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Vent and blowdown silencers

Design, engineering, manufacturing and worldwide delivery of blowdown and vent silencers by INERCO.



Vent silencers are equipment designed to reduce noise produced by high temperature and high-pressure gas flows during atmospheric expansions in safety valves, control valves, relief valves, purge systems and blow systems. Noise generated by these systems may be higher than 150 dBA, which can result in important issues for plant operations and maintenance.

INERCO has over 30 years of experience in the research, development, manufacturing, and innovation of noise reduction technologies. In order to predict the acoustic behavior of our equipment (sound attenuation) we use a specialized Finite Element Method (FEM) software to study the change of all the parameters. We also have a laboratory and an acoustic test chambers, where client prototypes are tested.

Our methodology is:

  • We obtain the pressure, velocities and turbulence fields inside the silencers using fluid-dynamic analysis. With these parameters, we calculate the self-noise (noise generated by the fluid through the silencer).
  • Using the pressure progress, a static-structural analysis is performed to study the maximum stress and deformations of the equipment. In this structural analysis, we apply fluid dynamic and external loads, as the effect of the wind, snow and gravity.
  • Once the static pre-stress is calculated, we carry out a harmonic analysis in order to study the resonance phenomena of the equipment casing. Then, we calculate natural frequencies and their associated vibration modes of the silencers. The aim of this analysis is to determinate casing vibrations according to loads applied and to check that the silencer is not going to suffer resonance phenomena.
  • Finally, we do the harmonic analysis to study the acoustic performance of the silencer.


INERCO's commitment with the supply:

  • Customized design for each case
  • Acoustic and fluid-dynamic design of the silencer
  • Mechanical and acoustic guarantee
  • Worldwide delivery
  • Own manufacturing to assure quality and delivery term
  • Manufacturing dossier and 3D drawings
  • Document and logistics management:
    • Welding homologation dossier
    • Material certificates
    • Inspection Test Plan
    • Painting procedure
    • Quality procedure
    • Non-destructive tests (penetrant dyes, X-rays)
    • Verification check-list
    • Nameplate
    • Packing
    • Packing-list
  • Fixed prices
  • Quality control and inspection of each silencer
  • Technical advice of the installation and maintenance
  • Operating, maintenance, stocking and packing handbook.



Vent silencers have three main components:

  • Inlet diffuser: reduces the noise generated and modifies the sound spectrum so it can be better controlled in the absorptive stages of the silencer. This is obtained by dividing the flow into hundreds of small jets. The highest pressure drop of the silencer will be produced inside this stage.
  • Absorbent plenum: is an expansion chamber designed to homogenize the gas flow before the reduction of acoustic energy that is obtained in the dissipative stage. The sound reduction principle consists in the waves reflection that reduce the noise level in low frequencies (until 250 Hz).
  • Dissipative stage: drives the fluid to a system of crowns (cylindrical design), or absorbent baffles (prismatic design) made of absorbent material and perforated steel sheet, reducing the noise in medium and high frequencies (from 250 Hz to 16.000 Hz). The sound reduction principle is based on the transformation of kinetic energy of the fluid into thermal energy caused by the friction with the absorbent material.


Design parameters:

The design of the vent silencers depends on the following factors:

  • Fluid conditions: type of fluid, mass flow rate, pressure and temperature.
  • Incident noise (noise spectrum at the inlet of the equipment).
  • Required attenuation, required noise level at the discharge of the silencer or at a specific distance of it.
  • Nominal diameter (DN), material and thickness of the connection pipe.
  • Pressure drop required.
  • Connection type: flanged or welded.
  • Type of operation: intermittent or continuous.
  • Physical space, weight or materials restrictions.
  • Position and location of the silencer.


Design reference normative:

  • ISO 9001:2008: our manufacturing system is according with quality requirements specified in this normative.
  • ASME section VIII: code for the design, manufacture and inspection of pressure equipment.
  • PED 2014/68/EU: Pressure equipment directive, for cases where pressure drop contributed by the silencer is more than 0,5 barg.
  • ASME Section IX: normative of welding procedure.
  • ASME B 16.5 y ASME B 16.25: welding procedure between flanged connections and welded connections (BW).
  • API 521, VDI 2713 y ISO 4126: generated noise level in the atmospheric discharge.


Customized design:

INERCO can adapt the design of the silencers to the client requirements:

  • Range of attenuations: between 15 and 60 dBA.
  • Material selection: carbon steel, stainless steel and alloy steel.
  • Temperature limit up to 650 ºC.
  • Protective coating and surface treatment.
  • Multiple inlets available.
  • Drainage to evacuate condensates.
  • Non-destructive test: penetrant dyes and X-Rays.
  • Phytosanitary packing.
  • Horizontal or vertical installation.
  • Accessories: flanges, counter flanges, expansion joints, nameplates, anti-bird mesh, insulation clips, top rain coat, swan neck, lifting lugs, side supports, bolts, etc....
  • Engineering: mechanical calculations (support reactions, vibration modes, stress and maximum strain, fatigue, etc....) and fluid dynamics (calculation of the distribution of pressure, velocities, self-noise and temperature).
  • Acoustic measurements.