This paper presents an investigation into pneumatic conveying mechanism of particulate plugs moving in horizontal pipes. A plug flow regime may exist in pneumatic conveying systems operating with high-pressure gradients and low gas velocities. The most significant advantages of transporting particulate materials in a plug form is low energy consumption, low particles attrition and low pipe erosion. However, due to inaccurate approximations of the required pressure gradient of the plug, these kind of conveying processes can lead to pipeline blockage. It is obvious that mechanical modeling of particulate plugs movement play a key role to assess pressure loss occurs in pneumatic conveying systems. The present study presents a fundamental physical model and targeted to provide complete information on the mechanics of plugs movement, while combines characteristics of three different types of plugs as they move inside vertical or horizontal pipes. By using the model, it is possible to compare the energy loses of different plug types at specific conveying conditions, and hence, to characterize the existence of possible type of plug shape. The present work provides a several examples for such kind of analysis. The results of the present work provide information to update major characteristic variables for pneumatic conveying systems operating in a plug flow mode. This will be useful for both the designers and for further research works. (C) 2015 Elsevier B.V. All rights reserved.