Compressor Blow-off valve and relief valve noise
Blow-off valves should be equipped with their own silencers. Because they may be intermittent in operation, the noise that they make may not be noticed during a noise survey. An occasional noise may be more annoying to the neighbours than one continually present.
Safety valves only rarely discharge to the atmosphere. For safety reasons they must not be fitted with silencers or any form of piping. Indeed it may be desirable that they should make a noise as a warning. If a safety valve is continually blowing there is a fault in the control system.