Specific Gravity vs Vibrating Screen: Which Grain Cleaner Do You Actually Need?

Published: May 11, 2026 · Xinyada Technology · 9 min read

If you have ever stood in front of two glossy brochures — one for a vibrating cleaning screen, one for a specific gravity separator — and tried to decide which one your facility actually needs, you are not alone. Both machines are sold as "grain cleaners." Both claim impressive throughput numbers. Both come with capacity tables that look interchangeable at first glance. And yet they do completely different jobs, and choosing the wrong one is one of the most common procurement mistakes we see in greenfield grain projects.

The short version: a vibrating screen separates kernels from impurities by size. A specific gravity screen separates them by density. They are complementary tools, not substitutes. Most professional cleaning lines need both — and the order in which they appear matters as much as the equipment itself.

This guide walks through how each machine works, what each is good at, where each fails, how to compare them on a technical proposal, and what FOB pricing looks like in 2026. By the end you should be able to tell — from your crop, your throughput, and your end use — whether you need a vibrating screen, a gravity screen, or (most often) a sensibly sequenced pair.

How a Vibrating Cleaning Screen Works

A vibrating cleaning screen is a rectangular deck — or stack of decks — of perforated metal or woven mesh, suspended on springs and shaken by one or two eccentric motors. As grain falls onto the top deck, the vibration throws kernels into a controlled, repeating hop across the screen. Material small enough to drop through the perforations falls to the next deck or to the clean-grain outlet; oversize material rides over the screen and exits the side as trash.

The whole separation is geometric. The screen does not care whether a kernel is heavy or light, healthy or hollow, sound or weather-damaged — it only asks whether that kernel fits through the holes. Two decks let you split the feed into three streams: oversize trash on top, on-spec grain in the middle, and fines or small weed seeds below. Add an aspiration channel and you also pull dust and lightweight chaff out of the falling product.

That sizing logic is exactly what you want when the impurities differ from grain in dimension: straw, stones, broken cobs, mud clods, small weed seeds, fine sand. It is exactly what you do not want when the impurities are the same size as the kernel — hollow kernels, sprouted grain, dead seed, ergot bodies, light grass seed of similar diameter — because the screen cannot see them.

How a Specific Gravity Cleaning Screen Works

A specific gravity screen — sometimes called a gravity separator, density table, or destoner depending on configuration — does the opposite. It does not care about the size of what passes over it. It cares about density.

Inside the cabinet sits an inclined perforated deck. A fan blows air upward through the deck while the deck itself oscillates back and forth on a controlled stroke. The combination fluidises the grain bed, suspending it in a thin cushion of air. Inside that cushion, denser particles settle toward the deck surface and travel along its incline; lighter particles float on top and migrate in a different direction. Adjustable splitters at the discharge end peel off heavy fraction, mid fraction, and light fraction streams.

Because the working principle is density rather than dimension, a gravity screen can do what no sizing screen can: pull a hollow kernel out of a stream of sound kernels of the same diameter, separate immature or weather-damaged grain from market-grade product, drop small stones out of paddy rice, or recover viable seed from a mix that includes dead or empty seed. For seed plants, malting facilities, food-grade processors, and anyone shipping under tight quality contracts, the gravity table is where the final upgrade happens.

Head-to-Head: What Each Machine Actually Separates

The cleanest way to think about it is in terms of what kind of impurity each can remove and what it cannot.

Vibrating screen — strong at: oversize trash (straw, stones, clods), undersize material (fines, small weed seeds, broken kernels), dust when fitted with aspiration, grading by kernel size. Cannot remove same-size hollow or damaged kernels.
Specific gravity screen — strong at: hollow and damaged kernels, immature seed, stones of grain size, ergot, light foreign material that survived earlier steps, seed-grade upgrading. Cannot remove gross trash or size-different impurities — those must be gone before the gravity table runs.

This is why almost every grain cleaning line you will see in a well-engineered facility looks roughly the same in sequence: drum or scalper first, then vibrating screen, then gravity table at the end. Each stage removes what the next stage cannot see.

Comparison Table

Separation principle. Vibrating: size. Gravity: density.
Typical capacity. Vibrating: 5–100 t/h depending on deck area. Gravity: 5–30 t/h on grain duty, 1–8 t/h on seed duty.
Position in the line. Vibrating: secondary, after primary scalping. Gravity: tertiary or final, after sizing.
Output streams. Vibrating: usually three (oversize / clean / fines). Gravity: usually three (heavy / mid / light), with adjustable cut points.
Tolerance for dirty feed. Vibrating: moderate — straw blinds it. Gravity: low — requires pre-cleaned, sized feed to work well.
Energy consumption. Vibrating: low — small motors, only the eccentric. Gravity: moderate — fan plus deck oscillation.
Operator skill. Vibrating: low — set and run. Gravity: higher — air, slope, stroke, and splitter positions all need tuning for each crop.
Footprint. Vibrating: long and flat. Gravity: tall and cabinet-shaped.
Best for. Vibrating: feed mills, country granaries, general bulk cleaning. Gravity: seed plants, malting, food-grade, paddy rice with stones, soy and pulse cleaning.

When You Need Each — And When You Need Both

Three rules of thumb cover most procurement decisions.

If your end use is bulk feed or commodity storage, a vibrating screen downstream of a drum or scalper will usually meet the spec. Animal-feed mills, country granaries, and intake operations at port silos rarely need a gravity table — the contract simply does not pay for that level of cleaning, and the grain leaves the facility before quality differences would show up.

If your end use is seed, malting, food-grade, or specialty crops, you need a gravity screen, and the vibrating screen exists mainly to feed it the right size fraction. Seed plants typically run drum, then air-screen (vibrating with aspiration), then gravity table — and sometimes a colour sorter or indented cylinder after that. Skipping the gravity table on seed-grade work is a false economy; you will either fail germination tests or get docked on price.

If your end use is paddy rice or soybean, the gravity table doubles as a destoner — it pulls out small stones that have the same diameter as the kernel and would otherwise survive every sizing step. For rice destined for milling, this single machine often pays for itself in protected mill components inside the first crop year.

Common Procurement Pitfalls

Buying a gravity screen first. A gravity table cannot handle dirty feed. If you install one upstream of a sizing screen, it will choke, mis-classify, and require constant cleaning. Always ask the supplier to confirm the full line layout, not just the single machine you are quoting.
Comparing nameplate capacities directly. A 30 t/h vibrating screen and a 30 t/h gravity screen are not comparable — the gravity rating is at a much higher cleaning standard. Always ask for capacity at your target quality, not the supplier's reference grade.
Underspecifying air on the gravity table. The whole machine works because air fluidises the bed. A weak fan or undersized duct ruins separation. Ask for fan airflow in m³/h, static pressure in Pa, and the recommended damper setting for each crop you plan to run.
Skipping aspiration on the vibrating screen. Without an aspiration channel, dust and light husk migrate downstream and overload the gravity table. Always specify aspiration as standard, not as an option.
Cheap screens. Woven-wire screens on a vibrating cleaner are a wear part. Stainless or hardened-wire screens last three to five times longer than plain steel on abrasive feeds — worth the small price premium.
No spare deck inserts. Gravity-deck cloths and vibrating-screen meshes have to be changed when crops change. Buy at least one spare set per crop you run; otherwise a changeover means waiting weeks for a replacement to ship.

Indicative Pricing (FOB China, 2026)

Vibrating cleaning screen, 10–20 t/h, single deck, with aspiration: USD 4,500–7,500 FOB
Vibrating cleaning screen, 30–50 t/h, double deck, with cyclone aspiration: USD 9,000–15,000 FOB
Specific gravity screen, 3–8 t/h, seed-grade configuration: USD 8,000–13,000 FOB
Specific gravity screen, 10–20 t/h, grain-grade configuration: USD 14,000–22,000 FOB
Combined vibrating + gravity cleaning line, 10–15 t/h finished seed: USD 28,000–45,000 FOB

Add 15 to 30 percent for DAP/DDP delivery depending on destination country. A combined cleaning line typically ships in one 40-ft container including ducting, spare screens, and a 12-month wear-parts kit.

Why Buyers Choose Xinyada

Xinyada Technology has been manufacturing grain cleaning and handling equipment in Hebei, China for nearly fifty years — the predecessor factory was founded in 1976 — and is a long-time supplier to China's national grain reserve and provincial grain bureau projects. We build both vibrating cleaning screens and specific gravity screens in-house, which means a single supplier can configure, integrate and commission the full cleaning line rather than handing off between vendors. Standard scope includes aspiration channels and cyclones, stainless screen cloths on request, brand-name drives, and a 12-month spare-parts kit shipped in the same container as the main machines. Commissioning checklists and operator manuals are available in English and Spanish.

Next Steps

If you are scoping a new cleaning line — or upgrading an existing one and not sure where the bottleneck really is — send us your project brief with the crops you handle, peak hourly throughput, your finished-grade target (commodity / feed / food / seed) and your destination port. Our engineering team will reply inside 24 hours with a sized configuration, layout drawing, and FOB / DDP quotes.

You can also browse our full cleaning screen lineup on the products page, or read the companion article on drum cleaning screens at intake if you are still designing the front end of the line.