Page 5
Appeal No. 1998-1373
Application No. 08/377,473
filter stages in series, and it would have been obvious to one of ordinary skill in the art to
provide the Heyl apparatus with a second filter stage in view of this teaching.
Clark discloses an apparatus for removing particles from the air (Abstract). It
discloses a housing (11) that is partitioned by a plate (21) on which is mounted a
motorized impeller (16). A first filter unit (41) is positioned on the downstream side of the
partition, and a second filter unit (63) is located upstream of the partition with its inlet in
communication with the outlet of the first filter unit. The impeller causes air to move through
the two filter units. The second filter unit receives the air that has passed through the first
filter unit, and comprises a HEPA filter which traps sub-micron particles (column 5, line 62
et seq.).
From our perspective, one or ordinary skill in the art would have been taught by
Clark that the use of a second filter unit in series with the first results in more effective
filtration, and therefore would have found it obvious to add a second filter unit to the Heyl
apparatus. Suggestion for such a modification is found not only in the explicit teaching of
Clark that a second filter will improve the efficiency of the filtering process, but also in the
self evident advantages of passing a product to be filtered through a plurality of filters
2
arranged serially, which would have been known to the artisan. It therefore is our
2Skill is presumed on the part of the artisan, rather than the lack thereof (see In re
Sovish, 769 F.2d 738, 742, 226 USPQ 771, 774 (Fed Cir. 1995)).
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