(1) Resonance noise elimination method
Only when the regulating valve resonates can there be energy superposition that produces a strong noise of more than 100 decibels. Some are characterized by strong vibration and low noise, while others are characterized by weak vibration and very high noise; Some have high vibration and noise. This noise produces a single tone sound with a frequency typically between 3000 and 7000 Hz. Obviously, by eliminating resonance, the noise naturally disappears.
(2) Cavitation noise elimination method
Cavitation is the main source of hydrodynamic noise. During cavitation, bubbles rupture and generate high-speed impacts, causing strong turbulence in local areas and generating cavitation noise. This noise has a wide frequency range and produces a grating sound similar to the sound produced by the presence of sand in the fluid. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
(3) Using the thick wall pipeline method
The use of thick wall tubes is one of the methods for acoustic path treatment. The use of thin walls can increase the noise by 5 decibels, while the use of thick wall tubes can reduce the noise by 0 to 20 decibels. The thicker the wall of the same pipe diameter, the larger the pipe diameter of the same wall thickness, and the better the noise reduction effect. For example, when the wall thicknesses of DN200 pipes are 6.25, 6.75, 8, 10, 12.5, 15, 18, 20, and 21.5 mm, the noise can be reduced to - 3.5, - 2 (i.e., increased), 0, 3, 6, 8, 11, 13, and 14.5 decibels, respectively. Of course, the thicker the wall, the higher the cost.
(4) Using sound absorbing material method
This is also a relatively common and most effective method of acoustic path processing. Sound absorbing materials can be used to wrap the noise source and the pipeline behind the valve. It must be pointed out that because noise can propagate over long distances through fluid flow, the effectiveness of noise elimination ends wherever sound absorbing materials are packaged and thick walled pipes are used. This method is suitable for situations where the noise is not very high and the pipeline is not very long, as it is a more expensive method.
(5) Series muffler method
This method is applicable to the attenuation of aerodynamic noise, which can effectively eliminate the noise inside the fluid and suppress the noise level transmitted to the solid boundary layer. This method is most effective and economical for places with high mass flow or high pressure drop ratio before and after the valve. The use of absorption type series silencers can significantly reduce noise. However, from an economic perspective, it is generally limited to attenuation to about 25 decibels.
(6) Soundproof box method
Use sound barriers, houses, and buildings to isolate noise sources inside, reducing the noise from the external environment to an acceptable range.
(7) Series throttle method
When the pressure ratio of the regulating valve is high (△ P/P1 ≥ 0.8), the series throttling method is used to disperse the total pressure drop between the regulating valve and the fixed throttling element behind the valve. For example, using diffusers and multi hole flow restrictors is the most effective way to reduce noise. In order to obtain the best diffuser efficiency, it is necessary to design the diffuser (physical shape and size) based on the installation of each piece, so that the noise level generated by the valve and the diffuser are the same.
(8) Select low noise valve
The low noise valve decelerates gradually according to the zigzag flow path (multi orifice, multi groove) of the fluid through the valve core and valve seat to avoid generating supersonic speeds at any point in the flow path. There are various forms and structures of low noise valves (some designed for special systems) for use. When the noise is not very high, select a low noise sleeve valve, which can reduce the noise by 10-20 decibels. This is the most economical low noise valve.