(1) Method of eliminating resonance noise
Only when the regulating valve resonates, can there be energy superposition and produce a strong noise of more than 100 decibels. Some show strong vibration and low noise, while others have weak vibration and very high noise; Some have high vibration and noise. This noise produces a single tone sound with a frequency of 3000 ~ 7000 Hz. Obviously, the elimination of resonance, the noise will naturally disappear.
(2) Method of eliminating cavitation noise
Cavitation is the main source of hydrodynamic noise. During cavitation, bubble rupture produces high-speed impact, causing strong turbulence and cavitation noise locally. This kind of noise has a wide frequency range and produces rattle sound, which is similar to the sound made by sand and stone in the fluid. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.
(3) Use thick wall pipeline method
Using thick wall pipe is one of the methods of sound path treatment. Using thin wall can increase the noise by 5 dB, and using thick wall tube can reduce the noise by 0 ~ 20 dB. 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 thickness of DN200 pipe is 6.25, 6.75, 8, 10, 12.5, 15, 18, 20 and 21.5mm respectively, the noise can be reduced by -3.5, -2 (i.e., increase), 0, 3, 6, 8, 11, 13 and 14.5 DB respectively. Of course, the thicker the wall, the higher the cost.
(4) Sound absorbing material method
This is also a common and most effective sound path processing method. The noise source and the pipeline behind the valve can be wrapped with sound-absorbing materials. It must be pointed out that because the noise will spread over a long distance through fluid flow, the effectiveness of noise elimination will end where the sound-absorbing material is packed and where the thick wall pipe is used. This method is applicable to the situation where the noise is not very high and the pipeline is not very long, because it is a more expensive method.
(5) Series silencer method
This method is applicable to the attenuation of aerodynamic noise. It can effectively eliminate the noise inside the fluid and suppress the noise level transmitted to the solid boundary layer. For places with high mass flow or high pressure drop ratio before and after the valve, this method is the most effective and economical. The noise can be greatly reduced by using absorption series silencer. However, from an economic point of view, the attenuation is generally limited to about 25 dB.
(6) Soundproof box method
Use loudspeakers, houses and buildings to isolate the noise source inside, so that the noise of the external environment can be reduced to an acceptable range.
(7) Series throttling method
When the pressure ratio of the regulating valve is high (△ p/p1 ≥ 0.8), the series throttling method is adopted, that is, the total pressure drop is dispersed on 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, the diffuser (physical shape and size) must be designed according to the installation of each piece, so that the noise level produced by the valve is the same as that produced by the diffuser.
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