Application
Shut-off and Isolation under Cement and Lime Silos
Answer in brief
Under a cement or lime silo the gate faces a powder that behaves like a liquid when aerated and like rock when it is not.
Aerated powder finds every gap in a closed gate, and consolidated powder resists the blade that has to cut through it.
- Specify for both states, aerated and consolidated.
- Expect seat wear from fine abrasive powder.
- Allow for temperature where the material arrives hot.
Reviewed October 21, 2026 · Updated October 21, 2026
The problem
Fine mineral powder leaks through a seat that is only dust tight on paper, and the same powder consolidates after a standstill into a bed the blade has to pass.
Hot material from a mill adds thermal expansion to the clearance question.
Desired outcome
A gate that closes against the real column, can be proven closed before anyone works downstream, and opens again without damage.
Process approach
Blade designs that withdraw from the flow path avoid cutting through a consolidated bed and keep the seat cleaner.
Seat materials and sealing arrangements are chosen for the aerated condition, because that is when leakage is worst.
Thermal expansion is included in the clearance calculation where the powder arrives hot.
- Seat sealing specified for aerated powder, not for settled powder.
- Blade geometry that avoids cutting a consolidated bed.
- Clearance calculation including temperature.
Selection factors
- Aeration state and whether fluidising pads are used in the silo.
- Consolidation after the longest standstill.
- Temperature of the material at the outlet.
- Seat wear expectation and the inspection interval.
- Isolation requirement for work below the silo.
Common failure modes
- Aerated powder leaking through a closed gate
- Blade unable to pass a consolidated bed after a standstill
- Thermal expansion closing the clearance on hot material
- Seat wear discovered only when the gate failed to seal
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