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 was to install an absorptive jet discharge silencer, approximately 2 m long, onto the pressure vessel discharge. This had the following features:
£400 per unit. (1995)
Details of the measured noise reductions are shown in the table:
Sound pressure level at 1 m from the pressure vessel
|A-weighted||Octave band centre frequency (Hz)|
Photographs courtesy of Marley Automotive Components Limited. Equipment designed by Ian Sharland Limited.