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Pneumatic Conveyor Systems
Low Density or High Density Conveyor Systems?
Pneumatic systems are used wherever the transport path is long and full of directional changes and — because they contain virtually no mechanical and moving parts — are considered to be extremely reliable, safe, almost maintenance-free and nearly free of wear.
An optimal design always takes into account the overall system, that is, the conveying system itself and its interface points, including the charging unit (discharge system) and the separator (filter) with their corresponding control and safety systems.
We differentiate between two basic designs: the low-pressure or low-density conveying system, which uses a radial fan as the compressor, and the high-pressure or high-density conveying system, which uses a rotary piston blower.
The low-pressure conveyor system with three design options:
1. Closed loop without separator:
Recommended for smaller amounts of material and shorter transport distances. The exhaust air is reused as transport air. The advantages of this design are the low investment costs, the absence of exhaust air, which eliminates the need for a filter, and direct injection of material into the silo or container. Decoupling is necessary for safety reasons.
2. Closed loop with centrifugal separator and rotary feeder:
This system is used for larger quantities of material and short transport distances. It has the same advantages as the previous design. In addition, decoupling is achieved through the use of the rotary feeder.
3. With a filtering separator:
The most economical system for large amounts of material and long distances. Filter options include either a static silo filter, whose casing strength must correspond to the silo’s interior pressure, or a bag filter with a rotary valve for decoupling. While the first variant has the advantage of lower investment costs and the disadvantage of overpressure in the silo, the second variant features a decoupled discharge system and a normal pressure ratio in the silo.
The high-pressure conveyor system
As transport distances and material loads increase, more criteria speak for the use of a high-pressure system. The most important components in this design are the rotary piston blower, which has a high operating efficiency and low energy costs, and S-valves or knife-edge valves. Even in the case of large amounts of material, the injectors ensure a low expenditure of energy for the required power. Thick-walled steel pipes and manifolds provide for a long service life.
High-pressure systems are predestined for use with transport quantities of 1 – 100 t/h, conveying systems up to 1,500 meters in length, and nominal widths between 88 and 500 millimeters. As a rule, they are designed as positive pressure units and are implemented for vacuum operation only when transporting materials with a low specific weight (e.g., fibers or insulating materials < 30 kg/m3).
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