The "just suspended" condition is an important criterion for the design of agitators in solid liquid mixing processes. This criterion is met when all the particles are in motion on the base of the vessel but not necessarily uniformly distributed throughout the liquid. Grenville et al. (2015) have proposed a new correlation for predicting the just suspension speed of axial flow impellers in standard, baffled vessels with dished bases. It is based on the physical model proposed by Davies (1986) and correlates data taken at three scales over a wide range of physical properties. Many previous workers have measured the just suspension speed for Rushton turbines, which produce a radial primary flow, and forced their data to the correlation proposed by Zwietering (1958) but without testing the statistical fit. The applicability of the Davies (1986) model and Grenville et al. (2015) correlation to radial flow impellers was recognized as an outstanding question and it is addressed in this paper. Chapman (1981) measured the just suspension speed for Rushton turbines at five vessel scales in standard baffled vessels with flat bases under gassed and ungassed conditions. The ungassed data have been successfully fitted to the Grenville et al. (2015) correlation but with a change in geometrical dependencies. The just suspension speed is independent of impeller clearance above the vessel base but strongly dependent on the impeller to vessel diameter ratio. These geometric effects are very different to the ones observed for axial impellers in dished base vessels and this suggests that further work should be carried out to reconcile these differences. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.