Dilute phase transport: negative pressure system Negative pressure systems generally use positive displacement (roots type) exhausters providing up to 50% vacuum to convey materials through a pipeline to the destination where the air and product are separated at a receiving vessel with a filter, or a cyclone.
The product enters the convey line directly, or if metering is required, via a special feeding device such as a rotary valve or screw feeder. The conveyed product is discharged from the receiving vessel either on a continuous basis by a rotary airlock or intermittently by valves to surge hoppers, storage vessels or other discharge points.
In vacuum conveying, no moving parts contact the materials and no dust can escape into the atmosphere. Because of this superior leak containment, they are often specified on the basis of cleanliness, particularly when handling hazardous materials.
The drawback of this system is that if the loading is high or the length of the system is large, the components must be designed for high vacuum. This adds cost to the components and must be considered when comparing methods of transport.
