The pneumatic conveying of granular bulk solids is one of the most popular methods of material transportation with advantages such as safety, low cost, flexibility of layout, ease of automation, security, low I11aintenance and ease of installation. The state diagram or conveying characteristics for granular materials shown in Fig. 1 consist of three boundary lines A, Band C and curve D delineating tile condition when particles begin to deposit on the bottom of the pipeline. So far, there are no design models that can predict all the boundaries reliably. Also, the formation of the unstable zone located between lines B and C in the state diagram is still lacking in understanding and appreciation.