Envelope Style Filter Bags

Clean Air Matrix

RoboVent engineers are experts in every category of air filtration and ventilation. The four categories below represent the major options for treating your contaminated air. RoboVent has designed solutions for each of these categories and has manufactured air filtration systems of unrivaled quality.

For more information about these categories, see Indoor Air Quality 101.


Large blowers and air filtration equipment draw contaminated air from the plant (typically at the ceiling level), filter it and return it to the plant. This is a proven solution in plants welding large parts with overhead cranes. It reduces the haze in the air, resulting in a cleaner working environment, with no negative pressure or heat loss.


Air in the immediate area of the welding activity is captured in a hood system, then filtered and returned to the plant. This is the best solution whenever possible. It allows for a more flexible system and removes the smoke directly from the operator's breathing zone. There are many types of source capture, including overhead hoods, crossflow hoods, fume arms and fume guns, some of which work better than others.


Large exhaust fans draw contaminated air from the plant and exhaust it directly into the environment, typically through the roof or walls. This is a traditional method and often results in negative air pressure. Also, it is very difficult to climate-control your plant and the system may not work well in the winter.

Air in the immediate area of the welding activity is captured in a hood, sent through ductwork, and exhausted directly into the environment. This is a lower capital cost alternative to filtration, but tends to result in high operating costs and large, unsightly ducting systems that work less efficiently with modifications. It also results in negative pressure problems.

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.


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