When it comes to limiting noise emission due to discharge, noise reduction of control valves can be obtained by means of a suitable silencer, installed in the end of the piping line.

Such silencers are generally composed of a diffuser (upstream) and of a dissipative stage (downstream).

The diffuser is a perforated element, at which a change occurs (that is desired to be downwards) of the turbulence noise and shock noise, the presence of small diameter perforations causing a peak in noise generation for  high frequency. In addition, the presence of the diffuser causes a total loss of pressure on which attention must be paid (*).

The dissipative stage, in turn, consists of a lining (preferably: with high sound absorption), often used as filling of splitters, sometimes concentric (else: transverse), allowing for noise attenuation in a frequency range more or less extended namely depending on the acoustic characteristics of the porous medium and of its possible surfacing, on the geometry of the dissipative stage and on the nature and passage speed of the fluid.

In addition, the presence of the dissipative floor causes a total loss of pressure (usually less compared to that of the diffuser) on which attention must be paid (*) and generates self noise for which it is important to make sure that it is compatible with the noise reduction target to be considered as part of a project for which the implementation of a silencer is envisaged.

* Especially vis-à-vis the operating conditions of the valve on the downstream pressure which affects (upward)

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