A reciprocating air compressor had been in use for several years, both in a workshop and in mobile noise control demonstrations. Noise levels measured 94dB at 1m and clearly noise reduction was required.
The noise reductions were all through maintenance.
Initial work involved improving the valve seating. The old valves were observed to have a rough surface and to seal poorly to the casing. New valves were purchased and observed to be similarly rough.
These were then dressed (polished) to achieve a much-improved seal. An oil additive (molybdenum disulphide) was added to the lubricating oil to "smooth out" the surface finish in the cylinder, thus helping to cushion "piston slap".
The average reverberant noise level was reduced by 6dB to 87dB and the operators' noise exposures were reduced by 4dB.
£150 (2005 rates).