Causes of the noise of the regulating valve and the solutions

March 05, 2019
Industry News

1) Elimination of resonance noise
Only when the regulating valve resonates, is there energy superposition that produces a strong noise of more than 100 decibels. Some produce strong vibration with low noise, while some weak vibration with very high noise, and the other produce strong vibration with high noise. This noise produces a single-tone sound that typically has a frequency of 3000 to 7000 Hz. Obviously, the resonance is eliminated and the noise naturally disappears.

2) Elimination of cavitation noise
Cavitation is the main source of hydrodynamic noise. At the time of cavitation, the steam bubble burst produces a high-speed impact, causing strong turbulence locally, resulting in cavitation noise. This noise has a wide frequency range that produces a gig sound similar to that of a fluid containing sand. Eliminating and reducing cavitation is an effective way to eliminate and reduce noise.

3) Using thick-walled pipeline
The use of thick-walled tubes is one of the sound path treatment methods. The use of thin walls increases noise by 5 decibels, and the use of thick-walled tubes reduces noise by 0 to 20 decibels. The thicker the pipe wall of same diameter is, or the larger the pipe diameter of the same wall thickness, the better the noise reduction effect is. Let's take an instance, for DN200 pipe, if the wall thickness is 6.25, 6.75, 8, 10, 12.5, 15, 18, 20, 21.5 mm, the noise can be reduced to -3.5, -2 (that is, increase), 0, 3, 6, 8, 11, 13, 14.5 decibels respectively. Of course, the thicker the wall is, the higher the cost is.

4) Using sound absorbing materials
This is also a more common and effective way to handle sound paths. The noise source and the post-valve pipeline can be wrapped with sound absorbing materials. It must be pointed out that since the noise will travel long distances through the fluid flow, the effectiveness of eliminating the noise is terminated where the sound absorbing material is wrapped and where the thick-walled pipe is used. This method is suitable for situations where the noise is not very high and the pipeline is not very long, because it is a more expensive method.

5) Using silencers in series
This method is applicable to the muffling 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 in places where the mass flow rate is high or the pressure drop ratio before and after the valve is high. Noise can be drastically reduced by using absorption type silencers in series. However, it is generally limited to reduce the noise to about 25 decibels economically.

6) Using sound insulation box
Use soundproof boxes, houses and buildings to isolate the noise source and reduce the noise of the external environment to an acceptable level.

7) Series throttling method
In the case where the pressure ratio of the regulating valve is high (ΔP/P1 ≥ 0.8), the series throttling method is adopted, that is, the total pressure drop is dispersed on the fixed throttle element on or behind the regulating valve. The most effective way to reduce noise is to use a diffuser or a porous restrictor. In order to achieve the best diffuser efficiency, the diffuser (tangible shape, size) must be designed according to the installation of each piece, so that the noise level generated by the valve is the same as the noise level generated by the diffuser.

8) Using valves with low noise
Inside a low-noise valve, the flow rate is gradually decelerated according to the tortuous flow path of the fluid through the valve core and the valve seat (porous channel, multi-channel) to avoid supersonic speed at any point in the flow path. There are low-noise valves in many forms and structures (designed for special systems) for use. When the noise is not very high, a low-noise sleeve valve can be used to reduce noise by 10 to 20 decibels, which is the most economical low-noise valve.