---
title: "Bridging"
description: "Bridging (also arching or arch formation) is the formation of a stable mechanical arch of bulk-solid material above the discharge outlet of a hopper or silo. Once a bridge forms, no material flows out of the outlet even though the vessel above is full. Bridging is the universal failure mode of bulk-solids storage."
canonical_url: "https://sylio.co/glossary/bridging"
last_updated: "2026-06-28T02:29:32.711Z"
---

**Bridging** (also *arching* or *arch formation*) is the formation of a stable mechanical arch of bulk-solid material above the discharge outlet of a [hopper](/glossary/hopper) or [silo](/glossary/silo). Once a bridge forms, no material flows out of the outlet even though the vessel above is full. Bridging is the universal failure mode of bulk-solids storage.

## How a bridge forms

Cohesive forces between particles — moisture films, electrostatic charge, chemical bonding — combine with the converging-flow geometry to lock particles into an arch shape. The arch is self-supporting against the load above. Cohesion increases with:

- Fine particle size (especially Geldart-C powders — see [Geldart classification](/glossary/geldart-classification))
- Moisture
- Hygroscopic chemistry (urea, ammonium nitrate, lime)
- Long residence time (consolidation under sustained load)
- Temperature cycling

## Diagnosing a bridge

- Outlet flow stops while the level above remains high
- Mass-flow indicators report no movement
- A simple tap on the hopper outside the discharge cone produces a hollow sound
- Borescope inspection from the inlet shows the arch directly

## Remedies

<table>
<thead>
  <tr>
    <th>
      Technique
    </th>
    
    <th>
      Notes
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      <a href="/glossary/sonic-horn">
        Sonic horn
      </a>
    </td>
    
    <td>
      Continuous prevention; non-contact; minimal infrastructure
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/air-cannon-air-blaster">
        Air cannon
      </a>
    </td>
    
    <td>
      High-intensity periodic; effective on hard bridges; structural stress
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/bin-vibrator">
        Bin vibrator
      </a>
    </td>
    
    <td>
      Continuous vibration; can compact powder further if poorly sized
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/whip-hammer">
        Whip hammer
      </a>
    </td>
    
    <td>
      Manual; legacy; HSE concerns
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/fluidisation-pad-aeration-pad">
        Fluidisation pad
      </a>
    </td>
    
    <td>
      Aerates the lower vessel; not suitable for wet material
    </td>
  </tr>
  
  <tr>
    <td>
      Mechanical screw extractor
    </td>
    
    <td>
      Bypasses the bridge entirely; high capex
    </td>
  </tr>
</tbody>
</table>

## Related terms

- [Hopper](/glossary/hopper)
- [Silo](/glossary/silo)
- [Rat-holing](/glossary/rat-holing)
- [Mass flow vs funnel flow](/glossary/mass-flow-vs-funnel-flow)
- [Sonic horn](/glossary/sonic-horn)