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Vent & Blowdown Silencers

Recommended Operating Velocity Limits:  (See Technical Section)

Blowdown Duration

Intermittent

15000 to 20000 FPM

Continuous

10000 to 15000 FPM
Max. Allowable 20000 FPM
Critical  Less than 10000 FPM

These velocity limits are based on fully expanded flow, i.e. ACFM at the operating temperature and downstream pressure.

Pressurized Volume - Blowdown Time Calculation:

V=

Pressurized Volume (cu. Ft.)

A=

Effective Area in Square Inches (Valve or Orifice Throat Area x Flow Coefficient). Use 0.85 Flow Coefficient unless known.

SG=

Specific Gravity of Gas

Z=

Compressibility Factor (at initial Pressure)

Ta=

Initial Temperature (˚R)

Pa=

Initial Pressure (psia)

Patm=

Atmospheric Pressure (psia)

Natural Logarithm or Log to Base e

 

Pressure Drop Factors (PDF)  (See Technical Section)

 

Model

 PDF
412 10.00
521 13.00
552 20.00
553 30.00
561 11.75
562 12.25

711

Pressure Reduction/

Diffuser

 10.00

 

 

Due to the many variables and the complexity of vent silencer sizing, selection, and design, computer optimization methods are employed. The size is generally dictated by velocity, required noise reduction, and allowable pressure drop.

 

The following information is required to optimize a vent silencer selection;

  1. Venting gas

  2. Molecular weight or specific gravity

  3. Flow rate (lbs. / hr, ACFM, SCFM)

  4. Upstream pressure & temperature

  5. Valve manufacture, size, model no.

  6. Unsilenced noise level (octave band analysis)

  7. Allowable pressure drop

  8. Noise reduction criteria (Overall level & distance)

  9. Installation particulars (horizontal, vertical)

10. Pipe sizes

11. Materials of Construction

12. Weight limits

13. Loading requirements (wind, seismic, nozzle.)

Vent Silencer

A vent silencer is a device that is intended to muffle or reduce the very high noise levels created when high-pressure gas or steam is expanded to atmosphere. This noise is produced by the rapid turbulence of the mixing gas jet and energy release of the compressed gas. Most of the noise occurs at the expansion across the valve and is emitted at the stack opening. The silencer is installed at the exit to muffle this noise.

There are two noise reduction principles used in a vent silencer.

The first is absorption of the high frequency audible noise into a sound absorbing material. 

The second principle is a reactive section to attenuate the low frequencies and provide broad band noise reduction.

VANEC vent silencers are typically a three element design, each providing a critical function:

-Redirects the flow 90° and expands flow into the plenum chamber

-Absorbs thrust forces

-Shifts frequencies into the audible range

-Disrupts the jet mixing zone

-Provides a pressure staged expansion to atmosphere

 

-Expands the gas and provides a reduced flow velocity

-Provides a reactive element to attenuate the low frequencies

-Redirect the flow through the upper splitter panel sections

-Where conditions dictate the plenum and head may be acoustically

lagged to improve the (TL) transmission loss and reduce radiated

noises

-Primary high frequency noise absorption section

-Panels consist of perforated metal surfaces through out the

perimeter with acoustic packing inside each section. The splitter

panel sections diameter thickness, open area spacing and lengths

are optimized for maximum (IL) insertion loss.

 

 

 

 

VANEC vent silencers are available in carbon steels, galvanized steels, stainless steels, or with numerous protective-coating systems.

 

Diffusers are highly engineered, designed and fabricated to ASME Section VIII requirements if specified, and may be multi-stage.

 

 

 

Made In

USA


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Rev:02/21/2012