Using a lock hopper feeding system, gravel and coal shale slurries containing particles of median diameter approximately 4 mm were transported at high concentrations through a pipe of I.D. 7.87 cm at velocities below 3.5 m/s−1. In addition to the usual measurements of velocity, delivered concentration and hydraulic gradient, in‐situ concentrations and particle velocities were determined. With these measurements, a two‐layer model of stratified flow of the type proposed by Wilson was examined and found to give satisfactory predictions. Coefficients of wall friction were found to vary with velocity. Minimum values of these coefficients agreed with the results of direct shear tests. This variation could be attributed to stick‐slip processes at low velocities and a change in the nature of the interparticle stress at higher velocities.

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A study of the literature on screw conveyers and feeders has been made. Most of the work is concerned with conveying material and in these cases the degree of fill in the trough is kept low to protect intermediate bearings and minimize power requirements. An equally important application for the screw, but one which has received less attention, is its use as a constant rate feeder and in this case the screw is run full. The object of the present work has been to find the effect of various parameters on screw performance at all degrees of fill. Experiments are described in which the effects of screw geometry, speed, filling, and the use of materials with different properties have been investigated.