Blog — Conveying · 8 min read
Types of powder
conveying systems
Dilute phase, dense phase, vacuum and mechanical — how to choose by powder, distance and duty.
In short
Powder conveying systems fall into four families: dilute phase pneumatic (powder suspended in a fast air stream), dense phase pneumatic (powder pushed as slugs at low velocity), vacuum conveying (powder drawn toward a receiver), and mechanical conveying (screws, vibratory feeders). The right choice depends on the powder's friability and abrasiveness, the route, and the required rate.
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Dilute phase — simple and fast
In a dilute (lean) phase system, a blower drives a high-volume air stream through a pipeline and a rotary valve meters powder into it. Air velocities of 15–30 m/s keep every particle in suspension from pickup to filter receiver.
It is the least expensive pneumatic option and handles high rates over complex routes. The cost is energy and impact: particles hit bends at speed, so friable products degrade and abrasive ones wear the pipework. Robust powders — flour, salt, sugar, granules — are its natural territory.
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Dense phase — gentle and wear-resistant
Dense phase systems use a pressure pot to push powder through the line as slugs at 1–8 m/s. Low velocity means low impact: agglomerated dairy powders keep their structure and bulk density, blends stay blended, and bends last years instead of months on abrasive duty.
The trade is a more involved system and cycle-based (rather than continuous) operation. Wherever product condition matters — milk powder, infant formula, coffee — dense phase usually earns its place.
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Vacuum — contained by physics
Vacuum systems draw powder toward a receiver under negative pressure. Any leak pulls air inward, never powder outward, which makes vacuum the default for hazardous, potent or hygiene-critical materials over short to medium distances — mixer feeding, packing-line supply, refill loops.
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Mechanical — screws and vibration
Mechanical conveyors move powder physically: rigid and flexible screws for contained transfer and metering, vibratory feeders for gentle, instantly controllable discharge. Over short runs they are the cheapest and most energy-efficient option, and screws double as dosing devices.
Their limit is geometry — mechanical routes are straight lines and gentle curves, not the three-dimensional paths a pipe can take.
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Choosing between them
Selection is a property of the material and the duty:
- Friable or agglomerated powder → dense phase or vacuum
- Abrasive material → dense phase or mechanical
- Long or complex route → pneumatic (phase per product)
- Short straight run, modest rate → flexible screw
- Precise metering into a process → rigid screw or vibratory
- Hazardous or high-value powder → vacuum
Common questions
Frequently asked questions.
- What are the methods of conveying powder?
- Four families: dilute phase pneumatic (suspension in fast air), dense phase pneumatic (low-velocity slugs), vacuum conveying (drawn under negative pressure), and mechanical conveying (screw and vibratory). Most plants combine two or more, chosen per material and duty.
- Which conveying method is gentlest on the product?
- Dense phase pneumatic and vibratory feeding. Dense phase moves powder at velocities an order of magnitude below dilute phase, so fragile agglomerates survive; vibratory feeders have no flights or pinch points at all over short distances.
Related
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