Application
Valve and Airlock Selection for Grain and Feed Plants
Answer in brief
In a grain or feed mill the airlock under a filter is often expected to do two jobs: discharge dust and stop an explosion from travelling.
Only a valve that is specifically designed and certified does the second, and assuming it is the most common mistake in these plants.
- Decide whether the valve carries an isolation duty, and buy accordingly.
- Expect stones, metal and string to arrive with the product.
- Keep the discharge dust tight, because leakage feeds the next dust layer.
Reviewed October 21, 2026 · Updated October 21, 2026
The problem
Grain and feed streams carry foreign material that jams rotors and damages seats, and the dust they generate is combustible.
Many plants fit an ordinary process rotary valve under a filter and record it as explosion isolation, which it is not.
Desired outcome
A valve that discharges reliably against the filter pressure, survives the foreign material that will reach it, and provides a documented isolation function where the protection concept requires one.
Process approach
Where the protection concept calls for isolation, the valve must be a certified type with defined clearance, pocket count and construction, installed within the distance the certification covers.
Where it is only a discharge device, the design question is dust tightness and tolerance of the occasional stone or bolt.
Slide gates on bins and intake pits see settled, consolidated grain and need a blade that is not required to cut through the bed.
- Shear protection or relief in the drive, so a foreign object stops the rotor instead of destroying it.
- Access for clearing a jam without entering the equipment.
- Dust tight shaft seals that stay tight after a jam.
Selection factors
- Whether the valve carries an explosion isolation duty and which certification applies.
- Expected foreign material and the upstream separation that removes it.
- Pressure difference across the valve under the filter.
- Abrasion from husk, sand and mineral additions in feed.
- Seasonal peak rate, which usually sets the sizing.
Common failure modes
- Standard process valve recorded as explosion isolation
- Rotor jammed by a stone or bolt and the drive damaged
- Dust leakage at the shaft seal adding to the layer on the floor
- Gate blade unable to cut through settled grain
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