Filter Bags: Pulse Jet Bags

Pulse jet bags are cleaned using compressed air to mechanically “pulse” or snap the bag periodically so that the built up filter cake is discharged and the flow through the media is returned to its higher “in service” permeability. Pulse jet bags are installed on wire cage supports and filter from the outside/ in. This holds true for either top load or bottom load design baghouses.

Bottom load design

In the bottom load design, filter bags are pre-installed on their cages and then attached to a mounting thimble or cup which hangs down from the underside of the tube sheet. The tube sheet is a metal plate with regularly spaced holes which serves as the top of the gas tight metal box known as a dust collector. The top edge of the bottom loading bag is normally tucked into the cage and the entire assembly is attached to the thimble or cup with a hose clamp.

Installation of bottom loading bags is more difficult because of being on the dirty side of the collector and having no catwalks or surfaces on which to stand. Some bottom loaders are on the top of large storage bins on tall silos which make installation potentially dangerous. Bottom loader collectors are frequently used when headroom above the collector is not adequate for top removal design bags.

Bottom loading bags are less expensive than comparable size top loaders because the top is plain with no special attachment features.

Top load design

The top load design bag is installed from the clean side or top of the tube sheet providing a cleaner and easier change out bags. In the top loader bag installation process, the bag is not put on the cage first but instead is snapped into a tube sheet hole using a flexible stainless steel band and a grooved gasket in a cuff assembly at the bag top. This snap band cuff design is gas tight and eliminates the need for any clamps. After the bag is snapped in place, the cage is inserted to complete the process (certain flange design top loaders such as Young, Torit RF and older Fuller and Barber Greene bags are mounted on the cage first and then installed from the top, clean side).

The optimum top load design collector has a covered plenum above the tube sheet which provides a safe, weather protected environment.

Since the tube sheet top can be walked on and used as a platform, there are fewer safety concerns as exist in the bottom loader collector, and installation is faster and cleaner.

Finally, top load design bags are more expensive than comparable design bottom loaders since the bag top has the special cuff design for attaching the bag and sealing the bag at the tube sheet.