Filter Bags: Envelope Bags

One way to put substantial media area into a relatively small space is to use rectangular shaped envelope or flat bags. Typical envelope bag collectors have been made by Sly, Torit, DCE Vokes and a number of European OEM’s. Older design envelope bags may be cleaned by shaking systems (manual or motor driven) while newer envelope bag collectors use air blow back or air pulsing systems.

Multi-bag envelope design filters have also been designed for smaller filters and are characterized by a number of flat bags sewn side to side to decrease spacing even further. In all cases, envelope bags have an insert designed to prevent collapsing as the filtration is always from the outside to the inside. In many envelope filters, light to medium weight wovens are used because of their flexibility and thinness. Some lightweight shaker felts may be found as well.

Major concerns related to envelope bags are cleanability (how effective the cleaning systems are), agglomerating dusts which do not release well and bridging of dust between tightly spaced bags. Traditionally, envelope bags are used in smaller collectors or confined to specific areas such as packing houses.