The Stockpile · Pile 03 — The Fix List
Why silos plug, what ratholes and bridges actually are, how professional cleaning works without confined-space entry — and how to keep the buildup from coming back.
A silo is a simple promise: put material in the top, take it out the bottom. Bulk solids break that promise constantly. Unlike liquids, powders and granular materials gain strength when they sit — particles interlock, moisture migrates and binds them, fine particles compact under the weight of the column above. Give a cohesive material enough time at rest, a little moisture, and a converging outlet, and it will find a way to stop moving.
Flow problems concentrate at the cone, where the cross-section shrinks and pressures rise. The material closest to the wall moves slowest — in many silos it barely moves at all — which is why buildup problems grow quietly for months before anyone notices the symptoms.
| Pattern | What is happening | What you see |
|---|---|---|
| Rathole | Flow narrows to a pipe down the center; the surrounding material stands still and hardens in place. | Silo reads half full but runs empty; live capacity shrinks month after month. |
| Bridge / arch | Material locks into a self-supporting arch over the outlet, strong enough to hold the column above it. | Discharge stops dead with tons still in the vessel; feed starts again unpredictably when the arch collapses. |
| Wall buildup | Layers cake onto the walls and cone, hardening over time — especially with moist, hygroscopic or hot materials. | Slower discharge, off-spec product as old layers finally let go, and rising dead load on the structure. |
A silo whip is a rotating cutting head on a flexible arm, lowered through the top of the silo and worked down the vessel. The head knocks buildup off the walls and breaks bridges and ratholes, and the material simply falls to the outlet. The equipment stays on top of the silo; the crew stays out of the vessel entirely. This is how ACT cleans silos — comprehensive evaluation first, factory-trained technicians, explosion-proof lighting, and strategic cleaning that works with the vessel’s flow pattern, not against it.
Some situations still require entry: unusual internal structures, certain hardened materials, inspection and repair work. Entry cleaning is a fundamentally different job — a permit-required confined space with engulfment hazard, requiring atmosphere monitoring, retrieval systems, and a trained standby crew. Whether entry is genuinely needed is determined during the proposal, never improvised on site.
“The ACT Group helped us clear a silo that had been plugged for 18 years, all without confined space entry.” — IGM. Eighteen years of buildup, removed with the crew standing on top of the vessel.
A cleaning restores capacity; what protects it is flow support. The standard toolkit:
Engulfment kills quickly and quietly: material that looks solid can collapse under a worker in seconds, and flowing material traps a person faster than anyone can react. That is why the entire method is built around not entering the vessel — and why, on occasions when entry is unavoidable, it happens under a full confined-space program (OSHA 30 and MSHA Part 46/48 trained crews, permits, atmosphere monitoring, retrieval) or it does not happen at all.
It depends on the material and duty. Sticky, moist or hygroscopic materials in daily service may need annual or semi-annual cleaning; free-flowing materials may go years. The practical trigger is measurement: when live capacity or discharge rate falls off noticeably, buildup is established and hardening.
Often, yes. Whip cleaning works from the top of the vessel, and in many cases the silo can be cleaned in sections or during normal low-demand windows rather than a full outage. Coordination is worked out during the proposal.
No — drawing the silo down as far as it will discharge is enough. The whip works from the top surface of the remaining material downward, and cleaned material discharges through the normal outlet as work progresses.
Most bulk solids: cement, fly ash, lime, aggregates, grain and feed, wood products, chemicals and more. Cutting heads are matched to the hardness of the buildup — from soft bridging to years-old hardened cake.
ACT quotes include a comprehensive evaluation of silo conditions during the proposal process, factory-trained technicians, explosion-proof lighting, and strategic cleaning to maximize flow and production. If confined-space entry is genuinely required, that is identified up front in the proposal — never decided on the fly.
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