aren’t very long, as it is a relatively costly method. (5) The soundproof box method uses soundproof boxes, houses, and buildings to enclose the noise source, thereby reducing the noise from the external environment to an acceptable level. (6) 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. This method is effective and economical for applications with high mass flow rates or a high pressure drop across the valve. Using absorptive series silencers can significantly reduce noise. However, from an economic standpoint, it is generally limited to a attenuation of about 25 decibels. (7) Series throttling method: In cases where the pressure ratio across the control valve is high (△P/P1 ≥ 0.8), the series throttling method is employed; this involves distributing the total pressure drop between the control valve and a fixed throttling element located downstream of the valve. Using diffusers or porous flow-restricting plates is an effective method for reducing noise. To achieve optimal diffuser efficiency, the diffuser must be designed (in terms of its physical shape and size) according to the installation conditions of each individual unit, so that the noise level generated by the valve is equal to that produced by the diffuser. (8) Use low-noise valves; these valves enable the fluid to slow down gradually as it passes through the tortuous flow paths (multiple channels or grooves) in the valve core and seat, thereby preventing supersonic speeds from occurring at any point within the flow path. There are various types and structures of low-noise valves available for selection (some of which are designed for specific systems). When the noise level is not very high, using a low-noise sleeve valve can reduce noise by 10 to 20 decibels; it is the most cost-effective low-noise valve available.