Distinguish a bridge from a rathole
A bridge spans the outlet and prevents material below it from being replenished. It can result from cohesive powder or interlocking particles. In ratholing, a central channel empties while material around it remains stationary. Once the channel is empty, discharge stops despite remaining stock.
Neither condition should be diagnosed from one level reading. Check the operating history, delivered mass and the downstream status before deciding the cause.
Storage changes the material
Compare a fresh delivery with material that has stood overnight or for several days. Note moisture exposure, temperature cycles, fines and any change of supplier or formulation. A material name alone does not describe its flow after storage.
For recurring problems, representative flow testing can examine cohesive strength and wall friction under relevant conditions. This helps assess hopper geometry, wall finish and outlet dimensions instead of choosing an arbitrary larger opening.
Correct the cause rather than repeat the intervention
A suitable flow aid may help a defined application, but it does not make every hopper geometry suitable. Persistent stagnant regions can require review of the hopper and feeder interface. Outlet changes and vibration loads must also be checked structurally.
Do not increase air or vibration without assessing the result: released material can arrive suddenly and exceed downstream capacity. Clearing an obstruction and achieving controlled ongoing discharge are different outcomes.
For a quote
Build a useful record of the event
- Material batch, moisture information and time since filling.
- Level indication, estimated stock and quantity discharged before stopping.
- Valve and feeder status when flow was lost.
- Whether the event repeats after the same storage duration.
This approach applies to cement, minerals, food powders, feed ingredients and chemicals, with their own hygiene and compatibility requirements. Keep people out of silos and away from unstable stored material; investigation must follow site isolation and confined-space procedures.
Send the material data and a photograph or layout of the installation so we can define the equipment and connection requirements.
Start with the general silo discharge guide to distinguish a storage-flow problem from an outlet or downstream-equipment restriction. When a silo will not discharge consistently.
