FILTER

摘要

A chemisorptive filter e.g. activated alumina or carbon, is held in a chamber (16) between two webs of expanded metal mesh (5, 6) provided with angled perforations. The webs are rigidified in the direction of air flow (4) by a central post joining them. This filter is provided with prefiltering by a mechanical filter layer (19), e.g. polyester polyurethane foam and a layer with both electret and electrostatic activity (21). The chamber (16) may be provided with a window so that any colour change indicative of the remaining capacity of the chemisorptive material can be seen.