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Design and Selection of Low-Noise Control Valves
Most noise in control valves occurs with compressible fluids, as some of the energy is converted into sound during the throttling process. A common rule of thumb for estimation is this: if the product of the Cv value and the inlet pressure exceeds 1,000, the control valve will generate significant noise under critical pressure drop conditions.
Release date:
2020-04-28
Most noise in control valves occurs in cases involving compressible fluids, as some of the energy is converted into sound during the throttling process. A common rule of thumb for estimation is: if the product of the Cv value and the inlet pressure exceeds 1,000, the control valve will generate significant noise under critical pressure drop conditions.
The two primary factors in designing a low-noise control valve are fluid velocity and noise frequency. At speeds below the speed of sound, the noise energy level increases by a factor of the fluid velocity raised to the eighth power—demonstrating just how critical this factor is. At the same noise energy level, increasing the average frequency proves advantageous, as higher frequencies experience greater attenuation when passing through the valve body and downstream pipe walls.
The control valve employs a multi-stage pressure-reducing internal structure—such as a labyrinth design—which significantly reduces noise. This design uses numerous steps to force the fluid to continuously change direction, creating high turbulence and increasing frictional energy losses. As a result, not only is noise greatly minimized, but wear on the valve’s internal components is also reduced, ultimately extending the service life of the control valve.
Direct-acting single-seat control valves, particularly those with windowed sleeve designs, can be optimized to shift the maximum noise frequency higher, making the sound less audible. Among all valve configurations, if the outlet velocity of the control valve reaches or exceeds the speed of sound, it can generate harmful noise in the downstream piping system. Therefore, when operating under high pressure differentials, special measures are required on the downstream side—such as installing one or more specialized throttling plates—which not only gradually reduce the flow velocity but also help raise the noise frequency. Additionally, various industrial silencers can be employed to further mitigate noise levels. To effectively contain noise within a specific area, soundproofing is a proven strategy; however, even beyond the soundproofed zone, harmful noise levels may still persist.
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Design and Selection of Low-Noise Control Valves
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