The choice of a conveyance system boils down to two considerations – safety and cost. Safety encompasses that of workers, the environment and of the material itself. Cost encompasses the productivity of the system (throughput), initial outlay, and ease of maintenance or modification.
Safety
In the food industry, for example, 90% of conveyor injuries to workers are caused by flat belt conveyors and their accessories.
Pneumatic conveying systems, especially vacuum ones, eliminate most opportunities for spillage and contamination, and as such, they protect both the material from the environment and vice versa. They’re also easier to purge and clean than the many components of mechanical conveyors.
By having fewer parts they also make less noise. This can be a significant health and safety, or planning consent consideration.
Costs
Pneumatic conveying systems simplify the installation, extension or modification of routing. They require fewer additional components, like elevators, and save space by being able to turn awkward corners and avoid obstacles. They can often be extended at little extra cost.
Pneumatic conveyors have fewer moving parts and that means lower maintenance costs, especially when the transported material is abrasive to moving parts.
Mechanical conveyors have often been cheaper to run in terms of power consumption but modern pneumatic systems, especially ones using lower pressures, can be far more efficient if properly designed.
Limitations
Pneumatic conveyors are most often used with non-abrasive, non-fragile materials of fairly low density like flour, carbon, sugar, zinc oxide, plastic granules or hydrated lime.
Mechanical conveyors are often not suitable for high value, pollutant, or sensitive materials such as foodstuffs that may attract vermin and insects, or materials that need protection from the elements, like wind and rain.
Many of the components of mechanical systems may be prohibited from contact with foodstuffs, such as aluminium, many plastics and types of rubber.
Vacuum conveyor systems
Using vacuum pressure rather than positive pressure is particularly safe and efficient for moving materials that shouldn’t leak . A company with experience of these systems is http://www.aptech.uk.com/pneumatic-conveying/vacuum-conveying/.
The kinds of materials often moved by this method range from hot pellets, to protect workers from burns and fumes, to fragile foodstuffs such as nuts, breakfast cereals or spaghetti hoops. With this method it’s relatively easy to send through in batches instead of continuous streams, which is useful for quality screening and for loading containers.