An experimental program was established to investigate boundaries in low-velocity slug-flow pneumatic conveying. A straight horizontal pipeline of L=21m and D=60.3mm ID was set up for actual conveying trials and a simple rig was designed and built specifically to simulate the boundaries of slug-flow. After running several tests in the simulation rig with a sample of the product, the slug-flow were able to be determined with good accuracy. Combined with the theoretical correlations developed to determine pressure drop in slug-flow, reliable operating conditions can be predicted. Good agreement was achieved after the predicted results were compared with the experimental results from the large-scale pipeline.