The justifications for vacuum conveying are its simplicity of operation, ability to negotiate lengthy and tortuous routes and the hygienic transfer of materials. Product is conveyed from a feed source to a delivery point suspended in a stream of gas - usually air. When particulate materials are metered into an air-stream at an optimum solids to air ratio, the differential air pressure generated via a vacuumpump creates a high enough velocity to move the materials within the conveying tube.