Generally speaking, there are 3 systems used to generate the high- velocity air stream:

⑴Suction or vacuum system .This system usually utilizes a vacuum created in the pipeline to draw the material with the surrounding air. See fig 28-1(a), it is the positive pressure exhauster that causes material to flow through a nozzle and a duct into a cyclone collector where it is separated from the conveying air. The exhaust air is introduced to a filter collector for complete recovery of the material, leaving through the exhauster into the atmosphere. And the material is discharged from the collectors through rotary airlock feeders.

Now let’s see the advantage and working condition of vacuum conveying. Usually vacuum conveying eliminates the dust problem and it is most successfully applied for unloading material at a number of points, using a number of pipes, and delivering it to a single point. The system can operate at a low pressure, which is about 0.4 to 0.5 ATM below atmosphere, and is utilized mostly in conveying light free-flowing materials over short distances.

⑵Pressure-type system. It is a system in which a positive pressure is used to push material from one point to the next. Material is guided into a pipeline (Fig28-1(b)) through a rotary air-lock feeder to be conveyed by transport air fed by a blower through a receiver and a moisture trap. At the destination, the air stream then enters a cyclone collector for the recovery of material and the exhaust air is passed through a filter collector for dust separation. The system is good for conveying material from one point to number of unloading ones. It often operates under a pressure of 6 ATM and is capable of handling heavy pulverized and lumpy materials over very long distances.

⑶Combination system. In this system, a suction system is used to convey material from a number of loading points and a pressure system is needed to deliver it to a number of unloading points.