HEPA Air Filter Gasket Considerations

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 inch and width of 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.