How to choose a conveying system

When you are manufacturing in bulk, the way you convey materials to and from the production line is a critical decision. The cost of infrastructure and its maintenance are considerable, and you’ll have to consider the environment too.

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Pneumatic conveying usually offers the best solution. Your materials are protected by enclosure, there are few components to go wrong, routing is flexible, and you can automate. However, you still have major decisions to take, particularly between a vacuum or pressure conveyor, and the density of its airflow.

Air pressure and velocity

In “dilute phase” systems, air is blown faster so that the ratio of moving material to moving air is low. Most materials are suitable for dilute transportation and 85% use it, but fragile or abrasive materials often need gentler “dense phase” movement. In dense phase, material does not become airborne.

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In practice, many factors affect the flow rates and pressures throughout your system including tube bore, conveyor length, air speed, material density and often, unique features of particular materials. Because it’s a complex calculation with many materials behaving in surprising ways, you need the services of experienced professionals like to help you design it, although this spreadsheet will give you the general idea:

Positive pressure or vacuum conveyor

Pulling materials through with low pressure, instead of blowing, is better for some materials. Materials prone to clump or stick are pulled apart by vacuums, but clumped together by pressure. In the event of a leak, material will not spill out. This matters when it’s expensive, or hazardous enough to endanger workers or the environment.

If you want material delivered in batches instead of continuously, this is easier to achieve using vacuum. This helps you load containers one at a time, or conduct intermittent quality screening. Vacuum systems are most convenient when you want to load from several locations or containers but deliver into one outlet.

Conversely, blowing material through makes it easier to deliver it to a choice or succession of outlets. Generally speaking, positive-pressure systems can handle higher quantities and longer runs more easily. Your fan and compressor assembly will typically be at the loading end of the system, which may save you space where you need it most, while vacuum equipment tends to be located close to delivery points where you may have other processing equipment.

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