The operation of an adsorption dryer is often associated with a high sound level. This sound level represents not only a disturbing or nuisance element; noise can damage hearing and is best reduced at its source. The adsorption dryer with heatless regeneration, involving a continuous pressure release at a cycle of a few minutes with a relatively high sound pressure level of about 90 - 100 dB(A), is fitted with an effective silencer in order to cut down the noise. Free "blow-off" of the dryer during regeneration must be assured for technical process reasons. Silencing hoods in addition to the silencers reduce the sound level by about 5 - 7 dB(A). Microfilter silencers further lower the sound level by about 7 - 11 dB(A). (It has to be borne in mind that the elements of microfilter silencers have to be changed regularly. Dryers with internal and external heat regeneration involve noise sources arising through the release valves, blower motor as well as suction and flow noises. Using a suction inlet silencer, these noises can be reduced to about 75 dB(A) without significant technical effort. Further reductions are possible through additional measures such as automatic silencing hoods. In adsorption dryers with heat regeneration, release is carried out in a throttled condition. This considerably reduces exhaust noises. Closed loop adsorption dryer systems, which regenerate at operating pressure and thus without depressurisations during operation, complete their cycles with little noise. At the site of installation, the compressor and dryer sound sources add up. When adding sources of equal sound level, the overall level Lt = 10 log np = L + 10 log n. 2 noise sources of equal level increase the value by 3 dB(A) 10 noise sources of equal level increase the value by 10 dB(A) 100 noise sources of equal level increase the value by 20 dB(A) When adding unequal noise sources, the overall level
Lt = 10 log [100.1p1 + 100.1p2 + 100.1p3 + ...]
