Setting Air Volume on an Air-Screen Cleaner Without Instruments

Air volume can be set without an instrument, but not by feel alone. Set it by reading three things at the same time: the material stream on the deck, the state of the bed, and what leaves the light-fraction outlet. Start on the low side, raise it in small steps, and stop one step before the point where the machine starts to look impressive. The impressive setting is usually the one that is throwing grain away.

Two rules run through everything below. Change one thing at a time, and bring the feed to a steady state before judging a change. An adjustment made while the feed is surging tells you nothing, because the surging feed dominates the result.

Read the stream, the bed and the outlet

The material stream. Sound grain travels down the deck at a steady speed in a continuous sheet, staying in contact with the surface. When the air is about right, the bed is loosened underneath while the top layer still moves forward evenly. When it is too high, grain begins to skip, hop and hang, and travel becomes uneven. When it is too low, the sheet looks dead and heavy, and the grain slides rather than being worked.

The bed. You are looking for a bed loose enough for fines to reach the deck and dense enough to keep a residence time. A bed that visibly boils is being over-aerated. A bed that sits flat and closed, with fines on top, is being under-aerated. Look along the full width as well: if one side boils and the other sits dead, the cause is air distribution or a leak, and no damper position will repair it.

The light-fraction outlet. This outlet gives the clearest verdict. Catch what comes out in a container and look at it. Chaff, dust, broken pieces, shrivelled kernels and light weed seeds are the intended product of that outlet. Whole sound grain in it is a loss and means the air is above the useful setting. If the machine has aspiration ducting, watch it too: grain travelling or circling in a duct is the same message arriving later and more expensively.

Too much air looks like a clean result

Over-aeration survives for a long time because the product looks better while the loss stays invisible. The evidence is all on the outlet side, in the fraction that nobody examines closely.

• Whole kernels in the light fraction, at a rate that is easy to dismiss when the outlet is judged by eye from a distance.
• Grain hanging or circling in the aspiration duct, or a rattle in the ducting.
• A deck near the discharge that looks oddly empty while the inlet half carries a heavy bed: the air is lifting more than fines.
• Exhaust dust that visibly contains kernels, especially during a feed surge.

On small and light material the margin between carrying away the light fraction and carrying away the product is narrow, and the two settings sit close together. That is why the approach is to come up from below rather than down from a high setting. Coming down, you have no reference point for what acceptable looks like.

Too little air costs more quietly

Under-aeration does not throw grain away, so it is treated as a quality problem rather than a loss. It still costs, through extra passes and through wear.

• Light impurities stay in the product, so the cleanliness target is missed and the material has to be run again.
• The bed sits closed, fines cannot reach the deck, and blinding begins. Once apertures seal, throughput and separation fall together.
• Dust hangs around the inlet and around the machine instead of being taken away, which affects the working area and loads the dust collection system.
• The deck carries a heavier, less fluidised bed, so the drive and the structure work harder for a worse result.

If you find yourself compensating for weak aspiration by increasing the feed or by shaking the deck harder, stop and look at the air path instead. The air path is where the cause sits.

The setting follows feed, moisture and the air path

A damper position is not a setting that carries over to another day. Air volume has to match what the machine is being asked to do.

• Feed rate. A thicker bed needs more air to work through it; a thinner bed needs less or grain is lifted. When the feed changes, the setting changes with it, and a steady feed is what makes any setting repeatable.
• Moisture and surface condition. Damp grain is heavier on the surface and sticks to itself and to the deck, so it needs different treatment. Expect the setting to move when the incoming crop changes.
• Leaks and short-circuit air. Unlatched inspection doors, worn seals, open covers and disconnected ducts send air where it was not meant to go. The symptom is a machine that responds poorly to the damper while something elsewhere is still losing grain. Check the enclosure before blaming the setting.
• Blocked or loaded air path. Dust on filter media, dust settling in horizontal duct runs and material building up at hood connections all reduce the air that reaches the deck. Air volume that falls gradually over a shift is a maintenance signal, not a damper problem.

Any work on the air path, the guards or the machine interior is done with the machine stopped and the supply isolated, locked out and the voltage verified at the point of work. Work inside the control panel, including fan starters and interlocks, is for a licensed electrician.

Set and re-set it in a fixed sequence

1. Stop the feed, let the deck empty, then restart at a reduced rate and let it stabilise. Do not judge anything while the feed is still rising.
2. Close the air down to an obviously low position and confirm the symptoms of too little air, so you know what the low end looks like on this material.
3. Open the damper in small steps. After each step, let the machine settle before judging.
4. At each step check all three: stream, bed and light-fraction outlet. Catch the outlet fraction in a container and look at it properly.
5. Stop when the light fraction is clear of what you want to remove and you begin to see signs of good grain being carried. Go back one step from there.
6. Check across the full width. If one side behaves differently from the other, stop adjusting and find the distribution or leak problem.
7. Mark the damper position and write down the feed rate, the material, the moisture condition and what the outlet contained. The mark is useful together with the note, not on its own.

Repeat the outlet check on a fixed routine, every shift and every time the incoming material changes. The adjustment takes a few minutes; the loss it prevents runs continuously.