(1) Elimination of resonance noise
When resonance occurs in the control valve, it will produce energy superposition, which in turn triggers a strong noise of up to 100 decibels. This noise may be manifested as a strong vibration accompanied by a small noise, or vibration may be weak but very noisy, there are also some cases of vibration and noise are quite obvious. This noise is usually monotonous and ranges in frequency from 3000 to 7000 Hz. Obviously, as long as the resonance is eliminated, the noise will disappear.
(2) Methods for reducing cavitation noise
Cavitation is the main source of hydrodynamic noise. When cavitation occurs, the vapor bubble rupture will produce a high-speed impact, resulting in strong local turbulence, resulting in cavitation noise. This noise has a wide frequency range and sounds like a grating sound, similar to the sound made when gravel is mixed in the fluid. Reduce and eliminate cavitation is an effective means of reducing noise.
(3) Method of using thick-walled piping
The use of thick-walled piping is an effective method for dealing with noise transmission paths. Compared to thin-walled piping, thick-walled piping can reduce noise by 0 to 20 dB. The larger the wall thickness of the pipe, or the larger the diameter of the pipe with the same wall thickness, the better the noise reduction effect. For example, DN200 pipes with different wall thicknesses of 6.25 mm to 21.5 mm can reduce noise values from -3.5 dB to 14.5 dB. Of course, the greater the wall thickness, the higher the cost required.
(4) Application of sound-absorbing materials
This is also a common and effective method of dealing with noise transmission paths. Sound-absorbing materials can be used to wrap the noise source and the pipe behind the valve. However, it should be noted that noise will spread over long distances with the flow of fluid, so the sound-absorbing material will only wrap to a certain position, and the noise reduction effect will only reach that position. This method is suitable for the case where the noise is not high and the pipeline is not long, because the cost is relatively high.
(5) Method of connecting silencers in series
This method is suitable for eliminating aerodynamic noise, and it effectively eliminates noise inside the fluid and suppresses noise transmission to the solid boundary layer. This method is both effective and economical where the mass flow rate is high or the pressure drop ratio before and after the valve is high. The use of absorption-type series silencers can significantly reduce noise, but from an economic point of view, generally attenuate to about 25 dB.
(6) Method of Soundproof Chamber
The use of soundproof chambers, houses or buildings to isolate the source of noise can reduce the noise of the external environment to an acceptable level.
(7) Series throttling method
In the case where the pressure of the regulating valve is relatively high (ΔP/P1 ≥ 0.8), the method of series throttling can be used. This method is to spread the total pressure drop over the fixed throttling element after the regulating valve and valve, such as diffuser or porous restrictor plate. This is one of the most effective methods of reducing noise. In order to obtain optimum diffuser efficiency, it is necessary to design the diffuser (shape and size of the solid body) to match the noise level generated by the valve and the noise level generated by the diffuser for each installation.
(8) Selection of low-noise valves
Low-noise valves gradually decelerate the fluid through the zigzag flow path (multiple orifices and slots) of the spool and seat to avoid generating supersonic velocity at any point in the flow path. Low noise valves are available in a wide range of forms and configurations, some even designed for specific systems. When the noise is not particularly loud, choosing a low-noise sleeve valve can reduce noise by 10 to 20 dB, which is the most economical choice.
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