Experiments hare been carried out to determine the characteristics of the reattaching flow downstream of deflectors placed in a duct with and without aeration. In Part 1 the presentation of experimental results pertaining to the mean velocities and wall pressure is restricted to flows without aeration. Fluctuations of pressures are presented in terms of their root-mean-square values and their probability distributions. The mean pressures presented will be of interest in the design of aerators. The mean velocities and wall pressures are analysed numerically by a discrete vortex model and the computed results are compared with the experimental results. It is hoped that information provided in this paper will also be useful in assessing the likelihood of cavitation in reattaching flows occurring within boundaries of similar geometry. How air injection affects the wall pressure field in the wake of deflectors will be reported separately in Part 2.