A conventional pneumatic conveying system uses gas to move bulk solids through a pipeline without specialized conditioning along the route, distinguishing it fundamentally from assisted low-velocity arrangements. Both architectures utilize gas for transport, but they differ significantly in how material is conditioned, how flow stability is maintained, and which specific equipment controls the process. This distinction is critical when specifying a Roots blower because the air source alone does not determine the final conveying regime.
In a conventional pneumatic conveying system, a feeder introduces material directly into a continuous conveying-air stream. A typical industrial installation includes a filtered air source, feeder, pipeline, bends, receiver, and vent filter. Rotary airlocks, screws, and suitable low-pressure feeding devices are commonly integrated according to material characteristics and system pressure.
Conventional dilute-phase conveying maintains high enough gas velocity to ensure continuous forward particle movement. While broadly applicable, unnecessarily high velocities can induce abrasive pipeline wear and product breakage. Conversely, conventional low-velocity conveying is viable only when the bulk material exhibits suitable natural behavior. Fine powders may retain aeration, whereas uniformly sized granules may permit air to pass steadily through the particle bed. Increasing system pressure or reducing blower speed does not automatically transform every product into a stable dense-phase material without these inherent properties.
Assisted Low-Velocity Conveying Technologies
Unlike a conventional pneumatic conveying system, an assisted architecture adds specialized equipment intended to control material behavior either at the feed point or along the pipeline. Depending on process requirements, this engineering can include:
- Pre-aeration or fluidization zones near the feeder.
- Parallel bypass-air lines.
- Localized air-injection points.
- Pulse-air sequencing controls.
- Specialized plug-forming or material-conditioning equipment.
- Pressure-based automated feeder control.
These integrations manage materials that do not convey reliably in a simple low-velocity line. They inherently introduce additional valves, instrumentation, control logic, maintenance requirements, and auxiliary air demand. Their performance must be evaluated as a complete, separate technology package rather than being attributed to the capabilities of the Roots blower.
Material Properties and Pressure Boundaries
Permeability, air retention, particle-size distribution, moisture, cohesion, and wall friction collectively dictate whether a material forms a mobile bed or a plug. A slight increase in fines can drastically reduce permeability, while elevated moisture increases cohesion and compaction risks. Representative material trials are highly valuable when proposing a low-velocity mode. The trial data must report solids rate, gas mass flow, pressure profiles, pipe bore, material condition, and the observed flow pattern.
Assisted systems frequently demand higher pressure than conventional low-pressure conveying lines. The complete pressure budget must account for feeder resistance, straight pipe, bends, vertical lift, material acceleration, filter loss, auxiliary injection, and a credible operating margin. Pasifik’s reviewed two-lobe and three-lobe positive-pressure Roots blowers are published for duties up to 1,000 mbar. If a calculated duty or conveying test exceeds this parameter, the project requires a different air-source technology or a redesigned route. The presence of an assisted-air line does not extend the approved differential pressure limits of the blower.
Procurement and Blower Selection
A roots blower displaces a nearly fixed volume per revolution within its permitted operating range, with delivered flow influenced by rotational speed, inlet density, internal leakage, and differential pressure. Rising resistance directly increases absorbed power and discharge temperature. The blower must be selected based on the actual combined duty, incorporating both the main conveying air and any auxiliary air supplied by the package.
A well-structured procurement enquiry should identify the proposed architecture, material test data, main and auxiliary air flows, maximum pressure, feeder leakage, pipeline route, receiver-filter loss, and control sequencing. Pasifik Blower evaluates the compatible positive-pressure portion of the system to confirm the exact model, optimal speed, motor power, and thermal limits using validated performance diagrams.
Glossary
Auxiliary air: Additional gas introduced separately from the main conveying-air supply.
Bypass air line: A parallel pipe used to distribute controlled air to specific points along a conveying route.
Conventional conveying: A system in which material is fed directly into the primary conveying-air stream without specialized conditioning along the pipeline route.
Local air injection: The controlled introduction of gas at a selected pipeline position to manage material flow.
Material conditioning: Mechanical or pneumatic treatment intended to modify bulk-solid behavior before or during the conveying process.
Plug-forming equipment: Specialized feeding or control equipment intended to create concentrated material plugs of a manageable size.
Pressure budget: The deliberate allocation of available differential pressure among all system resistances, including the necessary operating margin.
Pulse-air sequencing: The timed introduction of intermittent air, typically utilized by certain assisted conveying technologies.