Pneumatic conveying systems: how they work and how to choose
Pneumatic conveying systems are used across industries from food and beverage to construction and chemicals. Anywhere bulk dry materials need to be transported efficiently, cleanly and at scale. Choosing the right system has a direct impact on energy costs, product integrity and operational throughput.
In this guide, you will find an overview of how pneumatic conveying works, the main system types (pressure and vacuum), and the three conveying phases. You will also find a comparison of dilute and dense phase conveying to help you identify the right approach for your material and application.
What is pneumatic conveying?
A pneumatic conveying system uses compressed air or gas to transport bulk dry materials (such as flour, cement, sand or plastic pellets) through an enclosed pipeline. Material moves either by pressure (positive conveying) or suction (vacuum conveying), with the chosen phase (dilute, dense or transient) determined by the material's properties and the distance to be covered.
Pneumatic conveying applications
Pneumatic conveying covers a range of industrial processes, each with different pressure, distance and material requirements. The three most common applications are:
- Bulk unloading: the transfer of dry bulk materials from a truck or train into storage. This is one of the most common entry points for pneumatic conveying in food, chemical and construction facilities.
- Truck unloading: a specific form of bulk unloading where an onboard or stationary compressor pressurises the tanker, pushing material directly into a silo or hopper. The same principle is also used to transport material between two production steps, for example when moving it from intermediate storage to the next stage of the process.
- Silo fluidization: a related application is silo fluidization, where air is introduced at the base of a silo to keep stored material flowing freely and prevent bridging or compaction. While not a form of pneumatic conveying itself, it often complements conveying systems by ensuring consistent discharge.
Pressure vs vacuum conveying
Pressure conveying
Pressure conveying (also called positive conveying) uses compressed air to push bulk material (whether cement, plastic pellets or grain) through a pipeline from the starting point to the destination. The compressor or blower sits at the inlet and can be stationary or mobile. This method handles longer distances and higher temperatures well but generates more pipeline wear at higher velocities.
Vacuum conveying
Vacuum conveying (also called negative conveying) uses suction to pull material through the pipeline, with the compressor or blower placed at the endpoint. Because the air reaches the material before passing through the unit, it is cleaner and cooler than in pressure systems, with no risk of oil carryover or compression heat affecting the product. This makes it well suited to food-grade and temperature-sensitive materials. Distance range is more limited than with pressure conveying.
The different phases of pneumatic conveying
A phase in pneumatic conveying refers to the way the material moves through the piping network. There are three different phases in pneumatic conveying:
- (A) dilute
- (B) dense
- (C) transient
The table below compares the two most commonly specified phases to help you identify which suits your material and application.
| Dilute phase | Dense phase | |
|---|---|---|
| How it works | Material is suspended in high-velocity airstream | Material moves in slugs or plugs at low velocity |
| Air velocity | High (typically 18–35 m/s) | Low (typically 3–10 m/s) |
| Air pressure | Low (up to 1 bar) | High (1–4 bar) |
| Throughput | Lower | Higher |
| Material suitability | Free-flowing, non-abrasive materials | Fragile, abrasive or cohesive materials |
| Pipeline wear | Higher | Lower |
| Best for | Lighter materials over short-to-medium distances | Heavy or sensitive materials over longer distances |
Materials matter
Not all bulk materials behave the same way in a pneumatic conveying system. The wrong system choice can damage fragile materials, cause blockages, increase energy consumption, or create safety risks such as dust explosions in fine powder applications.
The key material properties that affect system selection are:
- Particle size and density: heavier or coarser materials typically require higher air pressure and are better suited to dense phase conveying.
- Abrasiveness: highly abrasive materials cause pipeline wear at high velocities, making low-velocity dense phase the safer long-term choice.
- Fragility: materials that break apart easily (such as grain or certain food ingredients) need gentle handling. Dense phase conveying at low velocity reduces product degradation.
- Moisture content: damp or sticky materials can clump and block pipelines. System design needs to account for this through pipe diameter, bends and air drying.
- Combustibility: fine dry powders can be explosive when suspended in air. Oil-free compressed air and enclosed pipelines are essential safety requirements for these applications.
Select your material below to find out which pneumatic conveying system is right for your application.
Not sure which system is right for you?
Every application is different. Our compressed air specialists can help you size the right pneumatic conveying system for your material, distance and throughput requirements.
