This paper aims to provide design information for Row aid systems in the pneumatic conveying of powders, specifically for the system involving the use of knockers when an inclined pipeline is choked with powder. Acrylic pipes with a length 60 cm and inside diameters ranging from 2.6 to 6.4 cm were filled with powder whose mass was in the range of 30-270 g. The pipe was set at angles 10-50 degrees to the horizontal, The impact stress, 1-4.1 g (where g is the acceleration due to gravity), was exerted on the pipe, and the mass of powder that fell from the lower end of the pipe W (due to the impact) was correlated satisfactorily in terms of a variable related to the shear stress at the pipe wall. Within the experimental range studied, W was found to decrease almost linearly with the compressibility of powders for given experimental conditions.