Discharge through a narrow flow channel while surrounding bulk material remains stationary.
Also called: rat hole; hopper channeling.
What is the difference between a rathole and a bridge?
A rathole is a discharge channel surrounded by comparatively stagnant powder; a bridge spans and blocks the outlet. The channel can carry flow until it empties without surrounding material refilling it, leaving much of the hopper inventory unused.
Record whether discharge continues through a channel or has ceased, rather than using the two terms for any low-feed alarm. A full-looking hopper can contain material that is not participating in discharge. Its geometric capacity and current visible inventory are therefore different questions from usable supply to the capsule filler.
No. A pile-angle test does not reproduce the flow pattern inside the hopper. Assess whether surrounding powder joins discharge under the relevant moisture, storage and operating conditions at the hopper/feeder interface.
Assess whether material from the surrounding regions joins discharge. Mass-flow hopper design addresses the overall flow pattern, while local feeder activation acts at a different scale.