How to Choose a Suction Type Destoner: A Destoner Is Not One More Screen

A destoner is not one more screen. Stones of similar size to grain are almost the same size as the grain, so a screen will not take them out, and they are far heavier than husk and chaff, so air classification will not carry them away either. They sit right in between, and separation has to rely on deck vibration plus an upward air flow that stratifies by density.

The difference between suction type and pressure type is one sentence: does the fan blow from below the deck (pressure or blower type), or draw from above the deck (suction type). Reverse the air direction and the structure, the dust path and the sealing requirements all change with it.

How suction type and pressure type differ

So the claim that suction type is better than pressure type does not hold, and neither does the reverse. The criterion is your workshop: if dust cannot be discharged, or you need centralised dust collection, take suction type; if ventilation is good and you would rather not add dust ducting, pressure type is simpler. Naming that condition during machine selection is more useful than arguing about which design is more advanced.

Four things that decide performance

• Air volume. The air loosens the bed so stones sink and grain floats. Too little air and the bed does not move, so stones travel along with the grain; too much and good grain is carried into the stone stream, which is where grain in the stones comes from.
• Deck angle. The angle sets how fast the material crosses the deck and how long it stays. Too steep and stones slide out before they can sink; too shallow and the bed piles up and the air cannot push through.
• Vibration (amplitude and frequency). Vibration moves the stratified material towards the outlet end and keeps the stones against the deck. The eccentric weights on both sides of the vibration motor must match; if they do not, the deck carries a thick bed on one side and a thin one on the other.
• The destoner deck plate. The deck is not a flat plate; it is a perforated plate with a specific aperture shape. Aperture shape and open area affect how the air passes and how the stones stay against the deck. Ask which deck plate is used and how it is replaced when worn.

These four are adjusted as a set, and changing one affects another. Add one precondition that is not a machine setting but decides the outcome: the feed must be even. If it surges, the bed depth on the deck changes and stratification stops immediately. That is why a destoner is better off with an adjustable small hopper or a vibrating feeder in front of it.

How many outlet streams, and what happens to the middlings

Three streams are common: grain (product), stones (heavy impurities) and middlings (in between, carrying both grain and stones). The first two are obvious; middlings are what gets overlooked.

Whether middlings are returned for a second pass or downgraded has to be settled at the machine selection stage: which side the return spout faces, which section it feeds, whether a small elevator is needed. Improvised ducting on site usually ends up at too shallow an angle, and in the end someone carries the material back by hand, which is how the machine capacity gets eaten.

When performance drops off

• Material moisture is high. Particles stick, flowability is poor and stratification does not happen. Fix the moisture first; do not expect extra air to force it through.
• The feed surges. Bed depth on the deck is unstable, so the separation result cannot be stable either.
• Raw grain stone content is high. That is outside the design working conditions, so run a rough cleaning pass before the destoner, or the deck fills up with stones quickly.
• Particle shape is unusual. Very flat or very long material rolls across the deck quite differently from round grain, so deck angle and vibration have to be set for it specifically; general parameters will not work.

How it divides work with the fine cleaner and the air classifier

The usual order is air classification and screening first, destoning in the middle, fine cleaning last. Feeding a destoner with material that has not been cleaned means the most expensive stage is doing the rough work.

What to watch in day-to-day adjustment

• Take samples, do not judge by eye. Catch a pan from the grain stream and a pan from the stone stream, and see how much grain is in the stones and how many stones are left in the grain.
• Too much grain in the stones: check the air volume first. It is usually too much air carrying good grain into the stone stream. Change one step at a time.
• Stones still in the grain: then set the angle and vibration. Too steep an angle moves material too fast for stones to sink.
• The deck gets sticky and separation suddenly worsens: clean the deck and the deck plate first. Blocked apertures give uneven air, which looks as if the parameters have gone wrong.
• After a change of material, a change of batch or a spell of damp weather, set all four again. That is not a fault, it is how this type of machine is used.

Five questions to ask the manufacturer

• Is this machine suction type or pressure type, and why is this one being recommended for me? Ask them to justify it against your workshop dust conditions and the dust collection you already have.
• What aperture shape and open area does the destoner deck plate have, and how is it replaced when worn? The deck plate is a core component, so ask about supply and replacement.
• How is air volume adjusted, and can it be adjusted on site? Ask about the damper arrangement and who provides adjustment guidance when the material changes.
• How many outlet streams are there, and where do middlings go? The return spout position and whether an elevator is needed should be written into the agreement.
• Which parameters go into the technical agreement? Throughput, deck dimensions and deck plate specification, fan and vibration motor configuration, inlet and outlet directions, dust connection, supply voltage. Also write down which material and which baseline the product quality and stone removal results are measured against. After-sales is per the technical agreement in the contract; verbal promises do not count.

Mistake one: using a destoner as a screen

A destoner separates by density, not by size. Using it to remove large impurities or weed seeds does not work well and tends to block the deck. Screening and air classification belong upstream.

Mistake two: treating no grain in the stones as the target

A little grain in the stone stream is normal running condition. Chasing a stone stream with no grain in it at all means cutting air volume and slowing the material on the deck, which drops capacity and still does not separate cleanly. Judge against the measured baseline in the technical agreement, not against one pan of material.

Mistake three: buy it and forget it

Changing material, changing batch, or damp weather after rain all mean re-setting air volume, deck angle and vibration. Before you buy, ask whether the manufacturer provides adjustment guidance; that is worth more than another fully automatic label.

Four measurements settle it: how many tonnes per hour go in, what the material is and roughly what moisture range it has, how much stone the raw grain carries, and the dust conditions in the workshop and whether dust ducting exists. Then add the length, width and height of the space, the inlet and outlet directions, and the on-site power supply.

One last point not to skip: dust conditions decide between suction type and pressure type. Get that the wrong way round and the structure has to be changed.

Suction type or pressure type destoner: which is better?

Neither is absolutely better. A pressure type fan blows upward from below the deck; the structure is simple, but the deck is under positive pressure and dust tends to escape from the inspection window and the inlet and outlet. A suction type draws air from above the deck, so the deck is under negative pressure and dust is collected with the air stream, but the duct sealing and air distribution demand more. Choose by your workshop dust conditions.

What impurities can a destoner remove?

Mainly heavy impurities of a size close to grain but of higher density, such as stones of similar size to grain and mud lumps. Husk, chaff and dust need air classification; large and small impurities need screening. A destoner replaces none of those three.

What if grain keeps turning up in the stone stream?

First check whether the air volume is too high, because too much air carries good grain into the stone stream. Then check deck angle and vibration; if material travels too fast, stones have no time to sink. Also check the deck plate for blocked apertures, since uneven air produces the same symptom.

We already have a fine cleaner. Do we still need a destoner?

It depends on the impurities and the capacity. A double gravity fine cleaner has a destoning section built in, so with low stone content in the raw grain it can be used without a separate destoner. Where stone content is high and capacity is large, a separate destoner in front handles it first, so the fine cleaner deck does not fill up with stones.

Quotations are built from the suction or pressure structure, deck dimensions and deck plate specification, fan and vibration motor configuration, frame type, number of outlet streams and dust connection. There is no single price list. Give us the material, capacity, stone content and dust conditions to get an accurate quote; after-sales is per the technical agreement in the contract.

Suction or pressure type: it depends on your workshop

Tell us the material, the capacity, the stone content of the raw grain and the dust conditions in the workshop, and we will tell you whether suction type or pressure type fits, then quote the specific configuration.

• Grain fine cleaner
• Combined air-screen and vibrating cleaner
• Drum cleaner
• How to choose a double gravity fine cleaner: destoning and gravity separation are not the same thing
• What material suits a combined air-screen and vibrating cleaner, and how it divides work with a drum cleaner and a double gravity fine cleaner