Envelope Style Filter Bags
Envelope style filters are commonly used in small transfer or pressure relief vents where the dust loading is not too heavy. There are shaker, pulse and reverse air envelope systems. The envelope system was used often in the past. In order to reduce the dust collector’s footprint, envelope style collectors were developed. The envelope pulse jet system is still being installed as an alternative to cartridge systems where the process demand and head room are a concern.
Rectangular multi-pocket fabric bags collect dust on the outside, their dimensions supported by wire frames or by porous foam to prevent collapse. To discharge an arm knocks the bags or shakes them, releasing dust to a hopper below. Envelope filters are typically made of felt or woven media and an inside support frame or high loft medium is used to maintain an open area across the bag’s depth.