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Technical
Service Bulletin 99-2
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Inner Air Elements Their Purpose and Function
Filter
manufacturers often receive inquires regarding the purpose and filtration
efficiency of inner air filter elements. Some users suspect that the inner
element is a secondary filter, such as you might find in some fuel systems
which utilize a primary and secondary fuel filter. They therefore believe
the purpose of the inner element is to remove very small contaminant that
may pass through the outer filter. This bulletin addresses this misconception
and explains the use and purpose of the inner air element.
While
some applications do not utilize an inner air element, there are numerous
heavy-duty engine applications that use a combination of inner and outer
air filter elements. The primary purpose of the inner element is to keep
dirt and other contaminant from falling directly into the air intake system
of the engine while the outer element is being serviced. Given the dimensional
limitations placed on inner filters, only a small amount of filter media
can be used in their design and manufacture. The same amount of air that
flows through the outer filter must also flow through the inner element.
Therefore, the filter media of the inner element must be much more open
than the filter media in the outer filter to permit necessary air flow.
This air flow requirement also results in the media having lower filtration
efficiency than that of the outer filter media. As a consequence of the
necessary differences in the filter media, inner elements MUST NEVER be
used by themselves.
As
stated previously, the primary purpose of the inner element is to keep
dirt and other contaminant from falling into the air intake system of
the engine while the outer filter is being serviced. General recommendations
are to replace the inner element every third time the outer is replaced.
Please see TSB 89-3R3 for further information
on servicing heavy-duty air filter elements.
For additional information, contact:
Filter Manufacturers
Council
P.O. Box 13966
Research Triangle Park, NC 27709-3966
Phone: 919/406-8817 Fax: 919/406-1306
www.filtercouncil.org
Administered by Motor & Equipment
Manufacturers Association
Created May 1999
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