Silencing pressure vessel discharges

The problem

Absorptive jet discharge silencer

A firm producing fibre mouldings for the automotive industry made use of a number of fibre pulp header tanks, pressurised to ensure a constant flow to the pulp presses. As the level of pulp in a tank was replenished, air pressure rose until a pre-set limit was reached, at which point the pressurised air was released to the atmosphere through a 50 mm port. This discharge contained moisture and, occasionally, some pulp from the header tank.

The tanks were located in working areas of the factory, exposing employees every 10 minutes to A-weighted noise levels of about 101 dB for about 3 to 4 seconds.

The solution

The solution was to install an absorptive jet discharge silencer, approximately 2 m long, onto the pressure vessel discharge. This had the following features:

  • straight-through format so that neither back pressure nor the build up of solid particle carry-over could occur;
  • adequate length to absorb the energy;
  • a wrapping of thin plastic film to protect the absorbent material from moisture and pulp carry-over;
  • removable end connections via a British Standard Pipethread to enable periodic internal cleaning.

The cost

£400 per unit. (1995)

The result

Details of the measured noise reductions are shown in the table:

Sound pressure level at 1 m from the pressure vessel

Noise reduction (dB) for A-weighted and octave band centre frequency noise
A-weighted Band centre
Band centre
Band centre
Band centre
Band centre
Band centre
Before treatment 101 88 92 94 96 94 93
After treatment 91.2 87 88 84 81 85 84
Attenuation 9.8 1 4 10 15 9 9


Photographs courtesy of Marley Automotive Components Limited. Equipment designed by Ian Sharland Limited.

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Updated 2021-02-05