Pre Filter Considerations in Air Cleaning System

Filtration Table of Contents

Prefilters are intended to remove large particles upstream of HEPA filters. HEPA filters are intended primarily for removal of sub-micrometer particles and should not be used as coarse dust collectors. They have relatively low dust-holding capacity, particularly for large particles and lint, and may plug rapidly when exposed to high concentrations of such material or smoke. Lint may tend to bridge the pleats of the filter, further reducing its capacity. The HEPA filter is also the most critical particulate-removal element in the air cleaning system from the standpoint of preserving confinement, and its failure will result in failure of system function.

Prefilters, installed either locally at the entrances to intake ducts, in the central exhaust filter house, or both, extend the life of HEPA air filters and provide at least a measure of protection against damage. Local duct entrance filters also minimize dust accumulation in ducts and reduce an otherwise potential fire hazard. The increase for a specific application depends, of course, on the quality of the prefilter selected and the nature and concentration of dusts and particulate matter in the system.