Rotary Airlock Bridging

Generally what happens is that the dust is less dense than designed for and it bridges in the hopper. Another cause can be the wrong RPM at the airlock which prevents efficient removal of the dust by the airlock.

The old way to break the bridge was with hopper rappers where there was a hammer that hit the side of the hopper wall from outside. They worked nicely except they were loud. About 40 years ago OSHA would not let them use that procedure so there were a lot of pneumatic operated gadgets that were adapted.

Carter Day sold a unit where they put a piece of fabric on the walls and inflated it to change the angle of the hopper to 90 degrees and this broke many bridges. This was primarily applied to grain collectors, which were very notorious in bridging.

In the woodworking industry the general approach was to put on bigger and bigger airlocks. They considered a 24 inch airlock as a small one on many woodworking jobs.

There are many vibrators now applied to hoppers to break the bridges. The truth is there is no guaranteed way and usually the gadgets are returned to the manufacturer if they do not do the job.

Dustex had two cheap ways of using the pulsing control from the timer. First was to drill a hole to the hopper and insert a capped pipe about two inches into the hopper wall. With a saw make a slit 1/8 inch thick to cut out a slot 30 degrees wide. The jet spreads at about a 20 degree angle. The height is the air lock size times 2.5.  A 12 inch air-lock would be using a height of 30 inches.. The other way is to put a pulse pipe with one hole in the center above the airlock. Design the velocity pressure to be 4”wc at 65 psig with a regulator if there needs to be a bigger boost. It is like designing a jet to clean a square cartridge.

For assistance with dust collector problems