Mini - Pleated Air Filter Design and Application

Filtration Table of Contents

Mini - Pleated Air filter construction methods utilize 7/8 to 1 1/4-inch deep pleats with very narrow air spaces (1/8-inch) between, making it possible to pack more filter paper into the standard frame sizes than can be done with deep-pleat, corrugated separators, or even by using separator-less construction methods. Abutting folds are separated by threads, ribbons, tapes, strips of medium, or continuous beads of glass, foam, or plastic spaced across the width of the medium. Mini-pleat filters contain almost twice as much filter paper as deep-pleat, corrugated separator filters of equal frame size. They are rated to have an airflow resistance of 0.25 Kilopascals (kPa) when operated at 3,060 cubic meters per hour (m3/hr), compared to the same resistance for a flow rate of 1,700 to -2,040 m³/hr for deep-pleat corrugated separator filters. This gives the user of mini-pleat filters the option of utilizing space-saving higher airflow rates or extending filter life by operating at lower than rated airflow capacity. This is called downrating a filter.

When a mini-pleat filter rated for 3,060 m³/hr is down rated to service at 1,700 m3/hr, it theoretically should extend service life more than threefold before it reaches its final permissible resistance increase. In practice, filter life extension was found to be merely 1.6-fold because of dust bridging across the very narrow air passages between the paper pleats to form a filter cake covering the face area. An efficient prefilter might be used to prevent the formation of a surface filter cake and extend the service life of the mini-pleat filter.

Cased mini-pleat HEPA air filters are formed from sub components assembled in a continuous V array. The sub components are panels that hold the pleated filter paper in metal frames approximately 23.62 inches wide, 11.81 inches high, and the depth of the paper pleats. A seal is made between framed filter packs and the standard frame using rubber based adhesives, polyurethane, or some other plastic-based material, all of which are chemically compounded to inhibit their support of combustion.

Another mini-pleat filter design is formed by molding narrow longitudinal ridges into the wet filter paper at approximately 1-inch intervals while the paper is still on the papermaking machine, then folding the paper as it comes off the machine into mini-pleats that may be 2, 4, or 6 inches deep.18 The filter pack is mounted into the filter case perpendicular to the airflow direction instead of mounting a number of shallow panels arranged inside the filter frame in a series of V formations The 6-inch-deep mini-pleat separator-less filter contains the same area of filter paper as the 12-inch-deep separator type.