Application
Shut-off and Isolation in Plastics Silos
Answer in brief
A gate on a pellet silo is simple until a pellet gets caught in the seat.
A trapped pellet keeps the gate from closing fully, which matters most when the gate is the isolation point for work below.
- Choose a design that clears the seat as it closes.
- Check the closed position before working downstream.
- Ground the assembly like the rest of the line.
Reviewed October 21, 2026 · Updated October 21, 2026
The problem
Pellets lodge between blade and seat, so the gate reports closed while a leakage path remains.
In grade changes, a few retained pellets in the gate pocket contaminate the next product.
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
Clear-action designs withdraw the blade from the flow path, which avoids trapping pellets and keeps the seat clean between grades.
Where the gate is the isolation point for silo entry, the closed position must be lockable and independently indicated, and entry procedures treat it accordingly.
Grounding and bonding apply here as everywhere in a dry polymer line.
- Seat geometry that does not trap pellets.
- Pocket-free design for grade changeover.
- Lockable closed position for entry permits.
Selection factors
- Pellet size and shape, including regrind.
- Number of grades and the carryover that is acceptable.
- Whether the gate is an entry isolation point.
- Static control across the assembly.
- Column height and the resulting actuation force.
Common failure modes
- Pellet trapped in the seat leaving a leakage path
- Previous grade retained in the gate pocket
- Silo entry on a gate that was not provably closed
- Static discharge at an ungrounded gate body
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