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Filtration Table of Contents
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Filter Supplier
HEPA air filters must be installed so that even the
smallest volume of air or gas does not escape filtration;
therefore, gaskets and alternative methods of sealing filter
units to the mounting frames play a critical role in the
satisfactory operation of HEPA Air filters. The most widely used
sealing method is a flexible gasket attached to the open face
of the filter case and pressed against the flat face of the
mounting framework. The second most popular method is
referred to as a “fluid seal.” This method uses a channel
formed or routed in the peripheral face of the filter case
that is filled with a highly viscous, very low volatility,
nonflammable (or self extinguishing), odor-free,
non-Newtonian fluid such as a silicone. The fluid flows
around and over imperfections, but does not relax or separate
from the surfaces it contacts. For installation, the matching
framework face is equipped with a continuously protruding
knife-edge that mates with the fluid-filled channel in the
filter case. The reverse arrangement of a protruding
knife-edge on the filter and a fluid-filled channel on the
mounting frame also may be employed. These two mounting
methods do not have interchangeable parts, so hybrid sealing
systems are not feasible. Gaskets generally must be oil and
ozone resistant.
Closed-cell sponge gaskets composed of
synthetic rubber (neoprene) that conforms to grade 2C3 or 2C4
of ASTM D1056, Sponge and Cellular Rubber Products have been
widely used. Gaskets should have a minimum thickness of ¼
inch and width of ¾ inch. The gasket face attached to the
filter case should be free of any adhesion-resistant
mold-release contaminant that may have been acquired when the
gasket material was molded. To ensure an absence of residual
mold release chemical, only cut surfaces are permitted on
both gasket faces.
Gaskets may be cut out of a sheet of stock as
a single piece or may be made of strips joined at the corners
by dovetail or other interlocking arrangement. Joints are
sealed against air leakage with a rubber-base adhesive,
usually the same adhesive used to attach the gasket to the
filter case. Manufacturers of neoprene gaskets recommend a
shelf life not to exceed 3 years.
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