The first spec decision is not the blower, the pipe, or the brand. It is the material: bulk density below 8 kg/L (500 lb/ft³) and particle size below 30 mm mark the upper limit for what an air-stream conveyor can realistically carry [S2]. Materials outside that envelope, like wet sand, gravel, or coarse crushed rock, are not the duty of a pneumatic conveyor and should be routed to mechanical conveyors instead.
Selection then narrows to four coupled variables: phase mode, pressure regime (positive vs vacuum), conveying-air velocity, and solids-to-air ratio. Getting any one wrong cascades into the next, so the exercise is best done as a single matching pass rather than as sequential component picks. Engineers who treat it as a packaged system, similar to how they would specify a pneumatic actuator cylinder package, end up with fewer field retrofits.
Match Phase Mode to Material Behaviour
Dilute (lean) phase conveying suspends the material in a high-velocity air stream and is the default for non-fragile, free-flowing powders such as cement, sugar, and plastic pellets [S2]. Dense phase moves the material as a slower plug or slug at higher pressure, and is the right call for fragile, abrasive, or friable products because the lower velocity and higher solids loading cut particle degradation and pipeline wear [S3].
Medium phase sits between the two, with higher velocity than dense phase but higher concentration than dilute, and is the practical option for materials that straddle both regimes. A useful quick check: if a Jenike & Johanson-style flowability test shows the material is cohesive or highly friable, default to dense phase; if it is free-flowing and non-degradable, dilute phase is simpler and cheaper. The mode you pick drives the entire downstream spec, so do not lock it in after the blower has been quoted.
Positive Pressure vs Vacuum: Pick by Layout
Positive-pressure systems push material from a high-pressure feed side through the line, and they are the natural choice for moving bulk solids over longer distances or from one building to another [S2]. Vacuum conveyors pull from a low-pressure receiving side and are preferred when the feed point is multiple, the line is short, or the system must stay sealed to a single vessel to keep dust out of the room.
For pharmaceutical and food-grade duty, vacuum is often the default because the receiving vessel can be a single enclosed receiver with integrated filter, and dust cannot escape back toward the operator. For cement, mineral, or plastics plants with one source and several destination silos, positive pressure is the cleaner layout. A four-element architecture (vacuum source or blower, feed device, conveying line, air-material separator) is common to both regimes [S2], so component selection after the regime decision is largely a matter of pressure rating, pipe diameter, and filter area.
Air Velocity, Solids Loading, and Pressure Drop
Conveying-air velocity is the single most common cause of pneumatic conveyor failure, and the failure mode depends on which side of the optimum the design lands. If velocity is too low, the material settles in the line and plugs; if it is too high, particles shatter, elbows erode through, and the blower pays for wasted kinetic energy [S3].
Pressure drop compounds quickly with line length and bend count, which is why long-radius elbows and the fewest possible direction changes are a near-mandatory design discipline [S3]. A practical rule that tracks with the physics literature on single-tube pneumatic conveyors [S1]: unsteady-state transitions (start-up, product changeover, filter loading) are where most operating-parameter drift happens, so a model that estimates parameter change along the duct length is worth more than a single steady-state calculation. The Tarasov and Mukhopad 2019 model in *Theoretical Foundations of Chemical Engineering* explicitly targets this transient regime, which most catalogue-only designs ignore [S1].
Material Properties That Drive the Spec
Four material properties dominate the design sheet: bulk density, particle size distribution, moisture content, and friability. Bulk density sets the energy the blower must deliver per ton conveyed, and high-density materials push the design toward positive pressure with higher air volume [S3].
Particle size sets the minimum conveying velocity (the saltation boundary) and dictates whether the material is even a candidate for the technology; anything above the 30 mm ceiling is mechanical-conveyor territory [S2]. Friable products (tablets, certain food powders, catalyst supports) require dense phase, lower velocity, and gentle long-radius bends to keep breakage rates inside the plant's release spec. Moisture content is the silent killer: even small rises above the material's surface-dry state can flip a borderline powder from fluidizable to cohesive and double the pressure drop overnight, so the conveyor's filter and dryer specification must be sized for the wettest expected shift, not the average.
Component Selection After the System Match
Once phase mode and pressure regime are fixed, the remaining picks fall into place. Blower or compressor selection follows the system's pressure requirement, with positive-pressure dilute-phase systems typically needing higher volumetric flow at lower pressure, and dense-phase plug systems needing the opposite profile [S3]. A pneumatic silencer on the exhaust is a near-default for indoor installations to bring OSHA-style noise exposure under control without resorting to a separate enclosure.
Feed devices (rotary valves, venturi eductors, screw feeders) are selected by phase: rotary valves for positive-pressure dense phase, venturi eductors for vacuum dilute phase, and screw feeders for metered abrasive duty. The air-material separator (typically a cyclone followed by a bag or cartridge filter) is sized off the line's peak mass flow, not the average, because the filter is what determines whether the plant passes a dust-emissions audit. Piping diameter is a derivative of the chosen velocity and mass flow, but the engineer should still verify the pneumatic fitting class matches the system's pressure class; mismatches at the joint are a routine field-failure cause.
Who Should NOT Specify Pneumatic Conveying
Pneumatic conveying is the wrong technology when the material is wet, sticky, or above 30 mm particle size, when bulk density exceeds 8 kg/L, or when the duty is high-tonnage over very long distances with no tolerance for degradation [S2]. In those cases, a belt, chain, or vibrating conveyor will move more tons per kWh and inflict less damage on the product; a spec-first belt/chain comparison is in the [belt conveyor vs chain conveyor guide](/news/belt-conveyor-vs-chain-conveyor-spec-driven-selection.html), and vibration duty is covered in vibrating conveyor specs for warehouse automation builds.
Pneumatic is also the wrong pick for any application where the conveying line must pass through a classified hazardous area without engineered purge and bonding; the energy in a pressurized powder-air mixture is its own ignition source, and ATEX/IECEx-rated grounding, bonding, and velocity-limiting become mandatory rather than optional. The supply-side risk picture, which is similar across pneumatic components, is mapped in Pneumatic Actuator Supply Chain 2026, and a broader supplier-tier view sits in Pneumatic Actuator Supplier Map 2026.
Shortlist Logic and Verification
A shortlist worth sending out for bid has three names on it, not seven, and is built from the same envelope. Filter on: bulk density under 8 kg/L, particle size under 30 mm, friability class, required tonnage, and total conveying distance; eliminate any vendor whose reference duty is outside that envelope [S2]. Then verify the quoted system against the transient-state behaviour, not the steady-state brochure: a system that performs at start-up, during filter loading, and on product changeover is the one that survives a year of production without a modification order [S1].
Trackable signals for the next planning cycle: vendors publishing measured unsteady-state pressure profiles rather than only steady-state curves, more ATEX/IECEx-certified dense-phase packages for pharmaceutical duty, and tighter integration between conveyor control loops and upstream pneumatic cylinder or pneumatic actuator systems feeding the receiver. For a baseline read on the technology, the pneumatic conveyor encyclopedia entry is the starting point.